Voltage‐Dependent Block of N‐Methyl‐d‐Aspartate Receptors by the Novel Anticonvulsant Dibenzylamine, a Bioactive Constituent of l‐(+)‐β‐Hydroxybutyrate

Abstract

Summary:Purpose: Previously we demonstrated that L-(+)-β-hydroxybutyrate (L-BHB), acetoacetate (ACA), acetone, and dibenzylamine (DBA) were anticonvulsant in an audiogenic seizure-susceptible model, and that DBA was a bioactive contaminant identified in commercial lots of L-BHB. In the present study, we asked whether these effects could be mediated by ionotropic glutamate or γ -aminobutyric acid A (GABA A ) receptors.Methods: We studied the effects of both stereoisomers of BHB (as well as the racemate), ACA, and DBA on N-methyl-Daspartate (NMDA), α-amino-3-hydroxy-5methyl-4-isoxazoleproprionic acid (AMPA), and GABA A receptors in cultured rodent neocortical neurons by using whole-cell voltage-clamp recording techniques.Results: Only L-BHB and DBA exerted a concentration-and voltage-dependent block of NMDA-evoked currents, whereas none of the tested substrates affected AMPA-or GABA-activated currents. The kinetics of whole-cell block by L-BHB and DBA were similar, providing additional evidence that DBA is responsible for the anticonvulsant activity of L-BHB.

The Neuropharmacology of the Ketogenic Diet

“…However, the fact that inhibition was also enhanced with calorie restriction alone suggests that it may be the calorie restriction in the ketogenic diet, and not ketosis per se, that is the critical factor in the effect on inhibitory synaptic function. This conclusion is compatible with the studies, already noted, in which ketone bodies did not influence GABA receptor responses [48,49].…”

“…It was proposed that these ketone bodies might act as GABA receptor agonists. However, studies in cultured rat hippocampal neurons [48] and rodent neocortical neurons [49] failed to demonstrate an effect of the ketone bodies on GABA receptor currents, making this proposed mechanism unlikely.…”

“…The ketogenic diet may have activity in the maximal electroshock test in mice, although not in rats (Table 1), raising the possibility that some aspect of the diet, perhaps ketone bodies themselves, could block ionotropic glutamate receptors. However, studies in cell culture have failed to observe effects of β-hydroxybutyrate or acetoacetate on N-methyl-D-aspartate or AMPA receptor-mediated synaptic currents [48] or on responses to exogenously applied N-methyl-D-aspartate or AMPA [49]. Whether acetone is similarly inactive on ionotropic glutamate receptors remains to be determined.…”

Depolarizing Actions of GABA in Immature Neurons Depend Neither on Ketone Bodies Nor on Pyruvate

“…DBA mediates effects thought previously to be attributable to DL-BHB blockade of cardiac K ϩ channels and anticonvulsive actions of ketone bodies (Doepner et al, 1997(Doepner et al, , 2001Rho et al, 2002;Donevan et al, 2003). Investigations using DL-BHB must take this parameter into account.…”

“…Therefore, DL-BHB (Acros Organics) reduces DF-GABA and alters GDPs. Because previous studies reported the presence of a contaminant in L-BHB (Donevan et al, 2003) (see Discussion), we decided to test whether a similar contaminant was also present in DL-BHB obtained from this source (Acros Organics). Using a GC-MS instrument, several contaminants were found in this source of DL-BHB, notably DBA as PFPA derivative identified in the DL-BHB from Acros Organics (supplemental Fig.…”