Neuroprotective effects of a potent bradykinin B2 receptor antagonist HOE-140 on microvascular permeability, blood flow disturbances, edema formation, cell injury and nitric oxide synthase upregulation following trauma to the spinal cord.

Abstract

Bradykinin is a mediator of vasogenic brain edema formation. Recent reports suggest that bradykinin interacts with nitric oxide synthase (NOS) system in the central nervous system (CNS). However, role of bradykinin in spinal cord injury (SCI) induced alterations in the blood-spinal cord barrier (BSCB), spinal cord blood flow (SCBF), edema formation and cell changes are still not well known. Our previous reports showed that SCI induces marked upregulation of neuronal NOS (nNOS) in the cord associated with BSCB disruption, edema formation and cell injury. Thus, a possibility exists that bradykinin participates in SCI induced nNOS upregulation and cord pathology. To explore this idea a potent bradykinin B2 receptor antagonist HOE-140 was used in our rat model of SCI and cord pathology. SCI was inflicted in Equithesin anesthetized rats by making a longitudinal incision (2mm deep and 5mm long) into the right dorsal horn of the T10-11 segment. The animals were allowed to survive 5h after injury. A focal SCI significantly disrupted BSCB to Evans blue and [131]I-sodium in the traumatized and adjacent segments. Interestingly, far remote spinal cord segments C4 and T5 segments also affected within 5h. These spinal cord segments also exhibited pronounced reductions in the SCBF (mean-30%), increased edematous swelling and profound neuronal damages. Upregulation of nNOS expression is seen in both the dorsal and ventral horns of the spinal cord exhibiting cord pathology. At the ultrastructural level, exudation of lanthanum is seen within the endothelial cell cytoplasm and occasionally in the basal lamina. Pretreatment with low doses of HOE-140 (0. 1mg to 1mg/kg, i.v.) 30min prior to SCI significantly enhanced the SCBF and reduced the BSCB disruption, edema formation, nNOS upregulation and cell injury. However, HOE-140 in doses ranging from 2mg to 5mg/kg, i.v. did not induce significant neuroprotection. These observations are the first to suggest that bradykinin B2 receptors play an important role in BSCB permeability, SCBF, edema formation, nNOS upregulation and cell injury following acute SCI, not reported earlier.