Dietary arsenic affects dimethylhydrazine-induced aberrant crypt formation and hepatic global DNA methylation and DNA methyltransferase activity in rats.

Cell culture studies have suggested that arsenic exposure results in decreased S-adenosylmethionine (SAM), causing DNA hypomethylation. Previously, we have shown that hepatic SAM is decreased and/or S-adenosylhomocysteine increased in arsenic-deprived rats; these rats tended to have hypomethylated DNA. To determine the effect of dietary arsenic on dimethylhydrazine (DMH)-induced aberrant crypt formation in the colon, Fisher 344 weanling male rats were fed diets containing 0, 0.5, or 50 microg As (as NaAsO2)/g. After 12 wk, dietary arsenic affected the number of aberrant crypts (p<0.02) and aberrant crypt foci (p<0.007) in the colon and the amount of global DNA methylation (p<0.04) and activity of DNA methyltransferase (DNMT) (p<0.003) in the liver. In each case, there were more aberrant crypts and aberrant crypt foci, a relative DNA hypomethylation, and increased activity of DNMT in the rats fed 50 microg As/g compared to those fed 0.5 microg As/g. The same phenomenon, an increased number of aberrant crypts and aberrant crypt foci, DNA hypomethylation, and increased DNMT tended to hold when comparing rats fed the diet containing no supplemental arsenic compared to rats fed 0.5 microg As/g. The data suggest that there is a threshold for As toxicity and that possibly too little dietary As could also be detrimental.