Changes In Brain Energy Metabolism Research Articles

A Comprehensive Review on Hepatic Encephalopathy: Pathophysiology, Symptoms, Epidemiology, Classification, Diagnosis and Treatment

The condition known as hepatic encephalopathy (HE) is a state of impaired brain function that can be reversed and is experienced by patients who are suffering from severe liver diseases. Neurotoxins, decreased neurotransmission as a result of metabolic anomalies in liver failure, changes in brain energy metabolism, systemic inflammatory response, and alterations of the blood brain barrier are the primary hypotheses that are still being explored in relation to the precise pathophysiology of hepatic encephalopathy (HE). There is a wide spectrum of severity regarding the neurological and mental symptoms that can be brought on by HE. For the purpose of diagnosing limited HE, abnormal psychometric tests are utilised. Alterations in personality, altered states of consciousness, gradual spatial and temporal disorientation, lethargy, stupor, and coma are some of the characteristics of HE that are clinically noticeable. For the purpose of diagnosis, specific testing is not required outside of clinical studies. HE is classified according to the underlying disease, the severity of symptoms, the length of time it has been present, and whether or not there are triggers that cause it to occur. Hepatic encephalopathy refers to a collection of neuropsychiatric illnesses that can be treated and are characterised by the presence of symptoms in individuals who have liver disease or who have undergone portosystemic shunting. Entephalopathy, a disabling result of cirrhosis, affects thirty-five percent to forty-five percent of cirrhotic patients. Before recently, the treatment choices for HE that were available in hospitals were depending on anecdotal evidence, the availability of medication, and the norms of the relevant institutions. An increasing number of randomised controlled trials (RCTs) are providing further confirmation of the central significance of the basic HE therapy techniques (lactulose, branched-chain amino acids, and rifaximin), as well as the rising body of evidence showing the large beneficial advantages associated with these strategies. The liver transplantation and embolisation of large PSSs are two treatments that have proven to be effective for a select group of patients who have been carefully selected. Not only does it have a significant influence on the day-to-day lives of patients and carers, but it is also associated with increased rates of sickness and death and consumes a significant amount of resources in the healthcare system. In this article, we examine the history of hepatic encephalopathy, as well as the current understanding of the condition and the potential treatments for it.

A Comprehensive Review on Hepatic Encephalopathy: Pathophysiology, Symptoms, Epidemiology, Classification, Diagnosis and Treatment

The condition known as hepatic encephalopathy (HE) is a state of impaired brain function that can be reversed and is experienced by patients who are suffering from severe liver diseases. Neurotoxins, decreased neurotransmission as a result of metabolic anomalies in liver failure, changes in brain energy metabolism, systemic inflammatory response, and alterations of the blood brain barrier are the primary hypotheses that are still being explored in relation to the precise pathophysiology of hepatic encephalopathy (HE). There is a wide spectrum of severity regarding the neurological and mental symptoms that can be brought on by HE. For the purpose of diagnosing limited HE, abnormal psychometric tests are utilised. Alterations in personality, altered states of consciousness, gradual spatial and temporal disorientation, lethargy, stupor, and coma are some of the characteristics of HE that are clinically noticeable. For the purpose of diagnosis, specific testing is not required outside of clinical studies. HE is classified according to the underlying disease, the severity of symptoms, the length of time it has been present, and whether or not there are triggers that cause it to occur. Hepatic encephalopathy refers to a collection of neuropsychiatric illnesses that can be treated and are characterised by the presence of symptoms in individuals who have liver disease or who have undergone portosystemic shunting. Entephalopathy, a disabling result of cirrhosis, affects thirty-five percent to forty-five percent of cirrhotic patients. Before recently, the treatment choices for HE that were available in hospitals were depending on anecdotal evidence, the availability of medication, and the norms of the relevant institutions. An increasing number of randomised controlled trials (RCTs) are providing further confirmation of the central significance of the basic HE therapy techniques (lactulose, branched-chain amino acids, and rifaximin), as well as the rising body of evidence showing the large beneficial advantages associated with these strategies. The liver transplantation and embolisation of large PSSs are two treatments that have proven to be effective for a select group of patients who have been carefully selected. Not only does it have a significant influence on the day-to-day lives of patients and carers, but it is also associated with increased rates of sickness and death and consumes a significant amount of resources in the healthcare system. In this article, we examine the history of hepatic encephalopathy, as well as the current understanding of the condition and the potential treatments for it.

