Inhibitory effects of adenine nucleotides on brain mitochondrial permeability transition

Disturbances in mitochondrial bioenergetics and control quality and unbalanced redox homeostasis in the liver of a mouse model of mucopolysaccharidosis type II

Mucopolysaccharidosis type II (MPS II; Hunter syndrome) is a lysosomal storage disease caused by mutations in the gene encoding the enzyme iduronate 2-sulfatase (IDS) and biochemically characterized by the accumulation of glycosaminoglycans (GAGs) in different tissues. It is a multisystemic disorder that presents liver abnormalities, the pathophysiology of which is not yet established. In the present study, we evaluated bioenergetics, redox homeostasis, and mitochondrial dynamics in the liver of 6-month-old MPS II mice (IDS-). Our findings show a decrease in the activity of α-ketoglutarate dehydrogenase and an increase in the activities of succinate dehydrogenase and malate dehydrogenase. The activity of mitochondrial complex I was also increased whereas the other complex activities were not affected. In contrast, mitochondrial respiration, membrane potential, ATP production, and calcium retention capacity were not altered. Furthermore, malondialdehyde levels and 2',7'-dichlorofluorescein oxidation were increased in the liver of MPS II mice, indicating lipid peroxidation and increased ROS levels, respectively. Sulfhydryl and reduced glutathione levels, as well as glutathione S-transferase, glutathione peroxidase (GPx), superoxide dismutase, and catalase activities were also increased. Finally, the levels of proteins involved in mitochondrial mass and dynamics were decreased in knockout mice liver. Taken together, these data suggest that alterations in energy metabolism, redox homeostasis, and mitochondrial dynamics can be involved in the pathophysiology of liver abnormalities observed in MPS II.

Disturbance of mitochondrial functions caused by N-acetylglutamate and N-acetylmethionine in brain of adolescent rats: Potential relevance in aminoacylase 1 deficiency

Aminoacylase 1 (ACY1) deficiency is a rare genetic disorder that affects the breakdown of short-chain aliphatic N-acetylated amino acids, leading to the accumulation of these amino acid derivatives in the urine of patients. Some of the affected individuals have presented with heterogeneous neurological symptoms such as psychomotor delay, seizures, and intellectual disability. Considering that the pathological mechanisms of brain damage in this disorder remain mostly unknown, here we investigated whether major metabolites accumulating in ACY1 deficiency, namely N-acetylglutamate (NAG) and N-acetylmethionine (NAM), could be toxic to the brain by examining their in vitro effects on important mitochondrial properties. We assessed the effects of NAG and NAM on membrane potential, swelling, reducing equivalents, and Ca2+ retention capacity in purified mitochondrial preparations obtained from the brain of adolescent rats. NAG and NAM decreased mitochondrial membrane potential, reducing equivalents, and calcium retention capacity, and induced swelling in Ca2+-loaded brain mitochondria supported by glutamate plus malate. Notably, these changes were completely prevented by the classical inhibitors of mitochondrial permeability transition (MPT) pore cyclosporin A plus ADP and by ruthenium red, implying the participation of MPT and Ca2+ in these effects. Our findings suggest that NAG- and NAM-induced disruption of mitochondrial functions involving MPT may represent relevant mechanisms of neuropathology in ACY1 deficiency.

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.

Disruption of mitochondrial functions involving mitochondrial permeability transition pore opening caused by maleic acid in rat kidney

Propionic acid (PA) predominantly accumulates in tissues and biological fluids of patients affected by propionic acidemia that may manifest chronic renal failure along development. High urinary excretion of maleic acid (MA) has also been described. Considering that the underlying mechanisms of renal dysfunction in this disorder are poorly known, the present work investigated the effects of PA and MA (1-5 mM) on mitochondrial functions and cellular viability in rat kidney and cultured human embryonic kidney (HEK-293) cells. Mitochondrial membrane potential (∆ψm), NAD(P)H content, swelling and ATP production were measured in rat kidney mitochondrial preparations supported by glutamate or glutamate plus malate, in the presence or absence of Ca²⁺. MTT reduction and propidium iodide (PI) incorporation were also determined in intact renal cells pre-incubated with MA or PA for 24 h. MA decreased Δψm and NAD(P)H content and induced swelling in Ca²⁺-loaded mitochondria either respiring with glutamate or glutamate plus malate. Noteworthy, these alterations were fully prevented by cyclosporin A plus ADP, suggesting the involvement of mitochondrial permeability transition (mPT). MA also markedly inhibited ATP synthesis in kidney mitochondria using the same substrates, implying a strong bioenergetics impairment. In contrast, PA only caused milder changes in these parameters. Finally, MA decreased MTT reduction and increased PI incorporation in intact HEK-293 cells, indicating a possible association between mitochondrial dysfunction and cell death in an intact cell system. It is therefore presumed that the MA-induced disruption of mitochondrial functions involving mPT pore opening may be involved in the chronic renal failure occurring in propionic acidemia.

