Piperine modulates permeability characteristics of intestine by inducing alterations in membrane dynamics: influence on brush border membrane fluidity, ultrastructure and enzyme kinetics.

Piperine (1-Piperoyl piperidine) is a major alkaloid of Piper nigrum Linn. and Piper longum Linn. It is shown to possess bioavailability-enhancing activity with various structurally and therapeutically diverse drugs. The mechanism of enhancing the bioavailability, is, however, not understood. We hypothesize that piperine's bioavailability-enhancing property may be attributed to increased absorption, which may be due to alteration in membrane lipid dynamics and change in the conformation of enzymes in the intestine. Results of membrane fluidity studies using an apolar fluorescent probe, pyrene (which measures the fluid properties of hydrocarbon core), showed an increase in intestinal brush border membrane (BBM) fluidity. Piperine also stimulated Leucine amino peptidase and Glycyl-glycine dipeptidase activity, due to the alteration in enzyme kinetics. This suggests that piperine could modulate the membrane dynamics due to its apolar nature by interacting with surrounding lipids and hydrophobic portions in the protein vicinity, which may decrease the tendency of membrane lipids to act as stearic constrains to enzyme proteins and thus modify enzyme conformation. Ultra structural studies with piperine showed an increase in microvilli length with a prominent increase in free ribosomes and ribosomes on the endoplasmic reticulum in enterocytes, suggesting that synthesis or turnover of cytoskeletal components or membrane proteins may be involved in the observed effect. In conclusion, it is suggested that piperine may be inducing alterations in membrane dynamics and permeation characteristics, along with induction in the synthesis of proteins associated with cytoskeletal function, resulting in an increase in the small intestine absorptive surface, thus assisting efficient permeation through the epithelial barrier.

Mechanism of action of 6, 7, 8, 9, 10, 12-hexahydro-azepino-[2, 1-b] quinazolin-12-one-(RLX)--a novel bronchodilator.

The present study presents a mode of action profile of RLX (6, 7, 8, 9, 10, 12-hexahydro-azepino-[2, 1-b]-quinazoline-12-one) a bronchodilator obtained by the chemical modification in the molecule of alkaloid vasicine (Ex: Adhatoda vesica). The effect of RLX (p.o.) was observed on: (a) mast cell degranulation, (b) release of histamine and prostaglandin E (PGE), (c) 45Ca uptake and (d) activities of cAMP phosphodiesterase (PDEase) and lipoxygenase enzymes in mesenteries/peritoneal mast cells/lung tissue homogenates in rats under systemic anaphylaxis. RLX (10 and 20 mg/kg) inhibited antigen-induced mast cell degranulation and released of histamine from target tissues. An increased outflow of PGE (lungs) and an inhibited 45Ca uptake (peritoneal mast cells) were noted. Lung PDEase and lipoxygenase activities were decreased. These results suggested that RLX could be acting like disodium cromoglycate and aminophyline with additional attributes its oral efficacy and long duration of action.

Piperine mediated alterations in lipid peroxidation and cellular thiol status of rat intestinal mucosa and epithelial cells.

Piperine (1-Piperoyl piperidine) is the major alkaloid of black and long peppers used widely in various systems of traditional medicine. The present study investigates the toxicity of piperine via free-radical generation by determining the degree of lipid peroxidation and cellular thiol status in the rat intestine. Lipid peroxidation content, measured as thiobarbituric reactive substances (TBARS), was increased with piperine treatment although conjugate diene levels were not altered. A significant increase in glutathione levels was observed, whereas protein thiols and glutathione reductase activity were not altered. The study suggests that increased TBARS levels may not be a relevant index of cytotoxicity, since thiol redox was not altered, but increased synthesis transport of intracellular GSH pool may play an important role in cell hemostasis and requires further study.

Permeability characteristics of piperine on oral absorption--an active alkaloid from peppers and a bioavailability enhancer.

Piperine, [1-[5-[1,3-benzodioxol-5-yl]-1-oxo-2,4, pentadienyl] piperidine], is a pungent alkaloid present in Piper nigrum Linn, and P. longum Linn. It is shown to enhance the bioavailability of various structurally and therapeutically diverse drugs. A concise mechanism responsible for its bioavailability enhancing action is poorly understood. This study is an effort to understand the absorption dynamics of piperine in intestine on oral absorption. It encompasses intestinal everted sacs as an experimental model. Cycloheximide treatment and exclusion of Na+ salts from incubating medium were the variables used. Absorption half life, absorption rate, absorption clearance and apparent permeability co-efficient were computed from the data. Experiments to denote physico-chemical characteristics of this moiety exhibited that it is a weak base, highly lipophilic in nature with partial solubility in aqueous media. It exhibited passive diffusion constituting non-saturable absorption kinetics. Transport of piperine was not resisted by UWL and was proposed to be absorbed through transcellular pathway. It displayed short absorption clearance and high apparent permeability co-efficient. Data thus obtained suggested that piperine is absorbed very fast across the intestinal barrier. It may act as an apolar molecule and form apolar complex with drugs and solutes. It may modulate membrane dynamics due to its easy partitioning thus helping in efficient permeability across the barriers.

Piperine modulation of carcinogen induced oxidative stress in intestinal mucosa.