Omega-3 alleviates behavioral and molecular changes in a mouse model of stress-induced juvenile depression

IntroductionDepression is increasingly diagnosed in adolescence, necessitating specific prevention and treatment methods. However, there is a lack of animal models mimicking juvenile depression. This study explores a novel model using ultrasound (US) stress in juvenile mice. MethodsWe employed the US stress model in one-month-old C57/BL6 mice, exposing them to alternating ultrasound frequencies (20–25 kHz and 25–45 kHz) for three weeks. These frequencies correspond to negative and neutral emotional states in rodents and can induce a depressive-like syndrome. Concurrently, mice received either an omega-3 food supplement (FS) containing eicosapentaenoic acid (EPA; 0.55 mg/kg/day) and docosahexaenoic acid (DHA; 0.55 mg/kg/day) or a vehicle. Post-stress, we evaluated anxiety- and depressive-like behaviors, blood corticosterone levels, brain expression of pro-inflammatory cytokines, and conducted metabolome analysis of brain, liver and blood plasma. ResultsUS-exposed mice treated with vehicle exhibited decreased sucrose preference, a sign of anhedonia, a key feature of depression, increased anxiety-like behavior, elevated corticosterone levels, and enhanced TNF and IL-1β gene expression in the brain. In contrast, US-FS mice did not display these changes. Omega-3 supplementation also reduced anxiety-like behavior in non-stressed mice. Metabolomic analysis revealed US-induced changes in brain energy metabolism, with FS increasing brain sphingomyelin. Liver metabolism was affected by both US and FS, while plasma metabolome changes were exclusive to FS. Brain glucose levels correlated positively with activity in anxiety tests. ConclusionChronic omega-3 intake counteracted depressive- and anxiety-like behaviors in a US model of juvenile depression in mice. These effects likely stem from the anti-inflammatory properties of the supplement, suggesting potential therapeutic applications in juvenile depression.

Hippocampal disruptions of synaptic and astrocyte metabolism are primary events of early amyloid pathology in the 5xFAD mouse model of Alzheimer\u2019s disease

Alzheimer’s disease (AD) is an unremitting neurodegenerative disorder characterized by cerebral amyloid-β (Aβ) accumulation and gradual decline in cognitive function. Changes in brain energy metabolism arise in the preclinical phase of AD, suggesting an important metabolic component of early AD pathology. Neurons and astrocytes function in close metabolic collaboration, which is essential for the recycling of neurotransmitters in the synapse. However, this crucial metabolic interplay during the early stages of AD development has not been sufficiently investigated. Here, we provide an integrative analysis of cellular metabolism during the early stages of Aβ accumulation in the cerebral cortex and hippocampus of the 5xFAD mouse model of AD. Our electrophysiological examination revealed an increase in spontaneous excitatory signaling in the 5xFAD hippocampus. This hyperactive neuronal phenotype coincided with decreased hippocampal tricarboxylic acid (TCA) cycle metabolism mapped by stable 13C isotope tracing. Particularly, reduced astrocyte TCA cycle activity and decreased glutamine synthesis led to hampered neuronal GABA synthesis in the 5xFAD hippocampus. In contrast, the cerebral cortex of 5xFAD mice displayed an elevated capacity for oxidative glucose metabolism, which may suggest a metabolic compensation in this brain region. We found limited changes when we explored the brain proteome and metabolome of the 5xFAD mice, supporting that the functional metabolic disturbances between neurons and astrocytes are early primary events in AD pathology. In addition, synaptic mitochondrial and glycolytic function was selectively impaired in the 5xFAD hippocampus, whereas non-synaptic mitochondrial function was maintained. These findings were supported by ultrastructural analyses demonstrating disruptions in mitochondrial morphology, particularly in the 5xFAD hippocampus. Collectively, our study reveals complex regional and cell-specific metabolic adaptations in the early stages of amyloid pathology, which may be fundamental for the progressing synaptic dysfunctions in AD.

