Itaconate and itaconate derivatives target JAK1 to suppress alternative activation of macrophages

Cholangiocarcinoma PDHA1 succinylation suppresses macrophage antigen presentation via alpha-ketoglutaric acid accumulation

Gemcitabine combined with cisplatin is the first-line chemotherapy for advanced cholangiocarcinoma, but drug resistance remains a challenge, leading to unsatisfactory therapeutic effect. Here, we elucidate the possibility of chemotherapy regimens sensitized by inhibiting succinylation in patients with cholangiocarcinoma from the perspective of post-translational modification. Our omics analysis reveals that succinylation of PDHA1 lysine 83, a key enzyme in the tricarboxylic acid cycle, alters PDH enzyme activity, modulates metabolic flux, and leads to alpha-ketoglutaric acid accumulation in the tumor microenvironment. This process activates the OXGR1 receptor on macrophages, triggering MAPK signaling and inhibiting MHC-II antigen presentation, which promotes immune escape and tumor progression. Moreover, we show that inhibiting PDHA1 succinylation with CPI-613 enhances the efficacy of gemcitabine and cisplatin. Targeting PDHA1 succinylation may be a promising strategy to improve treatment outcomes in cholangiocarcinoma and warrants further clinical exploration.

Injectable DMM/GelMA hydrogel for diabetic wound healing via regulating mitochondrial metabolism and macrophage repolarization

The chronic diabetic wounds represented by diabetes foot ulcers (DFUs) are a worldwide challenge. Excessive production of reactive oxygen species (ROS) and persistent inflammation caused by the impaired phenotype switch of macrophages from M1 to M2 during wound healing are the main culprits of non-healing diabetic wounds. Therefore, an injectable DMM/GelMA hydrogel as a promising wound dressing was designed to regulate the mitochondrial metabolism of macrophages via inhibiting succinate dehydrogenase (SDH) activity and to promote macrophage repolarization towards M2 type. DMM/GelMA hydrogel exhibited good biocompatibility, injectability and water absorption and retention capacity. In vitro studies showed that DMM/GelMA hydrogel inhibited SDH activity, recovered the decrease in mitochondrial membrane potential, and significantly reduced the production of ROS and inflammatory cytokines in the LPS-evoked macrophages. In vivo evaluations and RNA sequencing analysis demonstrated that DMM/GelMA hydrogel downregulated ROS generation, the ratio of M1/M2 macrophages and pro-inflammatory cytokine production in the full-thickness skin wound model in the diabetic mice. Additionally, DMM/GelMA hydrogel improved the wound-healing quality with thicker epidermis, more collagen deposition and higher ratio of collagen I/III by sustained release of DMM. These findings indicate this hydrogel has a great potential to be a biocompatible, injectable and anti-inflammatory dressing for better diabetic wound healing.

Macrophages recycle phagocytosed bacteria to fuel immunometabolic responses

Macrophages specialize in phagocytosis, a cellular process that eliminates extracellular matter, including microorganisms, through internalization and degradation1,2. Despite the critical role of phagocytosis during bacterial infection, the fate of phagocytosed microbial cargo and its impact on the host cell are poorly understood. In this study, we show that ingested bacteria constitute an alternative nutrient source that skews immunometabolic host responses. By tracing stable isotope-labelled bacteria, we found that phagolysosomal degradation of bacteria provides carbon atoms and amino acids that are recycled into various metabolic pathways, including glutathione and itaconate biosynthesis, and satisfies the bioenergetic needs of macrophages. Metabolic recycling of microbially derived nutrients is regulated by the nutrient-sensing mechanistic target of rapamycin complex C1 and is intricately tied to microbial viability. Dead bacteria, as opposed to live bacteria, are enriched in cyclic adenosine monophosphate, sustain the cellular adenosine monophosphate pool and subsequently activate adenosine monophosphate protein kinase to inhibit the mechanistic target of rapamycin complex C1. Consequently, killed bacteria strongly fuel metabolic recycling and support macrophage survival but elicit decreased reactive oxygen species production and reduced interleukin-1β secretion compared to viable bacteria. These results provide a new insight into the fate of engulfed microorganisms and highlight a microbial viability-associated metabolite that triggers host metabolic and immune responses. Our findings hold promise for shaping immunometabolic intervention for various immune-related pathologies.

Patenting perspective on Keap1 inhibitors (2019-2024)

INTRODUCTION

Kelch-like ECH-associated protein 1 (Keap1), an E3 ligase negatively regulating the nuclear factor erythroid 2-related factor 2 (Nrf2), has emerged as an auspicious drug target for treating ailments associated with oxidative stress and inflammation. Discovery of Keap1 inhibitors have attracted significant interest.

AREAS COVERED

This review covers patents on Keap1 inhibitors from 2019 to 2024, providing a comprehensive analysis of their structural characteristics, optimization strategies, pharmacological properties and clinical progress.

EXPERT OPINION

Extensive efforts have been devoted to enhance potency and drug-like properties of Keap1 inhibitors. Strategies such as ROS-cleavable prodrug design, bivalent inhibition and PROTACs are emerging. As the range of drug types and applications expands, Keap1 inhibitors are becoming a sagacious option for disease treating.

A Constant Filgotinib Delivery Adhesive Platform Based on Polyethylene Glycol (PEG) Hydrogel for Accelerating Wound Healing via Restoring Macrophage Mitochondrial Homeostasis

Skin wound healing is often hindered by disrupted mitochondrial homeostasis and imbalanced macrophage glucose metabolism, posing a critical challenge to improve patient outcomes. Developing new wound healing dressings capable of effectively regulating macrophage immune-metabolic functions remains a pressing issue. Herein, a highly adhesive polyethylene glycol (PEG) hydrogel loaded with the Janus kinase 1 (JAK1) inhibitor Filgotinib (Fil@GEL) is prepared to modulate macrophage metabolic reprogramming and restore normal mitochondrial function. Fil@GEL exhibits superior shear adhesion strength compared to commercially available tissue binder products, providing adequate adhesion for skin wound closure. Additionally, Fil@GEL exhibits the capacity to inhibit M1-type macrophage polarization by suppressing the JAK-STAT signaling pathway, and induces a metabolic shift in macrophages from aerobic glycolysis to oxidative phosphorylation, which results in decreased lactate production, reduced reactive oxygen species (ROS) levels, and the restoration of mitochondrial homeostasis. The Fil@GEL hydrogel significantly accelerates skin wound healing compared to the control group, reduces intra-wound inflammation, and promotes collagen regeneration. In summary, this highly adhesive hydrogel demonstrates exceptional performance as a drug carrier, exerting immunometabolic modulation through firm wound adhesion and sustained filgotinib release, underscoring its substantial potential as an effective wound dressing.

Preclinical insights into the potential of itaconate and its derivatives for liver disease therapy

Annually, approximately 3.5 % of the world's population dies of cirrhosis or liver cancer, and the burden of liver disease is steadily expanding owing to multiple factors such as alcohol consumption, irrational diets, viral transmission, and exposure to drugs and toxins. However, the lack of effective therapies and the adverse effects of some medications remain a threat to the management of liver disease. Recently, immunometabolism, as an emerging discipline, appears to be the focus of unprecedented research. As a natural metabolite that regulates cellular functions, itaconate is a crucial bridge connecting metabolism and immune response. Remodeling immune function through metabolic modulation may be a promising alternative for disease intervention strategies. In this review, we first briefly describe the historical origin of itaconate and the development of its derivatives. This was followed by a review of the molecular mechanisms by which itaconate regulated immune-metabolic responses. Furthermore, we analyzed the effects of itaconate regulation on immune cells of the hepatic system. Finally, we summarized the experimental evidence for itaconate and its derivatives in the therapeutic application of liver diseases. Itaconate is potentially an invaluable component of emerging therapeutic strategies for liver disease.

Metabolic reprogramming shapes post-translational modification in macrophages

Polarized macrophages undergo metabolic reprogramming, as well as extensive epigenetic and post-translational modifications (PTMs) switch. Metabolic remodeling and dynamic changes of PTMs lead to timely macrophage response to infection or antigenic stimulation, as well as its transition from a pro-inflammatory to a reparative phenotype. The transformation of metabolites in the microenvironment also determines the PTMs of macrophages. Here we reviewed the current understanding of the altered metabolites of glucose, lipids and amino acids in macrophages shape signaling and metabolism pathway during macrophage polarization via PTMs, and how these metabolites in some macrophage-associated diseases affect disease progression by shaping macrophage PTMs.

