The protection effect of rhodionin against methicillin-resistant Staphylococcus aureus-induced pneumonia through sortase A inhibition.

Methicillin-resistant Staphylococcus aureus (MRSA) is a zoonotic antibiotic-resistant pathogen that negatively impacts society from medical, veterinary, and societal standpoints. The search for alternative therapeutic strategies and innovative anti-infective agents is urgently needed. Among the pathogenic mechanisms of Staphylococcus aureus (S. aureus), sortase A is a virulence factor of great concern because it is highly linked with the ability of MRSA to invade the host. In this study, we identified that rhodionin, a natural compound of flavonoid glucosides, effectively inhibited the activity of SrtA without affecting the survival and growth of bacteria, and its half maximal inhibitory concentration (IC50) value was 22.85 µg/mL. In vitro, rhodionin prominently attenuated the virulence-related phenotype of SrtA by reducing the adhesion of S. aureus to fibrinogen, reducing the capacity of protein A (SpA) on the bacterial surface and biofilm formation. Subsequently, fluorescence quenching and molecular docking were performed to verify that rhodionin directly bonded to SrtA molecule with KA value of 6.22 × 105 L/mol. More importantly, rhodionin showed a significant protective effect on mice pneumonia model and improved the survival rate of mice. According to the above findings, rhodionin achieved efficacy in the treatment of MRSA-induced infections, which holds promising potential to be developed into a candidate used for MRSA-related infections.

Cyanidin chloride protects mice from methicillin-resistant Staphylococcus aureus-induced pneumonia by targeting Sortase A.

Methicillin-resistant Staphylococcus aureus (MRSA) has been developing rapidly in recent years. It poses a severe peril to global health care, and the new strategies to against the MRSA is urgently needed. Sortase A (SrtA) regulates the anchoring of many surface proteins. Compounds repress Staphylococcus aureus (S. aureus) cysteine transpeptidase SrtA are considered adequate potent virulence inhibitors. Then, we describe the identification of an effective SrtA inhibitor, cyanidin chloride, a bioflavonoid compound isolated from various plants. It has a reversible inhibitory effect on SrtA activity at an IC50 of 21.91 µg/mL. As a SrtA inhibitor, cyanidin chloride antagonizes SrtA-related virulence phenotypes due to its breadth and specificity, including fibrinogen adhesion, A549 cell invasion, biofilm formation, and surface protein (SpA) anchoring. Subsequently, molecular docking and fluorescence quenching revealed that SrtA and cyanidin chloride had robust mutual affinity. Further mechanistic studies revealed that Arg-197, Gly-167, and Sep-116 were the key-binding sites mediating the interaction between SrtA and cyanidin chloride. Notably, a significant therapeutic effect of cyanidin chloride in vivo was also observed on the mouse pneumonia model induced by MRSA. In conclusion, our study indicates that cyanidin chloride potentially represents a new candidate SrtA inhibitor for S. aureus and potentially be developed as a new antivirulence agent.

7,8-Dihydroxyflavone attenuates the virulence of Staphylococcus aureus by inhibiting alpha-hemolysin.

Staphylococcus aureus (S. aureus), a Gram-positive bacteria, is an incurable cause of hospital and community-acquired infections. Inhibition bacterial virulence is a viable strategy against S. aureus infections based on the multiple virulence factors secreted by S. aureus. Alpha-hemolysin (Hla) plays a crucial role in bacteria virulence without affecting bacterial viability. Here, we identified that 7,8-Dihydroxyflavone (7,8-DHF), a natural compound, was able to decrease the expression of and did not affect the in vitro growth of S. aureus USA300 at a concentration of 32 µg/mL. It was verified by western blot and RT-qPCR that the natural compound could inhibit the transcription and translation of Hla. Further mechanism studies revealed that 7,8-DHF has a negative effect on transcriptional regulator agrA and RNAIII, preventing the upregulation of virulence gene. Cytotoxicity assays showed that 7,8-DHF did not produce significant cytotoxicity to A549 cells. Animal experiments showed that the combination of 7,8-DHF and vancomycin had a more significant therapeutic effect on S. aureus infection, reflecting the synergistic effect of 7,8-DHF with antibiotics. In conclusion, 7,8-DHF was able to target Hla to protect host cells from hemolysis while limiting the development of bacterial resistance.

Tamarixetin Attenuated the Virulence of Staphylococcus aureus by Directly Targeting Caseinolytic Protease P.

