Neuronal inhibition and seizure suppression by acetoacetate and its analog, 2‐phenylbutyrate

Summary Objective The ketogenic diet is clinically used to treat drug‐resistant epilepsy. The diet treatment markedly increases ketone bodies (acetoacetate and β‐hydroxybutyrate), which work as energy metabolites in the brain. Here, we investigated effects of acetoacetate on voltage‐dependent Ca 2+ channels ( VDCC s) in pyramidal cells of the hippocampus. We further explored an acetoacetate analog that inhibited VDCC s in pyramidal cells, reduced excitatory postsynaptic currents ( EPSC s), and suppressed seizures in vivo. Methods The effects of acetoacetate and its analogs on VDCC s and EPSC s were evaluated using patch‐clamp recordings from CA 1 pyramidal cells of mouse hippocampal slices. The in vivo effects of these reagents were also evaluated using a chronic seizure model induced by intrahippocampal injection of kainate. Results Acetoacetate inhibited VDCC s in pyramidal cells of hippocampal slices, and reduced EPSC s in slices exhibiting epileptiform activity. More potent EPSC inhibitors were then explored by modifying the chemical structure of acetoacetate, and 2‐phenylbutyrate was identified as an acetoacetate analog that inhibited VDCC s and EPSC s more potently. Although acetoacetate is known to inhibit vesicular glutamate transporters ( VGLUT s), 2‐phenylbutyrate did not inhibit VGLUT s, showing that 2‐phenylbutyrate is an acetoacetate analog that preferably inhibits VDCC s. In addition, 2‐phenylbutyrate markedly reduced EPSC s in slices exhibiting epileptiform activity, and suppressed hippocampal seizures in vivo in a mouse model of epilepsy. The in vivo antiseizure effects of 2‐phenylbutyrate were more potent than those of acetoacetate. Finally, intraperitoneal 2‐phenylbutyrate was delivered to the brain, and its brain concentration reached the level enough to reduce EPSC s. Significance These results demonstrate that 2‐phenylbutyrate is an acetoacetate analog that inhibits VDCC s and EPSC s in pyramidal cells, suppresses hippocampal seizures in vivo, and has brain penetration ability. Thus 2‐phenylbutyrate provides a useful chemical structure as a lead compound to develop new antiseizure drugs originating from ketone bodies.