Differential effects of complex II on mitochondrial ROS production and their relation to cardioprotective pre- and postconditioning

Transcriptome analysis of porcine oocytes during postovulatory aging

Decreased oocyte quality is a significant contributor to the decline in female fertility that accompanies aging in mammals. Oocytes rely on mRNA stores to support their survival and integrity during the protracted period of transcriptional dormancy as they await ovulation. However, the changes in mRNA levels and interactions that occur during porcine oocyte maturation and aging remain unclear. In this study, the mRNA expression profiles of porcine oocytes during the GV, MII, and aging (24 h after the MII stage) stages were explored by transcriptome sequencing to identify the key genes and pathways that affect oocyte maturation and postovulatory aging. The results showed that 10,929 genes were coexpressed in porcine oocytes during the GV stage, MII stage, and aging stage. In addition, 3037 genes were expressed only in the GV stage, 535 genes were expressed only in the MII stage, and 120 genes were expressed only in the aging stage. The correlation index between the GV and MII stages (0.535) was markedly lower than that between the MII and aging stages (0.942). A total of 3237 genes, which included 1408 upregulated and 1829 downregulated genes, were differentially expressed during porcine oocyte postovulatory aging (aging stage vs. MII stage). Key functional genes, including ATP2A1, ATP2A3, ATP2B2, NDUFS1, NDUFA2, NDUFAF3, SREBF1, CYP11A1, CYP3A29, GPx4, CCP110, STMN1, SPC25, Sirt2, SYCP3, Fascin1/2, PFN1, Cofilin, Tmod3, FLNA, LRKK2, CHEK1/2, DDB1/2, DDIT4L, and TONSL, and key molecular pathways, such as the calcium signaling pathway, MAPK signaling pathway, TGF-β signaling pathway, PI3K/Akt signaling pathway, FoxO signaling pathway, gap junctions, and thermogenesis, were found in abundance during porcine postovulatory aging. These genes are mainly involved in the regulation of many biological processes, such as oxidative stress, calcium homeostasis, mitochondrial function, and lipid peroxidation, during porcine oocyte postovulatory aging. These results contribute to a more in-depth understanding of the biological changes, key regulatory genes and related biological pathways that are involved in oocyte aging and provide a theoretical basis for improving the efficiency of porcine embryo production in vitro and in vivo.

Chronic undernutrition impairs renal mitochondrial respiration accompanied by intense ultrastructural damage in juvenile rats

This study investigated whether chronic undernutrition alters the mitochondrial structure and function in renal proximal tubule cells, thus impairing fluid transport and homeostasis. We previously showed that chronic undernutrition downregulates the renal proximal tubules (Na++K+)ATPase, the main molecular machine responsible for fluid transport and ATP consumption. Male rats received a multifactorial deficient diet, the so-called Regional Basic Diet (RBD), mimicking those used in impoverished regions worldwide, from weaning to a juvenile age (3 months). The diet has a low content (8 %) of poor-quality proteins, low lipids, and no vitamins compared to control (CTR). We investigated citrate synthase activity, mitochondrial respiration (oxygraphy) in phosphorylating and non-phosphorylating conditions with different substrates/inhibitors, potential across the internal membrane (Δψ), and anion superoxide/H2O2 formation. The data were correlated with ultrastructural alterations evaluated using transmission electron microscopy (TEM) and focused ion beam scanning electron microscopy (FIB-SEM). Citrate synthase activity decreased (∼50 %) in RBD rats, accompanied by a similar reduction in respiration in non-phosphorylating conditions, maximum respiratory capacity, and ATP synthesis. The Δψ generation and its dissipation after carbonyl cyanide-4-(trifluoromethoxy) phenylhydrazone remained unmodified in the survival mitochondria. H2O2 production increased (∼100 %) after Complex II energization. TEM demonstrated intense matrix vacuolization and disruption of cristae junctions in a subpopulation of RBD mitochondria, which was also demonstrated in the 3D analysis of FIB-SEM tomography. In conclusion, chronic undernutrition impairs mitochondrial functions in renal proximal tubules, with profound alterations in the matrix and internal membrane ultrastructure that culminate with the compromise of ATP supply for transport processes.

Graphene Oxide Significantly Modifies Cardiac Parameters and Coronary Endothelial Reactivity in Healthy and Hypertensive Rat Hearts Ex Vivo

Interactions of graphene oxide (GO) with an ex vivo rat heart and its coronary vessels have not been studied yet. Moreover, the conflicting data on the "structure-properties" relationships do not allow for biomedical applications of GO. Herein, we study the impact of GO on the ex vivo isolated rat heart, normotensive and hypertensive, under the working heart and the constant-pressure perfusion (Langendorff) regimes. Four structural GO variants of the following initial morphology were used: few-layer (below 10-layer) GO1, O < 49%; predominantly single-layer GO2, O = 41-50%; 15-20-layer GO3, O < 11%; and few-layer (below 10-layer) NH4 +-functionalized GO4, O < 44%, N = 3-6%. The aqueous GO dispersions, sonicated and stabilized with bovine serum albumin in Krebs-Henseleit-like solution-uniformized in terms of the particle size-were eventually size-monodisperse as revealed by dynamic light scattering. To study the cardiotoxicity mechanisms of GO, histopathology, Raman spectroscopy, analysis of cardiac parameters (coronary and aortic flows, heart rate, aortic pressure), and nitric oxide (NO-)-dependent coronary flow response to bradykinin (blood-vessel-vasodilator) were used. GO1 (10 mg/L) exerted no effects on cardiac function and preserved an increase in coronary flow in response to bradykinin. GO2 (10 mg/L) reduced coronary flow, aortic pressure in normotensive hearts, and coronary flow in hypertensive hearts, and intensified the response to bradykinin in normal hearts. GO3 (10 mg/L) reduced all parameters in hypertensive hearts and coronary response to bradykinin in normal hearts. At higher concentrations (normotensive hearts, 30 mg/L), the coronary response to bradykinin was blocked. GO4 (10 mg/L) reduced the coronary flow in normal hearts, while for hypertensive hearts, all parameters, except the coronary flow, were reduced and the coronary response to bradykinin was blocked. The results showed that a low number of GO layers and high O-content were safer for normal and hypertensive rat hearts. Hypertensive hearts deteriorated easier upon perfusion with low-O-content GOs. Our findings support the necessity of strict control over the GO structure during organ perfusion and indicate the urgent need for personalized medicine in biomedical applications of GO.

Primary mitochondrial diseases: The intertwined pathophysiology of bioenergetic dysregulation, oxidative stress and neuroinflammation

OBJECTIVES AND SCOPE

Primary mitochondrial diseases (PMDs) are rare genetic disorders resulting from mutations in genes crucial for effective oxidative phosphorylation (OXPHOS) that can affect mitochondrial function. In this review, we examine the bioenergetic alterations and oxidative stress observed in cellular models of primary mitochondrial diseases (PMDs), shedding light on the intricate complexity between mitochondrial dysfunction and cellular pathology. We explore the diverse cellular models utilized to study PMDs, including patient-derived fibroblasts, induced pluripotent stem cells (iPSCs) and cybrids. Moreover, we also emphasize the connection between oxidative stress and neuroinflammation.

INSIGHTS

The central nervous system (CNS) is particularly vulnerable to mitochondrial dysfunction due to its dependence on aerobic metabolism and the correct functioning of OXPHOS. Similar to other neurodegenerative diseases affecting the CNS, individuals with PMDs exhibit several neuroinflammatory hallmarks alongside neurodegeneration, a pattern also extensively observed in mouse models of mitochondrial diseases. Based on histopathological analysis of postmortem human brain tissue and findings in mouse models of PMDs, we posit that neuroinflammation is not merely a consequence of neurodegeneration but a potential pathogenic mechanism for disease progression that deserves further investigation. This recognition may pave the way for novel therapeutic strategies for this group of devastating diseases that currently lack effective treatments.

SUMMARY

In summary, this review provides a comprehensive overview of bioenergetic alterations and redox imbalance in cellular models of PMDs while underscoring the significance of neuroinflammation as a potential driver in disease progression.

Novel formylpeptide receptor 1/2 agonist limits hypertension-induced cardiovascular damage

AIMS

Formylpeptide receptors (FPRs) play a critical role in the regulation of inflammation, an important driver of hypertension-induced end-organ damage. We have previously reported that the biased FPR small-molecule agonist, compound17b (Cmpd17b), is cardioprotective against acute, severe inflammatory insults. Here, we reveal the first compelling evidence of the therapeutic potential of this novel FPR agonist against a longer-term, sustained inflammatory insult, i.e. hypertension-induced end-organ damage. The parallels between the murine and human hypertensive proteome were also investigated.

METHODS AND RESULTS

The hypertensive response to angiotensin II (Ang II, 0.7 mg/kg/day, s.c.) was attenuated by Cmpd17b (50 mg/kg/day, i.p.). Impairments in cardiac and vascular function assessed via echocardiography were improved by Cmpd17b in hypertensive mice. This functional improvement was accompanied by reduced cardiac and aortic fibrosis and vascular calcification. Cmpd17b also attenuated Ang II-induced increased cardiac mitochondrial complex 2 respiration. Proteomic profiling of cardiac and aortic tissues and cells, using label-free nano-liquid chromatography with high-sensitivity mass spectrometry, detected and quantified ∼6000 proteins. We report hypertension-impacted protein clusters associated with dysregulation of inflammatory, mitochondrial, and calcium responses, as well as modified networks associated with cardiovascular remodelling, contractility, and structural/cytoskeletal organization. Cmpd17b attenuated hypertension-induced dysregulation of multiple proteins in mice, and of these, ∼110 proteins were identified as similarly dysregulated in humans suffering from adverse aortic remodelling and cardiac hypertrophy.

