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

Forssman and the staphylococcal hemolysins

Forssman was a Swedish pathologist and microbiologist who, in the 1920s and 1930s conducted a long series of experiments that led to unique insights into surface antigens of blood cells, as well as added to the discrimination of toxins produced by staphylococci that lyse red blood cells. This review takes offset in the studies published by Forssman in APMIS addressing the hemolytic properties of staphylococcal toxins displayed against erythrocytes of animal and human origin. In light of current knowledge, we will discuss the insights we now have and how they may pave the way for curing infections with pathogenic staphylococci, including Staphylococcus aureus.

Bacterial pore-forming toxin pneumolysin drives pathogenicity through host extracellular vesicles released during infection

Streptococcus pneumoniae is a global priority respiratory pathogen that kills over a million people annually. The pore-forming cytotoxin, pneumolysin (PLY) is a major virulence factor. Here, we found that recombinant PLY as well as wild-type pneumococcal strains, but not the isogenic PLY mutant, upregulated the shedding of extracellular vesicles (EVs) harboring membrane-bound toxin from human THP-1 monocytes. PLY-EVs induced cytotoxicity and hemolysis dose-dependently upon internalization by recipient monocyte-derived dendritic cells. Proteomics analysis revealed that PLY-EVs are selectively enriched in key inflammatory host proteins such as IFI16, NLRC4, PTX3, and MMP9. EVs shed from PLY-challenged or infected cells induced dendritic cell maturation and primed them to infection. In vivo, zebrafish administered with PLY-EVs showed pericardial edema and mortality. Adoptive transfer of bronchoalveolar-lavage-derived EVs from infected mice to healthy recipients induced lung damage and inflammation in a PLY-dependent manner. Our findings identify that host EVs released during infection mediate pneumococcal pathogenesis.

A structured biomimetic nanoparticle as inflammatory factor sponge and autophagy-regulatory agent against intervertebral disc degeneration and discogenic pain

Lower back pain (LBP) is a common condition closely associated with intervertebral disc degeneration (IDD), causing a significant socioeconomic burden. Inflammatory activation in degenerated discs involves pro-inflammatory cytokines, dysregulated regulatory cytokines, and increased levels of nerve growth factor (NGF), leading to further intervertebral disc destruction and pain sensitization. Macrophage polarization is closely related to autophagy. Based on these pathological features, a structured biomimetic nanoparticle coated with TrkA-overexpressing macrophage membranes (TMNP@SR) with a rapamycin-loaded mesoporous silica core is developed. TMNP@SR acted like sponges to adsorbe inflammatory cytokines and NGF and delivers the autophagy regulator rapamycin (RAPA) into macrophages through homologous targeting effects of the outer engineered cell membrane. By regulating autophagy activation, TMNP@SR promoted the M1-to-M2 switch of macrophages to avoid continuous activation of inflammation within the degenerated disc, which prevented the apoptosis of nucleus pulposus cells. In addition, TMNP@SR relieved mechanical and thermal hyperalgesia, reduced calcitonin gene-related peptide (CGRP) and substance P (SP) expression in the dorsal root ganglion, and downregulated GFAP and c-FOS signaling in the spinal cord in the rat IDD model. In summary, TMNP@SR spontaneously inhibits the aggravation of disc inflammation to alleviate disc degeneration and reduce the ingress of sensory nerves, presenting a promising treatment strategy for LBP induced by disc degeneration.

Antitoxin nanoparticles: design considerations, functional mechanisms, and applications in toxin neutralization

The application of nanotechnology has significantly advanced the development of novel platforms that enhance disease treatment and diagnosis. A key innovation in this field is the creation of antitoxin nanoparticles (ATNs), designed to address toxin exposure. These precision-engineered nanosystems have unique physicochemical properties and selective binding capabilities, allowing them to effectively capture and neutralize toxins from various biological, chemical, and environmental sources. In this review, we thoroughly examine their therapeutic and diagnostic potential for managing toxin-related challenges. We also explore recent advancements and offer critical insights into the design and clinical implementation of ATNs.

Customizable Zr-MOF nanoantidote-based multieffective arsenic detoxification and its extended low-toxic therapy

Arsenic (As) poisoning has become a global public problem threatening human health. Chelation therapy (CT) is the preferred treatment for arsenic poisoning. Nevertheless, efficient and safe arsenic removal in vivo remains a daunting challenge due to the limitations of chelators, including weak affinity, poor cell membrane penetration, and short half-life. Herein, a mercapto-functionalized and size-tunable hierarchical porous Zr-MOF (UiO-66-TC-SH) is developed, which possesses abundant arsenic chemisorption sites, effective cell uptake ability, and long half-life, thereby efficiently removing toxic arsenic in vivo. Moreover, the strong binding affinity of UiO-66-TC-SH for arsenic reduces systemic toxicity caused by off-target effects. In animal trials, UiO-66-TC-SH decreases the blood arsenic levels of acute arsenic poisoning mice to a normal value within 48 h, and the efficacy is superior to clinical drugs 2,3-dimercaptopropanesulfonic acid sodium salt (DMPS). Meanwhile, UiO-66-TC-SH also significantly mitigates the arsenic accumulation in the metabolic organs of chronic arsenic poisoning mice. Surprisingly, UiO-66-TC-SH also accelerates the metabolism of arsenic in organs of tumor-bearing mice and alleviates the side effects of arsenic drugs antitumor therapy. STATEMENT OF SIGNIFICANCE: Arsenic (As) contamination has become a global problem threatening public health. The present clinical chelation therapy (CT) still has some limitations, including the weak affinity, poor cell membrane permeability and short half-life of hydrophilic chelators. Herein, a metal-organic framework (MOF)-based multieffective arsenic removal strategy in vivo is proposed for the first time. Mercapto-functionalized and size-tunable hierarchical porous Zr-MOF nanoantidote (denoted as UiO-66-TC-SH) is accordingly designed and synthesized. After injection, UiO-66-TC-SH can form Zr-O-As bonds and As-S bonds with arsenic, thus enhancing arsenic adsorption capacity, cycling stability and systemic safety simultaneously. The acute arsenic poisoning model results indicate that UiO-66-TC-SH shows superior efficacy to the clinical drug sodium dimercaptopropanesulfonate (DMPS). More meaningfully, we find that UiO-66-TC-SH also accelerates the metabolism of arsenic in organs of tumor-bearing mice and alleviates side effects of arsenic drugs anti-tumor therapy.

Dry powder inhalation containing muco-inert ciprofloxacin and colistin co-loaded liposomes for pulmonary P. Aeruginosa biofilm eradication

Pseudomonas aeruginosa (PA), a predominant pathogen in lung infections, poses significant challenges due to its biofilm formation, which is the primary cause of chronic and recalcitrant pulmonary infections. Bacteria within these biofilms exhibit heightened resistance to antibiotics compared to their planktonic counterparts, and their secreted toxins exacerbate lung infections. Diverging from traditional antibacterial therapy for biofilm eradication, this study introduces a novel dry powder inhalation containing muco-inert ciprofloxacin and colistin co-encapsulated liposomes (Cipro-Col-Lips) prepared using ultrasonic spray freeze drying (USFD) technique. This USFD dry powder is designed to efficiently deliver muco-inert Cipro-Col-Lips to the lungs. Once deposited, the liposomes rapidly diffuse into the airway mucus, reaching the biofilm sites. The muco-inert Cipro-Col-Lips neutralize the biofilm-secreted toxins and simultaneously trigger the release of their therapeutic payload, exerting a synergistic antibiofilm effect. Our results demonstrated that the optimal USFD liposomal dry powder formulation exhibited satisfactory in vitro aerosol performance in terms of fine particle fraction (FPF) of 44.44 ± 0.78 %, mass median aerodynamic diameter (MMAD) of 4.27 ± 0.21 μm, and emitted dose (ED) of 99.31 ± 3.31 %. The muco-inert Cipro-Col-Lips effectively penetrate the airway mucus and accumulate at the biofilm site, neutralizing toxins and safeguarding lung cells. The triggered release of ciprofloxacin and colistin works synergistically to reduce the biofilm's antibiotic resistance, impede the development of antibiotic resistance, and eliminate 99.99 % of biofilm-embedded bacteria, including persister bacteria. Using a PA-beads induced biofilm-associated lung infection mouse model, the in vivo efficacy of this liposomal dry powder aerosol was tested, and the results demonstrated that this liposomal dry powder aerosol achieved a 99.7 % reduction in bacterial colonization, and significantly mitigated inflammation and pulmonary fibrosis. The USFD dry powder inhalation containing muco-inert Cipro-Col-Lips emerges as a promising therapeutic strategy for treating PA biofilm-associated lung infections.

