Demonstrating a link between diet, gut microbiota and brain: 14C radioactivity identified in the brain following gut microbial fermentation of 14C-radiolabeled tyrosine in a pig model.

Background: There is a need to better understand the relationship between the diet, the gut microbiota and mental health. Metabolites produced when the human gut microbiota metabolize amino acids may enter the bloodstream and have systemic effects. We hypothesize that fermentation of amino acids by a resistant protein-primed gut microbiota could yield potentially toxic metabolites and disturb the availability of neurotransmitter precursors to the brain. However, these mechanisms are challenging to investigate via typical in vitro and clinical methods. Methods: We developed a novel workflow using 14C radiolabeling to investigate complex nutrient-disease relationships. The first three steps of the workflow are reported here. α-Linolenic acid (ALA) was used as a model nutrient to confirm the efficacy of the workflow, and tyrosine (Tyr) was the test nutrient. 14C-Tyr was administered to male weanling pigs fed a high resistant protein diet, which primed the gut microbiota for fermenting protein. The hypotheses were; (1) that expected biodistribution of 14C-ALA would be observed, and (2) that radioactivity from 14C-Tyr, representing Tyr and other amino acids released from resistant protein following gut microbial fermentation, would be bioavailable to the brain. Results: Radioactivity from the 14C-ALA was detected in tissues reflecting normal utilization of this essential fatty acid. Radioactivity from the 14C-Tyr was detected in the brain (0.15% of original dose). Conclusion: Metabolites of gut-fermented protein and specifically amino acid precursors to neurotransmitters such as tyrosine, are potentially able to affect brain function. By extension, resistant proteins in the diet reaching the gut microbiota, also have potential to release metabolites that can potentially affect brain function. The high specificity of detection of 14C radioactivity demonstrates that the proposed workflow can similarly be applied to understand other key diet and health paradigms.

Fate of acrylamide during coffee roasting and in vitro digestion assessed with carbon 14- and carbon 13-labeled materials.

Acrylamide (AA) formation during coffee roasting happens rapidly, reaching a peak value within the first minutes of roasting followed by a fast decrease to reach an asymptote at approximately 200 µg/kg. Today, the mechanisms by which AA is reduced during roasting remain unclear. In this research, the fate of AA during roasting followed by drip brewed-like extraction was studied using 14C-radiolabeled (14C-AA) and 13C-labeled (13C3-AA) materials. Results showed that 28% of the spiked 14C-AA was lost during the roasting process, presumably by degradation to volatile compounds and 25% was non-extractable; therefore, appeared bound to the matrix. About 50% of initial AA went into the water extract, either unchanged or transformed by conjugation/binding. The release of bound acrylamide was further evidenced by increasing levels of 13C3-AA over prolonged roasting times. In addition, the absence of 14C activity in the hexane extracts suggested acrylamide not to bind to any lipophilic material.