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ARSENIC METHYLATION AND OXIDANT INJURY BY ESR IN VIVO AND IN VITRO
Citation:
Kadiiska, M. B., S. C. Nesnow, J. Liu, M. P. Waalkes, AND R. P. Mason. ARSENIC METHYLATION AND OXIDANT INJURY BY ESR IN VIVO AND IN VITRO. Presented at Society of Toxicology, Baltimore, MD, 03/21-25/04.
Description:
Arsenic Methylation and Oxidant Injury by ESR In Vivo and In Vitro.
Although arsenic is naturally occurring and present in the environment, it is a serious environmental concern worldwide, because of the large number of known contaminated sites and millions of people at risk from drinking arsenic-contaminated water. Inorganic arsenic undergoes metabolic conversion from pentavalent arsenate (AsV) to trivalent arsenite (As III) with subsequent methylation to generate organometallic forms of arsenic such as MMAV, MMAIII, DMAV, DMAIII and trimethylarsine oxide. Studies have shown that AsIII metabolites MMAIII and DMAIII are quite toxic to mammalian liver, skin, urinary bladder, lung cells and cause extensive damage to DNA in a variety of human tissues. It has been postulated that the in vivo toxicity and carcinogenicity result from the catalysis of free radical generation. Using electron spin resonance (ESR) in conjunction with the spin traps phenyl-N-tert-butylnitrone (PBN), alpha -(4-pyridyl 1-oxide)- N-tertbutylnitrone (POBN) and 5,5-dimethyl-l-pyrroline-N-oxide (DMPO) we investigated free radical production by sodium arsenite (AsIII ) and sodium arsenate (Asv) in a mouse model of acute poisoning. In addition, the role of free radicals in in vitro cytotoxicity of DMAIII using murine TRL 1215 liver cells was examined. In order to define the mode of action of DNA damage induced by DMAIII, this study investigated free radical generation by DMAIII in in vitro experiments with supercoiled thetaX174 DNA. Simultaneous administration of PBN and AsIII to adult male 129/Sv mice resulted in the generation of free radical metabolites detected in the liver lipid extract by ESR. Free radical generation was subsequently observed in TRL 1215 liver cells subjected to an acute high dose of DMAIII exposure. Finally, ESR was used to identify the nature of the radical being trapped by DMPO in the DMAIII-DNA damage studies. The complete system gave a characteristic spectrum of a DMPO-hydroxyl radical adduct. In conclusion, the present study provides the most direct ESR evidence for the generation of free radical metabolites by arsenicals both in vivo and in vitro.
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