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by Acad. Konstantin SKRYABIN, RAS "Bioinzheneria" (Bioengineering) Center; Acad. Igor TIKHONOVICH, RAS Institute of Agricultural Microbiology; Valery VARLAMOV, Dr. Sc. (Chem.), Enzymes Engineering Laboratory, RAS "Bioinzheneria" (Bioengineering) Center

Lately, in these last twenty years or so, research studies of chitin, a native polymer (second only to cellulose in occurrence) and of its derivative, chitosan, have given birth to a new science, chitinology. The miraculous properties of these two compounds have found many applications in farming, industries, medicine and even in cosmetics. Ecofriendly, both substances, have important spinoffs in ecology problem solving as well.

TWO CENTURIES OF RESEARCH

Chitin, a natural polysaccharide, was first discovered by Henri Braconnot of France in champignons back in 1811. Afterwards this biopolymer was also detected in the testae of crustaceans, in the cuticles of insects, in diatoms, sea sponges and elsewhere. As Charles Rouget of France demonstrated in 1859, chitin, if treated by caustic alkali, gives rise to its acidic water-soluble modification. Next, in 1886, Ernst Hoppe-Seyler, a German biochemist, when heating chitin in the presence of potassium hydroxide at 180 °C, obtained a substance well soluble in hydrochloric and acetic acids and named later chitosan. It and related biopolymers became an object of keen interest. Three Nobel prizewinners researched in this area: Emil Fischer of Germany (Nobel Prize, 1902, for experiments in sugar and purin groups); Paul

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Karrer of Switzerland (Nobel Prize, 1937, for work on carotenoids, flavins and Vitamins A and B); Walter Haworth of Britain (Nobel Prize, 1937, for research of carbohydrates and Vitamin C). Among other things, in 1903 Fischer synthesized glucosamine (a polysaccharide produced by joint cartilage); in 1929 Karrer degraded chitin in the presence of chitinase enzymes; and in 1939 Haworth gave an absolute configuration for glucosamine.

Structurally, chitin was found to be a linear polysaccharide composed of acetylated* glucosamine residues. As to chitosan (obtained from chitin in a simple reaction of acetyl group splitoff, it includes glucosamine as a monomer. A chitosan molecule contains a large number of free amino groups that let it bind hydrogen ions, and also "trap" and retain ions of metals (radioactive isotopes and toxic elements including). This polymer also "captures" much of the water-soluble substances, bacterial toxins among them.

This country's first works in chitin modification were guided by Pavel Shorygin, an organic chemist and member of the national Academy of Sciences. His results of 1934 and 1935 showed a very low activity of this

* With reference to acetylation, substitution of acetyl, CH3 CO, an acetic acid monoatomic radical (residue), for hydrogen (H) in organic compounds.-Ed.

native polymer both in acetylation and in methylation.

In the 1930s to 1970s our scientist found vast amounts of chitin formed in the Black Sea floor during the periodic sheddings of crustaceans (amphipods, or freshwater shrimps, in particular). Also, intensive studies were carried out in those years into chitosan biochemical transformations induced by sea bacteria.

Systematic studies of chitin and chitosan and their derivatives were launched in the 1950s by Stepan Danilov of the Institute of High-Molecular Compounds in Leningrad. His team looked also into their possible uses. Chitin was found to have a high sorption ability relative to uranium atoms. The Danilov laboratory was making a close study of chitosan, its physical and chemical characteristics. It developed an appropriate production technology and the Voikov Chemical Plant in Moscow produced the first chitosan batches that found a variety of applications. Thus, if treated with cyanethylchitosan, capacitor papers improved their dielectric characteristics. Since both chitin and chitosan possess a fiber-forming ability, they were used for making self-resolving surgical materials.

In 1961 the Moscow Biophysics Institute of the national Public Health Ministry also turned to chitin. The initiator of this work was Boris Belousov, who discovered in 1951 self-excited oscillations now known also

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as the Belousov-Zhabotinsky reaction. The aim of this research, to create antiactinic (antiradiation) preparations is as topical as ever. After full-scale studies into the action mechanism of chitosan, its pharmacological activity and toxicity, a group of researchers (under Acad. Leonid Ilyin) obtained two medical drugs code-named RC-10 and RC-11. Both demonstrated high efficiency and were officially approved for patients suffering from ionizing radiation aftereffects. Then the research team of the Biophysics Institute was joined by colleagues from the RAS "Bioinzheneria" (Bioengineering) Center with Acad. Konstantin Skryabin at the head. Effective forms of low-molecular chitosan were created and patented as radiation protector.

