Many spices used in food seasoning have broad spectrum of antimicrobial activity. Their antioxidant activity against lipid peroxidation enhances the keeping quality of food. Apart from the use as a popular spice and flavouring substance, black pepper as drug in the Indian and Chinese systems of medicine is well documented. In the Ayurvedic descriptions, pepper is described as katu (pungent), tikta (bitter), usbnaveerya (potency, leading to storing up of energy, easy digestion, diaphoresis, thirst and fatigue), to subdue vatta (all the biological phenomena controlled by CNS and autonomic nervous system) and kapha (implies the function of heat regulation, and also formation of various preservative fluids like mucus, synovia etc. The main functions of kapha is to provide co-ordination of the body system and regularization of all biological activities). Pepper is described as a drug which increases digestive power, improves appetite, cures cold, cough, dyspnoea, diseases of the throat, intermittent fever, colic, dysentery, worms and piles; also useful in tooth ache, pain in liver and muscle, inflammation, leucoderma and epileptic fits. Black pepper is called maricha or marica in Sanskrit, indicating its property to dispel poison. In Chinese medicine, it is used externally for snake and scorpion bite. These descriptions explain the diverse actions of pepper, which is being used in the Indian system of medicine either as such or as an ingredient in many formulations. But in the allopathic system, pepper or its active constituents did not find any therapeutic or clinical use. The above mentioned activities may be attributed to piperine and other phenolic amides and essential oil constituents. But in Ayurveda, the active principle-based specific activities of substances are not taken into consideration. Hence the pharmacological and toxicological aspects of pepper and its constituent secondary metabolites were not studied. Many of the clinical uses mentioned above were time tested and have been in use for generations. But to establish a scientific basis for many activities for which it has been used, pepper and its active constituents should be studied pharmacologically with well defined experimental protocols as used in modern drug development. Several studies were reported during the last ten or fifteen years, many of the results were encouraging and supported some of the clinical uses in the traditional Indian systems. Analgesic, antipyretic, antinflammatory, antimicrobial, and antineoplastic activities were reported both under in vitro and in vivo studies in experimental systems. Very promising results could be obtained in insecticidal and insect repellent activities. There seems to be scope for developing pepper based insecticides and insect repellents which are nontoxic to human beings.
Piperine is the major alkaloidal constituent of pepper. Systematic pharmacological studies on piperine have revealed its analgesic (alleviate pain), antipyretic (reduces fever), antinflammatory (reduces painful swelling caused by tissue injury) and central nervous system depressant activities. The essential oil constituents are mainly responsible for the antimicrobial actions.
Analgesic and Antipyretic Actions
The use of pepper and pepper containing preparations for the treatment of intermittent fever, neuritis, cold, pains and diseases of throat are practised in the Ayurvedic, Yunani, Siddha and folklore medicines in India. In the Chinese system, pepper and chenghan (Dichora febrifuga L, its active constituents, febrifugin and isofebrifugin, show anti-malarial property 50 times stronger than quinine) are used for the treatment of malaria. Pepper is also used as an antiperiodic in malarial fever. The curative effects claimed in the above cases can be attributed to the analgesic and antipyretic actions of the active constituents of black pepper. Lee et al. () have studied the analgesic and antipyretic actions of piperine on rabbit and mice and found strong antipyretic effect on typhoid vaccinated rabbits at a dose of 30 mg/kg body weight when administered orally. Acetaminophen was used as the reference substance. The antipyretic effect of piperine was found to be stronger than reference compound. For the determination of analgesic activity, acetaminophen and aminopyrine were used as reference compounds. Piperine gave a strong activity with an ED50 of 3.7 mg/kg on writhing method and 104.7 mg/kg on tailclip method.
The antinflammatory potential was studied by several groups. Lee et al. () reported that piperine showed a significant inhibition of increase in oedema volume in a carragenin induced test at an oral dose of 50 mg/kg body weight. Another group studied the effect on different acute and chronic experimental models. They evaluated the mechanism of antinflammatory activity by biochemical studies and concluded that piperine acted significantly on early acute changes in inflammatory process. The antinflammatory potential was supported by Kapoor et al. ().