Story of Pore-Forming Proteins from Deadly Disease-Causing Agents to Modern Applications with Evolutionary Significance

Animal venoms are a complex mixture of highly specialized toxic molecules. Among them, pore-forming proteins (PFPs) or toxins (PFTs) are one of the major disease-causing toxic elements. The ability of the PFPs in defense and toxicity through pore formation on the host cell surface makes them unique among the toxin proteins. These features made them attractive for academic and research purposes for years in the areas of microbiology as well as structural biology. All the PFPs share a common mechanism of action for the attack of host cells and pore formation in which the selected pore-forming motifs of the host cell membrane-bound protein molecules drive to the lipid bilayer of the cell membrane and eventually produces water-filled pores. But surprisingly their sequence similarity is very poor. Their existence can be seen both in a soluble state and also in transmembrane complexes in the cell membrane. PFPs are prevalent toxic factors that are predominately produced by all kingdoms of life such as virulence bacteria, nematodes, fungi, protozoan parasites, frogs, plants, and also from higher organisms. Nowadays, multiple approaches to applications of PFPs have been conducted by researchers both in basic as well as applied biological research. Although PFPs are very devastating for human health nowadays researchers have been successful in making these toxic proteins into therapeutics through the preparation of immunotoxins. We have discussed the structural, and functional mechanism of action, evolutionary significance through dendrogram, domain organization, and practical applications for various approaches. This review aims to emphasize the PFTs to summarize toxic proteins together for basic knowledge as well as to highlight the current challenges, and literature gap along with the perspective of promising biotechnological applications for their future research.

Toxin-triggered liposomes for the controlled release of antibiotics to treat infections associated with the gram-negative bacterium, Aggregatibacter actinomycetemcomitans

Antibiotic resistance has become an urgent threat to health care in recent years. The use of drug delivery systems provides advantages over conventional administration of antibiotics and can slow the development of antibiotic resistance. In the current study, we developed a toxin-triggered liposomal antibiotic delivery system, in which the drug release is enabled by the leukotoxin (LtxA) produced by the Gram-negative pathogen, Aggregatibacter actinomycetemcomitans. LtxA has previously been shown to mediate membrane disruption by promoting a lipid phase change in nonlamellar lipids, such as 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-methyl (N-methyl-DOPE). In addition, LtxA has been observed to bind strongly and nearly irreversibly to membranes containing large amounts of cholesterol. Here, we designed a liposomal delivery system composed of N-methyl-DOPE and cholesterol to take advantage of these interactions. Specifically, we hypothesized that liposomes composed of N-methyl-DOPE and cholesterol, encapsulating antibiotics, would be sensitive to LtxA, enabling controlled antibiotic release. We observed that liposomes composed of N-methyl-DOPE were sensitive to the presence of low concentrations of LtxA, and cholesterol increased the extent and kinetics of content release. The liposomes were stable under various storage conditions for at least 7 days. Finally, we showed that antibiotic release occurs selectively in the presence of an LtxA-producing strain of A. actinomycetemcomitans but not in the presence of a non-LtxA-expressing strain. Together, these results demonstrate that the designed liposomal vehicle enables toxin-triggered delivery of antibiotics to LtxA-producing strains of A. actinomycetemcomitans.

Biomembrane camouflaged nanoparticles: A paradigm shifts in targeted drug delivery system

Targeted drug delivery has emerged as a pivotal approach within precision medicine, aiming to optimize therapeutic efficacy while minimizing systemic side effects. Advanced biomimetic membrane-coated formulations have garnered significant interest from researchers as a promising strategy for targeted drug delivery, site-specific accumulation and heightened therapeutic outcomes. Biomimetic nanotechnology is able to retain the biological properties of the parent cell thus are able to exhibit superior targeting compared to conventional formulations. In this review, we have described different types of cell membrane camouflaged NPs. Mechanism of isolation and coating of the membranes along with the applications of each type of membrane and their mechanism to reach the desired site. Furthermore, a fusion of different membranes in order to prepare hybrid membrane biomimetic NPs which could possess better efficacy is discussed in detail in the review. Later, applications of the hybrid membrane-cloaked NPs along with current development were discussed in detail along with the challenges associated with it. Although membrane-cloaked NPs are currently in the preliminary stage of development, there is a huge potential to explore this biodegradable and biocompatible delivery system.

Targeted small molecule inhibitors blocking the cytolytic effects of pneumolysin and homologous toxins

Pneumolysin (PLY) is a cholesterol-dependent cytolysin (CDC) from Streptococcus pneumoniae, the main cause for bacterial pneumonia. Liberation of PLY during infection leads to compromised immune system and cytolytic cell death. Here, we report discovery, development, and validation of targeted small molecule inhibitors of PLY (pore-blockers, PB). PB-1 is a virtual screening hit inhibiting PLY-mediated hemolysis. Structural optimization provides PB-2 with improved efficacy. Cryo-electron tomography reveals that PB-2 blocks PLY-binding to cholesterol-containing membranes and subsequent pore formation. Scaffold-hopping delivers PB-3 with superior chemical stability and solubility. PB-3, formed in a protein-templated reaction, binds to Cys428 adjacent to the cholesterol recognition domain of PLY with a KD of 256 nM and a residence time of 2000 s. It acts as anti-virulence factor preventing human lung epithelial cells from PLY-mediated cytolysis and cell death during infection with Streptococcus pneumoniae and is active against the homologous Cys-containing CDC perfringolysin (PFO) as well.

Bacillus velezensis iturins inhibit the hemolytic activity of Staphylococcus aureus

Bovine mastitis caused by S. aureus has a major economic impact on the dairy sector. With the crucial need for new therapies, anti-virulence strategies have gained attention as alternatives to antibiotics. Here we aimed to identify novel compounds that inhibit the production/activity of hemolysins, a virulence factor of S. aureus associated with mastitis severity. We screened Bacillus strains obtained from diverse sources for compounds showing anti-hemolytic activity. Our results demonstrate that lipopeptides produced by Bacillus spp. completely prevented the hemolytic activity of S. aureus at certain concentrations. Following purification, both iturins, fengycins, and surfactins were able to reduce hemolysis caused by S. aureus, with iturins showing the highest anti-hemolytic activity (up to 76% reduction). The lipopeptides showed an effect at the post-translational level. Molecular docking simulations demonstrated that these compounds can bind to hemolysin, possibly interfering with enzyme action. Lastly, molecular dynamics analysis indicated general stability of important residues for hemolysin activity as well as the presence of hydrogen bonds between iturins and these residues, with longevous interactions. Our data reveals, for the first time, an anti-hemolytic activity of lipopeptides and highlights the potential application of iturins as an anti-virulence therapy to control bovine mastitis caused by S. aureus.

