Itaconate Suppresses the Activation of Mitochondrial NLRP3 Inflammasome and Oxidative Stress in Allergic Airway Inflammation

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.

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.

4-Octyl Itaconate Alleviates Airway Eosinophilic Inflammation by Suppressing Chemokines and Eosinophil Development

4-Octyl itaconate (4-OI) is a derivative of the Krebs cycle-derived metabolite itaconate and displays an array of antimicrobial and anti-inflammatory properties through modifying cysteine residues within protein targets. We have found that 4-OI significantly reduces the production of eosinophil-targeted chemokines in a variety of cell types, including M1 and M2 macrophages, Th2 cells, and A549 respiratory epithelial cells. Notably, the suppression of these chemokines in M1 macrophages was found to be NRF2-dependent. In addition, 4-OI can interfere with IL-5 signaling and directly affect eosinophil differentiation. In a model of eosinophilic airway inflammation in BALB/c mice, 4-OI alleviated airway resistance and reduced eosinophil recruitment to the lungs. Our findings suggest that itaconate derivatives could be promising therapeutic agents for the treatment of eosinophilic asthma.

Immuno-Responsive Gene-1: A mitochondrial gene regulates pathogenic Th17 in CNS autoimmunity mouse model

Pathogenic Th17 cells are crucial to CNS autoimmune diseases like multiple sclerosis (MS), though their control by endogenous mechanisms is unknown. RNAseq analysis of brain glial cells identified immuno-responsive gene 1 (Irg1), a mitochondrial-related enzyme-coding gene, as one of the highly upregulated gene under inflammatory conditions which were further validated in the spinal cord of animals with experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Moreover, Irg1 mRNA and protein levels in myeloid, CD4, and B cells were higher in the EAE group, raising questions about its function in CNS autoimmunity. We observed that Irg1 knockout (KO) mice exhibited severe EAE disease and greater mononuclear cell infiltration, including triple-positive CD4 cells expressing IL17a, GM-CSF, and IFNγ. Lack of Irg1 in macrophages led to higher levels of Class II expression and polarized myelin primed CD4 cells into pathogenic Th17 cells through the NLRP3/IL1β axis. Our findings show that Irg1 in macrophages plays an important role in the formation of pathogenic Th17 cells, emphasizing its potential as a therapy for autoimmune diseases, including MS.

Itaconic acid induces angiogenesis and suppresses apoptosis via Nrf2/autophagy to prolong the survival of multi-territory perforator flaps

Background

Perforator flaps are widely used in hand microsurgery to reconstruct and repair soft tissue injuries. However, ischemia and subsequent ischemia-reperfusion injury may cause distal necrosis of the flap. Itaconic acid (IA) is a modulator of macrophage function, which exerts anti-inflammatory effects in macrophage activation.

Methods

The necrotic area of the flap was detected by measuring the flap temperature with an infrared thermometer. Flap cell apoptosis was detected by TUNEL staining and Western blot analysis of the apoptosis-associated proteins Bcl-2 and Bax. HE staining was used to detect angiogenesis of the skin flaps. CD31 was detected to identify positive vascular expression, and the survival of choke vessels in different areas of the skin flap was assessed by arteriography. In addition, Western blot was performed to quantify the expressions of VEGF, Nrf2, LC3II, SQSTM1, and CTSD.

Results

Itaconic acid raises VEGF protein levels in skin flaps and the number of CD31-positive vessels. The skin flaps in the IA treatment group exhibited higher neovascularization and less necrosis than those in the control group. The results of TUNEL staining and Western blot revealed that Itaconic acid attenuated apoptosis in the ischemic area of flap. The combination of itaconic acid and Nrf2 inhibitor ML385 reversed this beneficial effect. The results revealed that itaconic acid attenuated apoptosis, enhanced angiogenesis, and enhanced autophagy.

Conclusion

In summary, our findings indicate that itaconic acid might be an effective treatment to reduce flap necrosis. Additionally, this study identified a novel mechanism for the effects of itaconic acid on flap survival.