Application of Polyhydroxyalkanoates in Medicine and the Biological Activity of Natural Poly(3-Hydroxybutyrate)

Biodegradable and biocompatible polymers, polyhydroxyalkanoates (PHAs), are actively used in medicine to produce a wide range of medical devices and dosage formulations. The medical industry mainly utilizes PHAs obtained by chemical synthesis, but interest in the medical application of natural PHAs obtained biotechnologically is also growing. Synthetic PHAs are the biomimetic analogs of bacterial poly(3-hydroxybutyrate) (PHB) and other natural PHAs. This paper addresses the issue of the presence of biological activity in synthetic and natural PHAs (stimulation of cell proliferation and differentiation, tissue regeneration) and their possible association with various biological functions of PHB in bacteria and eukaryotes, including humans.

Biosynthesis of poly(3-hydroxybutyrateco-3-hydroxy-4-methylvalerate) by Strain Azotobacter chroococcum 7B

Production of novel polyhydroxyalkanoates (PHAs), biodegradable polymers for biomedical applications, and biomaterials based on them is a promising trend in modern bioengineering. We studied the ability of an effective strain-producer Azotobacter chroococcum 7B to synthesize not only poly(3-hydroxybutyrate) homopolymer (PHB) and its main copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), but also a novel copolymer, poly(3-hydroxybutyrate-co-3-hydroxy-4-methylvalerate) (PHB4MV). For the biosynthesis of PHB copolymers, we used carboxylic acids as additional carbon sources and monomer precursors in the chain of synthesized copolymers. The main parameters of these polymers biosynthesis were determined: strain-producer biomass yield, polymer yield, molecular weight and monomer composition of the synthesized polymers, as well as the morphology of A. chroococcum 7B bacterial cells. The physico-chemical properties of the polymers were studied using nuclear magnetic resonance spectroscopy (NMR), differential scanning calorimetry (DSC), contact angle test, and other methods. In vitro biocompatibility of the obtained polymers was investigated using stromal cells isolated from the bone marrow of rats with the XTT cell viability test. The synthesis of the novel copolymer PHB4MV and its chemical composition were demonstrated by NMR spectroscopy: the addition of 4-methylvaleric acid to the culture medium resulted in incorporation of 3-hydroxy-4-methylvalerate (3H4MV) monomers into the PHB polymer chain (0.6 mol%). Despite the low molar content of 3H4MV in the obtained copolymer, its physico-chemical properties were significantly different from those of the PHB homopolymer: it has lower crystallinity and a higher contact angle, i.e. the physico-chemical properties of the PHB4MV copolymer containing only 0.6 mol% of 3H4MV corresponded to a PHBV copolymer with a molar content ranging from 2.5% to 7.8%. In vitro biocompatibility of the obtained PHB4MV copolymer, measured in the XTT test, was not statistically different from the cell growth of PHB and PHBV polymers, which make its use possible in biomedical research and development.

Biosynthesis of poly(3-hydroxybutyrateco-3-hydroxy-4-methylvalerate) by Strain Azotobacter chroococcum 7B

Production of novel polyhydroxyalkanoates (PHAs), biodegradable polymers for biomedical applications, and biomaterials based on them is a promising trend in modern bioengineering. We studied the ability of an effective strain-producer Azotobacter chroococcum 7B to synthesize not only poly(3-hydroxybutyrate) homopolymer (PHB) and its main copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), but also a novel copolymer, poly(3-hydroxybutyrate-co-3-hydroxy-4-methylvalerate) (PHB4MV). For the biosynthesis of PHB copolymers, we used carboxylic acids as additional carbon sources and monomer precursors in the chain of synthesized copolymers. The main parameters of these polymers' biosynthesis were determined: strain-producer biomass yield, polymer yield, molecular weight and monomer composition of the synthesized polymers, as well as the morphology of A. chroococcum 7B bacterial cells. The physico-chemical properties of the polymers were studied using nuclear magnetic resonance spectroscopy (NMR), differential scanning calorimetry (DSC), contact angle test, and other methods. In vitro biocompatibility of the obtained polymers was investigated using stromal cells isolated from the bone marrow of rats with the XTT cell viability test. The synthesis of the novel copolymer PHB4MV and its chemical composition were demonstrated by NMR spectroscopy: the addition of 4-methylvaleric acid to the culture medium resulted in incorporation of 3-hydroxy-4-methylvalerate (3H4MV) monomers into the PHB polymer chain (0.6 mol%). Despite the low molar content of 3H4MV in the obtained copolymer, its physico-chemical properties were significantly different from those of the PHB homopolymer: it has lower crystallinity and a higher contact angle, i.e. the physico-chemical properties of the PHB4MV copolymer containing only 0.6 mol% of 3H4MV corresponded to a PHBV copolymer with a molar content ranging from 2.5% to 7.8%. In vitro biocompatibility of the obtained PHB4MV copolymer, measured in the XTT test, was not statistically different from the cell growth of PHB and PHBV polymers, which make its use possible in biomedical research and development.