Reactive oxygen species (ROS) and reactive metabolic intermediates generated from various chemical carcinogens are known to play an important role in cell damage and in the initiation and progression of carcinogenesis. Many radical scavengers, interestingly naturally occuring antioxidants have been found to be effective in inhibiting the induction of carcinogenesis by a wide variety of chemical carcinogens. Studies have also indicated that various spice principles form an important group as antioxidants. In the present study our goal was to investigate whether piperine an pungent principle of black and long peppers was able to inhibit or reduce the oxidative changes induced by chemical carcinogens in rat intestinal model. Carcinogenesis was initiated in intestinal lumen of male rats with 7,12,dimethyl benzanthracene, dimethyl amino-methyl azobenzene and 3-methyl cholenthrene. Oxidative alterations were assessed by determining thiobarbituric reactive substances, mainly malonaldehyde (as a measure of lipid peroxidation), thiol status and expression of gamma-GT and Na+-K+-ATPase activity in intestinal mucosa. Data indicated that carcinogens treatment induced GSH depletion with substantial increase in thiobarbituric reactive substances and enzyme activities. Piperine treatment with carcinogens resulted in inhibition of thiobarbituric reactive substances. It mediated a significant increase in the GSH levels and restoration in gamma-GT and Na+-K+-ATPase activity. The studies thus indicate a protective role of piperine against the oxidative alterations by carcinogens. It may be suggested that piperine modulates the oxidative changes by inhibiting lipid peroxidation and mediating enhanced synthesis or transport of GSH thereby replenishing thiol redox.

An Ayurvedic formulation 'Trikatu' and its constituents.

'Trikatu' is an Ayurvedic preparation containing black pepper, long pepper and ginger, which is prescribed routinely for a variety of diseases as part of a multidrug prescription. These herbs along with piperine (alkaloid of peppers) have been shown to possess diverse biological activities in mammalian systems. A review is presented of these studies and it has been suggested that their use in the Indian system of medicine could be due to their bioavailability enhancing action on other medicaments.

Piperine-mediated changes in the permeability of rat intestinal epithelial cells. The status of gamma-glutamyl transpeptidase activity, uptake of amino acids and lipid peroxidation.

The effect of piperine (1-[5-(1,3-benzodioxol-5-yl)-1-oxo-2,4-pentadienyl]piperidin e), (from Piper nigrum) on the absorptive function of the intestine was studied. In vitro experiments showed that piperine (25-100 microM) significantly stimulated gamma-glutamyl transpeptidase (gamma-GT, EC 2.3.2.2.) activity, enhanced the uptake of radiolabelled L-leucine, L-isoleucine and L-valine, and increased lipid peroxidation in freshly isolated epithelial cells of rat jejunum. The kinetic behaviour of gamma-GT towards substrate and acceptor altered in the presence of piperine. In the presence of benzyl alcohol, an enhanced gamma-GT activity due to piperine was maintained. These results suggested that piperine may interact with the lipid environment to produce effects which lead to increased permeability of the intestinal cells.

Determination of estrogenic/antiestrogenic potential of antifertility substances using rat uterine peroxidase assay.

The effect of three compounds (clomiphene citrate, centchroman, embelin) and plant-derived methanolic extracts (Abutilon indicum and Butea monosperma) was studied on uterotropic and uterine peroxidase activities in ovariectomized rats. It was observed that these two parameters were highly correlated in response to treatment with these test materials and also to estradiol. It was suggested that the uterine peroxidase assay could be utilized as a biochemical parameter in the screening of new antifertility agents for their estrogenic/antiestrogenic properties.

Binding of potassium [3H]embelate to rat brain synaptosomes.

[3H]Embelate (potassium salt of 2,5-dihydroxy-3-undecyl-1,4- benzoquinone), a new analgesic compound, showed a specific and saturable binding in rat brain synaptosomes which was not influenced by naloxone and morphine. The binding characteristics were correlated with its non-narcotic central analgesic action.

Effect of piperine on bioavailability and pharmacokinetics of propranolol and theophylline in healthy volunteers.

The effect of piperine on the bioavailability and pharmacokinetics of propranolol and theophylline has been examined in a crossover study. Six subjects in each group received a single oral dose of propranolol 40 mg or theophylline (150 mg) alone or in combination with piperine 20 mg daily for 7 days. An earlier tmax and a higher Cmax and AUC were observed in the subjects who received piperine and propranolol. It produced a higher Cmax, longer elimination half-life and a higher AUC with theophylline. In clinical practice, the enhanced systemic availability of oral propranolol and theophylline could be exploited to achieve better therapeutic control and improved patient compliance.

Toxicity studies with potassium embelate, a new analgesic compound.

Potassium embelate, 2,5-dihydroxy, 3-undecyl-1, 4-benzoquinone, from Embelia ribes Burm. was subjected to toxicity evaluation which included subacute, chronic, reproductive toxicity testing and teratological investigations in laboratory animals (mice, rats and monkeys). The results did not indicate adverse effects suggesting that potassium embelate is a safe compound.

Kinetic fate of potassium embelate, a non-narcotic centrally acting analgesic after oral and intravenous administration.

The pharmacokinetics of oral and intravenous potassium embelate (20 mg/kg) was studied in rats. The results revealed that this compound follows a biexponential kinetic pattern. Absorption was complete (bioavailability 97%) and fast. The disposition half-life is 9.5 h on intravenous and 11 h on oral administration. High concentrations of the drug were found in brain between 0.25 and 2 h, which is in agreement with its pharmacological action. The kidney plays a major role in the excretion of the drug.

Possible interaction of potassium embelate, a putative analgesic agent, with opiate receptors.

The in vivo studies have been carried out in the rat brain for characterization of binding sites for potassium embelate (ex: Embelia ribes) a potent centrally acting analgesic compound. The results indicate that mixed mu and kappa binding sites in the brain may be involved in the analgesic action of this compound.