A Self-Assembled Metabolic Regulator Reprograms Macrophages to Combat Cytokine Storm and Boost Sepsis Immunotherapy

Sepsis, a life-threatening inflammatory disorder characterized by multiorgan failure, arises from a dysregulated immune response to infection. Modulating macrophage polarization has emerged as a promising strategy to control sepsis-associated inflammation. The endogenous metabolite itaconate has shown anti-inflammatory potential by suppressing the stimulator of interferon genes (STING) pathway, but its efficacy is inhibited by hyperactive glycolysis, which sustains macrophage overactivation. Here, we revealed a critical crosstalk between the itaconate-STING axis and glycolysis in macrophage-mediated inflammation. Building on this interplay, we developed a novel nanoparticle LDO (lonidamine disulfide 4-octyl-itaconate), a self-assembled metabolic regulator integrating an itaconate derivative with the glycolysis inhibitor Lonidamine. By concurrently targeting glycolysis and STING pathways, LDO reprograms macrophages to restore balanced polarization. In sepsis models, LDO effectively attenuates CCL2-driven cytokine storms, alleviates acute lung injury, and significantly enhances survival via metabolic reprogramming. This study offers a cytokine-regulatory strategy rooted in immunometabolism, providing a foundation for the translational development of immune metabolite-based sepsis therapies.

Insights into the itaconate family: Immunomodulatory mechanisms and therapeutic potentials

The itaconate family, comprising itaconate derivatives, endogenous isomers, and other related compounds, has demonstrated substantial immunoregulatory properties. These compounds exhibit significant therapeutic potential in various disease models by modulating metabolic pathways, signal transduction cascades, and post-translational modifications. In this review, we delineate the structural characteristics and biological functions of the members of the itaconate family and elucidate their immunomodulatory mechanisms. Additionally, we summarize the immunomodulatory effects of the itaconate family across various disease categories, including cardiovascular, liver, respiratory, bone and cartilage, neurological, and autoimmune diseases. This review aims to deepen our understanding of the itaconate family and its potential applications, providing new perspectives and therapeutic strategies for inflammatory disorders and autoimmune diseases.

Pharmacological inhibition of STING-mediated GPX4 autophagic degradation by 4-octyl itaconate ameliorates sepsis-induced acute kidney injury

The precise pathogenic mechanisms underlying sepsis-induced acute kidney injury (AKI) remain elusive. Emerging evidence suggests a link between tubular ferroptosis and the pathogenesis of AKI, though the regulatory pathways are not fully understood. Stimulator of interferon genes (STING), previously recognized as a pivotal mediator of innate immunity via DNA-sensing pathways, is increasingly associated with lipid peroxidation, a hallmark of ferroptosis, and 4-octyl itaconate (4-OI) has been shown to inhibit STING activation, exerting anti-inflammatory effects. This study investigates the protective mechanisms of 4-OI in sepsis-AKI. Following cecal ligation and puncture (CLP), inflammation, oxidative stress, and ferroptosis levels in kidney tissue increased. Both 4-OI and ferrostatin-1 (Fer-1) mitigated renal ferroptosis, exerting anti-inflammatory and antioxidant stress effects, and improved renal function. Consistently, in vitro experiments demonstrated that 4-OI reduced ferroptosis in human renal proximal tubule (HK-2) cells induced by lipopolysaccharide (LPS). Mechanistically, 4-OI suppressed LPS-induced activation of the STING pathway and reduced levels of inflammatory cytokines in a manner independent of NF-E2-related factor 2 (Nrf2). Additionally, 4-OI inhibited STING transcription through the activation of Nrf2. These dual actions effectively suppressed LPS-induced STING pathway activation, thereby inhibiting STING-mediated autophagic degradation of glutathione peroxidase 4 (GPX4), reducing reactive oxygen species (ROS) accumulation, and alleviating ferroptosis. In summary, 4-OI is a promising therapeutic candidate, functioning both as a STING inhibitor and a ferroptosis inhibitor, with potential applications in the treatment of sepsis.

Itaconate restrains acute proinflammatory activation of microglia after traumatic brain injury in mice

Traumatic brain injury (TBI) rapidly triggers proinflammatory activation of microglia, contributing to secondary brain damage post-TBI. Although the governing role of energy metabolism in shaping the inflammatory phenotype and function of immune cells has been increasingly recognized, the specific alterations in microglial bioenergetics post-TBI remain poorly understood. Itaconate, a metabolite produced by the enzyme aconitate decarboxylase 1 [IRG1; encoded by immune responsive gene 1 (Irg1)], is a pivotal metabolic regulator in immune cells, particularly in macrophages. Because microglia are macrophages of the brain parenchyma, the IRG1/itaconate pathway likely modulates microglial inflammatory responses. In this study, we explored the role of the IRG1/itaconate pathway in regulating microglial bioenergetics and inflammatory activation post-TBI using a mouse controlled cortical impact (CCI) model. We isolated microglia before and 4 and 12 hours after TBI and observed a swift but transient increase in glycolysis coupled with a prolonged disruption of mitochondrial metabolism after injury. Despite an up-regulation of Irg1 expression, itaconate in microglia declined after TBI. Microglia-specific Irg1 gene knockout (Irg1-Mi-KO) exacerbated metabolic changes, intensified proinflammatory activation and neurodegeneration, and worsened certain long-term neurological deficits. Supplementation with 4-octyl itaconate (OI) reinstated the use and oxidative metabolism of glucose, glutamine, and fatty acid, thereby enhancing microglial bioenergetics post-TBI. OI supplementation also attenuated proinflammatory activation and neurodegeneration and improved long-term neurological outcomes. These results suggest that therapeutically targeting the itaconate pathway could improve microglial energy metabolism and neurological outcomes after TBI.

Antifibrotic Function of Itaconate-Based Degradable Polyester Materials

Pathological fibrosis is a chronic disease, characterized by excessive extracellular matrix deposition, that remains a significant global health challenge. Despite its prevalence, current antifibrotic therapies are limited due to the complex interplay and signaling of profibrotic macrophages and fibroblast cells that underlies fibrotic tissue microenvironments. This study investigates a novel approach to combat fibrosis, harnessing the antifibrotic properties of the endogenous metabolite itaconate (IA) to target the pathological activation of the macrophage-fibroblast axis in fibrotic disease. To achieve therapeutic delivery relevant to the chronic nature of fibrotic conditions, we incorporated IA into the backbone of biodegradable polyester polymers, poly(dodecyl itaconate) (poly[IA-DoD]), capable of long-term localized release of IA. Degradation characterization of poly(IA-DoD) revealed that IA, as well as water-soluble IA-containing oligomeric groups, is released in a sustained manner. Treatment of murine bone marrow-derived macrophages and human dermal fibroblasts demonstrated that the degradation products of poly(IA-DoD) effectively modulated profibrotic behavior. Macrophages exposed to the degradation products exhibited reduced profibrotic responses, while fibroblasts showed decreased proliferation and myofibroblast α-smooth muscle actin expression. These findings suggest that poly(IA-DoD) has the potential to disrupt the fibrotic cycle by targeting key cellular players. This polymer-based delivery system offers a promising strategy for the treatment of fibrotic diseases.

The Trim32-DPEP2 axis is an inflammatory switch in macrophages during intestinal inflammation

The mechanisms via which inflammatory macrophages mediate intestinal inflammation are not completely understood. Herein, using merged analysis of RNA sequencing and mass spectrometry-based quantitative proteomics, we detected differences between proteomic and transcriptomic data in activated macrophages. Dipeptidase-2 (DPEP2), a member of the DPEP family, was highly expressed and then downregulated sharply at the protein level but not at the mRNA level in macrophages in response to inflammatory stimulation. Suppression of DPEP2 not only enhanced macrophage-mediated intestinal inflammation in vivo but also promoted the transduction of inflammatory pathways in macrophages in vitro. Mechanistically, overexpressed DPEP2 inhibited the transduction of inflammatory signals by resisting MAK3K7 in inactivated macrophages, whereas DPEP2 degradation by activated Trim32 resulted in strong activation of NF-κB and p38 MAPK signaling via the release of MAK3K7 in proinflammatory macrophages during the development of intestinal inflammation. The Trim32-DPEP2 axis accumulates the potential energy of inflammation in macrophages. These results identify DPEP2 as a key regulator of macrophage-mediated intestinal inflammation. Thus, the Trim32-DPEP2 axis may be a potential therapeutic target for the treatment of intestinal inflammation.

