Piperine-mediated inhibition of glucuronidation activity in isolated epithelial cells of the guinea-pig small intestine: evidence that piperine lowers the endogeneous UDP-glucuronic acid content.
Piperine (1-peperoyl piperidine), a major component of the Piper species was reported recently by us to inhibit the activities of rat hepatic monooxygenases and UDP-glucuronyltransferase. This study explores further the basis of inhibition of glucuronidation. The effect of piperine on the rate of glucuronidation of 3-hydroxybenzo(a) pyrene and UDP-glucuronic acid content in the intact isolated epithelial cells of the guinea-pig small intestine was studied. The cells offered a fairly good system to study the modulation of glucuronidation activity. Glucuronidation of 3-hydroxybenzo(a) pyrene was dependent on the time of incubation, cellular protein and substrate concentration. From the kinetics of glucuronidation of 3-hydroxybenzo(a)pyrene in the isolated cell preparation the Vmax of 0.5 nmol of BP-3-glucuronide formed per min/mg of protein and Km of 25 microM were observed. The endogeneous concentration of UDP-glucuronic acid observed was 1.6 to 2.3 nmol/mg of cellular protein. Piperine caused a concentration-related decrease in UDP-glucuronic acid content and the rate of glucuronidation in the cells. It required much lower concentrations of piperine than D-galactosamine to diminish the endogeneous level of UDP-glucuronic acid. Rate of glucuronidation of 3-hydroxybenzo (a) pyrene was dependent on the endogeneous level of UDP-glucuronic acid. At 50 microM piperine, the rate of glucuronidation was reduced to about 50% of the basal rate. Piperine caused noncompetitive inhibition of hepatic microsomal UDP-glucuronyltransferase with Ki of 70 microM. The studies demonstrate that piperine modifies the rate of glucuronidation by lowering the endogeneous UDP-glucuronic acid content and also by inhibiting the transferase activity.
Singh
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J
Dubey
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Atal
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D000470:Alkaloids; D000818:Animals; D052117:Benzodioxoles; D001580:Benzopyrenes / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D004848:Epithelium / Q000378:metabolism; D005688:Galactosamine / Q000494:pharmacology; D005965:Glucuronates / Q000378:metabolism*; D014453:Glucuronosyltransferase / Q000037:antagonists & inhibitors; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007421:Intestine, Small / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D010880:Piperidines / Q000494:pharmacology*; D053284:Polyunsaturated Alkamides; D014535:Uridine Diphosphate Glucuronic Acid / Q000032:analysis* / Q000378:metabolism; D014539:Uridine Diphosphate Sugars / Q000032:analysis*
D000470:Alkaloids; D052117:Benzodioxoles; D001580:Benzopyrenes; D005965:Glucuronates; D010880:Piperidines; D053284:Polyunsaturated Alkamides; D014539:Uridine Diphosphate Sugars; D014535:Uridine Diphosphate Glucuronic Acid; C021338:3-hydroxybenzo(a)pyrene; D005688:Galactosamine; D014453:Glucuronosyltransferase; C008922:piperine