Mycotoxins are of relevance for human and animal health if they fulfil two criteria. They are chemically and biologically stable and they are efficiently absorbed into humans and animals through the gut membrane (i.e., they have high “bioavailability). Unstable mycotoxins or those which are not taken up into the body typically do not lead to any adverse effects.

In nature mycotoxins are modified chemically by plants or bacteria or other fungi. These modifications include oxidation, de-epoxidation or the addition of glucose or acetyl groups. Some of these chemical modifications influence how easily the mycotoxin is taken up into the cell. Other chemical modification influence how toxic the mycotoxin is.

Our data show that some chemical derivatives of deoxynivalenol (e.g., nivalenol) retain their toxicity but show reduced bioavailability. Other derivatives (e.g., the de-epoxide DOM1) are absorbed effectively, but have lost their toxicity. Glucuronidated deoxynivalenol (carrying a glucose attached to the toxin) shows very poor bioavailability and therefore has negligible toxicity. However, some of these chemical modifications (e.g. glucuronidation) can be reversed by the gut microbiome, which can reactivate the toxin.

We have also assessed the effect of the mycotoxins deoxynivalenol and T2 on the oxidative stress response in mammalian cells. Several publications seemed to suggest that DON activates this stress response pathway. However, our data suggest that DON and T2 do not show an oxidative effect. Rather they activate a stress response pathway mediated by the aryl hydrocarbon receptor (Ahr). That pathway increases the expression of the protein Nrf2. While Nrf2 is a prerequisite for the response to oxidative stress, its expression does not constitute an oxidative cell stress response.

We have also explored the ribotoxic response to trichothecene mycotoxins in more detail. We asked the question whether an increase in the amount of ribotoxicity signalling molecules (specifically, the proteins ZAK-alpha and p38) in a mammalian cell can increase the response to mycotoxin exposure. In HEK293 cells, a popular cell culture model, this is not the case. This suggests that a sufficient amount of these two stress signalling molecules is already present in HEK293 cells to mediate a maximum response to DON exposure. Whether this is also true in other cell lines will be assessed in further experiments.

Overall, the data demonstrate that cell-based bioassays are able to report on [a] the uptake of toxins into cells and on [b] different stress responses which can be combined to develop sensitive and specific assays for mycotoxin detection. The cell-based assays will also be able to detect novel mycotoxins or toxin derivatives which are currently not fully characterised.

The food chain is subject to potential contamination with natural and industrial toxins. While acute food poisoning is relatively rare, long-term effects of food toxins are an area of concern and therefore routine testing of foods at different stages of agrifood processes is legally required (EU regulation 1881/2006). Toxin testing is typically carried out using chemical analysis methods (e.g., HPLC or LCMS) using commercially available standards, or immunological methods (e.g., ELISA or lateral flow assays).

The number of toxins with distinct chemistry, but similar toxicity, is often substantial. Mycotoxins is the collective description of a wide variety of chemicals which are secreted by a multitude of fungi. However, mycotoxins can by chemically modified by other organisms generating a group of agents with similar toxicity but different chemical properties. Some of these related substances may escape detection by the conventional analytical techniques.

The objective of this project is to develop cell assays which detect the harmful properties of toxins rather than their chemical structure. The assays can complement the existing chemical and immunological test. These cell-based assays can be carried out in conjunction with microbial biotransformation treatments and therefore permit the detection of masked toxins and toxin metabolites.

The current focus of the project is on mycotoxins which are of relevance to the Scottish agri-food industry and are a consequence of mould growth (especially on cereals). The current research approach seeks to identify cell types which have high sensitivity to mycotoxins and to assess which toxicity mechanisms have the best potential for rapid and sensitive toxin detection.

Historically the ingestion of mouldy foods containing mycotoxins led to food refusal and immune suppression. The prevalent mycotoxin deoxynivalenol is therefore also known colloquially as vomitoxin. The biochemical mechanisms which underly these toxic effects were tested as indicators of mycotoxin exposure in candidate cell lines. Candidate reporter systems were developed and tested. In addition, a comprehensive database analysis systematically appraised the currently available raw data on cellular responses to mycotoxin exposure (see publications and other outputs).

Our results demonstrate that one of the mechanisms of toxicity (called ribotoxicity) provides a rapid and sensitive readout for mycotoxin exposure in mammalian cell lines. This can be exploited for the development of robust cell-based assay systems.

Publications and other outputs

A science brief: Detection of mycotoxins using cell-based assays

A sytematic review of mycotoxin transcriptomics describing the available evidence for trichothecene mycotoxin effects in mammalian cells