Brain energy failure in dementia syndromes: Opportunities and challenges for glucagon-like peptide-1 receptor agonists.

Medications for type 2 diabetes (T2DM) offer a promising path for discovery and development of effective interventions for dementia syndromes. A common feature of dementia syndromes is an energy failure due to reduced energy supply to neurons and is associated with synaptic loss and results in cognitive decline and behavioral changes. Among diabetes medications, glucagon‐like peptide‐1 (GLP‐1) receptor agonists (RAs) promote protective effects on vascular, microglial, and neuronal functions. In this review, we present evidence from animal models, imaging studies, and clinical trials that support developing GLP‐1 RAs for dementia syndromes. The review examines how changes in brain energy metabolism differ in conditions of insulin resistance and T2DM from dementia and underscores the challenges that arise from the heterogeneity of dementia syndromes. The development of GLP‐1 RAs as dementia therapies requires a deeper understanding of the regional changes in brain energy homeostasis guided by novel imaging biomarkers.

Hippocampal Disruptions of Synaptic and Astrocyte Metabolism are Primary Events of Early Amyloid Pathology in the 5xFAD Mouse Model of Alzheimer's Disease

Alzheimer’s disease (AD) is an unremitting neurodegenerative disorder characterized by cerebral amyloid-β (Aβ) accumulation and gradual decline in cognitive function. Changes in brain energy metabolism arise in the preclinical phase of AD, suggesting an important metabolic component of early AD pathology. Neurons and astrocytes function in close metabolic collaboration, which is essential for the recycling of neurotransmitters in the synapse. However, this crucial metabolic interplay during the early stages of AD development has not been sufficiently investigated. Here, we provide an integrative analysis of cellular metabolism during the early stages of Aβ accumulation in the cerebral cortex and hippocampus of the 5xFAD mouse model of AD. Our electrophysiological examination revealed an increase in spontaneous excitatory signaling in the 5xFAD hippocampus. This hyperactive neuronal phenotype coincided with decreased hippocampal TCA cycle metabolism mapped by stable 13C isotope tracing. Particularly, reduced astrocyte TCA cycle activity led to decreased glutamine synthesis, in turn hampering neuronal GABA synthesis in the 5xFAD hippocampus. In contrast, the cerebral cortex of 5xFAD mice displayed an elevated capacity for oxidative glucose metabolism suggesting a metabolic compensation. We found limited changes when we explored the brain proteome and metabolome of the 5xFAD mice, supporting that the functional metabolic disturbances between neurons and astrocytes are early primary events in AD pathology. In addition, synaptic mitochondrial and glycolytic function was impaired selectively in the 5xFAD hippocampus, whereas non-synaptic mitochondrial function was maintained. These findings were supported by ultrastructural analyses demonstrating disruptions in mitochondrial morphology, particularly in the 5xFAD hippocampus. Collectively, our study reveals complex regional and cell-specific metabolic adaptations, in the early stages of amyloid pathology, which may be fundamental for the progressing synaptic dysfunction in AD.

Inflammation, insulin resistance and the pathophysiology of depression: implications for novel antidepressant developments

This review summarises the impact of chronic low grade inflammation as a causative factor in the pathophysiology of major depression. Evidence is presented to show that proinflammatory cytokines both directly, and indirectly by increasing hypercortisolaemia, desensitise insulin receptors and thereby decrease the transport of glucose into the brain (the diabetic brain). In addition, the proinflammatory cytokines activate the tryptophan-kynurenine pathway which results in the synthesis of the NMDA-glutamate receptor agonist quinolinic acid. This acts as a neurotoxin and facilitates neuronal apoptosis. As metabolic changes initiated by low grade inflammation underlie the pathophysiology of depression, drugs which attenuate the inflammatory cascade may present an approach to the novel development of antidepressants. The review concludes with a summary of drugs which might be considered for their novel therapeutic activity. Key points: 1. Chronic low grade inflammation commonly occurs in major depression and contributes to adverse changes in brain energy metabolism by decreasing insulin receptor function and thereby reducing glucose transport into the brain. 2. Low grade inflammation initiates an increase in the tryptophan-kynurenine pathway which enhances the NMDA-glutamate receptor function and thereby increases neuronal apoptosis. As many of the pathophysiological changes in depression result from dysfunctional brain metabolism caused by chronic low grade inflammation, it is concluded that drugs targeting the inflammatory pathways may offer new possibilities for the development of novel antidepressants.

