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Kamilova Iroda Abdurasulovna, Head of the Woman Wellness Center Tashkent Medical Academy, Uzbekistan E-mail: irodakamilova@mail.ru Yunusov Khaydar Ergashevich, DSc (Technical)
Institute of Polymer Chemistry and Physics, Uzbekistan Project Leader at the Cellulose and its Derivatives Chemistry and Technology Laboratory E-mail: haydar-yunusov@rambler.ru Sarymsakov Abdushukur Abdukhalilovich,
DSc (Technical)
Institute of Polymer Chemistry and Physics, Uzbekistan Professor, Head of Laboratory of Cellulose and its Derivatives Chemistry and Technology E-mail: polymer@academy.uz
HORIZONS AND CHALLENGES OF THE SILVER NANOPARTICLES APPLICATION IN THE PRACTICAL MEDICINE (REVIEW PAPER)
Abstract: Based in the literature review devoted to analysis of the current status of the issue of synthesis and stabilization of the silver nanoparticles (NP) and medical claims on their basis, it has been identified that transition from the macro-scale and micro-scale to the nanoscale causes emergence of qualitative modifications in the physical - chemical and medical - biological properties of compounds along with polymer systems obtained on their basis.
Synthesis and investigation of the silver NP stabilized in the polymer matrices are currently presenting promising trends in the polymer chemistry and medicine.
Keywords: nanotechnologies, nanoparticles, silver, silver nitrate, nanostructure, nanocluster, nanocomposites.
Since end of 80-s last century, the new terms with "nano" Over 20 recent years, globally, the technologies focused prefix appeared in scientific terminology, such as: nanotech- on obtainment and application of NP and nanostructures ma-nology, nanostructure, nanocomposite material, nanoclu- terials based mostly on the metals are being rapidly developed. ster, nanochemistry, nanophysics, nanobiotechnology, etc. In the present message we have considered the possibili-Scientific centres, institutes, chares and scientific schools ties of obtainment and research of physical - chemical, medi-dealing with nanotechnology problems were established. cal - biological properties and structure of the silver nanopar-The publications and journals exist in many countries for ticles formed in the various environments. publication of the outputs devoted to the nanomaterials en- Antibacterial properties of metallic silver and its com-tirely. Variety of review papers and monographs devoted to pounds have been known for ages. In small concentrations is nanotechnologies, nanostructures and nanomaterials have safe for the human cells but ruinous for the most of bacteria been written. Frequently, the new expertise with "nano" pre- and viruses; therefore it has been widespread for the water and fixs has been assigned to the well known objects or phenom- foodstuff decontamination in everyday life and for infection ena. However, the concepts not applied in the researchers' control in human treatment [15]. At this point, the unique toolkit already 25-30 years ago has been introduced in the antimicrobic and antiviral properties of the silver compounds practice and occupied rightful place; and the modern science have been extensively studied and several comprehensive redevelopment cannot be imagined without these concepts. views devoted [25; 33]. Unlikely, that microorganisms in the They include nanoparticles (NP) in their entire variety. Fre- course of mutations are able to produce silver resistance (ex-quently, the attempts are made to explain the properties of cept for the cases when it exists a priori), since its ions attack a nanoclusters, nanoparticles, nanostructures and nanocom- mass of various cell protein objects. This asset has become exposites only based on their sizes, which not always has been tremely crucial at present with emergence of growing quantity justified. of pathogenic bacteria strains resistant to narrow-spectrum
antibiotics and posing serious threat for the human life and health [25].
The studies on elaboration of the mechanism of the silver effect on microbial cell have been deployed in the Institute of Colloidal Chemistry and Water Chemistry under AS of the Ukraine under the leadership of L. A. Kulskiy. It is known, that the metal uptake by the cell can be done through three various ways [12]:
1. Metal adsorption by the cell surface;
2. Metal active transportation to the cell;
3. Biphasic process: first phase - adsorption rapidly removed with the second phase - active transportation of the metal to the cell.
Experiments accomplished by the above Institute employees demonstrated that the silver absorption by the microorganism cells had been made by the third way regardless their species composition.
It has been identified that the various species of microorganisms have the high silver adsorption by microbial cell; as a result, the cell stops breathing and dies (dries out). The silver ions adsorbed by the capsomeres (proteins) of the viral capsid (membrane) deprive the virus of capability to penetrate to the cells since the virus "becomes heavier" from the silver, its activity reduces and it is killed as a result [6; 12].
Antibacterial properties of the metal silver are associated with its slow oxidation and Ag+ ion release to environment; therefore, the use of nanosilver medicine as a special class of biocidal agents it is seemed as a promising one. Nanoparticles have the high antibacterial activity due to their extended surface providing the maximal contact with environment. Moreover, they are rather small and able to penetrate through the cell membranes and influence the intracellular processes internally [2; 5; 16].