Enhanced resistance to Ca2+-induced mitochondrial permeability transition in the long-lived red-footed tortoise Chelonoidis carbonaria

The interaction between supraphysiological cytosolic Ca2+ levels and mitochondrial redox imbalance mediates the mitochondrial permeability transition (MPT). The MPT is involved in cell death, diseases and aging. This study compared the liver mitochondrial Ca2+ retention capacity and oxygen consumption in the long-lived red-footed tortoise (Chelonoidis carbonaria) with those in the rat as a reference standard. Mitochondrial Ca2+ retention capacity, a quantitative measure of MPT sensitivity, was remarkably higher in tortoises than in rats. This difference was minimized in the presence of the MPT inhibitors ADP and cyclosporine A. However, the Ca2+ retention capacities of tortoise and rat liver mitochondria were similar when both MPT inhibitors were present simultaneously. NADH-linked phosphorylating respiration rates of tortoise liver mitochondria represented only 30% of the maximal electron transport system capacity, indicating a limitation imposed by the phosphorylation system. These results suggested underlying differences in putative MPT structural components [e.g. ATP synthase, adenine nucleotide translocase (ANT) and cyclophilin D] between tortoises and rats. Indeed, in tortoise mitochondria, titrations of inhibitors of the oxidative phosphorylation components revealed a higher limitation of ANT. Furthermore, cyclophilin D activity was approximately 70% lower in tortoises than in rats. Investigation of critical properties of mitochondrial redox control that affect MPT demonstrated that tortoise and rat liver mitochondria exhibited similar rates of H2O2 release and glutathione redox status. Overall, our findings suggest that constraints imposed by ANT and cyclophilin D, putative components or regulators of the MPT pore, are associated with the enhanced resistance to Ca2+-induced MPT in tortoises.

S-adenosylmethionine induces mitochondrial dysfunction, permeability transition pore opening and redox imbalance in subcellular preparations of rat liver

S-adenosylmethionine (AdoMet) predominantly accumulates in tissues and biological fluids of patients affected by liver dysmethylating diseases, particularly glycine N-methyltransferase, S-adenosylhomocysteine hydrolase and adenosine kinase deficiencies, as well as in some hepatic mtDNA depletion syndromes, whose pathogenesis of liver dysfunction is still poorly established. Therefore, in the present work, we investigated the effects of S-adenosylmethionine (AdoMet) on mitochondrial functions and redox homeostasis in rat liver. AdoMet decreased mitochondrial membrane potential and Ca²⁺ retention capacity, and these effects were fully prevented by cyclosporin A and ADP, indicating mitochondrial permeability transition (mPT) induction. It was also verified that the thiol-alkylating agent NEM prevented AdoMet-induced ΔΨm dissipation, implying a role for thiol oxidation in the mPT pore opening. AdoMet also increased ROS production and provoked protein and lipid oxidation. Furthermore, AdoMet reduced GSH levels and the activities of aconitase and α-ketoglutarate dehydrogenase. Free radical scavengers attenuated AdoMet effects on lipid peroxidation and GSH levels, supporting a role of ROS in these effects. It is therefore presumed that disturbance of mitochondrial functions associated with mPT and redox unbalance may represent relevant pathomechanisms of liver damage provoked by AdoMet in disorders in which this metabolite accumulates.

Ethylmalonic acid impairs bioenergetics by disturbing succinate and glutamate oxidation and induces mitochondrial permeability transition pore opening in rat cerebellum

Tissue accumulation and high urinary excretion of ethylmalonic acid (EMA) are found in ethylmalonic encephalopathy (EE), an inherited disorder associated with cerebral and cerebellar atrophy whose pathogenesis is poorly established. The in vitro and in vivo effects of EMA on bioenergetics and redox homeostasis were investigated in rat cerebellum. For the in vitro studies, cerebellum preparations were exposed to EMA, whereas intracerebellar injection of EMA was used for the in vivo evaluation. EMA reduced state 3 and uncoupled respiration in vitro in succinate-, glutamate-, and malate-supported mitochondria, whereas decreased state 4 respiration was observed using glutamate and malate. Furthermore, mitochondria permeabilization and succinate supplementation diminished the decrease in state 3 with succinate. EMA also inhibited the activity of KGDH, an enzyme necessary for glutamate oxidation, in a mixed manner and augmented mitochondrial efflux of α-ketoglutarate. ATP levels were markedly reduced by EMA, reflecting a severe bioenergetic disruption. Docking simulations also indicated interactions between EMA and KGDH and a competition with glutamate and succinate for their mitochondrial transporters. In vitro findings also showed that EMA decreased mitochondrial membrane potential and Ca²⁺ retention capacity, and induced swelling in the presence of Ca²⁺ , which were prevented by cyclosporine A and ADP and ruthenium red, indicating mitochondrial permeability transition (MPT). Moreover, EMA, at high concentrations, mildly increased ROS levels and altered antioxidant defenses in vitro and in vivo. Our data indicate that EMA-induced impairment of glutamate and succinate oxidation and MPT may contribute to the pathogenesis of the cerebellum abnormalities in EE.

