Chronic exposure to synthetic food colorant Allura Red AC promotes susceptibility to experimental colitis via intestinal serotonin in mice

Allura Red AC is a dye used in food products. Here the authors report that chronic, long-term exposure to Allura Red AC increases susceptibility to experimental colitis in mice dependent on the serotonin biosynthetic enzyme TPH1, while intermittent exposure more typical for the human setting did not increase susceptibility to experimental colitis. Chemicals in food are widely used leading to significant human exposure. Allura Red AC (AR) is a highly common synthetic colorant; however, little is known about its impact on colitis. Here, we show chronic exposure of AR at a dose found in commonly consumed dietary products exacerbates experimental models of colitis in mice. While intermittent exposure is more akin to a typical human exposure, intermittent exposure to AR in mice for 12 weeks, does not influence susceptibility to colitis. However, exposure to AR during early life primes mice to heightened susceptibility to colitis. In addition, chronic exposure to AR induces mild colitis, which is associated with elevated colonic serotonin (5-hydroxytryptamine; 5-HT) levels and impairment of the epithelial barrier function via myosin light chain kinase (MLCK). Importantly, chronic exposure to AR does not influence colitis susceptibility in mice lacking tryptophan hydroxylase 1 (TPH1), the rate limiting enzyme for 5-HT biosynthesis. Cecal transfer of the perturbed gut microbiota by AR exposure worsens colitis severity in the recipient germ-free (GF) mice. Furthermore, chronic AR exposure elevates colonic 5-HT levels in naive GF mice. Though it remains unknown whether AR has similar effects in humans, our study reveals that chronic long-term exposure to a common synthetic colorant promotes experimental colitis via colonic 5-HT in gut microbiota-dependent and -independent pathway in mice.

Automated summary

Chronic exposure to Allura Red AC increases susceptibility to colitis in mice dependent on the serotonin biosynthetic enzyme TPH1. Intermittent exposure, more typical for humans, does not increase susceptibility. The impact of chronic exposure to this common synthetic colorant on colitis is mediated through colonic 5-HT levels and is microbiota-dependent and -independent.