Liposome-integrated hydrogel hybrids: Promising platforms for cancer therapy and tissue regeneration

Drug delivery platforms have gracefully emerged as an indispensable component of novel cancer chemotherapy, bestowing targeted drug distribution, elevating therapeutic effects, and reducing the burden of unwanted side effects. In this context, hybrid delivery systems artfully harnessing the virtues of liposomes and hydrogels bring remarkable benefits, especially for localized cancer therapy, including intensified stability, excellent amenability to hydrophobic and hydrophilic medications, controlled liberation behavior, and appropriate mucoadhesion to mucopenetration shift. Moreover, three-dimensional biocompatible liposome-integrated hydrogel networks have attracted unprecedented interest in tissue regeneration, given their tunable architecture and physicochemical properties, as well as enhanced mechanical support. This review elucidates and presents cutting-edge developments in recruiting liposome-integrated hydrogel systems for cancer treatment and tissue regeneration.

Developments and Trends of Nanotechnology Application in Sepsis: A Comprehensive Review Based on Knowledge Visualization Analysis

Sepsis, a common life-threatening clinical condition, continues to have high morbidity and mortality rates, despite advancements in management. In response, significant research efforts have been directed toward developing effective strategies. Within this scope, nanotechnology has emerged as a particularly promising field, attracting significant interest for its potential to enhance disease diagnosis and treatment. While several reviews have highlighted the use of nanoparticles in sepsis, comprehensive studies that summarize and analyze the hotspots and research trends are lacking. To identify and further promote the development of nanotechnology in sepsis, a bibliometric analysis was conducted on the relevant literature, assessing research trends and hotspots in the application of nanomaterials for sepsis. Next, a comprehensive review of the subjectively recognized research hotspots in sepsis, including nanotechnology-enhanced biosensors and nanoscale imaging for sepsis diagnostics, and nanoplatforms designed for antimicrobial, immunomodulatory, and detoxification strategies in sepsis therapy, is elucidated, while the potential side effects and toxicity risks of these nanomaterials were discussed. Particular attention is given to biomimetic nanoparticles, which mimic the biological functions of source cells like erythrocytes, immune cells, and platelets to evade immune responses and effectively deliver therapeutic agents, demonstrating substantial translational potential. Finally, current challenges and future perspectives of nanotechnology applications in sepsis with a view to maximizing their great potential in the research of translational medicine are also discussed.

Secretion of the fungal toxin candidalysin is dependent on conserved precursor peptide sequences

The opportunistic fungal pathogen Candida albicans damages host cells via its peptide toxin, candidalysin. Before secretion, candidalysin is embedded in a precursor protein, Ece1, which consists of a signal peptide, the precursor of candidalysin and seven non-candidalysin Ece1 peptides (NCEPs), and is found to be conserved in clinical isolates. Here we show that the Ece1 polyprotein does not resemble the usual precursor structure of peptide toxins. C. albicans cells are not susceptible to their own toxin, and single NCEPs adjacent to candidalysin are sufficient to prevent host cell toxicity. Using a series of Ece1 mutants, mass spectrometry and anti-candidalysin nanobodies, we show that NCEPs play a role in intracellular Ece1 folding and candidalysin secretion. Removal of single NCEPs or modifications of peptide sequences cause an unfolded protein response (UPR), which in turn inhibits hypha formation and pathogenicity in vitro. Our data indicate that the Ece1 precursor is not required to block premature pore-forming toxicity, but rather to prevent intracellular auto-aggregation of candidalysin sequences.

Treatment of Staphylococcus aureus infection with sphingosine in ex vivo perfused and ventilated lungs

BACKGROUND

Ex vivo lung perfusion (EVLP) has expanded the donor pool for lung transplantation. Pulmonary Staphylococcus aureus infection, especially that caused by multidrug-resistant strains, is a severe threat to posttransplantation outcomes. Sphingosine is a lipid compound that exhibits broad-spectrum antibacterial activity. Therefore, we aimed to evaluate the effects of S aureus infection on EVLP and whether sphingosine administration during EVLP prevents infection with S aureus.

METHODS

Eighteen pigs were randomly assigned to 3 groups: uninfected, infected with S aureus with NaCl treatment, or infected with sphingosine treatment. Bacterial numbers were determined before and after treatment. Sphingosine concentrations in the lung tissues were determined using biochemical assays. Lung histology, lung physiological parameters, perfusate content, lung weight, and cell death were measured to analyze the effects of infection and sphingosine administration on EVLP.

RESULTS

Sphingosine administration significantly reduced the bacterial load. The concentration of sphingosine in the bronchial epithelium was elevated after sphingosine administration. S aureus infection increased pulmonary artery pressure and pulmonary vascular resistance. Lung edema, histology scores, lactate and lactate dehydrogenase levels in the perfusate, ΔPO2 in the perfusate, static lung compliance, and lung peak airway pressure did not differ among the groups.

CONCLUSIONS

Infection of S aureus did not affect the lung function during EVLP but induced higher pulmonary artery pressure and pulmonary vascular resistance. Administration of sphingosine effectively eliminated S aureus without side effects in isolated, perfused, and ventilated pig lungs.

Toxin-Triggered Liposomes for the Controlled Release of Antibiotics to Treat Infections Associated with Gram-Negative Bacteria

Antibiotic resistance has become an urgent threat to health care in recent years. The use of drug delivery systems provides advantages over conventional administration of antibiotics and can slow the development of antibiotic resistance. In the current study, we developed a toxin-triggered liposomal antibiotic delivery system, in which the drug release is enabled by the leukotoxin (LtxA) produced by the Gram-negative pathogen, Aggregatibacter actinomycetemcomitans. LtxA has previously been shown to mediate membrane disruption by promoting a lipid phase change in nonlamellar lipids, such as 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-methyl (N-methyl-DOPE). In addition, LtxA has been observed to bind strongly and nearly irreversibly to membranes containing large amounts of cholesterol. Here, we designed a liposomal delivery system composed of N-methyl-DOPE and cholesterol to take advantage of these interactions. Specifically, we hypothesized that liposomes composed of N-methyl-DOPE and cholesterol, encapsulating antibiotics, would be sensitive to LtxA, enabling controlled antibiotic release. We observed that liposomes composed of N-methyl-DOPE were sensitive to the presence of low concentrations of LtxA, and cholesterol increased the extent and kinetics of content release. The liposomes were stable under various storage conditions for at least 7 days. Finally, we showed that antibiotic release occurs selectively in the presence of an LtxA-producing strain of A. actinomycetemcomitans but not in the presence of a non-LtxA-expressing strain. Together, these results demonstrate that the designed liposomal vehicle enables toxin-triggered delivery of antibiotics to LtxA-producing strains of A. actinomycetemcomitans.

Red blood cell-mimicking liposomes loading curcumin promote diabetic wound healing

The excessive inflammatory response is known to be a major challenge for diabetic wound healing, while bacteria secreted toxin, α-hemolysin (Hlα), was recently reported to prolong inflammation and delay diabetic wound healing. In this study, we designed a red blood cell membrane (RBCM)-mimicking liposome containing curcumin (named RC-Lip) for the treatment of diabetic wounds. RC-Lips were successfully fabricated using the thin film dispersion method, and the fusion of RBC membrane with the liposomal membrane was confirmed via surface protein analysis. RC-Lips efficiently adsorbed Hlα, thereby reducing the damage and pro-apoptotic effects of Hlα on keratinocytes. Furthermore, they remarkably facilitated liposome uptake into macrophages with advanced curcumin release and regulation of M2 macrophage polarization. In a diabetic mouse and infected wound model, RC-Lips treatment significantly promoted wound healing and re-epithelialization while downregulating interleukin-1β (IL-1β) and upregulating interleukin-10 (IL-10). In summary, the results showed that the spongiform RC-Lips effectively modulate the inflammatory response after adsorbing Hlα and regulating M2 macrophage polarization, leading to a significant promotion of wound healing in diabetic mice. Hence, this study provides a prospective strategy of efficiently mediating inflammatory response for diabetic wounds.

