Vitamin C supplementation in patients on maintenance dialysis

Effects of vitamin C supplementation on oxidative stress and serum paraoxonase/arylesterase activities in patients on long-term hemodialysis

BACKGROUND

Oxidative stress increases oxidizability of apolipoprotein-B containing lipoproteins and decreases paraoxonase (PON) activity in hemodialysis (HD) patients and plays an important part in the development of atherosclerotic cardiovascular diseases. In HD patients, plasma ascorbic acid (AA) levels are decreased either due to the loss by hemodialysis membranes or due to malnutrition and contribute to the imbalance of antioxidant defense mechanisms. We hypothesized that long-term ascorbic acid (AA) supplementation recovers oxidizability of lipoproteins in HD patients by reinforcing PON activity.

METHODS

Twenty-nine adult patients were treated with 100mg and 500mg AA at the end of each HD session thrice a week for two consecutive 16 weeks-periods, respectively. Blood samples were obtained before the first HD session and prior to the first HD sessions following the 100mg AA-supplemented and the 500mg AA-supplemented periods.

RESULTS

PON activities were significantly increased after 100mg (p<0.05) and 500mg AA (p<0.001) supplementation periods compared to the basal level. Apo-B lipoprotein oxidizability (Δ-MDA) was significantly decreased after 500mg AA supplementation compared to both basal (p<0.05) and 100mg AA supplementation periods (p<0.05). Plasma AA concentrations were negatively correlated with Δ-MDA levels (R=-0.327; p<0.01).

CONCLUSION

Our results suggest that long-term parenteral 500mg AA supplementation improves PON activity alleviating apo B-containing lipoproteins oxidizability in HD patients.

Oxidative Stress in Hemodialysis Patients: Pathophysiological Mechanisms, Clinical Consequences and Basic Principles of Treatment

Cardiovascular diseases are the leading cause of death in patients who undergo regular hemodialysis. Oxidative stress is a non-traditional risk factor for the development of cardiovascular diseases in this population of patients. It is defined as tissue damage caused by balance disturbance between the formation of free radicals and the function of protective antioxidative systems. The superoxide anion and hydrogen peroxide are precursors in the formation of stronger oxidants, such as: hydroxyl radical, peroxynitrite and hypochloric acid. Superoxide dismutase is the first line of antioxidant protection while catalase, glutathione peroxidase, trace elements, vitamin C, vitamin E, N-acetylcysteine and coenzyme Q10 also have a significant antioxidative role. Hemo-dialysis is itself a trigger for the increased formation of oxygen free radicals. The two main pathophysiological mechanisms of the increased formation of free oxygen radicals during the hemo-dialysis session are: bionicompatibility of the dialysis membrane and the presence of endotoxins in the hemodialysis solution. The measurement of myeloperoxidase concentration in a patient’s serum during hemodialysis is an indicator of the severity of oxidative stress induced by the dialysis membrane (an indicator of the biocompatibility of the dialysis membrane). The main clinical consequences of oxidative stress include: atherosclerosis, erythropoietin resistance, malnutrition and amyloidosis associated with hemodialysis. The evaluation of oxidative stress in patients undergoing hemodialysis is performed by measuring the concentration of lipid peroxidation products (malonyldialdehyde, 4-hydroxynonenal, TBARS, F2-isoprostane, oxLDL), protein oxidation (AOPP), protein gelling (AGE), and oxidation of nucleic acids (8-OHdG). The antioxidant treatment strategy consists of replenishing vitamin C, vitamin E, selenium, N-acetylcysteine and coenzyme Q10. On-line hemodialysis, a biocompatible vitamin E-coated dialysis membrane, an ultra-pure solution for hemodialysis, prevent oxidative stress, reduce the rate of cardiovascular morbidity and mortality and improve life quality of patients treated with regular hemodialysis.