N-Acetylglutamate and N-acetylmethionine compromise mitochondrial bioenergetics homeostasis and glutamate oxidation in brain of developing rats: Potential implications for the pathogenesis of ACY1 deficiency.

Aminoacylase 1 (ACY1) deficiency is an inherited metabolic disorder biochemically characterized by high urinary concentrations of aliphatic N-acetylated amino acids and associated with a broad clinical spectrum with predominant neurological signs. Considering that the pathogenesis of ACY1 is practically unknown and the brain is highly dependent on energy production, the in vitro effects of N-acetylglutamate (NAG) and N-acetylmethionine (NAM), major metabolites accumulating in ACY1 deficiency, on the enzyme activities of the citric acid cycle (CAC), of the respiratory chain complexes and glutamate dehydrogenase (GDH), as well as on ATP synthesis were evaluated in brain mitochondrial preparations of developing rats. NAG mildly inhibited mitochondrial isocitrate dehydrogenase 2 (IDH2) activity, moderately inhibited the activities of isocitrate dehydrogenase 3 (IDH3) and complex II-III of the respiratory chain and markedly suppressed the activities of complex IV and GDH. Of note, the NAG-induced inhibitory effect on IDH3 was competitive, whereas that on GDH was mixed. On the other hand, NAM moderately inhibited the activity of respiratory complexes II-III and GDH activities and strongly decreased complex IV activity. Furthermore, NAM was unable to modify any of the CAC enzyme activities, indicating a selective effect of NAG toward IDH mitochondrial isoforms. In contrast, the activities of citrate synthase, α-ketoglutarate dehydrogenase, malate dehydrogenase, and of the respiratory chain complexes I and II were not changed by these N-acetylated amino acids. Finally, NAG and NAM strongly decreased mitochondrial ATP synthesis. Taken together, the data indicate that NAG and NAM impair mitochondrial brain energy homeostasis.

Sex-Based Impact of Creatine Supplementation on Depressive Symptoms, Brain Serotonin and SSRI Efficacy in an Animal Model of Treatment-Resistant Depression.

BACKGROUND: Rates of major depressive disorder (MDD) increase with living at altitude. In our model, rats housed at moderate altitude (in hypobaric hypoxia) exhibit increased depression-like behavior, altered brain serotonin and a lack of antidepressant response to most selective serotonin reuptake inhibitors (SSRIs). A forebrain deficit in the bioenergetic marker creatine is noted in people living at altitude or with MDD. METHODS: Rats housed at 4500 ft were given dietary creatine monohydrate (CRMH, 4% w/w, 5 weeks) vs. un-supplemented diet, and impact on depression-like behavior, brain bioenergetics, serotonin and SSRI efficacy assessed. RESULTS: CRMH significantly improved brain creatine in a sex-based manner. At altitude, CRMH increased serotonin levels in the female prefrontal cortex and striatum but reduced male striatal and hippocampal serotonin. Dietary CRMH was antidepressant in the forced swim test and anti-anhedonic in the sucrose preference test in only females at altitude, with motor behavior unchanged. CRMH improved fluoxetine efficacy (20 mg/kg) in only males at altitude: CRMH + SSRI significantly improved male striatal creatine and serotonin vs. CRMH alone. CONCLUSIONS: Dietary CRMH exhibits sex-based efficacy in resolving altitude-related deficits in brain biomarkers, depression-like behavior and SSRI efficacy, and may be effective clinically for SSRI-resistant depression at altitude. This is the first study to link CRMH treatment to improving brain serotonin.

Brain mitochondria in behavior: more than a powerhouse.

Rosenberg and colleagues developed a miniaturized assay of mitochondrial content and energy transformation capacity that allowed them to assess mitochondrial features and activities across the brain in male mice. Their findings provide a comprehensive brain-wide map of mitochondrial associations with stress-induced behaviors and highlight mitochondria as dynamic, spatially-organized organelles.

Brain bioenergetics in chronic hypertension: Risk factor for acute ischemic stroke.

