Toxicological significance of modified fumonisins

Fumonisins are toxins produced by moulds, so-called mycotoxins. Moulds of the genus Fusarium (or Aspergillus) can, under appropriate climatic conditions, grow and multiply on cereals, fruits or nuts. This also releases fumonisins, which can then also be found in processed food or feed. Fumonisins are strong kidney toxins, can promote the growth of tumours and cause birth defects in animals and humans. There are numerous strategies to minimise the occurrence of mycotoxins on cereals, but it is currently not possible to prevent them completely. In order to protect humans (and animals), EU-wide maximum levels (or guidance values) for food (and feed) have been introduced, which must not be exceeded. In Austria, the occurrence of fumonisins is problematic, especially in maize and maize products. Unfortunately, the unmodified fumonisins - originally produced by moulds - are not the only forms found in food and feed. Plants can, after they encounter toxins, convert them to other - possibly less toxic - compounds. A distinction is made between metabolic products (metabolites) and so-called "bound toxins". Very little is currently known about plant metabolites of fumonisins, with the exception of one form. Even less is known about bound fumonisins. Due to their chemical structure, fumonisins like to attach themselves to proteins and carbohydrates and escape the chemical analysis of their occurrence in food. Even more alarming is the fact that no data are available on the toxicity ("toxicological significance") of these bound fumonisins. The World Health Organization (WHO), together with the Food and Agriculture Organization of the United Nations (FAO), has recently recommended that studies should be conducted fill these gaps in knowledge. The aim of this project, therefore, is to find out to which forms fumonisins can be converted in maize and what the proportion of unmodified forms, metabolites and bound fumonisins actually is. For this purpose, fumonisins are produced by moulds, purified, applied to growing maize plants and the plants are subsequently analysed. The toxicity of bound fumonisins depends mainly on how many free toxins are released during digestion in the animal. This is to be found out by means of rats, which are administered the compounds. Afterwards, the animals` faeces and urine will be collected and measured. The concentration of the administered toxins is so low that the animals do not have to suffer. The generated data will be imperative to draw first conclusions about the toxicity of the compounds also for humans.

Fumonisins, produced by several Fusarium fungi, are major contaminants of food and feed. Maximum levels have been set by the European Union to ensure food safety, but those only take into account freely extractable fumonisins. So called "modified (masked and bound) fumonisins" also occur naturally, but their bioavailability and toxicity are unknown. The aim of the project was to thoroughly investigate the metabolism of the mycotoxin fumonisin B1 (FB1) in maize. (Radio-)labelled mycotoxins should facilitate these studies and biomarkers should be used to monitor the bioavailability of masked and bound fumonisins in rats. We aimed to produce (labelled) FB1, treat maize with (radio-)labelled fumonisins, exhaustively extract residues for the determination of masked and bound forms, perform toxicokinetic studies with rats and determine the bioavailability of masked and bound fumonisins with biomarker methods. First, we successfully produced and purified sufficient amounts of FB1, 13C-FB1 and 14C-FB1 for plant treatments. Mini-maize had to be used in the project, to minimize the amount of toxins. Unfortunately, the mini-maize proved difficult to propagate and grow. Upon several unsuccessful experiments in several growth chambers and outside we started growing the maize in a glass-house, but fluctuations in temperature and resulted in the partial loss of plants. Nonetheless, we started with the treatment and tested application via silks and cobs, as well as different concentrations. After hydrolysis, the bound forms were about 2-4 times higher than the native toxins. Unfortunately, the needed amount of fumonisin-treated maize to conduct the animal trial as planned could not be produced until the end of the project. The animal trial application was approved by the BOKU ethical committee and the Austrian Federal Ministry of Education, Science and Research. The trial with 16 rats had to be postponed as insufficient amount of diet was obtained and will be conducted in an already started European Union funded follow-up project. The project was extremely valuable to produce the needed (labelled) FB1 for the plant and the later animal trial. As a side-aspect, the purified substances allowed the work on fumonisin-resistance, resulting in two publications. Also, conditions to allow consistent growth and propagation of mini-maize were found and sufficient diet will be available soon to conduct the animal trial as planned, which is instrumental to answer the hypothesis that modified fumonisins are partly bioavailable and contribute to the overall toxicity. Two bachelor and one master thesis at BOKU were successfully completed within the project. The major impact of the project is yet to come. Regardless of how bio-available modified fumonisins prove to be, this will have an impact on the safety assessment conducted by the European Food Safety Authority and potentially on the maximum levels for fumonisins set by the European Union.