Engineered liposomes sequester bacterial exotoxins and protect from severe invasive infections in mice

Nanotechnology Integration for SARS-CoV-2 Diagnosis and Treatment: An Approach to Preventing Pandemic

The SARS-CoV-2 outbreak is the COVID-19 disease, which has caused massive health devastation, prompting the World Health Organization to declare a worldwide health emergency. The corona virus infected millions of people worldwide, and many died as a result of a lack of particular medications. The current emergency necessitates extensive therapy in order to stop the spread of the coronavirus. There are various vaccinations available, but no validated COVID-19 treatments. Since its outbreak, many therapeutics have been tested, including the use of repurposed medications, nucleoside inhibitors, protease inhibitors, broad spectrum antivirals, convalescence plasma therapies, immune-modulators, and monoclonal antibodies. However, these approaches have not yielded any outcomes and are mostly used to alleviate symptoms associated with potentially fatal adverse drug reactions. Nanoparticles, on the other hand, may prove to be an effective treatment for COVID-19. They can be designed to boost the efficacy of currently available antiviral medications or to trigger a rapid immune response against COVID-19. In the last decade, there has been significant progress in nanotechnology. This review focuses on the virus's basic structure, pathogenesis, and current treatment options for COVID-19. This study addresses nanotechnology and its applications in diagnosis, prevention, treatment, and targeted vaccine delivery, laying the groundwork for a successful pandemic fight.

Fructose-coated Ångstrom silver prevents sepsis by killing bacteria and attenuating bacterial toxin-induced injuries

Serious infection caused by multi-drug-resistant bacteria is a major threat to human health. Bacteria can invade the host tissue and produce various toxins to damage or kill host cells, which may induce life-threatening sepsis. Here, we aimed to explore whether fructose-coated Ångstrom-scale silver particles (F-AgÅPs), which were prepared by our self-developed evaporation-condensation system and optimized coating approach, could kill bacteria and sequester bacterial toxins to attenuate fatal bacterial infections.

Methods: A series of in vitro assays were conducted to test the anti-bacterial efficacy of F-AgÅPs, and to investigate whether F-AgÅPs could protect against multi-drug resistant Staphylococcus aureus (S. aureus)- and Escherichia coli (E. coli)-induced cell death, and suppress their toxins (S. aureus hemolysin and E. coli lipopolysaccharide)-induced cell injury or inflammation. The mouse models of cecal ligation and puncture (CLP)- or E. coli bloodstream infection-induced lethal sepsis were established to assess whether the intravenous administration of F-AgÅPs could decrease bacterial burden, inhibit inflammation, and improve the survival rates of mice. The levels of silver in urine and feces of mice were examined to evaluate the excretion of F-AgÅPs.

Results: F-AgÅPs efficiently killed various bacteria that can cause lethal infections and also competed with host cells to bind with S. aureus α-hemolysin, thus blocking its cytotoxic activity. F-AgÅPs inhibited E. coli lipopolysaccharide-induced endothelial injury and macrophage inflammation, but not by directly binding to lipopolysaccharide. F-AgÅPs potently reduced bacterial burden, reversed dysregulated inflammation, and enhanced survival in mice with CLP- or E. coli bloodstream infection-induced sepsis, either alone or combined with antibiotic therapy. After three times injections within 48 h, 79.18% of F-AgÅPs were excreted via feces at the end of the 14-day observation period.

Conclusion: This study suggests the prospect of F-AgÅPs as a promising intravenous agent for treating severe bacterial infections.

Recent advancements of nanomaterial-based therapeutic strategies toward sepsis: bacterial eradication, anti-inflammation, and immunomodulation

Sepsis is a life threatening disease that is caused by a dysregulated host immune response to infection, resulting in tissue damage and organ dysfunction, which account for a high in-hospital mortality (approximately 20%). However, there are still no effective and specific therapeutics for clinical sepsis management. Nanomaterial-based strategies have emerged as promising tools for improving the therapeutic efficacy of sepsis by combating lethal bacterial infection, modulating systemic inflammatory response, preventing multiple organ failure, etc. This review has comprehensively summarized the recent advancements in nanomaterial-based strategies for the management of sepsis and severe complications, in which those nanosystems act either as inherent therapeutics or as nanocarriers for the precise delivery of agents. These formulations mechanically possess antibacterial, anti-inflammatory, immunomodulatory, and anti-oxidative effects, achieving multifunctional synergistic treatment efficacy against sepsis. Furthermore, several cell membrane-derived biomimetic nanoplatforms have been used as decoys to trap and neutralize the pathogenic toxins. The critical role of other adjuvant therapies in sepsis management, including the combination of nanotechnology and stem cell therapy, is also highlighted. Overall, this review provides insights into innovative nanotechnology-based strategies applied in sepsis treatment.

A Nanoantidote Alleviates Glioblastoma Chemotoxicity without Efficacy Compromise

Cancer patients suffer from the toxicity of chemotherapy. Antidote, given as a remedy limiting poison, is an effective way to counteract toxicity. However, few antidotes abrogate chemotoxicity without compromising the therapeutic efficacy. Herein, a rationally designed nanoantidote can neutralize chemo-agents in normal cells but not enter tumors and thus would not interfere with the efficacy of tumor treatment. The nanoantidote, consisting of a dendrimer core wrapped by reductive cysteine, captures Temozolomide (TMZ, the glioblastoma standard chemotherapy). Meanwhile, thanks to the blood-brain barrier (BBB) and the size of the nanoantidote, the nanoantidote cannot enter glioblastoma. In murine models, the nanoantidote distributes in normal tissues without crossing the BBB, so it markedly reduces the chemotoxicity of TMZ and retains the original TMZ therapeutic efficacy. With most nanotechnologies focusing on antitumor treatment, this detoxicating strategy demonstrates a nanoplatform to reduce chemotoxicity using physiology barriers and introduces a new approach to nanomedicine for cancer chemotherapy.

Liposomes Prevent In Vitro Hemolysis Induced by Streptolysin O and Lysenin

The need for alternatives to antibiotics in the fight against infectious diseases has inspired scientists to focus on antivirulence factors instead of the microorganisms themselves. In this respect, prior work indicates that tiny, enclosed bilayer lipid membranes (liposomes) have the potential to compete with cellular targets for toxin binding, hence preventing their biological attack and aiding with their clearance. The effectiveness of liposomes as decoy targets depends on their availability in the host and how rapidly they are cleared from the circulation. Although liposome PEGylation may improve their circulation time, little is known about how such a modification influences their interactions with antivirulence factors. To fill this gap in knowledge, we investigated regular and long-circulating liposomes for their ability to prevent in vitro red blood cell hemolysis induced by two potent lytic toxins, lysenin and streptolysin O. Our explorations indicate that both regular and long-circulating liposomes are capable of similarly preventing lysis induced by streptolysin O. In contrast, PEGylation reduced the effectiveness against lysenin-induced hemolysis and altered binding dynamics. These results suggest that toxin removal by long-circulating liposomes is feasible, yet dependent on the particular virulence factor under scrutiny.

Nanobiosystems for Antimicrobial Drug-Resistant Infections

The worldwide increased bacterial resistance toward antimicrobial therapeutics has led investigators to search for new therapeutic options. Some of the options currently exploited to treat drug-resistant infections include drug-associated nanosystems. Additionally, the use of bacteriophages alone or in combination with drugs has been recently revisited; some studies utilizing nanosystems for bacteriophage delivery have been already reported. In this review article, we focus on nine pathogens that are the leading antimicrobial drug-resistant organisms, causing difficult-to-treat infections. For each organism, the bacteriophages and nanosystems developed or used in the last 20 years as potential treatments of pathogen-related infections are discussed. Summarizing conclusions and future perspectives related with the potential of such nano-antimicrobials for the treatment of persistent infections are finally highlighted.