The long-term drinking of potable water containing 50 mkg/l of silver (MAC level) by the human being does not affect negatively on the functions of organs of digestive system, including liver antitoxic function [6; 19].
In the course of identification of antimicrobial properties of ionized silver it has been established that its antibacterial effect is extremely higher compared to the carbolic acid, sublimate and chlorinated lime. The spectrum of the silver antimicrobial effect is significantly wider compared to many antibiotics and sulfanilamide. Antibacterial effect is manifested with the minimal doses [22].
The silver has the more prominent antimicrobial effect than penicillin and the other antibiotics, and causes the similar effect on antibiotic-resistant bacterial strains. The silver ions provide the various antimicrobial effect on aurococcus, Proteus vulgaris, blue pus bacillus and colon bacillus - from antibacterial to bacteriostatic one [2; 4; 22; 26].
The silver ions have the prominent capability to inactivate and depress the activity of the influenza viruses, some enteroviruses, adenoidal viruses and AIDS viruses. At that, the high advantage of the colloidal silver therapy compared to the conventional one has been identified [4; 13].
The studies of the German scientists has demonstrated the prominent antibacterial activity of the silver nanoparticles related to the antibiotic- resistant microorganisms (Staphylococcus epidermidis and Staphylococcu saureus) with their addition to the bone cement [27]. The integration of the nanosilver with imidasole suclophosphan has the same antimicrobial activity as 0.5% solution of the silver nitrate in terms of S. aureus, as well as E. coli, P. aeruginosa, C. albicans, A. niger and S. cerevisiae. This integration acute toxicity (LD50) in intravenous injection to the rats achieved 100 mg/kg [16; 17].
The information on necessity of the deepen analysis of toxicological aspects pf nanomedicines, including nanosilver, are emerging in scientific literature. D. Chen at al. [12] were studying effect of the silver nanoparticles and microparticles in their implantation in the rat spinal muscles. The positive biological effect in application of the silver nanoparticles and microparticles was obtained on the 7th and 14th day of observation. The inflammation effect was identified on the 30th day of observation in application of both silver medicines; this was associated with its high concentration in the muscles.
The research was devoted to the influence of the silver NP on the vital activity of gram-negative microorganisms Е. coli, V. cholera, P. aeruginosa and S. Typhys at logarithmic phase of growth with the state-of-the-art high-precision methods [28]. At that, V. cholera and P. aeruginosa manifested higher resistance compared to Е. coli and S. typhys, however, in case of silver concentration 75 mkg-ml-1 the growth cessation was identified in all samples. The electronic microscopy identified that the silver NPs were not only fixed on the cellular membrane but were also abletopenetrate through it and split up inside bacterium. Only individual NPs but not their agglomerates had this capability. Moreover, the sizes of NPs connected to membrane, as a rule, did not exceed the size of the particles inside the cell. Based on this, the conclusion was made that only clusters able to interact with the cellular membrane could penetrate in the cytoplasmic space [12; 28].
The mechanism of NP penetration inside the cell is still unclear at all. There have been reports presented on the high modifications in the bacterial membrane structure B. coli, increase of its penetrance and loss of microorganisms in interaction with the silver NPs. Bacterial wall comprises high quantity of sulphur and phosphorus containing molecules interacting with NPs and losing their activity. Inside bacterium NPs may interact with DNA, and at that, DNA is losing replication capability causing its loss as well [20].
The same team of researches was studying the influence of the silver NPs on activity of the human immunodeficiency virus (HIV-1) [20]. For this purpose, the test of the NP samples stabilized with foam carbon, poly (N-vinil-2-pyrrolidone) and bovine serum albumin was fulfilled.
The silver cysteinat is being suggested for eradication of immunodeficiency virus: "proteins with the link protein -metal are the important components of retroviruses of the human immunodeficiency virus (HIV) type. Therefore, the metals can be used as antiviral agents. However, most of the metals are poisonous for the human beings, excluding the silver which is the poison only for prokaryotic cells and viruses. Therefore, untoxic silver cysteinat can be applied as antiviral medicine and cysteine source. The silver is a very active antibacterial metal with minor toxicity for the human beings. It was also demonstrated that the silver can act as a powerful inhibitor of HIV protease. The silver is interacting with HIV proteins (for instance, with the surface receptors, gene or cellular biosynthesis of viruses) and, therefore, interrupting the cellular replication of HIV at the various stages [9; 26].