Biosynthesis of poly(3-hydroxybutyrate) copolymers by Azotobacter chroococcum 7B: A precursor feeding strategy

A precursor feeding strategy for effective biopolymer producer strain Azotobacter chroococcum 7B was used to synthesize various poly(3-hydroxybutyrate) (PHB) copolymers. We performed experiments on biosynthesis of PHB copolymers by A. chroococcum 7B using various precursors: sucrose as the primary carbon source, various carboxylic acids and ethylene glycol (EG) derivatives [diethylene glycol (DEG), triethylene glycol (TEG), poly(ethylene glycol) (PEG) 300, PEG 400, PEG 1000] as additional carbon sources. We analyzed strain growth parameters including biomass and polymer yields as well as molecular weight and monomer composition of produced copolymers. We demonstrated that A. chroococcum 7B was able to synthesize copolymers using carboxylic acids with the length less than linear 6C, including poly(3-hydroxybutyrate-co-3-hydroxy-4-methylvalerate) (PHB-4MHV) using Y-shaped 6C 3-methylvaleric acid as precursor as well as EG-containing copolymers: PHB-DEG, PHB-TEG, PHB-PEG, and PHB-HV-PEG copolymers using short-chain PEGs (with n ≤ 9) as precursors. It was shown that use of the additional carbon sources caused inhibition of cell growth, decrease in polymer yields, fall in polymer molecular weight, decrease in 3-hydroxyvalerate content in produced PHB-HV-PEG copolymer, and change in bacterial cells morphology that were depended on the nature of the precursors (carboxylic acids or EG derivatives) and the timing of its addition to the growth medium.

[Development and preclinical studies of insulating membranes based on poly-3-hydroxybutyrate-co-3-hydroxyvalerate for guided bone regeneration]

Bone tissue damages are one of the dominant causes of temporary disability and developmental disability. Currently, there are some methods of guided bone regeneration employing different osteoplastic materials and insulation membranes used in surgery. In this study, we have developed a method of preparation of porous membranes from the biopolymer poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV), produced by a strain of Azotobacter chroococcum 7B. The biocompatibility of the porous membranes was investigated in vitro using mesenchymal stem cells (MSCs) and in vivo on laboratory animals. The cytotoxicity test showed the possibility of cell attachment on membrane and histological studies confirmed good insulating properties the material. The data obtained demonstrate the high biocompatibility and the potential application of insulating membranes based on PHBV in bone tissue engineering.

[Prolonged release of chlorambucil and etoposide from poly-3-oxybutyrate-based microspheres]

Microspheres were obtained on the basis of poly(3-oxibutyrate) (POB) with the inclusion of the Chlorambucil and Etoposide cytostatic drugs in a polymer matrix, and the morphology, kinetics of drug release from microspheres, and the interaction between microspheres and tumor cells in vitro were studied. Data on the kinetics of drug release suggests that a prolonged release occurs by drug diffusion from the polymer matrix at the initial stage and at the expense of hydrolytic degradation of the polymer at a later stage. A study of the biocompatibility and biological activity of biopolymeric microspheres showed that chlorambucil operates actively and strongly inhibits the growth of cultured cells for a short time (24 h). Etoposide acts weaker (the percentage of cell growth suppression during 48 h does not exceed 50%), but subsequently it has a basis for the creation of new dosage forms with prolonged action of Etoposide and chlorambucil for cancer therapy.

