Melatonin prevents LPS-induced epithelial-mesenchymal transition in human alveolar epithelial cells via the GSK-3β/Nrf2 pathway

Nrf-2 as a novel target in radiation induced lung injury

Radiation-induced lung injury (RILI) is a common and fatal complication of chest radiotherapy. The underlying mechanisms include radiation-induced oxidative stress caused by damage to the deoxyribonucleic acid (DNA) and production of reactive oxygen species (ROS), resulting in apoptosis of lung and endothelial cells and recruitment of inflammatory cells and myofibroblasts expressing NADPH oxidase to the site of injury, which in turn contribute to oxidative stress and cytokine production. Nuclear factor erythroid 2-related factor 2 (Nrf-2) is a vital transcription factor that regulates oxidative stress and inhibits inflammation. Studies have shown that Nrf-2 protects against radiation-induced lung inflammation and fibrosis. This review discusses the protective role of Nrf-2 in RILI and its possible mechanisms.

Melatonin prevents pulmonary fibrosis caused by PM2.5 exposure by targeting epithelial-mesenchymal transition

Pulmonary fibrosis is a lung disorder characterized by the accumulation of abnormal extracellular matrix, scar tissue formation, and tissue stiffness. Type II alveolar epithelial cells (AEII) play a critical role in repairing lung tissue after injury, and repeated injury to these cells is a key factor in the development of pulmonary fibrosis. Chronic exposure to PM2.5, a type of air pollution, has been shown to increase the incidence and severity of pulmonary fibrosis by enhancing the activation of EMT in lung epithelial cells. Melatonin, a hormone with antioxidant properties, has been shown to prevent EMT and reduce fibrosis in previous studies. However, the mechanism through which melatonin targets EMT to prevent pulmonary fibrosis caused by PM2.5 exposure has not been extensively discussed before. In this current study, we found that melatonin effectively prevented pulmonary fibrosis caused by prolonged exposure to PM2.5 by targeting EMT. The study demonstrated changes in cellular morphology and expression of EMT markers. Furthermore, the cell migratory potential induced by prolonged exposure to PM2.5 was greatly reduced by melatonin treatment. Finally, in vivo animal studies showed reduced EMT markers and improved pulmonary function. These findings suggest that melatonin has potential clinical use for the prevention of pulmonary fibrosis.

Comprehensive review of potential drugs with anti-pulmonary fibrosis properties

Pulmonary fibrosis is a chronic and progressive lung disease characterized by the accumulation of scar tissue in the lungs, which leads to impaired lung function and reduced quality of life. The prognosis for idiopathic pulmonary fibrosis (IPF), which is the most common form of pulmonary fibrosis, is generally poor. The median survival for patients with IPF is estimated to be around 3-5 years from the time of diagnosis. Currently, there are two approved drugs (Pirfenidone and Nintedanib) for the treatment of IPF. However, Pirfenidone and Nintedanib are not able to reverse or cure pulmonary fibrosis. There is a need for new pharmacological interventions that can slow or halt disease progression and cure pulmonary fibrosis. This review aims to provide an updated overview of current and future drug interventions for idiopathic pulmonary fibrosis, and to summarize possible targets of potential anti-pulmonary fibrosis drugs, providing theoretical support for further clinical combination therapy or the development of new drugs.

Mechanisms of LPS-induced epithelial mesenchymal transition in bEECs

High-concentrate diets cause subacute ruminal acidosis, resulting in increased blood lipopolysaccharide (LPS) levels in cows. We found that the peak LPS in cows fed with high-concentrate diets coincides the period of embryo implantation in a large-scale dairy farm. As epithelial-mesenchymal transition (EMT) should be tightly regulated during normal embryo implantation in cows, we speculated that increased LPS may cause abnormal EMT, thereby inhibiting embryo implantation in cows. To confirm that elevated LPS levels induce abnormal EMT in cows, we treated bovine endometrial epithelial cells (bEECs) with LPS for 48 h and analyzed the protein levels of ZEB1, a major EMT-related transcription factor, which is positively regulated by the TGFβ/SMAD3 pathway. In addition, we analyzed the changes in expression of three EMT-related genes (E-cadherin, N-cadherin, and Vimentin), and examined the morphology and migratory ability of the cells. The results showed that elevated LPS levels increased protein expression of ZEB1, vimentin, and N-cadherin, and reduced that of E-cadherin. Elevated LPS also increased bEECs migration rate, and induced the cells to acquire a mesenchymal phenotype. Furthermore, benzyl butyl phthalate (BBP)-induced ZEB1 overexpression significantly decreased E-cadherin levels and increased N-cadherin levels. As LPS treatment also decreased the expression of Bta-miR-200b, we further found that Bta-miR-200b targets to the 3'UTR of ZEB1 through the confirmation of dual-luciferase reporter system. And the increased level of Bta-miR-200b by mimic enhanced the expression of E-cadherin and yet inhibited the expression of N-cadherin in protein, which exactly opposite to the results induced by LPS. In conclusion, LPS induced EMT in bEECs by upregulating ZEB1, while Bta-miR-200b could inhibit the occurrence of EMT by binding ZEB1 3'UTR. These results provide a new insight for low reproductive rate of dairy cows under the background of high-concentrate diets.

Isorhamnetin suppresses the epithelial-mesenchymal transition of the retinal pigment epithelium both in vivo and in vitro through Nrf2-dependent AKT/GSK-3β pathway

Age-related macular degeneration (AMD) is a major cause of blindness in the elderly worldwide. Multiple studies have shown that epithelial-mesenchymal transition (EMT) plays a pivotal role in the pathogenesis of AMD. Isorhamnetin (Isor) is a flavonoid compound that inhibits EMT in tumor cells. However, whether it can also attenuate EMT in the retinal pigment epithelium (RPE) is unknown. Therefore, our study was designed to probe the possible impact of Isor on EMT process in both mouse retina and ARPE-19 cells. C57BL/6 mice were utilized to establish a dry AMD model. Isor and LCZ (a mixture of luteine/β-carotene/zinc gluconate) were administered orally for 3 months. The effects of Isor on the retina were evaluated using fundus autofluorescence, optical coherence tomography, and transmission electron microscopy. Transwell and wound healing assay were employed to assess ARPE-19 cell migration. Western blotting and immunofluorescence were used to measure the protein expressions associated with EMT, Nrf2 and AKT/GSK-3β pathway. The findings indicated that Isor alleviated dry AMD-like pathological changes in vehicle mice retina, inhibited the migration of Ox-LDL-treated ARPE-19 cells, and repressed the EMT processes in vivo and in vitro. Furthermore, Isor activated Nrf2 pathway and deactivated AKT/GSK-3β pathway in both vehicle mice and ARPE-19 cells. Interestingly, when Nrf2 siRNA was transfected into ARPE-19 cells, the inhibitory effect of Isor on EMT and AKT/GSK-3β pathway was attenuated. These results suggested that Isor inhibited EMT processes via Nrf2-dependent AKT/GSK-3β pathway and is a promising candidate for dry AMD treatment.