Adenylate kinase derived ATP shapes respiration and calcium storage of isolated mitochondria

The ratio of ADP and ATP is a natural indicator of cellular bioenergetic state and thus a prominent analyte in metabolism research. Beyond adenylate interconversion via oxidative phosphorylation and ATPase activities, ADP and ATP act as steric regulators of enzymes, e.g. cytochrome C oxidase, and are major factors in mitochondrial calcium storage potential. Consideration of all routes of adenylate conversion is critical to successfully predict their abundance in an experimental system and to correctly interpret many aspects of mitochondrial function. We showcase here how adenylate kinases elicit considerable impact on the outcome of a variety of mitochondrial assays through their drastic manipulation of the adenylate profile. Parameters affected include cytochrome c oxidase activity, P/O ratio, and mitochondrial calcium dynamics. Study of the latter revealed that the presence of ATP is required for mitochondrial calcium to be shaped into a particularly dense form of mitochondrial amorphous calcium phosphate.

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.

Disturbance of mitochondrial functions associated with permeability transition pore opening induced by cis-5-tetradecenoic and myristic acids in liver of adolescent rats

Patients affected by very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency commonly present liver dysfunction whose pathogenesis is poorly known. We demonstrate here that major metabolites accumulating in this disorder, namely cis-5-tetradecenoic acid (Cis-5) and myristic acid (Myr), markedly impair mitochondrial respiration, decreasing ATP production in liver mitochondrial preparations from adolescent rats. Other parameters of mitochondrial homeostasis such as membrane potential (ΔΨm) and Ca²⁺retention capacity were strongly compromised by these fatty acids, involving induction of mitochondrial permeability transition. The present data indicate that disruption of mitochondrial bioenergetics and Ca²⁺homeostasis may contribute to the liver dysfunction of VLCAD deficient patients.

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.

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.

Bioenergetics dysfunction, mitochondrial permeability transition pore opening and lipid peroxidation induced by hydrogen sulfide as relevant pathomechanisms underlying the neurological dysfunction characteristic of ethylmalonic encephalopathy

Hydrogen sulfide (sulfide) accumulates at high levels in brain of patients with ethylmalonic encephalopathy (EE). In the present study, we evaluated whether sulfide could disturb energy and redox homeostasis, and induce mitochondrial permeability transition (mPT) pore opening in rat brain aiming to better clarify the neuropathophysiology of EE. Sulfide decreased the activities of citrate synthase and aconitase in rat cerebral cortex mitochondria, and of creatine kinase (CK) in rat cerebral cortex, striatum and hippocampus supernatants. Glutathione prevented sulfide-induced CK activity decrease in the cerebral cortex. Sulfide also diminished mitochondrial respiration in cerebral cortex homogenates, and dissipated mitochondrial membrane potential (ΔΨm) and induced swelling in the presence of calcium in brain mitochondria. Alterations in ΔΨm and swelling caused by sulfide were prevented by the combination of ADP and cyclosporine A, and by ruthenium red, indicating the involvement of mPT in these effects. Furthermore, sulfide increased the levels of malondialdehyde in cerebral cortex supernatants, which was prevented by resveratrol and attenuated by glutathione, and of thiol groups in a medium devoid of brain samples. Finally, we verified that sulfide did not alter cell viability and DCFH oxidation in cerebral cortex slices, primary cortical astrocyte cultures and SH-SY5Y cells. Our data provide evidence that bioenergetics disturbance and lipid peroxidation along with mPT pore opening are involved in the pathophysiology of brain damage observed in EE.