Bacteria-Anchoring Hybrid Liposome Capable of Absorbing Multiple Toxins for Antivirulence Therapy of Escherichia coli Infection

Antivirulence therapy by cell membrane coated nanoparticles has shown promise against bacterial infections. However, current approaches remain unsatisfactory when facing Escherichia coli (E. coli) infections, since the E. coli secretes multiple bacterial toxins including endotoxins and exotoxins that are challenging to eliminate simultaneously. What is worse, the absorptive scavengers normally rely on random contact of the diffuse toxins, which is not efficient. For the current cell membrane coated platform, the single type of cell membrane cannot fully meet the detoxing requirement facing multiple toxins. To address these problems, a polymyxin B (PMB)-modified, red blood cell (RBC)-mimetic hybrid liposome (P-RL) was developed. The P-RL was fabricated succinctly through fusion of PMB-modified lipids and the RBC membranes. By the strong interaction between PMB and the E. coli membrane, P-RL could attach and anchor to the E. coli; attributed to the fused RBC membrane and modified PMB, the P-RL could then efficiently neutralize both endotoxins and exotoxins from the toxin fountainhead. In vitro and in vivo results demonstrated the P-RL had a significant anchoring effect to E. coli. Moreover, compared with the existing RBC vesicles or PMB-modified liposomes, P-RL exhibited a superior therapeutic effect against RBC hemolysis, macrophage activation, and a mixed-toxin infection in mice. Potently, P-RL could inhibit E. coli O157:H7-induced skin damage, intestinal infection, and mouse death. Overall, the P-RL could potentially improve the detoxing efficiency and markedly expand the detoxification spectrum of current antivirulence systems, which provides different insights into drug-resistant E. coli treatment.

Biodistribution and Pharmacokinectics of Liposomes and Exosomes in a Mouse Model of Sepsis

Exosomes have attracted considerable attention as drug delivery vehicles because their biological properties can be utilized for selective delivery of therapeutic cargoes to disease sites. In this context, analysis of the in vivo behaviors of exosomes in a diseased state is required to maximize their therapeutic potential as drug delivery vehicles. In this study, we investigated biodistribution and pharmacokinetics of HEK293T cell-derived exosomes and PEGylated liposomes, their synthetic counterparts, into healthy and sepsis mice. We found that biodistribution and pharmacokinetics of exosomes were significantly affected by pathophysiological conditions of sepsis compared to those of liposomes. In the sepsis mice, a substantial number of exosomes were found in the lung after intravenous injection, and their prolonged blood residence was observed due to the liver dysfunction. However, liposomes did not show such sepsis-specific effects significantly. These results demonstrate that exosome-based therapeutics can be developed to manage sepsis and septic shock by virtue of their sepsis-specific in vivo behaviors.

Novel Diagnostics and Therapeutics in Sepsis

Sepsis management demands early diagnosis and timely treatment that includes source control, antimicrobial therapy, and resuscitation. Currently employed diagnostic tools are ill-equipped to rapidly diagnose sepsis and isolate the offending pathogen, which limits the ability to offer targeted and lowest-toxicity treatment. Cutting edge diagnostics and therapeutics in development may improve time to diagnosis and address two broad management principles: (1) source control by removing the molecular infectious stimulus of sepsis, and (2) attenuation of the pathological immune response allowing the body to heal. This review addresses novel diagnostics and therapeutics and their role in the management of sepsis.

Tailored liposomal nanotraps for the treatment of Streptococcal infections

BACKGROUND

Streptococcal infections are associated with life-threatening pneumonia and sepsis. The rise in antibiotic resistance calls for novel approaches to treat bacterial diseases. Anti-virulence strategies promote a natural way of pathogen clearance by eliminating the advantage provided to bacteria by their virulence factors. In contrast to antibiotics, anti-virulence agents are less likely to exert selective evolutionary pressure, which is a prerequisite for the development of drug resistance. As part of their virulence mechanism, many bacterial pathogens secrete cytolytic exotoxins (hemolysins) that destroy the host cell by destabilizing their plasma membrane. Liposomal nanotraps, mimicking plasmalemmal structures of host cells that are specifically targeted by bacterial toxins are being developed in order to neutralize-by competitive sequestration-numerous exotoxins.

RESULTS

In this study, the liposomal nanotrap technology is further developed to simultaneously neutralize the whole palette of cytolysins produced by Streptococcus pneumoniae, Streptococcus pyogenes and Streptococcus dysgalactiae subspecies equisimilis-pathogens that can cause life-threatening streptococcal toxic shock syndrome. We show that the mixture of liposomes containing high amounts of cholesterol and liposomes composed exclusively of choline-containing phospholipids is fully protective against the combined action of exotoxins secreted by these pathogens.

CONCLUSIONS

Unravelling the universal mechanisms that define targeting of host cells by streptococcal cytolysins paves the way for a broad-spectrum anti-toxin therapy that can be applied without a diagnostic delay for the treatment of bacterial infections including those caused by antibiotic-resistant pathogens.

Application of Nanotechnology in the COVID-19 Pandemic

COVID-19, caused by SARS-CoV-2 infection, has been prevalent worldwide for almost a year. In early 2000, there was an outbreak of SARS-CoV, and in early 2010, a similar dissemination of infection by MERS-CoV occurred. However, no clear explanation for the spread of SARS-CoV-2 and a massive increase in the number of infections has yet been proposed. The best solution to overcome this pandemic is the development of suitable and effective vaccines and therapeutics. Fortunately, for SARS-CoV-2, the genome sequence and protein structure have been published in a short period, making research and development for prevention and treatment relatively easy. In addition, intranasal drug delivery has proven to be an effective method of administration for treating viral lung diseases. In recent years, nanotechnology-based drug delivery systems have been applied to intranasal drug delivery to overcome various limitations that occur during mucosal administration, and advances have been made to the stage where effective drug delivery is possible. This review describes the accumulated knowledge of the previous SARS-CoV and MERS-CoV infections and aims to help understand the newly emerged SARS-CoV-2 infection. Furthermore, it elucidates the achievements in developing COVID-19 vaccines and therapeutics to date through existing approaches. Finally, the applicable nanotechnology approach is described in detail, and vaccines and therapeutic drugs developed based on nanomedicine, which are currently undergoing clinical trials, have presented the potential to become innovative alternatives for overcoming COVID-19.

Antivirulence Strategies for the Treatment of Staphylococcus aureus Infections: A Mini Review

Staphylococcus aureus is a Gram-positive bacterium capable of infecting nearly all host tissues, causing severe morbidity and mortality. Widespread antimicrobial resistance has emerged among S. aureus clinical isolates, which are now the most frequent causes of nosocomial infection among drug-resistant pathogens. S. aureus produces an array of virulence factors that enhance in vivo fitness by liberating nutrients from the host or evading host immune responses. Staphylococcal virulence factors have been identified as viable therapeutic targets for treatment, as they contribute to disease pathogenesis, tissue injury, and treatment failure. Antivirulence strategies, or treatments targeting virulence without direct toxicity to the inciting pathogen, show promise as an adjunctive therapy to traditional antimicrobials. This Mini Review examines recent research on S. aureus antivirulence strategies, with an emphasis on translational studies. While many different virulence factors have been investigated as therapeutic targets, this review focuses on strategies targeting three virulence categories: pore-forming toxins, immune evasion mechanisms, and the S. aureus quorum sensing system. These major areas of S. aureus antivirulence research demonstrate broad principles that may apply to other human pathogens. Finally, challenges of antivirulence research are outlined including the potential for resistance, the need to investigate multiple infection models, and the importance of studying antivirulence in conjunction with traditional antimicrobial treatments.

