Polyol pathway

Overview

The polyol pathway is a two-step metabolic pathway that converts glucose into fructose. This pathway is particularly active in tissues such as the lens of the eye, the nervous system, and the kidney. It plays a significant role in the development of complications in diabetes, particularly in the formation of cataracts and diabetic neuropathy.

Diagram of the polyol metabolic pathway

Steps of the Pathway

The polyol pathway consists of two main enzymatic reactions:

Aldose Reductase

The first step involves the enzyme aldose reductase, which reduces glucose to sorbitol, a type of sugar alcohol. This reaction uses NADPH as a cofactor. Aldose reductase is the rate-limiting enzyme of the polyol pathway and is found in various tissues.

Sorbitol Dehydrogenase

In the second step, sorbitol dehydrogenase oxidizes sorbitol to fructose. This reaction uses NAD+ as a cofactor. The conversion of sorbitol to fructose is crucial because sorbitol is osmotically active and can accumulate in cells, leading to osmotic stress.

Clinical Significance

The polyol pathway is implicated in the pathogenesis of diabetic complications. In conditions of hyperglycemia, such as in uncontrolled diabetes, excess glucose is shunted into the polyol pathway. This leads to the accumulation of sorbitol and fructose, which can cause osmotic and oxidative stress in cells.

Diabetic Neuropathy

In diabetic neuropathy, the accumulation of sorbitol in nerve cells can lead to nerve damage. The osmotic stress and oxidative damage from the polyol pathway are thought to contribute to the degeneration of nerve fibers.

Diabetic Retinopathy

In the eye, the accumulation of sorbitol in the lens can lead to the development of cataracts. The osmotic imbalance caused by sorbitol accumulation results in lens swelling and opacification.

Inhibition of the Polyol Pathway

Inhibitors of aldose reductase have been studied as potential therapeutic agents to prevent or reduce the complications of diabetes. By inhibiting the first step of the polyol pathway, these drugs aim to reduce the accumulation of sorbitol and its associated damage.

Related Pages

• Diabetes mellitus
• Aldose reductase
• Sorbitol
• Fructose
• Diabetic neuropathy
• Cataract