Isodon rubescens (Hemls.) Hara.: A Comprehensive Review on Traditional Uses, Phytochemistry, and Pharmacological Activities.

Isodon rubescens is a medicinal and food plant, often eaten as a wild vegetable in ancient China, and has been widely used for decades to treat sore throats, tonsillitis, colds and headaches, bronchitis, chronic hepatitis, joint rheumatism, snake and insect bites, and various cancers. This comprehensive and systematic review of the ethnomedicinal uses, phytochemical composition, pharmacological activity, quality control and toxicology of I. rubescens provides updated information for the further development and application in the fields of functional foods and new drugs research. To date, a total of 324 substances have been isolated and identified from the plant, including terpenoids, flavonoids, polyphenols, alkaloids, amino acids, and volatile oils. Among these substances, diterpenoids are the most important and abundant bioactive components. In the past decades pharmacological studies have shown that I. rubescens has significant biological activities, especially in the modulation of antitumor and multidrug resistance. However, most of these studies have been conducted in vitro. In-depth in vivo studies on the quality control of its crude extracts and active ingredients, as well as on metabolite identification are still very limited. Therefore, more well-designed preclinical and clinical studies are needed to confirm the reported therapeutic potential of I. rubescens.

Introduction

The genus Isodon (Lamiaceae family) consists of more than 150 species of perennial herbs that are widely distributed in tropical Africa, tropical and subtropical Asia, and East Central Siberia, with a few species in Malaysia, Australia, and the Pacific Islands. There are 90 species and 21 varieties in China, among which the largest number of species is found in the Southwest provinces. I. rubescens (Hemsl.) H. Hara is a perennial herb of the genus Isodon in the Labiaceae family. I. rubescens (Figure 1) is also known as Rabdosia rubescens var. lushiensis, I. rubescens var. eglandulosus, Rabdosia rubescens var. taihangensis, Rabdosia dichromophylla (The Plant List, 2013) as well as under local names such as “Donglingcao,” “Binglingcao,” “Xuehuacao,” “Poxuedan,” “Shanxiangcao,” “Yehuoxiang,” and “Liuyueling” in China (Wei, 2012).

FIGURE 1

The aerial part (A), Plant flower (B), Plant leaves (C) (http://ppbc.iplant.cn/), and I. rubescens tea (D).

I. rubescens is sweet and bitter in a prescription and slightly cold after the drug acting on the body, clears away heat, and has detoxifying, anti-inflammatory, analgesic, and antitumor effects. It has been used in the treatment of esophageal cancer in He’nan province in China for more than 50 years (Xiong, 2014). The aboveground parts of I. rubescens are commonly used in traditional Chinese medicine (TCM) for sore throats, tonsillitis, laryngothralgia, colds, headaches, fever, heating, choking, nausea, tracheitis, chronic hepatitis, joint rheumatism, and snake and insect bites. It is also used alone or in combination with other herbs to treat cardiac cancer, liver cancer, lung cancer, prostate cancer, and bladder cancer in TCM (Feng et al., 2008). I. rubescens was first recorded in the “Jiuhuang Bencao” (simplified Chinese: 救荒本草) compiled by Zhu Xun in the Ming Dynasty (A.D. 1368–1644), it was often used as a wild vegetable in ancient China. In addition, many kinds of products related to I. rubescens such as I. rubescens tea, have been developed in the past decades.

In recent years, I. rubescens has received increasing attention due to the diverse chemical constituents and extensive biological activities, as well as its excellent clinical antitumor efficacy (Xue et al., 2007; Xiong, 2014). Previous phytochemical studies of I. rubescens have led to the identification of numerous diterpenoids, triterpenoids, phenols, alkaloids, volatile oils and other compounds. Its crude extract and some of its compounds have antitumor, anti-inflammatory, antibacterial, antioxidant, immunomodulatory, hypoglycemic, diarrheal and other biological activities (Han et al., 2003a). In particular, hundreds of enantio-kaurane and spirofo-kaurane diterpenes discovered in recent years are attracting increasing attention because of their novel structures and diverse biological activities. They have significant anti-proliferative, multidrug resistance (MDR) reversal properties as well as anti-inflammatory and anti-cardiovascular activities (Han, 2018).

To date, 324 compounds have been isolated and identified from I. rubescens. The main compound type are diterpenes of which the most representative one is oronidin (1). The results showed that oronidin has multiple biological activities and especially antitumor activity (Bae et al., 2014). However, the existing literature lacks a systematic review of traditional uses, toxicity, quality assessment, human studies, and newly discovered compounds of I. rubescens. In this review, in light of the widely recognized curative effect of I. rubescens, and hundreds of terpenoids with significant pharmacological activity have been isolated from I. rubescens in the past decades, we attempted to systematically and critically summarize the traditional uses, phytochemical constituents, pharmacological activity, quality evaluation, and toxicity of I. rubescens based on a database of scientific reports on human studies of I. rubescens. We believe that this review will provide important guidance for the further research and development of I. rubescens and its active components.

Materials and Methods

Information for this review (until August 2021) was collected through several popular search engines and databases such as Web of Science, Scifinder Scholar, Google Scholar, ScienceDirect, ACS, PubMed, and classic texts of Chinese herbal medicines (e.g., Jiuhuang Bencao), and other web sources, such as the Flora of China, the Plant List, YaoZh website (https://db.yaozh.com/). The selection criteria of this article were: 1) Research involves the traditional application and modern pharmacological activity of I. rubescens; 2) research involves the preparation of crude extract and the separation and identification of monomer compounds; 3) research involves the determination of the activity of the crude extract and isolated compounds; 4) research involves the mechanism of action; 5) research involves the botany, toxicity, quality control, etc. Exclusion criteria of this review were: 1) Research did not properly address the topic of this review 2) research with obvious defects or unethical problems. Keywords used in the literature search were: “I. rubescens,” “冬凌草,” “phytochemistry,” “pharmacology,” “biological activity,” “traditional uses,” “clinical trial,” “safety,” “quality control,” “medicinal uses,” “toxicology,” and other related search terms. The chemical structures of these compounds isolated from I. rubescens were drawn using the software ChemBioDraw Ultra 14.0 (The world’s leading chemical structure drawing tool can draw various complex structural equations).

Botanical Description and Traditional Usages

Botanical Description

According to the Flora of China, I. rubescens is a shrub of up to 1.2 m in height; Rootstock woody, stem erect, glabrous, branched with inflorescences, young branches very densely tomentose, purplish red. Cauline leaves opposite, base-wide cuneate, lateral veins on both sides very obvious, often purplish red; Petiole gradually shortening toward the top of stem and branch. Cymes, peduncles and peduncles, and rachis densely puberulent, but often purplish red; Bracts tapering upward, much beyond cyme in lower panicle, calyx campanulate, calyx teeth slightly two-lipped, fruity calyx enlarged, tubular campanulate, outer corolla sparsely puberulent and glandular, inner surface glabrous, shallow saccate above corolla tube, corolla eaves two-lipped, filaments flattened, styles filiform, disk annular. Obovate-trigonal nutlets flower from July to October, and bear fruits from August to November. I. rubescens is widely distributed in the Yellow River and Yangtze River basins in the provinces of Hu’bei, Si’chuan, Gui’zhou, Guang’xi, Shan’xi, Gan’su, Shaan’xi, He’nan, He’bei, Zhe’jiang, An’hui, Jiang’xi, and Hu’nan in China (Figure 2) (http://ppbc.iplant.cn/sp/222546). Its main production area is located in the southern part of the Taihang Mountain in Jiyuan, He’nan, with 1,400 hectares cultivation in 2015, and has been recognised as “National Geographical Indication Protected Product” since 2006. I. rubescens has been more used in the local owning to its high quality and clear efficacy. It may be related to the higher content of oridonin (1) and ponicidin (2) in the local I. rubescens.

FIGURE 2

The red spots in the map depicted the main region of I. rubescens distribution in China.

Traditional Usages

The first known record of I. rubescens is found in “Jiuhuang Bencao” (simplified Chinese: 救荒本草) (Ming Dynasty, A.D. 1,406), which is an encyclopedia that specializes in endemic plants and combines edible aspects with famine relief. Moreover, I. rubescens is recorded in various versions of the Chinese Pharmacopoeia. In the Chinese pharmacopoeia 2020 edition, I. rubescens is sweet and bitter in a prescription and slightly cold after the drug acting on the body. To the lung, stomach, and liver meridian, it has the effects of clearing away heat, detoxification, activating blood and relieving pain, which are employed for the treatment of sore throats, scratches, snake bites and other diseases. In the Chinese Pharmacopoeia, the recommended dosage of I. rubescens is 30–60 g per day (China Pharmacopoeia, 2020). I. rubescens has also been included in many local herbal standards. For instance, according to the records of He’nan folks materia medica, I. rubescens is often used to treat sore throat, cold and headache, bronchitis, chronic hepatitis, rheumatism and joint pain, snake bites, as well as esophageal cancer, cardia cancer, liver cancer, lung cancer, prostate cancer, bladder cancer, colon cancer, cervical cancer and many other cancers.

According to the folk medicine from the Taihang Mountains area of China, “a bowl of I. rubescens can be consumed daily to prevent wrinkles, remove spots and nourish the appearance, brighten and clear the voice, and drive away the disease of the body and mind”. Relatively few ancient prescriptions of I. rubescens are reported, but since the 1980s, the number of studies on I. rubescens has been increasing. I. rubescens related drugs and compatible formulations have emerged one after the other. The relevant ingredients and contents of the treatment of diseases are shown in Table 1. In clinical practice, I. rubescens is usually used alone or in combination with other TCM herbs. Many TCM herbs or classical prescriptions containing I. rubescens have been used in the form of decoction, powders, granules, tablets, pills and drop pills. For example, Fufang Donglingcao Lozenge, a representative classic formula containing I. rubescens, Mentha canadensis, Platycodon grandiflorus, and Glycyrrhiza uralensis, improves throat dryness, burning and pain, chronic pharyngitis, and oral ulcers (Deng and Lv, 2017). Overall, I. rubescens may be further studied and applied as a dietary supplement and therapeutic agent.

TABLE 1

The prescriptions and efficacy indications of I. rubescens in China.

No	Preparation name	Main composition	Role of I. rubescens in prescription	Efficacy and indications	References
1	Donglingcao Diwan	I. rubescens	Leading role	Acute tonsillitis, acute pharyngitis, sore throat	Ren et al. (2009)
2	Donglingcao Pian	I. rubescens	Leading role	Tonsillitis, pharyngitis, stomatitis, hoarseness	Zhang et al. (2008)
3	Donglingcao Capsules	I. rubescens	Leading role	Acute and chronic tonsillitis, pharyngitis, laryngitis, stomatitis	Zhang, (2019)
4	Donglingcao Dispersible tablets	I. rubescens	Leading role	Acute and chronic tonsillitis, pharyngitis, laryngitis, stomatitis, cancer	Li et al. (2011)
5	Donglingcao tea	I. rubescens	Leading role	Pharyngitis, cancer prevention	Dai et al. (2015)
6	Fufang Donglingcao Lozenge	I. rubescens, Mentha canadensis, Platycodon grandiflorus, Glycyrrhiza uralensis	Leading role	Dryness, burning and pain in the pharynx, Chronic pharyngitis, oral ulcers	Deng and Lv, (2017)
7	Donglingcao Syrup	I. Rubescens, Sucrose, Sodium benzoate	Leading role	Chronic tonsillitis, pharyngitis, laryngitis, stomatitis	Li et al. (2001)
8	Yankang Lozenge	I. Rubescens, Scrophularia ningpoensis, Ophiopogon japonicus, Platycodon grandiflorus, Glycyrrhiza uralensis	Leading role	Acute and chronic pharyngitis caused by wind-heat in the lung meridian	Si et al. (1993)
9	Dongqie Granules	Solanum melongena, I. rubescens	Supporting role	Chronic bronchitis	Shi, (1984)
10	Donglingcao Toothpaste	I. rubescens, Glycerin, Sorbitol, Xylitol, Menthol	Leading role	Bleeding gums, periodontal abscess, caries	Yang and Shen, (1997)

Phytochemical Constituents

Many studies on the isolation and identification of I. rubescens have shown that I. rubescens contains a variety of secondary metabolites, including diterpenoids (1–255), triterpenoids (256–266), phenols (267–301), alkaloids (302–311), essential oils (312–317) and other compounds (318–324). The most important and abundant biologically active components isolated from I. rubescens are diterpenoids, which have excellent antitumor activity. These components should be considered as promising candidates for the future development. The phytochemicals present in I. rubescens, including their names, CAS numbers, formulas of the isolated compounds, are summarized in Table 2. The structures of compounds isolated from I. rubescens are illustrated in Figure 3 showing that diterpenoids are the main components of I. rubescens. To document the advances in the pharmacological study of the listed compounds, these active compounds are shown in Table 3.

