Nigella sativa

1.1. Sources

Nigella sativa (of the family ranunculaceae) is a plant that is synonymous with nigella cretica and is commonly called black cumin, fennel flower, or nutmeg flower despite being wholly unrelated to the common cumin (Cuminum cyminum), fennel (Foeniculum vulgare), and nutmeg (the Myristica genus). Other names include Kalonji seeds,^[5] and Ajaji, black caraway seed, and Habbatu Sawda.^[6] It appears to be a fairly well regarded medicinal herb, with some religious usage calling it the 'remedy for all diseases except death' (Prophetic hadith)^[7] and Habatul Baraka "the Blessed Seed".^[6] The seeds are the main medicinal component, although a seed oil pressed from the seeds (Black Cumin Oil or Black Seed Oil) also shares the same bioactives.

Medicinal usage of these seeds mostly centers around diarrhoea and abdominal pain, dyslipidaemia,^[8] asthma and coughs,^[6] headache, dysentery, renal calculi,^[6] infections, obesity, back pain, hypertension, and dermatological problems^[9][10][11] 

Nigella sativa is a simple spice used in food that appears to be a very well renowned seed, and is used for a large variety of medicinal purposes as well as general well being and longevity

Nigella sativa seeds are sometimes eaten alongside honey or simply used to spice food products such as breads^[6][9] and even in these food products it is considered medicinal since the recommended dosages are low, with the crushed seed powder (no further processing required) being recommended at 1-2g (Unani Pharmacopoeia of India), 1-3g (Ayurvedic Pharmacopoeia of India), or 0.5-4g (Siddha Pharmacopoeia of India).^[5]

Nigella sativa (Black Cumin or Kalonji) appears to be medicinally active in fairly low doses, and does not appear to require any particular extraction processes of sources to have medicinal properties. As such, it is a prime candidate for being a functional food product (something that can be eaten in the diet for benefits exceeding normal nourishment)

1.2. Composition

The seeds of nigella sativa are comprised of:

• An oil component (36-38%^[12][13]) which is mostly comprised of linoleic acid (50-60%), oleic (20-23.4%), dihomolinoleic acid (10%), palmitic acid (12.5%) and eicodadienoic acid (3%)^[7][12][14] with some other minor lipid constituents such as methylnonadeca-15,17-dienoate, pentyl hexadec-12-enoate, and pentyl pentadec-11-enoate^[15]

• An essential oil component (0.4-2.5%^[13] and a subset of the oil component)

• Protein at 20-23%^{[16][12][9][17]}

• Carbohydrates at 32-38%^[12][9][17]

• A moisture content of 4.64-6.5%^[12][17]

• A fiber content of 6.6-7.64%^[17][12]

• An ash content of 4.0-4.37%^[17][12]

The seeds themselves are a relatively balanced profile of proteins, fatty acids, and carbohydrates; a particular subset of the fatty acids, the essential oil ranging from 0.4-2.5% of the total seed weight, is seen as the active part of the seed due to containing the 'main' bioactive

While the seeds also contain the non-caloric components:

• Comferol (flavonoid) as diglucoside and digalactoside^[18]

• The isoquinoline alkaloids nigellicimine and its N-oxide^[7]

• Nigellidine and nigellicine^[19] as well as nigellidine-4-sulfite^[20]

• Nigellamines A1-A5 (A1 at 0.0096%, A2 at 0.0078%^[21]), B1-2 (0.0012% and 0.0036%, respectively), and C (dolabellane type diterpenoids)^[22][21]

• Alpha-hederin^[12][7]

• β-sitosterol and stigmasterol^[15] as well as some other sterols^[23]

• Thiamin (Vitamin B1) at 831mg/100g dry weight^[17]

• Riboflavin (Vitamin B2) at 63mg/100g dry weight^[17]

• Pyridoxine (Vitamin B6) at 789mg/100g dry weight^[17]

• Niacin at 6,311mg/100g dry weight^[17]

• Folic acid at 42mg/100g dry weight^[17]

• Vitamin E (as tocopherols) at 340-361mg/100g dry weight^[17][16]

• Potassium (Lowest estimate at 7.6+/-0.42mg/100g^[12] or 0.6-1% dry weight,^[24] with higher estimates between 808-1,180mg/100g dry weight ^[17][16])

• Phosphorus (1.8+/-0.23mg/100g^[12] or 0.5-0.7% dry weight^[24])

• Sodium (0.75+/-0.1mg/100g^[12] or 0.2-0.7%,^[24] with higher estimates of 17.6-85.3mg/100g dry weight^[17][16])

• Iron (Reported as low as 0.1-0.7% dry weight^[24] with highly variable estimates ranging between 0.15-57.5mg/100g dry weight^[12][17][16])

• zinc (0.06+/-0.015mg/100g^[12] or 0.01-0.1% dry weight^[24])

• Copper (0.02-0.03% dry weight^[24])

• calcium (Low estimates at 0.04+/-0.008mg/100g^[12] yet higher estimates between 188-570mg/100g dry weight^[17][16] or 7.4-10.6% dry weight^[24])

• magnesium (0.03+/-0.005mg/100g^[12] or 9.4-11.6%^[24])

There are a variety of molecules found in the seed itself that are not concentrated in the essential oil fragment, and these may play a part in the bioactivity of the seed. The mineral content seems pretty variable