Because of the growing catches of the Antarctic mol-lusks krills, a problem of test-containing waste disposal came to the fore. To address this problem a goal-oriented program, Krill, was forked out, with the national Research Institute of Fishing and Oceanography as the head body; many Science Academy research institutes joined up. The biological activity of chitosan and its practical uses in medicine and farming became much the trend in research. Production of this biopolymer was started in Moscow ("Sonat" firm) and in the Moscow region ("Bioprogress"), and in the Maritime Territory of the Far East.

To coordinate these activities a public organization was set up, the Russian Chitin Society (RCS), with Dr. Sc. Valery Varlamov as its head. RCS sponsors regular scientific conferences. In 2011 this public body had an honor of holding the Tenth International Conference of the European Chitin Society timed for the bicentennial of the discovery of chitin; leading chitinologists from many countries took part. This attests to a major contribution of our scientists to chitinology, a science now developing apace. The number of chitinology-related publications is rising fast: worldwide it stood at 24,300 in 2012 (27,300 patents). The accomplishments of Russian chitinologists over the past 10 to 15 years are summed up in a collective study, Chitosan (2013). The market of chitosan and related products is likewise expanding. In 2010 the total amount of chitosan on the world market was estimated at 13.7 thous. tons, and it is expected to be up to 21.4 thous. t by 2015. According to a Global Industry Analysis prognosis, the overall cost of the output of chitin and its derivatives is to reach as much as 63 bin dollars by the year 2015, and of chitosan products on the world market, 21,4 bin dollars.

CHITIN SOURCES

The testae of crustaceans, shrimps and crabs for the most part, are the main source of this native polymer. Their total catch in Russia is about 170,000 t. As much as two-thirds of this number falls on shrimps caught chiefly abroad; crabs account for 58,000 t fished chiefly in the Northeastern Atlantic (Barents Sea). The first crab

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Chitosan molecular structure. Gray balls, carbon atoms; white balls, hydrogen atoms; red balls, oxygen atoms; blue balls, nitrogen atoms.

canneries were commissioned in the Maritime Territory (Far East) 100 years ago or so. But the testa containing as much as 35 percent of chitin, 30 percent of protein as well minerals, lipids and other substances were thrown away to form huge dumps in the Pacific coastal zone. Hence a grave ecological hazard. Meanwhile in the late 1980s came a decision to build a chitin production plant at Partizansk (Maritime Territory, Far East).

Work got under way in the 1930s to acclimate the Kamchatka crab in the Norwegian Sea. This work received further impetus in the 1960s thanks to enthusiastic efforts of our scientists under the guidance of Yuri Orlov (of the Research Institute of Fishing and Oceanography). They brought to the Barents Sea females, fry and roe. The very possibility of acclimation was debated for a long time. But the project panned out-the crabs acclimated themselves well, though the expediency of this work is still questioned. The matter was clinched at the Norwegian Embassy in Moscow (2003) as Orlov got an invitation to visit it: the Norwegians thanked our country for the success of this great operation. Today the Kamchatka crab population is multiplying and exploited by Norway and Russia alike, giving, apart from delicious food, also a raw material for chitin and chitosan.

Apiculture (bee-keeping dead matter) is yet another source of chitin and chitosan. Lately, the Ural city of Perm was the venue of the 12th International RCS Conference held in June of 2014 under the auspices of

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the Tentorium Company (headed by Rail Khismatullin) specializing in apiculture products. In 2012 a plant was commissioned in Perm to treat bee-keeping dead matter. In 2001 Tentorium won a silver medal in Durban, South Africa, for the innovative technology of apisan production, with apisan being a chitosan product obtained from dead bees (Apis Mellifera).

