Vascular alterations in PDAPP mice after anti-Aß immunotherapy: Implications for amyloid-related imaging abnormalities.

ABSTRACT

BACKGROUND: Clinical studies of ß-amyloid (Aß) immunotherapy in Alzheimer's disease (AD) patients have demonstrated reduction of central Aß plaque by positron emission tomography (PET) imaging and the appearance of amyloid-related imaging abnormalities (ARIA). To better understand the relationship between ARIA and the pathophysiology of AD, we undertook a series of studies in PDAPP mice evaluating vascular alterations in the context of central Aß pathology and after anti-Aß immunotherapy. METHODS: We analyzed PDAPP mice treated with either 3 mg/kg/week of 3D6, the murine form of bapineuzumab, or isotype control antibodies for periods ranging from 1 to 36 weeks and evaluated the vascular alterations in the context of Aß pathology and after anti-Aß immunotherapy. The number of mice in each treatment group ranged from 26 to 39 and a total of 345 animals were analyzed. RESULTS: The central vasculature displayed morphological abnormalities associated with vascular Aß deposits. Treatment with 3D6 antibody induced clearance of vascular Aß that was spatially and temporally associated with a transient increase in microhemorrhage and in capillary Aß deposition. Microhemorrhage resolved over a time period that was associated with a recovery of vascular morphology and a decrease in capillary Aß accumulation. CONCLUSIONS: These data suggest that vascular leakage events, such as microhemorrhage, may be related to the removal of vascular Aß. With continued treatment, this initial susceptibility period is followed by restoration of vascular morphology and reduced vulnerability to further vascular leakage events. The data collectively suggested a vascular amyloid clearance model of ARIA, which accounts for the currently known risk factors for the incidence of ARIA in clinical studies.