The essential oil component (0.4-2.5% of the seeds by weight^[13] although most sources are in the more modest end of this range at 0.4-0.45%^[25][26]) includes:

• Thymoquinone at 27.8-57.0% of the essential oil^[27][13] yet only somewhere between 0.05%^[28] and 0.13-0.17%^[13] of the oil overall; also, the dimer known as dithymoquinone (Nigellone)^[29] which is not quantifiable in the oil^[28] and is instead reliant on conversion in the body

• Thymohydroquinone^[27][30] at 0.0008% of the oil overall^[28]

• Thymol at 0.009% of the oil overall^[28] and 0.09-0.25% of the essential oil^[27]

• p-Cymene at 7.1-15.5%^[13][14][27]

• Carvacrol at 5.8-11.6%^[13] and Carvone at 0.13-4%^[27][14]

• 4-terpineol at 2-6.6%,^[13] α-terpinene (less than 0.07%^[27]), and γ-terpinene (0.02-1.1%^[27])

• Longifoline at 1-8%^[13] and Longipinene (0.21-1.68%^[27])

• t-anethole at 0.25-4.28%^[27][13] although at times very high concentrations (38.3%) have been noted^[14]

• Limonene at 0.29-4.3%^[27][14]

The essential oil of the seeds (0.4-2.5% of the seed by weight) contains a variety of molecules of which include Thymoquinone, seen as the main component of the entire seed

2.1. Metabolism

Thymoquinone is known to readily convert into dithymoquinone, a dimer which is referred to as nigellone.^[28][10]

2.2. Cellular Kinetics

Thymoquinone and Dithymoquinone do not appear to be effluxed from cells via multidrug resistance protein (MDR),^[31] a transporter that is known to cause cells to become resistant to chemotherapy via promoting drug efflux.^[32]

2.3. Enzymatic Interactions

Metabolism of dextromethophan into its CYP3A4 and CYP2D6 mediated metabolites are inhibited by 60% and 80% at 100µg/mL of the basic seed extract, and oral ingestion of 2,500mg of the seed powder twice daily over a week has been confirmed to alter dextromethorphan kinetics (a minor increase in the ratio of CYP3A4 metabolite relative to the parent molecule to 1.6:1, but a significantly 127-fold increase in the CYP2D6 metabolite ratio relative to the parent molecule).^[1]

Oral ingestion of nigella sativa appears to not interfere with carbamazepine pharmacokinetics,^[33] which is a pharmaceutical able to induce CYP3A4, CYP1A2, and P-glycoprotein^[34] while it itself is metabolized by CYP3A4,^[35] and oral ingestion of 200mg/kg nigella sativa seed extract (rabbits) over eight days appears to reduce the C_max (35.5%) and AUC (55.9%) of cyclosporin^[36] which is mediated by both CYP3A4 and P-glycoprotein.^[37]

Systemic exposure to phenytoin can be reduced up to 87% with nigella sativa (week long supplementation followed by drug testing) ingestion in dogs,^[38] suggesting induction of CYP2C19 or CYP2C9 which metabolize phenytoin.^[39] Phenytoin is also known to induce CYP3A4 and CYP2B6.^[40]

Overall, it appears that nigella sativa retains the ability to inhibit CYP3A4 yet it doesn't appear to be practically relevant following oral ingestion (tentative statement). It may interact with P-glycoprotein by increasing its activity, and it does appear to inhibit CYP2D6 as well as either CYP2C19 or CYP2C9 (maybe both)

3.1. Ion Channels

Nigella sativa seeds appear to have calcium channel blocking abilities at 100-3,000µg/mL of the crude seed extract as assessed by relaxing rabbit intestinal cells, with 10-fold more potency in the petroleum extract.^[41]

3.2. AMPK

Adenosine monophosphate kinase (AMPK) is a protein that positively modulates glucose and lipid uptake into cells, and its activation is seen as hypolipidemic and antidiabetic.^[42] Nigella sativa extract at 200μg/mL appears to activate AMPK phosphorylation in muscle cells but not adipocytes with a potency comparable to 2mM AICAR.^[43]

Oral ingestion of 48mg/kg of the basic seed extract in Meriones shawi (equivalent to 2g of the seed extract in humans) over four weeks has been confirmed to increase ACC phosphorylation in skeletal muscle, indicative of increased AMPK activity.^[44]

Nigella sativa appears to activate AMPK in skeletal muscle and liver cells, but not in fat cells; this may be a mechanism relevant to oral supplementation of the seeds

Nigella sativa seed extract appears to cause mitochondrial uncoupling in isolated liver mitochondria in a concentration dependent manner between 25–200μg/mL which was not due to any known constituents (thymol, carvacrol, hederagenin, nigellimine and thymoquinone).^[43] This reached a potency of 81+/-5% at 160μg/mL of the water extract or 64+/-8% at 200μg/mL of the ethanolic extract.^[43]

Despite the aforementioned uncoupling, nigella sativa does not depress intracellular (cytosolic) ATP concentrations^[43] and the theoretical recompensatory increase in acidosis (from anaerobic glycolysis^[45]) from ATP depletion does not occur.^[43] This is similar to both Metformin^[46] and Berberine^[47] which activate AMPK vicariously through causing mitochondrial uncoupling in order to preserve cytoplasmic ATP concentrations.

