Chitin and its beneficial activity as an immunomodulator in allergic reactions

Abstract

Chitin is a linear polysaccharide consisting of β-(1-4)-N-acetyl D-glucosamine residues. It is widely distributed in nature and is the second most abundant polysaccharide in nature after cellulose. It may be regarded as cellulose with hydroxyl at position C-2 replaced by an acetamino group. Chitin is a white, hard, inelastic, nitrogenous polysaccharide found in the cell walls of bacteria and fungi, mushrooms, exoskeletons of crustaceans and insects, the microfilarial sheath of parasitic nematodes, and the lining of the digestive tracts of many insects. These organisms use chitin to protect the invader from the harsh conditions inside the animal or plant host (Elias et al. 2005). It can be degraded by chitinase. Chitin is highly hydrophobic and it is insoluble in water and most organic solvents. It exists mainly in two forms: α-chitin and β-chitin. α-chitin consists of sheets of tightly packed alternating parallel and antiparallel chains (Minke and Blackwell 1978). Meanwhile, β-chitin is arranged in parallel (Gardner and Blackwell 1975), which occurs less frequently in nature than α-chitin. Being non-toxic and environmentally safe, chitin has become of great interest not only as a utilized resource, but also as a new functional biomaterial of high potential in many fields, such as medical, agricultural, and cosmetic applications. It is readily obtained for commercial use from crustacean shell waste products generated by the seafood industry (Kurita 2006; Shahidi and Synowiecki 1991; Ravi Kumar 2000; Pillai et al. 2009). Chitosan, a partially deacetylated polymer of N-acetylglucosamine, is produced commercially by the deacetylation of chitin (Aranaz et al. 2009; Dutta et al. 2004). During the past several decades, chitosan has received considerable attention due to its biodegradable, non-toxic, and non-allergenic properties, which made it possible to be used in many fields, including food, cosmetics, biomedicine, agriculture, and environmental protection (Shahidi et al. 1999; Kim and Rajapaksea 2005). Recent studies have focused on the conversion of chitosan to chitooligosaccharides (COS), since COS are not only water-soluble (Yang et al. 2010) and possess higher oral absorption (Chae et al. 2005), but they also have various biological effects, including antimicrobial, antitumor, anticancer, antioxidant, anti-inflammatory, and anti-angiotensin I-converting enzyme activities (Kim and Rajapaksea 2005; Park and Kim 2010; Xia et al. 2011). Especially, chitin and its derivatives have been determined to be therapeutic agents against allergic diseases (Catalli and Kulka 2010).