Development and Evaluation of Azithromycin-Loaded Transethosomes for Enhanced Dermal Delivery and Antibacterial Efficacy

Background/Objectives: The topical delivery of antibiotics through transethosomes shows promise for enhancing its dermal delivery for the treatment of skin infections. This study aimed to develop and characterize azithromycin-loaded transethosomes to enhance topical drug delivery and improve the antibacterial activity of azithromycin. Methods: The prepared azithromycin formulations underwent assessment for various characteristics, including their vesicle dimensions, size distribution, zeta potential, encapsulation efficiency, and morphological features (via TEM analysis). Additionally, their thermal properties were examined through DSC analysis, and their stability was monitored over six months under refrigerated storage conditions. The sequential tape-stripping technique was employed to conduct ex vivo penetration studies on human skin. Interactions between transethosomes and stratum corneum lipids were examined using attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR). Additionally, the formulations were tested for their in vitro antibacterial efficacy against Staphylococcus aureus. Results: The findings revealed that AZ 1 and AZ 2 had vesicle sizes of 108.44 ± 5.72 nm and 70.42 ± 6.02 nm, zeta potential measurements of -11.897 ± 1.820 mV and -34.575 ± 4.535 mV, and high entrapment efficiencies of 99.259 ± 0.086% and 99.560 ± 0.014%, respectively. Transmission electron microscopy (TEM) analysis confirmed the spherical nature of the vesicles, whereas differential scanning calorimetry (DSC) confirmed the successful encapsulation of azithromycin in transethosomes. The formulations exhibited acceptable physical stability at 4 °C for six months. Ex vivo studies revealed a significantly higher deposition of azithromycin in the skin by both transethosome formulations than by the drug solution (p < 0.05), with low systemic absorption. Among the formulations, AZ 2 resulted in much deeper skin penetration, with deeper dermal and epidermal layer deposition (1.388 ± 0.242 µg/cm2) compared to AZ 1 (four-fold higher, p < 0.05) and to the control drug solution (12 times more, p < 0.05). Analysis using ATR-FTIR suggested that azithromycin-loaded transethosomes improve the drug penetration by increasing the lipid fluidity and extracting lipids from the stratum corneum. Moreover, the transethosomes loaded with azithromycin demonstrated enhanced antibacterial efficacy against Staphylococcus aureus, with minimum inhibitory concentration (MIC) values that were lower than those of the free drug solution. Conclusion: The results highlight the promising potential of transethosomes as a novel topical drug delivery system for azithromycin that offers improved therapeutic effects against skin infections.

Nanomaterial-enabled anti-biofilm strategies: new opportunities for treatment of bacterial infections

Biofilms play a pivotal role in bacterial pathogenicity and antibiotic resistance, representing a major challenge in the treatment of bacterial infections. The limited diffusion and inactivation efficacy of antibiotics within biofilms hinder their clearance, and while increasing dosage may enhance effectiveness, it also promotes antibiotic resistance. Nano-delivery systems that target antimicrobial agents directly to biofilms offer a promising strategy to overcome this challenge. This review summarizes the resistance mechanisms and therapeutic challenges associated with biofilms, with a focus on recent advances in nano-delivery systems such as liposomes, nanoemulsions, cell membrane vesicles (CMVs), polymers, dendrimers, nanogels, inorganic nanoparticles, and metal-organic frameworks (MOFs). Furthermore, the review explores the potential applications and challenges of nano-delivery systems in biofilm treatment and provides recommendations to guide future research and development in this field.

Effectiveness of a Novel Liposomal Methylglyoxal-Tobramycin Formulation in Reducing Biofilm Formation and Bacterial Adhesion

Background: The emergence of multidrug-resistant bacteria presents a significant global health threat. Liposomal antibiotics have shown a potential to improve antibiotic delivery and efficacy. This study aimed to develop liposomes encapsulating tobramycin (TOB) and methylglyoxal (MGO) to enhance TOB activity while reducing bacterial adhesion and biofilm formation. Methods: Clinical isolates of Pseudomonas aeruginosa and Klebsiella pneumoniae were characterized using whole-genome sequencing. Liposomes (Lip-MGO-TOB) were formulated using Manuka honey as a surfactant and loaded with MGO and TOB. Antibacterial activity, biofilm formation, and bacterial cell adhesion assays were performed to compare the efficacy of Lip-MGO-TOB against free TOB. Liposome characterization included analyses of morphology, zeta potential, TOB encapsulation efficiency, and stability under various biological conditions. Results: The Lip-MGO-TOB formulation, at a minimum inhibitory concentration (MIC) of 32 µg/mL, reduced the biofilm formation of the P. aeruginosa isolate (PA85) by 68%. Conversely, free TOB, at a MIC of 64 µg/mL, achieved only a 21% reduction. For the K. pneumoniae isolate (KP57), Lip-MGO-TOB inhibited bacterial adhesion to A549 cells at a lower concentration (256 µg/mL) compared to free TOB (512 µg/mL). Lip-MGO-TOB demonstrated sustained drug release over 24 h under tested conditions and retained over 99% of TOB. Conclusions: The Lip-MGO-TOB formulation significantly enhanced TOB activity against resistant bacteria compared to free TOB. Additionally, it provided a stable drug delivery system with controlled drug release. Liposomal TOB represents a promising advancement in combating antibiotic resistance by improving the efficacy and delivery of conventional antibiotics.