Chronic hypertension is one of the key modifiable risk factors for acute ischemic stroke, also contributing to determine greater neurological deficits and worse functional outcome when an acute cerebrovascular event would occur. A tight relationship exists between cerebrovascular autoregulation, neuronal activity and brain bioenergetics. In chronic hypertension, progressive adaptations of these processes occur as an attempt to cope with the demanding necessity of brain functions, creating a new steady-state homeostatic condition. However, these adaptive modifications are insufficient to grant an adequate response to possible pathological perturbations of the established fragile hemodynamic and metabolic homeostasis. In this narrative review, we will discuss the main mechanisms by which alterations in brain bioenergetics and mitochondrial function in chronic hypertension could lead to increased risk of acute ischemic stroke, stressing the interconnections between hemodynamic factors (i.e. cerebral autoregulation and neurovascular coupling) and metabolic processes. Both experimental and clinical pieces of evidence will be discussed. Moreover, the potential role of mitochondrial dysfunction in determining, or at least sustaining, the pathogenesis and progression of chronic neurogenic hypertension will be considered. In the perspective of novel therapeutic strategies aiming at improving brain bioenergetics, we propose some determinant factors to consider in future studies focused on the cause-effect relationships between chronic hypertension and brain bioenergetic abnormalities (and vice versa), so to help translational research in this so-far unfilled gap.

Mitochondria-Targeted Therapeutics for Alzheimer's Disease: The Good, the Bad, the Potential.

Significance: Alzheimer's disease (AD) is the leading cause of dementia. Thus far, 99.6% of clinical trials, including those targeting energy metabolism, have failed to exert disease-modifying efficacy. Altered mitochondrial function and disruption to the brain bioenergetic system have long-been documented as early events during the pathological progression of AD. Recent Advances: While therapeutic approaches that directly promote mitochondrial bioenergetic machinery or eliminate reactive oxygen species have exhibited limited translatability, emerging strategies targeting nonenergetic aspects of mitochondria provide novel therapeutic targets with the potential to modify AD risk and progression. Growing evidence also reveals a critical link between mitochondrial phenotype and neuroinflammation via metabolic reprogramming of glial cells. Critical Issues: Herein, we summarize major classes of mitochondrion-centered AD therapeutic strategies. In addition, the discrepancy in their efficacy when translated from preclinical models to clinical trials is addressed. Key factors that differentiate the responsiveness to bioenergetic interventions, including sex, apolipoprotein E genotype, and cellular diversity in the brain, are discussed. Future Directions: We propose that the future development of mitochondria-targeted AD therapeutics should consider the interactions between bioenergetics and other disease mechanisms, which may require cell-type-specific targeting to distinguish neurons and non-neuronal cells. Moreover, a successful strategy will likely include stratification by metabolic phenotype, which varies by sex and genetic risk profile and dynamically changes throughout the course of disease. As the network of mitochondrial integration expands across intracellular and systems level biology, assessment of intended, the good, versus unintended consequences, the bad, will be required to reach the potential of mitochondrial therapeutics.

Pharmacokinetics, Safety, and Tolerability of Orally Administered Ursodeoxycholic Acid in Patients With Parkinson's Disease-A Pilot Study.

Mitochondrial dysfunction is implicated in the pathogenesis of Parkinson's disease. Preliminary data have shown lower brain adenosine triphosphate (ATP) levels in Parkinson's disease versus age-matched healthy controls. Ursodeoxycholic acid (UDCA) may improve impaired mitochondrial function. Our objective was to evaluate UDCA tolerability, pharmacokinetics, and its effect on brain bioenergetics in individuals with Parkinson's disease. An open-label, prospective, multiple-ascending-dose study of oral UDCA in 5 individuals with Parkinson's disease was completed. A blood safety panel, plasma concentrations of UDCA and UDCA conjugates, and brain ATP levels were measured before and after therapy (week 1: 15 mg/kg/day; week 2: 30 mg/kg/day; and weeks 3-6: 50 mg/kg/day). UDCA and conjugates were measured using liquid chromatography-mass spectrometry. ATP levels and ATPase activity were measured using 7-Tesla 31 P magnetic resonance spectroscopy. Secondary measures included the Unified Parkinson's Disease Rating Scale and Montreal Cognitive Assessment. UDCA was generally well tolerated. The most frequent adverse event was gastrointestinal discomfort, rated by subjects as mild to moderate. Noncompartmental pharmacokinetic analysis resulted in (mean ± standard deviation) a maximum concentration of 8749 ± 2840 ng/mL and half-life of 2.1 ± 0.71 hr. Magnetic resonance spectroscopy data were obtained in 3 individuals with Parkinson's disease and showed modest increases in ATP and decreases in ATPase activity. Changes in Unified Parkinson's Disease Rating Scale (parts I-IV) and Montreal Cognitive Assessment scores (mean ± standard deviation) were -4.6 ± 6.4 and 2 ± 1.7, respectively. This is the first report of UDCA use in individuals with Parkinson's disease. Its pharmacokinetics are variable, and at high doses it appears reasonably well tolerated. Our findings warrant additional studies of its effect on brain bioenergetics.

