The role of succinate and ROS in reperfusion injury - A critical appraisal

Malate dehydrogenase-2 inhibition shields renal tubular epithelial cells from anoxia-reoxygenation injury by reducing reactive oxygen species

Ischemia-reperfusion (I-R) injury is the most common cause of acute kidney injury. In experiments involving primary human renal proximal tubular epithelial cells (RPTECs) exposed to anoxia-reoxygenation, we explored the hypothesis that mitochondrial malate dehydrogenase-2 (MDH-2) inhibition redirects malate metabolism from the mitochondria to the cytoplasm, towards the malate-pyruvate cycle and reversed malate-aspartate shuttle. Colorimetry, fluorometry, and western blotting showed that MDH2 inhibition accelerates the malate-pyruvate cycle enhancing cytoplasmic NADPH, thereby regenerating the potent antioxidant reduced glutathione. It also reversed the malate-aspartate shuttle and potentially diminished mitochondrial reactive oxygen species (ROS) production by transferring electrons, in the form of NADH, from the mitochondria to the cytoplasm. The excessive ROS production induced by anoxia-reoxygenation led to DNA damage and protein modification, triggering DNA damage and unfolded protein response, ultimately resulting in apoptosis and senescence. Additionally, ROS induced lipid peroxidation, which may contribute to the process of ferroptosis. Inhibiting MDH-2 proved effective in mitigating ROS overproduction during anoxia-reoxygenation, thereby rescuing RPTECs from death or senescence. Thus, targeting MDH-2 holds promise as a pharmaceutical strategy against I-R injury.

Understanding coenzyme Q

Coenzyme Q (CoQ), also known as ubiquinone, comprises a benzoquinone head group and a long isoprenoid side chain. It is thus extremely hydrophobic and resides in membranes. It is best known for its complex function as an electron transporter in the mitochondrial electron transport chain (ETC) but is also required for several other crucial cellular processes. In fact, CoQ appears to be central to the entire redox balance of the cell. Remarkably, its structure and therefore its properties have not changed from bacteria to vertebrates. In metazoans, it is synthesized in all cells and is found in most, and maybe all, biological membranes. CoQ is also known as a nutritional supplement, mostly because of its involvement with antioxidant defenses. However, whether there is any health benefit from oral consumption of CoQ is not well established. Here we review the function of CoQ as a redox-active molecule in the ETC and other enzymatic systems, its role as a prooxidant in reactive oxygen species generation, and its separate involvement in antioxidant mechanisms. We also review CoQ biosynthesis, which is particularly complex because of its extreme hydrophobicity, as well as the biological consequences of primary and secondary CoQ deficiency, including in human patients. Primary CoQ deficiency is a rare inborn condition due to mutation in CoQ biosynthetic genes. Secondary CoQ deficiency is much more common, as it accompanies a variety of pathological conditions, including mitochondrial disorders as well as aging. In this context, we discuss the importance, but also the great difficulty, of alleviating CoQ deficiency by CoQ supplementation.

Myeloperoxidase as a Promising Therapeutic Target after Myocardial Infarction

Coronary artery disease (CAD) and myocardial infarction (MI) remain leading causes of death and disability worldwide. CAD begins with the formation of atherosclerotic plaques within the intimal layer of the coronary arteries, a process driven by persistent arterial inflammation and oxidation. Myeloperoxidase (MPO), a mammalian haem peroxidase enzyme primarily expressed within neutrophils and monocytes, has been increasingly recognised as a key pro-inflammatory and oxidative enzyme promoting the development of vulnerable coronary atherosclerotic plaques that are prone to rupture, and can precipitate a MI. Mounting evidence also implicates a pathogenic role for MPO in the inflammatory process that follows a MI, which is characterised by the rapid infiltration of activated neutrophils into the damaged myocardium and the release of MPO. Excessive and persistent cardiac inflammation impairs normal cardiac healing post-MI, resulting in adverse cardiac outcomes and poorer long-term cardiac function, and eventually heart failure. This review summarises the evidence for MPO as a significant oxidative enzyme contributing to the inappropriate inflammatory responses driving the progression of CAD and poor cardiac healing after a MI. It also details the proposed mechanisms underlying MPO's pathogenic actions and explores MPO as a novel therapeutic target for the treatment of unstable CAD and cardiac damage post-MI.

Exposure to nanopollutants (nZnO) enhances the negative effects of hypoxia and delays recovery of the mussels' immune system

Aquatic environments face escalating challenges from multiple stressors like hypoxia and nanoparticle exposure, with impact of these combined stressors on mussel immunity being poorly understood. We investigated the individual and combined effects of short-term and long-term hypoxia and exposure to zinc oxide nanoparticles (nZnO) on immune system of the mussels (Mytilus edulis). Hemocyte functional traits (mortality, adhesion capacity, phagocytosis, lysosomal abundance, and oxidative burst), and transcript levels of immune-related genes involved in pathogen recognition (the Toll-like receptors, the complement system components, and the adaptor proteins MyD88) were assessed. Short-term hypoxia minimally affected hemocyte parameters, while prolonged exposure led to immunosuppression, impacting hemocyte abundance, viability, phagocytosis, and defensin gene expression. Under normoxia, nZnO stimulated immune responses of mussel hemocytes. However, combined nZnO and hypoxia induced more pronounced and rapid immunosuppression than hypoxia alone, indicating a synergistic interaction. nZnO exposure hindered immune parameter recovery during post-hypoxic reoxygenation, suggesting persistent impact. Opposing trends were observed in pathogen-sensing and pathogen-elimination mechanisms, with a positive correlation between pathogen-recognition system activation and hemocyte mortality. These findings underscore a complex relationship and potential conflict between pathogen-recognition ability, immune function, and cell survival in mussel hemocytes under hypoxia and nanopollutant stress, and emphasize the importance of considering multiple stressors in assessing the vulnerability and adaptability of mussel immune system under complex environmental conditions of anthropogenically modified coastal ecosystems.

Cellular succinate metabolism and signaling in inflammation: implications for therapeutic intervention

Succinate, traditionally viewed as a mere intermediate of the tricarboxylic acid (TCA) cycle, has emerged as a critical mediator in inflammation. Disruptions within the TCA cycle lead to an accumulation of succinate in the mitochondrial matrix. This excess succinate subsequently diffuses into the cytosol and is released into the extracellular space. Elevated cytosolic succinate levels stabilize hypoxia-inducible factor-1α by inhibiting prolyl hydroxylases, which enhances inflammatory responses. Notably, succinate also acts extracellularly as a signaling molecule by engaging succinate receptor 1 on immune cells, thus modulating their pro-inflammatory or anti-inflammatory activities. Alterations in succinate levels have been associated with various inflammatory disorders, including rheumatoid arthritis, inflammatory bowel disease, obesity, and atherosclerosis. These associations are primarily due to exaggerated immune cell responses. Given its central role in inflammation, targeting succinate pathways offers promising therapeutic avenues for these diseases. This paper provides an extensive review of succinate's involvement in inflammatory processes and highlights potential targets for future research and therapeutic possibilities development.

Mitochondrial responses to constant and cyclic hypoxia depend on the oxidized fuel in a hypoxia-tolerant marine bivalve Crassostrea gigas

Sessile benthic organisms like oysters inhabit the intertidal zone, subject to alternating hypoxia and reoxygenation (H/R) episodes during tidal movements, impacting respiratory chain activities and metabolome compositions. We investigated the effects of constant severe hypoxia (90 min at ~ 0% O2 ) followed by 10 min reoxygenation, and cyclic hypoxia (5 cycles of 15 min at ~ 0% O2 and 10 min reoxygenation) on isolated mitochondria from the gill and the digestive gland of Crassostrea gigas respiring on pyruvate, palmitate, or succinate. Constant hypoxia suppressed oxidative phosphorylation (OXPHOS), particularly during Complex I-linked substrates oxidation. It had no effect on mitochondrial reactive oxygen species (ROS) efflux but increased fractional electron leak (FEL). In mitochondria oxidizing Complex I substrates, exposure to cyclic hypoxia prompted a significant drop after the first H/R cycle. In contrast, succinate-driven respiration only showed significant decline after the third to fifth H/R cycle. ROS efflux saw little change during cyclic hypoxia regardless of the oxidized substrate, but Complex I-driven FEL tended to increase with each subsequent H/R cycle. These observations suggest that succinate may serve as a beneficial stress fuel under H/R conditions, aiding in the post-hypoxic recovery of oysters by reducing oxidative stress and facilitating rapid ATP re-synthesis. The impacts of constant and cyclic hypoxia of similar duration on mitochondrial respiration and oxidative lesions in the proteins were comparable indicating that the mitochondrial damage is mostly determined by the lack of oxygen and mitochondrial depolarization. The ROS efflux in the mitochondria of oysters was minimally affected by oxygen fluctuations indicating that tight regulation of ROS production may contribute to robust mitochondrial phenotype of oysters and protect against H/R induced stress.