Macrolide-loaded nanofibrous inserts with polycaprolactone and cellulose acetate base for sustained ocular delivery: Pharmacokinetic study in Rabbit's eye

The present study aimed to prepare nanofibrous inserts for sustained ocular drug delivery of Azithromycin (AZM) toward conquering the obstacles of conventional topical drug delivery. Nanofibers were fabricated by electrospinning using polycaprolactone (PCL) and cellulose acetate (CA) which are biocompatible and biodegradable polymers. Prepared nanofibers were evaluated in terms of physicochemical, morphological properties, pharmacokinetic study and ocular irritation. SEM images revealed average diameters of about 160 nm and 190 nm for CA and PCL nanofibers, respectively. These ocular drug delivery systems were strong, flexible, and stable under humid and dry conditions. Quantification was performed using microbiological assay by M. luteus as a microorganism. While PCL-based nanofibrous inserts released AZM in a two-step manner initiated by a burst release via Peppas kinetical model, CA-based inserts showed a gradual release profile without any burst release which followed the first-order model. Results showed that these inserts were non-cytotoxic and non-irritating. The nanofibers showed antibacterial efficacy against Escherichia coli and Staphylococcus aureus. In addition, according to a pharmacokinetic study in Rabbit's Eye, a higher Cmax and lower Tmax were achieved by PCL nanofibers compared to CA-based ones. The pharmacokinetic study of nanofibers in rabbit eyes showed that all formulations were able to maintain the effective concentration of AZM for about 6 days. In conclusion, the prepared nanofibers can be effectively utilized for prolonged ocular delivery of AZM in the treatment of conjunctival infections.

Overcoming resistance: Chitosan-modified liposomes as targeted drug carriers in the fight against multidrug resistant bacteria-a review

Antimicrobial resistance (AMR) poses a significant global health threat, rendering standard antibiotics ineffective against multi-drug resistant bacteria. To tackle this urgent issue, innovative approaches are essential. Liposomes, small spherical vesicles made of a phospholipid bilayer, present a promising solution. These vesicles can encapsulate various medicines and are both biocompatible and biodegradable. Their ability to be modified for targeted tissue or cell uptake makes them an ideal drug delivery system. By delivering antibiotics directly to infection sites, liposomes minimize side effects and reduce the development of resistance. However, challenges such as poor stability and rapid drug leakage limit their biological application. Chitosan, a biocompatible polymer, enhances liposome interaction with specific tissues or cells, enabling selective drug release at infection sites. Incorporating chitosan into liposome formulations alters and diversifies their surface characteristics through electrostatic interactions, resulting in improved stability and pH-sensitive drug release. These interactions are crucial for enhancing drug retention and targeted delivery, especially in varying pH environments like tumor sites or infection areas, thereby improving therapeutic outcomes and reducing systemic side effects. This review discusses recent advancements, challenges, and the need for further research to optimize liposome formulations and enhance targeted drug delivery for effective AMR treatment. Chitosan-modified liposomes offer a promising strategy to overcome AMR and improve antimicrobial therapies.

Research Progress on Strategies for Improving the Enzyme Properties of Bacteriophage Endolysins

Bacterial resistance to commonly used antibiotics is one of the major challenges to be solved today. Bacteriophage endolysins (Lysins) have become a hot research topic as a new class of antibacterial agents. They have promising applications in bacterial infection prevention and control in multiple fields, such as livestock and poultry farming, food safety, clinical medicine and pathogen detection. However, many phage endolysins display low bactericidal activities, short half-life and narrow lytic spectrums. Therefore, some methods have been used to improve the enzyme properties (bactericidal activity, lysis spectrum, stability and targeting the substrate, etc) of bacteriophage endolysins, including deletion or addition of domains, DNA mutagenesis, chimerization of domains, fusion to the membrane-penetrating peptides, fusion with domains targeting outer membrane transport systems, encapsulation, the usage of outer membrane permeabilizers. In this review, research progress on the strategies for improving their enzyme properties are systematically presented, with a view to provide references for the development of lysins with excellent performances.

Liposomal drug delivery strategies to eradicate bacterial biofilms: Challenges, recent advances, and future perspectives

Typical antibiotic treatments are often ineffectual against biofilm-related infections since bacteria residing within biofilms have developed various mechanisms to resist antibiotics. To overcome these limitations, antimicrobial-loaded liposomal nanoparticles are a promising anti-biofilm strategy as they have demonstrated improved antibiotic delivery and eradication of bacteria residing in biofilms. Antibiotic-loaded liposomal nanoparticles revealed remarkably higher antibacterial and anti-biofilm activities than free drugs in experimental settings. Moreover, liposomal nanoparticles can be used efficaciously for the combinational delivery of antibiotics and other antimicrobial compounds/peptide which facilitate, for instance, significant breakdown of the biofilm matrix, increased bacterial elimination from biofilms and depletion of metabolic activity of various pathogens. Drug-loaded liposomes have mitigated recurrent infections and are considered a promising tool to address challenges associated to antibiotic resistance. Furthermore, it has been demonstrated that surface charge and polyethylene glycol modification of liposomes have a notable impact on their antibacterial biofilm activity. Future investigations should tackle the persistent hurdles associated with development of safe and effective liposomes for clinical application and investigate novel antibacterial treatments, including CRISPR-Cas gene editing, natural compounds, phages, and nano-mediated approaches. Herein, we emphasize the significance of liposomes in inhibition and eradication of various bacterial biofilms, their challenges, recent advances, and future perspectives.

Inhaled dry powder liposomal azithromycin for treatment of chronic lower respiratory tract infection

A dry powder inhaled liposomal azithromycin formulation was developed for the treatment of chronic respiratory diseases such as cystic fibrosis and bronchiectasis. Key properties including liposome size, charge and encapsulation efficiency powder size, shape, glass transition temperature (Tg), water content and in vitro respiratory deposition were determined. Antimicrobial activity against cystic fibrosis (CF) respiratory pathogens was determined by MIC, MBC and biofilm assays. Cytotoxicity and cellular uptake studies were performed using A549 cells. The average liposome size was 105 nm, charge was 55 mV and encapsulation efficiency was 75 %. The mean powder particle size d[v,50] of 4.54 µm and Mass Median Aerodynamic Diameter (MMAD) was 5.23 µm with a mean Tg of 76˚C and water content of 2.1 %. These excellent physicochemical characteristics were maintained over one year. Liposomal loaded azithromycin demonstrated enhanced activity against P. aeruginosa clinical isolates grown in biofilm. The formulation was rapidly delivered into bacterial cells with > 75 % uptake in 1 h. Rapid uptake into A549 cells via a cholesterol-dependent endocytosis pathway with no cytotoxic effects apparent. These data demonstrate that this formulation could offer benefits over current treatment regimens for people with chronic respiratory infection.

