The AMPK Activator A769662 Blocks Voltage-Gated Sodium Channels: Discovery of a Novel Pharmacophore with Potential Utility for Analgesic Development.

Marina N Asiedu,Gregory Dussor,Theodore J Price,Sulayman D Dib-Hajj,Stephen G Waxman,Chongyang Han,Bradley Taylor

doi:10.1371/journal.pone.0169882

Abstract

Voltage-gated sodium channels (VGSC) regulate neuronal excitability by governing action potential (AP) generation and propagation. Recent studies have revealed that AMP-activated protein kinase (AMPK) activators decrease sensory neuron excitability, potentially by preventing sodium (Na+) channel phosphorylation by kinases such as ERK or via modulation of translation regulation pathways. The direct positive allosteric modulator A769662 displays substantially greater efficacy than other AMPK activators in decreasing sensory neuron excitability suggesting additional mechanisms of action. Here, we show that A769662 acutely inhibits AP firing stimulated by ramp current injection in rat trigeminal ganglion (TG) neurons. PT1, a structurally dissimilar AMPK activator that reduces nerve growth factor (NGF) -induced hyperexcitability, has no influence on AP firing in TG neurons upon acute application. In voltage-clamp recordings, application of A769662 reduces VGSC current amplitudes. These findings, based on acute A769662 application, suggest a direct channel blocking effect. Indeed, A769662 dose-dependently blocks VGSC in rat TG neurons and in Nav1.7-transfected cells with an IC50 of ~ 10 μM. A769662 neither displayed use-dependent inhibition nor interacted with the local anesthetic (LA) binding site. Popliteal fossa administration of A769662 decreased noxious thermal responses with a peak effect at 5 mins demonstrating an analgesic effect. These data indicate that in addition to AMPK activation, A769662 acts as a direct blocker/modulator of VGSCs, a potential mechanism enhancing the analgesic property of this compound.

Highlights

Pain hypersensitivity resulting from injury or disease is often paralleled by increased excitability of peripheral sensory neurons in either the dorsal root ganglion (DRG) or trigeminalPLOS ONE | DOI:10.1371/journal.pone.0169882 January 24, 2017A769662 Blocks Voltage-Gated Sodium Channels decision to publish, or preparation of the manuscript
We hypothesized that A769662 had a direct effect on Voltage-gated sodium channels (VGSC) in addition to its known mechanism of action as a positive allosteric modulator of AMPactivated protein kinase (AMPK)
Based on the results presented above, we hypothesized that A769662, but not other AMPK activators, should be capable of eliciting a local anesthetic effect in vivo due to its acute VGSC blocking properties

Summary

Introduction

Pain hypersensitivity resulting from injury or disease is often paralleled by increased excitability of peripheral sensory neurons in either the dorsal root ganglion (DRG) or trigeminal. The identification of activity-dependent changes in VGSCs in preclinical models [5,6] and the linkage of mutations in VGSCs to genetic pain disorders in humans [7,8,9,10,11] illustrates a key role for these channels in pain hypersensitivity in animals and humans. AMPK activators, including A769662, decrease DRG and TG neuron excitability as well as hyperexcitability induced by pain promoting endogenous mediators such as nerve growth factor (NGF) [33]. In addition to AMPK activation, A769662 acts as a direct blocker/modulator of VGSCs, including Nav1.7, and ameliorates pain behavior in an animal model

Materials and Methods

Results

Discussion