In the eye of the storm: mitochondrial damage during heart and brain ischaemia

Redox Regulation of Mitochondrial Potassium Channels Activity

Redox reactions exert a profound influence on numerous cellular functions with mitochondria playing a central role in orchestrating these processes. This pivotal involvement arises from three primary factors: (1) the synthesis of reactive oxygen species (ROS) by mitochondria, (2) the presence of a substantial array of redox enzymes such as respiratory chain, and (3) the responsiveness of mitochondria to the cellular redox state. Within the inner mitochondrial membrane, a group of potassium channels, including ATP-regulated, large conductance calcium-activated, and voltage-regulated channels, is present. These channels play a crucial role in conditions such as cytoprotection, ischemia/reperfusion injury, and inflammation. Notably, the activity of mitochondrial potassium channels is intricately governed by redox reactions. Furthermore, the regulatory influence extends to other proteins, such as kinases, which undergo redox modifications. This review aims to offer a comprehensive exploration of the modulation of mitochondrial potassium channels through diverse redox reactions with a specific focus on the involvement of ROS.

Exploring the Role of Surface and Mitochondrial ATP-Sensitive Potassium Channels in Cancer: From Cellular Functions to Therapeutic Potentials

ATP-sensitive potassium (KATP) channels are found in plasma membranes and mitochondria. These channels are a type of ion channel that is regulated by the intracellular concentration of adenosine triphosphate (ATP) and other nucleotides. In cell membranes, they play a crucial role in linking metabolic activity to electrical activity, especially in tissues like the heart and pancreas. In mitochondria, KATP channels are involved in protecting cells against ischemic damage and regulating mitochondrial function. This review delves into the role of KATP channels in cancer biology, underscoring their critical function. Notably responsive to changes in cellular metabolism, KATP channels link metabolic states to electrical activity, a feature that becomes particularly significant in cancer cells. These cells, characterized by uncontrolled growth, necessitate unique metabolic and signaling pathways, differing fundamentally from normal cells. Our review explores the intricate roles of KATP channels in influencing the metabolic and ionic balance within cancerous cells, detailing their structural and operational mechanisms. We highlight the channels' impact on cancer cell survival, proliferation, and the potential of KATP channels as therapeutic targets in oncology. This includes the challenges in targeting these channels due to their widespread presence in various tissues and the need for personalized treatment strategies. By integrating molecular biology, physiology, and pharmacology perspectives, the review aims to enhance the understanding of cancer as a complex metabolic disease and to open new research and treatment avenues by focusing on KATP channels. This comprehensive approach provides valuable insights into the potential of KATP channels in developing innovative cancer treatments.

Protective mechanisms of quercetin in neonatal rat brain injury induced by hypoxic-ischemic brain damage (HIBD)

Neonatal hypoxic-ischemic brain damage (HIBD) is a leading cause of infant mortality worldwide. This study explored whether quercetin (Que) exerts neuroprotective effects in a rat model of HIBD. A total of 36 seven-day-old Sprague-Dawley rats were divided into control, Que, HI, and HI + Que groups. The Rice method was used to establish HIBD in HI and HI + Que rats, which were treated with hypoxia (oxygen concentration of 8%) for 2 h after ligation of the left common carotid artery. The rats in the HI + Que group were intraperitoneally injected with Que (30 mg/kg) 1 h before hypoxia, and the rats in the Que group were only injected with the same amount of Que. Brain tissues were harvested 24 h postoperation and assessed by hematoxylin and eosin staining, 2,3,5-triphenyltetrazolium chloride staining, and terminal deoxynucleotidyl transferase dUTP nick-end labeling assay; relative gene and protein levels were evaluated by RT-qPCR, IHC, or western blot (WB) assay. Brain tissue morphologies were characterized by transmission electron microscopy (TEM); LC3B protein levels were assessed by immunofluorescence staining. Escape latencies and platform crossing times were significantly improved (p < .05) in HI + Que groups; infarct volume significantly decreased (p < .001), whereas the numbers of autophagic bodies and apoptotic cells increased and decreased, respectively. Meanwhile, NLRX1, ATG7, and Beclin1 expressions were significantly upregulated, and mTOR and TIM23 expressions, LC3B protein level, and LC 3II/LC 3I ratio were significantly downregulated. Que exerted neuroprotective effects in a rat model of HIBD by regulating NLRX1 and autophagy.

Molecular therapy of cardiac ischemia-reperfusion injury based on mitochondria and ferroptosis

Excessive death of myocardial cells can lead to various cardiovascular diseases and even develop into heart failure, so developing ideal treatment plans based on pathogenesis is of great significance for cardiopathy. After the heart undergoes ischemia‒reperfusion (I/R), myocardial cells accumulate a large amount of peroxides, leading to mitochondrial dysfunction and inducing ferroptosis. Ferroptosis is a form of iron-dependent regulatory cell death (RCD) caused by imbalanced redox and iron metabolism that leads to severe cell damage through the accumulation of peroxides. The mechanism of ferroptosis is highly correlated with mitochondrial metabolism. Myocardial cells are rich in a large number of mitochondria, which serve as energy supply centers and are prone to producing reactive oxygen species (ROS), providing opportunities for oxidative stress caused by ferroptosis. Ferroptosis is related to various cardiovascular diseases, and potential treatment methods designed around ferroptosis may alter the pathological progression of cardiovascular diseases. Therefore, this review investigates the regulatory mechanisms of ferroptosis, exploring the close pathological and physiological connections between ferroptosis and mitochondrial and cardiac I/R injury. Targeting ferroptosis and mitochondria for intervention may be an effective plan for preventing and treating cardiac I/R injury.

Enriched environment as a nonpharmacological neuroprotective strategy

The structure and functions of the central nervous system are influenced by environmental stimuli, which also play an important role in brain diseases. Enriched environment (EE) consists of producing modifications in the environment of standard laboratory animals to induce an improvement in their biological conditions. This paradigm promotes transcriptional and translational effects that result in ameliorated motor, sensory, and cognitive stimulation. EE has been shown to enhance experience-dependent cellular plasticity and cognitive performance in animals housed under these conditions compared with animals housed under standard conditions. In addition, several studies claim that EE induces nerve repair by restoring functional activities through morphological, cellular, and molecular adaptations in the brain that have clinical relevance in neurological and psychiatric disorders. In fact, the effects of EE have been studied in different animal models of psychiatric and neurological diseases, such as Alzheimer's disease, Parkinson's disease, schizophrenia, ischemic brain injury, or traumatic brain injury, delaying the onset and progression of a wide variety of symptoms of these disorders. In this review, we analyze the action of EE focused on diseases of the central nervous system and the translation to humans to develop a bridge to its application.

Relationship between Brain Metabolic Disorders and Cognitive Impairment: LDL Receptor Defect

The low-density-lipoprotein receptor (LDLr) removes low-density lipoprotein (LDL), an endovascular transporter that carries cholesterol from the bloodstream to peripheral tissues. The maintenance of cholesterol content in the brain, which is important to protect brain function, is affected by LDLr. LDLr co-localizes with the insulin receptor and complements the internalization of LDL. In LDLr deficiency, LDL blood levels and insulin resistance increase, leading to abnormal cholesterol control and cognitive deficits in atherosclerosis. Defects in brain cholesterol metabolism lead to neuroinflammation and blood–brain-barrier (BBB) degradation. Moreover, interactions between endoplasmic reticulum stress (ER stress) and mitochondria are induced by ox-LDL accumulation, apolipoprotein E (ApoE) regulates the levels of amyloid beta (Aβ) in the brain, and hypoxia is induced by apoptosis induced by the LDLr defect. This review summarizes the association between neurodegenerative brain disease and typical cognitive deficits.

