title: Ginkgo biloba leaf extract induces DNA damage by inhibiting topoisomerase II activity in human hepatic cells.
abstract: Ginkgo biloba leaf extract has been shown to increase the incidence in liver tumors in mice in a 2-year bioassay conducted by the National Toxicology Program. In this study, the DNA damaging effects of Ginkgo biloba leaf extract and many of its constituents were evaluated in human hepatic HepG2 cells and the underlying mechanism was determined. A molecular docking study revealed that quercetin, a flavonoid constituent of Ginkgo biloba, showed a higher potential to interact with topoisomerase II (Topo II) than did the other Ginkgo biloba constituents; this in silico prediction was confirmed by using a biochemical assay to study Topo II enzyme inhibition. Moreover, as measured by the Comet assay and the induction of γ-H2A.X, quercetin, followed by keampferol and isorhamnetin, appeared to be the most potent DNA damage inducer in HepG2 cells. In Topo II knockdown cells, DNA damage triggered by Ginkgo biloba leaf extract or quercetin was dramatically decreased, indicating that DNA damage is directly associated with Topo II. DNA damage was also observed when cells were treated with commercially available Ginkgo biloba extract product. Our findings suggest that Ginkgo biloba leaf extract- and quercetin-induced in vitro genotoxicity may be the result of Topo II inhibition.
authors.affiliation: Division of Genetic and Molecular Toxicology, National Center for Toxicological Research, Jefferson, AR 72079, USA.
authors.forename: Zhuhong
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Division of Biochemical Toxicology, National Center for Toxicological Research, Jefferson, AR 72079, USA.
authors.forename: Si
authors.initials: S
authors.lastname: Chen
authors.affiliation: College of Bioengineering, Chongqing University, Chongqing 400044, China.
authors.forename: Hu
authors.initials: H
authors.lastname: Mei
authors.affiliation: Division of Biochemical Toxicology, National Center for Toxicological Research, Jefferson, AR 72079, USA.
authors.forename: Jiekun
authors.initials: J
authors.lastname: Xuan
authors.affiliation: Division of Genetic and Molecular Toxicology, National Center for Toxicological Research, Jefferson, AR 72079, USA.
authors.forename: Xiaoqing
authors.initials: X
authors.lastname: Guo
authors.affiliation: Division of Biochemical Toxicology, National Center for Toxicological Research, Jefferson, AR 72079, USA.
authors.forename: Letha
authors.initials: L
authors.lastname: Couch
authors.affiliation: Division of Genetic and Molecular Toxicology, National Center for Toxicological Research, Jefferson, AR 72079, USA.
authors.forename: Vasily N
authors.initials: VN
authors.lastname: Dobrovolsky
authors.affiliation: Division of Biochemical Toxicology, National Center for Toxicological Research, Jefferson, AR 72079, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Guo
authors.affiliation: Division of Genetic and Molecular Toxicology, National Center for Toxicological Research, Jefferson, AR 72079, USA.
authors.forename: Nan
authors.initials: N
authors.lastname: Mei
mesh_terms: D004249:DNA Damage / Q000187:drug effects*; D004250:DNA Topoisomerases, Type II / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D055785:Gene Knockdown Techniques; D020868:Gene Silencing; D020441:Ginkgo biloba / Q000737:chemistry*; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000187:drug effects* / Q000502:physiology*; D006801:Humans; D008958:Models, Molecular; D008968:Molecular Conformation; D009153:Mutagens / Q000737:chemistry / Q000494:pharmacology / Q000633:toxicity; D010936:Plant Extracts / Q000737:chemistry / Q000494:pharmacology* / Q000633:toxicity; D018515:Plant Leaves / Q000737:chemistry*; D011794:Quercetin / Q000494:pharmacology / Q000633:toxicity; D059005:Topoisomerase II Inhibitors / Q000737:chemistry / Q000494:pharmacology / Q000633:toxicity
chemical_list: D009153:Mutagens; D010936:Plant Extracts; D059005:Topoisomerase II Inhibitors; D011794:Quercetin; D004250:DNA Topoisomerases, Type II