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

Itaconate: A Potential Therapeutic Strategy for Autoimmune Disease

Itaconate is a metabolite of the Krebs cycle, and endogenous itaconate is driven by a variety of innate signals that inhibit the production of inflammatory cytokines. The key mechanism of action of itaconate was initially found to be the competitive inhibition of succinate dehydrogenase (SDH), which inhibits the production of inflammatory factors, as well as its antioxidant effects. With increasing research, it was discovered that it modifies cysteine residues of related proteins through the Michael addition, such as modifying the Kelch-like ECH-associated protein 1 (KEAP1) protein and activating the nuclear factor erythroid 2-related factor 2 (NRF2) signalling pathway, as well as glycolytic enzymes and cellular pathway-associated factors that attenuate inflammatory responses and oxidative stress. It also acts on a variety of immune cells, affecting their function and activity, and has been increasingly shown to play a therapeutic role in a variety of inflammatory and autoimmune diseases through a combination of these mechanisms. In conclusion, there has been a great breakthrough in the research of itaconate, from the initial industrial application to the redefinition of the biological functions of itaconate. However, with the deepening of the research, we also found that there are more questions: the mechanism of action of itaconate, more functions of itaconate, clinical application of itaconate, and the use of itaconate still needs to be solved.

Animal models of infection-induced acute lung injury

Aim: Acute lung injury (ALI) is characterized by severe hypoxemia, reduced lung elasticity, and notable pulmonary edema, often caused by infections and potentially progressing to ARDS. This article explores animal models of ALI and clarifies its main pathogenic mechanisms.

Materials and Methods: we reviewed 20 years of ALI animal model advancements via PubMed, assessing clinical symptoms, histopathology, and reproducibility, and provided guidance on selecting models aligned with ALI pathogenesis.

Results: key proinflammatory mediators and interleukins play a significant role in ALI development, though their interactions are not fully understood. Preclinical models are essential for investigating ALI causes and testing treatments. Animal models mimic ALI from sources such as infections, drugs, and I/R events, but differences between mouse and human lungs necessitate careful validation of these findings.

Conclusions: A comprehensive strategy is essential to address clinical treatment and drug R&D challenges to prevent severe complications and reduce mortality rates.

The role and therapeutic potential of itaconate in lung disease

Lung diseases triggered by endogenous or exogenous factors have become a major concern, with high morbidity and mortality rates, especially after the coronavirus disease 2019 (COVID-19) pandemic. Inflammation and an over-activated immune system can lead to a cytokine cascade, resulting in lung dysfunction and injury. Itaconate, a metabolite produced by macrophages, has been reported as an effective anti-inflammatory and anti-oxidative stress agent with significant potential in regulating immunometabolism. As a naturally occurring metabolite in immune cells, itaconate has been identified as a potential therapeutic target in lung diseases through its role in regulating inflammation and immunometabolism. This review focuses on the origin, regulation, and function of itaconate in lung diseases, and briefly discusses its therapeutic potential.

Itaconate to treat acute lung injury: recent advances and insights from preclinical models

Acute lung injury (ALI) is defined as the acute onset of diffuse bilateral pulmonary infiltration, leading to PaO2/FiO2 ≤ 300 mmHg without clinical evidence of left atrial hypertension. Acute respiratory distress syndrome (ARDS) involves more severe hypoxemia (PaO2/FiO2 ≤ 200 mmHg). Treatment of ALI and ARDS has received renewed attention as the incidence of ALI caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has increased. Itaconate and its derivatives have shown therapeutic potential against ALI. This review provides an in-depth summary of the mechanistic research of itaconate in the field of acute lung injury, including inducing autophagy, preventing ferroptosis and pyroptosis, shifting macrophage polarization to an anti-inflammatory M2 phenotype, inhibiting neutrophil activation, regulating epigenetic modifications, and repressing aerobic glycolysis. These compounds merit further consideration in clinical trials. We anticipate that the clinical translation of itaconate-based drugs can be accelerated.