Update: Microdialysis for Monitoring Cerebral Metabolic Dysfunction after Subarachnoid Hemorrhage.

Cerebral metabolic dysfunction has been shown to extensively mediate the pathophysiology of brain injury after subarachnoid hemorrhage (SAH). The characterization of the alterations of metabolites in the brain can help elucidate pathophysiological changes occurring throughout SAH and the relationship between secondary brain injury and cerebral energy dysfunction after SAH. Cerebral microdialysis (CMD) is a tool that can measure concentrations of multiple bioenergetics metabolites in brain interstitial fluid. This review aims to provide an update on the implication of CMD on the measurement of metabolic dysfunction in the brain after SAH. A literature review was conducted through a general PubMed search with the terms "Subarachnoid Hemorrhage AND Microdialysis" as well as a more targeted search using MeSh with the search terms "Subarachnoid hemorrhage AND Microdialysis AND Metabolism." Both experimental and clinical papers were reviewed. CMD is a suitable tool that has been used for monitoring cerebral metabolic changes in various types of brain injury. Clinically, CMD data have shown the dramatic changes in cerebral metabolism after SAH, including glucose depletion, enhanced glycolysis, and suppressed oxidative phosphorylation. Experimental studies using CMD have demonstrated a similar pattern of cerebral metabolic dysfunction after SAH. The combination of CMD and other monitoring tools has also shown value in further dissecting and distinguishing alterations in different metabolic pathways after brain injury. Despite the lack of a standard procedure as well as the presence of limitations regarding CMD application and data interpretation for both clinical and experimental studies, emerging investigations have suggested that CMD is an effective way to monitor the changes of cerebral metabolic dysfunction after SAH in real-time, and alternatively, the combination of CMD and other monitoring tools might be able to further understand the relationship between cerebral metabolic dysfunction and brain injury after SAH, determine the severity of brain injury and predict the pathological progression and outcomes after SAH. More translational preclinical investigations and clinical validation may help to optimize CMD as a powerful tool in critical care and personalized medicine for patients with SAH.

Mitochondrial Supercomplexes: Physiological Organization and Dysregulation in Age-Related Neurodegenerative Disorders.

Several studies suggest that the assembly of mitochondrial respiratory complexes into structures known as supercomplexes (SCs) may increase the efficiency of the electron transport chain, reducing the rate of production of reactive oxygen species. Therefore, the study of the (dis)assembly of SCs may be relevant for the understanding of mitochondrial dysfunction reported in brain aging and major neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD). Here we briefly reviewed the biogenesis and structural properties of SCs, the impact of mtDNA mutations and mitochondrial dynamics on SCs assembly, the role of lipids on stabilization of SCs and the methodological limitations for the study of SCs. More specifically, we summarized what is known about mitochondrial dysfunction and SCs organization and activity in aging, AD and PD. We focused on the critical variables to take into account when postmortem tissues are used to study the (dis)assembly of SCs. Since few works have been performed to study SCs in AD and PD, the impact of SCs dysfunction on the alteration of brain energetics in these diseases remains poorly understood. The convergence of future progress in the study of SCs structure at high resolution and the refinement of animal models of AD and PD, as well as the use of iPSC-based and somatic cell-derived neurons, will be critical in understanding the biological relevance of the structural remodeling of SCs.