In the authors' opinion, not neutral metal atoms but Ag+ ions adsorbed on NP surface make decisive contribution to antibacterial activity of the silver NPs. The large silver NPs (62 ± 18 nm) were synthesized for identification of the influence of the size of oxidized NPs on their dispersion antibacterial effect. It was identified that with equal concentration of the metal NP dispersions with the mean diameter 9.8 nm were manifesting biological activity by 10 times exceeding activity of dispersions of the larger silver clusters. The outputs of research devoted to analysis of antibacterial activity of the large silver NPs (from 25 nm and bigger) can be found in the paper [26; 30]. In analyzing the influence of NPs on the bacterial stains resistant to the silver nitrate effect (mutants Е. coli - strains [33] AgNO3 R and J53(pMG101)), it was identified that these microorganisms stayed capable to propagate with NP concentrations maximally possible under experiment conditions. This fact indirectly proves that chemisorbed ions provide decisive influence on biocidal properties of the particles. Detailed information on silver resistant bacteria is presented in reviews and articles [25; 26; 30].
Studying of fundamental issues related to the mechanisms of antibacterial effect of the silver NPs is currently on the initial stage. However, the number of emerging publications is increasing with description of the use of antibacterial properties of the silver NPs for solution of applied medical and industrial objectives. Thus, it was reported [32] on the positive synerget-ic effect of nanosilver and various antibiotics in control of S. aureus and Е. coli. The simple and cheap procedure of creation of bio-compatible polyelectrolyte layer on the basis of laminated film ofpolyethylenterephtalate containing silver clusters
and having high anticoagulative and antibacterialactivite is described in the paper [21]. In the authors' opinion, such films can have potential application in surface modification of the various medical facilities, specifically, cardiovascular implants. The research authors [31] obtained and described properties of food packing materials based on the natural polymers able to bio-degradation and having antibacterial properties due to the silver-containing nanocomposite. A lot of papers have been devoted to infiltration of textile goods with solutions of the silver NPs in order to provide them with antibacterial properties [19]. The simple and efficient industrial method of infiltration of woven and nonwoven fiber with the silver nanoparticles (~2-3 nm) has been developed [24].
The recent period is characterized with the growth of the microbial infection number, including surgical and post-operational, in all countries of the world, regardless their economic development [7].
The number of water soluble metal containing nanobio-composites have been obtained; their composition includes the silver nanoparticles [3], stabilized with the natural polysaccharides: arabinogalactan, its functionalized derivatives and heparine. The parameters of synthesis of nonorganic -organic silver nanocomposites remaining physical - chemical properties of biogenic matrix were developed and optimized.
Obtained nanoparticles are [resented in form of homogeneous formations with the mean sizes 4-30 nm, and their shape has regular character and close to the oval one. Particle distribution by size appeared to be extremely limited, for instance, the sample argentoarabinogalactan is narrow disperse: the share of particles with the size within the range 6-12 nm is equal to 80% [3; 8; 18].
It has been identified that the minimal antibacterial concentration of argentoarabinogalactan and argentoheparine varies within the range from 1 to 100 mkg/ml in terms of the principle representatives of the surgical infections, including Staphylococcus aureus [1; 13].
The paper [5; 10] is suggesting the synthesis of sustainable concentrated (up to 3 g/l) highly dispersive silver aqua-sols stabilized with cetyltrimethylammonium bromide. The possibility of modification of polyethylenterephtalate previously deformed according to the creysing mechanism with the silver nanoparticles has been considered. Based on the outputs of microbiological tests with the use of bacteria Pseu-domonasaeruginosa it was identified that obtained nanocom-posites had prominent biocidal effect.
Recently, the ready-made bandages containing colloidal (ultra-disperse, nanocrystallic) silver [9; 19; 31] receive widespread acceptance; numerous studies prove efficient antimicrobial and wound-healthing properties of these products, however, the differences in manufacturing ways, con-
centrations, particle sixes, nature of carrier material, etc. are hindering the meaningfull comparison of the products. Despite the number of unsolved issues, these bandaging materials have passed successful trial in Germany, France and Italy; the studies accomplished in Canada demonstrated improved clinical parameters and reduction of the surface bioburden of the wound; at the same time, the flora of the deeper tissues remained unchanged [8; 11; 29]. The authors are also stating that the modern materials not only need to have antibacterial efficiency for the wound bandaging; they require additional properties accelerating the wound redressing; for instance, the material has been described which removes the products of bacteria metabolism from the treatment area and connects endotoxins formed in the course of the cell loss [14; 25; 33].
Hydrogel bandaging materials have been offered; they are based on chitosan and include the silver nanoparticles. The integrated research of antibacterial properties, toxicology, safety, sanitary - chemical properties and wound-healthing action of the new material has been accomplished [31].
