Impact of phase I metabolism on uptake, oxidative stress and genotoxicity of the emerging mycotoxin alternariol and its monomethyl ether in esophageal cells

Abstract

Studies on the genotoxicity of Alternaria mycotoxins focus primarily on the native compounds. Alternariol (AOH) and its methyl ether (AME) have been reported to represent substrates for cytochrome P450 enzymes, generating hydroxylated metabolites. The impact of these phase I metabolites on genotoxicity remains unknown. In the present study, the synthesis and the toxicological effects of the metabolites 4-hydroxy alternariol (4-OH-AOH) and 4-hydroxy alternariol monomethyl ether (4-OH-AME) are presented and compared to the effects of the parent molecules. Although the two phase I metabolites contain a catecholic structure, which is expected to be involved in redox cycling, only 4-OH-AOH increased reactive oxygen species (ROS) in human esophageal cells (KYSE510), 4 times more pronounced than AOH. No ROS induction was observed for 4-OH-AME, although the parent compound showed some minor impact. Under cell-free conditions, both metabolites inhibited topoisomerase II activity comparable to their parent compounds. In KYSE510 cells, both metabolites were found to enhance the level of transient DNA–topoisomerase complexes in the ICE assay. Although the level of ROS was significantly increased by 4-OH-AOH, neither DNA strand breaks nor enhanced levels of formamidopyrimidine-DNA-glycosylase (FPG)-sensitive sites were observed. In contrast, AOH induced significant DNA damage in KYSE510 cells. Less pronounced or even absent effects of hydroxylated metabolites compared to the parent compounds might at least partly be explained by their poor cellular uptake. Glucuronidation as well as sulfation appear to have only a minor influence. Instead, methylation of 4-OH-AOH seems to be the preferred way of metabolism in KYSE510 cells, whereby the toxicological relevance of the methylation product remains to be clarified.Electronic supplementary materialThe online version of this article (doi:10.1007/s00204-016-1801-0) contains supplementary material, which is available to authorized users.

Mycotoxins: Biotransformation and Bioavailability Assessment Using Caco-2 Cell Monolayer

“…AOH is known for its genotoxicity [ 118 ]. However, the phase I metabolites, 4-OH-AOH and 4-OH-AME, had minor effect compared to AOH or AME in topoisomerase inhibition and DNA strand-breaking effects [ 174 ]. Phase II metabolism includes conjugation with glucuronic acid and sulfate [ 119 ].…”

“…( A ): Demethylation; ( B , C , H ): Hydroxylation; ( D , I ): Methylation; ( E , F ): Sulfation, glycosylation, and glucuronidation; ( G ): Epoxide reduction. CYP: Cytochrome P; and UGTs: Uridine 5′-diphospho-glucuronosyltransferase [ 71 , 117 , 121 , 172 , 173 , 174 , 177 , 178 , 179 , 180 , 181 ].…”

Bioavailability, metabolism, and excretion of a complex Alternaria culture extract versus altertoxin II: a comparative study in rats

“…Moreover, Sarkanj et al (2018) reported AOH (up to 0.2 ng/mL) for the first time in human urine samples as new biomarkers of exposure. Catechols formed by hydroxylation of AOH and AME may be further methylated by catechol-O-methyltransferase (Pfeiffer et al 2007;Tiessen et al 2017), while AME was also reported to be demethylated by microsomes of rat, human, and porcine liver (Pfeiffer et al 2007). However, AOH and AME are thermally and chemically rather stable in food matrices and therefore persistent during food processing (Estiarte et al 2018;Siegel et al 2010).…”

Outcomes of Gallic Acid on Alternariol Induced Cyto-Morphic and Genotoxic In Vivo Changes in Parotid Gland: 4-HNE Incorporated

“…Fleck et al [47] reported that AOH-induced reactive catechols react covalently with DNA forming depurinating adducts at the N-7 of guanine and the N-3 of adenine. Tiessen et al [48] added that AOH exposure induced complex distributions of γH2AX histones which are paramount biomarkers of DNA double strand breaks (DSBs) and strong indicator that AOH-induced DSBs are important triggering signals for G2 arrest and autophagy [49]. AOH has been proved as a DNA topoisomerase poison with certain selectivity for its IIa isoform [50].…”