It is hypothesized that nigella sativa activates AMPK in a similar manner to berberine and Metformin, vicariously through causing mitochondrial uncoupling

3.3. Akt

In the livers of rats fed the petroleum extract of nigella sativa (equivalent to 2g/kg of the basic seed extract), Akt phosphorylation in response to insulin appears to be increased relative to control.^[48] This is also seen in muscle cells at 200 μg/mL^[43] but not in adipocytes.^[43]

The increase in GLUT4 content of skeletal muscle seen in animals fed a basic seed extract (equivalent ot 2g in humans) is thought to be indicative of increased Akt activity, or at least the increase in plasma insulin.^[44]

There is an increase in Akt activity following supplementation of nigella sativa, which should work to increase glucose uptake into liver and muscle cells. It is not sure what causes this increased Akt phosphorylation although increased insulin signalling is likely a factor

3.4. PPARs

In adipocytes, nigella sativa appears to activate PPARγ activity in the concentration range of 50-200μg/mL^[43] which may explain the increased glucose uptake and proliferation seen in adipocytes^[49] despite AMPK^[43] and Akt^[43] not contributing. The increase glucose uptake with this concentration of nigella sativa is comparable to a supraphysiological concentration of insulin (100nM) and was additive with it as well, while the increase in adipogenesis was comparable to 10μM rosiglitazone.^[43]

Nigella sativa may activate PPARγ and induce fat cell glucose uptake and proliferation, a proobesogenic yet insulin sensitizing mechanism common to the Thiazolidinedione drug class

3.5. MAPKs

In the livers of rats fed the petroleum extract of nigella sativa (equivalent to 2g/kg of the basic seed extract), p44/42ERK phosphorylation in response to insulin treatment appears to be enhanced as well as baseline p44/42ERK phosphorylation^[48] although in isolated H4IIE liver cells there was no influence;^[43] this increase in ERK1/2 phosphorylation has also been confirmed in muscle cells (C2C12 myocytes)^[43] yet failed to influence adipocytes.^[43]

ERK1/2 appears to be increased in activity, which is thought to just be secondary to insulin signalling in liver and skeletal muscle cells

4.1. GABAergic Neurotransmission

Nigella sativa has been found to inhibit picrotoxin (noncompetitive GABA_A antagonist^[50]) induced seizures and against bicuculline (competitive GABA_A antagonist^[51]), with an injection of 150mg/kg being more protective than 300mg/kg sodium valproate against picrotoxin.^[52] That being said, nigella sativa (via Thymoquinone) has been found to lower the ED₅₀ for sodium valproate^[52] suggesting that the GABA_A receptor is somehow enhanced via thymoquinone.

It is possible that thymoquinone has opioidergic signalling which increases GABAergic tone, which has been hypothesized^[52] based on some rat studies showing that both signalling pathways contribute to the observed effects.^[53][53] Alternatively, it has been noted that thymoquinone suppresses the stress-induced increase in brain nitrite concentrations (without an inhernet effect in unstressed mice),^[54] which may be related to the ability of thymoquinone to suppress iNOS activation^[55] which can dysregulate GABAergic signalling^[56] since cGMP (produced via nitric oxide) suppresses GABA_A function.^[57]

The anti-epileptic^[53] and anxiolytic^[54] properties of nigella sativa appear to be mediated via GABA signalling.

Thymoquinone appears to enhance GABA_A signalling, although the exact mechanism is not known; it may be somewhat indirectly via opioidergic signalling, nitrinergic signalling (nitric oxide pathways in the brain), or possibly both

At least one study has noted that administration of 20mg/kg thymoquinone to mice has resulted in an increase in brain GABA concentrations^[54] and that the addition of methylene blue (negative regulator of nitrinergic signalling^[58]) did not further the increase.

May increase GABA concentrations itself

4.2. Analgesia

Nigella sativa seeds at 500mg/kg appear to have analgesic properties in rats (hot plate test) with a potency statistically similar to aspirin at 100mg/kg, albeit trending to be less effective.^[59]

4.3. Appetite and Food Intake

One study using oral intake of nigella sativa petroleum extract over four weeks in rats has noted a 25% reduction in food intake after one week of ingestion (which attenuated but persisted) resulting in mild weight loss.^[48]

4.4. Attention and Focus

Supplementation of 500mg seed powder twice daily for nine weeks appears to improve attention processing (trail making test) and speed of processing without affecting processing accuracy in older subjects; the improvement being very modest in size.^[60]

4.5. Fever

In rats given a yeast induced fever, nigella sativa at 500mg/kg oral intake fails to prevent symptoms of fever despite the reference drug (100mg/kg aspirin) being effective.^[59]

4.6. Stroke and Tramautic Brain Injury

400mg/kg of nigella sativa seed extracts (petroleum ether and chloroform) daily in rats for a week prior to a middle cerebral artery occlusion (MCAO; a model for stroke) is able to fully preserve locomotor activity and grip strength (similar to the reference drug of 100mg/kg aspirin) and reduced oxidative changes and infarct size to a similar level.^[61]

Extracts of the seeds appear to be neuroprotective against stroke, and the potency seems comparable to aspirin

4.7. Epilepsy and Convulsions

Intraperitoneal injections of the water extract (50-75mg/kg intraperitoneal injections) but not seed oil appears to have anti-epileptic properties against pentylenetetrazole (PTZ), mostly due to thymoquinone which had an EC₅₀ (93.2mg/kg or 0.57mM/kg) lower than sodium valproate (161mg/kg).^[52] There are no significant protective properties against maximal electroshock induced seizures and thymoquinone can attenuate picrotoxin induced seizures^[52] as well as potentiate the protective effects of sodium valproate when coadministered.^[52]