Mevalonolactone disrupts mitochondrial functions and induces permeability transition pore opening in rat brain mitochondria: Implications for the pathogenesis of mevalonic aciduria

Mevalonic aciduria (MVA) is caused by severe deficiency of mevalonic kinase activity leading to tissue accumulation and high urinary excretion of mevalonic acid (MA) and mevalonolactone (ML). Patients usually present severe neurologic symptoms whose pathophysiology is poorly known. Here, we tested the hypothesis that the major accumulating metabolites are toxic by investigating the in vitro effects of MA and ML on important mitochondrial functions in rat brain and liver mitochondria. ML, but not MA, markedly decreased mitochondrial membrane potential (ΔΨm), NAD(P)H content and the capacity to retain Ca²⁺ in the brain, besides inducing mitochondrial swelling. These biochemical alterations were totally prevented by the classical inhibitors of mitochondrial permeability transition (MPT) cyclosporine A and ADP, as well as by ruthenium red in Ca²⁺-loaded mitochondria, indicating the involvement of MPT and an important role for mitochondrial Ca²⁺ in these effects. ML also induced lipid peroxidation and markedly inhibited aconitase activity, an enzyme that is highly susceptible to free radical attack, in brain mitochondrial fractions, indicating that lipid and protein oxidative damage may underlie some of ML-induced deleterious effects including MTP induction. In contrast, ML and MA did not compromise oxidative phosphorylation in the brain and all mitochondrial functions evaluated in the liver, evidencing a selective toxicity of ML towards the central nervous system. Our present study provides for the first time evidence that ML impairs essential brain mitochondrial functions with the involvement of MPT pore opening. It is therefore presumed that disturbance of brain mitochondrial homeostasis possibly contributes to the neurologic symptoms in MVA.

Disturbance of mitochondrial functions provoked by the major long-chain 3-hydroxylated fatty acids accumulating in MTP and LCHAD deficiencies in skeletal muscle

The pathogenesis of the muscular symptoms and recurrent rhabdomyolysis that are commonly manifested in patients with mitochondrial trifunctional protein (MTP) and long-chain 3-hydroxy-acyl-CoA dehydrogenase (LCHAD) deficiencies is still unknown. In this study we investigated the effects of the major long-chain monocarboxylic 3-hydroxylated fatty acids (LCHFA) accumulating in these disorders, namely 3-hydroxytetradecanoic (3HTA) and 3-hydroxypalmitic (3HPA) acids, on important mitochondrial functions in rat skeletal muscle mitochondria. 3HTA and 3HPA markedly increased resting (state 4) and decreased ADP-stimulated (state 3) and CCCP-stimulated (uncoupled) respiration. 3HPA provoked similar effects in permeabilized skeletal muscle fibers, validating the results obtained in purified mitochondria. Furthermore, 3HTA and 3HPA markedly diminished mitochondrial membrane potential, NAD(P)H content and Ca(2+) retention capacity in Ca(2+)-loaded mitochondria. Mitochondrial permeability transition (mPT) induction probably underlie these effects since they were totally prevented by cyclosporin A and ADP. In contrast, the dicarboxylic analogue of 3HTA did not alter the tested parameters. Our data strongly indicate that 3HTA and 3HPA behave as metabolic inhibitors, uncouplers of oxidative phosphorylation and mPT inducers in skeletal muscle. It is proposed that these pathomechanisms disrupting mitochondrial homeostasis may be involved in the muscle alterations characteristic of MTP and LCHAD deficiencies.

cis-4-Decenoic and decanoic acids impair mitochondrial energy, redox and Ca(2+) homeostasis and induce mitochondrial permeability transition pore opening in rat brain and liver: Possible implications for the pathogenesis of MCAD deficiency

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is biochemically characterized by tissue accumulation of octanoic (OA), decanoic (DA) and cis-4-decenoic (cDA) acids, as well as by their carnitine by-products. Untreated patients present episodic encephalopathic crises and biochemical liver alterations, whose pathophysiology is poorly known. We investigated the effects of OA, DA, cDA, octanoylcarnitine (OC) and decanoylcarnitine (DC) on critical mitochondrial functions in rat brain and liver. DA and cDA increased resting respiration and diminished ADP- and CCCP-stimulated respiration and complexes II-III and IV activities in both tissues. The data indicate that these compounds behave as uncouplers and metabolic inhibitors of oxidative phosphorylation. Noteworthy, metabolic inhibition was more evident in brain as compared to liver. DA and cDA also markedly decreased mitochondrial membrane potential, NAD(P)H content and Ca(2+) retention capacity in Ca(2+)-loaded brain and liver mitochondria. The reduction of Ca(2+) retention capacity was more pronounced in liver and totally prevented by cyclosporine A and ADP, as well as by ruthenium red, demonstrating the involvement of mitochondrial permeability transition (mPT) and Ca(2+). Furthermore, cDA induced lipid peroxidation in brain and liver mitochondria and increased hydrogen peroxide formation in brain, suggesting the participation of oxidative damage in cDA-induced alterations. Interestingly, OA, OC and DC did not alter the evaluated parameters, implying lower toxicity for these compounds. Our results suggest that DA and cDA, in contrast to OA and medium-chain acylcarnitines, disturb important mitochondrial functions in brain and liver by multiple mechanisms that are possibly involved in the neuropathology and liver alterations observed in MCAD deficiency.

