D-beta-hydroxybutyrate prevents glutamate-mediated lipoperoxidation and neuronal damage elicited during glycolysis inhibition in vivo

β-hydroxybutyrate and ischemic stroke: roles and mechanisms

Stroke is a significant global burden, causing extensive morbidity and mortality. In metabolic states where glucose is limited, ketone bodies, predominantly β-hydroxybutyrate (BHB), act as alternative fuel sources. Elevated levels of BHB have been found in the ischemic hemispheres of animal models of stroke, supporting its role in the pathophysiology of cerebral ischemia. Clinically, higher serum and urinary BHB concentrations have been associated with adverse outcomes in ischemic stroke, highlighting its potential utility as a prognostic biomarker. In both animal and cellular models, exogenous BHB administration has exhibited neuroprotective effects, reduction of infarct size, and improvement of neurological outcomes. In this review, we focus on the role of BHB before and after ischemic stroke, with an emphasis on the therapeutic potential and mechanisms of ketone administration after ischemic stroke.

Intermittent fasting and Alzheimer's disease-Targeting ketone bodies as a potential strategy for brain energy rescue

Alzheimer's disease (AD) lacks effective clinical treatments. As the disease progresses, the cerebral glucose hypometabolism that appears in the preclinical phase of AD gradually worsens, leading to increasingly severe brain energy disorders. This review analyzes the brain energy deficit in AD and its etiology, brain energy rescue strategies based on ketone intervention, the effects and mechanisms of IF, the differences in efficacy between IF and ketogenic diet and the duality of IF. The evidence suggests that brain energy deficits lead to the development and progression of AD pathology. IF, which improves brain energy impairments by promoting ketone metabolism, thus has good therapeutic potential for AD.

Is L-Glutamate Toxic to Neurons and Thereby Contributes to Neuronal Loss and Neurodegeneration? A Systematic Review

L-glutamate (L-Glu) is a nonessential amino acid, but an extensively utilised excitatory neurotransmitter with critical roles in normal brain function. Aberrant accumulation of L-Glu has been linked to neurotoxicity and neurodegeneration. To investigate this further, we systematically reviewed the literature to evaluate the effects of L-Glu on neuronal viability linked to the pathogenesis and/or progression of neurodegenerative diseases (NDDs). A search in PubMed, Medline, Embase, and Web of Science Core Collection was conducted to retrieve studies that investigated an association between L-Glu and pathology for five NDDs: Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD). Together, 4060 studies were identified, of which 71 met eligibility criteria. Despite several inadequacies, including small sample size, employment of supraphysiological concentrations, and a range of administration routes, it was concluded that exposure to L-Glu in vitro or in vivo has multiple pathogenic mechanisms that influence neuronal viability. These mechanisms include oxidative stress, reduced antioxidant defence, neuroinflammation, altered neurotransmitter levels, protein accumulations, excitotoxicity, mitochondrial dysfunction, intracellular calcium level changes, and effects on neuronal histology, cognitive function, and animal behaviour. This implies that clinical and epidemiological studies are required to assess the potential neuronal harm arising from excessive intake of exogenous L-Glu.

Ketone Bodies in the Brain Beyond Fuel Metabolism: From Excitability to Gene Expression and Cell Signaling

Ketone bodies are metabolites that replace glucose as the main fuel of the brain in situations of glucose scarcity, including prolonged fasting, extenuating exercise, or pathological conditions such as diabetes. Beyond their role as an alternative fuel for the brain, the impact of ketone bodies on neuronal physiology has been highlighted by the use of the so-called “ketogenic diets,” which were proposed about a century ago to treat infantile seizures. These diets mimic fasting by reducing drastically the intake of carbohydrates and proteins and replacing them with fat, thus promoting ketogenesis. The fact that ketogenic diets have such a profound effect on epileptic seizures points to complex biological effects of ketone bodies in addition to their role as a source of ATP. In this review, we specifically focus on the ability of ketone bodies to regulate neuronal excitability and their effects on gene expression to respond to oxidative stress. Finally, we also discuss their capacity as signaling molecules in brain cells.

Uncoupling Thermotolerance and Growth Performance in Chinook Salmon: Blood Biochemistry and Immune Capacity

Ocean warming and extreme sea surface temperature anomalies are threatening wild and domesticated fish stocks in various regions. Understanding mechanisms for thermotolerance and processes associated with divergent growth performance is key to the future success of aquaculture and fisheries management. Herein, we exposed Chinook salmon (Oncorhynchus tshawytscha) to environmentally relevant water temperatures (19–20 °C) approaching their upper physiological limit for three months and sought to identify blood biomarkers associated with thermal stress and resilience. In parallel, blood biochemical associations with growth performance were also investigated. Temperature stress-activated leukocyte apoptosis induced a minor immune response, and influenced blood ion profiles indicative of osmoregulatory perturbation, regardless of how well fish grew. Conversely, fish displaying poor growth performance irrespective of temperature exhibited numerous biomarker shifts including haematology indices, cellular-based enzyme activities, and blood clinical chemistries associated with malnutrition and disturbances in energy metabolism, endocrine functioning, immunocompetence, redox status, and osmoregulation. Findings provide insight into mechanisms of stress tolerance and compromised growth potential. Biochemical phenotypes associated with growth performance and health can potentially be used to improve selective breeding strategies.

Applications of Ketogenic Diets in Patients with Headache: Clinical Recommendations

Headaches are among the most prevalent and disabling neurologic disorders and there are several unmet needs as current pharmacological options are inadequate in treating patients with chronic headache, and a growing interest focuses on nutritional approaches as non-pharmacological treatments. Among these, the largest body of evidence supports the use of the ketogenic diet (KD). Exactly 100 years ago, KD was first used to treat drug-resistant epilepsy, but subsequent applications of this diet also involved other neurological disorders. Evidence of KD effectiveness in migraine emerged in 1928, but in the last several year's different groups of researchers and clinicians began utilizing this therapeutic option to treat patients with drug-resistant migraine, cluster headache, and/or headache comorbid with metabolic syndrome. Here we describe the existing evidence supporting the potential benefits of KDs in the management of headaches, explore the potential mechanisms of action involved in the efficacy in-depth, and synthesize results of working meetings of an Italian panel of experts on this topic. The aim of the working group was to create a clinical recommendation on indications and optimal clinical practice to treat patients with headaches using KDs. The results we present here are designed to advance the knowledge and application of KDs in the treatment of headaches.

