Cell-based bioassay solutions for food contaminant testing

Challenges

The food supply chain is subject to potential contamination with natural and industrial toxins. Food can contain pathogenic microorganisms, natural toxic compounds or industrial chemicals added intentionally or accidentally. 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. 

Toxin testing is typically carried out using analytic methods like high-performance liquid chromatography (HPLC) or liquid chromatography-mass spectrometry (LCMS), using commercially available standards, or immunological methods. Chemical and immunological analyses are very specific and typically detect a single analyte. Targeted LCMS also requires standards for the toxins under analysis.

The number of toxins with distinct chemistry, but similar toxicity, is often substantial. For example, there are 300 different known mycotoxins and 700 different pyrrolizidines. The related substances can be produced by the same pathogenic organism or by the metabolism of the toxin and may escape detection by normal analytical techniques. For some toxins, therefore, separate tests exist for the original and the metabolised toxin. Thus, it is impossible to test for such a wide range of mycotoxins using antibodies or LCMS.

Cell-based assays

Cell-based assays utilise whole cells as indicators of a specific biological process and can be used to detect chemicals which elicit toxicity. Cell-based assays can measure a variety of biological outcomes utilising parameters, including cell viability, transcriptional changes or signalling events involving protein-protein interactions. Cell-based analysis of signalling interactions can lead to the development of immunological tests, biochemical assays, and biosensors.

Cell-based assays are used in the pharmaceutical sector for pre-clinical screening of novel therapeutic compounds but have also been used for food toxicity testing. Examples include grain-borne mycotoxins, packaging-derived xenobiotics, shellfish toxins, or pyrrolizidine alkaloids in herbal extracts. Cell-based assays can simply measure cell viability (including toxicity or, conversely, growth stimulation by endocrine activity) but can also interrogate specific signalling events affected by toxins. Whole-cell bioassays based on bacterial cells, yeast and nematodes have been developed and are used for the detection of food and environmental toxins in some commercial settings. Cell-based assays can provide an alternative for and a complement to immunological and chemical testing. As for these established techniques toxin detection is influenced by food matrices.

The advantages of cell-based assays include:

• Automatic incorporation of bioavailability and viability testing.
• Ability to test for a group of chemicals with a similar toxicity profile.
• Ability to identify toxins for which no established standards currently exist.
• This is an active area of research, and the full potential of cell-based assays has not been fully realised yet. 

Questions

Solutions

The overall objective of the project is to develop cell-based assays based on the toxicity mechanism of toxins to complement the existing chemical and immunological tests. The assays are expected to enable the detection of masked toxins and toxin metabolites. 

Cell-based assays for mycotoxin detection

Mycotoxins are a major hazard in the food chain. The term mycotoxin includes a wide variety of fungus-derived toxins with a variety of mechanisms of toxicity. Humans and animals can be affected by mycotoxin poisoning in response to acute and chronic exposure. Cell-based assays for mycotoxin detection have concentrated on cell viability and endocrine receptor activation in the specific case of zearalenone. 

We are utilising 3 parallel approaches to develop cell-based assay systems for mycotoxins. They are based on two established toxicity responses (immune toxicity and food refusal toxicity) and one novel approach utilising the transcriptional response in a cell type which has shown high sensitivity to mycotoxin treatment. The cell-based assays have diagnostic relevance on their own, but they also inform the development of novel immunological and biosensor detection approaches by identifying undetected masked mycotoxin variants which share toxicity patterns with currently regulated compounds.

The development of these assay systems is primarily focusing on toxins currently relevant for the Scottish agri-food sector, but this approach can also be extended to include toxins which may become problems in the future due to climate change, an altered trade environment and testing requirements due to the UK’s European Union Exit, and the development of novel foods and food contact materials as a consequence of a focus on sustainability, increased biodiversity and a circular economy.

Project Partners

Progress