Positron Emission Tomography and Autoradiography Imaging of P-selectin Activation Using 68Ga-Fucoidan in Photothrombotic Stroke

Background: P-selectin is activated early after stroke, followed by a rapid decline. This time course can be used to generate important information on stroke onset. The latter is crucial for therapeutic decision-making of wake-up strokes (i.e. thrombolysis or not). Here, we evaluated the specific p-selectin inhibitor fucoidan labeled with gallium-68 (68Ga-Fucoidan) as an imaging biomarker for assessing p-selectin activation in acute ischemic stroke using Positron Emission Tomography (PET). Methods: 68Ga-Fucoidan was investigated in rats brain at 2-5 h (n=16), and additionally at 24-26 h (n=9) and 48 h (n=3) after induction of photothrombic stroke or in sham-operated animals (n=6). Correlation of cerebral 68Ga-Fucoidan uptake with p-selectin expression was determined by exposing freshly cut brain cryosections to autoradiography and immunostaining using specific antibodies against p-selectin. Results: PET scans showed an increased accumulation of 68Ga-Fucoidan in the histologically proven ischemic stroke, as compared to the corresponding contralateral hemisphere in all except one animal. The median ratio between the uptake in the ischemic lesion and the contralateral region was 1.95 (1.45-2.41) at 2-5 h, 1.38 (1.05-1.89) at 24-26 h, and 1.09 (0.81-1.38) at 48 h after stroke, compared to 1.22 (0.99-1.49) for sham-operated animals. In the ex vivo autoradiography, 68Ga-Fucoidan accumulation co-localized with p-selectin as assessed by immunostaining. Control animals and those scanned at 24-26 h and 48 h after stroke exhibited no elevated 68Ga-Fucoidan uptake in either hemisphere. Conclusion: PET imaging using 68Ga-Fucoidan represents a valuable tool for assessing p-selectin activation in vivo discriminating ischemic stroke early after stroke onset.