Acacetin inhibits Streptococcus pneumoniae virulence by targeting pneumolysin

Acacetin Attenuates Sepsis-induced Acute Lung Injury via NLRC3-NF-κB Pathway

Acacetin, a flavonoid derived compound has been recognized for its diverse biological activities, such as anti-oxidative and anti-inflammatory effects. Acute lung injury (ALI) is a severe condition characterized by respiratory insufficiency and tissue damage, commonly triggered by pneumonia and severe sepsis. These conditions induce an inflammatory response via Toll-like receptor 4 (TLR4) signaling activation. This study explored acacetin's therapeutic potential against lipopolysaccharide (LPS) induced ALI in mice, focusing on its ability to modulate the NF-κB pathway via regulation of the Nod-like receptor family CARD domain containing 3 (NLRC3), a signal sensor that plays an important role in the regulation of inflammation and the maintenance of homeostasis. Our findings revealed that high-dose acacetin reduced the mortality rate of ALI mice, significantly ameliorated LPS-induced lung pathological changes, reduced lung edema, and decreased the expression of inflammatory mediators in lung tissues. This protective impact of acacetin appears to stem form its capacity to enhance NLRC3 expression, which, intern, can inhibit the activation of NF-κB and subsequently inhibit the production of inflammatory mediators. NLRC3 deficiency inhibits the protective effect of acacetin on ALI mice. Molecular docking also verified that acacetin tightly bound acacetin to NLRC3. Additionally, acacetin was found to influence macrophage recruitment dynamics via NLRC3, inhibiting the overactivation of NLRC3-NF-κB related pathways. Taken together, our results indicate that acacetin inhibited LPS-induced acute lung injury and macrophage overrecruitment to the lungs in mice by upregulating NLRC3.

Outlining the Phytoconstituents of Greek Clover Herb Extract and Assessment of Its Effect against Foodborne Infections Caused by Salmonella typhimurium

Owing to the spread of resistance between pathogenic bacteria, searching for novel compounds with antibacterial activity is essential. Here, we investigated the potential antibacterial activity of Greek clover or Trigonella foenum-graecum herb extract on Salmonella typhimurium clinical isolates. The chemical profile of the herb was initially determined using LC-ESI-MS/MS, which explored 36 different compounds. Interestingly, the fenugreek extract possessed antibacterial action in vitro with minimum inhibitory concentrations of 64 to 512 µg/mL. The potential mechanism of action was studied by elucidating the effect of the fenugreek extract on the membrane properties of S. typhimurium bacteria, including the inner and outer membrane permeability and membrane integrity. Remarkably, the fenugreek extract had detrimental effects on the membrane properties in 40-60% of the isolates. Moreover, the in vivo antibacterial action was studied using a gastrointestinal infection model with S. typhimurium bacteria. Interestingly, the fenugreek extract (200 mg/kg) improved the infection outcomes in the tested mice. This was represented by the noteworthy decrease (p < 0.05) in the bacterial count in the small intestine and caecum tissues. The survival rate of the fenugreek-extract-treated mice significantly increased compared to the S. typhimurium-infected group. Additionally, there was an improvement in the histological and immunohistochemical features of tumor necrosis factor-alpha. In addition, using an ELISA and qRT-PCR, there was an improvement in the proinflammatory and oxidative stress markers in the fenugreek-extract-treated group. Consequently, fenugreek extract should be investigated further on other food pathogens.

Wogonin attenuates the pathogenicity of Streptococcus pneumoniae by double-target inhibition of Pneumolysin and Sortase A

Streptococcus pneumoniae (S. pneumoniae) is a major causative agent of respiratory disease in patients and can cause respiratory distress and other symptoms in severe cases. Pneumolysin (PLY) is a pore-forming toxin that induces host tissue injury and inflammatory responses. Sortase A (SrtA), a catalytic enzyme that anchors surface-associated virulence factors, is critical for S. pneumoniae virulence. Here, we found that the active ingredient of the Chinese herb Scutellaria baicalensis, wogonin, simultaneously inhibited the haemolytic activity of PLY and SrtA activity. Consequently, wogonin decreased PLY-mediated cell damage and reduced SrtA-mediated biofilm formation by S. pneumoniae. Furthermore, our data indicated that wogonin did not affect PLY expression but directly altered its oligomerization, leading to reduced activity. Furthermore, the analysis of a mouse pneumonia model further revealed that wogonin reduced mortality in mice infected with S. pneumoniae laboratory strain D39 and S. pneumoniae clinical isolate E1, reduced the number of colony-forming units in infected mice and decreased the W/D ratio and levels of the inflammatory factors TNF-α, IL-6 and IL-1β in the lungs of infected mice. Thus, wogonin reduces S. pneumoniae pathogenicity by inhibiting the dual targets PLY and SrtA, providing a treatment option for S. pneumoniae infection.

