Mode of action of elasnin as biofilm formation eradicator of methicillin-resistant Staphylococcus aureus

Expression of Syo_1.56 SARP Regulator Unveils Potent Elasnin Derivatives with Antibacterial Activity

Actinomycetes are prolific producers of natural products, particularly antibiotics. However, a significant proportion of its biosynthetic gene clusters (BGCs) remain silent under typical laboratory conditions. This limits the effectiveness of conventional isolation methods for the discovery of novel natural products. Genetic interventions targeting the activation of silent gene clusters are necessary to address this challenge. Streptomyces antibiotic regulatory proteins (SARPs) act as cluster-specific activators and can be used to target silent BGCs for the discovery of new antibiotics. In this study, the expression of a previously uncharacterized SARP protein, Syo_1.56, in Streptomyces sp. RK18-A0406 significantly enhanced the production of known antimycins and led to the discovery of 12 elasnins (1-12), 10 of which were novel. The absolute stereochemistry of elasnin A1 was assigned for the first time to be 6S. Unexpectedly, Syo_1.56 seems to function as a pleiotropic rather than cluster-specific SARP regulator, with the capability of co-regulating two distinct biosynthetic pathways, simultaneously. All isolated elasnins were active against wild-type and methicillin-resistant Staphylococcus aureus with IC50 values of 0.5-20 μg/mL, some of which (elasnins A1, B2, and C1 and proelasnins A1, and C1) demonstrated moderate to strong antimalarial activities against Plasmodium falciparum 3D7. Elasnins A1, B3, and C1 also showed in vitro inhibition of the metallo-β-lactamase responsible for the development of highly antibiotic-resistant bacterial strains.

Liposomal Rifabutin-A Promising Antibiotic Repurposing Strategy against Methicillin-Resistant Staphylococcus aureus Infections

Methicillin-resistant Staphylococcus aureus (M RSA) infections, in particular biofilm-organized bacteria, remain a clinical challenge and a serious health problem. Rifabutin (RFB), an antibiotic of the rifamycins class, has shown in previous work excellent anti-staphylococcal activity. Here, we proposed to load RFB in liposomes aiming to promote the accumulation of RFB at infected sites and consequently enhance the therapeutic potency. Two clinical isolates of MRSA, MRSA-C1 and MRSA-C2, were used to test the developed formulations, as well as the positive control, vancomycin (VCM). RFB in free and liposomal forms displayed high antibacterial activity, with similar potency between tested formulations. In MRSA-C1, minimal inhibitory concentrations (MIC) for Free RFB and liposomal RFB were 0.009 and 0.013 μg/mL, respectively. Minimum biofilm inhibitory concentrations able to inhibit 50% biofilm growth (MBIC50) for Free RFB and liposomal RFB against MRSA-C1 were 0.012 and 0.008 μg/mL, respectively. Confocal microscopy studies demonstrated the rapid internalization of unloaded and RFB-loaded liposomes in the bacterial biofilm matrix. In murine models of systemic MRSA-C1 infection, Balb/c mice were treated with RFB formulations and VCM at 20 and 40 mg/kg of body weight, respectively. The in vivo results demonstrated a significant reduction in bacterial burden and growth index in major organs of mice treated with RFB formulations, as compared to Control and VCM (positive control) groups. Furthermore, the VCM therapeutic dose was two fold higher than the one used for RFB formulations, reinforcing the therapeutic potency of the proposed strategy. In addition, RFB formulations were the only formulations associated with 100% survival. Globally, this study emphasizes the potential of RFB nanoformulations as an effective and safe approach against MRSA infections.

The biofilm proteome of Staphylococcus aureus and its implications for therapeutic interventions to biofilm-associated infections

