Mitochondrial ATP-sensitive K+ channel opening decreases reactive oxygen species generation

A glibenclamide analog lacking the cyclohexylurea portion fails to block ischemic preconditioning-induced mitochondrial and cardiac protection against ischemia/reperfusion injury

Despite significant research, there are no definitive therapies to prevent ischemia/reperfusion injury. During reperfusion, mitochondrial reactive oxygen species (ROS) cause cell damage. Ischemic preconditioning (IP), characterized by brief cycles of ischemia and reperfusion, activates mitochondrial ATP-sensitive potassium channels (mitoKATP) and provides cardioprotection. The aim of the present study is to investigate the impact of a truncated glibenclamide (lacking the cyclohexylurea portion - IMP-A) in ischemic preconditioning (IP)-mediated cardioprotection. Our study shows that IMP-A (2-5 μM) does not inhibit the protective effects of IP against ischemia/reperfusion damage in isolated rat hearts. In this context, IP hearts (with or without IMP-A) exhibited preserved cardiac function, as indicated by stable left ventricular developed pressure, maximal and minimal first derivatives, and rate-pressure product, along with a reduced infarct size following ischemia/reperfusion injury. Conversely, glibenclamide (2 μM - a well-characterized mitoKATP inhibitor) abolished the protective effects of IP against ischemia/reperfusion damage. Mitochondria isolated from reperfused IP hearts (treated or not with IMP-A) produced significantly lower levels of mitochondrial ROS and had lower susceptibility to Ca2+-induced swelling secondary to mitochondrial permeability transition pore (mPTP) opening. Additionally, IP hearts (treated or not with IMP-A) had preserved protein sulfhydryls. Glibenclamide elevated mitochondrial ROS production and negatively impacted mPTP and the sulfhydryl protection seen in IP hearts. Importantly, mitochondrial O2 consumption was preserved in IP hearts (treated or not with IMP-A), and this preservation was disrupted by glibenclamide but not by IMP-A. These findings suggest that the cyclohexylurea group of glibenclamide is essential for its ability to block IP-mediated cardioprotection, providing valuable insights for developing novel therapeutic strategies.

Stress-induced mitochondrial fragmentation in endothelial cells disrupts blood-retinal barrier integrity causing neurodegeneration

Increased vascular leakage and endothelial cell (EC) dysfunction are major features of neurodegenerative diseases. Here, we investigated the mechanisms leading to EC dysregulation and asked whether altered mitochondrial dynamics in ECs impinge on vascular barrier integrity and neurodegeneration. We show that ocular hypertension, a major risk factor to develop glaucoma, induced mitochondrial fragmentation in retinal capillary ECs accompanied by increased oxidative stress and ultrastructural defects. Analysis of EC mitochondrial components revealed overactivation of dynamin-related protein 1 (DRP1), a central regulator of mitochondrial fission, during glaucomatous damage. Pharmacological inhibition or EC-specific in vivo gene delivery of a dominant negative DRP1 mutant was sufficient to rescue mitochondrial volume, reduce vascular leakage, and increase expression of the tight junction claudin-5 (CLDN5). We further demonstrate that EC-targeted CLDN5 gene augmentation restored blood-retinal-barrier integrity, promoted neuronal survival, and improved light-evoked visual behaviors in glaucomatous mice. Our findings reveal that preserving mitochondrial homeostasis and EC function are valuable strategies to enhance neuroprotection and improve vision in glaucoma.

Ion channel-mediated mitochondrial volume regulation and its relationship with mitochondrial dynamics

The mitochondrion, one of the important cellular organelles, has the major function of generating adenosine triphosphate and plays an important role in maintaining cellular homeostasis, governing signal transduction, regulating membrane potential, controlling programmed cell death and modulating cell proliferation. The dynamic balance of mitochondrial volume is an important factor required for maintaining the structural integrity of the organelle and exerting corresponding functions. Changes in the mitochondrial volume are closely reflected in a series of biological functions and pathological changes. The mitochondrial volume is controlled by the osmotic balance between the cytoplasm and the mitochondrial matrix. Thus, any disruption in the influx of the main ion, potassium, into the cells can disturb the osmotic balance between the cytoplasm and the matrix, leading to water movement between these compartments and subsequent alterations in mitochondrial volume. Recent studies have shown that mitochondrial volume homeostasis is closely implicated in a variety of diseases. In this review, we provide an overview of the main influencing factors and research progress in the field of mitochondrial volume homeostasis.

The Protective Effect of Uridine in a Rotenone-Induced Model of Parkinson's Disease: The Role of the Mitochondrial ATP-Dependent Potassium Channel

The effect of the modulators of the mitochondrial ATP-dependent potassium channel (mitoKATP) on the structural and biochemical alterations in the substantia nigra and brain tissues was studied in a rat model of Parkinson's disease induced by rotenone. It was found that, in experimental parkinsonism accompanied by characteristic motor deficits, both neurons and the myelin sheath of nerve fibers in the substantia nigra were affected. Changes in energy and ion exchange in brain mitochondria were also revealed. The nucleoside uridine, which is a source for the synthesis of the mitoKATP channel opener uridine diphosphate, was able to dose-dependently decrease behavioral disorders and prevent the death of animals, which occurred for about 50% of animals in the model. Uridine prevented disturbances in redox, energy, and ion exchanges in brain mitochondria, and eliminated alterations in their structure and the myelin sheath in the substantia nigra. Cytochemical examination showed that uridine restored the indicators of oxidative phosphorylation and glycolysis in peripheral blood lymphocytes. The specific blocker of the mitoKATP channel, 5-hydroxydecanoate, eliminated the positive effects of uridine, suggesting that this channel is involved in neuroprotection. Taken together, these findings indicate the promise of using the natural metabolite uridine as a new drug to prevent and, possibly, stop the progression of Parkinson's disease.

Activation of mitoKATP channels induces penile vasodilation and inhibits mitochondrial respiration and ROS production: Role of NO

OBJECTIVE

Mitochondrial ATP-sensitive K+ (mitoKATP) channels are involved in neuronal and cardiac protection from ischemia and oxidative stress. Penile erection is a neurovascular event mediated by relaxation of the erectile tissue via nitric oxide (NO) released from nerves and endothelium. In the present study, we investigated whether mitoKATP channels play a role in the control of penile vascular tone and mitochondrial dynamics, and the involvement of NO.

METHODS

The effect of the selective mitoKATP activator BMS191095 was examined on vascular tone, on mitochondrial bioenergetics by real-time measurements with Agilent Seahorse and on ROS production by MitoSOX fluorescence in freshly isolated microarteries.

RESULTS

BMS191095 and diazoxide relaxed penile arteries, BMS191095 being one order of magnitude more potent. BMS191095-induced relaxations were reduced by mechanical endothelium removal and by inhibitors of the nitric oxide synthase (NOS) and PI3K enzymes. The NO-dependent component of the relaxation to BMS191095 was impaired in penile arteries from insulin resistant obese rats. The blockers of mitoKATP channel 5-HD, sarcolemma KATP (sarcKATP) channel glibenclamide, and large conductance Ca2+-activated K+ (BKCa) channel iberiotoxin, inhibited relaxations to BMS191095 and to the NO donor SNAP. BMS191095 reduced the mitochondrial bioenergetic profile of penile arteries and attenuated mitochondrial ROS production. Blockade of endogenous NO impaired and exogenous NO mimicked, respectively, the inhibitory effects of BMS191095 on basal respiration and oxygen consumed for ATP synthesis. Exogenous NO exhibited dual inhibitory/stimulatory effects on mitochondrial respiration.

CONCLUSIONS

These results demonstrate that selective activation of mitoKATP channels causes penile vasodilation, attenuates ROS production and inhibits mitochondrial respiration in part by releasing endothelial NO. These mechanisms couple blood flow and metabolism in penile arterial wall and suggest that activation of vascular mitoKATP channels may protect erectile tissue against ischemic injury.

