Triheptanoin reduces seizure susceptibility in a syndrome-specific mouse model of generalized epilepsy

Summary

Triheptanoin is a triglyceride containing heptanoate, an odd-chained medium fatty acid that is metabolized to produce propionyl-CoA and subsequently C4 intermediates of the citric acid cycle and therefore capable of anaplerosis. These metabolic products are believed to underlie triheptanoin's anticonvulsant effects in rodent seizure models. Here we investigate the anticonvulsive effects of oral triheptanoin in a syndrome-specific genetic mouse model of generalized epilepsy based on the GABA_Aγ2(R43Q) mutation. Mice were fed a diet supplemented with triheptanoin from weaning for three weeks prior to electrocortical recordings. Occurrence and durations of spike and wave discharges (SWDs) were measured. Triheptanoin did not alter body weight or basal blood glucose levels suggesting that it was well tolerated. Triheptanoin supplementation halved the time spent in seizures due to a reduction in both SWD occurrence and duration. An injection of insulin was used to reduce blood glucose, a metabolic stress known to precipitate seizures in the GABA_Aγ2(R43Q) mouse. The reduction in seizure count was also evident following insulin induced hypoglycemia with the triheptanoin treated group having significantly less SWDs than control animals under similar low blood glucose conditions. In summary, triheptanoin may be an effective and well tolerated dietary therapy for generalized epilepsy.

Introduction

The high-fat, low-carbohydrate ketogenic diet is widely accepted as a useful treatment option in epilepsy with reports of up to 90% reductions in seizure frequency in some patients (Bailey et al., 2005, Freeman et al., 1998). However, the ketogenic diet is poorly tolerated, requiring adherence to a very rigid regimen and causing significant side effects including growth retardation and kidney stones (Kang et al., 2004). Although the precise mechanism underlying the efficacy of the ketogenic diet is not known, one hypothesis is that the ketone bodies may provide energy substrates to the brain (McNally and Hartman, 2012). In this study, we investigate a metabolic therapy based on an anaplerotic approach achieved through triheptanoin supplementation.

Anaplerosis describes the replenishment of depleted metabolic cycle intermediates. Triheptanoin is a triglyceride containing three saturated seven carbon chain fatty acids and is used to treat metabolic disorders due to its anaplerotic capability in the citric acid cycle (CAC) (Mochel et al., 2005, Roe et al., 2002). Triheptanoin is initially broken down in the gastrointestinal tract into heptanoate which is then metabolized by the liver to two C5 ketone bodies, β-hydroxypentanoate and β-ketopentanoate. Heptanoate and C5 ketones can be taken up by the brain, the latter possibly via monocarboxylate transporters (Broer et al., 1998). In the brain, these metabolites undergo further fatty acid oxidation to acetyl-CoA and propionyl-CoA. Carboxylation of propionyl-CoA can be anaplerotic because it produces methyl-malonyl-CoA, which can then be metabolized to the CAC intermediate succinyl-CoA.

Recent experimental evidence in chronic and acute rodent seizure models show that oral triheptanoin is an anticonvulsant (Borges and Sonnewald, 2011, Thomas et al., 2012, Willis et al., 2010). The aim of this study is to evaluate anticonvulsant effects of oral triheptanoin on generalized epilepsy using a genetic mouse model based on a human epilepsy mutation (Tan et al., 2007). We also evaluated if triheptanoin was protective during metabolic stress induced by lowering blood glucose levels.