Cumin (Cuminum cyminum) and black cumin (Nigella sativa) seeds: traditional uses, chemical constituents, and nutraceutical effects

Abstract

Although the seeds of cumin (Cuminum cyminum L.) are widely used as a spice for their distinctive aroma, they are also commonly used in traditional medicine to treat a variety of diseases. The literature presents ample evidence for the biomedical activities of cumin, which have generally been ascribed to its bioactive constituents such as terpenes, phenols, and flavonoids. Those health effects of cumin seeds that are experimentally validated are discussed in this review. Black seeds (Nigella sativa), which are totally unrelated to C. cyminum, have nevertheless taken the name ‘Black cumin’ and used in traditional systems of medicine for many disorders. Numerous pre-clinical and clinical trials have investigated its efficacy using the seed oil, essential oil, and its main constituent thymoquinone (TQ). These investigations support its use either independently or as an adjunct along with conventional drugs in respiratory problems, allergic rhinitis, dyspepsia, metabolic syndrome, diabetes mellitus, inflammatory diseases, and different types of human cancer. Multiple studies made in the last decades validate its health beneficial effects particularly in diabetes, dyslipidemia, hypertension, respiratory disorders, inflammatory diseases, and cancer. Nigella sativa seeds also possess immune stimulatory, gastroprotective, hepatoprotective, nephroprotective, and neuroprotective activities. TQ is the most abundant constituent of volatile oil of N. sativa seeds, and most of the medicinal properties of N. sativa are attributed mainly to TQ. All the available evidence suggests that TQ should be developed as a novel drug in clinical trials.

Cuminum cyminum, Nigella sativa, digestive stimulant, antidiabetic, anti-inflammatory, cancer preventive, immune stimulatory, gastroprotective

Introduction

Cumin seeds (Figure 1) are obtained from the herb Cuminum cyminum, native from East Mediterranean to South Asia belonging to the family Apiaceae—a member of the parsley family. Cumin seeds are oblong and yellow–grey. Cumin seeds are liberally used in several cuisines of many different food cultures since ancient times, in both whole and ground forms. In India, cumin seeds have been used for thousands of years as a traditional ingredient of innumerable dishes including kormas and soups and also form an ingredient of several other spice blends. Besides food use, it has also many applications in traditional medicine. In the Ayurvedic system of medicine in India, cumin seeds have immense medicinal value, particularly for digestive disorders. They are used in chronic diarrhoea and dyspepsia (Table 1).

Figure 1

Different varieties of cumin.

Table 1.

Differences between seed spices closely related to cumin seeds.

Common name of the spice	Cumin	Black cumin (Nigella/kalonji)	Bitter cumin (Kashmiri jeera/ Shahi jeera)
Scientific name	Cuminum cyminum	Nigella sativa	Cuminum nigrum or Bunium persicum
Genus/family	Cuminum/Apiaceae (member of Parsley family)	Nigella/Ranunculaceae	Cuminum/Apiaceae
Native of countries growing	East Meditaranian to South Asia. Now mostly grown in Pakistan, India, Uzbekistan Iran, Turkey, Morocco, Egypt, Syria, Chile, Mexico, and China	South to Southwest Asia. Middle Eastern Mediterranean region, South Europe, Northern India, Pakistan, Syria, Turkey, Iran, and Saudi Arabia	Central Asia to Northern India. Mountainous regions of North India
Traditional uses	Both whole and ground seeds are used in the cuisines of many cultures for ages. It has also many uses in traditional medicine. They are used in chronic diarrhoea and dyspepsia	A spice in Indian and Middle Eastern cuisines. In the ancient Egypt, it was used as a preservative in mummification. Traditionally, it is used for asthma, diabetes, hypertension, fever, inflammation, bronchitis, dizziness, eczema, and gastrointestinal disturbances	A spice in Northern Indian cookery, often the Moghul cooking
Main constituents	Cuminaldehyde	Thymoquinone	Cuminaldehyde, p-mentha-1,3-dien-7-al and p-mentha-1,4-dien-7-al

Black seed (also known as black cumin; Nigella sativa) (Figure 1) is an annual flowering plant belonging to the family Ranunculaceae and is a native of Southern Europe, North Africa, and Southwest Asia. Black cumin is cultivated in the Middle Eastern Mediterranean region, Southern Europe, Northern India, Pakistan, Syria, Turkey, Iran, and Saudi Arabia. Nigella sativa seeds and their oil have a long history of folklore usage in Indian and Arabian civilization as food and medicine (Yarnell and Abascal, 2011). The seeds of N. sativa have a pungent bitter taste and aroma and are used as a spice in Indian and extensively in Middle Eastern cuisines. The dry-roasted nigella seeds flavour curries, vegetables, and pulses. Black seeds are used in food as a flavouring additive in breads and pickles. It is also used as an ingredient of the spice mixture (panch phoron) and also independently of many recipes in Bengali cuisine. Cumin was traditionally used as a preservative in mummification in the ancient Egyptian civilization. Black cumin has a long history of use as medicine in the Indian traditional system of medicine like Unani and Ayurveda (Sharma et al., 2005). The black cumin seeds have traditionally been used in the Southeast Asian and Middle East countries for the treatment of diseases such as asthma, bronchitis, rheumatism, and other inflammatory diseases. Nigella sativa has extensively been used because of its therapeutic potential and possesses a wide spectrum of activities, namely, diuretic, antihypertensive, antidiabetic, anticancer, immune-modulatory, antimicrobial, anthelmintic, analgesic and anti-inflammatory, spasmolytic, bronchodilator, gastroprotective, hepatoprotective, and renal protective properties. Traditionally, seeds of N. sativa are widely used for asthma, diabetes, hypertension, fever, inflammation, bronchitis, dizziness, rheumatism, skin disorders, and gastrointestinal disturbances (Table 1). It is also used as a liver tonic, digestive, antidiarrhoeal, emmenagogue, and to control parasitic infections and boost immune system (Goreja, 2003).

Bunium persicum (occasionally referred to as Cuminum nigrum; also known as Shahi jeera), belonging to Apiaceae (parsley family), is a smaller variety of cumin with a different flavour, popularly used in North Indian, Pakistani, and Iranian foods (Figure 1). Until now, there is only very little scientific information on this spice.

Chemical constituents

Cumin seeds are nutritionally rich; they provide high amounts of fat (especially monounsaturated fat), protein, and dietary fibre. Vitamins B and E and several dietary minerals, especially iron, are also considerable in cumin seeds. Cuminaldehyde (Figure 2), cymene, and terpenoids are the major volatile components of cumin (Bettaieb et al., 2011). Cumin has a distinctive strong flavour. Its warm aroma is due to its essential oil content. Its main constituent of aroma compounds are cuminaldehyde and cuminic alcohol. Other important aroma compounds of roasted cumin are the substituted pyrazines, 2-ethoxy-3-isopropylpyrazine, 2-methoxy-3-sec-butylpyrazine, and 2-methoxy-3-methylpyrazine. Other components include γ-terpinene, safranal, p-cymene, and β-pinene (Li and Jiang, 2004).

Figure 2.

Major bioactive compounds of cumin and black seeds.

Nigella sativa seeds contain protein (26.7%), fat (28.5%), carbohydrates (24.9%), crude fibre (8.4%), and total ash (4.8%). Nigella sativa seeds also contain a good amount of various vitamins and minerals like Cu, P, Zn, and Fe. Many active compounds have been identified in N. sativa. The most important active compounds of N. sativa are thymoquinone (TQ) (30%–48%) (Figure 2), thymohydroquinone, dithymoquinone (nigellone), p-cymene (7%–15%), carvacrol (6%–12%), 4-terpineol (2%–7%), t-anethole (1%–4%), sesquiterpene longifolene (1%–8%), α-pinene, and thymol. (Boskabady and Shirmohammadi, 2002; Ali and Blunden, 2003). Nigella sativa also contains other compounds such as carvone, limonene, citronellol in trace amounts, and two varieties of alkaloids, i.e. isoquinoline alkaloids (e.g. nigellicimine and nigellicimine-N-oxide) and pyrazole alkaloids (e.g. nigellidine and nigellicine). Nigella sativa seeds also contain α-hederin, a water soluble pentacyclic triterpene (Al-Jassir, 1992; Nickavar et al., 2003). The pharmacological properties of N. sativa are mainly attributable to its quinine constituents, TQ being the most abundant. The N. sativa seeds contain fatty oil rich in unsaturated fatty acids, constituting linoleic acid (50%–60%), oleic acid (20%), eicosadienoic acid (3%), and dihomolinoleic acid (10%), and saturated fatty acids (palmitic and stearic acids) constitute up to 30 per cent. α-Sitosterol is the major sterol, accounting for 44%–54% of the total sterols in N. sativa oils, followed by stigmasterol (6.57%–20.9% of total sterols) (Cheikh-Rouhou et al., 2008; Mehta et al., 2008).