3-Hydroxybutyrate as a Metabolite and a Signal Molecule Regulating Processes of Living Organisms

3-hydroxybutyrate (3-HB) as a very important metabolite occurs in animals, bacteria and plants. It is well known that in animals, 3-HB is formed as a product of the normal metabolism of fatty acid oxidation and can therefore be used as an energy source in the absence of sufficient blood glucose. In microorganisms, 3-HB mainly serves as a substrate for the synthesis of polyhydroxybutyrate, which is a reserve material. Recent studies show that in plants, 3-HB acts as a regulatory molecule that most likely influences the expression of genes involved in DNA methylation, thereby altering DNA methylation levels. Additionally, in animals, 3-HB is not only an intermediate metabolite, but also an important regulatory molecule that can influence gene expression, lipid metabolism, neuronal function, and overall metabolic rate. Some of these effects are the direct effects of 3-HB itself, while others are indirect effects, regulated by the metabolites into which 3-HB is converted. One of the most important regulatory functions of 3-HB is the inhibition of the activity of histone deacetylases and thus the epigenetic regulation of many genes. Due to the number of functions of this compound, it also shows promising therapeutic properties.

CNS glucose metabolism in Amyotrophic Lateral Sclerosis: a therapeutic target?

Amyotrophic lateral sclerosis (ALS) is a fatal progressive neurodegenerative disorder primarily characterized by selective degeneration of both the upper motor neurons in the brain and lower motor neurons in the brain stem and the spinal cord. The exact mechanism for the selective death of neurons is unknown. A growing body of evidence demonstrates abnormalities in energy metabolism at the cellular and whole-body level in animal models and in people living with ALS. Many patients with ALS exhibit metabolic changes such as hypermetabolism and body weight loss. Despite these whole-body metabolic changes being observed in patients with ALS, the origin of metabolic dysregulation remains to be fully elucidated. A number of pre-clinical studies indicate that underlying bioenergetic impairments at the cellular level may contribute to metabolic dysfunctions in ALS. In particular, defects in CNS glucose transport and metabolism appear to lead to reduced mitochondrial energy generation and increased oxidative stress, which seem to contribute to disease progression in ALS. Here, we review the current knowledge and understanding regarding dysfunctions in CNS glucose metabolism in ALS focusing on metabolic impairments in glucose transport, glycolysis, pentose phosphate pathway, TCA cycle and oxidative phosphorylation. We also summarize disturbances found in glycogen metabolism and neuroglial metabolic interactions. Finally, we discuss options for future investigations into how metabolic impairments can be modified to slow disease progression in ALS. These investigations are imperative for understanding the underlying causes of metabolic dysfunction and subsequent neurodegeneration, and to also reveal new therapeutic strategies in ALS.

Treatment with the Ketone Body D-β-hydroxybutyrate Attenuates Autophagy Activated by NMDA and Reduces Excitotoxic Neuronal Damage in the Rat Striatum In Vivo

BACKGROUND

The ketone bodies (KB), β-hydroxybutyrate (BHB) and acetoacetate, have been proposed for the treatment of acute and chronic neurological disorders, however, the molecular mechanisms involved in KB protection are not well understood. KB can substitute for glucose and support mitochondrial metabolism increasing cell survival. We have reported that the D-isomer of BHB (D-BHB) stimulates autophagic degradation during glucose deprivation in cultured neurons increasing cell viability. Autophagy is a lysosomal degradation process of damaged proteins and organelles activated during nutrient deprivation to obtain building blocks and energy. However, impaired or excessive autophagy can contribute to neuronal death.

OBJECTIVE

The aim of the present study was to test whether D-BHB can preserve autophagic function in an in vivo model of excitotoxic damage induced by the administration of the glutamate receptor agonist, N-methyl-Daspartate (NMDA), in the rat striatum.

METHODS

D-BHB was administered through an intravenous injection followed by either an intraperitoneal injection (i.v+i.p) or a continuous epidural infusion (i.v+pump), or through a continuous infusion of D-BHB alone. Changes in the autophagy proteins ATG7, ATG5, BECLIN 1 (BECN1), LC3, Sequestrosome1/p62 (SQSTM1/ p62) and the lysosomal membrane protein LAMP2, were evaluated by immunoblot. The lesion volume was measured in cresyl violet-stained brain sections.

RESULTS

Autophagy is activated early after NMDA injection but autophagic degradation is impaired due to the cleavage of LAMP2. Twenty-four h after NMDA intrastriatal injection, the autophagic flux is re-established, but LAMP2 cleavage is still observed. The administration of D-BHB through the i.v+pump protocol reduced the content of autophagic proteins and the cleavage of LAMP2, suggesting decreased autophagosome formation and lysosomal membrane preservation, improving autophagic degradation. D-BHB also reduced brain injury. The i.v+i.p administration protocol and the infusion of D-BHB alone showed no effect on autophagy activation or degradation.

Antiepileptic effects of exogenous β-hydroxybutyrate on kainic acid-induced epilepsy

The aim of the present study was to explore the potential anticonvulsant effects of β-hydroxybutyrate (BHB) in a kainic acid (KA)-induced rat epilepsy model. The KA-induced rat seizure model was established and BHB was administrated intraperitoneally at a dose of 4 mmol/kg 30 min prior to KA injection. Hippocampal tissues were then obtained 1, 3 and 7 days following KA administration, following which the expression levels of neuron-specific enolase (NSE) and glial fibrillary acidic protein (GFAP) were measured using a double immunofluorescence labeling method. In addition, the contents of glutathione (GSH), γ-aminobutyric acid (GABA) and ATP were measured using ELISA. Pretreatment with BHB markedly increased the expression of NSE after KA injection compared with that in the normal saline (NS) + KA group, suggesting that the application of BHB could alleviate neuronal damage in rats. The protective effect of BHB may be associated with suppressed inflammatory responses, which was indicated by the observed inhibition of GFAP expression in rats in the BHB + KA group compared with that in the NS + KA group. It was also found that GSH and GABA contents were notably increased after the rats were pretreated with BHB compared with those in the NS + KA group. To conclude, the application of exogenous BHB can serve as a novel therapeutic agent for epilepsy.

