QUANTITATIVE RT-PCR MEASUREMENT OF CYTOCHROMES P450 1A1, 1B1, AND 2B7, MICROSOMAL EPOXIDE HYDROLASE, AND NADPH OXIDOREDUCTASE EXPRESSION INLUNG-CELLS OF SMOKERS AND NONSMOKERS

Bronchial epithelial cells (BEG) are the progenitors of bronchogenic c arcinomas and are exposed to polycyclic aromatic hydrocarbon (PAH) pro carcinogens through inhalation of combustion products. PAH are convert ed to carcinogenic molecules through a combination of monoxygenation b y cytochrome p450 (CYP) enzymes in the presence of NADPH oxidoreductas e (OR) and hydrolysis by microsomal epoxide hydrolase (mEH). In artifi cial systems, the relative expression of these genes determines whethe r carcinogenic or noncarcinogenic species are generated during metabol ism. This relationship was explored in humans by using quantitative co mpetitive reverse transcriptase polymerase chain reaction amplificatio n to determine the range of expression of CYP1A1, CYP1B1, mEH, and NAD PH OR in BEC recovered from 10 nonsmokers and 9 smokers. CYP2B7 expres sion was evaluated because, although little is known of its substrate specificity, it is expressed at high levels in human lung tissue. CYP1 A1 and CYP1B1 were expressed in BEC at significantly different levels (P < 0.05) in the 9 smokers at 1.4 +/- 2.3 x 10(4) and 2.4 +/- 3.2 x 1 0(3) molecules/10(6) p-actin molecules (mean +/- STD), respectively, b ut each was measurable in only one of the 10 nonsmokers. There was sig nificant inter-individual variation (P < 0.05) in both CYP1A1 and CYP1 B1 expression among the subjects for whom sufficient data were obtaine d. The inducibility of human BEC CYP1A1 gene by PAH exposure was confi rmed in vitro by incubating cultured immortalized human BEC with beta- naphthoflavone and observing a > 6-fold induction of CYP1A1 after 24 h . In contrast to BEG, alveolar macrophages expressed CYP1A1 at low (30 -70 molecules/10(6) p-actin molecules) to unmeasurable levels in both smokers and nonsmokers. There was no significant difference in express ion of mEH, CYP2B7, or NADPH OR in smokers compared with nonsmokers. T he inter-individual variation in absolute and relative expression of P AH metabolism enzymes in BEC reported here supports the hypothesis tha t inter-individual variation in ability to activate/inactivate inhaled PAH carcinogens accounts for at least some of the inter-individual va riation in risk for bronchogenic carcinoma.