Monocarboxylate transporters facilitate succinate uptake into brown adipocytes

Uptake of circulating succinate by brown adipose tissue (BAT) and beige fat elevates whole-body energy expenditure, counteracts obesity and antagonizes systemic tissue inflammation in mice. The plasma membrane transporters that facilitate succinate uptake in these adipocytes remain undefined. Here we elucidate a mechanism underlying succinate import into BAT via monocarboxylate transporters (MCTs). We show that succinate transport is strongly dependent on the proportion that is present in the monocarboxylate form. MCTs facilitate monocarboxylate succinate uptake, which is promoted by alkalinization of the cytosol driven by adrenoreceptor stimulation. In brown adipocytes, we show that MCT1 primarily facilitates succinate import. In male mice, we show that both acute pharmacological inhibition of MCT1 and congenital depletion of MCT1 decrease succinate uptake into BAT and consequent catabolism. In sum, we define a mechanism of succinate uptake in BAT that underlies its protective activity in mouse models of metabolic disease.

Dynamin-related protein 1 is a critical regulator of mitochondrial calcium homeostasis during myocardial ischemia/reperfusion injury

Dynamin-related protein 1 (Drp1) is a cytosolic GTPase protein that when activated translocates to the mitochondria, meditating mitochondrial fission and increasing reactive oxygen species (ROS) in cardiomyocytes. Drp1 has shown promise as a therapeutic target for reducing cardiac ischemia/reperfusion (IR) injury; however, the lack of specificity of some small molecule Drp1 inhibitors and the reliance on the use of Drp1 haploinsufficient hearts from older mice have left the role of Drp1 in IR in question. Here, we address these concerns using two approaches, using: (a) short-term (3 weeks), conditional, cardiomyocyte-specific, Drp1 knockout (KO) and (b) a novel, highly specific Drp1 GTPase inhibitor, Drpitor1a. Short-term Drp1 KO mice exhibited preserved exercise capacity and cardiac contractility, and their isolated cardiac mitochondria demonstrated increased mitochondrial complex 1 activity, respiratory coupling, and calcium retention capacity compared to controls. When exposed to IR injury in a Langendorff perfusion system, Drp1 KO hearts had preserved contractility, decreased reactive oxygen species (ROS), enhanced mitochondrial calcium capacity, and increased resistance to mitochondrial permeability transition pore (MPTP) opening. Pharmacological inhibition of Drp1 with Drpitor1a following ischemia, but before reperfusion, was as protective as Drp1 KO for cardiac function and mitochondrial calcium homeostasis. In contrast to the benefits of short-term Drp1 inhibition, prolonged Drp1 ablation (6 weeks) resulted in cardiomyopathy. Drp1 KO hearts were also associated with decreased ryanodine receptor 2 (RyR2) protein expression and pharmacological inhibition of the RyR2 receptor decreased ROS in post-IR hearts suggesting that changes in RyR2 may have a role in Drp1 KO mediated cardioprotection. We conclude that Drp1-mediated increases in myocardial ROS production and impairment of mitochondrial calcium handling are key mechanisms of IR injury. Short-term inhibition of Drp1 is a promising strategy to limit early myocardial IR injury which is relevant for the therapy of acute myocardial infarction, cardiac arrest, and heart transplantation.

Preventing mitochondrial reverse electron transport as a strategy for cardioprotection

In the context of myocardial infarction, the burst of superoxide generated by reverse electron transport (RET) at complex I in mitochondria is a crucial trigger for damage during ischaemia/reperfusion (I/R) injury. Here we outline the necessary conditions for superoxide production by RET at complex I and how it can occur during reperfusion. In addition, we explore various pathways that are implicated in generating the conditions for RET to occur and suggest potential therapeutic strategies to target RET, aiming to achieve cardioprotection.

Energy substrate metabolism, mitochondrial structure and oxidative stress after cardiac ischemia-reperfusion in mice lacking UCP3

Myocardial ischemia-reperfusion (IR) injury may result in cardiomyocyte dysfunction. Mitochondria play a critical role in cardiomyocyte recovery after IR injury. The mitochondrial uncoupling protein 3 (UCP3) has been proposed to reduce mitochondrial reactive oxygen species (ROS) production and to facilitate fatty acid oxidation. As both mechanisms might be protective following IR injury, we investigated functional, mitochondrial structural, and metabolic cardiac remodeling in wild-type mice and in mice lacking UCP3 (UCP3-KO) after IR. Results showed that infarct size in isolated perfused hearts subjected to IR ex vivo was larger in adult and old UCP3-KO mice than in equivalent wild-type mice, and was accompanied by higher levels of creatine kinase in the effluent and by more pronounced mitochondrial structural changes. The greater myocardial damage in UCP3-KO hearts was confirmed in vivo after coronary artery occlusion followed by reperfusion. S1QEL, a suppressor of superoxide generation from site IQ in complex I, limited infarct size in UCP3-KO hearts, pointing to exacerbated superoxide production as a possible cause of the damage. Metabolomics analysis of isolated perfused hearts confirmed the reported accumulation of succinate, xanthine and hypoxanthine during ischemia, and a shift to anaerobic glucose utilization, which all recovered upon reoxygenation. The metabolic response to ischemia and IR was similar in UCP3-KO and wild-type hearts, being lipid and energy metabolism the most affected pathways. Fatty acid oxidation and complex I (but not complex II) activity were equally impaired after IR. Overall, our results indicate that UCP3 deficiency promotes enhanced superoxide generation and mitochondrial structural changes that increase the vulnerability of the myocardium to IR injury.

Unveiling the potential of mitochondrial dynamics as a therapeutic strategy for acute kidney injury

Acute Kidney Injury (AKI), a critical clinical syndrome, has been strongly linked to mitochondrial malfunction. Mitochondria, vital cellular organelles, play a key role in regulating cellular energy metabolism and ensuring cell survival. Impaired mitochondrial function in AKI leads to decreased energy generation, elevated oxidative stress, and the initiation of inflammatory cascades, resulting in renal tissue damage and functional impairment. Therefore, mitochondria have gained significant research attention as a potential therapeutic target for AKI. Mitochondrial dynamics, which encompass the adaptive shifts of mitochondria within cellular environments, exert significant influence on mitochondrial function. Modulating these dynamics, such as promoting mitochondrial fusion and inhibiting mitochondrial division, offers opportunities to mitigate renal injury in AKI. Consequently, elucidating the mechanisms underlying mitochondrial dynamics has gained considerable importance, providing valuable insights into mitochondrial regulation and facilitating the development of innovative therapeutic approaches for AKI. This comprehensive review aims to highlight the latest advancements in mitochondrial dynamics research, provide an exhaustive analysis of existing studies investigating the relationship between mitochondrial dynamics and acute injury, and shed light on their implications for AKI. The ultimate goal is to advance the development of more effective therapeutic interventions for managing AKI.

Identity, structure, and function of the mitochondrial permeability transition pore: controversies, consensus, recent advances, and future directions

The mitochondrial permeability transition (mPT) describes a Ca2+-dependent and cyclophilin D (CypD)-facilitated increase of inner mitochondrial membrane permeability that allows diffusion of molecules up to 1.5 kDa in size. It is mediated by a non-selective channel, the mitochondrial permeability transition pore (mPTP). Sustained mPTP opening causes mitochondrial swelling, which ruptures the outer mitochondrial membrane leading to subsequent apoptotic and necrotic cell death, and is implicated in a range of pathologies. However, transient mPTP opening at various sub-conductance states may contribute several physiological roles such as alterations in mitochondrial bioenergetics and rapid Ca2+ efflux. Since its discovery decades ago, intensive efforts have been made to identify the exact pore-forming structure of the mPT. Both the adenine nucleotide translocase (ANT) and, more recently, the mitochondrial F1FO (F)-ATP synthase dimers, monomers or c-subunit ring alone have been implicated. Here we share the insights of several key investigators with different perspectives who have pioneered mPT research. We critically assess proposed models for the molecular identity of the mPTP and the mechanisms underlying its opposing roles in the life and death of cells. We provide in-depth insights into current controversies, seeking to achieve a degree of consensus that will stimulate future innovative research into the nature and role of the mPTP.

