Exploring the evolutionary roots and physiological function of itaconate

Polyguluronate alleviates ulcerative colitis by targeting the gut commensal Lactobacillus murinus and its anti-inflammatory metabolites

Polyguluronate (PG) is a fermentable polysaccharide from edible algae. The present study was designed to investigate the therapeutic effect of PG on ulcerative colitis (UC) and its underlying mechanisms. Our results suggest that oral intake of PG attenuates UC and improves gut microbiota dysbiosis by promoting the growth of Lactobacillus spp. in dextran sulfate sodium-fed mice. Five different species of Lactobacillus were isolated from the feces of PG-treated mice and L. murinus was identified to have the best anti-colitis effect, suggesting a critical role for L. murinus in mediating the therapeutic effect of PG. Furthermore, PG was degraded potentially by the beta-glucuronidase from L. murinus and adding PG to the culture medium of L. murinus remarkably increased its production of anti-inflammatory metabolites, including itaconic acid, cis-11,14-eicosadienoic acid, and 3-amino-3-(2-chlorophenyl)-propionic acid. Additionally, L. salivarius, a human intestine-derived PG-utilizing species that is closely related to L. murinus, was also demonstrated to have potent anti-colitis effects, suggesting that it is a candidate target of PG in the human gut. Altogether, our study illustrates an unprecedented application of PG in the treatment of UC and establishes the basis for understanding its therapeutic effect from the perspective of L. murinus and its metabolites.

Engineering metabolism to modulate immunity

Metabolic programming and reprogramming have emerged as pivotal mechanisms for altering immune cell function. Thus, immunometabolism has become an attractive target area for treatment of immune-mediated disorders. Nonetheless, many hurdles to delivering metabolic cues persist. In this review, we consider how biomaterials are poised to transform manipulation of immune cell metabolism through integrated control of metabolic configurations to affect outcomes in autoimmunity, regeneration, transplant, and cancer. We emphasize the features of nanoparticles and other biomaterials that permit delivery of metabolic cues to the intracellular compartment of immune cells, or strategies for altering signals in the extracellular space. We then provide perspectives on the potential for reciprocal regulation of immunometabolism by the physical properties of materials themselves. Lastly, opportunities for clinical translation are highlighted. This discussion contributes to our understanding of immunometabolism, biomaterials-based strategies for altering metabolic configurations in immune cells, and emerging concepts in this evolving field.

The yin and yang of itaconate metabolism and its impact on the tumor microenvironment

The tumor microenvironment (TME) consists of a network of metabolically interconnected tumor and immune cell types. Macrophages influence the metabolic composition within the TME, which directly impacts the metabolic state and drug response of tumors. The accumulation of oncometabolites, such as succinate, fumarate, and 2-hydroxyglutarate, represents metabolic vulnerabilities in cancer that can be targeted therapeutically. Immunometabolites are emerging as metabolic regulators of the TME impacting immune cell functions and cancer cell growth. Here, we discuss recent discoveries on the potential impact of itaconate on the TME. We highlight how itaconate influences metabolic pathways relevant to immune responses and cancer cell proliferation. We also consider the therapeutic implications of manipulating itaconate metabolism as an immunotherapeutic strategy to constrain tumor growth.

Novel insights into the role of acetyl-CoA producing enzymes in epigenetic regulation

Inflammation-dependent changes in gene expression programs in innate immune cells, such as macrophages, involve extensive reprogramming of metabolism. This reprogramming is essential for the production of metabolites required for chromatin modifications, such as acetyl-CoA, and regulate their usage and availability impacting the macrophage epigenome. One of the most transcriptionally induced proinflammatory mediator is nitric oxide (NO), which has been shown to inhibit key metabolic enzymes involved in the production of these metabolites. Recent evidence indicates that NO inhibits mitochondrial enzymes such as pyruvate dehydrogenase (PDH) in macrophages induced by inflammatory stimulus. PDH is involved in the production of acetyl-CoA, which is essential for chromatin modifications in the nucleus, such as histone acetylation. In addition, acetyl-CoA levels in inflamed macrophages are regulated by ATP citrate lyase (ACLY) and citrate transporter SLC25A1. Interestingly, acetyl-CoA producing enzymes, such as PDH and ACLY, have also been reported to be present in the nucleus and to support the local generation of cofactors such as acetyl-CoA. Here, we will discuss the mechanisms involved in the regulation of acetyl-CoA production by metabolic enzymes, their inhibition by prolonged exposure to inflammation stimuli, their involvement in dynamic inflammatory expression changes and how these emerging findings could have significant implications for the design of novel therapeutic approaches.

