Altered plasma free and protein-bound sulfur amino acid levels in patients undergoing maintenance hemodialysis.

The plasma sulfur amino acid status of maintenance hemodialysis (MHD) patients has not previously been comprehensively investigated. We measured plasma sulfur amino acid levels in 24 MHD patients (12 fasted, 12 nonfasted) both before and after a routine 4-h hemodialysis and in 13 normal individuals (seven fasted, six nonfasted). Plasma free cystine, homocystine, cysteine-homocysteine-mixed disulfide (MDS), methionine, and taurine and protein-bound cysteine and homocysteine were measured. In nonfasted patients, plasma homocystine and MDS were not measured. Fasted patients predialysis had elevated plasma free cystine, homocystine, MDS, methionine, and taurine; all of these, except taurine, fell during dialysis. In nonfasted patients, plasma free cystine was elevated. Protein-bound cysteine and homocysteine were elevated predialysis and postdialysis in all patients; protein-bound cysteine fell during dialysis but remained above normal. In MHD patients predialysis, plasma free cystine levels correlated with plasma MDS, protein-bound cysteine, and age. These findings indicate pervasive alterations in plasma sulfur amino acid levels in MHD patients.