Uridine as a Regulator of Functional and Ultrastructural Changes in the Brain of Rats in a Model of 6-OHDA-Induced Parkinson's Disease

Using a model of Parkinson's disease (PD) induced by the bilateral injection of neurotoxin 6-hydroxydopamine (6-OHDA) into rat brain substantia nigra (SN), we showed uridine to exert a protective effect associated with activation of the mitochondrial ATP-dependent potassium (mitoK-ATP) channel. Injection of 4 µg neurotoxin evoked a 70% decrease in the time the experimental animal spent on the rod in the RotaRod test, an increase in the amount of lipid peroxides in blood serum and cerebral-cortex mitochondria and the rate of reactive oxygen species formation, and a decrease in Ca2+ retention in mitochondria. Herewith, lymphocytes featured an increase in the activity of lactate dehydrogenase, a cytosolic enzyme of glycolysis, without changes in succinate-dehydrogenase activity. Structural changes occurring in the SN and striatum manifested themselves in the destruction of mitochondria, degeneration of neurons and synapses, and stratification of myelin sheaths in them. Subcutaneous injections of 30 µg/kg uridine for 22 days restored the neurotoxin-induced changes in these parameters to levels close to the control. 5-Hydroxydecanoate (5 mg/kg), a specific mitoK-ATP channel inhibitor, eliminated the beneficial effect of uridine for almost all characteristics tested, indicating the involvement of the mitoK-ATP channel in the protective effect of uridine. The mechanism of the protective effect of uridine and its therapeutic applications for the prevention and treatment of PD are discussed.

Competitive interaction between ATP and GTP regulates mitochondrial ATP-sensitive potassium channels

Mitochondrial ATP-sensitive K⁺ channels (mitoKATP) have been recently characterized structurally, and possess a protein through which K⁺ enters mitochondria (MitoKIR), and a regulatory subunit (mitoSUR). The mitoSUR regulatory subunit is an ATP-binding cassette (ABC) protein isoform 8 (ABCB8). Opening these channels is known to be cardioprotective, but the molecular and physiological mechanisms that activate them are not fully known. Here, to better understand the molecular and physiological mechanisms of activators (GTP) and inhibitors (ATP) on the activity of mitoKATP, we exposed isolated mitochondria to both nucleotides. We also used molecular docking directed to the nucleotide-binding domain of human ABCB8/mitoSUR to test a comparative model of ATP and GTP effects. As expected, we find that ATP dose-dependently inhibits mitoKATP activity (IC₅₀ = 21.24 ± 1.4 mM). However, simultaneous exposure of mitochondria to GTP dose-dependently (EC₅₀ = 13.19 ± 1.33 mM) reversed ATP inhibition. Pharmacological and computational studies suggest that GTP reverses ATP activity competitively. Docking directed to the site of crystallized ADP reveals that both nucleotides bind to mitoSUR with high affinity, with their phosphates directed to the Mg²⁺ ion and the walker A motif of the protein (SGGGKTT). These effects, when combined, result in GTP binding, ATP displacement, mitochondrial ATP-sensitive K⁺ transport, and lower formation of reactive oxygen species. Overall, our findings demonstrate the basis for ATP and GTP binding in mitoSUR using a combination of biochemical, pharmacological, and computational experiments. Future studies may reveal the extent to which the balance between ATP and GTP actions contributes toward cardioprotection against ischemic events.

Regulation of Mitochondrial Permeability Transition Pore Opening by Monovalent Cations in Liver Mitochondria

The opening of the permeability transition pore (PTP) in mitochondria is a key event in the initiation of cell death in various pathologic states, including ischemia/reperfusion. The activation of K⁺ transport into mitochondria protects cells from ischemia/reperfusion. However, the role of K⁺ transport in PTP regulation is unclear. Here, we studied the role of K⁺ and other monovalent cations in the regulation of the PTP opening in an in vitro model. The registration of the PTP opening, membrane potential, Ca²⁺-retention capacity, matrix pH, and K⁺ transport was performed using standard spectral and electrode techniques. We found that the presence of all cations tested in the medium (K⁺, Na⁺, choline⁺, and Li⁺) strongly stimulated the PTP opening compared with sucrose. Several possible reasons for this were examined: the effect of ionic strength, the influx of cations through selective and non-selective channels and exchangers, the suppression of Ca²⁺/H⁺ exchange, and the influx of anions. The data obtained indicate that the mechanism of PTP stimulation by cations includes the suppression of K⁺/H⁺ exchange and acidification of the matrix, which facilitates the influx of phosphate. Thus, the K⁺/H⁺ exchanger and the phosphate carrier together with selective K⁺ channels compose a PTP regulatory triad, which might operate in vivo.

Disruption of mitochondrial bioenergetics and calcium homeostasis by phytanic acid in the heart: Potential relevance for the cardiomyopathy in Refsum disease

Refsum disease is an inherited peroxisomal disorder caused by severe deficiency of phytanoyl-CoA hydroxylase activity. Affected patients develop severe cardiomyopathy of poorly known pathogenesis that may lead to a fatal outcome. Since phytanic acid (Phyt) concentrations are highly increased in tissues of individuals with this disease, it is conceivable that this branched-chain fatty acid is cardiotoxic. The present study investigated whether Phyt (10-30 μM) could disturb important mitochondrial functions in rat heart mitochondria. We also determined the influence of Phyt (50-100 μM) on cell viability (MTT reduction) in cardiac cells (H9C2). Phyt markedly increased mitochondrial state 4 (resting) and decreased state 3 (ADP-stimulated) and uncoupled (CCCP-stimulated) respirations, besides reducing the respiratory control ratio, ATP synthesis and the activities of the respiratory chain complexes I-III, II, and II-III. This fatty acid also reduced mitochondrial membrane potential and induced swelling in mitochondria supplemented by exogenous Ca²⁺, which were prevented by cyclosporin A alone or combined with ADP, suggesting the involvement of the mitochondrial permeability transition (MPT) pore opening. Mitochondrial NAD(P)H content and Ca²⁺ retention capacity were also decreased by Phyt in the presence of Ca²⁺. Finally, Phyt significantly reduced cellular viability (MTT reduction) in cultured cardiomyocytes. The present data indicate that Phyt, at concentrations found in the plasma of patients with Refsum disease, disrupts by multiple mechanisms mitochondrial bioenergetics and Ca²⁺ homeostasis, which could presumably be involved in the cardiomyopathy of this disease.

Disruption of mitochondrial bioenergetics, calcium retention capacity and cell viability caused by D-2-hydroxyglutaric acid in the heart

Accumulation of D-2-hydroxyglutaric acid (D-2-HG) is the biochemical hallmark of D-2-hydroxyglutaric aciduria type I and, particularly, of D-2-hydroxyglutaric aciduria type II (D2HGA2). D2HGA2 is a metabolic inherited disease caused by gain-of-function mutations in the gene isocitrate dehydrogenase 2. It is clinically characterized by neurological abnormalities and a severe cardiomyopathy whose pathogenesis is still poorly established. The present work investigated the potential cardiotoxicity D-2-HG, by studying its in vitro effects on a large spectrum of bioenergetics parameters in heart of young rats and in cultivated H9c2 cardiac myoblasts. D-2-HG impaired cellular respiration in purified mitochondrial preparations and crude homogenates from heart of young rats, as well as in digitonin-permeabilized H9c2 cells. ATP production and the activities of cytochrome c oxidase (complex IV), alpha-ketoglutarate dehydrogenase, citrate synthase and creatine kinase were also inhibited by D-2-HG, whereas the activities of complexes I, II and II-III of the respiratory chain, glutamate, succinate and malate dehydrogenases were not altered. We also found that this organic acid compromised mitochondrial Ca²⁺ retention capacity in heart mitochondrial preparations and H9c2 myoblasts. Finally, D-2-HG reduced the viability of H9c2 cardiac myoblasts, as determined by the MTT test and by propidium iodide incorporation. Noteworthy, L-2-hydroxyglutaric acid did not change some of these measurements (complex IV and creatine kinase activities) in heart preparations, indicating a selective inhibitory effect of the enantiomer D. In conclusion, it is presumed that D-2-HG-disrupts mitochondrial bioenergetics and Ca²⁺ retention capacity, which may be involved in the cardiomyopathy commonly observed in D2HGA2.

