Molecular weight and pH aspects of the efficacy of oligochitosan against methicillin-resistant Staphylococcus aureus (MRSA)

The quantitative molecular weight-antimicrobial activity relationship for chitosan polymers, oligomers, and derivatives

Chitosan and chitosan derivatives can kill pathogenic microorganisms including bacteria and fungi. The antimicrobial activity is dependent on the degree of acetylation, substituent structure, and molecular weight. Over the past four decades, numerous studies have endeavored to elucidate the relationship between molecular weight and the activity against microorganisms. However, investigators have reported divergent and, at times, conflicting conclusions. Here a bilinear equation is proposed, delineating the relationship between antimicrobial activity, defined as log (1/MIC), and the molecular weight of chitosan and chitosan derivatives. Three constants AMin, AMax, and CMW govern the shape of the curve determined by the equation. The constant AMin denotes the minimal activity expected as the molecular weight tends towards zero while AMax represents the maximal activity observed for molecular weights exceeding CMW, the critical molecular weight required for max activity. This equation was applied to analyze data from seven studies conducted between 1984 and 2019, which reported MIC (Minimum Inhibitory Concentration) values against bacteria and fungi for various molecular weights of chitosan and its derivatives. All the 29 datasets exhibited a good fit (R2 ≥ 0.5) and half excellent (R2 ≥ 0.95) fit to the equation. The CMW generally ranged from 4 to 10 KD for datasets with an excellent fit to the equation.

Exploiting specific properties of squid pens for the preparation of oligochitosan hydrochloride

Herein, we describe in first the application of squid pens for the preparation of pharmaceutical-grade oligochitosan hydrochloride with the physicochemical characteristics corresponding with the requirements of the European Pharmacopoeia. It is shown that the use of specific properties of squid pens as a source of parent chitosan allows preparing the product with a high yield at relatively moderate process conditions used for squid pens treatments and chitosan depolymerization.

An insight into the effect of interaction with protein on antibacterial activity of chitosan derivatives

Antimicrobial activity of chitosan in protein-rich media is of a particular interest for various protein-based drug delivery and other systems. For the first time, bacteriostatic activity of chitosan derivatives in the presence of caseinate sodium (CAS) was studied and discussed. Complexation of chitosan derivatives soluble in acidic (CH and RCH) or alkalescent (RCH) media with CAS was confirmed by fluorescent spectroscopy, turbodimetry, light scattering data and measurement of electrical potentials of CAS/chitosan derivative complexes. An addition of CH and RCH caused a static quenching of CAS. Binding constants Kb determined for CH/CAS and RCH/CAS complexes at pH 6.0 were equal to 29.8 × 106 M-1 and 8.9 × 106 M-1, respectively. Kb value of RCH/CAS complex at pH 7.4 was equal to 1.1 × 105'M-1. The poisoned food method was used for counting the number and the direct measurement of the size of bacterial colonies on the surfaces of turbid agar media containing CAS/chitosan derivative complexex. Complete suppression of E. coli cells growth and restriction of S. aureus cells growth were observed on the surface of acidic media. A high concentration of CAS reduced the activity. The activity of RCH in alkalescent media is low or absent. These results can be promising for preparation of microbiologically stable protein-based drug delivery systems.

Formation Kinetics and Antimicrobial Activity of Silver Nanoparticle Dispersions Based on N-Reacetylated Oligochitosan Solutions for Biomedical Applications

