Pro-inflammatory response ensured by LPS and Pam3CSK4 in RAW 264.7 cells did not improve a fungistatic effect on Cryptococcus gattii infection

High-throughput single-cell analysis reveals Omp38-specific monoclonal antibodies that protect against Acinetobacter baumannii infection

Infections caused by Acinetobacter baumannii (A. baumannii) have emerged as a global public health concern because of high pathogenicity of this bacterium. Monoclonal antibodies (mAbs) have a lower likelihood of promoting drug resistance and offer targeted treatment, thereby reducing potential adverse effects; however, the therapeutic potential of mAbs targeting A. baumannii has not been fully characterized. In this study, mAbs against the outer membrane proteins (OMPs) of A. baumannii were isolated in a high-throughput manner. The ability of Omp38-specific mAbs to bind to A. baumannii strains from diverse sources was confirmed via enzyme-linked immunosorbent assay (ELISA). Intravenous administration of the Omp38-specific mAbs significantly improved the survival rate and reduced the bacterial load in a mouse model of lethal A. baumannii infection. Flow cytometry and ELISA confirmed that immune cell infiltration and cytokine production, respectively, decreased in a mouse model of sublethal A. baumannii infection. In addition, analysis of the Omp38-mAb C3 binding conformation revealed the potential mechanism of broad-spectrum binding activity of this mAb against A. baumannii. Taken together, these findings indicate that mAbs against Omp38 facilitate bacterial clearance from host, minimize inflammatory mediator release and reduce host damage, highlighting the potential of Omp38-specific mAbs in the clinical treatment of A. baumannii infection.

Antimicrobial and anti-inflammatory effects of antimicrobial peptide Lf-KR against carbapenem-resistant Escherichia coli

BACKGROUND

Carbapenem-resistant Escherichia coli (CREC) is one of the most significant clinical pathogens, primarily emerging owing to the widespread use of broad-spectrum antibiotics. Antimicrobial resistance is a major global health challenge that prolongs treatment duration and increases healthcare costs. This study evaluated the antibacterial and anti-inflammatory effects of the antimicrobial peptide Lf-KR against CREC.

METHODS

Broth microdilution method, growth curve analysis, and time-kill assays were performed to evaluate the antibacterial activity of Lf-KR against CREC. The working mechanism of Lf-KR was elucidated using N-phenyl-1-naphthylamine, propidium iodide fluorochrome, and lipopolysaccharide-binding assays. qRT-PCR was used to assess the peptide's effects on the expression of pro-inflammatory cytokines expression during infection. Furthermore, the safety and stability of Lf-KR were assessed by testing its cytotoxicity, hemolytic activity, and antibacterial stability under various conditions. The Galleria mellonella infection model was applied to evaluate the in vivo activity of Lf-KR.

RESULTS

In vitro tests showed that Lf-KR exhibited potent antibacterial activity against CREC, with the minimum inhibitory concentrations of ranging from 4-8 µg/mL and minimum bactericidal concentrations 4-16 µg/mL. Mechanistically, Lf-KR induced bacterial cell death by disrupting the bacterial membrane. Furthermore, Lf-KR significantly reduced the expression of pro-inflammatory cytokine genes, including IL-1β, IL-6, and TNF-α, in RAW 264.7 macrophage cells infected with CREC. Lf-KR concentrations < 128 µg/mL showed no significant cytotoxicity or erythrocyte hemolytic activity. Lf-KR antibacterial activity was stable across a wide temperature range (- 80 °C to 65 °C), although it was more susceptible to inhibition by fetal bovine serum. The G. mellonella infection model further demonstrated the robust antimicrobial activity of Lf-KR.

CONCLUSIONS

This study demonstrated that the antimicrobial peptide Lf-KR is a highly promising antimicrobial and anti-inflammatory agent against CREC, with potential applications in combating multi drug-resistant bacterial infections.