Integrated proteomic and metabolomic profiling of urine of renal anemia patients uncovers the molecular mechanisms of roxadustat

Roxadustat (FG-4592) is a hypoxia-inducible factor prolyl hydroxylase inhibitor (HIF-PHI) prescribed to patients with low hemoglobin associated with chronic kidney disease. Due to the various HIF-mediated adaptive responses, FG-4592 has attracted significant interest for therapeutic use against various diseases. However, the clinical application of Roxadustat remains limited due to a lack of understanding of its underlying mechanisms. Herein, we performed label-free quantitative liquid chromatography with tandem mass spectrometry (LC-MS-MS) proteomics and un-targeted metabolomics to study the protein and metabolite alterations in the urine of renal anemia patients before and after Roxadustat therapy. The results were validated by parallel reaction monitoring (PRM). A total of 46 proteins (including 15 upregulated and 31 downregulated proteins) and 207 metabolites were significantly altered after Roxadustat treatment in urine samples obtained from renal anemia patients. Then, the altered proteins were further validated by PRM. Finally, proteomics combined with metabolomics analysis revealed that the Ras signalling pathway, cysteine and methionine metabolism, arginine and proline metabolism, and cholesterol metabolism were the main pathways altered by Roxadustat treatment. The multi-omics analysis revealed that Roxadustat could alter the protein expression and reverse the potential metabolic changes to exert hypotensive, lipid metabolic regulation, and renoprotective effects in clinical practice.

Mitochondrial calcium and reactive oxygen species in cardiovascular disease

Cardiomyocytes are one of the most mitochondria-rich cell types in the body, with ∼30-40% of the cell volume being composed of mitochondria. Mitochondria are well established as the primary site of adenosine triphosphate (ATP) generation in a beating cardiomyocyte, generating up to 90% of its ATP. Mitochondria have many functions in the cell, which could contribute to susceptibility to and development of cardiovascular disease (CVD). Mitochondria are key players in cell metabolism, ATP production, reactive oxygen species (ROS) production, and cell death. Mitochondrial calcium (Ca2+) plays a critical role in many of these pathways, and thus the dynamics of mitochondrial Ca2+ are important in regulating mitochondrial processes. Alterations in these varied and in many cases interrelated functions play an important role in CVD. This review will focus on the interrelationship of mitochondrial energetics, Ca2+, and ROS and their roles in CVD. Recent insights into the regulation and dysregulation of these pathways have led to some novel therapeutic approaches.

Pharmacological Cardioprotection against Ischemia Reperfusion Injury-The Search for a Clinical Effective Therapy

Pharmacological conditioning aims to protect the heart from myocardial ischemia-reperfusion injury (IRI). Despite extensive research in this area, today, a significant gap remains between experimental findings and clinical practice. This review provides an update on recent developments in pharmacological conditioning in the experimental setting and summarizes the clinical evidence of these cardioprotective strategies in the perioperative setting. We start describing the crucial cellular processes during ischemia and reperfusion that drive acute IRI through changes in critical compounds (∆G_ATP, Na⁺, Ca²⁺, pH, glycogen, succinate, glucose-6-phosphate, mitoHKII, acylcarnitines, BH₄, and NAD⁺). These compounds all precipitate common end-effector mechanisms of IRI, such as reactive oxygen species (ROS) generation, Ca²⁺ overload, and mitochondrial permeability transition pore opening (mPTP). We further discuss novel promising interventions targeting these processes, with emphasis on cardiomyocytes and the endothelium. The limited translatability from basic research to clinical practice is likely due to the lack of comorbidities, comedications, and peri-operative treatments in preclinical animal models, employing only monotherapy/monointervention, and the use of no-flow (always in preclinical models) versus low-flow ischemia (often in humans). Future research should focus on improved matching between preclinical models and clinical reality, and on aligning multitarget therapy with optimized dosing and timing towards the human condition.

Electron transfer and ROS production in brain mitochondria of intertidal and subtidal triplefin fish (Tripterygiidae)

While oxygen is essential for oxidative phosphorylation, O₂ can form reactive species (ROS) when interacting with electrons of mitochondrial electron transport system. ROS is dependent on O₂ pressure (PO₂) and has traditionally been assessed in O₂ saturated media, PO₂ at which mitochondria do not typically function in vivo. Mitochondrial ROS can be significantly elevated by the respiratory complex II substrate succinate, which can accumulate within hypoxic tissues, and this is exacerbated further with reoxygenation. Intertidal species are repetitively exposed to extreme O₂ fluctuations, and have likely evolved strategies to avoid excess ROS production. We evaluated mitochondrial electron leakage and ROS production in permeabilized brain of intertidal and subtidal triplefin fish species from hyperoxia to anoxia, and assessed the effect of anoxia reoxygenation and the influence of increasing succinate concentrations. At typical intracellular PO₂, net ROS production was similar among all species; however at elevated PO₂, brain tissues of the intertidal triplefin fish released less ROS than subtidal species. In addition, following in vitro anoxia reoxygenation, electron transfer mediated by succinate titration was better directed to respiration, and not to ROS production for intertidal species. Overall, these data indicate that intertidal triplefin fish species better manage electrons within the ETS, from hypoxic-hyperoxic transitions.

Monocarboxylate transporters facilitate succinate uptake into brown adipocytes

Uptake of circulating succinate by brown adipose tissue (BAT) and beige fat elevates whole body energy expenditure, counteracts obesity, and antagonizes systemic tissue inflammation in mice. The plasma membrane transporters that facilitate succinate uptake in these adipocytes remain undefined. Here we elucidate a mechanism underlying succinate import into BAT via monocarboxylate transporters (MCTs). We show that succinate transport is strongly dependent on the proportion of it present in the monocarboxylate form. MCTs facilitate monocarboxylate succinate uptake, which is promoted by alkalinization of the cytosol driven by adrenoreceptor stimulation. In brown adipocytes, we show that MCT1 primarily facilitates succinate import, however other members of the MCT family can partially compensate and fulfill this role in the absence of MCT1. In mice, we show that acute pharmacological inhibition of MCT1 and 2 decreases succinate uptake into BAT. Conversely, congenital genetic depletion of MCT1 alone has little effect on BAT succinate uptake, indicative of additional transport mechanisms with high capacity in vivo . In sum, we define a mechanism of succinate uptake in BAT that underlies its protective activity in mouse models of metabolic disease.

Aorta- and liver-generated TMAO enhances trained immunity for increased inflammation via ER stress/mitochondrial ROS/glycolysis pathways

We determined whether gut microbiota-produced trimethylamine (TMA) is oxidized into trimethylamine N-oxide (TMAO) in nonliver tissues and whether TMAO promotes inflammation via trained immunity (TI). We found that endoplasmic reticulum (ER) stress genes were coupregulated with MitoCarta genes in chronic kidney diseases (CKD); TMAO upregulated 190 genes in human aortic endothelial cells (HAECs); TMAO synthesis enzyme flavin-containing monooxygenase 3 (FMO3) was expressed in human and mouse aortas; TMAO transdifferentiated HAECs into innate immune cells; TMAO phosphorylated 12 kinases in cytosol via its receptor PERK and CREB, and integrated with PERK pathways; and PERK inhibitors suppressed TMAO-induced ICAM-1. TMAO upregulated 3 mitochondrial genes, downregulated inflammation inhibitor DARS2, and induced mitoROS, and mitoTEMPO inhibited TMAO-induced ICAM-1. β-Glucan priming, followed by TMAO restimulation, upregulated TNF-α by inducing metabolic reprogramming, and glycolysis inhibitor suppressed TMAO-induced ICAM-1. Our results have provided potentially novel insights regarding TMAO roles in inducing EC activation and innate immune transdifferentiation and inducing metabolic reprogramming and TI for enhanced vascular inflammation, and they have provided new therapeutic targets for treating cardiovascular diseases (CVD), CKD-promoted CVD, inflammation, transplantation, aging, and cancer.

