Bread crust extract is a novel activator of aryl hydrocarbon receptor and modulator of NRF2 and NFκB in HepG2 and HCT 116 cells

Abstract

The Maillard reaction describes the non-enzymatic formation of advanced glycation end products (AGEs), e.g., during thermal food processing. Studies on the mode of action and health implications of food-derived AGEs are often contradictory and lack information on active components. We use bread crust extract (BCE) as a model for an AGE-rich diet. Despite the identified AGEs and known activated signaling pathways, it is still unclear which receptors can exert the various effects described for BCE. This study investigates whether BCE can induce the aryl hydrocarbon receptor (AHR), the downstream NRF2 and NFκB signaling pathways and if this activation can be attributed to individual, free AGEs or AHR-agonists present in BCE. HepG2 reporter cell results showed activation of AHR and NRF2 but not NFκB by BCE. However, the tested free AGEs did not show an activation. Known AHR-(pro-)agonists kynurenine (Kyn) and benzo[a]pyrene (BaP), both present in BCE, activated the reporter to a similar extent as BCE with distinct differences in target gene induction of CYP1A1, interleukin-8, heme oxygenase 1 and Manganese-superoxide dismutase. Furthermore, CYP1A1 ethoxyresorufin-O-deethylase enzymatic activity was also induced and could be modulated by AHR and NRF2-inhibition. In contrast, in HCT 116 pTRAF reporter cells, BCE activated AHR, NFκB and NRF2 and induced CYP1A1. We conclude that BCE contains potent AHR activators that influence cellular signaling activities. AHR most likely concerts cell line dependent NRF2 and NFκB-activation. The BCE effects are probably attributable to an interplay of AHR-agonists and AGEs.