7 Lessons Learned from 20 Years of Mycotoxin Detoxification Research
What mycotoxins have in common that they are toxic, secondary metabolites of fungi. However, they vary in their structures which leads to significant differences in their biochemical and physical properties. Many of the seven lessons below stem from these differences.
1. Not every mycotoxin can be adsorbed
Although a plethora of literature on binding of mycotoxins is available, so far only certain clays have been shown to efficiently bind aflatoxins in the gastrointestinal tract of animals. However, not every clay can sufficiently bind aflatoxins and therefore a standardized method for evaluating aflatoxin binders was suggested in the European Union.
Deoxynivalenol (DON) in particularly is known to be a non adsorbable mycotoxin as in vitro binding rates for clay based materials only is up to 20%. However, for DON activated carbon (AC) has been proposed as binding agents with higher binding rates. The downside of using activated carbon is that it impacts the uptake of essential nutrients in the animals—decreasing the nutritional value of feed. This leads to the next important lesson learned:
2. The additives should not have any negative impact on feed and animals
When activated carbon is used, animals are blackened which is not appreciated in the livestock industry. Furthermore, activated carbon is an unspecific binding agent which also binds vitamins and other nutrients. Taken over a longer period, depletions can take place.
Often, quaternary amines are used to treat the surface of clays to modify their adsorption properties and behavior. These organophilic clays (organoclays) were proposed to bind mycotoxins like zearalenone (ZEN) and fumonisins. However, these modified clays were described to entail toxic effects.
3. In vitro cannot be equated with in vivo
Organoclays actually have a very good binding behavior in vitro, but when examined in vivo both the selectivity and the specificity for mycotoxins is gone. In one of our test series we have evaluated two organoclays.
While the binding efficiency for zearalenone (ZEN) in vitro was very good (> 90%), no improvement of reproductive organ parameters could be seen in vivo. This illustrates that reaction conditions in vitro (buffer solution) are quite different from in vivo (complex environment). This also leads to the next important lesson:
4. Specificity is key
A detoxifying agent will only work in a complex environment such as the gastrointestinal tract if it has a high specificity for the respective target mycotoxin. This is not only true for clay minerals and aflatoxins (see above) but also for enzymes that cleave or transform mycotoxins into metabolites.
In our research we have been able to demonstrate that a ZEN detoxifying enzyme needs favorable kinetic parameters such as a low KM value, a high catalytic rate and specific activities to work in the gastrointestinal tract of animals. However, performance is not the most suitable endpoint for an in vivo experiment, and this leads to the next important learning:
5. Biomarker are key in assessing the efficacy of mycotoxin deactivators
Specific biomarkers should be taken for the in vivo assessment of the detoxification product applied. Biomarkers could be the mycotoxin itself, its metabolites or any other marker which is influenced by the presence of the mycotoxin, like an altered sphinganine / sphingosine ratio, when fumonisins are present.
In the case of testing the efficacy of ZEN-degrading enzymes, we used reproduction organ parameters, but also ZEN metabolites in urine and feces.
6. Prove that metabolites are non- or less toxic
When detoxifiers against mycotoxins are selected, it has to be assured that intermediates and end products are harmless for animals and the environment. Therefore, formed metabolites have to be investigated for any detrimental impact.
For instance, we tested the in vitro and in vivo toxicity of hydrolyzed fumonisin (HFB), a metabolite produced during detoxification of fumonisins with a specific carboxylesterase. Furthermore, we analyzed if metabolites produced by a ZEN hydrolase still have estrogenic potential.
7. Make sure that the deactivator is stable in the feed
Mycotoxin deactivators are always applied via the feed and for this reason products have to be formulated in a way that they are stable during processing and storage of feed.
For a fumonisin-degrading enzyme (FUMzyme®)we have applied genetic engineering in order to improve its pelleting stability. By exchanging several amino acids the stability of the enzyme could be increased to pelleting conditions at 90°C.