Cholesterol dependent cytolysins and the brain: Revealing a potential therapeutic avenue for bacterial meningitis

Bacterial meningitis is a catastrophic nervous system disorder with high mortality and wide range of morbidities. Some of the meningitis-causing bacteria occupy cholesterol dependent cytolysins (CDCs) to increase their pathogenicity and arrange immune-evasion strategy. Studies have observed that the relationship between CDCs and pathogenicity in these meningitides is complex and involves interactions between CDC, blood-brain barrier (BBB), glial cells and neurons. In BBB, these CDCs acts on capillary endothelium, tight junction (TJ) proteins and neurovascular unit (NVU). CDCs also observed to elicit intriguing effects on brain inflammation which involves microglia and astrocyte activations, along with neuronal damage as the end-point of pathological pathways in bacterial meningitis. As some studies mentioned potential advantage of CDC-targeted therapeutic mechanisms to combat CNS infections, it might be a fruitful avenue to deepen our understanding of CDC as a candidate for adjuvant therapy to combat bacterial meningitis.

Vaginal Epithelial Cell Membrane-Based Phototherapeutic Decoy Confers a "Three-in-One" Strategy to Treat against Intravaginal Infection of Candida albicans

Phototherapy is an effective strategy to control Candida albicans (C. albicans) infection without raising the concern of drug resistance. Despite its effectiveness, a higher dose of phototherapeutic power is required for C. albicans elimination compared to bacteria that have to be used, which is readily accompanied by off-target heat and toxic singlet oxygen to damage normal cells, thus limiting its usefulness for antifungal applications. Here to overcome this, we develop a "three-in-one" biomimetic nanoplatform consisting of an oxygen-dissolved perfluorocarbon camouflaged by a photosensitizer-loaded vaginal epithelial cell membrane. With a cell membrane coating, the nanoplatform is capable of specifically binding with C. albicans at the superficial or deep vaginal epithelium, thereby centering the phototherapeutic agents on C. albicans. Meanwhile, the cell membrane coating endows the nanoplatform to competitively protect healthy cells from candidalysin-medicated cytotoxicity. Upon candidalysin sequestration, pore-forming on the surface of the nanoplatform accelerates release of the preloaded photosensitizer and oxygen, resulting in enhanced phototherapeutic power for improved anti-C. albicans efficacy under near-infrared irradiation. In an intravaginal C. albicans-infected murine model, treatment with the nanoplatform leads to a significantly decreased C. albicans burden, particularly when leveraging candidalysin for further elevated phototherapy and C. albicans inhibition. Also, the same trends hold true when using the nanoplatform to treat the clinical C. albicans isolates. Overall, this biomimetic nanoplatform can target and bind with C. albicans and simultaneously neutralize the candidalysin and then transform such toxins that are always considered a positive part in driving C. albicans infection with the power of enhancing phototherapy for improved anti-C. albicans efficacy.

In situ gelling hydrogel loaded with berberine liposome for the treatment of biofilm-infected wounds

Background: In recent years, the impact of bacterial biofilms on traumatic wounds and the means to combat them have become a major research topic in the field of medicine. The eradication of biofilms formed by bacterial infections in wounds has always been a huge challenge. Herein, we developed a hydrogel with the active ingredient berberine hydrochloride liposomes to disrupt the biofilm and thereby accelerate the healing of infected wounds in mice. Methods: We determined the ability of berberine hydrochloride liposomes to eradicate the biofilm by means of studies such as crystalline violet staining, measuring the inhibition circle, and dilution coating plate method. Encouraged by the in vitro efficacy, we chose to coat the berberine hydrochloride liposomes on the Poloxamer range of in-situ thermosensitive hydrogels to allow fuller contact with the wound surface and sustained efficacy. Eventually, relevant pathological and immunological analyses were carried out on wound tissue from mice treated for 14 days. Results: The final results show that the number of wound tissue biofilms decreases abruptly after treatment and that the various inflammatory factors in them are significantly reduced within a short period. In the meantime, the number of collagen fibers in the treated wound tissue, as well as the proteins involved in healing in the wound tissue, showed significant differences compared to the model group. Conclusion: From the results, we found that berberine liposome gel can accelerate wound healing in Staphylococcus aureus infections by inhibiting the inflammatory response and promoting re-epithelialization as well as vascular regeneration. Our work exemplifies the efficacy of liposomal isolation of toxins. This innovative antimicrobial strategy opens up new perspectives for tackling drug resistance and fighting wound infections.

Dual Functioned Hexapeptide-Coated Lipid-Core Nanomicelles Suppress Toll-Like Receptor-Mediated Inflammatory Responses through Endotoxin Scavenging and Endosomal pH Modulation

Excessive activation of Toll-like receptor (TLR) signaling pathways and the circulating endotoxin are key players in the pathogenesis of many acute and chronic inflammatory diseases. Regulation of TLR-mediated inflammatory responses by bioactive nanodevices represents a promising strategy for treating these diseases. In searching for novel, clinically applicable nanodevices with potent TLR inhibitory activities, three types of hexapeptide-modified nano-hybrids with different cores of phospholipid nanomicelles, liposomes, and poly(lactic-co-glycolic acid) nanoparticles are constructed. Interestingly, only the peptide-modified lipid-core nanomicelles (M-P12) display potent TLR inhibitory activities. Further mechanistic studies disclose that lipid-core nanomicelles have a generic property to bind to and scavenge lipophilic TLR ligands including lipopolysaccharide to block the ligand-receptor interaction and down-regulate the TLR signaling extracellularly. In addition, the peptide modification enables M-P12 a unique capability to modulate endosomal acidification upon being endocytosed into macrophages, which subsequently regulates the endosomal TLR signal transduction. In an acute lung injury mouse model, intratracheal administration of M-P12 can effectively target lung macrophages and reduce lung inflammation and injuries. This work defines a dual mechanism of action of the peptide-modified lipid-core nanomicelles in regulating TLR signaling, and provides new strategies for the development of therapeutic nanodevices for treating inflammatory diseases.

Repurposing host-guest chemistry to sequester virulence and eradicate biofilms in multidrug resistant Pseudomonas aeruginosa and Acinetobacter baumannii

The limited diversity in targets of available antibiotic therapies has put tremendous pressure on the treatment of bacterial pathogens, where numerous resistance mechanisms that counteract their function are becoming increasingly prevalent. Here, we utilize an unconventional anti-virulence screen of host-guest interacting macrocycles, and identify a water-soluble synthetic macrocycle, Pillar[5]arene, that is non-bactericidal/bacteriostatic and has a mechanism of action that involves binding to both homoserine lactones and lipopolysaccharides, key virulence factors in Gram-negative pathogens. Pillar[5]arene is active against Top Priority carbapenem- and third/fourth-generation cephalosporin-resistant Pseudomonas aeruginosa and Acinetobacter baumannii, suppressing toxins and biofilms and increasing the penetration and efficacy of standard-of-care antibiotics in combined administrations. The binding of homoserine lactones and lipopolysaccharides also sequesters their direct effects as toxins on eukaryotic membranes, neutralizing key tools that promote bacterial colonization and impede immune defenses, both in vitro and in vivo. Pillar[5]arene evades both existing antibiotic resistance mechanisms, as well as the build-up of rapid tolerance/resistance. The versatility of macrocyclic host-guest chemistry provides ample strategies for tailored targeting of virulence in a wide range of Gram-negative infectious diseases.

Association Between Hypocholesterolemia and Mortality in Critically Ill Patients With Sepsis: A Systematic Review and Meta-Analysis

To ascertain the association between cholesterol and triglyceride levels on ICU admission and mortality in patients with sepsis.

