Therapeutic Potential of Ranunculus Species (Ranunculaceae): A Literature Review on Traditional Medicinal Herbs.

The genus Ranunculus includes approximately 600 species and is distributed worldwide. To date, several researchers have investigated the chemical and biological activities of Ranunculus species, and my research team has found them to have antimalarial effects. This review is based on the available information on the traditional uses and pharmacological studies of Ranunculus species. The present paper covers online literature, particularly from 2010 to 2021, and books on the ethnopharmacology and botany of Ranunculus species. Previous studies on the biological activity of crude or purified compounds from Ranunculus species, including R. sceleratus Linn., R. japonicus Thunb., R. muricatus Linn., R. ternatus Thunb., R. arvensis Linn., R. diffusus DC., R. sardous Crantz, R. ficaria Linn., R. hyperboreus Rotlb., and R. pedatus Waldst. & Kit., have provided new insights into their activities, such as antibacterial and antiprotozoal effects as well as antioxidant, immunomodulatory, and anticarcinogenic properties. In addition, the anti-inflammatory and analgesic effects of plants used in traditional medicine applications have been confirmed. Therefore, there is a need for more diverse studies on the chemical and pharmacological activities of highly purified molecules from Ranunculus species extracts to understand the mechanisms underlying their activities and identify novel drug candidates.

1. Introduction

The genus Ranunculus includes approximately 600 species globally. Recent taxonomic reports suggest that this genus has a monophyletic origin and is divided into two subgenera and seventeen sections [1]. Owing to its wide distribution, the genus has high genetic diversity. Several Ranunculus species have been used in folk medicine to treat various diseases or symptoms, such as jaundice, nebula, edema, malaria, asthma, pain, gout, rheumatism, inflammatory skin disorders, cancer, and hypertension. In addition, researchers have reported that Ranunculus extracts possess antioxidant, anti-inflammatory, antimutagenic, antimalarial, antibacterial, antitumoral, cardioprotective, and wound-healing properties [2,3,4,5,6,7].

Over the last decade, various studies have investigated the chemical components and pharmacological activities of Ranunculus species [8,9]. However, no recent review has been published detailing the aspects of the plants that have been investigated, including their biology, traditional uses, phytoconstituents, therapeutic activities, and clinical applications, since a previous review article was reported in 2012 [10]. Thus, this article aims to provide an up-to-date survey of the advances in and prospects of the research on the phytochemicals and pharmacological potential of Ranunculus species.

2. Search Strategy

This review article is based on the information available on the phytochemical, toxicological, and pharmacological studies on the traditional uses of Ranunculus species. The present paper covers online literature (Google Scholar, PubMed, ScienceDirect, Scopus, SpringerLink, and Web of Science), particularly from 2010 to 2021, and books on the ethnopharmacology and botany of Ranunculus species. The following words were used as key search terms: (“Ranunculus” OR “Ranunculus species”) AND (“herbal medicine” OR “herb medicine” OR “ethnopharmacological effects” OR “ethnopharmacological activity” OR “phytomedicine” OR “treatment” OR “drug”. The range of the article publication year for the search (from 2010 to 2021) was selected because the previous review by Aslam et al. covered almost all literature data published by 2012 [10].

3. Taxonomy, Distribution, and Morphology

Ranunculaceae Juss., or the buttercup family, has a worldwide distribution, representing a large group comprising more than 2500 species belonging to 59 genera. Its family members live under a wide range of ecological conditions, especially in the Northern Hemisphere [1,11]. Among the family, Ranunculus, comprising 600 species, is distributed across all continents [11]. Ranunculus species are highly genetically diverse; therefore, their classification is challenging. As a result, generic delimitation and infrageneric classification of these species are still under consideration.