In rats, direct intracerebroventricular injections of thymoquinone (200-400µM) is able to half the ability of pentylenetetrazole (PTZ) to induce seizures in a manner that is wholly reversible by flumazenil (a GABA_A antagonist) and is attenuated by naloxone (opioid antagonist)^[62] and this has been noted with intraperitoneal injections of the basic seed extract (40-80mg/kg).^[53]

The anti-epileptic abilities of thymoquinone appear to be mediated via enhancing signalling via the GABA_A (benzodiazepine) receptor, although opioid signalling may play a role

1mg/kg thymoquinone (twice daily 0.5mg/kg as a syrup) to children with poorly controlled epilepsy over the course of four weeks was associated with a reduction in seizure frequency by 53.91+/-38.756, and then the second part of the study (as it was a cross-over design) was associated with a 26.64+/-41.297 reduction; while both periods outperformed placebo, they were not significantly differnt due to the high variability.^[63] Overall, 54.5% of the subjects experienced a 50% or greater reduction in seizures.^[63]

Appears to have confirmed anti-epileptic effects in children following oral ingestion of isolated thymoquinone

4.8. Anxiety and Stress

Thymoquinone at 10-20mg/kg appears to exert anxiolytic properties in mice (much more effective in unstressed mice than stressed mice) with a potency statistically comparable to 2mg/kg diazepam and in a manner which is synergistic with methylene blue (negative regulator of nitrinergic signalling^[58]) despite methylene blue inherently being inactive.^[54] The increase in GABA and suppression of nitrite seen with thymoquinone were both not enhanced with methylene blue,^[54] suggesting that methylene blue acts downstream of nitrite.

Thymoquinone appears to have anxiety reducing properties, and it is thought that this is secondary to a suppression of nitric oxide signalling in the brain preserving the functions of GABA signalling

4.9. Depression

Depression is known to have an inflammatory link^[64][65] associated with microglia (support cells alongside neurons that mediate the inflammatory response in the brain^[66]) as increased inflammatory cytokine levels (IL-6, TNF-α, CRP) are known to be associated with depression^[67][68] and classical antidepressants have antiinflammatory properties.^[66]

In a model of LPS induced depression (which produced the aforementioned cytokines to cause depression^[69]), injections of nigella sativa (200-400mg/kg) is able to abolish the depressant effect in a forced swim test and open field test; isolated thymoquinone (40mg/kg) was also effective and 200mg/kg of nigella sativa appears to be more effective than the higher dose.^[70]

May have antidepressant effects in models of excessive inflammation (known to induce depression)

In otherwise healthy and nondepressed adolescent males given 500mg of encapsulated nigella sativa, it was noted that after four weeks of supplementation there was an elevation of mood state seen with supplementation relative to placebo treatment.^[71]

A mood enhancing property may exist with consumption of low doses of the seeds in otherwise healthy persons

4.10. Memory and Learning

In otherwise healthy rats given nigella sativa essential oil (60μg/kg) over 20 weeks, supplementation appears to be associated with improved memory formation as assessed by repeated (weekly) radial maze tests.^[72]

500mg of the nigella sativa seed extract twice daily over the course of nine weeks in otherwise healthy elderly persons outperformed placebo and was able to improve memory as assessed by logical memory tests (13.5-14.7% relative to baseline) and 30 minute recall (20.8%), but not digit span or the Rey-Osterrieth Complex Figure Test.^[60] Most improvements in cognition as assessed by the stroop test were also reported in this same of older persons.^[60]

May have mild memory enhancing properties in elderly persons; currently no studies conducted in youth

5.1. Cardiac Tissue

800mg/kg of nigella sativa to rats over the course of twelve weeks was able to improve the recovery of cardiac tissue following ischemia/reperfusion injury, thought to be due to its antioxidative properties.^[73]

5.2. Blood Pressure

In unconcious rats, the essential oil component at 4-32µg/mL causes dose-dependent reductions in blood pressure (5.1-29.2%) and heart rate (10-35%) via a mechanism inhibited by anticholinergics; these alterations normalized within 5 minutes.^[25]

Supplementation of 2g of the seed extract daily for six weeks in hypercholesterolemic subjects (with otherwise normal blood pressure) fails to modify systolic and diastolic blood pressure^[5] although a study in hypertensive persons using 100-200mg of a nigella sativa seed extract (concentrated via boiling) noted very minor reductions in blood pressure (1-2mmHg for both systolic and diastolic).^[74] In men with central obesity and mild hypertension, the reduction in blood pressure has reached 6% (9mHg) and diastolic was reduced 1.5% (1mmHg).^[75]

While injecting the essential oil seems to cause drastic reductions in blood pressure, this does not seem to apply to oral ingestion of the seeds. The actual therapeutic potency of the seeds in hypertensive persons, while present, is of very small magnitude

5.3. Triglycerides and Lipoproteins

The nigellamine molecules appear to have hypolipidemic properties, with nigellamine A5 being able to reduce triglyceride accumulation in hepatocytes at a concentration of 0.1-1µM (to 67% of control) which was comparable in potency to clofibrate (0.1µM down to 64%).^[22] Nigellamines A1 as well as B1-2 were comparable to clofibrate elsewhere in the same model at 0.1µM,^[21] although A3-4 and C were less effective than clofibrate in the 0.1-1µM concentration range.^[22]

