Chitosan

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Chitosan is a linear polysaccharide composed of randomly distributed ß-(1-4)-linked D-glucosamine (deacetylated unit) and N-acetyl-D-glucosamine (acetylated unit). It has a number of commercial and possible biomedical uses.

[edit] Manufacture and properties

Commercial chitosan is derived from the shells of shrimp and other sea crustaceans, including Pandalus borealis, pictured here.^[1]

Chitosan is produced commercially by deacetylation of chitin (can be produced from chitin also), which is the structural element in the exoskeleton of crustaceans (crabs, shrimp, etc.). The degree of deacetylation (%DA) can be determined by NMR spectroscopy, and the %DA in commercial chitosans is in the range 60-100 %.

The amino group in chitosan has a pKa value of ~6.5, thus, chitosan is positively charged and soluble in acidic to neutral solution with a charge density dependent on pH and the %DA-value. In other words, chitosan is bioadhesive and readily binds to negatively charged surfaces such as mucosal membranes. Chitosan enhances the transport of polar drugs across epithelial surfaces, and is biocompatible and biodegradable. Purified qualities of chitosans are available for biomedical applications.

Chitosan and its derivatives such as trimethylchitosan (where the amino group has been trimethylated) have been used in non-viral gene delivery. Trimethylchitosan, or quaternised chitosan, has been shown to transfect breast cancer cells; with increased degree of trimethylation increasing the cytotoxicity and at approximately 50% trimethylation the derivative is the most efficient at gene delivery. Oligomeric derivatives (3-6 kDa) are relatively non-toxic and have good gene delivery properties.^[2]

[edit] Usage

Chitosan is used primarily as a plant growth enhancer, and as a substance that boosts the ability of plants to defend against fungal infections. It is approved for use outdoors and indoors on many plants grown commercially and by consumers. The active ingredient is found in the shells of crustaceans, such as lobsters, crabs, and shrimp, and in certain other organisms. Given its low potential for toxicity and its abundance in the natural environment, chitosan is not expected to harm people, pets, wildlife, or the environment when used according to label directions.^[3]

Chitosan can also be used in water processing engineering as a part of a filtration process. Chitosan causes the fine sediment particles to bind together and is subsequently removed with the sediment during sand filtration. Chitosan also removes phosphorus, heavy minerals, and oils from the water. Chitosan is an important additive in the filtration process. Sand filtration apparently can remove up to 50% of the turbidity alone while the Chitosan with sand filtration removes up to 99% turbidity.^[4]

Chitosan is also useful in other filtration situations, where one may need to remove suspended particles from a liquid. Chitosan, in combination with bentonite, gelatin, silica gel, isinglass, or other fining agents is used to clarify wine, mead, and beer. Added late in the brewing process, chitosan improves flocculation, and removes yeast cells, fruit particles, and other detritus that cause hazy wine. Chitosan combined with colloidal silica is becoming a popular fining agent for white wines, because chitosan does not require acidic tannins (found primarily in red wines) to flocculate with.^[5]

[edit] Biomedical use

Chitosan's properties allow it to rapidly clot blood, and has recently gained approval in the USA for use in bandages. The bandages include a layer of carefully produced chitosan that, when applied to a wound, causes rapid clotting, stopping the bleeding. Chitosan is hypoallergenic, and has natural anti-bacterial properties, further supporting its use in field bandages.^[6]

[edit] Claimed benefits

Chitosan is frequently sold in tablet form at health stores as a 'fat attractor': It is supposed to have the capability of attracting fat from the digestive system and expelling it from the body so that users can, it is claimed, lose weight without eating less. However, some scientific research suggests that these claims are likely without substance. At best, unmodified chitosan would remove roughly 30 calories per day from a person's diet. Modfied chitosan is claimed to absorb anywhere up to three to six times its weight in fat and oils. Detractors claim that using chitosan may have the deleterious effect of rendering ineffective certain minerals found in foodstuffs and required by the body in order to remain healthy.

Other benefits which chitosan claims to have other than weight loss include inhibiting LDL cholesterol and boosting HDL cholesterol. It can also promote the healing of ulcers and lesions, help control blood pressure, reduce blood levels of uric acid, help prevent constipation, act as an antacid, help prevent irritable bowel syndrome, enhances calcium to strengthen bones, inhibits plaque/tooth decay, and offers anti-tumor action. None of these are supported by rigorous scientific evidence.

[edit] External links

• The Chitosanase Web Page – dedicated to the enzymatic hydrolysis of chitosan.
• ScienCentral News "But now, scientists have created a bandage that is actually able to clot a bullet wound in less than a minute. The bandages are laced with a mixture of ground shrimp shells and vinegar, a concoction that has been found to clot blood instantly. The key ingredient in the shrimp shells is called chitosan."
• A Critical look on ChitosanA critical look on the claims how chitosan can be used for weight management
• Revolutionizing Weight Loss? James Fritz' article on Chitosan's claim.
• Facts on Chitosan Chitosan fails to reduce the weight

[edit] Footnotes