Determination and metabolism of dithiol-chelating agents: electrolytic and chemical reduction of oxidized dithiols in urine.

The presence of oxidized species of the dithiol-chelating agents, meso-2,3-dimercaptosuccinic acid (DMSA) and 2,3-dimercaptopropane-1-sulfonic acid (DMPS), in human urine was determined by chemical and electrolytic reduction methods. Urine from a human given either DMSA or DMPS was treated with electrolysis, dithiothreitol, or sodium tetrahydridoborate (NaBH4). The SH groups were derivatized with monobromobimane for the determination of unaltered dithiols. Total dithiol (unaltered and oxidized) was determined by reduction followed by derivatization with monobromobimane. The bimane derivatives were identified and quantified by HPLC and fluorescence. Although all three reduction methods gave similar results, electrolytic reduction of oxidized DMSA and chemical reduction with NaBH4 of oxidized DMPS are recommended based upon both day to day reproducibility and recovery of standards. After reduction a 4-fold increase in DMSA and a 20-fold increase in DMPS were found in urine by 12 h after an oral dose of DMSA or DMPS. These new methods for the determination of dithiols and their oxidized forms should lead to a better understanding of the metabolic properties of these increasingly important orally effective chelating agents.