Graphical abstract

The aim of the present study is to develop physiologically-based kinetic (PBK) models for rat and human that include intestinal microbial and hepatic metabolism of zearalenone (ZEN) in order to predict systemic concentrations of ZEN and to obtain insight in the contribution of metabolism by the intestinal microbiota to the overall metabolism of ZEN. Methods and Results: In vitro derived kinetic parameters, apparent maximum velocities (V max ) and Michaelis-Menten constants (K m ) for liver and intestinal microbial metabolism of ZEN are included in the PBK models. The models include a sub-model for the metabolite, 𝜶-zearalenol (𝜶-ZEL), a metabolite known to be 60-times more potent as an estrogen than ZEN. Integrating intestinal microbial ZEN metabolism into the PBK models revealed that hepatic metabolism drives the formation of 𝜶-ZEL. Furthermore, the models predicted that at the tolerable daily intake (TDI) of 0.25 µg kg −1 bw the internal concentration of ZEN and 𝜶-ZEL are three-orders of magnitude below concentrations reported to induce estrogenicity in vitro. Conclusion: It is concluded that combining kinetic data on liver and intestinal microbial metabolism in a PBK model facilitates a holistic view on the role of the intestinal microbiota in the overall metabolism of the foodborne xenobiotic ZEN and its bioactivation to 𝜶-ZEL.

Zearalenone (ZEN) is a mycotoxin known for its estrogenic activities. The metabolism of ZEN plays a role in the interspecies differences in sensitivity to ZEN, and is known to occur in the liver and via the intestinal microbiota, although the relative contribution of these two pathways remains to be characterized. In the present study a fecal i n v i t r o model was optimized and used to quantify the interspecies differences in kinetics of the intestinal microbial metabolism of ZEN in rat, pig and human. Vmax, Km, and catalytic efficiencies (kcat) were determined, and results obtained reveal that the kcat values for formation of α-ZEL and β-ZEL amounted to 0.73 and 0.12 ml/h/kg bw for human microbiota, 2.6 and 1.3 ml/h/kg bw for rat microbiota and 9.4 and 6.3 ml/h/kg bw for pig microbiota showing that overall ZEN metabolism increased in the order human < rat < pig microbiota. Expressed per kg bw the kcat for ZEN metabolism by the liver surpassed that of the intestinal microbiota in all three species. In conclusion, it is estimated that the activity of the intestinal colon microbiome may be up to 36% of the activity of the liver, and that it can additionally contribute to the species differences in bioactivation and detoxification and thus the toxicity of ZEN in pigs and rats but not in humans. The results highlight the importance of the development of human specific models for the assessment of the metabolism of ZEN.