Inactivated AMPK-α2 promotes the progression of diabetic brain damage by Cdk5 phosphorylation at Thr485 site

Changes in brain energy metabolism in diabetes mellitus, including increased insulin resistance and mitochondrial dysfunction, are critically involved in diabetes-related neurodegeneration, and associate with early cognitive impairment as well. The aim of this study is to detect the specific phosphorylated-Thr485- AMP-activated protein kinase (AMPK-α2), regulated by cyclin-dependent kinase 5 (Cdk5) paly the inhibitory functional role of AMPK-α2, Which is maybe the link to the accelerated diabetic brain damage progression. Here, we used GK rats, the type 2 diabetic animal model for in vivo studies and performed In vitro kinase assay, high glucose treatment, -phosphorylated mutation and protein expression in both HEK-293T and HT-22 cell lines. In vitro, the results show that murine wild-type AMPK-α2 was phosphorylated by Cdk5 at a (S/T)PX(K/H/R) phosphorylation consensus sequence, which was associated with decreased AMPK-α2 activity. Surprisingly, mutation of Thr485 to alanine in AMPK-α2 results in the abolished Cdk5 effects, demonstrating that Thr485-phosphorylation is critical to AMPK-α2 inhibition by Cdk5. In addition, these alterations in AMPK-α2-phosphorylation and -activity induced by Cdk5 is specific at Thr485. Furthermore, in GK rats, the increased phosphorylated- Thr 485 of AMPK-α2 results in the decreased AMPK-α2 activity, which is correlated with the apoptosis of neurons in hippocamps. After high glucose treatment, the decreased survival showed in AMPK-α2T485A HT-22 cells compared to AMPK-α2WT. The down-regulated of p-CREB, SNAP25, synaptophysin as well as synapsin-1were shown in both GK rats and HT-22 cell line. Meanwhile, pre-treated with either the specific Cdk5-inhibitor (roscovitine) or the antidiabetic AMPK-α2-inhibitor (metformin) could restore the alterations in neuronal protein expression. Our results suggest that Cdk5-mediated phosphorylated- Thr485 in AMPK-α2 may be involved in the pathogenesis of diabetic brain damage.

Cerebral Metabolic Changes During Sleep.

The goal of the present paper is to review current literature supporting the occurrence of fundamental changes in brain energy metabolism during the transition from wakefulness to sleep. Latest research in the field indicates that glucose utilization and the concentrations of several brain metabolites consistently change across the sleep-wake cycle. Lactate, a product of glycolysis that is involved in synaptic plasticity, has emerged as a good biomarker of brain state. Sleep-induced changes in cerebral metabolite levels result from a shift in oxidative metabolism, which alters the reliance of brain metabolism upon carbohydrates. We found wide support for the notion that brain energetics is state dependent. In particular, fatty acids and ketone bodies partly replace glucose as cerebral energy source during sleep. This mechanism plausibly accounts for increases in biosynthetic pathways and functional alterations in neuronal activity associated with sleep. A better account of brain energy metabolism during sleep might help elucidate the long mysterious restorative effects of sleep for the whole organism.

Hepatic encephalopathy.

Hepatic encephalopathy (HE) is a reversible syndrome of impaired brain function occurring in patients with advanced liver diseases. The precise pathophysiology of HE is still under discussion; the leading hypothesis focus on the role of neurotoxins, impaired neurotransmission due to metabolic changes in liver failure, changes in brain energy metabolism, systemic inflammatory response and alterations of the blood brain barrier. HE produces a wide spectrum of nonspecific neurological and psychiatric manifestations. Minimal HE is diagnosed by abnormal psychometric tests. Clinically overt HE includes personality changes, alterations in consciousness progressive disorientation in time and space, somnolence, stupor and, finally, coma. Except for clinical studies, no specific tests are required for diagnosis. HE is classified according to the underlying disease, the severity of manifestations, its time course and the existence of precipitating factors. Treatment of overt HE includes supportive therapies, treatment of precipitating factors, lactulose and/or rifaximin. Routine treatment for minimal HE is only recommended for selected patients.