TABLE 2

The chemical constituents isolated from the I. rubescens.

No	Compounds	Molecular formula	CAS	Extracts	References
Diterpenoids
1	rubescensin A	C20H28O6	28957-04-2	EtOH	Cai, (2009)
2	rubescensin B	C20H26O6	52617-37-5	EtOH	Cai, (2009)
3	rubescensin C	C20H30O6	81661-34-9	EtOH	Cai, (2009)
4	rubescensin D	C20H26O6	88907-93-1	EtOH	Cai, (2009)
5	rubescensin E	C24H34O7	206659-93-0	EtOH	Cai, (2009)
6	rubescensin F	C20H30O7	521930-43-8	EtOH	Cai, (2009)
7	rubescensin G	C20H30O7	521930-45-0	EtOH	Cai, (2009)
8	rubescensin H	C21H30O7	306996-29-2	EtOH	Cai, (2009)
9	rubescensin I	C20H32O4	760948-08-1	Me2CO	Feng et al. (2008)
10	rubescensin J	C20H30O3	760948-09-2	Me2CO	Feng et al. (2008)
11	rubescensin K	C26H39NO4	760948-10-5	Me2CO	Feng et al. (2008)
12	rubescensin L	C26H40O8	760948-11-6	Me2CO	Feng et al. (2008)
13	rubescensin M	C40H58O9	760948-12-7	Me2CO	Feng et al. (2008)
14	rubescensin N	C19H26O4	602301-95-1	Me2CO	Feng et al. (2008)
15	rubescensin O	C21H32O7	602301-96-2	Me2CO	Feng et al. (2008)
16	rubescensin P	C20H32O4	760948-13-8	Me2CO	Feng et al. (2008)
17	rubescensin Q	C22H32O6	851868-64-9	Me2CO	Feng et al. (2008)
18	rubescensin R	C24H34O8	851868-65-0	Me2CO	Feng et al. (2008)
19	rubescensin S	C20H28O7	771485-56-4	Me2CO	Feng et al. (2008)
20	rubescensin T	C21H30O7	771531-48-7	Me2CO	Feng et al. (2008)
21	rubescensin U	C20H28O6	684278-34-0	Me2CO	Feng et al. (2008)
22	rubescensin V	C20H28O6	684278-35-1	Me2CO	Feng et al. (2008)
23	xindongnin A	C2 H32O7	97230-44-9	Et2O	Sun et al. (1985)
24	xindongnin B	C22H32O6	97230-45-0	Et2O	Sun et al. (1985)
25	xindongnin C	C24H34O7	725718-96-7	Me2CO	Feng et al. (2008)
26	xindongnin D	C26H38O8	725718-97-8	Me2CO	Feng et al. (2008)
27	xindongnin E	C24H36O7	725718-98-9	Me2CO	Feng et al. (2008)
28	xindongnin F	C22H32O6	725718-99-0	Me2CO	Feng et al. (2008)
29	xindongnin G	C25H38O8	725719-00-6	Me2CO	Feng et al. (2008)
30	xindongnin H	C22H30O6	769923-93-5	Me2CO	Feng et al. (2008)
31	xindongnin I	C20H28O5	769923-94-6	Me2CO	Feng et al. (2008)
32	xindongnin J	C20H28O5	97230-60-9	Me2CO	Feng et al. (2008)
33	xindongnin K	C21H32O6	769923-95-7	Me2CO	Feng et al. (2008)
34	xindongnin L	C23H34O7	769923-96-8	Me2CO	Feng et al. (2008)
35	xindongnin M	C48H70O16	692740-04-8	Me2CO	Feng et al. (2008)
36	xindongnin N	C48H68O15	692740-05-9	Me2CO	Feng et al. (2008)
37	xindongnin O	C48H68O15	692740-06-0	Me2CO	Feng et al. (2008)
38	xindongnin P	C44H64O12	857642-15-0	Me2CO	Feng et al. (2008)
39	lushanrubescensin A	C28H38O10	93078-70-7	Et2O	Liu et al. (2004a)
40	lushanrubescensin B	C26H36O9	110325-77-4	Et2O	Liu et al. (2004a)
41	lushanrubescensin C	C28H38O9	110325-78-5	Et2O	Liu et al. (2004a)
42	lushanrubescensin D	C22H32O6	110325-79-6	Et2O	Liu et al. (2004a)
43	lushanrubescensin E	C24H34O7	114020-54-1	Et2O	Liu et al. (2004a)
44	lushanrubescensin F	C2H32O7	640284-51-1	Me2CO	Feng et al. (2008)
45	lushanrubescensin G	C20H30O8	640284-54-2	Me2CO	Feng et al. (2008)
46	lushanrubescensin H	C22 H30O6	476640-22-9	Me2CO	Feng et al. (2008)
47	lushanrubescensin I	C22H30O7	640284-53-3	Me2CO	Feng et al. (2008)
48	lushanrubescensin J	C40H52O12	675603-42-6	Me2CO	Feng et al. (2008)
49	taibairubescensin A	C24H34O7	263910-37-8		Liu et al. (2004a)
50	taibairubescensin B	C24H34O7	263910-38-9		Liu et al. (2004a)
51	taibairubescensin C	C24H34O7	445256-93-9		Li et al. (2002)
52	hebeirubescensin A	C26H37NO8	887333-23-5	Me2CO	Huang et al. (2006)
53	hebeirubescensin B	C25H38O7	887333-24-6	Me2CO	Huang et al. (2006)
54	Hebeirubescensin C	C25H38O7	887333-25-7	Me2CO	Huang et al. (2006)
55	hebeirubescensin D	C26H34O7	887333-26-8	Me2CO	Huang et al. (2006)
56	hebeirubescensin E	C25H38O7	887333-27-9	Me2CO	Huang et al. (2006)
57	hebeirubescensin F	C25H40O7	887333-28-0	Me2CO	Huang et al. (2006)
58	hebeirubescensin G	C20H28O7	887333-29-1	Me2CO	Huang et al. (2006)
59	hebeirubescensin H	C20H28O7	887333-30-4	Me2CO	Huang et al. (2006)
60	hebeirubescensin I	C21H32O7	887333-31-5	Me2CO	Huang et al. (2006)
61	hebeirubescensin J	C21H32O6	887333-32-6	Me2CO	Huang et al. (2006)
62	hebeirubescensin K	C20H30O6	887333-33-7	Me2CO	Huang et al. (2006)
63	hebeirubescensin L	C26H36O8	887333-34-8	Me2CO	Huang et al. (2006)
64	ludongnin A	C20H24O6	93377-47-0	Et2O	Liu et al. (2004a)
65	ludongnin B	C20H26O5	110325-75-2	Et2O	Liu et al. (2004a)
66	ludongnin C	C20H26O5	609341-96-0	Et2O	Liu et al. (2004a)
67	ludongnin D	C20H26O5	609341-97-1	Et2O	Liu et al. (2004a)
68	ludongnin E	C20H26O6	100595-89-9	Et2O	Liu et al. (2004a)
69	ludongnin F	C21H30O5	623943-55-5	Me2CO	Feng et al. (2008)
70	ludongnin G	C21H30O5	623943-56-6	Me2CO	Feng et al. (2008)
71	ludongnin H	C21H30O5	623943-57-7	Me2CO	Feng et al. (2008)
72	ludongnin I	C21H30O5	623943-58-8	Me2CO	Feng et al. (2008)
73	ludongnin J	C21H28O5	623943-59-9	Me2CO	Feng et al. (2008)
74	guidongnins A	C20H26O6	119968-13-7	Me2CO	Han et al. (2003b)
75	guidongnins B	C20H26O5	596096-11-6	Me2CO	Han et al. (2003b)
76	guidongnins C	C20H26O6	93377-70-9	Me2CO	Han et al. (2003b)
77	guidongnins D	C20H26O7	596096-12-7	Me2CO	Han et al. (2003b)
78	guidongnins E	C20H28O5	102274-01-1	Me2CO	Han et al. (2003b)
79	guidongnins F	C20H28O5	596096-13-8	Me2CO	Han et al. (2003b)
80	guidongnins G	C20H28O6	596096-14-9	Me2CO	Han et al. (2003b)
81	guidongnins H	C21H30O5	596096-15-0	Me2CO	Han et al. (2003b)
82	hebeiabinin A	C20H26O5	934832-64-1	Me2CO	Huang et al. (2007)
83	hebeiabinin B	C20H34O5	934832-65-2	Me2CO	Huang et al. (2007)
84	hebeiabinin C	C20H28O3	934832-66-3	Me2CO	Huang et al. (2007)
85	hebeiabinin D	C40H60O11	934832-67-4	Me2CO	Huang et al. (2007)
86	hebeiabinin E	C40H56O9	934832-68-5	Me2CO	Huang et al. (2007)
87	kaurine A	C20H27NO5	1646821-73-9	EtOH	Liu, (2012)
88	kaurine B	C20H27NO5	1646821-74-0	EtOH	Liu, (2012)
89	kaurine C	C24H33NO8	1646821-75-1	EtOH	Liu, (2012)
90	jianshirubesin A	C20H28O7	1476061-46-7	EtOH	Liu, (2012)
91	jianshirubesin B	C20H28O7	1476061-47-8	EtOH	Liu, (2012)
92	jianshirubesin C	C20H28O8	1476061-48-9	EtOH	Liu, (2012)
93	jianshirubesin D	C20H26O6	1418183-49-9	EtOH	Liu, (2012)
94	jianshirubesin E	C20H28O6	1418183-50-2	EtOH	Liu, (2012)
95	jianshirubesin F	C20H28O5	1418183-51-3	EtOH	Liu, (2012)
96	jianshirubesin G	C20H32O4	1621268-64-1	EtOH	Liu, (2012)
97	jianshirubesin H	C26H34O9	1621268-65-2	EtOH	Liu, (2012)
98	jianshirubesin I	C22H30O7	1621268-66-3	EtOH	Liu, (2012)
99	jianshirubesin J	C20H26O6		EtOH	Liu, (2012)
100	jianshirubesin K	C22H30O6		EtOH	Liu, (2012)
101	jianshirubesin L	C24H34O8		EtOH	Liu, (2012)
102	jianshirubesin M	C24H36O8		EtOH	Liu, (2012)
103	hubeirubesin A	C22H32O6	1578156-49-6	EtOH	Liu, (2012)
104	hubeirubesin B	C24H32O6	1578156-51-0	EtOH	Liu, (2012)
105	hubeirubesin C	C28H36O10		EtOH	Liu, (2012)
106	hubeirubesin D	C26H34O10		EtOH	Liu, (2012)
