Targeted delivery of antibiotics to intracellular chlamydial infections using PLGA nanoparticles

Strategies for the eradication of intracellular bacterial pathogens

Intracellular pathogens affect a significant portion of world population and cause millions of deaths each year. They can invade host cells and survive inside them and are extremely resistant to immune systems and antibiotics. Current treatments have limitations, and therefore, new effective therapies are needed to combat this ongoing health challenge. Active research efforts have been made to develop many new strategies to eradicate these intracellular pathogens. In this review, we focus on the intracellular bacterial pathogens and first introduce several representative intracellular bacteria and the diseases they cause. We then discuss the challenges in eradicating these bacteria and summarize the current therapeutics for intracellular bacteria. Finally, recent advances in intracellular bacteria eradication are highlighted.

Enhanced clearance of C. muridarum infection using azithromycin-loaded liposomes

Chlamydia trachomatis is an intracellular bacterium which infects around 129 million people annually. Despite similar infection rates between sexes, most research investigating the effects of chlamydial infection on fertility has focused on females. There is now emerging evidence of a potential link between Chlamydia and impaired male fertility. The only treatments for chlamydial infection are antibiotics, with azithromycin (AZI) being one of the commonly used drugs. However, recent studies have suggested that optimizing the treatment regime is necessary, as higher concentrations of AZI may be required to effectively clear the infection in certain cell types, particularly testicular macrophages. To address this challenge, we have prepared liposomes consisting of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) loaded with AZI for clearing Chlamydia. These liposomes exhibited stability over time and were readily taken up by both macrophages and epithelial cells. Moreover, they demonstrated significant enhancement of chlamydial clearance in both cell types. In a mouse model, the drug-loaded liposomes cleared Chlamydia within the penile urethra more efficiently than the same dose of unencapsulated drug. Furthermore, the liposome-drug treatment showed significant protective effects on sperm motility and morphology, suggesting potential benefits in reducing sperm damage caused by the infection.

Nanoparticles-based therapeutics for the management of bacterial infections: A special emphasis on FDA approved products and clinical trials

Microbial resistance has increased in recent decades as a result of the extensive and indiscriminate use of antibiotics. The World Health Organization listed antimicrobial resistance as one of ten major global public health threats in 2021. In particular, six major bacterial pathogens, including third-generation cephalosporin-resistant Escherichia coli, methicillin-resistant Staphylococcus aureus, carbapenem-resistant Acinetobacter baumannii, Klebsiella pneumoniae, Streptococcus pneumoniae, and Pseudomonas aeruginosa, were found to have the highest resistance-related death rates in 2019. To respond to this urgent call, the creation of new pharmaceutical technologies based on nanoscience and drug delivery systems appears to be the promising strategy against microbial resistance in light of recent advancements, particularly the new knowledge of medicinal biology. Nanomaterials are often defined as substances having sizes between 1 and 100 nm. If the material is used on a small scale; its properties significantly change. They come in a variety of sizes and forms to help provide distinguishing characteristics for a wide range of functions. The field of health sciences has demonstrated a strong interest in numerous nanotechnology applications. Therefore, in this review, prospective nanotechnology-based therapeutics for the management of bacterial infections with multiple medication resistance are critically examined. Recent developments in these innovative treatment techniques are described, with an emphasis on preclinical, clinical, and combinatorial approaches.

Methylene Blue-Loaded NanoMOFs: Accumulation in Chlamydia trachomatis Inclusions and Light/Dark Antibacterial Effects

Metal-organic framework nanoparticles (nanoMOFs) are promising nanomaterials for biomedical applications. Some of them, including biodegradable porous iron carboxylates are proposed for encapsulation and delivery of antibiotics. Due to the high drug loading capacity and fast internalization kinetics, nanoMOFs are more beneficial for the treatment of intracellular bacterial infections compared to free antibacterial drugs, which poorly accumulate inside the cells because of the inability to cross membrane barriers or have low intracellular retention. However, nanoparticle internalization does not ensure their accumulation in the cell compartment that shelters a pathogen. This study shows the availability of MIL-100(Fe)-based MOF nanoparticles to co-localize with Chlamydia trachomatis, an obligate intracellular bacterium, in the infected RAW264.7 macrophages. Furthermore, nanoMOFs loaded with photosensitizer methylene blue (MB) exhibit complete photodynamic inactivation of C. trachomatis growth. Simultaneous infection and treatment of RAW264.7 cells with empty nanoMOFs resulted in a bacterial load reduction from 100 to 36% that indicates an intrinsic anti-chlamydial effect of this iron-containing nanomaterial. Thus, our findings suggest the use of iron-based nanoMOFs as a promising drug delivery platform, which contributes to antibacterial effect, for the treatment of chlamydial infections.

PLGA Particles in Immunotherapy

Poly(lactic-co-glycolic acid) (PLGA) particles are a widely used and extensively studied drug delivery system. The favorable properties of PLGA such as good bioavailability, controlled release, and an excellent safety profile due to the biodegradable polymer backbone qualified PLGA particles for approval by the authorities for the application as a drug delivery platform in humas. In recent years, immunotherapy has been established as a potent treatment option for a variety of diseases. However, immunomodulating drugs rely on targeted delivery to specific immune cell subsets and are often rapidly eliminated from the system. Loading of PLGA particles with drugs for immunotherapy can protect the therapeutic compounds from premature degradation, direct the drug delivery to specific tissues or cells, and ensure sustained and controlled drug release. These properties present PLGA particles as an ideal platform for immunotherapy. Here, we review recent advances of particulate PLGA delivery systems in the application for immunotherapy in the fields of allergy, autoimmunity, infectious diseases, and cancer.