2-Methylcitric acid impairs glutamate metabolism and induces permeability transition in brain mitochondria

Accumulation of 2-methylcitric acid (2MCA) is observed in methylmalonic and propionic acidemias, which are clinically characterized by severe neurological symptoms. The exact pathogenetic mechanisms of brain abnormalities in these diseases are poorly established and very little has been reported on the role of 2MCA. In the present work we found that 2MCA markedly inhibited ADP-stimulated and uncoupled respiration in mitochondria supported by glutamate, with a less significant inhibition in pyruvate plus malate respiring mitochondria. However, no alterations occurred when α-ketoglutarate or succinate was used as respiratory substrates, suggesting a defect on glutamate oxidative metabolism. It was also observed that 2MCA decreased ATP formation in glutamate plus malate or pyruvate plus malate-supported mitochondria. Furthermore, 2MCA inhibited glutamate dehydrogenase activity at concentrations as low as 0.5 mM. Kinetic studies revealed that this inhibitory effect was competitive in relation to glutamate. In contrast, assays of osmotic swelling in non-respiring mitochondria suggested that 2MCA did not significantly impair mitochondrial glutamate transport. Finally, 2MCA provoked a significant decrease in mitochondrial membrane potential and induced swelling in Ca(2+)-loaded mitochondria supported by different substrates. These effects were totally prevented by cyclosporine A plus ADP or ruthenium red, indicating induction of mitochondrial permeability transition. Taken together, our data strongly indicate that 2MCA behaves as a potent inhibitor of glutamate oxidation by inhibiting glutamate dehydrogenase activity and as a permeability transition inducer, disturbing mitochondrial energy homeostasis. We presume that 2MCA-induced mitochondrial deleterious effects may contribute to the pathogenesis of brain damage in patients affected by methylmalonic and propionic acidemias. We propose that brain glutamate oxidation is disturbed by 2-methylcitric acid (2MCA), which accumulates in tissues from patients with propionic and methylmalonic acidemias because of a competitive inhibition of glutamate dehydrogenase (GDH) activity. 2MCA also induced mitochondrial permeability transition (PT) and decreased ATP generation in brain mitochondria. We believe that these pathomechanisms may be involved in the neurological dysfunction of these diseases.

Increased Susceptibility of Gracilinanus microtarsus Liver Mitochondria to Ca²⁺-Induced Permeability Transition Is Associated with a More Oxidized State of NAD(P)

In addition to be the cell's powerhouse, mitochondria also contain a cell death machinery that includes highly regulated processes such as the membrane permeability transition pore (PTP) and reactive oxygen species (ROS) production. In this context, the results presented here provide evidence that liver mitochondria isolated from Gracilinanus microtarsus, a small and short life span (one year) marsupial, when compared to mice, are much more susceptible to PTP opening in association with a poor NADPH dependent antioxidant capacity. Liver mitochondria isolated from the marsupial are well coupled and take up Ca²⁺ but exhibited a much lower Ca²⁺ retention capacity than mouse mitochondria. Although the known PTP inhibitors cyclosporin A, ADP, and ATP significantly increased the marsupial mitochondria capacity to retain Ca²⁺, their effects were much larger in mice than in marsupial mitochondria. Both fluorescence and HPLC analysis of mitochondrial nicotinamide nucleotides showed that both content and state of reduction (mainly of NADPH) were lower in the marsupial mitochondria than in mice mitochondria despite the similarity in the activity of the glutathione peroxidase/reductase system. Overall, these data suggest that PTP opening is an important event in processes of Ca²⁺ signalling to cell death mediated by mitochondrial redox imbalance in G. microtarsus.

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.

Uncoupling, metabolic inhibition and induction of mitochondrial permeability transition in rat liver mitochondria caused by the major long-chain hydroxyl monocarboxylic fatty acids accumulating in LCHAD deficiency

Patients with long-chain 3-hydroxy-acyl-CoA dehydrogenase (LCHAD) deficiency commonly present liver dysfunction whose pathogenesis is unknown. We studied the effects of long-chain 3-hydroxylated fatty acids (LCHFA) that accumulate in LCHAD deficiency on liver bioenergetics using mitochondrial preparations from young rats. We provide strong evidence that 3-hydroxytetradecanoic (3HTA) and 3-hydroxypalmitic (3HPA) acids, the monocarboxylic acids that are found at the highest tissue concentrations in this disorder, act as metabolic inhibitors and uncouplers of oxidative phosphorylation. These conclusions are based on the findings that these fatty acids decreased ADP-stimulated (state 3) and uncoupled respiration, mitochondrial membrane potential and NAD(P)H content, and, in contrast, increased resting (state 4) respiration. We also verified that 3HTA and 3HPA markedly reduced Ca2+ retention capacity and induced swelling in Ca2+-loaded mitochondria. These effects were mediated by mitochondrial permeability transition (MPT) induction since they were totally prevented by the classical MPT inhibitors cyclosporin A and ADP, as well as by ruthenium red, a Ca2+ uptake blocker. Taken together, our data demonstrate that the major monocarboxylic LCHFA accumulating in LCHAD deficiency disrupt energy mitochondrial homeostasis in the liver. It is proposed that this pathomechanism may explain at least in part the hepatic alterations characteristic of the affected patients.