Research progress on effects of traditional Chinese medicine on myocardial ischemia-reperfusion injury: A review

Ischemic heart disease (IHD) is a high-risk disease in the middle-aged and elderly population. The ischemic heart may be further damaged after reperfusion therapy with percutaneous coronary intervention (PCI) and other methods, namely, myocardial ischemia-reperfusion injury (MIRI), which further affects revascularization and hinders patient rehabilitation. Therefore, the investigation of new therapies against MIRI has drawn great global attention. Within the long history of the prevention and treatment of MIRI, traditional Chinese medicine (TCM) has increasingly been recognized by the scientific community for its multi-component and multi-target effects. These multi-target effects provide a conspicuous advantage to the anti-MIRI of TCM to overcome the shortcomings of single-component drugs, thereby pointing toward a novel avenue for the treatment of MIRI. However, very few reviews have summarized the currently available anti-MIRI of TCM. Therefore, a systematic data mining of TCM for protecting against MIRI will certainly accelerate the processes of drug discovery and help to identify safe candidates with synergistic formulations. The present review aims to describe TCM-based research in MIRI treatment through electronic retrieval of articles, patents, and ethnopharmacology documents. This review reported the progress of research on the active ingredients, efficacy, and underlying mechanism of anti-MIRI in TCM and TCM formulas, provided scientific support to the clinical use of TCM in the treatment of MIRI, and revealed the corresponding clinical significance and development prospects of TCM in treating MIRI.

Succinate Activation of SUCNR1 Predisposes Severely Injured Patients to Neutrophil-mediated ARDS

OBJECTIVES

Identify the metabolites that are increased in the plasma of severely injured patients that developed ARDS versus severely injured patients that did not, and assay if these increased metabolites prime pulmonary sequestration of neutrophils (PMNs) and induce pulmonary sequestration in an animal model of ARDS. We hypothesize that metabolic derangement due to advanced shock in critically injured patients leads to the PMNs, which serves as the first event in the ARDS. Summary of Background Data: Intracellular metabolites accumulate in the plasma of severely injured patients.

METHODS

Untargeted metabolomics profiling of 67 critically injured patients was completed to establish a metabolic signature associated with ARDS development. Metabolites that significantly increased were assayed for PMN priming activity in vitro. The metabolites that primed PMNs were tested in a 2-event animal model of ARDS to identify a molecular link between circulating metabolites and clinical risk for ARDS.

RESULTS

After controlling for confounders, 4 metabolites significantly increased: creatine, dehydroascorbate, fumarate, and succinate in trauma patients who developed ARDS ( P < 0.05). Succinate alone primed the PMN oxidase in vitro at physiologically relevant levels. Intravenous succinate-induced PMN sequestration in the lung, a first event, and followed by intravenous lipopolysaccharide, a second event, resulted in ARDS in vivo requiring PMNs. SUCNR1 inhibition abrogated PMN priming, PMN sequestration, and ARDS. Conclusion: Significant increases in plasma succinate post-injury may serve as the first event in ARDS. Targeted inhibition of the SUCNR1 may decrease ARDS development from other disease states to prevent ARDS globally.

Effects of hypoxia and reoxygenation on mitochondrial functions and transcriptional profiles of isolated brain and muscle porcine cells

Oxygen fluctuations might occur in mammalian tissues under physiological (e.g. at high altitudes) or pathological (e.g. ischemia-reperfusion) conditions. Mitochondria are the key target and potential amplifiers of hypoxia-reoxygenation (H-R) stress. Understanding the mitochondrial responses to H-R stress is important for identifying adaptive mechanisms and potential therapeutic solutions for pathologies associated with oxygen fluctuations. We explored metabolic response to H-R stress in two tissue types (muscle and brain) with different degrees of hypoxia tolerance in a domestic pig Sus scrofa focusing on the cellular responses independent of the systemic regulatory mechanisms. Isolated cells from the skeletal muscle (masseter) and brain (thalamus) were exposed to acute short-term (15 min) hypoxia followed by reoxygenation. The mitochondrial oxygen consumption, reactive oxygen species (ROS) production rates and transcriptional profiles of hypoxia-responsive mRNA and miRNA were determined. Mitochondria of the porcine brain cells showed a decrease in the resting respiration and ATP synthesis capacity whereas the mitochondria from the muscle cells showed robust respiration and less susceptibility to H-R stress. ROS production was not affected by the short-term H-R stress in the brain or muscle cells. Transcriptionally, prolyl hydroxylase domain protein EGLN3 was upregulated during hypoxia and suppressed during reoxygenation in porcine muscle cells. The decline in EGLN3 mRNA during reoxygenation was accompanied by an upregulation of hypoxia-inducible factor subunit α (HIF1A) transcripts in the muscle cells. However, in the brain cells, HIF1A mRNA levels were suppressed during reoxygenation. Other functionally important transcripts and miRNAs involved in antioxidant response, apoptosis, inflammation, and substrate oxidation were also differentially expressed between the muscle and brain cells. Suppression of miRNA levels during acute intermittent hypoxia was stronger in the brain cells affecting ~ 55% of all studied miRNA transcripts than in the muscle cells (~ 25% of miRNA) signifying transcriptional derepression of the respective mRNA targets. Our study provides insights into the potential molecular and physiological mechanisms contributing to different hypoxia sensitivity of the studied tissues and can serve as a starting point to better understand the biological processes associated with hypoxia stress, e.g. during ischemia and reperfusion.

Current Status and Prospects of Research on Ischemia-Reperfusion Injury and Ferroptosis

The pathogenesis of ischemia-reperfusion injury is not fully understood, most of the current clinical treatment methods mainly relieve symptoms, and cannot prevent fundamentally. The mechanism of Ferroptosis has been extensively studied in recent years, but primarily focused on its therapeutic effects on tumors. After careful comparison, it is easy to find that the symptoms of ischemia-reperfusion injury often accompany by increased lipid peroxidation and increased intracellular iron level are the same as the manifestations of iron-dependent non-apoptotic Ferroptosis. Based on this “coincidence”, we launched this survey. After reading a lot of literature, we found that Ferroptosis is the first step of ischemia-reperfusion injury, and cell necrosis and inflammation are the subsequent steps secondary to Ferroptosis. In this review, we have collected and sorted out the current knowledge about the role and targets of Ferroptosis in the process of ischemia-reperfusion injury. And future studies may be biased towards exploring the use of ferroptosis inhibitors in combination with other treatment options.

Genetic impairment of succinate metabolism disrupts bioenergetic sensing in adrenal neuroendocrine cancer

Metabolic dysfunction mutations can impair energy sensing and cause cancer. Loss of function of the mitochondrial tricarboxylic acid (TCA) cycle enzyme subunit succinate dehydrogenase B (SDHB) results in various forms of cancer typified by pheochromocytoma (PC). Here we delineate a signaling cascade where the loss of SDHB induces the Warburg effect, triggers dysregulation of [Ca²⁺]_i, and aberrantly activates calpain and protein kinase Cdk5, through conversion of its cofactor from p35 to p25. Consequently, aberrant Cdk5 initiates a phospho-signaling cascade where GSK3 inhibition inactivates energy sensing by AMP kinase through dephosphorylation of the AMP kinase γ subunit, PRKAG2. Overexpression of p25-GFP in mouse adrenal chromaffin cells also elicits this phosphorylation signaling and causes PC. A potent Cdk5 inhibitor, MRT3-007, reverses this phospho-cascade, invoking a senescence-like phenotype. This therapeutic approach halted tumor progression in vivo. Thus, we reveal an important mechanistic feature of metabolic sensing and demonstrate that its dysregulation underlies tumor progression in PC and likely other cancers.