107	hubeirubesin E	C28H40O10		EtOH	Liu, (2012)
108	hubeirubesin F	C24H34O9		EtOH	Liu, (2012)
109	hubeirubesin G	C23H34O8		EtOH	Liu, (2012)
110	hubeirubesin H	C26H36O8		EtOH	Liu, (2012)
111	hubeirubesin I	C26H36O9		EtOH	Liu, (2012)
112	hubeirubesin J	C24H34O8		EtOH	Liu, (2012)
113	hubeirubesin K	C24H34O8		EtOH	Liu, (2012)
114	hubeirubesin L	C24H34O7		EtOH	Liu, (2012)
115	hubeirubesin M	C24H32O8		EtOH	Liu, (2012)
116	hubeirubesin N	C20H30O7		EtOH	Liu, (2012)
117	hubeirubesin O	C20H30O7		EtOH	Liu, (2012)
118	hubeirubesin P	C22H33O6		EtOH	Liu, (2012)
119	hubeirubesin Q	C22H32O5		EtOH	Liu, (2012)
120	hubeirubesin R	C20H30O7		EtOH	Liu, (2012)
121	hubeirubesin S	C24H34O8		EtOH	Liu, (2012)
122	hubeirubesin T	C20H28O6		EtOH	Liu, (2012)
123	hubeirubesin U	C22H32O6		EtOH	Liu, (2012)
124	hubeirubesin V	C20H28O6		EtOH	Liu, (2012)
125	hubeirubesin W	C24H34O9		EtOH	Liu, (2012)
126	hubeirubesin X	C20H30O6		EtOH	Liu, (2012)
127	hubeirubesin Y	C20H32O6		EtOH	Liu, (2012)
128	hubeirubesin Z	C22H32O6		EtOH	Liu, (2012)
129	epinodosin	C20H26O6	20086-60-6	EtOH	Liu, (2012)
130	rabdosin A	C21H28O6	84304-91-6	EtOH	Liu, (2012)
131	enmein	C20H26O6	3776-39-4	EtOH	Liu, (2012)
132	rabdosichuanin	C20H27O6		EtOH	Liu, (2012)
133	taibaijaponicain A	C21H30O7	C21H28O6	EtOH	Liu, (2012)
134	maoyecrystal K	C21H30O7	791837-58-6	EtOH	Liu, (2012)
135	isodocarpin	C20H26O5	10391-08-9	EtOH	Liu, (2012)
136	6β,15α-dihydroxy-6,7-seco-6,20-epoxy-1α,7-olide-ent-kaur-16-ene	C19H28O6		EtOH	Liu, (2012)
137	epinodosinol	C20H28O6	27548-88-5	EtOH	Liu, (2012)
138	6α,15α-dihydroxy-20-aldehyde-6,7-seco-6,11α-epoxy-ent-kaur 16-en-1α,7-olide	C20H25O6		EtOH	Liu, (2012)
139	laxiflorin C	C20H26O5	165337-72-4	EtOH	Liu, (2012)
140	laxiflorin D	C20H24O5	319914-45-9	EtOH	Liu, (2012)
141	laxiflorin E	C20H26O5	388122-19-8	EtOH	Liu, (2012)
142	rubescensin W	C21H30O6	780773-93-5	EtOH	Liu, (2012)
143	6β,7β,14β,15β,tetrahy-droxy-7α,20-epoxy-ent-kaur-16-ene	C20 H30O5	167894-11-3	EtOH	Liu, (2012)
144	maoecrystal X	C22H32O6	887471-86-5	EtOH	Liu, (2012)
145	maoyecrystal F	C24H34O7	79854-99-2	EtOH	Liu, (2012)
146	acetonide of maoyecrystal F	C22H32O7	664327-95-1	EtOH	Liu, (2012)
147	wikstroemioidin B	C23H34O6	152511-36-9	EtOH	Liu, (2012)
148	rabdoternin A	C20H28O6	128887-80-9	EtOH	Liu, (2012)
149	rabdoternin B	C20H28O7	128887-81-0	EtOH	Liu, (2012)
150	rabdoternin C	C24H34O7	128887-82-1	EtOH	Li et al. (2019)
151	rabdoternin D	C22H32O7	155969-81-6	EtOH	Liu, (2012)
152	rabdoternin F	C21H30O7	155977-87-0	EtOH	Liu, (2012)
153	shikokianin	C24H32O8	24267-69-4	EtOH	Liu, (2012)
154	lasiodin	C22H30O7	28957-08-6	EtOH	Liu, (2012)
155	lasiokaurinol	C22H32O7	52718-05-5	EtOH	Liu, (2012)
156	enmenin	C24H34O7	23811-50-9	EtOH	Liu, (2012)
157	enmenin monoacetate	C26H36O8	23807-57-0	EtOH	Liu, (2012)
158	rabdolongin A	C24H34O8	117229-55-7	EtOH	Liu, (2012)
159	parvifoline F	C20H26O6	882673-14-5	EtOH	Liu, (2012)
160	odonicin	C24H30O7	51419-51-3	EtOH	Liu, (2012)
161	parvifoline AA	C20H26O5	934370-61-3	EtOH	Liu, (2012)
162	ent-abierubesin A	C20H32O5	1578156-42-9	EtOH	Liu, (2012)
163	ent-abierubesin B	C20H34O5	1578156-43-0	EtOH	Liu, (2012)
164	ent-abierubesin C	C20H32O4	1578156-45-2	EtOH	Liu, (2012)
165	ent-abierubesin D	C20H32O4	1578156-46-3	EtOH	Liu, (2012)
166	ent-abierubesin E	C21H32O7	1578156-47-4	EtOH	Liu, (2012)
167	ent-abienervonin C	C20H32O5	1132681-75-4	EtOH	Liu, (2012)
168	rabdoepigibberellolide	C26H34O9	81398-21-2	EtOH	Liu, (2012)
169	neolaxiflorin U	C22H32O7	1821199-19-2	EtOH	Shu et al. (2017)
170	epinodosinol	C20H28O6	27548-88-5	EtOH	Shu et al. (2017)
171	rabdokaurin C	C24H34O8	150148-80-4	EtOH	Lu et al. (2007)
172	lasiokaurinol	C22H32O7	52718-05-5	EtOH	Lu et al. (2007)
173	lasiodonin	C20H28O6	38602-52-7	EtOH	Lu et al. (2007)
174	lasiokaurin	C22H30O7	28957-08-6	EtOH	Song et al. (2011)
175	lasiodonin acetonide	C23H32O6	851860-25-8	EtOH	Feng et al. (2008)
176	bisrubescensin A	C43H60O13	878481-77-7	Me2CO	Feng et al. (2008)
177	bisrubescensin B	C40H58O13	878481-78-8	Me2CO	Feng et al. (2008)
178	bisrubescensin C	C40H56O12	878481-79-9	Me2CO	Feng et al. (2008)
179	bisrubescensin D	C40H56O13	1052120-55-4	EtOH	Lu et al. (2008)
180	rubescrystal A	C22H28O7		Me2CO	Xie, (2012)
181	rubescrystal B	C20H24O6		Me2CO	Xie, (2012)
182	glaucocalactone	C22H26O7	123086-85-1	Me2CO	Xie, (2012)
183	rabdonervosin B	C21H30O6	248256-56-6	Me2CO	Xie, (2012)
184	acetonide of rubescensin J	C20H26O6		Me2CO	Xie, (2012)
185	maoyecrystal F	C22H32O7	664327-95-1	Me2CO	Xie, (2012)
186	1-α-O-β-D-glucopyran-osyl-enmenol	C26H40O6		Me2CO	Xie, (2012)
187	acetonide of maoyecrystal F	C25H36O7		Me2CO	Xie, (2012)
188	melissoidesin G	C24H34O7	256448-82-5	Me2CO	Feng et al. (2008)
189	dawoensin A	C26H36O8	137661-09-7	Me2CO	Feng et al. (2008)
190	glabcensin V	C24H34O7	197389-19-8	Me2CO	Feng et al. (2008)
191	angustifolin	C14H14O3	56881-08-4	Me2CO	Feng et al. (2008)
192	6-epiangustifolin	C21H28O6	369390-94-3	Me2CO	Feng et al. (2008)
193	sculponeatin J	C20H24O5	477529-69-4	Me2CO	Feng et al. (2008)
194	enmenol	C20H30O6	28957-06-4	EtOH	Cai, (2009)
195	dayecrystals B	C21H32O7	926010-25-5	EtOH	Cai, (2009)
196	rabdosianin A	C26H36O9	80138-69-8	MeOH	Li W et al. (2019)
197	parvifoline G	C26H34O9	882673-16-7	MeOH	Li et al. (2019)
198	suimiyain A	C22H32O6	143086-37-7	EtOH	Liu et al. (2004a)
199	effusanin E	C20H28O6	76470-15-0	EtOH	Liu et al. (2004a)
200	jaridon 6	C20H24O5		EtOH	Han, (2018)
201	16,17-exoepoxide-oridonin	C20H27O5		EtOH	Bai N S. et al. (2010)
202	11,15-O,O-diacetyl-rabdoternins D	C26H36O9		EtOH	Bai N S. et al. (2010)
203	rosthorin	C20H28O6	93772-27-1	EtOH	Bai N S. et al. (2010)
204	isolushinin A	C20H28O3	1233704-08-9	Me2CO	Luo et al. (2010)
205	isolushinin B	C22H32O6	1233704-09-0	Me2CO	Luo et al. (2010)
206	isolushinin C	C20H30O5	1233704-10-3	Me2CO	Luo et al. (2010)
207	isolushinin D	C23H32O6	1233704-11-4	Me2CO	Luo et al. (2010)
208	isolushinin E	C23H34O6	1233704-12-5	Me2CO	Luo et al. (2010)
209	isolushinin F	C21H30O6	1233704-13-6	Me2CO	Luo et al. (2010)
210	isolushinin G	C22H32O7	1233704-14-7	Me2CO	Luo et al. (2010)
211	isolushinin H	C22H32O6	1233704-15-8	Me2CO	Luo et al. (2010)
212	isolushinin I	C22H32O7	1233704-16-9	Me2CO	Luo et al. (2010)
213	isolushinin J	C20H30O6	1233704-17-0	Me2CO	Luo et al. (2010)
214	luanchunin A	C20H28O5	1242434-16-7	EtOH	Zhang et al. (2010a)
215	luanchunin B	C20H30O4	1242434-17-8	EtOH	Zhang et al. (2010b)
216	rubluanin A	C23H34O6	1252578-83-8	Me2CO	Zhang et al. (2010a)
217	rubluanin B	C21H32O5	1252578-85-0	Me2CO	Zhang et al. (2010b)
218	rubluanin C	C21H32O5	1252578-87-2	Me2CO	Zhang et al. (2010a)
219	rubluanin D	C21H32O7	1252578-88-3	Me2CO	Zhang et al. (2010b)
220	rubesanolide A	C20H30O4	1275523-36-8	MeOH	Zou et al. (2011)
221	rubesanolide B	C20H30O4	1275523-41-5	MeOH	Zou et al. (2011)