Bitter cumin (Shahi jeera) seeds contain calcium, vitamin A, potassium, sodium, iron, magnesium, and phosphorus. Bitter cumin (B. persicum) has 0.5 to 1.6 per cent essential oil, mainly carvone (45%–60%), limonene, and p-cymene. Oleoresin of bitter cumin is brownish to yellowish green. As there is not enough scientific information on the health effects of bitter cumin, this review is limited to C. cyminum (cumin seeds) and N. sativa (black seeds or black cumin)

Health effects of C. cyminum

Although the seeds of cumin (C. cyminum L.) are widely used as the spice for their distinctive aroma, they are also commonly used in traditional medicine to treat a variety of diseases, including chronic diarrhoea and dyspepsia, acute gastritis, diabetes, and cancer. The literature presents ample evidence for the biological and biomedical activities of cumin, which have generally been ascribed to its bioactive constituents such as terpenes, phenols, and flavonoids (Mnif and Aifa, 2015). Those health effects of cumin seeds that are experimentally validated (Figure 3) are discussed below.

Figure 3.

Multiple medicinal properties of Cuminum cyminum (cumin seeds).

Digestive stimulant action

In the context of cumin seeds being claimed in home remedies and traditional medicine, to aid digestion, an animal study has examined whether they have any stimulatory effect on the digestive enzymes. The influence of cumin seeds on the digestive enzymes of the rat pancreas and intestinal mucosa has particularly been investigated as a result of both continuous dietary intake and single oral administration (Platel and Srinivasan, 1996; 2000a) (Table 2). Dietary (1.25%) cumin lowered the activity of pancreatic lipase, whereas the activities of pancreatic trypsin, chymotrypsin, and amylase were significantly enhanced by the same (Platel and Srinivasan, 2000a). When given as a single oral dose, cumin exerted a lowering effect on pancreatic lipase, amylase, trypsin, and chymotrypsin. Among the terminal digestive enzymes, a small intestinal maltase activity was significantly higher in animals fed with cumin, whereas lactase and sucrose were unaffected (Platel and Srinivasan, 1996).

Table 2.

Digestive stimulant and antidiabetic effects of Cumin seeds.

Model/system	Effect observed	Researcher
Digestive stimulant action
Wistar rats	Dietary 1.25% cumin for 8 weeks significantly enhanced the activities of pancreatic trypsin, chymotrypsin, and amylase	Platel and Srinivasan, 2000a
Wistar rats	Dietary 1.25% cumin for 8 weeks significantly enhanced the small intestinal maltase activity	Platel and Srinivasan, 1996
Wistar rats	Dietary 1.25% cumin for 8 weeks had a significant stimulatory effect on bile flow rate and bile acid secretion	Platel and Srinivasan, 2000b
Wistar rats	Dietary 1.25% cumin for 8 weeks reduced gastrointestinal food transit time	Platel and Srinivasan, 2001
Antidiabetic action
Human NIDDM subjects	Fasting and post-prandial blood sugar was reduced when a formulation consisting cumin was orally administered for 24 weeks	Karnick, 1991
STZ-diabetic rats	Dietary cumin seeds for 8 weeks were observed to alleviate diabetes-related metabolic abnormalities	Willatgamuwa et al., 1998
Alloxan-diabetic rats	Hyperlipidemia associated with diabetes mellitus was also effectively countered by dietary cumin	Dandapani et al., 2002
Alloxan-diabetic rabbits	Cuminum nigrum seeds or their methanol/water extracts were found to be hypoglycemic	Akhtar and Ali, 1985
Alloxan-diabetic rabbits	The antihyperglycemic influence of Cuminum nigrum was produced by the fraction containing flavonoid compounds	Ahmad et al., 2000
Normal rabbits	Oral administration of C. cyminum decreased the area under the glucose tolerance curve and the hyperglycemic peak.	Roman-Ramos et al., 1995
STZ-diabetic rats	Methanolic extract of C. cyminum treated for 4 weeks mitigated oxidative stress and formation of AGEs	Jagtap and Patil, 2010
Sprague-Dawley rats	Cuminaldehyde isolated from C. cuminum inhibited lens aldose reductase and α-glucosidase of rats	Lee, 2005

Dietary cumin had a significant stimulatory effect on bile flow rate, the extent of increase in bile volume being 25 per cent, whereas its single oral dose did not have any effect on bile secretion rate (Platel and Srinivasan, 2000b). Dietary intake of cumin had a profound influence on bile acid output (quantity secreted per unit time), bile acid secretion being as high as 70 per cent over the control. Similar significant increases in bile acid secretion were seen in the case of cumin when administered as a single oral dose. Since bile juice makes a significant contribution to the overall process of digestion and absorption, essentially by supplying bile acids required for micelle formation, it is expected that cumin, which has a digestive stimulant action, could do so by stimulating biliary secretion of bile acids.

Another study has examined whether this digestive stimulant spice cumin also affects the duration of residence of food in the gastrointestinal tract of experimental rats (Platel and Srinivasan, 2001). Cumin produced a significant shortening of the food transit time by 25 per cent. The reduction in food transit time produced by dietary cumin roughly correlates with their beneficial influence either on digestive enzymes or bile secretion.

Antidiabetic effects

The antidiabetic effect of cumin seeds has been reported in human diabetics (Karnick, 1991) (Table 2). In this study, 80 patients with non-insulin dependent diabetes mellitus were orally administered for 24 weeks with an Ayurvedic formulation containing C. cyminum. Fasting and post-prandial blood sugar at 6-week intervals was significantly reduced in all the patients. Dietary cumin seeds were observed to alleviate diabetes-related metabolic abnormalities in STZ-diabetic rats (Willatgamuwa et al., 1998). An 8-week dietary regimen containing cumin powder (1.25%) was found to be remarkably beneficial, as indicated by a reduction in hyperglycaemia and glucosuria. Hyperlipidemia associated with diabetes mellitus was also effectively countered by dietary cumin in alloxan-diabetic rats (Dandapani et al., 2002).

Cuminum nigrum seeds or their water or methanol extracts have been observed to be hypoglycemic in alloxan-diabetic rabbits (Akhtar and Ali, 1985). The antihyperglycemic influence of C. nigrum has been attributed to the flavonoid compounds present in these seeds (Roman-Ramos et al., 1995; Ahmad et al., 2000). Methanolic extract of C. cyminum has been investigated in streptozotocin-diabetic rats on diabetes, oxidative stress, and formation of advanced glycated end products (AGE) in comparison with glibenclamide (Jagtap and Patil, 2010). In vitro studies indicated that cumin inhibited free radicals and AGE formation. The antidiabetic effect of cumin (treated for 4 weeks) was comparable to glibenclamide and even better in controlling oxidative stress and AGE formation, which is implicated in pathogenesis of diabetic microvascular complications. The inhibitory activity of C. cyminum seed–isolated component cuminaldehyde has been evaluated against lens aldose reductase and α-glucosidase isolated from Sprague-Dawley rats and compared with that of quercetin as an aldose reductase inhibitor and acarbose as an α-glucosidase inhibitor (Lee, 2005). Cuminaldehyde was about 1.8 and 1.6 times less in inhibitory activity than acarbose and quercetin, respectively. Nonetheless, cuminaldehyde may be useful for antidiabetic therapeutics.

Anti-inflammatory effects

Cumin essential oil was investigated for the anti-inflammatory effects in lipopolysaccharide (LPS)-stimulated RAW 264.7 cells and the underlying mechanisms (Wei et al., 2015) (Table 3). Volatile constituents were identified in essential oil using Gas Chromatography - Mass Spectrometry (GC-MS), the most abundant constituent being cuminaldehyde (48.8%). Cumin oil exerted anti-inflammatory effects in LPS-stimulated RAW cells through inhibiting NF-κB and mitogen-activated protein kinases suggesting its potential as an anti-inflammatory agent.

Table 3.

Cardioprotective, anti-inflammatory, and chemopreventive effects of cumin seeds.

