Ultrasmall superparamagnetic iron oxide nanoparticles coated with fucoidan for molecular MRI of intraluminal thrombus.

AIM: We have designed ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles associated with fucoidan (USPOI-FUCO), a natural sulfated polysaccharide with high affinity for activated platelets, to visualize by MRI arterial thrombi. MATERIALS & METHODS: USPIOs were prepared and sizes, zeta-potentials and relaxivities were measured. Elastase perfusion in the infrarenal aorta of Wistar rats induced intraluminal thrombus. They were scanned on 4.7 T MRI before and after injection of USPIO-FUCO or USPIO coated with anionic dextran. RESULTS: Surface plasmon resonance evidenced that fucoidan and USPIO-FUCO bind in vitro to immobilized P-selectin. All intraluminal hyposignals detected by MRI after injection of USPIO-FUCO on animals (13 out of 13) were correlated by histology with thrombi, whereas none could be identified with control USPIOs (0 out of 7). No signal was seen in absence of thrombus. Thrombi by MRI were correlated with P-selectin immunostaining and USPIO detection by electron microscopy. CONCLUSION: In vivo thrombi can thus be evidenced by MRI with USPIO-FUCO.

Abdominal aortic aneurysms targeted by functionalized polysaccharide microparticles: a new tool for SPECT imaging.

Aneurysm diagnostic is nowadays limited by the lack of technology that enables early detection and rupture risk prediction. New non invasive tools for molecular imaging are still required. In the present study, we present an innovative SPECT diagnostic tool for abdominal aortic aneurysm (AAA) produced from injectable polysaccharide microparticles radiolabeled with technetium 99m ((99m)Tc) and functionalized with fucoidan, a sulfated polysaccharide with the ability to target P-Selectin. P-Selectin is a cell adhesion molecule expressed on activated endothelial cells and platelets which can be found in the thrombus of aneurysms, as well as in other vascular pathologies. Microparticles with a maximum hydrodynamic diameter of 4 µm were obtained by crosslinking the polysaccharides dextran and pullulan. They were functionalized with fucoidan. In vitro interactions with human activated platelets were assessed by flow cytometry that demonstrated a specific affinity of fucoidan functionalized microparticles for P-Selectin expressed by activated platelets. For in vivo AAA imaging, microparticles were radiolabeled with (99m)Tc and intravenously injected into healthy and AAA rats obtained by elastase perfusion through the aorta wall. Animals were scanned by SPECT imaging. A strong contrast enhancement located in the abdominal aorta of AAA rats was obtained, while no signal was obtained in healthy rats or in AAA rats after injection of non-functionalized control microparticles. Histological studies revealed that functionalized radiolabeled polysaccharide microparticles were localized in the AAA wall, in the same location where P-Selectin was expressed. These microparticles therefore constitute a promising SPECT imaging tool for AAA and potentially for other vascular diseases characterized by P-Selectin expression. Future work will focus on validating the efficiency of the microparticles to diagnose these other pathologies and the different stages of AAA. Incorporation of a therapeutic molecule is also considered.

Radiolabeled fucoidan as a p-selectin targeting agent for in vivo imaging of platelet-rich thrombus and endothelial activation.

UNLABELLED: P-selectin expression is involved in the pathophysiology of biologically active arterial thrombus and endothelial activation after a transient ischemic event. Fucoidan is a polysaccharidic ligand of P-selectin, with a nanomolar affinity. In the present study, we propose a new approach of P-selectin molecular imaging based on radiolabeled fucoidan. METHODS: Two kinds of experimental models were selected to evaluate the ability of radiolabeled fucoidan to detect P-selectin expression: platelet-rich arterial thrombi (vegetations of infective endocarditis and arterial mural thrombus) and myocardial ischemia-reperfusion. These 2 settings were chosen because they were clinically relevant, and both were associated with an important overexpression of platelet and endothelial P-selectin, respectively. RESULTS: (99m)Tc-fucoidan SPECT was able to detect the presence of platelet-rich arterial thrombi in all animals, with a median target-to-background ratio of 5.2 in vegetations of endocarditis and 3.6 in mural aneurysmal thrombus, and to detect a persistent endothelial activation at 2 h after reperfusion. In this latter model, the magnitude of the signal was correlated with the extent of myocardium that underwent transient ischemia. The sensitivity of selectivity of the uptake and retention of (99m)Tc-fucoidan in both settings was excellent. CONCLUSION: This study supports (99m)Tc-fucoidan as a relevant imaging agent for in vivo detection of biologic activities associated with P-selectin overexpression, such as arterial thrombus and ischemic memory. Given the reported wide availability at a low cost, and its low toxicity, fucoidan seems to overcome some of the limitations of previous P-selectin-targeted imaging agents.