2004 Volume 48 Issue 1 Pages 407-414
Nutrient intake has significant effects on the toxicity and carcinogenesis caused by various chemicals. The toxicity and metabolism of arsenic is also thought to be affected by nutrients. This paper examines the effects of dietary cysteine (Cys) and enteromicroorganisms on the metabolism of arsenic in vitro and in vivo. Our previous study revealed that two unidentified metabolites, M-1 and M-2, were detected in urine and a further unidentified metabolite, M-3, in feces after long-term oral administration of dimethylarsinic acid (DMA(V)) to rats. M-2 was more cytotoxic than DMA (V), M-1, and M-3. DMA (V) was converted to M-2 and M-3 by E. coli. In this study, we examined the effects of Cys concentration on conversion of DMA (V) by E. coli in vitro. The maximum concentration of M-2 was observed at a Cys/DMA ratio of 2, and the maximum of M-3 was observed when the ratio exceeded 3. In the vivo experiment, we examined the urinary and fecal metabolites after 10 or 56 days of administration of 1 mM DMA (V) to 4 groups of rats, control rats (Cont-group), rats given E. coli (E. coli-group), rats given Cys-sufficient diet (Cys-group), and rats given E. coli and Cys-sufficient diet (Cys+ E. coli-group). The methylation rate in urinary metabolites was increased in the Cys-group and Cys+E. coli-group compared with the Cont-group after 10 days’ administration. The rate of M-2 and M-3 in feces was increased in the Cys-group and Cys+ E. coli-group after 56 days’ administration. These results indicate that dietary Cys and E. coli affect the production of M-2 and M-3.