Emerging Therapeutic Promise of Ketogenic Diet to Attenuate Neuropathological Alterations in Alzheimer's Disease

Alzheimer's disease (AD) is a multifactorial and chronic neurodegenerative disorder that interferes with memory, thinking, and behavior. The consumption of dietary fat has been considered a vital factor for AD as this disease is related to blood-brain barrier function and cholesterol signaling. The ε4 allele of apolipoprotein E (APOE4) is a primary genetic risk factor that encodes one of many proteins accountable for the transport of cholesterol and it is deemed as the leading cholesterol transport proteins in the brain. In case of AD development, the causative factor is the high level of serum/plasma cholesterol. However, this statement is arguable and, in the meantime, the levels of brain cholesterol in individuals with AD are extremely inconstant and levels of cholesterol in the brain and serum/plasma of AD individuals do not reflect cholesterol as a risk factor. In fact, APOE4 is neither fundamental nor sufficient for the advancement of AD; it just acts as a synergistic and increases the danger of AD. Another noticeable characteristic of AD is area-specific decreases in the metabolism of brain glucose. It has been found that the brain cells cannot efficiently metabolize fats; hence, they totally rely upon glucose as a vitality substrate. Thus, suppression of glucose metabolism can possess an intense effect on brain actions. Hypometabolism is frequently found in AD and has quite recently achieved impressive consideration as a plausible target for interfering in the progression of the disease. One promising approach is to keep up the normal supply of glucose to the brain with ketone bodies from the ketogenic diet signifies a potential therapeutic agent for AD. Therefore, this review represents the role of ketogenic diets to combat AD pathogenesis by considering the influence of APOE.

Selenium and antioxidant levels in children with intractable epilepsy receiving ketogenic diet

Ketogenic diet is a high-fat, low-carbohydrate, and adequate-protein diet. It is well-established as a treatment option for drug-resistant childhood epilepsies. Our study aimed to evaluate Selenium levels and oxidative stress in children receiving ketogenic diet for intractable seizures for 6 months. This is a comparative case-control study included 90 children under 6 years age. They were subdivided into three groups. Group I: Thirty patients with drug-resistant epilepsy under antiepileptic drugs only. Group II: Thirty patients with drug-resistant epilepsy under treatment with ketogenic diet for 6 months and antiepileptic drugs. Group III: Thirty age and sex-matched healthy children as controls. Full history taking with special emphasis on severity and frequency of seizures, neurological examination, anthropometric measurements and laboratory analysis for serum Malonaldehyde, and total antioxidant capacity and Selenium were done for all participants. The frequency and severity of seizures were significantly lower in group II receiving ketogenic diet than group I on antiepileptic drugs only. Selenium levels were significantly lower in epileptic patients in comparison to controls. However, it was markedly lower in the ketogenic diet group. Malonaldehyde levels were significantly higher in epileptic children in comparison to controls, with lower values among ketogenic diet group when compared to patients on antiepileptic drugs only. Total antioxidant capacity levels were significantly lower in epileptic patients in comparison to controls, with higher values among ketogenic diet group as compared to epileptic patients on pharmacological treatment. Ketogenic diet is an effective treatment for refractory epilepsy for its anti-epileptic mechanism. It also may exert antioxidant effects. The nutrient content of the ketogenic diet may not meet the recommended daily allowance for selenium. So, this should be taken into consideration for supplementation of minerals in adequate amounts for patients receiving this diet.

Impact of Hypoglycemia on Brain Metabolism During Diabetes

Diabetes is a metabolic disease afflicting millions of people worldwide. A substantial fraction of world's total healthcare expenditure is spent on treating diabetes. Hypoglycemia is a serious consequence of anti-diabetic drug therapy, because it induces metabolic alterations in the brain. Metabolic alterations are one of the central mechanisms mediating hypoglycemia-related functional changes in the brain. Acute, chronic, and/or recurrent hypoglycemia modulate multiple metabolic pathways, and exposure to hypoglycemia increases consumption of alternate respiratory substrates such as ketone bodies, glycogen, and monocarboxylates in the brain. The aim of this review is to discuss hypoglycemia-induced metabolic alterations in the brain in glucose counterregulation, uptake, utilization and metabolism, cellular respiration, amino acid and lipid metabolism, and the significance of other sources of energy. The present review summarizes information on hypoglycemia-induced metabolic changes in the brain of diabetic and non-diabetic subjects and the manner in which they may affect brain function.

Metabolic Dysfunctions in Amyotrophic Lateral Sclerosis Pathogenesis and Potential Metabolic Treatments

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease primarily characterized by loss of motor neurons in brain and spinal cord. The death of motor neurons leads to denervation of muscle which in turn causes muscle weakness and paralysis, decreased respiratory function and eventually death. Growing evidence indicates disturbances in energy metabolism in patients with ALS and animal models of ALS, which are likely to contribute to disease progression. Particularly, defects in glucose metabolism and mitochondrial dysfunction limit the availability of ATP to CNS tissues and muscle. Several metabolic approaches improving mitochondrial function have been investigated in vitro and in vivo and showed varying effects in ALS. The effects of metabolic approaches in ALS models encompass delays in onset of motor symptoms, protection of motor neurons and extension of survival, which signifies an important role of metabolism in the pathogenesis of the disease. There is now an urgent need to test metabolic approaches in controlled clinical trials. In addition, more detailed studies to better characterize the abnormalities in energy metabolism in patients with ALS and ALS models are necessary to develop metabolically targeted effective therapies that can slow the progression of the disease and prolong life for patients with ALS.

The inhibitory influence of 3-β-hydroxybutyrate on calf thymus DNA glycation by glucose

Glycation can change DNA structure and cause strand breaks, mutations, and changes in gene expression.

Ketone Body Therapy Protects From Lipotoxicity and Acute Liver Failure Upon Pparα Deficiency

Acute liver failure (ALF) is a severe and rapid liver injury, often occurring without any preexisting liver disease, which may precipitate multiorgan failure and death. ALF is often associated with impaired β-oxidation and increased oxidative stress (OS), characterized by elevated levels of hepatic reactive oxygen species (ROS) and lipid peroxidation (LPO) products. Peroxisome proliferator-activated receptor (PPAR)α has been shown to confer hepatoprotection in acute and chronic liver injury, at least in part, related to its ability to control peroxisomal and mitochondrial β-oxidation. To study the pathophysiological role of PPARα in hepatic response to high OS, we induced a pronounced LPO by treating wild-type and Pparα-deficient mice with high doses of fish oil (FO), containing n-3 polyunsaturated fatty acids. FO feeding of Pparα-deficient mice, in contrast to control sunflower oil, surprisingly induced coma and death due to ALF as indicated by elevated serum alanine aminotransferase, aspartate aminotransferase, ammonia, and a liver-specific increase of ROS and LPO-derived malondialdehyde. Reconstitution of PPARα specifically in the liver using adeno-associated serotype 8 virus-PPARα in Pparα-deficient mice restored β-oxidation and ketogenesis and protected mice from FO-induced lipotoxicity and death. Interestingly, administration of the ketone body β-hydroxybutyrate prevented FO-induced ALF in Pparα-deficient mice, and normalized liver ROS and malondialdehyde levels. Therefore, PPARα protects the liver from FO-induced OS through its regulatory actions on ketone body levels. β-Hydroxybutyrate treatment could thus be an option to prevent LPO-induced liver damage.

