Effect of inhibition of aldose reductase on glucose flux, diacylglycerol formation, protein kinase C, and phospholipase A2 activation.

Activation of the polyol pathway under hyperglycemic conditions is proposed to contribute to the development of diabetic nephropathy. The mechanisms by which this activation may lead to functional and structural changes within the kidney are yet to be definitively established. We have examined in vitro the steps linking increased polyol pathway activity resulting from hyperglycemia to prostaglandin production. Following the demonstration of increased prostaglandin E (PGE) levels in glomeruli from diabetic rats (14.9 +/- 2.5 v 59.1 +/- 19.4 ng PGE/mg protein), a specific inhibitor of aldose reductase, HOE-843, was used in vitro to analyze the response to hyperglycemia of the steps preceding prostaglandin production. In explants of glomeruli from control animals, increasing the glucose concentration in vitro from 5.6 mmol/L to 25 mmol/L resulted in a significant increase in the flux of glucose through the pentose phosphate pathway ([PPP] 1.29 +/- 0.08 v 2.00 +/- 0.11 nmol/h), de novo diacylglycerol synthesis (2.2 +/- 0.1 v 3.1 +/- 0.2 micromol/mg protein), membrane protein kinase C (PKC) activity (18.7 +/- 0.5 v 24.3 +/- 0.75 pmol/microg protein), and in vitro phospholipase A2 (PLA2) activity (2.18 +/- 0.46 v 3.83 +/- 1.07 nmol arachidonic acid hydrolyzed/min/mg cytosolic protein). For all parameters measured, the increase resulting from the increased glucose concentration could be prevented by in vitro addition of HOE-843 for 24 hours before measurement. These findings provide evidence to suggest a mechanism linking increased polyol pathway activity and an increase in PLA2 activity to increased prostaglandin production, which is observed in diabetes of recent onset and may ultimately lead to changes associated with the development of diabetic nephropathy.