Ca2+-induced permeabilization promotes free radical release from rat brain mitochondria with partially inhibited complex I

Severe Acute Liver Dysfunction Induces Delayed Hepatocyte Swelling and Cytoplasmic Vacuolization, and Delayed Cortical Neuronal Cell Death

Liver dysfunction is the main cause of hepatic encephalopathy. However, histopathological changes in the brain associated with hepatic encephalopathy remain unclear. Therefore, we investigated pathological changes in the liver and brain using an acute hepatic encephalopathy mouse model. After administering ammonium acetate, a transient increase in the blood ammonia level was observed, which returned to normal levels after 24 h. Consciousness and motor levels also returned to normal. It was revealed that hepatocyte swelling, and cytoplasmic vacuolization progressed over time in the liver tissue. Blood biochemistry also suggested hepatocyte dysfunction. In the brain, histopathological changes, such as perivascular astrocyte swelling, were observed 3 h after ammonium acetate administration. Abnormalities in neuronal organelles, especially mitochondria and rough endoplasmic reticulum, were also observed. Additionally, neuronal cell death was observed 24 h post-ammonia treatment when blood ammonia levels had returned to normal. Activation of reactive microglia and increased expression of inducible nitric oxide synthase (iNOS) were also observed seven days after a transient increase in blood ammonia. These results suggest that delayed neuronal atrophy could be iNOS-mediated cell death due to activation of reactive microglia. The findings also suggest that severe acute hepatic encephalopathy causes continued delayed brain cytotoxicity even after consciousness recovery.

Oncocyte Membrane-Camouflaged Multi-Stimuli-Responsive Nanohybrids for Synergistic Amplification of Tumor Oxidative Stresses and Photothermal Enhanced Cancer Therapy

The combination of various therapeutic modalities has received considerable attention for improving antitumor performance. Herein, an innovative nanohybrid, namely CaO₂@FePt-DOX@PDA@CM (CFDPM), was developed for synergistic chemotherapy/chemodynamic therapy/Ca²⁺ overloading-mediated amplification of tumor oxidative stress and photothermal enhanced cancer therapy. Camouflage of the 4T1 cell membrane enabled CFDPM to escape the immune surveillance and accumulate in the tumor tissue. Ca²⁺, released from CaO₂, could lead to mitochondrial dysfunction and facilitate the production of reactive oxygen species to amplify intracellular oxidative stress. Meanwhile, the increase of H₂O₂ concentration could enhance the efficiency of the chemodynamic therapy (CDT). Moreover, the hypoxic condition could be alleviated remarkably, which is attributed to the sufficient O₂ supply by CaO₂, resulting in the suppression of drug resistance and promotion of the chemotherapeutic effect. The nanohybrids involving Ca²⁺ overloading/CDT/chemotherapy could synergistically amplify the tumor oxidative stresses and remarkably aggravate the death of cancer cells. Significantly, the excellent photothermal conversion performance of CFDPM could further promote the tumoricidal effect. The in vitro and in vivo studies revealed that CFDPM could effectively advance the therapeutic efficiency via the cooperation of various therapeutic modalities to optimize their individual virtue, which would open a valuable avenue for effective cancer treatment.

Tumor Microenvironment-Responsive Cu/CaCO3 -Based Nanoregulator for Mitochondrial Homeostasis Disruption-Enhanced Chemodynamic/Sonodynamic Therapy

The efficiency of reactive oxygen species (ROS)-mediated cancer therapy is restrained by intrinsic characteristics in the tumor microenvironment (TME), such as overexpressed glutathione (GSH), hypoxia and limited efficiency of H₂ O₂ . In this work, intelligent copper-dropped calcium carbonate loading sonosensitizer Ce6 nanoparticles (Cu/CaCO₃ @Ce6, CCC NPs) are established to realize TME-responsive self-supply of oxygen and successively Ca²⁺ -overloading-strengthened chemodynamic therapy/sonodynamic therapy (CDT/SDT). CCC NPs release Ca²⁺ , Cu²⁺ , and Ce6 in weakly acid and GSH-excessive TME. Released Cu²⁺ can not only consume GSH and turn into Cu⁺ via a redox reaction, but also provide CDT-creating hydroxyl radicals through the Fenton-like reaction. Under ultrasound irradiation, the intracellular oxidative stress is amplified profoundly relying on singlet oxygen outburst from SDT. Moreover, Ca²⁺ influx aggravates the mitochondrial disruption, which further accelerates the oxidation level. The facile and feasible design of the Cu-dropped CaCO₃ -based nanoregulators will be further developed as a paradigm in ROS-contributed cancer therapy.

KCl-CaCO3 nanoclusters armoured with Pt nanocrystals for enhanced electro-driven tumor inhibition

Electrodynamic therapy (EDT) has recently emerged as an alternative approach for tumor therapy via the generation of ROS by platinum (Pt) nanoparticles under electric field. An interesting phenomenon observed during EDT is that the increased on-site concentration of chloride ions is highly beneficial for ROS generation and inhibition efficacy. Here, in this study, nanoclusters (KCC), consisting of potassium chloride (KCl) nanocrystals and amorphous calcium carbonate (CaCO₃), were synthesized and integrated with platinum nanoparticles (KCCP). In this system, KCC can dissolve and release calcium and chloride ions within tumor cells. The intracellular chloride ions considerably facilitated ROS generation by Pt nanoparticles under an electric field. More importantly, the excessive calcium ions and ROS formed a cycle of mutual promotion and self-amplification in cells, leading to agitated tumor inhibition, both in vitro and in vivo.

Calcium Peroxide-Based Nanosystem with Cancer Microenvironment-Activated Capabilities for Imaging Guided Combination Therapy via Mitochondrial Ca2+ Overload and Chemotherapy

Mitochondria are the "power plant" of the cell, providing a constant source of energy, and are involved in a variety of intracellular signaling pathways. Among these pathways, Ca²⁺ homeostasis is closely related to the normal function of mitochondria. By destroying the Ca²⁺ steady state of mitochondria and disrupting their multiple cellular activities, tumor cell killing can be achieved. In addition, the presence of an intracellular oxidative stress state triggers the closure of cellular calcium channels, which leads to intracellular Ca²⁺ retention and enrichment. We designed a targeted and tumor microenvironment (TME)-responsive CaO₂-based nanosystem that can selectively target cancer cells for pH-controlled degradation and drug release, alter cellular physiological mechanisms by disrupting Ca²⁺ homeostasis in an artificial manner, and introduce mitochondrial Ca²⁺ excess-mediated apoptosis. Meanwhile, the production of Ca(OH)₂ will raise the pH of the microenvironment and subsequently promote the oxidation process of glutathione by H₂O₂ released from CaO₂ degradation, achieving the goal of remodeling TME. Moreover, calcium overload of tumor cells and calcification of tissues can both inhibit tumor growth and act as a contrast agent for computed tomography imaging.