Inorganic and Polymeric Nanoparticles for Human Viral and Bacterial Infections Prevention and Treatment

Infectious diseases hold third place in the top 10 causes of death worldwide and were responsible for more than 6.7 million deaths in 2016. Nanomedicine is a multidisciplinary field which is based on the application of nanotechnology for medical purposes and can be defined as the use of nanomaterials for diagnosis, monitoring, control, prevention, and treatment of diseases, including infectious diseases. One of the most used nanomaterials in nanomedicine are nanoparticles, particles with a nano-scale size that show highly tunable physical and optical properties, and the capacity to a wide library of compounds. This manuscript is intended to be a comprehensive review of the available recent literature on nanoparticles used for the prevention and treatment of human infectious diseases caused by different viruses, and bacteria from a clinical point of view by basing on original articles which talk about what has been made to date and excluding commercial products, but also by highlighting what has not been still made and some clinical concepts that must be considered for futures nanoparticles-based technologies applications.

A soft anti-virulence liposome realizing the explosive release of antibiotics at an infectious site to improve antimicrobial therapy

Pore-forming toxins (PFTs), the most common virulence proteins, are promising therapeutic keys in bacterial infections. CAL02, consisting of sphingomyelin (Sm) and containing a maximum ratio of cholesterol (Ch), has been applied to sequester PFTs. However, Sm, a saturated phospholipid, leads to structural rigidity of the liposome, which does not benefit PFT combination. Therefore, in order to decrease the membrane rigidity and improve the fluidity of liposomes, we have introduced an unsaturated phospholipid, phosphatidylcholine (Pc), to the saturated Sm. In this report, a soft nanoliposome (called CSPL), composed of Ch, Sm and Pc, was artificially prepared. In order to further improve its antibacterial effect, vancomycin (Van) was loaded into the hydrophilic core of CSPL, where Van can be released radically at the infectious site through transmembrane pores formed by the PFTs in CSPL. This soft Van@CSPL nanoliposome with detoxification/drug release was able to inhibit the possibility of antibiotic resistance and could play a better role in treating severe invasive infections in mice.

The search for novel treatment strategies for Streptococcus pneumoniae infections

This review provides an overview of the most important novel treatment strategies against Streptococcus pneumoniae infections published over the past 10 years. The pneumococcus causes the majority of community-acquired bacterial pneumonia cases, and it is one of the prime pathogens in bacterial meningitis. Over the last 10 years, extensive research has been conducted to prevent severe pneumococcal infections, with a major focus on (i) boosting the host immune system and (ii) discovering novel antibacterials. Boosting the immune system can be done in two ways, either by actively modulating host immunity, mostly through administration of selective antibodies, or by interfering with pneumococcal virulence factors, thereby supporting the host immune system to effectively overcome an infection. While several of such experimental therapies are promising, few have evolved to clinical trials. The discovery of novel antibacterials is hampered by the high research and development costs versus the relatively low revenues for the pharmaceutical industry. Nevertheless, novel enzymatic assays and target-based drug design, allow the identification of targets and the development of novel molecules to effectively treat this life-threatening pathogen.

Role of the inflammatory response in community-acquired pneumonia: clinical implications

INTRODUCTION

Despite adequate antibiotic coverage, community-acquired pneumonia (CAP) remains a leading cause of hospitalization and mortality worldwide. It induces both a local pulmonary and a systemic inflammatory response, particularly significant in severe cases. The intensity of the dysregulated host response varies from patient to patient and has a negative impact on survival and other outcomes.

AREAS COVERED

This comprehensive review summarizes the pathophysiological aspects of the inflammatory response in CAP, briefly discusses the usefulness of biomarkers, and assesses the clinical evidence for modulating the inflammatory pathways. We searched PubMed for the most relevant studies, reviews, and meta-analysis until August 2020.

EXPERT OPINION

Notable efforts have been made to identify biomarkers that can accurately differentiate between viral and bacterial etiology, and indeed, to enhance risk stratification in CAP. However, none has proven ideal and no recommended biomarker-guided algorithms exist. Biomarker signatures from proteomic and metabolomic studies could be more useful for such assessments. To date, most studies have produced contradictory results concerning the role of immunomodulatory agents (e.g. corticosteroids, macrolides, and statins) in CAP. Adequately identifying the population who may benefit most from effective modulation of the inflammatory response remains a challenge.

Nanotools for Sepsis Diagnosis and Treatment

Sepsis is one of the leading causes of death worldwide with high mortality rates and a pathological complexity hindering early and accurate diagnosis. Today, laboratory culture tests are the epitome of pathogen recognition in sepsis. However, their consistency remains an issue of controversy with false negative results often observed. Clinically used blood markers, C reactive protein (CRP) and procalcitonin (PCT) are indicators of an acute-phase response and thus lack specificity, offering limited diagnostic efficacy. In addition to poor diagnosis, inefficient drug delivery and the increasing prevalence of antibiotic-resistant microorganisms constitute significant barriers in antibiotic stewardship and impede effective therapy. These challenges have prompted the exploration for alternative strategies that pursue accurate diagnosis and effective treatment. Nanomaterials are examined for both diagnostic and therapeutic purposes in sepsis. The nanoparticle (NP)-enabled capture of sepsis causative agents and/or sepsis biomarkers in biofluids can revolutionize sepsis diagnosis. From the therapeutic point of view, currently existing nanoscale drug delivery systems have proven to be excellent allies in targeted therapy, while many other nanotherapeutic applications are envisioned. Herein, the most relevant applications of nanomedicine for the diagnosis, prognosis, and treatment of sepsis is reviewed, providing a critical assessment of their potentiality for clinical translation.

Controlled Dendrimersome Nanoreactor System for Localized Hypochlorite-Induced Killing of Bacteria

Antibiotic resistance is a serious global health problem necessitating new bactericidal approaches such as nanomedicines. Dendrimersomes (DSs) have recently become a valuable alternative nanocarrier to polymersomes and liposomes due to their molecular definition and synthetic versatility. Despite this, their biomedical application is still in its infancy. Inspired by the localized antimicrobial function of neutrophil phagosomes and the versatility of DSs, a simple three-component DS-based nanoreactor with broad-spectrum bactericidal activity is presented. This was achieved by encapsulation of glucose oxidase (GOX) and myeloperoxidase (MPO) within DSs (GOX-MPO-DSs), self-assembled from an amphiphilic Janus dendrimer, that possesses a semipermeable membrane. By external addition of glucose to GOX-MPO-DS, the production of hypochlorite (-OCl), a highly potent antimicrobial, by the enzymatic cascade was demonstrated. This cascade nanoreactor yielded a potent bactericidal effect against two important multidrug resistant pathogens, Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa), not observed for H2O2 producing nanoreactors, GOX-DS. The production of highly reactive species such as -OCl represents a harsh bactericidal approach that could also be cytotoxic to mammalian cells. This necessitates the development of strategies for activating -OCl production in a localized manner in response to a bacterial stimulus. One option of locally releasing sufficient amounts of substrate using a bacterial trigger (released toxins) was demonstrated with lipidic glucose-loaded giant unilamellar vesicles (GUVs), envisioning, e.g., implant surface modification with nanoreactors and GUVs for localized production of bactericidal agents in the presence of bacterial growth.

