Itaconate as an inflammatory mediator and therapeutic target in cardiovascular medicine

Targeting the ACOD1-itaconate axis stabilizes atherosclerotic plaques

Inflammatory macrophages are key drivers of atherosclerosis that can induce rupture-prone vulnerable plaques. Skewing the plaque macrophage population towards a more protective phenotype and reducing the occurrence of clinical events is thought to be a promising method of treating atherosclerotic patients. In the current study, we investigate the immunomodulatory properties of itaconate, an immunometabolite derived from the TCA cycle intermediate cis-aconitate and synthesised by the enzyme Aconitate Decarboxylase 1 (ACOD1, also known as IRG1), in the context of atherosclerosis. Ldlr-/- atherogenic mice transplanted with Acod1-/- bone marrow displayed a more stable plaque phenotype with smaller necrotic cores and showed increased recruitment of monocytes to the vessel intima. Macrophages from Acod1-/- mice contained more lipids whilst also displaying reduced induction of apoptosis. Using multi-omics approaches, we identify a metabolic shift towards purine metabolism, in addition to an altered glycolytic flux towards production of glycerol for triglyceride synthesis. Overall, our data highlight the potential of therapeutically blocking ACOD1 with the aim of stabilizing atherosclerotic plaques.

Metabolism Serves as a Bridge Between Cardiomyocytes and Immune Cells in Cardiovascular Diseases

Metabolic disorders of cardiomyocytes play an important role in the progression of various cardiovascular diseases. Metabolic reprogramming can provide ATP to cardiomyocytes and protect them during diseases, but this transformation also leads to adverse consequences such as oxidative stress, mitochondrial dysfunction, and eventually aggravates myocardial injury. Moreover, abnormal accumulation of metabolites induced by metabolic reprogramming of cardiomyocytes alters the cardiac microenvironment and affects the metabolism of immune cells. Immunometabolism, as a research hotspot, is involved in regulating the phenotype and function of immune cells. After myocardial injury, both cardiac resident immune cells and heart-infiltrating immune cells significantly contribute to the inflammation, repair and remodeling of the heart. In addition, metabolites generated by the metabolic reprogramming of immune cells can further affect the microenvironment, thereby affecting the function of cardiomyocytes and other immune cells. Therefore, metabolic reprogramming and abnormal metabolite levels may serve as a bridge between cardiomyocytes and immune cells, leading to the development of cardiovascular diseases. Herein, we summarize the metabolic relationship between cardiomyocytes and immune cells in cardiovascular diseases, and the effect on cardiac injury, which could be therapeutic strategy for cardiovascular diseases, especially in drug research.

Metabolite signaling in the heart

The heart is the most metabolically active organ in the body, sustaining a continuous and high flux of nutrient catabolism via oxidative phosphorylation. The nature and relative contribution of these fuels have been studied extensively for decades. By contrast, less attention has been placed on how intermediate metabolites generated from this catabolism affect intracellular signaling. Numerous metabolites, including intermediates of glycolysis and the tricarboxylic acid (TCA) cycle, nucleotides, amino acids, fatty acids and ketones, are increasingly appreciated to affect signaling in the heart, via various mechanisms ranging from protein-metabolite interactions to modifying epigenetic marks. We review here the current state of knowledge of intermediate metabolite signaling in the heart.

Itaconate Isomers in Bread

The naturally occurring isomers itaconate, mesaconate and citraconate possess immunomodulatory, antioxidative and antimicrobial properties. However, it is not known whether they occur in commonly consumed human foods. Considering that they can arise as a result of heat conversion, we tested whether they occur in bread, representing a commonly consumed baked good. Using high-performance liquid chromatography−tandem mass spectrometry, we measured concentrations of the three isomers and their potential precursors, citrate and cis-aconitate, in unbaked sourdough and dough, and in crumb and crust of baked bread. All three isomers were detected at low concentrations (<20 pmol/mg dry weight) in sourdough, dough, crumb and crust. Concentrations of itaconate and citraconate were substantially higher in crust than in crumb of wheat and rye bread, and a modest increase in mesaconate was observed in crust of rye bread. In contrast, cis-aconitate concentrations were considerably lower in crust, which was consistent with the conversion of cis-aconitate to itaconate isomers due to higher temperature of the dough surface during baking. Based on data on the average consumption of bread and related baked goods in Germany, the daily intake of itaconate isomers was estimated to be roughly 7−20 µg. Thus, baked goods constitute a regular dietary source of low amounts of itaconate isomers. In order to enable studies on the impact of dietary intake of itaconate isomers on human health, their concentrations should be assessed in other foods that are subjected to high heating.

Research Progress on the Mechanism of Itaconate Regulating Macrophage Immunometabolism

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