PEGylated superparamagnetic iron oxide nanoparticles (SPIONs) ameliorate learning and memory deficit in a rat model of Alzheimer's disease: Potential participation of STIMs

The amyloid-beta (Aβ) fibrillation process seems to execute a principal role in the neuropathology of Alzheimer's disease (AD). Accordingly, novel therapeutic plans have concentrated on the inhibition or degradation of Aβ oligomers and fibrils. Biocompatible nanoparticles (NPs), e.g., gold and iron oxide NPs, take a unique capacity in redirecting Aβ fibrillation kinetics; nevertheless, their impacts on AD-related memory impairment have not been adequately evaluated in vivo. Here, we examined the effect of commercial PEGylated superparamagnetic iron oxide nanoparticles (SPIONs) on the learning and memory of an AD-animal model. The outcomes demonstrated the dose-dependent effect of SPIONs on Aβ fibrillation and learning and memory processes. In vitro and in vivo findings revealed that Low doses of SPIONs inhibited Aβ aggregation and ameliorated learning and memory deficit in the AD model, respectively. Enhanced level of hippocampal proteins, including brain-derived neurotrophic factor, BDNF, phosphorylated-cAMP response element-binding protein, p-CREB, and stromal interaction molecules, e.g., STIM1 and STIM2, were also observed. However, at high doses, SPIONs did not improve the detrimental impacts of Aβ fibrillation on spatial memory and hippocampal proteins expression. Overall, we revealed the potential capacity of SPIONs on retrieval of behavioral and molecular manifestations of AD in vivo, which needs further investigations to determine the mechanistic effect of SPIONs in the AD conundrum.

Plant Polyphenols as Neuroprotective Agents in Parkinson's Disease Targeting Oxidative Stress

Parkinson's disease (PD) is the second most prevalent progressive neurodegenerative disorder characterized by the degeneration of dopaminergic neurons in the human midbrain. Various ongoing research studies are competing to understand the pathology of PD and elucidate the mechanisms underlying neurodegeneration. Current pharmacological treatments primarily focused on improving dopamine metabolism in PD patients, despite the side effects of long-term usage. In recent years, it is recognized that oxidative stress-mediated pathways lead to neurodegeneration in the brain, which is associated with the pathophysiology of PD. The importance of oxidative stress is often less emphasized when developing potential therapeutic approaches. Natural plant antioxidants have been shown to mediate the oxidative stress-induced effects in PD, which has gained considerable attention in both in vitro and in vivo studies. Yet, clinical trials on natural polyphenol compounds are limited, restricting the potential use of these compounds as an alternative treatment for PD. Therefore, this review provides an understanding of the oxidative stress-induced effects in PD by elucidating the underlying events contributing to oxidative stress and explore the potential use of polyphenols in improving the oxidative status in PD. Preclinical findings have supported the potential of polyphenols in providing neuroprotection against oxidative stress-induced toxicity in PD. However, limiting factors, such as safety and bioavailability of polyphenols, warrant further investigations so as to make them the potential target for clinical applications in the treatment and management of PD.

EDNRB isoform 3 confers Temozolomide resistance in A375 melanoma cells by modulating membrane potential, reactive oxygen species and mitochondrial Ca2

Background

The role of endothelin receptor type B (EDNRB) isoform 3 involved in Temozolomide (TMZ)-induced melanoma cell death has not yet been elucidated.

Methods

The subcellular localization of EDNRB isoform 3 was determined by confocal and immunoblotting assays. Silencing EDNRB isoform 3 was performed by CRISPR/Cas9. Apoptosis was assessed by annexin V/propium iodide staining and caspases 3/7/9 activity. Mitochondrial membrane potential, reactive oxygen species and mitochondrial Ca²⁺ were measured by flow cytometry. Apoptosis protein array was applied.

Results

Confocal and immunoblot analyses indicate mitochondrial localization of EDNRB isoform 3 and the first N-terminal (1–22) amino acids are sufficient for its mitochondrial targeting. EDNRB isoform 3 depleted A375 cells significantly confers chemoresistance with mitochondrial depolarization, reduced reactive oxygen species, enhanced mitochondrial Ca²⁺ uptake and decreased caspase 9 activation. Additionally, apoptosis array shows that lack of EDNRB isoform 3 has relatively lower expression of phosphorylation of p53 at S392 and a slightly higher expression of Paraoxonase 2.

Conclusion

Our findings raise the possibility of targeting EDNRB isoform 3 as a new therapeutic strategy in combination with TMZ for melanoma treatment.

Effects of Phenelzine Administration on Mitochondrial Function, Calcium Handling, and Cytoskeletal Degradation after Experimental Traumatic Brain Injury

Traumatic brain injury (TBI) results in the production of peroxynitrite (PN), leading to oxidative damage of lipids and protein. PN-mediated lipid peroxidation (LP) results in production of reactive aldehydes 4-hydroxynonenal (4-HNE) and acrolein. The goal of these studies was to explore the hypothesis that interrupting secondary oxidative damage following a TBI via phenelzine (PZ), analdehyde scavenger, would protect against LP-mediated mitochondrial and neuronal damage. Male Sprague-Dawley rats received a severe (2.2 mm) controlled cortical impact (CCI)-TBI. PZ was administered subcutaneously (s.c.) at 15 min (10 mg/kg) and 12 h (5 mg/kg) post-injury and for the therapeutic window/delay study, PZ was administered at 1 h (10 mg/kg) and 24 h (5 mg/kg). Mitochondrial and cellular protein samples were obtained at 24 and 72 h post-injury (hpi). Administration of PZ significantly improved mitochondrial respiration at 24 and 72 h compared with vehicle-treated animals. These results demonstrate that PZ administration preserves mitochondrial bioenergetics at 24 h and that this protection is maintained out to 72 hpi. Additionally, delaying the administration still elicited significant protective effects. PZ administration also improved mitochondrial Ca2+ buffering (CB) capacity and mitochondrial membrane potential parameters compared with vehicle-treated animals at 24 h. Although PZ treatment attenuated aldehyde accumulation post-injury, the effects were insignificant. The amount of α-spectrin breakdown in cortical tissue was reduced by PZ administration at 24 h, but not at 72 hpi compared with vehicle-treated animals. In conclusion, these results indicate that acute PZ treatment successfully attenuates LP-mediated oxidative damage eliciting multiple neuroprotective effects following TBI.

Neuroprotective Effects of Cyclosporine in a Porcine Pre-Clinical Trial of Focal Traumatic Brain Injury

Mitochondrial dysfunction is thought to be a hallmark of traumatic brain injury (TBI) and plays a pivotal role in the resulting cellular injury. Cyclophilin D-mediated activation of the mitochondrial permeability transition pore has been suggested to contribute to this secondary injury cascade. Cyclosporine possesses neuroprotective properties that have been attributed to the desensitization of mitochondrial permeability transition pore activation. In vivo animal experiments have demonstrated neuroprotective effects of cyclosporine in more than 20 independent experimental studies in a multitude of different experimental models. However, the majority of these studies have been carried out in rodents. The aim of the present study was to evaluate the efficacy of a novel and cremophor/kolliphor EL-free lipid emulsion formulation of cyclosporine in a translational large animal model of TBI. A mild-to-moderate focal contusion injury was induced in piglets using a controlled cortical impact device. After initial step-wise analyses of pharmacokinetics and comparing with exposure of cyclosporine in clinical TBI trials, a 5-day dosing regimen with continuous intravenous cyclosporine infusion (20 mg/kg/day) was evaluated in a randomized and blinded placebo-controlled setting. Cyclosporine reduced the volume of parenchymal injury by 35%, as well as improved markers of neuronal injury, as measured with magnetic resonance spectroscopic imaging. Further, a consistent trend toward positive improvements in brain metabolism and mitochondrial function was observed in the pericontusional tissue. In this study, we have demonstrated efficacy using a novel cyclosporine formulation in clinically relevant and translatable outcome metrics in a large animal model of focal TBI.