Immunotherapy and vaccination against infectious diseases

Due to the overuse of antibiotics, infections, in particular those caused by multidrug-resistant bacteria, are becoming more and more frequent. Despite the worldwide introduction of antibiotic therapy, vaccines and constant improvements in hygiene, the burden of multidrug-resistant bacterial infections is increasing and is expected to rise in the future. The development of monoclonal therapeutic antibodies and specific immunomodulatory drugs represent new treatment options in the fight against infectious diseases. This article provides a brief overview of recent advances in immunomodulatory therapy and other strategies in the treatment of infectious disease.

Investigational and Experimental Drugs for Community-Acquired Pneumonia: the Current Evidence

Community-acquired pneumonia (CAP) is a common infection with a constantly evolving etiological spectrum. This changing etiology conditions the adequate selection of optimal therapeutic regimens, both in empirical and definitive treatments. In recent years, new antimicrobials have been approved by regulatory authorities for use in CAP, although it is necessary to continue incorporating new antimicrobial agents that improve the activity profile in relation to the appearance of bacterial resistance in certain pathogens, such as pneumococcus, Staphylococcus aureus or Pseudomonas aeruginosa. Delafloxacin, omadacycline and lefamulin are the most recently approved antibiotics for CAP. These three antibiotics have shown non-inferiority to their comparators for the treatment of CAP with an excellent safety profile. However, in the 2019 ATS/IDSA guidelines, it has been considered that more information is needed to incorporate these new drugs into community-based treatment. New antimicrobials, such as solithromycin and nemonoxacin, are currently being studied in Phase III clinical trials. Both drugs have shown non-inferiority against the comparators and an acceptable safety profile; however, they have not yet been approved by the regulatory authorities. Several drugs are being tested in Phase I and II clinical trials. These include zabofloxacin, aravofloxacin, nafithromycin, TP-271, gepotidacin, radezolid, delpazolid, and CAL02. The preliminary results of these clinical trials allow us to assure that most of these drugs may play a role in the future treatment of CAP.

Boosting nanotoxicity to combat multidrug-resistant bacteria in pathophysiological environments

Nanomaterials are promising novel antibiotics, but often ineffective. We found that nanomaterial-bacteria complex formation occurred with various nanomaterials. The bactericidal activity of NMs strongly depends on their physical binding to (multidrug-resistant) bacteria. Nanomaterials' binding and antibiotic effect was reduced by various pathophysiological biomolecule coronas strongly inhibiting their antibiotic effects. We show from analytical to in vitro to in vivo that nanomaterial-based killing could be restored by acidic pH treatments. Here, complex formation of negatively-charged, plasma corona-covered, nanomaterials with bacteria was electrostatically enhanced by reducing bacteria's negative surface charge. Employing in vivo skin infection models, acidic pH-induced complex formation was critical to counteract Staphylococcus aureus infections by silver nanomaterials. We explain why nano-antibiotics show reduced activity and provide a clinically practical solution.

Decoy nanoparticles protect against COVID-19 by concurrently adsorbing viruses and inflammatory cytokines

The COVID-19 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has highlighted the urgent need to rapidly develop therapeutic strategies for such emerging viruses without effective vaccines or drugs. Here, we report a decoy nanoparticle against COVID-19 through a powerful two-step neutralization approach: virus neutralization in the first step followed by cytokine neutralization in the second step. The nanodecoy, made by fusing cellular membrane nanovesicles derived from human monocytes and genetically engineered cells stably expressing angiotensin converting enzyme II (ACE2) receptors, possesses an antigenic exterior the same as source cells. By competing with host cells for virus binding, these nanodecoys effectively protect host cells from the infection of pseudoviruses and authentic SARS-CoV-2. Moreover, relying on abundant cytokine receptors on the surface, the nanodecoys efficiently bind and neutralize inflammatory cytokines including interleukin 6 (IL-6) and granulocyte-macrophage colony-stimulating factor (GM-CSF), and significantly suppress immune disorder and lung injury in an acute pneumonia mouse model. Our work presents a simple, safe, and robust antiviral nanotechnology for ongoing COVID-19 and future potential epidemics.

Alginate: From Food Industry to Biomedical Applications and Management of Metabolic Disorders

Initially used extensively as an additive and ingredient in the food industry, alginate has become an important compound for a wide range of industries and applications, such as the medical, pharmaceutical and cosmetics sectors. In the food industry, alginate has been used to coat fruits and vegetables, as a microbial and viral protection product, and as a gelling, thickening, stabilizing or emulsifying agent. Its biocompatibility, biodegradability, nontoxicity and the possibility of it being used in quantum satis doses prompted scientists to explore new properties for alginate usage. Thus, the use of alginate has been expanded so as to be directed towards the pharmaceutical and biomedical industries, where studies have shown that it can be used successfully as biomaterial for wound, hydrogel, and aerogel dressings, among others. Furthermore, the ability to encapsulate natural substances has led to the possibility of using alginate as a drug coating and drug delivery agent, including the encapsulation of probiotics. This is important considering the fact that, until recently, encapsulation and coating agents used in the pharmaceutical industry were limited to the use of lactose, a potentially allergenic agent or gelatin. Obtained at a relatively low cost from marine brown algae, this hydrocolloid can also be used as a potential tool in the management of diabetes, not only as an insulin delivery agent but also due to its ability to improve insulin resistance, attenuate chronic inflammation and decrease oxidative stress. In addition, alginate has been recognized as a potential weight loss treatment, as alginate supplementation has been used as an adjunct treatment to energy restriction, to enhance satiety and improve weight loss in obese individuals. Thus, alginate holds the promise of an effective product used in the food industry as well as in the management of metabolic disorders such as diabetes and obesity. This review highlights recent research advances on the characteristics of alginate and brings to the forefront the beneficial aspects of using alginate, from the food industry to the biomedical field.

Mannose receptor-derived peptides neutralize pore-forming toxins and reduce inflammation and development of pneumococcal disease

Cholesterol‐dependent cytolysins (CDCs) are essential virulence factors for many human pathogens like Streptococcus pneumoniae (pneumolysin, PLY), Streptococcus pyogenes (streptolysin O, SLO), and Listeria monocytogenes (Listeriolysin, LLO) and induce cytolysis and inflammation. Recently, we identified that pneumococcal PLY interacts with the mannose receptor (MRC‐1) on specific immune cells thereby evoking an anti‐inflammatory response at sublytic doses. Here, we identified the interaction sites between MRC‐1 and CDCs using computational docking. We designed peptides from the CTLD4 domain of MRC‐1 that binds to PLY, SLO, and LLO, respectively. In vitro, the peptides blocked CDC‐induced cytolysis and inflammatory cytokine production by human macrophages. Also, they reduced PLY‐induced damage of the epithelial barrier integrity as well as blocked bacterial invasion into the epithelium in a 3D lung tissue model. Pre‐treatment of human DCs with peptides blocked bacterial uptake via MRC‐1 and reduced intracellular bacterial survival by targeting bacteria to autophagosomes. In order to use the peptides for treatment in vivo, we developed calcium phosphate nanoparticles (CaP NPs) as peptide nanocarriers for intranasal delivery of peptides and enhanced bioactivity. Co‐administration of peptide‐loaded CaP NPs during infection improved survival and bacterial clearance in both zebrafish and mice models of pneumococcal infection. We suggest that MRC‐1 peptides can be employed as adjunctive therapeutics with antibiotics to treat bacterial infections by countering the action of CDCs.