222	15α-acetoxyl-6,11α-epoxy-6α-hydroxy-20-oxo-6,7-secoent-kaur-16-en-1,7-olide	C22H28O7		Me2CO	Xie et al. (2011)
223	15α-hydroxy-20-oxo-6,7-seco-ent-kaur-16-en-1,7α(6,11α)-diolide	C20H24O6		Me2CO	Xie et al. (2011)
224	bisrubescensin E	C40H54O13	1422357-49-0	MeOH	Lu and Liang, (2012)
225	isojiangrubesin A	C22H34O8		Me2CO	Zhang L et al. (2017)
226	isojiangrubesin B	C21H30O6		Me2CO	Zhang Y et al. (2017)
227	isojiangrubesin C	C21H30O6		Me2CO	Zhang L et al. (2017)
228	isojiangrubesin D	C20H30O6		Me2CO	Zhang Y et al. (2017)
229	isojiangrubesin E	C24H36O7		Me2CO	Zhang L et al. (2017)
230	isojiangrubesin F	C24H38O7		Me2CO	Zhang Y et al. (2017)
231	isojiangrubesin G	C24H38O7		Me2CO	Zhang L et al. (2017)
232	20(R)-6β,7β,15β-trihydroxy-20-methoxy-7α,20-epoxy-entkaur-16-en-1α,11β-acetonide	C24H36O7		Me2CO	Zhang Y et al. (2017)
233	nervosanin A	C21H32O6		Me2CO	Zhang L et al. (2017)
234	rabdoternin E	C21 H30O7	155969-82-7	Me2CO	Zhang Y et al. (2017)
235	6- epi-11-O-acetylangustifolin	C23H30O7		MeOH	Luo et al. (2017)
236	11- O-acetylangustifolin	C23H30O7		MeOH	Luo et al. (2017)
237	isodonrubescin A	C22H32O7		EtOH	Wen et al. (2019)
238	isodonrubescin B	C22H32O7		EtOH	Wen et al. (2019)
239	isodonrubescin C	C22H32O7		EtOH	Wen et al. (2019)
240	isodonrubescin D	C22H32O7		EtOH	Wen et al. (2019)
241	isodonrubescin E	C22H32O7		EtOH	Wen et al. (2019)
242	isodonrubescin F	C20H28O5		EtOH	Wen et al. (2019)
243	rubesanolide C	C20H30O4		MeOH	Zou et al. (2012)
244	rubesanolide D	C20H30O3		MeOH	Zou et al. (2012)
245	rubesanolide E	C20H30O2		MeOH	Zou et al. (2012)
246	jaridonin	C22H32O5	944826-54-4	Me2CO	Ma et al. (2013)
247	14-O-acetyl-oridonin	C22H31O7		EtOH	Bai N S. et al. (2010)
248	isodonoiol	C22H30O7	82460-75-1	Me2CO	Han et al. (2003d)
249	isodonal	C22H28O7	16964-56-0	Me2CO	Han et al. (2003d)
250	rabdosin B	C24H32O8	84304-92-7	Me2CO	Han et al. (2003d)
251	effusanin A	C20H28O5	30220-43-0	Me2CO	Zhang L et al. (2017)
252	longikaurin A	C20H28O5	75207-67-9	Me2CO	Zhang Y et al. (2017)
253	xerophinoid B	C21H30O6	946822-57-7	Me2CO	Zhang L et al. (2017)
254	7,14-O-(1-methylethy-lidene) oridonin	C23H32O6	331282-94-1	Me2CO	Zhang Y et al. (2017)
255	3β-hydroxy-6β-methoxy-6,7-seco-6,20-epoxy-1α,7-olide-ent-kaur-16-en-15-one	C21H28O6		EtOH	Wen et al. (2019)
Triterpenes
256	ursolic acid	C30H48O3	77-52-1	EtOH	Cai, (2009)
257	oleanic acid	C30H48O3	508-02-1	EtOH	Cai, (2009)
258	β-Sitosterol	C29H50O	64997-52-0	EtOH	Cai, (2009)
259	α-Amyrin	C30H50O	638-95-9	EtOH	Cai, (2009)
260	daucosterol	C35H60O6	474-58-8	EtOH	Cai, (2009)
261	betulin	C30H50O2	473-98-3	MeOH	Li et al. (2019)
262	betulinic acid	C30H48O3	472-15-1	MeOH	Li W et al. (2019)
263	eryihrodiol	C30H50O2	545-48-2	MeOH	Li et al. (2019)
264	friedelin	C30H50O	559-74-0	EtOH	Lu et al. (2013)
265	stigmasterol	C29H48O	83-48-7	EtOH	Yan et al. (2006)
266	2α,3α-dihydroxy-urs-12-en-28-oic acid	C30H48O4		EtOH	Cai et al. (2008)
Polyphenols
267	salicylic acid	C7H6O3	69-72-7	Me2CO	Feng et al. (2008)
268	caffeic acid	C9H8O4	331-39-5	Me2CO	Feng et al. (2008)
269	rosmarinic acid	C18H16O8	20283-92-5	Me2CO	Feng et al. (2008)
270	methyl rosmarinate	C19H18O8	99353-00-1	Me2CO	Feng et al. (2008)
271	danshensu	C9H10O5	76822-21-4	Me2CO	Feng et al. (2008)
272	chlorogenic acid	C16H18O9	327-97-9	EtOH	Du, (2008)
273	p-Hydroxybenzalde-hyde	C7H6O2	123-08-0	EtOH	Song et al. (2011)
274	acetovanillone	C9H10O3	498-02-2	Me2CO	Xie, (2012)
275	protocatechualdehyde	C7H6O3	139-85-5	EtOH	Lu et al. (2007)
276	ferulic Acid	C10H10O4	1,135-24-6	EtOH	Lu et al. (2007)
277	vanillic acid	C8H8O4	121-34-6	EtOH	Lu et al. (2007)
Flavonoids
278	cirsiliol	C17H14O7	34334-69-5	EtOH	Cai, (2009)
279	pedalitin	C16H12O7	22384-63-0	EtOH	Yan et al. (2006)
280	quercetin	C15H10O7	117-39-5	Me2CO	Gao and Wang, (2014)
281	sideritoflavone	C18H16O8	70360-12-2	Me2CO	Gao and Wang, (2014)
282	quercetin 3-O-rutinoside	C27H30O16	949926-49-2	Me2CO	Gao and Wang, (2014)
283	kaempferol 3,7-dirhamnoside	C27H30O14	482-38-2	Me2CO	Gao and Wang, (2014)
284	quercitrin	C21H20O11	522-12-3	Me2CO	Gao and Wang, (2014)
285	isorhamnetin	C16H12O7	480-19–3	Me2CO	Gao and Wang, (2014)
286	kaempferol 3-O-α-L-Rhamnoside	C21H20O10	482-39-3	Me2CO	Gao and Wang, (2014)
287	gardenin D	C19H18O8	29202-00-4	Me2CO	Gao and Wang, (2014)
288	5,3′,4' -trihydroxy- 6,7,8 trimethoxy flavone	C18H16O8		Me2CO	Gao and Wang, (2014)
289	kaempferol - 3,7 -O-α-L -dirhamnoside	C27H30O14	482-38-2	Me2CO	Gao and Wang, (2014)
290	apigenin -6,8 -di -C-β-D-glucopyranoside	C27H30O17		Me2CO	Gao and Wang, (2014)
291	5-Hydroxyl-3′4′6,7-Tetramethoxyflavone	C19H18O7		EtOH	Song et al. (2011)
292	5- Hydroxyl - 3′4′ 7 - Trimethoxyflavonoid	C18H16O6		EtOH	Song et al. (2011)
293	4′, 5, 7 - Trimethoxy flavonoid	C18H16O5		EtOH	Song et al. (2011)
294	5, 8, 4-trihydroxyl-6, 7, 3-trimethoxyl-flavone	C18H16O8		EtOH	Lu et al. (2013)
295	Tricin	C17H14O7	520-32-1	EtOH	Lu et al. (2013)
296	5, 3′, 4′ - trihydroxy-6, 7, 8-trimethoxyflavone	C18H16O8		Me2CO	Han et al. (2003c)
297	5, 4' - trihydroxy-6,7, 8, 3′- trimethoxy- flavone	C19H18O8		MeOH	Wang et al. (2010)
298	quercetin	C15H10O7	117-39-5	EtOH	Lu et al. (2007)
299	nodifloretin	C16H12O7	23494-48-6		Bai N et al. (2010)
300	penduletin	C18H16O7	569-80-2		Bai N et al. (2010)
301	luteolin	C15H10O6	491-70-3		Bai N et al. (2010)
Alkaloids
302	donglingine	C15H19N3O5		Me2CO	Guo et al. (2010)
303	aurantiamide acetate	C28H30N2O4		Me2CO	Guo et al. (2010)
304	N-(2-Aminoformyl-Phenyl)-2-hydroxybenzamide-5- O-β-D-allopyranoside	C20H22N2O9		EtOH	Liu et al. (2004b)
305	2- amino-3-phenylpropyl-2-benzamido-3-phenylpropanoate	C25H26N2O3		Me2CO	Guo et al. (2010)
306	4-Acetamidobutyric acid	C6H11NO3	3025-96-5	Me2CO	Guo et al. (2010)
307	2,6-Dihydroxypurine	C5H4N4O2	69-89-6	Me2CO	Guo et al. (2010)
308	7- Hydroxy-2-(1H)-quinolinone	C9H9NO2	22246-18-0	Me2CO	Guo et al. (2010)
309	pheophytin A	C55H74N4O5	603-17-8	EtOH	Lu and Xu (2008)
310	pheophytin B	C55H72N4O6	3147-18-0	EtOH	Lu and Xu (2008)
311	Urasil	C4H4N2O2	66-22-8	EtOH	Cai et al. (2008)
Monoterpenes and sesquiterpenes
312	α-Pinene	C10H61	80-56-8	EtOH	Cai, (2009)
313	β-Pinene	C10H16	2437-95-8	EtOH	Cai, (2009)
314	cinene	C10H16	138-86-3	EtOH	Cai, (2009)
315	1,8-Cineole	C10H18O	470-82-6	EtOH	Cai, (2009)
316	p-Cymene	C10H14	99-87-6	EtOH	Cai, (2009)
317	β-Elemene	C15H24	515-13-9	EtOH	Cai, (2009)
Other Compounds
318	nonanal	C9H18O	124-19-6	EtOH	Cai, (2009)
319	decanal	C10H20O	112-31-2	EtOH	Cai, (2009)
320	palmitic acid	C16H32O2	57-10-3	EtOH	Cai, (2009)
321	inositol	C6H12O6	87-89-8	EtOH	Cai, (2009)
322	a-D-fructofuranose	C6H12O6	10489-79-9	Me2CO	Feng et al. (2008)
323	tritriacontane	C33H68	630-05-7	EtOH	Liu et al. (2004a)
324	phytol	C20H40O	150-86-7	EtOH	Liu, (2012)