Therapeutic potential of melatonin in targeting molecular pathways of organ fibrosis

Fibrosis, the excessive deposition of fibrous connective tissue in an organ in response to injury, is a pathological condition affecting many individuals worldwide. Fibrosis causes the failure of tissue function and is largely irreversible as the disease progresses. Pharmacologic treatment options for organ fibrosis are limited, but studies suggest that antioxidants, particularly melatonin, can aid in preventing and controlling fibrotic damage to the organs. Melatonin, an indole nocturnally released from the pineal gland, is commonly used to regulate circadian and seasonal biological rhythms and is indicated for treating sleep disorders. While it is often effective in treating sleep disorders, melatonin's anti-inflammatory and antioxidant properties also make it a promising molecule for treating other disorders such as organ fibrosis. Melatonin ameliorates the necrotic and apoptotic changes that lead to fibrosis in various organs including the heart, liver, lung, and kidney. Moreover, melatonin reduces the infiltration of inflammatory cells during fibrosis development. This article outlines the protective effects of melatonin against fibrosis, including its safety and potential therapeutic effects. The goal of this article is to provide a summary of data accumulated to date and to encourage further experimentation with melatonin and increase its use as an anti-fibrotic agent in clinical settings.

Guggulsterone protects against lipopolysaccharide-induced inflammation and lethal endotoxemia via heme oxygenase-1

Guggulsterone (GS) is a phytosterol used to treat inflammatory diseases. Although many studies have examined the anti-inflammatory activities of GS, the detailed mechanisms of GS in lipopolysaccharide (LPS)-induced inflammation and endotoxemia have not yet been examined. Therefore, we investigated the anti-inflammatory effects of GS on LPS-induced inflammation. In murine peritoneal macrophages, the anti-inflammatory activity of GS was primarily mediated by heme oxygenase-1 (HO-1) induction. HO-1 induction by GS was mediated by GSH depletion and reactive oxygen species (ROS) production. The ROS generated by GS caused the phosphorylation of GSK3β (ser9/21) and p38, leading to the translocation of nuclear factor erythroid-related factor 2 (Nrf2), which ultimately induced HO-1. In addition, GS pretreatment significantly inhibited inducible nitric oxide synthase (iNOS), iNOS-derived NO, and COX-2 protein and mRNA expression, and production of COX-derived prostaglandin PGE2, interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α). In a mouse model of endotoxemia, GS treatment prolonged survival and inhibited the expression of inflammatory mediators, including IL-1β, IL-6, and TNF-α. GS treatment also inhibited LPS-induced liver injury. These results suggest that GS-induced HO-1 could exert anti-inflammatory effects via ROS-dependent GSK (ser21/9)-p38 phosphorylation and nuclear translocation of Nrf2.

Cyasterone ameliorates sepsis-related acute lung injury via AKT (Ser473)/GSK3β (Ser9)/Nrf2 pathway

BACKGROUND

Acute lung injury (ALI) is a severe disease that can lead to acute respiratory distress syndrome (ARDS), characterized by intractable hypoxemia, poor lung compliance, and respiratory failure, severely affecting patients' quality of life. The pathogenesis of ALI has not been fully elucidated yet, and sepsis is an important cause of ALI. Among the organ injuries caused by sepsis, the lungs are the earliest damaged ones. Radix cyathulae is reported to have analgesic, anti-inflammatory, and anti-aging effects. Cyasterone is extracted from Radix cyathulae. However, it is not known whether cyasterone has protective effects for ALI. This study aims to investigate the effect of cyasterone on sepsis-related ALI and its mechanism.

METHODS

We used the cecal ligation peferation (CLP) method to establish a mouse sepsis model, and cyasterone was given intraperitoneally on days 1-3 to observe its preventive effect on sepsis-related acute lung injury. Primary murine peritoneal macrophages were used to investigate the molecular mechanism of cyasterone in vitro.

RESULTS

Cyasterone pretreatment inhibits pro-inflammatory cytokine production, NLRP3 inflammasome activation, and oxidative stress in vivo and in vitro. In addition, cyasterone attenuates sepsis-induced ALI by activating nuclear factor erythroid2-related factor (Nrf2), which may be associated with AKT(Ser473)/GSK3β(Ser9) pathway activation.

CONCLUSIONS

Cyasterone defends against sepsis-induced ALI by inhibiting inflammatory responses and oxidative stress, which depends heavily on the upregulation of the Nrf2 pathway through phosphorylation of AKT(Ser473)/GSK3β(Ser9). These results suggest cyasterone may be a valuable drug candidate for preventing sepsis-related ALI.

The melatonin agonist ramelteon attenuates bleomycin-induced lung fibrosis by suppressing the NLRP3/TGF-Β1/HMGB1 signaling pathway

PURPOSE

The possible effects of ramelteon, a melatonin receptor agonist on bleomycin-induced lung fibrosis were analyzed via transforming growth factor β1 (TGF-β1), the high mobility group box 1 (HMGB1) and Nod-like receptor pyrin domain-containing 3 (NLRP3) which are related to the fibrosis process.

