Analgesic effects of chitin and chitosan

The analgesic effects of chitin and chitosan on inflammatory pain were evaluated using the acetic-acid-induced writhing test in mice. When chitin and chitosan suspensions were mixed with the 0.5% acetic acid solution (chitin-AC and chitosan-AC, respectively) and administered intraperitoneally in mice, both agents induced a dose-dependent decrease in the number of the abnormal behaviors (writhing) due to pain, including extension of the hind legs, abdominal rigidity, and abdominal torsion. This effect was greater in the animals administered the chitosan-AC than in those administered the chitin-AC. In vitro study indicated that addition of the chitin or chitosan suspension increased the pH of the AC, and that this effect was greater in the chitosan than the chitin. Furthermore, the level of bradykinin in the peritoneal lavage fluid in the animals administered the chitin-AC was lower than in the animals administered the chitosan-AC. In vitro study showed that the chitin particles absorbed bradykinin more extensively than the chitosan particles. These results suggest that the main analgesic effect of chitosan is the absorption of proton ions released in the inflammatory site, while that of chitin is the absorption of bradykinin.