Impaired Hippocampal Glutamate and Glutamine Metabolism in the db/db Mouse Model of Type 2 Diabetes Mellitus.

Type 2 diabetes mellitus (T2DM) is a risk factor for the development of Alzheimer's disease, and changes in brain energy metabolism have been suggested as a causative mechanism. The aim of this study was to investigate the cerebral metabolism of the important amino acids glutamate and glutamine in the db/db mouse model of T2DM. Glutamate and glutamine are both substrates for mitochondrial oxidation, and oxygen consumption was assessed in isolated brain mitochondria by Seahorse XFe96 analysis. In addition, acutely isolated cerebral cortical and hippocampal slices were incubated with [U-13C]glutamate and [U-13C]glutamine, and tissue extracts were analyzed by gas chromatography-mass spectrometry. The oxygen consumption rate using glutamate and glutamine as substrates was not different in isolated cerebral mitochondria of db/db mice compared to controls. Hippocampal slices of db/db mice exhibited significantly reduced 13C labeling in glutamate, glutamine, GABA, citrate, and aspartate from metabolism of [U-13C]glutamate. Additionally, reduced 13C labeling were observed in GABA, citrate, and aspartate from [U-13C]glutamine metabolism in hippocampal slices of db/db mice when compared to controls. None of these changes were observed in cerebral cortical slices. The results suggest specific hippocampal impairments in glutamate and glutamine metabolism, without affecting mitochondrial oxidation of these substrates, in the db/db mouse.

Improved cerebral energetics and ketone body metabolism in db/db mice

It is becoming evident that type 2 diabetes mellitus is affecting brain energy metabolism. The importance of alternative substrates for the brain in type 2 diabetes mellitus is poorly understood. The aim of this study was to investigate whether ketone bodies are relevant candidates to compensate for cerebral glucose hypometabolism and unravel the functionality of cerebral mitochondria in type 2 diabetes mellitus. Acutely isolated cerebral cortical and hippocampal slices of db/db mice were incubated in media containing [U-13C]glucose, [1,2-13C]acetate or [U-13C]β-hydroxybutyrate and tissue extracts were analysed by mass spectrometry. Oxygen consumption and ATP synthesis of brain mitochondria of db/db mice were assessed by Seahorse XFe96 and luciferin-luciferase assay, respectively. Glucose hypometabolism was observed for both cerebral cortical and hippocampal slices of db/db mice. Significant increased metabolism of [1,2-13C]acetate and [U-13C]β-hydroxybutyrate was observed for hippocampal slices of db/db mice. Furthermore, brain mitochondria of db/db mice exhibited elevated oxygen consumption and ATP synthesis rate. This study provides evidence of several changes in brain energy metabolism in type 2 diabetes mellitus. The increased hippocampal ketone body utilization and improved mitochondrial function in db/db mice, may act as adaptive mechanisms in order to maintain cerebral energetics during hampered glucose metabolism.

Functional Proteomics as Marker for Neurological and Psychiatric Disorders: The First Application to Dementia for an Immediate Future

Functional Proteomics is a useful technology to study the neuronal biochimism, allowing to evaluate the metabolic changes within neuronal cells and brain tissue that may imply some physiopathological modifications. In fact, changes in brain energy metabolism was shown to be causative of development/progression of both neurological and psychiatric disorders. In this paper, it is particularly described the role of brain energy metabolism as a key etiopathological factor in dementias, in the perspective of using functional Proteomics as a tool for novel biomarker discovery.

Molecular determinants of magnesium-dependent synaptic plasticity at electrical synapses formed by connexin36.