The paper presents the results of the synthesis, a detailed kinetics study, and an investigation of the biological activity of silver nanoparticles (AgNPs) in aqueous solutions of N-reacetylated oligochitosan hydrochloride. UV-visible spectrophotometry and dynamic light scattering were employed to control silver ion reduction. The process was observed to follow a pseudo-first-order law. Transmission and scanning electron microscopy demonstrated that AgNPs ranging in size from 10 to 25 nm formed aggregates measuring 60 to 90 nm, with the aggregate surface coated by a 2-4 nm chitosan shell. X-ray microanalysis and powder X-ray diffractometry were used to study the phase composition, identifying two crystalline phases, nanocrystalline silver and AgCl, present in the dispersions. The antibacterial effect was assessed using the serial dilution method for dispersions with varying degrees of Ag+ conversion. Nanodispersions exhibited significant activity against Escherichia coli, Pseudomonas aeruginosa, Bacillus cereus, and Staphylococcus aureus. Interestingly, the activity did not appear to be heavily influenced by the presence of the AgCl phase or the concentration of Ag+ ions. These synthesized dispersions hold promise for the development of materials tailored for biomedical applications.

Effect of Soft Preheating of Bovine Serum Albumin on the Complexation with Oligochitosan: Structure and Conformation of BSA in the Complex

Phase analysis, spectroscopic, and light scattering methods are applied to investigate the peculiarities of the interaction of oligochitosan (OCHI) with native and preheated bovine serum albumin (BSA) as well as the conformational and structural changes of BSA in BSA/OCHI complex. As shown, untreated BSA binds with OCHI mainly forming soluble electrostatic nanocomplexes, with the binding causing an increase in BSA helicity without a change in the local tertiary structure and thermal stability of BSA. In contrast, soft preheating at 56 °C enhances the complexation of BSA with OCHI and slightly destabilizes the secondary and local tertiary structures of BSA within the complex particles. Preheating at 64 °C (below the irreversible stage of BSA thermodenaturation) leads to further enhancement in the complexation and formation of insoluble complexes stabilized by both Coulomb forces and hydrophobic interactions. The finding can be promising for the preparation of biodegradable BSA/chitosan-based drug delivery systems.

Complexation between chitosan and carboxymethyl cellulose in weakly acidic, neutral, and weakly alcaline media

The interaction between carboxymethyl cellulose and partially reacetylated chitosan soluble in acidic and alkaline aqueous media is studied by light scattering and isothermal titration calorimetry in a wide pH range. It is shown that the formation of polyelectrolyte complexes (PEC) can occur in the pH range of 6-8, while this pair of polyelectrolytes loses the ability to complexation upon transition to a more alkaline medium. The revealed dependence of the observed enthalpy of interaction on the ionization enthalpy of the buffer indicates the participation of proton transfer from the buffer substance to chitosan and its additional ionization in the binding process. This phenomenon is first observed in a mixture of a weak polybase chitosan and a weak polyacid. The possibility to obtain soluble nonstoichiometric PEC by a direct mixing of the components in a weakly alkaline medium is shown. The resulting PECs are polymolecular particles in shape close to homogeneous spheres with a radius of about 100 nm. The obtained results are promising for creating of biocompatible and biodegradable drug delivery systems.

Complexation of oligochitosan with sodium caseinate in alkalescent and weakly acidic media

Сomplexation of oligochitosan (OCHI) having the degree of acetylation (DA 26 %) with sodium caseinate (SC) at pH 5.8 and 7.2 is described and compared with the complexation of OCHI (DA 2 %) at pH 5.8. In the alkalescent medium, the complexation of OCHI (DA 26 %) is weaker and dualistic depending on SC concentration in the system. In the diluted alkalescent system, the formation of only soluble complexes is observed at OCHI/SC ratio ≤0.9. In the semi diluted one, the complexation results in the formation of insoluble complexes those composition changes symbatically with the OCHI/SC ratio in the system. At pH 5.8, OCHI/SC ratio in insoluble complexes remains the same regardless of OCHI/SC ratio in the solution. At pH 5.8, the electrostatic complexation weakens with an increase in DA and is completely suppressed at a high ionic strength. These results can be promising for construction of biodegradable protein/chitosan drug delivery systems.