Initially, Ranunculus species were classified based on the descriptions of their achenes (e.g., the shape of their body and beak, pericarp structure, and indumentum), flowers (e.g., the number of sepals and honey-leaves, gloss and color of the petals, and shape of the nectaries), roots (e.g., whether they were uniform or dimorphic with fibrous and tuberous roots) [12], and fruit anatomy [13]. Later, Tamura classified the genera into seven subgenera based on the reassessment of the achene structure: Pallasiantha, Coptidium, Ficaria, Batrachium, Crymodes, Gampsoceras, and Ranunculus [1,11]. In this classification, the subgenera of Ranunculus were further subdivided into 20 sections [11].

Subsequently, DNA markers were utilized to delineate the phylogenetic relationships within Ranunculaceae [14,15,16,17,18,19,20,21,22,23]. The sequences of the internal transcribed spacer region of nuclear ribosomal DNA are mostly used as DNA barcode markers for phylogenetic studies at the generic/subgeneric level [24,25]. In combination with data from the chloroplast genome and other external data, this nuclear marker also offers insights into the reticulate patterns caused by hybridization [26,27]. Moreover, a complete study of the taxonomy of the genus using both DNA markers and morphological data suggested the separation of 226 species into two subgenera and 17 sections [20].

4. Phytochemical Investigations of Ranunculus Species

Ranunculus sceleratus Linn., commonly known as the celery-leaved buttercup, is a flowering plant species distributed over the Northern Hemisphere. The main constituents of R. sceleratus L. are flavonoids, steroids such as pyrogallol tannins, and the glycoside ranunculin [28]. Ranunculin is hydrolyzed after the leaves of R. sceleratus L. are dried or crushed and generates protoanemonin associated with the toxic properties of buttercups. Because of its instability, protoanemonin dimerizes to produce anemonin, a nonirritant form [29,30]. In addition, the 70% ethanolic extracts from the aerial parts of R. sceleratus L. have been found to be abundant in myristic acid [31], and sapigenin 4′-O-alpha-rhamnopyranoside, apigenin 7-O-beta-glucopyranosyl-4′-O-alpha-rhamnopyranoside, tricin 7-O-beta-glucopyranoside, tricin, and isoscopoletin have been identified as R. sceleratus-derived compounds in the extract [32].

Ranunculus ficaria Linn. is known as lesser celandine. The compositions found in R. ficaria L. were ranunculin and its enzymatic reaction products, flavonoids such as quercetin and rutoside, saponosides with hederagenin, oleanolic acid aglyca, macerate, and tinctures [33,34,35].

The components of R. japonicus Thunb. revealed by a Waters Acquity Ultra Performance liquid chromatography system were lactone glycosides, flavonoid glycosides, and aglycones including ranunculin, tricin, adonivernite, orientin, isorientin, vitexin, 6-C-β-D-glucosyl-8-C-α-L-arabinosylapigenin, and tricin-7-O-β-D-glucopyranoside [36].

Ranunculus muricatus Linn. is also known as spiny fruit buttercup. Phytochemical analysis of R. muricatus L. revealed the presence of saponins, tannins, phenols, flavonoids, alkaloids, cardiac glycosides, anthocyanins, carbohydrates, coumarins, and phytosterols [8,37,38]. The major constituents by HPLC were stigmast-4-ene-3,6-dione, stigmasterol, anemonin, β-sitosterol, protocatechuic aldehyde, protocatechuic acid, lutein, flavonoid glycosides, ranunculoside A, ranunculoside B, and ranunculone C, in addition to two potent antioxidants, caffeoyl-β-D-glucopyranoside, and 1,3-dihydroxy-2-tetracosanoylamino-4-(E)-nonadecene [9,39,40,41]. Moreover, four compounds, muriolide, muricazine, chalcone 4-benzyloxylonchocarpin, and new-to-nature anthraquinone muracatanes B, were recently isolated [42,43].

