Effect of the ultrastructure of chitosan nanoparticles in colloidal stability, quorum quenching and antibacterial activities

Nanomaterials Regulate Bacterial Quorum Sensing: Applications, Mechanisms, and Optimization Strategies

Anti-virulence therapy that interferes with bacterial communication, known as "quorum sensing (QS)", is a promising strategy for circumventing bacterial resistance. Using nanomaterials to regulate bacterial QS in anti-virulence therapy has attracted much attention, which is mainly attributed to unique physicochemical properties and excellent designability of nanomaterials. However, bacterial QS is a dynamic and multistep process, and there are significant differences in the specific regulatory mechanisms and related influencing factors of nanomaterials in different steps of the QS process. An in-depth understanding of the specific regulatory mechanisms and related influencing factors of nanomaterials in each step can significantly optimize QS regulatory activity and enhance the development of novel nanomaterials with better comprehensive performance. Therefore, this review focuses on the mechanisms by which nanomaterials regulate bacterial QS in the signal supply (including signal synthesis, secretion, and accumulation) and signal transduction cascade (including signal perception and response) processes. Moreover, based on the two key influencing factors (i.e., the nanomaterial itself and the environment), optimization strategies to enhance the QS regulatory activity are comprehensively summarized. Collectively, applying nanomaterials to regulate bacterial QS is a promising strategy for anti-virulence therapy. This review provides reference and inspiration for further research on the anti-virulence application of nanomaterials.

Application of nanomaterials as potential quorum quenchers for disease: Recent advances and challenges

Chemical signal molecules are used by bacteria to interact with one another. Small hormone-like molecules known as autoinducers are produced, released, detected, and responded to during chemical communication. Quorum Sensing (QS) is the word for this procedure; it allows bacterial populations to communicate and coordinate group behavior. Several research has been conducted on using inhibitors to prevent QS and minimize the detrimental consequences. Through the enzymatic breakdown of the autoinducer component, by preventing the formation of autoinducers, or by blocking their reception by adding some compounds (inhibitors) that can mimic the autoinducers, a technique known as "quorum quenching" (QQ) disrupts microbial communication. Numerous techniques, including colorimetry, electrochemistry, bioluminescence, chemiluminescence, fluorescence, chromatography-mass spectroscopy, and many more, can be used to test QS/QQ. They all permit quantitative and qualitative measurements of QS/QQ molecules. The mechanism of QS and QQ, as well as the use of QQ in the prevention of biofilms, are all elaborated upon in this writing, along with the fundamental study of nanoparticle (NP)in QQ. Q.

Design and in vitro assessment of chitosan nanocapsules for the pulmonary delivery of rifabutin

Tuberculosis (TB) is a life-threatening disease and a main cause of death worldwide. It mainly affects the lungs, and it is attributed to the infection with Mycobacterium tuberculosis (MTB). Current treatments consist of the oral administration of combinations of antibiotics including rifabutin, in high doses and for long periods of time. These therapeutic regimens are associated with many side effects and high rates of drug resistance. To overcome these problems, this study aims at developing a nanosystem for the improved delivery of antibiotics, with potential application in pulmonary delivery. Chitosan-based nanomaterials are widely used in biomedical applications, due to their biodegradability and biocompatibility, as well as their potential antimicrobial effects and lack of toxicity. In addition, this polymer is particularly attractive for mucosal delivery due to its bioadhesive properties. Therefore, the structure of the proposed nanocarrier consists of a chitosan shell and a lipid core with a combination of different oils and surfactants to allow optimal association of the hydrophobic drug rifabutin. These nanocapsules were characterized in terms of size, polydispersity index, surface charge, morphology, encapsulation efficiency and biological stability. The release kinetics of the drug-loaded nanostructures was evaluated in simulated lung media. Moreover, in vitro studies in different cell models (A549 and Raw 264.7 cells) demonstrated the safety of the nanocapsules as well as their efficient internalization. An antimicrobial susceptibility test was performed to evaluate the efficacy of the rifabutin-loaded nanocapsules against Mycobacterium phlei. This study indicated complete inhibition for antibiotic concentrations within the expected susceptibility range of Mycobacterium (≤ 0.25-16 mg/L).

