Free and total plasma malondialdehyde in chronic renal insufficiency and in dialysis patients

Background. Available data about oxidative status in patients with end-stage renal disease (ESRD) or on dialysis are contradictory. The present cross-sectional study aimed to investigate the role of renal insufficiency and dialysis on lipid peroxidation. To separate the effects of uraemia from dialysis-induced stress, we enrolled 26 patients with renal insufficiency on conservative treatment (ESRD), 23 on peritoneal dialysis (PD), 30 on haemodialysis (HD) and 30 controls. Methods. Plasma malondialdehyde (MDA) levels, both total (tMDA) and free (fMDA), were measured as indexes of oxidative stress by gas chromatography-mass spectrometry. Bound MDA (bMDA) levels were calculated as the difference between tMDA and fMDA. Results. Total and bMDA concentrations were significantly higher in patients than in controls (ESRD > HD > PD). In PD and HD patients, fMDA levels were similar and significantly higher than in ESRD. Multivariate analysis, with tMDA, fMDA and bMDA as dependent variables, showed similar and significant tMDA and bMDA relations with residual renal function (t = −2.160, P = 0.035) and albumin (t = −2.049, P = 0.045). Erythropoietin dose affected only fMDA values (t = −2.178, P = 0.034). Conclusions. Free and bMDA concentrations identified different MDA patterns. Bound MDA, not excreted by kidneys, accounts alone for high tMDA concentrations in ESRD patients, while both fMDA and bMDA contribute to tMDA values in dialysis patients. These findings show that increased tMDA could be indicative not only of recent lipid peroxidation, and they also highlight the importance of evaluating free, bound and total MDA in patients with reduced renal function in order to assess their oxidative status.