|Chitosan (other name: poliglusam)|
Chitosan (pronounced /ˈkaɪtɵsæn/) is a linear polysaccharide composed of randomly distributed β-(1-4)-linked D-glucosamine (deacetylated unit) and N-acetyl-D-glucosamine (acetylated unit). It has a number of commercial and possible biomedical uses.
Chitosan is produced commercially by deacetylation of chitin , which is the structural element in the exoskeleton ofcrustaceans (crabs, shrimp, etc.) and cell walls of fungi. The degree of deacetylation (%DD) can be determined by NMRspectroscopy, and the %DD in commercial chitosans is in the range 60-100 %.
|Commercial chitosan is derived from the shells|
of shrimp and other sea crustaceans, including
Pandalus borealis, pictured here.
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. This makes chitosan a bioadhesive which readily binds to negatively charged surfaces such as mucosal membranes. Chitosan enhances the transport of polar drugs across epithelial surfaces, and is biocompatibleand 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.
- Agricultural and horticultural use
- Natural biocontrol and elicitor
- In agriculture, chitosan is used primarily as a natural seed treatment and plant growth enhancer, and as a ecologically friendly biopesticide substance that boosts the innate ability of plants to defend themselves against fungal infections. The natural biocontrol active ingredients, chitin/chitosan, are found in the shells of crustaceans, such as lobsters, crabs, andshrimp, and many other organisms, including insects and fungi. It is one of the most abundant biodegradable materials in the world. Degraded molecules of chitin/chitosan exist in soil and water. Chitosan applications for plants and crops are regulated by the EPA, and the USDA National Organic Program regulates its use on organic certified farms and crops. EPA approved biodegradable chitosan products are allowed for use outdoors and indoors on plants and crops grown commercially and by consumers. The natural biocontrol ability of chitosan should not be confused with the effects of fertilizers or pesticides upon plants or the environment. Chitosan active biopesticides represent a new tier of cost effective biological control of crops for agriculture and horticulture
- The biocontrol mode of action of chitosan elicits natural innate defense responses within plant to resist insects, pathogens, and soil-borne diseases when applied to foliage or the soil. Chitosan increases photosynthesis, promotes and enhances plant growth, stimulates nutrient uptake, increases germination and sprouting, and boosts plant vigor. When used as seed treatment or seed coating on cotton, corn, seed potatoes, soybeans, sugar beets, tomatoes, wheat and many other seeds, it elicits an innate immunity response in developing roots which destroys parasitic cyst nematodes without harming beneficial nematodes and organisms. Agricultural applications of chitosan can reduce environmental stress due to drought and soil deficiencies, strengthen seed vitality, improve stand quality, increase yields, and reduce fruit decay of vegetables, fruits and citrus crops (see photo right). Horticultural applications of chitosan increases blooms and extends the life of cut flowers and Christmas trees. The US Forest Service has conducted research on chitosan to control pathogens in pine trees. and chitosan's ability to increase pine tree resin pitch outflow by 40% to resist pine beetle infestation.
- Chitosan has a rich history of being researched for applications in agriculture and horticulture dating back to the 1980s. By 1989, Bentech Labs patented chitosan salt solutions applied to crops for improved freeze protection or to crop seed for seed priming. Shortly thereafter, Bentech's chitosan salt received the first ever biopesticide label from the EPA. Numerous other chitosan patents for plants soon followed. Chitosan applications to protect plants have been used in space as well. NASA first flew a chitosan experiment to protect adzuki beans grown aboard the space shuttle and Mir space station in 1997 (see photo left). NASA results revealed chitosan induces increased growth (biomass) and pathogen resistance due to elevated levels of beta 1-3 glucanase enzymes within plant cells. NASA confirmed chitosan elicits the same effect in plants on earth. Over 20 years of R&D by DuPont/ConAgra Ventures (DCV) and AgriHouse Inc have gone into developing non-toxic low molecular weight chitosan polymer solutions safe enough for broad spectrum agricultural and horticultural use. In 2008, AgriHouse Inc, Denver (Berthoud), Colorado, was granted EPA natural broad spectrum elicitor status for YEA! Yield Enhancing Agent, a liquid solution containing an ultra low molecular active ingredient of 0.25% chitosan. YEA! is a next generation natural chitosan elicitor solution for agriculture and horticultural uses, and was granted an amended label for foliar and irrigation applications by the EPA in June, 2009. A milliliter of YEA! contains over 14.4 X 10¹³ bioactive low molecular weight chitosan molecules, and it is 600 times more effective than common chitosan. Given its low potential for toxicity and its abundance in the natural environment, chitosan does not harm people, pets, wildlife, or the environment when used according to label directions. Agricultural chitosan facts are located on USDA and EPA web sites.