Mechanism of Protein Carbonylation in Glutathione-Depleted Rat Brain Slices

This study was conducted to further our understanding about the link between lipid peroxidation and protein carbonylation in rat brain slices incubated with the glutathione (GSH)-depletor diethyl maleate. Using this in vitro system of oxidative stress, we found that there is a significant lag between the appearance of carbonylated proteins and GSH depletion, which seems to be due to the removal of oxidized species early on in the incubation by the mitochondrial Lon protease. Upon acute GSH depletion, protein carbonyls accumulated mostly in mitochondria and to a lesser degree in other subcellular fractions that also contain high levels of polyunsaturated lipids. This result is consistent with our previous findings suggesting that lipid hydroperoxides mediate the oxidation of proteins in this system. However, these lipid hydroperoxides are not produced by oxidation of free arachidonic acid or other polyunsaturated free fatty acids by lipooxygenases or cyclooxygenases. Finally, γ-glutamyl semialdehyde and 2-amino-adipic semialdehyde were identified by HPLC as the carbonyl-containing amino acid residues, indicating that proteins are carbonylated by metal ion-catalyzed oxidation of lysine, arginine and proline residues. The present findings are important in the context of neurological disorders that exhibit increased lipid peroxidation and protein carbonylation, such as Parkinson's disease, Alzheimer's disease, and multiple sclerosis.

Identification of 4-N-[2-(4-phenoxyphenyl)ethyl]quinazoline-4,6-diamine as a novel, highly potent and specific inhibitor of mitochondrial complex I

By probing the quinone substrate binding site of mitochondrial complex I with a focused set of quinazoline-based compounds, we identified substitution patterns as being critical for the observed inhibition. The structure activity relationship study also resulted in the discovery of the quinazoline 4-N-[2-(4-phenoxyphenyl)ethyl]quinazoline-4,6-diamine (EVP4593) as a highly potent inhibitor of the multisubunit membrane protein. EVP4593 specifically and effectively reduces the mitochondrial complex I-dependent respiration with no effect on the respiratory chain complexes II-IV. Similar to established Q-site inhibitors, EVP4593 elicits the release of reactive oxygen species at the flavin site of mitochondrial complex I. Recently, EVP4593 was nominated as a lead compound for the treatment of Huntingtons disease. Our results challenge the postulated primary mode-of-action of EVP4593 as an inhibitor of NF-κB pathway activation and/or store-operated calcium influx.

Exercise increases mitochondrial complex I activity and DRP1 expression in the brains of aged mice

Exercise is known to have numerous beneficial effects. Recent studies indicate that exercise improves mitochondrial energetics not only in skeletal muscle but also in other tissues. While exercise elicits positive effects on memory, neurogenesis, and synaptic plasticity, the effects of exercise on brain mitochondrial energetics remain relatively unknown. Herein, we studied the effects of exercise training in old and young mice on brain mitochondrial energetics, in comparison to known effects on peripheral tissues that utilize fatty acid oxidation. Exercise improved the capacity for muscle and liver to oxidize palmitate in old mice, but not young mice. In the brain, exercise increased rates of respiration and reactive oxygen species (ROS) production in the old group only while utilizing complex I substrates, effects that were not seen in the young group. Coupled complex I to III enzymatic activity was significantly increased in old trained versus untrained mice with no effect on coupled II to III enzymatic activity. Mitochondrial protein content and markers of mitochondrial biogenesis (PGC-1α and TFAM) were not affected by exercise training in the brain, in contrast to the skeletal muscle of old mice. Brain levels of the autophagy marker LC3-II and protein levels of other signaling proteins that regulate metabolism or transport (BDNF, HSP60, phosphorylated mTOR, FNDC5, SIRT3) were not significantly altered. Old exercised mice showed a significant increase in DRP1 protein levels in the brain without changes in phosphorylation, while MFN2 and OPA1 protein levels were unchanged. Our results suggest that exercise training in old mice can improve brain mitochondrial function through effects on electron transport chain function and mitochondrial dynamics without increasing mitochondrial biogenesis.

Regulation of Mitochondrial Function and Glutamatergic System Are the Target of Guanosine Effect in Traumatic Brain Injury

Traumatic brain injury (TBI) is a highly complex multi-factorial disorder. Experimental trauma involves primary and secondary injury cascades that underlie delayed neuronal dysfunction and death. Mitochondrial dysfunction and glutamatergic excitotoxicity are the hallmark mechanisms of damage. Accordingly, a successful pharmacological intervention requires a multi-faceted approach. Guanosine (GUO) is known for its neuromodulator effects in various models of brain pathology, specifically those that involve the glutamatergic system. The aim of the study was to investigate the GUO effects against mitochondrial damage in hippocampus and cortex of rats subjected to TBI, as well as the relationship of this effect with the glutamatergic system. Adult male Wistar rats were subjected to a unilateral moderate fluid percussion brain injury (FPI) and treated 15 min later with GUO (7.5 mg/kg) or vehicle (saline 0.9%). Analyses were performed in hippocampus and cortex 3 h post-trauma and revealed significant mitochondrial dysfunction, characterized by a disrupted membrane potential, unbalanced redox system, decreased mitochondrial viability, and complex I inhibition. Further, disruption of Ca²⁺ homeostasis and increased mitochondrial swelling was also noted. Our results showed that mitochondrial dysfunction contributed to decreased glutamate uptake and levels of glial glutamate transporters (glutamate transporter 1 and glutamate aspartate transporter), which leads to excitotoxicity. GUO treatment ameliorated mitochondrial damage and glutamatergic dyshomeostasis. Thus, GUO might provide a new efficacious strategy for the treatment acute physiological alterations secondary to TBI.

Traditional and novel tools to probe the mitochondrial metabolism in health and disease

Mitochondrial metabolism links energy production to other essential cellular processes such as signaling, cellular differentiation, and apoptosis. In addition to producing adenosine triphosphate (ATP) as an energy source, mitochondria are responsible for the synthesis of a myriad of important metabolites and cofactors such as tetrahydrofolate, α-ketoacids, steroids, aminolevulinic acid, biotin, lipoic acid, acetyl-CoA, iron-sulfur clusters, heme, and ubiquinone. Furthermore, mitochondria and their metabolism have been implicated in aging and several human diseases, including inherited mitochondrial disorders, cardiac dysfunction, heart failure, neurodegenerative diseases, diabetes, and cancer. Therefore, there is great interest in understanding mitochondrial metabolism and the complex relationship it has with other cellular processes. A large number of studies on mitochondrial metabolism have been conducted in the last 50 years, taking a broad range of approaches. In this review, we summarize and discuss the most commonly used tools that have been used to study different aspects of the metabolism of mitochondria: ranging from dyes that monitor changes in the mitochondrial membrane potential and pharmacological tools to study respiration or ATP synthesis, to more modern tools such as genetically encoded biosensors and trans-omic approaches enabled by recent advances in mass spectrometry, computation, and other technologies. These tools have allowed the large number of studies that have shaped our current understanding of mitochondrial metabolism. WIREs Syst Biol Med 2017, 9:e1373. doi: 10.1002/wsbm.1373 For further resources related to this article, please visit the WIREs website.

Manganese ions enhance mitochondrial H2O2 emission from Krebs cycle oxidoreductases by inducing permeability transition

Manganese-induced toxicity has been linked to mitochondrial dysfunction and an increased generation of reactive oxygen species (ROS). We could recently show in mechanistic studies that Mn²⁺ ions induce hydrogen peroxide (H₂O₂) production from the ubiquinone binding site of mitochondrial complex II (II_Q) and generally enhance H₂O₂ formation by accelerating the rate of superoxide dismutation. The present study with intact mitochondria reveals that manganese additionally enhances H₂O₂ emission by inducing mitochondrial permeability transition (mPT). In mitochondria fed by NADH-generating substrates, the combination of Mn²⁺ and different respiratory chain inhibitors led to a dynamically increasing H₂O₂emission which was sensitive to the mPT inhibitor cyclosporine A (CsA) as well as Ru-360, an inhibitor of the mitochondrial calcium uniporter (MCU). Under these conditions, flavin-containing enzymes of the mitochondrial matrix, e.g. the mitochondrial 2-oxoglutaratedehydrogenase (OGDH), were major sources of ROS. With succinate as substrate, Mn²⁺ stimulated ROS production mainly at complex II, whereby the applied succinate concentration had a marked effect on the tendency for mPT. Also Ca²⁺ increased the rate of H₂O₂ emission by mPT, while no direct effect on ROS-production of complex II was observed. The present study reveals a complex scenario through which manganese affects mitochondrial H₂O₂ emission: stimulating its production from distinct sites (e.g. site II_Q), accelerating superoxide dismutation and enhancing the emission via mPT which also leads to the loss of soluble components of the mitochondrial antioxidant systems and favors the ROS production from flavin-containing oxidoreductases of the Krebs cycle.

