The anti-inflammatory effect of bacterial short chain fatty acids is partially mediated by endocannabinoids.

The endocannabinoid (EC) system has pleiotropic functions in the body. It plays a key role in energy homeostasis and the development of metabolic disorders being a mediator in the relationship between the gut microbiota and host metabolism. In the current study we explore the functional interactions between the endocannabinoid system and the gut microbiome in modulating inflammatory markers. Using data from a 6 week exercise intervention (treatment n = 38 control n = 40) and a cross sectional validation cohort (n = 35), we measured the associations of 2-arachidonoylglycerol (2-AG), anandamide (AEA), -oleoylethanolamine (OEA) and -palmitoylethanolamine (PEA) with gut microbiome composition, gut derived metabolites (SCFAs) and inflammatory markers both cross-sectionally and longitudinally. At baseline AEA and OEA were positively associated with alpha diversity (β(SE) = .32 (.06), = .002; .44 (.04), < .001) and with SCFA producing bacteria such as (2-AG β(SE) = .21 (.10), < .01; PEA β(SE) = .23 (.08), < .01), and (PEA β(SE) = .29 (.11), = .01; .25 (.09), < .01) and negatively associated with (AEA β(SE) = -.31 (.12), = .004). Additionally, we found AEA to be positively associated with SCFA Butyrate (β(SE) = .34 (.15), = .01). AEA, OEA and PEA all increased significantly with the exercise intervention but remained constant in the control group. Changes in AEA correlated with SCFA butyrate and increases in AEA and PEA correlated with decreases in TNF-ɑ and IL-6 statistically mediating one third of the effect of SCFAs on these cytokines. Our data show that the anti-inflammatory effects of SCFAs are partly mediated by the EC system suggesting that there may be other pathways involved in the modulation of the immune system via the gut microbiome.