Chitosan hydrogel bandaging materials with the silver clusters were applied in the local treatment of the patients with the limb trophic ulcers and for the treatment of burns of II, III-a and III-b degrees. Based on the outputs, the conclusion was made on the high efficiency of traumatic dressings. This medical product cay be widely used in out-patient and clinical practice. The bandaging material provides the favourable course of traumatic process, facilitates tissue regeneration and results in reduction of the treatment duration. Chitosan hydrogel bandaging materials containing the silver clusters are promising for the use in surgical practice [2].
Compounds of colloidal (metallic) silver with the protein - trademarks "Argirol", "Protargol", "Collargol", etc. can be obtained through interaction of the silver oxide with gelatin or albumin (silver concentration 19-25%). Collargol and Protargol are applied externally in form of 1-2% solutions as astringent, antiseptic, anti-inflammation remedies in the treatment of ear, nose, throat; the possibility of these compounds application as antihypoxic drugs has been demonstrated [12].
The paper shows the low toxicity of the silver proteinate (rats, orally), however, the possibility of argyria development in case of overuse of these remedies has been manifested [8].
Along with the silver positive properties, its negative characteristics, for instance, toxicity, have to be taken into consideration. The numerous individual papers and surveys have been devoted to the problem of the silver toxicity. The scientific toxicological studies of silver in Russia are dated by the end ofXIX - beginning XX century. Thus, Rodzevich [24; 34] in 1903 analyzed the silver influence on blood using the extensive pilot material and demonstrated peculiarities of its effect
in case of various ways of the silver medicine introduction in the organism.
The silver (especially in ionic water soluble form) is toxic for aquatic organisms (aquatic fauna). At the same time, "the silver toxicity in terms ofmammals is relatively low. In the blood serum of human being, within 24 hours up 600 mkg/l of Ag concentration can be observed and in the urine - 1.100 mkg/l without clinical consequences. The fact that there has not been any reports known about any mutagenic or carcinogenic activity of the silver compounds [11] is the most important".
The authors predominantly agree that, unlike the salts of the other heavy metals, the silver is not dangerous for the external and internal medical application. Many scientists are warning about risk of overuse of the various products promoted in the market in form of biologically active supplements: "silver proteins", colloidal solutions and the other commercial (nonmedical) silver medicines. Apart from insufficient efficiency, the authors indicate the risk of argyria formation in case or oral application (argyria, argyrose or argyriasis, from the Greek word "argyros" - silver; brown or black and grey pigmentation of skin, mucous coat, tissues of internal organs and eyes caused by the silver settling).
WHO established the maximal silver dose which does not cause observable adverse effect on the human health (NOAEL level -No Observable Adverse Effect Level) - 10 grams. Therefore, according to the WHO methodology, the person "eating and drinking" totally 10 grams of silver over entire life (70 years) is reliably not supposed to have any associated health problems [31]. Based on this dimension the recommendations were developed on the tolerant (tolerable) silver content in the potable water - 100 mkg/l. Such concentration during 70 years of life gives the half of the NOAEL level, which is certainly safe for the health. According to the domestic "Sanitary Norms and Rules", MAC of silver in the potable water is equal to 50 mkg/l. The similar indicator was accepted as the silver maximum allowable level in the potable water for many states of America [26].
The silver practically "does not provide adverse effects on the human beings; argyria (change of the skin colour due to the silver subdermic settling) is a rare phenomenon and there is no any reason, mainly, for cosmetic concern". One of the recent articles [11; 29] categorically shows that "...the interest to the silver as the medicine for the wound treatment and redressingsy is experiencing Renaissance".
The analysis of the literature demonstrates that the silver compounds, specifically, silver nanoparticles with the narrow distribution by size and stabilized with polymeric systems are of a great interest in manufacturing of the new generation medical remedies and goods with unique new properties. Creation of antibacterial traumatic surfaces containing silver
nanoparticles in the structure of biodegradable and water soluble polymers is of a specific interest. Such polymers in form of powders, solutions, hydraulic gels and especially films to some extent simultaneously functioning as a skin are protecting the traumatic surface and do not injure it; and provide antibacterial wound redressingsing effect and are subject to biodegradation [11].
Based on the literature survey, devoted to the analysis of the current status of the issue on the methods of synthesis and
stabilization of the silver NPs and NP-based remedies properties it has been identified that transition from macro-scale and micro-scale to the nanoscale causes emergence of qualitative modifications in the physical - chemical and medical - biological properties of compounds along with polymer systems obtained on their basis.
Synthesis and investigation of the silver NP stabilized in the polymer matrices are currently presenting promising trends in the polymer chemistry and medicine.
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