RADIATION PROTECTION AND WATER PURIFICATION

In April of 1989 the Russian submarine Komsomolets sunk in the Norwegian Sea at a depth of 1,685 meters. That potential ecological disaster stimulated chitinology studies. In 1992 Vice-Admiral Tengiz Borisov, also a Dr. Sc, headed a team of experts to see what could be done to prevent a possible radiation leak. Since it was impossible to lift the submarine to the surface, the experts tested a great many technologies to make the sub airtight to exclude radiation leaks and preserve her there as she was. Ultimately one opted for capping devices composed of chitosan-containing polymers cross-linked by formal aldehyde. To fulfill this hard job chitosan output was stepped up in required volumes. Twenty-five years have passed since that tragic event; the capping devices installed by the mechanical arms of the Mir deep-sea explorer keep the Norwegian Sea safe from radioactive pollution as shown by tests by Norwegian and Russian scientists.

The good sorption characteristics of chitosan find application also in other areas of ecological problem solving. Thus, in many regions of this country there are problems of quality drinking water supply due to a high level of contamination and the poor condition of municipal pipelines. So, a bit of additional water purification is needed. The Sorption Laboratory of the Chemistry Institute in Vladivostok found an effective and safe method: two research scientists, Svetlana Bratskaya, Dr. Sc, and Denis Chervonetsky, suggested using water-soluble chitosan products, in particular, the "Chitofloc" flocculant and the composite "Instafloc". These reagents, if used in standard water purification systems, improve the potable water quality, boost the efficiency of water-treatment plants and bring down ecological hazards. Both purifiers are now in use at twenty enterprises of the Maritime Territory of the Far East, in private households and country cottages in the absence of central water supply when water is taken immediately from natural bodies or wells.

These reagents are just as effective in sewage treatment even if effluents contain heavy metal ions or oil emulsions. Chitosan as flocculant, if combined with sorption/filtration techniques, holds out good promise as shown by purification tests in Komsomolsk (a town in the Far East) for high-temperature emulsion effluents. This technique is also used at one of the Vladivostok-based enterprises in treating liquid radioactive wastes containing fuel oil impurities.

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Chitosan-containing flocculants were also tested at the Chernobyl Nuclear Station destroyed by a powerful blast in 1986. These tests were carried out within the framework of the International Atomic Energy Agency (IAEA) program providing for extraction of radioactive wastes and colloidal transuranium elements-their presence prevents treating such wastes conventionally. Both "Chitofloc" and "Instafloc" performed best in comparative tests against more than twenty other commercial synthetic flocculants. The purification factor versus transuranium elements topped 1,000, and the water thus treated may be fed for evaporation and cement grouting, as envisaged by the IAEI program. At the designing stage is an industrial plant for radioactive waste treatment ("Shelter") at Chernobyl.

It would be in place to note here that the work done by scientists of the Far East (RAS corresponding member Valentin Aframenko in particular) in radionuclide sorption and in obtaining the required sorbents caught the attention of Japanese nuclear physicists. A month after the Fukushima disaster of 2011, a group of Far Eastern experts received an invitation to visit Japan. The Japanese could see that the Russian sorbents and technologies are more effective than those of Japan. However, there was no headway in two-way cooperation. Unfortunately.

SPINOFFS IN MEDICINE

Russia offers a wide range of chitosan products for medicine, and many have no analogs elsewhere. For one, bandages and dressings for wet wounds and ulcers are put out among extra pure preparations in St. Petersburg; Dr. Sergei Antonov is in charge. Specific medicines added thereby help in speeding up skin and tissue reparative processes and in reducing side-effects. Used among potent compounds in dressings and bandages are the epidermal growth factor (rh-EGF), and the vascular endothelium growth factor (rh-VEGF). M.D. Igor Bol-shakov of Krasnoyarsk Medical University developed and patented original wound dressing along with products for eye doctors, dentists, and gynecologists (prevention and treatment of female genital inflammations).

Yet another Krasnoyarsk-made product: a skin substitute derived from collagen/chitosan for treating burns. Resorption (resolution) dressings are much more convenient in transplantation and in closing wound surfaces; furthermore, skin substitutes can be cultivated and subsequently used for transplantation of human epidermic skin cells and fibroblasts (connective tissue cells). It is best to use what we call pluripo-tent cells having virtually an infinite proliferation potential. Such cells can be well preserved if frozen and are always ready for transplantation. Krasnoyarsk medics have made use of imported (and certified) human embryonic cells and of embryonic animal cells (also of mice and rats). Joining hands with the Vavilov Genetics Institute in Moscow, the Krasnoyarsk scientists cultivated two new cell lines.