Staphylococcus aureus is a major healthcare concern due to its ability to inflict life-threatening infections and evolve antibiotic resistance at an alarming pace. It is frequently associated with hospital-acquired infections, especially device-associated infections. Systemic infections due to S. aureus are difficult to treat and are associated with significant mortality and morbidity. The situation is worsened by the ability of S. aureus to form social associations called biofilms. Biofilms embed a community of cells with the ability to communicate with each other and share resources within a polysaccharide or protein matrix. S. aureus establish biofilms on tissues and conditioned abiotic surfaces. Biofilms are hyper-tolerant to antibiotics and help evade host immune responses. Biofilms exacerbate the severity and recalcitrance of device-associated infections. The development of a biofilm involves various biomolecules, such as polysaccharides, proteins and nucleic acids, contributing to different structural and functional roles. Interconnected signaling pathways and regulatory molecules modulate the expression of these molecules. A comprehensive understanding of the molecular biology of biofilm development would help to devise effective anti-biofilm therapeutics. Although bactericidal agents, antimicrobial peptides, bacteriophages and nano-conjugated anti-biofilm agents have been employed with varying levels of success, there is still a requirement for effective and clinically viable anti-biofilm therapeutics. Proteins that are expressed and utilized during biofilm formation, constituting the biofilm proteome, are a particularly attractive target for anti-biofilm strategies. The proteome can be explored to identify potential anti-biofilm drug targets and utilized for rational drug discovery. With the aim of uncovering the biofilm proteome, this chapter explores the mechanism of biofilm formation and its regulation. Furthermore, it explores the antibiofilm therapeutics targeted against the biofilm proteome.

Pterosin sesquiterpenoids from Pteris laeta Wall. ex Ettingsh. protect cells from glutamate excitotoxicity by modulating mitochondrial signals

ETHNOPHARMACOLOGICAL RELEVANCE

The genus Pteris (Pteridaceae) has been used as a traditional herb for a long time. In particular, Pteris laeta Wall. ex Ettingsh. has been widely used in traditional Chinese medicine to treat nervous system diseases and some pterosin sesquiterpenes from Pteris show neuroprotective activity, but their underlying molecular mechanisms remain elusive. Therefore, to investigate the neuroprotective activity and working mechanism of pterosin sesquiterpenes from P. laeta Wall. ex Ettingsh. will provide a better understanding and guidance in using P. laeta Wall. ex Ettingsh. as a traditional Chinese medicine.

AIM OF THE STUDY

We aim to develop effective treatments for neurodegenerative diseases from pterosin sesquiterpenes by evaluating their neuroprotective activity and investigating their working mechanisms.

MATERIALS AND METHODS

Primary screening on the glutamate-induced excitotoxicity cell model was assessed by 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) assay. Fluorescent-activated cell sorting (FACS) was used to analyze the activation level of glutamate receptors and mitochondria membrane potential after treatment. Transcriptomics and proteomics analysis was performed to identify possible targets of pterosin B. The key pathways were enriched by the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis through the Database for Annotation, Visualization, and Integrated Discovery (DAVID). The core targets were visualized by a protein-protein interaction network using STRING. The mRNA and protein expressions were evaluated using real-time quantitative polymerase chain reaction (Q-PCR) and western blot, respectively. Immunocytochemistry was performed to monitor mitochondrial and apoptotic proteins. Cellular reactive oxygen species (ROS) were measured by ROS assay, and Ca²⁺ was stained with Fluo-4 AM to quantify intracellular Ca²⁺ levels.

RESULTS

We found pterosin B from Pteris laeta Wall. ex Ettingsh. showed significant neuroprotective activity against glutamate excitotoxicity, enhancing cell viability from 43.8% to 105% (p-value: <0.0001). We demonstrated that pterosin B worked on the downstream signaling pathways of glutamate excitotoxicity rather than directly blocking the activation of glutamate receptors. Pterosin B restored mitochondria membrane potentials, alleviated intracellular calcium overload from 107.4% to 95.47% (p-value: 0.0006), eliminated cellular ROS by 36.55% (p-value: 0.0143), and partially secured cells from LPS-induced inflammation by increasing cell survival from 46.75% to 58.5% (p-value: 0.0114). Notably, pterosin B enhanced the expression of nuclear factor-erythroid factor 2-related factor 2 (NRF2) and heme oxygenase-1 (HO-1) by 2.86-fold (p-value: 0.0006) and 4.24-fold (p-value: 0.0012), and down-regulated Kelch-like ECH-associated protein 1 (KEAP1) expression by 2.5-fold (p-value: 0.0107), indicating that it possibly promotes mitochondrial biogenesis and mitophagy to maintain mitochondria quality control and homeostasis, and ultimately inhibits apoptotic cell death.

CONCLUSIONS

Our work revealed that pterosin B protected cells from glutamate excitotoxicity by targeting the downstream mitochondrial signals, making it a valuable candidate for developing potential therapeutic agents in treating neurodegenerative diseases.