Plasma protein thiol oxidation and carbonyl formation in chronic renal failure

Background. Myeloperoxidase-catalyzed oxidative pathways have recently been identified as an important cause of oxidant stress in uremia and hemodialy sis (HD), and can lead to plasma protein oxidation. We have examined patter ns of plasma protein oxidation in vitro in response to hydrogen peroxide (H 2O2) and hypochlorous acid (HOCl). We measured thiol oxidation, amine oxida tion, and carbonyl concentrations in patients on chronic maintenance HD com pared with patients with chronic renal failure (CRF) and normal volunteers. We have also examined the effect of the dialysis procedure on plasma prote in oxidation using biocompatible and bioincompatible membranes. Methods. Plasma proteins were assayed for the level of free thiol groups us ing spectrophotometry, protein-associated carbonyl groups by enzyme-linked immunosorbent assay, and oxidation of free amine groups using a fluorescent spectrophotometer. Results. In vitro experiments demonstrate HOCl oxidation of thiol groups an d increased carbonyl formation. In vivo, there are significant differences in plasma-free thiol groups between normal Volunteers (279 +/- 12 mu mol/L) , CRF patients (202 +/- 20 mu mol/L, P = 0.005) and HD patients (178 +/- 18 mu mol/L, P = 0.0001). There are also significant differences in plasma pr otein carbonyl groups between normal volunteers (0.76 +/- 0.51 mu moI/L), C RF patients (13.73 +/- 4.45 mu mol/L, P = 0.015), and HD patients (16.95 +/ - 2.62 mu mol/L, P = 0.0001). There are no significant differences in amine group oxidation. HD with both biocompatible and bioincompatible membranes restored plasma protein thiol groups to normal levels, while minimally affe cting plasma protein carbonyl expression. Conclusions. First, both CRF and HD patients have increased plasma protein oxidation manifested by oxidation of thiol groups and formation of carbonyl groups. Second, HD with biocompatible and bioincompatible membranes restor ed plasma protein thiol groups to normal levels. Third, these experiments s uggest that there is a dialyzable low molecular weight toxin found in uremi a that is responsible for plasma protein oxidation.