Current Challenges of Mitochondrial Potassium Channel Research

In this paper, the current challenges of mitochondrial potassium channels research were critically reviewed. Even though recent progress in understanding K⁺ traffic in mitochondria has been substantial, some basic issues of this process remain unresolved. Here, we focused on the critical discussion of the molecular identity of various mitochondrial potassium channels. This point helps to clarify why there are different potassium channels in specific mitochondria. We also described interactions of mitochondrial potassium channel subunits with other mitochondrial proteins. Posttranslational modifications of mitochondrial potassium channels and their import are essential but unexplored research areas. Additionally, problems with the pharmacological targeting of mitochondrial potassium channel were illustrated. Finally, the limitation of the techniques used to measure mitochondrial potassium channels was explained. We believe that recognizing these problems may be interesting for readers but will also help to progress the field of mitochondrial potassium channels.

Vagus Nerve Stimulation Improves Mitochondrial Dysfunction in Post–cardiac Arrest Syndrome in the Asphyxial Cardiac Arrest Model in Rats

Cerebral mitochondrial dysfunction during post–cardiac arrest syndrome (PCAS) remains unclear, resulting in a lack of therapeutic options that protect against cerebral ischemia–reperfusion injury. We aimed to assess mitochondrial dysfunction in the hippocampus after cardiac arrest and whether vagus nerve stimulation (VNS) can improve mitochondrial dysfunction and neurological outcomes. In an asphyxial cardiac arrest model, male Sprague–Dawley rats were assigned to the vagus nerve isolation (CA) or VNS (CA + VNS) group. Cardiopulmonary resuscitation was performed 450 s after pulseless electrical activity. After the return of spontaneous circulation (ROSC), left cervical VNS was performed for 3 h in the CA + VNS group. Mitochondrial respiratory function was evaluated using high-resolution respirometry of the hippocampal tissue. The neurologic deficit score (NDS) and overall performance category (OPC) were assessed at 24, 48, and 72 h after resuscitation. The leak respiration and oxidative phosphorylation capacity of complex I (OXPHOS CI) at 6 h after ROSC were significantly higher in the CA + VNS group than in the CA group (p = 0.0308 and 0.0401, respectively). Compared with the trends of NDS and OPC in the CA group, the trends of those in the CA + VNS group were significantly different, thus suggesting a favorable neurological outcome in the CA + VNS group (p = 0.0087 and 0.0064 between times × groups interaction, respectively). VNS ameliorated mitochondrial dysfunction after ROSC and improved neurological outcomes in an asphyxial cardiac arrest rat model.

Cardioprotective Role of Estrogen in Takotsubo Cardiomyopathy

Takotsubo cardiomyopathy (TC) is a rare, reversible cause of left ventricular wall motion abnormality (LVWMA) that mimics the presentation of acute myocardial infarction (AMI). TC is usually preceded by an emotional or physical stressor and appears to be more common in postmenopausal women. Various pathophysiological hypotheses of TC have been proposed, but the exact mechanism of action remains elusive. Elevated levels of catecholamines leading to cardiac dysfunction are the most prevalent hypothesis. The protective role of estrogen in the development of cardiomyopathies has been studied extensively. International Takotsubo Diagnostic Criteria (InterTAK) and Mayo clinic diagnostic criteria both have the stipulation stating prevalence of TC is higher in postmenopausal women which hints towards the protective role of estrogen in the development of TC. To review the protective role of estrogen in the mechanism of this novel pathology, we searched Pubmed and Google scholar for the relevant articles by using keywords such as: “takotsubo cardiomyopathy”, “apical ballooning”, “broken heart syndrome”, “stress cardiomyopathy”, “left ventricle wall motion abnormality”, “estrogen”, “estradiol” and “sex hormones”. Our research revealed that although the prevalence of TC is greater in postmenopausal women as compared to men, the prognosis is worse in men. It also revealed the involvement of multiple cellular pathways under the influence of estrogen that could explain the cardioprotective effect of estrogen. Most of the articles found were based on animal studies, thus, there is an emphasis on future human studies. However, we strongly suggest evaluating estrogen levels as part of the initial workup for any patient presenting with signs and symptoms of cardiac pathology.

Anoxia-reoxygenation alters H2O2 efflux and sensitivity of redox centers to copper in heart mitochondria

Mitochondrial reactive oxygen species (ROS) have been implicated in organ damage caused by environmental stressors, prompting studies on the effect of oxygen deprivation and metal exposure on ROS metabolism. However, how anoxia and copper (Cu) jointly influence heart mitochondrial ROS metabolism is not understood. We used rainbow trout heart mitochondria to probe the effects of anoxia-reoxygenation and Cu on hydrogen peroxide (H₂O₂) emission during oxidation of palmitoylcarnitine (PC), succinate, or glutamate-malate. In addition, we examined the influence of anoxia-reoxygenation and Cu on site-specific H₂O₂ emission capacities and key antioxidant enzymes, glutathione peroxidase (GPx) and thioredoxin reductase (TrxR). Results showed that anoxia-reoxygenation suppressed H₂O₂ emission regardless of substrate type or duration of anoxia. Anoxia-reoxygenation reduced mitochondrial sensitivity to Cu during oxidation of succinate or glutamate-malate whereas high Cu concentration additively stimulated H₂O₂ emission in mitochondria oxidizing PC. Prolonged anoxia-reoxygenation stimulated H₂O₂ emission from sites O_F and I_F, inhibited emission from sites I_Q, II_F and III_Qo, and disparately altered the sensitivity of the sites to Cu. Interestingly, anoxia-reoxygenation increased GPx and TrxR activities, more prominently when reoxygenation followed a short duration of anoxia. Cu did not alter GPx but reduced TrxR activity in normoxic and anoxic-reoxygenated mitochondria. Overall, our study revealed potential mechanisms that may reduce oxidative damage associated with anoxia-reoxygenation and Cu exposure in heart mitochondria. The increased and decreased H₂O₂ emission from NADH/NAD⁺ and QH₂/Q isopotential sites, respectively, may represent a balance between H₂O₂ required for oxygen deprivation-induced signaling and prevention of ROS burst associated with anoxia-reoxygenation.

Mitochondrial dysfunction in perinatal asphyxia: role in pathogenesis and potential therapeutic interventions

Perinatal asphyxia (PA)-induced brain injury may present as hypoxic-ischemic encephalopathy in the neonatal period, and long-term sequelae such as spastic motor deficits, intellectual disability, seizure disorders and learning disabilities. The brain injury is secondary to both the hypoxic-ischemic event and oxygenation-reperfusion following resuscitation. Following PA, a time-dependent progression of neuronal insult takes place in terms of transition of cell death from necrosis to apoptosis. This transition is the result of time-dependent progression of pathomechanisms which involve excitotoxicity, oxidative stress, and ultimately mitochondrial dysfunction in developing brain. More precisely mitochondrial respiration is suppressed and calcium signalling is dysregulated. Consequently, Bax-dependent mitochondrial permeabilization occurs leading to release of cytochrome c and activation of caspases leading to transition of cell death in developing brain. The therapeutic window lies within this transition process. At present, therapeutic hypothermia (TH) is the only clinical treatment available for treating moderate as well as severe asphyxia in new-born as it attenuates secondary loss of high-energy phosphates (ATP) (Solevåg et al. in Free Radic Biol Med 142:113-122, 2019; Gunn et al. in Pediatr Res 81:202-209, 2017), improving both short- and long-term outcomes. Mitoprotective therapies can offer a new avenue of intervention alone or in combination with therapeutic hypothermia for babies with birth asphyxia. This review will explore these mitochondrial pathways, and finally will summarize past and current efforts in targeting these pathways after PA, as a means of identifying new avenues of therapeutic intervention.