Lipid-based nanomedicines for the treatment of bacterial respiratory infections: current state and new perspectives

The global threat posed by antimicrobial resistance demands urgent action and the development of effective drugs. Lower respiratory tract infections remain the deadliest communicable disease worldwide, often challenging to treat due to the presence of bacteria that form recalcitrant biofilms. There is consensus that novel anti-infectives with reduced resistance compared with conventional antibiotics are needed, leading to extensive research on innovative antibacterial agents. This review explores the recent progress in lipid-based nanomedicines developed to counteract bacterial respiratory infections, especially those involving biofilm growth; focuses on improved drug bioavailability and targeting and highlights novel strategies to enhance treatment efficacy while emphasizing the importance of continued research in this dynamic field.

Clarithromycin-Loaded Submicron-Sized Carriers: Pharmacokinetics and Pharmacodynamic Evaluation

The current study aims to improve clarithromycin bioavailability and effectiveness in complicated intra-abdominal infection management. Therefore, clarithromycin-loaded submicron dual lipid carriers (CLA-DLCs) were developed via hot high shear homogenization technique and evaluated for colloidal parameters, release behavior, stability study, and in-vitro antibiofilm activity. Bioavailability and therapeutic efficacy of optimized formulation on hampering cytokines storm induction was determined in E. coli-induced peritonitis. The developed CLA-DLCs (particle size 326.19 ± 24.14 nm, zeta potential -31.34 ± 2.81 mV, and entrapment efficiency 85.78 ± 4.01%) exhibited smooth spherical shapes and sustained in vitro release profiles. Long-term stability study of optimized CLA-DLCs ensured maintenance of colloidal parameters for 1 year at room temperature. In vitro antimicrobial studies revealed 3.43-fold higher anti-biofilm activity of CLA-DLCs compared with clarithromycin. In addition, the relative bioavailability of CLA-DLCs was enhanced 5.89-fold compared to pure drug in rats. The remarkable decrease in microbial burden in blood as well as tissues, along with oxidative stress markers (lipid peroxidation, myeloperoxidase activity, and carbonylated protein level) and immunological markers (total leukocyte count, neutrophil migration, NO, TNF-, and IL-6) on treatment with CLA-DLCs enhanced the survival in a rat model of peritonitis compared with the pure drug and untreated groups. In conclusion, CLA-DLCs hold promising potential in management of intra-abdominal infections and prevention of associated complications.

Development of the phage lysin-loaded liposomes as preservatives for live clams

Exogenous applications of phage lysins against Vibrio parahaemolyticus (V. parahaemolyticus) are a challenge due to the gram-negative bacteria outer membrane barrier. This study aimed to improve the antibacterial effect of V. parahaemolyticus phage lysin Lysqdvp001 (Lys), the best-characterized lysin with lytic activity against multiple species of Vibrios, by using liposome delivery. Various kinds of Lys-loaded liposome (Lys-lip) systems were designed and tested. The antibacterial activities of cationic guar gum (CGG) containing liposomes were much higher than the other liposomes, causing >5 log₁₀CFU/mL of reductions of V. parahaemolyticus in buffer and severely damaging the bacterial cell structure. Moreover, some CGG liposome formulations retained high antibacterial effect after both 60-80 °C heat treatments and freeze-drying. Besides, the most stable liposome formulation killed 99 % of V. parahaemolyticus in the seawater with live clams, and its depuration rate against the bacterial contaminated clams also reached 99 %.

Preparation of DRV Liposomes

Dried reconstituted vesicle (DRV) liposomes are formulated under mild conditions. The method has the capability to entrap substantially higher amounts of hydrophilic solutes, compared to other passive-loading liposome preparation methods. These characteristics make this liposome type ideal for entrapment of labile substances, such as peptides, proteins, or DNA's (or other nucleotides or oligonucleotides), or in general biopharmaceuticals and sensitive drugs. In this chapter, all possible types of DRV liposomes (in respect to the encapsulated molecule characteristics and/or their applications in therapeutics) are introduced, and preparation methodologies (for each type) are described in detail.

Pseudomonas aeruginosa: Recent Advances in Vaccine Development

Pseudomonas aeruginosa is an important opportunistic human pathogen. Using its arsenal of virulence factors and its intrinsic ability to adapt to new environments, P. aeruginosa causes a range of complicated acute and chronic infections in immunocompromised individuals. Of particular importance are burn wound infections, ventilator-associated pneumonia, and chronic infections in people with cystic fibrosis. Antibiotic resistance has rendered many of these infections challenging to treat and novel therapeutic strategies are limited. Multiple clinical studies using well-characterised virulence factors as vaccine antigens over the last 50 years have fallen short, resulting in no effective vaccination being available for clinical use. Nonetheless, progress has been made in preclinical research, namely, in the realms of antigen discovery, adjuvant use, and novel delivery systems. Herein, we briefly review the scope of P. aeruginosa clinical infections and its major important virulence factors.

Anti-Virulence Activity of 3,3′-Diindolylmethane (DIM): A Bioactive Cruciferous Phytochemical with Accelerated Wound Healing Benefits

Antimicrobial resistance is among the top global health problems with antibacterial resistance currently representing the major threat both in terms of occurrence and complexity. One reason current treatments of bacterial diseases are ineffective is the occurrence of protective and resistant biofilm structures. Phytochemicals are currently being reviewed for newer anti-virulence agents. In the present study, we aimed to investigate the anti-virulence activity of 3,3′-diindolylmethane (DIM), a bioactive cruciferous phytochemical. Using a series of in vitro assays on major Gram-negative pathogens, including transcriptomic analysis, and in vivo porcine wound studies as well as in silico experiments, we show that DIM has anti-biofilm activity. Following DIM treatment, our findings show that biofilm formation of two of the most prioritized bacterial pathogens Acinetobacter baumannii and Pseudomonas aeruginosa was inhibited respectively by 65% and 70%. Combining the antibiotic tobramycin with DIM enabled a high inhibition (94%) of P. aeruginosa biofilm. A DIM-based formulation, evaluated for its wound-healing efficacy on P. aeruginosa-infected wounds, showed a reduction in its bacterial bioburden, and wound size. RNA-seq was used to evaluate the molecular mechanism underlying the bacterial response to DIM. The gene expression profile encompassed shifts in virulence and biofilm-associated genes. A network regulation analysis showed the downregulation of 14 virulence-associated super-regulators. Quantitative real-time PCR verified and supported the transcriptomic results. Molecular docking and interaction profiling indicate that DIM can be accommodated in the autoinducer- or DNA-binding pockets of the virulence regulators making multiple non-covalent interactions with the key residues that are involved in ligand binding. DIM treatment prevented biofilm formation and destroyed existing biofilm without affecting microbial death rates. This study provides evidence for bacterial virulence attenuation by DIM.