Central Nervous System Depressant Activity
In the Ayurvedic medicine, pepper is used for the treatment of epileptic fits and to bring about sleep. In the pharmacological evaluations, the CNS depressant effect of pepper and piperine was established. It exhibited protection against pentetrazole seizure and showed weak protection against maximal electroshock seizure. The LD50 value for piperine was 287.1 mg/kg i.p. and 1638.8 mg/kg orally. In another study Shin et al. () showed that piperine at one-tenth of its LD50 value showed strong potentiating effect on hexobarbital induced hypnosis in mice. Decreased passivity, ptotic symptoms and decrease in body temperature were also observed. Protection against electroshock seizure and muscle relaxant effect were observed at relatively low dosage range with an ED50 of 15.1 mg/kg intraperitonial was reported. This was almost equipotent to the reference compound phenytoin. Petrol extract of pepper leaves was found to potentiate phenobarbitone-induced hypnosis in mice. Majumdar et al. () also reported that high dosage of piperine potentiates the phenobarbitone sleeping time by inhibiting the liver microsomal enzymes. It also acted partially through stimulation of pituitary adrenal axis. From the above studies it may be inferred that piperine may be effective in the treatment of petit mal.
A compound of great interest is antiepilepsirine (AE) isolated from white pepper. AE is 1-(3-benzodioxol-5yl)-1-oxo-2-propenyl)- piperidide. This is perhaps the only compound derived from pepper, clinically used, in the treatment of epilepsy. This is used as an alternative to dilantin therapy in Chinese hospitals. Reports on human clinical studies show that 83.3 per cent cases respond favourably leading to 50–90 per cent reduction of seizures. According to Zhou AE was most effective against grand mal seizures. No toxic effect was noticed, even in pregnant women. Liu et al. () suggests that AE may release 5-hydroxy tryptamine (5-HT) from nerve endings. Studies on rats showed that AE increases concentration of 5-HT in the brain and there by intensifies anticonvulsive activity. AE also raises tryptophan level in the brain, causing elevation of serontin and monoamine levels, a suggestive cause to seizure control
Action on Liver Enzymes
Neither pepper nor piperine produces any hepatic toxicity. In fact, it exerts liver protective action as evidenced by the studies of several workers. By enzyme modulation, piperine functions as a chemopreventive substance. Dalvi and Dalvi studied the hepatotoxic effect of piperine on rats by estimating the hepatic mixed function oxidases and serum enzymes as specific markers of hepatotoxicity. An intragastric dose of 100 mg/kg body weight caused an increase in hepatic microsomal enzymes, 24 hours after treatment (cytochrome p-450, cytochrome-b5, NADPH-cytochrome C reductase, benzphetamine N-demethylase, aminopyrine N-demethylase and aniline hydroxylase were estimated). On the other hand, an intraperitonial dose of 10 mg/kg did not produce any effect on the activities of the drug metabolizing enzymes. However, at higher doses of 800 mg/kg (intragastric) and 100 mg/kg (intraperitonial), significant decrease in the levels of the enzymes was noted. But these treatments did not affect those serum enzymes which are specific markers of liver toxic conditions. Piperine exerts significant protection against chemically induced hepatotoxicity. Kaul and Kapil, reports that this plant principle reduces in vitro and in vivo lipid peroxidation and prevents depletion of GSH and total thiols. Lipid peroxidation causes free radical production, which in turn produces tissue damage. GSH conjugates xenobiotics which are excreted out by subsequent glucuronidation. In this study, the hepato protective action was compared with a reference compound, silymarin, a known hepato protective drug, and found that piperine has slightly lower activity. A dose dependent increase in the levels of the hepatic biotransformation enzymes, (glutathione-s-transferase, cytochrome p-450, cytochrome b-5, acid soluble sulfhydril-SH), was obtained in a feeding experiment study using Swiss albino mice fed with a diet containing 1 per cent, 2 per cent and 5 per cent black pepper (w/w) for 10 and 20 days. A lowered level of glucuronidation due to the inhibition of the enzyme UDP-glucose dehydrogenase was observed by Reen et al. () in an in vitro study. While studying the hypoglycaemic action of several plants, Tripathi et al. () reported that pepper fruits are devoid of any significant hypoglycaemic action in rabbits. The aqueous extract of pepper leaves in a dose of 10–20 mg/kg led to a moderate increase in the blood pressure of dogs. Piperine as well as AE (antiepilepsirine) are reported to have detoxifying qualities, that may increase the bioavailability of other drugs, hence altering the pharmokinetic parameter of the epileptic.