Phytochemical analyses of R. ternatus Thunb. reported that the plant contains flavonoids, glycosides, benzine, organic acids, sterols, esters, amino acids, and constant and trace elements [44]. Furthermore, R. ternatus ethyl acetate extract constitutes contain sternbin, methylparaben, 3-[(4-O-d-glucopyranosyl)-phenyl]-2-propenoic acid, linocaffein, β-d-glucose, robustaflavone-4′-methylether, kayaflavone, podocarpus flavone A, bilobetin, isoginkgetin, amentoflavone, ternatoside A, ternatoside B, and 4-O-d-glucopyranosyl-p-coumaric acid [45,46,47]. Furthermore, methyl (R)-3-[2-(3,4-dihydroxybenzoyl)-4,5-dihydroxyphenyl]-2-hydroxypropanoate was isolated from R. ternatus roots [48].

Ranunculus arvensis Linn. is commonly known as field buttercup. Phytochemical analysis indicated that R. arvensis L. possesses rutin, caffeic acids, and classes of flavonoids and phenolics, including flavonol glycosides of quercetin, kaempferol, isorhamnetin, and their aglycons [49].

In Ranunculus species, several bioactive compounds and Ranunculus-specific constituents have been identified, such as ranunculosides, muricazine, and muracatanes. Although many other species related to Ranunculus have also been studied to evaluate their pharmacological activities, the novel bioactive compounds found in Ranunculus species with high pharmacological effects show nutraceutical and pharmaceutical potential. Pharmacological properties and molecular formula of Ranunculus species compounds reported in articles published from 2010 to 2021 are summarized in Table 1.

Table 1

Pharmacological properties and molecular formula of Ranunculus species compounds reported in articles published from 2010 to 2021.

Ranunculus Species	Molecule	Molecular Formula	Pharmacological Activity	Ref
Ranunculus japonicus Thunb.	berberine	C20H18NO4+	inhibited the migration capacity of RA-FLSs in a dose-dependent manner	[50]
	yangonin	C15H14O4
Ranunculus muricatusLinn.	muricazine	C16H10N2O4	antioxidant effect, lipoxygenase, and urease inhibitory activities.	[42]
	4-benzyloxylonchocarpin	C27H24O4	acetylcholinesterase inhibitory effect	[43]
	muracatane B	C14H8O5	alpha-glucosidase inhibitory effect	[43]
	4-methoxylonchocarpin	C21H20O4	moderate cytotoxic effects towards ovarian carcinoma, colorectal adenocarcinoma, breast cancer, and thyroid carcinoma	[43]
	muriolide	C15H15O8	antioxidant and lipoxygenase inhibitory activities	[42]
	caffeoyl-beta-D-glucopyranoside	C14H18O9	antioxidant effect	[41]
	1,3-dihydroxy-2-tetracosanoylamino-4-(E)-nonadecene	C43H80NO3	antioxidant effect	[41]
	ranuncoside	C22H11O7	antioxidant effect	[42]
Ranunculus ternatusThunb.	n-butyl-β-D-fructofuranoside	C10H20O6	inhibitory effect of multidrug-resistant tuberculosis	[48]

