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Ginkgo biloba leaf extract induces DNA damage by inhibiting topoisomerase II activity in human hepatic cells.

Zhang Z, Chen S, Mei H, Xuan J, Guo X, Couch L, Dobrovolsky VN, Guo L, Mei N - Sci Rep (2015)

Bottom Line: 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.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.Our findings suggest that Ginkgo biloba leaf extract- and quercetin-induced in vitro genotoxicity may be the result of Topo II inhibition.

View Article: PubMed Central - PubMed

Affiliation: Division of Genetic and Molecular Toxicology, National Center for Toxicological Research, Jefferson, AR 72079, USA.

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.

No MeSH data available.


Related in: MedlinePlus

DNA damage induced by quercetin in HepG2 cells.HepG2 cells were exposed to increasing concentrations (6.25–100 μM) of quercetin for 2, 4, 6, and 24 h. Total cellular protein was extracted at the indicated times and concentrations, and levels of phosphorylated (γ-H2A.X) were detected by Western blotting. GAPDH was used as a loading control. Similar results were obtained from three independent experiments.
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f6: DNA damage induced by quercetin in HepG2 cells.HepG2 cells were exposed to increasing concentrations (6.25–100 μM) of quercetin for 2, 4, 6, and 24 h. Total cellular protein was extracted at the indicated times and concentrations, and levels of phosphorylated (γ-H2A.X) were detected by Western blotting. GAPDH was used as a loading control. Similar results were obtained from three independent experiments.

Mentions: Quercetin has the highest potency for both Topo II inhibition and DNA damaging activity, compared to other Ginkgo biloba constituents tested, and quercetin is likely the major contributor to the genotoxicity caused by Ginkgo biloba leaf extract as demonstrated in our previous study6; we thus focused on quercetin for a detailed mechanistic study (Fig. 6). γ-H2A.X was induced in the cells treated with 100 μM quercetin as early as 2 h, and the induction was observed at lower concentrations at longer time treatments; for instance, γ-H2A.X was detected in the cells treated with 6.25 μM quercetin after a 24-h treatment. These results indicate the induction of phosphorylated H2A.X is time- and concentration-dependent.


Ginkgo biloba leaf extract induces DNA damage by inhibiting topoisomerase II activity in human hepatic cells.

Zhang Z, Chen S, Mei H, Xuan J, Guo X, Couch L, Dobrovolsky VN, Guo L, Mei N - Sci Rep (2015)

DNA damage induced by quercetin in HepG2 cells.HepG2 cells were exposed to increasing concentrations (6.25–100 μM) of quercetin for 2, 4, 6, and 24 h. Total cellular protein was extracted at the indicated times and concentrations, and levels of phosphorylated (γ-H2A.X) were detected by Western blotting. GAPDH was used as a loading control. Similar results were obtained from three independent experiments.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4588569&req=5

f6: DNA damage induced by quercetin in HepG2 cells.HepG2 cells were exposed to increasing concentrations (6.25–100 μM) of quercetin for 2, 4, 6, and 24 h. Total cellular protein was extracted at the indicated times and concentrations, and levels of phosphorylated (γ-H2A.X) were detected by Western blotting. GAPDH was used as a loading control. Similar results were obtained from three independent experiments.
Mentions: Quercetin has the highest potency for both Topo II inhibition and DNA damaging activity, compared to other Ginkgo biloba constituents tested, and quercetin is likely the major contributor to the genotoxicity caused by Ginkgo biloba leaf extract as demonstrated in our previous study6; we thus focused on quercetin for a detailed mechanistic study (Fig. 6). γ-H2A.X was induced in the cells treated with 100 μM quercetin as early as 2 h, and the induction was observed at lower concentrations at longer time treatments; for instance, γ-H2A.X was detected in the cells treated with 6.25 μM quercetin after a 24-h treatment. These results indicate the induction of phosphorylated H2A.X is time- and concentration-dependent.

Bottom Line: 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.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.Our findings suggest that Ginkgo biloba leaf extract- and quercetin-induced in vitro genotoxicity may be the result of Topo II inhibition.

View Article: PubMed Central - PubMed

Affiliation: Division of Genetic and Molecular Toxicology, National Center for Toxicological Research, Jefferson, AR 72079, USA.

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.

No MeSH data available.


Related in: MedlinePlus