What substance accumulates and causes cataracts, neuropathy, and retinopathy in diabetes mellitus?

In diabetes mellitus, the accumulation of sorbitol leads to various complications, including cataracts, neuropathy, and retinopathy. This process is primarily due to the activity of the enzyme aldose reductase, which converts glucose into sorbitol, a sugar alcohol. In the context of hyperglycemia, which is common in diabetes, there is an increased flux of glucose through this pathway, leading to excessive sorbitol production.

Sorbitol is not effectively transported out of cells, resulting in osmotic and oxidative stress. This accumulation of sorbitol is particularly implicated in the pathogenesis of diabetic complications: for instance, it plays a significant role in the development of cataracts via lens epithelial cell damage due to increased osmotic pressure, leads to neuropathy by affecting nerve tissues, and contributes to retinal damage in diabetic retinopathy.

In summary, elevated levels of sorbitol due to its formation from glucose under hyperglycemic conditions are key in causing the complications seen in diabetes mellitus, highlighting the importance of sorbitol in this context.