Triborheological Analysis of Reconstituted Gastrointestinal Mucus/Chitosan:TPP Nanoparticles System to Study Mucoadhesion Phenomenon under Different pH Conditions

Polymeric nanoparticles have attracted much attention as pharmaceutical delivery vehicles to prolong residence time and enhance the bioavailability of therapeutic molecules through the mucoadhesive phenomenon. In this study, chitosan:TPP nanoparticles were synthetized using the ionic gelation technique to analyze their mucoadhesive interaction with reconstituted porcine gastrointestinal mucus from a triborheological point of view under different pH conditions (pH = 2.0, 4.0, 6.0 and 7.0). The triborheological profile of the reconstituted mucus was evaluated at different pH environments through the oscillation frequency and the flow sweep tests, demonstrating that the reconstituted mucus exhibits shear thinning behavior regardless of pH, while its viscoelastic properties showed a change in behavior from a polymeric solution performance under neutral pH conditions to a viscoelastic gel under acidic conditions. Additionally, a rheological synergism analysis was performed to visualize the changes that occur in the viscoelastic properties, the viscosity and the coefficient of friction of the reconstituted mucus samples as a consequence of the interaction with the chitosan:TPP nanoparticles to determine or to discard the presence of the mucoadhesion phenomenon under the different pH values. Mucoadhesiveness evaluation revealed that chitosan:TPP exhibited strong mucoadhesion under highly acidic pH conditions, below its pKa value of 6.5. In contrast, at neutral conditions or close to its pKa value, the chitosan:TPP nanoparticles' mucoadhesiveness was negligible.

Cytocompatibility / Antibacterial Activity Trade-off for Knittable Wet-Spun Chitosan Monofilaments Functionalized by the In Situ Incorporation of Cu2+ and Zn2

The wet spinning of cytocompatible, bioresorbable, and knittable chitosan (CTS) monofilaments would be advantageous for a variety of surgical applications. The complexation capacity of chitosan with Cu²⁺ or Zn²⁺ can be leveraged to enhance its antibacterial activity, but not at the expense of cytocompatibility. In this work, a wet-spinning process was adapted for the in situ incorporation of Cu²⁺ or Zn²⁺ with chitosan dopes to produce monofilaments at different drawing ratios (τ_tot) with various cation/glucosamine molar ratios, evaluated in the fibers (r_Cu,f and r_Zn,f). Cytocompatibility and antibacterial activity of wet-spun monofilaments were, respectively, quantified by in vitro live-dead assays on balb 3T3 and by different evaluations of the proliferation inhibition of Staphylococcus epidermidis (Gram+) and Escherichia coli (Gram-). Knittability was tested by a specific tensile test using a knitting needle and evaluated with an industrial knitting machine. It was found that r_Cu,f = 0.01 and r_Zn,f = 0.03 significantly increase the antibacterial activity without compromising cytocompatibility. Wet spinning with τ_tot = 1.6 allowed the production of knittable CTS-Cu monofilaments, as confirmed by knitting assays under industrial conditions.

Decellularized nerve extracellular matrix/chitosan crosslinked by genipin to prepare a moldable nerve repair material

