Biocompatible antimicrobial colistin loaded calcium phosphate nanoparticles for the counteraction of biofilm formation in cystic fibrosis related infections

Liquid crystalline coatings loaded with colistin for preventing development of biofilms on orthopedic implants

The current antibacterial strategies focus on antibiotic therapy and extensive hygienic measures during orthopedic surgery. However, potential development of implant-associated infections remains a persistent clinical challenge. There is, therefore, a growing interest in introducing innovative safe antibacterial strategies for preventing and combating biofilm development on implants. Antibacterial coatings, particularly, are attractive for local delivery of antibacterial agents. We aim in this proof-of-concept study at introducing a novel and translatable implant coating approach, focusing on directed assembly of inverse non-lamellar lyotropic liquid crystalline (LLC) nanostructures on implants for prevention of initial bacterial attachment and biofilm formation through local delivery of the widely used cationic antibiotic colistin (COL). On exposure of dry lipid films deposited on model implants to aqueous solutions of COL prepared at different COL concentrations, a set of LLC coatings based on a commercial distilled monoglyceride product (or glycerol monooleate) were produced. In addition to small-angle X-ray scattering (SAXS) characterization investigations, in vitro studies were conducted for evaluating the antibacterial and antibiofilm properties of the LLC coatings against the Gram-negative bacteria Pseudomonas aeruginosa. The SAXS analysis indicated that all samples are inverse bicontinuous cubic Pn3m phases. Significant COL's antibacterial activity and efficient protection against bacterial adhesion were demonstrated on coating model implants with LLC surface films produced by using aqueous solutions containing COL at concentrations of 50 and 500 µg/mL. On exposure to serum, the detected structural alterations and changes in COL's antibacterial activity are also discussed. This study also highlights the implications of LLC self-assemblies for designing nanostructural coatings on orthopedic implants, which can prevent implant-associated biofilm infections through local delivery of antibacterial agents.

Antibacterial and Antibiofilm Activities of Colistin and Ceftazidime-Avibactam Conjugated Silver Nanoparticles

Multidrug-resistant (MDR) Gram-negative bacteria constitute a major global health concern, and the increasing resistance to last-line antimicrobial agents compels the urgent improvement of novel treatment strategies. The present study aims to produce colistin and ceftazidime-avibactam conjugated silver nanoparticles by eco-friendly synthesis method and to evaluate the antimicrobial and antibiofilm activities against MDR Gram-negative bacteria. The physicochemical characteristics of nanoparticles were analyzed through ultraviolet-visible spectrophotometry, high resolution-transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Broth microdilution assay was conducted to detect minimum inhibitory concentration (MIC) levels of nanoparticles against MDR bacteria and reference strains. The antibiofilm efficacy was assessed by the crystal violet staining method, and the cytotoxic activity was determined using the MTT assay. The characterization analyses demonstrated spherical morphology (5.6-41.6 nm in diameter) and crystalline structures for the nanoparticles. The MIC levels of antibiotic-conjugated nanoparticles against reference strains and MDR clinical isolates ranged from 0.125 to 4 µg/mL, showing inhibitory concentrations (2-1024 fold) lower than that of free antibiotics (p < 0.05). Nanoparticles exhibited more effective biofilm activity on Pseudomonas aeruginosa PAO1 strain compared to free antibiotics, and showed no substantial inhibitory impact on cell viability, even at increased concentrations. The nanoparticles obtained by the green synthesis method could be promising agents in fighting against MDR Gram-negative bacteria.

Bone Regeneration: Mini-Review and Appealing Perspectives

Bone is a natural mineral-organic nanocomposite protecting internal organs and allowing mobility. Through the ages, numerous strategies have been developed for repairing bone defects and fixing fractures. Several generations of bone repair biomaterials have been proposed, either based on metals, ceramics, glasses, or polymers, depending on the clinical need, the maturity of technologies, and knowledge of the natural constitution of the bone tissue to be repaired. The global trend in bone implant research is shifting toward osteointegrative, bioactive and possibly stimuli-responsive biomaterials and, where possible, resorbable implants that actively promote the regeneration of natural bone tissue. In this mini-review, the fundamentals of bone healing materials and clinical challenges are summarized and commented on with regard to progressing scientific discoveries. The main types of bone-healing materials are then reviewed, and their specific relevance to the field is reminded, with the citation of reference works. In the final part, we highlight the promise of hybrid organic-inorganic bioactive materials and the ongoing research activities toward the development of multifunctional or stimuli-responsive implants. This contribution is expected to serve as a commented introduction to the ever-progressing field of bone regeneration and highlight trends of future-oriented research.