Platelets and Their Role in the Pathogenesis of Cardiovascular Events in Patients With Community-Acquired Pneumonia

Community-acquired pneumonia (CAP) remains an important cause of morbidity and mortality throughout the world with much recent and ongoing research focused on the occurrence of cardiovascular events (CVEs) during the infection, which are associated with adverse short-term and long-term survival. Much of the research directed at unraveling the pathogenesis of these events has been undertaken in the settings of experimental and clinical CAP caused by the dangerous, bacterial respiratory pathogen, Streptococcus pneumoniae (pneumococcus), which remains the most common bacterial cause of CAP. Studies of this type have revealed that although platelets play an important role in host defense against infection, there is also increasing recognition that hyperactivation of these cells contributes to a pro-inflammatory, prothrombotic systemic milieu that contributes to the etiology of CVEs. In the case of the pneumococcus, platelet-driven myocardial damage and dysfunction is exacerbated by the direct cardiotoxic actions of pneumolysin, a major pore-forming toxin of this pathogen, which also acts as potent activator of platelets. This review is focused on the role of platelets in host defense against infection, including pneumococcal infection in particular, and reviews the current literature describing the potential mechanisms by which platelet activation contributes to cardiovascular complications in CAP. This is preceded by an evaluation of the burden of pneumococcal infection in CAP, the clinical features and putative pathogenic mechanisms of the CVE, and concludes with an evaluation of the potential utility of the anti-platelet activity of macrolides and various adjunctive therapies.

Biomimetic hybrid membrane-based nanoplatforms: synthesis, properties and biomedical applications

The rapid clearance and capture by the immune system pose a big challenge in targeted drug delivery using nanocarriers. Cell membrane coating endows nanoplatforms with prolonged blood circulation, enhanced immune escape, and improved targeting capability. However, monotypic cell membrane fails to meet the omnifarious needs of biomedical applications. The combination of different types of cell membranes provides a promising solution to provide multifunctional biomimetic nanoplatforms. In this review, we first discuss the feasibility of constructing biomimetic hybrid membranes and summarize current methods of preparing biomimetic hybrid membrane-based nanoplatforms (BHMNs) and their biomedical applications including drug delivery, cancer detection, detoxification, and cancer vaccines. Finally, the prospects and challenges of utilizing BHMNs for personalized medicine are also discussed.

Interaction of Macrophages and Cholesterol-Dependent Cytolysins: The Impact on Immune Response and Cellular Survival

Cholesterol-dependent cytolysins (CDCs) are key virulence factors involved in many lethal bacterial infections, including pneumonia, necrotizing soft tissue infections, bacterial meningitis, and miscarriage. Host responses to these diseases involve myeloid cells, especially macrophages. Macrophages use several systems to detect and respond to cholesterol-dependent cytolysins, including membrane repair, mitogen-activated protein (MAP) kinase signaling, phagocytosis, cytokine production, and activation of the adaptive immune system. However, CDCs also promote immune evasion by silencing and/or destroying myeloid cells. While there are many common themes between the various CDCs, each CDC also possesses specific features to optimally benefit the pathogen producing it. This review highlights host responses to CDC pathogenesis with a focus on macrophages. Due to their robust plasticity, macrophages play key roles in the outcome of bacterial infections. Understanding the unique features and differences within the common theme of CDCs bolsters new tools for research and therapy.

In vitro and in vivo Evaluation of in silico Predicted Pneumococcal UDPG:PP Inhibitors

Pneumonia, of which Streptococcus pneumoniae is the most common causative agent, is considered one of the three top leading causes of death worldwide. As seen in other bacterial species, antimicrobial resistance is on the rise for this pathogen. Therefore, there is a pressing need for novel antimicrobial strategies to combat these infections. Recently, uridine diphosphate glucose pyrophosphorylase (UDPG:PP) has been put forward as a potential drug target worth investigating. Moreover, earlier research demonstrated that streptococci lacking a functional galU gene (encoding for UDPG:PP) were characterized by significantly reduced in vitro and in vivo virulence. Therefore, in this study we evaluated the anti-virulence activity of potential UDPG:PP inhibitors. They were selected in silico using a tailor-made streptococcal homology model, based on earlier listerial research. While the compounds didn’t affect bacterial growth, nor affected in vitro adhesion to and phagocytosis in macrophages, the amount of polysaccharide capsule was significantly reduced after co-incubation with these inhibitors. Moreover, co-incubation proved to have a positive effect on survival in an in vivo Galleria mellonella larval infection model. Therefore, rather than targeting bacterial survival directly, these compounds proved to have an effect on streptococcal virulence by lowering the amount of polysaccharide and thereby probably boosting recognition of this pathogen by the innate immune system. While the compounds need adaptation to broaden their activity to more streptococcal strains rather than being strain-specific, this study consolidates UDPG:PP as a potential novel drug target.

Periphery-confined particulate systems for the management of neurodegenerative diseases and toxicity: Avoiding the blood-brain-barrier challenge

The blood-brain barrier prevents passage of large and hydrophilic molecules, undermining efforts to deliver most active molecules, proteins and other macromolecules. To date, nanoparticle-assisted delivery has been extensively studied to overcome this challenge but with limited success. On the other hand, for certain brain therapeutic applications, periphery-confined particles could be of immediate therapeutic usefulness. The modulation of CNS dysfunctions from the peripheral compartment is a promising approach, as it does not involve invasive interventions. From recent studies, three main roles could be identified for periphery-confined particles: brain tissue detoxification via the "sink-effect"; a "circulating drug-reservoir" effect to improve drug delivery to brain tissues, and finally, brain vascular endothelium targeting to diagnose or heal vascular-related dysfunctions. These applications are much easier to implement as they do not involve complex therapeutic and targeting strategies and do not require crossing biological barriers. Micro/nano-devices required for such applications will likely be simpler to synthesize and will involve fewer complex materials. Moreover, peripheral particles are expected to be less prone to neurotoxicity and issues related to their diffusion in confined space.

Liposomes for Antibiotic Encapsulation and Delivery

When antibiotics are administered, orally or intravenously, they pass through different organs and layers of tissue on their way to the site of infection; this can cause dilution and/or intoxication. To overcome these problems, drug delivery vehicles have been used to encapsulate and deliver antibiotics, improving their therapeutic index while minimizing their adverse effects. Liposomes are self-assembled lipid vesicles made from at least one bilayer of phospholipids with an inner aqueous compartment. Liposomes are attractive vehicles to deliver antibiotics because they can encapsulate both hydrophobic and hydrophilic antibiotics, they have low toxicity, and they can change the biodistribution of the drug. Furthermore, liposomes have been approved by regulatory agencies. However, most developmental and mechanistic research in the field has been focused on encapsulation and delivery of anticancer drugs, a class of molecules that differ significantly in chemistry from antibiotics. In this critical Review, we discuss the state of knowledge regarding the design of liposomes for encapsulation and delivery of antibiotics and offer insight into the challenges and promises of using liposomes for antibiotic delivery.

Increased pathogenicity of pneumococcal serotype 1 is driven by rapid autolysis and release of pneumolysin

Streptococcus pneumoniae serotype 1 is the predominant cause of invasive pneumococcal disease in sub-Saharan Africa, but the mechanism behind its increased invasiveness is not well understood. Here, we use mouse models of lung infection to identify virulence factors associated with severe bacteraemic pneumonia during serotype-1 (ST217) infection. We use BALB/c mice, which are highly resistant to pneumococcal pneumonia when infected with other serotypes. However, we observe 100% mortality and high levels of bacteraemia within 24 hours when BALB/c mice are intranasally infected with ST217. Serotype 1 produces large quantities of pneumolysin, which is rapidly released due to high levels of bacterial autolysis. This leads to substantial levels of cellular cytotoxicity and breakdown of tight junctions between cells, allowing a route for rapid bacterial dissemination from the respiratory tract into the blood. Thus, our results offer an explanation for the increased invasiveness of serotype 1.