Degeneration of spinal motor neurons by chronic AMPA-induced excitotoxicity in vivo and protection by energy substrates

INTRODUCTION

Several data suggest that excitotoxicity due to excessive glutamatergic neurotransmission may be an important factor in the mechanisms of motor neuron (MN) death occurring in amyotrophic lateral sclerosis (ALS). We have previously shown that the overactivation of the Ca(2+)-permeable α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) glutamate receptor type, through the continuous infusion of AMPA in the lumbar spinal cord of adult rats during several days, results in progressive rear limb paralysis and bilateral MN degeneration. Because it has been shown that energy failure and oxidative stress are involved in MN degeneration, in both ALS and experimental models of spinal MN degeneration, including excitotoxicity, in this work we tested the protective effect of the energy substrates pyruvate and β-hydroxybutyrate (βHB) and the antioxidants glutathione ethyl ester (GEE) and ascorbate in this chronic AMPA-induced neurodegeneration.

RESULTS

AMPA infusion induced remarkable progressive motor deficits, assessed by two motor tasks, that by day seven reach bilateral rear limb paralysis. These effects correlate with the death of >80% of lumbar spinal MNs in the infused and the neighbor spinal cord segments, as well as with notable astrogliosis in the ventral horns, detected by glial fibrillary acidic protein immunohistochemistry. Co-infusion with pyruvate or βHB notably prevented the motor deficits and paralysis, decreased MN loss to <25% and completely prevented the induction of astrogliosis. In contrast, the antioxidants tested were ineffective regarding all parameters analyzed.

CONCLUSIONS

Chronic progressive excitotoxicity due to AMPA receptors overactivation results in MN death and astrogliosis, with consequent motor deficits and paralysis. Because of the notable protection against these effects exerted by pyruvate and βHB, which are well established mitochondrial energy substrates, we conclude that deficits in mitochondrial energy metabolism are an important factor in the mechanisms of this slowly developed excitotoxic MN death, while the lack of protective effect of the antioxidants indicates that oxidative stress seems to be less significant factor. Because excitotoxicity may be involved in MN degeneration in ALS, these findings suggest possible preventive or therapeutic strategies for the disease.

Protection of hypoglycemia-induced neuronal death by β-hydroxybutyrate involves the preservation of energy levels and decreased production of reactive oxygen species

Glucose is the main energy substrate in brain but in certain circumstances such as prolonged fasting and the suckling period alternative substrates can be used such as the ketone bodies (KB), beta-hydroxybutyrate (BHB), and acetoacetate. It has been shown that KB prevent neuronal death induced during energy limiting conditions and excitotoxicity. The protective effect of KB has been mainly attributed to the improvement of mitochondrial function. In the present study, we have investigated the protective effect of D-BHB against neuronal death induced by severe noncoma hypoglycemia in the rat in vivo and by glucose deprivation (GD) in cortical cultures. Results show that systemic administration of D-BHB reduces reactive oxygen species (ROS) production in distinct cortical areas and subregions of the hippocampus and efficiently prevents neuronal death in the cortex of hypoglycemic animals. In vitro results show that D-BHB stimulates ATP production and reduces ROS levels, while the nonphysiologic isomer of BHB, L-BHB, has no effect on energy production but reduces ROS levels. Data suggest that protection by BHB, not only results from its metabolic action but is also related to its capability to reduce ROS, rendering this KB as a suitable candidate for the treatment of ischemic and traumatic injury.

Role of Medium Chain Triglycerides (Axona®) in the Treatment of Mild to Moderate Alzheimer's Disease

Treatment of Alzheimer's disease (AD) with acetylcholinesterase inhibitors or N-methyl-D-aspartate (NMDA) receptor antagonists provides symptomatic relief but do not prevent its progression. Thus, additional approaches aimed at slowing the progression of the disease have been investigated. Reports detailing reduced brain glucose metabolism in the early stages of AD led to the hypothesis that alternate energy sources aimed at increasing neuronal metabolism may protect neurons and thus benefit patients with AD. Medium-chain triglycerides (MCTs) are metabolized to ketone bodies that serve as an alternative source of energy for neurons. Data from clinical trials suggest that MCTs improve cognition in patients with mild to moderate AD in apolipoprotein E4-negative patients. Adverse events observed were mild and included minor gastrointestinal problems such as diarrhea, dyspepsia, and flatulence. However, since genomic profiles are not routinely conducted in patients with AD in a clinical setting, the role of MCTs in clinical practice seems to be minimal.

Energy substrates protect hippocampus against endogenous glutamate-mediated neurodegeneration in awake rats

Excitotoxicity due to excessive glutamatergic neurotransmission is a well-studied phenomenon that has been related to the mechanisms of neuronal death occurring in some disorders of the CNS. We have previously shown that the intrahippocampal perfusion by microdialysis of 4-aminopyridine (4-AP) in rats stimulates endogenous glutamate release from nerve endings and this results in excitotoxic effects such as immediate seizures and delayed neuronal death, due to the overactivation of N-methyl-D-aspartate (NMDA) receptors. To study whether mitochondrial energy dysfunction and oxidative stress could be involved in this 4-AP-induced excitotoxicity, we evaluated in awake rats the protective effect of several energy substrates and antioxidant compounds, using microdialysis, electroencephalographic (EEG) recording and histological analysis. The 4-AP-induced behavioral and EEG seizures, which progressed to status epilepticus in about 30 min, were prevented by the NMDA receptor antagonist MK-801, whereas acetoacetate, DL- and L-β-hydroxybutyrate did not protect against seizures but increased the latency to the onset of status epilepticus; pyruvate, α-ketoglutarate and glutathione ethyl ester did not show any protective effect. 4-AP also produced nearly complete loss of pyramidal neurons in CA1 and CA3 regions of the ipsilateral hippocampus 24 h after the experiment. MK-801 totally prevented this neuronal death and the energy substrates tested protected by about 50%, whereas the antioxidants showed only a weak protection. We conclude that ketone bodies possess weak anticonvulsant effects and that energy metabolism impairment plays a more important role than oxidative stress in the delayed hippocampal neurodegeneration resulting from the excitotoxic action of 4-AP mediated by endogenous glutamate.