Antimicrobial peptide A20L: in vitro and in vivo antibacterial and antibiofilm activity against carbapenem-resistant Klebsiella pneumoniae

Antimicrobial resistance has become a growing public health threat in recent years. Klebsiella pneumoniae is one of the priority pathogens listed by the World Health Organization. Antimicrobial peptides are considered promising alternatives to antibiotics due to their broad-spectrum antibacterial activity and low resistance. In this study, we investigated the antibacterial activity of antimicrobial peptide A20L against K. pneumoniae. In vitro antibacterial activity of A20L against K. pneumoniae was demonstrated by broth microdilution method. We confirmed the in vivo efficacy of A20L by Galleria mellonella infection model. In addition, we found that A20L also had certain antibiofilm activity by crystal violet staining. We also evaluated the safety and stability of A20L, and the results revealed that at a concentration of ≤128 µg/mL, A20L exhibited negligible toxicity to RAW264.7 cells and no substantial toxicity to G. mellonella. A20L was stable at different temperatures and with low concentration of serum [5% fetal bovine serum (FBS)]; however, Ca2+, Mg2+, and high serum concentrations reduced the antibacterial activity of A20L. Scanning electron microscope (SEM) and membrane permeability tests revealed that A20L may exhibit antibacterial action by damaging bacterial cell membranes and increasing the permeability of outer membrane. Taken together, our results suggest that A20L has significant development potential as a therapeutic antibiotic alternative, which provides ideas for the treatment of K. pneumoniae infection.

IMPORTANCE

A20L showed antibacterial and anti-infective efficacy in vitro and in vivo against Klebsiella pneumoniae. It can have an antibacterial effect by disrupting the integrity of cell membranes. A20L displayed anti-biofilm and anti-inflammatory activity against carbapenem-resistant K. pneumoniae and certain application potential in vivo, which provides a new idea for the clinical treatment of biofilm-associated infections.

PAM-1: an antimicrobial peptide with promise against ceftazidime-avibactam resistant Escherichia coli infection

Introduction

Antibiotic misuse and overuse have led to the emergence of carbapenem-resistant bacteria. The global spread of resistance to the novel antibiotic combination ceftazidime-avibactam (CZA) is becoming a severe problem. Antimicrobial peptide PAM-1 offers a novel approach for treating infections caused by antibiotic-resistant bacteria. This study explores its antibacterial and anti-biofilm activities and mechanisms against CZA-resistant Escherichia. Coli (E. coli), evaluating its stability and biosafety as well.

Methods

The broth microdilution method, growth curve analysis, crystal violet staining, scanning electron microscopy, and propidium iodide staining/N-phenyl-1-naphthylamine uptake experiments were performed to explore the antibacterial action and potential mechanism of PAM-1 against CZA-resistant E. coli. The biosafety in diverse environments of PAM-1 was evaluated by red blood cell hemolysis, and cytotoxicity tests. Its stability was further assessed under different temperatures, serum concentrations, and ionic conditions using the broth microdilution method to determine its minimum inhibitory concentration (MIC). Galleria mellonella infection model and RT-qPCR were used to investigate the in vivo antibacterial and anti-inflammatory effects.

Results and discussion

In vitro antibacterial experiments demonstrated that the MICs of PAM-1 ranged from 2 to 8 μg/mL, with its effectiveness sustained for a duration of 24 h. PAM-1 exhibited significant antibiofilm activities against CZA-resistant E. coli (p < 0.05). Furthermore, Membrane permeability test revealed that PAM-1 may exert its antibacterial effect by disrupting membrane integrity by forming transmembrane pores (p < 0.05). Red blood cell hemolysis and cytotoxicity tests revealed that PAM-1 exerts no adverse effects at experimental concentrations (p < 0.05). Moreover, stability tests revealed its effectiveness in serum and at room temperature. The Galleria mellonella infection model revealed that PAM-1 can significantly improve the survival rate of Galleria mellonella (>50%)for in vivo treatment. Lastly, RT-qPCR revealed that PAM-1 downregulates the expression of inflammatory cytokines (p < 0.05). Overall, our study findings highlight the potential of PAM-1 as a therapeutic agent for CZA-resistant E. coli infections, offering new avenues for research and alternative antimicrobial therapy strategies.

Octominin: An antimicrobial peptide with antibacterial and anti-inflammatory activity against carbapenem-resistant Escherichia coli both in vitro and in vivo

OBJECTIVES

The emergence of carbapenem-resistant Escherichia coli (CREC) is a global concern as its prevalence restricts treatment options and poses a considerable threat to public health. In this study, in vitro and in vivo activity of the antimicrobial peptide Octominin against CREC was investigated to reveal possible mechanisms of action. Furthermore, its safety and factors influencing its antibacterial effect were assessed. Additionally, the anti-inflammatory effects of Octominin were examined.