Influence of Microbial Metabolites and Itaconic Acid Involved in Bacterial Inflammation on the Activity of Mitochondrial Enzymes and the Protective Role of Alkalization

Human microbiota produces metabolites that may enter the bloodstream and exert systemic influence on various functions including mitochondrial. Mitochondria are not only a target for microbial metabolites, but also themselves, due to the inhibition of several enzymes, produce metabolites involved in infectious processes and immune response. The influence of indolic acids, microbial derivatives of tryptophan, as well as itaconic acid, formed in the tricarboxylic acid cycle under the action of bacterial lipopolysaccharides, on the activity of mitochondrial enzymes was studied by methyl thiazolyl tetrazolium (MTT), dichlorophenolindophenol (DCPIP) and pyridine nucleotide fluorescence assays. Thus, it was found that indolic acids suppressed succinate and glutamate oxidation, shifting the redox potential of pyridine nucleotides to a more oxidized state. Itaconic acid, in addition to the well-known inhibition of succinate oxidation, also decreased NAD reduction in reactions with glutamate as a substrate. Unlike itaconic acid, indolic acids are not direct inhibitors of succinate dehydrogenase and glutamate dehydrogenase as their effects could be partially eliminated by the thiol antioxidant dithiothreitol (DTT) and the scavenger of lipid radicals butyl-hydroxytoluene (BHT). Alkalization turned out to be the most effective means to decrease the action of these metabolites, including itaconic acid, which is due to the protective influence on redox-dependent processes. Thus, among mitochondrial oxidative enzymes, the most accessible targets of these microbial-related metabolites are succinate dehydrogenase and glutamate dehydrogenase. These are important in the context of the shifting of metabolic pathways involved in bacterial inflammation and sepsis as well as the detection of new markers of these pathologies.

Role of succinic acid in the regulation of sepsis

Sepsis is a life-threatening disease characterized by a defensive response to damage. The immune response in patients with sepsis is overenhanced in the early stages and suppressed in the later stages, leading to poor prognosis. Metabolic reprogramming and epigenetic changes play a role in sepsis. Metabolic intermediates such as elevated succinic acid levels are significantly altered in patients with sepsis. Succinic acid, a metabolic intermediate of the tricarboxylic acid cycle, participates in energy supply and plays a role in metabolic reprogramming. Simultaneously, as an epigenetic regulator, it participates in gene transcription, translation, and post-translational modifications. It also participates in the inflammatory response, hypoxia, and the production of reactive oxygen species via endocrine and paracrine pathways. In this review, we have discussed the effects of succinic acid on sepsis and its therapeutic potential.

Succinate as a New Actor in Pluripotency and Early Development?

Pluripotent cells have been stabilized from pre- and post-implantation blastocysts, representing respectively naïve and primed stages of embryonic stem cells (ESCs) with distinct epigenetic, metabolic and transcriptomic features. Beside these two well characterized pluripotent stages, several intermediate states have been reported, as well as a small subpopulation of cells that have reacquired features of the 2C-embryo (2C-like cells) in naïve mouse ESC culture. Altogether, these represent a continuum of distinct pluripotency stages, characterized by metabolic transitions, for which we propose a new role for a long-known metabolite: succinate. Mostly seen as the metabolite of the TCA, succinate is also at the crossroad of several mitochondrial biochemical pathways. Its role also extends far beyond the mitochondrion, as it can be secreted, modify proteins by lysine succinylation and inhibit the activity of alpha-ketoglutarate-dependent dioxygenases, such as prolyl hydroxylase (PHDs) or histone and DNA demethylases. When released in the extracellular compartment, succinate can trigger several key transduction pathways after binding to SUCNR1, a G-Protein Coupled Receptor. In this review, we highlight the different intra- and extracellular roles that succinate might play in the fields of early pluripotency and embryo development.

Inhibiting Succinate Release Worsens Cardiac Reperfusion Injury by Enhancing Mitochondrial Reactive Oxygen Species Generation

Background

The metabolite succinate accumulates during cardiac ischemia. Within 5 minutes of reperfusion, succinate returns to baseline levels via both its release from cells and oxidation by mitochondrial complex II. The latter drives reactive oxygen species (ROS) generation and subsequent opening of the mitochondrial permeability transition (PT) pore, leading to cell death. Targeting succinate dynamics (accumulation/oxidation/release) may be therapeutically beneficial in cardiac ischemia–reperfusion (IR) injury. It has been proposed that blocking MCT1 (monocarboxylate transporter 1) may be beneficial in IR injury, by preventing succinate release and subsequent engagement of downstream inflammatory signaling pathways. In contrast, herein we hypothesized that blocking MCT1 would retain succinate in cells, exacerbating ROS generation and IR injury.

Methods and Results

Using the mitochondrial ROS probe mitoSOX and a custom‐built murine heart perfusion rig built into a spectrofluorometer, we measured ROS generation in situ during the first moments of reperfusion. We found that acute MCT1 inhibition enhanced mitochondrial ROS generation at reperfusion and worsened IR injury (recovery of function and infarct size). Both of these effects were abrogated by tandem inhibition of mitochondrial complex II, suggesting that succinate retention worsens IR because it drives more mitochondrial ROS generation. Furthermore, using the PT pore inhibitor cyclosporin A, along with monitoring of PT pore opening via the mitochondrial membrane potential indicator tetramethylrhodamine ethyl ester, we herein provide evidence that ROS generation during early reperfusion is upstream of the PT pore, not downstream as proposed by others. In addition, pore opening was exacerbated by MCT1 inhibition.

Conclusions

Together, these findings highlight the importance of succinate dynamics and mitochondrial ROS generation as key determinants of PT pore opening and IR injury outcomes.

Pregnenolone Attenuates the Ischemia-Induced Neurological Deficit in the Transient Middle Cerebral Artery Occlusion Model of Rats

Neurosteroids are apparent to be connected in the cerebral ischemic injury for their potential neuroprotective effects. We previously demonstrated that progesterone induces neuroprotection via the mitochondrial cascade in the cerebral ischemic stroke of rodents. Here, we sought to investigate whether or not pregnenolone, a different neurosteroid, can protect the ischemic injury in the transient middle cerebral artery occlusion (tMCAO) rodent model. Male Wistar rats were chosen for surgery for inducing stroke using the tMCAO method. Pregnenolone (2 mg/kg b.w.) at 1 h postsurgery was administered. The neurobehavioral tests and (TTC staining) 2, 3, 5-triphenyl tetrazolium chloride staining were performed after 24 h of the surgery. The mitochondrial membrane potential and reactive oxygen species (ROS) were measured using flow cytometry. Oxygraph was used to examine mitochondrial bioenergetics. The spectrum of neurobehavioral tests and 2, 3, 5-triphenyltetrazolium chloride staining showed that pregnenolone enhanced neurological recovery. Pregnenolone therapy after a stroke lowered mitochondrial ROS following ischemia. Our data demonstrated that pregnenolone was not able to inhibit mitochondrial permeability transition pores. There was no effect on mitochondrial bioenergetics such as oxygen consumption and respiratory coupling. Overall, the findings demonstrated that pregnenolone reduced the neurological impairments via reducing mitochondria ROS but not through the inhibition of the mitochondria permeability transition pore (mtPTP).

Protective effects of natural products against myocardial ischemia/reperfusion: Mitochondria-targeted therapeutics

Patients with ischemic heart disease receiving reperfusion therapy still need to face left ventricular remodeling and heart failure after myocardial infarction. Reperfusion itself paradoxically leads to further cardiomyocyte death and systolic dysfunction. Ischemia/reperfusion (I/R) injury can eliminate the benefits of reperfusion therapy in patients and causes secondary myocardial injury. Mitochondrial dysfunction and structural disorder are the basic driving force of I/R injury. We summarized the basic relationship and potential mechanisms of mitochondrial injury in the development of I/R injury. Subsequently, this review summarized the natural products (NPs) that have been proven to targeting mitochondrial therapeutic effects during I/R injury in recent years and related cellular signal transduction pathways. We found that these NPs mainly protected the structural integrity of mitochondria and improve dysfunction, such as reducing mitochondrial division and fusion abnormalities, improving mitochondrial Ca²⁺ overload and inhibiting reactive oxygen species overproduction, thereby playing a role in protecting cardiomyocytes during I/R injury. This data would deepen the understanding of I/R-induced mitochondrial pathological process and suggested that NPs are expected to be transformed into potential therapies targeting mitochondria.

