Background: This study focused on the effect of vitamin C on the 8-hydroxy-2'-deoxyguanosine (8-OHdG) level of cellular DNA, as well as 8-oxoguanine-DNA glycosylase 1 (hOGG1) and human MutT homologue (hMTH1) gene expression in peripheral blood lymphocytes of chronic hemodialysis patients.
Methods: Sixty chronic hemodialysis patients (35 men and 25 women) were recruited to participate in a randomized, placebo-controlled study. Treatment order is block-randomized with intravenous sodium ascorbate (vitamin C, 300 mg) or placebo (0.9% saline), administered postdialysis three times a week. We evaluated 8-OHdG level, intracellular reactive oxygen species (ROS) production, and gene expression of hOGG1 and hMTH1 in peripheral blood lymphocytes by using high-performance liquid chromatography (HPLC) electrochemical detection method, flow cytometric analysis, and reverse transcription-polymerase chain reaction (RT-PCR), respectively.
Results: A total of 51 patients completed the study (26 in placebo group and 25 in vitamin C group). Mean 8-OHdG levels significantly decreased in total subjects following 8 weeks of vitamin C supplementation (22.9 vs. 18.8/10(6) dG, P < 0.01). The decrease in 8-OHdG levels after vitamin C supplementation was also noted in the patients with ferritin <500 or > or =500 microg/L and transferrin saturation (TSAT) <50 or > or =50% (P < 0.05). But 8-OHdG levels had no significant changes in total patients or in the four subgroups of patients treated with placebo as compared to their baselines. Intracellular ROS production by lymphocytes from the four subgroups of patients, either spontaneous (P < 0.05) or phorbol-12-myristate-13-acetate (PMA)-stimulated (P < 0.001), was significantly reduced after 8 weeks vitamin C supplementation. Steady-state hOGG1 mRNA levels were significantly up-regulated at 24 hours after vitamin C administration (P < 0.05), but hMTH1 mRNA levels were not. The changes in the spontaneous and PMA-stimulated ROS production, and an up-regulation of hOGG1 mRNA expression were not observed in patients treated with placebo as compared to their baselines.
Conclusion: Vitamin C supplementation in chronic hemodialysis patients can reduce the lymphocyte 8-OHdG levels and intracellular ROS production, as well as up-regulate hOGG1 gene expression for repair. There is no compelling evidence for an in vivo pro-oxidant effect of vitamin C on lymphocyte DNA base oxidation, even in the status of increased iron stores.