DATA SOURCES

Systematic review and meta-analysis of published studies on PubMed and Embase.

STUDY SELECTION

All observational studies reporting ICU admission cholesterol and triglyceride levels in critically ill patients with sepsis were included. Authors were contacted for further data.

DATA EXTRACTION

Eighteen observational studies were identified, including 1,283 patients with a crude overall mortality of 33.3%. Data were assessed using Revman (Version 5.1, Cochrane Collaboration, Oxford, United Kingdom) and presented as mean difference (MD) with 95% CIs, p values, and I 2 values.

DATA SYNTHESIS

Admission levels of total cholesterol (17 studies, 1,204 patients; MD = 0.52 mmol/L [0.27-0.77 mmol/L]; p < 0.001; I 2 = 91%), high-density lipoprotein (HDL)-cholesterol (14 studies, 991 patients; MD = 0.08 mmol/L [0.01-0.15 mmol/L]; p = 0.02; I 2 = 61%), and low-density lipoprotein (LDL)-cholesterol (15 studies, 1,017 patients; MD = 0.18 mmol/L [0.04-0.32 mmol/L]; p = 0.01; I 2 = 71%) were significantly lower in eventual nonsurvivors compared with survivors. No association was seen between admission triglyceride levels and mortality (15 studies, 1,070 patients; MD = 0.00 mmol/L [-0.16 to 0.15 mmol/L]; p = -0.95; I 2 = 79%).

CONCLUSIONS

Mortality was associated with lower levels of total cholesterol, HDL-cholesterol, and LDL-cholesterol, but not triglyceride levels, in patients admitted to ICU with sepsis. The impact of cholesterol replacement on patient outcomes in sepsis, particularly in at-risk groups, merits investigation.

Recent Approaches for Downplaying Antibiotic Resistance: Molecular Mechanisms

Antimicrobial resistance (AMR) is a ubiquitous public health menace. AMR emergence causes complications in treating infections contributing to an upsurge in the mortality rate. The epidemic of AMR in sync with a high utilization rate of antimicrobial drugs signifies an alarming situation for the fleet recovery of both animals and humans. The emergence of resistant species calls for new treatments and therapeutics. Current records propose that health drug dependency, veterinary medicine, agricultural application, and vaccination reluctance are the primary etymology of AMR gene emergence and spread. Recently, several encouraging avenues have been presented to contest resistance, such as antivirulent therapy, passive immunization, antimicrobial peptides, vaccines, phage therapy, and botanical and liposomal nanoparticles. Most of these therapies are used as cutting-edge methodologies to downplay antibacterial drugs to subdue the resistance pressure, which is a featured motive of discussion in this review article. AMR can fade away through the potential use of current cutting-edge therapeutics, advancement in antimicrobial susceptibility testing, new diagnostic testing, prompt clinical response, and probing of new pharmacodynamic properties of antimicrobials. It also needs to promote future research on contemporary methods to maintain host homeostasis after infections caused by AMR. Referable to the microbial ability to break resistance, there is a great ultimatum for using not only appropriate and advanced antimicrobial drugs but also other neoteric diverse cutting-edge therapeutics.

Meningitis-associated pneumococcal serotype 8, ST 53, strain is hypervirulent in a rat model and has non-haemolytic pneumolysin which can be attenuated by liposomes

Introduction

Streptococcus pneumoniae bacteria cause life-threatening invasive pneumococcal disease (IPD), including meningitis. Pneumococci are classified into serotypes, determined by differences in capsular polysaccharide and both serotype and pneumolysin toxin are associated with disease severity. Strains of serotype 8, ST 53, are increasing in prevalence in IPD in several countries.

Methods

Here we tested the virulence of such an isolate in a rat model of meningitis in comparison with a serotype 15B and a serotype 14 isolate. All three were isolated from meningitis patients in South Africa in 2019, where serotype 8 is currently the most common serotype in IPD.

Results and Discussion

Only the serotype 8 isolate was hypervirulent causing brain injury and a high mortality rate. It induced a greater inflammatory cytokine response than either the serotype 15B or 14 strain in the rat model and from primary mixed-glia cells isolated from mouse brains. It had the thickest capsule of the three strains and produced non-haemolytic pneumolysin. Pneumolysin-sequestering liposomes reduced the neuroinflammatory cytokine response in vitro indicating that liposomes have the potential to be an effective adjuvant therapy even for hypervirulent pneumococcal strains with non-haemolytic pneumolysin.

Recombinant Protein Micelles to Block Transduction by SARS-CoV-2 Pseudovirus

The continuing emergence of variants of the SARS-CoV-2 virus requires the development of modular molecular therapies. Here, we engineered a recombinant amphiphilic protein, oleosin, to spontaneously self-assemble into multivalent micellar nanostructures which can block the Spike S1 protein of SARS-CoV-2 pseudoviruses (PVs). Short recombinant proteins like oleosin can be formulated more easily than antibodies and can be functionalized with precision through genetic engineering. We cloned S1-binding mini-protein genes called LCBx, previously designed by David Baker's laboratory (UW Seattle), to the N-terminus of oleosin, expressing Oleo-LCBx proteins in E. coli. These proteins largely formed 10-100 nm micelles as verified by dynamic light scattering. Two proteins, Oleo-LCB1 and Oleo-LCB3, were seen to completely and irreversibly block transduction by both wild-type and delta variant PVs into 293T-hsACE2 cells at 10 μM. Presented in multivalent micelles, these proteins reduced transduction by PVs down to a functional protein concentration of 5 nM. Additionally, Oleo-LCB1 micelles outperformed corresponding synthetic LCB1 mini-proteins in reducing transduction by PVs. Tunable aqueous solubility of recombinant oleosin allowed incorporation of peptides/mini-proteins at high concentrations within micelles, thus enhancing drug loading. To validate the potential multifunctionality of the micelles, we showed that certain combinations of Oleo-LCB1 and Oleo-LCB3 performed much better than the individual proteins at the same concentration. These micelles, which we showed to be non-toxic to human cells, are thus a promising step toward the design of modular, multifunctional therapeutics that could bind to and inactivate multiple receptors and proteins necessary for the infection of the SARS-CoV-2 virus.

Toxin-Enabled "On-Demand" Liposomes for Enhanced Phototherapy to Treat and Protect against Methicillin-Resistant Staphylococcus aureus Infection

An effective therapeutic strategy against methicillin-resistant Staphylococcus aureus (MRSA) that does not promote further drug resistance is highly desirable. While phototherapies have demonstrated considerable promise, their application toward bacterial infections can be limited by negative off-target effects to healthy cells. Here, a smart targeted nanoformulation consisting of a liquid perfluorocarbon core stabilized by a lipid membrane coating is developed. Using vancomycin as a targeting agent, the platform is capable of specifically delivering an encapsulated photosensitizer along with oxygen to sites of MRSA infection, where high concentrations of pore-forming toxins trigger on-demand payload release. Upon subsequent near-infrared irradiation, local increases in temperature and reactive oxygen species effectively kill the bacteria. Additionally, the secreted toxins that are captured by the nanoformulation can be processed by resident immune cells to promote multiantigenic immunity that protects against secondary MRSA infections. Overall, the reported approach for the on-demand release of phototherapeutic agents into sites of infection could be applied against a wide range of high-priority pathogens.