The mechanisms behind the high invasiveness of Streptococcus pneumoniae serotype 1 are unclear. Here, Jacques et al. show that this feature is due to overproduction and rapid release of pneumolysin, which induces cytotoxicity and breakdown of tight junctions, allowing rapid bacterial dissemination from the respiratory tract into the blood.

Staging and Personalized Intervention for Infection and Sepsis

Background: Sepsis is defined as a dysregulated host response to infection, resulting in life-threatening organ dysfunction. It is now understood that this dysregulation not only constitutes excessive inflammation, but also sustained immune suppression. Immune-modulatory therapies thus have great potential for novel sepsis therapies. Here, we provide a review of biomarkers and functional assays designed to immunologically stage patients with sepsis as well as therapies designed to alter the innate and adaptive immune systems of patients with sepsis beneficially. Methods: A search of PubMed/MEDLINE and clinicaltrials.gov was performed between October 1, 2019 and December 22, 2019 using search terms such as "sepsis immunotherapy," "sepsis biomarkers," "sepsis clinical trials," and variations thereof. Results: Despite more than 30 years of research, there is still no Food and Drug Administration (FDA)-cleared biomarker that has proven to be effective in either identifying patients with sepsis who are at an increased risk of adverse outcomes or responsive to specific interventions. Similarly, past clinical trials investigating new treatment strategies have rarely stratified patients with sepsis. Overall, the results of these trials have been disappointing. Novel efforts to properly gauge an individual patient's immune response and choose an appropriate immunomodulatory agent based on the results are underway. Conclusion: Our evolving understanding of the different mechanisms perturbing immune homeostasis during sepsis strongly suggests that future successes will depend on finding the right therapy for the right patient and administering it at the right time. For such a personalized medicine approach, novel biomarkers and functional assays to properly stage the patient with sepsis will be crucial. The growing repertoire of immunomodulatory agents at our disposal, as well as re-appraisal of agents that have already been tested in unstratified cohorts of patients with sepsis, may finally translate into successful treatment strategies for sepsis.

Cell-Membrane-Mimicking Nanodecoys against Infectious Diseases

Infectious diseases are a leading cause of mortality worldwide, with viruses and bacteria in particular having enormous impacts on global healthcare. One major challenge in combatting such diseases is a lack of effective drugs or specific treatments. In addition, drug resistance to currently available therapeutics and adverse effects caused by long-term overuse are both serious public health issues. A promising treatment strategy is to employ cell-membrane mimics as decoys to trap and to detain the pathogens. In this Perspective, we briefly review the infection mechanisms adopted by different pathogens at the cellular membrane interface and highlight the applications of cell-membrane-mimicking nanodecoys for systemic protection against infectious diseases. We also discuss the implication of nanodecoy-pathogen complexes in the development of vaccines. We anticipate this Perspective will provide new insights on design and development of advanced materials against emerging infectious diseases.

Acid ceramidase of macrophages traps herpes simplex virus in multivesicular bodies and protects from severe disease

Macrophages have important protective functions during infection with herpes simplex virus type 1 (HSV-1). However, molecular mechanisms that restrict viral propagation and protect from severe disease are unclear. Here we show that macrophages take up HSV-1 via endocytosis and transport the virions into multivesicular bodies (MVBs). In MVBs, acid ceramidase (aCDase) converts ceramide into sphingosine and increases the formation of sphingosine-rich intraluminal vesicles (ILVs). Once HSV-1 particles reach MVBs, sphingosine-rich ILVs bind to HSV-1 particles, which restricts fusion with the limiting endosomal membrane and prevents cellular infection. Lack of aCDase in macrophage cultures or in Asah1^-/- mice results in replication of HSV-1 and Asah1^-/- mice die soon after systemic or intravaginal inoculation. The treatment of macrophages with sphingosine enhancing compounds blocks HSV-1 propagation, suggesting a therapeutic potential of this pathway. In conclusion, aCDase loads ILVs with sphingosine, which prevents HSV-1 capsids from penetrating into the cytosol.

Decoy exosomes provide protection against bacterial toxins

The production of pore-forming toxins that disrupt the plasma membrane of host cells is a common virulence strategy for bacterial pathogens such as methicillin-resistant Staphylococcus aureus (MRSA)^1-3. It is unclear, however, whether host species possess innate immune mechanisms that can neutralize pore-forming toxins during infection. We previously showed that the autophagy protein ATG16L1 is necessary for protection against MRSA strains encoding α-toxin⁴-a pore-forming toxin that binds the metalloprotease ADAM10 on the surface of a broad range of target cells and tissues^2,5,6. Autophagy typically involves the targeting of cytosolic material to the lysosome for degradation. Here we demonstrate that ATG16L1 and other ATG proteins mediate protection against α-toxin through the release of ADAM10 on exosomes-extracellular vesicles of endosomal origin. Bacterial DNA and CpG DNA induce the secretion of ADAM10-bearing exosomes from human cells as well as in mice. Transferred exosomes protect host cells in vitro by serving as scavengers that can bind multiple toxins, and improve the survival of mice infected with MRSA in vivo. These findings indicate that ATG proteins mediate a previously unknown form of defence in response to infection, facilitating the release of exosomes that serve as decoys for bacterially produced toxins.

Classical methods and perspectives for manipulating the human gut microbial ecosystem

A healthy Human Gut Microbial Ecosystem (HGME) is a necessary condition for maintaining the orderly function of the whole body. Major alterations in the normal gut microbial composition, activity and functionality (dysbiosis) by an environmental or host-related disruptive event, can compromise metabolic, inflammatory, and neurological processes, causing disorders such as obesity, inflammatory bowel disease, colorectal cancer, and depressive episodes. The restore or the maintaining of the homeostatic balance of Gut Microbiota (GM) populations (eubiosis) is possible through diet, the use of probiotics, prebiotics, antibiotics, and even Fecal Microbiota Transplantation (FMT). Although these "classic methods" represent an effective and accepted way to modulate GM, the complexity of HGME requires new approaches to control it in a more appropriate way. Among the most promising emergent strategies for modulating GM are the use of engineered nanomaterials (metallic nanoparticles (NP), polymeric-NP, quantum dots, micelles, dendrimers, and liposomes); phagotherapy (i.e., phages linked with the CRISPR/Cas9 system), and the use of antimicrobial peptides, non-antibiotic drugs, vaccines, and immunoglobulins. Here we review the current state of development, implications, advantages, disadvantages, and perspectives of the different approaches for manipulating HGME.

Cell membrane-coated nanoparticles: research advances

Cell membranes have been continuously imitated and used for the modification of nanoparticles (NPs) to improve NP biological properties. Cell membrane-coated NPs, where core NPs are wrapped with plasma membrane vesicles, show high biocompatibility, targeting specificity and low side effects. Compared with conventional strategies, this novel approach directly leverages intact and natural functions of cell membranes, instead of replicating these features via synthetic techniques. This top-down technique bestows NPs with enhanced biointerfacing capabilities with potential in the diagnosis and treatment of cancer, infection and other diseases. Herein, we report on the advances in cell membrane-coated NPs, including the preparation process, source cell membranes for wrapping and potential applications of these cell membrane-coated NPs.

Critical Parameters for the Development of Novel Therapies for Severe and Resistant Infections-A Case Study on CAL02, a Non-Traditional Broad-Spectrum Anti-Virulence Drug

Background: Poor outcomes in severe and resistant infections, together with the economic struggles of companies active in the field of anti-infective development, call for new solutions and front runners with novel approaches. Among “non-traditional” approaches, blocking virulence could be a game changer. Objectives: This review offers a perspective on parameters that have determined the development path of CAL02, a novel anti-virulence agent, with a view to steering clear of the obstacles and limitations that impede market sustainability for new anti-infective drugs. Conclusions and implications of key findings: This case study highlights four pillars that may support the development of other non-traditional drugs and, concurrently, provide a new model that could reshape the field. Therapeutic triggers, study designs, and economic parameters are discussed.

