Nature and biological significance of free radicals generated during bicarbonate hemodialysis

This study investigates evidence of oxidative stress during bicarbonate hemodialysis by measuring total glutathione and lipid peroxidation products in plasma, and characterizes the free radicals produced by neutrophils from healthy volunteers when incubated in vitro with increasing concentrations of bicarbonate. Blood samples were taken from nine hemodialysis patients before and after two hemodialysis sessions. Plasma hydroperoxides and total glutathione were measured. A significant increase was found in total glutathione (1.04 +/- 0.4 versus 2.11 +/- 0.9 microM, P < 0.001) and hydroperoxides by ferrous oxidation in xylenol orange version 2 method (4.6 +/- 0.53 versus 6.4 +/- 0.63 microM, P < 0.001) after hemodialysis, which indicated increased oxidative injury during hemodialysis. Normal neutrophils, activated by contact adhesion, produced a dose-dependent increase in free radical production (measured by luminol-enhanced chemiluminescence) when incubated with increasing concentrations of bicarbonate (up to 35 mM). Bicarbonate had the same effect on the chemiluminescence of a cell-free hypoxanthine/acetaldehyde system generating superoxide, but not on a glucose oxidase/myeloperoxidase system generating hydrogen peroxide and hypochlorous acid. These findings are consistent with (1) the hypothesis that superoxide generated during hemodialysis reacts with bicarbonate to form the toxic carbonate and formate radicals and (2) our previous observation that some patients undergoing bicarbonate (but not lactate) dialysis have increased plasma concentrations of formate after hemodialysis. It is suggested that the increased plasma total glutathione and hydroperoxide concentrations are a result of lipid peroxidation by these species. These reactive radicals can initiate lipid peroxidation and contribute to the cardiovascular complications of hemodialysis patients.