5. Pharmacological Activities of Ranunculus Species

5.1. Ranunculus sceleratus Linn.

All parts of Ranunculus sceleratus Linn. are poisonous when fresh; however, the plant is used in folk medicine to treat various diseases after heating or drying [7]. In recent decades, ethnopharmacological effects have been experimentally proven by several studies (Table 2). The two ranunculins, protoanemonin and anemonin, have shown fungicidal, antimicrobial, antimutanenic, and antipyretic properties [29,30,51], and have been used for ethnopharmacological purposes in many countries [52,53]. Sharif et al. performed an in vivo study to evaluate the effects of hypertension treatment using normotensive and fructose-induced hypertensive rats, in which the aqueous fraction produced the most interesting effects. Furthermore, mechanistic studies with various pharmacological antagonists have demonstrated that the hypotensive response induced by R. sceleratus L. is caused by the involvement of a muscarinic receptor, angiotensin-converting enzyme inhibition, ganglionic block, and nitric oxide release [54]. In addition, the 70% ethanolic extracts from the aerial parts of R. sceleratus L. revealed that abundant myristic acid in the extract inhibited nitrite concentration in LPS-stimulated RAW 264.7 macrophage cell line [31]. Moreover, R. sceleratus-derived compounds, sapigenin 4′-O-alpha-rhamnopyranoside, apigenin 7-O-beta-glucopyranosyl-4′-O-alpha-rhamnopyranoside, tricin 7-O-beta-glucopyranoside, tricin, and isoscopoletin, showed inhibitory activity against the hepatitis B virus [32]. In addition to the treatment effect of R. sceleratus extract, fresh R. sceleratus for TianJiu therapy, which involves adding Chinese medicinal herbal paste on designated acupoints, showed good therapeutic effect on intrahepatic cholestasis in rats, although the fresh form of R. sceleratus L. is known as an irritant [55]. Specific mechanisms by which the extract induces irritant or nonirritant responses have not been revealed. To eluciate this phenomenon, a methanolic extract of R. sceleratus L. was used to demonstrate the mechanism of both irritant and non-irritant properties induced by the extract in topical inflammation. When arachidonic acid elicited the inflammatory process, the effect of the extract was generally proinflammatory or neutral. However, if the response was caused by the application of an irritant, such as etradecanoylphorbol acetate, the extract mainly resulted in anti-inflammatory effects. This effect was mentioned as a counter-irritant, and the extract itself could be an irritant in physiological conditions but could also counteract the action of previously applied irritants [7].

Table 2

Therapeutic activity of Ranunculus species.

Ranunculus Species	Therapeutic Activity	Therapeutic Indications	Source	Ref.
Ranunculus sceleratusLinn.	Anti-inflammatory	Inhibits nitrite accumulation in macrophage	ethanolic extract of whole plant	[7,31]
	Hepatoprotective(treatment of cholestasis hepatitis)	Improves serum hepatic enzyme activity and hepatic pathologic changes in cholestatic rats	fresh R. sceleratus of whole plant	[55]
	Antihypertensive	Inhibits angiotensin converting enzyme (ACE) Involes muscarinic receptor, ganglionic block, and NO	aqueous fraction of aerial parts and roots	[28,54]
	Antiviral	Inhibits hepatitis B virus replication	isolated compounds of whole plant	[32]
Ranunculus japonicusThunb.	Antirheumatoid arthritis	Inhibits migration capacity of rheumatoid arthritis fibroblast-like synoviocytes	methanolic extract of whole plant	[50]
	Antimalarial	Inhibits parasite growth in Plasmodium falciparum and P. berghei improve hepatic and renal parameters	ethanolic extract of whole plant	[56]
	Antihypertrophic	Suppresses elevated expression of the ANP, BNP, and beta-MHC inhibits up-regulation of [Ca2+] i	total glycosides of whole plant	[57]
	Protective effect of myocardial ischemic-reperfusion injury	Improves heart function indexesReduces the area of myocardial infarction	total glycosides of whole plant	[58]
	Antihypertensive	Decreases blood pressure and reduces calcium ions level in cells	total glycosides of whole plant	[36]
Ranunculus muricatusLinn.	Antioxidant	Scavenges the DPPH free radical Inhibits lipoxygenase and urease enzyme activity	methanolic extract of whole plantethyl acetate fraction of whole plant	[41,42]
	Anticarcinogenic	Shows cytotoxic activity to cancer cellsInhibits acetylcholinesterase and alpha glucosidase	ethanolic extract of whole plant	[43]
	Anti-inflammatoryAnalgesic	Inhibits paw edema, paw licking and abdominal constrictions/stretching of hind limbs	methanolic extract of whole plant	[59]
	Cardiotonic (cardiovascular)	Increases perfusion pression and force of contractionIncreases heart rate	methanolic extract of whole plant	[60]
Ranunculus ternatusThunb.	Anticarcinogenic	Induces cell death depending on caspase-7	ethyl acetate extract of whole plant	[61]
	Antibacterial	Shows inhibitory activity against Mycobacterium tuberculosisInhibits multidrug-resistant tuberculosis	ethanolic extract of roots	[48]
Ranunculus arvensisLinn.	Antioxidant	Shows antioxidant activity in DPPH free radical scavenging assay	methanolic extract of whole plant	[49]
	Anticarcinogenic	Induces cell death	aqueous and methanolic extract of whole plant	[62]
Ranunculus diffusus DC.	Anti-inflammatory	Suppresses NF-kB signaling targeting Src and Syk	methanolic extract of aerial parts	[63,64]
Ranunculus sardous Crantz.	Anti-inflammatory	Inhibits nitrite accumulation in macrophage	ethanolic extract from aerial and root parts	[35]
Ranunculus ficaria Linn.	Anti-inflammatory	Inhibits nitrite accumulation in macrophage	ethanolic extract from aerial and root parts	[33,35]
Ranunculus hyperboreus Rotlb.	Anti-inflammatory	Decreases the elevated nitrate amountRegulates the expression and protein levels of inflammation-related enzymes, iNOS and COX-2, and proinflammatory cytokines, TNF-α, IL-1β, and IL-6Suppresses activation of MAPK pathway	aqueous and methanolic extract of whole plant	[65]
Ranunculus pedatus Waldst. & Kitt.	Anti-inflammatory	Inhibits increased capillary permeability induced by acetic-acid	methanolic extract of whole plant	[66]
	Wound healing	Shows fast dermal remodeling and re-epithelization in epidermis Enhances hydroxyproline content	methanolic and aqueous extractof whole plant
Ranunculus constantinapolitanus (DC.) d’Urv	Anti-inflammatory	Inhibits increased capillary permeability induced by acetic-acid	methanolic extract of whole plant	[66]
	Wound healing	Enhances hydroxyproline content	methanolic extractof whole plant

