The hypothesis that chronic feeding of the triglycerides of octanoate (trioctanoin) and decanoate (tridecanoin) in "a regular non-ketogenic diet" is anticonvulsant was tested and possible mechanisms of actions were subsequently investigated. Chronic feeding of 35E% of calories from tridecanoin, but not trioctanoin, was reproducibly anticonvulsant in two acute CD1 mouse seizure models. The levels of beta-hydroxybutyrate in plasma and brain were not significantly increased by either treatment relative to control diet. The respective decanoate and octanoate levels are 76 µM and 33 µM in plasma and 1.17 and 2.88 nmol/g in brain. Tridecanoin treatment did not alter the maximal activities of several glycolytic enzymes, suggesting that there is no reduction in glycolysis contributing to anticonvulsant effects. In cultured astrocytes, 200 µM of octanoic and decanoic acids increased basal respiration and ATP turnover, suggesting that both medium chain fatty acids are used as fuel. Only decanoic acid increased mitochondrial proton leak which may reduce oxidative stress. In mitochondria isolated from hippocampal formations, tridecanoin increased respiration linked to ATP synthesis, indicating that mitochondrial metabolic functions are improved. In addition, tridecanoin increased the plasma antioxidant capacity and hippocampal mRNA levels of heme oxygenase 1, and FoxO1.

There is mounting evidence that oxidative glucose metabolism is impaired in epilepsy and recent work has further characterized the metabolic mechanisms involved. In healthy people eating a traditional diet, including carbohydrates, fats and protein, the major energy substrate in brain is glucose. Cytosolic glucose metabolism generates small amounts of energy, but oxidative glucose metabolism in the mitochondria generates most ATP, in addition to biosynthetic precursors in cells. Energy is crucial for the brain to signal “normally,” while loss of energy can contribute to seizure generation by destabilizing membrane potentials and signaling in the chronic epileptic brain. Here we summarize the known biochemical mechanisms that contribute to the disturbance in oxidative glucose metabolism in epilepsy, including decreases in glucose transport, reduced activity of particular steps in the oxidative metabolism of glucose such as pyruvate dehydrogenase activity, and increased anaplerotic need. This knowledge justifies the use of alternative brain fuels as sources of energy, such as ketones, TCA cycle intermediates and precursors as well as even medium chain fatty acids and triheptanoin.

Although certain metabolic characteristics such as interictal glucose hypometabolism are well established for temporal lobe epilepsy (TLE), its pathogenesis still remains unclear. Here, we performed a comprehensive study of brain metabolism in a mouse model of TLE, induced by pilocarpine-status epilepticus (SE). To investigate glucose metabolism, we injected mice 3.5-4 weeks after SE with [1,2-13 C]glucose before microwave fixation of the head. Using 1 H and 13 C nuclear magnetic resonance spectroscopy, gas chromatography-mass spectrometry and high-pressure liquid chromatography, we quantified metabolites and 13 C labeling in extracts of cortex and hippocampal formation (HF). Hippocampal levels of glutamate, glutathione and alanine were decreased in pilocarpine-SE mice compared with controls. Moreover, the contents of N-acetyl aspartate, succinate and reduced nicotinamide adenine dinucleotide (phosphate) NAD(P)H were decreased in HF indicating impairment of mitochondrial function. In addition, the reduction in 13 C enrichment of hippocampal citrate and malate suggests decreased tricarboxylic acid (TCA) cycle turnover in this region. In cortex, we found reduced 13 C labeling of glutamate, glutamine and aspartate via the pyruvate carboxylation and pyruvate dehydrogenation pathways, suggesting slower turnover of these amino acids and/or the TCA cycle. In conclusion, mitochondrial metabolic dysfunction and altered amino-acid metabolism is found in both cortex and HF in this epilepsy model. Keywords: 13 C isotope; glutamate; mitochondria; neurometabolism; NMR spectroscopy; temporal lobe epilepsy Journal of Cerebral Blood INTRODUCTIONTemporal lobe epilepsy (TLE) is one of the most common forms of human epilepsy and is associated with a high level of drug resistance among patients. The mechanisms underlying the pathogenesis of TLE still remain unclear, although increasing evidence points to a disturbance in amino-acid neurotransmitter homeostasis and energy metabolism, as well as neuronal injury. Metabolic characteristics of human TLE include interictal glucose hypometabolism and a decrease in the levels of the neuronal marker N-acetyl aspartate (NAA) in the epileptogenic region. 1,2 Increased levels of extracellular glutamate in epileptogenic hippocampi have been reported before and during seizures 3 and interictally. 4 Moreover, it has been suggested that the uptake of glutamate from the extracellular space by astrocytes is slower in the epileptic brain as the expression of glutamine synthetase, the glial enzyme that converts glutamate to glutamine, was decreased in the epileptogenic hippocampi from patients with TLE. 5,6 Changes in brain metabolism in rat models of TLE resemble those reported in human TLE such as interictal glucose hypometabolism demonstrated in lithium-pilocarpine rats, 7 as well as alterations in NAA and glutamate reported in post-status epilepticus (SE) models induced by kainic acid and lithiumpilocarpine. [8][9][10] There are, however, few comprehensive studies on brain metabolism in mouse model...