Nanomedicine: New Frontiers in Fighting Microbial Infections

Microbes have dominated life on Earth for the past two billion years, despite facing a variety of obstacles. In the 20th century, antibiotics and immunizations brought about these changes. Since then, microorganisms have acquired resistance, and various infectious diseases have been able to avoid being treated with traditionally developed vaccines. Antibiotic resistance and pathogenicity have surpassed antibiotic discovery in terms of importance over the course of the past few decades. These shifts have resulted in tremendous economic and health repercussions across the board for all socioeconomic levels; thus, we require ground-breaking innovations to effectively manage microbial infections and to provide long-term solutions. The pharmaceutical and biotechnology sectors have been radically altered as a result of nanomedicine, and this trend is now spreading to the antibacterial research community. Here, we examine the role that nanomedicine plays in the prevention of microbial infections, including topics such as diagnosis, antimicrobial therapy, pharmaceutical administration, and immunizations, as well as the opportunities and challenges that lie ahead.

Targeted Drug Delivery Systems for Eliminating Intracellular Bacteria

The intracellular survival of pathogenic bacteria requires a range of survival strategies and virulence factors. These infections are a significant clinical challenge, wherein treatment frequently fails because of poor antibiotic penetration, stability, and retention in host cells. Drug delivery systems (DDSs) are promising tools to overcome these shortcomings and enhance the efficacy of antibiotic therapy. In this review, the classification and the mechanisms of intracellular bacterial persistence are elaborated. Furthermore, the systematic design strategies applied to DDSs to eliminate intracellular bacteria are also described, and the strategies used for internalization, intracellular activation, bacterial targeting, and immune enhancement are highlighted. Finally, this overview provides guidance for constructing functionalized DDSs to effectively eliminate intracellular bacteria.

Recent Developments in Drug Delivery for Treatment of Tuberculosis by Targeting Macrophages

Tuberculosis (TB) is among the greatest public health and safety concerns in the 21st century, Mycobacterium tuberculosis, which causes TB, infects alveolar macrophages and uses these cells as one of its primary sites of replication. The current TB treatment regimen, which consist of chemotherapy involving a combination of 3-4 antimicrobials for a duration of 6-12 months, is marked with significant side effects, toxicity, and poor compliance. Targeted drug delivery offers a strategy that could overcome many of the problems of current TB treatment by specifically targeting infected macrophages. Recent advances in nanotechnology and material science have opened an avenue to explore drug carriers that actively and passively target macrophages. This approach can increase the drug penetration into macrophages by using ligands on the nanocarrier that interact with specific receptors for macrophages. This review encompasses the recent development of drug carriers specifically targeting macrophages actively and passively. Future directions and challenges associated with development of effective TB treatment is also discussed.

PLGA-Based Composites for Various Biomedical Applications

Polymeric materials have been extensively explored in the field of nanomedicine; within them, poly lactic-co-glycolic acid (PLGA) holds a prominent position in micro- and nanotechnology due to its biocompatibility and controllable biodegradability. In this review we focus on the combination of PLGA with different inorganic nanomaterials in the form of nanocomposites to overcome the polymer’s limitations and extend its field of applications. We discuss their physicochemical properties and a variety of well-established synthesis methods for the preparation of different PLGA-based materials. Recent progress in the design and biomedical applications of PLGA-based materials are thoroughly discussed to provide a framework for future research.

Improving Antibacterial Activity of a HtrA Protease Inhibitor JO146 against Helicobacter pylori: A Novel Approach Using Microfluidics-Engineered PLGA Nanoparticles

Nanoparticle drug delivery systems have emerged as a promising strategy for overcoming limitations of antimicrobial drugs such as stability, bioavailability, and insufficient exposure to the hard-to-reach bacterial drug targets. Although size is a vital colloidal feature of nanoparticles that governs biological interactions, the absence of well-defined size control technology has hampered the investigation of optimal nanoparticle size for targeting bacterial cells. Previously, we identified a lead antichlamydial compound JO146 against the high temperature requirement A (HtrA) protease, a promising antibacterial target involved in protein quality control and virulence. Here, we reveal that JO146 was active against Helicobacter pylori with a minimum bactericidal concentration of 18.8–75.2 µg/mL. Microfluidic technology using a design of experiments approach was utilized to formulate JO146-loaded poly(lactic-co-glycolic) acid nanoparticles and explore the effect of the nanoparticle size on drug delivery. JO146-loaded nanoparticles of three different sizes (90, 150, and 220 nm) were formulated with uniform particle size distribution and drug encapsulation efficiency of up to 25%. In in vitro microdilution inhibition assays, 90 nm nanoparticles improved the minimum bactericidal concentration of JO146 two-fold against H. pylori compared to the free drug alone, highlighting that controlled engineering of nanoparticle size is important in drug delivery optimization.

Road map to the treatment of neglected tropical diseases: Nanocarriers interventions

Neglected tropical disease (NTD) is a set of 20 deadliest endemic diseases which shows its presence in most of the developing countries worldwide. Nearly 1 billion of the population are affected by it and suffered from poverty yearly. These diseases offer their own unique challenges and limitations towards effective prevention and treatment methods. Neglected tropical diseases are severe infections they may not kill the patient but debilitate the patient by causing severe skin deformities, disfigurement and horrible risks for several infections. Existing therapies for neglected diseases suffer from the loopholes like high degree of toxicity, side effects, low bioavailability, improper targeting and problematic application for affected populations. Progress in the field of nanotechnology in last decades suggested the intervention of nanocarriers to take over and drive the research and development to the next level by incorporating established drugs into the nanocarriers rather than discovering the newer drugs which is an expensive affair. These nanocarriers are believed to be a sure shot technique to fight infections at root level by virtue of its nanosize and ability to reach at cellular level. This article highlights the recent advances, rationale, targets and the challenges that are being faced to fight against NTDs and how the novel therapy tactics are able to contribute to its importance in prevention and treatment of NTDs.

