BACKGROUND

The number of studies on adiponectin, GPx-1 gene polymorphisms, and nonalcoholic fatty liver disease (NAFLD) susceptibility is increasing, but none have investigated the effect of cigarette smoking in combination with the gene polymorphisms on the susceptibility to NAFLD. In order to understand the distribution of adiponectin and GPx-1 in the local population, to explore the possible association of cigarette smoking with adiponectin and GPx-1 gene polymorphisms in the pathogenesis of NAFLD, we conducted this research, examining the distribution of polymorphisms of adiponectin and GPx-1 in NAFLD patients and healthy controls, analyzing the association between these polymorphisms and cigarette smoking.

METHODS

Two hundred nonalcoholic simple fatty liver (NAFL), 200 nonalcoholic steatohepatitis (NASH), and 200 nonalcoholic fatty hepatic cirrhosis (NAFHC) cases from the First Affiliated Hospital of Xinxiang Medical College in China from February 2011 to November 2014 were selected for this study, and 200 healthy individuals as a control group. No significant difference among the four groups in age, sex, ethnicity, and birthplace was observed. The genetic polymorphisms of adiponectin gene promoter-11377C/G and GPx-1 gene C594T were analyzed using polymerase chain reaction-restriction fragment length polymorphisms in peripheral blood leukocytes of the above-mentioned cases. The interaction between the two mutants and the gene-environment association of the genotypes with cigarette smoking were analyzed.

RESULTS

The frequencies of adiponectin gene promoter-11377C/G(CG), -11377C/G (GG), GPx-1 gene C594T (CT) and C594T (TT) were 24.50%, 26.00%, 24.00%, and 25.50% in the NAFL group, 34.50%, 37.00%, 35.00%, and 36.00% in the NASH group, 42.00%, 46.00%, 43.50%, and 45.50% in the NAFHC group, and 14.00%, 14.50%, 13.00%, and 14.00% in the control group, respectively. Statistical tests showed a significant difference in the frequencies among each group (p < 0.01). The risk of NAFLD significantly increased in patients with adiponectin gene promoter-11377C/G (CG) genotype [odds ratio (OR)NAFL = 2.5278; ORNASH = 6.1823; ORNAFHC = 17.8570), in those with -11377C/G (GG) genotype (ORNAFL = 2.5900; ORNASH = 6.4017; ORNAFHC = 18.9023), in those with GPx-1 gene C594T (CT) genotype (ORNAFL = 2.6687; ORNASH = 6.7772; ORNAFHC = 22.2063), and in those with C594T (TT) genotype (ORNAFL = 2.6330; ORNASH = 6.4729; ORNAFHC = 21.5682). Combined analysis of the polymorphisms showed that percentages of adiponectin gene promoter -11377C/G (GG)/GPx-1 gene C594T (TT) in the NAFL, the NASH, NAFHC, and control groups was 7.00%, 13.50%, 21.00%, and 2.00%, respectively (p < 0.01). The people who carried the adiponectin gene promoter -11377C/G (GG)/GPx-1 gene C594T (TT) had a high risk of NAFLD (ORNAFL = 7.2800; ORNASH = 41.2941; ORNAFHC = 363.9724), and statistical analysis suggested a positive association between -11377C/G (GG) and C594T (TT) in increasing the risk of NAFLD (γ2NAFL = 2.2071, γ4 NAFL = 2.0773; γ2 NASH = 2.1084; γ4NASH = 2.0543; γ2 NAFHC = 2.1387; γ4NAFHC = 2.0004). Likewise, there were also positive association in the pathogenesis of NAFLD between -11377C/G (CG) and C594T (TT), -11377C/G (CG) and C594T (CT), -11377C/G (GG), and C594T (TT) (CT).The frequencies of smoking index (SI) ≤ 400 and SI > 400 were 22.50% and 26.50% in the NAFL group, 29.00% and 40.50% in the NASH group, 34.00% and 51.50% in the NAFHC group, and 15.50% and 12.00% in the control group, respectively. Statistical tests showed a significant difference in the frequencies among each group (all p < 0.01). The risk of NAFLD significantly increased in patients with SI ≤ 400 (ORNAFL = 2.0636; ORNASH = 4.4474; ORNAFH C = 10.9677) and in those with SI > 400 (ORNAFL = 3.1393; ORNASH = 8.0225; ORNAFHC = 21.4583), and statistical analysis suggested a positive association between cigarette smoking and -11377C/G (CG), -11377C/G (GG), C594T (CT), and C594T (TT) in increasing the risk of NAFLD (all γ > 1).

CONCLUSION

Adiponectin gene promoter -11377C/G (CG), -11377C/G (GG), GPx-1 gene C594T (CT), C594T (TT), and cigarette smoking are risk factors in NAFLD, and the significant association between genetic polymorphisms of -11377C/G, C594T, and cigarette smoking amplify the risk of NAFLD.