Age dependent expression of cytochrome P-450_b and metabolism of the potent carcinogen 2-nirofluorene in the rat lung

Northern and Western blot analyses, and analyses of microsomal metabolism of the carcinogen 2-nitrofluorene (NF) were conducted with the aim of studying age dependent cytochrome P-450(b) levels in the rat lung. The level of P-450(b) homologous mRNA and corresponding protein is very low in lungs from fetal and newborn rats. The levels then increase between 3 and 4 weeks of age, and reach adult levels at 6-8 weeks. No sex differences were detected with regard to lung P-450(b) mRNA levels or catalytical activities. Lung microsomal metabolism of NF increased in parallel with the accumulation of P-450(b) homologous mRNA and microsomal cytochrome P-450(b) protein concentration. Formation of the major metabolite, and potent mutagen, 9-hydroxy-2-nitrofluorene (9-OHNF) was significantly inhibited by addition of polyclonal anti-P-450(b)-IgG, and by addition of the inhibitor proadifen to incubations with lung microsomal protein. It is postulated that the observed, profound age-related differences in level and activity of lung cytochrome P-450(b) are likely to affect both availability and the ratio of metabolic detoxification and activation of chemical carcinogens deposited in the lung.