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.

Mapping the Metabolic Niche of Citrate Metabolism and SLC13A5

The small molecule citrate is a key molecule that is synthesized de novo and involved in diverse biochemical pathways influencing cell metabolism and function. Citrate is highly abundant in the circulation, and cells take up extracellular citrate via the sodium-dependent plasma membrane transporter NaCT encoded by the SLC13A5 gene. Citrate is critical to maintaining metabolic homeostasis and impaired NaCT activity is implicated in metabolic disorders. Though citrate is one of the best known and most studied metabolites in humans, little is known about the consequences of altered citrate uptake and metabolism. Here, we review recent findings on SLC13A5, NaCT, and citrate metabolism and discuss the effects on metabolic homeostasis and SLC13A5-dependent phenotypes. We discuss the “multiple-hit theory” and how stress factors induce metabolic reprogramming that may synergize with impaired NaCT activity to alter cell fate and function. Furthermore, we underline how citrate metabolism and compartmentalization can be quantified by combining mass spectrometry and tracing approaches. We also discuss species-specific differences and potential therapeutic implications of SLC13A5 and NaCT. Understanding the synergistic impact of multiple stress factors on citrate metabolism may help to decipher the disease mechanisms associated with SLC13A5 citrate transport disorders.

Characterization and engineering of branched short-chain dicarboxylate metabolism in Pseudomonas reveals resistance to fungal 2-hydroxyparaconate

In recent years branched short-chain dicarboxylates (BSCD) such as itaconic acid gained increasing interest in both medicine and biotechnology. Their use as building blocks for plastics urges for developing microbial upcycling strategies to provide sustainable end-of-life solutions. Furthermore, many BSCD exhibit anti-bacterial properties or exert immunomodulatory effects in macrophages, indicating a medical relevance for this group of molecules. For both of these applications, a detailed understanding of the microbial metabolism of these compounds is essential. In this study, the metabolic pathway of BSCD degradation from Pseudomonas aeruginosa PAO1 was studied in detail by heterologously transferring it to Pseudomonas putida. Heterologous expression of the PA0878-0886 itaconate metabolism gene cluster enabled P. putida KT2440 to metabolize itaconate, (S)- and (R)-methylsuccinate, (S)-citramalate, and mesaconate. The functions of the so far uncharacterized genes PA0879 and PA0881 were revealed and proven to extend the substrate range of the core degradation pathway. Furthermore, the uncharacterized gene PA0880 was discovered to encode a 2-hydroxyparaconate (2-HP) lactonase that catalyzes the cleavage of the itaconate derivative 2-HP to itatartarate. Interestingly, 2-HP was found to inhibit growth of the engineered P. putida on itaconate. All in all, this study extends the substrate range of P. putida to include BSCD for bio-upcycling of high-performance polymers, and also identifies 2-HP as promising candidate for anti-microbial applications.

Mechanisms underlying the therapeutic effects of 4-octyl itaconate in treating sepsis based on network pharmacology and molecular docking

Objective: Through network pharmacology and molecular docking technology, the hub genes, biological functions, and signaling pathways of 4-Octyl itaconate (4-OI) against sepsis were revealed.

Methods: Pathological targets of sepsis were screened using GeneCards and GEO databases. Similarly, the pharmacological targets of 4-OI were obtained through Swiss TargetPrediction (STP), Similarity ensemble approach (SEA), and TargetNet databases. Then, all the potential targets of 4-OI anti-sepsis were screened by the online platform Draw Venn diagram, and the hub genes were screened by Cytoscape software. The identified hub genes were analyzed by GO and KEGG enrichment analysis, protein interaction (PPI) network, and molecular and docking technology to verify the reliability of hub gene prediction, further confirming the target and mechanism of 4-OI in the treatment of sepsis.

