Krizanac-Bengez Ljiljana, Mayberg Marc R, Cunningham Edwin, Hossain Mohammed, Ponnampalam Stephen, Parkinson Fiona E, Janigro Damir
Department of Neurological Surgery, Cerebrovascular Research Center, Cleveland, Ohio 44195, USA.
J Cell Physiol. 2006 Jan;206(1):68-77. doi: 10.1002/jcp.20429.
Brain ischemia is associated with an acute release of pro-inflammatory cytokines, notably TNF-alpha and IL-6 and failure of the blood-brain barrier. Shear stress, hypoxia-hypoglycemia, and blood leukocytes play a significant role in blood-brain barrier failure during transient or permanent ischemia. However, these mechanisms have not been studied as independent variables for in vitro ischemia. The present study, using a dynamic in vitro blood-brain barrier model, showed that flow cessation/reperfusion under normoxia-normoglycemia or hypoxia-hypoglycemia without blood leukocytes in the luminal perfusate had a modest, transient effect on cytokine release and blood-brain barrier permeability. By contrast, exposure to normoxic-normoglycemic flow cessation/reperfusion with blood leukocytes in the luminal perfusate led to a significant increase in TNF-alpha and IL-6, accompanied by biphasic blood-brain barrier opening. Enhanced permeability was partially prevented with an anti-TNF-alpha antibody. In leukocyte-free cartridges, the same levels of IL-6 had no effect, while TNF-alpha caused a moderate increase in blood-brain barrier permeability, suggesting that blood leukocytes are the prerequisite for cytokine release and blood-brain barrier failure during reduction or cessation of flow. These cells induce release of TNF-alpha early after ischemia/reperfusion; TNF-alpha triggers release of IL-6, since blockade of TNF-alpha prevents IL-6 release, whereas blockade of IL-6 induces TNF-alpha release. Pre-treatment of blood leukocytes with the cyclooxygenase (COX) inhibitor, ibuprofen, inhibited cytokine release and completely preserved blood-brain barrier permeability during the reperfusion period. In conclusion, loss of flow (flow cessation/reperfusion) independent of hypoxia-hypoglycemia plays a significant role in blood-brain barrier failure by stimulating leukocyte-mediated inflammatory mechanisms.
脑缺血与促炎细胞因子的急性释放有关，尤其是肿瘤坏死因子-α（TNF-α）和白细胞介素-6（IL-6），以及血脑屏障的破坏。在短暂性或永久性缺血期间，剪切应力、缺氧-低血糖和血液中的白细胞在血脑屏障破坏中起重要作用。然而，这些机制尚未作为体外缺血的独立变量进行研究。本研究使用动态体外血脑屏障模型表明，在常氧-常糖或缺氧-低血糖条件下，管腔内灌注液中无血液白细胞时的血流停止/再灌注对细胞因子释放和血脑屏障通透性有适度的短暂影响。相比之下，管腔内灌注液中有血液白细胞时暴露于常氧-常糖血流停止/再灌注会导致TNF-α和IL-6显著增加，同时伴有血脑屏障双相开放。抗TNF-α抗体可部分预防通透性增强。在无白细胞的灌注盒中，相同水平的IL-6没有影响，而TNF-α导致血脑屏障通透性适度增加，这表明血液白细胞是血流减少或停止期间细胞因子释放和血脑屏障破坏的先决条件。这些细胞在缺血/再灌注后早期诱导TNF-α释放；TNF-α触发IL-6释放，因为阻断TNF-α可防止IL-6释放，而阻断IL-6则诱导TNF-α释放。用环氧化酶（COX）抑制剂布洛芬预处理血液白细胞可抑制细胞因子释放，并在再灌注期间完全保持血脑屏障通透性。总之，与缺氧-低血糖无关的血流丧失（血流停止/再灌注）通过刺激白细胞介导的炎症机制在血脑屏障破坏中起重要作用。