Mitochondrial Adaptive Responses to Hypertriglyceridemia and Bioactive Lipids

Significance: Altered plasma triglyceride metabolism and changes in dietary fatty acid types and levels are major contributors to the development of metabolic and cardiovascular diseases such as fatty liver disease, obesity, diabetes, and atherosclerosis. Lipid accumulation in visceral adipose tissue and ectopically in other organs, as well as lipid-induced redox imbalance, is connected to mitochondrial dysfunction in a range of oxidative stress-associated metabolic and degenerative disorders. Recent Advances: Successful mitochondrial adaptive responses in the context of hypertriglyceridemia and dietary bioactive polyunsaturated fatty acids contribute to increase body energy expenditure and reduce oxidative stress, thus allowing several cell types to cope with metabolic challenges and stresses. These responses include mitochondrial redox signaling, mild uncoupling, and changes in network dynamic behavior. Critical Issues: Mitochondrial bioenergetics and redox changes in a lipid overload context are relatively well characterized. However, the turning point between adaptive and maladaptive mitochondrial responses remains a critical issue to be elucidated. In addition, the relationship between changes in fusion/fission machinery and mitochondrial function is less well understood. Future Directions: The effective mitochondrial responses described here support the research for new drug design and diet or nutraceutical formulations targeting mitochondrial mild uncoupling and effective quality control as putative strategies for cardiometabolic diseases. Antioxid. Redox Signal. 36, 953-968.

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.

Mitochondrial K+ Transport: Modulation and Functional Consequences

The existence of a K⁺ cycle in mitochondria has been predicted since the development of the chemiosmotic theory and has been shown to be crucial for several cellular phenomena, including regulation of mitochondrial volume and redox state. One of the pathways known to participate in K⁺ cycling is the ATP-sensitive K⁺ channel, MitoK_ATP. This channel was vastly studied for promoting protection against ischemia reperfusion when pharmacologically activated, although its molecular identity remained unknown for decades. The recent molecular characterization of MitoK_ATP has opened new possibilities for modulation of this channel as a mechanism to control cellular processes. Here, we discuss different strategies to control MitoK_ATP activity and consider how these could be used as tools to regulate metabolism and cellular events.

Diazoxide and Exercise Enhance Muscle Contraction during Obesity by Decreasing ROS Levels, Lipid Peroxidation, and Improving Glutathione Redox Status

Obesity causes insulin resistance and hyperinsulinemia which causes skeletal muscle dysfunction resulting in a decrease in contraction force and a reduced capacity to avoid fatigue, which overall, causes an increase in oxidative stress. KATP channel openers such as diazoxide and the implementation of exercise protocols have been reported to be actively involved in protecting skeletal muscle against metabolic stress; however, the effects of diazoxide and exercise on muscle contraction and oxidative stress during obesity have not been explored. This study aimed to determine the effect of diazoxide in the contraction of skeletal muscle of obese male Wistar rats (35 mg/kg), and with an exercise protocol (five weeks) and the combination from both. Results showed that the treatment with diazoxide and exercise improved muscular contraction, showing an increase in maximum tension and total tension due to decreased ROS and lipid peroxidation levels and improved glutathione redox state. Therefore, these results suggest that diazoxide and exercise improve muscle function during obesity, possibly through its effects as KATP channel openers.

Signaling pathways targeting mitochondrial potassium channels

In this review, we describe key signaling pathways regulating potassium channels present in the inner mitochondrial membrane. The signaling cascades covered here include phosphorylation, redox reactions, modulation by calcium ions and nucleotides. The following types of potassium channels have been identified in the inner mitochondrial membrane of various tissues: ATP-sensitive, Ca²⁺-activated, voltage-gated and two-pore domain potassium channels. The direct roles of these channels involve regulation of mitochondrial respiration, membrane potential and synthesis of reactive oxygen species (ROS). Changes in channel activity lead to diverse pro-life and pro-death responses in different cell types. Hence, characterizing the signaling pathways regulating mitochondrial potassium channels will facilitate understanding the physiological role of these proteins. Additionally, we describe in this paper certain regulatory mechanisms, which are unique to mitochondrial potassium channels.

Disturbance of bioenergetics and calcium homeostasis provoked by metabolites accumulating in propionic acidemia in heart mitochondria of developing rats

Propionic acidemia is caused by lack of propionyl-CoA carboxylase activity. It is biochemically characterized by accumulation of propionic (PA) and 3-hydroxypropionic (3OHPA) acids and clinically by severe encephalopathy and cardiomyopathy. High urinary excretion of maleic acid (MA) and 2-methylcitric acid (2MCA) is also found in the affected patients. Considering that the underlying mechanisms of cardiac disease in propionic acidemia are practically unknown, we investigated the effects of PA, 3OHPA, MA and 2MCA (0.05-5 mM) on important mitochondrial functions in isolated rat heart mitochondria, as well as in crude heart homogenates and cultured cardiomyocytes. MA markedly inhibited state 3 (ADP-stimulated), state 4 (non-phosphorylating) and uncoupled (CCCP-stimulated) respiration in mitochondria supported by pyruvate plus malate or α-ketoglutarate associated with reduced ATP production, whereas PA and 3OHPA provoked less intense inhibitory effects and 2MCA no alterations at all. MA-induced impaired respiration was attenuated by coenzyme A supplementation. In addition, MA significantly inhibited α-ketoglutarate dehydrogenase activity. Similar data were obtained in heart crude homogenates and permeabilized cardiomyocytes. MA, and PA to a lesser degree, also decreased mitochondrial membrane potential (ΔΨm), NAD(P)H content and Ca²⁺ retention capacity, and caused swelling in Ca²⁺-loaded mitochondria. Noteworthy, ΔΨm collapse and mitochondrial swelling were fully prevented or attenuated by cyclosporin A and ADP, indicating the involvement of mitochondrial permeability transition. It is therefore proposed that disturbance of mitochondrial energy and calcium homeostasis caused by MA, as well as by PA and 3OHPA to a lesser extent, may be involved in the cardiomyopathy commonly affecting propionic acidemic patients.

Study of Uridine Effect on the Development of Audiogenic Tonic Seizures in Krushinsky-Molodkina Strain Rats

The latency of tonic seizure in response to loud sound (in rats of the Krushinsky-Molodkina strain with audiogenic epilepsy) had been slightly (although statistically significantly) longer after chronic uridine injections (100 mg/kg, i.p., three times a day during 9 or 12 days). The recovery time from the tonic seizure was shorter after 12 days of injections in comparison to the 9-day injection period. At the same time, the intensity of tonic seizures provoked by loud sound did not change after chronic uridine injections. The lack of uridine anticonvulsive effect demonstrated in the audiogenic epilepsy model contradicts the anticonvulsant effects of uridine in experiments with other seizure models, in which the epileptic foci were localized in the forebrain structures.

High vulnerability of the heart and liver to 3-hydroxypalmitic acid-induced disruption of mitochondrial functions in intact cell systems

Patients affected by long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency predominantly present severe liver and cardiac dysfunction, as well as neurological symptoms during metabolic crises, whose pathogenesis is still poorly known. In this study, we demonstrate for the first time that pathological concentrations of 3-hydroxypalmitic acid (3HPA), the long-chain hydroxyl fatty acid (LCHFA) that most accumulates in LCHAD deficiency, significantly decreased adenosine triphosphate-linked and uncoupled mitochondrial respiration in intact cell systems consisting of heart fibers, cardiomyocytes, and hepatocytes, but less intense in diced forebrain. 3HPA also significantly reduced mitochondrial Ca²⁺ retention capacity and membrane potential in Ca²⁺ -loaded mitochondria more markedly in the heart and the liver, with mild or no effects in the brain, supporting a higher susceptibility of the heart and the liver to the toxic effects of this fatty acid. It is postulated that disruption of mitochondrial energy and Ca²⁺ homeostasis caused by the accumulation of LCHFA may contribute toward the severe cardiac and hepatic clinical manifestations observed in the affected patients.

Use the Protonmotive Force: Mitochondrial Uncoupling and Reactive Oxygen Species

Mitochondrial respiration results in an electrochemical proton gradient, or protonmotive force (pmf), across the mitochondrial inner membrane. The pmf is a form of potential energy consisting of charge (∆ψ_m) and chemical (∆pH) components, that together drive ATP production. In a process called uncoupling, proton leak into the mitochondrial matrix independent of ATP production dissipates the pmf and energy is lost as heat. Other events can directly dissipate the pmf independent of ATP production as well, such as chemical exposure or mechanisms involving regulated mitochondrial membrane electrolyte transport. Uncoupling has defined roles in metabolic plasticity and can be linked through signal transduction to physiologic events. In the latter case, the pmf impacts mitochondrial reactive oxygen species (ROS) production. Although capable of molecular damage, ROS also have signaling properties that depend on the timing, location, and quantity of their production. In this review, we provide a general overview of mitochondrial ROS production, mechanisms of uncoupling, and how these work in tandem to affect physiology and pathologies, including obesity, cardiovascular disease, and immunity. Overall, we highlight that isolated bioenergetic models-mitochondria and cells-only partially recapitulate the complex link between the pmf and ROS signaling that occurs in vivo.