Pneumolysin as a target for new therapies against pneumococcal infections: A systematic review

BACKGROUND

This systematic review evaluates pneumolysin (PLY) as a target for new treatments against pneumococcal infections. Pneumolysin is one of the main virulence factors produced by all types of pneumococci. This toxin (53 kDa) is a highly conserved protein that binds to cholesterol in eukaryotic cells, forming pores that lead to cell destruction.

METHODS

The databases consulted were MEDLINE, Web of Science, and Scopus. Articles were independently screened by title, abstract, and full text by two researchers, and using consensus to resolve any disagreements that occurred. Articles in other languages different from English, patents, cases report, notes, chapter books and reviews were excluded. Searches were restricted to the years 2000 to 2021. Methodological quality was evaluated using OHAT framework.

RESULTS

Forty-one articles describing the effects of different molecules that inhibit PLY were reviewed. Briefly, the inhibitory molecules found were classified into three main groups: those exerting a direct effect by binding and/or blocking PLY, those acting indirectly by preventing its effects on host cells, and those whose mechanisms are unknown. Although many molecules are proposed as toxin blockers, only some of them, such as antibiotics, peptides, sterols, and statins, have the probability of being implemented as clinical treatment. In contrast, for other molecules, there are limited studies that demonstrate efficacy in animal models with sufficient reliability.

DISCUSSION

Most of the studies reviewed has a good level of confidence. However, one of the limitations of this systematic review is the lack of homogeneity of the studies, what prevented to carry out a statistical comparison of the results or meta-analysis.

CONCLUSION

A panel of molecules blocking PLY activity are associated with the improvement of the inflammatory process triggered by the pneumococcal infection. Some molecules have already been used in humans for other purposes, so they could be safe for use in patients with pneumococcal infections. These patients might benefit from a second line treatment during the initial stages of the infection preventing acute respiratory distress syndrome and invasive pneumococcal diseases. Additional research using the presented set of compounds might further improve the clinical management of these patients.

Shionone-Targeted Pneumolysin to Ameliorate Acute Lung Injury Induced by Streptococcus pneumoniae In Vivo and In Vitro

Streptococcus pneumoniae (S. pneumoniae), as a Gram-positive bacterium, can cause severe bacterial pneumonia, and result in high morbidity and mortality in infected people. Meanwhile, isolated drug-resistant S. pneumoniae is growing, which raises concerns about strategies for combatting S. pneumoniae infection. To disturb S. pneumoniae pathogenicity and its drug-resistance, developing novel anti-infective strategies or compounds is urgent. In this study, the anti-infective effect of shionone was explored. A minimum inhibitory concentration (MIC) assay and growth curve determination were performed to evaluate the effect of the tetracyclic triterpenoid compound shionone against S. pneumoniae. Hemolysis tests, western blotting, oligomerization inhibition assays, and molecular docking were carried out to explore the anti-infective mechanism of shionone. Moreover, the protective effect of shionone was also confirmed in a mousepneumonia model. The results showed that the excellent hemolytic inhibitory activity of shionone was observed at less than 8 μg/mL. Meanwhile, shionone could disturb the oligomerization of pneumolysin (PLY) but did not interfere with PLY expression at less than 4 μg/mL. Molecular docking suggested that shionone targeted the ASP-59, ILE-60, THR-57, PHE-344, and ASN-346 amino acid sites to reduce S. pneumoniae pathogenicity. Furthermore, shionone alleviated lung histopathologic injury and decreased lung bacterial colonization in vivo. The above results showed that shionone could bind to the PLY active pocket under the concentrations of 8 μg/mL and neutralize PLY hemolysis activity to reduce S. pneumoniae pathogenicity in vitro and in vivo.