Interaction of the Psychiatric Risk Gene Cacna1c With Post-weaning Social Isolation or Environmental Enrichment Does Not Affect Brain Mitochondrial Bioenergetics in Rats.

The pathophysiology of neuropsychiatric disorders involves complex interactions between genetic and environmental risk factors. Confirmed by several genome-wide association studies, Cacna1c represents one of the most robustly replicated psychiatric risk genes. Besides genetic predispositions, environmental stress such as childhood maltreatment also contributes to enhanced disease vulnerability. Both, Cacna1c gene variants and stressful life events are associated with morphological alterations in the prefrontal cortex and the hippocampus. Emerging evidence suggests impaired mitochondrial bioenergetics as a possible underlying mechanism of these regional brain abnormalities. In the present study, we simulated the interaction of psychiatric disease-relevant genetic and environmental factors in rodents to investigate their potential effect on brain mitochondrial function using a constitutive heterozygous Cacna1c rat model in combination with a four-week exposure to either post-weaning social isolation, standard housing, or social and physical environmental enrichment. Mitochondria were isolated from the prefrontal cortex and the hippocampus to evaluate their bioenergetics, membrane potential, reactive oxygen species production, and respiratory chain complex protein levels. None of these parameters were considerably affected in this particular gene-environment setting. These negative results were very robust in all tested conditions demonstrating that Cacna1c depletion did not significantly translate into altered bioenergetic characteristics. Thus, further investigations are required to determine the disease-related effects on brain mitochondria.

Physical exercise mitigates doxorubicin-induced brain cortex and cerebellum mitochondrial alterations and cellular quality control signaling.

Doxorubicin (DOX) is a highly effective anti-neoplastic agent, whose clinical use is limited by a dose-dependent mitochondrial toxicity in non-target tissues, including the brain. Here we analyzed the effects of distinct exercise modalities (12-week endurance treadmill-TM or voluntary free-wheel activity-FW) performed before and during sub-chronic DOX treatment on brain cortex and cerebellum mitochondrial bioenergetics, oxidative stress, permeability transition pore (mPTP), and proteins involved in mitochondrial biogenesis, apoptosis and auto(mito)phagy. Male Sprague-Dawley rats were divided into saline-sedentary (SAL+SED), DOX-sedentary (DOX+SED; 7-week DOX (2 mg · kg(-1)per week)), DOX+TM and DOX+FW. Animal behavior and post-sacrifice mitochondrial function were assessed. Oxidative phosphorylation (OXPHOS) subunits, oxidative stress markers or related proteins (SIRT3, p66shc, UCP2, carbonyls, MDA, -SH, aconitase, Mn-SOD), as well as proteins involved in mitochondrial biogenesis (PGC1α and TFAM) were evaluated. Apoptotic signaling was followed through caspases 3, 8 and 9-like activities, Bax, Bcl2, CypD, ANT and cofilin expression. Mitochondrial dynamics (Mfn1, Mfn2, OPA1 and DRP1) and auto(mito)phagy (LC3II, Beclin1, Pink1, Parkin and p62)-related proteins were measured by semi-quantitative Western blotting. DOX impaired behavioral performance, mitochondrial function, including lower resistance to mPTP and increased apoptotic signaling, decreased the content in OXPHOS complex subunits and increased oxidative stress in brain cortex and cerebellum. Molecular markers of mitochondrial biogenesis, dynamics and autophagy were also altered by DOX treatment in both brain subareas. Generally, TM and FW were able to mitigate DOX-related impairments in brain cortex and cerebellum mitochondrial activity, mPTP and apoptotic signaling. We conclude that the alterations in mitochondrial biogenesis, dynamics and autophagy markers induced by exercise performed before and during treatment may contribute to the observed protective brain cortex and cerebellum mitochondrial phenotype, which is more resistant to oxidative damage and apoptotic signaling in sub-chronically DOX treated animals.

Effects of Creatine Monohydrate Augmentation on Brain Metabolic and Network Outcome Measures in Women With Major Depressive Disorder.

