LF16-0687 a novel non-peptide bradykinin B2 receptor antagonist reduces vasogenic brain edema from a focal lesion in rats.

Abstract

Head injury world wide is still the most frequent cause of morbidity and mortality among the population under 45 years. Approximately 50% of patients dying from severe head injury have a therapy refractory intracranial pressure rise (Baethmann 1998). Traumatic brain edema, e.g. resulting from disruption of the blood-brain barrier is viewed as an important factor of the increased intracranial pressure. Bradykinin, an active peptide of the kallikrein-kinin system is considered to enhance brain edema formation which is attributed to its permeabilizing effect on the blood-brain barrier and on dilation of arterial blood vessels in the brain mediated by B2-receptors facilitating extravasation. Currently, LF16-0687, a novel non-peptide bradykinin B2 receptor antagonist was experimentally tested as to its therapeutical potential on vasogenic brain edema from a cortical focal lesion. Following trephination of the skull in anaesthesia, male Sprague-Dawley rats were subjected to a focal cold injury of the left parietal cortex. Animals of two experimental groups were receiving either LF16-0687 as high or low dose, whereas one group of untreated animals with trauma was treated with 0.9% NaCl as continuous infusion beginning 10 min before until 24 h after lesion. 24 h after trauma the brain was removed from the skull, and the cerebral hemispheres were separated in the median plane for gravimetric assessment of hemispheric swelling. No significant reduction of hemispheric brain swelling (+7.4 +/- 2.9%) was found in animals receiving high-dose LF16-0687 as compared to the untreated controls. Brain swelling, however was significantly attenuated by the low-dose treatment, i.e. to +6.4 +/- 1.3%; vs. +9.3 +/- 1.1% found in the controls, (p < 0.05). The current data confirm that blocking of bradykinin B2-receptors by LF16-0687 is significantly attenuating vasogenic brain edema from a focal cold lesion. The therapeutical properties of the antagonist on brain edema formation cannot be attributed to a lowering of the blood pressure. Rather, specific blocking effects of B2-receptors in the brain appear to be involved. In conclusion, the understanding of secondary brain damage including brain edema in head injury has been markedly enhanced by the discovery of pathophysiologically active mediator compounds playing a role in its various manifestations. The current data confirm a pathophysiological function of bradykinin in vasogenic brain edema mediated by activation of B2-receptors. Currently it is studied whether LF16-0687 also reduces brain swelling when given after an insult.