Release of bradykinin and expression of kinin B2 receptors in the brain:: role for cell death and brain edema formation after focal cerebral ischemia in mice

Pharmacological studies using bradykinin B-2 receptor antagonists suggest that bradykinin, an early mediator of inflammation and the main metabolite of the kallikrein-kinin system, is involved in secondary brain damage after cerebral ischemia. However, the time-course of bradykinin production and kinin receptor expression as well as the conclusive role of bradykinin B-2 receptors for brain damage after experimental stroke have not been elucidated so far. C57/B16 mice were subjected to 45 mins of middle cerebral artery occlusion (MCAO) and 2, 4, 8, 24, and 48 h later brains were removed for the analysis of tissue bradykinin concentration and kinin B-2 receptor mRNA and protein expression. Brain edema, infarct volume, functional outcome, and long-term survival were assessed in WT and B-2(-/-) mice 24 h or 7 days after MCAO. Tissue bradykinin was maximally increased 12 h after ischemia (three-fold), while kinin B, receptor mRNA upregulation peaked 24 to 48 h after MCAO (10- to 12-fold versus naive brain tissue). Immunohistochemistry revealed that kinin B-2 receptors were constitutively and widely expressed in mouse brain, were upregulated 2 h after ischemia in cells showing signs of ischemic damage, and remained upregulated in the penumbra up to 24 h after ischemia. B-2(-/-) mice had improved motor function (P<0.05), smaller infarct volumes (-38%; P<0.01), developed less brain edema (-87%; P<0.05), and survived longer (P<0.01) as compared with wild-type controls. The current results show that bradykinin is produced in the brain, kinin B-2 receptors are upregulated on dying cells, and B-2 receptors are involved in cell death and brain edema formation after experimental stroke.