MATERIALS AND METHODS

Bleomycin (0.1 ​mL of 5 ​mg/kg) was administered by intratracheal instillation to induce pulmonary fibrosis (PF). Starting 24 ​h after bleomycin administration, a single dose of ramelteon was administered by oral gavage to the healthy groups, i.e. PF ​+ ​RM2 (pulmonary fibrosis model with bleomycin ​+ ​ramelteon at 2 ​mg/kg) and PF ​+ ​RM4 (pulmonary fibrosis model with bleomycin ​+ ​ramelteon at 4 ​mg/kg) at 2 and 4 ​mg/kg doses, respectively. Real-time polymerase chain reaction (real-time PCR) analyses, histopathological, and immunohistochemical staining were performed on lung tissues. Lung tomography images of the rats were also examined.

RESULTS

The levels of TGF-β1, HMGB1, NLRP3, and interleukin 1 beta (IL-1β) mRNA expressions increased as a result of PF and subsequently decreased with both ramelteon doses (p ​< ​0.0001). Both doses of ramelteon partially ameliorated the reduction in the peribronchovascular thickening, ground-glass appearances, and reticulations, and the loss of lung volume.

CONCLUSIONS

The severity of fibrosis decreased with ramelteon application. These effects of ramelteon may be associated with NLRP3 inflammation cascade.

Prolyl oligopeptidase inhibition ameliorates experimental pulmonary fibrosis both in vivo and in vitro

BACKGROUND

Pulmonary fibrosis is a progressive disease characterized by lung remodeling due to excessive deposition of extracellular matrix. Although the etiology remains unknown, aberrant angiogenesis and inflammation play an important role in the development of this pathology. In this context, recent scientific research has identified new molecules involved in angiogenesis and inflammation, such as the prolyl oligopeptidase (PREP), a proteolytic enzyme belonging to the serine protease family, linked to the pathology of many lung diseases such as pulmonary fibrosis. Therefore, the aim of this study was to investigate the effect of a selective inhibitor of PREP, known as KYP-2047, in an in vitro and in an in vivo model of pulmonary fibrosis.

METHODS

The in vitro model was performed using human alveolar A549 cells. Cells were exposed to lipopolysaccharide (LPS) 10 μg/ml and then, cells were treated with KYP-2047 at the concentrations of 1 μM, 10 μM and 50 μM. Cell viability was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) bromide colorimetric assay, while inflammatory protein expression was assessed by western blots analysis. The in vivo model was induced in mice by intra-tracheal administration of bleomycin (1 mg/kg) and then treated intraperitoneally with KYP-2047 at doses of 1, 2.5 and 5 mg/kg once daily for 12 days and then mice were sacrificed, and lung tissues were collected for analyses.

RESULTS

The in vitro results demonstrated that KYP-2047 preserved cell viability, reduced inflammatory process by decreasing IL-18 and TNF-α, and modulated lipid peroxidation as well as nitrosative stress. The in vivo pulmonary fibrosis has demonstrated that KYP-2047 was able to restore histological alterations reducing lung injury. Our data demonstrated that KYP-2047 significantly reduced angiogenesis process and the fibrotic damage modulating the expression of fibrotic markers. Furthermore, KYP-2047 treatment modulated the IκBα/NF-κB pathway and reduced the expression of related pro-inflammatory enzymes and cytokines. Moreover, KYP-2047 was able to modulate the JAK2/STAT3 pathway, highly involved in pulmonary fibrosis.

CONCLUSION

In conclusion, this study demonstrated the involvement of PREP in the pathogenesis of pulmonary fibrosis and that its inhibition by KYP-2047 has a protective role in lung injury induced by BLM, suggesting PREP as a potential target therapy for pulmonary fibrosis. These results speculate the potential protective mechanism of KYP-2047 through the modulation of JAK2/STAT3 and NF-κB pathways.

Melatonin Protects Against Hyperoxia-Induced Apoptosis in Alveolar Epithelial type II Cells by Activating the MT2/PI3K/AKT/ETS1 Signaling Pathway

PURPOSE

Hyperoxia-induced apoptosis in alveolar epithelial type II cells (AECIIs) plays a critical role in the development of bronchopulmonary dysplasia (BPD). Melatonin has been shown to improve BPD. However, the protective effect of melatonin on hyperoxia-induced apoptosis in AECIIs and the precise mechanisms involved remain unclear.

METHODS

Human alveolar epithelial type II A549 cells were treated with hyperoxia as an in vitro model to investigate the antiapoptotic mechanism of melatonin. CCK-8 assays were performed to investigate the viability of A549 cells. Hoechst 33,258 staining was carried out to quantify apoptosis in A549 cells. The protein expression levels of E26 oncogene homolog 1 (ETS1), Bcl-2, Bax, Bim, Wnt, β-catenin, AKT and phosphorylated AKT were measured by western blotting. LY294002, SC79 and the downregulation of ETS1, melatonin receptor 1 (MT1) and MT2 with specific siRNAs were used to investigate the role of the PI3K/AKT pathway, ETS1, MT1 and MT2 in hyperoxia-induced apoptosis in A549 cells.

RESULTS

Melatonin prevented hyperoxia-induced apoptosis in A549 cells, and the upregulation of E26 oncogene homolog 1 (ETS1) contributed to the antiapoptotic effect of melatonin. Melatonin activated the PI3K/AKT axis, which led to ETS1 upregulation and inhibited apoptosis in hyperoxia-exposed A549 cells. Furthermore, melatonin-induced activation of the PI3K/AKT axis, upregulation of ETS1 and inhibition of apoptosis were reversed by melatonin receptor 2 (MT2) siRNA in hyperoxia-exposed A549 cells.

CONCLUSION

Melatonin prevents hyperoxia-induced apoptosis by activating the MT2/PI3K/AKT/ETS1 axis in alveolar epithelial cells.

Melatonin reduces IL-33 and TSLP expression in human nasal epithelial cells by scavenging ROS directly

BACKGROUND

Chronic rhinosinusitis (CRS) is a chronic mucosal inflammation of the nasal cavity and sinuses. It is classified into CRS without nasal polyps and CRS with nasal polyps (CRSwNP). CRSwNP has high recurrence, especially CRSwNP with massive eosinophil infiltration which is mediated by type 2 inflammatory response. Melatonin is a hormone secreted by the pineal gland, it has powerful antioxidant and anti-inflammatory effects in addition to regulating biological rhythms. There are no studies on melatonin for the treatment of CRS, so we aimed to explore whether melatonin could be used for the treatment of CRS.

