Plants belonging to the genus Ocimum exhibit a great deal of different pharmacological activities of which the most important, as concluded by the number of research reports, will be discussed below. The activities to be discussed in more detail are anti-inflammatory, immunomodulating and adaptogenic, anticarcinogenic, hypoglycemic and blood lipid lowering, radioprotective, effect on the CNS, antiulcerogenic, hepatoprotective and the effect on smooth muscle. In addition to these activities a number of other activities are also reported in the literature, such as antioxidant, angioprotective effect, effect on the reproductive behaviour and antiwormal activity.
Ocimum sanctum L., popularly known as “Tulsi” in Hindi and “Holy Basil” in English, is a widely known sacred plant of Hindus. Different parts of the plant have been claimed to be valuable in a wide spectrum of diseases. For instance, it is used for the treatment of arthritis, rheumatism, pain and fever in the Ayurvedic system of medicine. Ocimum sanctum is now intensively studied in order to prove these activities by pharmacological evidence.
A methanol extract and an aqueous suspension of Ocimum sanctum leaves inhibited acute as well as chronic inflammation in rats as tested by carrageenan-induced paw edema and granuloma pouch, respectively. In both test procedures, the anti-inflammatory response of methanol extract (500 mg/kg) was statistically equivalent to the response observed with 300 mg/kg of sodium salicylate. The methanol extract and the aqueous suspension showed a statistically significant antipyretic action. However, the antipyretic action was weaker and of shorter duration than that of 300 mg/kg of sodium salicylate. These effects may, at least in part, be attributed to inhibition of the biosynthesis of prostaglandins.
Ocimum sanctum leaves and essential oil exhibited analgesic activity when studied with the hot plate, tail flick, acetic acid writhing and naloxone antagonism methods. No allied activities, e.g. antipyretic or CNS-depressant, were detected.
A 50% aqueous ethanol extract of dried and fresh leaves, and the volatile and fixed oils of Ocimum sanctum inhibited hind paw edema induced in rats by treatment with carrageenan, serotonin, histamine or PGE-2. The same extracts also showed anti-asthmatic activity against histamine- and acetylcholine-induced pre-convulsive dyspnea in guinea pigs.
The anti-inflammatory activity of Ocimum sanctum was studied using the water soluble portion of an alcoholic leaf extract. The test method used was carrageenan-induced paw edema in rats. The anti-inflammatory effect was dose dependent, showing a 57% inhibition at a dose of 400 mg/kg i.p. (). The same level of inhibition was found with 80 mg/kg phenylbutazone. The ED50-value was 270 mg/kg and LD50 4850 mg/kg, respectively.
Also the fixed oil of Ocimum sanctum seeds has been screened for its anti-inflammatory potential. It possessed significant anti-inflammatory activity against carrageenan- and different other mediator-induced paw edemas in rats. On the basis of these findings it seems that Ocimum sanctum fixed oil may have the potential to inhibit both the pathways causing inflammation, i.e. cydooxygenase and lipoxygenase, of the arachidonic acid metabolism (Singh et al., 1996a). Later the same year it was found that the pharmacological activity of the fixed oil could be attributed to its triglyceride fraction or the fatty acids. A year later it was determined that linolenic acid present in the fixed oil of Ocimum sanctum has the capacity to block both the cyclooxygenase and lipoxygenase pathways of the arachidonate metabolism.
Immunomodulating and Adaptogenic Effects
Certain plants widely used in the Ayurvedic and Unani systems of medicine for treatment of chronic infections and immunological disorders were studied on delayed type hypersensitivity, humoral responses to sheep red blood cells, skin allograft rejection, and phagocytic activity of the reticuloendothelial system in mice. An ethanolic extract of Ocimum gratissimum leaves (100 mg/kg p.0.) appeared to improve the phagocytic function without affecting the humoral or cell-mediated immune system.
A methanol extract and an aqueous suspension of Ocimum sanctum were investigated for their immunoregulatory profile to antigenic challenge in albino rats. The aqueous suspension represents the form usually employed in traditional medicine. Administration of the methanol extract at doses of 100 and 250 mg/kg (p.o.) and the aqueous suspension at 500 mg/kg caused a statistically significant increase in the antibody titre. This finding indicates that the methanol extract and the aqueous suspension of Ocimum sanctum leaves stimulates humoral response and this observed immunostimulation may account for the adaptogenic action of the plant.