[Sustained release of the antitumor drug paclitaxel from poly(3-hydroxybutyrate)-based microspheres]

Development of systems of medicines with sustained action on the basis of biodegradable polymers is a promising trend in modem pharmacology. Polyhydroxyalkanoates (POA) attract increasing attention due to their biodegradability and high biocompatibility, which make them suitable for development of novel drug dosage forms. We obtained microspheres on the basis of poly(3-hydroxybutyrate) (PHB) loaded with the antitumor drug paclitaxel. Morphology, drug release kinetics and effect on tumor cells in vitro of microspheres were studied. The data on the kinetics of drug release, biocompatibility and biological activity of the biopolymer microspheres in vitro showed that the studied system of prolonged drug release had lower toxicity and higher efficiency compared to the traditional dosage forms of paclitaxel.

[Poly(3-hydroxybutyrate) and biopolymer systems on the basis of this polyester]

Biodegradable biopolymers attract much attention in biology and medicine due to its wide application. The present review is designed to be a comprehensive source for research of biodegradable and biocompatible bacterial polymer, poly(3-hydroxybutyrate). This paper focuses on basic properties of biopolymer: biodegradability and biocompatibility, as well as on biopolymer systems: various materials, devices and compositions on the basis of biopolymer. Application of biopolymer systems based on poly(3-hydroxybutyrate) in medicine as surgical implants, in bioengineering as scaffold for cell cultures, and in pharmacy as drug dosage forms and drug systems is observed in the present review.

[Biosynthesis of poly-3-hydroxybutyrate-3-hydroxyvalerate copolymer by Azotobacter chroococcum strain 7B]

The ability of Azotobacter chroococcum strain 7B, producer of polyhydroxybutyrate (PHB), to synthesize its copolymer poly-3-hydroxybutyrate-3-hydroxyvalerate (PHB-HV) was studied. It was demonstrated, for the first time, that A. chroococcum strain 7B was able to synthesize PHB-HV with various molar rates of HV in the polymer chain when cultivated on medium with sucrose and carboxylic acids as precursors of HV elements in the PHB chain, namely, valeric (13.1-21.6 mol %), propanoic (3.1 mol %), and hexanoic (2.1 mol %) acids. Qualitative and functional differences between PHB and PHB-HV were demonstrated by example of the release kinetic of methyl red from films made of synthesized polymers. Maximal HV incorporation into the polymer chain (28.8 mol %) was recorded when the nutrient medium was supplemented with 0.1% peptone on the background of 20 mM valerate. These results suggest that that the studied strain can be regarded as a potential producer of not only PHB but also PHB-HV.

[A comparative study of biodegradation kinetics of biopolymer systems based on poly(3-hydroxybutyrate)]

The aim of this study was to evaluate and to compare of long-term kinetics curves of biodegradation of poly(3-hydroxybutyrate) (PHB), its copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and PHB/polylactic acid blend. The total weight loss and the change of average viscosity molecular weight were used as an index of biodegradation degree. The rate of biodegradation was analyzed in vitro in presence oflipase and in vivo when the films were implanted in animal tissues. The morphology of PHB films surface was studied by atomic force microscopy technique. It was shown that biodegradation of PHB is occurred by means of as polymer hydrolysis, and as its enzymatic biodegradation. The obtained data can be used for development of medical devices on the base of PHB.

[Effect of growth conditions on the molecular weight of poly-3-hydroxybutyrate produced by Azotobacter chroococcum 7B]

It has been shown that poly-3-hydroxybutyrate (PHB) of predetermined molecular weight can be obtained by varying the growth conditions of the producer strain, Azotobacter chroococcum 7B: pH, temperature, aeration, presence of sodium acetate as an additional carbon source, or growth on crude complex carbon sources (molasses, vinasse, or starch). High-molecular-weight polymer can be obtained at pH 7.0, optimal for the culture (1485 kDa), temperature 30-37 degrees C (1600-1450 kDa, respectively), and low aeration (2215 kDa). The following factors decrease PHB MW: pH deviation to the acidic (pH 6.0, 476 kDa) or alkaline (pH 8.0, 354 kDa) range or lower temperature (20 degrees C, 897 kDa). Introduction of additional carbon source (sodium acetate) at concentrations in the medium varying from 0 to 5 g/l provides an original method of production of PHB with predetermined MW in a wide range, from 270 to 1515 kDa, with high PHB content in the cell.

[Antimicrobial activity of core-sheath surgical sutures modified with poly-3-hydroxybutyrate]

To impart antimicrobial activity to surgical sutures, weaved polyester fibers are coated with poly-3-hydroxybutyrate (PHB), containing the antimicrobial agent furazolidone (FZ). The prolonged FZ effect (7-14 days) is achieved by two-step application of a sheath, constituting 10% of the suture weight and containing 2-6% FZ. The sheath structure and antimicrobial activity of sutures can be modified by the introduction of other biocompatible and biodegradable polymers.