Changes in ascorbate, glutathione and α-tocopherol concentrations in the brain regions during normal development and moderate hypoglycemia in rats

Ascorbate, glutathione and α-tocopherol are the major low molecular weight antioxidants in the brain. The simultaneous changes in these compounds during normal development, and under a pro-oxidant condition are poorly understood. Ascorbate, glutathione and α-tocopherol concentrations in the olfactory bulb, cerebral cortex, hippocampus, striatum, hypothalamus, midbrain, cerebellum, pons and medulla oblongata were determined in postnatal day (P) 7, P14 and P60 male rats. A separate group of P14 and P60 rats were subjected to acute hypoglycemia, a pro-oxidant condition, prior to tissue collection. The concentrations of all three antioxidants were 100-600% higher in the brain regions at P7 and P14, relative to P60. The neuron-rich anterior brain regions (cerebral cortex and hippocampus) had higher concentrations of all three antioxidants than the myelin-rich posterior regions (pons and medulla oblongata) at P14 and P60. Hypoglycemia had a differential effect on the antioxidants. Glutathione was decreased at both P14 and P60. However, the decrease was localized at P14 and global at P60. Hypoglycemia had no effect on ascorbate and α-tocopherol at either age. Higher antioxidant concentrations in the developing brain may reflect the risk of oxidant stress during the early postnatal period and explain the relative resistance to oxidant-mediated injury at this age.

Ketogenic diet improves forelimb motor function after spinal cord injury in rodents

High fat, low carbohydrate ketogenic diets (KD) are validated non-pharmacological treatments for some forms of drug-resistant epilepsy. Ketones reduce neuronal excitation and promote neuroprotection. Here, we investigated the efficacy of KD as a treatment for acute cervical spinal cord injury (SCI) in rats. Starting 4 hours following C5 hemi-contusion injury animals were fed either a standard carbohydrate based diet or a KD formulation with lipid to carbohydrate plus protein ratio of 3:1. The forelimb functional recovery was evaluated for 14 weeks, followed by quantitative histopathology. Post-injury 3:1 KD treatment resulted in increased usage and range of motion of the affected forepaw. Furthermore, KD improved pellet retrieval with recovery of wrist and digit movements. Importantly, after returning to a standard diet after 12 weeks of KD treatment, the improved forelimb function remained stable. Histologically, the spinal cords of KD treated animals displayed smaller lesion areas and more grey matter sparing. In addition, KD treatment increased the number of glucose transporter-1 positive blood vessels in the lesion penumbra and monocarboxylate transporter-1 (MCT1) expression. Pharmacological inhibition of MCTs with 4-CIN (α-cyano-4-hydroxycinnamate) prevented the KD-induced neuroprotection after SCI, In conclusion, post-injury KD effectively promotes functional recovery and is neuroprotective after cervical SCI. These beneficial effects require the function of monocarboxylate transporters responsible for ketone uptake and link the observed neuroprotection directly to the function of ketones, which are known to exert neuroprotection by multiple mechanisms. Our data suggest that current clinical nutritional guidelines, which include relatively high carbohydrate contents, should be revisited.

Effects of hypoglycaemia on neuronal metabolism in the adult brain: role of alternative substrates to glucose

Hypoglycaemia is characterized by decreased blood glucose levels and is associated with different pathologies (e.g. diabetes, inborn errors of metabolism). Depending on its severity, it might affect cognitive functions, including impaired judgment and decreased memory capacity, which have been linked to alterations of brain energy metabolism. Glucose is the major cerebral energy substrate in the adult brain and supports the complex metabolic interactions between neurons and astrocytes, which are essential for synaptic activity. Therefore, hypoglycaemia disturbs cerebral metabolism and, consequently, neuronal function. Despite the high vulnerability of neurons to hypoglycaemia, important neurochemical changes enabling these cells to prolong their resistance to hypoglycaemia have been described. This review aims at providing an overview over the main metabolic effects of hypoglycaemia on neurons, covering in vitro and in vivo findings. Recent studies provided evidence that non-glucose substrates including pyruvate, glycogen, ketone bodies, glutamate, glutamine, and aspartate, are metabolized by neurons in the absence of glucose and contribute to prolong neuronal function and delay ATP depletion during hypoglycaemia. One of the pathways likely implicated in the process is the pyruvate recycling pathway, which allows for the full oxidation of glutamate and glutamine. The operation of this pathway in neurons, particularly after hypoglycaemia, has been re-confirmed recently using metabolic modelling tools (i.e. Metabolic Flux Analysis), which allow for a detailed investigation of cellular metabolism in cultured cells. Overall, the knowledge summarized herein might be used for the development of potential therapies targeting neuronal protection in patients vulnerable to hypoglycaemic episodes.

Comparison of the immunoreactivities of NMDA receptors between the young and adult hippocampal CA1 region induced by experimentally transient cerebral ischemia

Young gerbils are much more resistant to transient cerebral ischemia than the adult. In the present study, we observed that about 90% of CA1 pyramidal cells in the adult hippocampus died 4days post-ischemia; however, about 56% of them in the young hippocampus died at 7days post-ischemia. To compare excitotoxicity between them, we carried out immunoreactivities of NMDA receptor 1 (NMDAR1) and NMDAR2A/B in the hippocampal CA1 region (CA1) induced by 5min of transient cerebral ischemia in the young and adult gerbils. Their immunoreactivities and protein levels in the young sham-group were much lower than those in the adult sham-group. Four days after ischemia-reperfusion, they were significantly decreased in the adult ischemia-group; however, in the young ischemia-group, they were much higher than those in the adult. Seven days after ischemia-reperfusion, NMDAR1 immunoreactivity and its level in the young were much higher than those in the adult; NMDAR2A/B immunoreactivity and its level in the young were lower than in the adult. In brief, the immunoreactivities of NMDARs were not decreased in the ischemic CA1 region of the young 4days after transient cerebral ischemia. This finding indicates that longer maintenance of NMDARs may contribute to less and more delayed neuronal death/damage in the young CA1.

d-β-Hydroxybutyrate inhibited the apoptosis of PC12 cells induced by H2O2 via inhibiting oxidative stress

Oxidative stress has an important role in neurodegenerative diseases and cerebral ischemic injury. It is reported that d-β-hydroxybutyrate (DβHB), the major component of ketone bodies, is neuroprotective in recent studies. Therefore, in the present work the neuroprotective effects of DβHB on H2O2-induced apoptosis mediated by oxidative stress was investigated. PC12 cells were exposed to H2O2 with different concentrations of H2O2 for different times after DβHB pretreatment. MTT assay, apoptotic rates, intracellular reactive oxygen species (ROS) level, GSH content, mitochondrial membrane potential (MMP) and caspase-3 activity were determined. The results showed that DβHB inhibited the decrease of cell viability induced by H2O2 in PC12 cells. DβHB decreased the apoptotic rates induced by H2O2. The changes of intracellular ROS, GSH, MMP and caspase-3 activity due to H2O2 exposure were partially reversed in PC12 cells. So DβHB inhibited the apoptosis of PC12 cells induced by H2O2 via inhibiting oxidative stress.