The Aconitate Decarboxylase 1/Itaconate Pathway Modulates Immune Dysregulation and Associates with Cardiovascular Disease Markers and Disease Activity in Systemic Lupus Erythematosus

The Krebs cycle enzyme aconitate decarboxylase 1 (ACOD1) mediates itaconate synthesis in monocytes and macrophages. Previously, we reported that administration of 4-octyl itaconate to lupus-prone mice abrogated immune dysregulation and clinical features. In this study, we explore the role of the endogenous ACOD1/itaconate pathway in the development of TLR7-induced lupus (imiquimod [IMQ] model). We found that, in vitro, ACOD1 was induced in mouse bone marrow-derived macrophages and human monocyte-derived macrophages following TLR7 stimulation. This induction was partially dependent on type I IFN receptor signaling and on specific intracellular pathways. In the IMQ-induced mouse model of lupus, ACOD1 knockout (Acod1-/-) displayed disruptions of the splenic architecture, increased serum levels of anti-dsDNA and proinflammatory cytokines, and enhanced kidney immune complex deposition and proteinuria, when compared with the IMQ-treated wild-type mice. Consistent with these results, Acod1-/- bone marrow-derived macrophages treated in vitro with IMQ showed higher proinflammatory features. Furthermore, itaconate serum levels in systemic lupus erythematosus patients were decreased compared with healthy individuals, in association with disease activity and specific perturbed cardiometabolic parameters. These findings suggest that the ACOD1/itaconate pathway plays important immunomodulatory and vasculoprotective roles in systemic lupus erythematosus, supporting the potential therapeutic role of itaconate analogs in autoimmune diseases.

Itaconate in host inflammation and defense

Immune cells undergo rapid and extensive metabolic changes during inflammation. In addition to contributing to energetic and biosynthetic demands, metabolites can also function as signaling molecules. Itaconate (ITA) rapidly accumulates to high levels in myeloid cells under infectious and sterile inflammatory conditions. This metabolite binds to and regulates the function of diverse proteins intracellularly to influence metabolism, oxidative response, epigenetic modification, and gene expression and to signal extracellularly through binding the G protein-coupled receptor (GPCR). Administration of ITA protects against inflammatory diseases and blockade of ITA production enhances antitumor immunity in preclinical models. In this article, we review ITA metabolism and its regulation, discuss its target proteins and mechanisms, and conjecture a rationale for developing ITA-based therapeutics to treat inflammatory diseases and cancer.

Itaconate promotes hepatocellular carcinoma progression by epigenetic induction of CD8+ T-cell exhaustion

Itaconate is a well-known immunomodulatory metabolite; however, its role in hepatocellular carcinoma (HCC) remains unclear. Here, we find that macrophage-derived itaconate promotes HCC by epigenetic induction of Eomesodermin (EOMES)-mediated CD8+ T-cell exhaustion. Our results show that the knockout of immune-responsive gene 1 (IRG1), responsible for itaconate production, suppresses HCC progression. Irg1 knockout leads to a decreased proportion of PD-1+ and TIM-3+ CD8+ T cells. Deletion or adoptive transfer of CD8+ T cells shows that IRG1-promoted tumorigenesis depends on CD8+ T-cell exhaustion. Mechanistically, itaconate upregulates PD-1 and TIM-3 expression levels by promoting succinate-dependent H3K4me3 of the Eomes promoter. Finally, ibuprofen is found to inhibit HCC progression by targeting IRG1/itaconate-dependent tumor immunoevasion, and high IRG1 expression in macrophages predicts poor prognosis in HCC patients. Taken together, our results uncover an epigenetic link between itaconate and HCC and suggest that targeting IRG1 or itaconate might be a promising strategy for HCC treatment.

Nrf2/PHB2 alleviates mitochondrial damage and protects against Staphylococcus aureus-induced acute lung injury

