PLASMA HOMOCYSTEINE AND THIOL COMPOUND FRACTIONS AFTER ORAL-ADMINISTRATION OF N-ACETYLCYSTEINE

The total concentration of the atherogenic aminothiol acid homocystein e in plasma of healthy volunteers was decreased after oral administrat ion of N-acetylcysteine (NAC), whereas the reduced and free (non-prote in bound) fractions of homocysteine were increased. The decrease of th e total fraction varied between 20 and 50% and was dose-related. Cyste inylglycine was also decreased after the administration of NAC, wherea s cysteine did not change. Administration of high amounts of NAC proba bly displaces homocysteine and cysteinylglycine from their protein bin ding sites by disulfide interchange reactions. This leads to the forma tion of mixed low molecular-weight cystein and NAC disulfides with hig h renal clearance and possibly also increased metabolic bio-availabili ty, thereby eliminating homocysteine and cysteinylglycine from plasma. Since only a small amount of additional urinary homocysteine was reco vered it is likely that this aminothiol acid is taken up by the tubula r cells and further metabolized.