Emerging Treatment Options for Infections by Multidrug-Resistant Gram-Positive Microorganisms

Antimicrobial agents are currently the mainstay of treatment for bacterial infections worldwide. However, due to the increased use of antimicrobials in both human and animal medicine, pathogens have now evolved to possess high levels of multi-drug resistance, leading to the persistence and spread of difficult-to-treat infections. Several current antibacterial agents active against Gram-positive bacteria will be rendered useless in the face of increasing resistance rates. There are several emerging antibiotics under development, some of which have been shown to be more effective with an improved safety profile than current treatment regimens against Gram-positive bacteria. We will extensively discuss these antibiotics under clinical development (phase I-III clinical trials) to combat Gram-positive bacteria, such as Staphylococcus aureus, Enterococcus faecium and Streptococcus pneumoniae. We will delve into the mechanism of actions, microbiological spectrum, and, where available, the pharmacokinetics, safety profile, and efficacy of these drugs, aiming to provide a comprehensive review to the involved stakeholders.

Bacterial pore-forming toxin pneumolysin: Cell membrane structure and microvesicle shedding capacity determines differential survival of cell types

Bacterial infectious diseases can lead to death or to serious illnesses. These outcomes are partly the consequence of pore-forming toxins, which are secreted by the pathogenic bacteria (eg, pneumolysin of Streptococcus pneumoniae). Pneumolysin binds to cholesterol within the plasma membrane of host cells and assembles to form trans-membrane pores, which can lead to Ca²⁺ influx and cell death. Membrane repair mechanisms exist that limit the extent of damage. Immune cells which are essential to fight bacterial infections critically rely on survival mechanisms after detrimental pneumolysin attacks. This study investigated the susceptibility of different immune cell types to pneumolysin. As a model system, we used the lymphoid T-cell line Jurkat, and myeloid cell lines U937 and THP-1. We show that Jurkat T cells are highly susceptible to pneumolysin attack. In contrast, myeloid THP-1 and U937 cells are less susceptible to pneumolysin. In line with these findings, human primary T cells are shown to be more susceptible to pneumolysin attack than monocytes. Differences in susceptibility to pneumolysin are due to (I) preferential binding of pneumolysin to Jurkat T cells and (II) cell type specific plasma membrane repair capacity. Myeloid cell survival is mostly dependent on Ca²⁺ induced expelling of damaged plasma membrane areas as microvesicles. Thus, in myeloid cells, first-line defense cells in bacterial infections, a potent cellular repair machinery ensures cell survival after pneumolysin attack. In lymphoid cells, which are important at later stages of infections, less efficient repair mechanisms and enhanced toxin binding renders the cells more sensitive to pneumolysin.

Antimicrobial lipids in nano-carriers for antibacterial delivery

Antimicrobial lipids have been recognised as broad-spectrum antibacterial agents. They can directly act on and lyse bacterial cell membrane, and inhibit bacterial growth through a range of mechanisms. Antimicrobial lipids include free fatty acids, monoglycerides, cholesteryl ester, sphingolipids and etc., with the first two being the most extensively studied. Their application is usually hindered by the low solubility of the compounds themselves, and nano-sized lipid-based carriers can endow druggability to these antimicrobial agents for they improve lipid solubility and dispersion in aqueous formulations. Nano-carriers also possess advantages in overcoming drug resistance. In this review we will discuss different kinds of antimicrobial lipids in nano-sized carriers for antibacterial delivery. CAL02 as a promising infection-controlling liposome consisted of cholesterol and sphingomyelin will also be included for it's a unique anti-infection approach, which signifies that the underlying antibacterial roles antimicrobial lipids needs to be further addressed. With the global emergence of antibiotic resistance, antimicrobial lipids formulated in nano-carriers might provide a novel alternative in combatting infectious diseases.

Current landscape in the discovery of novel antibacterial agents

BACKGROUND

Standard treatments against bacterial infections are becoming ineffective due to the rise of antibacterial resistance worldwide. Classical approaches to develop new antibacterial agents are not sufficient to fulfil the current pipeline, therefore new strategies are currently being devised in the field of antibacterial discovery.

OBJECTIVES

The objective of this narrative review is to compile the most successful strategies for drug discovery within the antibacterial context that are currently being pursued.

SOURCES

Peer-reviewed publications from the MEDLINE database with robust data addressing the discovery of new antibacterial agents in the current pipeline have been selected.

CONTENT

Several strategies to discover new antibacterials are described in this review: (i) derivatives of known antibacterial agents; the activity of a known antimicrobial agent can be improved through two strategies: (a) the modification of the original chemical structure of an antimicrobial agent to circumvent antibacterial resistance mechanisms and (b) the development of a compound that inhibits the mechanisms of resistance to an antibacterial agent; (ii) new antibacterial agents targeting new proteins; (iii) inhibitors of virulence factors; (iv) nanoparticles; (v) antimicrobial peptides and peptidomimetics; (vi) phage therapy and enzybiotics; and (vii) antisense oligonucleotides.

IMPLICATIONS

This review intends to provide a positive message affirming that several different strategies to design new antibacterial agents are currently being developed, and we are therefore confident that in the near future some of the most promising approaches will come to fruition.

Inhibition of Pore-Forming Proteins

Perforation of cellular membranes by pore-forming proteins can affect cell physiology, tissue integrity, or immune response. Since many pore-forming proteins are toxins or highly potent virulence factors, they represent an attractive target for the development of molecules that neutralize their actions with high efficacy. There has been an assortment of inhibitors developed to specifically obstruct the activity of pore-forming proteins, in addition to vaccination and antibiotics that serve as a plausible treatment for the majority of diseases caused by bacterial infections. Here we review a wide range of potential inhibitors that can specifically and effectively block the activity of pore-forming proteins, from small molecules to more specific macromolecular systems, such as synthetic nanoparticles, antibodies, antibody mimetics, polyvalent inhibitors, and dominant negative mutants. We discuss their mechanism of inhibition, as well as advantages and disadvantages.

Bioinspired and Biomimetic Nanotherapies for the Treatment of Infectious Diseases

There are still great challenges for the effective treatment of infectious diseases, although considerable achievement has been made by using antiviral and antimicrobial agents varying from small-molecule drugs, peptides/proteins, to nucleic acids. The nanomedicine approach is emerging as a new strategy capable of overcoming disadvantages of molecular therapeutics and amplifying their anti-infective activities, by localized delivery to infection sites, reducing off-target effects, and/or attenuating resistance development. Nanotechnology, in combination with bioinspired and biomimetic approaches, affords additional functions to nanoparticles derived from synthetic materials. Herein, we aim to provide a state-of-the-art review on recent progress in biomimetic and bioengineered nanotherapies for the treatment of infectious disease. Different biomimetic nanoparticles, derived from viruses, bacteria, and mammalian cells, are first described, with respect to their construction and biophysicochemical properties. Then, the applications of diverse biomimetic nanoparticles in anti-infective therapy are introduced, either by their intrinsic activity or by loading and site-specifically delivering various molecular drugs. Bioinspired and biomimetic nanovaccines for prevention and/or therapy of infectious diseases are also highlighted. At the end, major translation issues and future directions of this field are discussed.