Temporal lobe epilepsy is a common form of adult epilepsy and shows high resistance to treatment. Increasing evidence has suggested that metabolic dysfunction contributes to the development of seizures, with previous studies indicating impairments in brain glucose metabolism. Here we aim to elucidate which pathways involved in glucose metabolism are impaired, by tracing the hippocampal metabolism of injected [U-13C]glucose (i.p.) during the chronic stage of the pilocarpine-status epilepticus mouse model of epilepsy. The enrichment of 13C in the intermediates of glycolysis and the TCA cycle were quantified in hippocampal extracts using liquid chromatography–tandem mass spectroscopy, along with the measurement of the activities of enzymes in each pathway. We show that there is reduced incorporation of 13C in the intermediates of glycolysis, with the percentage enrichment of all downstream intermediates being highly correlated with those of glucose 6-phosphate. Furthermore, the activities of all enzymes in this pathway including hexokinase and phosphofructokinase were unaltered, suggesting that glucose uptake is reduced in this model without further impairments in glycolysis itself. The key findings were 33% and 55% losses in the activities of pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase, respectively, along with reduced 13C enrichment in TCA cycle intermediates. This lower 13C enrichment is best explained in part by the reduced enrichment in glycolytic intermediates, whereas the reduction of key TCA cycle enzyme activity indicates that TCA cycling is also impaired in the hippocampal formation. Together, these data suggest that multitarget approaches may be necessary to restore metabolism in the epileptic brain.

There is increasing evidence that energy metabolism is disturbed in Amyotrophic Lateral Sclerosis (ALS) patients and animal models. Treatment with triheptanoin, the triglyceride of heptanoate, is a promising approach to provide alternative fuel to improve oxidative phosphorylation and aid ATP generation. Heptanoate can be metabolized to propionyl-CoA, which after carboxylation can produce succinyl-CoA and thereby re-fill the tricarboxylic acid (TCA) cycle (anaplerosis). Here we tested the hypothesis that treatment with triheptanoin prevents motor neuron loss and delays the onset of disease symptoms in female mice overexpressing the mutant human SOD1G93A (hSOD1G93A) gene. When oral triheptanoin (35% of caloric content) was initiated at P35, motor neuron loss at 70 days of age was attenuated by 33%. In untreated hSOD1G93A mice, the loss of hind limb grip strength began at 16.7 weeks. Triheptanoin maintained hind limb grip strength for 2.8 weeks longer (p<0.01). Loss of balance on the rotarod and reduction of body weight were delayed by 13 and 11 days respectively (both p<0.01). Improved motor function occurred in parallel with alterations in the expression of genes associated with muscle metabolism. In gastrocnemius muscles, the mRNA levels of pyruvate, 2-oxoglutarate and succinate dehydrogenases and methyl-malonyl mutase were reduced by 24–33% in 10 week old hSOD1G93A mice when compared to wild-type mice, suggesting that TCA cycling in skeletal muscle may be slowed in this ALS mouse model at a stage when muscle strength is still normal. At 25 weeks of age, mRNA levels of succinate dehydrogenases, glutamic pyruvic transaminase 2 and the propionyl carboxylase β subunit were reduced by 69–84% in control, but not in triheptanoin treated hSOD1G93A animals. Taken together, our results suggest that triheptanoin slows motor neuron loss and the onset of motor symptoms in ALS mice by improving TCA cycling.