Evidence of covalent interaction of fumaric acid esters with sulfhydryl groups in peptides

Differential Effects of Itaconate and its Esters on the Glutathione and Glucose Metabolism of Cultured Primary Rat Astrocytes

Itaconate is produced as endogenous metabolite by decarboxylation of the citric acid cycle intermediate cis-aconitate. As itaconate has anti-microbial and anti-inflammatory properties, this substance is considered as potential therapeutic drug for the treatment of inflammation in various diseases including traumatic brain injury and stroke. To test for potential adverse effects of itaconate on the viability and metabolism of brain cells, we investigated whether itaconate or its membrane permeable derivatives dimethyl itaconate (DI) and 4-octyl itaconate (OI) may affect the basal glucose and glutathione (GSH) metabolism of cultured primary astrocytes. Acute exposure of astrocytes to itaconate, DI or OI in concentrations of up to 300 µM for up to 6 h did not compromise cell viability. Of the tested substances, only OI stimulated aerobic glycolysis as shown by a time- and concentration-dependent increase in glucose-consumption and lactate release. None of the tested itaconates affected the pentose-phosphate pathway-dependent reduction of the water-soluble tetrazolium salt 1 (WST1). In contrast, both DI and OI, but not itaconate, depleted cellular GSH in a time- and concentration-dependent manner. For OI this depletion was accompanied by a matching increase in the extracellular GSH content that was completely prevented in the presence of the multidrug resistance protein 1 (Mrp1)-inhibitor MK571, while in DI-treated cultures GSH was depleted both in cells and medium. These data suggest that OI stimulates Mrp1-mediated astrocytic GSH export, while DI reacts with GSH to a conjugate that is not detectable by the GSH assay applied. The data presented demonstrate that itaconate, DI and OI differ strongly in their effects on the GSH and glucose metabolism of cultured astrocytes. Such results should be considered in the context of the discussed potential use of such compounds as therapeutic agents.

New insights in the targets of action of dimethyl fumarate in endothelial cells: effects on energetic metabolism and serine synthesis in vitro and in vivo

Dimethyl fumarate is an ester from the Krebs cycle intermediate fumarate. This drug is approved and currently used for the treatment of psoriasis and multiple sclerosis, and its anti-angiogenic activity was reported some years ago. Due to the current clinical relevance of this compound and the recently manifested importance of endothelial cell metabolism on the angiogenic switch, we wanted to elucidate whether dimethyl fumarate has an effect on energetic metabolism of endothelial cells. Different experimental approximations were performed in endothelial cells, including proteomics, isotope tracing and metabolomics experimental approaches, in this work we studied the possible role of dimethyl fumarate in endothelial cell energetic metabolism. We demonstrate for the first time that dimethyl fumarate promotes glycolysis and diminishes cell respiration in endothelial cells, which could be a consequence of a down-regulation of serine and glycine synthesis through inhibition of PHGDH activity in these cells. Dimethyl fumarate alters the energetic metabolism of endothelial cells in vitro and in vivo through an unknown mechanism, which could be the cause or the consequence of its pharmacological activity. This new discovery on the targets of this compound could open a new field of study regarding the mechanism of action of dimethyl fumarate.

Dimethyl fumarate inhibits necroptosis and alleviates systemic inflammatory response syndrome by blocking the RIPK1-RIPK3-MLKL axis

