Exendin-4, but Not Oleoylethanolamide, Promotes Host-Mediated Alterations to the Gut Microbiome during Weight Loss

Gut-derived molecules like glucagon-like peptide-1 (GLP-1) and oleoylethanolamide (OEA) are prime targets for developing more effective obesity therapeutics due to their weight loss action. Hypophagia is commonly cited as the mechanism by which OEA and Exendin-4 (Ex4), a GLP-1 receptor agonist, reduce body weight. However, we recently showed in diet-induced obese (DIO) mice that the hypophagic action of Ex4 and OEA is transient and that weight loss continues even as food intake returns to pre-treatment levels. This was associated with increased energy expenditure (EE) in Ex4-, but not OEA-treated, mice. Given the emerging role for the gut microbiome as a regulator of energy balance, we hypothesized that the long-term, food intake-independent weight loss elicited by Ex4 is associated with alterations in the gut microbiome. In vivo and in vitro experiments coupled with 16S analysis were used to determine the effect of chronic Ex4 and OEA on the gut microbiome during weight loss. Male, DIO C57Bl/6J mice (60% high-fat diet for 15 weeks) were dosed 2x daily with Vehicle, OEA (5mg/kg) or Ex4 (100µg/kg) for 7 days. Fecal pellets were collected pre- and post-treatment for 16S analysis. Ex4 caused a change (p<0.05) in 11 bacterial species, including a 5.6-fold increase in L. johnsonii, a bacteria that has been shown to improve metabolic outcomes in DIO models. In contrast, though OEA reduced body weight, OEA treatment had relatively little effect on the microbiome. To determine whether Ex4 and OEA directly alter the gut bacteria profile, we cultured gut bacteria isolated from DIO mice and treated the cultures with Vehicle, OEA (10µM), or Ex4 (10nM) for 24 hours. 16S analysis of in vitro cultures revealed no change in bacteria profiles for either treatment. These results suggest that Ex4 indirectly alters the gut microbiome to promote weight loss. Future experiments will determine if microbiome alterations contribute to the Ex4-mediated elevation in EE and improvements in metabolic outcomes.