Anticonvulsant And Antiepileptogenic Effects Of FTY720in Experimental Epilepsy Models

Epilepsy is a disorder of the brain clinically characterized by unexpectedrecurrent seizures and long-time treatment of antiepileptic drugs (AEDs). It is acommon human disease and affects the whole age range from neonates toelderly people. Approximately50million people around the world suffer fromepilepsy, which imposes a heavy burden on society and their families. Thoughthe new generation of AEDs is developed, there is no evidence that the efficacyof new AEDs is better than the old agents. About30%of epilepsy is intractableepilepsy which can not be cured by present AEDs. Majority of intractableepilepsy is the symptomatic epilepsy followed by brain injuries. An initial braininsult triggers a cascade of cellular events which, after a latent period,contributes “normal brain” to “epileptic brain” and leads to neural networkhyperexcitability and occurrence of spontaneous recurrent seizures. This processis termed epileptogenesis. Recently, emerging evidence has suggestedinflammatory processes play an important role in seizure and epileptogenesis.Several anti-neuroinflammatory agents have anticonvulsant and antiepileptogenic actions in animal models and some anti-inflammatory drugsare administered as adjunctive agents in patients with intractable epilepsy. All ofthese facts indicate that anti-inflammation is a new probable pathway fortreatment of epilepsy.Fingolimod (FTY720) is a new anti-inflammatory drug approved for thetreatment of multiple sclerosis (MS) by the US Food and Drug Administration(FDA). Present data suggest that anti-neuroinflammatory effects of FTY720viavarious pathways are involved in its pharmacological properties. In our research,we studied FTY720′s anticonvulsant and antiepileptogenic actions in animalmodels and their underlying mechanisms through monitoring behavior,electrophysiological techniques and immunohistochemistry in vivo and vitro.We hope to provide a new pathway for treatment and prevention of epilepsy.Firstly, to demonstrate the effects of acute inflammation on epileptiformdischarges in vitro and reveal its underlying mechanisms, we observed changesof epileptiform activity, synaptic strength and neuronal excitability after addingLPS (an extensively used agent to induce brain inflammatory processes inexperiments in vivo and in vitro) to hippocampal slices. The results were asfollowings:1. Acute administration of LPS facilitated epileptiform activity inhippocampal CA1pyramidal neurons in vitro;2. Acute LPS exposure enhancedevoked excitatory postsynaptic currents (eEPSCs) but did not modify evokedinhibitory postsynaptic currents (eIPSCs);3. Exposure to LPS increased theexcitability of CA1pyramidal neurons but did not change the amplitude orhalf-width of the first action potential evoked by rheobase current. These resultssuggest strengthened excitatory synaptic transmission and neuronal excitabilityare most likely attributable to this facilitation of acute inflammation induced byLPS. It provides a model to study the effects of FTY720on abnormal excitatorysynaptic strength in the following experiment. Secondly, we evaluated anticonvulsant activity of FTY720in three animalmodels of epilepsy including MES model, s.c.PTZ model and pilocarpine model.In addition, we studied the underlying mechanisms in hippocampal slice in vitro.The results were as followings:1. At dosage of0.25mg/kg and1mg/kg,FTY720had not anticonvulsant activity in MES model.2. In s.c. PTZ model,0.25mg/kg FTY720had no effects on latency of minimal clonic seizure (MCS)or generalized tonic-clonic seizure (GTCS) or mortality of mice while reducedthe duration of GTCS.1mg/kg FTY720improved latency of MCS and GTCS,also decreased mortality and the duration of GTCS.3. In pilocarpine model,1mg/kg FTY720injection showed anticonvulsant activity demonstrated byreducing the latency to SE. However,1mg/kg FTY720did not decrease themortality and the number of rats developing SE.4. In vitro, LPS increasedamplitude of EPSP recorded in hippocampal CA1region. At100μM but not0.1-10μM concentration, FTY720-P suppressed increasing amplitude of EPSPinduced by LPS.100μM FTY720-P had no effect on normal EPSP in CA1region. These data indicate FTY720has anticonvulsant action and this action isdose-dependent. Ability of decreasing abnormal excitatory synaptic transmissionmay be one of underlying mechanisms.Due to FTY720′s anticonvulsion, decreasing abnormal EPSP andanti-inflammation reported by others, we hypothesized that FTY720maysuppress epileptogenesis and reduce spontaneous recurrent seizures (SRS) inchronic epilepsy. In the third experiment, to test this hypothesis,1mg/kgFTY720was administrated24h after onset of status epilepticus (SE) for14consecutive days. We examined whether FTY720might attenuatehyperexcitability of hippocampal neuronal circuits and SRS following SE, andwhether FTY720might decrease inflammatory responses, such as glialactivation, expression of IL-1β and TNFα. Furthermore, we evaluated whether neuronal degeneration and aberrant mossy fiber sprouting (MFS) inhippocampus could be reversed by administration of FTY720. The results wereas followings:1. During21-34days post SE, FTY720decreased incidence ofSRS. The frequency, duration of SRS and severity of seizures were also reducedin this period.2. At four days post SE, FTY720alleviated the concentration ofIL-1β and TNFα in hippocampus. The number of micriglia and astrocytes inCA1、CA3and hilus were decreased in FTY720treated SE rats compared tosaline treated SE rats. At this time point, FTY720had a neuroprotective effectaganist neurodegeneration in hippocampus.3. At seven days post SE, FTY720decreased hyperexcitability of hippocampal neuronal circuits.4.35days afterSE, there were less Timm score in SE+FTY720group than SE+saline group.These observations suggest that FTY720has antiepileptogenic action in ratsfollowing SE induced by Li-pilocarpine. Anti-inflammatory and neuroprotectiveeffects and suppression of MFS may all involve in the underlying mechanisms.In conclusion, mimic inflammatory environment by acute LPS exposurefacilitated epileptiform activity. Strengthened excitatory synaptic transmissionand neuronal excitability may contribute to this facilitation. FTY720exertsanticonvulsant action in animal epilepsy models and reducing abnormalexcitatory synaptic transmitter may be involved in its underlying mechanisms.In addition, FTY720plays an antiepileptic role in the Li-pilocarpine model inrats. This efficacy may result from anti-inflammation and suppression ofhyperexcitable circuit of FTY720. Our observations suggest inflammationaggravates epilepsy in electrophysiology and FTY720exerts anticonvulsant andantiepileptogenic actions in animal models of epilepsy.