Kasturi Lal Bedi

Characterization of a new rat urinary metabolite of piperine by LC/NMR/MS studies.

Potential of piperine, an active alkaloid of black and long peppers, to increase the bioavailability of drugs in humans is of great clinical significance owing to its omnipresence in food. In an attempt to further study the reported differences in its metabolism in rats and humans, a new major urinary metabolite was detected in rat urine and plasma using HPLC. The metabolite was partially purified using reverse phase column chromatography on Sephadex((R))-LH 20 and characterized as 5-(3, 4-methylenedioxy phenyl)-2E,4E-pentadienoic acid-N-(3-yl propionic acid)-amide with the help of LC/NMR/positive ESI-MS studies. Complete mass fragmentation pattern could be assigned with MS/MS studies. The metabolite has a unique structure compared to the previously reported metabolites in that it retains methylenedioxy ring and conjugated double bonds while the piperidine ring is modified to form propionic acid group. Mechanism of formation of the metabolite by oxidation and cleavage of piperidine ring is proposed. Kidney appears to be the major excretion route for piperine metabolites in rats as no metabolite could be detected in feces.

Simple high-performance liquid chromatography method for the simultaneous determination of ketoconazole and piperine in rat plasma and hepatocyte culture.

Piperine, a major alkaloid of black and long peppers has been reported to act as bioavailability enhancer of several drugs by inhibiting drug metabolising enzymes and/or by increasing oral absorption. Ketoconazole is a well established potent inhibitor of CYP 3A4 and P-glycoprotein. A simple and rapid HPLC method has been developed for the simultaneous analysis of ketoconazole and piperine in rat plasma and hepatocyte culture. Analysis was performed using a Symmetry C18 column (150x4.6 mm, 5 microm) and isocratic elution with 25 mM KH2PO4 (pH 4.5)-acetonitrile (50:50) with a flow-rate of 1 ml/min. Photodiode array detection was used to simultaneously monitor piperine at 340 nm and ketoconazole at 231 nm in a single sample. Calibration plots in spiked plasma, hepatocytes and Williams medium E were linear over the range studied (10-2000 ng for both drugs). The detection limits for piperine and ketoconazole are 2 and 4 ng, respectively, and the limits of quantitation are 10 and 12 ng, respectively. Intra- and inter-assay variations were less than 8%.

Synthesis and Structure-Activity Relationships of Vasicine Analogues as Bronchodilatory Agents

The series of vasicine (1) analogues, an alkaloid from Adhatoda vasica Nees., were synthesized with changes in A, B or C rings. Compounds 13-19 were evaluated for in vitro bronchodilatory activity using isolated guinea pig tracheal chain. Compounds 3-8 were also synthesized in good yields using microwave-mediated synthesis under solvent free conditions. Compounds 5 and 8 with seven-member C ring were more active than etofylline and caused 100% relaxation of both the histamine and acetycholine pre-contracted guinea pig tracheal chain. The structure-activity relationship studies showed that the quinazoline and oxo functionalities were essential for activity. The compounds without C ring and instead having aliphatic and phenyl substitutions in B ring showed relaxation against histamine pre-contracted tracheal chain only, 2-methyl substituted analogues, 12 and 13, being most active with 100% relaxation effect.

Improved Bioavailability of Dapsone in the Presence of Piperine in Rats

Piperine, an alkaloid present in a number of Piper species, selectively enhances the bioavailability of structurally and therapeutically different drugs, either by increasing the absorption or by delaying the metabolism of the drug or by a combination of both processes. Dapsone, a widely used anti-leprosy drug, is known to produce methaemoglo-binaemia as a serious side effect. Based on the reported interaction of piperine with drug-metabolizing enzymes, the present investigation was undertaken to study changes in bioavailability of dapsone and possible reduction in methaemoglobinaemia in the presence of piperine in rats. A Cmax value of 2.4±0.12 μg mL−1 was obtained with dapsone alone (10 mg kg−1), compared with 3.90 ± 0.16 μg mL−1 obtained with a combination of dapsone (10 mg kg−1) and piperine (10 mg kg−1). This represents an increase of 62% in peak plasma levels caused by the presence of piperine. Reduction in total clearance from 4.80 ± 0.31 to 3.81 ± 0.20 mL h−1, and a volume of distribution from 4.61 ± 0.19 to 3.08 ± 0.12 L resulted in a net increase of 35% in AUC (34.55 ± 1.83 to 46.70 ± 3.14) in the presence of piperine. We conclude that piperine significantly (P < 0.001) enhances the bioavailability of dapsone.