Antioxidant vitamin concentrations and LDL oxidation in nephrotic syndrome

The increased risk of atherosclerosis in nephrotic syndrome is attributable in part to the associated hyperlipidaemia. The importance of oxidation of LDL in the atherogenic process has been recognized over the last 15 years. However, there are few data on the balance of antioxidant defences and lipo protein oxidation in nephrotic syndrome. Plasma antioxidant vitamin concent rations and indices of LDL oxidation (LDL lipid hydroperoxide content and t he susceptibility of LDL to oxidation) were measured in two groups of patie nts; group I comprised 29 nephrotic patients and group II comprised 25 pati ents with haematuria. Plasma ascorbate concentration was significantly lowe r in group I (the nephrotic group) compared with group II (median 13.3 vers us 22.2 mu mol/L; P<0.001). Vitamin E concentrations were higher in group I but were not significantly different if corrected for total plasma cholest erol(6.12 versus 5.88 mu mol/mmol; P=0.33). However, these changes resulted in a low ascorbate:vitamin E ratio in group I (0.19 versus 0.87; P<0.0001) . Despite these changes in important antioxidant vitamin concentrations, we were unable to demonstrate any increased susceptibility to LDL oxidation i n vitro or any difference in LDL lipid hydroperoxide content. These data su ggest that there may be a relative defect of oxidant/antioxidant balance in nephrotic syndrome which could predispose to increased oxidative stress. H owever, measures of LDL oxidation were not significantly different between the two groups. LDL was protected from oxidation despite the severe hyperli pidaemia and the low circulating vitamin C concentrations.