Abstract 14759: Molecular Imaging of Activated Factor XIII for Early Detection of Coronary Microvascular Disease in Mice

Abstract

Background: Coronarary microvascular disease (MVD) remains a major clinical problem affecting women twofold more than men, and involves endothelial dysfunction and microthrombosis. We hypothesized that acute and sub-acute microthrombi could be identified using in vivo molecular imaging of technetium-labeled activated XIII (^99mTc-NC100668, GE Healthcare Limited, UK). To evaluate this approach we developed a novel MVD mouse model using photodynamic therapy (PDT).

Methods: 24 female mice were assigned to one of three groups: 1) thoracotomy with 100 µL intrajugular 10% Rose Bengal; 2) thoracotomy with 7 minutes 540nm green light; or 3) thoracotomy with their combination. For evaluation of microvascular injury at 24 hours post-surgery, mice in each group (n = 8) underwent coronary microCT angiography (n=4), electron microscopy (EM, n=2), or fluorescent myocardial perfusion (n=2). Toward development of a non-invasive approach for evaluation of coronary MVD, an additional 84 female mice underwent focal PDT followed by injection of either 0.1mCi ^99mTc-NC100668 or ^99mTc-AH110563 (an inactive analog), at 3 hours, 24 hours, 3, 7, or 14 days, for ex vivo gamma well counting (GWC, n=60) to assess regional myocardial activity as %injection dose/mg (id/mg), or in vivo microSPECT (n=24) to visualize MVD.

Results: All PDT mice developed photothrombotic coronary MVD, while no control mice developed MVD. microCT demonstrated microvascular rarefaction isolated to region of PDT without macrovascular changes. EM showed luminal microthrombi and loss of endothelial integrity in PDT-treated myocardium. Confocal microscopy discovered “no flow phenomena” in the PDT-targeted region. GWC demonstrated ^99mTc-NC100668 activity within endothelial-damaged myocardium compared to inactive tracer at early time points (3 hours: 93.3±19.8 vs. 6.89±1.97% id/mg, p<0.01; 3 days: 28.1±23.4 vs. 3.02±0.932% id/mg, p<0.05). In vivo microSPECT images showed focal myocardial uptake up to day 3, demonstrating potential of NC100668 imaging for non-invasive detection of activated FXIII.

Conclusions: We established a mouse model of focal coronary MVD using PDT. Targeted imaging of the activated FXIII allowed visualization of acute and subacute coronary micro-thrombi.