The various roles of TREM2 in cardiovascular disease

Triggering receptor expressed on myeloid cells-2 (TREM2) is a transmembrane immune receptor that is expressed mainly on macrophages. As a pathology-induced immune signaling hub, TREM2 senses tissue damage and activates immune remodeling in response. Previous studies have predominantly focused on the TREM2 signaling pathway in Alzheimer's disease, metabolic syndrome, and cancer. Recent research has indicated that TREM2 signaling is also activated in various cardiovascular diseases. In this review, we summarize the current understanding and the unanswered questions regarding the role of TREM2 signaling in mediating the metabolism and function of macrophages in atherosclerosis and various models of heart failure. In the context of atherosclerosis, TREM2 signaling promotes foam cell formation and is crucial for maintaining macrophage survival and plaque stability through efferocytosis and cholesterol efflux. Recent studies on myocardial infarction, sepsis-induced cardiomyopathy, and hypertensive heart failure also implicated the protective role of TREM2 signaling in cardiac macrophages through efferocytosis and paracrine functions. Additionally, we discuss the clinical significance of elevated soluble TREM2 (sTREM2) in cardiovascular disease and propose potential therapies targeting TREM2. The overall aim of this review is to highlight the various roles of TREM2 in cardiovascular diseases and to provide a framework for therapeutic strategies targeting TREM2.

Discovery of Orally Available Prodrugs of Itaconate and Derivatives

Itaconate, an endogenous immunomodulator from the tricarboxylic acid (TCA) cycle, shows therapeutic effects in various disease models, but is highly polar with poor cellular permeability. We previously reported a novel, topical itaconate derivative, SCD-153, for the treatment of alopecia areata. Here, we present the discovery of orally available itaconate derivatives for systemic and skin disorders. Four sets of prodrugs were synthesized using pivaloyloxymethyl (POM), isopropyloxycarbonyloxymethyl (POC), (5-methyl-2-oxo-1,3-dioxol-4-yl) methyl (ODOL), and 3-(hexadecyloxy)propyl (HDP) pro-moieties pairing with itaconic acid (IA), 1-methyl itaconate (1-MI), and 4-methyl itaconate (4-MI). Among these, POC-based prodrugs (P2, P9, P13) showed favorable stability, permeability, and pharmacokinetics. Notably, P2 and P13 significantly inhibited Poly(I:C)/IFNγ-induced inflammatory cytokines in human epidermal keratinocytes. Oral studies demonstrated favorable pharmacokinetics releasing micromolar concentrations of IA or 4-MI from P2 and P13, respectively. These findings highlight the potential of prodrug strategies to enhance itaconate's cellular permeability and oral bioavailability, paving the way for clinical translation.

Immunoresponsive gene 1 facilitates TLR4 agonist-induced augmentation of innate antimicrobial immunity

Treatment with the toll-like receptor 4 agonist monophosphoryl lipid A conditions innate immunocytes to respond robustly to subsequent infection, a phenotype termed innate immune memory. Our published studies show that metabolic reprogramming of macrophages is a prominent feature of the memory phenotype. We undertook studies to define the functional contributions of tricarboxylic acid cycle reprogramming to innate immune memory. We observed that priming of wild-type mice with monophosphoryl lipid A potently facilitated accumulation of the tricarboxylic acid cycle metabolite itaconate at sites of infection and enhanced microbial clearance. Augmentation of itaconate accumulation and microbial clearance was ablated in Irg1-deficient mice. We further observed that monophosphoryl lipid A potently induces expression of Irg1 and accumulation of itaconate in macrophages. Compared to wild-type macrophages, the ability of Irg1-deficient macrophages to kill Pseudomonas aeruginosa was impaired. We further observed that itaconate is directly antimicrobial against P. aeruginosa at pH 5, which is characteristic of the phagolysosome, and is facilitated by reactive oxygen species. Monophosphoryl lipid A-induced augmentation of glycolysis, oxidative phosphorylation, and accumulation of the tricarboxylic acid cycle metabolites succinate and malate was decreased in Irg1 knockout macrophages compared to wild-type controls. RNA sequencing revealed suppressed transcription of genes associated with phagolysosome function and increased expression of genes associated with cytokine production and chemotaxis in Irg1-deficient macrophages. This study identifies a contribution of itaconate to monophosphoryl lipid A-induced augmentation of innate antimicrobial immunity via facilitation of microbial killing as well as impact on metabolic and transcriptional adaptations.

4-octyl Itaconate Attenuates Acute Pancreatitis and Associated Lung Injury by Suppressing Ferroptosis in Mice

Acute pancreatitis (AP) is a common gastrointestinal emergency requiring hospitalization. In recent years, several studies have demonstrated a role for 4-octyl itaconate (4-OI) in anti-inflammatory and oxidative stress injury. However, the potential effects of 4-OI in AP have not been investigated. Caerulein and LPS were used to induce experimental AP models in mice and AR42J cells and then studied by histopathology, biochemical, and molecular analysis. Ferroptosis inhibitor ferrostatin-1 effectively improves pancreatic injury and reduces lipid peroxidation products in experimental AP mice. 4-OI treatment significantly alleviated pancreatic and AP-associated lung injury and inflammation in experimental AP mice by inhibiting ferroptosis. The ferroptosis activator Erastin blocked the protective effect of 4-OI against pancreatic injury in AP, validating that 4-OI alleviates pancreatitis injury through ferroptosis. In vitro experiments further confirmed that 4-OI treatment ameliorated AP-induced pancreatic injury by inhibiting ferroptosis. Our study, for the first time, found that 4-OI ameliorates AP and AP-related lung injury by inhibiting ferroptosis in experimental AP mice, providing a new therapeutic target for alleviating AP.

Itaconate and its derivatives as anti-pathogenic agents

Pathogenic microorganisms and viruses cause outbreaks and pandemics that affect millions of people worldwide. Despite recent advances in pharmacology and medicine, the ability of infectious diseases to spread in the modern era is accelerating due to various factors contributing to increased human-to-human and human-animal contacts. With the global rise of drug resistance among pathogens and frequently occurring viral outbreaks, alternative drugs and therapies that specifically inhibit microbial virulence or regulate immune responses are attracting growing interest. The present review focuses on itaconate and its derivatives as potential anti-pathogenic agents. It summarizes the current state of research on itaconate metabolism in bacteria, fungi and mammals. This is followed by a comprehensive review of recent advances studying itaconate and its derivatives as anti-inflammatory, immunoregulatory, antimicrobial and antiviral compounds, along with their mechanisms of action. Finally, the review emphasises the existing challenges and future research directions for the application of itaconate and its derivatives as anti-pathogenic agents.

Development of itaconate polymer microparticles for intracellular regulation of pro-inflammatory macrophage activation

Itaconate (IA) is an endogenous metabolite and a potent regulator of the innate immune system. Its use in immunomodulatory therapies has faced limitations due to inherent challenges in achieving controlled delivery and requirements for high extracellular concentrations to achieve internalization of the highly polar small molecule to achieve its intracellular therapeutic activity. Microparticle (MP)-based delivery strategies are a promising approach for intracellular delivery of small molecule metabolites through macrophage phagocytosis and subsequent intracellular polymer degradation-based delivery. Toward the goal of intracellular delivery of IA, degradable polyester polymer-(poly(itaconate-co-dodecanediol)) based IA polymer microparticles (IA-MPs) were generated using an emulsion method, forming micron-scale (∼ 1.5 µm) degradable microspheres. IA-MPs were characterized with respect to their material properties and IA release kinetics to inform particle fabrication. Treatment of murine bone marrow-derived macrophages with an optimized particle concentration of 0.1 mg/million cells enabled phagocytosis-mediated internalization and low levels of cytotoxicity. Flow cytometry demonstrated IA-MP-specific regulation of IA-sensitive inflammatory targets. Metabolic analyses demonstrated that IA-MP internalization inhibited oxidative metabolism and induced glycolytic reliance, consistent with the established mechanism of IA-associated inhibition of succinate dehydrogenase. This development of IA-based polymer microparticles provides a basis for additional innovative metabolite-based microparticle drug delivery systems for the treatment of inflammatory disease.

