Alterations in Cytosolic and Mitochondrial [U-¹³C]-Glucose Metabolism in a Chronic Epilepsy Mouse Model

Abstract

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 percent enrichment of all downstream intermediates highly correlated to 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 finding was a 33% and 55% loss 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 due to the reduced enrichment in glycolytic intermediates, while the reduction of key TCA cycle enzyme activity indicates that the TCA cycling is also impaired in the hippocampal formation. Together this study suggests that multi-target approaches may be necessary to restore metabolism in the epileptic brain.

Significance Statement The specific metabolic impairments that occur in the epileptic brain and can play a role in the development of seizures are mostly unknown. Glucose uptake has been shown to be reduced in epileptic brain areas in patients and models. By following ¹³C-glucose metabolism, we show that during the chronic epileptic stage in a murine model, there are further impairments to oxidative glucose metabolism along with reduced maximal activities of pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase, key enzymes of the TCA cycle in the hippocampus. Together with diminished glucose uptake, this will decrease the ability to produce ATP in epileptogenic areas, which may contribute to seizure development. This research identified new targets for new therapies to inhibit seizures in the “epileptic” brain.