galactitol

Galactitol, also known as dulcitol, is a hexitol sugar alcohol derived from galactose by reduction of the aldehyde group. It has the chemical formula C6H14O6 and is highly soluble in water. In mammals, galactitol is produced in the polyol pathway when galactose is present, via the action of the enzyme aldose reductase on galactose.

Biological and medical significance: Galactitol is not readily metabolized further in many tissues. When galactose levels are elevated, such as in galactosemia, galactitol can accumulate in tissues including the lens, kidney, and retina. Its accumulation increases osmotic pressure, drawing water into cells and contributing to osmotic stress; this mechanism is associated with cataract formation in affected individuals. In contrast to some other sugar alcohols, galactitol is not efficiently oxidized and cleared in humans, so its buildup can be more pronounced under high galactose exposure.

Occurrence in microorganisms: In certain bacteria, dulcitol can serve as a carbon source. Its uptake and metabolism are often encoded by the dulcitol (gat) operon, enabling growth on galactitol as a sole carbon source in organisms such as some strains of Escherichia coli.

Notes and context: Galactitol is one of several sugar alcohols formed by reduction of monosaccharides; others include sorbitol (from glucose) and mannitol (from mannose). Its biological relevance is primarily linked to conditions that elevate galactose levels, rather than routine metabolism.