CONCLUSION

We have demonstrated, for the first time, that the FPR agonist Cmpd17b powerfully limits hypertension-induced end-organ damage, consistent with proteome networks, supporting development of pro-resolution FPR-based therapeutics for treatment of systemic hypertension complications.

Cardiolipin oxidized by ROS from complex II acts as a target of gasdermin D to drive mitochondrial pore and heart dysfunction in endotoxemia

Cardiac dysfunction, an early complication of endotoxemia, is the major cause of death in intensive care units. No specific therapy is available at present for this cardiac dysfunction. Here, we show that the N-terminal gasdermin D (GSDMD-N) initiates mitochondrial apoptotic pore and cardiac dysfunction by directly interacting with cardiolipin oxidized by complex II-generated reactive oxygen species (ROS) during endotoxemia. Caspase-4/11 initiates GSDMD-N pores that are subsequently amplified by the upregulation and activation of NLRP3 inflammation through further generation of ROS. GSDMD-N pores form prior to BAX and VDAC1 apoptotic pores and further incorporate into BAX and VDAC1 oligomers within mitochondria membranes to exacerbate the apoptotic process. Our findings identify oxidized cardiolipin as the definitive target of GSDMD-N in mitochondria of cardiomyocytes during endotoxin-induced myocardial dysfunction (EIMD), and modulation of cardiolipin oxidation could be a therapeutic target early in the disease process to prevent EIMD.

Obstacles to implement machine perfusion technology in routine clinical practice of transplantation: Why are we not there yet?

Machine perfusion of solid human organs is an old technique, and the basic principles were presented as early as 1855 by Claude Barnard. More than 50 years ago, the first perfusion system was used in clinical kidney transplantation. Despite the well-known benefits of dynamic organ preservation and significant medical and technical development in the last decades, perfusion devices are still not in routine use. This article describes the various challenges to implement this technology in practice, critically analyzing the role of all involved stakeholders, including clinicians, hospitals, regulatory, and industry, on the background of regional differences worldwide. The clinical need for this technology is discussed first, followed by the current status of research and the impact of costs and regulations. Considering the need for strong collaborations between clinical users, regulatory bodies, and industry, integrated road maps and pathways required to achieve a wider implementation are presented. The role of research development, clear regulatory pathways, and the need for more flexible reimbursement schemes is discussed together with potential solutions to address the most relevant hurdles. This article paints an overall picture of the current liver perfusion landscape and highlights the role of clinical, regulatory, and financial stakeholders worldwide.

Study on the acute toxicity of trichlorfon and its breakdown product dichlorvos to goldfish (Carassius auratus) based on 1H NMR metabonomics

Trichlorfon, one of the most widely used organophosphate insecticides, is commonly employed in aquaculture and agriculture to combat parasitic infestations. However, its inherent instability leads to rapid decomposition into dichlorvos (DDVP), increasing its toxicity by eightfold. Therefore, the environmental effects of trichlorfon in real-world scenarios involve the combined effects of trichlorfon and its degradation product, DDVP. In this study, we systematically investigated the degradation of trichlorfon in tap water over time using HPLC and LC-MS/MS analysis. Subsequently, an experiment was conducted to assess the acute toxicity of trichlorfon and DDVP on goldfish (Carassius auratus), employing a 1H NMR-based metabolic approach in conjunction with serum biochemistry, histopathological inspection, and correlation network analysis. Exposure to trichlorfon and its degradation product DDVP leads to increased lipid peroxidation, reduced antioxidant activity, and severe hepatotoxicity and nephrotoxicity in goldfish. Based on the observed pathological changes and metabolite alterations, short-term exposure to trichlorfon significantly affected the liver and kidney functions of goldfish, while exerting minimal influence on the brain, potentially due to the presence of the blood-brain barrier. The changes in the metabolic profile indicated that trichlorfon and DDVP influenced several pathways, including oxidative stress, protein synthesis, energy metabolism, and nucleic acid metabolism. This study demonstrated the applicability and potential of 1H NMR-based metabonomics in pesticide environmental risk assessment, providing a feasible method for the comprehensive study of pesticide toxicity in water environments.

Succinate metabolism: a promising therapeutic target for inflammation, ischemia/reperfusion injury and cancer

Succinate serves as an essential circulating metabolite within the tricarboxylic acid (TCA) cycle and functions as a substrate for succinate dehydrogenase (SDH), thereby contributing to energy production in fundamental mitochondrial metabolic pathways. Aberrant changes in succinate concentrations have been associated with pathological states, including chronic inflammation, ischemia/reperfusion (IR) injury, and cancer, resulting from the exaggerated response of specific immune cells, thereby rendering it a central area of investigation. Recent studies have elucidated the pivotal involvement of succinate and SDH in immunity beyond metabolic processes, particularly in the context of cancer. Current scientific endeavors are concentrated on comprehending the functional repercussions of metabolic modifications, specifically pertaining to succinate and SDH, in immune cells operating within a hypoxic milieu. The efficacy of targeting succinate and SDH alterations to manipulate immune cell functions in hypoxia-related diseases have been demonstrated. Consequently, a comprehensive understanding of succinate's role in metabolism and the regulation of SDH is crucial for effectively targeting succinate and SDH as therapeutic interventions to influence the progression of specific diseases. This review provides a succinct overview of the latest advancements in comprehending the emerging functions of succinate and SDH in metabolic processes. Furthermore, it explores the involvement of succinate, an intermediary of the TCA cycle, in chronic inflammation, IR injury, and cancer, with particular emphasis on the mechanisms underlying succinate accumulation. This review critically assesses the potential of modulating succinate accumulation and metabolism within the hypoxic milieu as a means to combat various diseases. It explores potential targets for therapeutic interventions by focusing on succinate metabolism and the regulation of SDH in hypoxia-related disorders.

Glucose fluctuation promotes mitochondrial dysfunctions in the cardiomyocyte cell line HL-1

AIMS

Glycemic variability has been suggested as a risk factor for diabetes complications but the precise deleterious mechanisms remain poorly understood. Since mitochondria are the main source of energy in heart and cardiovascular diseases remain the first cause of death in patients with diabetes, the aim of the study was to evaluate the impact of glucose swings on mitochondrial functions in the cardiomyocyte cell line HL-1.

METHODS

HL-1 cells were exposed to low (LG, 2.8 mmol/l), normal (NG, 5.5 mmol/l), high (HG, 25 mmol/l) or intermittent high glucose (IHG, swing between low and high) every 2h during 12h (short-time treatment) or every 12h during 72h (long-time treatment). Anaerobic catabolism of glucose was evaluated by measuring glucose consumption and lactate production, oxidative phosphorylation was evaluated by polarography and ATP measurement, mitochondrial superoxide anions and the mitochondrial membrane potential (MMP) were analysed using fluorescent probes, and the protein oxidation was measured by oxyblot.

RESULTS

IHG and HG increased glucose consumption and lactate production compared to LG and NG but without any difference between short- and long-time treatments. After 72h and unlike to LG, NG and HG, we didn't observe any increase of the mitochondrial respiration in the presence of succinate upon IHG treatment. IHG, and to a lesser extent HG, promoted a time-dependent decrease of the mitochondrial membrane potential compared to LG and NG treatments. HG and IHG also increased superoxide anion production compared to LG and NG both at 12 and 72h but with a higher increase for IHG at 72h. At last, both HG and IHG stimulated protein oxidation at 72h compared to LG and NG treatments.

CONCLUSIONS

Our results demonstrated that exposure of HL-1 cells to glucose swings promoted time-dependent mitochondrial dysfunctions suggesting a deleterious effect of such condition in patients with diabetes that could contribute to diabetic cardiomyopathy.

Targeting mitochondrial energetics reverses panobinostat- and marizomib-induced resistance in pediatric and adult high-grade gliomas

In previous studies, we demonstrated that panobinostat, a histone deacetylase inhibitor, and bortezomib, a proteasomal inhibitor, displayed synergistic therapeutic activity against pediatric and adult high-grade gliomas. Despite the remarkable initial response to this combination, resistance emerged. Here, in this study, we aimed to investigate the molecular mechanisms underlying the anticancer effects of panobinostat and marizomib, a brain-penetrant proteasomal inhibitor, and the potential for exploitable vulnerabilities associated with acquired resistance. RNA sequencing followed by gene set enrichment analysis (GSEA) was employed to compare the molecular signatures enriched in resistant compared with drug-naïve cells. The levels of adenosine 5'-triphosphate (ATP), nicotinamide adenine dinucleotide (NAD)+ content, hexokinase activity, and tricarboxylic acid (TCA) cycle metabolites required for oxidative phosphorylation to meet their bioenergetic needs were analyzed. Here, we report that panobinostat and marizomib significantly depleted ATP and NAD+ content, increased mitochondrial permeability and reactive oxygen species generation, and promoted apoptosis in pediatric and adult glioma cell lines at initial treatment. However, resistant cells exhibited increased levels of TCA cycle metabolites, which required for oxidative phosphorylation to meet their bioenergetic needs. Therefore, we targeted glycolysis and the electron transport chain (ETC) with small molecule inhibitors, which displayed substantial efficacy, suggesting that resistant cell survival is dependent on glycolytic and ETC complexes. To verify these observations in vivo, lonidamine, an inhibitor of glycolysis and mitochondrial function, was chosen. We produced two diffuse intrinsic pontine glioma (DIPG) models, and lonidamine treatment significantly increased median survival in both models, with particularly dramatic effects in panobinostat- and marizomib-resistant cells. These data provide new insights into mechanisms of treatment resistance in gliomas.

Myocardial capacity of mitochondrial oxidative phosphorylation in response to prolonged electromagnetic stress

Introduction

Mitochondria are central energy generators for the heart, producing adenosine triphosphate (ATP) through the oxidative phosphorylation (OXPHOS) system. However, mitochondria also guide critical cell decisions and responses to the environmental stressors.

