Bioactive terpenoids and flavonoids from Ginkgo biloba extract induce the expression of hepatic drug-metabolizing enzymes through pregnane X receptor, constitutive androstane receptor, and aryl hydrocarbon receptor-mediated pathways.
OBJECTIVE
The objective of the current study is to investigate the hypothesis that bioactive terpenoids and flavonoids of Ginkgo biloba extract (GBE) induce human hepatic drug metabolizing enzymes (DMEs) and transporters through the selective activation of pregnane X receptor (PXR), constitutive androstane receptor (CAR), and aryl hydrocarbon receptor (AhR).


METHODS
Human primary hepatocyte (HPH), and HepG2 cells are used as in vitro models for enzyme induction and nuclear receptor activation studies. A combination of real-time RT-PCR, transient transfection, and cell-based reporter assays were employed.


RESULTS
In human primary hepatocytes, real-time PCR analysis showed induction of CYP2B6, CYP3A4, UGT1A1, MDR1, and MRP2 by EGb 761, ginkgolide A (GA) and ginkgolide B (GB), but not by bilobalide (BB) or the flavonoids (quercetin, kaempferol and tamarixetin) of GBE. Cell-based reporter assays in HepG2 revealed that GA and GB are potent activators of PXR; quercetin and kaempferol activate PXR, CAR, and AhR, whereas BB exerts no effects on these xenobiotic receptors. Notably, the flavonoids induced the expression of UGT1A1 and CYP1A2 in HepG2 cells but not in HPH.


CONCLUSIONS
Our results indicate that terpenoids and flavonoids of GBE exhibit differential induction of DMEs through the selective activation of PXR, CAR, and AhR.
Li
Linhao
L
Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland at Baltimore, 20 Penn Street, Baltimore, Maryland, 21201, USA.
Stanton
Joseph D
JD
Tolson
Antonia H
AH
Luo
Yuan
Y
Wang
Hongbing
H
D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000096:biosynthesis; D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis* / Q000235:genetics; D001189:Aryl Hydrocarbon Hydroxylases / Q000096:biosynthesis; D051792:Basic Helix-Loop-Helix Proteins; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D000090702:Constitutive Androstane Receptor; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A / Q000096:biosynthesis; D004790:Enzyme Induction; D004798:Enzymes / Q000096:biosynthesis* / Q000235:genetics; D005419:Flavonoids / Q000302:isolation & purification / Q000494:pharmacology*; D017930:Genes, Reporter; D020441:Ginkgo biloba; D014453:Glucuronosyltransferase / Q000096:biosynthesis; D022781:Hepatocytes / Q000187:drug effects* / Q000201:enzymology; D006801:Humans; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000096:biosynthesis; D010089:Oxidoreductases, N-Demethylating / Q000096:biosynthesis; D010936:Plant Extracts / Q000737:chemistry / Q000494:pharmacology*; D000077297:Pregnane X Receptor; D012333:RNA, Messenger / Q000096:biosynthesis; D018336:Receptors, Aryl Hydrocarbon / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D011987:Receptors, Steroid / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D013729:Terpenes / Q000302:isolation & purification / Q000494:pharmacology*; D014157:Transcription Factors / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D015854:Up-Regulation; D000099148:UGT1A1 Enzyme; D000096983:Ginkgo Extract
D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D001189:Aryl Hydrocarbon Hydroxylases; D051792:Basic Helix-Loop-Helix Proteins; D000090702:Constitutive Androstane Receptor; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A; D004798:Enzymes; D005419:Flavonoids; D014453:Glucuronosyltransferase; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D010089:Oxidoreductases, N-Demethylating; D010936:Plant Extracts; D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D013729:Terpenes; D014157:Transcription Factors; D000099148:UGT1A1 Enzyme; C513055:ABCB1 protein, human; C000715087:ABCC2 protein, human; C111235:AHR protein, human; C063170:Ginkgo biloba extract; D000096983:Ginkgo Extract; C585599:CYP2B6 protein, human; C510163:CYP3A4 protein, human