Results: After the target screening of 4-OI and sepsis, 264 pharmacological targets, 1953 pathological targets, and 72 genes related to 4-OI anti-sepsis were obtained, and eight hub genes were screened, namely MMP9, MMP2, SIRT1, PPARA, PTPRC, NOS3, TLR2, and HSP90AA1. The enrichment analysis results indicated that 4-OI might be involved in regulating inflammatory imbalance, immunosuppression, and oxidative stress in developing sepsis. 4-OI protects multiple organ dysfunction in sepsis by acting on hub genes, and MMP9 is a reliable gene for the prognosis and diagnosis of sepsis. The molecular docking results showed that 4-OI binds well to the hub target of sepsis.

Conclusion: 4-OI plays an antiseptic role by regulating MMP9, MMP2, SIRT1, PPARA, PTPRC, NOS3, TLR2 and HSP90AA1. These Hub genes may provide new insights into follow-up research on the target of sepsis treatment.

Dimethyl itaconate reprograms neurotoxic to neuroprotective primary astrocytes through the regulation of NLRP3 inflammasome and NRF2/HO-1 pathways

The activation of neurotoxic reactive astrocytes contributes to the pathogenesis of many neurodegenerative diseases. Itaconate, a product of cellular metabolism, is released from activated macrophage/microglia and has been shown to regulate inflammatory responses in several mammalian cells. This study was designed to investigate the impact of cell-permeable dimethyl itaconate (DI) on reactive astrocyte-dependent neurotoxicity. Primary murine astrocyte cells were isolated and stimulated with lipopolysaccharide (LPS) to generate reactive astrocytes. Treating these activated cells with DI was able to diminish the neurotoxic phenotype of reactive astrocytes, as we found reduced LPS-induced Nod-like receptor protein 3 (NLRP3) inflammasome activation and interleukin-1β (IL-1β) secretion. DI reduced the level of inflammasome components, attenuated inflammasome assembly and subsequently reduced caspase-1 cleavage and IL-1β levels. Additionally, DI attenuated nuclear factor-kappa B (NF-κB) phosphorylation in LPS-activated astrocytes and also protected astrocytes from LPS-induced cytotoxicity, including a lowering of Bax and caspase3. DI-treated reactive astrocytes showed an elevated GSH/GSSG ratio and improved antioxidant defense factors including catalase and superoxide dismutase, while lipid peroxidation was reduced. We found that DI activated the nuclear factor 2 (NRF2) and heme oxygenase-1 (HO-1) pathway in astrocytes and thereby potentially control redox-regulation and the inflammatory state of astrocytes. Collectively, these results indicate the neuroprotective role of DI by reprogramming astrocytes from neurotoxic A1 to neuroprotective A2 states and thereby reveal a novel potential strategy for the treatment of neurodegenerative diseases.

Itaconate: an antimicrobial metabolite of macrophages

Itaconate is a conjugated 1,4-dicarboxylate produced by macrophages. This small molecule has recently received increasing attention due to its role in modulating the immune response of macrophages upon exposure to pathogens. Itaconate has also been proposed to play an antimicrobial function; however, this has not been explored as intensively. Consistent with the latter, itaconate is known to show antibacterial activity in vitro and was reported to inhibit isocitrate lyase, an enzyme required for survival of bacterial pathogens in mammalian systems. Recent studies have revealed bacterial growth inhibition under biologically relevant conditions. In addition, an antimicrobial role for itaconate is substantiated by the high concentration of itaconate found in bacteria-containing vacuoles, and by the production of itaconate-degrading enzymes in pathogens such as Salmonella enterica ser. Typhimurium, Pseudomonas aeruginosa, and Yersinia pestis. This review describes the current state of literature in understanding the role of itaconate as an antimicrobial agent in host–pathogen interactions.