It became necessary to prove that embryo stem cells are viable when mounted on collagen/chitosan substrates. Indeed, embedded on such substrates and grown in a nutrient culture medium, they remain viable for a long time and capable of proliferation, with no signs of differentiation. If the culture medium is supplemented with embryonal fibroblasts or else if these cells are mounted on a monolayer, they produce a dermal/ epidermal skin equivalent in two weeks of cultivation. These innovative techniques have merited six federal patents, with two included in a list of 100 Russia's best inventions.

Yet another chitosan physical and chemical characteristic: it can produce nanoparticles through ionotropic gel formation or sedimental coacervation (separation of liquid media into bilayers); this work is being done by Dr. Alla Ilyina of the "Bioinzheneria" ("Bioengineer-ing") Center. The advantage of these two methods is in that they allow to generate nanoparticles without toxic cross-linking agents. Chitosan-based nanoparticles can help deliver biologically active substances into cells. As substrates they provide for targeted transportation of biologically active substances, reduce the dosage and prolong the effect. Such medication can be administered orally or nasally. Nanoparticles like that were used with much success in tumor therapy (by binding to the recombination alpha-2-interferon and in doxorubicin transport to tumor cells). Low-toxicity chitosan particles offer broad opportunities for targeted and controlled use of medication.

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ELUSIVE SIGNALS

Agrobiology, too, makes use of chitosan and its modifications. This is a research area of the Agricultural Microbiology Institute in St. Petersburg, with Acad. Igor Tikhonovich in charge. For many years St. Petersburg biologists have been studying how all the various microorganisms, useful and noxious alike, act upon plants. For instance, nodule bacteria were tested on leguminous plants as nitrogen suppliers (we know that nitrogen compounds are an essential nutrient). This symbiotic system is highly specific.

Say, soya plants need one kind of bacteria, pea plants are in want of other bacteria, and the lucerne, of yet another kind. And so on and so forth. There are billions of different microorganisms in soil, but a plant picks out only a definite bacterial strain to fix the molecular nitrogen.

Plants can pick and choose only on the basis of exact information. What kind of information? And how do they cope in the absence of seeing, hearing and olfaction? This question, a live issue in contemporary biology, came to the fore about thirty years ago. As it came out, plants and bacteria exchange signals. Professor Ben Lugtenberg of Leiden, Netherlands, and his pupils have found that nodule bacteria genes in control of symbiosis react to plant discharges (root exudates). Professor Sharon Long of Stanford University (USA) has made a close study of this phenomenon. Plants identify themselves by exuding certain compounds, the flavones and flavonoids, different in their structure. Plants select one or two signals with a set symbiotic genes. This is how the American researcher interpreted the very first signal. But what about the bacterial response? Geneticists said it comes from a nonprotein molecule. What in particular? At this point chemists joined in. Professor Denarie of France had a better run of luck. Bacteriologists were puzzled: it happened to be a chitin... oligomer-quite unexpectedly!

The best-known application of this compound in the farm industry is to prevent phytopathogenic attacks. Plants are quite sensitive to moieties of the chitin polymer and its deacylated derivatives-the

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chitosan. They, the plants, respond to the presence of oligosaccharides as a warning signal: there could be fungi, a source of phytopathogens, around. Picking up a signal like that, plants activate their protective systems to meet the attack in panoply. Incidentally, agrobiologists have made use of this response in designing many preparations. In the course of evolution symbiotic bacteria must have made use of the ability of plants to recognize chitin oligomers and consequently inserted their genome into a chain of chitin reproductive genes. Simultaneously, plant protective systems had to be switched off to let bacteria get in. They acquired a set of corresponding genetic determinants in the distant past, perhaps from the mucorrhiza-fungi symbiotic with the roots of higher plants; such fungi had an essential part to play hundreds of millions of years ago as plants ran roots on dry land.

