Nigella sativa in controlling Type 2 diabetes, cardiovascular, and rheumatoid arthritis diseases: Molecular aspects.

Oxidative stress is an important factor in the etiology of several chronic diseases that include cardiovascular disease (CVD), Type 2 diabetes (T2D), and rheumatoid arthritis (RA). Oxidative stress can lead to inflammation, and this can contribute to these chronic diseases. Reducing inflammation and oxidative stress may, therefore, be useful in the prevention and treatment of these conditions. One of the treatment options for chronic diseases is the use of traditional medicine and herbs, such as Nigella sativa. This is one of the herbs that have recently been assessed for its ability to reduce inflammation and oxidative stress. We have reviewed the reported effects of N. sativa on risk factors of chronic diseases (CVD, DM, and RA) with emphasis on molecular and cellular mechanisms in controlling inflammation and oxidative stress. Various mechanisms have been proposed to contribute to the beneficial properties of N. sativa, including a reduction of lipid peroxidation via its antioxidant properties; agonist of peroxisome proliferator-activated receptor gamma in adipose tissue; activation of AMP-activated protein kinase, increased antioxidants, inhibition of nuclear factor-kappa B pathway; increased in interleukin-10 expression, CD4+ T-cell percentage, T regulatory cell percentage (CD4+ CD25+ T-cell) in peripheral blood, and CD4+/CD8+ ratio, but to prove this claim, it is necessary to conduct experimental and well-designed clinical trial studies with a larger sample size on the effects of N. sativa on these chronic diseases. Copyright:

INTRODUCTION

Chronic diseases may be defined as a long-term illness with long treatment period that cannot currently be prevented by vaccines, or fully cured by medication and also causes physical changes in the body and reduces its performance.[1] According to the Centers for Disease Control (CDC) definition, cardiovascular disease (CVD), Type 2 diabetes (T2D), and rheumatoid arthritis (RA) are common chronic diseases globally.[12] CVD is associated with dysfunction of the heart and blood vessels and comprises disorders such as coronary heart disease and hypertension.[3] It has been estimated that the prevalence of hypertension and CVD reaches about 30% of the world's population by the year 2025.[456] T2D is the most common type of diabetes, accounting for 90% of all diabetes cases.[7] The number of people with T2D in the world was estimated to be approximately 125 million in 1997 and is expected to reach 300 million by 2025, and on average, the prevalence among adults is 8.5%.[89] RA is an autoimmune chronic disease that affects the small joints of the human body and affects approximately 1% of the population and is usually associated with severe disability.[10] Based on the National Health Council (NHC) reports, the burden of the cost of chronic diseases annually in the United States is about $ 1.3 trillion for seven common chronic diseases and now about 78% of total health care spending in the United States is spent on chronic diseases, and this trend is increasing.[11] It has been widely accepted that persistent oxidative stress leads to chronic inflammation and this inflammation can be effective in many chronic diseases such as CVD, T2D, and RA;[12] therefore, it is possible that reducing the level of inflammation and oxidative stress may ameliorate these diseases. One of the treatment options for chronic diseases is the use of traditional medicine and herbs, and it has been shown to be used in both prevention and treatment.[13] In general, the consumption of medicinal plants is increasing in different countries due to the evidence of the positive effects as well as the low side effects and availability of these plants.[141516] Nigella sativa is one of the herbs that have recently been used to reduce inflammation and oxidative stress in various chronic diseases.[17]

N. sativa is also known as black seed, black cumin, habbatus sauda, and black caraway seed. It is cultivated in countries such as India, Pakistan, and some parts of Iran. The plant is a local herb in southern Europe, North Africa, and Asia.[18192021] N. sativa, as a 1-year-old plant, has flowers whose stem is covered with very delicate fluff and grows to a height of 20–30 cm; this plant's flowers are solitary and pale blue or white with 5 petals, the fruits are shaped like a large capsule containing 3–7 follicles, and the seeds in each follicle are black in color and have a bitter, spicy flavor[22] [Figure 1].

Figure 1

Nigella sativa plant: Fruits, leaf, and flowers

N. sativa has been reported to contain more than 100 chemical compounds and has many reported therapeutic effects due to these compounds. N. sativa oil contains average, 35.6%–41.6% fat (constant oil), 22.7% protein, 32% carbohydrate, and 0.5%–1.6% essential fatty acid. The major fatty acid in this plant is linoleic acid (about 57.3% of fixed oil).[2324] It also contains other compounds such as crude fiber, reducing sugars, mucilage, resin, alkaloids, sterols, tannins, flavonoids, saponins, minerals (such as Fe, zinc, Na, phosphorus, and calcium), and vitamins (C, B1, B3, B6, and B9 as water-soluble vitamins and A and E as a couple of fat-soluble vitamins).[2425] The biological activity of N. sativa is attributed to the following proportions of forming components: volatile oils, such as thymoquinone (TQ) (30%–48%), P-cymene (7%–15%), carvacrol (6%–12%), 4-terpineol (2%–7%), trans-anethole (1%–4%), and sesquiterpene longifolene (1%–8%). A combination of four monoterpenes (d-limonene (carvone), carvone, pinene-α, and p-cymene), TQ, and its derivatives are the most pharmacologically active compounds.[242627] TQ is not only a type of inhibitor for chemically reactive species containing oxygen such as superoxide and hydroxyl radicals but also inhibits leukotriene C4 and B4 production in humans and has anti-inflammatory effects.[2728]