Nigellamines appear to have relatively potent lipid reducing properties, with some of them being comparable to the fibrate drug known as clofibrate

Supplementation of 2g of the crushed seeds from nigella sativa over the course of four weeks in persons with high cholesterol was associated with minor reductions in total cholesterol (4.78%) and LDL-C (7.6%) yet more significant reductions in triglycerides (16.65%).^[76] This has been noted elsewhere to a statistically insignificant degree in diagnosed hyperlipidemics^[5] and men with central obesity with high baseline lipids.^[75]

In type II diabetics, the addition of 2g of the crushed seeds appears to reduce total cholesterol (11.3% after four weeks, maintained over the next two months), LDL-C (16.3% within eight weeks), and triglycerides (20% within four weeks) and although the HDL:LDL ratio increased significantly there was no inhernet change in HDL-C.^[77] This hypocholesterolemic effect has been noted elsewhere in medicated diabetics with 2.5mL of the oil, although this study failed to find an influence on triglycerides.^[78]

One study has investigated the usage of nigella sativa paired with garlic as an adjuvant to simvastatin (a statin drug) and found that the improvments in LDL-C, total cholesterol, and triglycerides from simvastatin were enhanced with coadministration of the spices.^[3]

Nigella sativa appears to be able to improve the lipid profile in persons with impaired lipid profiles, but the magnitude of this effect is quite small. However, it seems to work nicely with pharmaceutical options as it has been used in medicated diabetics and dyslipidemics without problem

In hypertensive persons with no apparent alterations in lipid or glucose metabolism, supplementation of 100-200mg of a seed extract is ineffective in improving any biomarker for cholesterol or triglycerides.^[74]

There is no apparent influence on the lipid profile in persons who have a normal profile

5.4. Atherosclerosis

It is possible that nigella sativa extract could protect against the development of atherosclerosis, particularly related to the immune system (from when macrophages accumulate too much cholesterol and convert into foam cells^[79] that promote atherosclerosis^[80]) since nigella sativa both potentiates macrophage activity^[9] yet exerts antiinflammatory effects in these cells at 100µL.^[81] The development of foam cells has been noted to be reduced in vitro at a very reasonable IC₅₀ value of 180ng/mL.^[82]

The influence of foam cells on the development of artherosclerosis is likely reduced with supplementation of the seed oil of nigella sativa, and this occurs at low enough concentrations that it is probably relevant to oral supplementation

6.1. Insulin and the Pancreas

Nigella sativa seed oil, as well as two of its constituents (thymoquinone and nigellone) have failed to stimulate the secretion of insulin from pancreatic cells either in the presence or absence of glucose (3-11.1mM)^[83] although elsewhere the defatted seed extract and basic seed extract have shown an augmentation of glucose-stimulated insulin secretion (8.3mM glucose) in a concentration dependent manner between 0.1-5mg/mL.^[84] This latter study also noted that the acidic and neutral fractions failed to stimulate insulin at any dose except 5mg/mL,^[84] suggesting that the lipids are not active (although an ethanolic extract, rather than the seed oil, has been found to stimulate glucose-induced insulin secretion in vitro^[49]).

One study in Meriones shawi found that 48mg/kg of the basic seed extract (equivalent to 2g in an adult human) was actually able to increase plasma insulin in diabetics relative to the diabetic control and the reference drug (Metformin, which reduced insulin).^[44]

The seed extract and both water and ethanolic extracts, yet not the basic seed oil, appear to be able to augment insulin secretion from the pancreas when in the presence of glucose (ie. when a meal is ingested rather than a per se effect)

Nigella sativa has been found to, in vitro, accelerate pancreatic β-cell proliferation secondary to accelerating DNA synthesis in these cells by 13% relative to control (over an 18 hour incubation at 200μg/mL)^[49] and in diabetic rats injected with 0.20mL/kg of the essential oil for 30 days was able to attenuate the rate of β-cell destruction induced by the diabetic toxin (streptozotocin).^[85]

May be able to protect and regenerate pancreatic β-cells

6.2. Blood Glucose

Nigella sativa appears to be highly recommended among practitioners of traditional medicine for the purpose of treating diabetes^[86] and is known to reduce blood glucose (without influencing insulin levels in serum nor glucose absorption) when paired with the gums of ferula asafoetida and olibanum, commiphora myrrh, as well as aloe vera^[87] with a potency comparable to phenformin.^[88]

It is thought that most of the antidiabetic properties of nigella sativa come from AMPK activation^[44] similar to some drugs like Metformin or Berberine, although activation of PPARγ (200μg/mL of the seeds being similar in potency as 10μM rosiglitazone)^[43] may also play a role.

