We used the microbiota-derived IAA as we previously showed its decrease in IBD11 and metabolic syndrome.14 FICZ is an endogenous photoproduct of Trp metabolism with a potent AhR-activity.22 Butyrate, FICZ and IAA led to significant AhR activation on HepG2luc cells, but synergistically increased when they were combined with butyrate (Figures 2a and 2b). Here, AHR is linked to metabolic syndrome.