Effect of glycolysis inhibition on mitochondrial function in rat brain

Inhibition of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase enhances the neural vulnerability to excitotoxicity both in vivo and in vitro through an unknown mechanism possibly related to mitochondrial failure. However, as the effect of glycolysis inhibition on mitochondrial function in brain has not been studied, the aim of the present work was to evaluate the effect of glycolysis inhibition induced by iodoacetate on mitochondrial function and oxidative stress in brain. Mitochondria were isolated from brain cortex, striatum and cerebellum of rats treated systemically with iodoacetate (25 mg/kg/day for 3 days). Oxygen consumption, ATP synthesis, transmembrane potential, reactive oxygen species production, lipoperoxidation, glutathione levels, and aconitase activity were assessed. Oxygen consumption and aconitase activity decreased in the brain cortex and striatum, showing that glycolysis inhibition did not trigger severe mitochondrial impairment, but a slight mitochondrial malfunction and oxidative stress were present.

Hydroxybutyrate prevents protein aggregation in the halotolerant bacterium Pseudomonas sp. CT13 under abiotic stress

Polyhydroxybutyrate (PHB), a typical carbon and energy storage compound, is widely found in Bacteria and Archae domains. This polymer is produced in response to conditions of physiological stress. PHB is composed of repeating units of β-hydroxybutyrate (R-3HB). It has been previously shown that R-3HB functions as an osmolyte in extremophile strains. In this study, Pseudomonas sp. CT13, a halotolerant bacterium, and its PHB synthase-minus mutant (phaC) were used to analyze the chaperone role of R-3HB. The production of this compound was found to be essential to salt stress resistance and positively correlated with salt concentration, suggesting that PHB monomer acts as a compatible solute in Pseudomonas sp. CT13. R-3HB accumulation was also associated with the prevention of protein aggregation under combined salt and thermal stresses in Pseudomonas sp. CT13. Physiological concentrations of R-3HB efficiently reduced citrate synthase (CS) aggregation and stabilized the enzymatic activities of CS during thermal stress. Docking analysis of the CS/R-3HB interaction predicted the stability of this complex under physiological concentrations of R-3HB. Thus, in vivo, in vitro and in silico analyses suggest that R-3HB can act as a chemical chaperone.

Clinical review: ketones and brain injury

Although much feared by clinicians, the ability to produce ketones has allowed humans to withstand prolonged periods of starvation. At such times, ketones can supply up to 50% of basal energy requirements. More interesting, however, is the fact that ketones can provide as much as 70% of the brain's energy needs, more efficiently than glucose. Studies suggest that during times of acute brain injury, cerebral uptake of ketones increases significantly. Researchers have thus attempted to attenuate the effects of cerebral injury by administering ketones exogenously. Hypertonic saline is commonly utilized for management of intracranial hypertension following cerebral injury. A solution containing both hypertonic saline and ketones may prove ideal for managing the dual problems of refractory intracranial hypertension and low cerebral energy levels. The purpose of the present review is to explore the physiology of ketone body utilization by the brain in health and in a variety of neurological conditions, and to discuss the potential for ketone supplementation as a therapeutic option in traumatic brain injury.

Neuroprotection by acetoacetate and β-hydroxybutyrate against NMDA-induced RGC damage in rat--possible involvement of kynurenic acid

PURPOSE

This study investigated the effects of systemically administered lithium acetoacetate (ACA) and sodium β-hydroxybutyrate (BHB) in a rat model of N-methyl-D-aspartate (NMDA)-induced damage of retinal ganglion cells (RGC). Additionally, the influence of ACA and BHB on kynurenic acid (KYNA) production was assessed in vitro in bovine retinal slices.

METHODS

Female adult Brown-Norway rats in groups of 5-8 animals were used. ACA and BHB were administered intraperitoneally once a day for 21 consecutive days, and phosphate buffered saline (PBS) was administered to control animals. After 2 weeks, the animals received intraocular NMDA (2 μl of a 10 mM solution in PBS) or intraocular PBS as a control. On day 19, retinal ganglion cells were labeled retrogradely with hydroxystilbamidine. Two days later, RGC density (cells per mm(2)) was assessed on retinal flatmounts. Additionaly, bovine retinal slices were incubated with NMDA and ACA or BHB at concentrations of 1.0 mM and 3.0 mM, and de novo KYNA production was measured using HPLC.

RESULTS

Intraperitoneal ACA (250 mg/kg) or BHB (291.2 mg/kg) significantly protected RGC against NMDA-induced neurodegeneration. De novo KYNA production in bovine retinal slices was lowered by NMDA. Both ACA and BHB at a concentration of 3.0 mM significantly reduced the effects of NMDA.

CONCLUSIONS

ACA and BHB had a significant dose-dependent neuroprotective effect on RGC in a rat model of NMDA-induced RGC damage. Both ketone bodies also significantly attenuated NMDA-induced reduction of retinal KYNA production in vitro, suggesting that this mechanism may be essential for the neuroprotective effects of ACA and BHB in vivo. Our results imply that ketone bodies may represent an additional treatment option in chronic neurodegenerative disorders of the eye.

Role of beta-hydroxybutyric acid in the central regulation of energy balance

Although the phenomenon of beta-hydroxybutyric acid (BHBA) impact on satiety and thermogenesis has been described in the past decades, the underlying molecular mechanisms involved remain unresolved. Other metabolites such as glucose, fatty or branched chain amino acids are known to activate the AMP kinase pathway leading to an increase of anorexic and a decrease of orexigenic neuropeptides in the hypothalamus, one of the central regulators of energy homeostasis. Since BHBA is utilized as an energy source by the brain particularly in suckling newborns and under starving conditions, it is supposed to be a further central signal and energy providing substrate involved in the regulation of food intake. Moreover, BHBA might present a therapeutic approach for treating neuronal diseases because of its neuroprotective properties. Therefore, the purpose of this review is to summarize the known central effects of BHBA and to point out the importance of the identification of cellular pathways triggered in response to BHBA.

Glycolysis inhibition decreases the levels of glutamate transporters and enhances glutamate neurotoxicity in the R6/2 Huntington's disease mice

Excitotoxicity has been associated with the loss of medium spiny neurons (MSN) in Huntington's disease (HD). We have previously observed that the content of the glial glutamate transporters, glutamate transporter 1 (GLT-1) and glutamate-aspartate transporter (GLAST), diminishes in R6/2 mice at 14 weeks of age but not at 10 weeks, and that this change correlates with an increased vulnerability of striatal neurons to glutamate toxicity. We have also reported that inhibition of the glycolytic pathway decreases glutamate uptake and enhances glutamate neurotoxicity in the rat brain. We now show that at 10-weeks of age, glutamate excitotoxicity is precipitated in R6/2 mice, after the treatment with iodoacetate (IOA), an inhibitor of the glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH). IOA induces a larger inhibition of GAPDH in R6/2 mice, while it similarly reduces the levels of GLT-1 and GLAST in wild-type and transgenic animals. Results suggest that metabolic failure and altered glutamate uptake are involved in the vulnerability of striatal neurons to glutamate excitotoxicity in HD.