Nanomedicines for the topical treatment of vulvovaginal infections: Addressing the challenges of antimicrobial resistance

Recent years have, surprisingly, witnessed an increase in incidence of sexually transmitted infections (STIs). At the same time, antimicrobial therapy came under the threat of ever rising antimicrobial resistance (AMR), resulting in STIs with extremely limited therapy options. In this review, we addressed the challenges of treating vaginal infections in an era of AMR. We focused on published work regarding nanomedicine destined for localized treatment of vaginal infections. Localized therapy offers numerous advantages such as assuring high drug concentration at the infection site, limiting systemic drug exposure that can lead to faster development of AMR reduction in the systemic side effects and potentially safe therapy in pregnancy. We provided a state-of-the-art overview of nanoformulations proposed to topically treat STIs, emphasizing the challenges and advantages of each type of nanocarriers, as well as issues of potential toxicity.

Bioinspired drug delivery strategies for repurposing conventional antibiotics against intracellular infections

Bacteria have developed a wealth of strategies to avoid and resist the action of antibiotics, one of which involves pathogens invading and forming reservoirs within host cells. Due to the poor cell membrane permeability, stability and retention of conventional antibiotics, this renders current treatments largely ineffective, since achieving a therapeutically relevant antibiotic concentration at the site of intracellular infection is not possible. To overcome such challenges, current antibiotics are 'repurposed' via reformulation using micro- or nano-carrier systems that effectively encapsulate and deliver therapeutics across cellular membranes of infected cells. Bioinspired materials that imitate the uptake of biological particulates and release antibiotics in response to natural stimuli are recently explored to improve the targeting and specificity of this 'nanoantibiotic' approach. In this review, the mechanisms of internalization and survival of intracellular bacteria are elucidated, effectively accentuating the current treatment challenges for intracellular infections and the implications for repurposing conventional antibiotics. Key case studies of nanoantibiotics that have drawn inspiration from natural biological particles and cellular uptake pathways to effectively eradicate intracellular pathogens are detailed, clearly highlighting the rational for harnessing bioinspired drug delivery strategies.

Prevention of infection caused by enteropathogenic E. coli O157:H7 in intestinal cells using enrofloxacin entrapped in polymer based nanocarriers

Poor bioavailability of antibiotics, toxicity, and development of antibiotic-resistant bacteria jeopardize antibiotic treatments. To circumvent these issues, drug delivery using nanocarriers are highlighted to secure the future of antibiotic treatments. This work investigated application of nanocarriers, to prevent and treat bacterial infection, presenting minimal toxicity to the IPEC-J2 cell line. To accomplish this, polymer-based nanoparticles (NPs) of poly(lactide-co-glycolide) (PLGA) and lignin-graft-PLGA (LNP) loaded with enrofloxacin (ENFLX) were synthesized, yielding spherical particles with average sizes of 111.8 ± 0.6 nm (PLGA) and 117.4 ± 0.9 nm (LNP). The releases of ENFLX from PLGA and LNP were modeled by a theoretical diffusion model considering both the NP and dialysis diffusion barriers for drug release. Biocompatible concentrations of ENFLX, enrofloxacin loaded PLGA(Enflx) and LNP(Enflx) were determined based on examination of bacterial inhibition, toxicity, and ROS generation. Biocompatible concentrations were used for treatment of higher- and lower-level infections in IPEC-J2 cells. Prevention of bacterial infection by LNP(Enflx) was enhanced more than 50% compared to ENFLX at lower-level infection. At higher-level infection, PLGA(Enflx) and LNP(Enflx) demonstrated 25% higher prevention of bacteria growth compared to ENFLX alone. The superior treatment achieved by the nanocarried drug is accredited to particle uptake by endocytosis and slow release of the drug intracellularly, preventing rapid bacterial growth inside the cells.

Nanoantibiotics: Functions and Properties at the Nanoscale to Combat Antibiotic Resistance

One primary mechanism for bacteria developing resistance is frequent exposure to antibiotics. Nanoantibiotics (nAbts) is one of the strategies being explored to counteract the surge of antibiotic resistant bacteria. nAbts are antibiotic molecules encapsulated with engineered nanoparticles (NPs) or artificially synthesized pure antibiotics with a size range of ≤100 nm in at least one dimension. NPs may restore drug efficacy because of their nanoscale functionalities. As carriers and delivery agents, nAbts can reach target sites inside a bacterium by crossing the cell membrane, interfering with cellular components, and damaging metabolic machinery. Nanoscale systems deliver antibiotics at enormous particle number concentrations. The unique size-, shape-, and composition-related properties of nAbts pose multiple simultaneous assaults on bacteria. Resistance of bacteria toward diverse nanoscale conjugates is considerably slower because NPs generate non-biological adverse effects. NPs physically break down bacteria and interfere with critical molecules used in bacterial processes. Genetic mutations from abiotic assault exerted by nAbts are less probable. This paper discusses how to exploit the fundamental physical and chemical properties of NPs to restore the efficacy of conventional antibiotics. We first described the concept of nAbts and explained their importance. We then summarized the critical physicochemical properties of nAbts that can be utilized in manufacturing and designing various nAbts types. nAbts epitomize a potential Trojan horse strategy to circumvent antibiotic resistance mechanisms. The availability of diverse types and multiple targets of nAbts is increasing due to advances in nanotechnology. Studying nanoscale functions and properties may provide an understanding in preventing future outbreaks caused by antibiotic resistance and in developing successful nAbts.

