Protective mechanisms of picroside Ⅱ on aquaporin-4 expression in a rat model of cerebral ischemia/reperfusion injury

BACKGROUND:Aquaporin-4 (AQP-4) over-expression following cerebral ischemia results in cerebral edema. Picroside Ⅱ has been shown to exhibit a neuroprotective effect on neuronal apoptosis. However,few reports have addressed the neuroprotective mechanisms and therapeutic times following cerebral ischemic reperfusion injury. OBJECTIVE:To explore the neuroprotective effects and ideal treatment window for picroside II treatment of middle cerebral artery occlusion and reperfusion injury in rats. DESIGN,TIME AND SETTING:A randomized,controlled,animal experiment was performed at Institute of Cerebrovascular Diseases,Qingdao University Medical College from September 2008 to May 2009. MATERIALS:Picroside Ⅱ was purchased from Tianjin Kuiqing Medical Technology,China. METHODS:A total of 165 adult,healthy,male,Wistar rats were randomly assigned to sham-surgery (n = 15),model (n = 75),and treatment groups (n = 75). Rats in the model and treatment groups underwent middle cerebral artery occlusion and reperfusion through the use of an intraluminal monofilament suture on the left external-internal carotid artery. The treatment group was injected with 1.0% picroside Ⅱ (10 mg/kg) into the tail vein,and the model and sham-surgery groups were injected with 0.1 mol/L phosphate buffered saline (250 μL). MAIN OUTCOME MEASURES:Neurological functional scores were evaluated using the Longa’s method; cerebral infarction volume was detected through the use of tetrazolium chloride staining; cellular apoptosis was determined through the use of the in situ end-labeling method; aquaporin-4 expression was measured using fluorescence labeling analysis and reverse transcription polymerase chain reaction technique. RESULTS:At 0.5 hour following cerebral ischemic injury,neurological functional scores were low,and a small infarction focus was detected in the ischemic cortex of the model group. Along with prolonged ischemia and an increased number of apoptosis-positive cells,AQP-4 mRNA and protein expression was increased. At 1-2 hours after ischemia,neurological scores and infarction sizes were significantly increased in the model group. Apoptotic-positive cells were widespread in the ipsilateral cortex and striatum. In addition,AQP-4 mRNA and protein expression levels were increased. Picroside Ⅱ treatment significantly decreased neurological scores and infarction volume,and reduced AQP-4 mRNA and protein expression levels compared with the model group (P < 0.05 or P < 0.01). At 1 hour after ischemia,the therapeutic effect of picroside Ⅱ was notable (P < 0.01). CONCLUSION:Picroside Ⅱ played a protective role in cerebral ischemic reperfusion injury by inhibiting apoptosis and regulating AQP-4 expression. The best therapeutic time window was 1 hour after cerebral ischemic reperfusion.