PBK Model‐Based Prediction of Intestinal Microbial and Host Metabolism of Zearalenone and Consequences for its Estrogenicity

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.

Use of Physiologically Based Kinetic Modeling-Based Reverse Dosimetry to Predict In Vivo Nrf2 Activation by EGCG and Its Colonic Metabolites in Humans

“…Previous studies showed a proof of the principle for the inclusion of gut microbial metabolism in PBK modeling using kinetic parameters derived from in vitro anaerobic fecal incubations. 25,26 The model predicted the C max of GA and PG, after consumption of two capsules of the EGCG supplement (the recommended daily intake), to be less than 1.5% of the blood C max of EGCG and less than 14.1% when expressed in unbound EGCG equivalents in plasma. The increase in the percentage is due to both the REP values for GA and PG that are higher than the REP value of 1.0 for EGCG and the fact that the plasma fraction unbound values of GA and PG are 1.8 and 4.5 times that of EGCG, respectively.…”

“…The conceptual PBK model of EGCG, including sub-models for GA and PG, for humans is presented in Figure . The model is modified from PBK models developed and evaluated previously for zearalenone and daidzein also taking gut microbial metabolism into account. , The model includes a separate compartment for liver as the biliary excretion and metabolizing compartment, and compartments for stomach, fat, kidney, blood, small intestinal lumen, small intestine tissue, large intestinal lumen, slowly perfused tissue (muscle, skin, and bone), and rapidly perfused tissue. The model includes a stomach emptying process, and the small intestinal lumen was divided into seven sub-compartments, enabling the description of the transition within the small intestine .…”

“…The intestinal absorption rate of EGCG in the small intestine was subsequently determined using the following equation: absorption rate (μmol/h) = P app,in vivo (cm/h) × surface area of the human small intestine (cm 2 ) × luminal concentration of EGCG (mM = μmol/ cm 3 ). 26,36 The surface areas of human small and large intestines were 7200 and 4700 cm 2 , respectively. 26 The luminal concentrations of EGCG in the small intestine and large intestine were calculated by dividing the amount of EGCG by the volume of the small or large intestines, respectively.…”

“…26,36 The surface areas of human small and large intestines were 7200 and 4700 cm 2 , respectively. 26 The luminal concentrations of EGCG in the small intestine and large intestine were calculated by dividing the amount of EGCG by the volume of the small or large intestines, respectively. The transport of GA and PG formed by intestinal microbiota was modeled to go directly from the large intestinal lumen to the liver.…”

“…The aim of the present study was to develop a PBK model in humans including a separate microbial metabolism compartment to predict the in vivo kinetics of EGCG and to gain insights into the role of the gut microbiota in the bioactivation of EGCG. To characterize the PBK model parameters for the gut microbial conversion of EGCG, in vitro anaerobic fecal incubations were performed, previously shown to be an adequate way to generate kinetic PBK model parameters of colonic metabolism, including the respective kinetic constants V max and K m for microbial conversions. , Model predictions for blood levels of EGCG were evaluated against available in vivo kinetic data from the literature. Subsequently, PBK modeling-based reverse dosimetry was used to extrapolate the in vitro concentration–response curves from U2OS-Nrf2 CALUX reporter gene assays to in vivo dose–response curves for Nrf2 activation by EGCG in humans, taking the concentrations and relative activity of its major colonic metabolites GA and PG into account.…”