Cerebral and myocardial mitochondrial injury differ in a rat model of cardiac arrest and cardiopulmonary resuscitation

Brain mitochondria are more sensitive to global ischemia compared to heart mitochondria. Complex I in the electron transport chain (ETC) is sensitive to ischemic injury and is a major control point of the rate of ADP stimulated oxygen consumption. The purpose of this study was to explore whether changes in cerebral and myocardial mitochondria differ after cardiac arrest. Animals were randomized into 4 groups (n = 6): 1) Sham 2) VF 3) VF+CPR 4) ROSC 1hr. Ventricular Fibrillation (VF) was induced through a guide wire advanced from the right jugular vein into the ventricle and untreated for 8 min. Resuscitation was attempted with a 4J defibrillation after 8 min of cardiopulmonary resuscitation (CPR). Brain mitochondria and cardiac mitochondrial subpopulations were isolated. Calcium retention capacity was measured to assess susceptibility to mitochondrial permeability transition pore opening. ADP stimulated oxygen consumption and ETC activity assays were performed. Brain mitochondria are far more sensitive to injury during cardiac arrest and resuscitation compared to cardiac mitochondria. Complex I is highly sensitive to injury in brain mitochondria. With markedly decreased calcium retention capacity, mitochondria contribute to cerebral reperfusion injury. Therapeutic preservation of cerebral mitochondrial activity and mitochondrial function during cardiac arrest may improve post-resuscitation neurologic function.

Multidimensional Regulation of Cardiac Mitochondrial Potassium Channels

Mitochondria play a fundamental role in the energetics of cardiac cells. Moreover, mitochondria are involved in cardiac ischemia/reperfusion injury by opening the mitochondrial permeability transition pore which is the major cause of cell death. The preservation of mitochondrial function is an essential component of the cardioprotective mechanism. The involvement of mitochondrial K+ transport in this complex phenomenon seems to be well established. Several mitochondrial K+ channels in the inner mitochondrial membrane, such as ATP-sensitive, voltage-regulated, calcium-activated and Na+-activated channels, have been discovered. This obliges us to ask the following question: why is the simple potassium ion influx process carried out by several different mitochondrial potassium channels? In this review, we summarize the current knowledge of both the properties of mitochondrial potassium channels in cardiac mitochondria and the current understanding of their multidimensional functional role. We also critically summarize the pharmacological modulation of these proteins within the context of cardiac ischemia/reperfusion injury and cardioprotection.

No Direct Postconditioning Effect of Poloxamer 188 on Mitochondrial Function after Ischemia Reperfusion Injury in Rat Isolated Hearts

Myocardial infarction is a leading cause for morbidity and mortality worldwide. The only viable treatment for the ischemic insult is timely reperfusion, which further exacerbates myocardial injury. Maintaining mitochondrial function is crucial in preserving cardiomyocyte function in ischemia reperfusion (IR) injury. Poloxamer (P) 188 has been shown to improve cardiac IR injury by improving cellular and mitochondrial function. The aim of this study was to show if P188 postconditioning has direct protective effects on mitochondrial function in the heart. Langendorff prepared rat hearts were subjected to IR injury ex-vivo and reperfused for 10 min with 1 mM P188 vs. vehicle. Cardiac mitochondria were isolated with 1 mM P188 vs. 1 mM polyethylene glycol (PEG) vs. vehicle by differential centrifugation. Mitochondrial function was assessed by adenosine triphosphate synthesis, oxygen consumption, and calcium retention capacity. Mitochondrial function decreased significantly after ischemia and showed mild improvement with reperfusion. P188 did not improve mitochondrial function in the ex-vivo heart, and neither further P188 nor PEG induced direct mitochondrial protection after IR injury in this model.

Rational Application of β-Hydroxybutyrate Attenuates Ischemic Stroke by Suppressing Oxidative Stress and Mitochondrial-Dependent Apoptosis via Activation of the Erk/CREB/eNOS Pathway

Stroke is one of the leading causes of disability and death. Increasing evidence indicates that β-hydroxybutyrate (BHB) exerts beneficial effects in treating stroke, but the underlying mechanism remains largely unknown. In this study, we injected different doses of BHB into the lateral ventricle in middle cerebral artery occlusion (MCAO) model rats and neuronal cells were treated with different doses of BHB followed by oxygen-glucose deprivation (OGD). We found that a moderate dose of BHB enhanced mitochondrial complex I respiratory chain complex I activity, reduced oxidative stress, inhibited mitochondrial apoptosis, improved neurological scores, and reduced infarct volume after ischemia. We further showed that the effects of BHB were achieved by upregulating the dedicated BHB transporter SMCT1 and activating the Erk/CREB/eNOS pathway. These results provide us with a foundation for a novel understanding of the neuroprotective effects of BHB in stroke.

Energy substrate metabolism and mitochondrial oxidative stress in cardiac ischemia/reperfusion injury

The heart is the most metabolically flexible organ with respect to the use of substrates available in different states of energy metabolism. Cardiac mitochondria sense substrate availability and ensure the efficiency of oxidative phosphorylation and heart function. Mitochondria also play a critical role in cardiac ischemia/reperfusion injury, during which they are directly involved in ROS-producing pathophysiological mechanisms. This review explores the mechanisms of ROS production within the energy metabolism pathways and focuses on the impact of different substrates. We describe the main metabolites accumulating during ischemia in the glucose, fatty acid, and Krebs cycle pathways. Hyperglycemia, often present in the acute stress condition of ischemia/reperfusion, increases cytosolic ROS concentrations through the activation of NADPH oxidase 2 and increases mitochondrial ROS through the metabolic overloading and decreased binding of hexokinase II to mitochondria. Fatty acid-linked ROS production is related to the increased fatty acid flux and corresponding accumulation of long-chain acylcarnitines. Succinate that accumulates during anoxia/ischemia is suggested to be the main source of ROS, and the role of itaconate as an inhibitor of succinate dehydrogenase is emerging. We discuss the strategies to modulate and counteract the accumulation of substrates that yield ROS and the therapeutic implications of this concept.

