Gut microbiota and physiologic bowel ¹⁸F-FDG uptake

Background: We investigated the association between physiologic bowel FDG uptake and gut microbiota. FDG uptake in the normal large and small intestine is widely variable both in distribution and intensity. The etiology of physiologic bowel ¹⁸F-FDG activity remains unknown. Results: We included 63 healthy male subjects. After overnight fasting, blood samples and ¹⁸F-FDG PET/CT scans were taken. Fecal samples were collected, and gut microbiota were analyzed by 16S rRNA gene-pyrosequencing. The physiologic bowel FDG uptake was classified into three groups by visual assessment and measured using the maximum and mean standardized uptake value. We used the total bowel to liver uptake ratio (TBR_max and TBR_mean). There was no significant difference in age, BMI, or lipid profiles between groups. To identify specific microbial taxa associated with the bowel FDG uptake while accounting for age and BMI, we performed a generalized linear model. At the genus level, the group with focal or intense FDG uptake in the intestine was associated with low abundance of unclassified Clostridiales. The group with intestinal FDG uptake lower than the liver was associated with high abundance of Klebsiella. TBR_max and TBR_mean were negatively associated with abundance of unclassified Enterobacteriaceae. Conclusion: We cautiously speculate that physiologic bowel FDG activity might be caused by an increase in intestinal permeability and may reflect an impaired barrier function in the intestine.