Background
Unintentional reperfusion is considered a complication in a number of ischemic models. In the following study we evaluated whether this short-term reperfusions affects ischemic volume and blood brain barrier (BBB) integrity after permanent focal ischemia in rats.
Methods
Focal brain ischemia was induced in male SD rats using the intraluminal filament method. In groups 1, 2, and 3 a 20 second reperfusion period was allowed 0.5, 2 and 10 minutes after thread occlusion. In control animals reperfusion was omitted. Twenty-four hours after permanent middle cerebral artery occlusion animals were killed and the infarct volume and swelling examined on serial coronar silver nitrate stained sections. Vascular leakage was determined by immunhistochemical staining for the plasma protein thrombin. Expression of vascular endothelial growth factor (VEGF) and matrix-metalloproteinases (MMP) 2 and 9 was investigated using RT-PCR and zymography methodology.
Results
Short reperfusion already two minutes after thread occlusion lead to a significant increase of the ischemic volume and swelling (control animals: 423±32 mm3/12.4±8.5%, group 1: 428±62 mm3/24.7±7.0%*, group 2: 547±48 mm3*/36.7±4.8%*, group 3: 592±74 mm3*/33.8±4.9%*, ischemic volume/swelling, respectively, *p<0.05 vs. control animals). There was a severe leakage of the plasma protein thrombin determined immunohistochemically (Fig. 1). Quantifying the volume with the most severe thrombin leakage showed significant more leakage in animals with a short reperfusion after 10 minutes of MCA occlusion. The ratios of ipsilateral/contralateral VEGF mRNA expression and MMP 9 protein content tended to result in increased values (VEGF: group 4: 1.67±0.44 vs control: 1.06±0.10, p<0.1; MMP 9: group4: 4.40±1.54 vs control: 2.42±0.87, p<0.1).
Conclusions
Early transient reperfusion may be causal for increased disruption of the BBB in permanent ischemia. Similar reperfusion episodes during early ischemia in patients - due to incomplete clot adherence or clot distal movements - could be causal for increased BBB damage and hemorrhagic conversion in individual patients. Thus, screening for mechanisms of intermittent reperfusion injury may be worthwhile to detect patients at risk for BBB damage before initiating reperfusion therapy, which is associated with a high risk of further disruption of the BBB and subsequent intracerebral bleeding.