Free and protein-bound homocysteine and cysteine in cystathionine beta-synthase deficiency: interrelations during short- and long-term changes in plasma concentrations.
Homocysteine interacts in a complex way in the plasma with cysteine and plasma proteins. To explore the interrelations between free and protein-bound homocysteine and cysteine during short- and long-term changes in plasma levels, free and bound homocysteine and cysteine were measured in 13 patients with homocystinuria due to cystathionine beta-synthase deficiency. Levels were measured during oral methionine loads (4 g/m2 body surface area) and after oral betaine (3 g twice daily). In six pyridoxine-responsive patients, free and bound levels of homocysteine and cysteine, measured 4 to 24 hours after oral methionine, changed in a parallel manner. Similar close tracking occurred in fasting plasma samples collected from two pyridoxine-nonresponsive patients before and during betaine therapy. Oral betaine given to seven pyridoxine-nonresponsive patients decreased free and bound homocysteine and increased free and bound cysteine toward normal levels during monitoring periods of up to 300 days. In these studies as the level of homocysteine decreased, the proportion of protein-bound homocysteine and cysteine increased. The present study establishes that changes in bound and free levels of either homocysteine or cysteine track closely in the short-term (four hours or less) and generally also in the long-term (up to 300 days).
Department of Cardiovascular Medicine, University of New South Wales, Prince Henry Hospital, Little Bay, Sydney, Australia.
V C
VC
Wiley
N P
NP
Dudman
D E
DE
Wilcken
D000328:Adult; D001622:Betaine / Q000627:therapeutic use; D001798:Blood Proteins / Q000378:metabolism*; D003541:Cystathionine beta-Synthase / Q000172:deficiency*; D003545:Cysteine / Q000097:blood*; D006710:Homocysteine / Q000097:blood*; D006712:Homocystinuria / Q000097:blood / Q000188:drug therapy; D006801:Humans; D006836:Hydro-Lyases / Q000172:deficiency*; D007700:Kinetics; D008297:Male; D008715:Methionine; D011485:Protein Binding
D001798:Blood Proteins; D006710:Homocysteine; D001622:Betaine; D008715:Methionine; D006836:Hydro-Lyases; D003541:Cystathionine beta-Synthase; D003545:Cysteine