Evidence for Alterations in Circulating Low-Molecular-Weight Antioxidants and Increased Lipid Peroxidation in Smokers on Hemodialysis

Abstract

Background/Aim: Cardiovascular disease is the major cause of mortality in dialysis patients, accounting for about 40% of deaths in most large registries. Oxidative stress has been strongly implicated in the pathogenesis of these events. As end-stage renal disease is a state of elevated free radical activity, the aim of the present study was to investigate the negative impact of smoking in 57 male hemodialysis patients. Methods: The patients, who were 20–85 years of age (mean age 51.0 ± 14 years), had been on hemodialysis for at least 6 months before participating in this study. Fasting blood sampling for serum lipid, albumin, urate and lipophilic antioxidants such as tocopherols, carotenes, ascorbate and lipid peroxides was performed. Results: The plasma malondialdehyde (MDA) concentration was significantly higher in hemodialysis patients who smoked compared to hemodialysis patients who were nonsmokers (1.92 ± 0.52 vs. 1.59 ± 0.42 nmol/ml, p = 0.006). No association was found between levels of MDA in smokers and parameters such as body mass index, serum cholesterol, serum triglycerides and smoking index. There were no significant differences in the plasma levels of uric acid, α-tocopherol, γ-tocopherol, δ-tocopherol, α-carotene, β-carotene and retinol between the two groups. A significantly lower level of plasma ascorbate was observed in hemodialysis patients who smoked compared to the nonsmoking hemodialysis patients or healthy controls (4.59 ± 4.0 vs. 9.57 ± 4.0 and 10.16 ± 4.6 µg/ml, p < 0.05). Moreover, in smokers, the plasma levels of ascorbate were negatively correlated with the levels of plasma MDA (r = –0.43, p < 0.001) of each patient. Partial correlation analysis of the plasma levels of the measured antioxidants and the smoking index revealed a negative correlation between the plasma levels of lipid-normalized lycopene and the smoking index (r = –0.53, p < 0.05). Conclusion: Our data suggest that cigarette smoking further increases plasma-circulating products of lipid peroxidation, which are already increased in nonsmoking hemodialysis patients as compared to matched healthy controls. The lower plasma levels of ascorbate in hemodialysis patients who smoke suggest that these patients may be more susceptible to oxidative tissue damage caused by smoking.