NAD(H)-loaded nanoparticles for efficient sepsis therapy via modulating immune and vascular homeostasis

Sepsis is a life-threatening organ dysfunction responsible for nearly 270,000 deaths annually in the United States alone. Nicotinamide adenine dinucleotide (NAD+), an immunomodulator, can potentially treat sepsis; however, clinical application of NAD+ is hindered by its inability to be directly taken up by cells. To address this challenge, a family of nanoparticles (NPs) loaded with either NAD+ or the reduced form of NAD+ (NADH), hereafter NAD(H)-loaded NPs, were engineered to enable direct cellular transport and replenishment of NAD(H). The NAD(H)-loaded NPs improved cellular energy supply, suppressed inflammation and prevented inflammation-induced cell pyroptosis and apoptosis. Therefore, the NPs can help maintain immune homoeostasis and vascular function, two key factors in the pathogenesis of sepsis. The NAD(H)-loaded NPs demonstrated excellent therapeutic efficacies in treating endotoxemia and multidrug-resistant pathogen-induced bacteremia. In addition, the NAD(H)-loaded NPs prevented caecal ligation and puncture-induced multiorgan injury and improved outcomes of secondary Pseudomonas aeruginosa infections following caecal ligation and puncture, thus potentially leading to a highly innovative and translational approach to treat sepsis efficiently and safely.

Bacterial Toxin-Triggered Release of Antibiotics from Capsosomes Protects a Fly Model from Lethal Methicillin-Resistant Staphylococcus aureus (MRSA) Infection

Antibiotic resistance is a severe global health threat and hence demands rapid action to develop novel therapies, including microscale drug delivery systems. Herein, a hierarchical microparticle system is developed to achieve bacteria-activated single- and dual-antibiotic drug delivery for preventing methicillin-resistant Staphylococcus aureus (MRSA) bacterial infections. The designed system is based on a capsosome structure, which consists of a mesoporous silica microparticle coated in alternating layers of oppositely charged polymers and antibiotic-loaded liposomes. The capsosomes are engineered and shown to release their drug payloads in the presence of MRSA toxins controlled by the Agr quorum sensing system. MRSA-activated single drug delivery of vancomycin and synergistic dual delivery of vancomycin together with an antibacterial peptide successfully kills MRSA in vitro. The capability of capsosomes to selectively deliver their cargo in the presence of bacteria, producing a bactericidal effect to protect the host organism, is confirmed in vivo using a Drosophila melanogaster MRSA infection model. Thus, the capsosomes serve as a versatile multidrug, subcompartmentalized microparticle system for preventing antibiotic-resistant bacterial infections, with potential applications to protect wounds or medical device implants from infections.

Nanomaterial-Based Zinc Ion Interference Therapy to Combat Bacterial Infections

Pathogenic bacterial infections are the second highest cause of death worldwide and bring severe challenges to public healthcare. Antibiotic resistance makes it urgent to explore new antibacterial therapy. As an essential metal element in both humans and bacteria, zinc ions have various physiological and biochemical functions. They can stabilize the folded conformation of metalloproteins and participate in critical biochemical reactions, including DNA replication, transcription, translation, and signal transduction. Therefore, zinc deficiency would impair bacterial activity and inhibit the growth of bacteria. Interestingly, excess zinc ions also could cause oxidative stress to damage DNA, proteins, and lipids by inhibiting the function of respiratory enzymes to promote the formation of free radicals. Such dual characteristics endow zinc ions with unparalleled advantages in the direction of antibacterial therapy. Based on the fascinating features of zinc ions, nanomaterial-based zinc ion interference therapy emerges relying on the outstanding benefits of nanomaterials. Zinc ion interference therapy is divided into two classes: zinc overloading and zinc deprivation. In this review, we summarized the recent innovative zinc ion interference strategy for the treatment of bacterial infections and focused on analyzing the antibacterial mechanism of zinc overloading and zinc deprivation. Finally, we discuss the current limitations of zinc ion interference antibacterial therapy and put forward problems of clinical translation for zinc ion interference antibacterial therapy.

Cholesterol Microdomain Enhances the Biofilm Eradication of Antibiotic Liposomes

Resistance and tolerance of biofilms to antibiotics is the greatest challenge in the treatment of bacterial infections. Therefore, developing an effective strategy against biofilms is a top priority. Liposomes are widely used as antibiotic drug carriers; however, common liposomes lack affinity for biofilms. Herein, biofilm-targeted antibiotic liposomes are created by simply adjusting their cholesterol content. The tailored liposomes exhibit significantly enhanced bacterial inhibition and biofilm eradication effects that are positively correlated with the cholesterol content of liposomes. The experiments further demonstrate that this enhanced effect can be ascribed to the effective drug release through the pores, which are formed by the combination of cholesterol microdomains in liposomal lipid bilayers with membrane-damaged toxins in biofilms. Consequently, liposome encapsulation with a high cholesterol concentration improves noticeably the pharmacodynamics and biocompatibility of antibiotics after pulmonary administration. This work may provide a new direction for the development of antibiofilm formulations that can be widely used for the treatment of infections caused by bacterial biofilms.

Targeting the Pseudomonas aeruginosa Virulence Factor Phospholipase C With Engineered Liposomes

Engineered liposomes composed of the naturally occurring lipids sphingomyelin (Sm) and cholesterol (Ch) have been demonstrated to efficiently neutralize toxins secreted by Gram-positive bacteria such as Streptococcus pneumoniae and Staphylococcus aureus. Here, we hypothesized that liposomes are capable of neutralizing cytolytic virulence factors secreted by the Gram-negative pathogen Pseudomonas aeruginosa. We used the highly virulent cystic fibrosis P. aeruginosa Liverpool Epidemic Strain LESB58 and showed that sphingomyelin (Sm) and a combination of sphingomyelin with cholesterol (Ch:Sm; 66 mol/% Ch and 34 mol/% Sm) liposomes reduced lysis of human bronchial and red blood cells upon challenge with the Pseudomonas secretome. Mass spectrometry of liposome-sequestered Pseudomonas proteins identified the virulence-promoting hemolytic phospholipase C (PlcH) as having been neutralized. Pseudomonas aeruginosa supernatants incubated with liposomes demonstrated reduced PlcH activity as assessed by the p-nitrophenylphosphorylcholine (NPPC) assay. Testing the in vivo efficacy of the liposomes in a murine cutaneous abscess model revealed that Sm and Ch:Sm, as single dose treatments, attenuated abscesses by &gt;30%, demonstrating a similar effect to that of a mutant lacking plcH in this infection model. Thus, sphingomyelin-containing liposome therapy offers an interesting approach to treat and reduce virulence of complex infections caused by P. aeruginosa and potentially other Gram-negative pathogens expressing PlcH.

Exotoxin-Targeted Drug Modalities as Antibiotic Alternatives

The paradigm of antivirulence therapy dictates that bacterial pathogens are specifically disarmed but not killed by neutralizing their virulence factors. Clearance of the invading pathogen by the immune system is promoted. As compared to antibiotics, the pathogen-selective antivirulence drugs hold promise to minimize collateral damage to the beneficial microbiome. Also, selective pressure for resistance is expected to be lower because bacterial viability is not directly affected. Antivirulence drugs are being developed for stand-alone prophylactic and therapeutic treatments but also for combinatorial use with antibiotics. This Review focuses on drug modalities that target bacterial exotoxins after the secretion or release-upon-lysis. Exotoxins have a significant and sometimes the primary role as the disease-causing virulence factor, and thereby they are attractive targets for drug development. We describe the key pre-clinical and clinical trial data that have led to the approval of currently used exotoxin-targeted drugs, namely the monoclonal antibodies bezlotoxumab (toxin B/TcdB, Clostridioides difficile), raxibacumab (anthrax toxin, Bacillus anthracis), and obiltoxaximab (anthrax toxin, Bacillus anthracis), but also to challenges with some of the promising leads. We also highlight the recent developments in pre-clinical research sector to develop exotoxin-targeted drug modalities, i.e., monoclonal antibodies, antibody fragments, antibody mimetics, receptor analogs, neutralizing scaffolds, dominant-negative mutants, and small molecules. We describe how these exotoxin-targeted drug modalities work with high-resolution structural knowledge and highlight their advantages and disadvantages as antibiotic alternatives.