Recent studies have shown that N. sativa can be helpful and effective in the prevention and treatment of some chronic diseases, such as asthma, liver and kidney disease, influenza, and gastrointestinal problems.[2129] Previous studies reported that N. sativa was used as antihypertensive, liver tonics, diuretics, antidiarrheal, appetite stimulant, analgesics, digestive, antibacterial, and in skin disorders,[30] and also, its effects on neurological and mental illness, cardiovascular disorders, cancer, diabetes, and inflammatory conditions have been shown.[31] Effects of an aqueous extract from N. sativa on glucose tolerance and body weight in rats were studied by Meddan et al.[32] In a similar study, N. sativa was reported to reduce the risk of CVD in diabetic patients.[33] Some studies have also shown the anti-inflammatory and analgesic effects of N. sativa in RA.[34]

Despite the effects of N. sativa on some chronic disease risk factors in previous studies, the exact mechanism of these effects has not been identified and the results of some studies have been inconsistent. Therefore, this study aims to review the possible molecular and cellular effects of N. sativa on inflammation, oxidative stress, and other related risk factors of chronic diseases (CVD, T2D, and RA).

SEARCH STRATEGY

PubMed-Medline, Google Scholar, Scopus, and Web of Science databases were searched to identify the relevant articles. The keywords including “nigella sativa,” OR “black seed,” OR “black cumin,” OR “habbatus sauda,” OR “black–caraway seed” in combination with “diabetes,” “insulin resistance,” “glucose,” “hemoglobin A1C,” “dyslipidemia,” “lipid profile,” “blood pressure,” “cardiovascular disease,” “heart disease,” “rheumatoid arthritis,” “atherosclerosis,” “oxidative stress,” “anti-oxidant,” “inflammation,” and “inflammatory markers” were used for an electronic search strategy. All the identified studies and review articles were reviewed. Subsequently, the eligible experimental and clinical trials were selected. These are papers reporting original studies on the mechanisms of action of N. sativa and almost all available animal and human studies. However, we mentioned that this study is a narrative review and not in a systematic framework.

EFFECTS OF NIGELLA SATIVA IN CARDIOVASCULAR RISK FACTORS

Laboratory animal studies

Three doses of hydroalcoholic extract of N. sativa (200, 400, and 600 mg/kg) were injected intraperitoneally in hypertensive rats showed a protective effect on blood pressure (BP) after 30 min of injection that was induced by TQ and its effects on angiotensin II.[35] In another study, improvements of cardiovascular risk factors including body weight, red blood cell and white blood cell, lipid profile (triglyceride [TG], low-density lipoprotein [LDL], and high-density lipoprotein [HDL]) and immune response (IgM and IgG), total antioxidant capacity, and malondialdehyde (MDA) after 8-week supplementation with N. sativa seed at doses of 300 and 600 g/kg in rabbits were proved.[36] This effect was dose dependent. The cardioprotective effects of N. sativa are summarized in Table 1.

Table 1

Effects of Nigella sativa on cardiovascular, diabetes, and rheumatoid arthritis risk factors in experimental studies