Antibiotic-loaded lipid-based nanocarrier: a promising strategy to overcome bacterial infection

According to the World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC), bacterial infections are one of the greatest threats to global health, food production, and life expectancy. In this sense, the development of innovative formulations aiming at greater therapeutic efficacy, safety, and shorter treatment duration compared to conventional products is urgently needed. Lipid-based nanocarriers (LBNs) have demonstrated the potential to enhance the effectiveness of available antibiotics. Among them, liposome, nanoemulsion, solid lipid nanoparticle (SLN), and nanostructured lipid carrier (NLC) are the most promising due to their solid technical background for laboratory and industrial production. This review describes recent advances in developing antibiotic-loaded LBNs against susceptible and resistant bacterial strains and biofilm. LBNs revealed to be a promising alternative to deliver antibiotics due to their superior characteristics compared to conventional preparations, including their modified drug release, improved bioavailability, drug protection against chemical or enzymatic degradation, greater drug loading capacity, and biocompatibility. Antibiotic-loaded LBNs can improve current clinical drug therapy, bring innovative products and rescue discarded antibiotics. Thus, antibiotic-loaded LBNs have potential to open a window of opportunities to continue saving millions of lives and prevent the devastating impact of bacterial infection.

Membrane Organization Strategies in Vesicular Antibiotic Delivery

Small molecule antibiotics are often derived from microorganisms that thrive in competitive environments. Their importance as therapeutics for infectious disease in humans has been established over many years. It has now become clear that antibiotic-producing organisms use packaging and delivery in the form of vesicles in many cases. A similar strategy has evolved in recent decades in the pharmaceutical industry for formulation of antibiotic therapies. The top-down approach that has evolved over millions of years in various micro-organisms has generated complex, efficient delivery systems that we are just now beginning to understand. The bottom-up formulation approach involves simple, safe compositions, which are being continually enhanced by trying to add features of which the natural systems inform us. A comparison is made here of these paradigms. Despite the differences, there are a number of common features in the basic physical and biological requirements that must be satisfied. In this review, illustration and comparison of some of these requirements is given, demonstrating the ongoing challenges in this area of research.

The Analysis of Chitosan-Coated Nanovesicles Containing Erythromycin-Characterization and Biocompatibility in Mice

Nanoantibiotics have proved improved pharmacokinetic characteristics and antimicrobial features. Recent studies have shown non-toxicity, non-immunogenicity, antioxidant, anti-hyperlipidemic, and hepatocyte protective actions, among other advantages of chitosan-based nanoparticles. The purpose of our study was the structural analysis of novel chitosan-coated vesicles entrapping erythromycin (ERT) and the assessment of their biocompatibility in mice. According to the group in which they were randomly assigned, the mice were treated orally with one of the following: distilled water; chitosan; ERT; chitosan vesicles containing ERT. Original nanosystems entrapping ERT in liposomes stabilized with chitosan were designed. Their oral administration did not produce sizeable modifications in the percentages of the leukocyte formula elements, of some blood constants useful for evaluating the hepatic and renal function, respectively, and of some markers of oxidative stress and immune system activity, which suggests a good biocompatibility in mice. The histological examination did not reveal significant alterations of liver and kidney architecture in mice treated with chitosan liposomes entrapping ERT. The results indicate the designed liposomes are a promising approach to overcome disadvantages of conventional ERT treatments and to amplify their benefits and can be further studied as carrier systems.

The Impact of an Efflux Pump Inhibitor on the Activity of Free and Liposomal Antibiotics against Pseudomonas aeruginosa

The eradication of Pseudomonas aeruginosa in cystic fibrosis patients has become continuously difficult due to its increased resistance to treatments. This study assessed the efficacy of free and liposomal gentamicin and erythromycin, combined with Phenylalanine arginine beta-naphthylamide (PABN), a broad-spectrum efflux pump inhibitor, against P. aeruginosa isolates. Liposomes were prepared and characterized for their sizes and encapsulation efficiencies. The antimicrobial activities of formulations were determined by the microbroth dilution method. Their activity on P. aeruginosa biofilms was assessed, and the effect of sub-inhibitory concentrations on bacterial virulence factors, quorum sensing (QS) signals and bacterial motility was also evaluated. The average diameters of liposomes were 562.67 ± 33.74 nm for gentamicin and 3086.35 ± 553.95 nm for erythromycin, with encapsulation efficiencies of 13.89 ± 1.54% and 51.58 ± 2.84%, respectively. Liposomes and PABN combinations potentiated antibiotics by reducing minimum inhibitory and bactericidal concentrations by 4–32 fold overall. The formulations significantly inhibited biofilm formation and differentially attenuated virulence factor production as well as motility. Unexpectedly, QS signal production was not affected by treatments. Taken together, the results indicate that PABN shows potential as an adjuvant of liposomal macrolides and aminoglycosides in the management of lung infections in cystic fibrosis patients.