FIGURE 3

The chemical structure of compounds from I. rubescens.

TABLE 3

Biological activities of bioactive compounds and extracts of I. rubescens.

Biological activities	Compounds/extracts	Types	Testing subjects	Doses/Duration	Mechanisms/Effects	References
Anticancer activity
	oridonin (1)	In vitro	Human cancer cell lines (Hep G2, COLO 205, MCF-7, and HL-60)	5–100 µM for 24 h	IC50 values against 4 tumor cells were 26.90, 5.92, 50.32, and 6.42 μM, respectively	Bai N S. et al. (2010)
	14- O-acetyl-oridonin (247)	In vitro	Human cancer cell lines (Hep G2, COLO 205, MCF-7, and HL-60)	5–100 µM for 24 h	IC50 values against 4 tumor cells were 30.96, 14.59, 56.18, 11 and 11.95 μM, respectively	Bai N S. et al. (2010)
	rosthorin (203)	In vitro	Human cancer cell lines (Hep G2, COLO 205, MCF-7, and HL-60)	5–100 µM for 24 h	IC50 values against 4 tumor cells were 27.85, 6.63, 51.52, and 10.86 μM, respectively	Bai N S. et al. (2010)
	rubescensin B (2)	In vitro	Human cancer cell lines (Hep G2, COLO 205, MCF-7, and HL-60)	5–100 µM for 24 h	IC50 values against 4 tumor cells were 32.41, 6.47, 70.79, and 9.36 μM, respectively	Bai N S. et al. (2010)
	lushanrubescens-in H (46)	In vitro	Human cancer cell lines (K562 Bcap37, BGC823, and CA)	100, 10, 1, 0.1, 0.01 mg/ml for 48 h or 72 h	IC50 values against 4 tumor cells were 3.56, 13.42, 8.91, and 8.25 μM, respectively	Han et al. (2003d)
	lasiodonin (173)	In vitro	Human cancer cell lines (K562 and Bcap37)	100, 10, 1, 0.1, 0.01 mg/ml for 48 h or 72 h	IC50 values against 2 tumor cells were 5.35 and 112.53 μM, respectively	Han et al. (2003d)
	oridonin (1)	In vitro	Human cancer cell lines (K562 Bcap37, BIU87, CA, CNE, and Hela)	100, 10, 1, 0.1, 0.01 mg/ml for 48 h or 72 h	IC50 values against 5 tumor cells were 4.37, 8.32, 55.91, 0.06, 16.50, and 28.67 μM, respectively	Han et al. (2003d)
	ponicidin (2)	In vitro	Human cancer cell lines (K562 Bcap37, BGC823, BIU87, CA, CNE, and Hela)	100, 10, 1, 0.1, 0.01 mg/ml for 48 h or 72 h	IC50 values against 7 tumor cells were 2.26, 6.76, 55.17, 13.26, 0.06, 13.26, and 11.31 μM, respectively	Han et al. (2003d)
	isodonoiol (248)	In vitro	Human cancer cell lines (K562 and Bcap37)	100, 10, 1, 0.1, 0.01 mg/ml for 48 h or 72 h	IC50 values against 2 tumor cells were 10.15 and 101.32 μM, respectively	Han et al. (2003d)
	isodonal (249)	In vitro	Human cancer cell lines (K562 Bcap37, BGC823, and CA)	100, 10, 1, 0.1, 0.01 mg/ml for 48 h or 72 h	IC50 values against 4 tumor cells were 2.29, 28.64, 79.87, and 9.04 μM, respectively	Han et al. (2003d)
	rabdosin B (250)	In vitro	Human cancer cell lines (K562 Bcap37, and BGC823)	100, 10, 1, 0.1, 0.01 mg/ml for 48 h or 72 h	IC50 values against 3 tumor cells were 4.61, 15.84, and 10.93 μM, respectively	Han et al. (2003d)
	lushanrubescen-sin J (48)	In vitro	Human cancer cell lines K562	NM	IC50 values against K562 tumor cells were 0.93 μg/ml, respectively	Han et al. (2005)
	rabdosin A (130)	In vitro	Human cancer cell lines (HL-60, SMMC-7721, A-549, MCF-7, and SW-480)	NM	IC50 values against 5 tumor cells were 2.11, 2.15, 3.53, 2.82, and 2.85 μM, respectively	Liu, (2012)
	isodocarpin (135)	In vitro	Human cancer cell lines (HL-60, SMMC-7721, A-549, MCF-7, and SW-480)	NM	IC50 values against 5 tumor cells were 3.02, 2.57, 3.76, 3.07, and 3.05 μM, respectively	Liu, (2012)
	shikokianin (153)	In vitro	Human cancer cell lines (HL-60, SMMC-7721, A-549, MCF-7, and SW-480)	NM	IC50 values against 5 tumor cells were 3.98, 2.43, 5.22, 4.64, and 4.40 μM, respectively	Liu, (2012)
	lasiodin (154)	In vitro	Human cancer cell lines (HL-60, SMMC-7721, A-549, MCF-7, and SW-480)	NM	IC50 values against 5 tumor cells were 2.72, 2.81, 2.51, 3.58, and 3.14 μM, respectively	Liu, (2012)
	Parvifoline AA (161)	In vitro	Human cancer cell lines (HL-60, SMMC-7721, A-549, MCF-7, and SW-480)	NM	IC50 values against 5 tumor cells were 10.20, 10.20, 17.31, 17.61, and 24.11 μM, respectively	Liu et al. (2012)
	jaridon 6 (200)	In vitro	Drug resistant gastric cancer cells MGC803/5-Fu	0, 8, 16, 32 μM for 24 h	Induced apoptosis and increased the apoptosis rate by up- regulating the caspase-9, caspase-3, and caspase-7, down- regulating the p-PI3K, p-Akt, and p-GSK-3β	Han, (2018)
	jaridonin (246)	In vitro	Huma esophageal cancer cell lines (EC9706, EC109, EC1)	10, 20, 40 μM for 24 h	Induced apoptosis and increased the apoptosis rate by up- regulating the p21 and Bax	Ma et al. (2013)
	IsojiangrubesinB (226)	In vitro	Human cancer cell lines (HL-60, A-549, SMMC-7721, MCF-7, and SW-480)	0.064, 0.32, 1.6, 8, and 40 μM for 48 h	IC50 values against 5 tumor cells were 1.2, 5.3, 3.0, 2.9, and 0.8 μM, respectively	Zhang L et al. (2017)
	Isojiangrubesin C (227)	In vitro	Human cancer cell lines (HL-60, SMMC-7721, MCF-7, and SW-480)	0.064, 0.32, 1.6, 8, and 40 μM for 48 h	IC50 values against 4 tumor cells were 3.4, 8.6, 4.1, and 2.1 μM, respectively	Zhang Y et al. (2017)
	IsojiangrubesinE (229)	In vitro	Human cancer cell lines (HL-60, A-549, SMMC-7721, MCF-7, and SW-480)	0.064, 0.32, 1.6, 8, and 40 μM for 48 h	IC50 values against 5 tumor cells were 1.0, 5.8, 3.2, 3.4, and 1.9 μM, respectively	Zhang L et al. (2017)
	effusanin A (251)	In vitro	Human cancer cell lines (HL-60, A-549, SMMC-7721, MCF-7, and SW-480)	0.064, 0.32, 1.6, 8, and 40 μM for 48 h	IC50 values against 5 tumor cells were 1.8, 6.5, 3.2, 3.4, and 0.6 μM, respectively	Zhang Y et al. (2017)
	longikaurin A (252)	In vitro	Human cancer cell lines (HL-60, A-549, SMMC-7721, MCF-7, and SW-480)	0.064, 0.32, 1.6, 8, and 40 μM for 48 h	IC50 values against 5 tumor cells were 0.7, 2.9, 1.2, 2.7, and 0.5 μM, respectively	Zhang L et al. (2017)
	xerophinoid B (253)	In vitro	Human cancer cell lines (HL-60, MCF-7, and SW-480)	0.064, 0.32, 1.6, 8, and 40 μM for 48 h	IC50 values against 3 tumor cells were 3.6, 4.5, and 2.3 μM, respectively	Zhang Y et al. (2017)
	rabdoternin F (152)	In vitro	Human cancer cell lines (HL-60, and SW-480)	0.064, 0.32, 1.6, 8, and 40 μM for 48 h	IC50 values against 2 tumor cells were 3.2 and 2.3 μM, respectively	Zhang L et al. (2017)
	rabdoternin E (234)	In vitro	Human cancer cell lines (HL-60, and SW-480)	0.064, 0.32, 1.6, 8, and 40 μM for 48 h	IC50 values against 2 tumor cells were 2.7, and 3.0 μM, respectively	Zhang Y et al. (2017)
	Lasiodonin- acetonide (175)	In vitro	Human cancer cell lines (HL-60, SMMC-7721, MCF-7, and SW-480)	0.064, 0.32, 1.6, 8, and 40 μM for 48 h	IC50 values against 4 tumor cells were 0.9, 3.8, 2.9, and 0.9 μM, respectively	Zhang L et al. (2017)
	7,14-O-(1-met-hylethylidene) oridonin (254)	In vitro	Human cancer cell lines (HL-60, A-549, SMMC-7721, MCF-7, and SW-480)	0.064, 0.32, 1.6, 8, and 40 μM for 48 h	IC50 values against 5 tumor cells were 2.4, 3.8, 3.0, 3.9, and 1.1 μM, respectively	Zhang Y et al. (2017)
	6-epi-11-O-acetylangustifoli-n (235)	In vitro	Human lung cancer cell lines A549 and leukemia cell lines K562	NM	IC50 values against 2 tumor cells were 15.81 and 1.93 μM, respectively	Luo et al. (2017)
	11-O-acetylan-gustifolin (236)	In vitro	Human lung cancer cell lines A549 and leukemia cell lines K562	NM	IC50 values against 2 tumor cells were 9.89 and 0.59 μM, respectively	Luo et al. (2017)
Antibacterial activity
	oridonin (1)	In vitro	Methicillin-resistant Staphylococcus aureus (MRSA) strain USA300	0, 8, 16, 32, 64, and 128 μg/ml	The MIC was 64 μg/ml, and the MBC value was 512 μg/ml	Yuan et al. (2019)
	oridonin (1)	In vitro	C.albicans strains (CA2489, CA3208, CA10, and CA136)	0, 8, 16, and 32 μg/ml	Promote the sensitization to azoles for azoles-resistant C. albicans by affect the expression level of efflux-related genes, inhibits drug efflux, and induces apoptosis of C. albicans after entering cells	Chen et al. (2020)
Anti-inflammatory activity
	3β-hydroxy-6β-methoxy-6,7-seco-6,20-epoxy-1α,7-olide-ent-kaur-16-en-15-one (255)	In vitro	LPS-induced RAW 264.7 cells	NW	Inhibited NO production with IC50 values of 3.97 μM	Wen et al. (2019)
	enmein (131)	In vitro	LPS-induced RAW 264.7 cells	NW	Displayed NO production inhibitory effects with IC50 values of 17.43 μM	Wen et al. (2019)
	rabdosin A (130)	In vitro	LPS-induced RAW 264.7 cells	NW	Exhibited NO production inhibitory effects with IC50 values of 2.25 μM	Wen et al. (2019)
	epinodosin (129)	In vitro	LPS-induced RAW 264.7 cells	NW	Displayed NO production inhibitory effects with IC50 values of 18.25 μM	Wen et al. (2019)
	oridonin (1)	In vitro	LPS-induced RAW 264.7 cells	NW	Inhibited NO production with IC50 values of 6.51 μM	Wen et al. (2019)
	hubeirubesin I (111)	In vitro	LPS-induced RAW 264.7 cells	NW	Inhibited NO production with IC50 values of 1.48 μM	Wen et al. (2019)
	lasiokaurin (174)	In vitro	LPS-induced RAW 264.7 cells	NW	Inhibited NO production with IC50 values of 1.36 μM	Wen et al. (2019)
	pedalitin (270)	In vitro	LPS-induced RAW 264.7 cells	20, 40, 60, 80, and 100 μg/ml	Modestly active for inhibiting NO production in macrophage	Bai N et al. (2010)
	oridonin (1)	In vivo	Insulin resistance by fed a high-fat diet in mice	10 mg/kg/d	Reduced the levels of TNF-α, IL-6, IL-1β and MCP-1	Li et al. (2017)
	AEIRL	In vivo	Xylene induced mouse	0.32 g/kg	Effectively inhibit the inflammation and the pain of the treated mice, respectively	Tang et al. (2011)
Antioxidant activity
	oridonin (1)	In vitro	H2O2-mediated formation of ROS HaCaT cells	1–20 µM for 24 h	Protect keratinocytes against H2O2-induced apoptosis of 1–5 µM	Bae et al. (2014)
	AEAIR	In vitro	DPPH and ABTS radical	NW	Exhibited the scavenging activities against DPPH and ABTS radical, and the EC50 was 1.63 and 9.02 mg/ml, respectively	Feng and Xu, (2014)
	EPIRAPEE	In vitro	DPPH and hydroxyl radicals	800 μg/ml	The scavenging rates of DPPH free radicals and hydroxyl free radicals were 94.30% and 89.46% respectively	Jiu et al. (2018)
Anti-cardiovascular activity
	oridonin (1)	In vivo	Myocardial ischemia reperfusion rats	10 mg/kg for 7 d	Significantly decreased infarct size and reversed the abnormal elevated myocardial zymogram in serum	Zhang J. H et al. (2019)
	TFAIR	In vivo	BIT model mice	75 mg/kg, 150 mg/kg, 300 mg/kg for 5 days	Decrease the mortality and NSE level, increase the content of NO and the activity of NOS, and improve the pathological damage of cortex and hippocampus of mice	Kang et al. (2017)
Diarrhea treatment activity
	oridonin (1)	In vitro	ΔF508-CFTR cells	10–100 µM	IC50 = 46.8 µM	Luan et al. (2015)
Hypoglycemic activity
	AEIR	In vitro	HUVECs treated with high glucose	0.06 g/L, 0.13 g/L, 0.25 g/L, 0.50 g/L, and 1.00 g/L	Significant differences with that of the model group. 0.13 g/L-1.00 g/L had higher cell viability (101.37%–114.18%) than that of the positive control (102.49%)	Jintao et al. (2020)
Inhibit liver fibrosis activity
	EPIRWPEE	In vivo	CCl4-induced injury of chronic liver injury model mice	0.08, 0.04, and 0.02 g/(10 g·d)	Reduced the content of ALT, AST, TP, ALB, MDA, and increased SOD activity	Yao et al. (2010)
	oridonin (1)	In vivo	CCl4-induced injury of chronic liver injury model mice	5 mg/kg for 6 weeks	Down-regulated the levels of ALT and α-SMA	Liu et al. (2020)
Anti-Alzheimer’s activity
	oridonin (1)	In vivo	APP/PS1-21 mice	20 mg/kg for 10 days	Reduced the autophagosome formation and synaptic loss and improved cognitive dysfunction in MHE rats	Zhang et al. (2013)
	oridonin (1)	In vivo	Aβ1-42-induced AD mice	10 mg/kg for 15 days	Significant neuroprotective effects associated with the activation of the BDNF/TrkB/CREB signaling pathway	Wang et al. (2016)
Immunomodulatory activity
	RPPSIIa	In vitro	Con A-induced T lymphocyte	5, 10, 50, and 100 μg/m L	At a dose of 5 and 50 μg/ml, effectively enhance the lymphocyte proliferation response induced by Con A	Liu et al. (2011)
	oridonin (1)	In vivo	1 day-old male broiler chicken	50, 80, and 100 mg/kg	Reduced the release and the mRNA expression of IL-2, IL-4, IL-6, IL-10, and TNF-α in the spleen	Wu et al. (2018)
Antidepressant activity
	oridonin (1)	In vivo	mice	2.5, 9, and 12.5 mg/kg/d	Increased PPAR-γ protein expression and subsequent GluA1 (Ser845) phosphorylation and GluA1 levels	Liu and Du. (2020)

Note: NM, not mentioned; AEIRL, aqueous extract of I. rubescens leaves; AEAIR, acetone extract from the aerial part of I. rubescens; EPIRAPEE, Ethyl acetate part form the I. rubescens aerial part ethanol extract; TFAIR, Total flavonoid from the aerial part of I. rubescens; AEIR, aqueous extract of I. rubescens; EPIRWPEE, Ethyl acetate part form the I. rubescens whole plant ethanol extract; RPPSIIa, Rhamnose: Glucose = 7:93.

