Determination and metabolism of dithiol chelating agents: VI. Isolation and identification of the mixed disulfides of meso-2,3-Dimercaptosuccinic acid with l-cysteine in human urine☆

Virtually nothing is known about the biotransformation of the heavy metal chelating agent, meso-2,3-dimercaptosuccinic acid (DMSA). Two fasted, normal, young men wera given 10.0 mg DMSA/kg po, and their urines were collected over a 14-hr period. Urine samples were analyzed, before and after electrolytic reductive treatment, for DMSA and its biotransformants using bromobimane derivatization, HPLC separation, and fluorescence detection. Metabolites were isolated by HPLC, ion-pairing extraction, ion-exchange extraction, and TLC. By 14 hr after DMSA administration, 87% of the total DMSA and 95% of the total l-cysteine found in urine consisted of altered forms of these compounds. The urinary excretion of altered DMSA, at 1, 2, 4, 6, 9, and 14 hr after administration of DMSA, when compared to the urinary excretion of altered l-cysteine had a correlation coefficient of 0.952 and p < 0.003. Approximately 90% of the altered DMSA excreted in the 2- to 4-hr urine was found in disulfide linkage with l-cysteine. The remaining 10% was found as cyclic disulfides of DMSA. Of the mixed disulfides found in 4- to 6-hr urine, 97% consisted of two l-cysteine residues per one DMSA and the remaining 3% consisted of one l-cysteine per one DMSA. The 2:1 mixed disulfides (97%) were isolated as three distinct species by TLC, consisting of 77, 12, and 8% of the total mixed disulfides found. In addition to the novelty of these biotransformants of DMSA, the DMSA-cysteine mixed disulfides indicate a thiol-disulfide interchange between DMSA and l-cystine. The discovery of the formation of these water soluble DMSA-cysteine mixed disulfides should encourage the evaluation of DMSA in the treatment of cystinuria.