Liposomes-in-chitosan hydrogel boosts potential of chlorhexidine in biofilm eradication in vitro

Successful treatment of skin infections requires eradication of biofilms found in up to 90 % of all chronic wounds, causing delayed healing and increased morbidity. We hypothesized that chitosan hydrogel boosts the activity of liposomally-associated membrane active antimicrobials (MAA) and could potentially improve bacterial and biofilm eradication. Therefore, liposomes (∼300 nm) bearing chlorhexidine (CHX; ∼50 μg/mg lipid) as a model MAA were incorporated into chitosan hydrogel. The novel CHX-liposomes-in-hydrogel formulation was optimized for skin therapy. It significantly inhibited the production of nitric oxide (NO) in lipopolysaccharide (LPS)-induced macrophage and almost completely reduced biofilm formation. Moreover, it reduced Staphylococcus aureus and Pseudomonas aeruginosa adherent bacterial cells in biofilm by 64.2-98.1 %. Chitosan hydrogel boosted the anti-inflammatory and antimicrobial properties of CHX.

Current and novel therapeutic strategies for the management of cystic fibrosis

Introduction: Cystic fibrosis (CF), is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene and affects thousands of people throughout the world. Lung disease is the leading cause of death in CF patients. Despite the advances in treatments, the management of CF mainly targets symptoms. Recent CFTR modulators however target common mutations in patients, alleviating symptoms of CF. Unfortunately, there is still no approved treatments for patients with rare mutations to date.Areas covered: This paper reviews current treatments of CF that mitigate symptoms and target genetic defects. The use of gene and drug delivery systems such as viral or non-viral vectors and nano-compounds to enhance CFTR expression and the activity of antimicrobials against chronic pulmonary infections respectively, will also be discussed.Expert opinion: Nano-compounds tackle biological barriers to drug delivery and revitalize antimicrobials, anti-inflammatory drugs and even genes delivery to CF patients. Gene therapy and gene editing are of particular interest because they have the potential to directly target genetic defects. Nanoparticles should be formulated to more specifically target epithelial cells, and biofilms. Finally, the development of more potent gene vectors to increase the duration of gene expression and reduce inflammation is a promising strategy to eventually cure CF.

Polymeric Inserts Containing Eudragit® L100 Nanoparticle for Improved Ocular Delivery of Azithromycin

Polymeric inserts containing azithromycin-loaded Eudragit® L100 nanoparticles were developed to sustain the drug release and enhance its ocular performance. The solvent diffusion technique was employed to prepare nanoparticles. The developed nanoparticles (NPs) were fully characterized and investigated. The solvent casting method was used to prepare azithromycin ocular inserts (azithromycin, AZM film) by adding hydroxypropyl methylcellulose (HPMC) or hydroxyethyl cellulose (HEC) solutions after the incorporation of AZM-loaded Eudragit® L100 nanoparticles into plasticized PVA (polyvinyl alcohol) solutions. The optimized nanoparticles had a particle size of 78.06 ± 2.3 nm, zeta potential around -2.45 ± 0.69 mV, polydispersity index around 0.179 ± 0.007, and entrapment efficiency 62.167 ± 0.07%. The prepared inserts exhibited an antibacterial effect on Staphylococcus aureus and Escherichia coli cultures. The inserts containing AZM-loaded nanoparticles showed a burst release during the initial hours, followed by a sustained drug release pattern. Higher cumulative corneal permeations from AZM films were observed for the optimized formulation compared to the drug solution in the ex-vivo trans-corneal study. In comparison to the AZM solution, the inserts significantly prolonged the release of AZM in rabbit eyes (121 h). The mucoadhesive inserts containing azithromycin-loaded Eudragit® L100 nanoparticles offer a promising approach for the ocular delivery of azithromycin (antibacterial and anti-inflammatory) to treat ocular infections that require a prolonged drug delivery.

Enhancing azithromycin antibacterial activity by encapsulation in liposomes/liposomal-N-acetylcysteine formulations against resistant clinical strains of Escherichia coli

E. coli is an Enterobacteriaceae that could develop resistance to various antibiotics and become a multi-drug resistant (MDR) bacterium. Options for treating MDR E. coli are limited and the pipeline is somewhat dry when it comes to antibiotics for MDR bacteria, so we aimed to explore more options to help in treating MDR E. coli. The purpose of this study is to examine the synergistic effect of a liposomal formulations of co-encapsulated azithromycin and N-acetylcysteine against E. coli. Liposomal azithromycin (LA) and liposomal azithromycin/N-acetylcysteine (LAN) were compared to free azithromycin. A broth dilution was used to measure the MIC and MBC of both formulations. The biofilm reduction activity, thermal stability measurements, stability studies, and cell toxicity analysis were performed. LA and LAN effectively reduced the MIC of E. coli SA10 strain, to 3 μg/ml and 2.5 μg/ml respectively. LAN at 1 × MIC recorded a 93.22% effectiveness in reducing an E. coli SA10 biofilm. The LA and LAN formulations were also structurally stable to 212 ± 2 °C and 198 ± 3 °C, respectively. In biological conditions, the formulations were largely stable in PBS conditions; however, they illustrated limited stability in sputum and plasma. We conclude that the formulation presented could be a promising therapy for E. coli resistance circumstances, providing the stability conditions have been enhanced.

Nanoparticulate drug-delivery systems for fighting microbial biofilms: from bench to bedside

Biofilms are highly tolerant to antimicrobial agents and adverse environmental conditions being important reservoirs for chronic and hard-to-treat infections. Nanomaterials exhibit microbiostatic/microbicidal/antipathogenic properties and can be also used for the delivery of antibiofilm agents. However, few of the many promising leads offered by nanotechnology reach clinical studies and eventually, become available to clinicians. The aim of this paper was to review the progress and challenges in the development of nanotechnology-based antibiofilm drug-delivery systems. The main identified challenges are: most papers report only in vitro studies of the activity of different nanoformulations; lack of standardization in the methodological approaches; insufficient collaboration between material science specialists and clinicians; paucity of in vivo studies to test efficiency and safety.

