Fusarium mycotoxins deoxynivalenol (DON), NX-3 and butenolide are secondary metabolites formed by Fusarium graminearu. Evidence for formation of DON-glutathione adducts exists in plants, and also in human liver (HepG2) cells mass spectrometric evidence for GSH-adduct formation was reported

In the present study, they investigated whether NX-3 matches DON with respect to pro-oxidative properties in HepG2 cells, comparing cytotoxicity, intracellular ROS levels, the impact on the GSH/GSSG status as well as the induction of the redox-sensitive pathway Nrf2/ARE.

Researchers furthermore addressed the question whether the intracellular GSH level is relevant for DON, NX-3 and BUT-induced toxicity in mammalian cells and the possible combinatory effects of DON with potentially co-occurring fungal metabolites with pro-oxidative and GSH-depleting properties, exemplified for BUT.

Contamination of food and feed by mycotoxins produced by Fusarium fungi are a global food safety issue. Many of the toxic secondary Fusarium metabolites have been well characterized during the last decades, but so far this study is, to the best of our knowledge, the first to address combinatory effects of DON and the potentially co-occurring Fusarium metabolite BUT. Although BUT has been reported as low or moderately toxic in previous toxicological characterizations

BUT-induced toxicity

NX-3 is a DON derivative lacking structural features for Thiol-Michael addition, while BUT has the structural requirements (conjugated double bond and keto group). In the present study, they addressed whether these structural differences affect levels of intracellular reactive oxygen species in HepG2 cells and if intracellular GSH levels influence toxic effects induced by DON, NX-3, and BUT.

Pre-treatment with an inhibitor of GSH bio-synthesis, L-buthionine-[S, R]-sulfoximine, aggravated substantially BUT-induced cytotoxicity (≥50 μM, 24 h), but only marginally affected the cytotoxicity of DON and NX-3 indicating that GSH-mediated detoxification is of minor importance in HepG2 cells.

They further investigated whether BUT, a compound inducing alone low oral toxicity, might affect the toxicity of DON. Under different experimental designs with respect to pre- and/or co-incubations, BUT was found to contribute to the combinatorial cytotoxicity, exceeding the toxic effect of DON alone.

The observed combinatorial effects underline the potential contribution of secondary metabolites like BUT, considered to be alone of low toxicological relevance, to the toxicity of DON or structurally related trichothecenes, arguing for further studies on the toxicological relevance of naturally occurring mixtures.