Model/system	Effect observed	Researcher
Cardioprotective influence
Rat	Orally administered aqueous cumin extract (200 mg/kg body for 9 weeks) improved plasma nitric oxide and decreased the systolic blood pressure in hypertensive rats.	Kalaivani et al., 2013
Patients with hypercholesterolemia	Cumin extract significantly decreased the level of oxLDL while increasing the activities of paraoxonase, and arylesterase activities were increased in serum	Samani and Farrokhi, 2014
Anti-inflammatory effect
LPS-stimulated RAW 264.7 cells	Cumin essential oil exerted anti-inflammatory effects via inhibition of NF-κB and mitogen-activated protein kinases ERK and JNK	Wei et al., 2015
Chemopreventive effect
Mice	Dietary 2.5 and 5.0% cumin alleviated benzo(α)pyrene-induced forestomach tumourigenesis and 3-MCA-induced uterine cervix tumorigenesis, attributable to its ability to modulate carcinogen metabolism	Gagandeep et al. 2003
Rat	Dietary cumin (1.25% for 32 weeks) suppressed DMH-induced colon carcinogenesis. The excretion of fecal bile acids and neutral sterols was increased.	Nalini et al., 2006
HT29 colon cancer cells	Spent cumin from Ayurvedic industry was effective in arresting the cell cycle and inducing apoptosis	Arun et al., 2016
Miscellaneous nutraceutical effects
PC12 cells	C. cyminum essential oil inhibited the fibrillation of α-synuclein suggesting neuroprotective effects	Morshedi et al., 2015
Rat	Aqueous extract of cumin seeds showed anti-diarrhoeal effect when induced with castor oil	Sahoo et al., 2014

Cardio-protective influence through hypolipidemic and hypotensive effects

Cuminum cyminum is traditionally used for the treatment of indigestion and hypertension. The anti-hypertensive potential of aqueous extract of cumin seed and its role in arterial–endothelial nitric oxide synthase expression, inflammation, and oxidative stress have been evaluated in renal hypertensive rats (Kalaivani et al., 2013) (Table 3). Cumin administered orally (200 mg/kg body) for 9 weeks improved plasma nitric oxide and reduced the systolic blood pressure in hypertensive rats. This was accompanied by the up-regulation of the expression of inducible nitric oxide synthase (iNOS), Bcl-2, TRX1, and TRXR1 and down-regulation of the expression of Bax, TNF-α, and IL-6. These data suggest that cumin seeds augment endothelial functions and ameliorate inflammatory and oxidative stress in hypertensive rats.

Paraoxanase-1 plays a protective role against the oxidative modification of plasma lipoproteins and hydrolyzes lipid peroxides in human atherosclerotic lesions. Flavonoids present in cumin seeds are recognized to have antioxidant activity and improve the antioxidant system. A study demonstrated that cumin extract significantly decreased the level of oxidized Low-density lipoprotein (OxLDL) while increasing the activities of paraoxonase, and arylesterase activities were increased in serum (Samani and Farrokhi, 2014). The effect of cumin added to normal and hypercholesterolemia inducing diet on serum and liver cholesterol levels in rats has been studied (Sambaiah and Srinivasan, 1991). Dietary cumin did not show any cholesterol lowering effect when included in the diet (1.25%) at about 5-fold the normal consumption level.

Chemopreventive effects

Cancer chemopreventive potentials of dietary 2.5 and 5.0 per cent cumin were evaluated against benzo(α)pyrene-induced tumorigenesis in forestomach and 3-methylcholanthrene (MCA)-induced tumorigenesis in uterine cervix in mice (Gagandeep et al., 2003) (Table 3). Cumin produced a significant inhibition of stomach tumour. The effect on carcinogen/xenobiotic metabolizing phase I and phase II enzymes, antioxidant enzymes, and lipid peroxidation in the liver was also examined. Cytochrome P₄₅₀ and cytochrome b₅ were significantly augmented by dietary cumin. The phase II enzyme glutathione-S-transferase (GST) was increased by cumin, whereas the specific activities of superoxide dismutase (SOD) and catalase were significantly elevated. Lipid peroxidation was inhibited by cumin, suggesting that the cancer chemopreventive potential of cumin could be attributed to its ability to modulate carcinogen metabolism.

The effect of cumin (C. cyminum; dietary 1.25% for 32 weeks) was studied on colon cancer induced in rats by 1,2-dimethylhydrazine (DMH) s.c. 20 mg/kg of body weight (15 doses, at weekly intervals) (Nalini et al., 2006). Results showed that cumin suppresses colon carcinogenesis in the presence of the procarcinogen DMH. The excretion of fecal bile acids and neutral sterols was significantly increased in cumin+DMH-administered rats. Cholesterol and 3-hydroxy-3-methylglutaryl-CoA reductase activity were decreased in cumin+DMH-treated rats. Spent cumin generated from Ayurvedic industry was evaluated for its nutraceutical potential in terms of antioxidant (in terms of scavenging 2,2-Diphenyl-1-picryl-hydrazyl-hydrate [DPPH] radical), antidiabetic (in terms of better α-amylase inhibition and glucose uptake activity in L6 cells), and anticancer properties (in terms of arresting the cell cycle and inducing apoptosis in HT29 colon cancer cells) and compared with that of the raw cumin (Arun et al., 2016). The results suggested that nutraceutical food formulation made out of spent cumin could play a major role in the prevention or management of degenerative diseases.

Miscellaneous nutraceutical effects

Cumin seeds are traditionally used for the treatment of diarrhoea. The aqueous extract of cumin seeds (100, 250, and 500 mg/kg) has been examined against diarrhoea in albino rats induced with castor oil (Sahoo et al., 2014). The extract showed significant inhibition in the frequency of diarrhoea, delaying the defecation time, secretion of intestinal fluid, and intestinal propulsion in a dose-dependent manner. Fibrillation of α-synuclein (α-SN) is a critical process in the pathophysiology of several neurodegenerative diseases, especially Parkinson’s disease. A study on the inhibitory effects of C. cyminum essential oil on the fibrillation of α-SN indicated that the small abundant natural compound, cuminaldehyde can modulate α-SN fibrillation, suggesting that such natural active aldehyde could have potential therapeutic applications (Morshedi et al., 2015).

Health effects of N. sativa

Black cumin (N. sativa) has been in use in traditional systems of medicine for various medical disorders. Nigella sativa is used in Moroccan folk medicine for the treatment of diabetes mellitus. Many pre-clinical and clinical trials have investigated its efficacy, using the seed oil, essential oil, and its isolated main constituent TQ (Ali and Blunden, 2003). These investigations provide preliminary support for its use in asthma, allergic rhinitis, and atopic dermatitis (Yarnell and Abascal, 2011). Black cumin might help in dyspepsia, respiratory problems, diabetes mellitus, and metabolic syndrome (Yarnell and Abascal, 2011). A meta-analysis of clinical trials suggests that N. sativa has a short-term benefit in lowering systolic and diastolic blood pressure, and its various extracts can reduce triglycerides, LDL, and total cholesterol (Sahebkar et al., 2016a; 2016b). Several studies made in the last decades validate its health beneficial effects particularly in diabetes, dyslipidemia, hypertension, and obesity. A systematic review of all human trials has revealed that N. sativa supplementation might be effective in glycemic control in humans (Mohtashami and Entezari, 2016).

Antidiabetic effects

Nigella sativa seeds are traditionally used in the management of diabetes mellitus in indigenous systems of medicine and folk remedies. Defatted extract of N. sativa seed is reported to increase glucose-induced insulin release from isolated rat pancreatic islets in vitro (Rchid et al., 2004) (Table 4). The effect of N. sativa extracts (defatted fractions either containing acidic and neutral compounds or containing basic compounds) have been investigated on insulin secretion in vitro in rat pancreatic islets in the presence of glucose (8.3 mmol/l). Results showed that the antidiabetic properties of N. sativa seeds may partially be mediated by the stimulation of insulin release, especially by the basic subfraction of the seed. The possible insulinotropic property of N. sativa oil has also been studied in STZ plus nicotinamide (NA) induced diabetes mellitus in hamsters. Nigella sativa oil treatment for four weeks decreased blood glucose and increased serum insulin (Fararh et al., 2002). Immunohistochemical staining revealed the presence of insulin in the pancreas from N. sativa oil-treated group, suggesting that the hypoglycemic effect results, at least partly, from a stimulatory effect on β-cell function.

Table 4.

Antidiabetic effects of black cumin (Nigella sativa) seeds.