Staphylococcus aureus (SA) is a major cause of sepsis, leading to acute lung injury (ALI) characterized by inflammation and oxidative stress. However, the role of the Nrf2/PHB2 pathway in SA-induced ALI (SA-ALI) remains unclear. In this study, serum samples were collected from SA-sepsis patients, and a SA-ALI mouse model was established by grouping WT and Nrf2-/- mice after 6 h of intraperitoneal injection. A cell model simulating SA-ALI was developed using lipoteichoic acid (LTA) treatment. The results showed reduced serum Nrf2 levels in SA-sepsis patients, negatively correlated with the severity of ALI. In SA-ALI mice, downregulation of Nrf2 impaired mitochondrial function and exacerbated inflammation-induced ALI. Moreover, PHB2 translocation from mitochondria to the cytoplasm was observed in SA-ALI. The p-Nrf2/total-Nrf2 ratio increased in A549 cells with LTA concentration and treatment duration. Nrf2 overexpression in LTA-treated A549 cells elevated PHB2 content on the inner mitochondrial membrane, preserving genomic integrity, reducing oxidative stress, and inhibiting excessive mitochondrial division. Bioinformatic analysis and dual-luciferase reporter assay confirmed direct binding of Nrf2 to the PHB2 promoter, resulting in increased PHB2 expression. In conclusion, Nrf2 plays a role in alleviating SA-ALI by directly regulating PHB2 transcription and maintaining mitochondrial function in lung cells.

4-OI ameliorates bleomycin-induced pulmonary fibrosis by activating Nrf2 and suppressing macrophage-mediated epithelial-mesenchymal transition

OBJECTIVES

Pulmonary fibrosis (PF) is a chronic and refractory interstitial lung disease with limited therapeutic options. 4-octyl itaconate (4-OI), a cell-permeable derivative of itaconate, has been shown to have anti-oxidative and anti-inflammatory properties. However, the effect and the underlying mechanism of 4-OI on PF are still unknown.

METHODS

WT or Nrf2 knockout (Nrf2^-/-) mice were intratracheally injected with bleomycin (BLM) to establish PF model and then treated with 4-OI. The mechanism study was performed by using RAW264.7 cells, primary macrophages, and conditional medium-cultured MLE-12 cells.

RESULTS

4-OI significantly alleviated BLM-induced PF and EMT process. Mechanism studies have found that 4-OI can not only directly inhibit EMT process, but also can reduce the production of TGF-β1 by restraining macrophage M2 polarization, which in turn inhibits EMT process. Moreover, the effect of 4-OI on PF and EMT depends on Nrf2.

CONCLUSION

4-OI ameliorates BLM-induced PF in an Nrf2-dependent manner, and its role in alleviating PF is partly due to the direct inhibition on EMT, and partly through indirect inhibition of M2-mediated EMT. These findings suggested that 4-OI has great clinical potential to develop as a new anti-fibrotic agent for PF therapy.

4-Octyl itaconate attenuates LPS-induced acute kidney injury by activating Nrf2 and inhibiting STAT3 signaling

BACKGROUND

Septic acute kidney injury (S-AKI) is the leading form of acute kidney failure among hospitalized patients, and the inflammatory response is involved in this process. 4-octyl itaconate (4-OI) is a multi-target itaconate derivative with potent anti-inflammatory action. However, it remains elusive whether and how 4-OI contributes to the regulation of S-AKI.

METHODS

We employed a lipopolysaccharide (LPS)-induced AKI murine model and explored the potential renoprotective effect of 4-OI in vivo. In vitro experiments, BUMPT cells, a murine renal tubular cell line, were conducted to examine the effects of 4-OI on inflammation, oxidative stress, and mitophagy. Moreover, STAT3 plasmid was transfected in BUMPT cells to investigate the role of STAT3 signaling in the 4-OI-administrated state.

RESULTS

We demonstrate that 4-OI protects against S-AKI through suppressing inflammation and oxidative stress and enhancing mitophagy. 4-OI significantly reduced the levels of Scr, BUN, Ngal as well as the tubular injury in LPS-induced AKI mice. 4-OI restrained inflammation by reducing macrophage infiltration and suppressing the expression of IL-1β and NLRP3 in the septic kidney. 4-OI also reduced ROS levels, as well as cleaved caspase-3 and boosted antioxidants such as HO-1, and NQO1 in mice. In addition, the 4-OI treatment significantly promoted mitophagy. Mechanistically, 4-OI activated Nrf2 signaling and suppressed phosphorylated STAT3 in vivo and vitro. Molecular docking revealed the binding affinity of 4-OI towards STAT3. ML385, a specific Nrf2 inhibitor, partially repressed the anti-inflammatory and anti-oxidative effects of 4-OI and partially restricted the mitophagy induced by 4-OI in vivo and in vitro. Transfected with STAT3 plasmid partially suppressed mitophagy and the anti-inflammatory effect provoked by 4-OI in vitro.