Antioxidant effects of JM-20 on rat brain mitochondria and synaptosomes: mitoprotection against Ca²⁺-induced mitochondrial impairment

Because mitochondrial oxidative stress and impairment are important mediators of neuronal damage in neurodegenerative diseases and in brain ischemia/reperfusion, in the present study, we evaluated the antioxidant and mitoprotective effect of a new promising neuroprotective molecule, JM-20, in mitochondria and synaptosomes isolated from rat brains. JM-20 inhibited succinate-mediated H₂O₂ generation in both mitochondria and synaptosomes incubated in depolarized (high K(+)) medium at extremely low micromolar concentration and with identical IC₅₀ values of 0.91 μM. JM-20 also repressed glucose-induced H₂O₂ generation stimulated by rotenone or by antimycin A in synaptosomes incubated in high sodium-polarized medium at extremely low IC₅₀ values of 0.395 μM and 2.452 μM, respectively. JM-20 was unable to react directly with H₂O₂ or with superoxide anion radicals but displayed a cathodic reduction peak at -0.71V, which is close to that of oxygen (-0.8V), indicating high electron affinity. JM-20 also inhibited uncoupled respiration in mitochondria or synaptosomes and was a more effective inhibitor in the presence of the respiratory substrates glutamate/malate than in the presence of succinate. JM-20 also prevented Ca(2+)-induced mitochondrial permeability transition pore opening, membrane potential dissipation and cytochrome c release, which are key pathogenic events during stroke. This molecule also prevented Ca(2+) influx into synaptosomes and mitochondria; the former effect was a consequence of the latter because JM-20 inhibition followed the patterns of carbonyl cyanide p-trifluoromethoxyphenyl hydrazone (FCCP), which is a classic mitochondrial uncoupler. Because the mitochondrion is considered an important source and target of neuronal cell death signaling after an ischemic insult, the antioxidant and protective effects of JM-20 against the deleterious effects of Ca(2+) observed at the mitochondrial level in this study may endow this molecule with the ability to succeed in mitochondrion-targeted strategies to combat ischemic brain damage.

Mitochondrial bioenergetics deregulation caused by long-chain 3-hydroxy fatty acids accumulating in LCHAD and MTP deficiencies in rat brain: a possible role of mPTP opening as a pathomechanism in these disorders?

Long-chain 3-hydroxylated fatty acids (LCHFA) accumulate in long-chain 3-hydroxy-acyl-CoA dehydrogenase (LCHAD) and mitochondrial trifunctional protein (MTP) deficiencies. Affected patients usually present severe neonatal symptoms involving cardiac and hepatic functions, although long-term neurological abnormalities are also commonly observed. Since the underlying mechanisms of brain damage are practically unknown and have not been properly investigated, we studied the effects of LCHFA on important parameters of mitochondrial homeostasis in isolated mitochondria from cerebral cortex of developing rats. 3-Hydroxytetradecanoic acid (3 HTA) reduced mitochondrial membrane potential, NAD(P)H levels, Ca(2+) retention capacity and ATP content, besides inducing swelling, cytochrome c release and H2O2 production in Ca(2+)-loaded mitochondrial preparations. We also found that cyclosporine A plus ADP, as well as ruthenium red, a Ca(2+) uptake blocker, prevented these effects, suggesting the involvement of the mitochondrial permeability transition pore (mPTP) and an important role for Ca(2+), respectively. 3-Hydroxydodecanoic and 3-hydroxypalmitic acids, that also accumulate in LCHAD and MTP deficiencies, similarly induced mitochondrial swelling and decreased ATP content, but to a variable degree pending on the size of their carbon chain. It is proposed that mPTP opening induced by LCHFA disrupts brain bioenergetics and may contribute at least partly to explain the neurologic dysfunction observed in patients affected by LCHAD and MTP deficiencies.

