In vitro assessment of bacterial supernatants on hypothalamic gene expression: implications for appetite regulation

Bacterial metabolites, such as short-chain fatty acids (SCFAs), influence energy balance, appetite, and endocrine function. Investigating cell-free (CFSs) and cell-free conditioned supernatants (CCSs) containing SCFAs and other microbial metabolites may help unravel the mechanisms underpinning these potential benefits for metabolic health. This study evaluated the neuroactive potential of two bacterial species, Bifidobacterium longum APC1472 and Limosilactobacillus reuteri ATCC PTA 6475, known for their metabolic health benefits. In silico analysis predicted the capacity of these bacteria to produce neuroactive metabolites involved in gut-brain communication. Next, untargeted metabolomics was used to evaluate the predicted functional capability of these two species to produce metabolites under different growth conditions. CFSs and CCSs were tested on embryonic and adult mouse hypothalamic cells to assess their effects on appetite-regulating gene expression. Results revealed supernatant type- and species-specific metabolite profiles, identifying B. longum APC1472 and L. reuteri ATCC PTA 6475 as acetate producers, with B. longum APC1472 also identified as a tryptophan producer. The distinct metabolite profiles of CFSs and CCSs from these two species induced specific effects on the modulation of ghrelin receptor and glucagon-like receptor 1 gene expression in hypothalamic cells. These findings validate an in vitro approach to identify bacterial metabolites with potential neuroactive and metabolic health benefits, demonstrated through modulation of mouse hypothalamic gene expression.