Evaluation of glucagon-like peptide-1 receptor expression in non-diabetic and diabetic atherosclerotic mice using PET tracer 68 Ga-NODAGA-exendin-4.

Activation of glucagon-like peptide-1 receptor (GLP-1R) signaling attenuates development of atherosclerosis and vascular inflammation. However, the expression of GLP-1R in atherosclerotic arteries remains uncertain. We evaluated whether a positron emission tomography (PET) tracer 68Ga-NODAGA-exendin-4 enables detection and imaging of GLP-1R expression in the mouse atherosclerotic aorta. Hypercholesterolemic (LDLR-/-ApoB100/100), hypercholesterolemic and diabetic (IGF-II/LDLR-/-ApoB100/100) as well as healthy control (C57BL/6N) mice were utilized in the study. The uptake of 68Ga-NODAGA-exendin-4 in atherosclerotic lesions was studied by autoradiography of tissue sections followed by immunofluorescence evaluation of inflammatory and vascular cell markers and GLP-1R. A subset of mice was imaged with 68Ga-NODAGA-exendin-4 PET/computed tomography (CT). The aortas of both LDLR-/-ApoB100/100 and IGF-II/LDLR-/-ApoB100/100 mice contained prominent, macrophage-rich atherosclerotic lesions. Diabetic mice demonstrated hyperglycemia and glucose intolerance. We found that by autoradiography, 68Ga-NODAGA-exendin-4 uptake was focally increased in macrophage-rich lesion areas compared with corresponding healthy vessel wall (lesion-to-wall ratio 1.6 ± 0.10, p<0.0001) in both non-diabetic and diabetic hypercholesterolemic mice. Pre-injection of unlabeled exendin-4 peptide significantly reduced cellular uptake of 68Ga-NODAGA-exendin-4. Furthermore, PET/CT imaging showed 68Ga-NODAGA-exendin-4 accumulation in the atherosclerotic aorta. Immunofluorescence stainings demonstrated co-localization of GLP-1R with macrophage-rich areas in atherosclerotic lesions. Tracer uptake was low in the healthy vessel wall of C57BL/6N mice coupled with negative GLP-1R staining. In conclusion, 68Ga-NODAGA-exendin-4 detects GLP-1R expression in atherosclerotic lesions in both non-diabetic and diabetic hypercholesterolemic mice. These results provide evidence that GLP-1R expression is mainly localized in macrophage-rich area in atherosclerotic lesions and may have implications for studies of pharmacological modification of GLP-1R signaling in atherosclerosis.