Decellularized nerve extracellular matrix (NECM) composited with chitosan are moldable materials suitable for spinal cord repair. But the rapid biodegradation of the materials may interrupt neural tissue reconstruction in vivo. To improve the stability of the materials, the materials produced by NECM and chitosan hydrogels were crosslinked by genipine, glutaraldehyde or ultraviolet ray. Physicochemical property, degradation and biocompatibility of materials crosslinked by genipin, glutaraldehyde or ultraviolet ray were evaluated. The scaffold crosslinked by genipin possessed a porous structure, and the porosity ratio was 89.07 + 4.90%, the average diameter of pore was 85.32 + 5.34 μm. The crosslinked degree of the scaffold crosslinked by genipin and glutaraldehyde was 75.13 ± 4.87%, 71.25 ± 5.06% respectively; Uncrosslinked scaffold disintegrated when immerged in distilled water while the scaffold crosslinked by genipin and glutaraldehyde group retained their integrity. The scaffold crosslinked by genipin has better water absorption, water retention and anti-enzymatic hydrolysis ability than the other three groups. Cell cytotoxicity showed that the cytotoxicity of scaffold crosslinked by genipin was lower than that crosslinked by glutaraldehyde. The histocompatibility of scaffold crosslinked by genipin was also better than glutaraldehyde group. More cells grew well in the scaffold crosslinked by genipin when co-cultured with L929 cells. The decellularized nerve extracellular matrix/chitosan scaffold crosslinked by the genipin has good mechanical properties, micro structure and biocompatibility, which is an ideal scaffold for the spinal cord tissue engineering.

Screening of Bacterial Quorum Sensing Inhibitors in a Vibrio fischeri LuxR-Based Synthetic Fluorescent E. coli Biosensor

A library of 23 pure compounds of varying structural and chemical characteristics was screened for their quorum sensing (QS) inhibition activity using a synthetic fluorescent Escherichia coli biosensor that incorporates a modified version of lux regulon of Vibrio fischeri. Four such compounds exhibited QS inhibition activity without compromising bacterial growth, namely, phenazine carboxylic acid (PCA), 2-heptyl-3-hydroxy-4-quinolone (PQS), 1H-2-methyl-4-quinolone (MOQ) and genipin. When applied at 50 µM, these compounds reduced the QS response of the biosensor to 33.7% ± 2.6%, 43.1% ± 2.7%, 62.2% ± 6.3% and 43.3% ± 1.2%, respectively. A series of compounds only showed activity when tested at higher concentrations. This was the case of caffeine, which, when applied at 1 mM, reduced the QS to 47% ± 4.2%. In turn, capsaicin, caffeic acid phenethyl ester (CAPE), furanone and polygodial exhibited antibacterial activity when applied at 1mM, and reduced the bacterial growth by 12.8% ± 10.1%, 24.4% ± 7.0%, 91.4% ± 7.4% and 97.5% ± 3.8%, respectively. Similarly, we confirmed that trans-cinnamaldehyde and vanillin, when tested at 1 mM, reduced the QS response to 68.3% ± 4.9% and 27.1% ± 7.4%, respectively, though at the expense of concomitantly reducing cell growth by 18.6% ± 2.5% and 16% ± 2.2%, respectively. Two QS natural compounds of Pseudomonas aeruginosa, namely PQS and PCA, and the related, synthetic compounds MOQ, 1H-3-hydroxyl-4-quinolone (HOQ) and 1H-2-methyl-3-hydroxyl-4-quinolone (MHOQ) were used in molecular docking studies with the binding domain of the QS receptor TraR as a target. We offer here a general interpretation of structure-function relationships in this class of compounds that underpins their potential application as alternatives to antibiotics in controlling bacterial virulence.

Covalently and ionically, dually crosslinked chitosan nanoparticles block quorum sensing and affect bacterial cell growth on a cell-density dependent manner