Corilagin: A Novel Antivirulence Strategy to Alleviate Streptococcus pneumoniae Infection by Diminishing Pneumolysin Oligomers

Pneumolysin (PLY) is a significant virulence factor of Streptococcus pneumoniae (S. pneumoniae), able to break through the defense system of a host and mediate the occurrence of a series of infections. Therefore, PLY as the most ideal target to prevent S. pneumoniae infection has received more and more attention and research. Corilagin is a tannic acid that exhibits excellent inhibition of PLY oligomers without bacteriostatic activity to S. pneumoniae. Herein, hemolytic activity assays, cell viability tests and western blot experiments are executed to evaluate the antivirulence efficacy of corilagin against PLY in vitro. Colony observation, hematoxylin and eosin (H&E) staining and cytokines of bronchoalveolar lavage fluid (BALF) are applied to assess the therapeutic effect of corilagin in mice infected by S. pneumoniae. The results indicate the related genes of corilagin act mainly via enrichment in pathways associated with pneumonia disease. Furthermore, molecular docking and molecular dynamics simulations show that corilagin might bind with domains 3 and 4 of PLY and interfere with its hemolytic activity, which is further confirmed by the site-directed mutagenesis of PLY. Additionally, corilagin limits PLY oligomer production without impacting PLY expression in S. pneumoniae cultures. Moreover, corilagin effectively relieves PLY-mediated cell injury without any cytotoxicity, even then reducing the colony count in the lung and the levels of pro-inflammatory factors in BALF and remarkably improving lung lesions. All the results demonstrate that corilagin may be a novel strategy to cope with S. pneumoniae infection by inhibiting PLY oligomerization.

IL-4 plays an essential role in DnaJ-ΔA146Ply-mediated immunoprotection against Streptococcus pneumoniae in mice

The fusion protein DnaJ-ΔA146Ply is protective against pneumococcal infections in mice. However, we found that immunized IL-4-/- mice showed significant lower survival rates and higher bacterial loads than did wild-type (WT) mice after being challenged. We explored the role of IL-4 in the protective immunity conferred by DnaJ-ΔA146Ply. Our results showed that there were no significant differences in antibody titers between immunized WT mice and IL-4-/- mice. The bacterial loads of passively immunized IL-4-/- mice were significantly higher than those of WT mice, while mice immunized with anti-DnaJ-ΔA146Ply serum from WT and IL-4-/- mice showed similar capacity for bacterial clearance. DnaJ-ΔA146Ply-dependent phagocytosis of IL-4-/- neutrophils was significant decreased compared with that of WT neutrophils. The levels of Syk and phosphor-Syk in IL-4-/- neutrophils were decreased compared with those in WT neutrophils. Additionally, Splenocytes in IL-4-/- mice triggered significantly higher levels of IFN-γ and IL-17A than did splenocytes in WT mice. Taken together, our findings illustrate that IL-4 deficiency does not influence the antibody production or antibody effect, but change the cellular immune response induced by DnaJ-ΔA146Ply. Additionally, IL-4 can enhance the antibody-dependent phagocytosis of neutrophils partially by activating Syk and participate in the protective immunity induced by DnaJ-ΔA146Ply.

The role of flavonoids in inhibiting IL-6 and inflammatory arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease that primarily affects the synovial joints. RA has well-known clinical manifestations and can cause progressive disability and premature death along with socioeconomic burdens. Interleukin-6 (IL-6) has been implicated in the pathology of RA where it can stimulate pannus formation, osteoclastogenesis, and oxidative stress. Flavonoids are plant metabolites with beneficial pharmacological effects, including anti-inflammatory, antioxidant, antidiabetic, anticancer, and others. Flavonoids are polyphenolic compounds found in a variety of plants, vegetables, and fruits. Many flavonoids have demonstrated anti-arthritic activity mediated mainly through the suppression of pro-inflammatory cytokines. This review thoroughly discusses the accumulate data on the role of flavonoids on IL-6 in RA.

