Antioxidant system disturbances and mitochondrial dysfunction induced by 3-methyglutaric acid in rat heart are prevented by bezafibrate.

Barth syndrome (BTHS) and dilated cardiomyopathy with ataxia syndrome (DCMA) are biochemically characterized by high levels of 3-methylglutaric acid (MGA) in the urine and plasma of affected patients. Although cardiolipin abnormalities have been observed in these disorders, their pathophysiology is not fully established. We evaluated the effects of MGA administration on redox homeostasis and mitochondrial function in heart, as well as on vascular reactivity in aorta of Wistar rats without cardiolipin genetic deficiency. Potential cardioprotective effects of a pretreatment with bezafibrate (BEZ), a pan-PPAR agonist that induces mitochondrial biogenesis, were also determined. Our findings showed that MGA induced lipid peroxidation, altered enzymatic and non-enzymatic antioxidant defenses and reduced respiratory chain function in rat heart. MGA also increased Drp1 and reduced MFN1 levels, suggesting mitochondrial fission induction. Moreover, MGA altered MAPK and Akt signaling pathways, and had a strong tendency to reduce Sirt1 and PGC-1α, indicative of mitochondrial biogenesis impairment. Aorta vascular reactivity was further altered by MGA. Additionally, BEZ mitigated most alterations on antioxidant defenses and mitochondrial quality control proteins provoked by MGA. However, vascular reactivity disturbances were not prevented. It may be presumed that oxidative stress, mitochondrial bioenergetics and control quality disturbances, and vascular reactivity impairment caused by MGA may be involved in the cardiac failure observed in BTHS and DCMA, and that BEZ should be considered as a pharmacological candidate for the treatment of these disorders.

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.

In vivo evidence that bezafibrate prevents oxidative stress and mitochondrial dysfunction caused by 3-methylglutaric acid in rat liver.

High urinary excretion and tissue accumulation of 3-methylglutaric acid (MGA) are observed in patients affected by 3-hydroxy-3-methylglutaric (HMGA) and 3-methylglutaconic (MGTA) acidurias. The pathomechanisms underlying the hepatic dysfunction commonly observed in these disorders are not fully elucidated so that we investigated here the effects of intraperitoneal administration of MGA on redox homeostasis, mitochondrial bioenergetics, biogenesis and dynamics in rat liver. The effects of a pre-treatment with the protective compound bezafibrate (BEZ) were also determined. Our data showed that MGA induced lipid peroxidation and altered enzymatic and non-enzymatic antioxidant defenses in liver, indicating redox homeostasis disruption. BEZ prevented most of these alterations induced by MGA. MGA also decreased the activities of the respiratory chain complexes II and IV and increased of II-III, whereas BEZ prevented the alteration in complex II activity. Furthermore, MGA decreased levels of nuclear PGC-1α and Sirt1, and increased levels of AMPKα1 and cytosolic PPARγ, which were blocked by BEZ. MGA augmented the levels of mitofusin-1 and dynamin-related protein 1, suggesting that both fusion and fission mitochondrial processes are enhanced by MGA. BEZ was able to prevent only the changes in mitofusin-1 levels. Collectively, these findings indicate that oxidative stress and mitochondrial dysfunction are mechanisms involved in the hepatic dysfunction found in HMGA and MGTA. It is also presumed that mitochondrial biogenesis stimulation may constitute an attractive approach to reduce MGA toxicity in liver of individuals affected by HMGA and MGTA.

3-Hydroxy-3-Methylglutaric Acid Impairs Redox and Energy Homeostasis, Mitochondrial Dynamics, and Endoplasmic Reticulum-Mitochondria Crosstalk in Rat Brain.

3-Hydroxy-3-methylglutaryl-CoA lyase (HL) deficiency is a neurometabolic disorder characterized by predominant accumulation of 3-hydroxy-3-methylglutaric acid (HMG) in tissues and biological fluids. Patients often present in the first year of life with metabolic acidosis, non-ketotic hypoglycemia, hypotonia, lethargy, and coma. Since neurological symptoms may be triggered or worsened during episodes of metabolic decompensation, which are characterized by high urinary excretion of organic acids, this study investigated the effects of HMG intracerebroventricular administration on redox homeostasis, citric acid cycle enzyme activities, dynamics (mitochondrial fusion and fission), and endoplasmic reticulum (ER)-mitochondria crosstalk in the brain of neonatal rats euthanized 1 (short term) or 20 days (long term) after injection. HMG induced lipid peroxidation and decreased the activities of glutathione peroxidase (GPx) and citric acid cycle enzymes, suggesting bioenergetic and redox disruption, 1 day after administration. Levels of VDAC1, Grp75, and mitofusin-1, proteins involved in ER-mitochondria crosstalk and mitochondrial fusion, were increased by HMG. Furthermore, HMG diminished synaptophysin levels and tau phosphorylation, and increased active caspase-3 content, indicative of cell damage. Finally, HMG decreased GPx activity and synaptophysin levels, and changed MAPK phosphorylation 20 days after injection, suggesting that long-term toxicity is further induced by this organic acid. Taken together, these data show that HMG induces oxidative stress and disrupts bioenergetics, dynamics, ER-mitochondria communication, and signaling pathways in the brain of rats soon after birth. It may be presumed that these mechanisms underlie the onset and progression of symptoms during decompensation occurring in HL-deficient patients during the neonatal period.