Turn up the cellular power generator with vitamin E analogue formulation

The down regulation of the cellular power generator, adenosine triphosphate (ATP) synthase, in various cancer cells plays an obstructive role in mitochondria-mediated cell death. Cancer cells up-regulate ATPase inhibitory factor 1 (IF1) and down-regulate β-F1-ATPase of ATP synthase to enhance aerobic glycolysis for tumor growth via inhibiting total ATP synthase activity in the oxidative phosphorylation (OXPHOS) pathway. Alpha-tocopheryl succinate (α-TOS), one of the most bioactive derivatives of vitamin E, can selectively induce apoptosis in numerous cancer cells. The cancer cell selective apoptosis inducing property of α-TOS is correlated to: mitochondrial destabilization, inhibition of anti-apoptotic B cell lymphoma 2 (Bcl2) and protein kinase C (PKC), caspase 3 activation, production of mitochondrial reactive oxygen species (ROS), and inhibition of succinate dehydrogenase activity of mitochondrial complex II, and interaction with complex I to some extent. There is no report which elucidates the effects of α-TOS on the cellular power generator, complex V or ATP synthase. Here, we report the activation of mitochondrial ATP synthase using a suitably designed chemical formulation of α-TOS for the first time. A mitochondria targeted α-TOS nanoparticle formulation demonstrated enhanced cytotoxicity and mitochondrial activities in cancer cells by inhibiting Bcl2 protein and activating ATP synthase. The modulation of ATP synthase in cancer cells by the engineered formulation of α-TOS can be promising for solid cancers with compromised ATP synthase.

Interrelationship between Changes in the Amyloid β 42/40 Ratio and Presenilin 1 Conformation

The ratio of the longer (i.e., Aβ42/Aβ43) to shorter (i.e. Aβ40) species is a critical factor determining amyloid fibril formation, neurotoxicity and progression of the amyloid pathology in Alzheimer's disease. The relative levels of the different Aβ species are affected by activity and conformation of the γ-secretase complex catalytic component - presenilin 1 (PS1). The enzyme exists in a dynamic equilibrium of the conformational states, with so-called "close" conformation associated with the shift of the γ-secretase cleavage towards the production of longer, neurotoxic Aβ species. In the current study, fluorescence lifetime imaging microscopy, spectral Förster resonance energy transfer, calcium imaging and cytotoxicity assays were utilized to explore reciprocal link between the Aβ42 and Aβ40 peptides present at various ratios and PS1 conformation in primary neurons. We report that exposure to Aβ peptides at a relatively high ratio of Aβ42/40 causes conformational change within the PS1 subdomain architecture towards the pathogenic "closed" state. Mechanistically, the Aβ42/40 peptides present at the relatively high ratio increase intracellular calcium levels, which were shown to trigger pathogenic PS1 conformation. This indicates that there is a reciprocal crosstalk between the extracellular Aβ peptides and PS1 conformation within a neuron, with Aβ40 showing some protective effect. The pathogenic shift within the PS1 domain architecture may further shift the production of Aβ peptides towards the longer, neurotoxic Aβ species. These findings link elevated calcium, Aβ42 and PS1/γ-secretase conformation, and offer possible mechanistic explanation of the impending exacerbation of the amyloid pathology.

Acupuncture reversed hippocampal mitochondrial dysfunction in vascular dementia rats

Hippocampal mitochondrial dysfunction due to oxidative stress has been considered to play a major role in the pathogenesis of vascular dementia (VD). Previous studies suggested that acupuncture could improve cerebral hypoperfusion-induced cognitive impairments. However, whether hippocampal mitochondria are associated with this cognitive improvement remains unclear. In this study, an animal model of VD was established via bilateral common carotid arteries occlusion (BCCAO) to investigate the alterations of cognitive ability and hippocampal mitochondrial function. BCCAO rats showed impairments in hippocampal mitochondrial function, overproduction of reactive oxygen species (ROS) and learning and memory deficits. After two-week acupuncture treatment, BCCAO-induced spatial learning and memory impairments as shown in Morris water maze were ameliorated. Hippocampal mitochondrial respiratory complex enzymes (complex I, II, IV) activities and cytochrome c oxidase IV expression significantly increased, which might contribute to the reduction of hippocampal ROS generation. In addition, acupuncture significantly improve mitochondrial bioenergy parameters such as mitochondrial respiratory control rate and membrane potential not PDH A1 expression. Placebo-acupuncture did not produce similar therapeutic effects. These findings suggested that acupuncture reversed BCCAO-induced hippocampal mitochondrial dysfunction, which might contribute to its prevention on cognitive deficits.

The calcium uniporter regulates the permeability transition pore in isolated cortical mitochondria

To investigate the influence of the mitochondrial calcium uniporter on the mitochondrial permeability transition pore, the present study observed mitochondrial morphology in cortical neurons isolated from adult rats using transmission electron microscopy, and confirmed the morphology and activity of isolated mitochondria by detecting succinic dehydrogenase and monoamine oxidase, two mitochondrial enzymes. Isolated mitochondria were treated with either ruthenium red, an inhibitor of the uniporter, spermine, an activator of the uniporter, or in combination with cyclosporin A, an inhibitor of the mitochondrial permeability transition pore. Results showed that ruthenium red inhibited CaCl2-induced mitochondrial permeability transition pore opening, spermine enhanced opening, and cyclosporin A attenuated the effects of spermine. Results demonstrated that the mitochondrial calcium uniporter plays a role in regulating the mitochondrial permeability transition pore in mitochondria isolated from the rat brain cortex.

Brain edema in acute liver failure: mechanisms and concepts

Brain edema and associated increase in intracranial pressure continue to be lethal complications of acute liver failure (ALF). Abundant evidence suggests that the edema in ALF is largely cytotoxic brought about by swelling of astrocytes. Elevated blood and brain ammonia levels have been strongly implicated in the development of the brain edema. Additionally, inflammation and sepsis have been shown to contribute to the astrocyte swelling/brain edema in the setting of ALF. We posit that ammonia initiates a number of signaling events, including oxidative/nitrative stress (ONS), the mitochondrial permeability transition (mPT), activation of the transcription factor (NF-κB) and signaling kinases, all of which have been shown to contribute to the mechanism of astrocyte swelling. All of these factors also impact ion-transporters, including Na(+), K(+), Cl(-) cotransporter and the sulfonylurea receptor 1, as well as the water channel protein aquaporin-4 resulting in a perturbation of cellular ion and water homeostasis, ultimately resulting in astrocyte swelling/brain edema. All of these events are also potentiated by inflammation. This article reviews contemporary knowledge regarding mechanisms of astrocyte swelling/brain edema formation which hopefully will facilitate the identification of therapeutic targets capable of mitigating the brain edema associated with ALF.

