Quantitative Longitudinal Imaging of Vascular Inflammation and Treatment by Ezetimibe in apoE Mice by FMT Using New Optical Imaging Biomarkers of Cathepsin Activity and αvβ3 Integrin

Shu-An Lin,Donna Suresch,Milind Rajopadhye,Bohumil Bednar,Michael Klimas,Kevin Groves,Manishkumar Patel,Bagna Bao,Jeffrey D Peterson,Cyrille Sur,Brett Connolly

doi:10.1155/2012/189254

Abstract

Inflammation as a core pathological event of atherosclerotic lesions is associated with the secretion of cathepsin proteases and the expression of α v β 3 integrin. We employed fluorescence molecular tomographic (FMT) noninvasive imaging of these molecular activities using cathepsin sensing (ProSense, CatB FAST) and α v β 3 integrin (IntegriSense) near-infrared fluorescence (NIRF) agents. A statistically significant increase in the ProSense and IntegriSense signal was observed within the chest region of apoE−/− mice (P < 0.05) versus C57BL/6 mice starting 25 and 22 weeks on high cholesterol diet, respectively. In a treatment study using ezetimibe (7 mg/kg), there was a statistically significant reduction in the ProSense and CatB FAST chest signal of treated (P < 0.05) versus untreated apoE−/− mice at 31 and 21 weeks on high cholesterol diet, respectively. The signal of ProSense and CatB FAST correlated with macrophage counts and was found associated with inflammatory cells by fluorescence microscopy and flow cytometry of cells dissociated from aortas. This report demonstrates that cathepsin and α v β 3 integrin NIRF agents can be used as molecular imaging biomarkers for longitudinal detection of atherosclerosis, and cathepsin agents can monitor anti-inflammatory effects of ezetimibe with applications in preclinical testing of therapeutics and potentially for early diagnosis of atherosclerosis in patients.

Highlights

Atherosclerosis, a progressive inflammatory disease, results in the development of plaques within the arterial walls that may contain intracellular and extracellular lipids, a variety of inflammatory cells, extracellular matrix, smooth muscle cells, fibroblasts, and calcification [1,2,3,4]
The newly developed cathepsin agents ProSense FAST and Cat B FAST are based on low molecular weight substrate peptides with fluorochromes attached to the C- and N-termini of the peptide resulting in 95% of the fluorescence quenching and a hypsochromic (“blue”) shift of about 60 nm in the absorption spectra (Figures 1(c) and 1(d))
The quenching of the fluorophores in the ProSense agent is achieved by tight packing of the polymer coil, which slows the activation of this agent

Summary

Introduction

Atherosclerosis, a progressive inflammatory disease, results in the development of plaques within the arterial walls that may contain intracellular and extracellular lipids, a variety of inflammatory cells, extracellular matrix, smooth muscle cells, fibroblasts, and calcification [1,2,3,4]. The noninvasive detection of atherosclerotic plaque has been clinically limited mostly to the measurements of arterial stenosis in selected arterial beds [8,9,10,11]. Such measurements have been shown to be poor predictors of clinical outcomes, stimulating further research into the biology of atherosclerotic lesions and development of new biomarkers with a better predictive value for the formation of vulnerable plaques [12,13,14,15,16,17]

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Conclusion