MATERIALS AND METHODS

In this study, we used melatonin to treat a cell model of CRS. Subsequently, MTT assay was performed to examine the cell viability of human nasal epithelial cells (HNEpCs), a reactive oxygen species (ROS) kit to detect ROS production, a malondialdehyde (MDA) kit to detect the MDA content in the cell culture supernatant, and an apoptosis kit and Western blot analysis to detect apoptosis. The expressions of Nrf2, HO-1, IL-33, TSLP, and IL-25 were detected by Western blot analysis.

RESULTS

Melatonin improved the viability of HNEpCs, reduced lipopolysaccharide-induced ROS, reduced the MDA content, and inhibited their apoptosis. More importantly, melatonin reduced the expression of IL-33 and TSLP, an important phenomenon for the treatment of CRSwNP.

CONCLUSION

Melatonin protects HNEpCs from damage in inflammation and reduces IL-33 and TSLP expression of HNEpCs.

Activation of the NLRP3 inflammasome by HMGB1 through inhibition of the Nrf2/HO-1 pathway promotes bleomycin-induced pulmonary fibrosis after acute lung injury in rats

OBJECTIVE

Acute lung injury (ALI) is a common complication of critical diseases with high morbidity and mortality. This study explored the regulatory role and mechanism of high mobility histone box 1 protein (HMGB1) on pulmonary fibrosis (PF) after ALI in rats through nucleotide oligomerization domain-like receptor protein-3 (NLRP3) inflammasome.

METHODS

PF rat models after ALI were established by induction of bleomycin. Degree of fibrosis was assessed by Masson staining and Ashcroft scoring. Hydroxyproline (Hyp) contents in lung tissues and rat lung tissue morphology were detected by enzyme-linked-immunosorbent serologic assay (ELISA) and hematoxylin and eosin staining. The levels of NLRP3, major proteins of NLRP3 inflammasome (NLRP3/ASC/caspase-1), and downstream inflammatory cytokines interleukin (IL)-1 and IL-18 were determined using immunohistochemistry, Western blotting analysis, and ELISA. The nuclear/cytoplasmic nuclear factor erythroid 2-related factor 2 (Nrf2) levels and HO-1 levels were measured by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and Western blotting analysis. Rats was injected with lentivirus carrying short hairpin (sh)-HMGB1 and zinc protoporphyria (ZNPP) (HO-1 inhibitor) to assess the effects of HMGB1 and HO-1 on PF and NLRP3 inflammasome activation.

RESULTS

Bleomycin induced PF after ALI in rats, manifested as patchy fibrosis, atelectasis, and excessive expansion, and increased Aschcroft score and Hyp content. Bleomycin treatment enhanced levels of NLRP3, ASC, caspase-1, IL-1, and IL-18 in rat lung tissues, which promoted activation of NLRP3 inflammasome. HMGB1 was up-regulated in bleomycin-induced rats. HMGB1 knockdown partially reversed NLRP3 inflammasome activation and PF progression. HMGB1 knockdown promoted Nrf2 nuclear translocation and up-regulated HO-1. Suppression of HO-1 partially reversed inhibition of HMGB1 knockdown on NLRP3 inflammasome activation and PF.

CONCLUSION

HMGB1 can activate NLRP3 inflammasomes and promote PF by inhibiting the Nrf2/HO-1 pathway.

Sustained systemic inflammation increases autophagy and induces EMT/fibrotic changes in mouse liver cells: Protection by melatonin

The unending lifestyle stressors along with genetic predisposition, environmental factors and infections have pushed the immune system into a state of constant activity, leading to unresolved inflammation and increased vulnerability to chronic diseases. Liver fibrosis, an early-stage liver condition that increases the risk of developing liver diseases like cirrhosis and hepatocellular carcinoma, is among the various diseases linked to inflammation that dominate worldwide morbidity and mortality. We developed a mouse model with low-grade lipopolysaccharide (LPS) exposure that shows hepatic damage and a pro-inflammatory condition in the liver. We show that inflammation and oxidative changes increase autophagy in liver cells, a degradation process critical in maintaining cellular homeostasis. Our findings from in vivo and in vitro studies also show that induction of both inflammation and autophagy trigger epithelial-mesenchymal transition (EMT) and pro-fibrotic changes in hepatocytes. Inhibiting the inflammatory pathways with a naturally occurring NF-κB inhibitor and antioxidant, melatonin, could assuage the changes in autophagy and activation of EMT/fibrotic pathways in hepatocytes. Taken together, this study shows a pathway linking inflammation and autophagy which could be targeted for future drug development to delay the progression of liver fibrosis.

A novel mechanism for the protection against acute lung injury by melatonin: mitochondrial quality control of lung epithelial cells is preserved through SIRT3-dependent deacetylation of SOD2

The mitochondrial quality control of lung epithelial cells is disturbed during sepsis, which contributes to abnormal mitochondrial function and acute lung injury. Melatonin is one of the primary hormones secreted by the pineal gland, displaying favorable antioxidative actions in sepsis and cardiopulmonary disease. However, the potential roles and molecular basis of melatonin in lipopolysaccharide (LPS)-treated lung epithelial cells have not been explored and reported. Herein, we investigated whether melatonin could protect against sepsis-induced acute lung injury (ALI) and LPS-treated lung epithelial cells through the mitochondrial quality control as well as its possible molecular targets. Wild type and Sirt3 knockout mice were intratracheally instilled with LPS for 12 h to construct an in vivo acute lung injury model. Both A549 lung epithelial cells and primary alveolar type II (AT-II) cells were used to explore the possible roles of melatonin in vitro by incubating with small interfering RNA against Sirt3. To determine the involvement of the melatonin receptor, cells and mice were treated with si Mtnr1b and luzindole. Melatonin pretreatment significantly inhibited pathological injury, inflammatory response, oxidative stress, and apoptosis in LPS-treated lung tissues and LPS-treated lung epithelial cells. Furthermore, melatonin also shifted the dynamic course of mitochondria from fission to fusion, inhibited mitophagy and fatty acid oxidation in LPS-treated lung epithelial cells in vitro and in vivo. However, SIRT3 inhibition abolished the protective roles of melatonin in acute lung injury. Mechanistically, we found that melatonin increased the activity and expression of SIRT3, which further promoted the deacetylation of SOD2 at K122 and K68. More importantly, melatonin exerted pulmonary protection by activating MTNR1B but not MTNR1A during ALI. Collectively, melatonin could preserve the mitochondrial quality control of lung epithelial cells through the deacetylation of SOD2 in a SIRT3-dependent manner, which eventually alleviated sepsis-induced injury, inflammation, oxidative stress, and apoptosis. Thus, melatonin may serve as a promising candidate against ALI in the future.