METHODS

The antimicrobial activity of Octominin against 11 strains of CREC was determined using the broth microdilution method, growth curve, and time-kill assay. Its possible mechanism of action was unraveled using the propidium iodide and N-phenyl-1-naphthylamine fluorochrome and lipopolysaccharide-binding assays. To understand the safety and stability of Octominin, its cytotoxicity, hemolysis, and antibacterial activity under various conditions (i.e, temperature, ions) were estimated. Additionally, a Galleria mellonella infection model was utilized to evaluate the efficacy of Octominin in vivo, and qRT-PCR was performed to assess its effect on the expression of proinflammatory cytokines.

RESULTS

Octominin displayed a significant antibacterial effect, with MICs of 4-8 µg/mL and MBCs of 8-16 µg/mL. Octominin exerted its antibacterial effect by disrupting bacterial membranes. Cytotoxicity and hemolysis tests demonstrated the potential application of Octominin in vivo. The G. mellonella infection model asserted the in vivo efficacy of Octominin. Furthermore, Octominin inhibited the expression of proinflammatory cytokines. Although the temperature had little effect on its the activity, serum and ions reduced activity.

CONCLUSION

Octominin is a promising alternative agent with remarkable antibacterial and anti-inflammatory effects for treating infections caused by CREC.

Trichinella spiralis cystatin alleviates polymicrobial sepsis through activating regulatory macrophages

BACKGROUND

Sepsis is a life-threateningorgandysfunction caused by the cytokine storm induced by the severe bacterial infection. Excessive inflammatory responses are responsible for the lethal organ damage during the early stage of sepsis. Helminth infection and helminth-derived proteins have been identified to have the ability to immunomodulate the host immune system by reducing inflammation against inflammatory diseases. Trichinella spiralis cystatin (Ts-Cys) is a cysteine protease inhibitor with strong immunomodulatory functions on host immune system. Our previous studies have shown that excretory-secretory proteins of T. spiralis reduced sepsis-induced inflammation and Ts-Cys was able to inhibit macrophages to produce inflammatory cytokines. Whether Ts-Cys has a therapeutic effect on polymicrobial sepsis and related immunological mechanism are not yet known.

METHODS

Sepsis was induced in BALB/c mice using cecal ligation and puncture (CLP), followed by intraperitoneal injection of 15 µg recombinant Ts-Cys (rTs-Cys). The therapeutic effect of rTs-Cys on sepsis was evaluated by observing the 72-hour survival rates of CLP-induced septic mice and the acute injury of lung and kidney through measuring the wet/dry weight ratio of lung, the levels of blood urea nitrogen (BUN) and creatinine (Cr) in sera and the tissue section pathology. The potential underlying mechanism was investigated using mouse bone marrow-derived macrophages (BMDMs) by observing the effect of rTs-Cys on LPS-stimulated macrophage polarization. The expression of genes associated with macrophage polarization in BMDMs and tissues of septic mice was measured by Western Blotting and qPCR.

RESULTS

In this study, we demonstrated the treatment with rTs-Cys alleviated CLP-induced sepsis in mice with significantly reduced pathological injury in vital organs of lung and kidney and reduced mortality of septic mice. The further study identified that treatment with rTs-Cys promoted macrophage polarization from classically activated macrophage (M1) to alternatively activated macrophage (M2) phenotype via inhibiting TLR2/MyD88 signal pathway and increasing expression of mannose receptor (MR), inhibited pro-inflammatory cytokines (TNF-α, IL-6 and IL-1β) and increased regulatory anti-inflammatory cytokines (IL-10 and TGF-β) in sera and tissues (lung and kidney) of mice with polymicrobial sepsis.

CONCLUSIONS

Our results demonstrated that rTs-Cys had a therapeutic effect on sepsis through activating regulatory macrophages possibly via suppressing TLR2/MyD88 signal pathway. We also identified that rTs-Cys-induced M2 macrophage differentiation was associated with increased expression of MR on the surface of macrophages. Our results underscored the importance of MR in regulating macrophages during the treatment with rTs-Cys, providing another immunological mechanism in which helminths and their derived proteins modulate the host immune system. The findings in this study suggest that rTs-Cys is a potential therapeutic agent for the prevention and treatment of sepsis and other inflammatory diseases.