Necroptosis has been implicated in various inflammatory diseases including tumor-necrosis factor-α (TNF-α)-induced systemic inflammatory response syndrome (SIRS). Dimethyl fumarate (DMF), a first-line drug for treating relapsing-remitting multiple sclerosis (RRMS), has been shown to be effective against various inflammatory diseases. However, it is still unclear whether DMF can inhibit necroptosis and confer protection against SIRS. In this study, we found that DMF significantly inhibited necroptotic cell death in macrophages induced by different necroptotic stimulations. Both the autophosphorylation of receptor-interacting serine/threonine kinase 1 (RIPK1) and RIPK3 and the downstream phosphorylation and oligomerization of MLKL were robustly suppressed by DMF. Accompanying the suppression of necroptotic signaling, DMF blocked the mitochondrial reverse electron transport (RET) induced by necroptotic stimulation, which was associated with its electrophilic property. Several well-known anti-RET reagents also markedly inhibited the activation of the RIPK1-RIPK3-MLKL axis accompanied by decreased necrotic cell death, indicating a critical role of RET in necroptotic signaling. DMF and other anti-RET reagents suppressed the ubiquitination of RIPK1 and RIPK3, and they attenuated the formation of necrosome. Moreover, oral administration of DMF significantly alleviated the severity of TNF-α-induced SIRS in mice. Consistent with this, DMF mitigated TNF-α-induced cecal, uterine, and lung damage accompanied by diminished RIPK3-MLKL signaling. Collectively, DMF represents a new necroptosis inhibitor that suppresses the RIPK1-RIPK3-MLKL axis through blocking mitochondrial RET. Our study highlights DMF's potential therapeutic applications for treating SIRS-associated diseases.

Beyond Brooding on Oncometabolic Havoc in IDH-Mutant Gliomas and AML: Current and Future Therapeutic Strategies

Isocitrate dehydrogenases 1 and 2 (IDH1,2), the key Krebs cycle enzymes that generate NADPH reducing equivalents, undergo heterozygous mutations in >70% of low- to mid-grade gliomas and ~20% of acute myeloid leukemias (AMLs) and gain an unusual new activity of reducing the α-ketoglutarate (α-KG) to D-2 hydroxyglutarate (D-2HG) in a NADPH-consuming reaction. The oncometabolite D-2HG, which accumulates >35 mM, is widely accepted to drive a progressive oncogenesis besides exacerbating the already increased oxidative stress in these cancers. More importantly, D-2HG competes with α-KG and inhibits a large number of α-KG-dependent dioxygenases such as TET (Ten-eleven translocation), JmjC domain-containing KDMs (histone lysine demethylases), and the ALKBH DNA repair proteins that ultimately lead to hypermethylation of the CpG islands in the genome. The resulting CpG Island Methylator Phenotype (CIMP) accounts for major gene expression changes including the silencing of the MGMT (O⁶-methylguanine DNA methyltransferase) repair protein in gliomas. Glioma patients with IDH1 mutations also show better therapeutic responses and longer survival, the reasons for which are yet unclear. There has been a great surge in drug discovery for curtailing the mutant IDH activities, and arresting tumor proliferation; however, given the unique and chronic metabolic effects of D-2HG, the promise of these compounds for glioma treatment is uncertain. This comprehensive review discusses the biology, current drug design and opportunities for improved therapies through exploitable synthetic lethality pathways, and an intriguing oncometabolite-inspired strategy for primary glioblastoma.

Control of Oxidative Stress and Inflammation in Sickle Cell Disease with the Nrf2 Activator Dimethyl Fumarate

AIMS

Heme derived from hemolysis is pro-oxidative and proinflammatory and promotes vaso-occlusion in murine models of sickle cell disease (SCD), suggesting that enhanced detoxification of heme may be beneficial. Nuclear factor erythroid-2-related factor-2 (Nrf2) transcription pathway is the principal cellular defense system responding to pro-oxidative and proinflammatory stress. Dimethyl fumarate (DMF), a drug approved for treatment of multiple sclerosis, provides neuroprotection by activating Nrf2-responsive genes. We hypothesized that induction of Nrf2 with DMF would be beneficial in murine SCD models.