On-demand pH-sensitive surface charge-switchable polymeric micelles for targeting Pseudomonas aeruginosa biofilms development

Bacterial biofilm is the complicated clinical issues, which usually results in bacterial resistance and reduce the therapeutic efficacy of antibiotics. Although micelles have been drawn attention in treatment of the biofilms, the micelles effectively permeate and retain in biofilms still facing a big challenge. In this study, we fabricated on-demand pH-sensitive surface charge-switchable azithromycin (AZM)-encapsulated micelles (denoted as AZM-SCSMs), aiming to act as therapeutic agent for treating Pseudomonas aeruginosa (P. aeruginosa) biofilms. The AZM-SCSMs was composed of poly(l-lactide)-polyetherimide-hyd-methoxy polyethylene glycol (PLA-PEI-hyd-mPEG). It was noteworthy that the pH-sensitive acylhydrazone bond could be cleaved in acidic biofilm microenvironment, releasing the secondary AZM-loaded cationic micelles based on PLA-PEI (AZM-SCMs) without destroying the micellar integrity, which could tailor drug-bacterium interaction using micelles through electrostatic attraction. The results proved that positively charged AZM-SCMs could facilitate the enhanced penetration and retention inside biofilms, improved binding affinity with bacterial membrane, and added drug internalization, thus characterized as potential anti-biofilm agent. The excellent in vivo therapeutic performance of AZM-SCSMs was confirmed by the targeting delivery to the infected tissue and reduced bacterial burden in the abscess-bearing mice model. This study not only developed a novel method for construction non-depolymerized pH-sensitive SCSMs, but also provided an effective means for the treatment of biofilm-related infections.

Combatting intracellular pathogens using bacteriophage delivery

Intracellular pathogens reside in specialised compartments within the host cells restricting the access of antibiotics. Insufficient intracellular delivery of antibiotics along with several other resistance mechanisms weaken the efficacy of current therapies. An alternative to antibiotic therapy could be bacteriophage (phage) therapy. Although phage therapy has been in practice for a century against various bacterial infections, the efficacy of phages against intracellular bacteria is still being explored. In this review, we will discuss the advancement and challenges in phage therapy, particularly against intracellular bacterial pathogens. Finally, we will highlight the uptake mechanisms and approaches to overcome the challenges to phage therapy against intracellular bacteria.

Nanotechnology approaches for global infectious diseases

Infectious diseases are a major driver of morbidity and mortality globally. Treatment of malaria, tuberculosis and human immunodeficiency virus infection are particularly challenging, as indicated by the ongoing transmission and high mortality associated with these diseases. The formulation of new and existing drugs in nano-sized carriers promises to overcome several challenges associated with the treatment of these diseases, including low on-target bioavailability, sub-therapeutic drug accumulation in microbial sanctuaries and reservoirs, and low patient adherence due to drug-related toxicities and extended therapeutic regimens. Further, nanocarriers can be used for formulating vaccines, which represent a major weapon in our fight against infectious diseases. Here we review the current burden of infectious diseases with a focus on major drivers of morbidity and mortality. We then highlight how nanotechnology could aid in improving existing treatment modalities. We summarize our progress so far and outline potential future directions to maximize the impact of nanotechnology on the global population.

Degradable polymeric vehicles for postoperative pain management

Effective control of pain management has the potential to significantly decrease the need for prescription opioids following a surgical procedure. While extended release products for pain management are available commercially, the implementation of a device that safely and reliably provides extended analgesia and is sufficiently flexible to facilitate a diverse array of release profiles would serve to advance patient comfort, quality of care and compliance following surgical procedures. Herein, we review current polymeric systems that could be utilized in new, controlled post-operative pain management devices and highlight where opportunities for improvement exist.

Encapsulation of Andrographolide in poly(lactide-co-glycolide) Nanoparticles: Formulation Optimization and in vitro Efficacy Studies

Andrographolide is a potential chemopreventive and chemotherapeutic agent that suffers from poor aqueous solubility. Encapsulation in poly(lactide-co-glycolide) (PLGA) nanoparticles can overcome solubility issues and enable sustained release of the drug, resulting in improved therapeutic efficacy. In this study, andrographolide was encapsulated in PLGA nanoparticles via emulsion solvent evaporation technique. Effect of various formulation parameters including polymer composition, polymer molecular weight, polymer to drug ratio, surfactant concentration and the organic solvent used on nanoparticle properties were investigated. A selected formulation was used to determine the effect of encapsulation in nanoparticles on andrographolide's in vitro anticancer efficacy. Nanoparticles formulated using a polymer with 85:15 lactide to glycolide ratio and ethyl acetate as the organic solvent were found to be optimal based on average hydrodynamic particle size (135 ± 4 nm) and drug loading (2.6 ± 0.6%w/w). This formulation demonstrated sustained release of andrographolide over 48 h and demonstrated significantly greater in vitro anticancer efficacy compared to free drug in a metastatic breast cancer cell line. These results suggest that additional, more in-depth efficacy studies are warranted for the nanoparticle formulation of andrographolide.

Recent Advances in Polymeric Nanoparticle-Encapsulated Drugs against Intracellular Infections

Polymeric nanocarriers (PNs) have demonstrated to be a promising alternative to treat intracellular infections. They have outstanding performance in delivering antimicrobials intracellularly to reach an adequate dose level and improve their therapeutic efficacy. PNs offer opportunities for preventing unwanted drug interactions and degradation before reaching the target cell of tissue and thus decreasing the development of resistance in microorganisms. The use of PNs has the potential to reduce the dose and adverse side effects, providing better efficiency and effectiveness of therapeutic regimens, especially in drugs having high toxicity, low solubility in the physiological environment and low bioavailability. This review provides an overview of nanoparticles made of different polymeric precursors and the main methodologies to nanofabricate platforms of tuned physicochemical and morphological properties and surface chemistry for controlled release of antimicrobials in the target. It highlights the versatility of these nanosystems and their challenges and opportunities to deliver antimicrobial drugs to treat intracellular infections and mentions nanotoxicology aspects and future outlooks.

