A novel zwitterionic inhibitor of aldose reductase interferes with polyol pathway in ex vivo and in vivo models of diabetic complications.

Recently a zwitterionic principle has been suggested as an alternative to bioisosteric replacement for increasing low bioavailability of aldose reductase inhibitors bearing an acidic function. In the present work we studied the effect of a novel zwitterionic inhibitor of aldose reductase [(2-benzyl-2,3,4,5-tetrahydro-1 H-pyrido[4,3-b]indole-8-yl)-acetic acid, compound 1] on sorbitol accumulation in ex vivo and in vivo models of diabetic complications. The effect of 1 on sorbitol accumulation in isolated rat eye lenses incubated with high glucose and in selected organs of streptozotocin-induced diabetic rats was evaluated. Significantly increased sorbitol levels were recorded in the lenses incubated with 50 mM glucose in comparison with controls. Sorbitol production was inhibited by 1 at concentrations of 25 and 100 μM. Under in vivo conditions in diabetic rats, significant elevation of sorbitol levels in selected organs was recorded. Compound 1 administered i.g. for five consecutive days (twice a day 25 mg/kg) inhibited sorbitol accumulation in erythrocytes and the sciatic nerve, yet it was without effect in eye lenses. A similar picture of inhibition was observed after i.p. administration of 1. To conclude, the results suggest that the zwitterionic principle may represent a practicable way of improving bioavailability of aldose reductase inhibitors bearing an acidic function.