High-performance liquid chromatographic and carbon-13 nuclear magnetic resonance spectrometric determination of S-carboxymethyl-l-cysteine and its metabolites in human urine

Summary

Both HPLC separation with fluorometric detection and ¹³C NMR spectrometry were used to quantify carbocysteine (CMC) and its major metabolites directly in the urine of thirteen human subjects following oral administration of the isotopomer S-carboxy-[¹³C]methyl-l-cysteine (¹³C-CMC). Comparison of the data obtained by these two independent analytical methods provides unequivocal evidence that the excretion of significant amounts of previously described cysteinyl sulphoxide metabolites cannot be verified. Instead, the identification and reproducible quantitation of renally eliminated CMC and its major non-cysteinyl metabolites, thiodiglycolic acid and thiodiglycolic acid sulphoxide, has been accomplished. It has to be concluded from this study, therefore, that the proposed genetically determined polymorphism of CMC sulphoxidation does not exist.