Size and Charge Adaptive Clustered Nanoparticles Targeting the Biofilm Microenvironment for Chronic Lung Infection Management

Chronic lung infection caused by bacterial biofilms is an extremely serious clinical problem, which can lead to the failure of antibiotic therapy. Although nanoparticles have shown great potential in the treatment of biofilms, the efficient penetration and retention of nanoparticles in biofilms is still a big challenge. To address this issue, we herein fabricate size and charge adaptive azithromycin (AZM)-conjugated clustered nanoparticles (denoted as AZM-DA NPs) as therapeutic agents for treating biofilms. The AZM-DA NPs are prepared by electrostatic complexation between AZM conjugated amino-ended poly(amidoamine) dendrimer (PAMAM) and 2,3-dimethyl maleic anhydride (DA) modified poly(ethylene glycol)-block-polylysine (PEG-b-PLys). It is noteworthy that the AZM-DA NPs can disassemble in an acidic biofilm microenvironment (pH 6.0), leading to the release of secondary AZM-conjugated PAMAM nanoparticles (PAMAM-AZM NPs). PAMAM-AZM NPs with small size and positive charge are beneficial for improved penetration and retention inside biofilms, enhanced permeabilization of the bacterial membrane, and increased internalization of AZM, thus exhibiting excellent antibiofilm activities. AZM-DA NPs are also favorable as long-term antibacterial agents due to the reduced occurrence of drug resistance. In vivo therapeutic performance is confirmed by the reduced bacterial burden and the alleviated inflammation in the chronic lung infection model. This research not only develops an innovative strategy for antibiotic delivery in vivo but also provides an effective way for the management of biofilm-associated infections, including chronic lung infection.

Gut Check Time: Antibiotic Delivery Strategies to Reduce Antimicrobial Resistance

Antimicrobial resistance (AMR) has developed into a huge threat to global health, and reducing it is an urgent priority for public health authorities. The importance of a healthy and balanced gut microbiome has been identified as a key protective factor against AMR development, but this can be significantly affected by antibiotic therapy, resulting in dysbiosis and reduction of taxonomic richness. The way in which antibiotics are administered could form an important part of future antimicrobial stewardship strategies, where drug delivery is ideally placed to play a key role in the fight against AMR. This review focuses on drug delivery strategies for antibiotic administration, including avoidance of the gut microbiome and targeted delivery approaches, which may reduce AMR.

Oral pentamidine-loaded poly(d,l-lactic-co-glycolic) acid nanoparticles: an alternative approach for leishmaniasis treatment

Leishmaniasis is a group of diseases caused by a protozoa parasite from one of over 20 Leishmania species. Depending on the tissues infected, these diseases are classified as cutaneous, mucocutaneous and visceral leishmaniasis. For the treatment of leishmaniasis refractory to antimony-based drugs, pentamidine (PTM) is a molecule of great interest. However, PTM displays poor bioavailability through oral routes due to its two strongly basic amidine moieties, which restricts its administration by a parenteral route and limits its clinical use. Among various approaches, nanotechnology-based drug delivery systems (nano-DDS) have potential to overcome the challenges associated with PTM oral administration. Here, we present the development of PTM-loaded PLGA nanoparticles (NPs) with a focus on the characterization of their physicochemical properties and potential application as an oral treatment of leishmaniasis. NPs were prepared by a double emulsion methodology. The physicochemical properties were characterized through the mean particle size, polydispersity index (PdI), zeta potential, entrapment efficiency, yield process, drug loading, morphology, in vitro drug release and in vivo pharmacological activity. The PTM-loaded PLGA NPs presented with a size of 263 ± 5 nm (PdI = 0.17 ± 0.02), an almost neutral charge (-3.2 ± 0.8 mV) and an efficiency for PTM entrapment of 91.5%. The release profile, based on PTM dissolution, could be best described by a zero-order model, followed by a drug diffusion profile that fit to the Higuchi model. In addition, in vivo assay showed the efficacy of orally given PTM-loaded PLGA NPs (0.4 mg kg^-1) in infected BALB/c mice, with significant reduction of organ weight and parasite load in spleen (p-value < 0.05). This work successfully reported the oral use of PTM-loaded NPs, with a high potential for the treatment of visceral leishmaniasis, opening a new perspective to utilization of this drug in clinical practice.

Carbohydrate-based nanocarriers and their application to target macrophages and deliver antimicrobial agents

Many deadly infections are produced by microorganisms capable of sustained survival in macrophages. This reduces exposure to chemadrotherapy, prevents immune detection, and is akin to criminals hiding in police stations. Therefore, the use of glyco-nanoparticles (GNPs) as carriers of therapeutic agents is a burgeoning field. Such an approach can enhance the penetration of drugs into macrophages with specific carbohydrate targeting molecules on the nanocarrier to interact with macrophage lectins. Carbohydrates are natural biological molecules and the key constituents in a large variety of biological events such as cellular communication, infection, inflammation, enzyme trafficking, cellular migration, cancer metastasis and immune functions. The prominent characteristics of carbohydrates including biodegradability, biocompatibility, hydrophilicity and the highly specific interaction of targeting cell-surface receptors support their potential application to drug delivery systems (DDS). This review presents the 21^st century development of carbohydrate-based nanocarriers for drug targeting of therapeutic agents for diseases localized in macrophages. The significance of natural carbohydrate-derived nanoparticles (GNPs) as anti-microbial drug carriers is highlighted in several areas of treatment including tuberculosis, salmonellosis, leishmaniasis, candidiasis, and HIV/AIDS.