Author (year)	Country (reference number)	n	Type and dose of N.S administered	Duration	Outcome measures
Enayatfard et al. (2019)[35]	Iran	21 hypertensive rats	200, 400, and 600 mg/kg N.S	Once injection	Dose-dependent reduction in systolic blood pressure, mean arterial pressure, and heart rate
El-Gindy et al. (2019)[36]	Egypt	54 growing V-line unsexed rabbits	300 or 600 mg of N.S seed/kg	8 weeks	Significantly improved body weight, ↑RBCs and WBCs ↑IgG and IgM immune responses, ↓ serum total lipids, TG, LDL, and MDA, and ↑HDL and total antioxidant capacity.
Ahmed and Hassanein (2013)[94]	Egypt	45 Albino rats	N.S oil (4 ml/kg) orally	Once administration	↓heart rate, ST-segment change, pro-inflammatory cytokines, oxidative stress, and cardiac tissue damage
Randhawa (2013)[95]	India	16 Wistar albino rats	0.2 ml/kg/day, intraperitoneally	6 weeks	↓blood pressure, oxidative injury, improved left ventricular function
Babaei Bonab and Tofighi (2019)[96]	Iran	35 male Wistar rats with T2M	400mg/kg/day	8 weeks	Improvement in lipid profile (LDL, HDL, TC, and TG), FBG, HbA1c, and insulin resistance
Ahmad and Alkreathy (2018)[97]	Saudi Arabia	48 male Albino Wistar rats	2 ml/kg, p.o	7 days	Improvement in lipid profile (TC, LDL, HDL, and TG)
Muneera et al. (2015)[98]	Pakistan	30 Sprague Dawley rats	1000mg/kg/day	6 weeks	Improvement in the lipid profile of rats
Al-Hader et al. (1993)[99]	Jordan	Diabetic rabbits	50 mg/kg volatile oil extract of N.S	2, 4, and 6 h	Showed significant decreases in FBG levels
Meral et al. (2001)[44]	Turkey	15 New Zealand male rabbits	20 ml/kg aqueous extract of N.S	2 months	↑GSH and ceruloplasmin concentrations ↓MDA and glucose levels
El-Dakhakhny et al. (2002)[54]	Egypt	Diabetic rats	0.4g/kg N.S oil	2, 4, and 6 weeks	↓blood glucose concentration
Kanter et al. (2003)[59]	Turkey	46 male Wistar rats	0.2 ml/kg/day volatile oil of N.S	4 weeks	↓GSH, glucose level, and serum NO ↑Insulin level
Fararh et al. (2004)[74]	Japan	Male Syrian hamsters	400 mg/kg body weight/day of N.S oil	4 weeks	↓total glycated hemoglobin
Rchid et al. (2004)[61]	-	Rat pancreatic cells	0.01, 0.1, 1, and 5 mg/ml whole, basic, and acidic subfractions of N.S	30 min	A significant stimulatory effect on insulin release has been observed
Mansi et al. (2005)[55]	Jordan	Diabetic rats	20 ml/kg/day aqueous extract of N.S	15 days	↑Insulin level and ↓Glucose level
Mansi (2006)[100]	Jordan	Diabetic rats	20 ml/kg aqueous extract of N.S	3 weeks	↑Insulin level
Kaleem et al. (2006)[101]	India	Wister rats	300 mg/kg/day ethanol extract of N.S	4 weeks	↑Catalase, SOD and insulin levels ↓Lipid peroxidation, GPX and glutathione ↓Body weight
Houcher et al. (2007)[56]	Algeria	Diabetic rats	810 mg/kg/day 2.5 ml/kg/day methanol extract of N.S and N.S oil	25 days	↓Glucose level↑TAC
Kanter (2008)[58]	Turkey	diabetic rats	N.S in a dose of 400 mg/kg body weight and TQ 50 mg/kg body weight once a day	12 weeks	↓Serum glucose
AL-Logmani (2009)[102]	Saudi Arabia	40 diabetic male Wistar rats	N.S oil	3 weeks	↓Blood glucose
Meddah et al. (2009)[59]	Morocco	Rat jejunum	In vitro: 0.1 pg/ml to 100 ng/mlIn vivo: 2g/kg	6 weeks	In vivo: glucose tolerance and body weight improvementIn vitro: inhibition of glucose absorption
Benhaddou-Andaloussi et al. (2010)[103]	Morocco	C2C12 skeletal muscle cells and 3T3-L1 adiposities	Ethanol extract of N.S	18 h	↑Glucose uptake in skeletal cells and adiposities
Fararh et al. (2010)[53]	Egypt	Diabetic rats	50 mg/kg/day TQ	20 days	↓ Plasma glucose, TC, TG↑ Insulin concentration
Abdelmeguid et al. (2010)[62]	Egypt	Diabetic rats	2 mL⁄kg, i.p., 5% N. SExtract 0.2 mL⁄kg, i.p, N.S oil, or 3 mg⁄mL, i.p., TQ	30 days	↓ glucose and improve serum insulin levels
Salama (2011)[52]	Saudi Arabia	Diabetic rats	500 mg/kg N.S oil	4 weeks	↓Glucose concentration↑insulin, c-peptide, and TAC
Al-Logmani and Zari (2011)[104]	Saudi Arabia	Diabetic Wistar rats	Diet containing 5% N.S oil	7 weeks	N. sativa oil decreased blood glucose levels
Alimohammadi et al. (2013)[105]	Iran	Diabetic rats	5, 10, and 20 mg/kg hydroalcoholic N.S extract	32 days	5 mg/kg: ↓FBS↑Insulin secretion
Mohamed et al. (2015)[51]	Saudi Arabia	Nonalcoholic fatty liver in obese diabetic albino rats	100mg/kg aqueous extract of N.S seed	4 weeks	↓FBS↓TG, TC
Asaduzzaman et al. (2015)[106]	Bangladesh	Diabetic rats	300 mg/kg body weight of ethanol extract of N.S	28 days	↓TG, TC, LDL, and FBG↑HDL
Al-Trad et al. (2016)[107]	Jordan	Experimental diabetic rats	50 mg/kg TQ and 2 mL/kg N.S oil	10 weeks	N.S oil or TQ significantly reduced blood glucose level compared with that in untreated diabetic rats
Umar et al. (2012)[75]	India	Three groups of six Wistar albino rats each with collagen-induced arthritis	5 mg/ kg TQ PO	21 days	↓ IL-1β, IL-6, TNF-α, IFN- γ, PGE2, articular elastase, myeloperoxidase, lipoxygenase, and NO↑IL-10, SOD, GPX, and catalase
Vaillancourt et al. (2011)[76]	Canada	24 female Lewis rats with lipopolysaccharide (LPS)-induced arthritis	5 mg/ kg TQ PO	7 days	↓ LPS-induced IL-1β, TNF-α, MMP-13, Cox-2, and PGE2
Tekeoglu et al. (2006)[108]	Turkey	Five groups of seven Wistar albino rats each with collagen-induced arthritis	2.5 mg/kg and 5 mg/kg TQ PO	7 days	↓ TNF-α and IL-1β
Mohamed et al. (2003)[109]	Canada	24 mice with inducing inflammation	1 mg/kg TQ iv	5 days and 12 days	Mice received TQ at day 12: Higher levels of GSHSignificant reduction of symptoms of inflammation
Faisal et al. (2015)[110]	Pakistan	32 rats with collagen-induced arthritis	2mg/kg/day TQ by i.p injection	15 days	↓ in clinical score of inflammation and differentiation leucocyte counts
Zhong (2017)	China	60 rabbit osteoarthritis model	1mg/kg/day TQ by intra-articular injection	9 weeks	↓ in MMP-13 mRNA and cartilage lesions
Chen et al. (2010)[111]	China	20 rabbit osteoarthritis model	10 µmol/L TQintra-articular injection	4 weeks	Inhibited NF-kB p65↓ IL-1βSuppressed the MMP-1, MMP-3, and MMP-13 gene expression

