Galactosemic Cataract - Galactitol's Harmful Influence

Galactitol's Harmful Influence

In galactosemic cataracts, osmotic swelling of the lens epithelial cells (LEC) occurs. Osmosis is the movement of water from areas of low particle concentration to areas of high particle concentration, to establish equilibrium. Researchers concluded that this osmotic swelling must be the result of an accumulation of abnormal metabolites or electrolytes in the lens. Ruth Van Heyningen was the first to discover that the lens’s retention of dulcitol, synonymous for galactitol, induces this osmotic swelling in the galactosemic cataract. However, galactose concentration must be fairly high before the enzyme, aldose reductase, will convert significant amounts of the sugar to its galactitol form. As it turns out, the lens is a favorable site for galactose accumulation. The lens phosphorylates galactose at a relatively slow pace in comparison to other tissues. This factor, in combination with the low activity of galactose-metabolizing enzymes in galactosemic patients, allows for the accumulation of galactose in the lens. Aldose reductase is able to dip into this galactose reservoir and synthesize significant amounts of galactitol. As is mentioned above, galactitol is not a suitable substrate for the enzyme, polyol dehydrogenase, which catalyzes the next step in the carbohydrate metabolic cycle. Thus, the sugar alcohol idly begins to accumulate in the lens.