Total antioxidant capacity (TAC): is it an effective method to evaluate the oxidative stress in uraemia?

Lipoprotein abnormalities are common in uraemia and are considered important factors for development of atherosclerosis and progression of renal disease. Reduction of total antioxidant capacity (TAC) and lipid peroxidation (LP) probably play a major role in both processes. The aim of this study was to assess the effect of renal function, dietary manipulation and lipids on TAC of uraemic patients with different chronic renal failure (CRF). Sixty patients (36M, 24F), aged 60 +/- 12 years were divided into five groups according to serum creatinine levels (sCr,mg/dl)--CRFI, 1.5-3; CRFII, > 3-5.5; CRFIII, > 5.5; CRFIV, > 3 on vegetarian supplemented diet (SD); CRFV haemodialysis patients (HD)- and investigated for TAC by enhanced chemiluminescent assay, autoantibodies against oxidized LDL (oxLDLAb), lipids, apolipoprotein AI, B, Lp(a) and uric acid (UA). The results were compared to a control group of 19 people (8M, 11F), aged 52 +/- 11 years with sCr < 1.5. TAC increased significantly with the progression of CRF and was strongly related to both sCr and UA. Lipids and SD did not show any influence on TAC. Unexpectedly, lipid peroxidation did not correlate to TAC, neither to sCr or UA. HD accounted for a mild reduction of both TAC and LP. Patients on SD showed a marked reduction of LP as compared to patients with a similar degree of renal failure (CRF-III) but on conventional diet. Our results suggest that elevated TAC in uraemia is likely to be dependent on increased UA levels and does not seem to induce an effective protection in vivo from oxidative stress. In conclusion, TAC does not appear to be a reliable method for assessing the oxidative susceptibility of CRF patients.