Role of Chitinases in Human Stomachfor Chitin Digestion: AMCase in theGastric Digestion of Chitin and Chit inGastric Pathologies

Chitin-containing food is an interesting but underestimated source of locally available, in most cases sustainable, food although chitin digestion by humans has generally been questioned or denied. Only in recent times chitinases have been found in several human tissues and their role has been associated with defence against parasite infections as well as with some allergic conditions. We reflected that crustaceans, and to some extent molluscs, mushrooms and most arthropods containing chitin, are sometime a consistent part of food regimes for local communities. Finally, we demonstrated that AMCase is present in gastric juices and it is associated with chitin digestion. In most tropical and some temperate countries, such as Japan and Korea, a significant number of adult insects and larvae are consumed raw, or cooked along with diverse local specialities. At present, up to 2,000 species of insects and other terrestrial arthropods have been listed as edible in Africa, Asia, Central and South America, Australia and Europe. Both insects and crustaceans are covered by chitin teguments and mushrooms contain some chitin. In most cases, the hard covering of polysaccharide chitin on insects accounts for 5-20% of their dry weight. In general, chitinases can digest chitin and reduce it to simple compounds such as N-acetyl-glucosamine. Western society does not consider insects an important food, however: crustaceans, such as lobsters and crabs, are commonly eaten after discarding the hardened chitin-rich tegument, with the exception of small shrimps, which are generally eaten fried. Therefore, Western nutrition does not seem to depend on chitinases. These and other considerations, including the absence of chitin as a human body component, have led us to ask whether humans are capable of chitin digestion. To assess chitinases’ function as tools to digest chitin, we have examined 48 patient’s gastric juices, obtained during gastroscopy, at Padova University Hospital. We found that 14.6% of total samples studied showed AMCase activity from 36.270 to 3.540 nmol/ml/h. The majority of involved subjects (75%) had lower values, from 2.800 to 0.178 nmol/ml/h; while in 10.4% of subjects the chitinolitic activity varied from 0.086 to 0.013 nmol/ml/h, and could be considered absent. We reported superficial digestion of fly forewings, utilizing gastric juice of a patient with an AMCase activity of 19.410 nmol/ml/h. If AMCase enzyme, present in gastric juice, is truly involved in chitin digestion, we should expect a higher presence of expressed AMCase in populations currently accustomed to eating mushrooms and/or invertebrates bearing chitin. We also found a positive relationship between CHIT expression level in antral gastric mucosa and both flogosis and Helicobacter pylori infection.