CONCLUSION

These data suggest that 4-OI ameliorates LPS-induced AKI by suppressing inflammation and oxidative stress and enhancing mitophagy through the overactivation of the Nrf2 signaling pathway, and inactivation of STAT3. Our study identifies 4-OI as a promising pharmacologic for S-AKI.

4-Octyl itaconate attenuates glycemic deterioration by regulating macrophage polarization in mouse models of type 1 diabetes

BACKGROUND

Pancreatic beta cell dysfunction and activated macrophage infiltration are early features in type 1 diabetes pathogenesis. A tricarboxylic acid cycle metabolite that can strongly activate NF-E2-related factor 2 (Nrf2) in macrophages, itaconate is important in a series of inflammatory-associated diseases via anti-inflammatory and antioxidant properties. However, its role in type 1 diabetes is unclear. We used 4-octyl itaconate (OI), the cell-permeable itaconate derivate, to explore its preventative and therapeutic effects in mouse models of type 1 diabetes and the potential mechanism of macrophage phenotype reprogramming.

METHODS

The mouse models of streptozotocin (STZ)-induced type 1 diabetes and spontaneous autoimmune diabetes were used to evaluate the preventative and therapeutic effects of OI, which were performed by measuring blood glucose, insulin level, pro- and anti-inflammatory cytokine secretion, histopathology examination, flow cytometry, and islet proteomics. The protective effect and mechanism of OI were examined via peritoneal macrophages isolated from STZ-induced diabetic mice and co-cultured MIN6 cells with OI-pre-treated inflammatory macrophages in vitro. Moreover, the inflammatory status of peripheral blood mononuclear cells (PBMCs) from type 1 diabetes patients was evaluated after OI treatment.

RESULTS

OI ameliorated glycemic deterioration, increased systemic insulin level, and improved glucose metabolism in STZ-induced diabetic mice and non-obese diabetic (NOD) mice. OI intervention significantly restored the islet insulitis and beta cell function. OI did not alter the macrophage count but significantly downregulated the proportion of M1 macrophages. Additionally, OI significantly inhibited MAPK activation in macrophages to attenuate the macrophage inflammatory response, eventually improving beta cell dysfunction in vitro. Furthermore, we detected higher IL-1β production upon lipopolysaccharide stimulation in the PBMCs from type 1 diabetes patients, which was attenuated by OI treatment.

CONCLUSIONS

These results provided the first evidence to date that OI can prevent the progression of glycemic deterioration, excessive inflammation, and beta cell dysfunction predominantly mediated by restricting macrophage M1 polarization in mouse models of type 1 diabetes.

Is Nuclear Factor Erythroid 2-Related Factor 2 a Target for the Intervention of Cytokine Storms?

The term "cytokine storm" describes an acute pathophysiologic state of the immune system characterized by a burst of cytokine release, systemic inflammatory response, and multiple organ failure, which are crucial determinants of many disease outcomes. In light of the complexity of cytokine storms, specific strategies are needed to prevent and alleviate their occurrence and deterioration. Nuclear factor erythroid 2-related factor 2 (NRF2) is a CNC-basic region-leucine zipper protein that serves as a master transcription factor in maintaining cellular redox homeostasis by orchestrating the expression of many antioxidant and phase II detoxification enzymes. Given that inflammatory response is intertwined with oxidative stress, it is reasonable to assume that NRF2 activation limits inflammation and thus cytokine storms. As NRF2 can mitigate inflammation at many levels, it has emerged as a potential target to prevent and treat cytokine storms. In this review, we summarized the cytokine storms caused by different etiologies and the rationale of interventions, focusing mainly on NRF2 as a potential therapeutic target.