Comparison of Effects of Metformin, Phenformin, and Inhibitors of Mitochondrial Complex I on Mitochondrial Permeability Transition and Ischemic Brain Injury

Damage to cerebral mitochondria, particularly opening of mitochondrial permeability transition pore (MPTP), is a key mechanism of ischemic brain injury, therefore, modulation of MPTP may be a potential target for a neuroprotective strategy in ischemic brain pathologies. The aim of this study was to investigate whether biguanides-metformin and phenformin as well as other inhibitors of Complex I of the mitochondrial electron transfer system may protect against ischemia-induced cell death in brain slice cultures by suppressing MPTP, and whether the effects of these inhibitors depend on the age of animals. Experiments were performed on brain slice cultures prepared from 5-7-day (premature) and 2-3-month old (adult) rat brains. In premature brain slice cultures, simulated ischemia (hypoxia plus deoxyglucose) induced necrosis whereas in adult rat brain slice cultures necrosis was induced by hypoxia alone and was suppressed by deoxyglucose. Phenformin prevented necrosis induced by simulated ischemia in premature and hypoxia-induced-in adult brain slices, whereas metformin was protective in adult brain slices cultures. In premature brain slices, necrosis was also prevented by Complex I inhibitors rotenone and amobarbital and by MPTP inhibitor cyclosporine A. The latter two inhibitors were protective in adult brain slices as well. Short-term exposure of cultured neurons to phenformin, metformin and rotenone prevented ionomycin-induced MPTP opening in intact cells. The data suggest that, depending on the age, phenformin and metformin may protect the brain against ischemic damage possibly by suppressing MPTP via inhibition of mitochondrial Complex I.

Protective effects of anthocyanins against brain ischemic damage

Anthocyanins are considered as bioactive components of plant-based diets that provide protection against ischemic cardiovascular pathologies by mechanisms dependent on their antioxidant and reductive capacities. However, it is not clear whether similar anthocyanin-mediated mechanisms can provide protection against ischemia-induced brain mitochondrial injury and cell death. In this study, we compared effects of three cyanidin-3-glycosides - glucoside (Cy3G), galactoside (Cy3Gal) and rutinoside (Cy3R), with pelargonxidin-3-glucoside (Pg3G) and found that at 10-20 μM concentrations they have no direct effect on respiratory functions of mitochondria isolated from normal or ischemia-damaged rat brain slices. However, intravenous injection of Cy3Gal and Cy3G (0,025 mg/kg or 0,05 mg/kg what matches 10 μM or 20 μM respectively) but not Cy3R in rats protected against ischemia-induced caspase activation and necrotic cell death, and reduced infarct size in cerebral cortex and cerebellum. These effects correlated with cytochrome c reducing capacity of cyanidin-3-glycosides. In contrast, intravenous injection of 0,025 mg/kg Pg3G which has the lowest cytochrome c reducing capacity among investigated anthocyanins, had no effect on ischemia-induced caspase activation and necrosis but reduced brain infarct size whereas intravenous injection of 0,05 mg/kg of Pg3G slightly promoted necrosis in the brain. Our data suggest that reductive rather than antioxidant capacities of anthocyanins may be important components in providing protection against ischemic brain damage.

Changes in Mitochondria-Associated Protein Expression and Mitochondrial Function in Response to 2 Weeks of Enriched Environment Training After Cerebral Ischaemia-Reperfusion Injury

An enriched environment (EE) can stimulate the recovery of neurological function following a cerebral ischaemia-reperfusion injury; however, the impact of EE's on mitochondrial function has been insufficiently studied. Our research aimed to assess whether EE's therapeutic impact involved the enhancement of mitochondrial dysfunction. Following 2 weeks of EE training, we tested both mitochondrial function and mitochondria-associated protein expression within the cerebral cortex following cerebral ischaemia-reperfusion injury. We subjected Sprague-Dawley rats to transient focal cerebral ischaemia and categorized the rats into three separate groups, i.e. an enriched environment (EE) group, a standard condition (SC) group and a sham control group (no middle cerebral artery embolization). The rats within the EE group were raised in enriched conditions for 2 weeks, while the rats within the SC group, in comparison, were reared in standard conditions for 2 weeks. After 2 weeks, the cerebral cortices of the rats were removed. We then measured a series of indices, i.e. the protein expression of peroxisome proliferator-activated receptor gamma coactivator (PGC-1α), nuclear respiratory factor-1 (NRF-1), mitochondrial transcription factor A (TFAM) and mitochondrial protein cytochrome C oxidase subunit IV (COX IV). Furthermore, the number of mitochondria was evaluated through electron microscopy.EE upregulated the protein expression of PGC-1α, NRF-1 as well as TFAM, which function as the master regulators of mitochondrial biogenesis, in comparison with the SC group. The EE group's COX IV protein expression also exhibited an increase. Moreover, the amount of mitochondria in the peri-infarct region of the cortex increased as result of EE training. Over 2 weeks, EE training significantly increased mitochondrial biogenesis-associated protein expression and mitochondrial function. A possible mechanism of the EE leading to the improvement of neurological function is that it increases brain mitochondrial biogenesis after the rats' cerebral ischaemia-reperfusion injury. Mitochondrial biogenesis stimulation or enhancement could become an innovative strategy for neuroprotection in future treatment.

Natural Bioactive Compounds As Protectors Of Mitochondrial Dysfunction In Cardiovascular Diseases And Aging

Diet, particularly the Mediterranean diet, has been considered as a protective factor against the development of cardiovascular diseases, the main cause of death in the world. Aging is one of the major risk factors for cardiovascular diseases, which have an oxidative pathophysiological component, being the mitochondria one of the key organelles in the regulation of oxidative stress. Certain natural bioactive compounds have the ability to regulate oxidative phosphorylation, the production of reactive oxygen species and the expression of mitochondrial proteins; but their efficacy within the mitochondrial physiopathology of cardiovascular diseases has not been clarified yet. The following review has the purpose of evaluating several natural compounds with evidence of mitochondrial effect in cardiovascular disease models, ascertaining the main cellular mechanisms and their potential use as functional foods for prevention of cardiovascular disease and healthy aging.

Anthocyanins: From plant pigments to health benefits at mitochondrial level

Anthocyanins are water-soluble pigments providing certain color for various plant parts, especially in edible berries. Earlier these compounds were only known as natural food colorants, the stability of which depended on pH, light, storage temperature and chemical structure. However, due to the increase of the in vitro, in vivo experimental data, as well as of the epidemiological studies, today anthocyanins and their metabolites are also regarded as potential pharmaceutical compounds providing various beneficial health effects on either human or animal cardiovascular system, brain, liver, pancreas and kidney. Many of these effects are shown to be related to the free-radical scavenging and antioxidant properties of anthocyanins, or to their ability to modulate the intracellular antioxidant systems. However, it is generally overlooked that instead of acting exclusively as antioxidants certain anthocyanins affect the activity of mitochondria that are the main source of energy in cells. Therefore, the aim of the present review is to summarize the major knowledge about the chemistry and regulation of biosynthesis of anthocyanins in plants, to overview the facts on bioavailability, and to discuss the most recent experimental findings related to the beneficial health effects emphasizing mitochondria.

Integrating multi-omics and regular analyses identifies the molecular responses of zebrafish brains to graphene oxide: Perspectives in environmental criteria

With the broad application of nanoparticles, nanotoxicology has attracted substantial attention in environmental science. However, the methods for detecting few and targeted genes or proteins, even single omics approaches, may miss other responses, including the major responses induced by nanoparticles. To determine the actual toxicological mechanisms of zebrafish brains induced by graphene oxide (GO, a popular carbon-based nanomaterial applied in various fields) at nonlethal concentrations, multi-omics and regular analyses were combined. The biomolecule responses were remarkable, although GO was not obviously observed in brain tissues. The trends for gene and protein changes were the same and accounted for 3.53% and 5.36% of all changes in the genome and proteome, respectively, suggesting a limitation of single omics analysis. Transcriptomics and proteomics analyses indicated that GO affected the functions or pathways of the troponin complex, actin cytoskeleton, monosaccharide transmembrane transporter activity, oxidoreductase activity and focal adhesion. Both metabolomics and proteomics revealed mitochondrial dysfunction and disruption of the citric acid cycle. The integrated analysis of omics, transmission electron microscopy and immunostaining confirmed that GO induced energy disruptions and mitochondrial damage by downregulating tubulin. The combination of multi-omics and regular analyses provides insights into the actual and highly influential mechanisms underlying nanotoxicity.

