Abstract 215: A Systemic Inflammation-Induced Mouse Model of Cerebral Microbleeds

Abstract

Introduction: Cerebral microhemorrhages (CMH) are tiny deposits of blood degradation products in the brain and are the pathological substrate of cerebral microbleeds (MB). The existing animal models of MB are either β-amyloid-, anti-amyloid antibody-, or hypertension-induced; however, MB may develop independent of hypertension or amyloid deposition. In fact, MB are associated with normal aging, sepsis and neurodegenerative conditions. One common factor among the above pathologies is inflammation, and recent studies show a link between systemic inflammation and MB. Hence, we hypothesize that systemic inflammation (induced by lipopolysaccharide; LPS) will result in MB development, and an inflammation-induced animal model will be appropriate to study MB. In the current study we used two different dosing regimens for LPS and observed rapid and robust development of CMH and MB. Methods: Adult C57BL/6 mice were injected with LPS (1mg/kg or 3mg/kg, i.p.) or saline at 0, 6, and 24h. At 2 or 7 days after first LPS injection, brains were harvested. Hematoxylin and eosin (H&E) and Prussian blue (PB) were used to stain fresh (acute) hemorrhages and hemosiderin (subacute hemorrhages), respectively. Results: No surface and negligible H&E-positive CMH were observed in saline controls (n=4). LPS (3mg/kg; n=13) resulted in significantly higher number (p<0.01), size (p<0.05) and area (p<0.01) of H&E-positive CMH at 2 days. Negligible PB-positive CMH were observed at 2 days after LPS (3 or 1 mg/kg) injection. However, LPS (1mg/kg) resulted in robust development of PB-positive CMH at 7 days, with significantly higher number (p<0.05), size (p<0.05) and area (p<0.01) in LPS (n=9) versus saline (n=4) treated mice. MRI confirmed the presence of MB in this model. The number of CMH was significantly higher in the cerebellum (p<0.05) compared to cortical or subcortical regions. Conclusion: In summary, LPS produced rapid development of H&E-positive CMH (at 2 and 7 days) and PB-positive CMH (at 7 days) with low mortality. Thus, this appears to be an appropriate model to study the pathophysiology of CMH and MB.