Deficiency of immune-responsive gene 1 exacerbates interleukin-1beta-elicited the inflammatory response of chondrocytes via enhancing the activation of NLRP3 inflammasome

Immune-responsive gene 1 (IRG1) is a multifunctional protein that mediates inflammatory responses in numerous pathological conditions. However, whether IRG1 has a relevance with osteoarthritis remains unaddressed. The inflammatory response of chondrocytes contributes to the progression of osteoarthritis. This study focused on assessing the functional link between IRG1 and interleukin-1beta (IL-1β)-elicited the inflammatory response of chondrocytes. The expression levels of IRG1 increased markedly in osteoarthritis cartilage compared to normal healthy cartilage. IRG1 level also increased after IL-1β stimulation in chondrocytes. The knockdown of IRG1 exacerbated IL-1β-elicited apoptosis and degradation of the extracellular matrix in chondrocytes. The nucleotide-binding oligomerization domain-like receptor 3 (NLRP3) inflammasome activation evoked by IL-1β stimulation was enhanced in IRG1-deficient chondrocytes. Importantly, restraint of the NLRP3 inflammasome was able to diminish IRG1-deficiency-amplified effects on IL-1β-stimulated chondrocytes. Additionally, the supplement of itaconate could ameliorate IL-1β-induced the inflammatory response of chondrocytes and reverse any IRG1-deficiency-induced effects. Altogether, our findings document a vital role for IRG1/itaconate in settling the inflammatory response of chondrocytes via effects on the NLRP3 inflammasome.

Modulation of the Itaconate Pathway Attenuates Murine Lupus

OBJECTIVE

Itaconic acid, a Krebs cycle-derived immunometabolite, is synthesized by myeloid cells in response to danger signals to control inflammasome activation, type I interferon (IFN) responses, and oxidative stress. As these pathways are dysregulated in systemic lupus erythematosus (SLE), we investigated the role of an itaconic acid derivative in the treatment of established murine lupus.

METHODS

Female (NZW × NZB)F1 lupus-prone mice were administered 4-octyl itaconate (4-OI) or vehicle starting after clinical onset of disease (30 weeks of age) for 4 weeks (n = 10 mice /group). At 34 weeks of age (peak disease activity), animals were euthanized, organs and serum were collected, and clinical, metabolic, and immunologic parameters were evaluated.

RESULTS

Proteinuria, kidney immune complex deposition, renal scores of severity and inflammation, and anti-RNP autoantibodies were significantly reduced in the 4-OI treatment group compared to the vehicle group. Splenomegaly decreased in the 4-OI group compared to vehicle, with decreases in activation markers in innate and adaptive immune cells, increases in CD8+ T cell numbers, and inhibition of JAK1 activation. Gene expression analysis in splenocytes showed significant decreases in type I IFN and proinflammatory cytokine genes and increased Treg cell-associated markers in the 4-OI group compared to the vehicle group. In human control and lupus myeloid cells, 4-OI in vitro treatment decreased proinflammatory responses and B cell responses.

CONCLUSIONS

These results support targeting immunometabolism as a potentially viable approach in autoimmune disease treatment, with 4-OI displaying beneficial roles attenuating immune dysregulation and organ damage in lupus.

Research Progress on the Mechanism of Itaconate Regulating Macrophage Immunometabolism

The field of immunology is undergoing rapid and dramatic changes. Immunometabolism, a change in metabolic pathways within immune cells, is a key determinant in the activation of immune cells, and intermediates of immunometabolic processes which can influence inflammatory gene expression and play a role in inflammation. Itaconate is one of the most representative metabolites, produced in the tricarboxylic acid cycle (TCA cycle), which links macrophage metabolism, oxidative stress response and immune response to regulate macrophage activity, playing an important role in the function of macrophages. In this paper, we review the mechanisms of the metabolite itaconate and its derivatives in the regulation of macrophage immune metabolism, intending to gain further insight into the role and mechanisms of this metabolite in macrophages and provide new ideas for the mechanisms and treatment of clinical diseases.

