Effect of Human OGG 1 1245 C 3 G Gene Polymorphism on 8-Hydroxy-2 '-Deoxyguanosine Levels of Leukocyte DNA among Patients Undergoing Chronic Hemodialysis

The effects of the human OGG1 gene (hOGG1) 1245C3G polymorphism on the 8-hydroxy-2'-deoxyguanosine (8-OHdG) contents of peripheral leukocyte DNA were investigated among chronic hemodialysis patients. First, the hOGG1 1245C3G transversion was assessed, by using a PCR-restriction fragment length polymorphism method, among 210 hemodialysis patients and 156 healthy individuals. Second, the 8-OHdG contents in leukocyte DNA were measured, by using an HPLC-electrochemical detection method, for 112 hemodialysis patients and 112 age-, gender-, and genotype-matched healthy control subjects. The three genotypes (as dummy variables) and age, gender, dialysis duration, dialyzer membrane type, blood antioxidant levels, and iron parameters were used as independent variables and the natural logarithm of the leukocyte 8-OHdG concentration was used as a dependent variable in a forward, stepwise, multiple-regression model. The results demonstrated that the allelic frequency of hOGG1 1245G was 64.1% among 210 hemodialysis patients and 62.2% in the whole control population. The genotypic frequencies (CC/CG/GG ratio, 10%/51.9%/38.1%) for the hemodialysis patients did not differ significantly from those (16.7%/42.3%/41.0%) for the control subjects (P 0.05, 2 test). The mean leukocyte 8-OHdG levels for the patients were significantly higher than those for the healthy control subjects (P 0.001). Leukocyte 8-OHdG levels were further increased among patients with the 1245GG genotype, compared with patients with the 1245CG or CC genotype (P 0.001, ANOVA), but levels were similar among healthy control subjects irrespective of the hOGG1 gene polymorphism. It was also observed that patients who underwent dialysis with cellulose membranes exhibited significantly higher leukocyte 8-OHdG levels than did patients who underwent dialysis with polymethylmethacrylate, polysulfone, or vitamin E-bonded membranes (P 0.001, ANOVA). The multivariate regression analysis revealed that hOGG1 1245C3G polymorphism and dialysis membrane type were the two independent predictors of 8-OHdG contents in leukocyte DNA from hemodialysis patients. This study demonstrated that the extent of oxidative DNA damage among chronic hemodialysis patients not only is influenced by overproduction of reactive oxygen species resulting from leukocyte contacts with complement-activating membranes and by impaired antioxidant defense mechanisms but also is genetically determined. Reactive oxygen species (ROS) and peroxides are involved in the pathogenesis of many human diseases, including atherosclerosis and inflammatory diseases, and are thought to participate in the aging process and carcinogenesis (1–3). Oxidative damage occurs in a cell when the production of ROS exceeds the antioxidant defense capacity. A growing body of evidence indicates that ROS, which are generated by oxidative metabolism in activated phagocytes during hemodialysis, cause damage to cellular constituents, such as membrane lipids (4,5), proteins (6,7), and DNA (8,9). Membrane lipids and proteins are protected against oxidation by low-molecular weight antioxidants, as well as antioxidant enzymes, whereas DNA is not as well protected against ROS. Therefore, a marker of oxidative DNA damage would be useful for estimation of the extent of oxidative stress among hemodialysis subjects. Among the many types of oxidative DNA damage, 8-hydroxy-2'-deoxyguanosine (8-OHdG) is one of the most abundant oxidative products of cellular DNA (2). 8-OHdG is capable of reflecting extremely low levels of oxidative damage, because it can be detected, using HPLC-electrochemical detection methods, in the femtomole range. We have identified peripheral leukocytes of hemodialysis patients as being suitable for the monitoring of 8-OHdG levels in cellular DNA, because they are not only the source but also the target of endogenous ROS (8,9). In our previous work, leukocyte 8-OHdG levels were demonstrated to Received January 23, 2001. Accepted May 9, 2001. Correspondence to Dr. Yau-Huei Wei, Department of Biochemistry and Center for Cellular and Molecular Biology, National Yang-Ming University, No. 155, Section 2, Li-Nung Street, Taipei 112, Taiwan. Phone: 886-2-2826-7118; Fax: 886-2-2826-1132; E-mail: joeman@mailsrv.ym. edu.tw