Background: Environmental tobacco smoke (ETS) is the primary etiologic factor responsible for lung cancer. However, only 10-15 % of smokers develop lung cancer, suggesting a genetic role in modifying individual susceptibility to lung cancer. Antioxidant enzymes and genetic polymorphisms should be considered.
Aim: The present study aimed to evaluate the role of antioxidant enzyme activity and genetic polymorphisms in modifying the susceptibility to lung cancer among individuals exposed to ETS.
Subjects and methods: A total of 150 male subjects were divided into three groups: 50 lung cancer patients, 50 chronic smokers, and 50 passive smokers. Genotyping of microsomal epoxide hydrolase (mEH) exon 3 (Tyr(113)Hist) and exon 4 (Hist(139)Arg) polymorphisms were done by the polymerase chain reaction-restriction fragment length polymorphism technique. MnSOD (Val(16)Ala) polymorphism was detected by the real time-TaqMan assay. Erythrocyte MnSOD activity was measured spectrophotometrically.
Results: ETS-exposed individuals (both active and passive smokers) who carried the His allele of mEH exon3 have a 2.9-fold increased risk of lung cancer (odds ratio [OR] 2.9, P < 0.001). In addition, ETS-exposed carriers of the Arg allele of mEH exon 4 have a 2.1-fold increased risk of lung cancer (OR 2.1, P = 0.024). However, no association between the MnSOD Val(16)Ala polymorphism and lung cancer was detected among ETS-exposed individuals (OR 1.6, P = 0.147), although the lung cancer group had significantly lower MnSOD activity than the chronic or passive smoker groups (P = 0.03).
Conclusions: Exons 3 and 4 polymorphisms of the mEH gene may contribute to lung cancer susceptibility through disturbed antioxidant balance. However, this was not the case with the MnSOD Val(16)Ala single-nucleotid polymorphism. Antioxidant enzymes may modulate the influence of ETS exposure on lung cancer risk.