A Physiologically Based in Silico Model for trans-2-Hexenal Detoxification and DNA Adduct Formation in Rat

Abstract

trans-2-Hexenal (2-hexenal) is an α,β-unsaturated aldehyde that occurs naturally in a wide range of fruits, vegetables, and spices. 2-Hexenal as well as other α,β-unsaturated aldehydes that are natural food constituents or flavoring agents may raise a concern for genotoxicity due to the ability of the α,β-unsaturated aldehyde moiety to react with DNA. Controversy remains, however, on whether α,β-unsaturated aldehydes result in significant DNA adduct formation in vivo at realistic dietary exposure. In this study, a rat physiologically based in silico model was developed for 2-hexenal as a model compound to examine the time- and dose-dependent detoxification and DNA adduct formation of this selected α,β-unsaturated aldehyde. The model was developed based on in vitro and literature-derived parameters, and its adequacy was evaluated by comparing predicted DNA adduct formation in the liver of rats exposed to 2-hexenal with reported in vivo data. The model revealed that at an exposure level of 0.04 mg/kg body weight, a value reflecting estimated daily human dietary intake, 2-hexenal is rapidly detoxified predominantly by conjugation with glutathione (GSH) by glutathione S-transferases. At higher dose levels, depletion of GSH results in a shift to 2-hexenal oxidation and reduction as the major pathways for detoxification. The level of DNA adduct formation at current levels of human dietary intake was predicted to be more than 3 orders of magnitude lower than endogenous DNA adduct levels. These results support that rapid detoxification of 2-hexenal reduces the risk arising from 2-hexenal exposure and that at current dietary exposure levels, DNA adduct formation is negligible.

An integrated QSAR-PBK/D modelling approach for predicting detoxification and DNA adduct formation of 18 acyclic food-borne α,β-unsaturated aldehydes

“…The PBK/D models for trans-2-hexenal for rat and human revealed that DNA adduct formation in the liver due to intake of trans-2-hexenal at human dietary exposure levels would be three to six orders of magnitude lower than the natural background levels of structurally similar 1,N 2 -exocyclic deoxyguanosine adducts in disease free human liver. Based on this observation we concluded that at realistic dietary exposure levels the DNA adduct formation may be negligible (Kiwamoto et al, 2012;Kiwamoto et al, 2013). trans-2-Hexenal is, however, only one of the many α,β-unsaturated aldehydes present in diet and it remains unknown whether the results would be similar for other acyclic α,β-unsaturated aldehydes.…”

“…c o m / l o c a t e / y t a a p detoxification is indeed sufficient to prevent significant DNA adduct formation of acyclic α,β-unsaturated aldehydes in vivo. Using trans-2-hexenal as model compound, we have previously shown that physiologically based kinetic/dynamic (PBK/D) modelling gives insights in detoxification and DNA adduct formation of α,β-unsaturated aldehydes in vivo (Kiwamoto et al, 2012;Kiwamoto et al, 2013). The PBK/D models for trans-2-hexenal for rat and human revealed that DNA adduct formation in the liver due to intake of trans-2-hexenal at human dietary exposure levels would be three to six orders of magnitude lower than the natural background levels of structurally similar 1,N 2 -exocyclic deoxyguanosine adducts in disease free human liver.…”

“…The UPLC methods applied are presented in supplementary information 1. A calibration curve to quantify the GSH conjugates was obtained for each aldehyde by reacting an aldehyde (10 mM) with different lower concentrations of GSH (100-500 μM) in 0.1 M Tris-HCl (pH 8.6) (Kiwamoto et al, 2012). The conjugates were quantified based on the peak areas determined at a wavelength of 200 nm.…”

Scientific Opinion on Flavouring Group Evaluation 200 (FGE.200): 74 α,β‐unsaturated aldehydes and precursors from subgroup 1.1.1 of FGE.19

“…Thus, dietary exposure to doses that do not deplete glutathione, and therefore do not lead either to tissue damage or DNA adducts would not be expected to pose a mutagenic or carcinogenic hazard (Kiwamoto et al, 2012(Kiwamoto et al, , 2013. However, the Panel considered that PBK/D studies are not sufficient due to the lack of validation.…”

“…The Panel noted that all the metabolic parameters were obtained from in vitro studies using rat (Kiwamoto et al, 2012) or human (Kiwamoto et al, 2013) liver S9-mix or small intestine S9-mix and cofactors or liver mitochondrial fraction to determine the kinetic constants for ALDH-mediated oxidation, AR-mediated reduction and GST-catalysed conjugation of GSH with trans-2-hexenal in these different tissue fractions. Due to the fact that data were obtained only in vitro, such a model is limited.…”