Sulfite disrupts brain mitochondrial energy homeostasis and induces mitochondrial permeability transition pore opening via thiol group modification

Sulfite oxidase (SO) deficiency is biochemically characterized by the accumulation of sulfite, thiosulfate and S-sulfocysteine in tissues and biological fluids of the affected patients. The main clinical symptoms include severe neurological dysfunction and brain abnormalities, whose pathophysiology is still unknown. The present study investigated the in vitro effects of sulfite and thiosulfate on mitochondrial homeostasis in rat brain mitochondria. It was verified that sulfite per se, but not thiosulfate, decreased state 3, CCCP-stimulated state and respiratory control ratio in mitochondria respiring with glutamate plus malate. In line with this, we found that sulfite inhibited the activities of glutamate and malate (MDH) dehydrogenases. In addition, sulfite decreased the activity of a commercial solution of MDH, that was prevented by antioxidants and dithiothreitol. Sulfite also induced mitochondrial swelling and reduced mitochondrial membrane potential, Ca(2+) retention capacity, NAD(P)H pool and cytochrome c immunocontent when Ca(2+) was present in the medium. These alterations were prevented by ruthenium red, cyclosporine A (CsA) and ADP, supporting the involvement of mitochondrial permeability transition (MPT) in these effects. We further observed that N-ethylmaleimide prevented the sulfite-elicited swelling and that sulfite decreased free thiol group content in brain mitochondria. These findings indicate that sulfite acts directly on MPT pore containing thiol groups. Finally, we verified that sulfite reduced cell viability in cerebral cortex slices and that this effect was prevented by CsA. Therefore, it may be presumed that disturbance of mitochondrial energy homeostasis and MPT induced by sulfite could be involved in the neuronal damage characteristic of SO deficiency.

A lectin from Bothrops leucurus snake venom raises cytosolic calcium levels and promotes B16-F10 melanoma necrotic cell death via mitochondrial permeability transition

BlL, a galactose-binding C-type lectin purified from Bothrops leucurus snake venom, exhibits anticancer activity. The current study was designed to elucidate the cellular mechanisms by which BlL induces melanoma cell death. The viabilities of B16-F10 melanoma cells and HaCaT keratinocytes treated with BlL were evaluated. Necrotic and apoptotic cell death, cytosolic Ca(2+) levels, mitochondrial Ca(2+) transport and superoxide levels were assessed in B16-F10 melanoma cells exposed to BlL. We found that treatment with BlL caused dose-dependent necrotic cell death in B16-F10 melanoma cells. Conversely, the viability of non-tumorigenic HaCaT cells was not affected by similar doses of BlL. BlL-induced B16-F10 necrosis was preceded by a significant (2-fold) increase in cytosolic calcium concentrations and a significant (3-fold) increase in mitochondrial superoxide generation. It is likely that BlL treatment triggers B16-F10 cell death via mitochondrial permeability transition (MPT) pore opening because the pharmacological MPT inhibitors bongkrekic acid and Debio 025 greatly attenuated BlL-induced cell death. Experiments evaluating mitochondrial Ca(2+) transport in permeabilized B16-F10 cells strongly supported the hypothesis that BlL rapidly stimulates cyclosporine A-sensitive Ca(2+)-induced MPT pore opening. We therefore conclude that BlL causes selective B16-F10 melanoma cell death via dysregulation of cellular Ca(2+) homeostasis and Ca(2+)-induced opening of MPT pore.

Ethylmalonic acid induces permeability transition in isolated brain mitochondria

Predominant accumulation of ethylmalonic acid (EMA) in tissues and biological fluids is a characteristic of patients affected by short chain acyl-CoA dehydrogenase deficiency and ethylmalonic encephalopathy. Neurological abnormalities are frequently found in these disorders, but the mechanisms underlying the brain injury are still obscure. Since hyperlacticacidemia is also found in many affected patients indicating a mitochondrial dysfunction; in the present work, we evaluated the in vitro and ex vivo effects of EMA plus Ca(2+) on mitochondrial integrity and redox balance in succinate-supported brain organelles. We verified that the evaluated parameters were disturbed only when EMA was associated with exogenous micromolar Ca(2+) concentrations. Thus, we found that this short chain organic acid plus Ca(2+) dissipated the membrane potential and provoked mitochondrial swelling, as well as impaired the mitochondrial Ca(2+) retention capacity, resulting in a rapid Ca(2+) release and decreased NAD(P)H matrix content. In contrast, EMA was not able to stimulate mitochondrial hydrogen peroxide generation. We also observed that all these effects were prevented by the mitochondrial Ca(2+) uptake inhibitor ruthenium red and the mitochondrial permeability transition (MPT) inhibitors cyclosporin A (CsA) and ADP. Furthermore, mitochondria isolated from rat brains after in vivo intrastriatal administration of EMA was more susceptible to Ca(2+)-induced swelling, which was fully prevented by CsA and ADP. Finally, EMA significantly decreased striatal slice viability, which was attenuated by CsA. The data strongly indicate that EMA reduced the mitochondrial threshold for Ca(2+)-induced MPT reinforcing the role of this cation in EMA-induced disruption of mitochondrial bioenergetics. It is, therefore, presumed that EMA acting synergistically with Ca(2+) compromises mitochondrial energy homeostasis in the central nervous system that may explain at least in part the neurologic alterations presented by patients with abnormal levels of this organic acid.

