REABSORPTION OF NATIVE AND GLYCATED ALBUMIN BY RENAL PROXIMAL TUBULAREPITHELIAL-CELLS

The proximal tubule epithelial handling of native and glycated albumin was evaluated by quantitative immunocytochemistry. Native bovine seru m albumin (BSA) and its glycated form (gBSA), tagged to different hapt ens, were simultaneously injected in anesthetized mice and maintained in circulation for 10 or 60 min. Both albumins were localized within t he capillary lumen, in glomerular and peritubular basement membranes, the urinary space, and cellular compartments of the proximal tubular e pithelial cells. In these cells, both forms of albumin were concomitan tly found within the same endocytic-lysosomal system. Morphometric eva luations have indicated higher proportions of gBSA in the urinary spac e, reflecting probably a significant glomerular filtration of this for m of albumin combined to a lesser reabsorptive clearance. Indeed, high er proportions of native BSA were found in the endocytic compartment o f the tubular epithelial cells, suggesting its preferential reabsorpti on. The present study thus supports a preferential glomerular filtrati on of gBSA with a facilitated filtration of native BSA in the presence of the glycated one. It also demonstrates the tubular reabsorption of BSA and gBSA through a common endocytic pathway, in which the native BA is preferentially reabsorbed with respect to its glycated form.