Mitochondria, oxidative stress, and temporal lobe epilepsy

Mitochondrial oxidative stress and dysfunction are contributing factors to various neurological disorders. Recently, there has been increasing evidence supporting the association between mitochondrial oxidative stress and epilepsy. Although certain inherited epilepsies are associated with mitochondrial dysfunction, little is known about its role in acquired epilepsies such as temporal lobe epilepsy (TLE). Mitochondrial oxidative stress and dysfunction are emerging as key factors that not only result from seizures, but may also contribute to epileptogenesis. The occurrence of epilepsy increases with age, and mitochondrial oxidative stress is a leading mechanism of aging and age-related degenerative disease, suggesting a further involvement of mitochondrial dysfunction in seizure generation. Mitochondria have critical cellular functions that influence neuronal excitability including production of adenosine triphosphate (ATP), fatty acid oxidation, control of apoptosis and necrosis, regulation of amino acid cycling, neurotransmitter biosynthesis, and regulation of cytosolic Ca(2+) homeostasis. Mitochondria are the primary site of reactive oxygen species (ROS) production making them uniquely vulnerable to oxidative stress and damage which can further affect cellular macromolecule function, the ability of the electron transport chain to produce ATP, antioxidant defenses, mitochondrial DNA stability, and synaptic glutamate homeostasis. Oxidative damage to one or more of these cellular targets may affect neuronal excitability and increase seizure susceptibility. The specific targeting of mitochondrial oxidative stress, dysfunction, and bioenergetics with pharmacological and non-pharmacological treatments may be a novel avenue for attenuating epileptogenesis.

D-beta-hydroxybutyrate prevents MPP+-induced neurotoxicity in PC12 cells

Numerous studies show that D-beta-Hydroxybutyrate (DbetaHB) is neuroprotective. The present study was to explore the neuroprotective effects of DbetaHB against the cell death and apoptosis induced by 1-methyl-4-phenylpyridinium ion (MPP+) in PC12 cells. PC12 cells were pretreated with DbetaHB and followed by MPP+ exposure. The cell viability was determined by MTT assay. The morphological characteristics of apoptosis was observed by Acridine Orange (AO) staining and apoptotic rates were measured by flow cytometer. The product of lipid peroxidation, malondialdehyde (MDA), was measured using thiobarbituric acid method. The mitochondrial membrane potential (MMP), intracellular ROS and total glutathione were detected by microplate reader. In PC12 cells, pretreatment with DbetaHB significantly reduced MPP+-induced the decrease of cell viability. AO staining and flow cytometric analysis found DbetaHB inhibited MPP+-induced apoptosis. The measurement of MDA formation showed that DbetaHB alleviated lipid peroxidation induced by MPP+. The loss of MMP induced by MPP+ was preventive by DbetaHB. The changes of intracellular ROS and total glutathione induced by MPP+ were reversed by DbetaHB. DbetaHB protected PC12 cells against MPP+-induced death and apoptosis.

Study of the ketogenic agent AC-1202 in mild to moderate Alzheimer's disease: a randomized, double-blind, placebo-controlled, multicenter trial

BACKGROUND

Alzheimer's disease (AD) is characterized by early and region-specific declines in cerebral glucose metabolism. Ketone bodies are produced by the body during glucose deprivation and are metabolized by the brain. An oral ketogenic compound, AC-1202, was tested in subjects with probable AD to examine if ketosis could improve cognitive performance.

METHODS

Daily administration of AC-1202 was evaluated in 152 subjects diagnosed with mild to moderate AD in a US-based, 90-day, randomized, double-blind, placebo-controlled, parallel-group study. Subjects were on a normal diet and continued taking approved AD medications. Primary cognitive end points were mean change from Baseline in the AD Assessment Scale-Cognitive subscale (ADAS-Cog), and global scores in the AD Cooperative Study - Clinical Global Impression of Change (ADCS-CGIC). AC-1202 was compared to Placebo in several population groups, including: intention-to-treat (ITT), per protocol, and dosage compliant groups. Results were also stratified by APOE4 carriage status (a predefined analysis based on the epsilon 4 (E4) variant of the apolipoprotein E gene). This trial was registered with ClinicalTrials.gov, registry number NCT00142805, information available at http://clinicaltrials.gov/ct2/show/NCT00142805

RESULTS

AC-1202 significantly elevated a serum ketone body (beta-hydroxybutyrate) 2 hours after administration when compared to Placebo. In each of the population groups, a significant difference was found between AC-1202 and Placebo in mean change from Baseline in ADAS-Cog score on Day 45: 1.9 point difference, p = 0.0235 in ITT; 2.53 point difference, p = 0.0324 in per protocol; 2.6 point difference, p = 0.0215 in dosage compliant. Among participants who did not carry the APOE4 allele (E4(-)), a significant difference was found between AC-1202 and Placebo in mean change from Baseline in ADAS-Cog score on Day 45 and Day 90. In the ITT population, E4(-) participants (N = 55) administered AC-1202 had a significant 4.77 point difference in mean change from Baseline in ADAS-Cog scores at Day 45 (p = 0.0005) and a 3.36 point difference at Day 90 (p = 0.0148) compared to Placebo. In the per protocol population, E4(-) participants receiving AC-1202 (N = 37) differed from placebo by 5.73 points at Day 45 (p = 0.0027) and by 4.39 points at Day 90 (p = 0.0143). In the dosage compliant population, E4(-) participants receiving AC-1202 differed from placebo by 6.26 points at Day 45 (p = 0.0011, N = 38) and 5.33 points at Day 90 (p = 0.0063, N = 35). Furthermore, a significant pharmacologic response was observed between serum beta-hydroxybutyrate levels and change in ADAS-Cog scores in E4(-) subjects at Day 90 (p = 0.008). Adverse events occurred more frequently in AC-1202 subjects, were primarily restricted to the gastrointestinal system, and were mainly mild to moderate in severity and transient in nature.

CONCLUSION

AC-1202 rapidly elevated serum ketone bodies in AD patients and resulted in significant differences in ADAS-Cog scores compared to the Placebo. Effects were most notable in APOE4(-) subjects who were dosage compliant.