Identification of RyR2-PBmice and the effects of transposon insertional mutagenesis of the RyR2 gene on cardiac function in mice

Ryanodine receptor 2 (RyR2) plays an important role in maintaining the normal heart function, and mutantions can lead to arrhythmia, heart failure and other heart diseases. In this study, we successfully identified a piggyBac translocated RyR2 gene heterozygous mouse model (RyR2-PBmice) by tracking red fluorescent protein (RFP) and genotyping PCR. Cardiac function tests showed that there was no significant difference between the RyR2-PBmice and corresponding wild-type mice (WTmice), regardless of whether they were in the basal state or injected with epinephrine and caffeine. However, the sarcoplasmic reticulum Ca²⁺ content was significantly reduced in the cardiomyocytes of RyR2-PBmice as assessed by measuring caffeine-induced [Ca²⁺]_i transients; the cardiac muscle tissue of RyR2-PBmice displayed significant mitochondrial swelling and focal dissolution of mitochondrial cristae, and the tissue ATP content in the RyR2-PBmice heart was significantly reduced. To further analyze the molecular mechanism behind these changes, we tested the expression levels of related proteins using RT-PCR and Western blot analyses. The mRNA level of RyR2 in RyR2-PBmice cardiac tissue decreased significantly compared with the WTmice, and the protein expression associated with the respiratory chain was also downregulated. These results suggested that the piggyBac transposon inserted into the RyR2 gene substantively affected the structure and function of mitochondria in the mouse cardiomyocytes, leading to disorders of energy metabolism.

B355252, A Novel Small Molecule, Confers Neuroprotection Against Cobalt Chloride Toxicity In Mouse Hippocampal Cells Through Altering Mitochondrial Dynamics And Limiting Autophagy Induction

Cerebral hypoxia as often occurs in cases of stroke, hemorrhage, or other traumatic brain injuries, is one of the leading causes of death worldwide and a main driver of disabilities in the elderly. Using a chemical mimetic of hypoxia, cobalt chloride (CoCl2), we tested the ability of a novel small molecule, 4-chloro-N-(naphthalen-1-ylmethyl)-5-(3-(piperazin-1-yl)phenoxy)thiophene-2-sulfonamide (B355252), to alleviate CoCl2-induced damage in mouse hippocampal HT22 cells. A dose-dependent decrease in cell viability was observed during CoCl2 treatment along with increases in mitochondrial membrane potential and generation of reactive oxygen species (ROS). B355252 conferred protection against these changes. We further found that mitochondrial dynamics, the balance between mitochondrial fusion and fission, were perturbed by CoCl2 treatment. Mitochondrial fusion, which was assessed by measuring the expression of proteins optic atrophy protein 1 (OPA1) and mitofusin 2 (Mfn2), declined due to CoCl2 exposure, but B355252 addition was able to elevate Mfn2 expression while OPA1 expression was unchanged. Mitochondrial fission, measured by phosphorylated dynamin-related protein 1 (p-DRP1) and fission protein 1 (FIS1) expression, also decreased following CoCl2 exposure, and was stabilized by B355252 addition. Finally, autophagy was assessed by measuring the conversion of cytosolic microtubule-associated protein 1A/1B-light chain three-I (LC3-I) to autophagosome-bound microtubule-associated protein 1A/1B-light chain three-II (LC3-II) and was found to be increased by CoCl2. B355252 addition significantly reduced autophagy induction. Taken together, our results indicate B355252 has therapeutic potential to reduce the damaging effects caused by CoCl2 and should be further evaluated for applications in cerebral ischemia therapy.

The role of decreased cardiolipin and impaired electron transport chain in brain damage due to cardiac arrest

Ischemic brain damage is the major cause of mortality in cardiac arrest (CA). However, the molecular mechanism responsible for brain damage is not well understood. We previously found that mitochondrial state-3 respiration, which had been decreased following CA, was recovered in the kidney and liver, but not in the brain following cardiopulmonary bypass (CPB) resuscitation. Examination of mitochondria from these tissues may shed light on why the brain is the most vulnerable. In this study, adult male Sprague-Dawley rats were subjected to asphyxia-induced CA for 30 min or 30 min followed by 60 min CPB resuscitation. Mitochondria were then isolated from brain, heart, kidney, and liver tissues for examination using spectrophotometry and mass spectrometry to measure the activities of mitochondrial electron transport complexes and the cardiolipin content. We found significantly decreased complex I activity in mitochondria isolated from all four organs following CA, while complex III and IV activities remained intact. Following CPB resuscitation, complex I activity was normalized in kidney and liver, but unrecovered in brain and heart mitochondria. In addition, complex III activity in brain mitochondria was decreased by 22% with a concomitant decrease in cardiolipin following CPB resuscitation. These results suggest that of the tissues tested only brain mitochondria suffer reperfusion injury in addition to ischemic alterations, resulting in diminished overall mitochondrial respiration following resuscitation.

Mitochondria and Reactive Oxygen Species Contribute to Neurogenic Hypertension

Beyond its primary role as fuel generators, mitochondria are engaged in a variety of cellular processes, including redox homeostasis. Mitochondrial dysfunction, therefore, may have a profound impact on high-energy-demanding organs such as the brain. Here, we review the roles of mitochondrial biogenesis and bioenergetics, and their associated signaling in cellular redox homeostasis, and illustrate their contributions to the oxidative stress-related neural mechanism of hypertension, focusing on specific brain areas that are involved in the generation or modulation of sympathetic outflows to the cardiovascular system. We also highlight future challenges of research on mitochondrial physiology and pathophysiology.

2,4 Dinitrophenol Attenuates Mitochondrial Dysfunction and Improves Neurobehavioral Outcomes Postanoxia in Neonatal Rats

Following anoxia, a rapid and marked mitochondrial-linked cell death occurs in the cerebral cortex of newborn rats which leads to insult advancement within a couple of days and causes lifelong neurobehavioral abnormalities. The present study investigated the role of 2,4 dinitrophenol (2,4 DNP) in three doses, i.e.,1, 2.5, and 5 mg/kg on anoxia-induced time-dependent mitochondrial dysfunction and associated neurobehavioral outcome using a well-established global model of anoxia. Briefly, rat pups of 30-h age (P2) were subjected to two episodes of anoxia (10 min each) at 24 h of the time interval in an enclosed chamber supplied with 100% N₂ and immersed in a water bath (35-37 °C) to avoid hypothermia. Results demonstrated that the uncoupler 2,4 DNP, in the dose 2.5 and 5 mg/kg injected i.p. within 5 min after second anoxic episode significantly (P < 0.05) preserved mitochondrial function on day 7 preferentially by maintaining mitochondrial membrane potential (MMP) and inhibiting mitochondrial permeability transition (MPT) pore. Further, 2,4 DNP preserved mitochondrial function by improving different states of mitochondrial respiration (s2, s3, s4, s5), respiratory control ratio (RCR), antioxidant enzyme system like superoxide dismutase (SOD) and catalase (CAT), and mitochondrial complex enzymes (I, II, IV, V) after anoxia. Furthermore, a marked decrease in the levels of expression of cytochrome C (cyt C) and pro-apoptotic (Bcl-2 family) and apoptotic (caspase-9/3) proteins was observed on day 7 indicating that the treatment with 2,4 DNP prevented mitochondrial dysfunction and further insult progression (day 1 to day 7). Moreover, 2,4 DNP decreased the apoptotic cell death on day 7 and overall improved the neurobehavioral outcomes like reflex latency and hanging latency which suggests its role in treating neonatal anoxia.