Enhanced hydrogen peroxide generation accompanies the beneficial bioenergetic effects of methylene blue in isolated brain mitochondria

The redox dye methylene blue (MB) is proven to have beneficial effects in various models of neurodegenerative diseases. Here we investigated the effects of MB (100 nM, 300 nM, and 1 μM) on key bioenergetic parameters and on H2O2 production/elimination in isolated guinea pig brain mitochondria under normal as well as respiration-impaired conditions. As measured by high-resolution Oxygraph the rate of resting oxygen consumption was increased, but the ADP-stimulated respiration was unaffected by MB with any of the substrates (glutamate malate, succinate, or α-glycerophosphate) used for supporting mitochondrial respiration. In mitochondria treated with inhibitors of complex I or complex III MB moderately but significantly increased the rate of ATP production, restored ΔΨm, and increased the rate of Ca(2+) uptake. The effects of MB are consistent with transferring electrons from upstream components of the electron transport chain to cytochrome c, which is energetically favorable when the flow of electrons in the respiratory chain is compromised. On the other hand, MB significantly increased the production of H2O2 measured by Amplex UltraRed fluorimetry under all conditions, in resting, ATP-synthesizing, and respiration-impaired mitochondria, with each substrate combination supporting respiration. Furthermore, it also decreased the elimination of H2O2. Generation of H2O2 without superoxide formation, observed in the presence of MB, is interpreted as a result of reduction of molecular oxygen to H2O2 by the reduced MB. The elevated generation and impaired elimination of H2O2 should be considered for the overall oxidative state of mitochondria treated with MB.

Caffeine intake may modulate inflammation markers in trained rats

Caffeine is presented in many commercial products and has been proven to induce ergogenic effects in exercise, mainly related to redox status homeostasis, inflammation and oxidative stress-related adaptation mechanisms. However, most studies have mainly focused on muscle adaptations, and the role of caffeine in different tissues during exercise training has not been fully described. The aim of this study was therefore, to analyze the effects of chronic caffeine intake and exercise training on liver mitochondria functioning and plasma inflammation markers. Rats were divided into control, control/caffeine, exercise, and exercise/caffeine groups. Exercise groups underwent four weeks of swimming training and caffeine groups were supplemented with 6 mg/kg/day. Liver mitochondrial swelling and complex I activity, and plasma myeloperoxidase (MPO) and acetylcholinesterase (AChE) activities were measured. An anti-inflammatory effect of exercise was evidenced by reduced plasma MPO activity. Additionally, caffeine intake alone and combined with exercise decreased the plasma AChE and MPO activities. The per se anti-inflammatory effect of caffeine intake should be highlighted considering its widespread use as an ergogenic aid. Therefore, caffeine seems to interfere on exercise-induced adaptations and could also be used in different exercise-related health treatments.

Effects of diphenyl diselenide on methylmercury toxicity in rats

This study investigates the efficacy of diphenyl diselenide [(PhSe)2] in attenuating methylmercury- (MeHg-)induced toxicity in rats. Adult rats were treated with MeHg [5 mg/kg/day, intragastrically (i.g.)] and/ or (PhSe)2 [1 mg/kg/day, intraperitoneally (i.p.)] for 21 days. Body weight gain and motor deficits were evaluated prior to treatment, on treatment days 11 and 21. In addition, hepatic and cerebral mitochondrial function (reactive oxygen species (ROS) formation, total and nonprotein thiol levels, membrane potential (ΔΨm), metabolic function, and swelling), hepatic, cerebral, and muscular mercury levels, and hepatic, cerebral, and renal thioredoxin reductase (TrxR) activity were evaluated. MeHg caused hepatic and cerebral mitochondrial dysfunction and inhibited TrxR activity in liver (38,9%), brain (64,3%), and kidney (73,8%). Cotreatment with (PhSe)2 protected hepatic and cerebral mitochondrial thiols from depletion by MeHg but failed to completely reverse MeHg's effect on hepatic and cerebral mitochondrial dysfunction or hepatic, cerebral, and renal inhibition of TrxR activity. Additionally, the cotreatment with (PhSe)2 increased Hg accumulation in the liver (50,5%) and brain (49,4%) and increased the MeHg-induced motor deficits and body-weight loss. In conclusion, these results indicate that (PhSe)2 can increase Hg body burden as well as the neurotoxic effects induced by MeHg exposure in rats.

Concentration dependent effect of calcium on brain mitochondrial bioenergetics and oxidative stress parameters

Mitochondrial dysfunction following traumatic brain and spinal cord injury (TBI and SCI) plays a pivotal role in the development of secondary pathophysiology and subsequent neuronal cell death. Previously, we demonstrated a loss of mitochondrial bioenergetics in the first 24 h following TBI and SCI initiates a rapid and extensive necrotic event at the primary site of injury. Within the mitochondrial derived mechanisms, the cross talk and imbalance amongst the processes of excitotoxicity, Ca²⁺ cycling/overload, ATP synthesis, free radical production and oxidative damage ultimately lead to mitochondrial damage followed by neuronal cell death. Mitochondria are one of the important organelles that regulate intracellular calcium (Ca²⁺) homeostasis and are equipped with a tightly regulated Ca²⁺ transport system. However, owing to the lack of consensus and the link between downstream effects of calcium in published literature, we undertook a systematic in vitro study for measuring concentration dependent effects of calcium (100–1000 nmols/mg mitochondrial protein) on mitochondrial respiration, enzyme activities, reactive oxygen/nitrogen species (ROS/RNS) generation, membrane potential (ΔΨ) and oxidative damage markers in isolated brain mitochondria. We observed a dose- and time-dependent inhibition of mitochondrial respiration by calcium without influencing mitochondrial pyruvate dehydrogenase complex (PDHC) and NADH dehydrogenase (Complex I) enzyme activities. We observed dose-dependent decreased production of hydrogen peroxide and total ROS/RNS species generation by calcium and no significant changes in protein and lipid oxidative damage markers. These results may shed new light on the prevailing dogma of the direct effects of calcium on mitochondrial bioenergetics, free radical production and oxidative stress parameters that are primary regulatory mitochondrial mechanisms following neuronal injury.

New therapeutic approach: diphenyl diselenide reduces mitochondrial dysfunction in acetaminophen-induced acute liver failure

The acute liver failure (ALF) induced by acetaminophen (APAP) is closely related to oxidative damage and depletion of hepatic glutathione, consequently changes in cell energy metabolism and mitochondrial dysfunction have been observed after APAP overdose. Diphenyl diselenide [(PhSe)₂], a simple organoselenium compound with antioxidant properties, previously demonstrated to confer hepatoprotection. However, little is known about the protective mechanism on mitochondria. The main objective of this study was to investigate the effects (PhSe)₂ to reduce mitochondrial dysfunction and, secondly, compare in the liver homogenate the hepatoprotective effects of the (PhSe)₂ to the N-acetylcysteine (NAC) during APAP-induced ALF to validate our model. Mice were injected intraperitoneal with APAP (600 mg/kg), (PhSe)₂ (15.6 mg/kg), NAC (1200 mg/kg), APAP+(PhSe)₂ or APAP+NAC, where the (PhSe)₂ or NAC treatment were given 1 h following APAP. The liver was collected 4 h after overdose. The plasma alanine and aspartate aminotransferase activities increased after APAP administration. APAP caused a remarkable increase of oxidative stress markers (lipid peroxidation, reactive species and protein carbonylation) and decrease of the antioxidant defense in the liver homogenate and mitochondria. APAP caused a marked loss in the mitochondrial membrane potential, the mitochondrial ATPase activity, and the rate of mitochondrial oxygen consumption and increased the mitochondrial swelling. All these effects were significantly prevented by (PhSe)₂. The effectiveness of (PhSe)₂ was similar at a lower dose than NAC. In summary, (PhSe)₂ provided a significant improvement to the mitochondrial redox homeostasis and the mitochondrial bioenergetics dysfunction caused by membrane permeability transition in the hepatotoxicity APAP-induced.