Model/system	Effect observed	Researcher
STZ-diabetic rats	The oil of N. sativa significantly lowered blood glucose in STZ-diabetic rats after 2, 4, and 6 weeks	El-Dakhakhny et al., 2002
Rat pancreatic islets	Defatted extract of N. sativa seed increased glucose induced insulin release from isolated rat pancreatic islets in vitro	Rchid et al., 2004
STZ/NA-diabetic hamsters	N. sativa oil treatment for 4 weeks decreased blood glucose and increased serum insulin	Fararh et al., 2002
STZ-diabetic hamsters	The hypoglycemic effect of N. sativa oil (400 mg/kg by p.o.) is partially due to a decrease in hepatic gluconeogenesis	Fararh et al., 2004
Hepatocytes (HepG2)	Defatted extract of N. sativa seeds increased glucose consumption by hepatocytes (HepG2) in vitro through activation of AMPK	Yuan et al., 2014
Diabetic rabbits	N. sativa extract (orally for 2 months) decreased lipid peroxidation and increased antioxidant defense system	Meral et al., 2001
STZ-diabetic rats	Daily oral administration of ethanol extract of N. sativa seeds (300 mg/kg for 30 days) reduced hyperglycemia and improved altered levels of lipid peroxidation products and antioxidant enzymes in liver and kidney	Kaleem et al., 2006
STZ-diabetic rats	N. sativa oil (0.2 ml/kg for 30 days) decreased hyperglycemia and restored lowered serum insulin with partial regeneration of pancreatic β-cells	Kanter et al., 2003
STZ-diabetic rats	N. sativa treatment exerts a protective effect on diabetes by decreasing oxidative stress and preserving pancreatic β-cell integrity	Kanter et al., 2004
STZ-diabetic rats fed with high-fat diet	Daily administration of N. sativa oil significantly induced the gene expression of insulin receptor and upregulated the expression of insulin-like growth factor-1	Balbaa et al., 2016
STZ-diabetic rats	N. sativa seed oil down-regulated the expression of apoptotic markers in the aortic medial layer of diabetic rats, thus preventing apoptosis in vascular structures	Cüce et al., 2015
STZ-diabetic rats	Protective effects of N. sativa oil on insulin sensitivity and ultrastructural changes of pancreatic β-cells	Kanter et al., 2009
STZ-diabetic rats	N. sativa extract, oil, and TQ decreased the diabetes-induced lipid peroxides and hyperglycemia, and significantly increased serum insulin and SOD activity in tissues	Abdelmeguid et al., 2010
STZ-NA–induced diabetic rats	Oral administration of TQ dose-dependently improved the glycemic status; levels of insulin and Hb increased; altered activities of carbohydrate metabolizing enzymes were restored	Pari and Sankaranarayanan, 2009
Patients with diabetes	N. sativa oil showed a beneficial effect on various clinical and biochemical parameters of the insulin resistance syndrome	Najmi et al., 2008
Patients with type 2 diabetes	N. sativa (2 g/day) brought reductions in fasting blood glucose, postprandially, and glycosylated haemoglobin.	Bamosa et al., 2010

The oil of N. sativa significantly lowered blood glucose in STZ-diabetic rats after 2, 4, and 6 weeks (El-Dakhakhny et al., 2002). A study of the effect of N. sativa oil on insulin secretion from isolated rat pancreatic islets in the presence of glucose indicated that its hypoglycemic effect might be mediated by extra-pancreatic actions rather than by stimulation of insulin release. The hypoglycemic effect of N. sativa oil (400 mg/kg by p.o.) is partly due to decreased hepatic gluconeogenesis (Fararh et al., 2004). Indazole-type alkaloid 17-O-(β-D-glucopyranosyl)-4-O-methyl nigellidine present in the defatted extract of N. sativa seeds increased glucose consumption by hepatocytes (HepG2 cells) in vitro through activation of AMP-activated protein kinase (AMPK) (Yuan et al., 2014).

Nigella sativa extract given orally for 2 months decreased lipid peroxidation and increased antioxidant defence system and also prevented the lipid peroxidation-induced liver damage in diabetic rabbits (Meral et al., 2001). Daily oral administration of ethanol extract of N. sativa seeds (300 mg/kg) to STZ-diabetic rats for 30 days reduced the elevated levels of blood glucose, lipids, plasma insulin, and improved altered levels of lipid peroxidation products and antioxidant enzymes in liver and kidney (Kaleem et al., 2006). This suggested that in addition to antidiabetic activity, N. sativa seeds may control diabetic complications through antioxidant effects. Treatment of N. sativa oil (0.2 ml/kg, i.p.) for 30 days decreased the elevation in serum glucose and restored lowered serum insulin with partial regeneration or proliferation of pancreatic β-cells in STZ-diabetic rats (Kanter et al., 2003). The possible protective effects of N. sativa (0.2 ml/kg, i.p.) against β-cell damage from STZ-diabetes in rats have been evidenced by the observed decrease in lipid peroxidation and serum nitric oxide and increase in the activities of antioxidant enzymes in the pancreas (Kanter et al., 2004). Increased staining for insulin and preservation of β-cell numbers were evident in N. sativa–treated diabetic rats. This suggests that N. sativa treatment exerts a protective effect on diabetes by decreasing oxidative stress and preserving pancreatic β-cell integrity.

Nigella sativa oil administration (daily) to STZ-induced diabetic rats maintained on a high-fat diet significantly induced the gene expression of insulin receptor (Balbaa et al., 2016). Nigella sativa oil upregulated the expression of IGF-1 and phosphoinositide-3 kinase, whereas the expression of ADAM-17 was downregulated. Also, the N. sativa oil significantly reduced blood glucose level, individual lipid profile, oxidative stress markers, serum insulin or insulin receptor ratio, and the TNF-α, confirming that N. sativa oil has an antidiabetic activity. Thus, the daily N. sativa oil treatment improves insulin-induced signalling.

Hyperglycaemia is an important risk factor for the development and progression of the macrovascular and microvascular complications that occur in diabetes. The expression of apoptotic markers in the medial aortic layer of diabetic rats and the effects of N. sativa seed oil on the expression of these markers have been investigated (Cüce et al., 2015). It is understood that N. sativa seed oil is effective against diabetes and merits further treatment strategies for preventing apoptosis in vascular structures.

Treatment of streptozotocin-diabetic rats with N. sativa extract, N. sativa oil, and TQ, significantly decreased the diabetes-induced lipid peroxides and hyperglycemia, and significantly increased serum insulin and SOD activity in tissues. Nigella sativa oil and TQ have therapeutic potential and are protective against STZ-diabetes by decreasing oxidative stress, thus preserving pancreatic β-cell integrity, leading to increased insulin levels (Abdelmeguid et al., 2010). The protective effects of N. sativa oil on insulin sensitivity and ultrastructural changes of pancreatic β-cells in STZ-induced diabetic rats are reported (Kanter et al., 2009). It is evident that N. sativa treatment exerts a protective effect on diabetes by decreasing morphological changes and preserving the pancreatic β-cell integrity (Kanter et al., 2009). The anti-hyperglycemic potential of TQ and the effect on the activities of key enzymes of carbohydrate metabolism in STZ-NA–induced diabetic rats have been evaluated (Pari and Sankaranarayanan, 2009). Oral administration of TQ (20, 40, and 80 mg/kg body weight for 45 days) dose-dependently improved the glycemic status in STZ/NA-induced diabetic rats. The levels of insulin and haemoglobin increased along with a decrease in glucose and HbA1c levels. The altered activities of carbohydrate-metabolizing enzymes were also restored (Pari and Sankaranarayanan, 2009).

In a clinical study, the adjuvant effect of N. sativa oil on various clinical and biochemical parameters of the insulin resistance syndrome in patients with diabetes and dyslipidemia has been evidenced (Najmi et al., 2008). Nigella sativa accentuates glucose-induced secretion of insulin besides negatively affecting glucose absorption. Hence, it is of immense therapeutic benefit in diabetic individuals (Kapoor, 2009). The effect of N. sativa seeds used as an adjuvant therapy in addition to the anti-diabetic medications on the glycemic control of patients with type 2 diabetes mellitus was investigated (Bamosa et al., 2010). Nigella sativa at a dose of 2 g/day caused significant reductions in fasting blood glucose, 2-hour post-prandially, and glycosylated haemoglobin. The results indicate that a dose of 2 g/day of N. sativa could serve as a useful adjuvant to oral hypoglycemic drugs in patients with type 2 diabetes mellitus.

Ameliorative effects of N. sativa on dyslipidemia

Dyslipidemia is an established risk factor for ischemic heart disease. Nigella sativa has been used for the treatment and prevention of hyperlipidemia (Asgary et al., 2015). Different preparations of N. sativa including seed powder (100 mg–20 g daily), seed oil (20–800 mg daily), TQ (3.5–20 mg daily), and methanolic extract reduced plasma levels of total cholesterol, low-density lipoprotein cholesterol, and triglycerides. In clinical trials, N. sativa was found to be effective when added as an adjunct to conventional hypolipidemic and antidiabetic medications. Inhibition of dietary cholesterol absorption, decreased hepatic cholesterol synthesis, and up-regulation of LDL receptors contribute to lipid-lowering effects of N. sativa. Overall, the evidence from an experimental and a clinical study suggests that N. sativa seeds are promising natural therapy for patients with dyslipidemia.

