Assessment of atherosclerotic lesions permeability in ApoE(-/-) mice using fluorescent blood pool agent

Introduction. Atherosclerosis, the major cause of death in Western society, is an artery degenerative disease resulting in plaques leading to stenosis, embolization and thrombosis.The FP7 project “NanoAthero” was funded to... [ view full abstract ]

Introduction. Atherosclerosis, the major cause of death in Western society, is an artery degenerative disease resulting in plaques leading to stenosis, embolization and thrombosis.

The FP7 project “NanoAthero” was funded to develop novel nanosystems for imaging and therapy of atherosclerotic diseases, with the contribution of several European research labs.

Currently, most of imaging techniques are not able to predict acute event based on plaque composition. A diagnostic tool aimed to stratify plaques with respect to different permeability could help clinicians to evaluate the response to nanosystem-based therapies.

The aim of this study was the investigation by Optical Imaging of the permeability of lesions in ApoE(-/-) mice, that develop hypercholesterolemia and atherosclerosis. To this purpose, the fluorescence signals of two blood-pool agents, Human Serum Albumin Cyanine5-conjugated (HSA-Cy5) or the albumin binder B26170, containing an aminodeoxycholic acid conjugated with IrDye800CW, were analysed on plaques of ApoE(-/-) mice at different stage of development.

Methods. ApoE(-/-)mice, under high-cholesterol diet, were administered with HSA-Cy5 or B26170. OI images were acquired ex vivo on excised aortic trees and the fluorescent signal was analysed on lesions compared to surrounding tissue. Hematoxylin/eosin staining and immunostaining for macrophages and endogenous Mouse Serum Albumin (MSA) were performed on cryosections of plaques.

Results. The fluorescence signal of both HSA-Cy5 and B26170, decreases with the progression of pathology, thus with ageing and loss of plaque permeability. Moreover, the highest signals were found in lesions at early development with widespread presence of macrophages, characterizing inflamed plaques, and with large MSA content, reflecting the endothelial permeability to serum protein. Conversely, fibro-calcific plaques, with rare macrophages and low MSA content, displayed the lowest signal.

Discussion. The permeability of an atherosclerotic lesion to albumin, using HSA-Cy5 or the albumin-binder B26170, reflects plaque morphology and composition, with respect to different staging. The proof of concept obtained with OI, could be proposed for a clinical tool in MRI, to establish which plaques are suitable for an anti-inflammatory nanoparticles-based therapy.

In this sense, the gadolinium-based contrast agent B22956/1, a MRI albumin binder analogue to B26170, could enable clinicians to define plaques features and to establish a proper therapeutic regimen.