Hybrid Nanosystems of Antibiotics with Metal Nanoparticles-Novel Antibacterial Agents

The appearance and increasing number of microorganisms resistant to the action of antibiotics is one of the global problems of the 21st century. Already, the duration of therapeutic treatment and mortality from infectious diseases caused by pathogenic microorganisms have increased significantly over the last few decades. Nanoscale inorganic materials (metals and metal oxides) with antimicrobial potential are a promising solution to this problem. Here we discuss possible mechanisms of pathogenic microorganisms' resistance to antibiotics, proposed mechanisms of action of inorganic nanoparticles on bacterial cells, and the possibilities and benefits of their combined use with antibacterial drugs. The prospects of using metal and metal oxide nanoparticles as carriers in targeted delivery systems for antibacterial compositions are also discussed.

Cryostructuring of Polymeric Systems: 62 Preparation and Characterization of Alginate/Chondroitin Sulfate Cryostructurates Loaded with Antimicrobial Substances

Targeted drug release is a significant research focus in the development of drug delivery systems and involves a biocompatible polymeric carrier and certain medicines. Cryostructuring is a suitable approach for the preparation of efficient macroporous carriers for such drug delivery systems. In the current study, the cryogenically structured carriers based on alginate/chondroitin sulfate mixtures were prepared and their physicochemical properties and their ability to absorb/release the bactericides were evaluated. The swelling parameters of the polysaccharide matrix, the amount of the tightly bound water in the polymer and the sulfur content were measured. In addition, FTIR and UV spectroscopy, optical and scanning microscopy, as well as a standard disk diffusion method for determining antibacterial activity were used. It was shown that alginate/chondroitin sulfate concentration and their ratios were significant factors influencing the swelling properties and the porosity of the resultant cryostructurates. It was demonstrated that the presence of chondroitin sulfate in the composition of a polymeric matrix slowed down the release of the aminoglycoside antibiotic gentamicin. In the case of the NH₂-free bactericide, dioxidine, the release was almost independent of the presence of chondroitin sulfate. This trend was also registered for the antibacterial activity tests against the Escherichia coli bacteria, when examining the drug-loaded biopolymeric carriers.

Nanoparticles of Bioactive Metals/Metal Oxides and Their Nanocomposites with Antibacterial Drugs for Biomedical Applications

The increasing appearance of new strains of microorganisms resistant to the action of existing antibiotics is a modern problem that requires urgent decision. A promising potential solution is the use of nanoparticles of bioactive metals and their oxides as new antibacterial agents, since they are capable of affecting pathogenic microorganisms by mechanisms different from the mechanisms of action of antibiotics. Inorganic nanoparticles possess a wide spectrum of antibacterial activity. These particles can be easily conjugated with drug molecules and become carriers in targeted drug-delivery systems. This paper discusses the benefits and prospects of the application of nanoparticles from metals and metal oxides and their nanocomposites with antibacterial drugs.

A C∧S-Cyclometallated Gold(III) Complex as a Novel Antibacterial Candidate Against Drug-Resistant Bacteria

The worldwide emergence and spread of infections caused by multidrug-resistant bacteria endangers the efficacy of current antibiotics in the clinical setting. The lack of new antibiotics in the pipeline points to the need of developing new strategies. Recently, gold-based drugs are being repurposed for antibacterial applications. Among them, gold(III) complexes have received increasing attention as metal-based anticancer agents. However, reports on their antibacterial activity are scarce due to stability issues. The present work demonstrates the antibacterial activity of the gold(III) complex 2 stabilized as C∧S-cycloaurated containing a diphenylphosphinothioic amide moiety, showing minimum inhibitory concentration (MIC) values that ranged from 4 to 8 and from 16 to 32 mg/L among Gram-positive and Gram-negative multidrug-resistant (MDR) pathogens, respectively. Complex 2 has a biofilm inhibitory activity of only two to four times than its MIC. We also describe for the first time a potent antibacterial synergistic effect of a gold(III) complex combined with colistin, showing a bactericidal effect in less than 2 h; confirming the role of the outer membrane as a permeability barrier. Complex 2 shows a low rate of internalization in Staphylococcus aureus and Acinetobacter baumannii; it does not interact with replication enzymes or efflux pumps, causes ultrastructural damages in both membrane and cytoplasmic levels, and permeabilizes the bacterial membrane. Unlike control antibiotics, complex 2 did not generate resistant mutants in 30-day sequential cultures. We detected lower cytotoxicity in a non-tumoral THLE-2 cell line (IC50 = 25.5 μM) and no acute toxicity signs in vivo after an i.v. 1-mg/kg dose. The characterization presented here reassures the potential of complex 2 as a new chemical class of antimicrobial agents.

Cryostructuring of Polymeric Systems. 55. Retrospective View on the More than 40 Years of Studies Performed in the A.N.Nesmeyanov Institute of Organoelement Compounds with Respect of the Cryostructuring Processes in Polymeric Systems

The processes of cryostructuring in polymeric systems, the techniques of the preparation of diverse cryogels and cryostructurates, the physico-chemical mechanisms of their formation, and the applied potential of these advanced polymer materials are all of high scientific and practical interest in many countries. This review article describes and discusses the results of more than 40 years of studies in this field performed by the researchers from the A.N.Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences-one of the key centers, where such investigations are carried out. The review includes brief historical information, the description of the main effects and trends characteristic of the cryostructuring processes, the data on the morphological specifics inherent in the polymeric cryogels and cryostructurates, and examples of their implementation for solving certain applied tasks.

Influence of succinylation of a wide-pore albumin cryogels on their properties, structure, biodegradability, and release dynamics of dioxidine loaded in such spongy carriers

The goal of this study was to reveal how the chemical modification, succinylation in this case, of the wide-pore serum-albumin-based cryogels affects on their osmotic characteristics (swelling extent), biodegradability and ability to be loaded with the bactericide substance - dioxidine, as well as on its release. The cryogels were prepared via the cryogenic processing (freezing - frozen storage - thawing) of aqueous solutions containing bovine serum albumin (50 g/L), denaturant (urea or guanidine hydrochloride, 1.0 mol/L) and reductant (cysteine, 0.01 mol/L). Freezing/frozen storage temperatures were either -15, or -20, or -25 °C. After defrosting, spongy cryogels were obtained that possessed the system of interconnected gross pores, whose shape and dimensions were dependent on the freezing temperature and on the type of denaturant introduced in the feed solution. Subsequent succinylation of the resultant cryogels caused the growth of the swelling degree of the pore walls of these spongy materials, resulted in strengthening of their resistance against of trypsinolysis and gave rise to an increase in their loading capacity with respect to dioxidine. With that, the microbiological tests showed a higher bactericidal activity of the dioxidine-loaded sponges based on the succinylated albumin cryogels as compared to that of the drug-carriers based on the non-modified protein sponges.