Potential application of liposomal nanodevices for non-cancer diseases: an update on design, characterization and biopharmaceutical evaluation

Liposomes, lipid-based vesicular systems, have attracted major interest as a means to improve drug delivery to various organs and tissues in the human body. Recent literature highlights the benefits of liposomes for use as drug delivery systems, including encapsulating of both hydrophobic and hydrophilic cargos, passive and active targeting, enhanced drug bioavailability and therapeutic effects, reduced systemic side effects, improved cargo penetration into the target tissue and triggered contents release. Pioneering work of liposomes researchers led to introduction of long-circulating, ligand-targeted and triggered release liposomes, as well as, liposomes containing nucleic acids and vesicles containing combination of cargos. Altogether, these findings have led to widespread application of liposomes in a plethora of areas from cancer to conditions such as cardiovascular, neurologic, respiratory, skin, autoimmune and eye disorders. There are numerous review articles on the application of liposomes in treatment of cancer, which seems the primary focus, whereas other diseases also benefit from liposome-mediated treatments. Therefore, this article provides an illustrated detailed overview of liposomal formulations, in vitro characterization and their applications in different disorders other than cancer. Challenges and future directions, which must be considered to obtain the most benefit from applications of liposomes in these disorders, are discussed.

Lipid-Based Antimicrobial Delivery-Systems for the Treatment of Bacterial Infections

Many nanotechnology-based antimicrobials and antimicrobial-delivery-systems have been developed over the past decades with the aim to provide alternatives to antibiotic treatment of infectious-biofilms across the human body. Antimicrobials can be loaded into nanocarriers to protect them against de-activation, and to reduce their toxicity and potential, harmful side-effects. Moreover, antimicrobial nanocarriers such as micelles, can be equipped with stealth and pH-responsive features that allow self-targeting and accumulation in infectious-biofilms at high concentrations. Micellar and liposomal nanocarriers differ in hydrophilicity of their outer-surface and inner-core. Micelles are self-assembled, spherical core-shell structures composed of single layers of surfactants, with hydrophilic head-groups and hydrophobic tail-groups pointing to the micellar core. Liposomes are composed of lipids, self-assembled into bilayers. The hydrophilic head of the lipids determines the surface properties of liposomes, while the hydrophobic tail, internal to the bilayer, determines the fluidity of liposomal-membranes. Therefore, whereas micelles can only be loaded with hydrophobic antimicrobials, hydrophilic antimicrobials can be encapsulated in the hydrophilic, aqueous core of liposomes and hydrophobic or amphiphilic antimicrobials can be inserted in the phospholipid bilayer. Nanotechnology-derived liposomes can be prepared with diameters <100-200 nm, required to prevent reticulo-endothelial rejection and allow penetration into infectious-biofilms. However, surface-functionalization of liposomes is considerably more difficult than of micelles, which explains while self-targeting, pH-responsive liposomes that find their way through the blood circulation toward infectious-biofilms are still challenging to prepare. Equally, development of liposomes that penetrate over the entire thickness of biofilms to provide deep killing of biofilm inhabitants still provides a challenge. The liposomal phospholipid bilayer easily fuses with bacterial cell membranes to release high antimicrobial-doses directly inside bacteria. Arguably, protection against de-activation of antibiotics in liposomal nanocarriers and their fusogenicity constitute the biggest advantage of liposomal antimicrobial carriers over antimicrobials free in solution. Many Gram-negative and Gram-positive bacterial strains, resistant to specific antibiotics, have been demonstrated to be susceptible to these antibiotics when encapsulated in liposomal nanocarriers. Recently, also progress has been made concerning large-scale production and long-term storage of liposomes. Therewith, the remaining challenges to develop self-targeting liposomes that penetrate, accumulate and kill deeply in infectious-biofilms remain worthwhile to pursue.

Azithromycin-liposomes as a novel approach for localized therapy of cervicovaginal bacterial infections

Background

Efficient localized cervicovaginal antibacterial therapy, enabling the delivery of antibiotic to the site of action at lower doses while escaping systemic drug effects and reducing the risk of developing microbial resistance, is attracting considerable attention. Liposomes have been shown to allow sustained drug release into vaginal mucosa and improve delivery of antibiotics to bacterial cells and biofilms. Azithromycin (AZI), a potent broad-spectrum macrolide antibiotic, has not yet been investigated for localized therapy of cervicovaginal infections, although it is administered orally for the treatment of sexually transmitted diseases. Encapsulation of AZI in liposomes could improve its solubility, antibacterial activity, and allow the prolonged drug release in the cervicovaginal tissue, while avoiding systemic side effects.

Purpose

The objective of this study was to develop AZI-liposomes and explore their potentials for treating cervicovaginal infections.

Methods

AZI-liposomes that differed in bilayer elasticity/rigidity and surface charge were prepared and evaluated under simulated cervicovaginal conditions to yield optimized liposomes, which were assessed for antibacterial activity against several planktonic and biofilm-forming Escherichia coli strains and intracellular Chlamydia trachomatis, ex vivo AZI vaginal deposition/penetration, and in vitro cytotoxicity toward cervical cells.

Results

Negatively charged liposomes with rigid bilayers (CL-3), propylene glycol liposomes (PGL-2) and deformable propylene glycol liposomes (DPGL-2) were efficient against planktonic E. coli ATCC 700928 and K-12. CL-3 was superior for preventing the formation of E. coli ATCC 700928 and K-12 biofilms, with IC₅₀ values (concentrations that inhibit biofilm viability by 50%) up to 8-fold lower than those of the control (free AZI). DPGL-2 was the most promising for eradication of already formed E. coli biofilms and for treating C. trachomatis infections. All AZI-liposomes were biocompatible with cervical cells and improved localization of the drug inside vaginal tissue compared with the control.

Conclusion

The performed studies confirm the potentials of AZI-liposomes for localized cervicovaginal therapy.

