Correlation studies of plasma paraoxonase activity and uric acid concentration with AAPH-Induced erythrocyte hemolysis in hemodialysis patients.

Uric acid possesses antioxidant properties and is an important determinant of total plasma antioxidant capacity. Uric acid concentrations tend to be elevated in patients with renal failure requiring maintenance hemodialysis but are abruptly reduced by the dialysis procedure itself. Paraoxonase (PON1), an enzyme which circulates in association with high density lipoprotein (HDL), confers protection against free radicals by limiting the oxidation of phospholipids. The relationship between pre- and postdialysis uric acid concentration, PON1 activity, and high density lipoprotein cholesterol (HDL-C) level and the resistance of erythrocytes from hemodialysis patients to hemolysis induced by the free radical generator 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) was studied. Red cells were washed free of plasma prior to the assay, and no plasma was added to the hemolysis assay tubes. Postdialysis erythrocytes were found to be more susceptible to hemolysis compared to blood samples obtained at the initiation of the session (784 +/- 713 vs. 256 +/- 256 micro mol/L hemoglobin released after 60 min incubation and 1530 +/- 696 vs. 1354 +/- 757 micro mol/L at 90 min). Hemolysis correlated negatively with the concentration of uric acid and positively with PON1 arylesterase activity but not with HDL-C level in the corresponding plasma samples. There was a strong negative correlation between uric acid and PON1 in predialysis blood samples (r2 = 0.4, P < 0.001). The conclusion is that the reciprocal relationship between uric acid and PON1 may reflect a mechanism that protects erythrocytes from subsequent oxidative stress.