Serum Bilirubin and Ferritin Levels Link Between Heme Oxygenase-1 Gene Promoter Polymorphism and Susceptibility to Coronary Artery Disease in Diabetic Patients

Abstract

Objective Heme oxygenase (HO) leads to the generation of free iron, carbon monoxide, and bilirubin. A length polymorphism of GT repeat in the promoter of human HO-1 gene has been shown to modulate gene transcription. This study aims to assess the association of the length of (GT)n repeats in HO-1 gene promoter with serum bilirubin, markers of iron status, and the development of coronary artery disease (CAD).

Research design and methods We screened the allelic frequencies of (GT)ⁿ repeats in the HO-1 gene promoter in 986 unrelated individuals that underwent coronary angiography. Serum bilirubin and markers of iron status were evaluated.

Results The distribution of numbers of (GT)_n repeats was divided into 2 subclasses: class S included shorter (<27) repeats, and class L included longer (≥27) repeats. Among those with diabetes, subjects with L/L genotype had significantly lower bilirubin levels than those with S/S and S/L genotypes (0.70±0.22 vs. 0.81±0.24 mg/dL, P=0.001) and higher serum ferritin values (4.76±0.72 vs. 4.28±1.05 μg/L for log-ferritin, P=0.001). Compared with those carrying S allele, diabetic subjects with L/L genotype had an almost three-fold increase in CAD risk after controlling for conventional risk factors (odds ratio 2.81, 95% confidence interval [CI] 1.22 to 6.47, P=0.015). Adjusting for both serum bilirubin and ferritin, the effect of HO-1 promoter polymorphism on susceptibility to CAD disappeared.

Conclusions Length polymorphism in the HO-1 gene promoter is correlated with susceptibility to CAD in diabetic patients and such effect might be conveyed through its influence on serum bilirubin and ferritin.