Rat kidney aldose reductase and aldehyde reductase and polyol production in rat kidney

Mounting evidence indicates that aldose reductase catalyzed reduction of excess glucose to sorbitol initiates the onset of certain diabetic complications. However, the kidney contains a large amount of aldehyde reductase, another NADPH-dependent reductase. The study was designed to assess the importance of these reductases to sugar alcohol (polyol) production in the kidney. To study the ability to reduce aldoses to polyols, both aldose and aldehyde reductases were purified from rat kidneys. Incubation studies with purified enzymes clearly demonstrated the polyol formation by both enzymes. Galactose feeding induced polyol accumulation in both medulla and cortex of the rat kidney. Al 1576, a potent inhibitor of both enzymes, reduced this polyol accumulation in both cortex and medulla, while the selective inhibitors Ponalrestat or FK 366 resulted in greater inhibition in medulla than cortex. These results suggest that kidney polyols may be generated by both aldose and aldehyde reductases and that aldehyde reductase contributes to polyol production in the kidney cortex, the predominant site of diabetes-linked kidney lesions.