Role of murine cytochrome P-4502F2 in metabolic activation of naphthalene and metabolism of other xenobiotics

Despite their substantially lower levels relative to hepatic tissue, pulmon ary cytochrome P-450 (CYP) monooxygenases play an important role in the met abolic activation of substrates that cause lung injury. The target- and spe cies-selective toxicity of a number of pulmonary toxicants has been attribu ted to the presence and distribution of activating enzymes with high k(cat) in target airways of susceptible species. However, experimental demonstrat ion of these concepts and quantitative assessment of the contribution of in dividual CYP isoforms is lacking. This study was undertaken to characterize the catalytic activities of CYP2F2 with naphthalene, a murine Clara cell t oxicant, as well as with other xenobiotics that either undergo metabolic ac tivation to cytotoxic intermediates or that function as "isoform-selective' ' substrates. Recombinant CYP2F2 was produced using the baculovirus express ion vector system in Spodoptera frugiperda and Trichoplusia ni cells, accou nting up to similar to 20% of the total cellular protein. Incubations conta ining naphthalene, recombinant CYP2F2, NADPH-cytochrome P-450 oxidoreductas e, and NADPH-regenerating system metabolized naphthalene with a high degree of stereoselectivity to 1R,2S-naphthalene oxide (66:1 enantiomeric ratio). The K-m and k(cat) values, along with the specificity constant, for naphth alene metabolism by recombinant CYP2F2 were 3 mu M, 104 min(-1), and 5.8 x 10(5) M-1 s(-1), respectively. Recombinant CYP2F2 also metabolized ethoxyre sorufin, pentoxyresorufin, p-nitrophenol, and 1-nitronaphthalene at easily detectable levels. The results from this work suggest that CYP2F2 1) plays a key role in the species- and cell-selective toxicity of naphthalene and 2 ) efficiently metabolizes a number of other substrates, including the lung toxicant 1-nitronaphthalene.