Mycotoxins are secondary metabolites produced by toxigenic fungi that are frequently found as foods and animal feeds contaminants (Gruber-Dorninger et al., 2019). Thus, the ingestion of these is the main exposure to mycotoxins for animals (Liew and Mohd-Redwan, 2018) and can compromise their intestinal health.
The gastrointestinal tract has the function of digesting and absorbing nutrients and energy, while being an important part of the immune system and acting as a protective barrier against possible infectious or non-infectious agents such as mycotoxins. In this context, intestinal health is characterized by a state of balance (homeostasis) between the different components of the intestinal barrier, including the microbiota, the mucosa and the immune system, which promotes the health, well-being and performance of the animals. (Celi et al., 2017).
However, mycotoxins can alter this homeostasis and affect the functions of the gastrointestinal tract, compromising the absorption of nutrients and the intestinal barrier. In general, mycotoxins have a direct antimicrobial effect in addition to a secondary effect of toxicity on intestinal cells that produces changes in the intestinal microbiota. In turn, the microbial population of the intestine itself can disturb the adsorption of mycotoxins and their structure, forming secondary metabolites that can affect the health of the animals. Thus, a bidirectional scenario has been described between mycotoxins and the intestinal microbiota (Guerre, 2020). On the other hand, mycotoxins can disturb intestinal integrity.
Trichothecenes such as DON or T-2 toxin have been described as the mycotoxins with the greatest toxicity on intestinal health. Trichothecenes decrease the expression of tight junctions (increased permeability) and glucose transporters, while inducing enterocyte apoptosis by reducing villus height and, therefore, increasing intestinal permeability and reducing nutrient absorption. In addition, these mycotoxins reduce the number of goblet cells, mucin-secreting cells with an important protective function, and cytokines. In summary, trichothecenes negatively affect intestinal absorption, integrity, and immunity. In addition, they induce the release of satiety hormones that compromise production parameters and induce oxidative stress and liver damage.
Fumonisins reduce the expression of tight junctions and induce cell apoptosis in the intestine (by accumulation of sphinganine), increasing intestinal permeability that allows the translocation of bacteria into the bloodstream. On the other hand, and unlike the trichothecenes, the fumonisins stimulate the continuous hypersecretion of mucin by the goblet cells, depleting them and compromising the mucosal barrier. Also, fumonisins limit the immune response. Thus, in general, fumonisins increase cell apoptosis and compromise the intestinal barrier, including the immune system.
Ochratoxins are characterized by being one of the most common toxins in animal production and, although the kidney is their target organ, they have negative effects on the gastrointestinal tract: they increase intestinal permeability by reducing the expression of tight junctions and inducing oxidative stress and the consequent apoptosis of enterocytes. Consequently, the height of the villi is compromised, and, at the same time, the immune system is altered (decreasing the expression of cytokines). In this scenario, the animal becomes more vulnerable to secondary infections. Thus, ochratoxins compromise intestinal integrity and decrease nutrient absorption.
Aflatoxins, among which aflatoxin B1 stands out, have the liver as their target organ. These mycotoxins are characterized by having a great hepatotoxicity and, in addition, compromising the productive performance and the immune system. However, its toxicity on the gastrointestinal tract is comparable to that of other mycotoxins: it increases permeability and degenerates the intestinal morphological structure while altering the immune system, increasing the infiltration of leukocytes and lymphocytes in the intestinal mucosa.
The described effects of zearalenone on the gastrointestinal tract are not as detrimental compared to the other mycotoxins. In fact, differences between zearalenone and its metabolites have been described, although in both cases the reproductive system is the main target of this mycotoxin.
However, it is important to take into account the high frequency of multi-contamination with mycotoxins and the possible synergistic or additive effect (Fusilier et al., 2022) by altering the functions of the gastrointestinal tract, compromising the absorption of nutrients and the intestinal barrier that, in turn, can negatively affect the health and productive performance of animals.
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