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INVESTIGATIONS INTO THE MODE OF ACTION (MOA) OF ARSENIC USING THE SINGLE CELL GEL (SCG) ASSAY AND CYTOGENETICS
Citation:
KLIGERMAN, A. D., A. H. TENNANT, AND J. CAMPBELL. INVESTIGATIONS INTO THE MODE OF ACTION (MOA) OF ARSENIC USING THE SINGLE CELL GEL (SCG) ASSAY AND CYTOGENETICS. Presented at 38th Annual Meeting of the Environmental Mutagen Society, Atlanta, GA, October 20 - 24, 2007.
Impact/Purpose:
In this presentation we provide data that indicate that reactive oxygen species (ROS) are responsible for the induction of DNA damage and present a model to explain the cytogenetic effects of arsenic exposure.
Description:
Arsenic is a globally important pollutant found in the air, food, and in many water systems causing significant human exposure and in some cases illness. While there is no doubt that arsenic is a human carcinogen, there is no consensus on its carcinogenic MOA. Numerous hypotheses have been offered including arsenic's ability to inhibit DNA repair, disrupt cell signalling, induce chromosome aberrations (CAs), induce cell death and proliferation, and alter DNA methylation patterns. These may not be mutually exclusive. In this presentation we provide data that indicate that reactive oxygen species (ROS) are responsible for the induction of DNA damage and present a model to explain the cytogenetic effects of arsenic exposure. The alkaline SCG assay was used to determine if mouse lymphocytes from superoxide dismutasel (SOD1)-knockout mice (Sod1tm1Leb) were abnormally sensitive to the DNA-damaging effects of arsenicals. Spleens from wildtype and SOD1 knockout mice were removed, splenic lymphocytes isolated and exposed for 2 h to DMAIII in complete medium. Following exposure, cells were embedded in low melting point agarose, and DNA damage was assayed using the alkaline SCG assay. DNA damage in cells exposed to 2.5, 5.0 or 10 μM DMA3 was significantly higher in cells with deleted SOD1 activity. In the second part of our study, we propose a testable cytogenetic model to explain the cytogenetic MOA of arsenic, and then present data from various cytogenetic assays to test this model. Cytogenetically active arsenicals were found to be ineffective in inducing SCEs or CAs in Go. However, active arsenicals could induce SCEs and are extremely clastogenic when exposure occurs during or just before S-phase. DNA repair inhibition studies in Go using cytosine arabinoside (ara-C) indicate that rapid repair of DNA damage is likely responsible for the lack of a clastogenic Go-effect. These observations coupled with the lack of DNA adduction caused by arsenicals indicate that free radical damage is a plausible explanation for the cytogenetic effects produced by arsenicals.