Staphylococcus aureus, especially drug-resistant S. aureus infections, is a worldwide healthcare challenge. There is a growing focus on antivirulence therapy against S. aureus. Caseinolytic protease p (ClpP) is a protein hydrolase essential for pathogenicity in S. aureus. A flavonoid compound, tamarixetin, which was screened in this work, was specifically able to inhibit the hydrolytic activity of ClpP on the fluorescent substrate Suc-LY-AMC with an IC50 of 49.73 µM, without affecting the growth of methicillin-resistant S. aureus strain USA300 and was without obvious cytotoxicity. Further assays found that tamarixetin inhibited the transcription of hla, agr, RNAIII, pvl, PSM-α, and spa genes as well as suppressed the protein expression levels of Hla and PVL. Moreover, tamarixetin was observed to dramatically inhibit the hemolytic activity of hla in S. aureus. Consistent with that of S. aureus USA300-ΔclpP, tamarixetin was shown to increase urease expression. The thermal shift and cellular thermal shift assays showed that tamarixetin markedly changed the thermal stability of ClpP. The dissociation constant (KD) value of tamarixetin with ClpP was 2.52 × 10-6 M measured by surface plasmon resonance. The molecular docking and ClpP point mutation results also demonstrated that tamarixetin had a strong interaction with ClpP. In vivo study showed that tamarixetin was effective in protecting mice from S. aureus pneumonia by increasing survival, reducing lung tissue load, and slowing down the infiltration of inflammatory factors. In addition, tamarixetin was able to enhance the antibacterial activity of cefotaxime in combination. In conclusion, tamarixetin was promising as a ClpP inhibitor for S. aureus infections.

Hinokiflavone Attenuates the Virulence of Methicillin-Resistant Staphylococcus aureus by Targeting Caseinolytic Protease P.

Drug-resistant bacteria was the third leading cause of death worldwide in 2019, which sounds like a cautionary note for global public health. Therefore, developing novel strategies to combat Methicillin-resistant Staphylococcus aureus (MRSA) infections is the need of the hour. Caseinolytic protease P (ClpP) represents pivotal microbial degradation machinery in MRSA involved in bacterial homeostasis and pathogenicity, considered an ideal target for combating S. aureus infections. Herein, we identified a natural compound, hinokiflavone, that inhibited the activity of ClpP of MRSA strain USA300 with an IC50 of 34.36 µg/mL. Further assays showed that hinokiflavone reduced the virulence of S. aureus by inhibiting multiple virulence factors expression. Results obtained from cellular thermal transfer assay (CETSA), thermal shift assay (TSA), local surface plasmon resonance (LSPR) and molecular docking (MD) assay enunciated that hinokiflavone directly bonded to ClpP with confirmed docking sites, including SER-22, LYS-26 and ARG-28. In vivo, the evaluation of anti-infective activity showed that hinokiflavone in combination with vancomycin effectively protected mice from MRSA-induced fatal pneumonia, which was more potent than vancomycin alone. As mentioned above, hinokiflavone, as an inhibitor of ClpP, could be further developed into a promising adjuvant against S. aureus infections.

Scutellarin potentiates vancomycin against lethal pneumonia caused by methicillin-resistant Staphylococcus aureus through dual inhibition of sortase A and caseinolytic peptidase P.

The strategy of targeting virulence factor has received great attention as it barely develops bacterial resistance. Sortase A (SrtA) and caseinolytic peptidase P (ClpP), as important virulence factors, are considered to be ideal pharmacological targets for methicillin-resistant Staphylococcus aureus (MRSA) infection. Through screening hundreds of compounds, we found scutellarin, a natural flavonoid, markedly inhibited SrtA and ClpP activities of MRSA strain USA300 with an IC50 of 53.64 µg/mL and 107.00 µg/mL, respectively. Subsequently, we observed that scutellarin could inhibit the SrtA-related virulence of MRSA. To demonstrate whether scutellarin directly binding to SrtA, fluorescence quenching assay and molecular docking were performed and the results indicated that scutellarin directly bonded to SrtA molecule with a KA value of 7.58 × 104 L/mol. In addition to direct SrtA inhibition, scutellarin could also inhibit hemolytic activity of S. aureus by inhibiting the expression of Hla in a SrtA-independent manner. Further assays confirmed that scutellarin inhibited hemolysis by inhibiting ClpP. The combination of scutellarin and vancomycin showed enhancing inhibition of USA300 in vitro and in vivo, evidenced by decreased MIC from 3 µg/mL to 0.5 µg/mL and increased survival and improvement of lung pathology in pneumonia mice. Taken together, these results suggest that scutellarin exhibited di-inhibitory effects on SrtA and ClpP of USA300. The di-inhibition of virulence factors by scutellarin combined with vancomycin to prevent MRSA invasion of A549 cells and pneumonia in mice, indicating that scutellarin is expected to be a potential adjuvant against MRSA in the future.

Analysis of Long Noncoding RNAs in Aila-Induced Non-Small Cell Lung Cancer Inhibition.

Non-small cell lung cancer (NSCLC) has the highest morbidity and mortality among all carcinomas. However, it is difficult to diagnose in the early stage, and current therapeutic efficacy is not ideal. Although numerous studies have revealed that Ailanthone (Aila), a natural product, can inhibit multiple cancers by reducing cell proliferation and invasion and inducing apoptosis, the mechanism by which Aila represses NSCLC progression in a time-dependent manner remains unclear. In this study, we observed that most long noncoding RNAs (lncRNAs) were either notably up- or downregulated in NSCLC cells after treatment with Aila. Moreover, alterations in lncRNA expression induced by Aila were crucial for the initiation and metastasis of NSCLC. Furthermore, in our research, expression of DUXAP8 was significantly downregulated in NSCLC cells after treatment with Aila and regulated expression levels of EGR1. In conclusion, our findings demonstrate that Aila is a potent natural suppressor of NSCLC by modulating expression of DUXAP8 and EGR1.