Mapping Fusogenicity of Ciprofloxacin-Loaded Liposomes with Bacterial Cells

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.

Innovative Phospholipid Carriers: A Viable Strategy to Counteract Antimicrobial Resistance

The overuse and misuse of antibiotics have led to the emergence and spread of multidrug-resistant (MDR), extensively drug-resistant (XDR), and pan-drug-resistant (PDR) bacteria strains, usually associated with poorer patient outcomes and higher costs. In order to preserve the usefulness of these life-saving drugs, it is crucial to use them appropriately, as also recommended by the WHO. Moreover, innovative, safe, and more effective approaches are being investigated, aiming to revise drug treatments to improve their pharmacokinetics and distribution and to reduce the onset of drug resistance. Globally, to reduce the burden of antimicrobial resistance (AMR), guidelines and indications have been developed over time, aimed at narrowing the use and diminishing the environmental spread of these life-saving molecules by optimizing prescriptions, dosage, and times of use, as well as investing resources into obtaining innovative formulations with better pharmacokinetics, pharmacodynamics, and therapeutic results. This has led to the development of new nano-formulations as drug delivery vehicles, characterized by unique structural properties, biocompatible natures, and targeted activities such as state-of-the-art phospholipid particles generally grouped as liposomes, virosomes, and functionalized exosomes, which represent an attractive and innovative delivery approach. Liposomes and virosomes are chemically synthesized carriers that utilize phospholipids whose nature is predetermined based on their use, with a long track record as drug delivery systems. Exosomes are vesicles naturally released by cells, which utilize the lipids present in their cellular membranes only, and therefore, are highly biocompatible, with investigations as a delivery system having a more recent origin. This review will summarize the state of the art on microvesicle research, liposomes, virosomes, and exosomes, as useful and effective tools to tackle the threat of antibiotic resistance.

Liposomes Co-Delivering Curcumin and Colistin to Overcome Colistin Resistance in Bacterial Infections

Antibiotic colistin is the last line of defense against multidrug-resistant (MDR) Gram-negative bacterial infections. Emergence of colistin resistance in microbes is a critical challenge. Herein, curcumin is discovered, for the first time, to reverse the resistance phenotype of colistin-resistant bacteria via a checkerboard assay. For the co-delivery of curcumin and colistin, negatively charged poly(ethylene glycol)-functionalized liposomes encapsulating both drugs (Lipo-cc) are prepared. Killing kinetics and live/dead assays confirm the antibacterial activity of Lipo-cc against colistin-resistant bacteria, which is more potent than that of the free curcumin and colistin combination. Mechanistical studies reveal that Lipo-cc restores the affinity of colistin for the bacterial membrane and improves the uptake of curcumin, which leads to reduced efflux pump activity, achieving a synergistic effect of colistin and curcumin. At the effective antibacterial dose, Lipo-cc does not exhibit any toxicity. The therapeutic efficacy of Lipo-cc is further demonstrated in an intestinal bacterial infection model induced with colistin-resistant Escherichia coli. Lipo-cc reduces the bacterial burden with over 6-log reduction and alleviated inflammation caused by infection. Importantly, unlike colistin, Lipo-cc does not affect the homeostasis of the intestinal flora. Taken together, Lipo-cc successfully overcame colistin resistance, indicating its potential for the treatment of colistin-resistant bacterial infections.

Development and Evaluation of EDTA-Treated Rabbits for Bioavailability Study of Chelating Drugs Using Levofloxacin, Ciprofloxacin, Hemiacetal Ester Prodrugs, and Tetracycline

