Effect of Ginkgo biloba extract on rat hepatic microsomal CYP1A activity: role of ginkgolides, bilobalide, and flavonols.
The present study investigated the in vitro effect of Ginkgo biloba extracts and some of the individual constituents (ginkgolides, bilobalide, and flavonols such as kaempferol, quercetin, isorhamnetin, and their glycosides) on CYP1A-mediated 7-ethoxyresorufin O-dealkylation in hepatic microsomes isolated from rats induced with beta-naphthoflavone. G. biloba extract competitively inhibited CYP1A activity, with an apparent Ki value of 1.6 +/- 0.4 microg/mL (mean +/- SE). At the concentrations present in the G. biloba extracts, ginkgolides A, B, C, and J and bilobalide did not affect CYP1A activity, whereas kaempferol (IC50 = 0.006 +/- 0.001 microg/mL, mean +/- SE), isorhamnetin (0.007 +/- 0.001 microg/mL), and quercetin (0.050 +/- 0.003 microg/mL) decreased this activity. The monoglycosides (1 and 10 microg/mL) and diglycosides (10 microg/mL) of kaempferol and quercetin but not those of isorhamnetin also inhibited CYP1A activity. The order of inhibitory potency was kaempferol approximately equal to isorhamnetin > quercetin, and for each of these flavonols the order of potency was aglycone >> monoglycoside > diglycoside. In summary, G. biloba extract competitively inhibited rat hepatic microsomal CYP1A activity, but the effect was not due to ginkgolides A, B, C, or J, bilobalide, kaempferol, quercetin, isorhamnetin, or the respective flavonol monoglycosides or diglycosides.
Kuo
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Faculty of Pharmaceutical Sciences, University of British Columbia, 2146 East Mall, Vancouver, BC V6T 1Z3, Canada.
Chen
Jie
J
Chang
Thomas K H
TK
D000818:Animals; D003517:Cyclopentanes / Q000494:pharmacology*; D019363:Cytochrome P-450 CYP1A1 / Q000378:metabolism*; D019388:Cytochrome P-450 CYP1A2 / Q000378:metabolism*; D004224:Diterpenes / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D044948:Flavonols / Q000494:pharmacology*; D005663:Furans / Q000494:pharmacology*; D020441:Ginkgo biloba; D046934:Ginkgolides; D007783:Lactones / Q000494:pharmacology; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects* / Q000201:enzymology; D010936:Plant Extracts / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley
D003517:Cyclopentanes; D004224:Diterpenes; D044948:Flavonols; D005663:Furans; D046934:Ginkgolides; D007783:Lactones; D010936:Plant Extracts; C058295:ginkgolide C; D019363:Cytochrome P-450 CYP1A1; D019388:Cytochrome P-450 CYP1A2; C073710:bilobalide