Use of the Caco-2 cell model to assess the relative lead-chelating abilityof diasterioisomers of 2,3-dimercaptosuccinic acid

The purpose of this study was to examine the mechanisms of lead (Pb) uptake by human intestinal cells and to compare the intestinal transport and rela tive lead-chelating ability of two diastereoisomeric forms (i.e., meso and racemic) of 2,3-dimercaptosuccinic acid (DMSA). The model used was the huma n adenocarcinoma (Caco-2) cell monolayer. The Caco-2 cells were cultured in flasks for examination of cellular uptake of lead and subsequent chelation of the lead by the DMSA isomers. For assessment of the comparative intesti nal transport of the diastereoisomers, the Caco-2 cells were cultured on se mipermeable supports. The effects of N-ethylmaleimide and 1,25-dihydroxyvit amin D-3 (vitamin D-3) on the uptake of lead by the Caco-2 monolayer were e xamined to determine the contributions of sulfhydryl-binding and calcium-bi nding protein, respectively, to the lead uptake process. Analysis of lead w as performed using both macro- and micro-proton-induced X-ray emission (PIX E), and DMSA was measured spectrophotometrically following derivatization w ith 5,5'-dithiobis-2-nitrobenzoic acid. Results from micro-PIXE imaging sug gest that lead is bound on the surface of the cell, and that sulfhydryl bin ding may be an important step in the uptake of lead by the Caco-2 cells. Ma cro-PIXE results indicate that the racemic form of DMSA may be more effecti ve in chelating lead from within the fell. Comparison of the transport of t he two DMSA diastereoisomers indicates that the racemic form is transported across the Caco-2 monolayer more readily than the meso form.