Metabolite accumulation in VLCAD deficiency markedly disrupts mitochondrial bioenergetics and Ca2+ homeostasis in the heart

We studied the effects of the major long-chain fatty acids accumulating in very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency, namely cis-5-tetradecenoic acid (Cis-5) and myristic acid (Myr), on important mitochondrial functions in isolated mitochondria from cardiac fibers and cardiomyocytes of juvenile rats. Cis-5 and Myr at pathological concentrations markedly reduced mitochondrial membrane potential (ΔΨ_m ), matrix NAD(P)H pool, Ca²⁺ retention capacity, ADP- (state 3) and carbonyl cyanide 3-chlorophenyl hydrazine-stimulated (uncoupled) respiration, and ATP generation. By contrast, these fatty acids increased resting (state 4) respiration (uncoupling effect) with the involvement of the adenine nucleotide translocator because carboxyatractyloside significantly attenuated the increased state 4 respiration provoked by Cis-5 and Myr. Furthermore, the classical inhibitors of mitochondrial permeability transition (MPT) pore cyclosporin A plus ADP, as well as the Ca²⁺ uptake blocker ruthenium red, fully prevented the Cis-5- and Myr-induced decrease in ΔΨ_m in Ca²⁺ -loaded mitochondria, suggesting, respectively, the induction of MPT pore opening and the contribution of Ca²⁺ toward these effects. The findings of the present study indicate that the major long-chain fatty acids that accumulate in VLCAD deficiency disrupt mitochondrial bioenergetics and Ca²⁺ homeostasis, acting as uncouplers and metabolic inhibitors of oxidative phosphorylation, as well as inducers of MPT pore opening, in the heart at pathological relevant concentrations. It is therefore presumed that a disturbance of bioenergetics and Ca²⁺ homeostasis may contribute to the cardiac manifestations observed in VLCAD deficiency.

Energetic, oxidative and ionic exchange in rat brain and liver mitochondria at experimental audiogenic epilepsy (Krushinsky-Molodkina model)

The role of brain and liver mitochondria at epileptic seizure was studied on Krushinsky-Molodkina (KM) rats which respond to sound with an intensive epileptic seizure (audiogenic epilepsy). We didn't find significant changes in respiration rats of brain and liver mitochondria of KM and control rats; however the efficiency of АТР synthesis in the KM rat mitochondria was 10% lower. In rats with audiogenic epilepsy the concentration of oxidative stress marker malondialdehyde in mitochondria of the brain (but not liver) was 2-fold higher than that in the control rats. The rate of H2O2 generation in brain mitochondria of КМ rats was twofold higher than in the control animals when using NAD-dependent substrates. This difference was less pronounced in liver mitochondria. In KM rats, the activity of mitochondrial ATP-dependent potassium channel was lower than in liver mitochondria of control rats. The comparative study of the mitochondria ability to retain calcium ions revealed that in the case of using the complex I and complex II substrates, permeability transition pore is easier to trigger in brain and liver mitochondria of KM and КМs rats than in the control ones. The role of the changes in the energetic, oxidative, and ionic exchange in the mechanism of audiogenic epilepsy generation in rats and the possible correction of the epilepsy seizures are discussed.

Bioenergetic and volume regulatory effects of mitoKATP channel modulators protect against hypoxia-reoxygenation-induced mitochondrial dysfunction

The mitochondrial ATP-sensitive K(+) (mitoKATP) channel plays a significant role in mitochondrial physiology and protects against ischemic reperfusion injury in mammals. Although fish frequently face oxygen fluctuations in their environment, the role of the mitoKATP channel in regulating the responses to oxygen stress is rarely investigated in this class of animals. To elucidate whether and how the mitoKATP channel protects against hypoxia-reoxygenation (H-R)-induced mitochondrial dysfunction in fish, we first determined the mitochondrial bioenergetic effects of two key modulators of the channel, diazoxide and 5-hydroxydecanoate (5-HD), using a wide range of doses. Subsequently, the effects of low and high doses of the modulators on mitochondrial bioenergetics and volume under normoxia and after H-R using buffers with and without magnesium and ATP (Mg-ATP) were tested. In the absence of Mg-ATP (mitoKATP channel open), both low and high doses of diazoxide improved mitochondrial coupling, but only the high dose of 5-HD reversed the post-H-R coupling-enhancing effect of diazoxide. In the presence of Mg-ATP (mitoKATP channel closed), diazoxide at the low dose improved coupling post-H-R, and this effect was abolished by 5-HD at the low dose. Interestingly, both low and high doses of diazoxide reversed H-R-induced swelling under mitoKATP channel open conditions, but this effect was not sensitive to 5-HD. Under mitoKATP channel closed conditions, diazoxide at the low dose protected the mitochondria from H-R-induced swelling and 5-HD at the low dose reversed this effect. In contrast, diazoxide at the high dose failed to reduce the swelling caused by H-R, and the addition of the high dose of 5-HD enhanced mitochondrial swelling. Overall, our study showed that in the presence of Mg-ATP, both opening of mitoKATP channels and bioenergetic effects of diazoxide were protective against H-R in fish mitochondria, while in the absence of Mg-ATP only the bioenergetic effect of diazoxide was protective.

Modulation of Potassium Channel Activity in the Balance of ROS and ATP Production by Durum Wheat Mitochondria-An Amazing Defense Tool Against Hyperosmotic Stress

In plants, the existence of a mitochondrial potassium channel was firstly demonstrated about 15 years ago in durum wheat as an ATP-dependent potassium channel (PmitoKATP). Since then, both properties of the original PmitoKATP and occurrence of different mitochondrial potassium channels in a number of plant species (monocotyledonous and dicotyledonous) and tissues/organs (etiolated and green) have been shown. Here, an overview of the current knowledge is reported; in particular, the issue of PmitoKATP physiological modulation is addressed. Similarities and differences with other potassium channels, as well as possible cross-regulation with other mitochondrial proteins (Plant Uncoupling Protein, Alternative Oxidase, Plant Inner Membrane Anion Channel) are also described. PmitoKATP is inhibited by ATP and activated by superoxide anion, as well as by free fatty acids (FFAs) and acyl-CoAs. Interestingly, channel activation increases electrophoretic potassium uptake across the inner membrane toward the matrix, so collapsing membrane potential (ΔΨ), the main component of the protonmotive force (Δp) in plant mitochondria; moreover, cooperation between PmitoKATP and the K(+)/H(+) antiporter allows a potassium cycle able to dissipate also ΔpH. Interestingly, ΔΨ collapse matches with an active control of mitochondrial reactive oxygen species (ROS) production. Fully open channel is able to lower superoxide anion up to 35-fold compared to a condition of ATP-inhibited channel. On the other hand, ΔΨ collapse by PmitoKATP was unexpectedly found to not affect ATP synthesis via oxidative phosphorylation. This may probably occur by means of a controlled collapse due to ATP inhibition of PmitoKATP; this brake to the channel activity may allow a loss of the bulk phase Δp, but may preserve a non-classically detectable localized driving force for ATP synthesis. This ability may become crucial under environmental/oxidative stress. In particular, under moderate hyperosmotic stress (mannitol or NaCl), PmitoKATP was found to be activated by ROS, so inhibiting further large-scale ROS production according to a feedback mechanism; moreover, a stress-activated phospholipase A2 may generate FFAs, further activating the channel. In conclusion, a main property of PmitoKATP is the ability to keep in balance the control of harmful ROS with the mitochondrial/cellular bioenergetics, thus preserving ATP for energetic needs of cell defense under stress.

