In vitro and ex vivo effects of the air pollutants SO2 and NOx on benzo(a)pyrene activating enzymes of the rat liver.

In the course of a larger project aimed at studying possible combination effects between common air pollutants and carcinogens, previous studies of our laboratory had shown that the genotoxic activity of benzo(a)pyrene (B(a)p) in fetal lung cells of the Syrian hamster is decreased by NOx and SO2. This particular study was performed to assess whether the gases may cause this depression by affecting the net yield of active B(a)p metabolites. Using the S. typhimurium assay as a model-system the gaseous exposure of subcellular activation systems to SO2 and NOx did not affect the yield of B(a)p induced mutants of S. typhimurium. Also the pretreatment of animals with SO2 or NOx in vitro did not result in a measurable induction or inhibition of B(a)p metabolizing enzymes, as was assessed also with S. typhimurium. Accordingly, neither direct enzymic interactions nor complex systemic pathways reflected possible mechanisms of combination effects between B(a)p and the air pollutants.