Rifampicin-Loaded Mesoporous Silica Nanoparticles for the Treatment of Intracellular Infections

Infectious diseases remain a major burden in today’s world, causing high mortality rates and significant economic losses, with >9 million deaths per year predicted by 2030. Invasion of host cells by intracellular bacteria poses treatment challenges due to the poor permeation of antimicrobials into the infected cells. To overcome these limitations, mesoporous silica nanoparticles (MSNP) loaded with the antibiotic rifampicin were investigated as a nanocarrier system for the treatment of intracellular bacterial infection with specific interest in the influence of particle size on treatment efficiency. An intracellular infection model was established using small colony variants (SCV) of S. aureus in macrophages to systemically evaluate the efficacy of rifampicin-loaded MSNP against the pathogen as compared to a rifampicin solution. As hypothesized, the superior uptake of MSNP by macrophages resulted in an enhanced treatment efficacy of the encapsulated rifampicin as compared to free antibiotic. This study provides a potential platform to improve the performance of currently available antibiotics against intracellular infections.

Promising Recent Strategies with Potential Clinical Translational Value to Combat Antibacterial Resistant Surge

Multiple drug resistance (MDR) for the treatment of bacterial infection has been a significant challenge since the beginning of the 21st century. Many of the small molecule-based antibiotic treatments have failed on numerous occasions due to a surge in MDR, which has claimed millions of lives worldwide. Small particles (SPs) consisting of metal, polymer or carbon nanoparticles (NPs) of different sizes, shapes and forms have shown considerable antibacterial effect over the past two decades. Unlike the classical small-molecule antibiotics, the small particles are less exposed so far to the bacteria to trigger a resistance mechanism, and hence have higher chances of fighting the challenge of the MDR process. Until recently, there has been limited progress of clinical treatments using NPs, despite ample reports of in vitro antibacterial efficacy. In this review, we discuss some recent and unconventional strategies that have explored the antibacterial efficacy of these small particles, alone and in combination with classical small molecules in vivo, and demonstrate possibilities that are favorable for clinical translations in near future.

Effect of erythromycin and modulating effect of CeO2 NPs on the toxicity exerted by the antibiotic on the microalgae Chlamydomonas reinhardtii and Phaeodactylum tricornutum

Erythromycin is an antibiotic employed in the treatment of infections caused by Gram positive microorganisms and the increasing use has made it a contaminant of emerging concern in aqueous ecosystems. Cerium oxide nanoparticles (CeO₂ NPs), which are known to have catalytic and antioxidant properties, have also become contaminants of emerging concern. Due to the high reactivity of CeO₂ NPs, they can interact with erythromycin magnifying their effects or on the other hand, considering the redox potential of CeO₂ NPs, it can alleviate the toxicity of erythromycin. The present study was carried out to assess the toxicity of both single compounds as well as mixed on Chlamydomonas reinhardtii and Phaeodactylum tricornutum (freshwater and marine microalgae respectively) employed as target species in ecotoxicological tests. Mechanisms of oxidative damage and those harmful to the photosynthetic apparatus were studied in order to know the toxic mechanisms of erythromycin and the joint effects with CeO₂ NPs. Results showed that erythromycin inhibited the microalgae population growth and effective quantum yield of PSII (E.Q.Y.) in both microalgae. However, the freshwater microalgae Chlamydomonas reinhardtii was more sensitive than the marine diatom Phaeodactylum tricornutum. Responses related to the photosynthetic apparatus such as E.Q.Y. was affected by the exposure to erythromycin of both microalgae, as chloroplasts are target organelle for this antibiotic. Mixed experiments (CeO₂ NPs + erythromycin) showed the protective role of CeO₂ NPs in both microalgae preventing erythromycin toxicity in toxicological responses such as the growth of the microalgae population and E.Q.Y.

Combination drug therapy via nanocarriers against infectious diseases

Current drug therapy against infections is threatening to become obsolete due to the poor physical, chemical, biological and pharmacokinetic properties of drugs, followed by high risk of acquiring resistance. Taking into account the significant benefits of nanotechnology, nano-based delivery of anti-infectious agents is emerging as a potential approach to combat several lethal infections. Co-delivery of multiple anti-infectious agents in a single nano-based system is beginning to show significant advantages over mono-therapy, such as synergism, enhanced anti-microbial activity, broad anti-microbial spectrum, reduced resistance development, and improved and cost-effective treatment. The current review provides a detailed update on the status of various lipid and polymer based nano-systems used to co-deliver multiple anti-infectious agents against bacterial, HIV and malarial infections. It also identifies current key challenges and suggests strategies to overcome them, thus guiding formulation scientists to further optimize nano-based co-drug delivery as an approach to fight infections effectively.

Antimycobacterial susceptibility evaluation of rifampicin and isoniazid benz-hydrazone in biodegradable polymeric nanoparticles against Mycobacterium tuberculosis H37Rv strain

INTRODUCTION

Tuberculosis (TB) is the single largest infectious disease which requires a prolonged treatment regime with multiple drugs. The present treatment for TB includes frequent administration of a combination of four drugs for a duration of 6 months. This leads to patient's noncompliance, in addition to developing drug-resistant strains which makes treatment more difficult. The formulation of drugs with biodegradable polymeric nanoparticles (NPs) promises to overcome this problem.

