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AN EVALUATION OF THE RELATIVE GENOTOXICITY OF ARSENITE, ARSENATE, AND FOUR METHYLATED METABOLITES IN VITRO USING THE ALKALINE SINGLE CELL GEL ASSAY
Citation:
Tennant, A H., M J. Mass, AND A D. Kligerman. AN EVALUATION OF THE RELATIVE GENOTOXICITY OF ARSENITE, ARSENATE, AND FOUR METHYLATED METABOLITES IN VITRO USING THE ALKALINE SINGLE CELL GEL ASSAY. Presented at 2001 Environmental Mutagen Society Mtg, San Diego, CA, March 16-21/2001.
Description:
An Evaluation of the Relative Genotoxicity of Arsenite, Arsenate, and Four Methylated
Metabolites In Vitro Using the Alkaline Single Cell Gel Assay (ASCG).
Arsenic ( As) is a genotoxic and carcinogenic metal found in many drinking water systems throughout the world. Though it is a human carcinogen, it has been difficult to unravel its mode of action. The metabolism (methylation) of As involves a series of oxidative-reduction reactions during which the valence of arsenic changes from (III) to (V). Up until now, it was thought that during this process, arsenic was detoxified by methylation on route to excretion in the urine. We decided to investigate the genotoxicity of three As (III) forms: sodium arsenite, monomethylarsine oxide, dimethyliodoarsine; and three As (V) forms: sodium arsenate, monomethylarsonic acid, and dimethylarsinic acid using the ASCG assay to detect single strand breaks and/or alkaline-labile sites. Human whole blood samples from five donors were exposed to up to 7 concentrations of each arsenic compound for 2 h. The cells were then washed in buffered saline, embedded in agarose, lysed, denatured at pH 13 and exposed to an electric field (1.67 volts/cm) in an electrophoresis chamber. Following neutralization and dehydraton were stained with SYBR Green I(R), and analyzed using the Komet 3.0(R) system. Monomethylarsonic acid (V) was nongenotoxic causing no significant induction in comet tail moment. Both arsenite and arsenate were only weakly genotoxic, with arsenate being slightly more potent than arsenite. However, contrary to generally accepted ideas on the activity of arsenicals, both dimethylated compounds as well as t4e monomethylarsine oxide (III) were quite potent inducers of DNA damage. Dimethyliodoarsine (III) was by far the most potent compound tested being over 500-fold more potent than the unmethylated arsenicals, almost 10-fold more potent than the dimethyl As (V) derivative, and over 6-fold more potent than the momo- methylarsine oxide (III). These results strongly suggest that in the process of detoxifying arsenic through methylation, highly reactive genotoxic intermediates are formed that may indeed be responsible for the carcinogenic properties of this metal.
This is an abstract of a proposed presentation and does not necessarily represent EPA policy.