The protective effect of natural medicines against excessive inflammation and oxidative stress in acute lung injury by regulating the Nrf2 signaling pathway

Acute lung injury (ALI) is a common critical disease of the respiratory system that progresses into acute respiratory distress syndrome (ARDS), with high mortality, mainly related to pulmonary oxidative stress imbalance and severe inflammation. However, there are no clear and effective treatment strategies at present. Nuclear factor erythroid 2-related factor 2(Nrf2) is a transcription factor that interacts with multiple signaling pathways and regulates the activity of multiple oxidases (NOX, NOS, XO, CYP) related to inflammation and apoptosis, and exhibits antioxidant and anti-inflammatory roles in ALI. Recently, several studies have reported that the active ingredients of natural medicines show protective effects on ALI via the Nrf2 signaling pathway. In addition, they are cheap, naturally available, and possess minimal toxicity, thereby having good clinical research and application value. Herein, we summarized various studies on the protective effects of natural pharmaceutical components such as polyphenols, flavonoids, terpenoids, alkaloids, and polysaccharides on ALI through the Nrf2 signaling pathway and demonstrated existing gaps as well as future perspectives.

Melatonin ameliorates bleomycin-induced pulmonary fibrosis via activating NRF2 and inhibiting galectin-3 expression

Pulmonary fibrosis (PF) is a chronic interstitial lung disease with no effective therapies. Galectin-3 (Gal-3), a marker of oxidative stress, plays a key role in the pathogenesis of PF. Fibroblast-myofibroblast differentiation (FMD) is an important source of fibrotic cells in PF. Previous studies showed that melatonin (MT) exerted anti-fibrotic effect in many diseases including PF through its antioxidant activity. In the present study we investigated the relationships among Gal-3, NRF2, ROS in FMD and their regulation by MT. We established an in vitro model of FMD in TGF-β1-treated human fetal lung fibroblast1 (HFL1) cells and a PF mouse model via bleomycin (BLM) intratracheal instillation. We found that Gal-3 expression was significantly increased both in vitro and in vivo. Knockdown of Gal-3 in HFL1 cells markedly attenuated TGF-β1-induced FMD process and ROS accumulation. In TGF-β1-treated HFL1 cells, pretreatment with NRF2-specific inhibitor ML385 (5 μM) significantly increased the levels of Gal-3, α-SMA and ROS, suggesting that the expression of Gal-3 was regulated by NRF2. Treatment with NRF2-activator MT (250 μM) blocked α-SMA and ROS accumulation accompanied by reduced Gal-3 expression. In BLM-induced PF model, administration of MT (5 mg·kg⁻¹·d⁻¹, ip for 14 or 28 days) significantly attenuated the progression of lung fibrosis through up-regulating NRF2 and down-regulating Gal-3 expression in lung tissues. These results suggest that Gal-3 regulates TGF-β1-induced pro-fibrogenic responses and ROS production in FMD, and MT activates NRF2 to block FMD process by down-regulating Gal-3 expression. This study provides a useful clue for a clinical strategy to prevent PF.

Calycosin Ameliorates Bleomycin-Induced Pulmonary Fibrosis via Suppressing Oxidative Stress, Apoptosis, and Enhancing Autophagy

Calycosin (CA) is a flavonoid extracted from the root of Astragalus membranaceus and has antioxidant, anti-inflammation, and antiapoptosis properties. The objective of this study was to investigate the efficacy of CA in protecting against pulmonary fibrosis. CA (14 mg/kg) and SB216763 (20 mg/kg) were administrated to bleomycin-induced pulmonary fibrosis mice for 3 weeks. The results concluded that CA alleviated the inflammation and collagen deposition in pulmonary fibrosis. In addition, CA reduced MDA level, enhanced SOD and TAC activities, and increased the activity of the Nrf2/HO-1 pathway. CA also regulated the expressions of apoptosis-related proteins. Moreover, CA enhanced autophagy via upregulating LC3, beclin1, PINK1, and reducing p62. CA also increased expression of LAMP1 and TFEB, and inhibited the release of lysosome enzymes from ruptured lysosomes. These results provide new evidence that CA protects against pulmonary fibrosis through inhibiting oxidative stress and apoptosis. In addition, autophagy abnormality and lysosome dysfunction are restored by CA.

The Role of Nrf2 in Pulmonary Fibrosis: Molecular Mechanisms and Treatment Approaches

Pulmonary fibrosis is a chronic, progressive, incurable interstitial lung disease with high mortality after diagnosis and remains a global public health problem. Despite advances and breakthroughs in understanding the pathogenesis of pulmonary fibrosis, there are still no effective methods for the prevention and treatment of pulmonary fibrosis. The existing treatment options are imperfect, expensive, and have considerable limitations in effectiveness and safety. Hence, there is an urgent need to find novel therapeutic targets. The nuclear factor erythroid 2-related factor 2 (Nrf2) is a central regulator of cellular antioxidative responses, inflammation, and restoration of redox balance. Accumulating reports reveal that Nrf2 activators exhibit potent antifibrosis effects and significantly attenuate pulmonary fibrosis in vivo and in vitro. This review summarizes the current Nrf2-related knowledge about the regulatory mechanism and potential therapies in the process of pulmonary fibrosis. Nrf2 orchestrates the activation of multiple protective genes that target inflammation, oxidative stress, fibroblast–myofibroblast differentiation (FMD), and epithelial–mesenchymal transition (EMT), and the mechanisms involve Nrf2 and its downstream antioxidant, Nrf2/HO−1/NQO1, Nrf2/NOX4, and Nrf2/GSH signaling pathway. We hope to indicate potential for Nrf2 system as a therapeutic target for pulmonary fibrosis.