MATERIALS AND METHODS

In this study, we focus on two important drugs used for TB treatment - rifampicin (RIF) and isoniazid (INH) - and report a detailed study of RIF-loaded poly lactic-co-glycolic acid (PLGA) NPs and INH modified as INH benz-hydrazone (IH2) which gives the same therapeutic effect as INH but is more stable and enhances the drug loading in PLGA NPs by 15-fold compared to INH. The optimized formulation was characterized using particle size analyzer, scanning electron microscopy and transmission electron microscopy. The drug release from NPs and stability of drug were tested in different pH conditions.

RESULTS

It was found that RIF and IH2 loaded in NPs release in a slow and sustained manner over a period of 1 month and they are more stable in NPs formulation compared to the free form. RIF- and IH2-loaded NPs were tested for antimicrobial susceptibility against Mycobacterium tuberculosis H37Rv strain. RIF loaded in PLGA NPs consistently inhibited the growth at 70% of the minimum inhibitory concentration (MIC) of pure RIF (MIC level 1 µg/mL), and pure IH2 and IH2-loaded NPs showed inhibition at MIC equivalent to the MIC of INH (0.1 µg/mL).

CONCLUSION

These results show that NP formulations will improve the efficacy of drug delivery for TB treatment.

MPEG-PCL Copolymeric Micelles for Encapsulation of Azithromycin

Macrolide antibiotics are lipophilic drugs with some limitations including low solubility, limited cellular permeation, patients discomfort, etc. With amphiphilic methoxy poly(ethylene glycol)-b-poly(ε-caprolactone) (MPEG-PCL) copolymer and azithromycin (AZT) as drug carrier and model drug, AZT-loaded micelles were prepared via thin-membrane hydration method in order to overcome these limitations. Encapsulation efficiency of AZT-loaded micelles was 94.40% with good storage stability for 28 days, and AZT's water solubility was enhanced to 944 μg/mL. Fourier transform infrared spectrum and x-ray diffraction analysis indicated that AZT was enveloped into the micelles in amorphous form due to its interaction with the copolymer. AZT's in vitro release from the AZT-loaded micelles demonstrated a slow and continuous behavior when compared with raw AZT. The release dynamics was accorded with Weibull equation, meaning that release amount of AZT lowered with time and was proportional to remaining amount of drug in the AZT-loaded micelles. Korsmeyer-Peppas fitting result suggested that drug release process was a classical Fickian diffusion-controlled manner. With Staphylococcus aureus as bacterial strain, antibacterial activity of the AZT-loaded micelles displayed was comparable with raw AZT. In conclusion, MPEG-PCL should be a promising carrier for macrolide antibiotic delivery in treatment of bacterial infections.

A programmable lipid-polymer hybrid nanoparticle system for localized, sustained antibiotic delivery to Gram-positive and Gram-negative bacterial biofilms

Bacteria enmeshed in an extracellular matrix, biofilms, exhibit enhanced antibiotic tolerance. Coupled with the rapid emergence of multidrug-resistant strains, the current cohorts of antibiotics are becoming ineffective. Alternative antimicrobial approaches are therefore urgently needed to overcome recalcitrant biofilm infections. Here, we propose the use of a non-toxic lipid-polymer hybrid nanoparticle (LPN) system composed of a solid polymer core (i.e. PLGA; poly lactic-co-glycolic acid) and a cationic lipid shell (i.e. DOTAP) for localized, sustained release of antimicrobial agents to bacterial biofilms. LPNs were synthesized through a simple, robust self-assembly approach. LPNs of uniform particle size (i.e. 100-130 nm), efficiently encapsulated (up to 95%) bioimaging molecules or antibiotics and provided controlled release of the latter. The cationic lipid coating enabled the LPN to anchor onto surfaces of a diverse range of Gram-positive and Gram-negative bacterial pathogens, either in the planktonic or biofilm form. Consistently, the LPN formulations reduced more than 95% of biofilm activity at concentrations that were 8 to 32-fold lower than free antibiotics. These data clearly indicate that these novel formulations could be a useful strategy to enhance the efficacy of antimicrobials against planktonic cells and biofilms of diverse species.

Nanoparticle-based local antimicrobial drug delivery

Despite the wide success of antibiotics in modern medicine, the treatment of bacterial infections still faces critical challenges, especially due to the rapid emergence of antibiotic resistance. As a result, local antimicrobial treatment aimed at enhancing drug concentration at the site of infection while avoiding systemic exposure is becoming increasingly attractive, as it may alleviate resistance development. Meanwhile, therapeutic nanoparticles, especially liposomes, polymeric nanoparticles, dendrimers, and inorganic nanoparticles, are gaining traction to improve the therapeutic efficacy with many applications specifically focused on local antimicrobial treatment. This review highlights topics where nanoparticle-based strategies hold significant potential to advance treatment against local bacterial infections, including (1) promoting antibiotic localization to the pathogen, (2) modulating drug-pathogen interaction against antibiotic resistance, and (3) enabling novel anti-virulence approaches for 'drug-free' antimicrobial activity. In each area, we highlight the innovative antimicrobial strategies tailored for local applications and review the progress made for the treatment of bacterial infections.

Targeting the hard to reach: challenges and novel strategies in the treatment of intracellular bacterial infections

Infectious diseases continue to threaten human and animal health and welfare globally, impacting millions of lives and causing substantial economic loss. The use of antibacterials has been only partially successful in reducing disease impact. Bacterial cells are inherently resilient, and the therapy challenge is increased by the development of antibacterial resistance, the formation of biofilms and the ability of certain clinically important pathogens to invade and localize within host cells. Invasion into host cells provides protection from both antibacterials and the host immune system. Poor delivery of antibacterials into host cells causes inadequate bacterial clearance, resulting in chronic and unresolved infections. In this review, we discuss the challenges associated with existing antibacterial therapies with a focus on intracellular pathogens. We consider the requirements for successful treatment of intracellular infections and novel platforms currently under development. Finally, we discuss novel strategies to improve drug penetration into host cells. As an example, we discuss our recent demonstration that the cell penetrating cationic polymer polyhexamethylene biguanide has antibacterial activity against intracellular Staphylococcus aureus.