Characterization of Citrus Pectin Oligosaccharides and Their Microbial Metabolites as Modulators of Immunometabolism on Macrophages

We characterized the structure of prepared citrus pectin oligosaccharides (POS) and investigated the immunometabolism-modulating effects of POS and their microbial metabolites on human macrophages. Both POS and metabolites activated immune responses and exhibited anti-inflammatory properties in the presence of lipopolysaccharide (LPS) via regulating expressions of inflammatory cytokines and nuclear factor-kappa B. Cholesterol efflux was also facilitated via increased gene expressions of the liver X receptor-α-adenosine triphosphate-binding cassette transporter (ABC) A1/ABCG1 pathway and suppressed cholesterol synthesis via suppressing expressions of 3-hydroxy-3-methylglutaryl-coenzyme A reductase. Microbial degradation prevented POS from attenuating palmitoyl-3-cysteine-serine-lysine-4-induced inflammation and promoting M2 polarization, but it is capable of inhibiting cholesterol uptake-related genes CD36 and SR-A. These findings indicate that immunometabolism-modulating effects of POS are not solely microbiota-dependent effects. Both POS and their microbial metabolites are potential immunometabolism modulators via different mechanisms.

Luteolin transforms the polarity of bone marrow-derived macrophages to regulate the cytokine storm

Background

Macrophages are indispensable regulators of inflammatory responses. Macrophage polarisation and their secreted inflammatory factors have an association with the outcome of inflammation. Luteolin, a flavonoid abundant in plants, has anti-inflammatory activity, but whether luteolin can manipulate M1/M2 polarisation of bone marrow-derived macrophages (BMDMs) to suppress inflammation is still unclear. This study aimed to observe the effects of luteolin on the polarity of BMDMs derived from C57BL/6 mice and the expression of inflammatory factors, to explore the mechanism by which luteolin regulates the BMDM polarity.

Methods

M1-polarised BMDMs were induced by lipopolysaccharide (LPS) + interferon (IFN)-γ and M2-polarisation were stimulated with interleukin (IL)-4. BMDM morphology and phagocytosis were observed by laser confocal microscopy; levels of BMDM differentiation and cluster of differentiation (CD)11c or CD206 on the membrane surface were assessed by flow cytometry (FCM); mRNA and protein levels of M1/M2-type inflammatory factors were performed by qPCR and ELISA, respectively; and the expression of p-STAT1 and p-STAT6 protein pathways was detected by Western-blotting.

Results

The isolated mouse bone marrow cells were successfully differentiated into BMDMs, LPS + IFN-γ induced BMDM M1-phenotype polarisation, and IL-4 induced M2-phenotype polarisation. After M1-polarised BMDMs were treated with luteolin, the phagocytosis of M1-polarized BMDMs was reduced, and the M1-type pro-inflammatory factors including IL-6, tumour necrosis factor (TNF)-α, inducible nitric oxide synthase (iNOS), and CD86 were downregulated while the M2-type anti-inflammatory factors including IL-10, IL-13, found in inflammatory zone (FIZZ)1, Arginase (Arg)1 and CD206 were upregulated. Additionally, the expression of M1-type surface marker CD11c decreased. Nevertheless, the M2-type marker CD206 increased; and the levels of inflammatory signalling proteins phosphorylated signal transducer and activator of transcription (p-STAT)1 and p-STAT6 were attenuated and enhanced, respectively.

Conclusions

Our study suggests that luteolin may transform BMDM polarity through p-STAT1/6 to regulate the expression of inflammatory mediators, thereby inhibiting inflammation. Naturally occurring luteolin holds promise as an anti-inflammatory and immunomodulatory agent.

A crosstalk between type 2 innate lymphoid cells and alternative macrophages in lung development and lung diseases (Review)

Type 2 innate lymphoid cells (ILC2s) are important innate immune cells that are involved in type 2 inflammation, in both mice and humans. ILC2s are stimulated by factors, including interleukin (IL)-33 and IL-25, and activated ILC2s secrete several cytokines that mediate type 2 immunity by inducing profound changes in physiology, including activation of alternative (M2) macrophages. M2 macrophages possess immune modulatory, phagocytic, tissue repair and remodeling properties, and can regulate ILC2s under infection. The present review summarizes the role of ILC2s as innate cells and M2 macrophages as anti-inflammatory cells, and discusses current literature on their important biological significance. The present review also highlights how the crosstalk between ILC2s and M2 macrophages contributes to lung development, induces pulmonary parasitic expulsion, exacerbates pulmonary viral and fungal infections and allergic airway diseases, and promotes the development of lung diseases, such as pulmonary fibrosis, chronic obstructive pulmonary disease and carcinoma of the lungs.