Regional brain uptake of ketone bodies and glucose in elderly humans: A 11C-acetoacetate and 18F-FDG PET study

The brain relies on glucose as its primary energy substrate. However, ketone bodies, i.e. acetoacetate and hydroxybutyrate, are the main replacement fuels for brain activity during fasting or on a ketogenic (very high fat, low carbohydrate) diet. We report here a study of ketone and glucose metabolism in human brain in young (mean 26 years) and aged (mean 73 years) healthy individuals as measured with positron emission tomography (PET), using the radiotracers ¹¹C-acetoacetate and ¹⁸F-fluorodeoxyglucose (FDG). Three blood samples were withdrawn during the two scans and were analyzed for plasma radioactivity and for concentration of acetoacetate, hydroxybutyrate and glucose. In the eighteen selected brain regions for this study, although the standard uptake values (SUV) were lower in the elderly subjects compared to the young subjects, the ratio of SUV in aged on young were almost similar in glucose and ketone metabolism. This protocol for brain fuel measurement by PET can be combined with treatment or on ketogenic diet to further study brain metabolism in neurodegenerative pathologies.