Purpose
Mechanisms of early cerebral edema following SAH are poorly understood. Previously, we demonstrated a peak of edema evolution at 24 hours after experimental SAH in rats. Furthermore, brain water content correlated with neurological deficits of animals. In focal cerebral ischemia, alteration of the microvascular basal lamina, a constituent of the blood-brain barrier, and its relevance for development of cerebral edema and hemorrhagic transformation has previously been demonstrated. The present study was designed to demonstrate microvascular basal lamina damage in the context of blood-brain barrier dysfunction as a potential target for therapeutical interventions to reduce vasogenic brain edema following SAH.
Methods
54 rats were subjected to SAH by an endovascular filament. Animals were randomly assigned to 1 sham (n=9) and 4 SAH groups (n=9 each; 6, 24, 48, and 72 h survival). Microvascular basal lamina alteration was quantified by anticollagen type IV immunochemistry with subsequent counting of stained cerebral microvessels/region of interest (ROI) in cortex and subcortical regions of both hemispheres; Western Blot was used to define the collagen type IV protein content. Bovine serum albumin (BSA) extravasation was quantified by Western Blot technique to assess blood-brain barrier permeability.
Results
Significant (p<0.001) reduction of Collagen Type IV stained microvessels/ROI occurred in all SAH groups with the most pronounced decline until 24 hours following SAH. Consistently, Collagen type IV protein content was significantly reduced after 6 and 24 hours. Microvascular damage was found within the cortex bilaterally with predominance of the ipsilateral hemisphere. There was no alteration of the microvascular basal lamina in subcortical regions (hippocampus, basal ganglia, brain stem, cerebellum), neither evaluated by immunohistochemistry nor by Western Blot for collagen type IV. BSA Western Blot revealed maximum and significant extravasation 24 hours after SAH, correlating with microvascular damage.
Conclusion
This is the first study to demonstrate that microvascular basal lamina injury after experimental SAH is linked to blood-brain barrier permeability in a time-dependent manner. Documented loss of basal lamina integrity might contribute to the development of vasogenic brain edema. Consequently, proteolytic systems that are known to be involved in the digestion of basal lamina antigens after focal cerebral ischemia need to be investigated and their role as targets for therapeutic interventions to prevent development of cerebral edema following SAH need to be defined.