When investigating the potency of this effect, oral ingestion of 48mg/kg of the basic seed extract in Meriones shawi (equivalent to 2g of the seed extract in humans) over four weeks is able to reduce blood glucose to a level similar to control and of equal potency to 300mg/kg Metformin, although Metformin acting within 1 week and nigella sativa required all four weeks to reach equal potency.^[44] Insulin sensitivity in response to an oral glucose tolerance test was also improved, albeit to a lesser degree than Metformin.^[44]

Nigella sativa appears to be recommended for anti-diabetic purposes, which appears to mostly be associated with the AMPK activation seen with the seeds although PPARγ activation may also play a role. This appears to be biologically relevant at an oral dose of the supplement that is commonly recommended to humans

In persons with high cholesterol but no apparent problems with blood glucose, supplementation of 2g of the crushed seeds daily for four weeks failed to modify fasting blood glucose^[76] and this failure has been noted over six weeks in the same cohort of persons^[5] and over eight weeks in hypertensive that are not also diabetic.^[74]

Three months of supplementation with nigella sativa seed powder (1-3g) in type II diabetics in addition to their medication noted that only the 2g dosage was associated with significant improvements in HbA1c (1.52% from baseline) and blood glucose^[77] and similar effects have been noted in unmedicated men with central obesity (no diagnosed diabetes, but elevated blood glucose) where a mild 1.9% reduction in blood glucose was noted after three months of 3g nigella sativa.^[75] 2.5mL of the oil itself in medicated type II diabetics has also noted improvements in blood glucose relative to the medicated control given placebo, with a reduction 58% greater than control (although no changes in postprandial glucose were noted).^[78]

When looking at human studies assessing blood glucose uptake, there appears to be a relatively potent reduction in blood glucose in diabetic persons (who have elevated blood glucose) while there is no hypoglycemic effect in persons with normal blood glucose

7.1. Adipokines

In diabetic animals given the human equivalent of 2g of nigella seeds over four weeks, there was no significant influence of supplementation on plasma levels of adiponectin or leptin.^[44]

7.2. Interventions

Nigella sativa appears to be traditionally recommended as an anti-obesity agent^[89]

Supplementation of 2g of the seed extract daily over six weeks in overweight and hypercholesterolemic persons has failed to significantly reduce BMI and waist circumference^[5] which has been noted elsewhere.^[74] Only one trial has been conducted and noted significant weightloss, although the persons in this study (men with central obesity) also experienced a reduction in appetite; since food intake was not recorded it is possible that they consumed less food.^[75]

8.1. Mechanisms

Nigella sativa (200µg/mL) appears to increase glucose uptake into muscle cells at 2.1-fold higher rates than a supraphysiological concentration of insulin (100nM),^[49]

9.1. Macrophages

50-100µL of a seed extract from nigella sativa has been noted to cause 68.64-91.65% inhibition of nitric oxide release from macrophages exposed to LPS in vitro^[81] which appears to be due to thymoquinone causing inhibition of the iNOS enzyme with an IC₅₀ value of 1.4-2.76µM;^[55] the components in the methanolic extract (with the highest antioxidant capacity) seem most effective.^[90]

Thre appears to be relatively potent anti-inflammatory properties on macrophages, which occurs at a relatively low concentration and may be relevant following oral ingestion. This is through inhibiting iNOS induction in response to inflammatory stressors,

Nigella sativa can increase IL-1β secretion in vitro^[91] although likely secondary to the suppression of iNOS secretion of IL-6, nitric oxide, and TNF-α are suppressed.^[92]

May alter cytokine secretion from macrophages in a manner that reflects an antiinflammatory state

Supplementation of 2g of nigella sativa seeds for 30 days in addition to immunotherapy (compared against immunotherapy itself) appears to be able to enhance phagocytic activity of macrophages, increasing a 32% boost to 75%.^[9] Intracellular killing activity increased to a similar level.^[9]

Oral ingestion of nigella sativa appears to boost the ability of macrophages to destroy invaders

9.2. T Cells

Nigella sativa is able to increase secretion of IL-3 from lymphocytes when cultured with pooled allogeneic cells, without necessarily increasing mitogenic potential of lymphocytes when incubated with PHA, concanavalin-A, or pokeweed mitogen.^[91]

9.3. Natural Killer Cells

The ability of NK cells to cause cytotoxicity to tumor cells (YAC-1 cell line) appears to be enhanced in vitro with incubation of nigella sativa extract.^[92]

9.4. Eicosanoids

Thymoquinone appears to potently suppress 5-LOX (IC₅₀ less than 1µg/mL) and COX (IC₅₀ of 3.5µg/mL) enzyme activity in leukocytes, and while it is the most active component it does not appear to fully explain the observed effects with the oil.^[13]

9.5. Allergies

Nigellone (dithymoquinone) appears to be able to inhibit mast cell histamine release in response to A23187 and compound 48/80^[11] and injections of 8mg/kg thymoquinone can reduce histamine release in rat RPMCs senstized to ovalbumin by 41%.^[93]

Injections of compound 48/80 (induces mortality secondary to mast cell degranulation) are significantly attenuated with injections of thymoquinone at 10-100mg/kg.^[93]

The main bioactive appears to inhibit the release of histamine from mast cells

Injections of 3mg/kg thymoquinone for five days prior to ovalbumin sensitization in guinea pigs is able to reduce the sensitivity of the trachea to contractions by histamine (74%) and acetylcholine (71%), suggesting anti-asthmatic effects in response to allergins.^[93]

May have an anti-asthmatic effect in allergic asthma

In allergic rhinitus, the oil of nigella sativa failed to alter nasal concentrations of IgE and eosinophils yet reduced subjective symptoms of rhinitus over the course of thirty days (itching, runny nose, sneezing, and congestion)^[94] which has been noted previously in a general cohort of persons with allergic diseases (allergic rhinitis, bronchial asthma, atopic eczema) given 40-80mg/kg of the seed oil daily^[95] and when using the standard 2g dosage of seed extract as an adjuvant therapy.^[9]