LINKED ARTICLES

This article is part of a themed section on Drug Metabolism and Antibiotic Resistance in Micro-organisms. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.14/issuetoc.

Antimicrobial Polymers in the Nano-World

Infections are one of the main concerns of our era due to antibiotic-resistant infections and the increasing costs in the health-care sector. Within this context, antimicrobial polymers present a great alternative to combat these problems since their mechanisms of action differ from those of antibiotics. Therefore, the microorganisms' resistance to these polymeric materials is avoided. Antimicrobial polymers are not only applied in the health-care sector, they are also used in many other areas. This review presents different strategies that combine nanoscience and nanotechnology in the polymer world to combat contaminations from bacteria, fungi or algae. It focuses on the most relevant areas of application of these materials, viz. health, food, agriculture, and textiles.

Freeze concentration-induced PLGA and polystyrene nanoparticle aggregation: Imaging and rational design of lyoprotection

Long-term storage of stable nanoparticulate systems is critical to the utilization of nanotechnology in biomedical applications. Freeze-drying or lyophilization is the most commonly used approach to preparing stable injectable nano formulations. A detailed understanding of the freezing stress on nanoparticles is essential to the successful preservation of original particle attributes and to the development of reliable lyophilization processes. However, visualization of the freezing process and the underlying mechanisms that result in particle aggregation remains challenging. Here, we show a clear causal relationship between the freeze-concentration event and particle aggregation by employing correlative imaging techniques, encompassing both real-time dynamic visualization and super-resolution imaging for frozen systems. Direct evidence was obtained to corroborate the particle isolation hypothesis. Moreover, ice-ice, ice-air and ice-container interfaces were identified as hotspots for generating freezing stress on susceptible nanoparticles. In light of these observations, sphere close packing models were explored. Based on the relationship between jammed particles and void fraction within a confined interfacial space, we are able to define the boundary condition of the minimal 'cryoprotectant to particle ratio' required for effective design space of particle isolation and cryoprotection. These findings clearly demonstrated the utility of visualization techniques and modeling in elucidating the mechanism of freezing stress and protection, providing guiding tools to the rational design of cryoprotectant containing nano formulations and processes.

Antileishmanial activities of caffeic acid phenethyl ester loaded PLGA nanoparticles against Leishmania infantum promastigotes and amastigotes in vitro

OBJECTIVE

To investigate and compare the antileishmanial effects of CAPE and (CAPE)_{PLGA NPs} on Leishmania infantum (L. infantum) promastigotes and amastigotes in vitro.

METHODS

Efficacies of CAPE, (CAPE)_{PLGA NPs} and free PLGA nanoparticles (NPs) on promastigotes were evaluated using MTT and promastigote count assays, and their anti-amastigote effects were determined via infection index analysis. Griess reaction was also performed to calculate nitric oxide production of macrophages exposed to investigated molecules.

RESULTS

It was determined that CAPE and (CAPE)_{PLGA NPs} demonstrated significant inhibitory effects on L. infantum promastigotes and amastigotes, while free NPs did not exhibit any meaningful antileishmanial effectiveness. The IC₅₀ values of CAPE for L. infantum promastigotes and amastigotes were assessed as (51.0 ± 0.8) and (19.0 ± 1.4) μg/mL, respectively (P < 0.05). On the other side, it was revealed that (CAPE)_{PLGA NPs} had superior antileishmanial activity on both forms of parasites since its IC₅₀ values for L. infantum promastigotes and amastigotes were (32.0 ± 1.3) and (8.0 ± 0.9) μg/mL, respectively (P < 0.05). It was also determined that both agents strongly stimulated nitric oxide production of macrophages.

CONCLUSIONS

The obtained results show that (CAPE)_{PLGA NPs} have a great potential to be especially used in treatment of visceral leishmaniasis; however, in vivo antileishmanial screening of these molecules should be performed in the near future.

Junior G, Pilon LE, B. Junior W, Giglioti R, Mosqueira VCF. Uso de antimicrobiano nanoparticulado para o tratamento da mastite subclínica de ovelhas de corte no período seco

Resumo: A inflamação da glândula mamária é uma das principais causas de prejuízo na ovinocultura. Este estudo teve como objetivo investigar as taxas de cura do tratamento da mastite subclínica após infusão intramamária de princípio ativo antimicrobiano no momento da secagem, em formulações convencional e nanoparticulada. Os rebanhos estavam localizados em São Carlos, São Paulo, Brasil. Analisou-se um total de 584 glândulas mamárias de 307 ovelhas de aptidão para produção de carne. Triagem prévia dos casos subclínicos de mastite foi efetuada por meio do California Mastitis Test (CMT) e/ou da contagem de células somáticas (CCS). Análises microbiológicas foram realizadas para confirmação da etiologia infecciosa. As glândulas mamárias com mastite subclínica foram distribuídas em três grupos: G1 (Controle; glândulas mamárias que não receberam tratamento antimicrobiano); G2 (glândulas mamárias em que foi administrado 100 mg de cloxacilina benzatina em estrutura convencional) e G3 (glândulas mamárias em que foi administrado 50 mg de cloxacilina benzatina em estrutura nanoencapsulada). O tratamento aplicado ao G3 mostrou-se mais eficiente (P=0,047) na cura de glândulas mamárias com mastite subclínica. O uso da cloxacilina nanoencapsulada no momento da secagem de ovelhas de corte auxilia no controle da mastite subclínica infecciosa e reduz os prejuízos consequentes.