RESULTS

DMF (30 mg/kg/day) or vehicle (0.08% methyl cellulose) was administered for 3-7 days to NY1DD and HbSS-Townes SCD mice. Vaso-occlusion, a hallmark of SCD, measured in sickle mice with dorsal skinfold chambers, was inhibited by DMF. The inhibitory effect of DMF was abrogated by the heme oxygenase-1 (HO-1) inhibitor tin protoporphyrin. DMF increased nuclear Nrf2 and cellular mRNA of Nrf2-responsive genes in livers and kidneys. DMF increased heme defenses, including HO-1, haptoglobin, hemopexin, and ferritin heavy chain, although plasma hemoglobin and heme levels were unchanged. DMF decreased markers of inflammation, including nuclear factor-kappa B phospho-p65, adhesion molecules, and toll-like receptor 4. DMF administered for 24 weeks to HbSS-Townes mice decreased hepatic necrosis, inflammatory cytokines, and irregularly shaped erythrocytes and increased hemoglobin F, but did not alter hematocrits, reticulocyte counts, lactate dehydrogenase, plasma heme, or spleen weights, indicating that the beneficial effects of DMF were not attributable to decreased hemolysis.

INNOVATION

These studies identify Nrf2 activation as a new therapeutic target for the treatment of SCD.

CONCLUSION

DMF activates Nrf2, enhances antioxidant defenses, and inhibits inflammation and vaso-occlusion in SCD mice. Antioxid. Redox Signal. 26, 748-762.

Therapeutic decisions in multiple sclerosis: moving beyond efficacy

Several innovative disease-modifying treatments (DMTs) for relapsing-remitting multiple sclerosis have been licensed recently or are in late-stage development. The molecular targets of several of these DMTs are well defined. All affect at least 1 of 4 properties, namely (1) trafficking, (2) survival, (3) function, or (4) proliferation. In contrast to β-interferons and glatiramer acetate, the first-generation DMTs, several newer therapies are imbued with safety issues, which may be attributed to their structure or metabolism. In addition to efficacy, understanding the relationship between the mechanism of action of the DMTs and their safety profile is pertinent for decision making and patient care. In this article, we focus primarily on the safety of DMTs in the context of understanding their pharmacological characteristics, including molecular targets, mechanism of action, chemical structure, and metabolism. While understanding mechanisms underlying DMT toxicities is incomplete, it is important to further develop this knowledge to minimize risk to patients and to ensure future therapies have the most advantageous benefit-risk profiles. Recognizing the individual classes of DMTs described here may be valuable when considering use of such agents sequentially or possibly in combination.

Detection of fumarate-glutathione adducts in the portal vein blood of rats: evidence for rapid dimethylfumarate metabolism

Dimethylfumarate (DMF), the essential ingredient of the drug product Fumaderm®, is used to treat psoriasis with a recognized favorable long-term safety profile. Interestingly, the mode of action and the pharmacokinetics of DMF in psoriasis or multiple sclerosis are not fully explored. It is known that DMF as an α,β-unsaturated carboxylic acid ester forms an adduct with the antioxidant glutathione in vitro via a Michael-type addition within a very short period of time. In addition, it was shown that this reaction also takes place in vivo since the mercapturic acid of DMF was detected in urine of psoriasis patients after oral intake of Fumaderm®. To verify the hypothesis that DMF reacts with GSH already in or even before entering the portal vein blood an in vivo study in rats was initiated and portal vein blood was analyzed for the presence of DMF, MMF, GS-DMS and break down products, after DMF was given directly into the small intestine. The results show that no free DMF could be detected in the rat portal vein blood at any time point. MMF was the dominant metabolite and GS-DMS was also detectable in portal vein blood. In the rat mucosa the glutathione adducts of DMF and MMF were present. The data obtained provide evidence that the modulation of immune-mediated inflammatory pathways responsible for development of psoriasis and MS are targeted by DMF regulating redox-sensitive pathways for which the reaction with glutathione by DMF plays a crucial role.

