Intestinal transport and metabolism of oxidized ascorbic acid (dehydroascorbic acid)

The transport and metabolic properties of dehydroascorbic acid have been evaluated in the small intestine of one ascorbic acid-dependent animal species (guinea pig) and one ascorbic acid-synthesizing animal species (rat). Loops of guinea pig jejunum in vitro brought about net transepithelial absorption of L-[14C]dehydroascorbic acid with most of the absorbed substrate appearing in the reduced form (ascorbic acid). Saturation of brush-border transport occurs at a lower concentration than saturation of the enzymatic reduction. Rat intestine did not bring about net transepithelial transport. The intestines of both guinea pigs and rats took up substantial dehydroascorbic acid from the serosal bathing solution, with the majority appearing in the mucosa as ascorbic acid. It is proposed that in guinea pig intestinal mucosa, dehydroascorbic acid reductase has a nutritional role in extracting the vitamin from chyme and reducing it for subsequent use in the body. The intestines of both guinea pig and rat appear to take up dehydroascorbic acid across the basolateral surface and reduce it, thus maintaining a substantial endogenous level of ascorbic acid in the mucosa. The transport and metabolic properties described might play an important role as a protective antioxidant mechanism in intestinal mucosa.