Ketone bodies as a therapeutic for Alzheimer's disease

An early feature of Alzheimer's disease (AD) is region-specific declines in brain glucose metabolism. Unlike other tissues in the body, the brain does not efficiently metabolize fats; hence the adult human brain relies almost exclusively on glucose as an energy substrate. Therefore, inhibition of glucose metabolism can have profound effects on brain function. The hypometabolism seen in AD has recently attracted attention as a possible target for intervention in the disease process. One promising approach is to supplement the normal glucose supply of the brain with ketone bodies (KB), which include acetoacetate, beta-hydroxybutyrate, and acetone. KB are normally produced from fat stores when glucose supplies are limited, such as during prolonged fasting. KB have been induced both by direct infusion and by the administration of a high-fat, low-carbohydrate, low-protein, ketogenic diets. Both approaches have demonstrated efficacy in animal models of neurodegenerative disorders and in human clinical trials, including AD trials. Much of the benefit of KB can be attributed to their ability to increase mitochondrial efficiency and supplement the brain's normal reliance on glucose. Research into the therapeutic potential of KB and ketosis represents a promising new area of AD research.

Excitotoxic neuronal death and the pathogenesis of Huntington's disease

Huntington's disease (HD) is a neurodegenerative hereditary illness originated by the mutation of the gene encoding the huntingtin-protein (htt). Mutated htt (mhtt) is characterized by an increased number of glutamine repeats in the N-terminal end; when 40 or more glutamine residues are present, the disease is manifested. Expression of mhtt leads to the selective death of the medium spiny neurons (MSN) in the neostriatum, resulting in the appearance of generalized involuntary movements, the main phenotypic alteration of HD. The relationship between the expression of mhtt and the death of the MSN is not fully understood. Nonetheless, according to experimental evidence indicating that MSN are selectively vulnerable to the toxicity of glutamate (excitotoxicity) or its analogues, excitotoxic neuronal death is suggested to be involved in neurodegeneration associated with HD. Support for this hypothesis comes from studies in HD postmortem tissue and transgenic mice models, suggesting a correlation between mhtt expression and altered glutamatergic neurotransmission, mainly altered conductance of the N-methyl-D-aspartate (NMDA) glutamate receptor subtype and decreased levels of glutamate transporters. On the other hand, alterations in energy metabolism are well documented in HD patients, which might facilitate excitotoxicity. Throughout this review we will discuss relevant evidence suggesting that altered glutamatergic neurotransmission plays a role in neurodegeneration associated with HD, as well as the possible contribution of deficient energy metabolism to the development of an excitotoxic cell death cascade in MSN. We show data supporting protection by energy substrates against neuronal damage in a rat model combining energy deficit and glutamate toxicity.

Antioxidant capacity contributes to protection of ketone bodies against oxidative damage induced during hypoglycemic conditions

Ketone bodies play a key role in mammalian energy metabolism during the suckling period. Normally ketone bodies' blood concentration during adulthood is very low, although it can rise during starvation, an exogenous infusion or a ketogenic diet. Whenever ketone bodies' levels increase, their oxidation in the brain rises. For this reason they have been used as protective molecules against refractory epilepsy and in experimental models of ischemia and excitotoxicity. The mechanisms underlying the protective effect of these compounds are not completely understood. Here, we studied a possible antioxidant capacity of ketone bodies and whether it contributes to the protection against oxidative damage induced during hypoglycemia. We report for the first time the scavenging capacity of the ketone bodies, acetoacetate (AcAc) and both the physiological and non-physiological isomers of beta-hydroxybutyrate (D- and L-BHB, respectively), for diverse reactive oxygen species (ROS). Hydroxyl radicals (.OH) were effectively scavenged by D- and L-BHB. In addition, the three ketone bodies were able to reduce cell death and ROS production induced by the glycolysis inhibitor, iodoacetate (IOA), while only D-BHB and AcAc prevented neuronal ATP decline. Finally, in an in vivo model of insulin-induced hypoglycemia, the administration of D- or L-BHB, but not of AcAc, was able to prevent the hypoglycemia-induced increase in lipid peroxidation in the rat hippocampus. Our data suggest that the antioxidant capacity contributes to protection of ketone bodies against oxidative damage in in vitro and in vivo models associated with free radical production and energy impairment.

Cerebral metabolic adaptation and ketone metabolism after brain injury

The developing central nervous system has the capacity to metabolize ketone bodies. It was once accepted that on weaning, the 'post-weaned/adult' brain was limited solely to glucose metabolism. However, increasing evidence from conditions of inadequate glucose availability or increased energy demands has shown that the adult brain is not static in its fuel options. The objective of this review is to summarize the body of literature specifically regarding cerebral ketone metabolism at different ages, under conditions of starvation and after various pathologic conditions. The evidence presented supports the following findings: (1) there is an inverse relationship between age and the brain's capacity for ketone metabolism that continues well after weaning; (2) neuroprotective potentials of ketone administration have been shown for neurodegenerative conditions, epilepsy, hypoxia/ischemia, and traumatic brain injury; and (3) there is an age-related therapeutic potential for ketone as an alternative substrate. The concept of cerebral metabolic adaptation under various physiologic and pathologic conditions is not new, but it has taken the contribution of numerous studies over many years to break the previously accepted dogma of cerebral metabolism. Our emerging understanding of cerebral metabolism is far more complex than could have been imagined. It is clear that in addition to glucose, other substrates must be considered along with fuel interactions, metabolic challenges, and cerebral maturation.

Glutamate-induced retinal lipid and protein damage: the protective effects of catechin

Glutamate toxicity has been implicated in various retinal diseases. Green tea leaf extract catechin has protective effects against cellular toxicity. This study investigated the effects of catechin on the glutamate-treated retina. Porcine retinal homogenates were incubated with glutamate (20 nmol) at 37 degrees C for 60 min. Catechin was co-incubated with the glutamate-treated retina in the same condition. The malondialdehyde (MDA) levels were determined as an index of lipid peroxidation (LPO). Differential protein expressions were derived from two-dimensional gel electrophoresis. Mass spectrometry was conducted to identify the proteins. Glutamate increased the retinal MDA (p<0.0001) and catechin reversed the effect (p<0.0001). There were significant changes in seven proteins after the glutamate treatment (p<0.05), namely, heterogeneous ribonucleoprotein, thioredoxin peroxidase, 5-hydroxytryptamine receptor, pyruvate dehydrogenase, ARHA protein, peroxiredoxin 6 and proteasome. Catechin significantly reversed the changes in thioredoxin peroxidase, 5-hydroxytryptamine receptor, peroxiredoxin 6 and pyruvate dehydrogenase (p<0.05). Our study shows that (a) retinal glutamate toxicity is mediated by LPO and protein modification, and (b) catechin ameliorates the toxicity.