5.2. Ranunculus ficaria Linn.

Ranunculus ficaria Linn. is an herbal astringent commonly used to treat hemorrhoids internally or externally [67]. Various methods have been applied for ethnopharmacological use. Infusion or decoction of the leaves and roots of R. ficaria was known to have trophic and anti-inflammatory effects in varicose veins, hemorrhoids, and skin disorders in Romania. The macerate and tinctures obtained from this plant are used to treat hemorrhoids by stimulating blood circulation as a traditional medication [67]. The compositions found in R. ficaria could inhibit nitrite accumulation, and thus may be useful for preventing inflammatory diseases mediated by the excessive production of nitric oxide, according to an in vitro macrophage study. However, a previous report suggested that clinicians should consider using lesser celandine (pilewort, R. ficaria) as a causative agent owing to its hepatotoxicity [35,68].

5.3. Ranunculus japonicus Thunb.

Ranunculus japonicus Thunb. has been used to treat malaria, jaundice, migraines, stomachaches, arthralgia, crane-like arthropathy, ulcers, toothaches, and eye inflammation since Zhou Hou Bei Ji Fang was first recorded more than 1800 years ago [69]. Since then, studies have demonstrated various phytomedicinal activities, such as the protective effect on heart diseases including myocardial ischemic-reperfusion injury, hypertrophy in cardiomyocytes, and high blood pressure by alleviating chronic [Ca2+] i overload, as well as therapeutic effects on rheumatoid arthritis and decreasing intracellular [Ca2+] i in vascular smooth muscle cells [50,57,58]. In addition, R. japonicus extracts showed antimalarial effects in in vitro culture of Plasmodium falciparum and in vivo rodent malaria experimental systems of Plasmodium berghei [56].