Label-free visible colorimetric biosensor for detection of multiple pathogenic bacteria based on engineered polydiacetylene liposomes

Bacterial infections are considered as a critical healthcare concern worldwide. Timely infection detection is crucial to effective antibiotic administration which can reduce the severity of infection and the occurrence of antibiotic resistance. We have developed label-free polydiacetylene (PDA) liposome-based colorimetric biosensor to detect and identify bacterial cultures at the genus and species level with naked eyes by simple color change. We found that among the various liposomal systems, moderate concentration of PDA, phospholipids and cholesterol in liposome assemblies can greatly influence the sensitivity to different bacteria, exhibiting unique chromatic properties of each bacterial strain. The strikingly different chromatic color change was due to the various mechanisms of interactions between bacterial toxins and biomimetic lipid bilayers. Furthermore, increase of cholesterol in liposome assemblies greatly enhanced the sensitivity of bacterial strains related to membrane destruction mediated by pore-formation mechanism such as S. aureus and E.coli, whereas the detection of the two bacterial strains was believed to rely on the specific recognition elements coupled with PDA moiety. As a proof of concept, a colorimetric finger-print array for distinguishing 6 bacterial species was studied. Particularly, the proposed bacterial detection platform is achieved through the interaction between bacterially secreted toxins and liposome bilayers instead of specific recognition of receptors-ligands. The results of both response time and sensitivity of label-free-liposome-based system show superior to previous reports on chromatic bacterial detection assays. By combing these results, the label-free-liposome-based colorimetric sensing platform shows great importance as a bacterial-sensing and discrimination platform.

Engineered Liposomes Protect Immortalized Immune Cells from Cytolysins Secreted by Group A and Group G Streptococci

The increasing antibiotic resistance of bacterial pathogens fosters the development of alternative, non-antibiotic treatments. Antivirulence therapy, which is neither bacteriostatic nor bactericidal, acts by depriving bacterial pathogens of their virulence factors. To establish a successful infection, many bacterial pathogens secrete exotoxins/cytolysins that perforate the host cell plasma membrane. Recently developed liposomal nanotraps, mimicking the outer layer of the targeted cell membranes, serve as decoys for exotoxins, thus diverting them from attacking host cells. In this study, we develop a liposomal nanotrap formulation that is capable of protecting immortalized immune cells from the whole palette of cytolysins secreted by Streptococcus pyogenes and Streptococcus dysgalactiae subsp. equisimilis—important human pathogens that can cause life-threatening bacteremia. We show that the mixture of cholesterol-containing liposomes with liposomes composed exclusively of phospholipids is protective against the combined action of all streptococcal exotoxins. Our findings pave the way for further development of liposomal antivirulence therapy in order to provide more efficient treatment of bacterial infections, including those caused by antibiotic resistant pathogens.

Nanomedicine to fight infectious disease

The ubiquity and potency of antibiotics may give the false impression that infection is a solved problem. Unfortunately, even bacterial infections, the target of antibiotics, remain a major cause of illness and death. Several major unmet needs persist: biofilms, such as those on implanted hardware, largely resist antibiotics; the inflammatory host response to infection often produces more damage than the infection itself; and systemic antibiotics often decimate the gut microbiome, which can predispose to additional infections and even predispose to non-infectious diseases. Additionally, there is an increasing threat from multi-drug resistant microorganisms, though market forces may continue to inhibit innovation in this realm. These numerous unmet infection-related needs provide attractive goals for innovation of targeted drug delivery technologies, especially those of nanomedicine. Here we review several of those innovations in pre-clinical development, the two such therapies which have made it to clinical use, and the opportunities for further technology development for treating infections.

Intracellularly Released Cholesterol from Polymer-Based Delivery Systems Alters Cellular Responses to Pneumolysin and Promotes Cell Survival

Cholesterol is highly abundant within all human body cells and modulates critical cellular functions related to cellular plasticity, metabolism, and survival. The cholesterol-binding toxin pneumolysin represents an essential virulence factor of Streptococcus pneumoniae in establishing pneumonia and other pneumococcal infections. Thus, cholesterol scavenging of pneumolysin is a promising strategy to reduce S. pneumoniae induced lung damage. There may also be a second cholesterol-dependent mechanism whereby pneumococcal infection and the presence of pneumolysin increase hepatic sterol biosynthesis. Here we investigated a library of polymer particles varying in size and composition that allow for the cellular delivery of cholesterol and their effects on cell survival mechanisms following pneumolysin exposure. Intracellular delivery of cholesterol by nanocarriers composed of Eudragit E100–PLGA rescued pneumolysin-induced alterations of lipid homeostasis and enhanced cell survival irrespective of neutralization of pneumolysin.

Nano-metal-organic-frameworks for treating H2O2-Secreting bacteria alleviate pulmonary injury and prevent systemic sepsis

As a vital bacteria-secreted toxin, hydrogen peroxide (H₂O₂) can destroy infected tissues and increase vascular permeability, leading to life-threatening systemic bacteremia or sepsis. No strategy that can alleviate H₂O₂-induced injury and prevent systemic sepsis has been reported. Herein, as a proof of concept, we demonstrate the use of H₂O₂-reactive metal-organic framework nanosystems (MOFs) for treating H₂O₂-secreting bacteria. In mice infected with Streptococcus pneumoniae (S. pneumoniae) isolated from patients, MOFs efficiently accumulate in the lungs after systemic administration due to infection-induced alveolar-capillary barrier dysfunction. Moreover, MOFs sequester pneumococcal H₂O₂, reduce endothelial DNA damage, and prevent systemic dissemination of bacteria. In addition, this nanosystem exhibits excellent chemodynamic bactericidal effects against drug-resistant bacteria. Through synergistic therapy with the antibiotic ampicillin, MOFs eliminate over 98% of invading S. pneumoniae, resulting in a survival rate of greater than 90% in mice infected with a lethal dose of S. pneumoniae. This work opens up new paths for the clinical treatment of toxin-secreting bacteria.

The Case against Antibiotics and for Anti-Virulence Therapeutics

Although antibiotics have been indispensable in the advancement of modern medicine, there are downsides to their use. Growing resistance to broad-spectrum antibiotics is leading to an epidemic of infections untreatable by first-line therapies. Resistance is exacerbated by antibiotics used as growth factors in livestock, over-prescribing by doctors, and poor treatment adherence by patients. This generates populations of resistant bacteria that can then spread resistance genes horizontally to other bacterial species, including commensals. Furthermore, even when antibiotics are used appropriately, they harm commensal bacteria leading to increased secondary infection risk. Effective antibiotic treatment can induce bacterial survival tactics, such as toxin release and increasing resistance gene transfer. These problems highlight the need for new approaches to treating bacterial infection. Current solutions include combination therapies, narrow-spectrum therapeutics, and antibiotic stewardship programs. These mediate the issues but do not address their root cause. One emerging solution to these problems is anti-virulence treatment: preventing bacterial pathogenesis instead of using bactericidal agents. In this review, we discuss select examples of potential anti-virulence targets and strategies that could be developed into bacterial infection treatments: the bacterial type III secretion system, quorum sensing, and liposomes.

