Effects of exogenous methionine on arsenic burden and NO metabolism in brain of mice exposed to arsenite through drinking water

Abstract

The aim of this study was to explore the effects of exogenous methionine (Met) on arsenic burden and metabolism of nitric oxide (NO) in the brain of mice exposed to arsenite via drinking water. Mice were exposed to sodium arsenite through drinking water contaminated with 50 mg/L arsenic for four consecutive weeks, and treated intraperitoneally with saline solution, 100 mg/kg body weight (b.w), 200 mg/kg b.w or 400 mg/kg b.w of Met, respectively at the fourth week. Levels of inorganic arsenic (iAs), monomethylarsenic acid (MMAs), and dimethylarsenic acid (DMAs) in the liver, blood and brain were determined by method of hydride generation coupled with atomic absorption spectrophotometry. Nitric oxide synthase (NOS) activities and NO levels in the brain were determined by colorimetric method. Compared with mice exposed to arsenite alone, administration of Met increased significantly the primary methylation ratio in the liver, which resulted in decrease of percent iAs and increase of percent DMAs in the liver, and decrease of iAs, MMAs and total arsenic levels (TAs) in the blood and DMAs and TAs in the brain. NOS activities and NO levels in the brain of mice exposed to arsenite alone were significantly lower than those in control, however administration of Met could increase significantly NO levels. Findings from this study suggested that exogenous Met could benefit the primary arsenic methylation in the liver, which might increase the production of methylated arsenicals and facilitate arsenic excretion. As a consequence, arsenic burden in both blood and brain was reduced, and toxic effects on NO metabolism in the brain were ameliorated.