Induction of genotoxic damage is not correlated with the ability to methylate arsenite in vitro in the leukocytes of four mammalian species

Superoxide dismutase protects cells from DNA damage induced by trivalent methylated arsenicals

Superoxide dismutase (SOD) catalyzes the conversion of superoxide to hydrogen peroxide. Heterozygous mice of strain B6;129S7-Sod1(tm1Leb)/J were obtained from Jackson Laboratories and bred to produce offspring that were heterozygous (+/Sod1(tm1Leb)), homozygous wild-type (+/+), and homozygous knockout (Sod1(tm1Leb) /Sod1(tm1Leb)) for the Cu/Zn superoxide dismutase (Sod1) gene. Splenocytes from these mice were exposed to several concentrations of either sodium arsenite (As3 [0-200 μM]), monomethylarsonous acid (MMA3 [0-10 μM]), or dimethylarsinous acid (DMA3 [0-10 μM]) for 2 hr. Cells were then examined for DNA damage using the alkaline single cell gel electrophoresis assay. Methyl methanesulfonate (MMS) was used as a positive control. Splenocytes from each of the three genotypes for Sod1 were equally sensitive to MMS and As3. However, at equimolar concentrations, DMA3 and MMA3 produced significantly more DNA damage in the homozygous knockout mouse splenocytes than in the splenocytes from the wild-type or heterozygous mice. These findings suggest that superoxide is involved either directly or indirectly in producing DNA damage in cells exposed to trivalent methylated arsenicals. These arsenicals may generate reactive oxygen species that damage DNA. This DNA damage may be a key factor in initiating cancer in vivo.

Oxidation and methylation status determine the effects of arsenic on the mitotic apparatus

We investigated the spindle inhibitory properties of six arsenicals differing in their methylation or oxidation state. Human lymphoblasts were exposed for 6 h to either sodium arsenate (NaAs(V)), sodium arsenite (NaAs(III)), monomethylarsonic acid (MMA(V)), monomethylarsonous acid (MMA(III)), dimethylarsinic acid (DMA(V)), or dimethylarsinous acid (DMA(III)). After exposure slides were prepared, and the mitotic indices (MI) were assessed. We also exposed tubulin directly to each arsenical and spectrophotometrically measured its effect on polymerization. NaAs(V) caused a small but significant increase in MI. MMA(V) also caused only a slight increase in MI that just reached statistical significance. In contrast, DMA(V) caused a significant increase in MI, producing approximately 75% the MI of demecolcine and approximately 4 times the MI of the control. NaAs(III) had no significant effect on MI and was quite toxic. MMA(III) induced more than a twofold increase in MI compared to the control, which was about 40% that caused by demecolcine. On a micromolar basis, MMA(III) was the most potent of the arsenicals tested. DMA(III) gave inconsistent results. None of the pentavalent arsenicals had a substantial effect (either inhibition or enhancement) on GTP-induced polymerization of tubulin. In contrast, NaAs(III) inhibited polymerization at concentrations of 1 mM and above and MMA(III) and DMA(III) at 10 microM and above. Taken together, these results present a complex picture of how arsenicals may affect cells. These studies demonstrate that the metabolites of arsenic are active not only as chromosome breaking and DNA damaging agents but can also interfere with cell division via tubulin disruption.

Speciation of dimethylarsinous acid and trimethylarsine oxide in urine from rats fed with dimethylarsinic acid and dimercaptopropane sulfonate

Speciation of arsenic in urine from rats treated with dimethylarsinic acid (DMA(V)) alone or in combination with dimercaptopropane sulfonate (DMPS) were studied. Methods were developed for the determination of the methylarsenic metabolites, especially trace levels of dimethylarsinous acid (DMA(III)) and trimethylarsine oxide (TMAO), in the presence of a large excess of DMA(V). Success was achieved by using improved ion-exchange chromatographic separation combined with hydride generation atomic fluorescence detection. Micromolar concentrations of DMA(III) were detected in urine of rats fed with a diet supplemented with either 100 microg/g of DMA(V) or a mixture of 100 microg/g of DMA(V) and 5600 microg/g of DMPS. No significant difference in the DMA(III) concentration was observed between the two groups; however, there was a significant difference in TMAO concentrations. Urine from rats fed with the diet supplemented with DMA(V) alone contained 73 +/- 30 microM TMAO, whereas urine from rats fed with the diet supplemented with both DMA(V) and DMPS contained only 2.8 +/- 1.4 microM TMAO. Solutions containing mixtures of 100 microg/L DMA(V) or TMAO and 5600 microg/L DMPS did not show reduction of DMA(V) and TMAO. The significant decrease (p < 0.001) of the TMAO concentration in rats administered with both DMA(V) and DMPS suggests that DMPS inhibits the biomethylation of arsenic.