Peculiarities of the interaction of sodium dodecyl sulfate with chitosan in acidic and alkaline media

In this work, the interaction between the negatively charged surfactant sodium dodecyl sulfate (SDS) and partially N-reacetylated chitosan (RA-CHI), which is soluble at pH range up to pH 12, is studied in a wide pH range including alkaline media by light scattering (LS) and isothermic titration calorimetry (ITC). It is shown that in the weakly alkaline medium (pH 7.4), RA-CHI/SDS interaction is exothermic and cooperative. This interaction is found to be coupled with proton transfer from the buffer substance to chitosan as it is revealed by the dependence of the measured heat release on the ionization enthalpy of the buffer. At higher pH values (pH > 8), another mechanism of interaction is observed that include SDS micellization induced by hydrophobic interactions with polymer segments, so that no phase separation occurred in these mixtures. The results obtained can contribute to expand the knowledge about application of chitosan for preparation of pharmaceutical and cosmetic compositions containing anionic surfactants.

Fundamental and Practical Aspects in the Formulation of Colloidal Polyelectrolyte Complexes of Chitosan and siRNA

The formation of electrostatic interactions between polyanionic siRNA and polycations gives an easy access to the formation of colloidal particles capable of delivering siRNA in vitro or in vivo. Among the polycations used for siRNA delivery, chitosan occupies a special place due to its unique physicochemical and biological properties. In this chapter we describe the fundamental and practical aspects of the formation of colloidal complexes between chitosan and siRNA. The basis of the electrostatic complexation between oppositely charged polyelectrolytes is first introduced with a focus on the specific conditions to obtain stable colloid complex particles. Subsequent, the properties that make chitosan so special are described. In a third part, the main parameters influencing the colloidal properties and stability of siRNA/chitosan complexes are reviewed with emphasis on some practical aspects to consider in the preparation of complexes.

Molecular features of the interaction and antimicrobial activity of chitosan in a solution containing sodium dodecyl sulfate

Molecular interaction of chitosan with sodium dodecyl sulfate (SDS) is a more complicated process than it has been imagined so far. For the first time it has been shown that the shorter chitosan chains are, the more preferably they interact with the SDS and the larger-in-size microparticles they form. The influence of ionic strength, urea and temperature on microparticles formation allows interpreting the mechanism of microparticles formation as a cooperative electrostatic interaction between SDS and chitosan with simultaneous decrease in the surface charge of the complexes initiating the aggregation of microparticles. It is shown that hydrogen bonding is mainly responsible for the aggregation while hydrophobic interaction has a lesser effect. Chitosan demonstrates a high bacteriostatic activity in the presence of SDS in solution and can be promising for preparation of microbiologically stable pharmaceutical hydrocolloids, cosmetic products and chitosan-based Pickering emulsions containing strong anionic surfactants.

Biodegradable thermoresponsive oligochitosan nanoparticles: Mechanisms of phase transition and drug binding-release

Oligochitosan, a low molecular weight derivative of the cationic biopolymer, chitosan, currently shows a great potential of application as a biodegradable non-toxic stimuli-sensitive drug carrier. This paper aimed to elucidate the thermoresponsive potential of oligochitosan and the temperature-controlled drug binding and release to shed light on oligochitosan potential in stimuli-responsive drug delivery. Mechanisms of thermoresponsive behavior of oligochitosan induced by β-glycerophosphate (GP) were investigated using ITC, DSC, and DLS. Upon heating, the aqueous oligochitosan solution underwent a cooperative transition of the microphase separation type resulting in the formation of stable nano-sized particles. Energetics of the GP-oligochitosan interaction (evaluated by ITC) revealed a positive enthalpy of the GP binding to oligochitosan, which pointed to a notable contribution of dehydration and the related rearrangement of the polysaccharide hydration shell. Energetics of the thermal phase transition of oligochitosan was investigated by DSC upon variation of the solvent dielectric constant and GP concentration. The dependences of the transition parameters on these variables were determined and used for the analysis of the oligochitosan thermoresponsivity mechanism. The binding of ibuprofen to the thermotropic oligochitosan nanogel particles and its release from them were evaluated under near-physiological conditions. Relevantly, the oligochitosan nanoparticles surpassed some reference macromolecular adsorbers by the affinity for the drug and by the delayed release kinetics.