Anti-inflammatory property and analgesic activity

The antinociceptive and anti-inflammatory effects of TQ (Table 6), supporting the common perception of N. Sativa as a potent analgesic and anti-inflammatory agent, have been recently reviewed (Amin and Hosseinzadeh, 2016). Many protective properties are attributed to radical scavenging activity as well as an interaction with molecular targets involved in inflammation (proinflammatory enzymes and cytokines). Further investigations are needed to understand the precise mechanisms responsible for the antinociceptive and anti-inflammatory effects of its active constituents.

Table 6.

Anti-inflammatory/analgesic effects and immunomodulatory property of black cumin (Nigella sativa) seeds.

Model/system	Effect observed	Researcher
Anti-inflammatory property and analgesic activity
Rats	N. sativa essential oil produced a significant analgesic effect on acetic acid-induced writhing, formalin, and light tail flick tests	Hajhashemi et al., 2004
Rats	Intraperitoneal injection of N. sativa oil from 100 to 400 µl/kg significantly inhibited carrageenan-induced paw oedema	Hajhashemi et al., 2004
BV-2 murine microglia cells	TQ showed an effective anti-inflammatory effect on LPS-stimulated microglial cells	Taka et al., 2015
Human trials	Anti-osteoporotic effects of N. sativa and TQ are evidenced by observing inhibition of inflammatory cytokines (interleukin-1 and 6) and the transcription factor (NFκB)	Shuid et al., 2012
Pancreatic ductal adenocarcinoma (PDA) cells	TQ inhibited proliferation in these cells by inhibiting proinflammatory pathways; this anti-inflammatory potential involved modulation of the expression of different pro-inflammatory cytokines and chemokines	Chehl et al., 2009
Rats	Oral administration of TQ (5 mg/kg body/day for 21 days) showed anti-arthritic activity by significantly reducing pro-inflammatory mediators	Umar et al., 2012
Immunomodulatory action
BALB/c mice and C57/BL6 primary cells	Aqueous extract of N. sativa significantly enhanced the total white blood cells count and increased spleen weight in BALB/c mice and enhanced splenocyte proliferation	Ghonime et al., 2011
Long-Evans rat	Treatment with N. sativa oil significantly decreased the antibody production in response to typhoid vaccination	Torres et al., 2010
Pigeons	Co-administration of N. sativa (2.5%) with oxytetracycline (OXT) completely blocked the decreasing effects on total leukocyte and lymphocyte counts elicited by OXT and produced immunostimulant effects	Abel-Salam, 2012
Rats	N. sativa oil showed a promising radioprotective action against immunosuppressive and oxidative effects of γ-radiation	Assayed, 2010
Mice	N. sativa seed extract significantly improved symptoms and immune parameters in murine OVA-induced allergic diarrhoea	Duncker et al. 2012

Development of solid tumour malignancies is closely associated with inflammation. The steam-distilled essential oil of N. sativa, which mainly contains p-cymene (37.3%) and TQ (13.7%), investigated for its analgesic and antiinflammatory properties in rats was found to produce a significant analgesic effect on acetic acid-induced writhing, formalin, and light tail flick tests (Hajhashemi et al., 2004). Intraperitoneal injection of 100, 200, and 400 µl/kg significantly inhibited carrageenan-induced paw oedema. Mechanism(s) other than opioid receptors are believed to be involved in this analgesic effect of the Nigella essential oil. Its administration showed anti-inflammatory activity probably attributable to TQ, one of the major components of black cumin. The anti-inflammatory effect of TQ on LPS-stimulated BV-2 murine microglia cells has been reported, wherein TQ was effective in reducing nitrate with parallel decline of iNOS protein expression evidenced (Taka et al., 2015). TQ also reduced LPS-mediated elevation in gene expression of Cxcl10 and some of other cytokines. The anti-inflammatory properties of TQ in LPS-activated microglial cells suggested the applicability of TQ in delaying the onset of inflammation-mediated neurodegenerative disorders.

The aqueous extract of N. sativa has been found to possess anti-inflammatory and analgesic activities in animal models. Although osteoporosis is linked to oxidative stress and inflammation, the anti-osteoporotic effects of N. sativa and TQ are evidenced by observing the inhibition of inflammatory cytokines (interleukin (IL)-1 and 6) and the transcription factor (NFκB). Both N. sativa and TQ have shown potential as an anti-osteoporotic agent (Shuid et al., 2012). TQ induced apoptosis and inhibited proliferation in pancreatic ductal adenocarcinoma (PDA) cells. This anti-inflammatory potential involved an effect on the expression of different proinflammatory cytokines and chemokines. TQ dose-dependently reduced PDA cell synthesis of MCP-1, TNF-α, IL-1β, and Cox-2. TQ as an inhibitor of proinflammatory pathways provides an effective strategy that combines anti-inflammatory and proapoptotic modes of action (Chehl et al., 2009). A clinical trial was conducted to investigate the anti-inflammatory effects of N. sativa in patients with allergic rhinitis symptoms. The anti-allergic effects of N. sativa components could be attributed to allergic rhinitis (Nikakhlagh et al., 2011). The anti-arthritic activity of orally administered TQ (5 mg/kg body once daily for 21 days) in collagen-induced arthritic Wistar rats was evidenced with significantly reduced proinflammatory mediators [IL-1β, IL-6, TNF-α, IFN-γ, and PGE₂] and increased IL-10 (Umar et al., 2012).

Immunomodulatory action

The immunomodulatory properties of N. sativa and its major active ingredient, TQ in terms of their experimentally documented ability to modulate cellular and humoral adaptive immune responses (Table 6) have comprehensively been reviewed (Majdalawieh and Fayyad, 2015). The molecular and cellular mechanisms underlying such immunomodulatory effects of N. sativa and TQ are highlighted, and the signal transduction pathways implicated in the immunoregulatory functions are suggested. Experimental evidence suggests that N. sativa extracts and TQ can therapeutically be employed in the regulation of immune reactions in infectious and non-infectious conditions such as allergy, autoimmunity, and cancer.

The potential immunomodulatory effects of aqueous extract of N. sativa investigated in BALB/c mice and C57/BL6 primary cells with respect to splenocyte proliferation, macrophage function, and anti-tumor activity demonstrated that N. sativa significantly enhances splenocyte proliferation in a dose-responsive manner (Ghonime et al., 2011). Aqueous extract of N. sativa significantly suppressed the secretion of key proinflammatory mediators (IL-6, TNF-α, and NO) by primary macrophages indicating anti-inflammatory effects in vitro. Nigella sativa methanolic extract treatment (intraperitoneal) enhanced the total white blood cells count and increased spleen weight in BALB/c mice, suggesting the immunomodulatory activity of N. sativa seeds (Ghonime et al., 2011). Treatment with N. sativa oil significantly decreased the antibody production in response to typhoid vaccination (antigen typhoid TH) in a Long-Evans rat model. These results indicated that the N. sativa seeds could be considered as a potential immunosuppressive cytotoxic agent (Torres et al., 2010). Co-administration of N. sativa (2.5%) with oxytetracycline completely blocked the leukocyte and lymphocyte decreasing effects elicited by oxytetracycline and produced immunostimulant effects in pigeons indicating an immune-protective effect (Abel-Salam, 2012). Nigella sativa oil is also shown to have a promising radioprotective action against immunosuppressive and oxidative effects of γ-radiation in rats (Assayed, 2010). Nigella sativa seed extract significantly improved symptoms and immune parameters in murine ovalbumin-induced allergic diarrhoea in mice (Duncker et al., 2012).

Antioxidant and antimicrobial activity

An evaluation of the essential oil of N. sativa seeds, for antioxidants, showed that TQ and other components (carvacrol, t-anethole, and 4-terpineol) have a radical scavenging property. These constituents and the essential oil showed variable antioxidant activity when tested in the diphenylpicrylhydrazyl assay; they also effectively scavenged OH radical in the assay for non-enzymatic lipid peroxidation.

TQ has been shown to suppress the ferric nitrilotriacetate-induced oxidative stress in Wistar rats (Khan and Sultana, 2005). Dietary N. sativa seeds inhibited the oxidative stress caused by oxidized corn oil in rats (Al-Othman et al., 2006). Dietary N. sativa (10%) neutralized the oxidative stress induced by hepatocarcinogens such as dibutylamine and sodium nitrate in albino rats by normalizing glutathione and nitric oxide levels (Gendy et al., 2007). The N. sativa seed oil and TQ (intraperitoneal) are shown to have protective effects on lipid peroxidation process during ischemia-reperfusion injury in rat hippocampus (Hosseinzadeh et al., 2007). Treating broiler chicks with N. sativa seed for 6 weeks reduced the oxidative stress in the liver by increasing the activities of myeloperoxidase, glutathione-S-transferase, CAT, adenosine deaminase, and by decreasing hepatic lipid peroxidation (Sogut et al., 2008). The TQ pre-treatment countered the increased level of lipid peroxidation and augmented the antioxidant enzyme activities in the erythrocyte during 1,2-dimethylhydrazine-induced colon carcinogenesis in Wistar rats (Harzallah et al., 2012).