IRG1/itaconate enhances efferocytosis by activating Nrf2-TIM4 signaling pathway to alleviate con A induced autoimmune liver injury

Immune response gene 1 (IRG1) is highly expressed in mitochondria of macrophages in a pro-inflammatory state. IRG1 and its metabolites play important roles in infection, immune-related diseases and tumor progression by exerting resistance of pathogens, attenuating inflammation and producing antioxidant substances through various pathways and mechanisms. IRG1 deficiency aggravates liver injury. Efferocytosis is a vital mechanism for preventing the progression of inflammatory tissue damage. However, the mechanism by how IRG1/itaconate regulates efferocytosis in autoimmune hepatitis has yet to be fully understood. Therefore, we explored the influence of IRG1-/- on efferocytosis and its effects on regulating the nuclear factor erythroid 2-associated factor 2 (Nrf2)-T-cell immunoglobulin domain and mucin domain 4 (TIM4) pathway and autoimmune liver injury. An autoimmune hepatitis model was established by injecting Con A into wild-type and IRG1-/- mice via the tail vein. Liver injury and inflammatory response were assessed. The efferocytosis role of IRG1-/- macrophages and its potential regulatory mechanisms were also analysed. Exogenous 4-octyl itaconate (OI) supplementation promoted the expression of Nrf2 and TIM4 and restored IRG1-/- bone marrow-derived macrophage (BMDM) efferocytosis, whereas inhibition of Nrf2 mediated by ML385 led to impaired efferocytosis of BMDMs, decreased expression of TIM4, and aggravated liver inflammation injury. Additionally, after supplementing Nrf2-/- BMDMs with exogenous OI, we evaluated the changes in its efferocytosis effect, efferocytosis did not change, and the protective effect of OI disappeared. However, when TIM4 was blocked, the efferocytotic effect of BMDMs was attenuated, inflammatory liver injury and oxidative stress were aggravated. OI promoted the transformation of macrophages into M2 macrophages, and this was inhibited when TIM4 was blocked. To our best understanding, this is the initial exploration to show that TIM4, a downstream molecule of the IRG1/itaconate-Nrf2 pathway, regulates macrophage efferocytosis. These findings suggest a new mechanism and potential treatment for promoting the resolution of inflammation and efferocytosis in autoimmune hepatitis.

Itaconate transporter SLC13A3 confers immunotherapy resistance via alkylation-mediated stabilization of PD-L1

Itaconate is a metabolite catalyzed by cis-aconitate decarboxylase (ACOD1), which is mainly produced by activated macrophages and secreted into the extracellular environment to exert complex bioactivity. In the tumor microenvironment, itaconate is concentrated and induces an immunosuppressive response. However, whether itaconate can be taken up by tumor cells and its mechanism of action remain largely unclear. Here, we identified solute carrier family 13 member 3 (SLC13A3) as a key protein transporting extracellular itaconate into cells, where it elevates programmed cell death ligand 1 (PD-L1) protein levels and decreases the expression of immunostimulatory molecules, thereby promoting tumor immune evasion. Mechanistically, itaconate alkylates the cysteine 272 residue on PD-L1, antagonizing PD-L1 ubiquitination and degradation. Consequently, SLC13A3 inhibition enhances the efficacy of anti-CTLA-4 (cytotoxic T lymphocyte-associated antigen-4) immunotherapy and improves the overall survival rate in syngeneic mouse tumor models. Collectively, our findings identified SLC13A3 as a key transporter of itaconate and revealed its immunomodulatory role, providing combinatorial strategies to overcome immunotherapy resistance in tumors.

Metabolic Regulation of Inflammation: Exploring the Potential Benefits of Itaconate in Autoimmune Disorders

Itaconic acid and its metabolites have demonstrated significant therapeutic potential in various immune diseases. Originating from the tricarboxylic acid cycle in immune cells, itaconic acid can modulate immune responses, diminish inflammation, and combat oxidative stress. Recent research has uncovered multiple mechanisms through which itaconic acid exerts its effects, including the inhibition of inflammatory cytokine production, activation of anti-inflammatory pathways, and modulation of immune cell function by regulating cellular metabolism. Cellular actions are influenced by the modulation of metabolic pathways, such as inhibiting succinate dehydrogenase (SDH) activity or glycolysis, activation of nuclear-factor-E2-related factor 2 (Nrf2), boosting cellular defences against oxidative stress, and suppression of immune cell inflammation through the NF-κB pathway. This comprehensive review discusses the initiation, progression, and mechanisms of action of itaconic acid and its metabolites, highlighting their modulatory effects on various immune cell types. Additionally, it examines their involvement in immune disease like rheumatoid arthritis, multiple sclerosis, type 1 diabetes mellitus, and autoimmune hepatitis, offering greater understanding for creating new therapies for these ailments.

Examining the Impact of Microglia on Ischemic Stroke With an Emphasis on the Metabolism of Immune Cells

BACKGROUND

Ischemic stroke, a major cause of disability and the second leading cause of death, poses a significant public health challenge. Post-stroke inflammation can harm the blood-brain barrier and worsen neurological deficits, which are key factors in neuronal damage in patients with ischemic stroke. Microglia are crucial in the central nervous system, involved in inflammation, neuronal damage, and repair after cerebral ischemia. While cellular immune metabolism has been widely studied, its role in ischamic stroke remains unclear.

AIM

This review aims to examine how inflammation affects the phenotypic characteristics of immune cells after ischemic stroke and to explore the effects of the immune metabolic microenvironment on the phenotypic profiles and functions of microglia in ischemic stroke.

METHOD

The review refers to the available literature in PubMed, searching for critical terms related to Ischemic stroke, neuroinflammation, microglia, and immunometabolism.

RESULT

In this review, we found that during stroke progression, microglia can dynamically switch between pro-inflammatory and anti-inflammatory phenotypes. Microglial glycometabolism includes oxidative phosphorylation and glycolysis, and lipid metabolism involves lipid synthesis and breakdown. Modulating the production of inflammatory mediator precursors can induce an anti-inflammatory phenotype in microglia.

CONCLUSION

Thus, studying microglial metabolic pathways and their products may offer new insights for ischemic stroke treatment.

Dissecting S-itaconation at host-pathogen interactions with chemical proteomics tools

The molecular essence of the battle between host and pathogens lies in the protein-protein or protein-metabolite interactions. Itaconate is one of the most upregulated immunometabolites, regulating immune responses through either noncovalent binding or covalent modification in the host. We herein briefly review recent progresses in the discoveries of physiological and pathological roles of itaconate and applications of chemical proteomic technologies in exploring itaconate modifications on cysteines (S-itaconation) at the interface of host-pathogen interactions. Key challenges are also proposed as future outlook.

The cell autonomous and non-autonomous roles of itaconate in immune response

Itaconate which is discovered as a mammalian metabolite possessing antimicrobial and immunoregulatory activity has attracted much attention in the field of immunometabolism. Itaconate is synthesized by myeloid cells under conditions of pathogen infection and sterile inflammation. In addition to regulating immune response of myeloid cells, itaconate secreted from myeloid cells can also be taken up by non-myeloid cells to exert immunoregulatory effects in a cell non-autonomous manner. In this review, we recap the discovery of itaconate as a distinct immunologic regulator and effector, describe the development of itaconate biosensor, and detail the recent findings that decipher the mechanism underlying intercellular transport of itaconate. Based on these knowledges, we propose itaconate is a messenger transmitting immunologic signals from myeloid cells to other types of cells during host inflammation and immune defense.

