Brain Imaging of the GLP-1 Receptor in Obesity Using 68Ga-NODAGA-Exendin-4 PET

Stimulation of glucagon-like peptide-1 (GLP-1) receptors increases the insulin release in the pancreas during high glucose levels, and also stimulates a feeling of satiety. Likewise, synthetic GLP-1 receptor agonists derived from exendin are used successfully in the treatment of type-2 diabetes mellitus and obesity. Interestingly, preclinical and clinical studies further suggest that GLP-1 receptor agonists may decrease motor, behavioral, and cognitive symptoms in (animal models) Parkinson's disease and Alzheimer's disease and may slow down neurodegeneration. These observations suggest stimulation of GLP-1 receptors in the brain. The GLP-1 positron emission tomography (PET) tracer Ga-68-NODAGA-exendin-4 has been developed and successfully used for imaging in humans. In an ongoing study on the effects of bariatric surgery on GLP-1 receptor expression, we performed Ga-68-NODAGA-exendin-4 PET in obese subjects. Here we evaluated whether GLP-1 receptor binding could be visualized in the central nervous system in 10 obese subjects (seven woman; body mass index: mean +/- SD: 39 +/- 4.4 kg/m(2)) before bariatric surgery. Although we observed clear uptake in the pituitary area (mean SUVmax 4.3 +/- 2.3), we found no significant uptake in other parts of the brain. We conclude that Ga-68-NODAGA-exendin-4 PET cannot be used to analyze GLP-1 receptors in the brain of obese subjects.