The bioactive compounds of N. sativa essential oil identified using GC and GC-MS included p-cymene, TQ, α-thujene, longifolene, β-pinene, α-pinene, and carvacrol. Nigella sativa essential oil exhibited different biological activities including antifungal, antibacterial, and antioxidant potentials. Nigella sativa essential oil completely inhibited different Gram-negative and Gram-positive bacteria (Morsi, 2000). Nigella sativa oil also exhibited stronger radical scavenging activity against DPPḢ radical in comparison with synthetic antioxidants.

Anti-cancer properties

The anti-cancer effect of N. sativa has extensively been studied in different in vitro and in vivo models (Table 5). Nigella sativa is able to exert antioxidant, anti-mutagenic, cytotoxic, pro-apoptotic, anti-proliferative, and anti-metastatic effects in various primary cancer cells and cancer cell lines (Majdalawieh and Fayyad, 2016). The available studies strongly suggest that N. sativa could serve as an effective agent to control tumour initiation, growth, and metastasis independently or in combination with conventional chemotherapeutic drugs.

Table 5.

Anti-cancer effects of black cumin (Nigella sativa) seeds.

Model/system	Effect observed	Researcher
Mice—B()P-induced forestomach cancer	N. sativa extract ameliorated benz(a-)pyrene-induced carcinogenesis in the forestomach	Aruna and Sivarama-krishnan, 1990
Rat—DMH-induced colon cancer	Orally administered N.sativa oil (14 weeks) reduced the induction and development of 1,2-dimethylhydrazine-induced aberrant crypt foci (ACF), putative preneoplastic lesions for colon cancer	Salim and Fukushima, 2003
Rats—gastric ulcer induced by necrotizing agents	N. sativa aqueous suspension significantly ameliorated the ulcer severity and basal gastric acid secretion. The anti-ulcer effect is possibly prostaglandin- mediated and/or through its antioxidant and anti-secretory activities	Al Mofleh et al., 2008
Wistar rats—colon cancer induced with carcinogens	1000 or 4000 ppm N. sativa volatile oil in the diet for 30 weeks significantly reduced malignant and benign colon tumour sizes, incidences and multiplicities	Salim, 2010
Rats—colitis induced with TNBS	Oral N. sativa oil, by preventing inflammatory status in the blood, partly protected colonic tissue against experimental ulcerative colitis	Isik et al., 2011
Rat—DMBA-induced breast cancer	Orally administered (1—10 mg/kg) N. sativa oil or thymoquinone thrice in a week for 4 months exerted a protective effect against DMBA-induced breast cancer	Linjawi et al., 2015
Children with acute lymphoblastic leukaemia	Black cumin seeds (80 mg/kg/day for 1 week) decreased methotrexane hepatotoxicity and improved survival in children with leukaemia	Hagag et al., 2015
Cancer cells	Thymoquinone suppressed tumour cell proliferation in colorectal carcinoma, breast adenocarcinoma, osteosarcoma, ovarian carcinoma, myeloblastic leukaemia, and pancreatic carcinoma	Gali-Muhtasib et al., 2006
Cancer cells	TQ suppressed tumor cell proliferation in the case of breast adenocarcinoma, pancreatic carcinoma, colorectal carcinoma, ovarian carcinoma, osteosarcoma, and myeloblastic leukaemia	Allahghadri et al., 2010
Prostate cancer (PC-3) cell	TQ is shown to prevent tumour angiogenesis in a xenograft human cancer model	Yi et al., 2008
MCF-7 cells	N. sativa lipid extract and aqueous extract exhibited cytotoxicity to MCF-7 cells with LC50 of 2.7 and 50 mg/ml	Mahmoud and Torchilin, 2012
Human cervical squamous carcinoma cells (SiHa)	TQ was with IC50 values of 10.7 µg/ml; elimination of SiHa cells via apoptosis with down-regulation of the Bcl-2 protein	Ng et al., 2011
Human osteosarcoma cell line SaOS-2	Anti-tumour and anti-angiogenic activity of TQ possibly mediated by an inhibition of NF-κB and downstream effector molecules	Peng et al., 2013
Breast cancer MDA-MB-231 cells	TQ exerted a strong anti-proliferative effect on breast cancer cells via its potential effect on the PPAR-γ activation pathway; migration and invasion were also reduced	Woo et al. 2011
Pancreatic cancer cells	Treatment with TQ down-regulated MUC4 expression and induced apoptosis; increased apoptosis, decreased motility, and decreased migration of pancreatic cancer cells	Torres et al., 2010
Panc-1 cells	TQ dose-dependently suppressed the migration and invasion of panc-1 cells by down-regulating NF-kB and MMP-9	Wu et al., 2011
PC-3 cells	Administration of N. sativa reduced the carcinogenic effects of DMBA in mammary carcinoma	Shafi et al., 2008
Gastric cancer cells	Pre-treatment with TQ significantly increased the apoptotic effects induced by 5-FU in gastric cancer cell lines in vitro	Lei et al., 2012

Nigella sativa extract ameliorated the benz(α-)pyrene-induced carcinogenesis in the forestomach in mice (Aruna and Sivaramakrishnan, 1990). This is partly attributed to the ability to influence phase II enzymes. Orally administered N. sativa oil (14 weeks) interfered with the induction of aberrant crypt foci (ACF) by 1,2-dimethylhydrazine, putative preneoplastic lesions for colon cancer in rats (Salim and Fukushima, 2003). This inhibition may be associated, in part, with the suppression of cell proliferation in the colonic mucosa. Nigella sativa aqueous suspension significantly prevented gastric ulcer formation experimentally induced by necrotizing agents and also significantly ameliorated the severity of ulcer and gastric acid secretion in pylorus-ligated Shay rats (Al Mofleh et al., 2008).

The chemopreventive potential of N. sativa oil on tumour formation has been revealed in a study using a rat multiorgan carcinogenesis model induced by five different carcinogens (Salim, 2010). Post-initiation administration of 1000 or 4000 ppm N. sativa volatile oil in the diet for 30 weeks significantly reduced colon tumour sizes, incidences, and multiplicities. Nigella sativa volatile oil also significantly decreased the incidences and multiplicities of tumours in the lungs and alimentary canal (particularly the oesophagus and forestomach). Thus, N. sativa exerts potential inhibitory effects on tumour development in multiple organ sites (Salim, 2010). Nigella sativa oil (orally administered for 3 days) decreased the proinflammatory cytokines (TNF-α, IL-1β, and IL-6) in the blood of rats with experimental colitis induced with trinitrobenzene sulfonic acid (Isik et al., 2011). Nigella sativa oil, by preventing inflammatory status in the blood, partly protected colonic tissue against experimental ulcerative colitis. Oral TQ (1–10 mg/kg) or N. sativa oil (thrice in a week for 4 months) exerted a protective effect against breast cancer in female rats induced by 7,12-dimethylbenz[α-]anthracene as revealed by tumour markers, histopathological alterations, and the regulation of several genes (Brca1, Brca2, Id-1, and P53 mutation) related to breast cancer (Linjawi et al., 2015).

Acute lymphoblastic leukaemia (ALL) is a common childhood malignancy and is conventionally treated with methotrexate which also produces hepatotoxicity. The therapeutic value of N. sativa oil in methotrexate-induced hepatotoxicity has been assessed in 40 Egyptian children with ALL under methotrexate therapy (Hagag et al., 2015). Nigella sativa oil (80 mg/kg/day for 1 week) produced significant differences in remission, relapse, death, and disease-free survival. Nigella sativa seeds decreased methotrexate hepatotoxicity and improved survival. This report is suggestive of its application as an adjuvant drug in patients under methotrexate therapy.