Why succinate? Physiological regulation by a mitochondrial coenzyme Q sentinel

Metabolites once considered solely in catabolism or anabolism turn out to have key regulatory functions. Among these, the citric acid cycle intermediate succinate stands out owing to its multiple roles in disparate pathways, its dramatic concentration changes and its selective cell release. Here we propose that succinate has evolved as a signaling modality because its concentration reflects the coenzyme Q (CoQ) pool redox state, a central redox couple confined to the mitochondrial inner membrane. This connection is of general importance because CoQ redox state integrates three bioenergetic parameters: mitochondrial electron supply, oxygen tension and ATP demand. Succinate, by equilibrating with the CoQ pool, enables the status of this central bioenergetic parameter to be communicated from mitochondria to the rest of the cell, into the circulation and to other cells. The logic of this form of regulation explains many emerging roles of succinate in biology, and suggests future research questions.

Attenuated succinate accumulation relieves neuronal injury induced by hypoxia in neonatal mice

Hypoxia causes neonatal neuronal damage. However, the underlying mechanism remains unclear. This study aimed to explore the changes in succinate levels and identify the mechanisms underlying their contribution to hypoxia-induced damage in newborn mice. The neonatal C57BL/6J mouse hypoxia model was used in our study. We evaluated the levels of succinate, iron, reactive oxygen species (ROS), and mitochondrial ROS, and assessed mitophagy, neuronal damage, and learning and memory function, after hypoxia treatment. The neonatal mice showed increased succinate levels in the early hypoxia stage, followed by increased levels of oxidative stress, iron stress, neuronal damage, and cognitive deficits. Succinate levels were significantly reduced following treatment with inhibitors of succinate dehydrogenase (SDH), purine nucleotide cycle (PNC), and malate/aspartate shuttle (MAS), with the corresponding attenuation of oxidative stress, iron stress, neuronal damage, and cognitive impairment. Reversal catalysis of SDH through fumarate from the PNC and MAS pathways might be involved in hypoxia-induced succinate accumulation. Succinate accumulation in the early period after hypoxia may crucially contribute to oxidative and iron stress. Relieving succinate accumulation at the early hypoxia stage could prevent neuronal damage and cognitive impairment in neonatal hypoxia.

The GenoDiabMar Registry: A Collaborative Research Platform of Type 2 Diabetes Patients

The GenoDiabMar registry is a prospective study that aims to provide data on demographic, biochemical, and clinical changes in type 2 diabetic (T2D) patients attending real medical outpatient consultations. This registry is also used to find new biomarkers related to the micro- and macrovascular complications of T2D, with a particular focus on diabetic nephropathy. With this purpose, longitudinal serum and urine samples, DNA banking, and data on 227 metabolomics profiles, 77 immunoglobulin G glycomics traits, and other emerging biomarkers were recorded in this cohort. In this study, we show a detailed longitudinal description of the clinical and analytical parameters of this registry, with a special focus on the progress of renal function and cardiovascular events. The main objective is to analyze whether there are differential risk factors for renal function deterioration between sexes, as well as to analyze cardiovascular events and mortality in this population. In total, 650 patients with a median age of 69 (14) with different grades of chronic kidney disease—G1−G2 (eGFR > 90−60 mL/min/1.73 m2) 50.3%, G3 (eGFR; 59−30 mL/min/1.73 m2) 31.4%, G4 (eGFR; 29−15 mL/min/1.73 m2) 10.8%, and G5 (eGFR < 15 mL/min/1.73 m2) 7.5%—were followed up for 4.7 (0.65) years. Regardless of albuminuria, women lost 0.93 (0.40−1.46) fewer glomerular filtration units per year than men. A total of 17% of the participants experienced rapid deterioration of renal function, 75.2% of whom were men, with differential risk factors between sexes—severe macroalbuminuria > 300 mg/g for men OR [IQ] 2.40 [1.29:4.44] and concomitant peripheral vascular disease 3.32 [1.10:9.57] for women. Overall mortality of 23% was detected (38% of which was due to cardiovascular etiology). We showed that kidney function declined faster in men, with different risk factors compared to women. Patients with T2D and kidney involvement have very high mortality and an important cardiovascular burden. This cohort is proposed as a great tool for scientific collaboration for studies, whether they are focused on T2D, or whether they are interested in comparing differential markers between diabetic and non-diabetic populations.

Fighting in a wasteland: deleterious metabolites and antitumor immunity

As cancers progress, they produce a local environment that acts to redirect, paralyze, exhaust, or otherwise evade immune detection and destruction. The tumor microenvironment (TME) has long been characterized as a metabolic desert, depleted of essential nutrients such as glucose, oxygen, and amino acids, that starves infiltrating immune cells and renders them dysfunctional. While not incorrect, this perspective is only half the picture. The TME is not a metabolic vacuum, only consuming essential nutrients and never producing by-products. Rather, the by-products of depleted nutrients, "toxic" metabolites in the TME such as lactic acid, kynurenine, ROS, and adenosine, play an important role in shaping immune cell function and cannot be overlooked in cancer immunotherapy. Moreover, while the metabolic landscape is distinct, it is not unique, as these toxic metabolites are encountered in non-tumor tissues, where they evolutionarily shape immune cells and their response. In this Review, we discuss how depletion of essential nutrients and production of toxic metabolites shape the immune response within the TME and how toxic metabolites can be targeted to improve current cancer immunotherapies.

Ratiometric Mass Spectrometry Imaging for Stain-Free Delineation of Ischemic Tissue and Spatial Profiling of Ischemia-Related Molecular Signatures

Mass spectrometry imaging (MSI) serves as an emerging tool for spatial profiling of metabolic dysfunction in ischemic tissue. Prior to MSI data analysis, commonly used staining methods, e.g., triphenyltetrazole chloride (TTC) staining, need to be implemented on the adjacent tissue for delineating lesion area and evaluating infarction, resulting in extra consumption of the tissue sample as well as morphological mismatch. Here, we propose an in situ ratiometric MSI method for simultaneous demarcation of lesion border and spatial annotation of metabolic and enzymatic signatures in ischemic tissue on identical tissue sections. In this method, the ion abundance ratio of a reactant pair in the TCA cycle, e.g., fumarate to malate, is extracted pixel-by-pixel from an ambient MSI dataset of ischemic tissue and used as a surrogate indicator for metabolic activity of mitochondria to delineate lesion area as if the tissue has been chemically stained. This method is shown to be precise and robust in identifying lesions in brain tissues and tissue samples from different ischemic models including heart, liver, and kidney. Furthermore, the proposed method allows screening and predicting metabolic and enzymatic alterations which are related to mitochondrial dysfunction. Being capable of concurrent lesion identification, in situ metabolomics analysis, and screening of enzymatic alterations, the ratiometric MSI method bears great potential to explore ischemic damages at both metabolic and enzymatic levels in biological research.

Mitochondrial Metabolism in Myocardial Remodeling and Mechanical Unloading: Implications for Ischemic Heart Disease

Ischemic heart disease refers to myocardial degeneration, necrosis, and fibrosis caused by coronary artery disease. It can lead to severe left ventricular dysfunction (LVEF ≤ 35–40%) and is a major cause of heart failure (HF). In each contraction, myocardium is subjected to a variety of mechanical forces, such as stretch, afterload, and shear stress, and these mechanical stresses are clinically associated with myocardial remodeling and, eventually, cardiac outcomes. Mitochondria produce 90% of ATP in the heart and participate in metabolic pathways that regulate the balance of glucose and fatty acid oxidative phosphorylation. However, altered energetics and metabolic reprogramming are proved to aggravate HF development and progression by disturbing substrate utilization. This review briefly summarizes the current insights into the adaptations of cardiomyocytes to mechanical stimuli and underlying mechanisms in ischemic heart disease, with focusing on mitochondrial metabolism. We also discuss how mechanical circulatory support (MCS) alters myocardial energy metabolism and affects the detrimental metabolic adaptations of the dysfunctional myocardium.