Ciclosporin does not attenuate intracranial hypertension in rats with acute hyperammonaemia

AIM: To investigate the neuroprotective potential of ciclosporin during acute liver failure. We evaluated the effect of intrathecally administered ciclosporin on intracranial pressure, brain water content and aquaporin-4 expression in a rat model with acute hyperammonaemia.

METHODS: Twenty-four male Wistar rats with portacaval anastomosis were randomised into four groups receiving ciclosporin or vehicle and ammonia or saline infusion. Ciclosporin or vehicle was given intrathecally prior to the ammonia or saline infusion. The ammonia or saline infusion was given intravenously for 4 h, while intracranial pressure and arterial pressure was recorded. At the end of the experiment, cerebral cortex and cerebellar brain tissue was analysed for water and aquaporin-4 content.

RESULTS: The following intracranial pressures were found at the end of the experiment: ammonia + ciclosporin: 10.0 ± 1.7 mmHg, ammonia + vehicle: 6.8 ± 1.0 mmHg, saline + ciclosporin: 3.1 ± 0.5 mmHg, saline + vehicle: 3.3 ± 0.6 mmHg. Ammonia infusion had a significant effect on intracranial pressure and brain water content, which both were higher in the groups receiving ammonia (P < 0.001, two-way analysis of variance). Treatment with ciclosporin resulted in relevant tissue concentrations of ciclosporin (> 0.2 micromolar) but did not reduce intracranial pressure after 4 h. Furthermore, ciclosporin did not attenuate the increase in cerebral water content, and did not affect aquaporin-4 expression.

CONCLUSION: Intrathecal administration of ciclosporin does not attenuate intracranial hypertension or brain oedema in rats with portacaval anastomosis and 4 h of ammonia infusion.

African eggplant (Solanum anguivi Lam.) fruit with bioactive polyphenolic compounds exerts in vitro antioxidant properties and inhibits Ca(2+)-induced mitochondrial swelling

OBJECTIVE

To evaluate the antioxidant and radical scavenging activities of Solanum anguivi fruit (SAG) and its possible effect on mitochondrial permeability transition pore as well as mitochondrial membrane potential (ΔΨm) isolated from rat liver.

METHODS

Antioxidant activity of SAG was assayed by using 2,2-diphenyl-1-picrylhydrazyl (DPPH), reducing power, iron chelation and ability to inhibit lipid peroxidation in both liver and brain homogenate of rats. Also, the effect of SAG on mitochondrial membrane potential and mitochondrial swelling were determined. Identification and quantification of bioactive polyphenolics was done by HPLC-DAD.

RESULTS

SAG exhibited potent and concentration dependent free radical-scavenging activity (IC50/DPPH=275.03±7.8 μg/mL). Reductive and iron chelation abilities also increase with increase in SAG concentration. SAG also inhibited peroxidation of cerebral and hepatic lipids subjected to iron oxidative assault. SAG protected against Ca(2+) (110 μmol/L)-induced mitochondrial swelling and maintained the ΔΨm. HPLC analysis revealed the presence of gallic acid [(17.54±0.04) mg/g], chlorogenic acid (21.90±0.02 mg/g), caffeic acid (16.64±0.01 mg/g), rutin [(14.71±0.03) mg/g] and quercetin [(7.39±0.05) mg/g].

CONCLUSIONS

These effects could be attributed to the bioactive polyphenolic compounds present in the extract. Our results suggest that SAG extract is a potential source of natural antioxidants that may be used not only in pharmaceutical and food industry but also in the treatment of diseases associated with oxidative stress.

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.

nNOS(+) striatal neurons, a subpopulation spared in Huntington's Disease, possess functional NMDA receptors but fail to generate mitochondrial ROS in response to an excitotoxic challenge

Huntington's disease (HD) is a neurodegenerative condition characterized by severe neuronal loss in the cortex and striatum that leads to motor and behavioral deficits. Excitotoxicity is thought to be involved in HD and several studies have indicated that NMDA receptor (NMDAR) overactivation can play a role in the selective neuronal loss found in HD. Interestingly, a small subset of striatal neurons (less than 1% of the overall population) is found to be spared in post-mortem HD brains. These neurons are medium-sized aspiny interneurons that highly express the neuronal isoform of nitric oxide synthase (nNOS). Intriguingly, neurons expressing large amounts of nNOS [hereafter indicated as nNOS(+) neurons] show reduced vulnerability to NMDAR-mediated excitotoxicity. Mechanisms underlying this reduced vulnerability are still largely unknown and may shed some light on pathogenic mechanisms involved in HD. One untested possibility is that nNOS(+) neurons possess fewer or less functioning NMDARs. Employing single cell calcium imaging we challenged this hypothesis and found that cultured striatal nNOS(+) neurons show NMDAR-evoked responses that are identical to the ones observed in the overall population of neurons that express lower levels of nNOS [nNOS(−) neurons]. NMDAR-dependent deregulation of intraneuronal Ca²⁺ is known to generate high levels of reactive oxygen species of mitochondrial origin (mt-ROS), a crucial step in the excitotoxic cascade. With confocal imaging and dihydrorhodamine (DHR; a ROS-sensitive probe) we compared mt-ROS levels generated by NMDAR activation in nNOS(+) and (−) cultured striatal neurons. DHR experiments revealed that nNOS(+) neurons failed to produce significant amounts of mt-ROS in response to NMDA exposure, thereby providing a potential mechanism for their reduced vulnerability to excitotoxicity and decreased vulnerability in HD.

Nelfinavir inhibits intra-mitochondrial calcium influx and protects brain against hypoxic-ischemic injury in neonatal mice

Nelfinavir (NLF), an antiretroviral agent, preserves mitochondrial membranes integrity and protects mature brain against ischemic injury in rodents. Our study demonstrates that in neonatal mice NLF significantly limits mitochondrial calcium influx, the event associated with protection of the brain against hypoxic-ischemic insult (HI). Compared to the vehicle-treated mice, cerebral mitochondria from NLF-treated mice exhibited a significantly greater tolerance to the Ca²⁺-induced membrane permeabilization, greater ADP-phosphorylating activity and reduced cytochrome C release during reperfusion. Pre-treatment with NLF or Ruthenium red (RuR) significantly improved viability of murine hippocampal HT-22 cells, reduced Ca²⁺ content and preserved membrane potential (Ψm) in mitochondria following oxygen-glucose deprivation (OGD). Following histamine-stimulated Ca²⁺ release from endoplasmic reticulum, in contrast to the vehicle-treated cells, the cells treated with NLF or RuR also demonstrated reduced Ca²⁺ content in their mitochondria, the event associated with preserved Ψm. Because RuR inhibits mitochondrial Ca²⁺ uniporter, we tested whether the NLF acts via the mechanism similar to the RuR. However, in contrast to the RuR, in the experiment with direct interaction of these agents with mitochondria isolated from naïve mice, the NLF did not alter mitochondrial Ca²⁺ influx, and did not prevent Ca²⁺ induced collapse of the Ψm. These data strongly argues against interaction of NLF and mitochondrial Ca²⁺ uniporter. Although the exact mechanism remains unclear, our study is the first to show that NLF inhibits intramitochondrial Ca²⁺ flux and protects developing brain against HI-reperfusion injury. This novel action of NLF has important clinical implication, because it targets a fundamental mechanism of post-ischemic cell death: intramitochondrial Ca²⁺ overload → mitochondrial membrane permeabilization → secondary energy failure.