Methods

This study evaluated whether prolonged electromagnetic stress affects the mitochondrial OXPHOS system and structural modifications of the myocardium. To induce prolonged electromagnetic stress, mice were exposed to 915 MHz electromagnetic fields (EMFs) for 28 days.

Results

Analysis of mitochondrial OXPHOS capacity in EMF-exposed mice pointed to a significant increase in cardiac protein expression of the Complex I, II, III and IV subunits, while expression level of α-subunit of ATP synthase (Complex V) was stable among groups. Furthermore, measurement of respiratory function in isolated cardiac mitochondria using the Seahorse XF24 analyzer demonstrated that prolonged electromagnetic stress modifies the mitochondrial respiratory capacity. However, the plasma level of malondialdehyde, an indicator of oxidative stress, and myocardial expression of mitochondria-resident antioxidant enzyme superoxide dismutase 2 remained unchanged in EMF-exposed mice as compared to controls. At the structural and functional state of left ventricles, no abnormalities were identified in the heart of mice subjected to electromagnetic stress.

Discussion

Taken together, these data suggest that prolonged exposure to EMFs could affect mitochondrial oxidative metabolism through modulating cardiac OXPHOS system.

Machine perfusion of the liver and bioengineering

With the increasing number of accepted candidates on waiting lists worldwide, there is an urgent need to expand the number and the quality of donor livers. Dynamic preservation approaches have demonstrated various benefits, including improving liver function and graft survival, and reducing liver injury and post-transplant complications. Consequently, organ perfusion techniques are being used in clinical practice in many countries. Despite this success, a proportion of livers do not meet current viability tests required for transplantation, even with the use of modern perfusion techniques. Therefore, devices are needed to further optimise machine liver perfusion - one promising option is to prolong machine liver perfusion for several days, with ex situ treatment of perfused livers. For example, stem cells, senolytics, or molecules targeting mitochondria or downstream signalling can be administered during long-term liver perfusion to modulate repair mechanisms and regeneration. Besides, today's perfusion equipment is also designed to enable the use of various liver bioengineering techniques, to develop scaffolds or for their re-cellularisation. Cells or entire livers can also undergo gene modulation to modify animal livers for xenotransplantation, to directly treat injured organs or to repopulate such scaffolds with "repaired" autologous cells. This review first discusses current strategies to improve the quality of donor livers, and secondly reports on bioengineering techniques to design optimised organs during machine perfusion. Current practice, as well as the benefits and challenges associated with these different perfusion strategies are discussed.

Modulators of mitochondrial ATP-sensitive potassium channel affect cytotoxicity of heavy metals: Action on isolated rat liver mitochondria and AS-30D ascites hepatoma cells

Heavy metals are ubiquitous environmental pollutants that are extremely dangerous for public health, but the molecular mechanisms of their cytotoxic action are still not fully understood. In the present work, the possible contribution of the mitochondrial ATP-sensitive potassium channel (mK(ATP)), which is usually considered protective for the cell, to hepatotoxicity caused by heavy metals was investigated using polarography and swelling techniques as well as flow cytometry. Using isolated liver mitochondria from adult male Wistar rats and various potassium media containing or not containing penetrating anions (KNO₃, KSCN, KAcet, KCl), we studied the effect of mK(ATP) modulators, namely its blockers (5-hydroxydecanoate, glibenclamide, ATP, ADP) and activators (diazoxide, malonate), on respiration and/or membrane permeability in the presence of hepatotoxins such as Cd²⁺, Hg²⁺, and Cu²⁺. It has been shown for the first time that, contrary to Hg²⁺ and depending on media used, the mK(ATP) modulators affect Cd²⁺- and/or Cu²⁺-induced alterations in mitochondrial swelling and respiration rates, although differently, nevertheless, in the ways compatible with mK(ATP) participation in both these cases. On rat AS-30D ascites hepatoma cells, it was found that, unlike Cd²⁺, an increase in the production of reactive oxygen species was observed with the simultaneous use of Cu²⁺ and diazoxide; in addition, there was no protective effect of diazoxide against cell death, which also occurred in the presence of Cu²⁺. In conclusion, the relationships (functional, structural and/or regulatory) between mK(ATP), components of the mitochondrial electron transport chain (CI, CII-CIII and/or ATP synthase, CV) and mitochondrial permeability transition pores were discussed, as well as the role of these molecular structures in the mechanisms of the cytotoxic action of heavy metals.

Thermal modulation of mitochondrial function is affected by environmental nickel in rainbow trout (Oncorhynchus mykiss)

In this study, we investigated the combined effects of temperature and nickel (Ni) contamination on liver mitochondria electron transport system (ETS) enzymes, citrate synthase (CS), phospholipid fatty acid composition and lipid peroxidation in rainbow trout (Oncorhynchus mykiss). Juvenile trout were acclimated for two weeks to two different temperatures (5˚C and 15˚C) and exposed to nickel (Ni; 520 μg/L) for three weeks. Using ratios of ETS enzymes and CS activities, our data suggest that Ni and an elevated temperature acted synergistically to induce a higher capacity for reduction status of the ETS. The response of phospholipid fatty acid profiles to thermal variation was also altered under nickel exposure. In control conditions, the proportion of saturated fatty acids (SFA) was higher at 15˚C than at 5˚C, while the opposite was observed for monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA). However, in nickel contaminated fish, the proportion of SFA was higher at 5˚C than at 15˚C, while PUFA and MUFA followed the opposite direction. A higher PUFA ratio is associated with higher vulnerability to lipid peroxidation. Thiobarbituric Acid Reactive Substances (TBARS) content was higher when the PUFA were in higher proportions, except for Ni-exposed, warm-acclimated fish, in which we reported the lowest level of TBARS but the highest proportion of PUFA. We suspect that the interaction of nickel and temperature on lipid peroxidation is due to their synergistic effects on aerobic energy metabolism, as supported by the decrease in the activity of complex IV of the ETS enzyme activity in those fish, or on antioxidant enzymes and pathways. Overall, our study demonstrates that Ni exposure in heat-challenged fish can lead to the remodelling of the mitochondrial phenotype and potentially stimulate alternative antioxidant mechanisms.

DNA-PKcs and ATM modulate mitochondrial ADP-ATP exchange as an oxidative stress checkpoint mechanism

DNA-PKcs is a key regulator of DNA double-strand break repair. Apart from its canonical role in the DNA damage response, DNA-PKcs is involved in the cellular response to oxidative stress (OS), but its exact role remains unclear. Here, we report that DNA-PKcs-deficient human cells display depolarized mitochondria membrane potential (MMP) and reoriented metabolism, supporting a role for DNA-PKcs in oxidative phosphorylation (OXPHOS). DNA-PKcs directly interacts with mitochondria proteins ANT2 and VDAC2, and formation of the DNA-PKcs/ANT2/VDAC2 (DAV) complex supports optimal exchange of ADP and ATP across mitochondrial membranes to energize the cell via OXPHOS and to maintain MMP. Moreover, we demonstrate that the DAV complex temporarily dissociates in response to oxidative stress to attenuate ADP-ATP exchange, a rate-limiting step for OXPHOS. Finally, we found that dissociation of the DAV complex is mediated by phosphorylation of DNA-PKcs at its Thr2609 cluster by ATM kinase. Based on these findings, we propose that the coordination between the DAV complex and ATM serves as a novel oxidative stress checkpoint to decrease ROS production from mitochondrial OXPHOS and to hasten cellular recovery from OS.

Active Nrf2 signaling flexibly regulates HO-1 and NQO-1 in hypoxic Gansu Zokor (Eospalax cansus)

Gansu zokor (Eospalax cansus) is a typical subterranean rodent species with resistance to ambient hypoxia. The nuclear factor erythroid 2-related factor 2 (Nrf2) signaling plays a key role in regulating redox homeostasis. However, little is known about the regulation of Nrf2 signaling in Gansu zokor. We exposed Gansu zokors and SD rats to chronic hypoxia (44 h at 10.5% O₂) or acute hypoxia (6 h at 6.5% O₂) andmeasured the activities of heme oxygenase-1 (HO-1) and NAD(P)H quinone oxidoreductase-1 (NQO-1)，gene expression of HO-1, NQO-1, Nrf2, Kelch-like ECH-associated protein-1 (KEAP1), and β-transducin repeat-containing protein (β-TRCP) in the brain and liver. We found that Gansu zokor increased the NQO-1 protein content and activity, HO-1 protein content in the brain, and increased HO-1 activity and mRNA level, NQO-1 activity and protein content in the liver by up regulating Nrf2 gene expression under chronic hypoxia. Although acute hypoxia enhanced the expression of Nrf2 gene, only the level of HO-1 mRNA in the liver increased. Besides, the HO-1 and NQO-1 genes in the brain, HO-1 genes and NQO-1 mRNA in the Gansu zokor liver were significantly higher than those in SD rats under normoxia. Negative regulators of Nrf2 signaling were tissue specific: KEAP1 protein decreased in the brain, and β-TRCP decreased in the liver. The Nrf2 signaling and expression of downstream antioxidant enzymes were different under different oxygen concentrations, reflecting the flexible characteristics of Gansu zokor to deal with the hypoxic environment.

Hypoxia-induced ROS aggravate tumor progression through HIF-1α-SERPINE1 signaling in glioblastoma

Hypoxia, as an important hallmark of the tumor microenvironment, is a major cause of oxidative stress and plays a central role in various malignant tumors, including glioblastoma. Elevated reactive oxygen species (ROS) in a hypoxic microenvironment promote glioblastoma progression; however, the underlying mechanism has not been clarified. Herein, we found that hypoxia promoted ROS production, and the proliferation, migration, and invasion of glioblastoma cells, while this promotion was restrained by ROS scavengers N-acetyl-L-cysteine (NAC) and diphenyleneiodonium chloride (DPI). Hypoxia-induced ROS activated hypoxia-inducible factor-1α (HIF-1α) signaling, which enhanced cell migration and invasion by epithelial-mesenchymal transition (EMT). Furthermore, the induction of serine protease inhibitor family E member 1 (SERPINE1) was ROS-dependent under hypoxia, and HIF-1α mediated SERPINE1 increase induced by ROS via binding to the SERPINE1 promoter region, thereby facilitating glioblastoma migration and invasion. Taken together, our data revealed that hypoxia-induced ROS reinforce the hypoxic adaptation of glioblastoma by driving the HIF-1α-SERPINE1 signaling pathway, and that targeting ROS may be a promising therapeutic strategy for glioblastoma.

