Is chitin biodegradable in human tissues?
Chitin-degrading enzymes are very widespread in nature, and they also occur in humans. Three human chitinases are known. The best known human enzyme with chitinase activity is lysozyme occurring e.g. in tears. Probably the primary substrate for lysozyme is polysaccharide backbone of peptidoglycan in bacterial cell walls. Peptidoglycan is a linear polymer of β-1,4-glycosidically linked N-acetylglucosamine and N-acetylmuramic acid residues, the latter one being a lactic acid ether of N-acetylglucosamine. Thus, its structure resembles that of chitin, so that lysozymes can often degrade both polymers. The other two chitin-degrading enzymes in humans are true chitinases, namely chitotriosidase which is produced and secreted mostly by macrophages and, thus, also occurs in blood, and acidic mammalian chitinase which is probably expressed mostly in the human lung (while it seems to be much more abundant in other mammalians such as mice). These chitin-degrading enzymes are responsible that e.g. chitin-based surgical suture materials are slowly decomposing in the tissue, yielding the natural monomer N-acetylglucosamine which can be taken up by the human cells and re-used for the synthesis of e.g. glycosaminoglycans.