The effects of alcoholic extracts of Eleutberococcus senticosus and Ocimum sanctum, regarded as anti-stress agents, were studied on the changes in central neurotransmitter (adrenaline, noradrenaline, dopamine, 5-hydroxytryptamine) levels and enzyme (monoamine oxidase) activity in the brain induced by stressors. There was an increase in the levels of dopamine and 5-hydroxytryptamine and decrease in adrenaline, noradrenaline and monoamine oxidase in stressed rats. Both plants prevented the decrease in adrenaline, noradrenaline and monoamine oxidase and facilitated the increase in dopamine. It was concluded that prevention of changes in brain neurotransmitters and enzymes by anti-stress agents appear to enhance the stress-adaption and the organism copes better with stressful situations. The antistress activity of Ocimum sanctum was compared to E.senticosus and Panax ginseng in albino mice and rats in different experimental models of stress. All of them were found effective. An anti-stress unit was determined by the ED50-values obtained in the tests. Taking the anti-stress unit of Ocimum sanctum as 1, the relative effect of E.senticosus was 0.83 and P.ginseng 0.53. Ocimum sanctum also had the highest margin of safety.
Effects of stress and its modulation by Ocimum sanctum and eugenol were evaluated on some biochemical and biophysical parameters in rats. Ocimum sanctum and eugenol lowered cholesterol levels and enzyme activities induced by stress. Also stress induced changes in membrane functions were affected by administration of Ocimum sanctum and eugenol. The antistress effects of an ethanol extract of Ocimum sanctum leaves was screened against acute and chronic noise stress in albino rats by investigating the plasma corticosterone level. Treatment of the animals with the Ocimum sanctum extract prevented the changes in the plasma level of corticosterone.
In a search for plant products against cancer the protective effect of ursolic acid from Ocimum sanctum was studied against free radical induced damage. Ascorbic acid, carbon tetrachloride and ADP/iron were used to induce lipid peroxidation in isolated rat liver microsomes. Ursolic acid provided a 60% protection against lipid peroxidation. Ursolic acid was further studied against adriamycin induced lipid peroxidation in liver and heart microsomes in vitro. It showed 13% and 17% protection in liver and heart microsomes, respectively.
Basil leaves (Ocimum sanctum) significantly decreased the incidence of both benzopyrene induced neoplasia and 3′-methyl-4-dimethylaminoazobenzene induced hepatomas in mice.
An ethanolic extract of the leaves of Ocimum sanctum showed chemopreventive effects on 7,12-dimethylbenzanthracene induced skin papillomagenesis in male Swiss albino mice. A significant reduction in the tumor incidence, average number of tumors/ tumor bearing mice and the cumulative number of papillomas was observed in mice treated topically with the leaf extract of Ocimum sanctum ().
An alcoholic extract from the leaves of Ocimum sanctum at doses of 400 and 800 mg/kg (p.o.) for 15 days significantly elevated the activity of cytochrome P-450, cytochrome b , aryl hydrocarbon hydroxylase and glutathione S-transferase in mice. The effect was d5ose-responsive. The above mentioned enzymes are important in the detoxification of carcinogens and mutagens. Glutathione S-transferase represents an important defense mechanism in protecting cells against oxygen-derived free radicals and also from cellular lethality after exposure to anticancer drugs or ionizing radiation. These findings suggest that Ocimum leaf extract has the potential to block or suppress the events associated with chemical carcinogenesis.
Hypoglycemic and Blood Lipid Lowering Effect
One of the traditional uses for Ocimum sanctum is for treating diabetes. Experimental studies performed in the 1960’s showed that basil leaves can decrease blood glucose in hyperglycemic rats. These results were confirmed kter by other studies which showed that oral administration of alcoholic extracts of Ocimum sanctum leaves led to a marked lowering of blood sugar level in normal, glucose fed hyperglycemic and streptozotocin induced diabetic rats. In a randomized placebo-controlled, single blind trial performed on humans a significant decrease in fasting and postprandial blood glucose levels was found. The medication consisted of 2.50 g dried leaf powder of fresh leaves of Ocimum sanctum and was given for 61 days. The fasting blood glucose fell by 21.0 mg/dl and postprandial blood glucose fell by 15.8 mg/dl. The urine glucose levels showed a similar trend. In addition the total cholesterol showed a mild reduction during the basil treatment period.