Mitochondrial handling of excess Ca2+ is substrate-dependent with implications for reactive oxygen species generation

The mitochondrial electron transport chain is the major source of reactive oxygen species (ROS) during cardiac ischemia. Several mechanisms modulate ROS production; one is mitochondrial Ca(2+) uptake. Here we sought to elucidate the effects of extramitochondrial Ca(2+) (e[Ca(2+)]) on ROS production (measured as H(2)O(2) release) from complexes I and III. Mitochondria isolated from guinea pig hearts were preincubated with increasing concentrations of CaCl(2) and then energized with the complex I substrate Na(+) pyruvate or the complex II substrate Na(+) succinate. Mitochondrial H(2)O(2) release rates were assessed after giving either rotenone or antimycin A to inhibit complex I or III, respectively. After pyruvate, mitochondria maintained a fully polarized membrane potential (ΔΨ; assessed using rhodamine 123) and were able to generate NADH (assessed using autofluorescence) even with excess e[Ca(2+)] (assessed using CaGreen-5N), whereas they remained partially depolarized and did not generate NADH after succinate. This partial ΔΨ depolarization with succinate was accompanied by a large release in H(2)O(2) (assessed using Amplex red/horseradish peroxidase) with later addition of antimycin A. In the presence of excess e[Ca(2+)], adding cyclosporin A to inhibit mitochondrial permeability transition pore opening restored ΔΨ and significantly decreased antimycin A-induced H(2)O(2) release. Succinate accumulates during ischemia to become the major substrate utilized by cardiac mitochondria. The inability of mitochondria to maintain a fully polarized ΔΨ under excess e[Ca(2+)] when succinate, but not pyruvate, is the substrate may indicate a permeabilization of the mitochondrial membrane, which enhances H(2)O(2) emission from complex III during ischemia.

The role of the mitochondrial calcium uniporter in cerebral ischemia/reperfusion injury in rats involves regulation of mitochondrial energy metabolism

The mitochondrial calcium uniporter (MCU) maintains intracellular Ca2+ homeostasis by transporting Ca2+ from the cell cytosol into the mitochondrial matrix and is important for shaping Ca2+ signals and the activation of programmed cell death. Inhibition of MCU by ruthenium red (RR) or Ru360 has previously been reported to protect against neuronal death. The aim of the present study was to analyze the mechanisms underlying the effects of MCU activity in a rat model of cerebral ischemia/reperfusion (I/R) injury. Adult male Wistar rats were divided into 4 groups; sham, I/R, I/R + RR and I/R + spermine (Sper) and were subjected to reversible middle cerebral artery occlusion for 2 h followed by 24 h of reperfusion. A bolus injection of RR administered 30 min prior to ischemia was found to significantly decrease the total infarct volume and reduce neuronal damage and cell apoptosis compared with ischemia/reperfusion values. However, treatment with Sper, an activator of the MCU, increased the injury induced by I/R. Analysis of energy metabolism revealed that I/R induced progressive inhibition of complexes I‑IV of the electron transport chain, decreased ATP production, dissipated the mitochondrial membrane potential and increased the generation of reactive oxygen species. Treatment with RR ameliorated the condition, while spermine had the opposite effect. In conclusion, blocking MCU was demonstrated to exert protective effects against I/R injury and this process may be mediated by the prevention of energy failure.

Nitric oxide synthase inhibitors protect against rotenone-induced, oxidative stress mediated parkinsonism in rats

Rotenone is known to cause progressive dopaminergic neuronal loss in rodents, but it remains unclear how this mitochondrial complex-I inhibitor mediates neurodegeneration specific to substantia nigra pars compacta (SNpc). One of the proposed mechanisms is increased free radical generation owing to mitochondrial electron transport chain dysfunction following complex-I inhibition. The present study examined the role of nitric oxide (NO) and hydroxyl radicals (OH) in mediating rotenone-induced dopaminergic neurotoxicity. Indications of NO involvement are evidenced by inducible nitric oxide synthase (NOS) over-expression, and increased NADPH-diaphorase staining in SNpc neurons 96h following rotenone administration. Treatment of these animals with specific neuronal NOS inhibitor, 7-nitroindazole (7-NI) and non-specific NOS inhibitor, N-ω-nitro-l-argenine methyl ester (l-NAME) caused reversal of rotenone-induced striatal dopamine depletion, and attenuation of the neurotoxin-induced decrease in the number of tyrosine hydroxylase immunoreactive neurons in SNpc, as well as in apomorphine and amphetamine-induced unilateral rotations. Interestingly, the study also demonstrated the contribution of OH in mediating rotenone nigral toxicity since there appeared a significant generation of the reactive oxygen species in vivo 24h following rotenone administration, a copious loss of reduced and oxidized glutathione, and increased superoxide dismutase and catalase activities in the cytosolic fractions of the ipsilateral SNpc area on the 5th day. An OH scavenging capacity of 7-NI and l-NAME in a Fenton-like reaction, as well as complete reversal of the rotenone-induced increases in the antioxidant enzyme activities, and the loss in reduced and oxidized glutathione contents in the SNpc supported OH involvement in rotenone-induced dopaminergic neurotoxicity. While these results strongly suggest the contribution of both OH and NO, resulting in acute oxidative stress culminating in dopaminergic neurodegeneration caused by rotenone, the course of events indicated generation of OH as the primary event in the neurotoxic processes.

High Ca2+ load promotes hydrogen peroxide generation via activation of α-glycerophosphate dehydrogenase in brain mitochondria

H(2)O(2) generation associated with α-glycerophosphate (α-GP) oxidation was addressed in guinea pig brain mitochondria challenged with high Ca(2+) load (10 μM). Exposure to 10 μM Ca(2+) induced an abrupt 2.5-fold increase in H(2)O(2) release compared to that measured in the presence of a physiological cytosolic Ca(2+) concentration (100 nM) from mitochondria respiring on 5 mM α-GP in the presence of ADP (2 mM). The Ca(2+)-induced stimulation of H(2)O(2) generation was reversible and unaltered by the uniporter blocker Ru 360, indicating that it did not require Ca(2+) uptake into mitochondria. Enhanced H(2)O(2) generation by Ca(2+) was also observed in the absence of ADP when mitochondria exhibited permeability transition pore opening with a decrease in the NAD(P)H level, dissipation of membrane potential, and mitochondrial swelling. Furthermore, mitochondria treated with the pore-forming peptide alamethicin also responded with an elevated H(2)O(2) generation to a challenge with 10 μM Ca(2+). Ca(2+)-induced promotion of H(2)O(2) formation was further enhanced by the complex III inhibitor myxothiazol. With 20 mM α-GP concentration, stimulation of H(2)O(2) formation by Ca(2+) was detected only in the presence, not in the absence, of ADP. It is concluded that α-glycerophosphate dehydrogenase, which is accessible to and could be activated by a rise in the level of cytosolic Ca(2+), makes a major contribution to Ca(2+)-stimulated H(2)O(2) generation. This work highlights a unique high-Ca(2+)-stimulated reactive oxygen species-forming mechanism in association with oxidation of α-GP, which is largely independent of the bioenergetic state and can proceed even in damaged, functionally incompetent mitochondria.

Mitochondrial dysfunction and oxidative stress in Parkinson's disease and monogenic parkinsonism

The pathogenic mechanisms that underlie Parkinson's disease remain unknown. Here, we review evidence from both sporadic and genetic forms of Parkinson's disease that implicate both mitochondria and oxidative stress as central players in disease pathogenesis. A systemic deficiency in complex I of the mitochondrial electron transport chain is evident in many patients with the disease. Oxidative stress caused by reactive metabolites of dopamine and alterations in the levels of iron and glutathione in the substantia nigra accompany this mitochondrial dysfunction. Recent evidence from studies on the genetic forms of parkinsonism with particular stress on DJ-1, parkin, and PINK-1 also suggest the involvement of mitochondria and oxidative stress.

