TRPV1 antagonist capsazepine suppresses 4-AP-induced epileptiform activity in vitro and electrographic seizures in vivo

Abstract

Transient receptor potential vanilloid 1 (TRPV1) is a cation-permeable ion channel found in the peripheral and central nervous systems. The membrane surface expression of TRPV1 is known to occur in neuronal cell bodies and sensory neuron axons. TRPV1 receptors are also expressed in the hippocampus, the main epileptogenic region in the brain. Although, previous studies implicate TRPV1 channels in the generation of epilepsy, suppression of ongoing seizures by TRPV1 antagonists has not yet been attempted. Here, we evaluate the role of TRPV1 channels in the modulation of epileptiform activity as well as the anti-convulsant properties of capsazepine (CZP), an established TRPV1 competitive antagonist, using in vitro and in vivo models. To this end, we used 4-aminopyridine (4-AP) to trigger seizure-like activity. We found that CZP suppressed 4-AP induced epileptiform activity in vitro (10–100 µM) and in vivo (50 mg/kg s.c.). In contrast, capsaicin enhanced 4-AP induced epileptiform activity in vitro (1–100 µM) and triggered bursting activity in vivo (100 µM dialysis perfusion), which was abolished by the TRPV1 antagonist CZP. To further investigate the mechanisms of TRPV1 modulation, we studied the effect in capcaisin and CPZ on evoked potentials. Capsaicin (1–100 µM) and CZP (10–100 µM) increased and decreased, respectively, the amplitude of extracellular field evoked potentials in a concentration-dependent manner. Additional in vitro studies showed that the effect of the TRPV1 blocker on evoked potentials was similar whether the response was orthodromic or antidromic, suggesting that the effect involves interference with membrane depolarization on cells bodies and axons. The fact that CPZ could act directly on axons was confirmed by decreased amplitude of the compound action potential and by an increased delay of both the antidromic potentials and the axonal response. Histological studies using transgenic mice also show that, in addition to the known neural expression, TRPV1 channels are widely expressed in alvear oligodendrocytes in the hippocampus. Taken together, these results indicate that activation of TRPV1 channels leads to enhanced excitability, while their inhibition can effectively suppress ongoing electrographic seizures. These results support a role for TRPV1 channels in the suppression of convulsive activity, indicating that antagonism of TRPV1 channels particularly in axons may possibly be a novel target for effective acute suppression of seizures.

Cannabidiol exerts antiepileptic effects by restoring hippocampal interneuron functions in a temporal lobe epilepsy model

“…Agonism of human http://www.guidetopharmacology.org/GRAC/ObjectDisplayForward?objectId=507 expressed in HEK293 cells by CBD has been popularly reported with different potencies (3–10 μm) (Bisogno et al, 2001; De Petrocellis et al, 2011). The existing literature surrounding the role of TRPV1 in epilepsy is conflicted between different studies which indicate that activation of TRPV1 has no involvement (von Ruden et al, 2015), a proconvulsant (Manna and Umathe, 2012) or an anticonvulsant (Chen et al, 2013; Gonzalez‐Reyes et al, 2013) effect in epilepsy. Whether CBD is directly modulating http://www.guidetopharmacology.org/GRAC/FamilyDisplayForward?familyId=75 or targeting a novel postsynaptic cannabinoid receptor or alternatively working in synchrony with other previously established targets, for example, GRP55 or TRPV receptors (De Petrocellis et al, 2011; 2012; Hill et al, 2012b; Iannotti et al, 2014), remains to be investigated.…”

Analysis in conditional cannabinoid 1 receptor-knockout mice reveals neuronal subpopulation-specific effects on epileptogenesis in the kindling paradigm

“…Neonatal TRPV1 deficient mice are less susceptible to PTZ-induced seizures following hyperthermia (Kong et al, 2014). Moreover, agonists like capsaicin and OLDA enhanced epileptiform activity, whereas antagonists like capsazepine and AMG9810 abolished these effects (Bhaskaran and Smith, 2010;Gonzalez-Reyes et al, 2013;Shirazi et al, 2014). Capsazepine is a competitive antagonist of capsaicin with species-specific activity (McIntyre et al, 2001;Savidge et al, 2002).…”

Molecular Targets of Cannabidiol in Neurological Disorders

“…However, it remains unclear whether the increased TRPV1 expression described reflects an uninvolved and downstream consequence of disease or an integral part of the process. The preclinical literature describing TRPV1 involvement in epilepsy is conflicted where studies suggest no involvement [126,127], a proconvulsant effect, or an anticonvulsant effect of TRPV1 activation [128][129][130][131][132][133][134]. Overall, a larger number of studies suggest that the consequences of TRPV1 activation in epilepsy are detrimental which, given the large number of validated studies asserting overwhelmingly anticonvulsant effects of CBD in these animal models, suggests that TRPV1 activation by CBD is not part of its antiepileptic mechanism of action.…”