Zenarestat

Polyneuropathy, damage of peripheral neurons, is common in diabetes mellitus patients and causes pain, sensory and motor deficits in the limbs. Zenarestat is an aldose reductase inhibitor which inhibits the metabolism of glucose by the polyol pathway, which possibly slows or reduces progression of polyneuropathy. Chronic hyperglycemia affects peripheral nerves by an extracellular mechanism with many types of glycation reactions and chemical rearrangements, and an intracellular route involving increased amounts of glucose passing through the polyol pathway. The polyol pathway allows cells to produce fructose from glucose, and has two steps, which require energy and enzymes. Aldose reductase catalyzes the conversion of glucose to sorbitol in the first step, while the second involves the oxidation of nicotinamide adenine dicnucleotide phosphate (conversion of NADPH to NADP). Chronic hyperglycemia causes damage by overactivity of the polyol pathway, causing a decrease in cellular NADPH levels, reducing the amount of glutathione (a free radical scavenger), and nitric oxide (a vasodilator), as well as increasing cellular sorbital levels, causing decreased levels of myo-inositol (necessary for Na-K ATPase function) and increased fructose, thus increasing AGE (advanced glycosylation end products), the byproduct of the polyol pathway. The suppression of the first step in the polyol pathway by zenarestat prevents these deleterious processes from occuring.