Bezafibrate In Vivo Administration Prevents 3-Methylglutaric Acid-Induced Impairment of Redox Status, Mitochondrial Biogenesis, and Neural Injury in Brain of Developing Rats.

3-Methylglutaric acid (MGA) is an organic acid that accumulates in 3-methylglutaconic (MGTA) and 3-hydroxy-3-methylglutaric (HMGA) acidurias. Patients affected by these disorders present with neurological dysfunction that usually appears in the first years of life. In order to elucidate the pathomechanisms underlying the brain injury in these disorders, we evaluated the effects of MGA administration on redox homeostasis, mitochondrial respiratory chain activity, and biogenesis in the cerebral cortex of developing rats. Neural damage markers and signaling pathways involved in cell survival, and death were also measured after MGA administration. Furthermore, since the treatment for MGTA and HMGA is still limited, we tested whether a pre-treatment with the pan-peroxisome proliferator-activated receptor (PPAR) agonist bezafibrate could prevent the alterations caused by MGA. MGA provoked lipid peroxidation, increased heme oxygenase-1 content, and altered the activities of antioxidant enzymes, strongly suggestive of oxidative stress. MGA also impaired mitochondrial function and biogenesis by decreasing the activities of succinate dehydrogenase and various respiratory chain complexes, as well as the nuclear levels of PGC-1α and NT-PGC-1α, and cell content of Sirt1. AMPKα1 was further increased by MGA. Neural cell damage was also observed following the MGA administration, as verified by decreased Akt and synaptophysin content and reduced ERK phosphorylation, and by the increase of active caspase-3 and p38 and Tau phosphorylation. Importantly, bezafibrate prevented MGA-elicited toxic effects towards mitochondrial function, redox homeostasis, and neural cell injury, implying that this compound may be potentially used as an adjunct therapy for MGTA and HMGA and other disorders with mitochondrial dysfunction.

Evidence that thiol group modification and reactive oxygen species are involved in hydrogen sulfide-induced mitochondrial permeability transition pore opening in rat cerebellum.

We report here the effects of hydrogen sulfide (sulfide), that accumulates in ETHE1 deficiency, in rat cerebellum. Sulfide impaired electron transfer and oxidative phosphorylation. Sulfide also induced mitochondrial swelling, and decreased ΔΨm and calcium retention capacity in cerebellum mitochondria, which were prevented by cyclosporine A (CsA) plus ADP, and ruthenium red, suggesting mitochondrial permeability transition (mPT) induction. Melatonin (MEL) and N-ethylmaleimide also prevented sulfide-induced alterations. Prevention of sulfide-induced decrease of ΔΨm and viability by CsA and MEL was further verified in cerebellum neurons. The data suggest that sulfide induces mPT pore opening via thiol modification and ROS generation.

Evidence that Thiosulfate Inhibits Creatine Kinase Activity in Rat Striatum via Thiol Group Oxidation.

Sulfite oxidase, molybdenum cofactor, and ETHE1 deficiencies are autosomal recessive disorders that affect the metabolism of sulfur-containing amino acids. Patients with these disorders present severe neurological dysfunction and basal ganglia abnormalities, accompanied by high levels of thiosulfate in biological fluids and tissues. Aiming to better elucidate the pathophysiology of basal ganglia damage in these disorders, we evaluated the in vivo effects of thiosulfate administration on bioenergetics, oxidative stress, and neural damage in rat striatum. The in vitro effect of thiosulfate on creatine kinase (CK) activity was also studied. In vivo findings showed that thiosulfate administration decreased the activities of CK and citrate synthase, and increased the activity of catalase 30 min after administration. Activities of other antioxidant enzymes, citric acid cycle, and respiratory chain complex enzymes, as well as glutathione concentrations and markers of neural damage, were not altered by thiosulfate 30 min or 7 days after its administration. Thiosulfate also decreased the activity of CK in vitro in striatum of rats, which was prevented by the thiol reducing agents dithiothreitol (DTT), the antioxidants glutathione (GSH), melatonin, trolox (hydrosoluble analogue of vitamin E), and lipoic acid. DTT and GSH further prevented thiosulfate-induced decrease of the activity of a purified CK in a medium devoid of biological samples. These data suggest that thiosulfate inhibits CK activity by altering critical sulfhydryl groups of this enzyme. It may be also presumed that bioenergetics impairment and ROS generation induced by thiosulfate are mechanisms underlying the neuropathophysiology of disorders in which this metabolite accumulates.

Disruption of Energy Transfer and Redox Status by Sulfite in Hippocampus, Striatum, and Cerebellum of Developing Rats.

