The Neuroprotective Effect Of Parthenolide And The Underlying Mechanism In Experimental Ischemic Stroke

Objective: Cerebral ischemia is the most common type of cerebrovasculardisease, which is the first leading cause of death and the most frequent causeof permanent disability in adults. The pathological mechanisms that triggerischemic brain damage could be related to inflammation, oxidative stress,apoptosis, and so on. The excessive inflammatory response has been shownduring ischemic pathology, which resides in necrosis and ischemic region andresults in brain damage. Therefore, inhibitory actions on inflammation may bebeneficial in rescuing neuronal cells, exposed to ischaemia. General speaking,it is a main measure to treat acute cerebral infarction by anti-inflammationtherapy. Caspase-1, one of initiator subclass members of caspase family, playsa key role in inflammatory pathways by processing pro-IL-1β into the activecytokine mature IL-1with inflammatory damage. The mitogen-activatedprotein kinases (MAPKs), involving p38MAPK, and the transcription factornuclear factor nuclear factor-kappa B (NF-κB) contribute to activating somecytokines and inducing inflammation, with an amplified inflammatory cascade.The p38MAPK and NF-κB activation can be induced by caspase-1independently of its enzymatic activity. Our efforts focus on caspase-1,because its "apical" position within the inflammatory cascade makes itpotentially important therapeutic target. Parthenolide (PN), the majorsesquiterpene lactone, has demonstrated a wide range of pharmacological andbiological activities, including anti-inflammatory, anti-oxidation, anti-tumor,anti-apoptosis, and so on. Recent studies suggest that PN also exerts aprotective effect on schemia/reperfusion damage in heart. However, theunderlying mechanism of the neuroprotection of PN remains unclear in theacute phase of ischemic stroke. And the relationship between parthenolide andcaspase-1and p38MAPK expression in cerebral ischemia has not been investigated so far. We therefore investigated the potential neuroprotectiveeffects of parthenolide and the underlying mechanisms during ischemic stroke.Methods: Male, healthy Sprague-Dawley rats were used and subjected tomodified permanent middle cerebral artery occlusion (pMCAO), as describedby Longa previously. All the rats were randomly divided into6groups: thesaline treated groups: rats received sham operation or MCAO and equalvolume of normal sodium; the vehicle-treated groups: rats received shamoperation (Sham) or MCAO (MCAO) and equal volume of equal volume of0.05%Tween80; and PN groups: rats were treated with PN at250μg/kg(Low dose) or500μg/kg (High dose) intraperitoneally immediately afterMCAO. Neurological behavior was evaluated, brain water content wasmeasured by wet-dry method and infarct volume was analyzed with2,3,5-triphenyltetrazolium chloride (TTC) staining. In preliminary experiments,neurological deficit, infarct volume, and brain water content were measuredbetween the saline-and vehicle-treated groups, to exclude any biologicaleffect of the vehicle. Because neurological deficit, infarct volume, and brainwater content were comparable among the Sham+normal sodium andSham+0.05%Tween80and the MCAO+normal sodium and MCAO+0.05%Tween80respectively. Therefore, only the MCAO+0.05%Tween80(MCAO)group and Sham+0.05%Tween80(Sham) were used for another experiments.Immunohistochemistry and western blotting were used to analyze the proteinexpression of caspase-1, phospho-p38MAPK and NF-κB. Reversetranscription-polymerase chain reaction (RT-PCR) was used to analyze themRNA expression of caspase-1, NF-κB, TNF-α and IL-1β. The expression ofclaudin-5was measured by western blot and RT-PCR.Results:1Rats in Sham group had no palsy and a neurological score of zero. Rats inMCAO group, high dose group and low dose group performed a left palsy.Compared with MCAO group, there was a significant improvement inneurological function scores in the high group (P <0.05). By contrast, thescores in low dose group were not lowered by parthenolide (P>0.05). 2The two doses of parthenolide decreased the percentage of brain watercontent in ipsilateral hemispheres after stroke. Compared with MCAO group,high dose group reduced significantly the brain water content (High vs.MCAO:82.44±0.44%vs.85.25±0.50%, P <0.05). However, there was nosignificant reduction in the low group compared with MCAO group (Low vs.MCAO:84.61±0.34%vs.85.25±0.50%, P>0.05).3The high group decreased the infarct volume after MCAO (High vs.MCAO:82.44±0.48%vs.85.29±0.53%, P <0.05). Although the infarctvolume in the low group was reduced, there was no significant difference inthe infarct volume between the low group and MCAO group (P>0.05).4Compared with Sham group, MCAO induced sharply up-regulation ofcaspase-1, phospho-p38MAPK and nuclear NF-κB p65. Meanwhile, TNF-αand IL-1β mRNA were also up-regulated after MCAO. The expression ofcaspase-1, phospho-p38MAPK and nuclear NF-κB p65were inhibited afterMCAO by administration of high dose of PN (P <0.05). RT-PCR showed thatTNF-α and IL-1β were attenuated after PN treatment (P <0.05).5Compared with Sham group, claudin-5was reduced sharply after MCAO(P <0.05). The expression of claudin-5in cerebral ischemia was significantlyup-regulated at both protein and mRNA levels after treatment with high doseof PN. However, the low group did not display the up-regulation of claudin-5(P>0.05).Conclusions: Systemic administration of high dose of PN is effectivewhich can ameliorate the neurological deficit, improve the brain edema,decrease the infarct size and suppress inflammatory response under cerebralischemic conditions. The underlying mechanism of this neuroprotection maybe involved down-regulation caspase-1, phospho-p38MAPK and NF-κB andup-regulation claudin-5expression.