Item – Theses Canada

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OCLC number
1033183819
Link(s) to full text
LAC copy
Author
Yeung, Eugene Y. H.
Title
Activation of pregnane X receptor by Ginkgo biloba extract.
Degree
Master of Science - MSc -- University of British Columbia, 2008
Publisher
Vancouver : University of British Columbia, 2008.
Description
1 online resource
Notes
Includes bibliographical references.
Abstract
Pregnane X receptor (PXR) is a ligand-activated transcription factor that plays a role in a broad array of biological processes, including drug metabolism and transport. Ginkgo biloba is an herb commonly used to improve cognitive function. In primary cultures of rat hepatocytes, Ginkgo biloba induces the mRNA expression of CYP3A23, a target gene for rat PXR. The present study tested the hypothesis that Ginkgo biloba activates PXR. Cultured HepG2 human hepatoma cells were transfected with the full-length human PXR (pCR3-hPXR), the full-length mouse PXR (pCR3-mPXR), or an empty vector (pCR3) in addition to a reporter plasmid (XREM-CYP3A4-LUC; firefly luciferase) and an internal control plasmid (phRL-TK; Renilla luciferase). At 24 h after transfection, cells were treated for 24 h with Ginkgo biloba extract and luciferase activity was measured. The extract at 200 ♯g/ml increased mouse and human PXR activity by 3.0-fold and 9.5-fold, respectively, indicating that Ginkgo biloba more effectively activates human PXR. Dose-response experiments showed that the extract produced a log-linear increase over the range of 200-800 ♯g/ml. To determine whether Ginkgo biloba extract induces human PXR target gene expression, cultured LS180 human colon adenocarcinoma cells were treated for 72 h with the extract. Total cellular RNA was isolated and reverse transcribed. CYP3A4, CYP3A5, and ABCB1 cDNAs were amplified by real-time PCR. Ginkgo biloba extract at 200, 400, and 800 ♯g/ml increased CYP3A4 mRNA expression by 1.7-, 2.4-, and 2.5-fold, respectively. The extract at the same concentrations increased the mRNA expression of CYP3A5 (1.3 to 3.6-fold) and ABCB1 (2.7 to 6.4-fold). To determine whether the increased expression involved PXR activation, cells were treated with a PXR antagonist, L-sulforaphane, and Ginkgo biloba extract. L-sulforaphane at 5, 10, and 20 ♯M decreased CYP3A4 mRNA expression by 54%, 78%, and 93%, respectively, in cells co-treated with the extract. A similar pattern of response was obtained with CYP3A5 and ABCB1. In cells co-treated with the extract, L-sulforaphane (5 and 10 ♯M) was not cytotoxic and did not decrease PXR mRNA expression. Our data from cell culture experiments indicate that Ginkgo biloba activates PXR and increases CYP3A4, CYP3A5, and ABCB1 mRNA expression.
Other link(s)
hdl.handle.net
circle.ubc.ca
Subject
Pregnane X receptor.
Ginkgo biloba extract.