Melatonin: Regulation of Viral Phase Separation and Epitranscriptomics in Post-Acute Sequelae of COVID-19

The relentless, protracted evolution of the SARS-CoV-2 virus imposes tremendous pressure on herd immunity and demands versatile adaptations by the human host genome to counter transcriptomic and epitranscriptomic alterations associated with a wide range of short- and long-term manifestations during acute infection and post-acute recovery, respectively. To promote viral replication during active infection and viral persistence, the SARS-CoV-2 envelope protein regulates host cell microenvironment including pH and ion concentrations to maintain a high oxidative environment that supports template switching, causing extensive mitochondrial damage and activation of pro-inflammatory cytokine signaling cascades. Oxidative stress and mitochondrial distress induce dynamic changes to both the host and viral RNA m6A methylome, and can trigger the derepression of long interspersed nuclear element 1 (LINE1), resulting in global hypomethylation, epigenetic changes, and genomic instability. The timely application of melatonin during early infection enhances host innate antiviral immune responses by preventing the formation of "viral factories" by nucleocapsid liquid-liquid phase separation that effectively blockades viral genome transcription and packaging, the disassembly of stress granules, and the sequestration of DEAD-box RNA helicases, including DDX3X, vital to immune signaling. Melatonin prevents membrane depolarization and protects cristae morphology to suppress glycolysis via antioxidant-dependent and -independent mechanisms. By restraining the derepression of LINE1 via multifaceted strategies, and maintaining the balance in m6A RNA modifications, melatonin could be the quintessential ancient molecule that significantly influences the outcome of the constant struggle between virus and host to gain transcriptomic and epitranscriptomic dominance over the host genome during acute infection and PASC.

Antifibrotic effect of AD-1 on lipopolysaccharide-mediated fibroblast injury in L929 cells and bleomycin-induced pulmonary fibrosis in mice

20(R)-25-methoxyl-dammarane-3β,12β,20-triol (25-OCH₃-PPD, AD-1) is a dammarane ginsenoside that is isolated from Panax notoginseng. The present study aimed to explore its anti-pulmonary fibrosis (PF) effect in vitro and in vivo. L929 cells were treated with 10 μg mL^-1 lipopolysaccharide (LPS) to establish a PF model in vitro and mice were administered with 3.5 mg kg^-1 bleomycin (BLM) by endotracheal intubation to establish a PF model in vivo for investigating the anti-PF effect and its potential mechanism. The results demonstrated that AD-1 reduced the injury, extracellular matrix (ECM) buildup and α-smooth muscle actin (α-SMA) protein expression levels of L929 induced by LPS. Oral administration of AD-1 downregulated the expression of interleukins (such as IL-1β, IL-6 and IL-18), increased the expression of superoxide dismutase (SOD) and glutathione (GSH), reduced the lung coefficient and the content of hydroxyproline (HYP), and mediated the Bax/Bcl-2 protein ratio and P-p53, β-catenin and SIRT3 expression in the lung tissue of mice. Furthermore, AD-1 inhibited the expression levels of TGF-β1, TIMP-1 and α-SMA and reduced inflammatory cell infiltration and collagen deposition in the lung tissue of PF mice. These results indicated that AD-1 could alleviate PF both in vitro and in vivo, and the underlying mechanism may be related to the decrease in ECM deposition and inflammation, the enhancement of antioxidant capacity, and the mediation of lung cell apoptosis and the TGF-β1/TIMP-1/α-SMA signaling pathway, which provide a theoretical basis for the rehabilitation treatment of PF.

Melatonin and multiple sclerosis: antioxidant, anti-inflammatory and immunomodulator mechanism of action

BACKGROUND

Melatonin is an indole hormone secreted primarily by the pineal gland that showing anti-oxidant, anti-inflammatory and anti-apoptotic capacity. It can play an important role in the pathophysiological mechanisms of various diseases. In this regard, different studies have shown that there is a relationship between Melatonin and Multiple Sclerosis (MS). MS is a chronic immune-mediated disease of the Central Nervous System.

AIM

The objective of this review was to evaluate the mechanisms of action of melatonin on oxidative stress, inflammation and intestinal dysbiosis caused by MS, as well as its interaction with different hormones and factors that can influence the pathophysiology of the disease.

RESULTS

Melatonin causes a significant increase in the levels of catalase, superoxide dismutase, glutathione peroxidase, glutathione and can counteract and inhibit the effects of the NLRP3 inflammasome, which would also be beneficial during SARS-CoV-2 infection. In addition, melatonin increases antimicrobial peptides, especially Reg3β, which could be useful in controlling the microbiota.

CONCLUSION

Melatonin could exert a beneficial effect in people suffering from MS, running as a promising candidate for the treatment of this disease. However, more research in human is needed to help understand the possible interaction between melatonin and certain sex hormones, such as estrogens, to know the potential therapeutic efficacy in both men and women.

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.

The Relevance of Circadian Clocks to Stem Cell Differentiation and Cancer Progression

The molecular mechanism of circadian clocks depends on transcription-translation feedback loops (TTFLs) that have known effects on key cellular processes. However, the distinct role of circadian TTFLs in mammalian stem cells and other less differentiated cells remains poorly understood. Neural stem cells (NSCs) of the brain generate neurons and glia postnatally but also may become cancer stem cells (CSCs), particularly in astrocytomas. Evidence indicates clock TTFL impairment is needed for tumor growth and progression; although, this issue has been examined primarily in more differentiated cancer cells rather than CSCs. Similarly, few studies have examined circadian rhythms in NSCs. After decades of research, it is now well recognized that tumors consist of CSCs and a range of other cancer cells along with noncancerous stromal cells. The circadian properties of these many contributors to tumor properties and treatment outcome are being widely explored. New molecular tools and ones in development will likely enable greater discrimination of important circadian and non-circadian cells within malignancies at multiple stages of cancer progression and following therapy. Here, we focus on adult NSCs and glioma CSCs to address how cells at different stages of differentiation may harbor unique states of the molecular circadian clock influencing differentiation and cell fate.