N.S=Nigella sativa; TQ=thymoquinone; i.p=intraperitoneal; RBC=Red blood cells; WBC=White blood cells; TG=Triglyceride; TC=Total cholesterol; LDL=Low-density lipoprotein; HDL=High-density lipoprotein; MDA=Malondialdehyde; IgG=Immunoglobulin G; IgM=Immunoglobulin M; FBG=Fasting blood glucose; HbA1C=Glycated hemoglobin; IL-1β=Interleukin-1 beta; IL-6=Interleukin-6; TNF-α=Tumor necrosis factor-alpha; IFN- γ=Interferon-gamma; PGE2=Prostaglandin E2; GSH=Glutathione; NO=Nitric oxide, GPX=Glutathione peroxidase; TAC=Total antioxidant capacity; IL-10=Interleukin-10; LPS=Lipopolysaccharide; MMP=Matrix metalloproteinase; Cox-2=Cyclooxygenase 2; NFkB= Nuclear factor-κB

Clinical studies

Clinical trials in human subjects showed similar results. Sabzghabaee et al.[37] have reported that 2 g/d N. sativa for 4 weeks in hyperlipidemic patients significantly reduced total cholesterol (TC), TG, and LDL compared to control group [Table 2]. Furthermore, 500 mg/d N. sativa in metabolic syndrome patients decreased systolic and diastolic BP and LDL-cholesterol (LDL-C) compared to control group.[38]

Table 2

Effects of Nigella sativa on cardiovascular, diabetes, and rheumatoid arthritis risk factors in clinical trial studies