Integration of transcriptional and metabolic control in macrophage activation

Macrophages react to microbial and endogenous danger signals by activating a broad panel of effector and homeostatic responses. Such responses entail rapid and stimulus-specific changes in gene expression programs accompanied by extensive rewiring of metabolism, with alterations in chromatin modifications providing one layer of integration of transcriptional and metabolic regulation. A systematic and mechanistic understanding of the mutual influences between signal-induced metabolic changes and gene expression is still lacking. Here, we discuss current evidence, controversies, knowledge gaps, and future areas of investigation on how metabolic and transcriptional changes are dynamically integrated during macrophage activation. The cross-talk between metabolism and inflammatory gene expression is in part accounted for by alterations in the production, usage, and availability of metabolic intermediates that impact the macrophage epigenome. In addition, stimulus-inducible gene expression changes alter the production of inflammatory mediators, such as nitric oxide, that in turn modulate the activity of metabolic enzymes thus determining complex regulatory loops. Critical issues remain to be understood, notably whether and how metabolic rewiring can bring about gene-specific (as opposed to global) expression changes.

Establishment, Validation, and Initial Application of a Sensitive LC-MS/MS Assay for Quantification of the Naturally Occurring Isomers Itaconate, Mesaconate, and Citraconate

Itaconate is derived from the tricarboxylic acid (TCA) cycle intermediate cis-aconitate and links innate immunity and metabolism. Its synthesis is altered in inflammation-related disorders and it therefore has potential as clinical biomarker. Mesaconate and citraconate are naturally occurring isomers of itaconate that have been linked to metabolic disorders, but their functional relationships with itaconate are unknown. We aimed to establish a sensitive high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) assay for the quantification of itaconate, mesaconate, citraconate, the pro-drug 4-octyl-itaconate, and selected TCA intermediates. The assay was validated for itaconate, mesaconate, and citraconate for intra- and interday precision and accuracy, extended stability, recovery, freeze/thaw cycles, and carry-over. The lower limit of quantification was 0.098 µM for itaconate and mesaconate and 0.049 µM for citraconate in 50 µL samples. In spike-in experiments, itaconate remained stable in human plasma and whole blood for 24 and 8 h, respectively, whereas spiked-in citraconate and mesaconate concentrations changed during incubation. The type of anticoagulant in blood collection tubes affected measured levels of selected TCA intermediates. Human plasma may contain citraconate (0.4-0.6 µM, depending on the donor), but not itaconate or mesaconate, and lipopolysaccharide stimulation of whole blood induced only itaconate. Concentrations of the three isomers differed greatly among mouse organs: Itaconate and citraconate were most abundant in lymph nodes, mesaconate in kidneys, and only citraconate occurred in brain. This assay should prove useful to quantify itaconate isomers in biomarker and pharmacokinetic studies, while providing internal controls for their effects on metabolism by allowing quantification of TCA intermediates.

Itaconate Alters Succinate and Coenzyme A Metabolism via Inhibition of Mitochondrial Complex II and Methylmalonyl-CoA Mutase

Itaconate is a small molecule metabolite that is endogenously produced by cis-aconitate decarboxylase-1 (ACOD1) in mammalian cells and influences numerous cellular processes. The metabolic consequences of itaconate in cells are diverse and contribute to its regulatory function. Here, we have applied isotope tracing and mass spectrometry approaches to explore how itaconate impacts various metabolic pathways in cultured cells. Itaconate is a competitive and reversible inhibitor of Complex II/succinate dehydrogenase (SDH) that alters tricarboxylic acid (TCA) cycle metabolism leading to succinate accumulation. Upon activation with coenzyme A (CoA), itaconyl-CoA inhibits adenosylcobalamin-mediated methylmalonyl-CoA (MUT) activity and, thus, indirectly impacts branched-chain amino acid (BCAA) metabolism and fatty acid diversity. Itaconate, therefore, alters the balance of CoA species in mitochondria through its impacts on TCA, amino acid, vitamin B₁₂, and CoA metabolism. Our results highlight the diverse metabolic pathways regulated by itaconate and provide a roadmap to link these metabolites to potential downstream biological functions.