Streptolysin O concentration and activity is central to in vivo phenotype and disease outcome in Group A Streptococcus infection

Group A Streptoccocus (GAS) is among the most diverse of all human pathogens, responsible for a range of clinical manifestations, from mild superficial infections such as pharyngitis to serious invasive infections such as necrotising fasciitis and sepsis. The drivers of these different disease phenotypes are not known. The GAS cholesterol-dependent cytolysin, Streptolysin O (SLO), has well established cell and tissue destructive activity. We investigated the role of SLO in determining disease outcome in vivo, by using two different clinical lineages; the recently emerged hypervirulent outbreak emm type 32.2 strains, which result in sepsis, and the emm type 1.0 strains which cause septic arthritis. Using clinically relevant in vivo mouse models of sepsis and a novel septic arthritis model, we found that the amount and activity of SLO was vital in determining the course of infection. The emm type 32.2 strain produced large quantities of highly haemolytic SLO that resulted in rapid development of sepsis. By contrast, the reduced concentration and lower haemolytic activity of emm type 1.0 SLO led to translocation of bacteria from blood to joints. Importantly, sepsis associated strains that were attenuated by deletion or inhibition of SLO, then also translocated to the joint, confirming the key role of SLO in determining infection niche. Our findings demonstrate that SLO is key to in vivo phenotype and disease outcome. Careful consideration should be given to novel therapy or vaccination strategies that target SLO. Whilst neutralising SLO activity may reduce severe invasive disease, it has the potential to promote chronic inflammatory conditions such as septic arthritis.

Staphylococcus aureus Toxins: An Update on Their Pathogenic Properties and Potential Treatments

Staphylococcus aureus is a clinically important pathogen that causes a wide range of human infections, from minor skin infections to severe tissue infection and sepsis. S. aureus has a high level of antibiotic resistance and is a common cause of infections in hospitals and the community. The rising prevalence of community-acquired methicillin-resistant S. aureus (CA-MRSA), combined with the important severity of S. aureus infections in general, has resulted in the frequent use of anti-staphylococcal antibiotics, leading to increasing resistance rates. Antibiotic-resistant S. aureus continues to be a major health concern, necessitating the development of novel therapeutic strategies. S. aureus uses a wide range of virulence factors, such as toxins, to develop an infection in the host. Recently, anti-virulence treatments that directly or indirectly neutralize S. aureus toxins have showed promise. In this review, we provide an update on toxin pathogenic characteristics, as well as anti-toxin therapeutical strategies.

Bioactive Lipids and Their Derivatives in Biomedical Applications

Lipids, which along with carbohydrates and proteins are among the most important nutrients for the living organism, have a variety of biological functions that can be applied widely in biomedicine. A fatty acid, the most fundamental biological lipid, may be classified by length of its aliphatic chain, and the short-, medium-, and long-chain fatty acids and each have distinct biological activities with therapeutic relevance. For example, short-chain fatty acids have immune regulatory activities and could be useful against autoimmune disease; medium-chain fatty acids generate ketogenic metabolites and may be used to control seizure; and some metabolites oxidized from long-chain fatty acids could be used to treat metabolic disorders. Glycerolipids play important roles in pathological environments, such as those of cancers or metabolic disorders, and thus are regarded as a potential therapeutic target. Phospholipids represent the main building unit of the plasma membrane of cells, and play key roles in cellular signaling. Due to their physical properties, glycerophospholipids are frequently used as pharmaceutical ingredients, in addition to being potential novel drug targets for treating disease. Sphingolipids, which comprise another component of the plasma membrane, have their own distinct biological functions and have been investigated in nanotechnological applications such as drug delivery systems. Saccharolipids, which are derived from bacteria, have endotoxin effects that stimulate the immune system. Chemically modified saccharolipids might be useful for cancer immunotherapy or as vaccine adjuvants. This review will address the important biological function of several key lipids and offer critical insights into their potential therapeutic applications.

Gram-Positive Pneumonia: Possibilities Offered by Phage Therapy

Pneumonia is an acute pulmonary infection whose high hospitalization and mortality rates can, on occasion, bring healthcare systems to the brink of collapse. Both viral and bacterial pneumonia are uncovering many gaps in our understanding of host–pathogen interactions, and are testing the effectiveness of the currently available antimicrobial strategies. In the case of bacterial pneumonia, the main challenge is antibiotic resistance, which is only expected to increase during the current pandemic due to the widespread use of antibiotics to prevent secondary infections in COVID-19 patients. As a result, alternative therapeutics will be necessary to keep this disease under control. This review evaluates the advantages of phage therapy to treat lung bacterial infections, in particular those caused by the Gram-positive bacteria Streptococcus pneumoniae and Staphylococcus aureus, while also highlighting the regulatory impediments that hamper its clinical use and the difficulties associated with phage research.

Nanocapsules modify membrane interaction of polymyxin B to enable safe systemic therapy of Gram-negative sepsis

Systemic therapy of Gram-negative sepsis remains challenging. Polymyxin B (PMB) is well suited for sepsis therapy due to the endotoxin affinity and antibacterial activity. However, the dose-limiting toxicity has limited its systemic use in sepsis patients. For safe systemic use of PMB, we have developed a nanoparticulate system, called D-TZP, which selectively reduces the toxicity to mammalian cells but retains the therapeutic activities of PMB. D-TZP consists of an iron-complexed tannic acid nanocapsule containing a vitamin D core, coated with PMB and a chitosan derivative that controls the interaction of PMB with endotoxin, bacteria, and host cells. D-TZP attenuated the membrane toxicity associated with PMB but retained the ability of PMB to inactivate endotoxin and kill Gram-negative bacteria. Upon intravenous injection, D-TZP protected animals from pre-established endotoxemia and polymicrobial sepsis, showing no systemic toxicities inherent to PMB. These results support D-TZP as a safe and effective systemic intervention of sepsis.

Immunobiology and nanotherapeutics of severe acute respiratory syndrome 2 (SARS-CoV-2): a current update

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) constitutes the most significant global public health challenge in a century. It has reignited research interest in coronavirus. While little information is available, research is currently in progress to comprehensively understand the general biology and immune response mechanism against SARS-CoV-2. The spike proteins (S protein) of SARS-CoV-2 perform a crucial function in viral infection establishment. ACE2 and TMPRSS2 play a pivotal role in viral entry. Upon viral entry, the released pro-inflammatory proteins (cytokines and chemokines) cause the migration of the T cells, monocytes, and macrophages to the infection site. IFNϒ released by T cells initiates a loop of pro-inflammatory feedback. The inflammatory state may further enhance with an increase in immune dysfunction responsible for the infection's progression. A treatment approach that prevents ACE2-mediated viral entry and reduces inflammatory response is a crucial therapeutic intervention strategy, and nanomaterials and their conjugates are promising candidates. Nanoparticles can inhibit viral entry and replication. Nanomaterials have also found application in targeted drug delivery and also in developing a vaccine against SARS-CoV-2. Here, we briefly summarize the origin, transmission, and clinical features of SARS-CoV-2. We then discussed the immune response mechanisms of SARS-CoV-2. Finally, we further discussed nanotechnology's potentials as an intervention strategy against SARS-CoV-2 infection. All these understandings will be crucial in developing therapeutic strategies against SARS-CoV-2.

Cell-mimicking nanodecoys neutralize SARS-CoV-2 and mitigate lung injury in a non-human primate model of COVID-19

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has grown into a global pandemic, and only a few antiviral treatments have been approved to date. Angiotensin-converting enzyme 2 (ACE2) plays a fundamental role in SARS-CoV-2 pathogenesis because it allows viral entry into host cells. Here we show that ACE2 nanodecoys derived from human lung spheroid cells (LSCs) can bind and neutralize SARS-CoV-2 and protect the host lung cells from infection. In mice, these LSC-nanodecoys were delivered via inhalation therapy and resided in the lungs for over 72 h post-delivery. Furthermore, inhalation of the LSC-nanodecoys accelerated clearance of SARS-CoV-2 mimics from the lungs, with no observed toxicity. In cynomolgus macaques challenged with live SARS-CoV-2, four doses of these nanodecoys delivered by inhalation promoted viral clearance and reduced lung injury. Our results suggest that LSC-nanodecoys can serve as a potential therapeutic agent for treating COVID-19.