Cardiovascular risk factors
Author (year)	Country (reference number)	Study design (sex)	Participant numbers	Type and dose of N.S administered	Duration (mean age of subjects)	Outcome measures
Darand et al. (2019)[112]	Iran	RCT (male/female)	50 patients with NAFLD	2 g/day	12 weeks	↓serum glucose and serum insulin↑quantitative insulin sensitivity
Sabzghabaee et al. (2012)[37]	Iran	RCT (male/female)	88 Hyperlipidemia patients	2 g/d (capsule contained N.S crushed seeds)	4 weeks	↓TC, TG, and LDL, no significant difference in HDL, FBG
Dehkordi and Kamkhah (2008)[113]	Iran	RCT (male/female)	Patients with mild hypertension	Two test groups received 100 and 200 mg of N.S extract twice a day	8 weeks	Significant dose-dependent decline in the levels of TC, TG, LDL, systolic and diastolic blood pressure
Najimi et al. (2013)[38]	India	Open labeled RCT (male/female)	90 patients of metabolic syndrome	500 mg capsule of N.S per day	8 weeks	Significant improvement with reference to systolic and diastolic blood pressure and LDL-cholesterol, no significant difference in HDL, TG
Ibrahim et al. (2014)[114]	Malaysia	RCT (female)	37 hyperlipidemic menopausal women	500 mg capsule of N.S per day	2 months	↓ TC, LDL and TG, and increased HDL and FBG. No significant difference in diastolic and systolic blood pressure
Tasawar et al. (2011)[115]	Pakistan	RCT (male/female)	80 patients with coronary artery diseases	500 mg capsule of N.S per day	6 months	↓TC, LDL, VLDL, and TG↑HDL-C
Bamosa et al. (1997)[116]	Saudi Arabia	CT (male)	16 male adolescents	2 capsules of 500 mg N.S twice daily	2 weeks	↓ glucoseNo significant difference for TG change
Farzaneh et al. (2014)[117]	Iran	RCT (female)	20 sedentary overweight females	3 capsules of 500 mg N.S daily	8 weeks	↓TC, LDL, TG, and body mass index, and ↑HDL-C
Najimi et al. (2008)[118]	India	CT (male/female)	60 patients of metabolic syndrome	N.S oil 2.5 ml twice daily	6 weeks	↑TC, LDL, FBGNo effect on TG, HDL, postprandial glucose, body weight, BMI, and waist circumference
Mahdavi et al. (2015)[119]	Iran	RCT (female)	90 obese women	3 g per day (1 g before each meal) N.S oil	8 weeks	↓VLD, TG, and BMINo effect on HDL, TC, and LDL
Rashidmayvan et al. (2019)[66]	Iran	RCT (male/female)	44 patients with NAFLD	N.S oil	8 weeks	↓FBS, TG, TC, LDL, VLDL, AST and ALT, hs-CRP, IL-6, TNF-α↑HDL-CN.S oil had no significant effect on serum levels of insulin, blood pressure, and GGT
Pelegrin et al. (2019)[69]	France	Pilot RCT (male)	30 healthy male volunteers	N.S powder (1 g/day)	4 weeks	↓TC, LDL
Farhangi et al. (2018)[120]	Iran	RCT (male/female)	40 patients with Hashimoto’s thyroiditis	2 g N.S powder per day	8 weeks	↓ BMI, LDL, and TG↑ HDL
Bhatti et al. (2016)[121]	Pakistan	CT (male/female)	60 hyperlipidemic smokers	1 g of N.S (kalonji) seed	30 days	↓TC, LDL, and TG, ↑ HDL
Diabetes risk factors
Bamosa et al. (2010)[64]	Saudi Arabia	RCT (male/female)	94 patients with T2D	Capsules containing N.S (1, 2, and 3 g/day)	12 weeks	↓ FBS, 2hPG, and HbA1c
Kaatabi et al. (2012)[122]	Saudi Arabia	94 diabetic patients	CT (F)	1, 2, and 3 g/day of powdered N.S	12 weeks	1gr: ↑HDL-C2gr: ↑ HDL; ↓TC, TG, and LDL-C; 3gr: ↑HDL; ↓ TC, TG, and LDL-C
Hosseini et al. (2013)[123]	Iran	RCT (male/female)	70 patients with T2D	5 ml/day N.S oil	12 weeks	↓FBS, 2hPG, BMI
Mirmiran et al. (2015)[68]	Iran	RCT (male/female)	43 patients with T2D	1000 mg extract of black seed oil	8 weeks	↓FBS, LDL, total cholesterol, and LDL/HDL
Heshmati et al. (2015)[124]	Iran	RCT (male/female)	72 patients with	3 g/day N.S oil or soft gel capsules	12 weeks	↓FBS, HbA1c, ↓LDL-C, and TG
Farhangi et al. (2018)[120]	Iran	RCTmale/female)	40 patients with Hashimoto’s thyroiditis	2 g N.S powder per day	8 weeks	↓BMI ↑HDL ↓Serum concentrations of LDL and tri-TG
Rashidmayvan et al. (2019)[66]	Iran	RCT (male/female)	44 patients with NAFLD	1000 mg N.S oil per day	8 weeks	↓ FBS level↓TG, TC, LDL, VLDL↑ HDL
Pelegrin et al. (2019)[69]	France	Pilot RCT (male)	30 healthy male volunteers	N.S powder (1 g/day)	4-weeks	Ineffective on glucose-induced insulin secretion and insulin sensitivity
Rheumatoid arthritis risk factors
Hadi et al. (2016)[77]	Iran	RCT (female)	45 patients with rheumatoid arthritis	two capsules 500 mg/day N.S oil	8 weeks	↓ MDA, NO↑ Serum level of IL-10
Kheirouri et al. (2016)[91]	Iran	RCT (female)	45 patients with rheumatoid arthritis	two capsules 500 mg/day N.S oil	8 weeks	↓ hs-CRP level, cytotoxic T-cells (CD8+), DAS-28 score, and an improved number of swollen joints.↓ Serum level of CD4+ T-cell percentage, T regulatory cell percentage (CD4+CD25+ T-cell) and CD4+/CD8+ ratio
Gheita and Kenawy (2012)[78]	Egypt	RCT (female)	40 patients with rheumatoid arthritis	Two capsules 500 mg/day N.S oil	4 weeks	↓DAS-28, joint inflammation, and morning stiffness
Kooshki et al. (2016)[125]	Iran	RCT (male/female)	40 elderly patients with knee osteoarthritis	Topical application of 3cc N.S oil on knee	3 weeks	Pain reduction in the black seed group was greater than that of the acetaminophen group

N.S=Nigella sativa; RCT=Randomized controlled trial; TG=Triglyceride; TC=Total cholesterol; LDL=Low-density lipoprotein; HDL=High-density lipoprotein; VLDL=Very-lowdensity lipoprotein; FBG=Fasting blood glucose; BMI=Body mass index; AST=Aspartate aminotransferase; ALT=Alanine aminotransferase; GGT=Gamma-glutamyltransferase; hs-CRP; high-sensitive C-reactive protein; IL-6=Interleukin-6; TNF-α=Tumor necrosis factor-α; T2D=Type 2 diabetes; FBS=Fasting blood sugar; 2hPG=2-h postprandially glucose; HbA1c=Glycosylated hemoglobin; NAFLD=Nonalcoholic fatty liver disease; MDA=Malondialdehyde; NO=Nitric oxide; DAS-28=Disease Activity Score-28

Effect on lipid profile

Improvements in serum lipid profile were investigated in human and animal studies. The meta-analysis on the effect of N. sativa on lipid profiles indicated that the levels of TC and LDL-C dropped significantly.[3940] Sahebkar et al. showed significant reductions in serum TG.[40] Daryabeygi-Khotbehsara et al.[39] found that N. sativa seed oil reduced serum TG, while seed powder increased TG levels what may be a consequence for different preparation processes of crushed seeds and extracted oil in addition to chemical composition.[39] Another systematic review revealed that N. sativa supplementation might be effective in glycemic control, but its effects on anthropometric parameters and lipid profile were controversial.[41]

