URINARY-EXCRETION MEASUREMENT OF CYSTEINE AND HOMOCYSTEINE IN THE FORM OF THEIR S-PYRIDINIUM DERIVATIVES BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH ULTRAVIOLET DETECTION

Several human diseases, in particular metabolic disorders, often lead to the accumulation of characteristic metabolites in plasma, urine and cells. The selected diseases of this type include cystinuria and homo cystinuria. In the typical laboratory diagnosis of these two diseases, a positive nitroprusside test is followed by quantitative analysis of urine cysteine and homocysteine in order to differentiate between cys tinuria and homocystinuria. A sensitive and reproducible assay for tot al urine cysteine and homocysteine has been developed. The essential s teps in the assay include conversion of disulphides to free thiols wit h tributylphosphine, conjugation of the thiols with 2-chloro-1-methyl pyridinium iodide, separation of S-pyridinium derivatives of cysteine and homocysteine from other endogenous urine thiol derivatives by reve rsed-phase high-performance liquid chromatography, and detection and q uantitation by spectrophotometry. The method has a sensitivity of 4 pm ol and is reproducible, intra-and inter-day coefficients of variation are from 1.37 to 4.14% and from 2.38 to 5.01%, respectively. The mean concentration of total urine cysteine and homocysteine in healthy dono rs (7 men and 7 women) were for women, 92.0+/-45.8 and 16.4+/-4.8 resp ectively, and for men 120.9+/-46.6 and 21.5+/-7.4 nmol/ml, respectivel y. Total urine homocysteine represents approximately 17.7% of cysteine in the urine of normal individuals. (C) 1998 Elsevier Science B.V.