Tissue- and substrate-dependent mitochondrial responses to acute hypoxia-reoxygenation stress in a marine bivalve Crassostrea gigas (Thunberg, 1793)

Hypoxia is a major stressor for aquatic organisms, yet intertidal organisms like the oyster Crassostrea gigas are adapted to frequent oxygen fluctuations by metabolically adjusting to shifts in oxygen and substrate availability during hypoxia-reoxygenation (H/R). We investigated the effects of acute H/R stress (15 min at ∼0% O2, and 10 min reoxygenation) on isolated mitochondria from the gill and the digestive gland of C. gigas respiring on different substrates (pyruvate, glutamate, succinate, palmitate and their mixtures). Gill mitochondria showed better capacity for amino acid and fatty acid oxidation compared to the mitochondria from the digestive gland. Mitochondrial responses to H/R stress strongly depended on the substrate and the activity state of mitochondria. In mitochondria oxidizing NADH-linked substrates exposure to H/R stress suppressed oxygen consumption and ROS generation in the resting state, whereas in the ADP-stimulated state, ROS production increased despite little change in respiration. As a result, electron leak (measured as H2O2 to O2 ratio) increased after H/R stress in the ADP-stimulated mitochondria with NADH-linked substrates. In contrast, H/R exposure stimulated succinate-driven respiration without an increase in electron leak. Reverse electron transport (RET) did not significantly contribute to succinate-driven ROS production in oyster mitochondria except for a slight increase in the OXPHOS state during post-hypoxic recovery. A decrease in NADH-driven respiration and ROS production, enhanced capacity for succinate oxidation and resistance to RET might assist in post-hypoxic recovery of oysters mitigating oxidative stress and supporting rapid ATP re-synthesis during oxygen fluctuations such as commonly observed in estuaries and intertidal zones.

Astragalin Protects against Spinal Cord Ischemia Reperfusion Injury through Attenuating Oxidative Stress-Induced Necroptosis

Spinal cord ischemia/reperfusion (SCI/R) injury is a devastating complication usually occurring after thoracoabdominal aortic surgery. However, it remains unsatisfactory for its intervention by using pharmacological strategies. Oxidative stress is a main pharmacological process involved in SCI/R, which will elicit downstream programmed cell death such as the novel defined necroptosis. Astragalin is a bioactive natural flavonoid with a wide spectrum of pharmacological activities. Herein, we firstly evaluated the effect of astragalin to oxidative stress as well as the possible downstream necroptosis after SCI/R in mice. Our results demonstrated that astragalin improves the ethological score and histopathological deterioration of SCI/R mice. Astragalin mitigates oxidative stress and ameliorates inflammation after SCI/R. Astragalin blocks necroptosis induced by SCI/R. That is, the amelioration of astragalin to the motoneuron injury and histopathological changes. Indicators of oxidative stress, inflammation, and necroptosis after SCI/R were significantly blocked. Summarily, we firstly illustrated the protection of astragalin against SCI/R through its blockage to the necroptosis at downstream of oxidative stress.

The Antioxidant Transcription Factor Nrf2 in Cardiac Ischemia-Reperfusion Injury

Nuclear factor erythroid-2 related factor 2 (Nrf2) is a transcription factor that controls cellular defense responses against toxic and oxidative stress by modulating the expression of genes involved in antioxidant response and drug detoxification. In addition to maintaining redox homeostasis, Nrf2 is also involved in various cellular processes including metabolism and inflammation. Nrf2 activity is tightly regulated at the transcriptional, post-transcriptional and post-translational levels, which allows cells to quickly respond to pathological stress. In the present review, we describe the molecular mechanisms underlying the transcriptional regulation of Nrf2. We also focus on the impact of Nrf2 in cardiac ischemia-reperfusion injury, a condition that stimulates the overproduction of reactive oxygen species. Finally, we analyze the protective effect of several natural and synthetic compounds that induce Nrf2 activation and protect against ischemia-reperfusion injury in the heart and other organs, and their potential clinical application.

Ultra-Performance Liquid Chromatography-Q-Exactive Orbitrap-Mass Spectrometry Analysis for Metabolic Communication between Heart and Kidney in Adriamycin-Induced Nephropathy Rats

BACKGROUND/AIMS

Although the adriamycin-induced nephropathy model is frequently employed in the study of nephrotic syndrome and focal segmental glomerulosclerosis, the accompanying myocardial damage has always been a cause for concern. Therefore, there is a great need to study cardiorenal communication in this model.

METHODS

An adriamycin-induced nephropathy model was established via tail vein injection. The levels of the biochemical indicators serum albumin, serum globulin, serum total protein, serum cholesterol, serum creatinine (SCr), urinary protein, and urinary creatinine (UCr) were measured, and histopathological changes in the heart and kidneys were assessed using hematoxylin-eosin staining. Metabolomic changes in the heart, blood, and kidneys were analyzed using the metabolomics method based on ultra-performance liquid chromatography Q-Exactive Orbitrap mass spectrometry.

RESULTS

Compared with the control group, the model group showed significant decreases in serum protein and total protein levels, albumin/globulin ratio, and creatinine clearance rate as well as significant increases in serum cholesterol, SCr, urinary protein, and UCr levels. Significant pathological changes were observed in the renal pathology sections in the model group, including diffusely merged glomerular epithelial cells, inflammatory infiltration, and vacuolated glomerular cells. Additionally, thickened myocardial fibers, swollen nuclei, inflammatory infiltration, and partial myocardial necrosis could be seen in the cardiac pathology sections in the model group. Based on multivariate statistical analysis, a total of 20 differential metabolites associated with 15 metabolic pathways were identified in the heart, 7 differential metabolites with 7 metabolic pathways were identified in the blood, and 16 differential metabolites with 21 metabolic pathways were identified in the kidney. Moreover, 6 common metabolic pathways shared by the heart and kidney were identified: arginine and proline metabolism; arginine biosynthesis; glutathione metabolism; alanine, aspartate, and glutamate metabolism; beta-alanine metabolism; and histidine metabolism. Among these metabolic pathways, alanine, aspartate, and glutamate metabolism was shared by the heart, blood, and kidney. Succinic acid was found to be the key regulatory metabolite in cardiorenal metabolic communication.

CONCLUSION

Six metabolic pathways were found to be involved in cardiorenal metabolic communication in an adriamycin-induced nephropathy model, in which alanine, aspartate, and glutamate metabolism may be the metabolic link between the heart and kidney in the development and maintenance of oxidative stress and inflammation. Succinic acid may serve as a key regulatory metabolic switch or marker of cardiac and renal co-injury, as shown in an adriamycin-induced nephropathy model.

Cardiac PANK1 deletion exacerbates ventricular dysfunction during pressure overload

Coenzyme A (CoA) is an essential cofactor required for intermediary metabolism. Perturbations in homeostasis of CoA have been implicated in various pathologies; however, whether CoA homeostasis is changed and the extent to which CoA levels contribute to ventricular function and remodeling during pressure overload has not been explored. In this study, we sought to assess changes in CoA biosynthetic pathway during pressure overload and determine the impact of limiting CoA on cardiac function. We limited cardiac CoA levels by deleting the rate-limiting enzyme in CoA biosynthesis, pantothenate kinase 1 (Pank1). We found that constitutive, cardiomyocyte-specific Pank1 deletion (cmPank1-/-) significantly reduced PANK1 mRNA, PANK1 protein, and CoA levels compared with Pank1-sufficient littermates (cmPank1+/+) but exerted no obvious deleterious impact on the mice at baseline. We then subjected both groups of mice to pressure overload-induced heart failure. Interestingly, there was more ventricular dilation in cmPank1-/- during the pressure overload. To explore potential mechanisms contributing to this phenotype, we performed transcriptomic profiling, which suggested a role for Pank1 in regulating fibrotic and metabolic processes during the pressure overload. Indeed, Pank1 deletion exacerbated cardiac fibrosis following pressure overload. Because we were interested in the possibility of early metabolic impacts in response to pressure overload, we performed untargeted metabolomics, which indicated significant changes to metabolites involved in fatty acid and ketone metabolism, among other pathways. Collectively, our study underscores the role of elevated CoA levels in supporting fatty acid and ketone body oxidation, which may be more important than CoA-driven, enzyme-independent acetylation in the failing heart.NEW & NOTEWORTHY Changes in CoA homeostasis have been implicated in a variety of metabolic diseases; however, the extent to which changes in CoA homeostasis impacts remodeling has not been explored. We show that limiting cardiac CoA levels via PANK deletion exacerbated ventricular remodeling during pressure overload. Our results suggest that metabolic alterations, rather than structural alterations, associated with Pank1 deletion may underlie the exacerbated cardiac phenotype during pressure overload.