[The effect of combined and separate inoculation of alfalfa plants with Azospirillum lipoferum and Sinorhizobium meliloti on denitrification and nitrogen-fixing activities]

The effects of associative nitrogen fixer Azospirillum lipoferum strain 137 and root nodule bacteria Sinorhizobium meliloti after combined and separate inoculation of alfalfa seedlings on the background of mineral nitrogen applied at various times were studied. It was demonstrated that exudates of the alfalfa seedlings with the first pair of cotyledonary leaves already provide a high activity of these bacteria in the rhizosphere. To 74.6% of the introduced nitrate was transformed into N2O when the binary preparation of these bacteria was used. In an extended experiment (30 days), an active reduction of nitrates to N2O (11 micromol N2O/pot x 24 h) with inhibition of nitrogen fixation was observed in all of the experimental variants during the formation of legume-rhizobial and associative symbioses and simultaneous introduction of nitrates and bacteria. The most active enzyme fixation was observed in the case of a late (after 14 days) application of nitrates in the variants with both separate inoculations and inoculation with the binary preparation of A. lipoferum and S. meliloti. Separation in time of the application of bacterial preparations and mineral nitrogen assisted its preservation in all of the experimental variants. The variant of alfalfa inoculation with the binary preparation of A. lipoferum and S. meliloti and application of nitrates 2 weeks after inoculation was optimal for active nitrogen fixation (224.7 C2H4 nmol/flask x 24 h) and low denitrification activity (1.8 x micromol N2O/flask x 24 h). These results are useful in applied developments aimed at the use of bacterial and mineral fertilizers for leguminous plants.

[Preparation of biodegradable porous films for use as wound coverings]

We studied the preparation of polymeric films formed from solutions of poly-3-hydroxybutyrate and poly-epsilon-caprolactone in chloroform and methylene chloride. A morphological study of film chips (electron microscopy) showed that solvent evaporation results in the formation of a heterogeneous structure with interpenetrating pores (1-20 microm). We proposed a new method for introducing the proteolytic enzyme and the aminopolysaccharide chitosan into the composition of polyester films. Composite films possessed necrolytic activity and were characterized by increased hydrophilicity. Properties of enzyme-containing films from a mixture of polymers (proteolytic activity, porous structure, and increased hydrophilicity) account for their use in the preparation of biodegradable wound coverings.

[New poly-(3-hydroxybutyrate)-based systems for controlled release of dipyridamole and indomethacin]

New poly-(3-hydroxybutyrate)-based systems for controlled release of anti-inflammatory and antithrombogenic drugs have been studied. The release occurs via two mechanisms (diffusion and degradation) operating simultaneously. Dipyridamole and indomethacin diffusion processes determine the rate of the release at the early stages of the contact of the system with the environment (the first 6-8 days). The coefficient of the release diffusion of a drug depends on its nature, the thickness of the poly-(3-hydroxybutyrate) films containing the drug, the concentrations of dipyridamole and indomethacin, and the molecular weight of the poly-(3-hydroxybutyrate). The results obtained are critical for developing systems of release of diverse drugs, thus, enabling the attainment of the requisite physiological effects on tissues and organs of humans.

Aerobic and anaerobic microbial degradation of poly-beta-hydroxybutyrate produced by Azotobacter chroococcum

Food industry wastewater served as a carbon source for the synthesis of poly-beta-hydroxybutyrate (PHB) by Azotobacter chroococcum. The content of polymer in bacterial cells grown on the raw materials reached 75%. PHB films were degraded under aerobic, microaerobic, and anaerobic conditions in the presence and absence of nitrate by microbial populations of soil, sludges from anaerobic and nitrifying/denitrifying reactors, and sediment from a sludge deposit site. Changes in molecular mass, crystallinity, and mechanical properties of PHB were studied. Anaerobic degradation was accompanied by acetate formation, which was the main intermediate utilized by denitrifying bacteria or methanogenic archaea. On a decrease in temperature from 20 to 5 degrees C in the presence of nitrate, the rate of PHB degradation was 7.3 times lower. Under anaerobic conditions and in the absence of nitrate, no PHB degradation was observed, even at 11 degrees C. The enrichment cultures of denitrifying bacteria obtained from soil and anaerobic sludge degraded PHB films for a short time (3-7 d). The dominant species in the enrichment culture from soil were Pseudomonas fluorescens and Pseudomonas stutzeri. The rate of PHB degradation by the enrichment cultures depended on the polymer molecular weight, which reduced with time during biodegradation.