- Water Filtration
- 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. Chitosan has been used to precipitate caseins from bovine milk and cheese making. 
- 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) with which to flocculate.
- Industrial use
- Scientists have recently developed a polyurethane coating that heals its own scratches when exposed to sunlight, offering the promise of scratch-free cars and other products. The self-healing coating uses chitosan incorporated into traditional polymer materials, such as those used in coatings on cars to protect paint. When a scratch damages the chemical structure, the chitosan responds to ultraviolet light by forming chemical chains that begin bonding with other materials in the substance, eventually smoothing the scratch. The process can take less than an hour.
- Marek W. Urban, a scientist working on this project, said the polymer can only repair itself in the same spot once, and would not work after repeated scratches.
- Biomedical use
- Chitosan's properties allow it to rapidly clot blood, and has recently gained approval in the United States and Europe for use in bandages and other hemostatic agents. Chitosan hemostatic products have been shown in testing by the U.S. Marine Corps to quickly stop bleeding, and result in 100% survival of otherwise lethal arterial wounds in swine and to reduce blood loss. Chitosan hemostatic products reduce blood loss in comparison to gauze dressings and increase patient survival. Chitosan hemostatic products have been sold to theU.S. Army and are currently used by the UK military. Both the US and UK have already used the bandages on the battlefields of Iraq and Afghanistan. Chitosan is hypoallergenic and has natural antibacterial properties, which further support its use in field bandages.
- Claimed health benefits
- Chitosan is frequently sold in tablet form at health stores as a "fat binder": It is supposed to have the capability to interact with lipids (fat) from the digestive system and limit their absorption in the body. Therefore, chitosan can be an effective complement to help lose weight during diet period or to stabilise one's weight. In the 2007 Cochrane meta-analysiswhich evaluated all available clinical trials performed with chitosan on the subject of weight loss, it was concluded that body weight and all parameters related to cholesterol changed in favor of chitosan compared to placebo. The mean difference in body weight was −1.7 kg (range: −2.1 to −1.3) in favor of chitosan. This change in body weight was statistically significant. There was no difference between chitosan and placebo concerning side effects. The various qualities (in terms of duration, sample size, doses, subject characteristics, type of diet, chitosan quality and characteristics, etc.) of the clinical trials performed to evaluate the effect of chitosan on body weight might account for some of the disparities observed in clinical trial results  and the subsequent critics regarding the real efficacy of chitosan. In an experimental model of the stomach and duodenum tract, chitosan has shown to interact with oil, which inhibited duodenal absorption and enhanced lipid excretion. However, the mechanism of interaction between chitosan and fat is not very well understood and has not been really proved clinically yet. This is certainly the reason why the FDA has issued in 2004 Warning Letters to 2 companies who made inappropriate claims according to the regulator. Although detractors claim that using chitosan may have the deleterious effect of rendering ineffective certain minerals found in foodstuffs, several animal studies contradicted this statement by showing no or little effect. In mice, dietary ingestion of chitosan did not depress the level of iron, zinc or copper. Moreover, there is no proof of any adverse events, in particular regarding nutrient absorption, in humans.
Chitosan is currently the focus of much medical research, as it is a polyglucosamine (the second-most-common dietary fiber, after cellulose). Studies have shown chitosan has the following properties:
- As a soluble dietary fiber, it increases gastrointestinal lumen viscosity and slows down the emptying of the stomach.
- It alters bile acid composition, increasing the excretion of sterols and reducing the digestibility of ileal fats. It is unclear how chitosan does this, but the currently favored hypotheses involve the increase of intestinal viscosity or bile acid-binding capacity.
- Chitosan is relatively insoluble in water, but can be dissolved by dilute acids, which would make it a highly-viscous dietary fiber. Such fibers might inhibit the uptake of dietarylipids by increasing the thickness of the boundary layer of the intestinal lumen, which has been observed in animal experiments.
- Having very few acetyl groups, chitosan contains cationic groups. This may cause chitosan to have bile acid-binding capacity, which causes mixed micelles to be entrapped or disintegrated in the duodenum and ileum. This would interrupt bile acid circulation, causing reduced lipid absorption and increased sterol excretion, which has also been observed in animal experiments.
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