The anti-inflammatory effects of dimethyl fumarate in astrocytes involve glutathione and haem oxygenase-1

DMF (dimethyl fumarate) exerts anti-inflammatory and pro-metabolic effects in a variety of cell types, and a formulation (BG-12) is being evaluated for monotherapy in multiple sclerosis patients. DMF modifies glutathione (GSH) levels that can induce expression of the anti-inflammatory protein HO-1 (haem oxygenase-1). In primary astrocytes and C6 glioma cells, BG-12 dose-dependently suppressed nitrite production induced by either LI [LPS (lipopolysaccharide) at 1 μg/ml plus IFNγ (interferon γ) at 20 units/ml] or a mixture of pro-inflammatory cytokines, with greater efficacy in C6 cells. BG-12 reduced NOS2 (nitric oxide synthase 2) mRNA levels and activation of a NOS2 promoter, reduced nuclear levels of NF-κB (nuclear factor κB) p65 subunit and attenuated loss of IκBα (inhibitory κBα) in both cell types, although with greater effects in astrocytes. In astrocytes, LI decreased mRNA levels for GSHr (GSH reductase) and GCL (c-glutamylcysteine synthetase), and slightly suppressed GSHs (GSH synthetase) mRNAs. Co-treatment with BG-12 prevented those decreased and increased levels above control values. In contrast, LI reduced GSHp (GSH peroxidase) and GCL in C6 cells, and BG-12 had no effect on those levels. BG-12 increased nuclear levels of Nrf2 (nuclear factor-erythroid 2 p45 subunit-related factor 2), an inducer of GSH-related enzymes, in astrocytes but not C6 cells. In astrocytes, GSH was decreased by BG-12 at 2 h and increased at 24 h. Prior depletion of GSH using buthionine-sulfoximine increased the ability of BG-12 to reduce nitrites. In astrocytes, BG-12 increased HO-1 mRNA levels and effects on nitrite levels were blocked by an HO-1 inhibitor. These results demonstrate that BG-12 suppresses inflammatory activation in astrocytes and C6 glioma cells, but with distinct mechanisms, different dependence on GSH and different effects on transcription factor activation.

Dimethylfumarate inhibits NF-{kappa}B function at multiple levels to limit airway smooth muscle cell cytokine secretion

The antipsoriatic dimethylfumarate (DMF) has been anecdotically reported to reduce asthma symptoms and to improve quality of life of asthma patients. DMF decreases the expression of proinflammatory mediators by inhibiting the transcription factor NF-kappaB and might therefore be of interest for the therapy of inflammatory lung diseases. In this study, we determined the effect of DMF on platelet-derived growth factor (PDGF)-BB- and TNFalpha-induced asthma-relevant cytokines and NF-kappaB activation by primary human asthmatic and nonasthmatic airway smooth muscle cells (ASMC). Confluent nonasthmatic and asthmatic ASMC were incubated with DMF (0.1-100 microM) and/or dexamethasone (0.0001-0.1 microM), NF-kappaB p65 siRNA (100 nM), the NF-kappaB inhibitor helenalin (1 microM) before stimulation with PDGF-BB or TNFalpha (10 ng/ml). Cytokine release was measured by ELISA. NF-kappaB, mitogen and stress-activated kinase (MSK-1), and CREB activation was determined by immunoblotting and EMSA. TNFalpha-induced eotaxin, RANTES, and IL-6 as well as PDGF-BB-induced IL-6 expression was inhibited by DMF and by dexamethasone from asthmatic and nonasthmatic ASMC, but the combination of both drugs showed no glucocorticoid sparing effect in either of the two groups. NF-kappaB p65 siRNA and/or the NF-kappaB inhibitor helenalin reduced PDGF-BB- and TNFalpha-induced cytokine expression, suggesting the involvement of NF-kappaB signaling. DMF inhibited TNFalpha-induced NF-kappaB p65 phosphorylation, NF-kappaB nuclear entry, and NF-kappaB-DNA complex formation, whereas PDGF-BB appeared not to activate NF-kappaB within 60 min. Both stimuli induced the phosphorylation of MSK-1, NF-kappaB p65 at Ser276, and CREB, and all were inhibited by DMF. These data suggest that DMF downregulates cytokine secretion not only by inhibiting NF-kappaB but a wider range of NF-kappaB-linked signaling proteins, which may explain its potential beneficial effect in asthma.