Deregulation of mitochondrial functions provoked by long-chain fatty acid accumulating in long-chain 3-hydroxyacyl-CoA dehydrogenase and mitochondrial permeability transition deficiencies in rat heart--mitochondrial permeability transition pore opening as a potential contributing pathomechanism of cardiac alterations in these disorders

Mitochondrial trifunctional protein and long-chain 3-hydroxyacyl-CoA dehydrogenase deficiencies are fatty acid oxidation disorders biochemically characterized by tissue accumulation of long-chain fatty acids and derivatives, including the monocarboxylic long-chain 3-hydroxy fatty acids (LCHFAs) 3-hydroxytetradecanoic acid (3HTA) and 3-hydroxypalmitic acid (3HPA). Patients commonly present severe cardiomyopathy for which the pathogenesis is still poorly established. We investigated the effects of 3HTA and 3HPA, the major metabolites accumulating in these disorders, on important parameters of mitochondrial homeostasis in Ca(2+) -loaded heart mitochondria. 3HTA and 3HPA significantly decreased mitochondrial membrane potential, the matrix NAD(P)H pool and Ca(2+) retention capacity, and also induced mitochondrial swelling. These fatty acids also provoked a marked decrease of ATP production reflecting severe energy dysfunction. Furthermore, 3HTA-induced mitochondrial alterations were completely prevented by the classical mitochondrial permeability transition (mPT) inhibitors cyclosporin A and ADP, as well as by ruthenium red, a Ca(2+) uptake blocker, indicating that LCHFAs induced Ca(2+)-dependent mPT pore opening. Milder effects only achieved at higher doses of LCHFAs were observed in brain mitochondria, implying a higher vulnerability of heart to these fatty acids. By contrast, 3HTA and docosanoic acids did not change mitochondrial homeostasis, indicating selective effects for monocarboxylic LCHFAs. The present data indicate that the major LCHFAs accumulating in mitochondrial trifunctional protein and long-chain 3-hydroxyacyl-CoA dehydrogenase deficiencies induce mPT pore opening, compromising Ca(2+) homeostasis and oxidative phosphorylation more intensely in the heart. It is proposed that these pathomechanisms may contribute at least in part to the severe cardiac alterations characteristic of patients affected by these diseases.

Modulation of mitochondrial respiratory function and ROS production by novel benzopyran analogues

A substantial body of evidence indicates that pharmacological activation of mitochondrial ATP-sensitive potassium channels (mKATP) in the heart is protective in conditions associated with ischemia/reperfusion injury. Several mechanisms have been postulated to be responsible for cardioprotection, including the modulation of mitochondrial respiratory function. The aim of the present study was to characterize the dose-dependent effects of novel synthetic benzopyran analogues, derived from a BMS-191095, a selective mKATP opener, on mitochondrial respiration and reactive oxygen species (ROS) production in isolated rat heart mitochondria. Mitochondrial respiratory function was assessed by high-resolution respirometry, and H2O2 production was measured by the Amplex Red fluorescence assay. Four compounds, namely KL-1487, KL-1492, KL-1495, and KL-1507, applied in increasing concentrations (50, 75, 100, and 150 μmol/L, respectively) were investigated. When added in the last two concentrations, all compounds significantly increased State 2 and 4 respiratory rates, an effect that was not abolished by 5-hydroxydecanoate (5-HD, 100 μmol/L), the classic mKATP inhibitor. The highest concentration also elicited an important decrease of the oxidative phosphorylation in a K+ independent manner. Both concentrations of 100 and 150 μmol/L for KL-1487, KL-1492, and KL-1495, and the concentration of 150 μmol/L for KL-1507, respectively, mitigated the mitochondrial H2O2 release. In isolated rat heart mitochondria, the novel benzopyran analogues act as protonophoric uncouplers of oxidative phosphorylation and decrease the generation of reactive oxygen species in a dose-dependent manner.

RTG1- and RTG2-dependent retrograde signaling controls mitochondrial activity and stress resistance in Saccharomyces cerevisiae

Mitochondrial retrograde signaling is a communication pathway between the mitochondrion and the nucleus that regulates the expression of a subset of nuclear genes that codify mitochondrial proteins, mediating cell response to mitochondrial dysfunction. In Saccharomyces cerevisiae, the pathway depends on Rtg1p and Rtg3p, which together form the transcription factor that regulates gene expression, and Rtg2p, an activator of the pathway. Here, we provide novel studies aimed at assessing the functional impact of the lack of RTG-dependent signaling on mitochondrial activity. We show that mutants defective in RTG-dependent retrograde signaling present higher oxygen consumption and reduced hydrogen peroxide release in the stationary phase compared to wild-type cells. Interestingly, RTG mutants are less able to decompose hydrogen peroxide or maintain viability when challenged with hydrogen peroxide. Overall, our results indicate that RTG signaling is involved in the hormetic induction of antioxidant defenses and stress resistance.

Intermittent fasting results in tissue-specific changes in bioenergetics and redox state

Intermittent fasting (IF) is a dietary intervention often used as an alternative to caloric restriction (CR) and characterized by 24 hour cycles alternating ad libitum feeding and fasting. Although the consequences of CR are well studied, the effects of IF on redox status are not. Here, we address the effects of IF on redox state markers in different tissues in order to uncover how changes in feeding frequency alter redox balance in rats. IF rats displayed lower body mass due to decreased energy conversion efficiency. Livers in IF rats presented increased mitochondrial respiratory capacity and enhanced levels of protein carbonyls. Surprisingly, IF animals also presented an increase in oxidative damage in the brain that was not related to changes in mitochondrial bioenergetics. Conversely, IF promoted a substantial protection against oxidative damage in the heart. No difference in mitochondrial bioenergetics or redox homeostasis was observed in skeletal muscles of IF animals. Overall, IF affects redox balance in a tissue-specific manner, leading to redox imbalance in the liver and brain and protection against oxidative damage in the heart.

Effect of potential-dependent potassium uptake on production of reactive oxygen species in rat brain mitochondria

The effect of potential-dependent potassium uptake on reactive oxygen species (ROS) generation in mitochondria of rat brain was studied. It was found that the effect of K+ uptake on ROS production in the brain mitochondria under steady-state conditions (state 4) was determined by potassium-dependent changes in the membrane potential of the mitochondria (ΔΨm). At K+ concentrations within the range of 0-120 mM, an increase in the initial rate of K(+)-uptake into the matrix resulted in a decrease in the steady-state rate of ROS generation due to the K(+)-induced depolarization of the mitochondrial membrane. The selective blockage of the ATP-dependent potassium channel (K(ATP)(+)-channel) by glibenclamide and 5-hydroxydecanoate resulted in an increase in ROS production due to the membrane repolarization caused by partial inhibition of the potential-dependent K+ uptake. The ATP-dependent transport of K+ was shown to be ~40% of the potential-dependent K+ uptake in the brain mitochondria. Based on the findings of the experiments, the potential-dependent transport of K+ was concluded to be a physiologically important regulator of ROS generation in the brain mitochondria and that the functional activity of the native K(ATP)(+)-channel in these organelles under physiological conditions can be an effective tool for preventing ROS overproduction in brain neurons.

Effects of flavonoid-containing preparation Extralife on hydrogen peroxide production and functioning of mitochondrial ATP-dependent potassium channel

Extralife, a Pentaphylloides fruticos extract, in concentrations of 0.005-10 μg/ml dose-dependently increased H2O2 production in rat heart mitochondria in the presence of respiration substrates. Extralife decreased ATP-induced accumulation of H2O2 related to inhibition of mitochondrial ATP-dependent potassium channel. This effect was observed only at low doses of the adaptogen (0.05-3 μg/ml). High doses of the substance (5-10 μg/ml) did not abolish ATP-dependent production of H2O2 and increased the rate of H2O2 generation by the mitochondria. We concluded that Extralife in trace concentrations could activate mitochondrial ATP-dependent potassium channel and decrease H2O2 accumulation in the mitochondria.

Mild uncoupling of respiration and phosphorylation as a mechanism providing nephro- and neuroprotective effects of penetrating cations of the SkQ family

It is generally accepted that mitochondrial production of reactive oxygen species is nonlinearly related to the value of the mitochondrial membrane potential with significant increment at values exceeding 150 mV. Due to this, high values of the membrane potential are highly dangerous, specifically under pathological conditions associated with oxidative stress. Mild uncoupling of oxidative phosphorylation is an approach to preventing hyperpolarization of the mitochondrial membrane. We confirmed data obtained earlier in our group that dodecylrhodamine 19 (C(12)R1) (a penetrating cation from SkQ family not possessing a plastoquinone group) has uncoupling properties, this fact making it highly potent for use in prevention of pathologies associated with oxidative stress induced by mitochondrial hyperpolarization. Further experiments showed that C(12)R1 provided nephroprotection under ischemia/reperfusion of the kidney as well as under rhabdomyolysis through diminishing of renal dysfunction manifested by elevated level of blood creatinine and urea. Similar nephroprotective properties were observed for low doses (275 nmol/kg) of the conventional uncoupler 2,4-dinitrophenol. Another penetrating cation that did not demonstrate protonophorous activity (SkQR4) had no effect on renal dysfunction. In experiments with induced ischemic stroke, C(12)R1 did not have any effect on the area of ischemic damage, but it significantly lowered neurological deficit. We conclude that beneficial effects of penetrating cation derivatives of rhodamine 19 in renal pathologies and brain ischemia may be at least partially explained by uncoupling of oxidation and phosphorylation.