ADP protects cardiac mitochondria under severe oxidative stress

ADP is not only a key substrate for ATP generation, but also a potent inhibitor of mitochondrial permeability transition pore (mPTP). In this study, we assessed how oxidative stress affects the potency of ADP as an mPTP inhibitor and whether its reduction of reactive oxygen species (ROS) production might be involved. We determined quantitatively the effects of ADP on mitochondrial Ca(2+) retention capacity (CRC) until the induction of mPTP in normal and stressed isolated cardiac mitochondria. We used two models of chronic oxidative stress (old and diabetic mice) and two models of acute oxidative stress (ischemia reperfusion (IR) and tert-butyl hydroperoxide (t-BH)). In control mitochondria, the CRC was 344 ± 32 nmol/mg protein. 500 μmol/L ADP increased CRC to 774 ± 65 nmol/mg protein. This effect of ADP seemed to relate to its concentration as 50 μmol/L had a significantly smaller effect. Also, oligomycin, which inhibits the conversion of ADP to ATP by F0F1ATPase, significantly increased the effect of 50 μmol/L ADP. Chronic oxidative stress did not affect CRC or the effect of 500 μmol/L ADP. After IR or t-BH exposure, CRC was drastically reduced to 1 ± 0.2 and 32 ± 4 nmol/mg protein, respectively. Surprisingly, ADP increased the CRC to 447 ± 105 and 514 ± 103 nmol/mg protein in IR and t-BH, respectively. Thus, it increased CRC by the same amount as in control. In control mitochondria, ADP decreased both substrate and Ca(2+)-induced increase of ROS. However, in t-BH mitochondria the effect of ADP on ROS was relatively small. We conclude that ADP potently restores CRC capacity in severely stressed mitochondria. This effect is most likely not related to a reduction in ROS production. As the effect of ADP relates to its concentration, increased ADP as occurs in the pathophysiological situation may protect mitochondrial integrity and function.

Mitochondria as a source of reactive oxygen and nitrogen species: from molecular mechanisms to human health

Mitochondrially generated reactive oxygen species are involved in a myriad of signaling and damaging pathways in different tissues. In addition, mitochondria are an important target of reactive oxygen and nitrogen species. Here, we discuss basic mechanisms of mitochondrial oxidant generation and removal and the main factors affecting mitochondrial redox balance. We also discuss the interaction between mitochondrial reactive oxygen and nitrogen species, and the involvement of these oxidants in mitochondrial diseases, cancer, neurological, and cardiovascular disorders.

The higher susceptibility of congenital analbuminemic rats to Ca2+-induced mitochondrial permeability transition is associated with the increased expression of cyclophilin D and nitrosothiol depletion

Congenital analbuminemia is a rare autosomal recessive disorder characterized by a trace level of albumin in blood plasma and mild clinical symptoms. Analbuminemic patients generally present associated abnormalities, among which dyslipidemia is a hallmark. In this study, we show that mitochondria isolated from different tissues (liver, heart and brain) from 3-month-old analbuminemic rats (NAR) present a higher susceptibility to Ca(2+)-induced mitochondrial permeability transition (MPT), as assessed by either Ca(2+)-induced mitochondrial swelling, dissipation of membrane potential or mitochondrial Ca(2+) release. The Ca(2+) retention capacity of the liver mitochondria isolated from 3-month-old NAR was about 50% that of the control. Interestingly, the assessment of this variable in 21-day-old NAR indicated that the mitochondrial Ca(2+) retention capacity was preserved at this age, as compared to age-matched controls, which indicates that a reduced capacity for mitochondrial Ca(2+) retention is not a constitutive feature. The search for putative mediators of MPT sensitization in NAR revealed a 20% decrease in mitochondrial nitrosothiol content and a 30% increase in cyclophilin D expression. However, the evaluation of other variables related to mitochondrial redox status showed similar results between the controls and NAR, i.e., namely the contents of reduced mitochondrial membrane protein thiol groups and total glutathione, H(2)O(2) release rate, and NAD(P)H reduced state. We conclude that the higher expression of cyclophilin D, a major component of the MPT pore, and decreased nitrosothiol content in NAR mitochondria may underlie MPT sensitization in these animals.