BACKGROUND: Creatine monohydrate (creatine) augmentation has the potential to accelerate the clinical responses to and enhance the overall efficacy of selective serotonin reuptake inhibitor treatment in women with major depressive disorder (MDD). Although it has been suggested that creatine augmentation may involve the restoration of brain energy metabolism, the mechanisms underlying its antidepressant efficacy are unknown. METHODS: In a randomized, double-blind, placebo-controlled trial, 52 women with MDD were assigned to receive either creatine augmentation or placebo augmentation of escitalopram; 34 subjects participated in multimodal neuroimaging assessments at baseline and week 8. Age-matched healthy women (n = 39) were also assessed twice at the same intervals. Metabolic and network outcomes were measured for changes in prefrontal N-acetylaspartate and changes in rich club hub connections of the structural brain network using proton magnetic resonance spectroscopy and diffusion tensor imaging, respectively. RESULTS: We found MDD-related metabolic and network dysfunction at baseline. Improvement in depressive symptoms was greater in patients receiving creatine augmentation relative to placebo augmentation. After 8 weeks of treatment, prefrontal N-acetylaspartate levels increased significantly in the creatine augmentation group compared with the placebo augmentation group. Increment in rich club hub connections was also greater in the creatine augmentation group than in the placebo augmentation group. CONCLUSIONS: N-acetylaspartate levels and rich club connections increased after creatine augmentation of selective serotonin reuptake inhibitor treatment. Effects of creatine administration on brain energy metabolism and network organization may partly underlie its efficacy in treating women with MDD.

Cardiolipin profile changes are associated to the early synaptic mitochondrial dysfunction in Alzheimer's disease.

Brain mitochondria are fundamental to maintaining healthy functional brains, and their dysfunction is involved in age-related neurodegenerative disorders such as Alzheimer's disease (AD). In this study, we conducted a research on how both non-synaptic and synaptic mitochondrial functions are compromised at an early stage of AD-like pathologies and their correlation with putative changes on membranes lipid profile, using 3 month-old nontransgenic and 3xTg-AD mice, a murine model of experimental AD. Bioenergetic dysfunction in 3xTg-AD brains is evidenced by a decrease of brain ATP levels resulting, essentially, from synaptic mitochondria functionality disruption as indicated by declined respiratory control ratio associated with a 50% decreased complex I activity. Lipidomics studies revealed that synaptic bioenergetic deficit of 3xTg-AD brains is accompanied by alterations in the phospholipid composition of synaptic mitochondrial membranes, detected either in phospholipid class distribution or in the phospholipids molecular profile. Globally, diacyl- and lyso-phosphatidylcholine lipids increase while ethanolamine plasmalogens and cardiolipins content drops in relation to nontransgenic background. However, the main lipidomic mark of 3xTg-AD brains is that cardiolipin cluster-organized profile is lost in synaptic mitochondria due to a decline of the most representative molecular species. In contrast to synaptic mitochondria, results support the idea that non-synaptic mitochondria function is preserved at the age of 3 months. Although the genetically construed 3xTg-AD mouse model does not represent the most prevalent form of AD in humans, the present study provides insights into the earliest biochemical events in AD brain, connecting specific lipidomic changes with synaptic bioenergetic deficit that may contribute to the progressive synapses loss and the neurodegenerative process that characterizes AD.

Cannabinoid control of brain bioenergetics: Exploring the subcellular localization of the CB1 receptor.

Brain mitochondrial activity is centrally involved in the central control of energy balance. When studying mitochondrial functions in the brain, however, discrepant results might be obtained, depending on the experimental approaches. For instance, immunostaining experiments and biochemical isolation of organelles expose investigators to risks of false positive and/or false negative results. As an example, the functional presence of cannabinoid type 1 (CB1) receptors on brain mitochondrial membranes (mtCB1) was recently reported and rapidly challenged, claiming that the original observation was likely due to artifact results. Here, we addressed this issue by directly comparing the procedures used in the two studies. Our results show that the use of appropriate controls and quantifications allows detecting mtCB1 receptor with CB1 receptor antibodies, and that, if mitochondrial fractions are enriched and purified, CB1 receptor agonists reliably decrease respiration in brain mitochondria. These data further underline the importance of adapted experimental procedures to study brain mitochondrial functions.