[The effect of ATP-dependent K(+)-channel opener on transmembrane potassium exchange and reactive oxygen species production upon the opening of mitochondrial pore]

The effect of mitochondrial ATP-dependent K(+)-channel (K(+)ATP-channel) opener diazoxide (DZ) on transmembrane potassium exchange and reactive oxygen species (ROS) formation under the opening of mitochondrial permeability transition pore (MPTP) was studied in rat liver mitochondria. The activation of K(+)-cycling (K(+)-uptake and K(+)/H(+)-exchange) by DZ was established with peak effect at < or = 500 nM. It was shown that MPTP opening as well resulted in the activation of K(+)-cycling together with simultaneous activation of Ca(2+)-cycle in mitochondria. In the absence of depolarization Ca(2+)-cycle is supported by MPTP and Ca(2+)-uniporter. The stimulation of K(+)/H(+)-exchange by MPTP opening led to the activation of K(+)-cycle, but further activation of K(+)/H(+)-exchange resulted in MPTP inhibition. Under the same conditions the decrease in mitochondrial ROS production was observed. It was proposed that the decrease in ROS formation together with K(+)/H(+)-exchange activation could be the constituents of the complex effect of MPTP inhibition induced by K(+)ATP-channel opener.

Mitochondrial channels: ion fluxes and more

The field of mitochondrial ion channels has recently seen substantial progress, including the molecular identification of some of the channels. An integrative approach using genetics, electrophysiology, pharmacology, and cell biology to clarify the roles of these channels has thus become possible. It is by now clear that many of these channels are important for energy supply by the mitochondria and have a major impact on the fate of the entire cell as well. The purpose of this review is to provide an up-to-date overview of the electrophysiological properties, molecular identity, and pathophysiological functions of the mitochondrial ion channels studied so far and to highlight possible therapeutic perspectives based on current information.

Mitochondrial Channel Opener Diazoxide Attenuates Hypoxia-Induced sFlt-1 Release in Human Choriocarcinoma Cells

Objectives

To examine the effect of diazoxide on hypoxia-induced soluble fms-like tyrosin kinase-1 (sFlt-1) release in JEG-3 choriocarcinoma cells.

Methods

Cells were cultured under normoxia (20% O₂) or hypoxia (1% O₂), and expression of sFlt-1 mRNA and protein release was determined by quantitative real-time reverse-transcriptase polymerase chain reaction (qRT-PCR) assays and enzyme-linked immunosorbent assay (ELISA).

Results

Tumor necrosis factor-alpha (TNF-α) as well as hypoxia stimulated sFlt-1 release and diazoxide inhibited both of them. The selective inhibitor of mitochondrial adenosine triphosphat (ATP)-sensitive K⁺ channel opener (K_ATP) 5-hydroxydecanoate (5-HD) completely reversed the diazoxide-induced inhibition of hypoxia-stimulated sFlt-1 release. qRT-PCR and Western blot analyses showed that diazoxide up-regulated the heme oxygenase-1 (HO-1) expression. In addition, the HO-1 inducer cobalt protoporphyrin (CoPP) and the metabolic product of HO-1 bilirubin mimicked diazoxide to inhibit sFlt-1 release and reactive oxygen species (ROS) production under hypoxia, whereas the HO-1 inhibitor zinc protoporphyrin IX (ZnPP IX) antagonized the effect of diazoxide. In cells transfected with the HO-1 siRNA, diazoxide did not exert any effect on sFlt-1 release and ROS production under hypoxia.

Conclusion

These results, taken together, strongly suggest that up-regulation of the HO-1 expression is the crucial mechanism responsible for the diazoxide-induced inhibition of the sFlt-1 release and ROS production under hypoxia.

Protective effects elicited by levosimendan against liver ischemia/reperfusion injury in anesthetized rats

As in other organs, oxidative stress-induced injury and cell death may result from free oxygen radical-dependent mechanisms and alterations in signal transduction pathways leading to apoptosis. Among the new suggested therapies for injuries caused by oxidative stress, the use of levosimendan has been reported to be quite promising. In the present study, we aimed to examine the protective effects of levosimendan against liver oxidative stress in anesthetized rats and to analyze the involvement of mitochondrial adenosine triphosphate-dependent potassium (mitoK(ATP)) channels and nitric oxide (NO). In 50 anesthetized rats, liver ischemia/reperfusion (I/R) was performed via nontraumatic portal occlusion. In some animals, levosimendan was infused into the portal vein at the onset of reperfusion, whereas other rats received the vehicle only. Moreover, in some rats, levosimendan was given after the intraportal administration of L-Nω-nitro-arginine methyl ester (L-NAME) or 5-hydroxydecanoate (5HD). The portal vein blood flow was measured, and blood samples were taken for the determination of transaminases, thiobarbituric acid reactive substances (TBARS), and reduced glutathione (GSH); liver biopsy samples were used for B cell lymphoma 2-associated X protein, caspase-9, Akt, and endothelial nitric oxide synthase (eNOS) activation through western blotting. Also, caspase-3 activity was measured. In rats, I/R caused an increase in apoptotic markers, transaminases, and TBARS and a decrease in GSH and Akt activation. Levosimendan administration was able to counteract oxidative damage and apoptosis in a dose-dependent way and to increase GSH, Akt, and eNOS activation. All effects of levosimendan were abolished by pretreatment with L-NAME and 5HD. In conclusion, the results of the present study show that levosimendan can exert protection against ischemic liver damage through mechanisms related to NO production and mitoKATP channel function. These data provide interesting perspectives into the use of levosimendan in hepatic surgery and transplantation.

Oxidative phosphorylation and ion transport in the mitochondria of two strains of rats varying in their resistance to stress and hypoxia

The role of mitochondria in the inherited or ontogenetically acquired reactions of organism to stress is not studied enough. In the present work, we examined the functional state of the coupled respiratory chain, potassium and calcium transport and rate of hydrogen peroxide production on two rat lines: August and Wistar-which possess different resistance to emotional stress and hypoxia. It was established that the respiration rate and efficiency of oxidative phosphorylation were higher in August rats than in Wistar ones. In August rats, the rate of potassium transport and ATP-dependent mitochondrial swelling as well as the concentration of the ion in the mitochondrial matrix were almost twice as higher comparatively to those parameters in Wistar rats. The rate of H2O2 production was found to be decreased in the mitochondria of August rats. It was also demonstrated that the two rat lines differed by their resistance to the opening of the palmitate/Ca(2+)-induced pore and by their ability to retain calcium within mitochondria. The paper discusses the involvement of the mitochondrial ATP-dependent potassium channel in the adaptation of animals to adverse effects.

Extracts from Astragalus membranaceus limit myocardial cell death and improve cardiac function in a rat model of myocardial ischemia

ETHNOPHARMACOLOGICAL RELEVANCE

The root of Astragalus membranaceus, known as "huang-qi", is one of the most widely used Chinese herbal medicines for the prevention and treatment of myocardial ischemic diseases. However, the mechanisms governing its therapeutic effects are largely unknown.

AIMS OF THE STUDY

The aims of the present study were to investigate the cardioprotective effect of the root extract of Astragalu membranaceus (EAM) in myocardial ischemia and to explore its underlying mechanisms in ROS-mediated signaling cascade in vivo and in vitro.

MATERIALS AND METHODS

The saponins in EAM were analyzed using HPLC. The tests for the cardioprotective effects of EAM and its mechanisms were performed in vivo and in vitro. In vivo, the rat model of persistent myocardial ischemia was produced by occlusion of the left anterior descending (LAD) coronary artery. In vitro, the cardiomyocyte model of oxidative stress was mimicked by the direct free radical donor, H2O2.