Mutagenic and Carcinogenic Effects
Investigations into the mutagenic and carcinogenic activities of pepper gave encouraging results on its beneficial effects. It was found to be nonmutagenic by Ames test. Pepper prevents chemical carcinogenesis by stimulating the xenobiotic biotransformation enzymes. The antioxidant properties of piperine and associated unsaturated amides play a preventive role in carcinogenesis. Dietary intake of natural antioxidants could be an important aspect of the body’s defense mechanism against the degradative changes caused by mutagens. In addition to that, the essential oil constituents inhibits DNA adduct formation by xenobiotics. This observation shows the anticarcinogenic potential of pepper. However, studies with pepper extracts showed an increased incidence of tumour in mice and, an elevated level of DNA damage caused by piperine in cell culture investigations. Hexane, water and alcohol extracts of pepper were tested for mutagenicity on Salmonella typhimurium strains TA 98 and TA 100 by Ames assay and the results indicated the nonmutagenic effects of the extracts.
This study also gave evidence that the water extract exerts an antimutagenic action on carcinogen induced mutagenesis. Pepper as well as its constituents increases the activity of biotransformation enzymes in the liver in a dose dependent manner, thereby playing a chemoprotective role. The phenolic amides elicits a very significant antioxidant activity. It is well known that antioxidants exert a preventive mode of action in carcinogenesis. Hashim et al. () studied the modulating effects of the essential oil of pepper and found that this also has an inhibitory activity. The volatile oil and its constituents suppress the formation of DNA adducts with aflatoxin B1. This action was modulated through the microsomal enzymes. When mice was fed with powdered pepper in diet (1.66% w/w of food) no impact on carcinogenesis was noticed, whereas feeding and painting of mice with solvent extract of pepper, 2 mg for 3 days per week for 3 months, resulted in an increase in the incidence of tumour bearing mice. The pepper terpenoid d-limonene was found to reduce the carcinogenic activity of methycholanthrene, a potent carcinogenic compound. Two minor constituents of pepper, safrole and tannic acid, are attributed with minor carcinogenic activity. In a tissue culture study using V-79 lung fibroblast cell lines, Chu et al. () reported that piperine treated cell lines showed increased DNA damage compared to untreated ones. Piperine treatment lowered the activities of the enzymes glutathione-s-transferase and uridine diphosphate glucuronyl transferase indicating the cytotoxic potential. The in vivo formation of n-nitroso compounds from naturally occurring amines and amides contribute to the carcinogenic potential of certain foods and food additives. Piperine and other phenolic amides present in pepper are also known for their conversion to n-nitroso compounds in acidic conditions and hence treated as carcinogenic. But it can be inferred that the presence of conjugated unsaturated system in the phenolic amide prevents the oxidation of the amide nitrogen to n-nitroso compounds to a large extent. Moreover, the essential oil constituents of pepper also contribute to its anticarcinogenic potential preventing DNA damage. Investigations reveal both carcinogenic and anticarcinogenic nature. However, black pepper as such exhibited antimutagenic and anticarcinogenic effects. This is the form in which it is usually used as spice and also in various medicinal formulations of the Indian System.
Antioxidants scavenge free radicals and control lipid peroxidation in mammalian system. Lipid peroxidation is a chain reaction, providing continuous supply of free radicals that initiate further peroxidation. This is responsible not only for the deterioration of food but also for damage of tissue in vivo where it may cause inflammatory diseases, ageing, atherosclerosis, cancer etc. Investigations revealed that pepper and the phenolic amides present in it, possess good antioxidant property. Tocopherol and vitamin-C are two important natural antioxidants. Chiapault et al. () studied the antioxidant effectiveness of spices in a two phase aqueous fat system. Pepper has an antioxidant index of 6.1, compared to 103.0 for clove and 29.6 for turmeric. Saito and Asari, in a study on different spices, reported that pepper exhibit antioxidant activity and they attributed it to the tocopherol content of pepper. But in an earlier work on the effect of the pepper oleoresin on fish oil, Revankar and Sen stated that the antioxidant property is due to the polyphenolic content. The autoxidation of unsaturated fatty acids and proteins was delayed by addition of pepper, and significant protection against oxidative degradation was obtained as evidenced by the studies of Abdel-Fattah and El-Zeany. From an investigation on the family Piperaceae, Nakatani et al. () established that all the five phenolic amides present in P. nigrum possess very good antioxidant property, which is superior to that of the synthetic antioxidants like butylated hydroxy toluene and butylated hydroxy anisole.
