Mechanisms of 2DGs Antiepileptic Effects

Wm S. Middleton Memorial Veterans Hosp, Madison WI

Investigators

Abstract

DESCRIPTION (provided by applicant): Epilepsy occurs in about 1% of Veteran patients and is not controlled by current anti-epileptic drugs (AEDs) in approximately one third of patients. For the third who do not have their seizures controlled and for those who find AEDs to have unacceptable side effects, new treatment approaches are needed. An alternative treatment can be metabolic and a protein and high fat diet without glucose, the ketogenic diet, can improve seizure control in those patients who do not respond to conventional AEDs. The ketogenic diet inhibits glycolysis, the breakdown of sugar, and seizure control is lost when glucose ingested. A novel alternative to the diet is to inhibit glycolysis using 2-deoxy-D-glucose (2DG), a glucose analog that interferes with the initial isomerization step in the glycolytic pathway. 2DG is being evaluated as investigational new drug and offers a new therapy option. 2DG has been shown to decrease the development of epilepsy in the kindling model as well as having acute antiepileptic effects in the 6 Hz and audiogenic stimulation models, and against chemoconvulsants in hippocampal slices. We will try to determine what effects 2DG has on neuronal excitability at a single neuron level and at the neuronal network level. By defining mechanisms of 2DG's antiepileptic properties, we expect new approaches to therapy of epilepsy will follow. 2DG also appears to have disease-modifying actions, and this proposal will study the use-dependent action of 2DG's effects. Our underlying hypothesis is that inhibition of glycolysis by 2DG results in antiepileptic effects, and we will address possible mechanisms as they relate to neuronal membrane excitability and changes in synaptic transmission. We will assess the following 2 specific aims: Aim 1: To identify changes in membrane excitability produced by 2DG treatment. We will evaluate a number of possible mechanisms of action as they relate to inhibition of glycolysis and a change in energy substrate near the membrane. This will include analysis of action potential generation which may be changed by a decrease in sodium-potassium pump, enhancement in the adenosine triphosphate (ATP) sensitive potassium channel that is activated with a decrease in ATP levels, and changes in the afterhyperpolarization that follows action potential generation. Aim 2: To assess 2DG's effect on synaptic transmission mediated by presynaptic mechanisms that alter the network excitability of the CA3 region of the hippocampus. Specifically we will see how 2DG alters the abnormal synaptic activity that occurs after prolonged activation of group I metabotropic glutamate receptor activation and produces CA3 epileptiform synchronization. We will also define changes in synaptic transmission using minimal stimulation and analysis of miniature post synaptic currents. All studies will use the CA3 region of the hippocampus which is vulnerable to epileptiform synchronization, in part related to the properties of the CA3 neurons and their recurrent excitatory synaptic network. We will assess CA3 neuron firing characteristics using sharp intracellular electrode recordings and how they change after 2DG. We will also use patch and whole-cell voltage clamp recordings to study intrinsic and postsynaptic currents. Our approach will test for specific changes in single neuron and network synaptic function that are modified by 2DG and will elucidate potential mechanisms of action for the antiepileptic effects of glycolytic inhibition. In the proposed study, we will be performing experiments that will increase neuronal activity to load neurons with DG and monitor for use-dependent effects that may explain any disease modifying features of 2DG treatment. Defining these actions will give new therapeutic targets for antiepileptic drug development as well as understanding the mechanism of 2DG's acute antiepileptic action.