Free cysteine is increased in plasma from hemodialysis patients

Free cysteine is increased in plasma from hemodialysis patients. Background Although only the total thiol concentration, which includes bound and free forms, has been determined in most previous clinical studies, the free form may be a better predictor of cardiovascular risk. Methods We measured the apparent concentration of free homocysteine (Hcy) and cysteine (Cys) in filtered and acid-soluble fractions of plasma in healthy control subjects and in patients with chronic renal failure just before and after a hemodialysis session. Results In control, filtered Hcy and acid-soluble Hcy were similar, while filtered Cys was much smaller than in acid-soluble Cys. In prehemodialysis samples, filtered Cys was more than 60 times as abundant (259.2 ± 26.2 μmol/L) as in control samples (4.1 ± 0.7 μmol/L). Free-to-total ratios for filtered Cys were 1.6 ± 0.3% in controls, but 40.9 ± 2.7% in prehemodialysis patients. Conclusions The filtered fraction of thiols can be used to estimate solute transport across the dialysis membrane. In addition, the possible involvement of cysteine in the pathogenesis of atherosclerosis in hemodialysis patients should be reexamined.