Hyaluronan-colistin conjugates: Synthesis, characterization, and prospects for medical applications

The development of nanotechnology-based antibiotic delivery systems (nanoantibiotics) is an important challenge in the effort to combat microbial multidrug resistance. These systems have improved biopharmaceutical characteristics by increasing local bioavailability and reducing systemic toxicity and the number and frequency of drug side effects. Conjugation of low -molecular -weight antibacterial agents with natural polysaccharides is an effective strategy for developing optimal targeted delivery systems with programmed release and reduced cytotoxicity. This study describes the synthesis of conjugates of colistin (CT) and hyaluronic acid (HA) using carbodiimide chemistry to conjugate the amino groups of CT with the carboxyl groups of HA. The obtained polysaccharide carriers had a degree of substitution (DS) with CT molecules of 3-10 %, and the CT content was 129-377 μg/mg. The size of the fabricated particles was 300-600 nm; in addition, there were conjugates in the form of single macromolecules (30-50 nm). The ζ-potential of developed systems was about -20 mV. In vitro release studies at pH 7.4 and pH 5.2 showed slow hydrolysis of amide bonds, with a CT release of 1-5 % after 24 h. The conjugates retained antimicrobial activity depending on the DS: at DS 8 %, the minimum inhibitory concentration (MIC) of the conjugate corresponded to the MIC of free CT. The resulting systems also reduced CT nephrotoxicity by 20-50 %. These new conjugates of CT with HA are promising for the development of nanodrugs for safe and effective antimicrobial therapy.

Structural characterization of a homopolysaccharide produced by Weissella cibaria FMy 2-21-1 and its potential application as a green corrosion inhibiting film

Steel corrosion is a global issue that affects safety and the economy. Currently, the homopolysaccharide (HoPS) structure of a novel lactic acid bacterium (LAB) is under study, as well as its application as a green corrosion inhibitor. Weissella cibaria FMy 2-21-1 is a LAB strain capable of producing HoPS in sucrose enriched media. The isolated and purified HoPS was characterized by different spectroscopic analyses as a linear α-1,6 dextran adopting a random coil conformation, with high molecular weight and extended size in water. The polysaccharide showed a semi-crystalline organization, which is a requirement for film formation. Its biocoating showed a grainy network structure, with a slightly lesser hydrophobic role in the aqueous environment than in the ionic one. The electrochemical measurements of the steel-HoPS coating showed that the biopolymer layer acts as an anodic-type corrosion inhibitor, with high resistance to corrosion by water and with chloride ions which prevent pitting, a corrosion process typical of bare steel. Few reports have cited the application of LAB HoPS as corrosive coating inhibitors. This work is the first to explore the influence of a structurally characterized dextran from Weissella cibaria strain as a potential steel corrosion inhibitor in ionic environments.

Chitosan functionalized with heptadentate dinucleating ligand applied to removal of nickel, copper and zinc

The preconcentration of metal ions present at low concentration levels in aqueous systems and the selective removal of potentially toxic metals are important applications of adsorption processes. In this study, a heptadentate dinucleating ligand was anchored to chitosan for use in adsorption studies on Zn(II), Cu(II) and Ni(II) ions. The novel adsorbent was characterized by ¹³C NMR and FT-IR spectroscopy, TGA and BET surface area analysis. The degree of substitution of the ligand in chitosan, obtained from CHN analysis, was 0.73. The adsorption kinetics followed a pseudo-second-order model. The rate constants and the adsorption capacities for multicomponent systems decreased in the order Cu(II) >> Ni(II) ∼ Zn(II), indicating the preferential adsorption of Cu(II). For Cu(II) ions, the Langmuir model provided the best fitting to the experimental data, and the monolayer Cu(II) adsorption capacity was 0.404 mmol g^-1, while the linear isotherm described Zn(II) and Ni(II) ion adsorption.

Interfacial Properties of Chitosan in Interfacial Shear and Capsule Compression

The time-dependent behavior of surface-active adsorption layers at the oil/water interface can dictate emulsion behavior at both the micro- and macroscale. In addition, self-healing behavior of the adsorption layer may benefit emulsion stability subject to large deformation under processing or during final application. We explore the behavior of chitosan, a known hydrophilic emulsifier, which forms nanoparticle aggregates when the concentration of acetate buffer exceeds 0.3 M. We observe a Pickering adsorption layer building and strain-dependent behavior of the chitosan at the medium chain triglyceride oil/water interface. We compare this to the behavior of identical chitosan layers coated on oil droplets via atomic force microscopy colloidal probe compression in both linear and oscillatory compressions. In both interfacial shear rheometry and the capsule compression, a thick, elastic layer with strong time-dependent recovery behavior is observed, suggesting that the layer has some self-healing capabilities.

Nanoparticles of Short Cationic Peptidopolysaccharide Self-Assembled by Hydrogen Bonding with Antibacterial Effect against Multidrug-Resistant Bacteria

Cationic antimicrobial peptides (AMPs) and polymers are active against many multidrug-resistant (MDR) bacteria, but only a limited number of these compounds are in clinical use due to their unselective toxicity. The typical strategy for achieving selective antibacterial efficacy with low mammalian cell toxicity is through balancing the ratio of cationicity to hydrophobicity. Herein, we report a cationic nanoparticle self-assembled from chitosan-graft-oligolysine (CSM5-K5) chains with ultralow molecular weight (1450 Da) that selectively kills bacteria. Further, hydrogen bonding rather than the typical hydrophobic interaction causes the polymer chains to be aggregated together in water into small nanoparticles (with about 37 nm hydrodynamic radius) to concentrate the cationic charge of the lysine. When complexed with bacterial membrane, these cationic nanoparticles synergistically cluster anionic membrane lipids and produce a greater membrane perturbation and antibacterial effect than would be achievable by the same quantity of charge if dispersed in individual copolymer molecules in solution. The small zeta potential (+15 mV) and lack of hydrophobicity of the nanoparticles impedes the insertion of the copolymer into the cell bilayer to improve biocompatibility. In vivo study (using a murine excisional wound model) shows that CSM5-K5 suppresses the growth of methicillin-resistant Staphylococcus aureus (MRSA) bacteria by 4.0 orders of magnitude, an efficacy comparable to that of the last resort MRSA antibiotic vancomycin; it is also noninflammatory with little/no activation of neutrophils (CD11b and Ly6G immune cells). This study demonstrates a promising new class of cationic polymers-short cationic peptidopolysaccharides-that effectively attack MDR bacteria due to the synergistic clustering of, rather than insertion into, bacterial anionic lipids by the concentrated polymers in the resulting hydrogen-bonding-stabilized cationic nanoparticles.