Cell-specific loss of cytochrome P4502B1 in rat lung following treatment with pneumotoxic and non-pneumotoxic trialkylphosphorothioates

This study was designed to test the hypothesis that the reduction in cytoch rome P450 (CYP) 2B1 content and activity of rat lung microsomes, following dosing with pneumotoxic trimethylphosphorothioates, results from damage to specific cell types. Of the lung cells exhibiting immunolabelling for CYP2B 1, only type I cells showed signs of susceptibility to the pneumotoxins O,O .S-trimethylphosphorothioate and O,S, S-trimethylphosphorodithioate. While most type I cells became necrotic, type II and Clara cells showed no signs of injury, despite their gradual loss of CYP2B1, as detected by immunogold labelling. This loss of labelling was accompanied by a 75% reduction in the immunoreactive CYP2B1 content and an 85% reduction in pentoxyresorufin O-d ealkylase activity in lung microsomes. In contrast, the non-pneumotoxic ana logue O,O,S-Trimethylphosphorodithioate, differing from O,O,S-trimethylphos phorothioate by only the presence of a P = S rather than a P = O moiety, ca used an even more rapid fall in pulmonary pentoxyresorufin O-dealkylase act ivity, but only a slight reduction in the microsomal content of CYP2B1. The recovery of this activity began within 12 hr of dosing. O,O,S-Trimethylpho sphorodithioate, which acts as a suicidal inhibitor of pulmonary CYP2B1, di d not cause any detectable lung injury or increase in cell division. These results are consistent with the initial reduction in both enzyme content an d activity caused by the P = O - containing pneumotoxins resulting, almost entirely, from death of type I cells. Subsequent reductions that occur long after clearance of the toxin may be exacerbated by the onset of mitosis in Clara and type II cells. (C) 2001 Elsevier Science Inc. All rights reserve d.