In asthmatic persons, a boiled extract of the seeds (15mL/kg) over three months was able to significantly improve all asthmatic symptoms and pulmonary function tests causing a concomitant reduction in the requirement for anti-ashtmatic medications.^[96]

Nigella sativa appears to have anti-allergic properties, and may also be useful as an adjuvant therapy alongside other immune boosters for the treatment of mostly rhinitus and asthma although some benefit may exist for eczema (other allergic symptoms mostly unstudied)

9.6. Rheumatoid Arthritis

The main bioactive of nigella sativa, thymoquinone, is known as a relatively potent antiinflammatory agent in vitro^[97] and can reduce the release of inflammatory cytokines.^[8] Due to this and its inhibitory effects on nitric oxide production in macrophages^[81] it has been investigated for its role in rheumatoid arthritis

Due to the general antiinflammatory properties of thymoquinone, it is being investgiated for its role in some autoimmune diseases. This includes rheumatoid arthritis

Supplementation of 500mg nigella sativa oil twice daily for one month in patients with rheumatoid arthritis noted that while placebo was unable to affect rheumatoid arthritis that the seed oil reduced the disease activity score (DAS-28) from 4.98+/-0.79 to 4.55+/-0.82; a 9% reduction.^[98] This study also noted significant reductions in joint pain and swelling as well as morning stiffness in affected joints.^[98]

Standard doses of the oil may provide modest benefit to persons with rheumatoid arthritis

9.7. Virology

Nigella sativa has shown antiviral properties in vitro at 35µM (against infectious laryngotrachietis virus)^[99] and in mice (cytomegalovirus virus),^[100] leading to its testing in humans with viral diseases.

In patients with hepatitis C who were not on IFN-α therapy, 450mg of the seed oil of nigella sativa thrice daily over the course of three months was associated with a significant reduction in HCV RNA levels (to 38.6% of baseline) as well as a restoration of many serum parameters (red and white blood cell count, platelets, albumin, etc.).^[101] Interestingly, lower leg edema and ascites were both significantly reduced.^[101]

Nigella sativa appears to be able to reduce viral load in persons with hepatitis C

10.1. Testosterone

In rats, nigella sativa has been noted to increase testosterone concentrations following oral ingestion of the seed extract at 5% of the drinking water. Benefits applied to the experimental group with diabetes (14.3% increase) as well as control rats (33.1%).^[102] Elsewhere, rats given 100mg/kg of the seed oil failed to significantly increase testosterone (although a nonsignificant trend to increase testosterone by 9.6% was noted).^[103]

In men with central obesity given 3g of nigella sativa seeds daily for three months, supplementation failed to significantly increase free testosterone concentrations.^[75]

11.1. Mechanisms

Nigella sativa essential oil appears to have antioxidant properties (in a DPPH assay) associated with the components carvacrol, t-anethole, and 4-terpineol.^[27]

12.1. Seminal Parameters

Nigella sativa seed oil (100mg/kg) nonsignificantly increased sperm motility and morphology while significantly increasing sperm concentration, trending to be more potent than olive oil and less potent than pomegranate seed oil.^[103]

There may be some benefits to seminal count and motility associated with black cumin seed oil, but this does not appear to be to that large of a degree

13.1. Lungs and Trachea

Two flavonoids in nigella sativa (comferol diglucoside and digalactoside) appear to be capable of relaxing precontracted brachial muscles at 50-200µg/mL, which was lower than the reference drug theophylline (200-800µM); specifically, the lower concentrations were comparable and 200µg/mL was comparable to 400µM theophylline, with 600-800µM being significantly more potent.^[18]

The water and n-hexane extracts has been noted to be less active in vitro relative to chloroform or petroleum^[104] (although still somewhat active^[105]) and the relaxing effects seem to be present when brachial cells are contracted with methacholine but not KCl.^[106][104] The active extracts (chloroform, methanolic, petroleum^{[104][18][106]}) seem to contain two flavonoids known as comferol (diglucosie and digalactoside) which can cause relaxation in the 50-200µg/mL range.^[18]

Due to the inefficacy on cells precontracted with potassium but not other agonists, it is thought that the bioactives work via opening potassium channels. Calcium channel blocking does not seem relevant^[106] but a phosphodiesterase inhibiting activity (and increasing cAMP) has been hypothesized^[104] as have anticholinergic properties.^[107][106] Its overall potency is less than theophylline as reference drug.^[104][18]

Components of nigella sativa appear to be able to have bronchodilatory properties. It seems moderately potent in vitro, and seems to be dependent on potassium channels. The exact mechanism is not known, but is thought to be indirect involvement of potassium channels or muscarinic acetylcholine receptors possibly related to PDE enzyme inhibition (and increases in cAMP)

Asthmatic symptoms have been noted to be improved in persons who suffer from allergic asthma at 40-80mg/kg of the seed extract^[95] and general asthma (relation to allergies not stated) with a boiled extract at a concentration of 0.1g% and 15mL/kg.^[96]

In chemical war victims that had impaired respiratory function, supplementation of a boiled extract from the seeds of nigella sativa (50g% at 0.375mL/kg) for two months was able to significantly improve respiratory function as assessed by symptoms such as wheezing and pulmonary function tests (PFTs).^[108]