Luteolin Alleviates Epithelial-Mesenchymal Transformation Induced by Oxidative Injury in ARPE-19 Cell via Nrf2 and AKT/GSK-3β Pathway

Oxidative stress plays a critical role in age-related macular degeneration (AMD), and epithelial-mesenchymal transition (EMT) is involved in this process. The aim of this study was to investigate the protective effects of luteolin, a natural flavonoid with strong antioxidant activity, on H₂O₂-induced EMT in ARPE-19 cells. ARPE-19 cells were incubated with H₂O₂ at 200 μΜ to induce oxidative stress-associated injury. Cell viability assay showed that luteolin at 20 and 40 μM significantly promoted cell survival in H₂O₂-treated ARPE-19 cells. Luteolin also markedly protected ARPE-19 cells from H₂O₂-induced apoptosis. Cell migration assay presented that luteolin significantly reduced H₂O₂-induced migration in APRE-19 cells. EMT in ARPE-19 cells was detected by western blotting and immunofluorescence. The results showed that H₂O₂ significantly upregulated the expression of α-SMA and vimentin and downregulated the expression of ZO-1 and E-cadherin, while cells pretreated with luteolin showed a reversal. Meanwhile, the assessment of effects of luteolin on the Nrf2 pathway indicated that luteolin promoted Nrf2 nuclear translocation and upregulated the expressions of HO-1 and NQO-1. In addition, luteolin significantly increased the activities of SOD and GSH-PX and decreased intracellular levels of ROS and MDA in H₂O₂-treated ARPE-19 cells. Meanwhile, we observed that the expression of TGF-β2, p-AKT, and p-GSK-3β was upregulated in H₂O₂-treated ARPE-19 cells and downregulated in luteolin-treated cells, revealing that luteolin inhibited the activation of the AKT/GSK-3β pathway. However, these effects of luteolin were all annulled by transfecting ARPE-19 cells with Nrf2 siRNA. Our current data collectively indicated that inhibition of luteolin on EMT was induced by oxidative injury in ARPE-19 cell through the Nrf2 and AKT/GSK-3β pathway, suggesting that luteolin could be a potential drug for the treatment of dry AMD.

Exploring the Anti-Pulmonary Fibrosis Mechanism of Jingyin Granule by Network Pharmacology Strategy

Pulmonary fibrosis (PF) is a clinically common disease caused by many factors, which will lead to lung function decline and even respiratory failure. Jingyin granule has been confirmed to have anti-inflammatory and antiviral effects by former studies, and has been recommended for combating H1N1 influenza A virus (H1N1) infection and Coronavirus disease 2019 (COVID-19) in China. At present, studies have shown that patients with severe COVID-19 infection developed lung fibrotic lesions. Although Jingyin granule can improve symptoms in COVID-19 patients, no study has yet reported whether it can attenuate the process of PF. Here, we explored the underlying mechanism of Jingyin granule against PF by network pharmacology combined with in vitro experimental validation. In the present study, the active ingredients as well as the corresponding action targets of Jingyin granule were firstly collected by TCMSP and literature data, and the disease target genes of PF were retrieved by disease database. Then, the common targets were subjected to Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses, and then a PPI network and an ingredient–target network were constructed. Next, UPLC-MS was used to isolate and identify selected representative components in Jingyin granule. Finally, LPS was used to induce the A549 cell fibrosis model to verify the anti-PF effect of Jingyin granule in vitro. Our results indicated that STAT3, JUN, RELA, MAPK3, TNF, MAPK1, IL-6, and AKT1 were core targets of action and bound with good affinity to selected components, and Jingyin granule may alleviate PF progression by Janus kinase 2/signal transducers and activators of transcription (JAK2/STAT3), the mammalian nuclear factor-κB (NF-κB), the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt), tumor necrosis factor (TNF), and the extracellular signal-regulated kinases 1 and 2 (ERK1/2) signaling pathways. Overall, these results provide future therapeutic strategies into the mechanism study of Jingyin granule on PF.

Targeting Oxidative Stress as a Therapeutic Approach for Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic interstitial lung disease characterized by an abnormal reepithelialisation, an excessive tissue remodelling and a progressive fibrosis within the alveolar wall that are not due to infection or cancer. Oxidative stress has been proposed as a key molecular process in pulmonary fibrosis development and different components of the redox system are altered in the cellular actors participating in lung fibrosis. To this respect, several activators of the antioxidant machinery and inhibitors of the oxidant species and pathways have been assayed in preclinical in vitro and in vivo models and in different clinical trials. This review discusses the role of oxidative stress in the development and progression of IPF and its underlying mechanisms as well as the evidence of oxidative stress in human IPF. Finally, we analyze the mechanism of action, the efficacy and the current status of different drugs developed to inhibit the oxidative stress as anti-fibrotic therapy in IPF.

NF-κB-Dependent Snail Expression Promotes Epithelial-Mesenchymal Transition in Mastitis

Simple Summary

Mastitis is a common and important clinical disease in ruminants, resulting in decreased milk production, infertility and delayed conception. If not treated promptly, mastitis may result in fibrotic mastitis. Although epithelial–mesenchymal transition (EMT) is a typical characteristic of fibrotic diseases, the relationship between EMT and mastitis remains largely unknown. NF-κB and Snail are key regulators of the EMT. In the present study, we found that lipopolysaccharide (LPS) induced EMT in primary goat mammary epithelial cells (GMECs). Additionally, the expression of Snail was induced by LPS and was inhibited by the suppression of the TLR4/NF-κB signaling pathway. The knockdown of Snail alleviated LPS-induced EMT and altered the expression of inflammatory cytokines. Finally, we found that the expression of key molecules of the TLR4/NF-κB/Snail signaling pathway was increased in mastitic tissues. This study provides evidence that LPS induces EMT in GMECs through the TLR4/NF-κB/Snail signaling pathway and lays a theoretical foundation for further exploration of the pathological mechanism and treatment of mastitis.

