Reduced uptake of 18F-FDG and 15O-H2O in Alzheimer's disease-related regions after glucose loading.

Increased plasma glucose levels are known to reduce fluorine-18-labeled fluorodeoxyglucose ((18)F-FDG) uptake in Alzheimer's disease (AD)-related regions, resulting in the appearance of an AD-like pattern. However, the relationships of its appearance with cerebral blood flow and insulin levels are uncertain. We performed (18)F-FDG and oxygen-15-labeled water ((15)O-H2O) positron emission tomography in the fasting and glucose-loading conditions on nine young healthy volunteers with no cognitive impairments. Measurement of plasma glucose and insulin levels confirmed that all subjects were free of insulin resistance, and that glucose loading significantly increased plasma glucose and insulin levels. Fluorine-18-labeled fluorodeoxyglucose and (15)O-H2O images were compared between the two conditions, focusing on AD-related regions: precuneus/posterior cingulate (PP), lateral parietal cortex (LPC), and frontal cortex (FC). Volume-of-interest analyses showed significantly lower uptake of both (18)F-FDG and (15)O-H2O in PP, LPC, and FC after glucose loading (P<0.05). Whole-brain voxel-wise analyses also revealed the PP, LPC, and FC areas where uptake of both (18)F-FDG and (15)O-H2O decreased (P<0.05, familywise error rate-corrected). We concluded that increased plasma glucose and insulin levels can cause the appearance of the AD-like pattern in both (18)F-FDG and (15)O-H2O images, and this phenomenon can occur even in subjects without insulin resistance.