Cytochrome c is an oxidative stress-activated plasmalogenase that cleaves plasmenylcholine and plasmenylethanolamine at the sn-1 vinyl ether linkage

Plasmalogens are phospholipids critical for cell function and signaling that contain a vinyl ether linkage at the sn-1 position and are highly enriched in arachidonic acid (AA) at the sn-2 position. However, the enzyme(s) responsible for the cleavage of the vinyl ether linkage in plasmalogens has remained elusive. Herein, we report that cytochrome c, in the presence of either cardiolipin (CL), O₂ and H₂O₂, or oxidized CL and O₂, catalyzes the oxidation of the plasmalogen vinyl ether linkage, promoting its hydrolytic cleavage and resultant production of 2-AA-lysolipids and highly reactive α-hydroxy fatty aldehydes. Using stable isotope labeling in synergy with strategic chemical derivatizations and high-mass-accuracy MS, we deduced the chemical mechanism underlying this long sought-after reaction. Specifically, labeling with either ¹⁸O₂ or H₂¹⁸O, but not with H₂¹⁸O₂, resulted in M + 2 isotopologues of the α-hydroxyaldehyde, whereas reactions with both ¹⁸O₂ and H₂¹⁸O identified the M + 4 isotopologue. Furthermore, incorporation of ¹⁸O from ¹⁸O₂ was predominantly located at the α-carbon. In contrast, reactions with H₂¹⁸O yielded ¹⁸O linked to the aldehyde carbon. Importantly, no significant labeling of 2-AA-lysolipids with ¹⁸O₂, H₂¹⁸O, or H₂¹⁸O₂ was present. Intriguingly, phosphatidylinositol phosphates (PIP₂ and PIP₃) effectively substituted for cardiolipin. Moreover, cytochrome c released from myocardial mitochondria subjected to oxidative stress cleaved plasmenylcholine in membrane bilayers, and this was blocked with a specific mAb against cytochrome c Collectively, these results identify the first plasmalogenase in biology, reveal the production of previously unanticipated signaling lipids by cytochrome c, and present new perspectives on cellular signaling during oxidative stress.

Neuroprotective properties of anthocyanidin glycosides against H2O2-induced glial cell death are modulated by their different stability and antioxidant activity in vitro

The neuroprotective effect of several anthocyanins in combination with their stability and antioxidant/pro-oxidant activity has been investigated against H₂O₂-induced oxidative stress in C6 glial cells. First it was found that delphinidin (Dp) 3-O-glucoside and 3-O-rutinoside were degraded within an hour, and at the same time stimulated the production of H₂O₂ in the micromolar concentration range. The stability of peonidin, pelargonidin (Pg), malvidin (Mv) and cyanidin (Cy) 3-O-glucosides and Cy 3-O-rutinoside was significantly higher than that of Dp 3-O-glycosides, with Pg3G showing the highest percent recovery over time. Based on these findings and chemical difference (according to the set of functional groups on the B-ring) of tested anthocyanins Cy3G, Mv3G and Pg3G were selected as candidates for the protection of glial cells against H₂O₂-induced oxidative stress. It was revealed that Cy3G (5-20μM) and Mv3G (10-20μM) but not Pg3G protected glial cells against H₂O₂-induced necrotic cell death. Moreover, these anthocyanins sustained the glutathione antioxidant defence system. Finally, to the extent of our knowledge we were the first to demonstrate the protective effect of Cy3G on the resting mitochondrial respiration rate in H₂O₂-affected glial cells. The results suggest that Cy3G, as the most prominent antioxidant among tested anthocyanins, could be a potential adjuvant for the prevention or reduction of necrotic glial cell death during the oxidative stress conditions met in neurodegenerative diseases. However, further elucidation of other possible mechanisms for anthocyanins to protect the nervous system is encouraged.

Olesoxime Inhibits Cardioplegia-Induced Ischemia/Reperfusion Injury. A Study in Langendorff-Perfused Rabbit Hearts

Objective: During cardioplegia, which is often used in cardiac surgery, the heart is subjected to global ischemia/reperfusion injury, which can result in a post-operative impairment of cardiac function. Mitochondria permeability transition pores (MPTP) play a key role in cardiomyocyte survival after ischemia/reperfusion injury. It was shown in clinical settings that blockers of MPTP like cyclosporine might have a positive influence on cardiac function after cardioplegic arrest. Olesoxime, which is a new drug with MPTP blocking activity, has been introduced as a neuroprotective therapeutic agent. This drug has not been investigated on a possible positive effect in ischemia/reperfusion injury in hearts. Therefore, the aim of our study was to investigate possible effects of olesoxime on cardiac recovery after cardioplegic arrest.

Methods: We evaluated 14 mature Chinchilla bastard rabbits of 1,500–2,000 g. Rabbit hearts were isolated and perfused with constant pressure according to Langendorff. After induction of cardioplegic arrest (30 ml 4°C cold Custodiol cardioplegia without and with 5 μmol/L olesoxime, n = 7 each) the hearts maintained arrested for 90-min. Thereafter, the hearts were re-perfused for 60 min. At the end of each experiment left ventricular samples were frozen in liquid nitrogen for ATP measurements. Furthermore, heart slices were embedded in paraffin for histological analysis. During the entire experiment hemodynamic and functional data such as left ventricular pressure (LVP), dp/dt(max) and (min), pressure rate product (PRP), coronary flow, pO₂, and pCO₂ were also assessed.

Results: Histological analysis revealed that despite the same ischemic burden for both groups markers of nitrosative and oxidative stress were significantly lower in the olesoxime group. Moreover, hearts of the olesoxime-group showed a significantly faster and better hemodynamic recovery during reperfusion. In addition, tissue ATP-levels were significantly higher in the olesoxime treated hearts.

Conclusions: Olesoxime significantly protected the cardiac muscle from ischemia/reperfusion injury.

Study of Age-Dependent Structural and Functional Changes of Mitochondria in Skeletal Muscles and Heart of Naked Mole Rats (Heterocephalus glaber)

Morphometric analysis of mitochondria in skeletal muscles and heart of 6- and 60-month-old naked mole rats (Heterocephalus glaber) revealed a significant age-dependent increase in the total area of mitochondrial cross-sections in studied muscle fibers. For 6- and 60-month-old animals, these values were 4.8 ± 0.4 and 12.7 ± 1.8%, respectively. This effect is mainly based on an increase in the number of mitochondria. In 6-month-old naked mole rats, there were 0.23 ± 0.02 mitochondrial cross-sections per µm² of muscle fiber, while in 60-month-old animals this value was 0.47 ± 0.03. The average area of a single mitochondrial cross-section also increased with age in skeletal muscles - from 0.21 ± 0.01 to 0.29 ± 0.03 µm². Thus, naked mole rats show a drastic enlargement of the mitochondrial apparatus in skeletal muscles with age due to an increase in the number of mitochondria and their size. They possess a neotenic type of chondriome accompanied by specific features of mitochondrial functioning in the state of oxidative phosphorylation and a significant decrease in the level of matrix adenine nucleotides.