Diterpenoids

Diterpenoids are the main compounds identified from I. rubescens, and 255 diterpenoids have been isolated and identified from the whole plant of I. rubescens. Enantio-kaurikane diterpenes are the most diverse type of terrestrial plant diterpenes with the most diverse molecular structures and biological activities among natural products. Recent studies have shown that some members of this family have antibacterial and antitumor activities. The structural feature of the enantiomer-kauritan type is that the rings A and B share two carbon atoms at positions 5 and 10, forming a bridged ring (Li et al., 2019). Such tetracyclic diterpene molecules can be transformed into complex molecular skeletons through intramolecular cyclization, oxidative cleavage and degradation rearrangement. Therefore, more than 1,500 natural enantiomer-kauritan diterpenoids have been isolated and identified. Among these enantiomer-kauritan diterpenoids, 7, 20-epoxy enantiomer kaureane diterpene has the largest number of isolated compounds and the best activity. The most widely studied enantiomer-kauritan diterpenoid is oridonin (1), and it has been reported that it has an inhibitory effect on a variety of tumor cells including liver cancer, laryngeal cancer, esophageal cancer, colon cancer, gastric cancer, breast cancer, leukemia, pancreatic cancer and other cancers. Oridonin also has anti-dementia, antidepressant, antibacterial and antiviral activities (Ding et al., 2016; Pi et al., 2017; Yang et al., 2018; Zhang D. et al., 2019). Among these bioactive constituents, oridonin (1), ponicidin (2), lushanrubescensin H (46), lushanrubescensin J (48), rabdosin A (130), isodocarpin (135), rabdoternin F (152), shikokianin (153), lasiodin (154), parvifoline AA (161), lasiodonin (173), lasiodoninacetonide (175), rosthorin (203), isojiangrubesin C (227), isojiangrubesin E (229), rabdoternin E (234), 11-O-acetylangustifolin (236), jaridonin (246), 14-O-acetyl-oridonin (247), isodonoiol (248), isodonal (249), rabdosin B (250), effusanin A (251), xerophinoid B (253), and 7,14-O-(1-methylethylidene) oridonin (254), are best known for their antitumor, antioxidant, anti-inflammatory, antibacterial, anti-cardiovascular, anti-dementia, and immune regulatory activities. The components of diterpenes and their derivatives are shown in Table 2, and their structures are shown in Figure 3.

Triterpenes

Triterpenes and their derivatives are well-known in the research of natural phytochemistry for their excellent antitumor activity. Before 2009, 11 triterpenoids (256–266), including ursolic acid (256), oleanic acid (257), β-sitosterol (258), α-amyrin (259), daucosterol (260), betulin (261), eryihrodiol (263), and stigmasterol (265), were isolated and identified from I. rubescens. Among these triterpenoids, ursolic acid is a common triterpenoid compound that exists in natural plants. It has sedative, anti-inflammatory, antibacterial, anti-diabetic, anti-ulcer, blood sugar lowering, and other pharmacological activities and can be used as medicine or emulsifier (Cai, 2009). However, few studies have been recently reported on the biological activities of other triterpenoids.

Phenols

Phenols are important secondary metabolites in nature with a wide range of pharmaceutical activities, such as antioxidant, anti-inflammatory, antibacterial, and antiviral activities. At present, 35 phenolic compounds (267–301) have been separated from the whole plant of I. rubescens and structurally characterized. Salicylic acid (267) is an important raw material for aspirin, salicylamide and other drugs, and can also be used as a disinfectant. Caffeic acid (268), danshensu (271), ferulic acid (276), and other compounds with catechol structure have strong antibacterial, antiviral, antioxidant, and anti-cardiovascular biological activities.

Flavonoids are an important component of phenols. The flavonoid structure is characterized by two benzene rings (A and B-rings) with phenolic hydroxyl groups connected with each other through the central three carbon atoms, with 2-phenylchromone as the basic nucleus. Biologically important secondary metabolites have attracted wide attention due to their extensive pharmacological activities. Up to date, 24 flavonoids (278–301) have been isolated and identified from the whole plant of I. rubescens. Some of these flavonoids form flavonoid glycosides with the hydroxyl groups of monosaccharides or disaccharides at positions 3, 5, 6 and 7 through O-glycosidic bonds. Compounds (282–284, 286, and 289–290) are flavonoids and compounds (278–281, 285, 287–288, and 291–301) are flavonoid glycosides. Among these flavonoid glycosides, 5, 8, 4′-trihydroxyl-6, 7, 3′-trimethoxyl-flavone (294) and pedalitin (279) are modestly active in the inhibition of the nitrite production in macrophages, and 5, 4′- trihydroxy-6, 7, 8, 3′ trimethoxyflavone (297) was demonstrated to be selectively active against HL-60 cells with an IC50 value of 7.55 μM (Bai N. et al., 2010). Phenols are also an important material basis for the antioxidant effect of I. rubescens. A focus of future research should be on the phenols of I. rubescens and the promotion of their development for cosmetics, functional foods and medicine.

Alkaloids

Approximately nine alkaloids (302–311) have been isolated from the whole plant of I. rubescens (Guo et al., 2010). However, the pharmacological activity of most of these alkaloids is still unclear.

Essential Oil and Other Compounds

The stalks and leaves of I. rubescens also contain a series of essential oils. These volatile oils are mainly divided into monoterpenes and sesquiterpene compounds such as α-pinene (312), β-pinene (313), cinene (314), 1,8-cineole (315), p-cymene (316), and β-elemene (317) (Cai, 2009). In addition, fatty compounds (318–320, 323–324) have also been identified from the essential oil of I. rubescens by GC-MS. Moreover, inositol (321) and α-D-fructofuranose (322) have also been identified from I. rubescens (Cai, 2009).

Pharmacological Activities

The crude extracts and several compounds isolated from I. rubescens have been evaluated for their antitumor, antioxidant, anti-inflammatory, antibacterial, anti-dementia, and immune regulatory effects as well as their abilities in the prevention and treatment of cardiovascular and cerebrovascular diseases. Among these effects, the antitumor, antibacterial and anti-inflammatory activities of diterpenoids are the most important and also the most studied effects. Modern pharmacological studies are discussed below, and the main active ingredients are summarized in Table 3. In addition, the main molecular mechanism of the biological activity of I. rubescens is shown in Figure 4.

FIGURE 4

Graphical summary of pharmacological properties of I. rubescens.

Antitumor Activity

In several published papers, aqueous and alcoholic extracts of I. rubescens have shown inhibitory activity against a variety of cancer cells, including esophageal, gastric, liver, bladder pain, pancreatic, intestinal, and breast cancers (Ding et al., 2016). The most widely studied and important anticancer active compound in I. rubescens is oridonin (1), whose pharmacological activity has been proven to have significant cytotoxicity against various cancers such as liver, larynx, colon, pancreatic, breast, leukemia, lung, stomach, ovarian and bladder cancers (Ding et al., 2016; Jiang et al., 2017). The compound 14-O-acetyl-oridonin (247) showed a significant influence on the viability of the human cancer cell lines (HepG2, COLO 205, MCF-7, and HL-60), with IC50 values of 30.96, 14.59, 56.18, and 11.95 μM, respectively. Rosthorin (203) exhibited a better activity than 14-O-acetyl-oridonin under the same conditions, with IC50 values of 27.85, 6.63, 51.52, and 10.86 μM, respectively (Bai N. S. et al., 2010). Lushanrubescensin H (46) has significant anti-proliferative activity against tumor cell lines (K562, Bcap37, BGC823, and CA) at the concentrations of 100, 10, 1, 0.1, and 0.01 mg/ml after incubation for 48 or 72 h, and the corresponding IC50 values were 3.56, 13.42, 8.91, and 8.25 μM, respectively (Feng et al., 2008). Lushanrubescensin J (48) is a novel asymmetric ent-kauranoid dimer, which exhibited potent inhibitory activity against K562 cells with IC50 is 0.93 μg/ml (Han et al., 2005). In 2012, Liu et al. conducted a large number of phytochemical studies on I. rubescens and isolated 47 new diterpenoids. Pharmacological studies have shown that rabdosin A (130), isodocarpin (135), shikokianin (153), and lasiodin (154) showed in vitro cytotoxic activity against five species HL-60, SMMC-7721, A-549, MCF-7, and SW-480, which was equal to or stronger than that of the positive drug cisplatin. The structure-activity relationship confirms that unsaturated cyclopentanone is the active center responsible for the cytotoxic activity of enantio-kauri diterpene. The structure of kaurine A (87) is identical to that of oridonin (1) exhibiting unsaturated cyclopentanone fragments, but the nitrogen of kaurinea is replaced with oxygen in oridonin, which results in a greatly different activity. We speculate that the acid pKa value of the imine conjugate is around 9, which leads to cell culture conditions around pH 7, where only about one percent of the unprotonated molecules can cross the membrane and enter the interior of the cell, such as other enantiotopic kauri diterpenes, which do not contain nitrogen (Liu, 2012). The drug resistance caused by chemotherapy during the treatment of malignant tumors has an important effect on the efficacy and prognosis of tumor patients. Jaridon 6 (200) is a novel diterpenoid isolated from I. rubescens, which can promote the early apoptosis of MGC803/5-FU cells. At the same time, it inhibited the proliferation of MGC-803 cells in a dose and time-dependent manner by blocking the G0/G1 phase. It decreased the protein expression levels of p-PI3K, p-AKT and p-GSK-3β in MGC803/5-Fu cells, increased the expression of cleaved caspase-9, cleaved caspase-3, and cleaved caspase-7 cleaved PARP-1 protein activated the intracellular caspase pathway and promoted apoptosis (Han, 2018). Jaridonin (246) exhibited strong anti-proliferative and pro-apoptotic effects in human EC cell lines by the activation of the mitochondria mediated apoptotic pathway, induction of G2/M arrest, as well as increased expression of p53 and p21 (Ma et al., 2013). Similarly, isojiangrubesin B (226), isojiangrubesin E (229), effusanin A (251), and 7, 14-O-(1-methylethylidene) oridonin (254) exhibited a significant inhibitory ability against all cell lines (HL-60, A-549, SMMC-7721, MCF-7, and SW-480), with IC50 values ranging from 0.5 to 6.5 μM. Their cytotoxic activity was better than that of cisplatin, but worse than that of paclitaxel (Zhang L. et al., 2017). These reported antitumor activities are consistent with the traditional usage such as the treatment of liver cancer, esophageal cancer, cardia cancer, lung cancer, prostate cancer, bladder cancer, colon cancer, breast cancer, cervical cancer, and gastric cancer. The pharmacological studies of the inhibition of tumor cells of esophageal cancer and oral cancer by I. rubescens also confirmed the traditional application of I. rubescens in the treatment of sore throat, tonsillitis, pharyngitis and stomatitis. Therefore, I. rubescens tea can be consumed as a daily health drink by patients with pharyngitis.

In short, I. rubescens has significant antitumor activity and good health and medical effects on humans. However, it is worth noting that most of the research on its antitumor activity is still in its infancy, and the use of in vitro methods, further in-vivo and mechanism of action investigations and clinical research should therefore be encouraged and strengthened. Among the compounds isolated from I. rubescens, diterpenoids showed excellent antitumor activity in vitro, but the specific mechanism of action is not well understood yet, and further studies on the mechanism of action are needed in the later stage. The antitumor activity of other compounds, such as flavonoids and triterpenoids, needed to be urgently enhanced.