Nigella sativa seed oil and TQ have been understood to exert antioxidant and chemopreventive properties (Allahghadri et al., 2010). TQ could suppress tumour cell proliferation in the case of breast adenocarcinoma, pancreatic carcinoma, colorectal carcinoma, osteosarcoma, ovarian carcinoma, and myeloblastic leukaemia (Allahghadri et al., 2010). The cancer chemopreventive ability of TQ has been explained by its ability to modulate cell division in cancer cells, involving downregulation of Bcl-xL, cyclin D1, and VEGF (Aggarwal et al., 2008). TQ is reported to be effective in inhibiting human umbilical vein EC migration and invasion, suggesting its role in angiogenesis (Gali-Muhtasib et al., 2006). TQ is shown to prevent tumour angiogenesis in a xenograft human prostate cancer (PC-3) model (Yi et al., 2008). Nigella sativa, its oil, and TQ are effective against cancer in the blood system, lung, kidney, liver, prostate, breast, cervix, and skin. Some studies attribute the anti-cancer effect of TQ to its role as an antioxidant, ability to improve body’s immune system, and ability to induce apoptosis and control Akt pathway (Khan et al., 2011).

The cytotoxic effects of N. sativa seed extract as an adjuvant therapy to doxorubicin on human MCF-7 breast cancer cells are reported. Nigella sativa lipid extract was found to be cytotoxic to MCF-7 cells with LC₅₀ of 2.7 mg/ml, whereas its aqueous extract exhibited cytotoxicity at about 50 mg/ml (Mahmoud and Torchilin, 2012). TQ was found to be cytotoxic to human cervical squamous carcinoma cells (SiHa) with IC₅₀ values of 10.7 µg/ml as determined by MTT assay, whereas it was less cytotoxic towards the normal cells. Cell cycle analysis indicated induction of apoptosis by the compound and elimination of SiHa cells via apoptosis with down-regulation of the Bcl-2 protein (Ng et al., 2011). An investigation of the anti-tumour and anti-angiogenic effects of TQ on osteosarcoma in vitro and in vivo showed that TQ induced higher growth inhibition and apoptosis in the human osteosarcoma cell line SaOS-2. TQ significantly blocked human umbilical vein endothelial cell tube formation in a dose-dependent manner. The anti-tumour and anti-angiogenic activity of TQ in osteosarcoma is possibly mediated by inhibition of NF-κB and downstream effector molecules (Peng et al., 2013).

TQ exerted a strong anti-proliferative effect in breast cancer cells via its potential effect on the PPAR-γ activation pathway, and in combination with doxorubicin and 5-fluorouracil, TQ’s cytotoxicity was found to be increased. Migration and invasion of MDA-MB-231 cells were also reduced by TQ, which was found to increase PPAR-γ activity and down-regulate the expression of Bcl-2, Bcl-xL, and survivin in breast cancer cells (Woo et al., 2011). An investigation of the effect of TQ on pancreatic cancer cells and on MUC4 expression revealed down-regulated MUC4 expression and induced apoptosis in pancreatic cancer cells. The decrease in MUC4 expression was accompanied by increased apoptosis, decreased motility, and decreased migration of pancreatic cancer cells (Torres et al., 2010).

The administration of N. sativa reduced the carcinogenic effects of DMBA in mammary carcinoma which indicated its protective role in mammary carcinoma (Shafi et al., 2008). TQ dose-dependently suppressed the migration and invasion of Panc-1 cells. TQ also significantly down-regulated NF-kB and MMP-9 in Panc-1 cells. Administration of TQ significantly reduced tumour metastasis. Furthermore, the expression of NF-kB and MMP-9 protein in tumour tissues was down-regulated after treatment with TQ, thus exerting anti-metastatic activity on pancreatic cancer both in vitro and in vivo (Wu et al., 2011). The chemo-sensitizing effect of TQ and 5-fluorouracil (5-FU) on gastric cancer cells both in vitro and in vivo is reported (Lei et al., 2012). Pre-treatment with TQ significantly increased the apoptotic effects induced by 5-FU in gastric cancer cell lines in vitro. The combined treatment of TQ with 5-FU was more effective in anti-tumour action than either of them individually in a xeno-graft tumour mouse model. The TQ/5-FU-combined treatment induces apoptosis by enhancing the activation of both caspase-3 and caspase-9 in gastric cancer cells (Lei et al., 2012).

In summary, N. sativa oil and TQ are found to inhibit experimental carcinogenesis in different animal models. It has been shown to arrest the growth of various cancer cells in culture as well as xenograft tumours in vivo. The mode of anticancer effects of TQ includes inhibition of carcinogen-metabolizing enzyme activity and oxidative damage to cellular macromolecules, amelioration of inflammation, inhibition of cell cycle and apoptosis in tumour cells, inhibition of tumour angiogenesis, and suppression of migration, invasion, and metastasis of cancer cells. TQ improves anti-cancer effects when combined with conventionally used chemotherapeutic agents. At the molecular level, TQ targets intracellular signalling pathways, particularly a variety of kinases and transcription factors, which are activated during tumourigenesis.

Gastroprotective effect

Nigella sativa oil and its constituents are proved to exert gastroprotective effect (Table 7); some of the potential mechanisms exhibited by N. sativa in preventing or curing gastric ulcers are reviewed recently (Khan et al., 2016). The mechanism of gastroprotective effect of TQ has been assessed in rats injected with TQ (10 and 20 mg/kg) and subsequently subjected to ischemia or reperfusion insult. TQ restored the altered acid secretion, gastric mucosal content, lipid peroxide, and the activity of myeloperoxidase, reduced glutathione, and total nitric oxide along with ulcer index, the efficacy being comparable with that of the reference drug omeprazole. TQ exerted gastroprotection via inhibiting proton pump, acid secretion and neutrophil infiltration, while enhancing mucin secretion, and nitric oxide production, in addition to the antioxidant influences (Magdy et al., 2012).

Table 7.

Gastroprotectove, hepatoprotective, nephroprotective, and pulmonary-protective effects of black cumin (Nigella sativa) seeds.

Model/system	Effect observed	Researcher
Gastroprotective effect
Rats	N. sativa (2.5 and 5.0 ml/kg)/TQ administration (10, 20, 50, and 100 mg/kg) exerted gastro-protection when subjected to ischemia/reperfusion insult	El-Abhar et al., 2003 and Magdy et al., 2012
Rats	Anti-ulcer potential of N. sativa aqueous suspension on experimentally induced gastric ulcers (with various necrotizing chemicals) has been evidenced	Al Mofleh et al., 2008
Hypothyroidal rats	N. sativa and TQ protect gastric mucosa against the ulcerating effect of alcohol	Khaled, 2009
Newborn Sprague-Dawley rats	N. sativa oil (2 ml/kg daily; i.p.) showed beneficial effect in rats with necrotizing enterocolitis	Tayman et al., 2012
Mice	Treatment with TQ (5–25 mg/kg) ameliorated colonic inflammation in experimental inflammatory bowel disease (C57BL/6 murine colitis induced with dextran sodium sulfate)	Lei et al., 2012
Nephroprotective effect
Rabbits	Nephro-protective effect of N. sativa oil was observed against gentamicin-associated nephrotoxicity	Saleem et al., 2012
Rats	Protective effect of N. sativa oil against methotrexate-induced nephrotoxicity	Yaman and Balikci, 2010
Rats	Protective effects of N. sativa oil in the prevention of chronic cyclosporine A-induced nephrotoxicity by attenuation of the oxidative stress	Uz et al., 2008
Rats	TQ supplementation prevented the development of gentamycin-induced degenerative changes in kidney tissues	Sayed-Ahmed and Nagi, 2007
Hepatoprotective effect
Rats	N. sativa (0.2 ml/kg) relieves the deleterious effects of ischemia-reperfusion injury on the liver	Yildiz et al., 2008
Mice	Pre-treatment with TQ (10 µmol/l) showed a significant protection on the hepatotoxicity of Cd++ particularly by relieving the depletion of non-enzymatic and enzymatic antioxidants	Zafeer et al., 2012
Pulmonary protective effect
Wistar rats	N. sativa treatment showed beneficial effects on experimental lung injury; inhibited the inflammatory pulmonary responses	Kanter, 2009
Rats	N. sativa oil significantly reduced the severity of lung damage due to hyperoxia	Tayman et al., 2012
Patients with asthma	N. sativa (15 ml/kg of 0.1 g% boiled extract for 3 months) significantly alleviated symptoms and frequency of asthma symptoms, chest wheezing, and pulmonary function tests	Boskabady et al., 2007

The anti-ulcer potential of N. sativa aqueous suspension on gastric ulcers experimentally induced with various noxious chemicals (indomethacin, 80% ethanol, and 0.2 M NaOH) in Wistar rats was examined (Al Mofleh et al., 2008). Nigella sativa significantly prevented gastric ulcer formation induced by necrotizing agents by significantly replenishing the depleted gastric wall mucus content and gastric mucosal non-protein sulfhydryl concentration. The anti-ulcer effect of N. sativa was exerted through its antioxidant and anti-secretory activities (Al Mofleh et al., 2008). Both N. sativa (2.5 and 5.0 ml/kg, p.o.) and TQ (5, 20, 50, and 100 mg/kg, p.o.) were found to possess gastro-protective activity against gastric mucosal injury induced by ischemia or reperfusion in Wistar rats (El-Abhar et al., 2003). Lipid peroxidation and lactate dehydrogenase, elevated by the ischemia or reperfusion insult and decreased glutathione and activity of SOD accompanied by an increased formation of gastric lesions, were countered by N. sativa or TQ treatment, indicating their gastroprotective effect, probably by conservation of the gastric mucosal redox state.