In our efforts to improve the quality and stability of chitosan nanoparticles (NPs), we describe here a new type of chitosan NPs dually crosslinked with genipin and sodium tripolyphosphate (TPP) that display quorum quenching activity. These NPs were created using a simplified and robust procedure that resulted in improved physicochemical properties and enhanced stability. This procedure involves the covalent crosslinking of chitosan with genipin, followed by the formation of chitosan NPs by ionic gelation with TPP. We have optimized the conditions to obtain genipin pre-crosslinked nanoparticles (PC-NPs) with positive ς-potential (~ +30 mV), small diameter (~130 nm), and low size distributions (PdI = 0.1-0.2). PC-NPs present physicochemical properties that are comparable to those of other dually crosslinked chitosan NPs fabricated with different protocols. In contrast to previously characterized NPs, however, we found that PC-NPs strongly reduce the acyl homoserine lactone (AHL)-mediated quorum sensing response of an Escherichia coli fluorescent biosensor. Thus, PC-NPs combine, in a single design, the stability of dually crosslinked chitosan NPs and the quorum quenching activity of ionically crosslinked NPs. Similar to other chitosan NPs, the mode of action of PC-NPs is consistent with the existence of a "stoichiometric ratio" of NP/bacterium, at which the positive charge of the NPs counteracts the negative ς-potential of the bacterial envelope. Notably, we found that the time of the establishment of the "stoichiometric ratio" is a function of the NP concentration, implying that these NPs could be ideal for applications aiming to target of bacterial populations at specific cell densities. We are confident that our PC-NPs are up-and-coming candidates for the design of efficient anti-quorum sensing and a new generation antimicrobial strategies.

Biomolecular uptake effects on chitosan/tripolyphosphate micro- and nanoparticle stability

Colloidal chitosan/tripolyphosphate (TPP) particles have attracted significant attention as potential delivery vehicles for drugs, genes and vaccines. Yet, there have been several fundamental studies that showed these particles to disintegrate at physiological pH and ionic strength levels. To reconcile these findings with the published drug, gene and vaccine delivery research where chitosan/TPP particle disintegration was not reported, it has been postulated that the particles could be stabilized by their bioactive payloads. To test this hypothesis, here we examine whether the association of chitosan/TPP particles with model anionic proteins, α-lactalbumin (α-LA) and bovine serum albumin (BSA), and polynucleotides (DNA) enhances chitosan/TPP particle stability at physiological ionic strengths, using 150 mM NaCl (pH 5.5) and 1× PBS (pH 6.0) as the dissolution media. Light scattering and UV-vis spectroscopy revealed that anionic protein uptake had no impact on particle stability, likely due to the relatively weak protein/particle binding at near-physiological ionic strengths, which caused the protein to be rapidly released. This result occurred regardless of whether the protein was loaded during or after particle formation. Conversely, DNA uptake (at least at some compositions) increased the chitosan fractions persisting in a complexed/particulate form in model dissolution media, with the DNA remaining largely complexed to the chitosan at all investigated conditions. Collectively, these findings suggest that, while most bioactive payloads do not interact with chitosan strongly enough to stabilize chitosan/TPP particles, these chitosan particles can be stabilized to dissolution through the incorporation of polyanions.

Preparation of Puerarin Chitosan Oral Nanoparticles by Ionic Gelation Method and Its Related Kinetics

In this paper, as an active ingredient, puerarin chitosan nanoparticles (Pur-CS/TPP-NPs) are prepared by an ionic gelation method. The chitosan (CS) concentration, pH of the CS solution, sodium tripolyphosphate (TPP) concentration, stirring speed, stirring time, ultrasonic power, and dosage are used as single factors for investigation, and the encapsulation efficiency, drug loading capacity, particle size, and polydispersity index (PDI) are used as indicators for investigation. The optimal prescription is determined using the Box–Behnken effect surface design method. The characterization of the best formulation, which is determined via an in vitro release assay and liquid chromatography/tandem mass spectrometry (LC-MS/MS) analysis methods, is used here for pharmacokinetic studies. An in situ single-pass intestinal perfusion model is used to investigate drug absorption in the intestine. After characterization, the morphologies of the nanoparticles are intact. It can be seen from the in vitro release experiments that the equation fitted by the nanoparticles is the Higuchi model, the nanoparticle release process is very stable and without sudden release, indicating that the nanoparticles are well-released in vitro. The pharmacokinetic results and the in situ single-pass intestinal perfusion model study show that the bioavailability and absorption of Pur-CS/TPP-NPs were significantly higher than Pur. Thus, all the results show that the prepared nanoparticles can significantly improve the bioavailability of Pur, and we hope to lay the foundation for the development of new products of Pur.