Review
Combined hazard assessment of mycotoxins and their modified forms applying relative potency factors: Zearalenone and T2/HT2 toxin

https://doi.org/10.1016/j.fct.2019.110599Get rights and content

Highlights

  • Modified forms of ZEN and T2/HT2 have been described and their to occurrence in food quantified.

  • Toxicity of ZEN and T2/HT2 has been assessed and HBGVs were established.

  • Potency factors relative to ZEN and T2/HT2 were established for modified forms to compensate for the lack of toxicity data.

  • The methodology developed can be applied for other groups of structurally related substances.

Abstract

This paper describes a methodology for hazard assessment of groups of related substances for which toxicity data are insufficient, and which utilises, next to conventional toxicological assessments and mechanistic information, the derivation of relative toxicity potency factors (RPFs). Zearalenone (ZEN) and T-2 toxin (T2) and HT-2 toxin (HT2) and their modified forms have been used as examples. A tolerable daily intake (TDI) for ZEN of 0.25 μg/kg bw was established. In vitro and in vivo studies suggested that modified forms of ZEN act via the same mode of action as ZEN (oestrogenicity). Results from in vivo uterotrophic assays were used to establish RPFs, allowing inclusion the different modified forms in a group TDI with ZEN. A TDI for the sum of T2/HT2 of 0.02 μg/kg bw per day and an acute reference dose (ARfD) of 0.3 μg/kg bw for the sum of T2/HT2 was established. In vitro studies show that phase I metabolites of T2/HT2 act via a similar mode of action as their parent compounds, namely protein synthesis inhibition with immune- and haematotoxicity. The phase I metabolites as well as conjugates of T2/HT2 and their phase I metabolites can be included in a group TDI with T2/HT2 applying RPFs.

Introduction

Fusarium toxins are produced by fungi of the genus Fusarium that grow in the field and frequently contaminate crops used for food and feed. Zearalenone (ZEN), T2-toxin (T2) and HT2-toxin (HT2) are major representatives this toxin class. Both infected plants and the fungi themselves can form metabolites of these toxins, which can occur in considerable amounts in plants together with their parent compounds (EFSA CONTAM Panel, 2016, 2017). In addition, metabolites of ZEN have been shown to occur in animal derived food products such as cow's milk (Xia et al., 2009; Huang et al., 2014; Dänicke and Winkler, 2015). These mycotoxin derivatives have been defined as “modified forms” of mycotoxins (Rychlik et al., 2014). Modified forms include both phase I metabolites formed by oxidation, reduction or hydrolysis as well as phase II metabolites, i.e. glucose or sulfate conjugates of parent compounds or their phase I metabolites (EFSA CONTAM Panel, 2016, 2017). Although some modified fusarium toxins may still possess biological activity and exert considerable toxicity, to date, modified forms of fusarium toxins are neither considered in dietary risk assessments nor in the EU legislative framework on contaminants. The data collected and evaluated in two recent EFSA opinions (EFSA CONTAM Panel, 2016, 2017) were used as a starting point for the present scientific review. The objective of this scientific review is the introduction of a methodology for hazard assessment of groups of structurally related mycotoxins or other contaminants for which robust toxicity data are lacking, for several forms establishing relative potency factors (RPFs) for compounds of a substance group for which adequate toxicity data are not available. ZEN, T2 and HT2 and their modified forms have been used as examples.

Section snippets

Approach used for a combined assessment

The following approach was adopted to conduct a combined hazard assessment of mycotoxins and their modified forms in food. Several issues had to be considered to decide whether it is appropriate to set a combined health-based guidance value (HBGV) for a mycotoxin and its modified forms. Firstly, the modified forms of a certain mycotoxin were identified and described. Secondly, the occurrence of these modified forms in food commodities was verified, as a prerequisite for their relevance in

Modified forms of ZEN

ZEN (CAS No. 17,924-92-4, C18H22O5, MW 318) is found in cereal crops such as maize, wheat, barley, sorghum and rye, primarily in the field, but it may also occur upon poor storage conditions (EFSA CONTAM Panel, 2011a). It is produced by various Fusarium species under moist and cool conditions, but in particular by F. graminearum, F. culmorum, F. equiseti and F. verticillioides (Sweeney et al., 1998; Doohan et al., 2003). ZEN has the ring system of a macrocyclic β-resorcylic acid lactone (RAL).

Occurrence of modified forms of ZEN

In fungi, α- and β-ZEL are formed from ZEN, but these can be further conjugated by either fungi and/or infected plants to α- and β-ZEL glucosides, that were co-occurring with ZEN and α- and β-ZEL in cereal-based products (De Boevre et al., 2013; Nathanail et al., 2015). In cereal based foods, the concentrations of α-ZEL and β-ZEL added another 40% (mean concentration 19 μg/kg) and 30% (mean concentration 14 μg/kg), respectively, to the amount of ZEN present (mean concentration 47 μg/kg).

Toxicity of ZEN

In 2000, the Joint FAO/WHO Expert Committee on Food Additives (JECFA) (FAO/WHO, 2000) derived a no observed effect level (NOEL) of 40 μg/kg bw per day for ZEN based on oestrogenic effects (prolonged inter-oestrous interval and maintenance of corpora lutea and increased progesterone concentrations in plasma) in a study where gilts received oral doses of 0, 40, 200 and 400 μg ZEN/kg bw per day, between day 5 and day 20 of the oestrus (Edwards et al., 1987). Based on this NOEL, a provisional

Discussion and conclusions

The question of the relevance of modified mycotoxins regarding both their occurrence in food and their toxicity has received increased attention by the scientific community and also by European regulators over the last decade. This is also reflected in the increased number of publications dealing with this relatively new scientific field. Previous reviews have highlighted various aspects of modified mycotoxins including their relevance, addressing in particular modified Fusarium toxins (see for

Conflicts of interest

The authors have no conflict of interest.

Acknowledgements

This work was supported by the European Food Safety Authority (EFSA).

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