Preparation and characterization of endolysin-containing liposomes and evaluation of their antimicrobial activities against gram-negative bacteria

The overuse and misuse of antibiotics in treating bacterial infections cause the rapid emergence of drug-resistant bacteria, suggesting that the development of alternative strategies to control antibiotic-resistant bacteria is urgently needed. Endolysins are bacteriophage-encoded enzymes that can degrade peptidoglycan in bacterial cell walls, and they have great potential as alternative antimicrobial agents. However, exogenous application of recombinant endolysin is limited to Gram-positive bacteria because endolysins cannot penetrate the outer membrane of Gram-negative bacteria. Here, a liposome-mediated endolysin encapsulation system was developed, and its ability to penetrate the outer membrane of Gram-negative bacteria was tested. The phage-derived endolysin BSP16Lys was isolated, characterized, and used for encapsulation into a cationic liposome comprised of dipalmitoylphosphatidylcholine (DPPC), cholesterol, and hexadecylamine. The BSP16Lys-encapsulated liposome had a high zeta potential value (over 30 mV) with an average diameter of 303 nm. The encapsulation efficiency of BSP16Lys into the liposome was 35.27%. Salmonella Typhimuriumand Escherichia coli cells treated with BSP16Lys-encapsulated liposomes showed 2.2-log CFU/mL and 1.6-log CFU/mL reductions in the viable cell numbers, respectively, without treatment of a membrane permeabilizer. These results showed potential for liposome-mediated delivery of endolysin for exogenous application against Gram-negative bacteria.

Lipid-Based Antimicrobial Delivery-Systems for the Treatment of Bacterial Infections

Many nanotechnology-based antimicrobials and antimicrobial-delivery-systems have been developed over the past decades with the aim to provide alternatives to antibiotic treatment of infectious-biofilms across the human body. Antimicrobials can be loaded into nanocarriers to protect them against de-activation, and to reduce their toxicity and potential, harmful side-effects. Moreover, antimicrobial nanocarriers such as micelles, can be equipped with stealth and pH-responsive features that allow self-targeting and accumulation in infectious-biofilms at high concentrations. Micellar and liposomal nanocarriers differ in hydrophilicity of their outer-surface and inner-core. Micelles are self-assembled, spherical core-shell structures composed of single layers of surfactants, with hydrophilic head-groups and hydrophobic tail-groups pointing to the micellar core. Liposomes are composed of lipids, self-assembled into bilayers. The hydrophilic head of the lipids determines the surface properties of liposomes, while the hydrophobic tail, internal to the bilayer, determines the fluidity of liposomal-membranes. Therefore, whereas micelles can only be loaded with hydrophobic antimicrobials, hydrophilic antimicrobials can be encapsulated in the hydrophilic, aqueous core of liposomes and hydrophobic or amphiphilic antimicrobials can be inserted in the phospholipid bilayer. Nanotechnology-derived liposomes can be prepared with diameters <100-200 nm, required to prevent reticulo-endothelial rejection and allow penetration into infectious-biofilms. However, surface-functionalization of liposomes is considerably more difficult than of micelles, which explains while self-targeting, pH-responsive liposomes that find their way through the blood circulation toward infectious-biofilms are still challenging to prepare. Equally, development of liposomes that penetrate over the entire thickness of biofilms to provide deep killing of biofilm inhabitants still provides a challenge. The liposomal phospholipid bilayer easily fuses with bacterial cell membranes to release high antimicrobial-doses directly inside bacteria. Arguably, protection against de-activation of antibiotics in liposomal nanocarriers and their fusogenicity constitute the biggest advantage of liposomal antimicrobial carriers over antimicrobials free in solution. Many Gram-negative and Gram-positive bacterial strains, resistant to specific antibiotics, have been demonstrated to be susceptible to these antibiotics when encapsulated in liposomal nanocarriers. Recently, also progress has been made concerning large-scale production and long-term storage of liposomes. Therewith, the remaining challenges to develop self-targeting liposomes that penetrate, accumulate and kill deeply in infectious-biofilms remain worthwhile to pursue.

Azithromycin-loaded liposomes for enhanced topical treatment of methicillin-resistant Staphyloccocus aureus (MRSA) infections

Antibiotic delivery via liposomal encapsulation represents a promising approach for the efficient topical treatment of skin infections. The present study aimed to investigate the potential of using different types of azithromycin (AZT)-loaded liposomes to locally treat skin infections caused by methicillin-resistant Staphylococcus aureus (MRSA) strains. Conventional liposomes (CLs), deformable liposomes (DLs), propylene glycol-containing liposomes (PGLs) and cationic liposomes (CATLs) encapsulating AZT were prepared, and their physical characteristics, drug release profiles, ex vivo skin penetration/deposition abilities, in vitro anti-MRSA activities (planktonic bacteria and biofilm) and cell biocompatibilities were assessed. The (phospho)lipid composition and presence of surfactant or propylene glycol affected the physical characteristics of the liposomes, the release profile of AZT, its deposition inside the skin, as well as in vitro antibacterial efficacy and tolerability with the skin cells. All the liposomes retained AZT inside the skin more efficiently than did the control and were biocompatible with keratinocytes and fibroblasts. CATLs, DLs and PGLs efficiently inhibited MRSA strain growth and were superior to free AZT in preventing biofilm formation, exhibiting minimal inhibitory concentrations and minimal biofilm inhibitory concentrations up to 32-fold lower than those of AZT solution, thus confirming their potential for improved topical treatment of MRSA-caused skin infections.

DPI formulations for high dose applications - Challenges and opportunities

This opinion piece gives reasons for high dose DPI applications, points out challenges and shows opportunities and possible solutions for high dose DPI. This piece of work shall set the stage for more in-depth reviews of state of the art and research papers addressing the challenges of high dose DPI which shall be included in the special issue of IJP.

