Zonisamide Attenuates α-Synuclein Neurotoxicity by an Aggregation-Independent Mechanism in a Rat Model of Familial Parkinson’s Disease

Shigeki Arawaka,Hiroyasu Sato,Shingo Fukushima,Shingo Koyama,Takeo Kato,Kaori Koga,Asuka Sasaki,Philipp J Kahle

doi:10.1371/journal.pone.0089076

Abstract

The anti-epileptic agent zonisamide (ZNS) has been shown to exert protective effects in neurotoxin-based mouse models of Parkinson disease. However, it is unknown whether ZNS can attenuate toxicity of familial Parkinson’s disease-causing gene products. In this study, we investigated the effects of ZNS on neurodegeneration induced by expression of A53T α-synuclein in the rat substantia nigra using a recombinant adeno-associated virus vector. Expression of A53T α-synuclein yielded severe loss of nigral dopamine neurons and striatal dopamine nerve terminals from 2 weeks to 4 weeks after viral injection. Oral administration of ZNS (40 mg/kg/day) significantly delayed the pace of degeneration at 4 weeks after viral injection as compared with the vehicle group. This effect lasted until 8 weeks after viral injection, the final point of observation. ZNS treatment had no impact on the survival of nigrostriatal dopamine neurons in rats expressing green fluorescent protein. Quantification of striatal Ser129-phosphorylated α-synuclein-positive aggregates showed that these aggregates rapidly formed from 2 weeks to 4 weeks after viral injection. This increase was closely correlated with loss of nigrostriatal dopamine neurons. However, ZNS treatment failed to alter the number of all striatal Ser129-phosphorylated α-synuclein-positive aggregates, including small dot-like and large round structures. The number of these aggregates was almost constant at 4 weeks and 8 weeks after viral injection, although ZNS persistently prevented loss of nigrostriatal dopamine neurons during this period. Also, ZNS treatment did not affect the number of striatal aggregates larger than 10 µm in diameter. These data show that ZNS attenuates α-synuclein-induced toxicity in a manner that is independent of the formation and maturation of α-synuclein aggregates in an in vivo model of familial Parkinson’s disease, suggesting that ZNS may protect nigrostriatal dopamine neurons by modulating cellular damage or a cell death pathway commonly caused by neurotoxins and α-synuclein.

Highlights

Parkinson’s disease is a common neurodegenerative disorder characterized clinically by bradykinesia, rigidity, tremor, and gait dysfunction [1]
To elucidate whether ZNS has potential as a neuroprotective agent for the treatment of Parkinson’s disease, the present study focused on the effects of ZNS on a-synuclein-induced loss of nigrostriatal dopamine neurons and a-synuclein aggregation in a rat model, which expressed A53T a-synuclein using rAAV2
ZNS treatment significantly delayed the pace of degeneration at 4 weeks after viral injection, and this protective effect lasted over 8 weeks of observation after viral injection

Summary

Introduction

Parkinson’s disease is a common neurodegenerative disorder characterized clinically by bradykinesia, rigidity, tremor, and gait dysfunction [1]. There are many candidate agents showing neuroprotective effects in laboratory models using the neurotoxins, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrydine (MPTP) and 6-hydroxy dopamine (6-OHDA) [5,6]. As one of the reasons for this disconnect, there is difficulty in discriminating the neuroprotective effects of candidate agents from their symptomatic effects by elevation of synaptic dopamine levels or stimulation of dopamine receptors in clinical trials [4]. It is unclear whether neurotoxin-based animal models precisely reflect the pathogenesis of Parkinson’s disease [4,7]. There has been little study to clarify whether candidate agents can protect against neurodegeneration caused by familial Parkinson’s disease-linked gene products in genetic animal models

Methods

Results

Conclusion