We assayed the redox forms of
cysteine (reduced [CSH], oxidized [CSSC], and bound to
protein [CS-SP]),
cysteinylglycine (CGSH; cysteinylgycine
disulfide [CGSSGC] and
cysteinylglycine-
protein mixed
disulfide [CGS-SP]),
glutathione (GSH;
glutathione disulfide [
GSSG] and
glutathione-
protein mixed
disulfide [GS-SP]),
homocysteine (Hcy;
homocystine [HcyS] and
homocystine-
protein mixed
disulfides [bHcy]), and
protein sulfhydryls in the plasma of healthy subjects (divided into 8 groups ranging in age from birth to 70 years) and patients with mild
hyperhomocysteinemia associated with
cardiovascular disease (heart-transplant patients) or vascular
atherosclerosis, with or without
renal failure. In healthy individuals, levels of
disulfides and
protein-mixed
disulfides were more abundant than those of
thiols, and those of
protein-
thiol mixed
disulfides were higher than
disulfides. Concentrations of CSH, GSH, and CGSH in the various groups had profiles characterized by a maximum over time. The concentration of Hcy was unchanged up to the age of 30 years, after which it increased. CSSC concentration increased gradually with age, whereas concentrations of the other
disulfides were essentially unchanged. By contrast, the concentrations of all
protein-
thiol mixed
disulfides, especially those with CSH, increased gradually with age. Ranks of distribution of the reduced forms changed with age (at birth, CSH > CGSH > GSH > Hcy; in 1- to 2-year-olds, CSH > GSH > CGSH > Hcy; and in 51- to 70-year-olds, CSH > CGSH = GSH > Hcy), whereas those of
disulfides and
protein-
thiol mixed
disulfides were substantially unchanged (in all age groups, CSSC > CGSSGC >
GSSG = HcyS and CS-SP > CGS-SP > bHcy > GS-SP). In patients with pathologic conditions, plasma levels of
disulfide forms CSSC, HcyS, CS-SP, and bHcy were significantly increased, whereas other redox forms of
thiols were unchanged or showed variations opposite (increasing or decreasing) to control values. Maximal increases in
disulfides and
protein-
thiol mixed
disulfides were associated with
renal failure. Our data suggest that increases in plasma bHcy concentrations in subjects with pathologic conditions were more likely the result of activation of
thiol-
disulfide exchange reactions between free reduced Hcy and CS-SP than of a direct action of
reactive oxygen species.