Arsenite uptake and metabolism by rat hepatocyte primary cultures in comparison with kidney- and hepatocyte-derived rat cell lines

Biotransformation by methylation to monomethylarsonic acid (MMA) and dimeth ylarsinic acid (DMA) influences inorganic arsenical toxicity, which is ofte n investigated in cultured cells. Arsenic (III) uptake and methylation was assessed in rat hepatocytes in primary culture and in three established rat cell lines (hepatoma-derived McA-RH 7777 cells and H4-II-EC-3 cells, and k idney epithelium-derived NRK-52E cells) to compare their use as model syste ms for arsenite metabolism. Incubation of all cell types with 0.27, 0.67, 1 .33, 2.67, or 6.67 mu M As(III) concentrations resulted in concentration-de pendent arsenic uptake and biomethylation. Arsenic uptake by the NRK-52E ce lls was initially slower than that of the other cells, but by 8 h, total up take was similar in all cell types. At the lowest arsenite concentration, t he percentages of total arsenic methylated to MMA and DMA by the hepatocyte s and the McA-RH 7777 cells were similar (67 and 66%); methylation by the H 4-II-EC3 cells was somewhat lower (52%), and methylation by the kidney-deri ved NRK-52E cells was much lower (15%). Total arsenic methylation was inhib ited in the cell lines, but not in the hepatocytes, at the highest arsenite concentrations. In all cases, exposure to increased arsenite concentration s inhibited conversion of MMA to DMA much more than it affected the initial methylation step (inorganic arsenite to MMA). These results indicate that rat hepatocytes in primary culture and established rat hepatoma-derived cel l lines are similar in their abilities to accumulate and methylate arsenic to MMA and DMA at environmentally relevant arsenic concentrations in the me dium. They differed from the kidney epithelium-derived cells, which exhibit ed substantially lower biomethylation activity.