Neuronal gap junction (GJ) channels composed of connexin36 (Cx36) play an important role in neuronal synchronization and network dynamics. Here we show that Cx36-containing electrical synapses between inhibitory neurons of the thalamic reticular nucleus are bi-directionally modulated by changes in intracellular free magnesium concentration ([Mg2+]i). Chimeragenesis demonstrates that the first extracellular loop of Cx36 contains a Mg2+-sensitive domain, and site-directed mutagenesis shows that the pore-lining residue D47 is critical in determining high Mg2+-sensitivity. Single channel analysis of Mg2+-sensitive chimeras and mutants reveals that [Mg2+]i controls the strength of electrical coupling mostly via gating mechanisms. In addition, asymmetric transjunctional [Mg2+]i induces strong instantaneous rectification, providing a novel mechanism for electrical rectification in homotypic Cx36 GJs. We suggest that Mg2+-dependent synaptic plasticity of Cx36-containing electrical synapses could underlie neuronal circuit reconfiguration via changes in brain energy metabolism that affects neuronal levels of intracellular ATP and [Mg2+]i.

Homeostatic Adaptations in Brain Energy Metabolism in Mouse Models of Huntington Disease

Impairment of energy metabolism is a key feature of Huntington disease (HD). Recently, we reported longitudinal neurochemical changes in R6/2 mice measured by in-vivo proton magnetic resonance spectroscopy ((1)H MRS; Zacharoff et al, 2012). Here, we present similar (1)H MRS measurements at an early stage in the milder Q111 mouse model. In addition, we measured the concentration of ATP and inorganic phosphate (P(i)), key energy metabolites not accessible with (1)H MRS, using (31)P MRS both in Q111 and in R6/2 mice. Significant changes in striatal creatine and phosphocreatine were observed in Q111 mice at 6 weeks relative to control, and these changes were largely reversed at 13 weeks. No significant change was detected in ATP concentration, in either HD mouse, compared with control. Calculated values of [ADP], phosphorylation potential, relative rate of ATP synthase (v/V(max)(ATP)), and relative rate of creatine kinase (v/V(max)(CK)) were calculated from the measured data. ADP concentration and v/V(max)(ATP) were increased in Q111 mice at 6 weeks, and returned close to normal at 13 weeks. In contrast, these parameters were normal in R6/2 mice. These results suggest that early changes in brain energy metabolism are followed by compensatory shifts to maintain energetic homeostasis from early ages through manifest disease.

Glucose Transporters Regulation on Ischemic Brain: Possible Role as Therapeutic Target

Ischemic stroke is a major cause of death worldwide that provokes a high society cost. Deprivation of blood supply, with the subsequent deficiency of glucose and oxygen, triggers an important number of mechanisms (e.g. excitotoxicity, oxidative stress and inflammation) leading to irreversible neuronal injury. Consequently, ischemia increases the energy demand which is associated with profound changes in brain energy metabolism. Glucose transport activity may adapt to ensure the delivery of glucose to maintain normal cellular function, even at the low glucose levels observed in plasma during ischemia. In the brain, the main glucose transporters (GLUTs) are GLUT3 in neurons and GLUT1 in the microvascular endothelial cells of the blood brain barrier and glia. The intracellular signaling pathways involved in GLUT regulation in cerebral ischemia remain unclear; however, it has been established that ischemia induces changes in their expression. In this review, we describe the effect of glutamate-induced excitotoxicity, mitochondrial damage, glucose deprivation, and hypoxia on GLUTs expression in the brain. Additionally, we discuss the possible role of GLUTs as therapeutic target for ischemia. Despite of the intense research, current therapeutics options for stroke are very limited, therefore it is especially important to find new options. Few studies have examined the neuroprotective potential of GLUT up-regulation in ischemic stroke; however, evidence suggests that augmented GLUTs could be related to a protective mechanism. Increased understanding of the beneficial effects of GLUTs activation provides the rationale for targeting GLUT in the development of new therapeutic strategies.

