5-Methoxytryptophan ameliorates endotoxin-induced acute lung injury in vivo and in vitro by inhibiting NLRP3 inflammasome-mediated pyroptosis through the Nrf2/HO-1 signaling pathway.

Endotoxin-induced acute lung injury (ALI) is a complicated and fatal condition with no specific or efficient clinical treatments. 5-Methoxytryptophan (5-MTP), an endogenous metabolite of tryptophan, was revealed to block systemic inflammation. However, the specific mechanism by which 5-MTP affects ALI still needs to be clarified. The purpose of this study was to determine whether 5-MTP protected the lung by inhibiting NLRP3 inflammasome-mediated pyroptosis through the Nrf2/HO-1 signaling pathway. We used lipopolysaccharide (LPS)-stimulated C57BL/6 J mice and MH-S alveolar macrophages to create models of ALI, and 5-MTP (100 mg/kg) administration attenuated pathological lung damage in LPS-exposed mice, which was associated with decreased inflammatory cytokines and oxidative stress levels, upregulated protein expression of Nrf2 and HO-1, and suppressed Caspase-1 activation and NLRP3-mediated pyroptosis protein levels. Moreover, Nrf2-deficient mice or MH-S cells were treated with 5-MTP to further confirm the protective effect of the Nrf2/HO-1 pathway on lung damage. We found that Nrf2 deficiency partially eliminated the beneficial effect of 5-MTP on reducing oxidative stress levels and inflammatory responses and abrogating the inhibition of NLRP3-mediated pyroptosis induced by LPS. These findings suggested that 5-MTP could effectively ameliorate ALI by inhibiting NLRP3-mediated pyroptosis via the Nrf2/HO-1 signaling pathway.

Ma Y ，Wang Z ，Wu X ，Ma Z ，Shi J ，He S ，Li S ，Li X ，Li X ，Li Y ，Yu J ... -  《-》

Paeoniflorin attenuates particulate matter-induced acute lung injury by inhibiting oxidative stress and NLRP3 inflammasome-mediated pyroptosis through activation of the Nrf2 signaling pathway.

Particulate matter (PM), the main component of air pollutants, emerges as a research hotspot, especially in the area of respiratory diseases. Paeoniflorin (PAE), known as anti-inflammatory and immunomodulatory effects, has been reported to alleviate acute lung injury (ALI). However, the effect of PAE on PM-induced ALI and the underlying mechanisms are still unclear yet. In this study, we established the PM-induced ALI model using C57BL/6J mice and BEAS-2B cells to explore the function of PAE. In vivo, mice were intraperitoneally injected with PAE (100 mg/kg) or saline 1 h before instilled with 4 mg/kg PM intratracheally and were euthanized on the third day. For lung tissues, HE staining and TUNEL staining were used to evaluate the degree of lung injury, ELISA assay was used to assess inflammatory mediators and oxidative stress level, Immunofluorescence staining and western blotting were applied to explore the role of pyroptosis and Nrf2 signaling pathway. In vitro, BEAS-2B cells were pretreated with 100 μM PAE before exposure to 200 μg/ml PM and were collected after 24h for the subsequent experiments. TUNEL staining, ROS staining, and western blotting were conducted to explore the underlying mechanisms of PAE on PM-induced ALI. According to the results, PAE can attenuate the degree of PM-induced ALI in mice and reduce PM-induced cytotoxicity in BEAS-2B cells. PAE can relieve PM-induced excessive oxidative stress and NLRP3 inflammasome-mediated pyroptosis. Additionally, PAE can also activate Nrf2 signaling pathway and inhibition of Nrf2 signaling pathway can impair the protective effect of PAE by aggravating oxidative stress and pyroptosis. Our findings demonstrate that PAE can attenuate PM-induced ALI by inhibiting oxidative stress and NLRP3 inflammasome-mediated pyroptosis, which is mediated by Nrf2 signaling pathway.

Zhou W ，Zuo H ，Qian Y ，Miao W ，Chen C ... -  《-》

Inhibition of endotoxin-induced acute lung injury in rats by bone marrow-derived mesenchymal stem cells: Role of Nrf2/HO-1 signal axis in inhibition of NLRP3 activation.

