Impairment of UDP-glucose dehydrogenase and glucuronidation activities in liver and small intestine of rat and guinea pig in vitro by piperine.
The effects of piperine, a major ingredient of black pepper, on UDP-glucose dehydrogenase (UDP-GDH) and glucuronidation potentials of rat and guinea pig liver and intestine were studied. Piperine caused a concentration-related strong inhibition of UDP-GDH (50% at 10 microM) reversibly and equipotently, in both tissues. Partially purified rat liver UDP-GDH was used to obtain the kinetic values at pH optima of 9.4 and 8.6. At pH 9.4: KmUDP-glucose = 15 microM, Vmax = 5.2 nmol NADH/min/mg protein, Ki = 6 microM. With NAD, a Ki of 16 microM was obtained. At pH 8.6: Km = 35 microM, Vmax = 7.5 nmol, Ki = 15 microM. In all of these cases, piperine caused non-competitive inhibition. Data from structure-activity comparisons of piperine analogs indicated that the presence of conjugated double bonds in the side chain of the molecule is a factor in piperine inhibition. However, the UDP-glucuronic acid (UDPGA) contents were decreased less effectively by piperine in isolated rat hepatocytes compared with enterocytes of guinea pig small intestine. Piperine at 50 microM caused a marginal decrease of UDPGA in hepatocytes when the rate of glucuronidation of 3-hydroxybenzo[a]pyrene (3-OH-BP) decreased by about 40%. The decrease obtained at 10 microM piperine in intestinal cells was comparable to that obtained at 50-100 microM in hepatocytes. UDP-glucuronosyltransferase (UGT) activities towards 3-OH-BP (UGT1A1) and 4-OH-biphenyl (UGT2B1) were also determined. Piperine did not affect the rate of glucuronidation of 4-OH-biphenyl in rat liver, whereas that of 3-OH-BP was impaired significantly. In guinea pig small intestine, both these activities were inhibited significantly requiring less than 25 microM piperine to produce a more than 50% inhibition of UGT(s). The results suggested that (i) piperine is a potent inhibitor of UDP-GDH, (ii) inhibition is offered exclusively by the conjugated double bonds of the molecule, and (iii) piperine exerts stronger effects on intestinal glucuronidation than in rat liver.
Reen
R K
RK
Biochemistry Section, Council of Scientific and Industrial Research (CSIR), Jammu Tawi, India.
Jamwal
D S
DS
Taneja
S C
SC
Koul
J L
JL
Dubey
R K
RK
Wiebel
F J
FJ
Singh
J
J
D000470:Alkaloids; D000818:Animals; D052117:Benzodioxoles; D002478:Cells, Cultured; D005966:Glucuronidase / Q000378:metabolism*; D006168:Guinea Pigs; D007421:Intestine, Small / Q000201:enzymology*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology; D010880:Piperidines / Q000494:pharmacology*; D053284:Polyunsaturated Alkamides; D051381:Rats; D013329:Structure-Activity Relationship; D014533:Uridine Diphosphate Glucose Dehydrogenase / Q000032:analysis / Q000037:antagonists & inhibitors*
D000470:Alkaloids; D052117:Benzodioxoles; D010880:Piperidines; D053284:Polyunsaturated Alkamides; D014533:Uridine Diphosphate Glucose Dehydrogenase; D005966:Glucuronidase; C008922:piperine