Inflammatory Mediators of Cerebral Endothelium: A Role in Ischemic Brain Inflammation

Abstract

Brain inflammation has been implicated in the development of brain edema and secondary brain damage in ischemia and trauma. Adhesion molecules, cytokines and leukocyte chemoattractants released/presented at the site of blood‐brain barrier (BBB) play an important role in mobilizing peripheral inflammatory cells into the brain. Cerebral endothelial cells (CEC) are actively engaged in processes of microvascular stasis and leukocyte infiltration by producing a plethora of pro‐inflammatory mediators. When challenged by external stimuli including cytokines and hypoxia, CEC have been shown to release/express various products of arachidonic acid cascade with both vasoactive and pro‐inflammatory properties, including prostaglandins, leukotrienes, and platelet‐activating factor (PAF). These metabolites induce platelet and neutrophil activation and adhesion, changes in local cerebral blood flow and blood rheology, and increases in BBB permeability. Ischemic CEC have also been shown to express and release bioactive inflammatory cytokines and chemokines, including IL‐Iβ, IL‐8 and MCP‐1. Many of these mediators and ischemia in vitro and in vivo have been shown to up‐regulate the expression of both selectin and Ig‐families of adhesion molecules in CEC and to facilitate leukocyte adhesion and transmigration into the brain. Collectively, these studies demonstrate a pivotal role of CEC in initiating and regulating inflammatory responses in cerebral ischemia. Summary: Inflammatory genes/mediators are involved in molecular/biochemical cascades determining stroke outcome. Cerebral endothelial cells, targeted by inflammatory mediators produced in ischemic brain, undergo pro‐inflammatory activation by expressing/secreting various inflammatory mediators, thus becoming a source of inflammation themselves. A unique position of the cerebral endothelial cells at the interface between blood and brain establishes their role as principal regulators of peripheral inflammatory cell recruitment into the brain during stroke. Cerebral endothelial cells also exhibit ability to regulate vasomotor responses of brain microcirculation and the permeability of the BBB, both important components of inflammation. Therefore, approaches to attenuate consequences of stroke must take into consideration cerebral endothelial cells as an easily accessible target to interfere with the ischemic brain inflammation.