Hybrid Hydroxyapatite-Metal Complex Materials Derived from Amino Acids and Nucleobases

Calcium phosphates (CaPs) and their substituted derivatives encompass a large number of compounds with a vast presence in nature that have aroused a great interest for decades. In particular, hydroxyapatite (HAp, Ca10(OH)2(PO4)6) is the most abundant CaP mineral and is significant in the biological world, at least in part due to being a major compound in bones and teeth. HAp exhibits excellent properties, such as safety, stability, hardness, biocompatibility, and osteoconductivity, among others. Even some of its drawbacks, such as its fragility, can be redirected thanks to another essential feature: its great versatility. This is based on the compound's tendency to undergo substitutions of its constituent ions and to incorporate or anchor new molecules on its surface and pores. Thus, its affinity for biomolecules makes it an optimal compound for multiple applications, mainly, but not only, in biological and biomedical fields. The present review provides a chemical and structural context to explain the affinity of HAp for biomolecules such as proteins and nucleic acids to generate hybrid materials. A size-dependent criterium of increasing complexity is applied, ranging from amino acids/nucleobases to the corresponding macromolecules. The incorporation of metal ions or metal complexes into these functionalized compounds is also discussed.

Pulmonary delivery systems for antimicrobial peptides

Bacterial infections of the respiratory tract cause millions of deaths annually. Several diseases exist wherein (1) bacterial infection is the main cause of disease (e.g., tuberculosis and bacterial pneumonia), (2) bacterial infection is a consequence of disease and worsens the disease prognosis (e.g., cystic fibrosis), and (3) bacteria-triggered inflammation propagates the disease (e.g., chronic obstructive pulmonary disease). Current approaches to combat infections generally include long and aggressive antibiotic treatments, which challenge patient compliance, thereby making relapses common and contributing to the development of antibiotic resistance. Consequently, the proportion of infections that cannot be treated with conventional antibiotics is rapidly increasing, and novel therapies are urgently needed. In this context, antimicrobial peptides (AMPs) have received considerable attention as they may exhibit potent antimicrobial effects against antibiotic-resistant bacterial strains but with modest toxicity. In addition, some AMPs suppress inflammation and provide other host defense functions (motivating the alternative term host defense peptides (HDPs)). However, the delivery of AMPs is complicated because they are large, positively charged, and amphiphilic. As a result of this, AMP delivery systems have recently attracted attention. For airway infections, the currently investigated delivery approaches range from aerosols and dry powders to various self-assembly and nanoparticle carrier systems, as well as their combinations. In this paper, we discuss recent developments in the field, ranging from mechanistic mode-of-action studies to the application of these systems for combating bacterial infections in the airways.

One-Pot Synthesis of Bioinspired Peptide-Decorated Apatite Nanoparticles for Nanomedicine

Hybrid organic-inorganic bio-inspired apatite nanoparticles (NPs) are attractive for biomedical applications and especially in nanomedicine. Unfortunately, their applications in nanomedicine are limited by their broad particle size distributions and uncontrolled drug loading due to their multistep synthesis process.  Besides, very few attempts at exposing bioactive peptides on apatite NPs are made. In this work, an original one-pot synthesis of well-defined bioactive hybrid NPs composed of a mineral core of bioinspired apatite surrounded by an organic corona of bioactive peptides is reported. Dual stabilizing-bioactive agents, phosphonated polyethylene glycol-peptide conjugates, are prepared and directly used during apatite precipitation i) to form the organic corona during apatite precipitation, driving the size and shape of resulting hybrid NPs with colloidal stabilization and ii) to expose peptide moieties (RGD or YIGSR sequences) at the NPs periphery in view of conferring additional surface properties to enhance their interaction with cells. Here, the success of this approach is demonstrated, the functionalized NPs are fully characterized by Fourier-transform infrared, Raman, X-ray diffraction, solid and liquid state NMR, transmission electron microscopy, and dynamic light scattering, and their interaction with fibroblast cells is followed, unveiling a synergistic proliferative effect.

New Antimicrobial Strategies to Treat Multi-Drug Resistant Infections Caused by Gram-Negatives in Cystic Fibrosis

People with cystic fibrosis (CF) suffer from recurrent bacterial infections which induce inflammation, lung tissue damage and failure of the respiratory system. Prolonged exposure to combinatorial antibiotic therapies triggers the appearance of multi-drug resistant (MDR) bacteria. The development of alternative antimicrobial strategies may provide a way to mitigate antimicrobial resistance. Here we discuss different alternative approaches to the use of classic antibiotics: anti-virulence and anti-biofilm compounds which exert a low selective pressure; phage therapies that represent an alternative strategy with a high therapeutic potential; new methods helping antibiotics activity such as adjuvants; and antimicrobial peptides and nanoparticle formulations. Their mechanisms and in vitro and in vivo efficacy are described, in order to figure out a complete landscape of new alternative approaches to fight MDR Gram-negative CF pathogens.