Activation of 2-amino-3-methylimidazo (4,5-f) quinoline in rat and human hepatocyte/Salmonella mutagenicity assays: the contribution of hepatic conjugation.

The capacity of human liver S9 and hepatocytes to metabolically activate 2-amino-3-methylimidazo (4,5-f) quinoline (IQ) in Salmonella mutagenicity assays more closely resembles that of preparations from Aroclor-induced rat than control rat. The extent to which hepatocyte conjugating enzymes contribute to activation in these assays has been studied. Omission of sulphate or addition of a 'specific' sulphotransferase inhibitor (2,6-DCNP) did not significantly reduce mutagenicity, nor did PAPS enhance S9-mediated bacterial mutagenicity. Conversely, mutagenicity was significantly inhibited by PCP (an inhibitor of both sulphotransferase and acetyltransferase) and an acetylation-deficient Salmonella (TA98/1,8DNP6) was unresponsive to the mutagenicity of IQ. These data suggest that acetylation but not sulphation is important in IQ bacterial mutagenesis. The addition of acetyl CoA, PAPS-generating system or ATP paradoxically reduces the mutagenicity of IQ in S9/Salmonella TA98 assays. Therefore, activation by esterification in hepatocytes does not contribute to the mutagenicity of IQ in Salmonella typhimurium possibly due to restricted access of conjugates into the bacterial cell.