Both the Nuclear factor-erythroid 2 p45-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) antioxidant pathway and Nucleotide-binding oligomerization domain (NOD)-like receptor protein 3 (NLRP3) pathway are considered essential for the development of acute lung injury (ALI)/ARDS induced by sepsis. Our aim was to study the role of Nrf2/HO-1 pathway on activation of the NLRP3 in the protective effect of marrow mesenchymal stem cells (BMSCs) on LPS-induced ALI. We found that BMSCs ameliorated ALI as evidenced by 1) decreased histopathological injury, wet/dry ratio, and protein permeability index in lung; 2) decreased reactive oxygen species (ROS), malondialdehyde (MDA), and protein carbonyl content and restored the activity of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) in lung tissue; 3) reduced LPS-induced increase in inflammatory cell count and promotion of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 levels in bronchoalveolar lavage fluid (BALF); 4) improvement in the four-day survival rate of animals; and 5) enhanced expression of Nrf2 and HO-1 and decreased expression of NOD-like receptor protein 3(NLRP3) and caspase-1 (p20) in lung tissue. Of note, Nrf2 transcription factor inhibitor brusatol and HO-1 inhibitor tin protoporphyrin IX (SnppIX) reversed BMSCs induced down-expression of NLRP3 and caspase-1 (p20), and inhibited the protective effects of BMSCs. These findings demonstrated that the Nrf2-mediated HO-1 signaling pathway plays a critical role in the protective effects of BMSCs on LPS-induced ALI. BMSCs may play an anti-inflammatory effect partly through the Nrf2/HO-1-dependent NLRP3 pathway.

Lei L ，Guo Y ，Lin J ，Lin X ，He S ，Qin Z ，Lin Q ... -  《-》

Melatonin attenuates LPS-induced pyroptosis in acute lung injury by inhibiting NLRP3-GSDMD pathway via activating Nrf2/HO-1 signaling axis.

Acute lung injury (ALI)/ acute respiratory distress syndrome (ARDS) is featured by intensive inflammatory responses and oxidative stress, which lead to cytokine storms and pyroptosis. Here, we aimed to investigate whether melatonin was capable of alleviating LPS-induced ALI via activating the nuclear factor erythroid 2-related factor 2/heme oxygenase 1 (Nrf2/HO-1) signaling axis and inhibiting pyroptosis. Mice were injected with melatonin (30 mg/kg) intraperitoneally for consecutive five days before LPS instillation intratracheally, and human alveolar epithelial cell (AECⅡ) A549 cell lines and murine macrophages Raw264.7 cell lines were pretreated with melatonin (400 μM) before LPS (10 μg/ml) stimulation. The result demonstrated that LPS induced obvious lung injury characterized by alveolar damage, neutrophil infiltration and lung edema as well as the reduction of the survival rate of mice, which were totally reversed by melatonin pretreatment. Mechanistically, melatonin pretreatment activated nuclear factor erythroid2-related factor (Nrf) 2 signaling, subsequently, drove antioxidant pathways including significant increases in the expression of Nrf2, HO-1, NQO1, Mn-SOD and Catalase in vivo and in vitro. Simultaneously, melatonin inhibited ROS and MDA overproduction, iNOS expression as well as TNF-α and IL-1β expression and release. Furthermore, melatonin inhibited LPS-induced pyroptosis by reversing the overexpression of NLRP3, Caspase-1, IL-1β, IL-18 and GSDMD-N, as well as LDH release and TUNEL-positive cells in A549 cells and Raw264.7 cells. Overall, the current study suggests that melatonin exerts protective roles on LPS-induced ALI and pyroptosis by inhibiting NLRP3-GSDMD pathway via activating Nrf2/HO-1 signaling axis.

Kang JY ，Xu MM ，Sun Y ，Ding ZX ，Wei YY ，Zhang DW ，Wang YG ，Shen JL ，Wu HM ，Fei GH ... -  《-》

Tetramethylpyrazine ameliorates endotoxin-induced acute lung injury by relieving Golgi stress via the Nrf2/HO-1 signaling pathway.

Li S ，Xu Y ，He S ，Li X ，Shi J ，Zhang B ，Zhu Y ，Li X ，Wang Y ，Liu C ，Ma Y ，Dong S ，Yu J ... -  《BMC Pulmonary Medicine》