Neuroprotective Strategies during Cardiac Surgery with Cardiopulmonary Bypass

Aortocoronary bypass or valve surgery usually require cardiac arrest using cardioplegic solutions. Although, in principle, in a number of cases beating heart surgery (so-called off-pump technique) is possible, aortic or valve surgery or correction of congenital heart diseases mostly require cardiopulmonary arrest. During this condition, the heart-lung machine also named cardiopulmonary bypass (CPB) has to take over the circulation. It is noteworthy that the invention of a machine bypassing the heart and lungs enabled complex cardiac operations, but possible negative effects of the CPB on other organs, especially the brain, cannot be neglected. Thus, neuroprotection during CPB is still a matter of great interest. In this review, we will describe the impact of CPB on the brain and focus on pharmacological and non-pharmacological strategies to protect the brain.

Reduction of apoptosis and preservation of mitochondrial integrity under ischemia/reperfusion injury is mediated by estrogen receptor β

Background

Estrogen improves cardiac recovery after ischemia/reperfusion (I/R) by yet incompletely understood mechanisms. Mitochondria play a crucial role in I/R injury through cytochrome c-dependent apoptosis activation. We tested the hypothesis that 17β-estradiol (E2) as well as a specific ERβ agonist improve cardiac recovery through estrogen receptor (ER)β-mediated mechanisms by reducing mitochondria-induced apoptosis and preserving mitochondrial integrity.

Methods

We randomized ovariectomized C57BL/6N mice 24h before I/R to pre-treatment with E2 or a specific ERβ agonist (ERβA). Isolated hearts were perfused for 20min prior to 30min global ischemia followed by 40min reperfusion.

Results

Compared with controls, ERβA and E2 treated groups showed a significant improvement in cardiac recovery, i.e. an increase in left ventricular developed pressure, dP/dtmax and dP/dtmin. ERβA and E2 pre-treatment led to a significant reduction in apoptosis with decreased cytochrome c release from the mitochondria and increased mitochondrial levels of anti-apoptotic Bcl2 and ACAA2. Protein levels of mitochondrial translocase inner membrane (TIM23) and mitochondrial complex I of respiratory chain were increased by ERβA and E2 pre-treatment. Furthermore, we found a significant increase of myosin light chain 2 (MLC2) phosphorylation together with ERK1/2 activation in E2, but not in ERβA treated groups.

Conclusions

Activation of ERβ is essential for the improvement of cardiac recovery after I/R through the inhibition of apoptosis and preservation of mitochondrial integrity and can be a achieved by a specific ERβ agonist. Furthermore, E2 modulates MLC2 activation after I/R independent of ERβ.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-016-0104-8) contains supplementary material, which is available to authorized users.

Modeling the detailed kinetics of mitochondrial cytochrome c oxidase: Catalytic mechanism and nitric oxide inhibition

Cytochrome c oxidase (CcO) catalyzes the exothermic reduction of O₂ to H₂O by using electrons from cytochrome c, and hence plays a crucial role in ATP production. Although details on the enzyme structure and redox centers involved in O₂ reduction have been known, there still remains a considerable ambiguity on its mechanism of action, e.g., the number of sequential electrons donated to O₂ in each catalytic step, the sites of protonation and proton pumping, and nitric oxide (NO) inhibition mechanism. In this work, we developed a thermodynamically constrained mechanistic mathematical model for the catalytic action of CcO based on available kinetic data. The model considers a minimal number of redox centers on CcO and couples electron transfer and proton pumping driven by proton motive force (PMF), and accounts for the inhibitory effects of NO on the reaction kinetics. The model is able to fit well all the available kinetic data under diverse experimental conditions with a physiologically realistic unique parameter set. The model predictions show that: 1) the apparent K_m of O₂ varies considerably and increases from fully reduced to fully oxidized cytochrome c depending on pH and the energy state of mitochondria, and 2) the intermediate enzyme states depend on pH and cytochrome c redox fraction and play a central role in coupling mitochondrial respiration to PMF. The developed CcO model can easily be integrated into existing mitochondrial bioenergetics models to understand the role of the enzyme in controlling oxidative phosphorylation in normal and disease conditions.

Mitochondrial dysfunction and cell death in neurodegenerative diseases through nitroxidative stress

Mitochondria are important for providing cellular energy ATP through the oxidative phosphorylation pathway. They are also critical in regulating many cellular functions including the fatty acid oxidation, the metabolism of glutamate and urea, the anti-oxidant defense, and the apoptosis pathway. Mitochondria are an important source of reactive oxygen species leaked from the electron transport chain while they are susceptible to oxidative damage, leading to mitochondrial dysfunction and tissue injury. In fact, impaired mitochondrial function is commonly observed in many types of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease, alcoholic dementia, brain ischemia-reperfusion related injury, and others, although many of these neurological disorders have unique etiological factors. Mitochondrial dysfunction under many pathological conditions is likely to be promoted by increased nitroxidative stress, which can stimulate post-translational modifications (PTMs) of mitochondrial proteins and/or oxidative damage to mitochondrial DNA and lipids. Furthermore, recent studies have demonstrated that various antioxidants, including naturally occurring flavonoids and polyphenols as well as synthetic compounds, can block the formation of reactive oxygen and/or nitrogen species, and thus ultimately prevent the PTMs of many proteins with improved disease conditions. Therefore, the present review is aimed to describe the recent research developments in the molecular mechanisms for mitochondrial dysfunction and tissue injury in neurodegenerative diseases and discuss translational research opportunities.

Anthocyanins in cardioprotection: A path through mitochondria

Constantly growing experimental data from in vitro, in vivo and epidemiological studies show the great potential of anthocyanin-containing fruit and berry extracts or pure individual anthocyanins as cardioprotective food components or pharmacological compounds. In general it is regarded that the cardioprotective activity of anthocyanins is related to their antioxidant properties. However there are recent reports that certain anthocyanins may protect the heart against ischemia/reperfusion-induced injury by activating signal transduction pathways and sustaining mitochondrial functions instead of acting solely as antioxidants. In this review, we summarize the proposed mechanisms of direct or indirect actions of anthocyanins within cardiac cells with the special emphasis on recently discovered their pharmacological effects on mitochondria in cardioprotection: reduction of cytosolic cytochrome c preventing apoptosis and sustainment of electron transfer between NADH dehydrogenase and cytochrome c supporting oxidative phosphorylation in ischemia-damaged mitochondria.