[Reduction of nitrates by cultures of Azotobacter indicum and Azotobacter chroococcum ]

The capacity for denitrification was studied in Azotobacter bacteria, which are free-living nitrogen-fixing obligatory aerobes. Data on the nitrate reduction to nitrites and nitric oxide by A. indicum under anaerobic conditions were obtained for the first time for genus Azotobacter.

[The biodegradation of poly-beta-hydroxybutyrate (PHB) by a model soil community: the effect of cultivation conditions on the degradation rate and the physicochemical characteristics of PHB]

The biodegradation of films made of poly-beta-hydroxybutyrate (PHB) with a molecular mass of 1500 kDa was studied using a model soil community in the presence and absence of nitrate and at different concentrations of oxygen in the gas phase. The biodegradation of PHB was investigated with respect to changes in its molecular mass, crystallinity, and some mechanical properties.

[Determination of the nitrogen-fixing activity of Rhizobium japonicum under sterile microvegetative conditions]

The nitrogen fixing activity of Rhizobium japonicum in symbiosis with soya grown in the sterile microvegetative conditions at an air humidity of 70%, at a temperature of 20 degrees C and a length of light day of 16 hours was assayed using the acetylene technique. The plants were cultivated in phytotron in glass tubes (245 cm3) illuminated with xenon lamps. This technique can be used, apparently, to determine the nitrogen fixing activity of other legumes and cereals.

Action of metabolites of isolated plant tissues on the nitrogenase activity of Rhizobium vigna and Rhizobium meliloti

The dependence of the nitrogenase activity of Rhizobium meliloti on the strain peculiarities of the cultures, the composition of the media used, and the metabolites of legume tissue cultures was demonstrated by the acetylene method. The nitrogenase activity is significantly higher in R. vigna than in R. meliloti, under the same experimental conditions. Enrichment of the Murashige-Skoog medium with arabinose (25 mM), succinate (25 mM), glutamine (2 mM nitrogen), and yeast extract (0.1%) substantially stimulated the nitrogenase activity of a pure culture of R. vigna. The maximum nitrogenase activity on this medium was noted when metabolites of sweet clover tissue were introduced.

[Nitrogenase activity of Rhizobium meliloti and Rhizobium vigna in a root tisse culture of leguminous and nonleguminous plants]

As was shown using the acetylene technique, the nitrogenase activity of Rhizobium meliloti and Rhizobium vigna increased when they were cultivated with the root tissue cultures of legumes (lucerne, sweetclover) and non-legumes (tobacco, glasswort, carrot), particularly in the case of the former. The maximum activity of nitrogenase was found in R. meliloti. The tissue cultures of legumes had no effect on the growth of Rhizobium whereas the tissues of non-legumes stimulated their biomass accumulation though the activity of nitrogenase in both Rhizobium cultures was low in this case. Therefore, the metabolites of legumes produced a specific action on the nitrogenase of nodule bacteria.

[Role of leguminous plants in effective symniosis with nodule bacteria]

Experiments were conducted with five clover varieties and six lucerne varieties infected with their specific strains of nodule bacteria with a high or low activity. The role of plants in active symbiosis with nodule bacteria was established. The nitrogen fixing activity of nodule bacteria varied within a wide range depending on the plant variety. Not only the activity of the strain, but the variety of the plant too, should be taken into account for industrial purposes.

[Oxidative phosphorylation in Propionibacterium]

Oxidative phosphorylation during electron transport in the respiratory chain was found in two propionic bacteria, P. shermanii and P. petersonii. Its effectiveness, with oxygen as the terminal acceptor of electrons, was higher in P. petersonii, a more aerobic culture, than in P. shermanii. Oxidative phosphorylation with the participation of the electron transport chain was not found in P. petersonii in the absence of oxygen. Oxidative phosphorylation can take place together with the reactions of propionic fermentation in P. shermanii upon a small rearrangement of the respiration chain (if fumarate reductase is substituted for cytochrome oxidase).