EFFECTS OF SULFITE ON THE UPTAKE AND BINDING OF BENZO[A]PYRENE DIOL EPOXIDE IN CULTURED MURINE RESPIRATORY EPITHELIAL-CELLS

Sulfur dioxide (SO2) may act as a cocarcinogen with benzo[a] pyrene (BaP)in the respiratory tract. We have modeled this effect by examining the interactions of 7r,8t-dihy-droxy-9t, 10t-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE) with sulfite, the physiological form of SO2, in a murine respiratory epithelial cell line (C10). We exposed C10 cells to [H-3]-anti-BPDE and determined the effects of 1 and 10 mM sulfite on the uptake and subcellular localization of labeled products. Autoradiographic analysis showed that sulfite doubled the nuclear localization of anti-BPDE-derived materials after a 4-hr incubation period. The net nuclear localization of anti-BPDE-derived materials was not affected by sulfite during the first 60 min, but nuclear localization continued to increase in the sulfite-containing incubations throughout the 4-hr incubation period. Little increase in nuclear localization of anti-BPDE-derived material was note in the incubations without sulfite after 60 min. Subcellular fractionation was performed to determine the amount of label associated with cytosolic and nuclear fractions and to determine covalent binding to protein and DNA. Sulfite produced a modest increase in the amount of [H-3]-anti-BPDE-derived products bound to protein; however, binding to nuclear DNA increase by more than 200% with 10 mM sulfite. Analysis of the supernatants from the cytosolic and nuclear fractions of cells exposed to anti-BPDE and sulfite demonstrated the presence of 7r,8t, 9t-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene-10c-sulfonate (BPT-10-sulfonate). [H-3]-BPT-10-sulfonate was unable to enter C10 cells, suggesting that it is formed intracellularly. Once formed, this compound may be unable to leave the cell. The observed intracellular formation of BPT-10-sulfonate, a more stable DNA-modifying BaP derivative that BODE and one which probably cannot leave the cell, could be responsible for this extended time course of nuclear localization and DNA modification.