An interaction between Nrf 2 polymorphisms and smoking status affects annual decline in FEV 1 : a longitudinal retrospective cohort study

Background: An Nrf2-dependent response is a central protective mechanism against oxidative stress. We propose that particular genetic variants of the Nrf2 gene may be associated with a rapid forced expiratory volume in one second (FEV1) decline induced by cigarette smoking. Methods: We conducted a retrospective cohort study of 915 Japanese from a general population. Values of annual decline in FEV1 were computed for each individual using a linear mixed-effect model. Multiple clinical characteristics were assessed to identify associations with annual FEV1 decline. Tag single-nucleotide polymorphisms (SNPs) in the Nrf2 gene (rs2001350, rs6726395, rs1962142, rs2364722) and one functional SNP (rs6721961) in the Nrf2 promoter region were genotyped to assess interactions between the Nrf2 polymorphisms and smoking status on annual FEV1 decline. Results: Annual FEV1 decline was associated with smoking behavior and inversely correlated with FEV1/FVC and FEV1 % predicted. The mean annual FEV1 declines in individuals with rs6726395 G/G, G/A, or A/A were 26.2, 22.3, and 20.8 mL/year, respectively, and differences in these means were statistically significant (pcorr = 0.016). We also found a significant interaction between rs6726395 genotype and smoking status on the FEV1 decline (p for interaction = 0.011). The haplotype rs2001350T/rs6726395A/rs1962142A/rs2364722A/rs6721961T was associated with lower annual decline in FEV1 (p = 0.004). Conclusions: This study indicated that an Nrf2-dependent response to exogenous stimuli may affect annual FEV1 decline in the general population. It appears that the genetic influence of Nrf2 is modified by smoking status, suggesting the presence of a gene-environment interaction in accelerated decline in FEV1. Background Among pulmonary function test (PFT) measurements, forced expiratory volume in one second (FEV1) is the most reproducible [1]. Therefore, it is suitable for analyzing changes in pulmonary function over time. Accelerated decline in FEV1 is considered as an important predictor for the development of inflammatory obstructive lung diseases, such as asthma and chronic obstructive pulmonary disease (COPD) [2,3]. A rapid decline in FEV1 may be affected by multiple factors, including environmental and genetic factors. The most important environmental factor for FEV1 decline is cigarette smoking. In their landmark study, Fletcher et al. [4] demonstrated that smokers had a steeper decline in FEV1 than non-smokers. Subsequent studies have revealed that the rate of decline in FEV1 depends on pack-years smoked and that the accelerated decline in FEV1 in smokers slows to normal rates of decline upon smoking cessation [4-6]. Cigarette smoke contains high concentrations of oxidants, including reactive oxygen species and reactive nitrogen species [7]. Oxidative stress due to cigarette smoking promotes direct injury to airway epithelium, expression of genes encoding proinflammatory * Correspondence: t-saka@md.tsukuba. ac.jp Division of Respiratory Medicine, Institute of Clinical Medicine, University of Tsukuba, Ibaraki, Japan Full list of author information is available at the end of the article Masuko et al. BMC Medical Genetics 2011, 12:97 http://www.biomedcentral. com/1471-2350/12/97 © 2011 Masuko et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. mediators, and protease/antiprotease imbalance [8], all of which induce chronic inflammation in the lung of smokers that results in deterioration of lung function. However, only 10-15% of smokers develop a severe impairment of lung function [4]. In addition to environmental factors, genetic determinants play an important role in rapid decline in lung function. A pedigree-based study has shown that FEV1 levels have a heritability that is independent of cigarette smoking and disease status such as asthma [9]. Furthermore, recent large-scale genome-wide association studies have identified several loci associated with FEV1 and the FEV1/forced vital capacity (FVC) ratio [10,11]. It is possible that oxidant/antioxidant imbalance in the lungs of smokers results in an accelerated loss of lung function. Nrf2 is a major regulator of the antioxidant response [12]. Nrf2 regulates the expression of several genes encoding antioxidant and detoxification proteins [13]. In animal models, Nrf2 plays an important role in reducing inflammation associated with elastase-induced emphysema [14]. In human studies, attenuation of Nrf2 due to the down-regulation of the Nrf2 mRNA has been detected in alveolar macrophages of COPD patients [15]. Moreover, 3 single-nucleotide polymorphisms (SNPs) in the promoter region of the Nrf2 gene have an influence on the gene’s transcriptional activity, and one of these SNPs is associated with the development of acute lung injury [16]. Recently, one SNP (rs2364723) in the first intron of Nrf2 has been shown to be related to a lower FEV1 [17]. All of these findings indicate that an Nrf2-dependent adaptive response is important in inhibiting the oxidant-induced lung inflammation that results in a rapid decline in lung function. Therefore, we conducted a longitudinal retrospective cohort study of a general Japanese population in order to analyze associations between Nrf2 polymorphisms and annual decline in FEV1. We also assessed whether an interaction between the Nrf2 polymorphisms and smoking status affects FEV1 decline.