Multistationary and oscillatory modes of free radicals generation by the mitochondrial respiratory chain revealed by a bifurcation analysis

The mitochondrial electron transport chain transforms energy satisfying cellular demand and generates reactive oxygen species (ROS) that act as metabolic signals or destructive factors. Therefore, knowledge of the possible modes and bifurcations of electron transport that affect ROS signaling provides insight into the interrelationship of mitochondrial respiration with cellular metabolism. Here, a bifurcation analysis of a sequence of the electron transport chain models of increasing complexity was used to analyze the contribution of individual components to the modes of respiratory chain behavior. Our algorithm constructed models as large systems of ordinary differential equations describing the time evolution of the distribution of redox states of the respiratory complexes. The most complete model of the respiratory chain and linked metabolic reactions predicted that condensed mitochondria produce more ROS at low succinate concentration and less ROS at high succinate levels than swelled mitochondria. This prediction was validated by measuring ROS production under various swelling conditions. A numerical bifurcation analysis revealed qualitatively different types of multistationary behavior and sustained oscillations in the parameter space near a region that was previously found to describe the behavior of isolated mitochondria. The oscillations in transmembrane potential and ROS generation, observed in living cells were reproduced in the model that includes interaction of respiratory complexes with the reactions of TCA cycle. Whereas multistationarity is an internal characteristic of the respiratory chain, the functional link of respiration with central metabolism creates oscillations, which can be understood as a means of auto-regulation of cell metabolism.

The Na+/H+ exchanger-1 inhibitor cariporide prevents glutamate-induced necrotic neuronal death by inhibiting mitochondrial Ca2+ overload

In the brain, Na+/H+ exchanger-1 (NHE-1) activation has a significant impact on ischemic injury, and, in recent studies, NHE-1 inhibition has been found to protect neurons from ischemic injury. This protective effect has been ascribed to the prevention of apoptosis, but neuronal cell death following ischemia is a consequence of both necrotic and apoptotic cell death. Here, we evaluated the ability of the potent NHE-1 inhibitor cariporide to prevent necrotic cell death in an in vitro model of excitotoxic neuronal death. Cariporide (100 nM) was found to reduce both glutamate-induced necrotic and apoptotic neuronal cell death. Ca2+ concentrations were observed to peak twice in cytosol and mitochondria in cultured neuronal cells after glutamate exposure, and cariporide was found to reduce the second Ca2+ concentration increase, but not the first. Furthermore, glutamate-mediated mitochondrial death pathways involving loss of mitochondrial membrane potential and reactive oxygen species (ROS) accumulation were found to be attenuated by cariporide. In addition, cariporide effectively prevented necrosis following exposure to glutamate and ameliorated the mitochondrial Ca2+ and ROS production increases implicated in necrotic cell death. These results suggest that NHE-1 participates in the necrotic cell death process and that its inhibition offers a means of preventing both necrosis and apoptosis.

Protein carbonylation and aggregation precede neuronal apoptosis induced by partial glutathione depletion

While the build-up of oxidized proteins within cells is believed to be toxic, there is currently no evidence linking protein carbonylation and cell death. In the present study, we show that incubation of nPC12 (neuron-like PC12) cells with 50 μM DEM (diethyl maleate) leads to a partial and transient depletion of glutathione (GSH). Concomitant with GSH disappearance there is increased accumulation of PCOs (protein carbonyls) and cell death (both by necrosis and apoptosis). Immunocytochemical studies also revealed a temporal/spatial relationship between carbonylation and cellular apoptosis. In addition, the extent of all three, PCO accumulation, protein aggregation and cell death, augments if oxidized proteins are not removed by proteasomal degradation. Furthermore, the effectiveness of the carbonyl scavengers hydralazine, histidine hydrazide and methoxylamine at preventing cell death identifies PCOs as the toxic species. Experiments using well-characterized apoptosis inhibitors place protein carbonylation downstream of the mitochondrial transition pore opening and upstream of caspase activation. While the study focused mostly on nPC12 cells, experiments in primary neuronal cultures yielded the same results. The findings are also not restricted to DEM-induced cell death, since a similar relationship between carbonylation and apoptosis was found in staurosporine- and buthionine sulfoximine-treated nPC12 cells. In sum, the above results show for the first time a causal relationship between carbonylation, protein aggregation and apoptosis of neurons undergoing oxidative damage. To the best of our knowledge, this is the first study to place direct (oxidative) protein carbonylation within the apoptotic pathway.

Brain energy metabolism and mitochondrial dysfunction in acute and chronic hepatic encephalopathy

One proposed mechanism for acute and chronic hepatic encephalopathy (HE) is a disturbance in cerebral energy metabolism. It also reviews the current status of this mechanism in both acute and chronic HE, as well as in other hyperammonemic disorders. It also reviews abnormalities in glycolysis, lactate metabolism, citric acid cycle, and oxidative phosphorylation as well as associated energy impairment. Additionally, the role of mitochondrial permeability transition (mPT), a recently established factor in the pathogenesis of HE and hyperammonemia, is emphasized. Energy failure appears to be an important pathogenetic component of both acute and chronic HE and a potential target for therapy.

Post-injury administration of the mitochondrial permeability transition pore inhibitor, NIM811, is neuroprotective and improves cognition after traumatic brain injury in rats

Mitochondrial dysfunction is known to play a pivotal role in cell death mechanisms following traumatic brain injury (TBI). N-methyl-4-isoleucine-cyclosporin (NIM811), a non-immunosuppressive cyclosporin A (CsA) analog, inhibits the mitochondrial permeability transition pore (mPTP) and has been shown to be neuroprotective following TBI in mice. However, the translation of the neuroprotective effects of mPTP inhibitors, including CsA and NIM811, into improved cognitive end points has yet to be fully investigated. Therefore, to build upon these results, a severe unilateral controlled cortical impact model of TBI was used in the present study to establish a dose-response curve for NIM811 in rats. The findings demonstrate that the neuroprotection afforded by NIM811 is dose dependent, with the 10 mg/kg dose being the most effective dose. Once the dose response was established, we evaluated the effect of the optimal dose of NIM811 on behavior, mitochondrial bioenergetics, and mitochondrial oxidative damage following TBI. For behavioral studies, rats were administered NIM811 at 15 min and 24 h post-injury, with cognitive testing beginning 10 days post-injury. Mitochondrial studies involved a single injection of NIM811 at 15 min post-injury followed by mitochondrial isolation at 6 h post-injury. The results revealed that the optimal dose of NIM811 improves cognition, improves mitochondrial functioning, and reduces oxidative damage following TBI.

Mitochondrial membrane potential probes and the proton gradient: a practical usage guide

Fluorescent probes for monitoring mitochondrial membrane potential are frequently used for assessing mitochondrial function, particularly in the context of cell fate determination in biological and biomedical research. However, valid interpretation of results obtained with such probes requires careful consideration of numerous controls, as well as possible effects of non-protonic charges on dye behavior. In this context, we provide an overview of some of the important technical considerations, controls, and parallel complementary assays that can be employed to help ensure appropriate interpretation of results, thus providing a practical usage guide for monitoring mitochondrial membrane potentials with cationic probes. In total, this review will help illustrate both the strengths and potential pitfalls of common mitochondrial membrane potential dyes, and highlight best-usage approaches for their efficacious application in life sciences research.