The Responses of Tissues from the Brain, Heart, Kidney, and Liver to Resuscitation following Prolonged Cardiac Arrest by Examining Mitochondrial Respiration in Rats

Cardiac arrest induces whole-body ischemia, which causes damage to multiple organs. Understanding how each organ responds to ischemia/reperfusion is important to develop better resuscitation strategies. Because direct measurement of organ function is not practicable in most animal models, we attempt to use mitochondrial respiration to test efficacy of resuscitation on the brain, heart, kidney, and liver following prolonged cardiac arrest. Male Sprague-Dawley rats are subjected to asphyxia-induced cardiac arrest for 30 min or 45 min, or 30 min cardiac arrest followed by 60 min cardiopulmonary bypass resuscitation. Mitochondria are isolated from brain, heart, kidney, and liver tissues and examined for respiration activity. Following cardiac arrest, a time-dependent decrease in state-3 respiration is observed in mitochondria from all four tissues. Following 60 min resuscitation, the respiration activity of brain mitochondria varies greatly in different animals. The activity after resuscitation remains the same in heart mitochondria and significantly increases in kidney and liver mitochondria. The result shows that inhibition of state-3 respiration is a good marker to evaluate the efficacy of resuscitation for each organ. The resulting state-3 respiration of brain and heart mitochondria following resuscitation reenforces the need for developing better strategies to resuscitate these critical organs following prolonged cardiac arrest.

Sirtuin 3 mediates neuroprotection of ketones against ischemic stroke

Stroke is one of the leading causes of death. Growing evidence indicates that ketone bodies have beneficial effects in treating stroke, but their underlying mechanism remains unclear. Our previous study showed ketone bodies reduced reactive oxygen species by using NADH as an electron donor, thus increasing the NAD(+)/NADH ratio. In this study, we investigated whether mitochondrial NAD(+)-dependent Sirtuin 3 (SIRT3) could mediate the neuroprotective effects of ketone bodies after ischemic stroke. We injected mice with either normal saline or ketones (beta-hydroxybutyrate and acetoacetate) at 30 minutes after ischemia induced by transient middle cerebral artery (MCA) occlusion. We found that ketone treatment enhanced mitochondria function, reduced oxidative stress, and therefore reduced infarct volume. This led to improved neurologic function after ischemia, including the neurologic score and the performance in Rotarod and open field tests. We further showed that ketones' effects were achieved by upregulating NAD(+)-dependent SIRT3 and its downstream substrates forkhead box O3a (FoxO3a) and superoxide dismutase 2 (SOD2) in the penumbra region since knocking down SIRT3 in vitro diminished ketones' beneficial effects. These results provide us a foundation to develop novel therapeutics targeting this SIRT3-FoxO3a-SOD2 pathway.

Glutathione metabolism links FOXRED1 to NADH:ubiquinone oxidoreductase (complex I) deficiency: A hypothesis

FOXRED1 mutations result in complex I (NADH:ubiquinone oxidoreductase) deficiencies and Leigh syndrome (subacute necrotizing encephalomyelopathy). FOXRED1 is a mitochondrial flavoprotein related to N-methyl amino acid dehydrogenases. How is FOXRED1 required for the biogenesis of complex I? I present a hypothesis that suggests FOXRED1 catalytic activity as a sarcosine oxidase protects the developing fetus from oxidative stress during pregnancy. Loss of FOXRED1, coupled with protein, choline and/or folate-deficient diets results in the depletion of glutathione, the dysregulation of nitric oxide metabolism and the peroxynitrite-mediated inactivation of complex I.

High-Resolution Respirometry for Simultaneous Measurement of Oxygen and Hydrogen Peroxide Fluxes in Permeabilized Cells, Tissue Homogenate and Isolated Mitochondria

Whereas mitochondria are well established as the source of ATP in oxidative phosphorylation (OXPHOS), it is debated if they are also the major cellular sources of reactive oxygen species (ROS). Here we describe the novel approach of combining high-resolution respirometry and fluorometric measurement of hydrogen peroxide (H₂O₂) production, applied to mitochondrial preparations (permeabilized cells, tissue homogenate, isolated mitochondria). The widely used H₂O₂ probe Amplex Red inhibited respiration in intact and permeabilized cells and should not be applied at concentrations above 10 µM. H₂O₂ fluxes were generally less than 1% of oxygen fluxes in physiological substrate and coupling states, specifically in permeabilized cells. H₂O₂ flux was consistently highest in the Complex II-linked LEAK state, reduced with CI&II-linked convergent electron flow and in mitochondria respiring at OXPHOS capacity, and were further diminished in noncoupled mitochondria respiring at electron transfer system capacity. Simultaneous measurement of mitochondrial respiration and H₂O₂ flux requires careful optimization of assay conditions and reveals information on mitochondrial function beyond separate analysis of ROS production.

Disruption of cytochrome c heme coordination is responsible for mitochondrial injury during ischemia

BACKGROUND

It was recently suggested that electron flow into cyt c, coupled with ROS generation, oxidizes cyt c Met(80) to Met(80) sulfoxide (Met-O) in isolated hearts after ischemia-reperfusion, and converts cyt c to a peroxidase. We hypothesize that ischemia disrupts Met(80)-Fe ligation of cyt c, forming pentacoordinated heme Fe(2+), which inhibits electron transport (ET) and promotes oxygenase activity.

METHODS

SS-20 (Phe-D-Arg-Phe-Lys-NH2) was used to demonstrate the role of Met(80)-Fe ligation in ischemia. Mitochondria were isolated from ischemic rat kidneys to determine sites of respiratory inhibition. Mitochondrial cyt c and cyt c Met-O were quantified by western blot, and cristae architecture was examined by electron microscopy.

RESULTS

Biochemical and structural studies showed that SS-20 selectively targets cardiolipin (CL) and protects Met(80)-Fe ligation in cyt c. Ischemic mitochondria showed 17-fold increase in Met-O cyt c, and dramatic cristaeolysis. Loss of cyt c was associated with proteolytic degradation of OPA1. Ischemia significantly inhibited ET initiated by direct reduction of cyt c and coupled respiration. All changes were prevented by SS-20.

CONCLUSION

Our results show that ischemia disrupts the Met(80)-Fe ligation of cyt c resulting in the formation of a globin-like pentacoordinated heme Fe(2+) that inhibits ET, and converts cyt c into an oxygenase to cause CL peroxidation and proteolytic degradation of OPA1, resulting in cyt c release.

GENERAL SIGNIFICANCE

Cyt c heme structure represents a novel target for minimizing ischemic injury. SS-20, which we show to selectively target CL and protect the Met(80)-Fe ligation, minimizes ischemic injury and promotes ATP recovery.

Anthocyanins as substrates for mitochondrial complex I - protective effect against heart ischemic injury

Anthocyanins, a subclass of flavonoids, are known to protect against myocardial ischemia; however, little is known about their direct, acute effects on mitochondria injured by the ischemic insult. In this study, the effects of delphinidin 3-O-glucoside (Dp3G), cyanidin 3-O-glucoside (Cy3G) and pelargonidin 3-O-glucoside (Pg3G) on the activity of complex I of the mitochondrial respiratory chain were studied in mitochondria isolated from normal rat hearts and rat hearts subjected to ischemia for 45 min. Cy3G and Dp3G increased the activity of complex I, measured in the presence or absence of coenzyme Q1 (CoQ1 ), in ischemia-damaged mitochondria, whereas in nonischemic mitochondria the effect was observed only in the absence of CoQ1 . Dp3G and Cy3G but not Pg3G increased state 3 respiration and ATP synthesis with NADH-dependent substrates in mitochondria after ischemia. The results suggest that certain anthocyanins can act as electron acceptors at complex I, and bypass ischemia-induced inhibition, resulting in increased ATP production after ischemia. This study provides new information on a possible role of certain anthocyanins in the regulation of energy metabolism in mammalian cells.