Abstract

Mastitis is a common and important clinical disease in ruminants. This may be associated with inflammatory fibrosis if not treated promptly. Inflammation-derived fibrosis is usually accompanied by epithelial–mesenchymal transition (EMT) in epithelial cells. However, the precise molecular mechanism underlying mastitis-induced fibrosis remains unclear. Nuclear factor kappa-B (NF-κB) and Snail are key regulators of EMT. In this study, primary goat mammary epithelial cells (GMECs) were treated with 10 μg/mL lipopolysaccharide (LPS) for 14 d to mimic the in vivo mastitis environment. After LPS treatment, the GMECs underwent mesenchymal morphological transformation and expressed mesenchymal cell markers. Snail expression was induced by LPS and was inhibited by suppression of the TLR4/NF-κB signaling pathway. Snail knockdown alleviated LPS-induced EMT and altered the expression of inflammatory cytokines. Finally, we found that the expression of key molecules of the TLR4/NF-κB/Snail signaling pathway was increased in mastitis tissues. These results suggest that Snail plays a vital role in LPS-induced EMT in GMECs and that the mechanism is dependent on the activation of the TLR4/NF-κB signaling pathway.

Melatonin Promotes In Vitro Maturation of Vitrified-Warmed Mouse Germinal Vesicle Oocytes, Potentially by Reducing Oxidative Stress through the Nrf2 Pathway

Simple Summary

Cryopreservation of oocytes can cause high oxidative stress, reduce the quality of vitrified-warmed oocytes, and seriously hinder the application of oocyte cryopreservation technology in production and medicine. In this work, we found for the first time that melatonin can exert antioxidant effects through receptors and regulate the Nrf2 antioxidant pathway to respond to oxidative stress of vitrified-warmed oocytes, thereby improving both oocyte quality and the potential for subsequent development. The results illustrated the molecular mechanism of melatonin’s antioxidant effect in vitrified-warmed oocytes and provided a theoretical basis for the application of melatonin in the cryopreservation of oocytes. These findings are of great significance for the further application of oocyte cryopreservation technology to production and assisted reproduction in the future.

Abstract

Previously it was reported that melatonin could mitigate oxidative stress caused by oocyte cryopreservation; however, the underlying molecular mechanisms which cause this remain unclear. The objective was to explore whether melatonin could reduce oxidative stress during in vitro maturation of vitrified-warmed mouse germinal vesicle (GV) oocytes through the Nrf2 signaling pathway or its receptors. During in vitro maturation of vitrified-warmed mouse GV oocytes, there were decreases (p < 0.05) in the development rates of metaphase I (MI) oocytes and metaphase II (MII) and spindle morphology grades; increases (p < 0.05) in the reactive oxygen species (ROS) levels; and decreases (p < 0.05) in expressions of Nrf2 signaling pathway-related genes (Nrf2, SOD1) and proteins (Nrf2, HO-1). However, adding 10⁻⁷ mol/L melatonin to both the warming solution and maturation solutions improved (p < 0.05) these indicators. When the Nrf2 protein was specifically inhibited by Brusatol, melatonin did not increase development rates, spindle morphology grades, genes, or protein expressions, nor did it reduce vitrification-induced intracellular oxidative stress in GV oocytes during in vitro maturation. In addition, when melatonin receptors were inhibited by luzindole, the ability of melatonin to scavenge intracellular ROS was decreased, and the expressions of genes (Nrf2, SOD1) and proteins (Nrf2, HO-1) were not restored to control levels. Therefore, we concluded that 10⁻⁷ mol/L melatonin acted on the Nrf2 signaling pathway through its receptors to regulate the expression of genes (Nrf2, SOD1) and proteins (Nrf2, HO-1), and mitigate intracellular oxidative stress, thereby enhancing in vitro development of vitrified-warmed mouse GV oocytes.

β-Glucan from Saccharomyces cerevisiae alleviates oxidative stress in LPS-stimulated RAW264.7 cells via Dectin-1/Nrf2/HO-1 signaling pathway

β-Glucan from Saccharomyces cerevisiae has been described to be effective antioxidants, but the specific antioxidation mechanism of β-glucan is unclear. The objectives of this research were to determine whether the β-glucan from Saccharomyces cerevisiae could regulate oxidative stress through the Dectin-1/Nrf2/HO-1 signaling pathway in lipopolysaccharides (LPS)-stimulated RAW264.7 cells. In this study, we examined the effects of β-glucan on the enzyme activity or production of oxidative stress indicators in LPS-stimulated RAW264.7 cells by biochemical analysis and the protein expression of key factors of Dectin-1/Nrf2/HO-1 signaling pathway by immunofluorescence and western blot. The biochemical analysis results showed that β-glucan increased the LPS-induced downregulation of enzyme activity of intracellular heme oxygenase (HO), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) while decreasing the production of reactive oxygen species (ROS) and malondialdehyde (MDA). Furthermore, immunofluorescence results showed that β-glucan can activate the nuclear factor erythroid 2-related factor 2 (Nrf2). The antioxidant mechanism study indicated that β-glucan activated dendritic-cell-associated C-type lectin 1 (Dectin-1) receptors mediated Nrf2/HO-1 signaling pathway, thereby downregulating the production of ROS and thus produced the antioxidant effects in LPS-stimulated RAW 264.7 cells. In conclusion, these results indicate that β-glucan potently alleviated oxidative stress via Dectin-1/Nrf2/HO-1 in LPS-stimulated RAW 264.7 cells.

Protective Effect of Mitochondria-Targeted Antioxidants against Inflammatory Response to Lipopolysaccharide Challenge: A Review

Lipopolysaccharide (LPS), the major component of the outer membrane of Gram-negative bacteria, is the most abundant proinflammatory agent. Considerable evidence indicates that LPS challenge inescapably causes oxidative stress and mitochondrial dysfunction, leading to cell and tissue damage. Increased mitochondrial reactive oxygen species (mtROS) generation triggered by LPS is known to play a key role in the progression of the inflammatory response. mtROS at excessive levels impair electron transport chain functioning, reduce the mitochondrial membrane potential, and initiate lipid peroxidation and oxidative damage of mitochondrial proteins and mtDNA. Over the past 20 years, a large number of mitochondria-targeted antioxidants (mito-AOX) of different structures that can accumulate inside mitochondria and scavenge free radicals have been synthesized. Their protective role based on the prevention of oxidative stress and the restoration of mitochondrial function has been demonstrated in a variety of common diseases and pathological states. This paper reviews the current data on the beneficial application of different mito-AOX in animal endotoxemia models, in either in vivo or in vitro experiments. The results presented in our review demonstrate the promising potential of approaches based on mito-AOX in the development of new treatment strategies against Gram-negative infections and LPS per se.