Dimethyl itaconate induces long-term innate immune responses and confers protection against infection.

Itaconate is an immunomodulatory metabolite produced by immune cells under microbial stimulation and certain pro-inflammatory conditions and triggers antioxidant and anti-inflammatory responses. We show that dimethyl itaconate, a derivative of itaconate previously linked to suppression of inflammation and widely employed as an alternative to the endogenous metabolite, can induce long-term transcriptional, epigenomic, and metabolic changes, characteristic of trained immunity. Dimethyl itaconate alters glycolytic and mitochondrial energetic metabolism, ultimately leading to increased responsiveness to microbial ligand stimulation. Subsequently, mice treated with dimethyl itaconate present increased survival to infection with Staphylococcus aureus. Additionally, itaconate levels in human plasma correlate with enhanced ex vivo pro-inflammatory cytokine production. Collectively, these findings demonstrate that dimethyl itaconate displays short-term anti-inflammatory characteristics and the capacity to induce long-term trained immunity. This pro-and anti-inflammatory dichotomy of dimethyl itaconate is likely to induce complex immune responses and should be contemplated when considering itaconate derivatives in a therapeutic context.

d-2-Hydroxyglutarate is an anti-inflammatory immunometabolite that accumulates in macrophages after TLR4 activation.

Macrophages undergo extensive metabolic rewiring upon activation which assist the cell in roles beyond energy production and synthesis of anabolic building blocks. So-called immunometabolites that accumulate upon immune activation can serve as co-factors for enzymes and can act as signaling molecules to modulate cellular processes. As such, the Krebs-cycle-associated metabolites succinate, itaconate and alpha-ketoglutarate (αKG) have emerged as key regulators of macrophage function. Here, we describe that 2-hydroxyglutarate (2HG), which is structurally similar to αKG and exists as two enantiomers, accumulates during later stages of LPS-induced inflammatory responses in mouse and human macrophages. D-2HG was the most abundant enantiomer in macrophages and its LPS-induced accumulation followed the induction of Hydroxyacid-Oxoacid Transhydrogenase (HOT). HOT interconverts αKG and gamma-hydroxybutyrate into D-2HG and succinic semialdehyde, and we here identified this enzyme as being immune-responsive and regulated during the course of macrophage activation. The buildup of D-2HG may be further explained by reduced expression of D-2HG Dehydrogenase (D2HGDH), which converts D-2HG back into αKG, and showed inverse kinetics with HOT and D-2HG levels. We tested the immunomodulatory effects of D-2HG during LPS-induced inflammatory responses by transcriptomic analyses and functional profiling of D-2HG-pre-treated macrophages in vitro and mice in vivo. Together, these data suggest a role for D-2HG in the negative feedback regulation of inflammatory signaling during late-stage LPS-responses in vitro and as a regulator of local and systemic inflammatory responses in vivo. Finally, we show that D-2HG likely exerts distinct anti-inflammatory effects, which are in part independent of αKG-dependent dioxygenase inhibition. Together, this study reveals an immunometabolic circuit resulting in the accumulation of the immunomodulatory metabolite D-2HG that can inhibit inflammatory macrophage responses.

Immune modulatory effects of progesterone on oxLDL-induced trained immunity in monocytes.

Atherosclerotic cardiovascular diseases (CVD) are among the leading causes of death in the world. Monocyte-derived macrophages are key players in the pathophysiology of atherosclerosis. Innate immune memory following exposure of monocytes to atherogenic compounds, such as oxidized low-density lipoproteins (oxLDL), termed trained immunity, can contribute to atherogenesis. The current study aimed to elucidate intracellular mechanisms of oxLDL-induced trained immunity. Using untargeted intracellular metabolomics in isolated human primary monocytes, we show that oxLDL-induced trained immunity results in alterations in the balance of intracellular steroid hormones in monocytes. This was reflected by a decrease in extracellular progesterone concentrations following LPS stimulation. To understand the potential effects of steroid hormones on trained immunity, monocytes were costimulated with oxLDL and the steroid hormones progesterone, hydrocortisone, dexamethasone, ß-estradiol, and dihydrotestosterone. Progesterone showed a unique ability to attenuate the enhanced TNFα and IL-6 production following oxLDL-induced trained immunity. Single nucleotide polymorphisms in the nuclear glucocorticoid, progesterone, and mineralocorticoid receptor were shown to correlate with ex vivo oxLDL-induced trained immunity in 243 healthy volunteers. Pharmacologic inhibition experiments revealed that progesterone exerts the suppression of TNFα in trained immunity via the nuclear glucocorticoid and mineralocorticoid receptors. Our data show that progesterone has a unique ability to suppress oxLDL-induced trained immunity. We hypothesize that this effect might contribute to the lower incidence of CVD in premenopausal women.

Macrophage mitochondrial superoxides as a target for atherosclerotic disease treatment.

Cardiovascular diseases (CVD) are the leading cause of death worldwide. Although many effective therapies exist, a substantial portion of patients remain unprotected by current measures. Recent advances in the understanding of the underpinning cause of CVD, atherosclerosis, have demonstrated the important causative role of inflammation in disease progression. Monocytes are important protagonists of atherosclerosis, and they have been shown to have elevated reliance on mitochondrial metabolism producing elevated levels of superoxides as a noxious byproduct. There exists a key link between mitochondrial superoxides production and inflammatory output in monocytes in the context of atherosclerosis. In this review we describe mitochondrial superoxide lowering strategies in order to broaden the scope of treatment strategies for CVD. We further explore strategies for more effective and selective targeting of the involved monocytes and macrophages in order to increase potency of effect and diminish side effects.