The effects of N. sativa on lipid profile may be related to its antioxidant properties,[42] and its agonist effects on peroxisome proliferator-activated receptor gamma (PPAR-γ),[43] reducing lipid peroxidation,[42] upregulation of the LDL receptor in the hepatocytes subsequently, cholesterol removal, and suppression of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA R) gene and cholesterol synthase.[44]

Effect on blood pressure

N. sativa lowers BP sharply according to meta-analysis.[45] This may be connected to some factors such as diuretic effect, calcium channel-blocking properties, and cardiac depressant effect of N. sativa that are likely related to various components of N. sativa involved in this effect, including TQ, and fatty acids that contain substantial quantities of linoleic, oleic, and arachidonic acids, nigellicine, flavonoids, trans-anethole, p-cymene, α-pinene, limonene, carvone, and soluble fiber[4146] volatile oils extracted from N. sativa and TQ may directly or indirectly reduce both BP and heart rate, by their serotoninergic and muscarinic properties.[47] N. sativa compounds are also reported to have endothelium-independent relaxation effects that may be due to suppression of Ca2+ release from the sarcoplasmic reticulum across the smooth muscle cell membrane and reduction of Ca2+ sensitivity and influx.[48] Furthermore, N. sativa may reduce BP by its diuretic effects and regulate the electrolytes and water content, and also control of blood volume; subsequently, cardiac output is reduced, an important regulator of BP.[49] Figure 2 shows the potential mechanisms of the effect of N. sativa on CVD.

Figure 2

Potential mechanisms of the effect of N. sativa on cardiovascular disease. PPAR-γ = Peroxisome proliferator-activated receptor gamma; LDL receptor = Low-density lipoprotein receptor; HMG-CR = 3-Hydroxy-3-methylglutaryl-coenzyme A reductase

EFFECTS OF NIGELLA SATIVA IN TYPE 2 DIABETES

T2D mellitus is marked by hyperglycemia, dyslipidemia and increased oxidative markers that may be caused insulin resistance, and finally, overt diabetes.[50] Seeds of N. sativa have been used as a natural treatment for various diseases. Hypoglycemic, hypolipidemic, and antioxidant effects of N. sativa have been reported.[515253] Numerous studies have been done in diabetic animal models. El-Dakhakhny et al. have shown that 0.4 g/kg N. sativa oil significantly diluted blood glucose concentration in diabetic rats after 6 weeks.[54] Insulin levels in diabetic rats treated with a dose of 20 ml/kg aqueous extract of N. sativa rose after 15 days.[55] Houcher et al. reported that intraperitoneally, a daily dosage of 810 mg/kg methanol extract and 2.5 ml/kg of N. sativa oil not only lowered glucose but also increased total antioxidant capacity levels in diabetic rats after treated for 25 days.[56] Kantar et al. showed that 50 mg/kg TQ administered orally grew both energy metabolism and insulin levels in diabetic rats after 20 days of insertion.[575859] These studies also showed that a single daily dosage of 400 mg/kg and 50 mg/kg body weight N. sativa and TQ, respectively, administered orally in diabetic rats decreased serum glucose after the intervention.[58] Salama et al. in an animal study reported that oral 500 mg/kg N. sativa oil increased serum C-peptide, insulin, and total antioxidant capacity (TAC) concentration and decreased glucose level in a diabetic rat model.[52] Some studies assert that these antidiabetic properties of N. sativa are due to insulinotropic action,[6061] hepatic gluconeogenesis inhibition, and its antioxidant effects.[52566263] Many studies have been done to confirm the properties of N. sativa on insulin sensitivity and release.[55] Several attempts have been worked on N. sativa, and they suggest that this plant improves insulin sensitivity by preventing the severity of oxidative stress. Insulin secretory effects of N. sativa have been probed on in vitro isolated rat pancreatic islets and saw that the secretion of insulin is increased in the presence of N. sativa. Table 1 summarizes the effects of N. sativa on diabetes in experimental studies.

There have been several clinical studies that have evaluated the effects of oral N. sativa supplementation in different subject groups. Bamosa et al. in a clinical trial on 94 patients with diabetes showed that 2 g/day of N. sativa seed supplementation decreased fasting blood glucose (FBG), 2 h postprandially glucose, glycosylated hemoglobin (HbA1c), and insulin resistance after 12 weeks.[64] Hosseini et al. have reported a significant decrease in FBG, 2 h postprandial glucose, and HbA1c in 70 patients with T2D consuming (5 ml/day for 12 weeks) N. sativa oil.[65] The hypolipidemic and hypoglycemic effects of N. sativa oil (1000 mg/day for 8 weeks) were confirmed by Rashidmayvan et al. in a randomized, double-blind, placebo-controlled clinical trial performed in patients with nonalcoholic fatty liver.[66] Najmi et al. have been reported that the administration of N. sativa oil (2.5 mL twice a day for 6 weeks) to patients with metabolic syndrome significantly decreased FBG and LDL and increased HDL levels.[67] Hadi et al. in a clinical trial study investigated the effect 1000 mg/days extract of N. sativa oil supplementation on 43 patients with T2D. The results after 12-week supplementation of N. sativa oil have been shown a significant reduction in serum level of fasting blood sugar, HbA1c, LDL-C, and TG.[68] Table 2 summarizes clinical trials that evaluated the effects of N. sativa supplementation on healthy and patient subjects.