Acacetin Alleviates Listeria monocytogenes Virulence Both In Vitro and In Vivo via the Inhibition of Listeriolysin O

Listeria monocytogenes is a ubiquitous Gram-positive foodborne pathogen that is responsible for listeriosis in both humans and several animal species. The bacterium secretes a pore-forming cholesterol-dependent cytolysin, listeriolysin O (LLO), a major virulence factor involved in the activation of cellular processes. The ability of LLO to lyse erythrocytes is a measure of LLO activity. We used hemolytic activity assay to screen the LLO inhibitors. Acacetin was found to be an LLO inhibitor, which is a di-hydroxy and mono-methoxy flavone present in various plants, including Black locust, Damiana, and Silver birch. As the features of acacetin are of low toxicity and have less acquired resistance, it comes to a hotspot in drug development. In our study, we report that acacetin antagonized the hemolytic activity of L. monocytogenes culture supernatants and purified LLO by directly interfering with the formation of oligomers without inhibiting the bacterial growth and the expression of LLO. Acacetin also relieved the injury of alveolar epithelial cells by inhibiting LLO activity. Further, acacetin significantly promoted the clearance of L. monocytogenes and alleviated the histopathological damage, thereby raising survival rate, which conferred mice with effective protection against L. monocytogenes infection. Using molecular docking and dynamics simulation, we further proved the mechanism of acacetin antagonizing LLO pore-forming activity by direct binding to the second membrane-inserting helix bundle (HB2) of LLO domain 3. These data suggested that acacetin recedes the virulence of L. monocytogenes both in vivo and in vitro, and this study provided a promising candidate and potential alternative for the prevention and treatment of L. monocytogenes infections.

"Fei Yan No. 1" as a Combined Treatment for COVID-19: An Efficacy and Potential Mechanistic Study

There has been a large global outbreak of coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), representing a major public health issue. In China, combination therapy, including traditional Chinese medicine (TCM) as a treatment for COVID-19 has been used widely. “Fei Yan No. 1” (QFDYG) is a formula recommended by the Hubei Government to treat COVID-19. A retrospective study of 84 COVID-19 patients from Hubei Provincial Hospital of TCM and Renmin Hospital of Hanchuan was conducted to explore the clinical efficacy of QFDYG combination therapy. TCMSP and YaTCM databases were used to determine the components of all Chinese herbs in QFDYG. Oral bioavailability (OB) ≥ 30% and drug-like (DL) quality ≥ 0.18 were selected as criteria for screening the active compounds identified within the TCMSP database. The targets of active components in QFDYG were determined using the Swiss TargetPrediction (SIB) and Targetnet databases. The STRING database and the Network Analyzer plugin in Cytoscape were used to obtain protein-protein interaction (PPI) network topology parameters and to identify hub targets. Gene Ontology (GO) enrichment was conducted using FunRich version 3.1.3, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment using ClueGO version 2.5.6 software. PPI and compound-pathway (C-T) networks were constructed using Cytoscape 3.6.0. Compared with the control group, combined treatment with QFDYG resulted in a significantly higher rate of patients recovering from symptoms and shorter the time. After 14 days of treatment, QFDYG combined treatment increased the proportion of patients testing negative for SARS-CoV-2 nucleic acid by RT-PCR. Compared with the control group, promoting focal absorption and inflammation as viewed on CT images. GO and KEGG pathway enrichment indicated that QFDYG principally regulated biological processes, such as inflammation, an immune response, and apoptosis. The present study revealed that QFDYG combination therapy offered particular therapeutic advantages, indicating that the theoretical basis for the treatment of COVID-19 by QFDYG may play an antiviral and immune response regulation through multiple components, targets, and pathways, providing reference for the clinical treatment of COVID-19.

Pneumolysin: Pathogenesis and Therapeutic Target

Streptococcus pneumoniae is an opportunistic pathogen responsible for widespread illness and is a major global health issue for children, the elderly, and the immunocompromised population. Pneumolysin (PLY) is a cholesterol-dependent cytolysin (CDC) and key pneumococcal virulence factor involved in all phases of pneumococcal disease, including transmission, colonization, and infection. In this review we cover the biology and cytolytic function of PLY, its contribution to S. pneumoniae pathogenesis, and its known interactions and effects on the host with regard to tissue damage and immune response. Additionally, we review statins as a therapeutic option for CDC toxicity and PLY toxoid as a vaccine candidate in protein-based vaccines.