Fresh leaves of Ocimum sanctum (1 and 2 g/100 g diet) given for 4 weeks, brought about significant changes in the blood lipid profile of normal albino rats. Serum total cholesterol, triglycerides, phospholipids and LDL-cholesterol decreased and HDL-cholesterol and total faecal sterol content increased.
Prompted by the adaptogenic properties of Ocimum sanctum Devi and Ganasoundari undertook a study to investigate the radioprotective effect of Ocimum sanctum leaf extracts. Fresh leaves were extracted with water or water-alcohol and the extracts were administered i.p. either as a single dose or multiple doses to albino mice before whole-body exposure to gamma radiation. The optimum dose of water extract was 50 mg/kg. The water extract was more effective and less toxic than the aqueous alcohol extract. The acute LD50-values for the water and the aqueous alcohol extracts were 6200 mg/kg and 4600 mg/kg, respectively. Ocimum sanctum aqueous extract seems to provide protection against changes in the bone marrow and chromosome damage induced by radiation. Albino mice receiving both Ocimum sanctum extract and radiation showed fewer changes than groups receiving only radiation. The mechanism for protection is likely based on free radical scavenging.
Effects on the Central Nervous System
An ethanolic extract of the leaves of Ocimum sanctum was screened for its effects on the central nervous system. It prolonged the sleeping time induced by pentobarbital, reduced the recovery time and severity of elektroshock- and pentylenetetrazole-induced convulsions and decreased the apomorphine-induced fighting response and open-field activity. All these actions resemble the activity of low doses of barbiturates. The mechanism of action for the Ocimum extract may involve dopaminergic neurones.
Aqueous and methanolic extracts of Ocimum basilicum showed antiulcerogenic effects when administered to rats with aspirin-induced gastric ulcers. The ulcer index was decreased by both extracts. The acid output was decreased only by the methanolic extract, which indicate that the active principles are soluble in methanol. The pepsin output was decreased by both the aqueous and methanolic extract in ulcerated, but not in normal animals. The aqueous extract of Ocimum basilicum also increased the hexosamine concentration in normal rats, which might contribute to its antiulcer effect.
The antiulcerogenic effects of extracts, volatile oils and flavonoid glycosides of Ocimum basilicum leaves were studied in normal as well as aspirin-, acetic acid- and stress-induced ulcerated rats. Their effect on the output of gastric acid, pepsin and hexosamines was recorded. The aqueous, methanol and water-methanol extracts and flavonoid glycosides decreased the ulcer index, inhibited gastric acid and pepsin secretion and enhanced hexosamines. It appears that the antiulcerogenic compounds of Ocimum basilicum are extractable both into water and methanol and that they may include flavonoid glycosides. These substances may act by augmenting the gastric barrier.
A study on Ocimum sanctum showed that the extract reduced the ulcer index, free and total acidity on acute and chronic administration. It also increased the mucous secretion.
Ocimum sanctum leaves are part of a preparation sold in India for liver ailments. To prove the hepatoprotective action Ocimum sanctum leaf extract (200 mg/kg orally) was given to rats with paracetamol induced hepatic damage. The serume enzyme levels were significantly reduced and liver GSH level significantly higher in animals receiving both paracetamol and Ocimum sanctum leaf extract than in those given paracetamol alone. Histopathological studies showed marked reduction in fatty degeneration in animals receiving both paracetamol and Ocimum sanctum compared to the control group.
Ocimum gratissimum and Ocimum basilicum are used in a Taiwanese herbal remedy believed to possess anti-inflammatory and detoxication activities. The crude extracts was studied against CC1 – and D-GalN-induced acute hepatitis and were found to be hepatoprotective.
Effects on Smooth Muscle
A crude lipid extract of Ocimum gratissimum leaves caused contractions in a guinea pig ileum, rat colon and raised the mean arterial blood pressure in rats. The compounds seem to be related to lipids and fairly polar.
The volatile oil of basil (Ocimum basilicum) had relaxant effects on tracheal and ileal smooth muscles of the guinea pig. Of 22 oils examined basil belonged to the most potent group consisting of 16 oils. The EC -value for tracheal muscle was 19 mg/1 and for ileal muscle 32 mg/1, respectively.