MECHANISMS OF HYPOGLYCEMIC EFFECT OF NIGELLA SATIVA

N. sativa promotes glucose homeostasis and improves the lipid profile in diabetic animals and humans with T2M through several routes. Mainly, N. sativa improve peripheral insulin sensitivity and circulating insulin.[525369] It also enhances the activation of the AMP-activated protein kinase (AMPK) pathway in skeletal muscle and liver and to increased GLUT-4 in skeletal muscle.[70] Acetyl-CoA carboxylase (ACC) is a key component of the insulin-independent, metabolic sensing, and AMPK pathway. In fact, it has been reported that N. sativa stimulates ACC and the AMPK pathways in both hepatocyte cell lines and skeletal muscles in vitro.[70] Andaloussi et al. reported that in vivo N. sativa treatment can elevate the phosphorylation of ACC in skeletal muscle tissues and liver. The phosphorylation of ACC decreases its activity and shows a reduction of lipogenesis in the liver, whereas it increases fatty acid oxidation in skeletal muscle. These effects on lipid metabolism can justify the functionality of N. sativa to decrease plasma and tissue TG. Finally, it is known that the activation of the AMPK pathway can lead to growing synthesis of GLUT-4[71] [Figure 3]. Many researches suggested that the anti-hyperglycemia and anti-hyperlipidemia features of N. sativa are due to antioxidant components.[4452677273] TQ and dithymoquinone are the main antioxidant components of N. sativa. Several studies have reported that N. sativa can enhance antioxidant enzymes and decrease lipid peroxidation.[73] When oxidative stress is reduced, this may help to regeneration of pancreatic beta-cells, increase number of islets, keep the integrity of pancreatic beta-cells, reduction in insulin resistance, increase insulin secretion and inhibition of advanced glycation end product.[59] N. sativa oil has been shown to decrease hepatic glucose production from gluconeogenic precursors (alanine, glycerol, and lactate) in STZ-induced diabetic hamster.[74] Furthermore, an in vitro study indicated direct inhibition of electrogenic intestinal absorption of glucose by N. sativa extract.[32]

Figure 3

Potential mechanisms of the effect of N. sativa on diabetes. ACC = Acetyl-CoA carboxylase; AMPK = AMP-activated protein kinase

EFFECTS OF NIGELLA SATIVA IN RHEUMATOID ARTHRITIS

The anti-RA properties of N. sativa and its active ingredient TQ in an animal model were evaluated in experimentally induced arthritis. Findings of a study indicated that treatment with TQ orally (5 mg/kg once daily for 21 days) decreased levels of inflammatory cytokines (IL-1β, IL-6, tumor necrosis factor-α [TNF-α], interferon-gamma [IFN-γ], and prostaglandin E2 [PGE2]) and oxidative stress indices such as articular elastase, myeloperoxidase, lipoxygenase, nitric oxide (NO) significantly and increased levels of anti-inflammatory cytokine IL-10 and the activity of superoxide dismutase (SOD), glutathione peroxidase (GPX), and catalase (CAT).[75] The results of a study to elucidate the molecular mechanism of the protective effects of TQ showed that the administration of 5 mg/kg TQ orally for 7 days significantly reduced LPS-induced IL-1β, TNF-α, cyclooxygenase-2 (COX-2), metalloproteinase 13 (MMP-13), and PGE2.[76] Some of the studies reported on the effect of N. sativa on anti-RA are summarized in Table 1.

Clinical trial studies in patients with RA have shown similar results. Hadi et al. and Kheirouri et al. indicated that two capsules of 500 mg/day N. sativa oil for 8 weeks in patients with RA is significantly reduced in MDA, NO, high-sensitivity C-reactive protein (hs-CRP) level, cytotoxic T-cells (CD8+), Disease Activity Score-28 (DAS-28), and a decreased number of swollen joints in comparison with baseline and placebo groups. Furthermore, N. sativa oil is significantly increased in serum level of IL-10, CD4+ T-cell percentage, T regulatory cell percentage (CD4+ CD25+ T-cell), and CD4+/CD8+ ratio. These findings suggest that N. sativa by shifting T-helper lymphocyte cells type 1 (Th1) to T-helper lymphocyte cells type 2 (Th2) can improve RA.[77] In another study, the administration of twice capsules 500 mg/day N. sativa oil for 4 weeks significantly reduced DAS-28, joint inflammation, and morning stiffness, which could be attributed to the effect of N. sativa on the immunomodulatory system.[78] Table 2 summarizes studies investigating the effects of N. sativa and its main active ingredient TQ on the anti-RA and anti-inflammatory in clinical studies.

A MECHANISM OF IMMUNO-MODULATORY PROPERTIES OF NIGELLA SATIVA

Several mechanisms for the anti-RA effects of N. sativa have been proposed. N. sativa with antioxidant, anti-inflammatory, and immunomodulatory properties can be effective.[77] Figure 4 shows the probable mechanisms of the effect of N. sativa on RA.

