Preparation and biological activities of chitosan oligosaccharides

Chitosan oligosaccharides (COSs) are the degraded products prepared from the deacetylation and depolymerization of chitin or chitosan using physical, chemical, or enzymatic hydrolysis. In comparison to chitosan and chitin, COS, the hydrolyzed form, has lower molecular weight, lower degree of polymerization (DP), higher degree of deacetylation (DD), less viscosity, more solubility, absorbability though GI tract, biodegradability, biocompatibility, and exposed N-glucosamine units. These properties provide beneficial effects and great potential for biomedical and life science applications. The prominent biological activities of COSs include anti-bacteria, anti-fungi, anti-tumor, immunoregulation, antioxidant, and anti-inflammation that are effective for the therapy and prevention of many life-threatening diseases, such as cancer, heart disease, diabetes mellitus, and serious infections. Compared with chitin, COSs have outstanding advantages: 1) they are easily soluble in water; 2) they have no antigenicity; 3) they have weak accumulation effect in host body. Moreover, COSs have excellent biological activities in various aspects. Therefore, the development prospect is very broad. However, the research on the preparation and mechanism of COSs is not deep enough so far. The COSs prepared by the present methods are very limited, so they are expensive, and their application is limited. How to produce these COSs on a large scale with low cost and high yield, elucidating their mechanism of action, and preparing into the medicament that is easy to dissolve, easy to absorb and easy to use in the body environment, have become the focus of current research. It is believed that with the efforts of many scholars, COSs will benefit mankind in the near future.