Mitochondrial ROS induced by ML385, an Nrf2 inhibitor aggravates the ferroptosis induced by RSL3 in human lung epithelial BEAS-2B cells

Ferroptosis is a new type of cell death marked by iron and lipid ROS accumulation. GPX4 is one of the glutathione peroxidases known to regulate ferroptosis tightly. On the other hand, Nrf2 also plays a vital role in ferroptosis as it targets genes related to oxidant defense. Herein, we employed beas-2 human epithelial cells treated with a low concentration of RSL3 to induce ferroptosis. To study the protective role of Nrf2, we used ML385 as its specific inhibitor. A combination of ML385 and a low concentration of RSL3 synergistically induced more toxicity to RSL3. Furthermore, we found that mitochondrial ROS is elevated in ML385 and RSL3 combination group. In addition, Mito TEMPOL application successfully prevents the upregulation of mitochondrial ROS, lipid ROS, reduces the toxicity of RSL3, restores the antioxidant capacity of the cells, and mitochondrial functions reflected by mitochondrial membrane potential and mitochondrial oxidative phosphorylation system (OXPHOS) expression. Altogether, our study demonstrated that Nrf2 inhibition by ML385 induces more toxicity when combined with RSL3 through the elevation of mitochondrial ROS and disruption of mitochondrial function.

Polarization and β-Glucan Reprogram Immunomodulatory Metabolism in Human Macrophages and Ex Vivo in Human Lung Cancer Tissues

Immunomodulatory (IM) metabolic reprogramming in macrophages (Mϕs) is fundamental to immune function. However, limited information is available for human Mϕs, particularly in response plasticity, which is critical to understanding the variable efficacy of immunotherapies in cancer patients. We carried out an in-depth analysis by combining multiplex stable isotope-resolved metabolomics with reversed phase protein array to map the dynamic changes of the IM metabolic network and key protein regulators in four human donors' Mϕs in response to differential polarization and M1 repolarizer β-glucan (whole glucan particles [WGPs]). These responses were compared with those of WGP-treated ex vivo organotypic tissue cultures (OTCs) of human non-small cell lung cancer. We found consistently enhanced tryptophan catabolism with blocked NAD+ and UTP synthesis in M1-type Mϕs (M1-Mϕs), which was associated with immune activation evidenced by increased release of IL-1β/CXCL10/IFN-γ/TNF-α and reduced phagocytosis. In M2a-Mϕs, WGP treatment of M2a-Mϕs robustly increased glucose utilization via the glycolysis/oxidative branch of the pentose phosphate pathway while enhancing UDP-N-acetyl-glucosamine turnover and glutamine-fueled gluconeogenesis, which was accompanied by the release of proinflammatory IL-1β/TNF-α to above M1-Mϕ's levels, anti-inflammatory IL-10 to above M2a-Mϕ's levels, and attenuated phagocytosis. These IM metabolic responses could underlie the opposing effects of WGP, i.e., reverting M2- to M1-type immune functions but also boosting anti-inflammation. Variable reprogrammed Krebs cycle and glutamine-fueled synthesis of UTP in WGP-treated OTCs of human non-small cell lung cancer were observed, reflecting variable M1 repolarization of tumor-associated Mϕs. This was supported by correlation with IL-1β/TNF-α release and compromised tumor status, making patient-derived OTCs unique models for studying variable immunotherapeutic efficacy in cancer patients.

Melatonin drives apoptosis in head and neck cancer by increasing mitochondrial ROS generated via reverse electron transport

The oncostatic effects of melatonin correlate with increased reactive oxygen species (ROS) levels, but how melatonin induces this ROS generation is unknown. In the present study, we aimed to elucidate the two seemingly opposing actions of melatonin regarding its relationship with free radicals. We analyzed the effects of melatonin on head and neck squamous cell carcinoma cell lines (Cal-27 and SCC-9), which were treated with 0.5 or 1 mM melatonin. We further examined the potential effects of melatonin to induce ROS and apoptosis in Cal-27 xenograft mice. Here we report that melatonin mediates apoptosis in head and neck cancer by driving mitochondrial reverse electron transport (RET) to induce ROS production. Melatonin-induced changes in tumoral metabolism led to increased mitochondrial activity, which, in turn, induced ROS-dependent mitochondrial uncoupling. Interestingly, mitochondrial complex inhibitors, including rotenone, abolished the ROS elevation indicating that melatonin increased ROS generation via RET. Melatonin also increased membrane potential and CoQ₁₀ H₂ /CoQ₁₀ ratio to elevate mitochondrial ROS production, which are essential conditions for RET. We found that genetic manipulation of cancer cells with alternative oxidase, which transfers electrons from QH₂ to oxygen, inhibited melatonin-induced ROS generation, and apoptosis. RET restored the melatonin-induced oncostatic effect, highlighting the importance of RET as the site of ROS production. These results illustrate that RET and ROS production are crucial factors in melatonin's effects in cancer cells and establish the dual effect of melatonin in protecting normal cells and inducing apoptosis in cancer cells.

A Hypothesis Concerning the role of PPAR family on Cardiac Energetics in Adriamycin-Induced Cardiomyopathy

Adriamycin is an effective anti-neoplastic drug against a variety of cancer types. However, the drug causes adverse side-effects in a number of organ systems. Cardiomyopathy is one of the life-threatening side-effects of Adriamycin. In the current work, we have derived the possible involvement of PPAR family members in the development of Adriamycin-induced cardiomyopathy. Dysregulation of PPAR family by Adriamycin causes impairment in the transport and β-oxidation of fatty acids, the key substrate for ATP synthesis in heart. Evidences suggest that dysregulation of PPAR family results in alters the recruitment of glucose transporters. Furthermore, Hemeoxygenase-1 is a crucial enzyme regulating the iron homeostasis in the heart whose expression is regulated by PPAR family. Inverse relationship exists between the expression levels of PPARγ and hemeoxygenase-1. Adriamycin upregulates the expression of hemeoxygenase-1 which in turn disrupts the iron homeostasis in cardiomyocytes. Our molecular docking results show that Adriamycin has high affinity for iron binding sites of hemeoxygenase-1, thereby hindering formation of iron-sulfur complex. Lack of iron-sulfur complex impairs the electron transport chain. In addition, succinate dehydrogenase subunit A is downregulated by Adriamycin. The lack of this subunit uncouples Krebs cycle from ETC. Further lack of this subunit causes increases the concentration of succinate which further alters the mitochondrial membrane potential. Overall, in the present work we hypothesize that alteration in the expression of PPAR family members is one of the major causes of metabolic chaos and oxidative stress caused by Adriamycin during the development of cardiomyopathy.

Hyperoxia Reprogrammes Microvascular Endothelial Cell Response to Hypoxia in an Organ-Specific Manner

Organ function relies on microvascular networks to maintain homeostatic equilibrium, which varies widely in different organs and during different physiological challenges. The endothelium role in this critical process can only be evaluated in physiologically relevant contexts. Comparing the responses to oxygen flux in primary murine microvascular EC (MVEC) obtained from brain and lung tissue reveals that supra-physiological oxygen tensions can compromise MVEC viability. Brain MVEC lose mitochondrial activity and undergo significant alterations in electron transport chain (ETC) composition when cultured under standard, non-physiological atmospheric oxygen levels. While glycolytic capacity of both lung and brain MVEC are unchanged by environmental oxygen, the ability to trigger a metabolic shift when oxygen levels drop is greatly compromised following exposure to hyperoxia. This is particularly striking in MVEC from the brain. This work demonstrates that the unique metabolism and function of organ-specific MVEC (1) can be reprogrammed by external oxygen, (2) that this reprogramming can compromise MVEC survival and, importantly, (3) that ex vivo modelling of endothelial function is significantly affected by culture conditions. It further demonstrates that physiological, metabolic and functional studies performed in non-physiological environments do not represent cell function in situ, and this has serious implications in the interpretation of cell-based pre-clinical models.

Changes in Metabolism and Mitochondrial Bioenergetics during Polyethylene-Induced Osteoclastogenesis

Changes in mitochondrial bioenergetics are believed to take place during osteoclastogenesis. This study aims to assess changes in mitochondrial bioenergetics and reactive oxygen species (ROS) levels during polyethylene (PE)-induced osteoclastogenesis in vitro. For this purpose, RAW264.7 cells were cultured for nine days and allowed to differentiate into osteoclasts in the presence of PE and RANKL. The total TRAP-positive cells, resorption activity, expression of osteoclast marker genes, ROS level, mitochondrial bioenergetics, glycolysis, and substrate utilization were measured. The effect of tocotrienols-rich fraction (TRF) treatment (50 ng/mL) on those parameters during PE-induced osteoclastogenesis was also studied. During PE-induced osteoclastogenesis, as depicted by an increase in TRAP-positive cells and gene expression of osteoclast-related markers, higher proton leak, higher extracellular acidification rate (ECAR), as well as higher levels of ROS and NADPH oxidases (NOXs) were observed in the differentiated cells. The oxidation level of some substrates in the differentiated group was higher than in other groups. TRF treatment significantly reduced the number of TRAP-positive osteoclasts, bone resorption activity, and ROS levels, as well as modulating the gene expression of antioxidant-related genes and mitochondrial function. In conclusion, changes in mitochondrial bioenergetics and substrate utilization were observed during PE-induced osteoclastogenesis, while TRF treatment modulated these changes.