Patients with sulfite oxidase (SO) deficiency present severe brain abnormalities, whose pathophysiology is not yet elucidated. We evaluated the effects of sulfite and thiosulfate, metabolites accumulated in SO deficiency, on creatine kinase (CK) activity, mitochondrial respiration and redox status in hippocampus, striatum and cerebellum of developing rats. Our in vitro results showed that sulfite and thiosulfate decreased CK activity, whereas sulfite also increased malondialdehyde (MDA) levels in all brain structures evaluated. Sulfite further diminished mitochondrial respiration and increased DCFH oxidation and hydrogen peroxide production in hippocampus. Sulfite-induced CK activity decrease was prevented by melatonin (MEL), resveratrol (RSV), and dithiothreitol while increase of MDA levels was prevented by MEL and RSV. Regarding the antioxidant system, sulfite increased glutathione concentrations in hippocampus and striatum. In addition, sulfite decreased the activities of glutathione peroxidase in all brain structures, of glutathione S-transferase in hippocampus and cerebellum, and of glutathione reductase in cerebellum. In vivo experiments performed with intrahippocampal administration of sulfite demonstrated that this metabolite increased superoxide dismutase activity without altering other biochemical parameters in rat hippocampus. Our data suggest that impairment of energy metabolism and redox status may be important pathomechanisms involved in brain damage observed in individuals with SO deficiency.

In vitro evidence that sulfite impairs glutamatergic neurotransmission and inhibits glutathione metabolism-related enzymes in rat cerebral cortex.

Sulfite oxidase (SOX) deficiency is an inherited neurometabolic disorder biochemically characterized by tissue accumulation and high urinary excretion of sulfite and thiosulfate. Affected patients present severe neurological dysfunction accompanied by seizures, whose pathophysiology is poorly known. In the present study we evaluated the in vitro effects of sulfite and thiosulfate on important parameters of glutamatergic neurotransmission and redox homeostasis in rat cerebral cortex slices. We verified that sulfite, but not thiosulfate, significantly decreased glutamate uptake when cerebral cortex slices were exposed during 1h to these metabolites. We also observed that thiosulfate inhibited glutamine synthetase (GS) activity. A pronounced trend toward GS inhibition induced by sulfite was also found. Regarding redox homeostasis, sulfite, at the concentration of 10 µM, increased thiobarbituric acid-reactive substances and decreased glutathione concentrations after 1h of exposure. In contrast, thiosulfate did not alter these parameters. We also found that 500 µM sulfite increased sulfhydryl group content in rat cerebral cortex slices and increased GSH levels in a medium containing oxidized GSH (GSSG) and devoid of cortical slices, suggesting that sulfite reacts with disulfide bonds to generate sulfhydryl groups. Moreover, sulfite and thiosulfate did not alter the activities of glutathione peroxidase (GPx), glutathione reductase (GR), glutathione S-transferase (GST) and glucose-6-phosphate dehydrogenase (G6PDH) after 1h of incubation. However, sulfite inhibited the activities of GPx, GST and G6PDH when cortical slices were exposed for 3h to sulfite. We finally verified that sulfite did not induce cell death after 1h of incubation. Our data show that sulfite impairs glutamatergic neurotransmission and redox homeostasis in cerebral cortex. Therefore, it may be presumed that these pathomechanisms contribute, at least in part, to the seizures observed in patients affected by SOX deficiency.

Evidence that glycine induces lipid peroxidation and decreases glutathione concentrations in rat cerebellum.

Patients with non-ketotic hyperglycinemia (NKH) present severe neurological symptoms and brain abnormalities involving cerebellum. Although the pathomechanisms underlying the cerebellum damage have not been studied, high tissue levels of glycine (GLY), the biochemical hallmark of this disorder have been suggested to contribute to the neuropathology of this disease. We investigated the in vitro effects of GLY on important parameters of oxidative stress and energy metabolism in cerebellum of 30-day-old rats. Our results show that GLY increased 2',7'-dichlorofluorescin oxidation, suggesting that reactive species production are augmented by GLY in the cerebellum. However, hydrogen peroxide generation was not altered by GLY. GLY also increased thiobarbituric acid-reactive substances (TBA-RS) levels and reduced the glutathione (GSH) content, indicating that this amino acid provokes lipid oxidative damage and compromises the non-enzymatic antioxidant defenses, respectively, in cerebellum. The antioxidants melatonin and trolox (the hydrosoluble analog of vitamin E) prevented the GLY-induced increase of TBA-RS and decrease of GSH in cerebellum, indicating the involvement of hydroxyl and peroxyl radicals in these effects. The NMDA receptor antagonist MK-801 also attenuated GLY-induced decrease of GSH, suggesting that this effect is mediated through NMDA receptor. In contrast, GLY did not alter the protein carbonyl formation and total and protein-bound sulfhydryl group content, as well as catalase and superoxide dismutase activities. Furthermore, GLY did not alter the activities of the respiratory chain complexes and creatine kinase. Our present data indicate that oxidative stress elicited by GLY in vitro may be a potential pathomechanism involved in the cerebellar dysfunction observed in NKH.