Anti-Inflammatory Metabolites in the Pathogenesis of Bacterial Infection

Host and pathogen metabolism have a major impact on the outcome of infection. The microenvironment consisting of immune and stromal cells drives bacterial proliferation and adaptation, while also shaping the activity of the immune system. The abundant metabolites itaconate and adenosine are classified as anti-inflammatory, as they help to contain the local damage associated with inflammation, oxidants and proteases. A growing literature details the many roles of these immunometabolites in the pathogenesis of infection and their diverse functions in specific tissues. Some bacteria, notably P. aeruginosa, actively metabolize these compounds, others, such as S. aureus respond by altering their own metabolic programs selecting for optimal fitness. For most of the model systems studied to date, these immunometabolites promote a milieu of tolerance, limiting local immune clearance mechanisms, along with promoting bacterial adaptation. The generation of metabolites such as adenosine and itaconate can be host protective. In the setting of acute inflammation, these compounds also represent potential therapeutic targets to prevent infection.

Hepatoprotective Role of 4-Octyl Itaconate in Concanavalin A-Induced Autoimmune Hepatitis

4-Octyl itaconate (OI) is a novel anti-inflammatory metabolite that exerts protective effects in many various disease models. However, its function in autoimmune hepatitis- (AIH-) associated hepatic injury has not been investigated. In this study, we successfully used concanavalin A (Con A) to establish an AIH-associated liver injury model. Furthermore, we investigated the effect of OI in Con A-induced liver injury and found that OI mitigated Con A-induced histopathological damage. OI administration reduced serum levels of alanine transaminase and aspartate transaminase in Con A-treated mice and attenuated the infiltration of macrophages induced by Con A. Moreover, OI effectively inhibited the expression of proinflammatory cytokines including interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), and IL-1β induced by Con A. Furthermore, OI decreased hepatocyte apoptosis and malondialdehyde levels and increased the reduced glutathione/oxidized glutathione ratio in the Con A-induced liver injury model. In addition, we found that OI inhibited Con A-induced hepatocyte apoptosis in vitro, while Nrf2 deletion eliminated this effect. Furthermore, we administrated the Nrf2 inhibitor ML385 in OI+Con A-treated mice and found that ML385 eliminated the protective effect of OI in vivo. In addition, OI inhibited Con A-induced activation of nuclear factor-kappa B (NF-𝜅B) and the expression of proinflammatory cytokines in macrophages. Therefore, OI protected mice from Con A-induced liver damage and may be associated with Nrf2 activation and NF-𝜅B inhibition. Finally, our study revealed that OI inhibited TNF-α, or supernatants from Con A-treated RAW264.7 cells induced hepatocyte apoptosis. In conclusion, our study indicated that OI alleviated Con A-induced hepatic damage by reducing inflammatory response, oxidative stress, and apoptosis.

Immune-responsive gene 1 protects against liver injury caused by concanavalin A via the activation Nrf2/HO-1 pathway and inhibition of ROS activation pathways

Itaconate is produced by an enzyme encoded by the immune-responsive gene 1 (IRG1) and exerts antibacterial, anti-inflammatory, and antioxidant effects via multiple mechanisms. However, the role of IRG1/itaconate in liver injury caused by Concanavalin A (Con A) is not fully understood. In this study, we explored the therapeutic effect of IRG1/four-octyl itaconate (4-OI), a derivative of itaconate, on liver injury caused by Con A and its possible underlying mechanisms. In vivo experiments, we found that Con A promoted IRG1 expression in the liver tissue. Deletion of IRG1 in mice aggravated Con A-induced liver injury. Compared to wild-type (WT) mice, the inflammatory response, hepatocyte apoptosis, and serum cytokine levels were significantly increased, while the antioxidant capacity was significantly attenuated in IRG1^-/- mice. In addition, we found that Con A promoted the nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 inflammasome, caspase-1, and gasdermin D activation, and pyroptosis was more obvious in IRG1^-/- mice, while 4-OI inhibited pyroptosis. In vivo experiments showed that Con A promoted hepatocyte apoptosis by promoting reactive oxygen species (ROS) expression, and 4-OI reduced ROS-mediate apoptosis in NCTC 1469 cells. In RAW264.7 cells, we demonstrated that 4-OI inhibited the inflammatory response by promoting the nuclear factor erythroid 2 [NF-E2]-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) pathway and inhibiting the nuclear factor-kappa B (NF-κB)/mitogen-activated protein kinases signaling pathway. To further confirm that Nrf2 is the target of itaconate, we pretreated WT mice with ML385, an Nrf2 inhibitor, and found that ML385 could weaken the protection of 4-OI in Con A-induced liver injury mouse model. Furthermore, when we knocked down the Nrf2 gene in NCTC 1469 and RAW264.7 cells, the effect of 4-OI in inhibiting inflammation and apoptosis also decreased. In conclusion, our study shows the importance of IRG1 in inflammation and oxidative stress, and suggests that it plays a vital protective role in Con A-induced liver injury. These findings indicate IRG1/itaconate is a potential therapeutic strategy for immune liver injury, which requires further clinical exploration.