Effects of Chain Length of Chitosan Oligosaccharides on Solution Properties and Complexation with siRNA

In the context of gene delivery, chitosan has been widely used as a safe and effective polycation to complex DNA, RNA and more recently, siRNA. However, much less attention has been paid to chitosan oligosaccharides (COS) despite their biological properties. This study proposed to carry out a physicochemical study of COS varying in degree of polymerization (DP) from 5 to 50, both from the point of view of the solution properties and the complexing behavior with siRNA. The main parameters studied as a function of DP were the apparent pKa, the solubility versus pH, the binding affinity with siRNA and the colloidal properties of complexes. Some parameters, like the pKa or the binding enthalpy with siRNA, showed a marked transition from DP 5 to DP 13, suggesting that electrostatic properties of COS vary considerably in this range of DP. The colloidal properties of siRNA/COS complexes were affected in a different way by the COS chain length. In particular, COS of relatively high DP (≥50) were required to form small complex particles with good stability.

The Effect of Molecular Weight on the Antibacterial Activity of N,N,N-Trimethyl Chitosan (TMC)

N,N,N-trimethyl chitosan (TMC) with 93% degree of trimethylation was synthesized. TMC and the chitosan starting material were subjected to acidic hydrolysis to produce 49 different samples with a reduced average molecular weight (Mw) ranging from 2 to 144 kDa. This was done to allow the investigation of the relationship between antibacterial activity and Mw over a wide Mw range. NMR investigation showed that hydrolysis did not affect the degree of trimethylation (DSTRI) or the structure of the polymer backbone. The activity of TMC against Staphylococcus aureus (S. aureus) increased sharply with Mw until a certain Mw value (critical Mw for high activity, CMW) was reached. After the CMW, the activity was not affected by a further increase in the Mw. A similar pattern of activity was observed for chitosan. The CMW was determined to be 20 kDa for TMC and 50 kDa for chitosan.

[Comparative evaluation of antimicrobial activity of oligochitosans against Klebsiella pneumoniae]

Antibacterial activity of chitosan with different molecular weight at different pH values against gram-negative Klebsiella pneumoniae was studied. It was found that the dependence of inhibition activity of chitosan on its molecular weight was inversed when the medium pH was increased above 7.0. In acidic media higher molecular weight chitosan had the higher antibacterial activity was occured while and in weak alkaline media oligomeric forms of chitosan displayed the inhibition effect only. Our results showed that the antibacterial activity of chitosan against Klebsiella pneumoniae was closely connected with its polycationic nature, and was dependent on the degree of protonation of chitosan amino groups, which at the same time depended on the degree of polymerization and solution pH values.

Molecular weight dependence of structure and properties of chitosan oligomers

Molecular weight dependence of water solubility of COS.

Antifungal activity of oligochitosans (short chain chitosans) against some Candida species and clinical isolates of Candida albicans: molecular weight-activity relationship

A series of oligochitosans (short chain chitosans) prepared by acidic hydrolysis of chitosan and characterized by their molecular weight, polydispersity and degree of deacetylation were used to determine their anticandidal activities. This study has demonstrated that oligochitosans show a high fungistatic activity (MIC 8-512 μg/ml) against Candida species and clinical isolates of Candida albicans, which are resistant to a series of classic antibiotics. Flow cytometry analysis showed that oligochitosan possessed a high fungicidal activity as well. For the first time it was shown that even sub-MIC oligochitosan concentration suppressed the formation of C. albicans hyphal structures, cause severe cell wall alterations, and altered internal cell structure. These results indicate that oligochitosan should be considered as a possible alternative/additive to known anti-yeast agents in pharmaceutical compositions.