Lung function may be improved secondary to treating symptoms of asthma, which is mostly indicative of the anti-allergic potential of nigella sativa seeds. However, a direct benficial influence on the lungs cannot be ruled out as it has shown benefit in persons without asthma

13.2. Stomach

Nigella sativa is known to have antibacterial properties in vitro^[109] and have shown efficacy against both gram positive and gram negative bacteria as well as yeast^[110] which has been noted to influence anti-biotic resistant bacteria.^[111] Due to all the aforementioned and how an in vitro study noted complete eradication of heliobacter pylori within an hour^[112] it has been investigated for reducing this particular bacteria in humans where supplementation of 2g of the seed extract of nigella sativa (in addition to 40mg omeprazole) was able to eradicate two thirds (66.7%) of a heliobacter pylori infection, whereas lower (1g) and higher (3g) doses were less effective at 47.6-47.8%.^[4] The reference therapy (clarithromycin, amoxicillin, omeprazole) reached 82.6% eradication but was statistically comparable to 2g nigella sativa.^[4] The combination of an antibiotic or two with a proton pump inhibitor (omeprazole) tends to be standard therapy for the eradication of heliobacter pylori^[113] and nigella sativa has not yet been tested in isolation.

Nigella sativa appears to have anti-ulcer properties against the heliobacter pylori bacteria, with a potency somewhat comparable to a clarithromycin and amoxicillin combination therapy. It has not yet been tested in isolation, but alongside a proton pump inhibitor (omeprazole)

13.3. Kidney

Kidney stones (of which calcium stones are most common^[114][115]) are deposits of minerals or other solid products in kidney tissue, which can then be urinated out (somewhat painfully) or cause direct kidney damage before that^[115] and are a risk factor for kidney disease;^[116] dissolution of kidney stones is desired due to preventing any possible kidney damage and reducing the risk of painful kidney stone urination, and nigella sativa seeds have been traditionally used for the treatment and prevention of kidney stones.^[6]

In rats who got calcium oxalate stones induced (1% ethylene glycol), ingestion of either a water extract of n-butanol extract at 250mg/kg for 28 days alongside the 1% ethylene glycol was able to attenuate formation of calcium stones, with the water extract (54% reduction) underperforming relative to the n-butanol extracts (83-88% reduction).^[117] An ethanolic extract of nigella sativa also appears effective both when started alongside ethylene glycol (64% reduction) or when started 14 days later in a therapeutic manner (56% reduction).^[118]

Preliminary evidence in rats suggest quite potent anti-kidney stone properties, with the standard dose (250mg/kg correlating to a human dose of around 3g for a 150lb person) of all extracts more than halving kidney stone formation and the n-butanol extract nearly abolishing it

14.1. Pancreatic

Isolated thymoquinone at 50-75µM (not so much 25µM) in pancreatic cancer cells (specifically, pancreatic ductal adenocarcinoma (PDA) cells which are one of the more lethal variants^[119] which may be linked to or at least influenced by inflammation^[120][121]) is able to time and concentration-dependently reduce the ability of TNF-α to induce proinflammatory signalling, with 75µM over 24 hours fully abolishing the induction of TNF-α, MCP-1, COX2, and IL-1β mRNA.^[97] These effects were secondary to interfering with the ability of TNF-α to induce translocation of NF-kB,^[97] which is constituitively active in PDA cells^[122] but not noncancerous cells^[123] and mediates cellular defenses. Interestingly, thymoquinone not only prevented TNF-α induced NF-kB activity but, over time, reduced the production of NF-kB to 80% of control.^[97]

14.2. Liver

In rats given hepatocellular carcinomas after a two week preload of 1g/kg nigella sativa methanolic extract (), the increase in liver weight was significantly attenuated and the alterations in hepatic enzymes (serum levels and hepatic activity of hexokinase, glucose-6-phosphate dehydrogenase, and glyceraldehyde-3-phosphate dehydrogenase) was similarly attenuated by more than half.^[124]

14.3. Cervical

In vitro, thymoquinone appears to be cytotoxic towards cervical squamous carcinoma cells (SiHa) with an IC₅₀ of 9.33-10.67μg/mL; this was more effective than the reference drug cisplatin while it exerted less toxicity on non-cancerous cells (3T3-L1 adipocytes and Vero kidney cells).^[125] Thymoquinone appeared to induce apoptosis and increase expression of p53 and decreasing Bcl-2 (no influence on Bax), and at a concentration of 30μg/mL there was near complete accumulation in the sub G1 phase of the cell cycle (from 4.22% in control to 93.66%).^[125]

Similar cytotoxicity has been seen with the basic methanolic extract with an IC₅₀ of 93.2μL/mL reaching 88.3% inhibition at 125μL/mL^[126] and elsewhere thymoquinone has shown cytotoxicity against other cervical cancer cells such as HeLa.^[127]

In vitro, Thymoquinone appears to outperform the reference drug in causing cytotoxicity of SiHa cervical cancer cells

15.1. General

Isolated thymoquinone appears to be relatively safe, with an oral LD₅₀ of 794.3mg/kg in rats and 870.9mg/kg in mice; approximately 100-150 times higher than its therapeutic level.^[128]

15.2. Case Studies

There have been some isolated cases of topical usage of nigella sativa causing contact dermatitis, suggesting that it is possible to be allergic to the seed oil.^[8]