RESULTS

In vivo, the increased myocardial infarct size and the increased serum levels of lactate dehydrogenase (LDH), creatine kinase isoform MB (CK-MB), and cardiac troponin (cTnI) were significantly decreased by pre-treatment with EAM. Moreover, cardiac function, as assessed by±dP/dt, left ventricular developed pressure (LVDP), and left ventricular end-diastolic pressure (LVEDP), was dramatically improved. An oxidative stress biomarker, malondialdehyde (MDA), was reduced, and the antioxidant enzyme superoxide dismutase (SOD) was induced. In vitro, H2O2-triggered myocardial cell death and cytoplasm Ca(2+) overload were blocked by treatment with EAM. Furthermore, the KATP channel blocker (5-HD, glibenclamide) blocked the anti-apoptotic protective effect of EAM on cardiomyocytes injured by H2O2.

CONCLUSIONS

The cardioprotection of EAM was manifested as a protection of tissue structure and as a decrease in serum markers of ischemic injury. The mechanisms underlying the EAM-mediated protective effects may involve improving cardiac function, attenuating the oxidative injury via a decrease in MDA, a maintenance in SOD, and a reduction in free radical-induced myocardial cell injury. Additionally, EAM enhanced the myocardial cell viability via arresting the influx of Ca(2+) to block cell death and opening mitochondrial KATP channels to reduce cell apoptosis.

A silybin-phospholipids complex counteracts rat fatty liver degeneration and mitochondrial oxidative changes

AIM

To investigate the effectiveness of antioxidant compounds in modulating mitochondrial oxidative alterations and lipids accumulation in fatty hepatocytes.

METHODS

Silybin-phospholipid complex containing vitamin E (Realsil(®)) was daily administered by gavage (one pouch diluted in 3 mL of water and containing 15 mg vitamin E and 47 mg silybin complexed with phospholipids) to rats fed a choline-deprived (CD) or a high fat diet [20% fat, containing 71% total calories as fat, 11% as carbohydrate, and 18% as protein, high fat diet (HFD)] for 30 d and 60 d, respectively. The control group was fed a normal semi-purified diet containing adequate levels of choline (35% total calories as fat, 47% as carbohydrate, and 18% as protein). Circulating and hepatic redox active and nitrogen regulating molecules (thioredoxin, glutathione, glutathione peroxidase), NO metabolites (nitrosothiols, nitrotyrosine), lipid peroxides [malondialdehyde-thiobarbituric (MDA-TBA)], and pro-inflammatory keratins (K-18) were measured on days 0, 7, 14, 30, and 60. Mitochondrial respiratory chain proteins and the extent of hepatic fatty infiltration were evaluated.

RESULTS

Both diet regimens produced liver steatosis (50% and 25% of liver slices with CD and HFD, respectively) with no signs of necro-inflammation: fat infiltration ranged from large droplets at day 14 to disseminated and confluent vacuoles resulting in microvesicular steatosis at day 30 (CD) and day 60 (HFD). In plasma, thioredoxin and nitrosothiols were not significantly changed, while MDA-TBA, nitrotyrosine (from 6 ± 1 nmol/L to 14 ± 3 nmol/L day 30 CD, P < 0.001, and 12 ± 2 nmol/L day 60 HFD, P < 0.001), and K-18 (from 198 ± 20 to 289 ± 21 U/L day 30 CD, P < 0.001, and 242 ± 23 U/L day 60 HFD, P < 0.001) levels increased significantly with ongoing steatosis. In the liver, glutathione was decreased (from 34.0 ± 1.3 to 25.3 ± 1.2 nmol/mg prot day 30 CD, P < 0.001, and 22.4 ± 2.4 nmol/mg prot day 60 HFD, P < 0.001), while thioredoxin and glutathione peroxidase were initially increased and then decreased. Nitrosothiols were constantly increased. MDA-TBA levels were five-fold increased from 9.1 ± 1.2 nmol/g to 75.6 ± 5.4 nmol/g on day 30, P < 0.001 (CD) and doubled with HFD on day 60. Realsil administration significantly lowered the extent of fat infiltration, maintained liver glutathione levels during the first half period, and halved its decrease during the second half. Also, Realsil modulated thioredoxin changes and the production of NO derivatives and significantly lowered MDA-TBA levels both in liver (from 73.6 ± 5.4 to 57.2 ± 6.3 nmol/g day 30 CD, P < 0.01 and from 27.3 ± 2.1 nmol/g to 20.5 ± 2.2 nmol/g day 60 HFD, P < 0.01) and in plasma. Changes in mitochondrial respiratory complexes were also attenuated by Realsil in HFD rats with a major protective effect on Complex II subunit CII-30.

CONCLUSION

Realsil administration effectively contrasts hepatocyte fat deposition, NO derivatives formation, and mitochondrial alterations, allowing the liver to maintain a better glutathione and thioredoxin antioxidant activity.

Long-chain 3-hydroxy fatty acids accumulating in long-chain 3-hydroxyacyl-CoA dehydrogenase and mitochondrial trifunctional protein deficiencies uncouple oxidative phosphorylation in heart mitochondria

Cardiomyopathy is a common clinical feature of some inherited disorders of mitochondrial fatty acid β-oxidation including mitochondrial trifunctional protein (MTP) and isolated long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiencies. Since individuals affected by these disorders present tissue accumulation of various fatty acids, including long-chain 3-hydroxy fatty acids, in the present study we investigated the effect of 3-hydroxydecanoic (3 HDCA), 3-hydroxydodecanoic (3 HDDA), 3-hydroxytetradecanoic (3 HTA) and 3-hydroxypalmitic (3 HPA) acids on mitochondrial oxidative metabolism, estimated by oximetry, NAD(P)H content, hydrogen peroxide production, membrane potential (ΔΨ) and swelling in rat heart mitochondrial preparations. We observed that 3 HTA and 3 HPA increased resting respiration and diminished the respiratory control and ADP/O ratios using glutamate/malate or succinate as substrates. Furthermore, 3 HDDA, 3 HTA and 3 HPA decreased ΔΨ, the matrix NAD(P)H pool and hydrogen peroxide production. These data indicate that these fatty acids behave as uncouplers of oxidative phosphorylation. We also verified that 3 HTA-induced uncoupling-effect was not mediated by the adenine nucleotide translocator and that this fatty acid induced the mitochondrial permeability transition pore opening in calcium-loaded organelles since cyclosporin A prevented the reduction of mitochondrial ΔΨ and swelling provoked by 3 HTA. The present data indicate that major 3-hydroxylated fatty acids accumulating in MTP and LCHAD deficiencies behave as strong uncouplers of oxidative phosphorylation potentially impairing heart energy homeostasis.

Mitochondria: A mirror into cellular dysfunction in heart disease

Cardiovascular (CV) disease is the single most significant cause of morbidity and mortality worldwide. The emerging global impact of CV disease means that the goals of early diagnosis and a wider range of treatment options are now increasingly pertinent. As such, there is a greater need to understand the molecular mechanisms involved and potential targets for intervention. Mitochondrial function is important for physiological maintenance of the cell, and when this function is altered, the cell can begin to suffer. Given the broad range and significant impacts of the cellular processes regulated by the mitochondria, it becomes important to understand the roles of the proteins associated with this organelle. Proteomic investigations of the mitochondria are hampered by the intrinsic properties of the organelle, including hydrophobic mitochondrial membranes; high proportion of basic proteins (pI greater than 8.0); and the relative dynamic range issues of the mitochondria. For these reasons, many proteomic studies investigate the mitochondria as a discrete subproteome. Once this has been achieved, the alterations that result in functional changes with CV disease can be observed. Those alterations that lead to changes in mitochondrial function, signaling and morphology, which have significant implications for the cardiomyocyte in the development of CV disease, are discussed.

The neuroprotective effect of diazoxide is mediated by mitochondrial ATP-dependent potassium channels in a rat model of acute subdural hematoma

Acute subdural hematoma (ASDH) results in neuronal death due to mitochondrial dysfunction and a subsequent cascade of apoptotic and necrotic events. We previously demonstrated that mitochondrial ATP-dependent potassium (mitoK(ATP)) channels have a major role in cerebral ischemic preconditioning in vivo and in vitro. However, the role of the mitoK(ATP) channel has not been investigated in the context of ASDH. Thus, the purpose of this study was to determine whether the mitoK(ATP) channel mediates neuroprotection in a rat model of ASDH. Male Wistar rats were subjected to subdural infusion of 400 μL autologous venous blood. The rats were assigned to four experimental groups pretreated intraventricularly 15 minutes before ASDH with (1) vehicle (n=10); (2) the mitoK(ATP) channel agonist diazoxide (n=9); (3) diazoxide plus the selective mitoK(ATP) channel antagonist 5-hydroxydecanoate (5-HD) (n=6); or (4) 5-HD alone (n=6). Infarct volume was assessed at 4 days after ASDH. Brain edema formation was also measured. Pretreatment with diazoxide significantly reduced infarct volume and brain edema formation after ASDH. However, the effects of diazoxide were abolished by co-treatment with 5-HD. 5-HD alone increased infarct volume. These data suggest that the mitoK(ATP) channel is an important mediator of the neuroprotective effects of cerebral preconditioning in a rat model of ASDH.

