Aminothiols and allantoin in chronic dialysis patients: effects of hemodialysis sessions.

Background: To investigate the possible relationship between homocysteine and allantoin levels in hemodialyzed patients, serum levels of thiols and purine compounds were analyzed before and after dialysis sessions. Methods: 16 clinically stable non-diabetic patients hemodialyzed on polysulfone membranes were compared with 36 control subjects. Serum samples were collected before and after hemodialysis sessions. Total homocysteine, cysteine, glutathione, cysteinylglycine, uric acid, hypoxanthine, and allantoin were measured by capillary electrophoresis. Results: Pre-dialysis homocysteine, allantoin, and uric acid were significantly elevated in dialysis patients as compared to controls. Cysteine, glutathione, and hypoxanthine levels were similar in both groups. Homocysteine significantly decreased, but did not normalize after dialysis sessions. Glutathione and cysteinylglycine levels remained unchanged after dialysis sessions, whereas cysteine decreased. Uric acid, hypoxanthine, and allantoin levels were significantly reduced by dialysis sessions. The allantoin/uric acid ratio was higher in dialyzed patients before hemodialysis (0.049 +/- 0.023 vs. 0.016 +/- 0.012 in controls; p < 0.001), and became elevated after a dialysis session (0.084 +/- 0.033; p = 0.002). Conclusions: Despite the use of biocompatible membranes, homeostasis of thiols and purine compounds is disturbed in hemodialysed patients. We suggest that allantoin could be used as a marker for oxidative stress in hemodialyzed patients.