Antibacterial Activity

Ethanol extract of I. rubescens has an obvious antibacterial effect on Staphylococcus aureus and Streptococcus A hemolyticus. The minimum effective concentration was in the range of 1:128–1:256. The effect of the ethanol extract of I. rubescens on Escherichia coli was very weak, and the inhibitory effect of the water extract of I. rubescens on Staphylococcus aureus and Escherichia coli indicated that the effective antimicrobial component of I. rubescens was soluble in alcohol. Total diterpenes of I. rubescens also showed a strong inhibitory activity against Staphylococcus aureus and Staphylococcus albicans, and 80% acetone and ethanol extracts of I. rubescens had relatively higher antibacterial activities against Gram-positive strains with the lowest minimum inhibitory concentration and minimum bactericidal concentrations of 5 and 10 mg/ml, respectively (Feng and Xu, 2014). In vitro experiments showed that the extracts of I. rubescens had a certain inhibitory effect on Verticillium groundnut, and its n-butanol site had the best inhibitory activity with an inhibition rate of 94.61% and an EC50 value of 0.67 mg/ml which is the focus of antibacterial activity tracking. Extracts of I. rubescens had the best inhibitory activity against Zygomycetes of maize, wheat, tobacco, apple with EC50 values of 0.261, 0.689, 0.487, and 0.419 mg/ml, respectively. The efficacy of I. rubescens against Rhizoctonia verticillioides was studied, showing that the n-butanol part had the best control effect with an efficacy of 75.52%, and the ethyl acetate part had a better effect on powdery mildew of goldenrod with a long effect time. The possible mechanism is the inhibition of the bacterial growth by the I. rubescens extract by disrupting cell membrane permeability while disrupting the cellular metabolism (Li, 2020). The K-B method was used to screen the antibacterial active ingredients of I. rubescens, and the ethyl acetate part with the highest activity was separated by chromatography.

Several studies have demonstrated a significant inhibitory activity of the isolated compound of I. rubescens against a variety of bacterial strains. Of particular importance is the application of oridonin (1) to prevent methicillin resistance of Staphylococcus aureus (SA), Methcillin-resistant Staphylococcus aureus (MRSA), and β-lactamase-positive Staphylococcus aureus (ESBLs-SA), showing a certain antibacterial activity (MIC is 3.125, 6.25, 6.25 μg/disc) which is strong but still weaker than that of the positive control berberine (MIC is 0.156 μg/disc). Ferulic acid (276) has a certain antibacterial activity against SA and MRSA (MIC is 50 and 50 μg/disc), while salicylic acid (267) has only antibacterial activity against SA (MIC is 50 μg/disc) (Li et al., 2014). The MIC and MBC values of oridonin (1) against the MRSA strain USA300 were 64 and 512 μg/ml, respectively, and the mechanism underlying the antibacterial activity was related to changes in the cell membrane and cell wall permeability, disturbance in the protein and DNA metabolism, and influence on the bacterial morphology (Yuan et al., 2019). In addition, the combination of oridonin (1) and azoles has a synergistic effect on drug-resistant Candida albicans. The mechanism of reversing FLC resistance comprises changes of the expression level of efflux-related genes, inhibition of drug efflux, and induction of apoptosis upon entry of Candida albicans into cells (Chen et al., 2020). The results suggest its potential to provide new leads for the development of highly antimicrobial drugs, which are a source of new lead compounds for the development of novel antimicrobial agents.

Cholera is an acute diarrheal infectious disease caused by the contamination of ingested food or water with Vibrio cholerae. Each year, there are an estimated 3–5 million cases of cholera. CFTR chloride channels are new molecular targets for the treatment of secretory diarrhea. It was shown that oridonin (1) significantly reduced the inward flow of iodine ions in wt-CFTR and F508-CFTR FRT epithelial cells in a dose-dependent manner, and also reduced cholera toxin-induced humoral secretion, making it a candidate compound for the treatment of cholera toxin-induced secretory diarrhea (Luan et al., 2015).

However, many antimicrobial studies have only provided preliminary information. The isolation of bioactivity-oriented antimicrobial compounds and their potential mechanisms of antimicrobial action need to be further investigated.

Anti-Inflammatory Activity

Studies have shown that I. rubescens shows better efficacy on some inflammatory diseases. In the xylene induced auricular edema mouse model, the aqueous extract of I. rubescens was administered orally at a dose of 0.32 g/kg, and the results showed that the anti-inflammatory activity of aspirin was significantly higher than that of the blank group, while the anti-inflammatory activity of the aqueous extract at this dose was significantly higher than that of aspirin at a dose of 30 mg/kg (Tang et al., 2011). The compounds, oridonin (1), hubeirubesin I (111), rabdosin A (130) and lasiokaurin (174) isolated from I. rubescens exhibited obvious NO production inhibitory effects with IC50 values of 6.51, 1.48, 2.25, and 1.36 μM, respectively. In the present study, 6, 7-seco-ent-kaurane diterpenoids, such as compounds 225 and 130 with an α, β-unsaturated ketone moiety, exhibited NO production inhibitory effects, indicating that the α, β-unsaturated ketone moiety is an essential pharmacophore (Wen et al., 2019). The therapeutic effect of the oral administration of oridonin (1) on acetic acid-induced ulcerative colitis in mice was reported in the literature related to the anti-inflammatory effect of oridonin. In addition, the expression levels of TNF-α, IL-1β and IL-6 mRNA in RAW 264.7 cells were significantly reduced after administration of oridonin (10 μmol/L), and Western blot assay showed significantly reduced the expression levels of TNF-α, IL-1β and IL-6 mRNA in RAW 264.7 cells. These results suggest that oridonin can down-regulate the expression of LPS-induced pro-inflammatory factors in RAW 264.7 cells, and its anti-inflammatory immune mechanism is related to the activation of the TLR4-NF-κB signaling pathway. In vivo experimental results suggest that oridonin may target the p38-MAPK and NF-κB signaling pathways to inhibit the development of inflammation and significantly reduce the clinical symptoms of kidney injury in diabetic mice, including increased urine protein, creatinine and blood urea nitrogen levels, thus protecting from diabetic nephropathy (Kang and Liu, 2019). These findings suggest that I. rubescens diterpenoids are potent inhibitors of inflammation and may be useful in the development of anti-inflammatory drugs for the treatment of various inflammation-related diseases. However, studies on the crude extracts of I. rubescens and in vivo models are very limited, and more in-depth studies on the anti-inflammatory effects as well as possible mechanistic studies are urgently needed.

Antioxidant Activity

The crude extracts of I. rubescens have a certain scavenging activity for DPPH radicals, hydroxyl radicals and superoxide anion radicals. Studies showed that the scavenging rate of ethyl acetate extract was better than those of petroleum ether, chloroform and n-butanol extracts for DPPH radicals, hydroxyl radicals and superoxide anion radicals. At a mass concentration of 800 μg/ml, the ethyl acetate extraction site showed better scavenging of DPPH radicals, hydroxyl radicals and superoxide anion radicals of 94.30%, 89.46%, and 87.47% respectively. At the same mass concentration, the scavenging rates of DPPH radicals, hydroxyl radicals and superoxide anion radicals were 72.89%, 71.99%, and 50.60% for the n-butanol extraction site, but only 84.47%, 65.21%, and 20.37% for petroleum ether extraction site, respectively, while the scavenging rates of DPPH radical, hydroxyl radical and superoxide anion radical for the chloroform extraction site were only 62.47%, 63.03%, and 46.31%, respectively. The scavenging rates of DPPH radical, hydroxyl radical and superoxide anion radical by chloroform extraction site were only 62.47%, 63.03%, and 46.31%, respectively. The IC50 values of the ethyl acetate extraction site for DPPH radicals, hydroxyl radicals and superoxide anion radicals was significantly lower than those of the petroleum ether, chloroform and n-butanol extraction sites, but slightly higher than those of VC on DPPH radicals and hydroxyl radicals. The active ingredients of the ethyl acetate extract of I. rubescens were mostly identified by GC-MS as polyphenols, ketones and organic acids, among which the percentage of polyphenols reached 39.15%, which was consistent with the antioxidant activity (Jiu et al., 2018). In 2014, Feng et al. found that the 80% acetone extracts had the highest content of total polyphenols (equivalent to 8.09 mg GAE/g) and flavonoids (equivalent to 5.69 mg RE/g) and the strongest antioxidant activities, followed by those of 80% methanol and 80% ethanol, and finally hexane extracts (Feng and Xu, 2014). Determination of the total phenolic and flavonoid contents revealed that the ethanol extract of I. rubescens was equivalent to 8.40 mg GAE/g and 9.51 mg QE/g of dry weight, and the radical scavenging activities of the ethanol extracts were evaluated based on DPPHC and ABTSC+ radicals. The free radical scavenging capacities of the ethanol extracts were 198.90 and 303.74 μM, respectively, equivalent to the amount of ascorbic acid. Phenolic and total flavonoid contents are important factors that determine the antioxidant activity of the extracts which lays the foundation for the development and utilization of antioxidant products of I. rubescens (Zhang Y. et al., 2017). In addition, oridonin isolated from I. rubescens has antioxidant properties and protects human keratin-forming cells from hydrogen peroxide-induced oxidative stress. Low doses of oridonin (1–5 µM) protected keratin-forming cells from hydrogen peroxide-induced apoptosis in a concentration and time-dependent manner and significantly reduced the production of H2O2-induced reactive oxygen species in cells (Bae et al., 2014).

Natural antioxidants have attracted much attention because of their high efficiency and low toxicity. It has become an inevitable trend in the development of modern medicine and health care industries to find new antioxidants from natural products that can remove free radicals in the body. Numerous antioxidant experiments have confirmed that I. rubescens has the potential to become a natural antioxidant. It can eliminate free radicals or inhibit the activity of free radicals, thereby helping the body maintain sufficient antioxidant status.

Hypoglycemic Activity

In 2020, Xue et al. found that ethanolic and aqueous extracts (0.06–1.00 g/L) of I. rubescens could increase the activity of DMEM-treated human umbilical vein endothelial cells (HUVECs). Treatment with the aqueous extract (0.13–1.00 g/L) resulted in a higher cell viability (101.37%–114.18%) than the positive control (102.49%), while the cell viability of the positive control was higher than that of cells treated with alcohol extracts (90.07%–103.44%). Furthermore, the ethanol extract did not reduce fasting blood glucose in diabetic rats. The results of cell and animal experiments showed that the main hypoglycemic components of I. rubescens are hydrophilic substances (polar components), while alcohol-soluble substances I. rubescens (non-polar components) have no significant hypoglycemic effect. Based on network pharmacology screening, 25 hypoglycemic components of I. rubescens, such as rabdoternin A (148), rabdoternin B (149), and epinodosinol (137), were identified. These components activate six hypoglycemic targets, including 3-hydroxy-3-methyl glutaraldehyde coenzyme A reductase (HMGCR), integrin α-L (ITGAL), integrin β-2 (ITGB2), progesterone receptor (PGR), glucocorticoid receptor (NR3C1) and nuclear receptor subfamily 1I member 2 (NR1I2). These targets are involved in 94 signaling pathways, such as Rap1, PI3K-Akt and HIF-1 signaling pathways (Jintao et al., 2020).

Hepatoprotective Activity

The Global Hepatitis Report 2017, published by the World Health Organization, shows that approximately 325 million people worldwide were infected with chronic hepatitis B virus or hepatitis C virus in 2017. Moreover, 80% of liver cancers are caused by hepatitis B. Chronic hepatitis is the prevalent disease in China, usually caused by liver injury, which evolves into liver fibrosis and eventually leads to cirrhosis and liver cancer. Therefore, the prevention and treatment of liver injury and liver fibrosis receive much research attention. In 2010, Yao et al. found that I. rubescens extract had a protective effect against carbon tetrachloride-induced chronic liver injury and early hepatic fibrosis in mice. It significantly reduced the levels of serum alanine aminotransferase (ALT) and glutathione aminotransferase (AST), decreased the levels of total protein (TP), albumin (ALB), and malondialdehyde (MDA), increased the activity of superoxide dismutase (SOD), reduced the degree of liver tissue degeneration and necrosis, and alleviated the pathological changes of liver tissue (Yao et al., 2010). In 2019, Liu et al. discovered that oridonin (1) can reduce ALT levels in model mice and the expression of α-smooth muscle actin (α-SMA) in the liver of mice with fibrosis. It also reduced the expression of NLRP3, caspase-1, and IL-1β and the infiltration of inflammatory cells. Therefore, oridonin (1) is a potential drug for the treatment of liver fibrosis (Liu et al., 2020). Overall, the findings of these studies lay a research direction that points to prospective therapeutic efficacy of I. rubescens against hepatitis.

