Gut microbial modulation of 3-hydroxyanthranilic acid and dopaminergic signalling influences attention in obesity

Background Obesity-related alterations in the gut microbiota have been linked to cognitive decline, yet their relationship with attention remains poorly understood. Objective To evaluate the possible relationships among gut metagenomics, plasma metabolomics and attention. Design We conducted faecal shotgun metagenomics and targeted plasma tryptophan metabolomics across three independent cohorts (n=156, n=124, n=804) with functional validations in preclinical models, including three faecal microbiota transplantation (FMT) experiments in mice and Drosophila melanogaster . Results Obesity was consistently associated with reduced attention. Metagenomics analyses identified Proteobacteria species and microbial functions related to tryptophan biosynthesis from anthranilic acid (AA) as negatively associated with attention in obesity. Plasma tryptophan metabolic profiling and machine learning revealed that 3-hydroxyanthranilic acid (3-HAA) was positively associated with attention, particularly in obesity, while AA showed a negative association. Bariatric surgery improved attention and enriched microbial species linked to attention. In mice, diet-induced obesity (DIO) and microbiota depletion reduced 3-HAA and 5-hydroxy-indole acetic acid (5-HIAA) concentrations in the prefrontal cortex (PFC), which were restored by FMT. Global metabolic profiling (>600 metabolites) of PFC from the FMT group identified 3-HAA and the tryptophan and tyrosine pathways among the most significant in mice receiving microbiota from high-attention donors. A second FMT experiment also revealed a consistent enrichment of the tryptophan and tyrosine metabolism at the transcriptional level in the PFC, with Haao (3-hydroxyantrhanilic acid dioxygenase) and Aox4 (aldehyde oxidase 4), key in 3-HAA and 5-HIAA degradation, among the significantly regulated genes. In a third FMT study, attentional traits were transmitted from humans to mice alongside modulation of serotonergic and dopaminergic pathways. In Drosophila , mono-colonisation with Enterobacter cloacae and DIO induced attention deficit-like behaviours, which were mitigated by 3-HAA supplementation. Conclusions We have identified the microbiota and 3-HAA as potential therapeutic targets to improve attention, especially in obesity.