In vitro intestinal degradation and absorption of chondroitin sulfate, a glycosaminoglycan drug.

Chondroitin sulfate (CAS 24967-93-9, CS) is a natural polymer of a disaccharide consisting of glucuronic acid and N-acetyl glucosamine which is sulfated either in the 4 or 6 position. It is administered orally as a slow acting drug to treat osteoarthritis, though there is much debate about its effectiveness and its mode of action, given that macromolecules are not normally absorbed in the gastrointestinal (GI) tract. Initially using a spectrophotometric assay, the stability of CS was tested in the presence of both tissues and lumenal contents of stomach, small intestine, cecum and colon. There was no degradation by the contents of the stomach or small intestine or in any of the tissues. Degradation only took place in the contents of the colon and particularly the cecum. Using 14C-radiolabelled CS it was shown that the cecum contents degraded CS down to the component disaccharides. The 14C-radiolabelled CS was also used to investigate the transport of CS across the different parts of the GI tract in vitro. The CS was transported across the small intestine in low amounts in the intact form, probably by the mechanism of endocytosis. In the colon and the cecum, higher amounts of radioactivity were transported, but most of the radioactivity was in the form of the degradation products, the disaccharides. This study shows that small amounts of CS may cross the upper intestine intact, but in the distal GI tract the molecule is effectively degraded, presumably by the enzymes in the intestinal flora.