Nrf2 activation reprograms macrophage intermediary metabolism and suppresses the type I interferon response

To overcome oxidative, inflammatory, and metabolic stress, cells have evolved cytoprotective protein networks controlled by nuclear factor-erythroid 2 p45-related factor 2 (Nrf2) and its negative regulator, Kelch-like ECH associated protein 1 (Keap1). Here, using high-resolution mass spectrometry we characterize the proteomes of macrophages with altered Nrf2 status revealing significant differences among the genotypes in metabolism and redox homeostasis, which were validated with respirometry and metabolomics. Nrf2 affected the proteome following lipopolysaccharide (LPS) stimulation, with alterations in redox, carbohydrate and lipid metabolism, and innate immunity. Notably, Nrf2 activation promoted mitochondrial fusion. The Keap1 inhibitor, 4-octyl itaconate remodeled the inflammatory macrophage proteome, increasing redox and suppressing type I interferon (IFN) response. Similarly, pharmacologic or genetic Nrf2 activation inhibited the transcription of IFN-β and its downstream effector IFIT2 during LPS stimulation. These data suggest that Nrf2 activation facilitates metabolic reprogramming and mitochondrial adaptation, and finetunes the innate immune response in macrophages.

4-Octyl-Itaconate and Dimethyl Fumarate Inhibit COX2 Expression and Prostaglandin Production in Macrophages

Prostaglandins (PGs) are important proinflammatory lipid mediators, the significance of which is highlighted by the widespread and efficacious use of non-steroidal anti-inflammatory drugs (NSAIDs) in the treatment of inflammation. 4-Octyl itaconate (4-OI), a derivative of the Krebs cycle-derived metabolite itaconate, has recently garnered much interest as an anti-inflammatory agent. Here we show that 4-OI limits PG production in macrophages stimulated with the Toll-like receptor 1/2 (TLR1/2) ligand Pam3CSK4. This decrease in PG secretion is due to a robust suppression of COX2 expression by 4-OI, with both mRNA and protein levels decreased. Dimethyl fumarate (DMF), a fumarate derivative used in the treatment of multiple sclerosis (MS), with properties similar to itaconate, replicated the phenotype observed with 4-OI. We also demonstrate that the decrease in COX2 expression and inhibition of downstream prostaglandin production occurs in an NRF2-independent manner. Our findings provide a new insight into the potential of 4-OI as an anti-inflammatory agent and also identifies a novel anti-inflammatory function of DMF.

Auranofin: Past to Present, and repurposing

Auranofin (AF), a gold compound, has been used to treat rheumatoid arthritis (RA) for more than 40 years; however, its mechanism of action remains unknown. We revealed that AF inhibited the induction of proinflammatory proteins and their mRNAs by the inflammatory stimulants, cyclooxygenase-2 and inducible nitric oxide synthase, and their upstream regulator, NF-κB. AF also activated the proteins peroxyredoxin-1, Kelch-like ECH-associated protein 1, and NF-E2-related factor 2, and inhibited thioredoxin reductase, all of which are involved in oxidative or electrophilic stress under physiological conditions. Although the cell membrane was previously considered to be permeable to AF because of its hydrophobicity, the mechanisms responsible for transporting AF into and out of cells as well as its effects on the uptake and excretion of other drugs have not yet been elucidated. Antibodies for cytokines have recently been employed in the treatment of RA, which has had an impact on the use of AF. Trials to repurpose AF as a risk-controlled agent to treat cancers or infectious diseases, including severe acute respiratory syndrome coronavirus 2/coronavirus disease 2019, are ongoing. Novel gold compounds are also under development as anti-cancer and anti-infection agents.

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.