Leishmania parasites exchange drug-resistance genes through extracellular vesicles

Leishmania are eukaryotic parasites that have retained the ability to produce extracellular vesicles (EVs) through evolution. To date, it has been unclear if different DNA entities could be associated with Leishmania EVs and whether these could constitute a mechanism of horizontal gene transfer (HGT). Herein, we investigate the DNA content of EVs derived from drug-resistant parasites, as well as the EVs' potential to act as shuttles for DNA transfer. Next-generation sequencing and PCR assays confirm the enrichment of amplicons carrying drug-resistance genes associated with EVs. Transfer assays of drug-resistant EVs highlight a significant impact on the phenotype of recipient parasites induced by the expression of the transferred DNA. Recipient parasites display an enhanced growth and better control of oxidative stress. We provide evidence that eukaryotic EVs function as efficient mediators in HGT, thereby facilitating the transmission of drug-resistance genes and increasing the fitness of cells when encountering stressful environments.

Impact of Machine Perfusion on the Immune Response After Liver Transplantation – A Primary Treatment or Just a Delivery Tool

The frequent use of marginal livers forces transplant centres to explore novel technologies to improve organ quality and outcomes after implantation. Organ perfusion techniques are therefore frequently discussed with an ever-increasing number of experimental and clinical studies. Two main approaches, hypothermic and normothermic perfusion, are the leading strategies to be introduced in clinical practice in many western countries today. Despite this success, the number of studies, which provide robust data on the underlying mechanisms of protection conveyed through this technology remains scarce, particularly in context of different stages of ischemia-reperfusion-injury (IRI). Prior to a successful clinical implementation of machine perfusion, the concept of IRI and potential key molecules, which should be addressed to reduce IRI-associated inflammation, requires a better exploration. During ischemia, Krebs cycle metabolites, including succinate play a crucial role with their direct impact on the production of reactive oxygen species (ROS) at mitochondrial complex I upon reperfusion. Such features are even more pronounced under normothermic conditions and lead to even higher levels of downstream inflammation. The direct consequence appears with an activation of the innate immune system. The number of articles, which focus on the impact of machine perfusion with and without the use of specific perfusate additives to modulate the inflammatory cascade after transplantation is very small. This review describes first, the subcellular processes found in mitochondria, which instigate the IRI cascade together with proinflammatory downstream effects and their link to the innate immune system. Next, the impact of currently established machine perfusion strategies is described with a focus on protective mechanisms known for the different perfusion approaches. Finally, the role of such dynamic preservation techniques to deliver specific agents, which appear currently of interest to modulate this posttransplant inflammation, is discussed together with future aspects in this field.

Tumor necrosis factor induces pathogenic mitochondrial ROS in tuberculosis through reverse electron transport

Tumor necrosis factor (TNF) is a critical host resistance factor against tuberculosis. However, excess TNF produces susceptibility by increasing mitochondrial reactive oxygen species (mROS), which initiate a signaling cascade to cause pathogenic necrosis of mycobacterium-infected macrophages. In zebrafish, we identified the mechanism of TNF-induced mROS in tuberculosis. Excess TNF in mycobacterium-infected macrophages elevates mROS production by reverse electron transport (RET) through complex I. TNF-activated cellular glutamine uptake leads to an increased concentration of succinate, a Krebs cycle intermediate. Oxidation of this elevated succinate by complex II drives RET, thereby generating the mROS superoxide at complex I. The complex I inhibitor metformin, a widely used antidiabetic drug, prevents TNF-induced mROS and necrosis of Mycobacterium tuberculosis-infected zebrafish and human macrophages; metformin may therefore be useful in tuberculosis therapy.

Luseogliflozin preserves the pancreatic beta-cell mass and function in db/db mice by improving mitochondrial function

We aimed to determine the mechanism by which the sodium glucose co-transporter 2 inhibitor, luseogliflozin, preserves pancreatic beta-cell mass and function in db/db mice. Six-week-old db/db mice were fed to standard chow or standard chow containing 0.01% luseogliflozin. After 4 weeks, DNA microarray analysis, real-time PCR analysis, and measurement of mitochondrial respiratory capacity and reactive oxygen species (ROS) generation were performed using isolated islets. Immunohistochemistry and electron microscopic analysis were performed using pancreatic tissues. Metabolites extracted from the islets were measured by capillary electrophoresis mass spectrometry. The expression of genes involved in the tricarboxylic acid (TCA) cycle and electron transport chain was upregulated by luseogliflozin. Luseogliflozin improved the mitochondrial complex II-linked oxidative phosphorylation capacity and reduced ROS generation. Mitochondrial morphology was normally maintained by luseogliflozin. Luseogliflozin increased NK6 homeobox 1 (NKX6.1) expression and TCA cycle metabolites. Relief of glucotoxicity by luseogliflozin may involve lower mitochondrial ROS generation and an improvement in complex II-linked mitochondrial respiration. Reducing ROS generation through preventing complex II damage likely increases NKX6.1 expression and ameliorate glucose metabolism in the TCA cycle, contributing to the protection of pancreatic beta-cells. Protection of complex II in pancreatic beta-cells represents a novel therapeutic target for type 2 diabetes.

Hypothesis: Why Different Types of SDH Gene Variants Cause Divergent Tumor Phenotypes

Despite two decades of paraganglioma-pheochromocytoma research, the fundamental question of how the different succinate dehydrogenase (SDH)-related tumor phenotypes are initiated has remained unanswered. Here, we discuss two possible scenarios by which missense (hypomorphic alleles) or truncating (null alleles) SDH gene variants determine clinical phenotype. Dysfunctional SDH is a major source of reactive oxygen species (ROS) but ROS are inhibited by rising succinate levels. In scenario 1, we propose that SDH missense variants disrupt electron flow, causing elevated ROS levels that are toxic in sympathetic PPGL precursor cells but well controlled in oxygen-sensing parasympathetic paraganglion cells. We also suggest that SDHAF2 variants, solely associated with HNPGL, may cause the reversal of succinate dehydrogenase to fumarate reductase, producing very high ROS levels. In scenario 2, we propose a modified succinate threshold model of tumor initiation. Truncating SDH variants cause high succinate accumulation and likely initiate tumorigenesis via disruption of 2-oxoglutarate-dependent enzymes in both PPGL and HNPGL precursor tissues. We propose that missense variants (including SDHAF2) cause lower succinate accumulation and thus initiate tumorigenesis only in very metabolically active tissues such as parasympathetic paraganglia, which naturally show very high levels of succinate.

Differential hepatic mitochondrial function and gluconeogenic gene expression in 2 Holstein strains in a pasture-based system

The objective of this study was to assess hepatic ATP synthesis in Holstein cows of North American and New Zealand origins and the gluconeogenic pathway, one of the pathways with the highest ATP demands in the ruminant liver. Autumn-calving Holstein cows of New Zealand and North American origins were managed in a pasture-based system with supplementation of concentrate that represented approximately 33% of the predicted dry matter intake during 2017, 2018, and 2019, and hepatic biopsies were taken during mid-lactation at 174 ± 23 days in milk. Cows of both strains produced similar levels of solids-corrected milk, and no differences in body condition score were found. Plasma glucose concentrations were higher for cows of New Zealand versus North American origin. Hepatic mitochondrial function evaluated measuring oxygen consumption rates showed that mitochondrial parameters related to ATP synthesis and maximum respiratory rate were increased for cows of New Zealand compared with North American origin. However, hepatic gene expression of pyruvate carboxylase, phosphoenolpyruvate carboxykinase, and pyruvate dehydrogenase kinase was increased in North American compared with New Zealand cows. These results altogether suggest an increased activity of the tricarboxylic cycle in New Zealand cows, leading to increased ATP synthesis, whereas North American cows pull tricarboxylic cycle intermediates toward gluconeogenesis. The fact that this occurs during mid-lactation could account for the increased persistency of North American cows, especially in a pasture-based system. In addition, we observed an augmented mitochondrial density in New Zealand cows, which could be related to feed efficiency mechanisms. In sum, our results contribute to the elucidation of hepatic molecular mechanisms in dairy cows in production systems with higher inclusion of pastures.

The physiological role of complex V in ATP synthesis: Murzyme functioning is viable whereas rotary conformation change model is untenable

Complex V or F_oF₁-ATPase is a multimeric protein found in bioenergetic membranes of cells and organelles like mitochondria/chloroplasts. The popular perception on Complex V deems it as a reversible molecular motor, working bi-directionally (breaking or making ATP) via a conformation-change based chemiosmotic rotary ATP synthesis (CRAS) mechanism, driven by proton-gradients or trans-membrane potential (TMP). In continuance of our pursuits against the CRAS model of cellular bioenergetics, herein we demonstrate the validity of the murburn model based in diffusible reactive (oxygen) species (DRS/DROS). Supported by new in silico derived data (that there are ∼12 adenosine nucleotide binding sites on the F₁ bulb and not merely 3 sites, as perceived earlier), available structural information, known experimental observations, and thermodynamic/kinetic considerations (that de-solvation of protons from hydronium ions is facile), we deduce that Complex V serves as a physiological chemostat and a murzyme (enzyme working via murburn scheme, employing DRS). That is- Complex V uses ATP (via consumption at ε or proteins of F₁ module) as a Michaelis-Menten substrate to serve as a pH-stat by inletting protons via the c-ring of F_o module. Physiologically, Complex V also functions as a murzyme by presenting ADP/Pi (or their reaction intermediates) on the αβ bulb, thereby enabling greater opportunities for DRS/proton-assisted ATP formation. Thus, the murburn paradigm succeeds the CRAS hypothesis for explaining the role of oxygen in mitochondrial physiologies of oxidative phosphorylation, thermogenesis, TMP and homeostasis.Communicated by Ramaswamy H. Sarma.

