Normal bronchial epithelial cell expression of glutathione transferase P1, glutathione transferase M3, and glutathione peroxidase is low in subjects with bronchogenic carcinoma.

ABSTRACT

Normal bronchial epithelial cells (NBECs) are at risk for damage from inhaled and endogenous oxidative species and from epoxide metabolites of inhaled polycyclic aromatic hydrocarbons. Epidemiological and in vitro data suggest that interindividual variation in this risk may result from variation in NBEC expression of enzymes that inactivate reactive species by conjugating them to glutathione. Quantitative competitive reverse transcription-PCR was used to measure mRNA levels of glutathione transferases (GSTs) and glutathione peroxidases (GSHPxs) in primary NBECs from subjects with or without bronchogenic carcinoma. Mean expression levels (mRNA/10(3) beta-actin mRNA) in NBECs from 23 subjects without bronchogenic carcinoma compared to those from 11 subjects with bronchogenic carcinoma respectively (in parentheses) were mGST (26.0, 6.11), GSTM3 (0.29, 0.09), combined GSTM1,2,4,5 (0.98, 0.60), GSTT1 (0.84, 0.76), GSTP1 (287, 110), GSHPx (140, 62.1), and GSHPxA (0.43, 0.34). Levels of GSTP1, GSTM3, and GSHPx were significantly (P < 0.05) lower in NBECs from subjects with bronchogenic carcinoma. Further, the gene expression index formed by multiplying the values for mGST x GSTM3 x GSHPx x GSHPxA x GSTP1 had a sensitivity (90%) and specificity (76%) for detecting NBECs from bronchogenic carcinoma subjects that was better than any individual gene. In cultured NBECs derived from eight individuals without bronchogenic carcinoma and incubated under identical conditions such that environmental effects were minimized, the mean level of expression and degree of interindividual variation for each gene evaluated was less than that observed in primary NBECs. Data from these studies support the hypotheses that (a) interindividual variation in risk for bronchogenic carcinoma results in part from interindividual variation in NBEC expression of antioxidant genes; (b) gene expression indices will better identify individuals at risk for bronchogenic carcinoma than individual gene expression values; and (c) both hereditary and environmental exposures contribute to the level of and interindividual variation in gene expression observed in primary NBECs. Many epidemiological studies have been designed to evaluate risk associated with polymorphisms or gene expression levels of putative susceptibility genes based on measurements in surrogate tissues, such as peripheral blood lymphocytes. Based on data presented here, it will be important to include the assessment of NBECs in future studies. Measurement of antioxidant gene expression in NBECs may identify the 5-10% of individuals at risk for bronchogenic carcinoma. Bronchoscopic sampling of NBECs from smokers and ex-smokers then will allow susceptible individuals to be entered into surveillance and/or chemoprevention studies.