It should be noted that many of the spices possess antiseptic, antibacterial and antifungal effects. These properties are mainly due to the presence of volatile oil principles present in them. Volatile oils are mixtures of several constituents and it is logical to attribute the activity to more than one terpenoid constituents of the oil. The high value placed upon pepper as an important spice is due to its bactericidal and bacteriostatic activity. The addition of pepper to foods and processed foods increases their keeping quality and prevents their spoilage. The antimicrobial properties of pepper is due to its volatile oil as evidenced by several studies. Even the leaf extract possess activity, which was established even 40 years back. The extract of pepper was not inhibitory to E. coli., Aerobacter aerugenosa, Lactobacillus casei, Staphylococcus faecalis, S. aureus and S. sonnei (). The essential oil obtained from pepper was found to be active against penicillin-G resistant strain of Staphylococcus aureus. Jain and Kar reported the inhibitory action of pepper oil on Vibrio cholerae, Staphylococcus albus, Clostridium diphthereae, Shigella dysenteriae, Streptomyces faecalis, S. pyogenes, Bacillus pumilis, B. subtlis, Micrococcus sp., Pseudomonas pyogenes, P. solanacearum and Salmonella typhimurium. The antibacterial action was determined by the agar well diffusion technique using cephazolin as standard. Pepper oil stopped the mycelial growth and aflatoxin synthesis by Aspergillus parasiticus at a concentration of 0.2 per cent to 1 per cent. The leaf oil exhibits antifungal activity against Candida albicans () and Aspergillus flavus (). Salzer et al. () studied the antibacterial effects of pepper extract, essential oil and isolated piperine in vitro against sausage micro flora (Lactobacillus plantrum, Micrococcus specialis and Streptococcus faecalis) and found that only isolated piperine had growth inhibiting effect at normal doses. Pepper powder and extract were active only at high concentrations. An alcoholic extract was found active against the deadly food borne bacterium, Clostridium botulinum (). Another potential activity was revealed by a study carried out using tincture of pepper by Houghten et al. (). They have studied nine strains of Mycobacterium tuberculosis and found significant antibacterial activity against all the nine strains.
Pepper increases the bioavailability of medicaments and uptake of proteins and amino acids from food. In a study using Trikatu, an ayurvedic preparation containing Piper nigrum, P. longum and Z. officinale, it was found that pepper containing preparations enhance the bioavailability of other medicaments. Piperine at a dose of 25–100 micromolar quantity, enhanced the uptake of l-leucine, l-isoleucine and l-valine and increased lipid peroxidation in an in vitro study using rat intestinal epithelial cells. These results suggest that piperine may interact to increase the permeability of intestinal cells. Predeep and Geervani reported that the protein uptake from pulses was enhanced by the addition of spices (pepper and other common spices used in Indian cooking) at a level of about 1.5 per cent of the diet.
Investigations on Human Subjects
Only a very few studies using human subjects were reported. In high doses, the gastric mucosal injury caused by pepper is comparable to that of aspirin. This rinding was obtained in a double blind study of intragastric administration of pepper to human volunteers. Healthy human volunteers were given meals containing 1.5 g of pepper; aspirin (655 mg) and distilled water were used as the positive and negative control. However, the long-term effects of daily pepper ingestion are not known.
Vezyuez Olivincia et al. () studied the effect of intestinal peristalsis by measuring the orocaecal transit time, utilising a lactulose hydrogen breath test on healthy human subjects. They were given 1.5 g of pepper in gelatine capsule and the OCTT was measured on several days and found that orocecal transit time increased significantly after pepper administration. This finding has clinical importance in the management of various gastrointestinal tract disorders. Another significant study reveals the usefulness of pepper extract volatiles in smoking cessation treatment. The results of the study by Rose and Behm on human subjects revealed that, cigarette substitutes, delivering pepper volatile constituents, alleviated smoking withdrawal symptoms. The results of these two studies with human subjects are encouraging, which has the potential to be exploited for future therapeutic use.