Early Effects of Extracellular Vesicles Secreted by Adipose Tissue Mesenchymal Cells in Renal Ischemia Followed by Reperfusion: Mechanisms Rely on a Decrease in Mitochondrial Anion Superoxide Production

Acute kidney injury (AKI) caused by ischemia followed by reperfusion (I/R) is characterized by intense anion superoxide (O₂^•−) production and oxidative damage. We investigated whether extracellular vesicles secreted by adipose tissue mesenchymal cells (EVs) administered during reperfusion can suppress the exacerbated mitochondrial O₂^•− formation after I/R. We used Wistar rats subjected to bilateral renal arterial clamping (30 min) followed by 24 h of reperfusion. The animals received EVs (I/R + EVs group) or saline (I/R group) in the kidney subcapsular space. The third group consisted of false-operated rats (SHAM). Mitochondria were isolated from proximal tubule cells and used immediately. Amplex Red™ was used to measure mitochondrial O₂^•− formation and MitoTracker™ Orange to evaluate inner mitochondrial membrane potential (Δψ). In vitro studies were carried out on human renal proximal tubular cells (HK-2) co-cultured or not with EVs under hypoxic conditions. Administration of EVs restored O₂^•− formation to SHAM levels in all mitochondrial functional conditions. The gene expression of catalase and superoxide dismutase-1 remained unmodified; transcription of heme oxygenase-1 (HO-1) was upregulated. The co-cultures of HK-2 cells with EVs revealed an intense decrease in apoptosis. We conclude that the mechanisms by which EVs favor long-term recovery of renal structures and functions after I/R rely on a decrease of mitochondrial O₂^•− formation with the aid of the upregulated antioxidant HO-1/Nuclear factor erythroid 2-related factor 2 system, thus opening new vistas for the treatment of AKI.

MDH2 produced OAA is a metabolic switch rewiring the fuelling of respiratory chain and TCA cycle

The mitochondrial respiratory chain (RC) enables many metabolic processes by regenerating both mitochondrial and cytosolic NAD⁺ and ATP. The oxidation by the RC of the NADH metabolically produced in the cytosol involves redox shuttles as the malate-aspartate shuttle (MAS) and is of paramount importance for cell fate. However, the specific metabolic regulations allowing mitochondrial respiration to prioritize NADH oxidation in response to high NADH/NAD⁺ redox stress have not been elucidated. The recent discovery that complex I (NADH dehydrogenase), and not complex II (Succinate dehydrogenase), can assemble with other respiratory chain complexes to form functional entities called respirasomes, led to the assumption that this supramolecular organization would favour NADH oxidation. Unexpectedly, characterization of heart and liver mitochondria demonstrates that the RC systematically favours electrons provided by the 'respirasome free' complex II. Our results demonstrate that the preferential succinate driven respiration is tightly controlled by OAA levels, and that OAA feedback inhibition of complex II rewires RC fuelling increasing NADH oxidation capacity. This new regulatory mechanism synergistically increases RC's NADH oxidative capacity and rewires MDH2 driven anaplerosis of the TCA, preventing malate production from succinate to favour oxidation of cytosolic malate. This regulatory mechanism synergistically adjusts RC and TCA fuelling in response to extramitochondrial malate produced by the MAS.

Substrate-dependent differential regulation of mitochondrial bioenergetics in the heart and kidney cortex and outer medulla

The kinetics and efficiency of mitochondrial oxidative phosphorylation (OxPhos) can depend on the choice of respiratory substrates. Furthermore, potential differences in this substrate dependency among different tissues are not well-understood. Here, we determined the effects of different substrates on the kinetics and efficiency of OxPhos in isolated mitochondria from the heart and kidney cortex and outer medulla (OM) of Sprague-Dawley rats. The substrates were pyruvate+malate, glutamate+malate, palmitoyl-carnitine+malate, alpha-ketoglutarate+malate, and succinate±rotenone at saturating concentrations. The kinetics of OxPhos were interrogated by measuring mitochondrial bioenergetics under different ADP perturbations. Results show that the kinetics and efficiency of OxPhos are highly dependent on the substrates used, and this dependency is distinctly different between heart and kidney. Heart mitochondria showed higher respiratory rates and OxPhos efficiencies for all substrates in comparison to kidney mitochondria. Cortex mitochondria respiratory rates were higher than OM mitochondria, but OM mitochondria OxPhos efficiencies were higher than cortex mitochondria. State 3 respiration was low in heart mitochondria with succinate but increased significantly in the presence of rotenone, unlike kidney mitochondria. Similar differences were observed in mitochondrial membrane potential. Differences in H2O2 emission in the presence of succinate±rotenone were observed in heart mitochondria and to a lesser extent in OM mitochondria, but not in cortex mitochondria. Bioenergetics and H2O2 emission data with succinate±rotenone indicate that oxaloacetate accumulation and reverse electron transfer may play a more prominent regulatory role in heart mitochondria than kidney mitochondria. These studies provide novel quantitative data demonstrating that the choice of respiratory substrates affects mitochondrial responses in a tissue-specific manner.

Differential remodelling of mitochondrial subpopulations and mitochondrial dysfunction are a feature of early stage diabetes

Mitochondrial dysfunction is a feature of type I and type II diabetes, but there is a lack of consistency between reports and links to disease development. We aimed to investigate if mitochondrial structure–function remodelling occurs in the early stages of diabetes by employing a mouse model (GENA348) of Maturity Onset Diabetes in the Young, exhibiting hyperglycemia, but not hyperinsulinemia, with mild left ventricular dysfunction. Employing 3-D electron microscopy (SBF-SEM) we determined that compared to wild-type, WT, the GENA348 subsarcolemma mitochondria (SSM) are ~ 2-fold larger, consistent with up-regulation of fusion proteins Mfn1, Mfn2 and Opa1. Further, in comparison, GENA348 mitochondria are more irregular in shape, have more tubular projections with SSM projections being longer and wider. Mitochondrial density is also increased in the GENA348 myocardium consistent with up-regulation of PGC1-α and stalled mitophagy (down-regulation of PINK1, Parkin and Miro1). GENA348 mitochondria have more irregular cristae arrangements but cristae dimensions and density are similar to WT. GENA348 Complex activity (I, II, IV, V) activity is decreased but the OCR is increased, potentially linked to a shift towards fatty acid oxidation due to impaired glycolysis. These novel data reveal that dysregulated mitochondrial morphology, dynamics and function develop in the early stages of diabetes.

Role of Bioactive Compounds in the Regulation of Mitochondrial Dysfunctions in Brain and Age-Related Neurodegenerative Diseases

Mitochondria are multifunctional organelles that participate in a wide range of metabolic processes, including energy production and biomolecule synthesis. The morphology and distribution of intracellular mitochondria change dynamically, reflecting a cell’s metabolic activity. Oxidative stress is defined as a mismatch between the body’s ability to neutralise and eliminate reactive oxygen and nitrogen species (ROS and RNS). A determination of mitochondria failure in increasing oxidative stress, as well as its implications in neurodegenerative illnesses and apoptosis, is a significant developmental process of focus in this review. The neuroprotective effects of bioactive compounds linked to neuronal regulation, as well as related neuronal development abnormalities, will be investigated. In conclusion, the study of secondary components and the use of mitochondrial features in the analysis of various neurodevelopmental diseases has enabled the development of a new class of mitochondrial-targeted pharmaceuticals capable of alleviating neurodegenerative disease states and enabling longevity and healthy ageing for the vast majority of people.

Why do cells need oxygen? Insights from mitochondrial composition and function

Mitochondrial membrane-embedded redox proteins are classically perceived as deterministic "electron transport chain" (ETC) arrays cum proton pumps; and oxygen is seen as an "immobile terminal electron acceptor." This is untenable because: (1) there are little free protons to be pumped out of the matrix; (2) proton pumping would be highly endergonic; (3) ETC-chemiosmosis-rotary ATP synthesis proposal is "irreducibly complex"/"non-evolvable" and does not fit with mitochondrial architecture or structural/distribution data of the concerned proteins/components; (4) a plethora of experimental observations do not conform to the postulates/requisites; for example, there is little evidence for viable proton-pumps/pH-gradient in mitochondria, trans-membrane potential (TMP) is non-fluctuating/non-trappable, oxygen is seen to give copious "diffusible reactive (oxygen) species" (DRS/DROS) in milieu, etc. Quite contrarily, the newly proposed murburn model's tenets agree with known principles of energetics/kinetics, and builds on established structural data and reported observations. In this purview, oxygen is needed to make DRS, the principal component of mitochondrial function. Complex V and porins respectively serve as proton-inlet and turgor-based water-exodus portals, thereby achieving organellar homeostasis. Complexes I to IV possess ADP-binding sites and their redox-centers react/interact with O₂ /DRS. At/around these complexes, DRS cross-react or activate/oxidize ADP/Pi via fast thermogenic one-electron reaction(s), condensing to form two-electron stabilized products (H₂ O₂ /H₂ O/ATP). The varied architecture and distribution of components in mitochondria validate DRS as (i) the coupling agent of oxidative reactions and phosphorylations, and (ii) the primary reason for manifestation of TMP in steady-state. Explorations along the new precepts stand to provide greater insights on mitochondrial function and pathophysiology.

Lovastatin attenuates glyoxal-induced toxicity on rat liver mitochondria

Alpha-dicarbonyls such as glyoxal (GO) trigger mitochondrial dysfunction resulting in the development of different diabetic complications. The present study investigated the effects of lovastatin against GO-induced toxicity on rat liver mitochondria. The rat liver mitochondria (0.5 mg protein/mL) were treated with various concentrations of lovastatin (1, 5, 10 µM) at 37°C for 30 min and then exposed to GO (3 mM) at 37°C for 30 min. Oxidative stress markers including MDA, reactive oxygen species (ROS), glutathione (GSH) and protein carbonylation (PC) level were measured. Mitochondrial complex II activity and mitochondrial membrane potential (MMP) were assessed for evaluating mitochondrial function. Glyoxal significantly increased the level of ROS, PC and MDA. This effect was associated with the reduction of MMP, complex II activity and GSH content. Pre-treatment with lovastatin potentially reversed GO-induced mitochondrial toxicity. These results suggest that lovastatin have a protective effect against GO-induced toxicity in isolated rat liver mitochondria.

