Plasma homocysteine and thiol compound fractions after oral administration of N-acetylcysteine

Abstract

The total concentration of the atherogenic aminothiol acid homocysteine in plasma of healthy volunteers was decreased after oral administration of N-acetylcysteine (NAC), whereas the reduced and free (non-protein bound) fractions of homocysteine were increased. The decrease of the total fraction varied between 20 and 50% and was dose-related. Cysteinylglycine was also decreased after the administration of NAC, whereas cysteine did not change. Administration of high amounts of NAC probably displaces homocysteine and cysteinylglycine from their protein binding sites by disulfide interchange reactions. This leads to the formation of mixed low molecular-weight cystein and NAC disulfides with high renal clearance and possibly also increased metabolic bio-availability, thereby eliminating homocysteine and cysteinylglycine from plasma. Since only a small amount of additional urinary homocysteine was recovered it is likely that this aminothiol acid is taken up by the tubular cells and further metabolized.

Key Words:

• cysteine
• cysteinylglycine
• homocysteine
• N-acetylcysteine
• plasma
• urine