Inhibition of Mitochondrial Succinate Dehydrogenase with Dimethyl Malonate Promotes M2 Macrophage Polarization by Enhancing STAT6 Activation

Macrophages exhibit diverse phenotypes depending on environment status, which contribute to physiological and pathological processes of immunological diseases, including sepsis, asthma, multiple sclerosis and colitis. The alternative activation of macrophages is tightly regulated to avoid excessive activation and damage of tissues and organs. Certain works characterized that succinate dehydrogenase (SDH) altered function of macrophages and promoted inflammatory response in M1 macrophages via mitochondrial reactive oxygen species (ROS). However, the effect of succinate dehydrogenase on M2 macrophage polarization remains incompletely understood. We employed dimethyl malonate (DMM) to inhibit succinate dehydrogenase activity and took use of RNA-seq to analyze the changes of inflammatory response of LPS-activated M1 macrophages or IL 4-activated M2 macrophages. Our data revealed that inhibition of SDH with DMM increased expression of M2 macrophages-associated signature genes, including Arg1, Ym1 and Mrc1. Consistent with previous work, we also observed that inhibition of SDH decreased the expression of IL-1β and enhanced the levels of IL-10 in M1 macrophages. Additionally, inhibition of SDH with DMM inhibited the production of chemokines, such as Cxcl3, Cxcl12, Ccl20 and Ccl9. DMM also amplified the M2 macrophages-related signature genes in IL-13-activated M2 macrophages. Mechanistic studies revealed that DMM promoted M2 macrophages polarization through mitochondrial ROS dependent STAT6 activation. Blocking ROS with mitoTEMPO or inhibiting STAT6 activation with ruxolitinib abrogated the promotion effect of DMM on M2 macrophages. Finally, dimethyl malonate treatment promoted peritoneal M2 macrophages differentiation and exacerbated OVA-induced allergy asthma in vivo. Collectively, we identified SDH as a braker to suppress M2 macrophage polarization via mitochondrial ROS, suggesting a novel strategy to treatment of M2 macrophages-mediated inflammatory diseases.

Macrophage polarization in sepsis: Emerging role and clinical application prospect

Sepsis is a severe, potentially fatal condition defined by organ dysfunction due to excessive inflammation. Its complex pathogenesis and poor therapeutic outcomes pose significant challenges in treatment. Macrophages, with their high heterogeneity and plasticity, play crucial roles in both the innate and adaptive immune systems. They can polarize into M1-like macrophages, which promote pro-inflammatory responses, or M2-like macrophages, which mediate anti-inflammatory responses, positioning them as critical mediators in the immune response during sepsis.Macrophages are the main regulators of inflammatory responses, and their polarization is also regulated by inflammatory signaling pathways. This review highlights recent advances in the inflammatory signaling pathways involved in sepsis, mechanism of macrophage polarization mediated by inflammation-related signaling pathways in sepsis, and the role of signaling pathway mediated macrophage polarization in organ dysfunction involved in sepsis. We also explore the therapeutic potential of targeting macrophage polarization for immunotherapy, offering new perspectives on macrophage-targeted treatments for sepsis.

Click Chemistry in Detecting Protein Modification

Click chemistry, also known as "link chemistry," is an important molecular connection method that can achieve simple and efficient connections between specific small molecular groups at the molecular level. Click chemistry offers several advantages, including high efficiency, good selectivity, mild conditions, and few side reactions. These features make it a valuable tool for in-depth analysis of various protein posttranslational modifications (PTMs) caused by changes in cell metabolism during viral infection. This chapter considers the palmitoylation, carbonylation, and alkylation of STING and presents detailed information and experimental procedures for measuring PTMs using click chemistry.

Itaconate facilitates viral infection via alkylating GDI2 and retaining Rab GTPase on the membrane

Metabolic reprogramming of host cells plays critical roles during viral infection. Itaconate, a metabolite produced from cis-aconitate in the tricarboxylic acid cycle (TCA) by immune responsive gene 1 (IRG1), is involved in regulating innate immune response and pathogen infection. However, its involvement in viral infection and underlying mechanisms remain incompletely understood. Here, we demonstrate that the IRG1-itaconate axis facilitates the infections of VSV and IAV in macrophages and epithelial cells via Rab GTPases redistribution. Mechanistically, itaconate promotes the retention of Rab GTPases on the membrane via directly alkylating Rab GDP dissociation inhibitor beta (GDI2), the latter of which extracts Rab GTPases from the membrane to the cytoplasm. Multiple alkylated residues by itaconate, including cysteines 203, 335, and 414 on GDI2, were found to be important during viral infection. Additionally, this effect of itaconate needs an adequate distribution of Rab GTPases on the membrane, which relies on Rab geranylgeranyl transferase (GGTase-II)-mediated geranylgeranylation of Rab GTPases. The single-cell RNA sequencing data revealed high expression of IRG1 primarily in neutrophils during viral infection. Co-cultured and in vivo animal experiments demonstrated that itaconate produced by neutrophils plays a dominant role in promoting viral infection. Overall, our study reveals that neutrophils-derived itaconate facilitates viral infection via redistribution of Rab GTPases, suggesting potential targets for antiviral therapy.

Metabolic Reprograming of Macrophages: A New Direction in Traditional Chinese Medicine for Treating Liver Failure

Acute liver failure (ALF) is a fulminant clinical syndrome that usually leads to multiple organ failure and high mortality. Macrophages play a crucial role in the initiation, development, and recovery of ALF. Targeting macrophages through immunotherapy holds significant promise as a therapeutic strategy. These cells exhibit remarkable plasticity, enabling them to differentiate into various subtypes based on changes in their surrounding microenvironment. M1-type macrophages are associated with a pro-inflammatory phenotype and primarily rely predominantly on glycolysis. In contrast, M2-type macrophages, which are characterized by anti-inflammatory phenotype, predominantly obtain their energy from oxidative phosphorylation (OXPHOS) and fatty acid oxidation (FAO). Shifting macrophage metabolism from glycolysis to OXPHOS inhibits M1 macrophage activation and promotes M2 macrophage activation, thereby exerting anti-inflammatory and reparative effects. This study elucidates the relationship between macrophage activation and glucose metabolism reprograming from an immunometabolism perspective. A comprehensive literature review revealed that several signaling pathways may regulate macrophage polarization through energy metabolism, including phosphatidyl-inositol 3-kinase/protein kinase B (PI3K/AKT), mammalian target of rapamycin (mTOR)/hypoxia-inducible factor 1α (HIF-1α), nuclear factor-κB (NF-κB), and AMP-activated protein kinase (AMPK), which exhibit crosstalk with one another. Additionally, we systematically reviewed several traditional Chinese medicine (TCM) monomers that can modulate glucose metabolism reprograming and influence the polarization states of M1 and M2 macrophages. This review aimed to provide valuable insights that could contribute to the development of new therapies or drugs for ALF.

CAR-Macrophage Therapy Alleviates Myocardial Ischemia-Reperfusion Injury

BACKGROUND

Given the growing acknowledgment of the detrimental effects of excessive myocardial fibrosis on pathological remodeling after myocardial ischemia-reperfusion injury (I/R), targeting the modulation of myocardial fibrosis may offer protective and therapeutic advantages. However, effective clinical interventions and therapies that target myocardial fibrosis remain limited. As a promising chimeric antigen receptor (CAR) cell therapy, whether CAR macrophages (CAR-Ms) can be used to treat I/R remains unclear.

METHODS

The expression of FAP (fibroblast activation protein) was studied in mouse hearts after I/R. FAP CAR-Ms were generated to target FAP-expressing cardiac fibroblasts in mouse hearts after I/R. The phagocytosis activity of FAP CAR-Ms was tested in vitro. The efficacy and safety of FAP CAR-Ms in treating I/R were evaluated in vivo.

RESULTS

FAP was significantly upregulated in activated cardiac fibroblasts as early as 3 days after I/R. Upon demonstrating their ability to engulf FAP-overexpressing fibroblasts, we intravenously administered FAP CAR-Ms to mice at 3 days after I/R and found that FAP CAR-Ms significantly improved cardiac function and reduced myocardial fibrosis in mice after I/R. No toxicities associated with FAP CAR-Ms were detected in the heart or other organs at 2 weeks after I/R. Finally, we found that FAP CAR-Ms conferred long-term cardioprotection against I/R.

CONCLUSIONS

Our proof-of-concept study demonstrates the therapeutic potential of FAP CAR-Ms in alleviating myocardial I/R and potentially opens new avenues for the treatment of a range of heart diseases that include a fibrotic phenotype.