Mitochondrial capacity and reactive oxygen species production during hypoxia and reoxygenation in the ocean quahog, Arctica islandica

Oxygen fluctuations are common in marine waters, and hypoxia-reoxygenation (H-R) stress can negatively affect mitochondrial metabolism. The long-lived ocean quahog, Arctica islandica, is known for its hypoxia tolerance associated with metabolic rate depression, yet the mechanisms that sustain mitochondrial function during oxygen fluctuations are not well understood. We used top-down metabolic control analysis (MCA) to determine aerobic capacity and control over oxygen flux in the mitochondria of quahogs exposed to short-term hypoxia (24 h <0.01% O2) and subsequent reoxygenation (1.5 h 21% O2) compared with normoxic control animals (21% O2). We demonstrated that flux capacity of the substrate oxidation and proton leak subsystems were not affected by hypoxia, while the capacity of the phosphorylation subsystem was enhanced during hypoxia associated with a depolarization of the mitochondrial membrane. Reoxygenation decreased the oxygen flux capacity of all three mitochondrial subsystems. Control over oxidative phosphorylation (OXPHOS) respiration was mostly exerted by substrate oxidation regardless of H-R stress, whereas control by the proton leak subsystem of LEAK respiration increased during hypoxia and returned to normoxic levels during reoxygenation. During hypoxia, reactive oxygen species (ROS) efflux was elevated in the LEAK state, whereas it was suppressed in the OXPHOS state. Mitochondrial ROS efflux returned to normoxic control levels during reoxygenation. Thus, mitochondria of A. islandica appear robust to hypoxia by maintaining stable substrate oxidation and upregulating phosphorylation capacity, but remain sensitive to reoxygenation. This mitochondrial phenotype might reflect adaptation of A. islandica to environments with unpredictable oxygen fluctuations and its behavioural preference for low oxygen levels.

Mitochondrial respiratory chain and Krebs cycle enzyme function in human donor livers subjected to end-ischaemic hypothermic machine perfusion

INTRODUCTION

Marginal human donor livers are highly susceptible to ischaemia reperfusion injury and mitochondrial dysfunction. Oxygenation during hypothermic machine perfusion (HMP) was proposed to protect the mitochondria but the mechanism is unclear. Additionally, the distribution and uptake of perfusate oxygen during HMP are unknown. This study aimed to examine the feasibility of mitochondrial function analysis during end-ischaemic HMP, assess potential mitochondrial viability biomarkers, and record oxygenation kinetics.

METHODS

This was a randomised pilot study using human livers retrieved for transplant but not utilised. Livers (n = 38) were randomised at stage 1 into static cold storage (n = 6), hepatic artery HMP (n = 7), and non-oxygen supplemented portal vein HMP (n = 7) and at stage 2 into oxygen supplemented and non-oxygen supplemented portal vein HMP (n = 11 and 7, respectively). Mitochondrial parameters were compared between the groups and between low- and high-risk marginal livers based on donor history, organ steatosis and preservation period. The oxygen delivery efficiency was assessed in additional 6 livers using real-time measurements of perfusate and parenchymal oxygen.

RESULTS

The change in mitochondrial respiratory chain (complex I, II, III, IV) and Krebs cycle enzyme activity (aconitase, citrate synthase) before and after 4-hour preservation was not different between groups in both study stages (p > 0.05). Low-risk livers that could have been used clinically (n = 8) had lower complex II-III activities after 4-hour perfusion, compared with high-risk livers (73 nmol/mg/min vs. 113 nmol/mg/min, p = 0.01). Parenchymal pO2 was consistently lower than perfusate pO2 (p ≤ 0.001), stabilised in 28 minutes compared to 3 minutes in perfusate (p = 0.003), and decreased faster upon oxygen cessation (75 vs. 36 minutes, p = 0.003).

CONCLUSIONS

Actively oxygenated and air-equilibrated end-ischaemic HMP did not induce oxidative damage of aconitase, and respiratory chain complexes remained intact. Mitochondria likely respond to variable perfusate oxygen levels by adapting their respiratory function during end-ischaemic HMP. Complex II-III activities should be further investigated as viability biomarkers.

Simulated Galactic Cosmic Rays Modify Mitochondrial Metabolism in Osteoclasts, Increase Osteoclastogenesis and Cause Trabecular Bone Loss in Mice

Space is a high-stress environment. One major risk factor for the astronauts when they leave the Earth's magnetic field is exposure to ionizing radiation from galactic cosmic rays (GCR). Several adverse changes occur in mammalian anatomy and physiology in space, including bone loss. In this study, we assessed the effects of simplified GCR exposure on skeletal health in vivo. Three months following exposure to 0.5 Gy total body simulated GCR, blood, bone marrow and tissue were collected from 9 months old male mice. The key findings from our cell and tissue analysis are (1) GCR induced femoral trabecular bone loss in adult mice but had no effect on spinal trabecular bone. (2) GCR increased circulating osteoclast differentiation markers and osteoclast formation but did not alter new bone formation or osteoblast differentiation. (3) Steady-state levels of mitochondrial reactive oxygen species, mitochondrial and non-mitochondrial respiration were increased without any changes in mitochondrial mass in pre-osteoclasts after GCR exposure. (4) Alterations in substrate utilization following GCR exposure in pre-osteoclasts suggested a metabolic rewiring of mitochondria. Taken together, targeting radiation-mediated mitochondrial metabolic reprogramming of osteoclasts could be speculated as a viable therapeutic strategy for space travel induced bone loss.

Protective effects of medium chain triglyceride diet in a mouse model of Dravet syndrome

OBJECTIVE

Dravet syndrome (DS) is a severe developmental and epileptic encephalopathy with early childhood onset. Patients with DS do not respond well to antiepileptic drugs and have only a few treatment options available. Here, we evaluated the effect of medium chain triglyceride (MCT) diet therapy in a mouse model of DS.

METHODS

Scn1a^R1407X/+ DS mice were given diets supplemented with MCTs with varying ratios of decanoic (C10) and octanoic (C8) acid or a control diet for 4 weeks. Video monitoring was performed to evaluate spontaneous convulsive seizure frequency. Susceptibility to hyperthermia-induced seizures was also examined. Medium chain fatty acids, and mitochondrial and antioxidant markers were assessed in brain homogenate.

RESULTS

Dietary intervention with MCTs significantly prolonged survival and reduced convulsive seizure frequency during the critical period of highest seizure occurrence in the Scn1a^R1407X/+ DS mice. Moreover, MCT diet therapy showed protective effects against hyperthermia-induced seizures. We demonstrated that coadministration of C10/C8 was effective at reducing both seizures and mortality, whereas C10 alone only reduced mortality, suggesting that the ratio of C10 to C8 in the MCT is an important factor for efficacy. When C10 and C8 are supplemented at an 80:20 ratio in the diet, C10 accumulates in the brain in high enough concentrations to enhance brain energy metabolism by both stimulating mitochondrial enrichment and increasing its antioxidant status.

SIGNIFICANCE

The results from this study indicate that MCT diet therapy may provide therapeutic benefits in DS. Future clinical studies would elucidate whether these positive effects are mirrored in human patients.

Exploring the Leukemogenic Potential of GATA-1S, the Shorter Isoform of GATA-1: Novel Insights into Mechanisms Hampering Respiratory Chain Complex II Activity and Limiting Oxidative Phosphorylation Efficiency

GATA-1 is a key regulator of hematopoiesis. A balanced ratio of its two isoforms, GATA-1_FL and GATA-1_S, contributes to normal hematopoiesis, whereas aberrant expression of GATA-1_S alters the differentiation/proliferation potential of hematopoietic precursors and represents a poor prognostic factor in myeloid leukemia. We previously reported that GATA-1_S over-expression correlates with high levels of the succinate dehydrogenase subunit C (SDHC). Alternative splicing variants of the SDHC transcript are over-expressed in several tumors and act as potent dominant negative inhibitors of SDH activity. With this in mind, we investigated the levels of SDHC variants and the oxidative mitochondrial metabolism in myeloid leukemia K562 cells over-expressing GATA-1 isoforms. Over-expression of SDHC variants accompanied by decreased SDH complex II activity and oxidative phosphorylation (OXPHOS) efficiency was found associated only with GATA-1_S. Given the tumor suppressor role of SDH and the effects of OXPHOS limitations in leukemogenesis, identification of a link between GATA-1_S and impaired complex II activity unveils novel pro-leukemic mechanisms triggered by GATA-1_S. Abnormal levels of GATA-1_S and SDHC variants were also found in an acute myeloid leukemia patient, thus supporting in vitro results. A better understanding of these mechanisms can contribute to identify novel promising therapeutic targets in myeloid leukemia.