Rethinking succinate: an unexpected hormone-like metabolite in energy homeostasis

There has been an explosion of interest in the signaling capacity of energy metabolites. A prime example is the Krebs cycle substrate succinate, an archetypal respiratory substrate with functions beyond energy production as an intracellular and extracellular signaling molecule. Long associated with inflammation, emerging evidence supports a key role for succinate in metabolic processes relating to energy management. As the natural ligand for SUCNR1, a G protein-coupled receptor, succinate is akin to hormones and likely functions as a reporter of metabolism and stress. In this review, we reconcile new and old observations to outline a regulatory role for succinate in metabolic homeostasis. We highlight the importance of the succinate-SUCNR1 axis in metabolic diseases as an integrator of macrophage immune response, and we discuss new metabolic functions recently ascribed to succinate in specific tissues. Because circulating succinate has emerged as a promising biomarker in chronic metabolic diseases, a better understanding of the physiopathological role of the succinate-SUCNR1 axis in metabolism might open new avenues for clinical use in patients with obesity or diabetes.

SUMOylation as a Therapeutic Target for Myocardial Infarction

Myocardial infarction is a prevalent and life-threatening cardiovascular disease. The main goal of existing interventional therapies is to restore coronary reperfusion while few are designed to ameliorate the pathology of heart diseases via targeting the post-translational modifications of those critical proteins. Small ubiquitin-like modifier (SUMO) proteins are recently discovered to form a new type of protein post-translational modifications (PTM), known as SUMOylation. SUMOylation and deSUMOylation are dynamically balanced in the maintenance of various biological processes including cell division, DNA repair, epigenetic transcriptional regulation, and cellular metabolism. Importantly, SUMOylation plays a critical role in the regulation of cardiac functions and the pathology of cardiovascular diseases, especially in heart failure and myocardial infarction. This review summarizes the current understanding on the effects of SUMOylation and SUMOylated proteins in the pathophysiology of myocardial infarction and identifies the potential treatments against myocardial injury via targeting SUMO. Ultimately, this review recommends SUMOylation as a key therapeutic target for treating cardiovascular diseases.

Succinate accumulation contributes to oxidative stress and iron accumulation in pentylenetetrazol-induced epileptogenesis and kainic acid-induced seizure

This study explored the role of succinate accumulation in the oxidative stress and iron accumulation in both pentylenetetrazol (PTZ)-induced epileptogenesis and kainic acid (KA)-induced status epilepticus (SE). The levels of succinate, oxidative stress, iron content, iron-related protein expression, and the severity of neuronal injury and seizures were measured in both models. We found that increased concentrations of succinate were associated with increased levels of oxidative stress, iron content, iron regulator protein, and iron importer divalent metal transporter 1, as well as decreased levels of iron exporter ferropotin 1. Aggravated neuronal injury was observed in the hippocampi and cortices of both models. The cell-permeable molecule dimethyl malonate (DM), a competitive inhibitor of succinate dehydrogenase (SDH), significantly attenuated succinate accumulation, reduced the oxidative stress and iron levels, and mitigated the severity of the seizures and neuronal injury. Our results thus indicate that the accumulation of succinate due to the reverse catalysis of SDH may exacerbate oxidative stress and thus induce iron accumulation and neuronal injury in both models. Targeting succinate accumulation may achieve neuroprotective and anti-seizure effects.

LncRNA PART1 alleviated myocardial ischemia/reperfusion injury via suppressing miR-503-5p/BIRC5 mediated mitochondrial apoptosis

BACKGROUND

Long non-coding RNA (lncRNA) is crucial for heart development and for adult heart structural maintenance and function. Herein, we performed a study to explore the effect of lncRNA PART1 on myocardial ischemia-reperfusion (I/R) injury by targeting BIRC5 through miR-503-5p pathway.

METHODS

I/R model was created in vivo and vitro. The level of gene and protein was detected by RT-PCR and western blot. The apoptosis level was assessed by TUNEL and flow cytometry. Cell viability was determined by MTT. Mitochondrial function was evaluated by ATP content, ROS production, GSH level, and mitochondrial membrane potential. Cardiac function was confirmed by echocardiography, TTC staining, and H&E staining.

RESULTS

Here, we found that the expression of lncRNA PART1 was down-regulated in the I/R hearts and H/R cardiomyocytes. Forced expression of PART1 remitted cardiac I/RI and H/R cardiomyocyte injury. Silencing of PART1 aggravated apoptosis and mitochondrial damage in cardiomyocytes. We found that PART1 functioned as a competing endogenous RNA of miR-503-5p, which decreased the expression of miR-503-5p. We further established BIRC5 as a target of miR-503-5p. Furthermore, PART1 prevented apoptosis and improved mitochondrial function in myocardial I/RI by targeting miR-503-5p/BIRC5.

CONCLUSIONS

In summary, PART1 protected mitochondrial function via miR-503-5p/BIRC5 pathway in MI/RI, which may provide the new theoretical basis for MI/RI treatment in the clinic.

Ischemia-Reperfusion Injuries Assessment during Pancreas Preservation

Maintaining organ viability between donation and transplantation is of critical importance for optimal graft function and survival. To date in pancreas transplantation, static cold storage (SCS) is the most widely practiced method of organ preservation. The first experiments in ex vivo perfusion of the pancreas were performed at the beginning of the 20th century. These perfusions led to organ oedema, hemorrhage, and venous congestion after revascularization. Despite these early hurdles, a number of factors now favor the use of perfusion during preservation: the encouraging results of HMP in kidney transplantation, the development of new perfusion solutions, and the development of organ perfusion machines for the lung, heart, kidneys and liver. This has led to a resurgence of research in machine perfusion for whole organ pancreas preservation. This review highlights the ischemia-reperfusion injuries assessment during ex vivo pancreas perfusion, both for assessment in pre-clinical experimental models as well for future use in the clinic. We evaluated perfusion dynamics, oedema assessment, especially by impedance analysis and MRI, whole organ oxygen consumption, tissue oxygen tension, metabolite concentrations in tissue and perfusate, mitochondrial respiration, cell death, especially by histology, total cell free DNA, caspase activation, and exocrine and endocrine assessment.

The Redox Modulating Sonlicromanol Active Metabolite KH176m and the Antioxidant MPG Protect Against Short-Duration Cardiac Ischemia-Reperfusion Injury

Purpose

Sonlicromanol is a phase IIB clinical stage compound developed for treatment of mitochondrial diseases. Its active component, KH176m, functions as an antioxidant, directly scavenging reactive oxygen species (ROS), and redox activator, boosting the peroxiredoxin-thioredoxin system. Here, we examined KH176m’s potential to protect against acute cardiac ischemia-reperfusion injury (IRI), compare it with the classic antioxidant N-(2-mercaptopropionyl)-glycine (MPG), and determine whether protection depends on duration (severity) of ischemia.

Methods

Isolated C56Bl/6N mouse hearts were Langendorff-perfused and subjected to short (20 min) or long (30 min) ischemia, followed by reperfusion. During perfusion, hearts were treated with saline, 10 μM KH176m, or 1 mM MPG. Cardiac function, cell death (necrosis), and mitochondrial damage (cytochrome c (CytC) release) were evaluated. In additional series, the effect of KH176m treatment on the irreversible oxidative stress marker 4-hydroxy-2-nonenal (4-HNE), formed during ischemia only, was determined at 30-min reperfusion.

Results

During baseline conditions, both drugs reduced cardiac performance, with opposing effects on vascular resistance (increased with KH176m, decreased with MPG). For short ischemia, KH176m robustly reduced all cell death parameters: LDH release (0.2 ± 0.2 vs 0.8 ± 0.5 U/min/GWW), infarct size (15 ± 8 vs 31 ± 20%), and CytC release (168.0 ± 151.9 vs 790.8 ± 453.6 ng/min/GWW). Protection by KH176m was associated with decreased cardiac 4-HNE. MPG only reduced CytC release. Following long ischemia, IRI was doubled, and KH176m and MPG now only reduced LDH release. The reduced protection against long ischemia was associated with the inability to reduce cardiac 4-HNE.

Conclusion

Protection against cardiac IRI by the antioxidant KH176m is critically dependent on duration of ischemia. The data suggest that with longer ischemia, the capacity of KH176m to reduce cardiac oxidative stress is rate-limiting, irreversible ischemic oxidative damage maximally accumulates, and antioxidant protection is strongly diminished.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10557-021-07189-9.