Increased expression of glucose transporter 3 in gerbil brains following magnesium sulfate treatment and focal cerebral ischemic injury

Glucose is the primary energy substrate for neurons. Glucose transporter 3 (Glut3) localizes at the neuronal cellular membrane, which transports glucose from the extracelluar space into neurons. Ischemia results in an increased energy demand that is associated with profound changes in brain energy metabolism. Magnesium sulfate (MgSO(4)) ameliorates ischemia-induced neuronal death in the rat and gerbil model. We investigated the effects of MgSO(4) administration on the expression of Glut3 in cortex and hippocampus of gerbils during ischemia. The focal cerebral ischemia was produced by unilateral occlusion of the right common carotid artery and right middle cerebral artery. Following ischemia, Glut3 expression increased significantly versus non-ischemic (contra-lateral) cortex and hippocampus. MgSO(4) treatment significantly increased the level of Glut3 expression in the non-ischemic and ischemic cortex and hippocampus. We found that the MgSO(4)-induced increase in Glut3 expression was not reversed by administration of U0126, a MEK kinase inhibitor. These results suggest that other factors may function to modulate the MgSO(4)-induced Glut3 response. In all, our data showed that MgSO(4) increases the expression of Glut3 in the cortex and hippocampus of gerbil brains both in non-ischemia and ischemia status. However, the MEK signaling pathway might not be involved in MgSO(4)-induced Glut3 expression following focal ischemia.

Omega-3 fatty acids and brain energy metabolism: Impact on the expression of glucose transporters and glucose transport activity in endothelial cells in culture

Alterations in cognitive performance and neuronal activity in animals defi cient in n-3 polyunsaturated fatty acids (PUFA) have been linked to the decrease in docosahexaenoic acid (22:6n-3, DHA) level in brain membranes. These alterations could partly result from changes in brain energy metabolism and namely in glucose transport activity. Indeed, we reported that several brain areas of rats raised on a diet defi cient in n-3 PUFAs have below-normal rates of glucose utilization [1]. We postulated that the quantity of glucose transporter GLUT1 in defi cient rats was functionally abnormal as its immunoreactivity was low. We present experimental data that evaluated: 1) the in vivo impact of an n-3 PUFA-defi cient diet on expression of the main glucose transporters of rat cerebral cortex (endothelial 55-kDa GLUT1, astrocytic 45-kDa GLUT1, and neuronal GLUT3); and 2) the in vitro impact of the three main long-chain n-6 and n-3 PUFAs, arachidonic acid (20:4n-6), eicosapentaenoic acid (20:5n-3) and DHA, on the fatty acid composition of membrane phospholipids and glucose uptake in two models of rat brain endothelial cells (primary cultures (RBEC), and immortalized cell line RBE4). In vivo study Rats raised with a n-3 PUFA defi cient diet throughout one generation were compared with rats fed a diet with adequate amounts of n-6 and n-3 PUFA. The fatty acid profi le of brain microvessels was determined in order to identify the alterations in n-6 and n-3 PUFA in endothelial cells compared to their profi le in neural cells from the cerebral cortex. The main glucose transporters were quantifi ed by western immunoblotting and by real time quantitative RT-PCR. Specifi c binding of cytochalasin B to GLUT1 of isolated microvessels was also determined. In vitro study The three PUFA studied were added to the culture medium (15μM) as sodium salts on the fi rst day of culture and until the cells were used. Glucose uptake was measured on monolayers of RBEC and RBE4 cells using the non-metabolisable radiolabelled glucose analogue 3-o-methylglucose ([3H]-3-o-MG). In vivo data showed that the 55-kDa GLUT1 protein quantity decreased by 25% in the n-3 PUFA-defi cient microvessels, as did 45 kDa-GLUT1 in the homogenate (30% decrease). Results from cytochalasin B binding confi rmed these data, showing a lower level of its maximum binding to GLUT1. However, GLUT3 protein quantity did not change as GLUT1 and GLUT3 mRNA level. In vitro data demonstrated that both cerebral endothelial cells had low n-6 (mainly 20:4n-6) and n-3 (mainly 22:6n-3) PUFA concentrations under standard conditions of culture. RBEC and RBE4 cells grown in medium supplemented with 20:4n-6, 20:5n-3 or 22:6n-3 (15 μM, physiological concentrations), avidly incorporated these PUFAs into their membrane phospholipids to approach the contents of cerebral microvessels of control rats (considered as physiological references). However RBE4 cells did not incorporate suffi cient 20:4n-6 compared to physiological concentrations. Supplementation with 20:5n-3 and 22:6n-3 increased the basal glucose transport in RBEC ([3H]-3-O-methylglucose uptake) by 50% and 35% respectively, while 20:4n-6 had no effect. On the other hand, none of the PUFA supplements had a signifi cant effect on glucose uptake by RBE4. We demonstrated that incorporation of n-3 long-chain PUFAs in RBEC membranes acts on glucose transport activity. We suggest that the decreased glucose utilization in the cerebral cortex of n-3 PUFA-defi cient rats is in part due to reduced amounts of the two GLUT1 isoforms, possibly issuing from post-transcriptional down-regulation of GLUT1 protein synthesis. In vitro studies suggest that n-3 PUFA can directly modulate the activity of glucose transport in endothelial cells by altering their membrane phospholipid content.