Nigella sativa and TQ are reported to protect gastric mucosa against the ulcerating effect of alcohol on hypothyroidal rats and mitigate most of the biochemical adverse effects on gastric mucosa, viz., increase in lipid peroxidation and reduced gastric glutathione content, and enzyme activities of gastric SOD and GST (Khaled, 2009). The beneficial effect of N. sativa oil (2 ml/kg daily, i.p.) in rats with necrotizing enterocolitis (NEC) was studied in newborn Sprague-Dawley rats (Tayman et al., 2012). Histopathologic and apoptosis evaluation indicated that the bowel damage was less severe in the N. sativa oil–treated group. Nigella sativa oil had a beneficial preserving effect on tissue antioxidant enzymes, whereas lipid peroxide levels were significantly lower than those in the NEC control group. In a mouse model of inflammatory bowel disease (C57BL/6 murine colitis induced with dextran sodium sulfate), treatment with TQ (5, 10, or 25 mg/kg) ameliorated colonic inflammation (Lei et al., 2012). The treatment of mice with TQ prevented and reduced the occurrence of diarrhoea and body weight loss, associated with amelioration of colitis-related damage. Also, there was a significant reduction in colonic myeloperoxidase activity and malondialdehyde levels and an increase in glutathione levels (Lei et al., 2012).

Nephroprotective effect

The nephroprotective effect of N. sativa oil is observed in gentamicin-induced nephrotoxicity in rabbits (Saleem et al., 2012) (Table 7). Vitamin C and N. sativa oil when given as combination showed a synergistic nephroprotective effect (Saleem et al., 2012). Oral treatment of N. sativa oil (0.5, 1.0, or 2.0 ml/kg/day for 10 days) produced a dose-dependent amelioration of gentamycin-induced nephrotoxicity in rats as assessed by the biochemical and histological indices of nephrotoxicity (Ali, 2004). The protective effect of N. sativa oil on methotrexate-induced nephrotoxicity has been reported in albino rats which is medicated through restoring the antioxidant status (Abul-Nasr et al., 2001; Yaman and Balikci, 2010). The protective effects of N. sativa oil in the prevention of chronic cyclosporine A-induced nephrotoxicity in rats were evidenced by attenuation of the oxidative stress (Uz et al., 2008). TQ supplementation prevented the development of gentamycin-induced degenerative changes in kidney tissues and cisplatin-induced renal injury in rats as indicated by lipid peroxides and renal organic anion and cation transporters (Sayed-Ahmed and Nagi, 2007; Ulu et al., 2012). Nigella sativa significantly prevented renal ischemia- or reperfusion-induced functional and histological injuries in Wistar rats (Mousavi, 2015). Nigella sativa showed protective effects against ischemia-perfusion damage on kidney tissue based on the total antioxidant capacity, oxidative status index, and activities of catalase and myeloperoxidase in the kidney tissue (Yildiz et al., 2010).

Hepatoprotective effect

It is reported that N. sativa (i.p. 0.2 ml/kg) relieves the deleterious effects of ischemia-reperfusion injury on liver in rats, as indicated by titers of marker enzymes, total antioxidant capacity, total oxidative status, and myeloperoxidase in the liver tissue (Yildiz et al., 2008) (Table 7). The protective effect of TQ on the Cd⁺⁺-induced hepatotoxicity in mice, particularly the perturbation of non-enzymatic and enzymatic antioxidants, has been reported (Zafeer et al., 2012). Pre-treatment with TQ (10 µmol/l) showed a significant protection as indicated by an attenuation of protein oxidation and recovery of the depleted antioxidants, suggesting that TQ exerts modulatory influence on the antioxidant defence system when subjected to toxic insult.

Pulmonary-protective activity and anti-asthmatic effects

Nigella sativa has been investigated for the possible beneficial effects on experimental lung injury in rats after pulmonary aspiration (Kanter, 2009) (Table 7) and found that N. sativa treatment inhibits the inflammatory pulmonary responses. Nigella sativa therapy resulted in a significant reduction in the activity of iNOS and an increase in surfactant protein D in the lung tissue of different pulmonary aspiration models. It is concluded that N. sativa treatment might be beneficial in lung injury that merits potential clinical use. The ameliorative effect of N. sativa oil in rats with hyperoxia-induced lung injury has also been reported (Tayman et al., 2012).

The prophylactic effect of an extract of N. sativa (15 ml/kg of 0.1 g% boiled extract for 3 months) has been examined in asthmatic adults. All asthma symptoms, the frequency of symptoms, chest wheezing, and pulmonary function tests (PFT values) were significantly improved as a result of N. sativa treatment, generally suggesting a prophylactic effect on asthma disease (Boskabady et al., 2007). TQ potently and dose-dependently inhibited the formation of leukotrienes—supposedly important mediators in asthma and inflammatory processes, in human blood cells (Mansour and Tornhamre, 2004).

Miscellaneous nutraceutical effects

During the last three decades, several in vitro and in vivo animal studies have ascertained the pharmacological properties of N. sativa, including its antioxidant, antibacterial, anti-proliferative, proapoptotic, anti-inflammatory, and antiepileptic properties, and its beneficial effect in conditions of atherogenesis, endothelial dysfunction, glucose dyshomeostasis, and disrupted lipid metabolism. Nigella sativa and its constituents are found to have antioxidant, antidiabetic, anti-inflammatory, and anti-tumour properties as well as therapeutic effects on metabolic syndrome, and gastrointestinal, neuronal, cardiovascular, and respiratory disorders in clinical trials (Gholamnezhad et al., 2016). Experimental and clinical studies have evidenced therapeutic effects of N. sativa seed extracts, oil, and TQ on different disorders. Standard clinical trials are however needed for N. sativa supplementation for its promotion as an adjuvant therapy.

Long-term administration of N. sativa increased brain serotonin levels and improved learning ability and memory in rats (Perveen et al., 2008). Chronic administration of N. sativa decreased serotonin turnover and produced anxiolytic effects in rats. Tryptophan concentration in brain and plasma also increased significantly following repeated oral administration of N. sativa oil, suggesting that this oil is useful for the treatment of anxiety (Perveen et al., 2009). Anti-anxiety-like effects of TQ (20 mg/kg) was observed in mice, which involved modulation of GABA and NO levels. The anxiolytic effect was accompanied by a significant decrease in plasma nitrite and countering of decreased γ-aminobutyric acid content in the brain (Gilhotra and Dhingra, 2011). The neuroprotective effects of the aqueous extract of N. sativa have been recorded during cerebral ischemia in rats; this could be resulting from its free radical scavenging, antioxidant (elevation in reduced glutathione, SOD, and catalase (CAT) activities), and anti-inflammatory properties (Akhtar et al., 2012).

The incidence of kidney stone may increase the vulnerability of patients to renal failure. Nigella sativa and its main bioactive component—TQ showed positive effects on the prevention or dissolution of kidney stones and renal failure. This involves antioxidative, anti-inflammatory, and immunomodulatory effects. Thus, N. sativa and its components are beneficial in the prevention and curing of nephrolithiasis and renal damages (Hayatdavoudi et al., 2016).

Conclusions

A number of therapeutic influences of N. sativa and TQ have been scientifically investigated. This includes antidiabetic, anti-allergic, anti-microbial, immune-modulatory, anti-inflammatory, and anti-tumour effects (Figure 4). Nigella sativa and TQ also possess gastro-protective, hepatoprotective, nephroprotective, and neuroprotective activities. The scientific studies conducted so far have confirmed the pharmacological potential of N. sativa seeds, its oil, extracts, and its active principles, particularly TQ. TQ is the most abundant constituent of the volatile oil of N. sativa seeds, and most of the medicinal properties of N. sativa are attributable mainly to TQ. All the available evidence suggests that TQ should be developed as a drug or adjuvant in clinical trials. Nigella sativa seeds, its oil, and constituents like TQ could be used in suitable combinations with conventional therapeutic agents for maximizing the effectiveness in the treatment of many infectious diseases and also to circumvent the drug resistance problem. Further investigations are recommended to explore the specific cellular and molecular targets of various constituents of N. sativa, particularly TQ.

Figure 4.

Multiple medicinal properties of Nigella sativa (black cumin seeds).