Activity of mitochondrial ATP-dependent potassium channel in animals with different resistance to hypoxia before and after the course of hypoxic training

Activity of mitochondrial ATP-dependent potassium channel in rats with high genetically determined resistance to hypoxia was higher than in sensitive animals. Adaptation of low resistant rats to hypoxia was accompanied by activation of the channel, facilitation of potassium recycling in mitochondria, and a decrease in the rate of H2O2 formation. Our results indicate that mitochondrial ATP-dependent potassium channel plays an important role in the delayed mechanisms of animal's adaptation to hypoxia.

Diazoxide attenuates ischemia/reperfusion injury via upregulation of heme oxygenase-1 after liver transplantation in rats

AIM: To evaluate the effects of diazoxide on ischemia/reperfusion (I/R)-injured hepatocytes and further elucidate its underlying mechanisms.

METHODS: Male Sprague-Dawley rats were randomized (8 for donor and recipient per group) into five groups: I/R group (4 h of liver cold ischemia followed by 6 h of reperfusion); heme oxygenase-1 (HO-1) small interfering RNA (siRNA) group (injection of siRNA via donor portal vein 48 h prior to harvest); diazoxide (DZ) group (injection of DZ via donor portal vein 10 min prior to harvest); HO-1 siRNA + DZ group; and siRNA control group. Blood and liver samples were collected at 6 h after reperfusion. The mRNA expressions and protein levels of HO-1 were determined by reverse transcription polymerase chain reaction and Western blotting, and tissue morphology was examined by light and transmission electron microscopy. Serum transaminases level and cytokines concentration were also measured.

RESULTS: We observed that a significant reduction of HO-1 mRNA and protein levels in HO-1 siRNA and HO-1 siRNA + DZ group when compared with I/R group, while the increases were prominent in the DZ group. Light and transmission electron microscopy indicated severe disruption of tissue with lobular distortion and mitochondrial cristae damage in the HO-1 siRNA and HO-1 siRNA + DZ groups compared with DZ group. Serum alanine aminotransferase, aspartate transaminase, tumor necrosis factor-α and interleukin-6 levels increased in the HO-1 siRNA and HO-1 siRNA + DZ groups, and decreased in the DZ group.

CONCLUSION: The protective effect of DZ may be induced by upregulation of HO-1. By inhibiting expression of HO-1, this protection pretreated with DZ was abolished.

Phytanic acid disturbs mitochondrial homeostasis in heart of young rats: a possible pathomechanism of cardiomyopathy in Refsum disease

Phytanic acid (Phyt) accumulates in tissues and biological fluids of patients affected by Refsum disease. Although cardiomyopathy is an important clinical manifestation of this disorder, the mechanisms of heart damage are poorly known. In the present study, we investigated the in vitro effects of Phyt on important parameters of oxidative stress in heart of young rats. Phyt significantly increased thiobarbituric acid-reactive substances levels (P < 0.001) and carbonyl formation (P < 0.01), indicating that this fatty acid induces lipid and protein oxidative damage, respectively. In contrast, Phyt did not alter sulfhydryl oxidation. Phyt also decreased glutathione (GSH) concentrations (P < 0.05), an important non-enzymatic antioxidant defense. Moreover, Phyt increased 2',7'-dichlorofluorescin oxidation (DCFH) (P < 0.01), reflecting increased reactive species generation. We also found that the induced lipid and protein oxidative damage, as well as the decreased GSH levels and increased DCFH oxidation provoked by this fatty acid were prevented or attenuated by the reactive oxygen species scavengers melatonin, trolox, and GSH, but not by the nitric oxide inhibitor N: (ω)-nitro-L: -arginine methyl ester, suggesting that reactive oxygen species were involved in these effects. Next, we verified that Phyt strongly inhibited NADH-cytochrome c oxidoreductase (complex I-III) activity (P < 0.001) in heart supernatants, and decreased membrane potential and the NAD(P)H pool in heart mitochondria, indicating that Phyt acts as a metabolic inhibitor and as an uncoupler of the electron transport chain. Therefore, it can be presumed that disturbance of cellular energy and redox homeostasis induced by Phyt may possibly contribute to the cardiomyopathy found in patients affected by Refsum disease.

Lindera strychnifolia is Protective Against Post-ischemic Myocardial Dysfunction Through Scavenging Hydroxyl Radicals and Opening the Mitochondrial KATP Channels in Isolated Rat Hearts

Lindera strychnifolia (Tendai-Uyaku), a medicinal plant, has long been used for the treatment of cardiac, renal and rheumatic diseases in Japan. We aim to clarify (1) whether L. strychnifolia is protective against post-ischemic myocardial dysfunction, and (2) whether its effect is related to scavenging hydroxyl radicals and opening the mitochondrial K ATP channels in isolated rat hearts. Male Sprague-Dawley rats were orally given 1 ml/day of L. strychnifolia, which was extracted from 0.75 and 1.5 g/kg of roots of L. strychnifolia for 4 days. The rat hearts were excised and perfused on a Langendorff apparatus with Krebs-Henseleit solution with a gas mixture of 95% O 2 and 5% CO 2. The hearts were paced at 320 beats/min except during ischemia. Left ventricular developed pressure (LVDP, mmHg), ± dP/dt (mmHg/sec) and coronary flow (ml/min) were continuously monitored. All hearts were perfused for a total of 120 minutes consisting of a 30-minute pre-ischemic period followed by 30 minutes of global ischemia and 60 minutes of reperfusion with or without 5-HD, a mitochondrial K ATP channel blocker. The levels of lactate, LDH and 2,5-DHBA, an indicator of hydroxyl radicals, in the perfusate during reperfusion period were also measured. Treatment with L. strychnifolia significantly improved LVDP and ± dP/dt without altering coronary flow during reperfusion. The 100 μM of 5-HD in Krebs-Henseleit solution was perfused during the 10 minutes of pre-ischemic periods. Pretreatment with 5-HD abolished the improvement of LVDP and ± dP/dt by L. strychnifolia. L. strychnifolia significantly attenuated the levels of lactate, LDH and 2,5-DHBA during reperfusion, and which were restored by pretreatment with 5-HD. In conclusion, L. strychnifolia is protective against post-ischemic left ventricular dysfunction through scavenging hydroxyl radicals and opening the K ATP channels in the isolated rat heart.

Mitochondrial therapeutics for cardioprotection

Mitochondria represent approximately one-third of the mass of the heart and play a critical role in maintaining cellular function-however, they are also a potent source of free radicals and pro-apoptotic factors. As such, maintaining mitochondrial homeostasis is essential to cell survival. As the dominant source of ATP, continuous quality control is mandatory to ensure their ongoing optimal function. Mitochondrial quality control is accomplished by the dynamic interplay of fusion, fission, autophagy, and mitochondrial biogenesis. This review examines these processes in the heart and considers their role in the context of ischemia-reperfusion injury. Interventions that modulate mitochondrial turnover, including pharmacologic agents, exercise, and caloric restriction are discussed as a means to improve mitochondrial quality control, ameliorate cardiovascular dysfunction, and enhance longevity.

Physiology of potassium channels in the inner membrane of mitochondria

The inner membrane of the ATP-producing organelles of endosymbiotic origin, mitochondria, has long been considered to be poorly permeable to cations and anions, since the strict control of inner mitochondrial membrane permeability is crucial for efficient ATP synthesis. Over the past 30 years, however, it has become clear that various ion channels--along with antiporters and uniporters--are present in the mitochondrial inner membrane, although at rather low abundance. These channels are important for energy supply, and some are a decisive factor in determining whether a cell lives or dies. Their electrophysiological and pharmacological characterisations have contributed importantly to the ongoing elucidation of their pathophysiological roles. This review gives an overview of recent advances in our understanding of the functions of the mitochondrial potassium channels identified so far. Open issues concerning the possible molecular entities giving rise to the observed activities and channel protein targeting to mitochondria are also discussed.