Modeling Brain Energy Metabolism and Function: A Multiparametric Monitoring Approach

Mathematical modeling of brain function is an important tool needed for a better understanding of experimental results and clinical situations. In the present study, we are constructing and testing a mathematical model capable of simulating changes in brain energy metabolism that develop in real time under various pathophysiological conditions. The model incorporates the following parameters: cerebral blood flow, partial oxygen pressure, mitochondrial NADH redox state, and extracellular potassium. Accordingly, all the model variables are only time dependent (;point-model' approach). Numerical runs demonstrate the ability of the model to mimic pathological conditions, such as complete and partial ischemia, cortical spreading depression under normoxic and partial ischemic conditions. They also show that, when properly tuned, a model of this type permits the monitoring of only one or two crucial variables and the computation of the remaining variables in real time during clinical or experimental procedures.

Brain Energy Metabolism in a Sub-Acute Rat Model of Manganese Neurotoxicity: An Ex Vivo Nuclear Magnetic Resonance Study Using [1- [formula omitted]]Glucose

Ex vivo high-resolution NMR spectroscopy combined with in vivo injection of [1- 13C ]glucose was applied to gain insight into the mechanism(s) leading to energy failure in manganese neurotoxicity. In rats treated for 4 days with 50 mg/kg MnCl 2 (intraperitoneally, i.p.), the concentration of 13C -labeled lactate increased to 154% compared to control rats. Changes in the absolute amounts of lactate were much less, resulting in increased fractional 13C -enrichments in lactate (indicating relative changes of de novo synthesis from glucose via the glycolytic pathway) to 143% of control values ( P<0.001). Analysis of samples obtained from blood plasma and peripheral organs demonstrate a selective increase of lactate synthesis from [1- 13C ]glucose in the brain, which is released into the circulation. In parallel, manganese treatment resulted in stimulation of flux through pyruvate dehydrogenase (PDH), leading to accumulation of [4- 13C ]glutamate, [4- 13C ]glutamine and [2- 13C ]GABA to 168, 247 and 144% of control, respectively. The relative flux of glucose through astrocytic pyruvate carboxylase (PC), on the other hand, was impaired by manganese, as evident from a decreased ratio of [2- 13C ]/[4- 13C ]glutamate or [2- 13C ]/[4- 13C ]glutamine. Consistent with stimulated glucose oxidative metabolism, the fractional 13C -enrichment in [2- 13C ]acetyl-CoA entering the tricarboxylic acid (TCA) cycle and contributing to glutamate and glutamine synthesis increased to 138 and 156% of control, respectively ( P<0.001). In parallel, the TCA cycling ratio increased to 134% compared to control rats, prior to the label ending up in glutamate. In contrast, glutamine is synthesized mainly during the first TCA cycle turn. The present data provide new evidence in support of changes in brain energy metabolism playing an important role in manganese neurotoxicity. In particular, increased glycolytic flux and lactate synthesis may contribute to the deleterious effects of manganese in the brain. Furthermore, stimulated astrocytic glucose oxidation and glutamine synthesis may be associated with astrocytic pathology and altered astrocytic–neuronal metabolic trafficking in manganese neurotoxicity.