4-Octyl itaconate blocks GSDMB-mediated pyroptosis and restricts inflammation by inactivating granzyme A

GSDMB-mediated pyroptosis facilitates a pro-inflammatory immune microenvironment and needs to be tightly regulated to avoid excessive inflammation. Here, we provide evidence that itaconate and its cell-permeable derivative 4-octyl itaconate (4-OI) can significantly inhibit GSDMB-rendered pyroptotic activity independent of Nrf2. 4-OI interferes proteolytic process of GSDMB by directly modifying Cys54, Cys148 and Ser212 on granzyme A (GrzA), a serine protease that site-specifically cleaves the inter-domain linker of GSDMB, instead of interaction with GSDMB, thereby blocking pyroptosis and exerts anti-inflammatory effects. Moreover, 4-OI alleviates inflammation by suppressing GSDMB-induced pyroptotic cell death during acute colitis models in intestinal epithelial GSDMB conditional transgenic mice. Our data expand the role of 4-OI as a crucial immunometabolic derivative that regulates innate immunity and inflammation through a newly identified posttranslational modification, and targeting of pyroptosis by 4-OI therefore holds potent therapeutic potential for primarily inflammatory and/or autoimmune diseases.

Association Between the Ionized-to-Total Calcium Ratio and the Risk of Acute Kidney Injury in Patients With Severe Autoimmune Diseases: A Retrospective Analysis From the MIMIC-IV Database

AIM

To investigate the relationship between the ionized-to-total calcium ratio and the incidence of acute kidney injury (AKI) in critically ill patients with autoimmune diseases.

METHODS

A retrospective study was conducted utilizing data from the Medical Information Mart for Intensive Care IV database. In-hospital AKI was the primary outcome. Patients were classified into four distinct categories depending on the calcium ratio. Cox proportional hazards model and restricted cubic spline (RCS) analysis were applied to assess the association between the calcium ratio and AKI risk. Subgroup analyses were conducted to evaluate the consistency of this association across various patient characteristics.

RESULTS

A total of 1054 critically ill patients with autoimmune diseases were enrolled and stratified by calcium ratio quartiles into four groups (< 0.515; 0.515-0.546; 0.546-0.576; > 0.576). Cumulative incidence curves showed significant difference in AKI risk among the four groups. Patients in the highest calcium ratio quartile experienced a markedly reduced likelihood of AKI versus those in the lowest, especially in the fully adjusted model (HR = 0.66, 95% CI 0.51-0.84, p < 0.001). RCS analysis demonstrated an obvious nonlinear relationship, showing a steep decline in AKI risk with increasing calcium ratio, which eventually plateaued. This protective effect of higher calcium ratios against AKI was consistent across subgroups, except in those with chronic kidney disease at baseline.

CONCLUSION

The ionized-to-total calcium ratio proves to be significantly associated with the development of AKI in critically ill patients with autoimmune diseases, with its elevation indicating a reduced AKI risk.

Itaconate suppresses house dust mite-induced allergic airways disease and Th2 cell differentiation

Itaconate was initially identified as an antimicrobial compound produced by myeloid cells. Beyond its antimicrobial role, itaconate may also serve as a crucial metabolic and immune modulator. We therefore examined the roles of aconitate decarboxylase 1 (Acod1) and itaconate in house dust mite (HDM)-sensitized and -challenged mice, a model of T helper 2 (Th2)-driven allergic airways disease. HDM treatment induced lung Acod1 mRNA expression and bronchoalveolar lavage (BAL) itaconate levels in wild-type C57BL/6 mice. Acod1 knockout mice (Acod1-KO) with negligible BAL itaconate showed heightened HDM-induced type 2 cytokine expression, increased serum IgE, and enhanced recruitment of Th2 cells in the lung, indicating a shift towards a more pronounced Th2 immune response. Acod1-KO mice also showed increased eosinophilic airway inflammation and hyperresponsiveness. Experiments in chimeric mice demonstrated that bone marrow from Acod1-KO mice is sufficient to increase type 2 cytokine expression in wild-type mice, and that restitution of bone marrow from wild type mice attenuates mRNA expression of Th2 cytokines in Acod1-KO mice. Specific deletion of Acod1 in lysozyme-secreting macrophages (LysM-cre+Acod1flox/flox) recapitulated the exaggerated phenotype observed in whole-body Acod1-KO mice. Adoptive transfer of Acod1-KO bone marrow-derived macrophages also increased lung mRNA expression of Th2 cytokines. In addition, treatment of Th2-polarized CD4 cells with itaconate impeded Th2 cell differentiation, as shown by reduced expression of Gata3 and decreased release of IL-5 and IL-13. Finally, public datasets of human samples show lower Acod1 expression in subjects with allergic asthma, consistent with a protective role of itaconate in asthma pathogenesis. Together, these data suggest that itaconate plays a protective, immunomodulatory role in limiting airway type 2 inflammation after allergen challenge by attenuating T cell responses.

Itaconate uptake via SLC13A3 improves hepatic antibacterial innate immunity

Itaconate is an immunoregulatory metabolite produced by the mitochondrial enzyme immune-responsive gene 1 (IRG1) in inflammatory macrophages. We recently identified an important mechanism by which itaconate is released from inflammatory macrophages. However, it remains unknown whether extracellular itaconate is taken up by non-myeloid cells to exert immunoregulatory functions. Here, we used a custom-designed CRISPR screen to identify the dicarboxylate transporter solute carrier family 13 member 3 (SLC13A3) as an itaconate importer and to characterize the role of SLC13A3 in itaconate-improved hepatic antibacterial innate immunity. Functionally, liver-specific deletion of Slc13a3 impairs hepatic antibacterial innate immunity in vivo and in vitro. Mechanistically, itaconate uptake via SLC13A3 induces transcription factor EB (TFEB)-dependent lysosomal biogenesis and subsequently improves antibacterial innate immunity in mouse hepatocytes. These findings identify SLC13A3 as a key itaconate importer in mouse hepatocytes and will aid in the development of potent itaconate-based antibacterial therapeutics.

Itaconate drives mtRNA-mediated type I interferon production through inhibition of succinate dehydrogenase

Itaconate is one of the most highly upregulated metabolites in inflammatory macrophages and has been shown to have immunomodulatory properties. Here, we show that itaconate promotes type I interferon production through inhibition of succinate dehydrogenase (SDH). Using pharmacological and genetic approaches, we show that SDH inhibition by endogenous or exogenous itaconate leads to double-stranded mitochondrial RNA (mtRNA) release, which is dependent on the mitochondrial pore formed by VDAC1. In addition, the double-stranded RNA sensors MDA5 and RIG-I are required for IFNβ production in response to SDH inhibition by itaconate. Collectively, our data indicate that inhibition of SDH by itaconate links TCA cycle modulation to type I interferon production through mtRNA release.

Cancer cell-intrinsic biosynthesis of itaconate promotes tumor immunogenicity

The Krebs cycle byproduct itaconate has recently emerged as an important metabolite regulating macrophage immune functions, but its role in tumor cells remains unknown. Here, we show that increased tumor-intrinsic cis-aconitate decarboxylase (ACOD1 or CAD, encoded by immune-responsive gene 1, Irg1) expression and itaconate production promote tumor immunogenicity and anti-tumor immune responses. Furthermore, we identify thimerosal, a vaccine preservative, as a specific inducer of IRG1 expression in tumor cells but not in macrophages, thereby enhancing tumor immunogenicity. Mechanistically, thimerosal induces itaconate production through a ROS-RIPK3-IRF1 signaling axis in tumor cells. Further, increased IRG1/itaconate upregulates antigen presentation-related gene expression via promoting TFEB nuclear translocation. Intratumoral injection of thimerosal induced itaconate production, activated the tumor immune microenvironment, and inhibited tumor growth in a T cell-dependent manner. Importantly, IRG1 deficiency markedly impaired tumor response to thimerosal treatment. Furthermore, itaconate induction by thimerosal potentiates the anti-tumor efficacy of adoptive T-cell therapy and anti-PD1 therapy in a mouse lymphoma model. Hence, our findings identify a new role for tumor intrinsic IRG1/itaconate in promoting tumor immunogenicity and provide a translational means to increase immunotherapy efficacy.

