Aldose reductase, glomerular metabolism, and diabetic nephropathy

To explore a possible link between diabetic nephropathy and the enhanced activity of the polyol pathway known to occur in diabetes, we examined several pertinent metabolic parameters in glomeruli isolated from control and streptozotocin-diabetic rats and assessed whether changes observed in diabetic glomeruli could be prevented by the oral administration of the aldose reductase inhibitor sorbinil. We found that glomerular polyol content is significantly increased in diabetes, whereas glomerular myo-inositol content is significantly reduced. The sorbitol accumulation and myo-inositol depletion were both completely prevented by sorbinil, which was given throughout the duration of diabetes. Activity of the membrane-bound sodium/potassium adenosine triphosphatase (Na-K-ATPase) was decreased in diabetic samples; this change was also completely prevented by sorbinil. Erythrocyte deformability is another factor that has been implicated in the pathogenesis of microangiopathic complications. The ability of red blood cells to undergo an adaptation in shape that permits passage through the smallest vessels is impaired in diabetes. Using blood from control, diabetic, and sorbinil-treated diabetic rats, we found that erythrocyte deformability was decreased in diabetic samples and that sorbinil treatment significantly improved this parameter. Thus, if the glomerular consequences of sorbitol accumulation, myo-inositol depletion, reduced Na-K-ATPase activity, and decreased erythrocyte deformability are pathogenetically implicated in diabetic nephropathy, the ability of sorbinil to impact on these changes suggests that it could favorably impact on the nephropathic process.