Affiliations: Department of Molecular and Cell Biology, University
of California, Berkeley, USA. Present addresses: School of Food Biosciences,
Hugh Sinclair Human Nutrition Unit, University of Reading, UK | Department of Internal Medicine, University of
California, Davis, USA | Department of Applied Chemistry and Biotechnology,
Faculty of Engineering, Yamanashi University, Takeda, Kofu, Japan | Department of Molecular Pharmacology and Toxicology,
University of Southern California, Los Angeles, USA | Free Radical Research Group, National Institute for
Food and Nutrition Research, Rome, Italy
Note: [] PhD, School of Food Biosciences, Hugh Sinclair Human Nutrition
Unit, University of Reading, P.O. Box 226, Whiteknights, Reading, RG6 6AP, UK.
Tel.: +44 118 931 6463; Fax: +44 118 931 0080; E-mail:
G.H.Rimbach@afnovell.reading.ac.uk
Abstract: The objective of the present study was to characterize the action of
Ginkgo biloba extract (EGb761) and its sub-fractions on glutathione homeostasis
in a human keratinocyte cell culture model. Cells were incubated with EGb761,
its purified flavonoid (quercetin, kaempferol, rutin) or terpenoids
(gingkolides A, B, C, J, bilobalide) constituents or the vehicle for up to 72
hours. Incubation of keratinocytes with the purified flavonoids or terpenoids
did not affect cellular GSH levels. However, EGb761 treatment (up to 200
μg/ml) resulted in a dose-dependent increase of cellular
GSH. Western blot analysis of extracts from cells treated with EGb761 revealed
increased levels of the catalytic subunit of
γglutamylcysteinyl synthetase
(γGCS), the rate-limiting enzyme in GSH synthesis. The
abundance of mRNA for the catalytic subunit (assayed by RT-PCR) was also
increased by the treatment with EGb761. Increased levels of cellular GSH by
EGb761 were also observed in other cell lines including those from human
bladder and liver as well as in murine macrophages indicating that the
induction of γGCS mRNA, protein and GSH may be an
ubiquitous effect of EGb761 in mammalian cells.