A multifunctional self-reinforced injectable hydrogel for enhancing repair of infected bone defects by simultaneously targeting macrophages, bacteria, and bone marrow stromal cells

Injectable hydrogels (IHs) have demonstrated huge potential in promoting repair of infected bone defects (IBDs), but how to endow them with desired anti-bacterial, immunoregulatory, and osteo-inductive properties as well as avoid mechanical failure during their manipulation are challenging. In this regard, we developed a multifunctional AOHA-RA/Lap nanocomposite IH for IBDs repair, which was constructed mainly through two kinds of reversible cross-links: (i) the laponite (Lap) crystals mediated electrostatic interactions; (ii) the phenylboronic acid easter bonds between the 4-aminobenzeneboronic acid grafted oxidized hyaluronic acid (AOHA) and rosmarinic acid (RA). Due to the specific structural composition, the AOHA-RA/Lap IH demonstrated superior injectability, self-recoverability, spatial adaptation, and self-reinforced mechanical properties after being injected to the bone defect site. In addition, the RA molecules could be locally released from the hydrogel following a Weibull model for over 10 days. Systematic in vitro/vivo assays proved the strong anti-bacterial activity of the hydrogel against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Moreover, its capability of inducing M2 polarization of macrophages (Mφ) and osteogenic differentiation of bone marrow stromal cells (BMSCs) was verified either, and the mechanism of the former was identified to be related to the JAK1-STAT1 and PI3K-AKT signaling pathways and that of the latter was identified to be related to the calcium signaling pathway, extracellular matrix (ECM) receptor interaction and TGF-β signaling pathway. After being implanted to a S. aureus infected rat skull defect model, the AOHA-RA/Lap IH significantly accelerated repair of IBDs without causing significant systemic toxicity. STATEMENT OF SIGNIFICANCE: Rosmarinic acid and laponite were utilized to develop an injectable hydrogel, promising for accelerating repair of infected bone defects in clinic. The gelation of the hydrogel was completely driven by two kinds of reversible cross-links, which endow the hydrogel superior spatial adaption, self-recoverability, and structural stability. The as-prepared hydrogel demonstrated superior anti-bacterial/anti-biofilm activity and could induce M2 polarization of macrophages and osteogenic differentiation of BMSCs. The mechanism behind macrophages polarization was identified to be related to the JAK1-STAT1 and PI3K-AKT signaling pathways. The mechanism behind osteogenic differentiation of BMSCs was identified to be related to the ECM receptor interaction and calcium signaling/TGF-β signaling pathways.

Metabolic Dysregulation and Metabolite Imbalances in Acute-on-chronic Liver Failure: Impact on Immune Status

Liver failure encompasses a range of severe clinical syndromes resulting from the deterioration of liver function, triggered by factors both within and outside the liver. While the definition of acute-on-chronic liver failure (ACLF) may vary by region, it is universally recognized for its association with multiorgan failure, a robust inflammatory response, and high short-term mortality rates. Recent advances in metabolomics have provided insights into energy metabolism and metabolite alterations specific to ACLF. Additionally, immunometabolism is increasingly acknowledged as a pivotal mechanism in regulating immune cell functions. Therefore, understanding the energy metabolism pathways involved in ACLF and investigating how metabolite imbalances affect immune cell functionality are crucial for developing effective treatment strategies for ACLF. This review methodically examined the immune and metabolic states of ACLF patients and elucidated how alterations in metabolites impact immune functions, offering novel perspectives for immune regulation and therapeutic management of liver failure.

Itaconate is a metabolic regulator of bone formation in homeostasis and arthritis

OBJECTIVES

Bone remodelling is a highly dynamic process dependent on the precise coordination of osteoblasts and haematopoietic-cell derived osteoclasts. Changes in core metabolic pathways during osteoclastogenesis, however, are largely unexplored and it is unknown whether and how these processes are involved in bone homeostasis.

METHODS

We metabolically and transcriptionally profiled cells during osteoclast and osteoblast generation. Individual gene expression was characterised by quantitative PCR and western blot. Osteoblast function was assessed by Alizarin red staining. immunoresponsive gene 1 (Irg1)-deficient mice were used in various inflammatory or non-inflammatory models of bone loss. Tissue gene expression was analysed by RNA in situ hybridisation.

RESULTS

We show that during differentiation preosteoclasts rearrange their tricarboxylic acid cycle, a process crucially depending on both glucose and glutamine. This rearrangement is characterised by the induction of Irg1 and production of itaconate, which accumulates intracellularly and extracellularly. While the IRG1-itaconate axis is dispensable for osteoclast generation in vitro and in vivo, we demonstrate that itaconate stimulates osteoblasts by accelerating osteogenic differentiation in both human and murine cells. This enhanced osteogenic differentiation is accompanied by reduced proliferation and altered metabolism. Additionally, supplementation of itaconate increases bone formation by boosting osteoblast activity in mice. Conversely, Irg1-deficient mice exhibit decreased bone mass and have reduced osteoproliferative lesions in experimental arthritis.

CONCLUSION

In summary, we identify itaconate, generated as a result of the metabolic rewiring during osteoclast differentiation, as a previously unrecognised regulator of osteoblasts.

Caulerpa chemnitzia polysaccharide exerts immunomodulatory activity in macrophages by mediating the succinate/PHD2/HIF-1α/IL-1β pathway

Algal polysaccharide is an important food functional factor with diverse bioactive and low toxicity. Previous studies have confirmed Caulerpa chemnitzia polysaccharides (CRVP) have immunomodulatory activity, but the immunomodulatory mechanism of CRVP in macrophages has not been thoroughly explored yet. In our research, we found that CRVP has outstanding immunomodulatory activity in macrophages, which is reflected in promoting cell proliferation, upregulating cytokines (IL-1β, IL-6, and TNF-α) expression, and increasing NO and ROS levels. Additionally, the result of joint analysis of untargeted metabolomics showed metabolism played a major role in the immunomodulatory of CRVP and suggested succinic acid was a key metabolite. Further verification indicated that the accumulation of succinic acid in macrophages after administered with CRVP, induced the down-regulation of prolyl hydroxylase domain 2 (PHD2) and up-regulation of hypoxia-inducible factor-1α (HIF-1α), thereby enhancing IL-1β expression. Together, the immunomodulatory activity of CRVP in macrophages via succinate/PHD2/HIF-1α/IL-1β pathway.

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.

Future applications of host direct therapies for infectious disease treatment

New and emerging pathogens, such as SARS-CoV2 have highlighted the requirement for threat agnostic therapies. Some antibiotics or antivirals can demonstrate broad-spectrum activity against pathogens in the same family or genus but efficacy can quickly reduce due to their specific mechanism of action and for the ability of the disease causing agent to evolve. This has led to the generation of antimicrobial resistant strains, making infectious diseases more difficult to treat. Alternative approaches therefore need to be considered, which include exploring the utility of Host-Directed Therapies (HDTs). This is a growing area with huge potential but difficulties arise due to the complexity of disease profiles. For example, a HDT given early during infection may not be appropriate or as effective when the disease has become chronic or when a patient is in intensive care. With the growing understanding of immune function, a new generation of HDT for the treatment of disease could allow targeting specific pathways to augment or diminish the host response, dependent upon disease profile, and allow for bespoke therapeutic management plans. This review highlights promising and approved HDTs that can manipulate the immune system throughout the spectrum of disease, in particular to viral and bacterial pathogens, and demonstrates how the advantages of HDT will soon outweigh the potential side effects.

JAK inhibitor selectivity: new opportunities, better drugs?

Cytokines function as communication tools of the immune system, serving critical functions in many biological responses and shaping the immune response. When cytokine production or their biological activity goes awry, the homeostatic balance of the immune response is altered, leading to the development of several pathologies such as autoimmune and inflammatory disorders. Cytokines bind to specific receptors on cells, triggering the activation of intracellular enzymes known as Janus kinases (JAKs). The JAK family comprises four members, JAK1, JAK2, JAK3 and tyrosine kinase 2, which are critical for intracellular cytokine signalling. Since the mid-2010s multiple JAK inhibitors have been approved for inflammatory and haematological indications. Currently, approved JAK inhibitors have demonstrated clinical efficacy; however, improved selectivity for specific JAKs is likely to enhance safety profiles, and different strategies have been used to accomplish enhanced JAK selectivity. In this update, we discuss the background of JAK inhibitors, current approved indications and adverse effects, along with new developments in this field. We address the issue of JAK selectivity and its relevance in terms of efficacy, and describe new modalities of JAK targeting, as well as new aspects of JAK inhibitor action.