The glutathionylation agent disulfiram augments superoxide/hydrogen peroxide production when liver mitochondria are oxidizing ubiquinone pool-linked and branched chain amino acid substrates

Our group has previously observed that protein S-glutathionylation serves as an integral feedback inhibitor for the production of superoxide (O₂^●-)/hydrogen peroxide (H₂O₂) by α-ketoglutarate dehydrogenase (KGDH), pyruvate dehydrogenase (PDH), and complex I in muscle and liver mitochondria, respectively. In the present study, we hypothesized that glutathionylation would fulfill a similar role for the O₂^●-/H₂O₂ sources sn-glycerol-3-phosphate dehydrogenase (G3PDH), proline dehydrogenase (PRODH), and branched chain keto acid dehydrogenase (BCKDH). Surprisingly, we found that inducing glutathionylation with disulfiram increased the production of O₂^●-/H₂O₂ by mitochondria oxidizing glycerol-3-phosphate (G3P), proline (Pro), or α-keto-β-methylvaleric acid (KMV). Treatment of mitochondria oxidizing G3P or Pro with rotenone or myxothiazol increased the rate of ROS production after incubating in 1000 nM disulfiram. Incubating mitochondria treated with disulfiram in both rotenone and myxothiazol prevented this increase in O₂^●-/H₂O₂ production. In addition, when adminstered together, ROS production decreased below control levels. Disulfiram-treated mitochondria displayed higher rates of ROS production when oxidizing succinate, which was inhibited by rotenone, myxothiazol, and malonate, respectively. Disulfiram also increased ROS production by mitocondria oxidizing KMV. Treatment of mitochondria oxidizing KMV with disulfiram and rotenone or myxothiazol did not alter the rate O₂^●-/H₂O₂ production further when compared to mitochondria treated with disulfiram only. Analysis of BCKDH activity following disulfiram treatment revealed that glutathionylation does not inhibit the enzyme complex, indicating this α-keto acid dehydrogenase is not a target for glutathione modification. However, treatment of mitochondria with rotenone and myxothiazol without disulfiram also augmented ROS production. Overall, we were able to demonstrate for the first time that glutathionylation augments ROS production by the respiratory chain during forward electron transfer (FET) and reverse electron transfer (RET) from the UQ pool. Additionally, we were able to show that BCKDH is not a target for glutathione modification and that glutathionylation can also increase ROS production in mitochondria oxidizing branched chain amino acids following the modification of enzymes upstream of BCKDH.

Redox signaling in heart failure and therapeutic implications

Heart failure is a growing health burden worldwide characterized by alterations in excitation-contraction coupling, cardiac energetic deficit and oxidative stress. While current treatments are mostly limited to antagonization of neuroendocrine activation, more recent data suggest that also targeting metabolism may provide substantial prognostic benefit. However, although in a broad spectrum of preclinical models, oxidative stress plays a causal role for the development and progression of heart failure, no treatment that targets reactive oxygen species (ROS) directly has entered the clinical arena yet. In the heart, ROS derive from various sources, such as NADPH oxidases, xanthine oxidase, uncoupled nitric oxide synthase and mitochondria. While mitochondria are the primary source of ROS in the heart, communication between different ROS sources may be relevant for physiological signalling events as well as pathologically elevated ROS that deteriorate excitation-contraction coupling, induce hypertrophy and/or trigger cell death. Here, we review the sources of ROS in the heart, the modes of pathological activation of ROS formation as well as therapeutic approaches that may target ROS specifically in mitochondria.

Metabolic and Redox Regulation of Cardiovascular Stem Cell Biology and Pathology

Significance: Cardiovascular stem cells are important for regeneration and repair of damaged tissue. Recent Advances: Pluripotent stem cells have a unique metabolism, which is adopted for their energetic and biosynthetic demand as rapidly proliferating cells. Stem cell differentiation requires an exceptional metabolic flexibility allowing for metabolic remodeling between glycolysis and oxidative phosphorylation. Critical Issues: Respiration is associated with the generation of reactive oxygen species (ROS) by the mitochondrial respiratory chain. But also the membrane-bound protein nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase, NOX) contributes to ROS levels. ROS not only play a significant role in stem cell differentiation and tissue renewal but also cause senescence and contribute to tissue aging. Future Directions: For utilization of stem cells in therapeutic approaches, a deep understanding of the molecular mechanisms how metabolism and the cellular redox state regulate stem cell differentiation is required. Modulating the redox state of stem cells using antioxidative agents may be suitable to enhance activity of endothelial progenitor cells. Antioxid. Redox Signal. 35, 163-181.

Activity of ROS-induced processes in the combined preconditioning with amtizol before and after cerebral ischemia in rats

Introduction: The dose-dependent effect of reactive oxygen species (ROS) in tissues in preconditioning (PreC) and oxidative stress, as well as NO-synthase participation in mitochondrial ROS production determined the study aim – to assess the impact of the neuroprotective method of combined preconditioning (CPreC) on free radical reactions (FRRs) in brain in normoxia and in cerebral ischemia, including in NO-synthase blockade.

Materials and methods: The intensity of FRR by iron-induced chemiluminescence (CL), the content of lipid peroxidation products and antioxidant enzyme activity were investigated 1 hr (early period) and 48 hrs (delayed period) after CPreC (amtizol and hypobaric hypoxia) in Wistar rat brain. Some animal groups were operated (common carotid artery bilateral ligation) 1 hr and 48 hrs after CPreC, as well as with preliminary introduction of L-NAME and aminoguanidine.

Results and discussion: In normoxia, CPreC led to increase the CL maximum level (Fmax) in the delayed PreC period. The amount of thiobarbituric acid reactive products (TBA-RP), activity of superoxide dismutase (SOD) and catalase in mitochondrial fraction of rat brain did not change in comparison with the intact control in both PreC periods. In cerebral ischemia, oxidative stress was observed. The CPreC use before ischemia caused a decrease in CL parameters and TBA-RP in brain, the maintenance of SOD and high catalase activity. NO-synthase inhibitors partially abolished the antioxidant effect of CPreC in ischemia.

Conclusion: CPreC had no influence on FRRs in brain tissue in normoxia, but prevented their excessive activation after ischemia, especially in the delayed period. NO-synthase was involved in the CPreC neuroprotection.

Western Diet Decreases the Liver Mitochondrial Oxidative Flux of Succinate: Insight from a Murine NAFLD Model

Mitochondria play an essential role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Previously, we found that succinate-activated respiration was the most affected mitochondrial parameter in mice with mild NAFLD. In this study, we focused on the role of succinate dehydrogenase (SDH) in NAFLD pathogenesis. To induce the progression of NAFLD to nonalcoholic steatohepatitis (NASH), C57BL/6J mice were fed a Western-style diet (WD) or control diet for 30 weeks. NAFLD severity was evaluated histologically and the expression of selected proteins and genes was assessed. Mitochondrial respiration was measured by high-resolution respirometry. Liver redox status was assessed using glutathione, malondialdehyde, and mitochondrial production of reactive oxygen species (ROS). Metabolomic analysis was performed by GC/MS. WD consumption for 30 weeks led to reduced succinate-activated respiration. We also observed decreased SDH activity, decreased expression of the SDH activator sirtuin 3, decreased gene expression of SDH subunits, and increased levels of hepatic succinate, an important signaling molecule. Succinate receptor 1 (SUCNR1) gene and protein expression were reduced in the livers of WD-fed mice. We did not observe signs of oxidative damage compared to the control group. The changes observed in WD-fed mice appear to be adaptive to prevent mitochondrial respiratory chain overload and massive ROS production.

An update on methods and approaches for interrogating mitochondrial reactive oxygen species production

The chief ROS formed by mitochondria are superoxide (O2·−) and hydrogen peroxide (H₂O₂). Superoxide is converted rapidly to H₂O₂ and therefore the latter is the chief ROS emitted by mitochondria into the cell. Once considered an unavoidable by-product of aerobic respiration, H₂O₂ is now regarded as a central mitokine used in mitochondrial redox signaling. However, it has been postulated that O2·− can also serve as a signal in mammalian cells. Progress in understanding the role of mitochondrial H₂O₂ in signaling is due to significant advances in the development of methods and technologies for its detection. Unfortunately, the development of techniques to selectively measure basal O2·− changes has been met with more significant hurdles due to its short half-life and the lack of specific probes. The development of sensitive techniques for the selective and real time measure of O2·− and H₂O₂ has come on two fronts: development of genetically encoded fluorescent proteins and small molecule reporters. In 2015, I published a detailed comprehensive review on the state of knowledge for mitochondrial ROS production and how it is controlled, which included an in-depth discussion of the up-to-date methods utilized for the detection of both superoxide (O2·−) and H₂O₂. In the article, I presented the challenges associated with utilizing these probes and their significance in advancing our collective understanding of ROS signaling. Since then, many other authors in the field of Redox Biology have published articles on the challenges and developments detecting O2·− and H₂O₂ in various organisms [[1], [2], [3]]. There has been significant advances in this state of knowledge, including the development of novel genetically encoded fluorescent H₂O₂ probes, several O2·− sensors, and the establishment of a toolkit of inhibitors and substrates for the interrogation of mitochondrial H₂O₂ production and the antioxidant defenses utilized to maintain the cellular H₂O₂ steady-state. Here, I provide an update on these methods and their implementation in furthering our understanding of how mitochondria serve as cell ROS stabilizing devices for H₂O₂ signaling.

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Details on the toolkit for interrogating the 12 sites for mitochondrial ROS production.

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Approaches to assess mitochondrial ROS clearance.

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Novel genetically encoded H₂O₂ sensors.

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Small chemical probes for sensitive detection of O2·−.

Emerging cellular-based therapies in carbon monoxide poisoning

Carbon monoxide (CO) is an odorless and colorless gas with multiple sources that include engine exhaust, faulty furnaces, and other sources of incomplete combustion of carbon compounds such as house fires. The most serious complications for survivors of consequential CO exposure are persistent neurological sequelae occurring in up to 50% of patients. CO inhibits mitochondrial respiration by specifically binding to the heme a₃ in the active site of CIV-like hydrogen sulfide, cyanide, and phosphides. Although hyperbaric oxygen remains the cornerstone for treatment, it has variable efficacy requiring new approaches to treatment. There is a paucity of cellular-based therapies in the area of CO poisoning, and there have been recent advancements that include antioxidants and a mitochondrial substrate prodrug. The succinate prodrugs derived from chemical modification of succinate are endeavored to enhance delivery of succinate to cells, increasing uptake of succinate into the mitochondria, and providing metabolic support for cells. The therapeutic intervention of succinate prodrugs is thus potentially applicable to patients with CO poisoning via metabolic support for fuel oxidation and possibly improving efficacy of HBO therapy.