5.4. Ranunculus muricatus Linn.

Ranunculus muricatus Linn. has tremendous medicinal potentials [70]. It is used by the local population as a folk medicine for cough, asthma, heart disease, jaundice, diarrhea, dysentery, urinary infection, eczema, lymphatic tuberculosis, dental diseases, ringworm infection, and leprosy [71,72]. In addition, it exhibits antioxidant, anti-inflammatory, antibacterial, antifungal, analgesic, and cytotoxic activities [37,59,60,73]. Therefore, among Ranunculus species, R. muricatus L. is the most extensively studied. Several constituents identified in R. muricatus L. exhibit phytochemical activities. For example, the major isolated constituents are stigmast-4-ene-3,6-dione, stigmasterol, anemonin, β-sitosterol, protocatechuic aldehyde, protocatechuic acid, lutein, flavonoid glycosides, ranunculoside A, ranunculoside B, and ranunculone C, in addition to the two potent antioxidants, caffeoyl-β-D-glucopyranoside and 1,3-dihydroxy-2-tetracosanoylamino-4-(E)-nonadecene [9,39,40,41]. Moreover, two recently isolated compounds, muriolide, a new lactone, and muricazine, a new hydrazine derivative, exhibited robust free radical scavenging properties and exerted an inhibitory effect on lipoxygenase [42]. Finally, chalcone 4-benzyloxylonchocarpin, which inhibits AcheE, and the new-to-nature anthraquinone muracatanes B, which inhibits α-glucosidase, were isolated from R. muricatus L. [43].

5.5. Ranunculus diffusus DC.

The phytomedicinal effects of Ranunculus diffusus DC. have recently been reported. The methanol extract of R. diffusus showed photoaging protective effects on ultraviolet B radiation-induced skin by inhibiting the p38-AP-1 signal cascade. In addition, the extract exerted anti-inflammatory effects without toxicity by suppressing Src and Syk, which are targets of NF-κB signaling [63,64].

5.6. Ranunculus ternatus Thunb.

Ranunculus ternatus Thunb. has been used in traditional Chinese medicine [74] because of its effects on malignant lymphoma, leukemia, pulmonary tuberculosis, breast tumors, goiters, esophageal tumors, lung disease, gastric problems, and other health conditions [75,76,77]. Constituents of R. ternatus, such as amentoflavone and podocarpus flavone A, induce apoptosis [78,79]; however, their mechanisms have not been evaluated. Furthermore, n-butyl-β-D-fructofuranoside, isolated from R. ternatus roots, demonstrated significant therapeutic activity against tuberculosis [48]. Finally, the ethyl acetate extract of R. ternatus exerts caspase-7-dependent apoptosis in a cancer model [61].

5.7. Ranunculus arvensis Linn.

Ranunculus arvensis Linn. has been widely used to treat arthritis, asthma, hay fever, rheumatism, psoriasis, gut diseases, and rheumatic diseases [49]. Moreover, R. arvensis extracts showed antioxidant and anticarcinogenic activities [49,62]. However, topical use of the plant may cause contact dermatitis, such as skin inflammation, skin burns, and injury of mucous membranes [80,81,82].

5.8. Ranunculus hyperboreus Rotlb.

Ranunculus hyperboreus Rotlb. is a subarctic and subalpine plant that lives in extreme environmental conditions. R. hyperboreus extract induces anti-inflammatory activity by regulating the gene expression and protein levels of inflammation-related enzymes, such as iNOS and COX-2, and proinflammatory cytokines, such as TNF-α, IL-1β, and IL-6 [65].

5.9. Ranunculus pedatus Waldst. & Kit.

The wound healing activity of Ranunculus pedatus Waldst. & Kitt. was evaluated using its methanolic extract and was found to exert significant effects on wound healing with robust anti-inflammatory activity in both incision and excision wound animal models [66].

6. Conclusions

The chemical and biological activities of Ranunculus species have been investigated using plant extracts. Contemporary research on the biological activity of the extracts of the species mentioned above has uncovered many activities, including antibacterial, antiviral, and antiprotozoal effects, as well as antioxidant and anticarcinogenic properties. In addition, these studies have demonstrated that herbal extracts exert hepatoprotective, hypoglycemic, and thyroid regulatory effects. Moreover, the anti-inflammatory and analgesic effects of the plants, known from the application of traditional medicine, have been confirmed. Furthermore, the molecules isolated from Ranunculus species showed promising pharmacological activity. Therefore, it is expected that effective purified molecules could be discovered from Ranunculus species to develop novel drugs through intensive research.