Pharmacological upregulation of macrophage-derived itaconic acid by pubescenoside C attenuated myocardial ischemia-reperfusion injury

INTRODUCTION

Myocardial ischemia-reperfusion injury (MIRI) remains a prevalent clinical challenge globally, lacking an ideal therapeutic strategy. Macrophages play a pivotal role in MIRI pathophysiology, exhibiting dynamic inflammatory and resolutive functions. Macrophage polarization and metabolism are intricately linked to MIRI, presenting potential therapeutic targets. Pubescenoside C (PBC) from Ilex pubescens showed significantly anti-inflammatory effects, however, the effect of PBC on MIRI is unknown.

OBJECTIVES

This study aimed to assess the cardioprotective effects of PBC against MIRI and elucidate the underlying mechanisms.

METHODS

Sprague-Dawley rats, H9c2 and RAW264.7 macrophages were used to establish the in vitro and in vivo models of MIRI. TTC/Evans blue staining, immunohistochemical staining, metabonomics analysis, chemical probe, surface plasmon resonance (SPR), co-immunoprecipitation (CO-IP) assays were used for pharmacodynamic and mechanism study.

RESULTS

PBC administration effectively reduced myocardial infarct size, decreased ST-segment elevation, and lowered CK-MB levels, concurrently promoting macrophage M2 polarization in MIRI. Furthermore, PBC-treated macrophages and their conditioned culture medium attenuated the apoptosis of H9c2 cells induced by oxygen-glucose deprivation/reoxygenation (OGD/R). Metabonomics analysis revealed that PBC increased the production of itaconic acid (ITA) and malic acid (MA) in macrophages, which conferred protection against OGD/R injury in H9c2 cells. Mechanistic investigations indicated that ITA exerted its effects by covalently modifying pyruvate kinase M2 (PKM2) at Cys474, Cys424, and Lys151, thereby facilitating PKM2's mitochondrial translocation and enhancing the PKM2/Bcl2 interaction, subsequently leading to decreased degradation of Bcl2. SPR assays further revealed that PBC bound to HSP90, facilitating the interaction between HSP90 and GSK3β and resulting in the inactivation of GSK3β activity and upregulation of key metabolic enzymes for ITA and MA production (Acod1 and Mdh2).

CONCLUSION

PBC alleviates MIRI-induced cardiomyocyte apoptosis by modulating the HSP90/ITA/PKM2 axis. Furthermore, pharmacological upregulation of ITA emerges as a promising therapeutic approach for MIRI, hinting at PBC's potential as a candidate drug for MIRI therapy.

Itaconate induces tolerance of Staphylococcus aureus to aminoglycoside antibiotics

INTRODUCTION

Staphylococcus aureus is one of the chief pathogens that cause chronic and recurrent infections. Failure of the antibiotics to curb the infections contributes to relapse and is an important reason for the high mortality rate. Treatment failure may also be due to antibiotic tolerance. Accumulating evidence suggests that t the host immune environment plays an important role in inducing antibiotic tolerance of S. aureus, but research in this area has been limited.

METHODS

In this study,the minimum inhibitory concentration (MIC) of the antibiotics against S. aureus was determined using the standard broth microdilution method.The study evaluated whether itaconate induces antibiotic tolerance in S. aureus through an antibiotic bactericidal activity assay.The effect of itaconate on the growth of S. aureus was evaluated by monitoring the growth of S. aureus in medium supplemented with itaconate. Additionally, RNA sequencing and metabolomics analyses were used to determine transcriptional and metabolic changes in S. aureus when exposed to itaconate.

RESULTS AND DISCUSSION

According to the study,we found that the immune metabolite itaconate can induce tolerance in both methicillin-resistant and -susceptible S. aureus to aminoglycosides. When S. aureus was exposed to itaconate, its growth slowed down and transcriptomic and metabolomic alterations associated with decreased energy metabolism, including the tricarboxylate cycle, glycolysis, pyruvate metabolism, and arginine biosynthesis, were observed. These changes are associated with aminoglycoside tolerance. This study highlights the role of immune signaling metabolites in bacterial antibiotic tolerance and suggests new strategies to improve antibiotic treatment by modulating the host immune response and stimulating the metabolism of bacteria.

In situ chemoproteomic profiling reveals itaconate inhibits de novo purine biosynthesis in pathogens

Itaconate serves as an immune-specific metabolite that regulates gene transcription and metabolism in both host and pathogens. S-itaconation is a post-translational modification that regulates immune response; however, its antimicrobial mechanism under the physiological condition remains unclear. Here, we apply a bioorthogonal itaconate probe to perform global profiling of S-itaconation in living pathogens, including S. Typhimurium, S. aureus, and P. aeruginosa. Some functional enzymes are covalently modified by itaconate, including those involved in the de novo purine biosynthesis pathway. Further biochemical studies demonstrate that itaconate suppresses this specific pathway to limit Salmonella growth by inhibiting the initiator purF to lower de novo purine biosynthesis and simultaneously targeting the guaABC cluster to block the salvage route. Our chemoproteomic study provides a global portrait of S-itaconation in multiple pathogens and offers a valuable resource for finding susceptible targets to combat drug-resistant pathogens in the future.

Toward decoding spatiotemporal signaling activities of reactive immunometabolites with precision immuno-chemical biology tools

Immune-cell reprogramming driven by mitochondria-derived reactive electrophilic immunometabolites (mt-REMs-e.g., fumarate, itaconate) is an emerging phenomenon of major biomedical importance. Despite their localized production, mt-REMs elicit significantly large local and global footprints within and across cells, through mechanisms involving electrophile signaling. Burgeoning efforts are being put into profiling mt-REMs' potential protein-targets and phenotypic mapping of their multifaceted inflammatory behaviors. Yet, precision indexing of mt-REMs' first-responders with spatiotemporal intelligence and locale-specific function assignments remain elusive. Highlighting the latest advances and overarching challenges, this perspective aims to stimulate thoughts and spur interdisciplinary innovations to address these unmet chemical-biotechnological needs at therapeutic immuno-signaling frontiers.

Metabolic Messengers: itaconate

The metabolite itaconate has emerged as an important immunoregulator with roles in antibacterial defence, inhibition of inflammation and, more recently, as an inhibitory factor in obesity. Itaconate is one of the most upregulated metabolites in inflammatory macrophages. It is produced owing to the disturbance of the tricarboxylic acid cycle and the diversion of aconitate to itaconate via the enzyme aconitate decarboxylase 1. In immunology, initial studies concentrated on the role of itaconate in inflammatory macrophages where it was shown to be inhibitory, but this has expanded as the impact of itaconate on other cell types is starting to emerge. This review focuses on itaconate as a key immunoregulatory metabolite and describes its diverse mechanisms of action and its many impacts on the immune and inflammatory responses and in cancer. We also examine the clinical relevance of this immunometabolite and its therapeutic potential for immune and inflammatory diseases.

Endogenously produced itaconate negatively regulates innate-driven cytokine production and drives global ubiquitination in human macrophages

A wide variety of electrophilic derivatives of itaconate, the Kreb's cycle-derived metabolite, are immunomodulatory, yet these derivatives have overlapping and sometimes contradictory activities. Therefore, we generated a genetic system to interrogate the immunomodulatory functions of endogenously produced itaconate in human macrophages. Endogenous itaconate is driven by multiple innate signals restraining inflammatory cytokine production. Endogenous itaconate directly targets cysteine 13 in IRAK4 (disrupting IRAK4 autophosphorylation and activation), drives the degradation of nuclear factor κB, and modulates global ubiquitination patterns. As a result, cells unable to make itaconate overproduce inflammatory cytokines such as tumor necrosis factor alpha (TNFα), interleukin-6 (IL-6), and IL-1β in response to these innate activators. In contrast, the production of interferon (IFN)β, downstream of LPS, requires the production of itaconate. These data demonstrate that itaconate is a critical arbiter of inflammatory cytokine production downstream of multiple innate signaling pathways, laying the groundwork for the development of itaconate mimetics for the treatment of autoimmunity.