Salvinorin A protects against methicillin resistant staphylococcus aureus-induced acute lung injury via Nrf2 pathway

IL-9 promotes methicillin-resistant Staphylococcus aureus pneumonia by regulating the polarization and phagocytosis of macrophages

In this study, we examined the effect of Il9 deletion on macrophages in methicillin-resistant Staphylococcus aureus (MRSA) infection. MRSA-infected mice were employed for the in vivo experiments, and RAW264.7 cells were stimulated with MRSA for the in vitro experiments. Macrophage polarization was determined by flow cytometry and quantitative real-time PCR; macrophage phagocytosis was assessed by flow cytometry and laser scanning confocal microscopy; cell apoptosis was assessed by flow cytometry and western blotting. Il9 deletion markedly elevated macrophage phagocytosis and M2 macrophages in MRSA infection, which was accompanied by elevated expression of Il10 and Arg1 and reduced expression of Inos, tumor necrosis factor-α (Tnfα), and Il6. Il9 deletion also inhibited macrophage apoptosis in MRSA infection, which was manifested by elevated B-cell lymphoma 2 (BCL-2) protein level and reduced protein levels of cleaved cysteine protease 3 (CASPASE-3) and BCL2-Associated X (BAX). Both the in vivo and in vitro experiments further showed the activation of phosphoinositide 3-kinase (PI3K)/AKT (also known as protein kinase B, PKB) signaling pathway in MRSA infection and that the regulation of Il9 expression may be dependent on Toll-like receptor (TLR) 2/PI3K pathway. The above results showed that Il9 deletion exhibited a protective role against MRSA infection by promoting M2 polarization and phagocytosis of macrophages and the regulation of Il9 partly owing to the activation of TLR2/PI3K pathway, proposing a novel therapeutic strategy for MRSA-infected pneumonia.

Glycyrrhetinic acid prevents carbapenem-resistant Klebsiella pneumoniae-induced cell injury by inhibiting mitochondrial dysfunction via Nrf-2 pathway

OBJECTIVES

Due to the abuse of antibiotics, the high reoccurrence of drug-resistance strains, such as carbapenem-resistant Klebsiella pneumoniae (CRKP), deteriorates CRKP-infected pneumonia in the clinic, suggesting it is necessary to find new alternatives. Glycyrrhetinic acid (GA), an active ingredient of Yinhuapinggan granule, has antioxidant & anti-inflammatory capacity. Little, however, is known about the effects of GA on CRKP-induced epithelial injury.

METHODS

In this research, we examined the protective effects of GA against pulmonary epithelium damage caused by CRKP infection and potential molecular mechanisms.

RESULTS

Our results noted GA significantly promoted cell survival and reduced pro-inflammatory cytokines production, during CRKP-induced human pulmonary epithelial cell. Mechanically, GA alleviated mitochondrial-damage-induced apoptosis amid CRKP infection by inhibiting mitochondrial damage. Additionally, we found GA inhibited the expression of pro-apoptotic proteins Cyto-c, the Bax, and Caspase-3 while increasing the expression of anti-apoptotic protein Bcl-2. Further exploration found GA could trigger Nrf-2 expression at both gene and protein levels, activating antioxidative proteins to diminish CRKP-induced oxidative stress.

CONCLUSION

Together, our results demonstrated that GA was a promising candidate to alleviate CRKP-infected lung injury as well as a synergist to treat CRKP infection with antibiotics.

Dehydrocostus Lactone Attenuates Methicillin-Resistant Staphylococcus aureus-Induced Inflammation and Acute Lung Injury via Modulating Macrophage Polarization

Dehydrocostus lactone (DHL), a natural sesquiterpene lactone isolated from the traditional Chinese herbs Saussurea lappa and Inula helenium L., has important anti-inflammatory properties used for treating colitis, fibrosis, and Gram-negative bacteria-induced acute lung injury (ALI). However, the effects of DHL on Gram-positive bacteria-induced macrophage activation and ALI remains unclear. In this study, we found that DHL inhibited the phosphorylation of p38 MAPK, the degradation of IκBα, and the activation and nuclear translocation of NF-κB p65, but enhanced the phosphorylation of AMP-activated protein kinase (AMPK) and the expression of Nrf2 and HO-1 in lipoteichoic acid (LTA)-stimulated RAW264.7 cells and primary bone-marrow-derived macrophages (BMDMs). Given the critical role of the p38 MAPK/NF-κB and AMPK/Nrf2 signaling pathways in the balance of M1/M2 macrophage polarization and inflammation, we speculated that DHL would also have an effect on macrophage polarization. Further studies verified that DHL promoted M2 macrophage polarization and reduced M1 polarization, then resulted in a decreased inflammatory response. An in vivo study also revealed that DHL exhibited anti-inflammatory effects and ameliorated methicillin-resistant Staphylococcus aureus (MRSA)-induced ALI. In addition, DHL treatment significantly inhibited the p38 MAPK/NF-κB pathway and activated AMPK/Nrf2 signaling, leading to accelerated switching of macrophages from M1 to M2 in the MRSA-induced murine ALI model. Collectively, these data demonstrated that DHL can promote macrophage polarization to an anti-inflammatory M2 phenotype via interfering in p38 MAPK/NF-κB signaling, as well as activating the AMPK/Nrf2 pathway in vitro and in vivo. Our results suggested that DHL might be a novel candidate for treating inflammatory diseases caused by Gram-positive bacteria.

Itaconate ameliorates methicillin-resistant Staphylococcus aureus-induced acute lung injury through the Nrf2/ARE pathway

Background

Methicillin-resistant Staphylococcus aureus (MRSA) are a critical predisposing factor of sepsis in the clinic. As a product of human energy metabolism and immune response, itaconate can effectively reduce inflammation in the body. This research employed 4-octyl itaconate (4-OI) to illustrate that itaconate exerted anti-inflammatory effects to protect the body from acute lung injury (ALI) induced by MRSA.

Methods

HE staining and immunohistochemistry are used to evaluate the MRSA-induced ALI in mice. WB and qPCR were used to verify the effect of 4-OI on inflammation and oxidative stress caused by MRSA. Molecular docking was used to verify the binding sites of 4-OI and Keap1.

Results

We demonstrated that 4-OI treatment increased the survival ratio, attenuated the pathological damage, inhibited neutrophil infiltration, and reduced lung bacterial burden in the mouse MRSA pneumonia model. 4-OI decreased the expression of inflammatory factors by stimulating the Nrf2 in vivo and in vitro. Furthermore, 4-OI exerted its effect by promoting nuclear transport of Nrf2 in vitro. The results of molecular docking indicated that 4-OI bound to the pocket of Keap1 and exerted a stable interaction. Both Nrf2 inhibitors (ML385) and Nrf2^−/− mice abolished the protective effect of 4-OI on MRSA-induced inflammation both in vitro and in vivo.

Conclusions

4-OI prevents lung damage caused by MRSA bacteremia via activating Nrf2/ARE pathway.