Background: Animal models and human data have suggested macrophage-driven immune dysregulation in diabetic gastroparesis (DG). Translocator protein (TSPO) upregulation has been suggested to indicate activated state of macrophages and ER176 is a high affinity third generation TSPO-specific radioligand. The aim of this study was to determine feasibility of dynamic (11) C-ER 176 PET to identify macrophage activation in DG. Methods: Twelve patients, all females, were recruited (4 DG, 4 diabetics, and 4 healthy volunteers) for (11) C-ER 176 PET/CT scanning. The standardized uptake value (SUVmax ) in the gastric fundus, body, pylorus, and descending part of the duodenum were compared between three groups using Kruskal-Wallis test to perform the comparisons, and a p-value of 0.05 was considered statistically significant. Key results: Age was comparable among the three groups with a median of 53 years. The uptake was higher in pylorus in diabetics compared to DG and healthy (SUVmax healthy 4.6 +/- 0.2, diabetics 8.4 +/- 4.1, DG 5.5 +/- 1.0, p = 0.04). The uptake was similar in gastric fundus (9.0 +/- 1.6, 13.1 +/- 8.3, 7.8 +/- 1.9 respectively, p = 0.3), body (7.7 +/- 1.9, 13 +/- 9.2, 7.8 +/- 1.9 respectively, p = 0.8), and duodenum (6.2 +/- 2.1, 9.5 +/- 6.8, 7.0 +/- 1.8 respectively, p = 0.6). No correlation was observed between SUVmax uptake and either HbA1C or fasting blood glucose. Conclusions and inferences: Female diabetic gastroparesis patients did not demonstrate increased TSPO ligand (11) C-ER 176 uptake in the stomach. Possible explanations include lack of specificity of ligand for specific macrophage phenotypes in DG, sex effect, or small sample size. Further studies investigating non-invasive ways of analyzing immune dysregulation in neurogastrointestinal disorders are warranted.
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