Abstract 588: Noninvasive Monitoring the Biology of Atherosclerotic Plaque Development With Radiolabeled Annexin V and Matrix Metalloproteinase Inhibitor in Spontaneous Atherosclerotic Mice
Objectives: Increased apoptosis and expression of metalloproteinases are found in vulnerable atherosclerotic plaques. We compared 99mTc-labeled broad-based matrix metalloproteinase inhibitor (RP805) (MPI) and 99mTc-annexin V (AN) to detect more advanced lesions in apoE−/−mice.
Methods: Eight 6 –9 wk apoE−/− mice, 10 apoE−/− mice at 20 wk and 12 apoE−/− at 40 wk were injected with both tracers in alternating sequence separated by 48 h, and underwent high-resolution whole body planar imaging and were sacrificed. Radiotracer uptake was quantified from the scans as % whole body (%WB) and from tissue as % injected dose per gram (%ID/g). The extent of atherosclerosis was assessed visually and hearts and aortas and carotids were explanted for ex-vivo gamma well counting and histology.
Results: At 6 wk mice showed no tracer uptake in the chest or neck and had no lesions. At 20 wk, 5 of 10 (50%) mice showed focal uptake of AN in aortic (ao) region and 2/10 (20%) uptake of MPI and at 40 wk there was predominant neck activity for both tracers with more intense and extensive uptake of MPI. These observations were confirmed by %WB uptake as shown in table⇓. Localization of in-vivo activity to vascular territories was confirmed by ex-vivo tissue counting. Between 20 and 40 wk ao lesion area increased from 37±12 to 46±7% with greater increases in % MMP-2 and -9 + cells than % caspase + cells. The carotid lesion area at 40 wk was 74±9% with greater % cells + for MMP’s than caspase. For the ao lesions individual values for % ID/g AN correlated with % macrophages (macs) (R2= 0.60, P< 0.01), and with caspase-3 + cells (R2= 0.49, P< 0.05) and values for % ID/g MPI correlated with % macs (R2= 0.77, P< 0.01) and with MMP-9 + cells (R2= 0.64, P< 0.01). Caspase-3, MMP-2, and MMP-9 colocalized predominantly with macs.
Conclusions: These data indicate that in apoE−/− mice MMP expression is greater than apoptosis as the disease progresses and may be a better imaging agent for more advanced disease.