Global assessment of serum antioxidant status in hemodialysis patients

Since chronic renal failure (CRF) was described as a state of oxidant/antioxidant imbalance augmented after hemodialysis (HD) initiation, we assessed the total antioxidant activity and single antioxidants in sera from uremic patients dialyzed or not, compared to subjects with normal renal function.

Serum total antioxidant activity (TAA--measured as Trolox equivalent antioxidant capacity; mmol/L), total plasma free thiols (Pt-SH; micromol/g protein), albumin (g/dL) and uric acid (mg/dL) were determined in 19 hemodialyzed patients, 15 CRF non-dialyzed patients (serum creatinine (Cr) = 4.4 +/- 2.7 mg/dL) and in 16 healthy controls. The "antioxidant gap" (mmol/L), as a measure of the combined activity of plasma antioxidants other than albumin and uric acid, was calculated.

TAA and the "antioxidant gap" were higher in HD patients (1.21 +/- 0.12 vs. 0.96 +/- 0.13 in the non-HD group, p<0.001, and vs. 0.9 +/- 0.14 in controls, p<0.001, respectively, for TAA; 0.46 +/- 0.15 vs. 0.2 +/- 0.15, p<0.001, and vs. 0.21 +/- 0.16, p<0.001, respectively, for residual antioxidant activity). However, no differences existed in major plasma antioxidant levels (albumin and uric acid) among uremic patients, hemodialyzed or not. Pt-SH were reduced in nondialyzed patients as compared to controls (6.21 +/- 1.1 vs. 7.33 +/- 0.83, p=0.002), but were elevated in HD patients (11.9 +/- 1.1).

These results suggest that HD patients appear to have improved plasma antioxidant status, hyperuricemia not being the sole contributor. Therefore, it seems reasonable to speculate that other antioxidants (thiols or some as yet unrecognized substances) could also be contributors. However, more reliable assays for extracellular antioxidant defense evaluation are required to validate this hypothesis.