Efficacy of neutral and negatively charged liposome-loaded gentamicin on planktonic bacteria and biofilm communities

We investigated the efficacy of liposomal gentamicin formulations of different surface charges against Pseudomonas aeruginosa and Klebsiella oxytoca. The liposomal gentamicin formulations were prepared by the dehydration-rehydration method, and their sizes and zeta potential were measured. Gentamicin encapsulation efficiency inside the liposomal formulations was determined by microbiologic assay, and stability of the formulations in biologic fluid was evaluated for a period of 48 h. The minimum inhibitory concentration and the minimum bactericidal concentration were determined, and the in vitro time kill studies of the free form of gentamicin and liposomal gentamicin formulations were performed. The activities of liposomal gentamicin in preventing and reducing biofilm-forming P. aeruginosa and K. oxytoca were compared to those of free antibiotic. The sizes of the liposomal formulations ranged from 625 to 806.6 nm in diameter, with the zeta potential ranging from -0.22 to -31.7 mV. Gentamicin encapsulation efficiency inside the liposomal formulation ranged from 1.8% to 43.6%. The liposomes retained >60% of their gentamicin content during the 48 h time period. The minimum inhibitory concentration of neutral formulation was lower than that of free gentamicin (0.25 versus 1 mg/L for P. aeruginosa and 0.5 versus 1 mg/L for K. oxytoca). The negatively charged formulation exhibited the same bacteriostatic concentration as that of free gentamicin. The minimum bactericidal concentration of neutral liposomes on planktonic bacterial culture was twofold lower than that of free gentamicin, whereas the negatively charged formulations were comparable to free gentamicin. The killing time curve values for the neutral negatively charged formulation against planktonic P. aeruginosa and K. oxytoca were better than those of free gentamicin. Furthermore, liposomal formulations prevent the biofilm-formation ability of these strains better than free gentamicin. In summary, liposomal formulations could be an effective lipid nanoparticle to combat acute infections where planktonic bacteria are predominant.

Acquired resistance to macrolides inPseudomonas aeruginosafrom cystic fibrosis patients

Cystic fibrosis (CF) patients receive chronic treatment with macrolides for their antivirulence and anti-inflammatory properties. We, however, previously showed thatPseudomonas aeruginosa, considered as naturally resistant to macrolides, becomes susceptible when tested in a eukaryotic medium rather than a conventional broth.

We therefore looked for specific macrolide resistance determinants in 333 CF isolates from four European CF centres in comparison with 48 isolates from patients suffering from hospital-acquired pneumonia (HAP).

Minimum inhibitory concentrations (MICs) of macrolides and ketolides measured in eukaryotic medium (RPMI-1640) were higher towards CF than HAP isolates. Gene sequencing revealed mutations at three positions (2045, 2046 and 2598) in domain V of 23S rRNA of 43% of sequenced CF isolates, but none in HAP isolates. Enzymes degrading extracellular polymeric substances also reduced MICs, highlighting a role of the mucoid, biofilm-forming phenotype in resistance. An association between high MICs and chronic azithromycin administration was evidenced, which was statistically significant for patients infected by the Liverpool Epidemic Strain.

Thus, ribosomal mutations are highly prevalent in CF isolates and may spread in epidemic clones, arguing for prudent use of oral macrolides in these patients. Measuring MICs in RPMI-1640 could be easily implemented in microbiology laboratories to phenotypically detect resistance.

Stability study of sodium colistimethate-loaded lipid nanoparticles

In the last decades, the encapsulation of antibiotics into nanoparticulate carriers has gained increasing attention for the treatment of infectious diseases. Sodium colistimethate-loaded solid lipid nanoparticles (Colist-SLNs) and nanostructured lipid carriers (Colist-NLCs) were designed aiming to treat the pulmonary infection associated to cystic fibrosis patients. The nanoparticles were freeze-dried using trehalose as cryoprotectant. The stability of both nanoparticles was analysed over one year according to the International Conference of Harmonisation (ICH) guidelines by determining the minimum inhibitory concentration (MIC) against clinically isolated Pseudomonas aeruginosa strains and by studying their physico-chemical characteristics. The results showed that Colist-SLNs lost their antimicrobial activity at the third month; on the contrary, the antibacterial activity of Colist-NLCs was maintained throughout the study within an adequate range (MIC ≤16 μg/mL). In addition, Colist-NLCs exhibited suitable physico-chemical properties at 5 °C and 25 °C/60% relative humidity over one year. Altogether, Colist-NLCs proved to have better stability than Colist-SLNs.

Inhalable Antimicrobials for Treatment of Bacterial Biofilm-Associated Sinusitis in Cystic Fibrosis Patients: Challenges and Drug Delivery Approaches

Bacterial biofilm-associated chronic sinusitis in cystic fibrosis (CF) patients caused by Pseudomonas aeruginosa infections and the lack of available treatments for such infections constitute a critical aspect of CF disease management. Currently, inhalation therapies to combat P. aeruginosa infections in CF patients are focused mainly on the delivery of antimicrobials to the lower respiratory tract, disregarding the sinuses. However, the sinuses constitute a reservoir for P. aeruginosa growth, leading to re-infection of the lungs, even after clearing an initial lung infection. Eradication of P. aeruginosa from the respiratory tract after a first infection has been shown to delay chronic pulmonary infection with the bacteria for up to two years. The challenges with providing a suitable treatment for bacterial sinusitis include: (i) identifying a suitable antimicrobial compound; (ii) selecting a suitable device to deliver the drug to the sinuses and nasal cavities; and (iii) applying a formulation design, which will mediate delivery of a high dose of the antimicrobial directly to the site of infection. This review highlights currently available inhalable antimicrobial formulations for treatment and management of biofilm infections caused by P. aeruginosa and discusses critical issues related to novel antimicrobial drug formulation design approaches.

Current Trends in Development of Liposomes for Targeting Bacterial Biofilms

Biofilm targeting represents a great challenge for effective antimicrobial therapy. Increased biofilm resistance, even with the elevated concentrations of very potent antimicrobial agents, often leads to failed therapeutic outcome. Application of biocompatible nanomicrobials, particularly liposomally-associated nanomicrobials, presents a promising approach for improved drug delivery to bacterial cells and biofilms. Versatile manipulations of liposomal physicochemical properties, such as the bilayer composition, membrane fluidity, size, surface charge and coating, enable development of liposomes with desired pharmacokinetic and pharmacodynamic profiles. This review attempts to provide an unbiased overview of investigations of liposomes destined to treat bacterial biofilms. Different strategies including the recent advancements in liposomal design aiming at eradication of existing biofilms and prevention of biofilm formation, as well as respective limitations, are discussed in more details.