Laboratory rabbits are fed foods rich with cationic metals, and while fasting cannot empty gastric contents because of their coprophagic habits. This implies that, in rabbits, the oral bioavailability of chelating drugs could be modulated by the slow gastric emptying rates and the interaction (chelation, adsorption) with gastric metals. In the present study, we tried to develop a rabbit model with low amounts of cationic metals in the stomach for preclinical oral bioavailability studies of chelating drugs. The elimination of gastric metals was achieved by preventing food intake and coprophagy and administering a low concentration of EDTA 2Na solution one day before experiments. Control rabbits were fasted but coprophagy was not prevented. The efficacy of rabbits treated with EDTA 2Na was evaluated by comparing the gastric contents, gastric metal contents and gastric pH between EDTA-treated and control rabbits. The treatment with more than 10 mL of 1 mg/mL EDTA 2Na solution decreased the amounts of gastric contents, cationic metals and gastric pH, without causing mucosal damage. The absolute oral bioavailabilities (mean values) of levofloxacin (LFX), ciprofloxacin (CFX) and tetracycline hydrochloride (TC), chelating antibiotics, were significantly higher in EDTA-treated rabbits than those in control rabbits as follows: 119.0 vs. 87.2%, 9.37 vs. 13.7%, and 4.90 vs. 2.59%, respectively. The oral bioavailabilities of these drugs were significantly decreased when Al(OH)₃ was administered concomitantly in both control and EDTA-treated rabbits. In contrast, the absolute oral bioavailabilities of ethoxycarbonyl 1-ethyl hemiacetal ester (EHE) prodrugs of LFX and CFX (LFX-EHE, CFX-EHE), which are non-chelating prodrugs at least in in vitro condition, were comparable between control and EDTA-treated rabbits irrespective of the presence of Al(OH)₃, although some variation was observed among rabbits. The oral bioavailabilities of LFX and CFX from their EHE prodrugs were comparable with LFX and CFX alone, respectively, even in the presence of Al(OH)₃. In conclusion, LFX, CFX and TC exhibited higher oral bioavailabilities in EDTA-treated rabbits than in control rabbits, indicating that the oral bioavailabilities of these chelating drugs are reduced in untreated rabbits. In conclusion, EDTA-treated rabbits were found to exhibit low gastric contents including metals and low gastric pH, without causing mucosal damage. Ester prodrug of CFX was effective in preventing chelate formation with Al(OH)₃ in vitro and in vivo, as well as in the case of ester prodrugs of LFX. EDTA-treated rabbits are expected to provide great advantages in preclinical oral bioavailability studies of various drugs and dosage formulations. However, a marked interspecies difference was still observed in the oral bioavailability of CFX and TC between EDTA-treated rabbits and humans, possibly due to the contribution of adsorptive interaction in rabbits. Further study is necessary to seek out the usefulness of the EDTA-treated rabbit with less gastric contents and metals as an experimental animal.

Development of Ulvan-Containing Liposomes as Antibacterial Drug Delivery Platforms

Liposomes, due to their safety profile and targeting ability, are among the most studied nanocarriers as antimicrobial delivery systems. However, due to lack of stability and the non-specific interaction of liposomes with cells and proteins, their use is relatively limited. Aiming to overcome these drawbacks, it was envisaged that incorporation of ulvan, a bioactive marine sulfated polysaccharide isolated from green algae, in liposomes could improve their physicochemical properties and overall stability. Thus, we initially studied the interactions of ulvan with neutral, negatively, and positively charged lipids using Differential Scanning Calorimetry and subsequently, based on the obtained results, we prepared the respective ulvan–containing neutral and charged liposomes, where ulvan interacts with both lipid chains and polar groups in the liposomal bilayer. In a further step, we entrapped in the liposomes fusidic acid, used as a model antibacterial drug, and proceeded with the evaluation of their antibacterial activity against Staphylococcus aureus. The physicochemical properties (size and ζ-potential), stability, morphology, and entrapment efficiency of the prepared liposomal formulations were determined.

Nanocarriers for combating biofilms: advantages and challenges

Bacterial biofilms are highly resistant to antibiotics and pose a great threat to human and animal health. The control and removal of bacterial biofilms have become an important topic in the field of bacterial infectious diseases. Nanocarriers show great anti-biofilm potential because of their small particle size and strong permeability. In this review, the advantages of nanocarriers for combating biofilms are analyzed. Nanocarriers can act on all stages of bacterial biofilm formation and diffusion. They can improve the scavenging effect of biofilm by targeting biofilm, destroying extracellular polymeric substances, and enhancing the biofilm permeability of antimicrobial substances. Nanocarriers can also improve the antibacterial ability of antimicrobial drugs against bacteria in biofilm by protecting the loaded drugs and controlling the release of antimicrobial substances. Additionally, we emphasize the challenges faced in using nanocarrier formulations and translating them from a preclinical level to the clinical setting.