Figure 4

Probable mechanisms of the effect of N. sativa on rheumatoid arthritis. NF-κB = Inhibition of the nuclear factor-kappa B; TNF-α = Tumor necrosis factor-alpha; IL-1β = Interleukin-1β; IL-6 = Interleukin-6; IFN-γ = Interferon-gamma; MMP-3 = Matrix metalloproteinase 3; COX = Cyclooxygenase; iNOS = Inducible nitric oxide synthase; GSH = Glutathione; CAT = Catalase; GPX = Glutathione peroxidase; GSTs = Glutathione S-transferases; SOD = Superoxide dismutase; NO = Nitric oxide; MDA = Malondialdehyde; ROS = Reactive oxygen species; RNS = Reactive nitrogen species; Th1 = Type 1 helper T-cells; Th2 = Type 2 helper T-cells; IL-10 = Interleukin-10; IL-13 = Interleukin-13

Antioxidant properties

According to the results of studies, reactive oxygen species (ROS), such as O2, OH, and reactive nitrogen species (RNS) such as NO, play an important role in the enhancement of inflammation and progression of RA.[75798081] Therefore, strengthening the antioxidant defense system is very important in reducing chronic diseases.[82] Numerous studies have shown the potentiation of the antioxidant system of N. sativa.[34] N. sativa exerts its antioxidant properties by direct and indirect antioxidant mechanisms and inhibits the expression of oxidative-producing enzymes (inducible NO synthase [iNOS]). Direct antioxidant activities of N. sativa may restore other antioxidants including glutathione (GSH), Vitamin E and Vitamin A, metal chelators, and scavenger free radicals (ROS and RNS). N. sativa also exerts its indirect antioxidant role by activating transcription factors involved in the expression of antioxidant enzymes including SOD, glutathione S-transferases (GSTs), GPX, and CAT.[83]

Anti-inflammatory properties

Inhibition of the nuclear factor-kappa B (NF-κB) pathway is a known mechanism marking anti-inflammatory effects of N. sativa.[84] NF-κB is a transcription factor that causes an exacerbation of inflammatory status. This transcription factor is present in the cytosol and has two subunits called P50 and P65. It also binds to the inhibitor of κB (IκBα) inhibitory protein. Factors such as ROS, TNFα, interleukin-1 beta (IL-1B), and bacterial lipopolysaccharides (LPSs) induce NF-κB activity.[85] These factors via activation of IκB kinase (IKK) results in the phosphorylation and destruction of IκBα which results in the activation of NF-κB and its transfer to the nucleus. NF-κB is located in a nucleus on a specific gene sequence that will eventually lead to increased expression of various types of inflammatory cytokines (IL-1β, IL-6, TNF-α, IFN-γ, and MMP3), COX-2, and iNOS.[86] These inflammatory cytokines are not only upregulated by NF-κB but also activate NF-κB leading to continuity of inflammatory status.[87] Therefore, N. sativa may probably rupture these interactions by NF-κB suppression and plays an important duty in its anti-inflammatory activity.[88] Inhibition of the NF-κB pathway by N. sativa can be done in several ways: (1) preventing NF-κB transfer from the cytosol to the nucleus, (2) blocking the NF-KB subunit P50 bonded to the promoter of genes expressing inflammatory factors, especially TNF-α, (3) inhibition of NF-κB p65 subunit nuclear expression, and (4) prevention of phosphorylation and degradation of I-KBα (binding of I-KBα to NF-κB causes inactivation of this transcription factor).[87]

Immunomodulatory properties

Studies suggest that N. sativa can regulate immune responses.[82] In RA, decreased expression of IL-10 produced by Th2 can be accountable for the dominance of T-helper 1 over T-helper 2 cells at sites of inflamed synovium and in the peripheral blood and reduce in Th2 may exacerbate the inflammatory process in RA. N. sativa probably shifts the immune response from Th1 that produces pro-inflammatory cytokines such as TNF-α, IL-1β, and IL-6 to Th2 that results in anti-inflammatory cytokines such as IL-10 and IL-3. Studies have shown that an increase in IL-10 and IL-3 leads to an increase in T regulatory cell percentage (CD4+CD25+T-cell).[899091] T regulatory cells reduce the abnormal proliferation of immune cells, such as cytotoxic T-cells (CD8+) and Th1 cells, which is responsible for the secretion of many inflammatory cytokines.[919293] Therefore, N.sativa by regulation of T-lymphocytes leading to improve clinical symptoms of RA.[91]

CONCLUSION

This review article demonstrated that N. sativa could reduce oxidative stress and inflammation with various mechanisms have been proposed to contribute to the beneficial properties of N. sativa, including a reduction of lipid peroxidation via its antioxidant properties; agonist of PPAR-γ in adipose tissue; activation of AMPK, increased antioxidants inhibition of NF-κB pathway; increased in IL-10 expression, CD4+ T-cell percentage, T regulatory cell percentage in peripheral blood, and CD4+/CD8+ ratio. Therefore, N. sativa may be beneficial in chronic diseases (CVD, T2D, and RA) and can be used as an adjunct therapy. Furthermore, clinical studies have shown a positive effect of N. sativa on BP, FBG, and lipid profile, but to prove this claim, it is necessary to conduct experimental and well-designed clinical trial studies with a larger sample size on the effects of N. sativa on these chronic diseases.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.