Multivalent Inhibitors of Channel-Forming Bacterial Toxins

Rational design of multivalent molecules represents a remarkable modern tool to transform weak non-covalent interactions into strong binding by creating multiple finely-tuned points of contact between multivalent ligands and their supposed multivalent targets. Here, we describe several prominent examples where the multivalent blockers were investigated for their ability to directly obstruct oligomeric channel-forming bacterial exotoxins, such as the pore-forming bacterial toxins and B component of the binary bacterial toxins. We address problems related to the blocker/target symmetry match and nature of the functional groups, as well as chemistry and length of the linkers connecting the functional groups to their multivalent scaffolds. Using the anthrax toxin and AB5 toxin case studies, we briefly review how the oligomeric toxin components can be successfully disabled by the multivalent non-channel-blocking inhibitors, which are based on a variety of multivalent scaffolds.

Sphingosine-coating of plastic surfaces prevents ventilator-associated pneumonia

Ventilator-associated pneumonia (VAP) is a major cause of morbidity and mortality in critically ill patients. Here, we employed the broad antibacterial effects of sphingosine to prevent VAP by developing a novel method of coating surfaces of endotracheal tubes with sphingosine and sphingosine analogs. Sphingosine and phytosphingosine coatings of endotracheal tubes prevent adherence and mediate killing of Pseudomonas aeruginosa, Acinetobacter baumannii, and Staphylococcus aureus, even in biofilms. Most importantly, sphingosine-coating of endotracheal tubes also prevented P. aeruginosa and S. aureus pneumonia in vivo. Coating of the tubes with sphingosine was stable, without obvious side effects on tracheal epithelial cells and did not induce inflammation. In summary, we describe a novel method to coat plastic surfaces and provide evidence for the application of sphingosine and phytosphingosine as novel antimicrobial coatings to prevent bacterial adherence and induce killing of pathogens on the surface of endotracheal tubes with potential to prevent biofilm formation and VAP. KEY MESSAGES: Novel dip-coating method to coat plastic surfaces with lipids. Sphingosine and phytosphingosine as novel antimicrobial coatings on plastic surface. Sphingosine coatings of endotracheal tubes prevent bacterial adherence and biofilms. Sphingosine coatings of endotracheal tubes induce killing of pathogens. Sphingosine coatings of endotracheal tubes ventilator-associated pneumonia.

CAL02, a novel antitoxin liposomal agent, in severe pneumococcal pneumonia: a first-in-human, double-blind, placebo-controlled, randomised trial

BACKGROUND

Severe community-acquired pneumonia caused by Streptococcus pneumoniae is associated with high morbidity and mortality rates. CAL02, a novel antitoxin agent with an unprecedented mode of action, consists of liposomes that capture bacterial toxins known to dysregulate inflammation, cause organ damage, and impede immune defence. We aimed to assess the safety of CAL02 as an add-on therapy to antibiotics.

METHODS

This randomised, double-blind, multicentre, placebo-controlled trial was done in ten intensive care units (ICUs) in France and Belgium (but only six units enrolled patients), in patients with severe community-acquired pneumococcal pneumonia who required ICU admission and had been identified as being infected with S pneumoniae. We randomly assigned participants in two stages-the first stage randomly assigned six patients (1:1) to either low-dose CAL02 or placebo, and the second stage randomly assigned 18 patients (14:4) to either high-dose CAL02 or placebo, and stratified in four blocks (4:1, 4:1, 3:1, and 3:1), in addition to standard of care. Block randomisation was done with a computer-generated random number list. Participants, investigators, other site study personnel, the sponsor, and the sponsor's designees involved in study management and monitoring were masked to the randomisation list and treatment assignment. Patients were treated with low-dose (4 mg/kg) or high-dose (16 mg/kg) CAL02 or placebo (saline), in addition to standard antibiotic therapy. Two intravenous doses of study treatment were infused, with a 24 h interval, at a concentration of 10 mg/mL, stepwise, over a maximum of 2 h on days 1 and 2. The primary objective of the study was to assess the safety and tolerability of low-dose and high-dose CAL02 in patients with severe community-acquired pneumonia treated with standard antibiotic therapy, and the primary analysis was done on the safety population (all patients who received at least one dose of the study treatment). Efficacy was a secondary outcome. This trial is registered with ClinicalTrials.gov, number NCT02583373.

FINDINGS

Between March 21, 2016, and Jan 13, 2018, we screened 280 patients with community-acquired pneumonia. 19 patients were enrolled and randomly assigned, resulting in 13 patients in the CAL02 groups (three assigned to low-dose CAL02 and ten assigned to high-dose CAL02) and six in the placebo group. One patient randomly assigned to placebo was allocated to the wrong treatment group and received high-dose CAL02 instead of placebo. Thus, 14 patients received CAL02 (three received low-dose CAL02 and 11 received high-dose CAL02) and five patients received placebo, constituting the safety population. At baseline, the mean APACHE II score for the total study population was 21·5 (SD 4·9; 95% CI 19·3-23·7) and 11 (58%) of 19 patients had septic shock. Adverse events occurred in 12 (86%) of 14 patients in the CAL02 treatment groups combined and all five (100%) patients in the placebo group. Serious adverse events occurred in four (29%) of 14 patients in the CAL02 treatment groups combined and two (40%) of five patients in the placebo group. One non-serious adverse event (mild increase in triglycerides) in a patient in the high-dose CAL02 group was reported as related to study drug. However, analysis of the changes in triglyceride levels in the CAL02 groups compared with the placebo group revealed no correlation with administration of CAL02. No adverse events were linked to local tolerability events. All patients, apart from one who died in the low CAL02 group (death not related to the study drug) achieved clinical cure at the test of cure visit between days 15 and 22. The sequential organ failure assessment score decreased by mean 65·0% (95% CI 50·7-79·4) in the combined CAL02 groups compared with 29·2% (12·8-45·5) in the placebo group between baseline and day 8.

INTERPRETATION

The nature of adverse events was consistent with the profile of the study population and CAL02 showed a promising safety profile and tolerability. However, the difference between high-dose and low-dose CAL02 could not be assessed in this study. Efficacy was in line with the expected benefits of neutralising toxins. The results of this study support further clinical development of CAL02 and provide a solid basis for a larger clinical study.

FUNDING

Combioxin.

Erythroliposomes: Integrated Hybrid Nanovesicles Composed of Erythrocyte Membranes and Artificial Lipid Membranes for Pore-Forming Toxin Clearance

Pore-forming toxins (PFTs) are the most common bacterial virulence proteins and play a significant role in the pathogenesis of bacterial infections; thus, PFTs are an attractive therapeutic target in bacterial infections. Inspired by the pore-forming process and mechanism of PFTs, we designed an integrated hybrid nanovesicle-the erythroliposome (called the RM-PL)-for PFT detoxification by fusing natural red blood cell (RBC) membranes with artificial lipid membranes. The lipid and RBC membranes were mutually beneficial when integrated into a hybrid nanovesicle structure. The RBC membrane endowed RM-PLs with the capacity for detoxification, while the PEGylated lipid membrane stabilized the RM-PLs and greatly improved the detoxification capacity of the RBC membrane. With α-hemolysin (Hlα) as a model PFT, we demonstrated that RM-PLs could not only significantly reduce the toxicity of Hlα to erythrocytes in vitro but also effectively sponge Hlα in vivo and rescue mice from Hlα-induced damage. Moreover, the high detoxification capacity of RM-PLs was shown to be partly related to the expression of the Hlα receptor protein, a disintegrin and metalloproteinase domain-containing protein 10 on the RBC membrane. Consequently, as a component integrating natural and artificial materials, the erythroliposome nanoplatform inspires potential strategies for antivirulence therapy.