Prof. Denarie surprised the research community once again by demonstrating chitooligosaccharides as signals for plants in mycorrhiza symbiosis. Let us stress that the mycorrhiza is a very old acquisition. The oldest vestiges of fungal symbiosis are discovered in strata at least 500 mln years old. Nodular symbiosis is much younger, just 70 mln years; yet it was time enough to let soil bacteria fix nitrogen and make use of signaling. The sensitivity of plants to signals is really astounding-the first symbiotic reactions of a plant occur at concentrations of 10-12 M. Such molecules can be counted. Thus the chain of "chitin relationships" tied up pathogens and pests with symbiotic fungi and bacteria. Nature was not choosy overmuch and opted for a ready scenario. Hence the significance of polysaccharides-one cannot regulate interrelations between microorganisms and plants without mastering an oligosaccharide modification technology.

Obtaining chitin oligomers is a hard job for chemists. Their main method: the polymer's chemical hydrolysis resulting in a reaction mixture of different structure. However, it contains large chitin fragments (20 to 30 monomeric residues), with the output of the end product being very low. Since compounds of preas-signed structure and in large amounts were needed for

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pretreatment of plants, scientists had to explore for new modes of obtaining chitin oligomers. Microbes coped fine. A research team under Acad. Igor Tikhonovich and Dr. Yelena Dolgikh (All-Russia Institute of Agricultural Microbiology) suggested using enzymes of nodule bacteria. One such enzyme encoded by the nodC gene controls this process. Used thereby were bacterial enzymes that synthesize compounds of five or six monomers (such oligomers act like elicitors, or growth and root formation bioregulators). The final choice was the nodC enzyme of two nodule bacteria-the Mesorhizo-bium loti (leguminous symbion) and the Rhizobium sp. GRH2 (acacia symbion).

The nodC gene of these two nodule bacterial species were then implanted as plasmid into E.coli bacteria. E.coli is a pet object of contemporary biotechnology: this bacterium is a must if a sufficient amount of the product is to be obtained. Chitooligosaccharides thus produced proved to be biologically active in inducing protective reaction and in enhancing plant resistance to fungic infections.

Thus, with the aid of their knowledge of signaling molecules that control the symbiosis of plants and microorganisms, biologists succeeded in solving the problem of synthesizing substances for the farm industry first and foremost. These compounds, too, may be wanted in pharmacology. Biologically quite neutral and not charged, a chitooligosaccharide molecule can get across cell membranes and, consequently, is convenient for medication delivery.

An interesting run-on of this research: the biosynthesis of terminally N-deacetylated chitin oligomers mediated by Rhizobium soil bacteria enzymes. E.coli strains were thus obtained with genetic structures required for the synthesis of terminally deacetylated chitooligosaccharides. These works were awarded a gold medal at a St. Petersburg-held exhibition in 2011.

"NARCISSUS", "POLYCHIT" AND OTHERS

The works on chitin and chitosan helped in realizing many research projects in biotechnology, in agriculture and the food industry. The production of these biopoly-mers, their derivatives and composites is under way at Shchelkovo, Moscow. This project was launched at the All-Russia Research and Technology Institute of the Biological Industry under Dr. Anatoly Samuilenko and Dr. Alexei Albulov. The output of enterosorbents is on to treat intestinal diseases of livestock youngsters. These drugs have been tested on calves in the Kursk, Tula and Moscow administrative regions. The output of the chitosan-containing preparations Narziss and AgroChit has been launched; these products stimulate the growth of grain, potato and hothouse crops and make them pest-resistant.

The Bioprogress Company has opened a production line for the output of biologically active food additives of more than twenty trademarks: ChitAN, PolyChit, Phyto-Chitodez-02 and other related products. This enterprise has produced chitosan sorbents for the output of low-allergenic milk foods. Elimination of the allergenic protein β-lactoglobulin from whey via chitosan-medi-ated sorption has made it possible to put out hypoal-lergenic milk foods for children (since 2013 such foods have been produced in Voronezh). The prior research was conducted by "Bioinzheneria" in keeping with a federal contract.

Many products and technologies developed by us have no analogs elsewhere in the world and are among major achievements of Russian scientists. We have received over 100 federal patents and published more than 300 articles at home and abroad in high-rating journals.

For the project providing for the output of chitin-based products for practical uses in medicine, the food industry and biotechnology the research collective headed by Acad. Tikhonovich has merited a 2013 federal government prize in science and engineering.

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