Cardiovascular Protective Activity

Cardiovascular disease is a common disease that seriously threatens human health and is characterized by a high prevalence, disability rate, and mortality rate. Cardiovascular diseases kill up to 15 million people worldwide each year, ranking first among all causes of death. In 2017, Kang et al. demonstrated that total flavonoids of I. rubescens can stimulate endogenous protective mechanisms and induce the release of low levels of the cytokines NO and NOS, thereby reducing the release of serum NSE, alleviating ischemia-reperfusion injury in brain tissue and further improving the protective effect of ischemic preconditioning on brain injury (Kang et al., 2017). Moreover, oridonin (1) ameliorated the abnormal elevation of ECG ST segment caused by myocardial ischemia-reperfusion injury. Furthermore, the myocardial infarct area was significantly reduced and serum CK-MB levels were decreased. Oridonin (1) exerted significant cardioprotective effects by regulating energy and amino acid metabolism. Research on the composition and mechanism of action of other components of I. rubescens for cardiovascular protection should be enhanced.

Anti-Alzheimer’s and Antidepressant Activity

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by β-amyloid aggregation, tau protein hyperphosphorylation, and neuroinflammation. In 2013, Zhang et al. found that oridonin significantly attenuated β-amyloid deposition, plaque-associated APP expression and microglial activation in the brain of transgenic mice, and additional in vitro studies indicated that oridonin effectively attenuated the inflammatory reaction of macrophages and microglial cell lines (Zhang et al., 2013). In 2014, Wang et al. found that oridonin could inhibit the mRNA levels of IL-1β, IL-6, COX-2, iNOS, TNF-a, and MCP-1 induced by Aβ, which also up-regulated the expression of IL-10 in Aβ1-42-induced AD mice (Wang et al., 2014). Oridonin (1) was also found to rescue Aβ1-42-induced synaptic loss, increase the expression of PSD-95 and synaptophysin in the synaptosomes of AD mice, and promote mitochondrial activity. In addition, oridonin also activated the BDNF/TrkB/CREB signaling pathway in the hippocampus of AD mice and improved the behavioral symptoms of AD mice (Wang et al., 2016). In summary, oridonin is a candidate compound with anti-Alzheimer’s activity. Recently, oridonin was reported to regulate the PPAR-γ/AMPA receptor signaling pathway in the prefrontal cortex and identified as a novel antidepressant with clinical potential (Liu et al., 2020).

Immunomodulatory Activity

In 2011, Liu et al. isolated the polysaccharide fraction RPPSIIa from I. rubescens, analyzed its structural properties and explored its immunological activity. Structure analysis revealed that the polysaccharide RPPSIIa is a homogeneous compound composed of the monosaccharides rhamnose and glucose in the ratio of 7: 93. It can effectively stimulate the proliferation of mouse spleen lymphocytes in a concentration range of 5–100 μg/ml. Moreover, RPPSIIa at the concentrations of 5 and 50 μg/ml can effectively enhance lymphocyte proliferation induced by Con A (Liu et al., 2011). Moreover, oridonin also inhibits the transcriptional activation of the BAFF promoter in macrophages by significantly suppressing BAFF expression and secretion in macrophages. Lupus symptoms and tissue damage in MRL-lpr/lpr mice were effectively reduced by inhibiting BAFF (Zhou et al., 2013).

Quality Control

In the past decades, different methods including TLC, HPLC, UPLC, and UV have been used to analyze the chemical constituents of and control the quality of derivatives isolated from I. rubescens. In 2007, Zou et al. established a reversed-phase high performance liquid chromatography (RP-HPLC) method to determine the content of ursolic acid and oleanolic acid in I. rubescens by using the chromatographic column NUCLEO-DURC18RP (250 × 4.6 mm, 5 μm), a methanol-water mobile phase (87: 13), a flow rate of 0.8 ml/min, and a photodiode array detector (detection wavelength: 210 nm; column temperature: 25°C). The sample recovery rates of ursolic acid and oleanolic acid were 96.2% and 98.7%, and the RSD were 1.9% and 0.9%, respectively (Zou and Chen, 2007). In the 2020 edition of the Chinese Pharmacopoeia, only oridonin was used as the standard for the evaluation of the I. rubescens quality in the pharmaceutical market. According to this source, chromatography was performed using octadecylsilane bonded silica gel as filler and methanol-water (55: 45) as the mobile phase, and the detection wavelength was 239 nm. HPLC analysis of oridonin in the dried aboveground parts of I. rubescens revealed a content of more than 0.25% (Chinese Pharmacopoeia, 2020). In fact, diterpenoids especially oridonin (1) and ponicidin (2), are considered to be the main active ingredients of I. rubescens. Therefore, ponicidin (2) should be also used as quality control marker for I. rubescens and its medicinal extracts.

Due to different cultivation areas and climatic conditions, significant differences in the chemical compositions of Chinese herbal medicines may be found, and the interactions of multiple chemical compounds may contribute to the therapeutic effects of Chinese medicine. Therefore, a simple quantitative analysis of one or two active ingredients in herbal medicines cannot represent their overall quality, and the simultaneous quantitative analysis of active ingredients has become the most direct and important method for the quality of drugs control of TCM. Thus, it is necessary to establish standards for controlling the quality because of the need for its clinical application. In 2011, Zhang et al. established an ultra-high performance liquid chromatography (UPLC) method for the simultaneous determination of the contents of the five main active ingredients in I. rubescens by using a Waters UPLC chromatographic system, an ACQUITY BEH Shield PR18 column (2.1 × 100 mm, 1.7 μm), a mobile phase of 0.1% formic acid methanol solution (A)-0.1% formic acid aqueous solution (B) with a flow rate of 0.2 ml/min (detection wavelengths: 250 and 210 nm; column temperature: 23°C). The chromatographic analysis of the five components of oridonin, ponicidin, rosmarinic acid, oleanolic acid and ursolic acid could be completed within 22 min, the chromatographic peak of each component had a good resolution, and all calibration curves showed good linearity (r2 > 0.9991) in the test ranges (Zhang et al., 2011). In 2013, Yuan et al. established an HPLC method for the simultaneous determination of rosmarinic acid, oridonin and chrysoplenetin in I. rubescens. With this method, phenolic acids, diterpenes and flavonoids can be simultaneously determined to obtain more comprehensive information about the intrinsic quality of I. rubescens (Yuan et al., 2013).

I. rubescens has complex components, some of which are low in content, and most diterpenes have weak or no UV absorption. It is particularly difficult to use conventional quality control methods for TCM such as HPLC, UPLC, UV, and TLC for the simultaneous determination of to determine more active ingredients. HPLC-MS/MS provides a good alternative for routine analysis due to its rapidness, sensitivity and specificity, and can be used as a reliable method for the quality evaluation of I. rubescens. In 2010, Du et al. established a new HPLC-MS/MS method for the qualitative identification and quantitative determination of 19 diterpenoids, 6 phenolic acids, and 3 flavonoids in I. rubescens (Du et al., 2010). The separation was carried out on a C18 column with a linear gradient of 0.1% formic acid/methanol containing 0.1% formic acid at a flow rate of 0.7 ml/min. This method has been successfully applied to the qualitative and quantitative analysis of 28 chemical components in natural and planted I. rubescens samples from different sources, providing strong support for the quality control of I. rubescens. Although the commonly used method for the determination of the content of I. rubescens is HPLC, considering the multiple components and efficacy of TCM, new determination methods should be studied and developed.

Toxicity

Information on the side effects and safety evaluations of I. rubescens and its active ingredients is limited, and no major side effects have yet been discovered. The 2020 edition of the Chinese Pharmacopoeia recommends an exact dose of 30–60 g per day of I. rubescens (China Pharmacopoeia, 2020). In 2000, the chronic toxicity of I. rubescens tablets was measured by the intragastric administration of SD mice with a dose of 20 or 40 g/kg/day for 21 days, the results showed that the long-term administration of I. rubescens tablets had no toxic side effects on the organism (Hu et al., 2000). In 2011, Hu et al. observed the acute toxicity of the active parts of I. rubescens, and the mass fraction of oronidin in I. rubescens extract determined by HPLC was 62.4%. The maximum tolerated dose (MTD) of the effective parts of I. rubescens was 20 g/kg/d, which is 480 times the dose commonly used in human clinical administration, suggesting that the effective parts of I. rubescens had no toxicity in mice (Hu et al., 2011). In another safety evaluation experiment, the results of the acute oral toxicity test showed that the MTD of a concentrated solution of I. rubescens was greater than 20.3 g/kg/bw in Kunming mice of both sexes. The genetic toxic effects of different I. rubescens concentrations were verified in the three genetic toxicity tests of micronucleus test, sperm malformation test and Ames test of the cells, in vivo and in vitro in three aspects, revealing negative results. The 90 days feeding test showed that I. rubescens powder had no obvious toxic and side effects on the observed indexes of rats, and the maximum dose of I. rubescens powder was 5.0 g/kg/bw (Ma, 2010). In conclusion, the toxicity study of I. rubescens and its active components and traditional Chinese medicine preparations showed no toxicity, allowing for the development of I. rubescens related drugs and health food.

Conclusion and Future Perspectives

TCM is an important part of ancient medicine because of its wide range of uses, numerous types of chemical components, extensive pharmacological activity and reliable clinical effects. Moreover, it is an important source of lead compounds from numerous types of chemical components for modern drug development. In this review, we summarize the research progress in botany, ethnobotanical uses, phytochemistry, pharmacology, quality control and toxicity of I. rubescens. In ancient and modern China, I. rubescens was widely used to treat various diseases. Traditionally and ethnobotanically, I. rubescens was used for the treatment of esophageal, cardiac, liver, breast, rectal and other cancers, as well as sore throat, cold and headache, tracheitis, chronic hepatitis and snake and insect bites. To date, 324 compounds have been isolated and identified from this plant. A variety of biological activities have been reported for these components, especially their excellent and broad antitumor activity. Among these components, diterpenoids are the major bioactive component, but a large number of studies have focused on the pharmacology of enantio-kaurane type diterpenoids, such as oridonin (1) and ponicidin (2), and oridonin was touted as the second best bioactive component after paclitaxel. A variety of Chinese medicinal preparations including I. rubescens tablets and dropping pills, have been marketed, and clinical studies on the effective ingredient oridonin have also been carried out. It can be expected that further studies may reveal more enantio-kaurane type diterpenes. Based on the described pharmacological activities of I. rubescens, many studies have been conducted using different in vivo and in vitro experimental biological techniques that support most of its traditional medicinal uses. However, scientific research on I. rubescens still exhibits gaps. Therefore, we summarize several topics herein that should be prioritized for future detailed investigation.

Firstly, diterpenoids have always been considered to be the most important active compounds in I. rubescens, because of their wide variety and extensive pharmacological studies. However, research on new saponins, alkaloids and flavonoids isolated from I. rubescens is still neglected, which seriously limits the diversity of I. rubescens research and application. Secondly, current research mainly focuses on antitumor pharmacological activities, and research on other traditional applications of I. rubescens in the treatment of bronchitis, rheumatic joint pain, snake and insect bites, etc. needs to be strengthened. Thirdly, the metabolism and serum pharmacology of I. rubescens and its active components should be further studied by in vivo and in vitro methods. Fourth, the diterpenoids in I. rubescens generally have antitumor activity. Research on structure-activity relationships should be increased to find the core chemical structure of antitumor drugs, and provide effective molecules for the creation of new drugs of I. rubescens. Last but not least, similar pharmacological activities of these different components that contribute to the pharmacological activity of crude I. rubescens have been reported, but the relationship between these components including synergistic or antagonistic effects should be clarified in future studies.

In conclusion, I. rubescens is a valuable medicinal resource. However, more comprehensive studies on the pharmacodynamics, metabolism, pharmacokinetics, toxicity and side effects as well as clinical trials are required to demonstrate the efficacy and safety of extracts of active compounds of I. rubescens. We also expect to find new skeletons and new active molecules of I. rubescens.