Varicella-Zoster Viruses Associated with Post-Herpetic Neuralgia Induce Sodium Current Density Increases in the ND7-23 Nav-1.8 Neuroblastoma Cell Line

Peter G E Kennedy,Paul Montague,G H Ashrafi,Edward G Rowan,Esther Grinfeld,Judith Breuer,Fiona Scott,Joseph Charles Glorioso

doi:10.1371/journal.pone.0051570

Abstract

Post-herpetic neuralgia (PHN) is the most significant complication of herpes zoster caused by reactivation of latent Varicella-Zoster virus (VZV). We undertook a heterologous infection in vitro study to determine whether PHN-associated VZV isolates induce changes in sodium ion channel currents known to be associated with neuropathic pain. Twenty VZV isolates were studied blind from 11 PHN and 9 non-PHN subjects. Viruses were propagated in the MeWo cell line from which cell-free virus was harvested and applied to the ND7/23-Nav1.8 rat DRG x mouse neuroblastoma hybrid cell line which showed constitutive expression of the exogenous Nav 1.8, and endogenous expression of Nav 1.6 and Nav 1.7 genes all encoding sodium ion channels the dysregulation of which is associated with a range of neuropathic pain syndromes. After 72 hrs all three classes of VZV gene transcripts were detected in the absence of infectious virus. Single cell sodium ion channel recording was performed after 72 hr by voltage-clamping. PHN-associated VZV significantly increased sodium current amplitude in the cell line when compared with non-PHN VZV, wild-type (Dumas) or vaccine VZV strains ((POka, Merck and GSK). These sodium current increases were unaffected by acyclovir pre-treatment but were abolished by exposure to Tetrodotoxin (TTX) which blocks the TTX-sensitive fast Nav 1.6 and Nav 1.7 channels but not the TTX-resistant slow Nav 1.8 channel. PHN-associated VZV sodium current increases were therefore mediated in part by the Nav 1.6 and Nav 1.7 sodium ion channels. An additional observation was a modest increase in message levels of both Nav1.6 and Nav1.7 mRNA but not Nav 1.8 in PHN virally infected cells.

Highlights

VZV is a neurotropic human alpha herpes virus that causes varicella as a primary infection following which it becomes latent in neurons in the dorsal root ganglia (DRG) and trigeminal ganglia (TG) [1,2]
Nav1.3 transcriptional activity was barely detectable in non-infected ND7/23-Nav1.8 cells consistent with its documented transcriptional activity during CNS fetal development [29] and there was no discernible change in the mRNA abundance in VZV infected cells
A one-way ANOVA-Bonferroni Multiple Comparison Test was performed on the data sets identified a modest but statistically significant increase in the transcriptional activity of the Nav1.6 and Nav1.7 genes between the non-post-herpetic neuralgia (PHN) and PHN groupings and contrasted to the Nav1.8 mRNA abundance levels which remained essentially invariant between the non-PHN and PHN groups (Figure 1)

Summary

Introduction

VZV is a neurotropic human alpha herpes virus that causes varicella (chickenpox) as a primary infection following which it becomes latent in neurons in the dorsal root ganglia (DRG) and trigeminal ganglia (TG) [1,2]. The most important complication of zoster is post-herpetic neuralgia (PHN) which causes severe pain in the affected dermatome which persists for more than 3 months after the rash, and occurs in about 50% of individuals over 60 years [3]. It has a high morbidity, the mechanism causing PHN remains unknown, its occurrence cannot be predicted at the time of zoster and its treatment is still highly unsatisfactory and generally ineffective [4]. A key question is how the virus exerts its effects on neuronal cells

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