A complex battlefield: Mycotoxins in the GIT

Most grains are susceptible to mycotoxin contamination. These toxic secondary metabolites are produced by fungi before or after harvest and cause severe economic losses. For livestock, negative consequences include acute effects, such as impaired liver and kidney function, vomiting, or anorexia, as well as chronic effects, such as immunosuppression, growth retardation and reproductive problems.

But how is it that mycotoxins cause so much damage in the first place?

This article delves into the complex processes that take place when mycotoxins come into contact with the gastrointestinal tract (GIT). The intestinal epithelium is the first tissue to be exposed to mycotoxins and often at higher concentrations than other tissues. A deeper understanding of how mycotoxins affect the GIT allows us to appreciate the cascading effects on animal health and performance, why such damage already occurs at contamination levels well below official safety thresholds – and what can be done about it.

Busy triage site

When mycotoxins are ingested, they encounter the GIT’s intestinal epithelium (Figure 1). This single layer of cells lining the intestinal lumen serves 2 conflicting functions:

1. on the one hand, it must be permeable enough to allow the absorption of nutrients
2. on the other, it constitutes the primary physiological barrier against harmful agents, such as viruses, micro-organisms, and toxins.

Figure 1 – The intestinal epithelium.

Within the intestinal epithelium, several types of highly specialised cells are involved in epithelial regeneration, nutrient absorption, innate defence, transport of immunoglobulins and immune surveillance. The selective barrier function is maintained due to the formation of complex networks of proteins that link adjacent cells and seal the intercellular space. Besides, the intestinal epithelium is covered with mucus produced by goblet cells, which isolates its surface preventing the adhesion of pathogens to the enterocytes (intestinal absorptive cells). Due to its dual involvement in digestive and immune processes, the intestinal epithelium plays a pivotal role in the animal’s overall health. Importantly, the epithelium is directly exposed to the entire load of ingested mycotoxins. Hence their effects can be problematic even at low concentrations.

Attack on the intestinal epithelium

Most mycotoxins are absorbed in the proximal part of the gastrointestinal tract (Table 1). This absorption can be high, as in the case of aflatoxins (~90%), but also very limited, as in the case of fumonisins (<1%); moreover, it depends on the species. importantly, a significant portion of unabsorbed toxins remains in the lumen of the gastrointestinal tract. some of the mycotoxins that enter the intestinal lumen can be bio-transformed into less toxic compounds by the action of certain bacteria. this action, however, predominantly happens in the large intestine – therefore, no detoxification takes place before absorption in the upper parts of the git. some of the absorbed mycotoxins can also re-enter the intestine, reaching the cells from the basolateral side via the bloodstream. they can also re-enter through enterohepatic circulation (the circulation of substances between the liver and small intestine). both actions increase the gastrointestinal tract’s overall exposure to the toxins.

The damaging impact of mycotoxins on the intestinal epithelium initially occurs through:

• A decrease in protein synthesis, which reduces barrier and immune function.
• Increased oxidative stress at the cellular level, which leads to lipid peroxidation, affecting cell membranes.
• Changes in gene expression and the production of chemical messengers (cytokines), with effects on the immune system and cellular growth and differentiation.
• The induction of programmed cell death (apoptosis), affecting the reposition of immune and absorptive cells.

Importantly, studies based on realistic mycotoxin challenges show that the mycotoxin levels necessary to trigger these processes are lower than the levels reported as safe by EFSA, the Food Safety Agency of the European Union. The ultimate consequences range from diminished nutrient absorption to inflammatory responses and pathogenic disorders in the animal (Figure 2).

Figure 2 – Mycotoxins’ impact on the GIT and consequences for monogastric animals.

Alteration of the intestinal barrier

The mycotoxins DON, fumonisin, and T2 induce a reduction in the rate of epithelial cell proliferation and differentiation. This causes a decrease in the height and the surface of the intestinal villi, which in turn leads to a reduction in nutrient absorption. Additionally, some nutrient transporters are inhibited by the action of mycotoxins, such as DON and T2, for example, negatively affecting the transport of glucose. Several studies indicate that mycotoxins such as aflatoxin B1, DON, fumonisin B1, ochratoxin A, and T2, can increase the permeability of the intestinal epithelium of poultry. This is mostly a consequence of the inhibition of protein synthesis. As a result, there is an increase in the passage of antigens into the bloodstream (e.g., bacteria, viruses and toxins). This increases the animal’s susceptibility to infectious enteric diseases. Moreover, the damage that mycotoxins cause to the intestinal barrier means that they are also being absorbed at a higher rate.

All grains used for animal feed, in compound feed and as an extra, are prone to mycotoxins. Photo: Ronald Hissink

Impaired immune function

The intestine is a very active immune site where several immuno-regulatory mechanisms simultaneously defend the body from harmful agents. Immune cells are affected by mycotoxins through the initiation of apoptosis, the inhibition or stimulation of cytokines and the induction of oxidative stress. Studies demonstrate that aflatoxin, DON, fumonisin, T2, and zearalenone interact with the intestinal immune system in such a manner that the animal’s susceptibility to viral and bacterial infections increases. Moreover, by increasing their faecal elimination, the horizontal transmission of pathogens is extended.

In poultry production one of the most severe enteric problems of bacterial origin is necrotic enteritis which is caused by Clostridium perfringens toxins. Any agent capable of disrupting the gastrointestinal epithelium – e.g., mycotoxins such as DON, T2 and ochratoxin – promotes the development of necrotic enteritis. The inhibition of the intestinal immune system, caused by mycotoxins such as aflatoxin, DON, and T2, also contributes to the development of this disease.

Alteration of the microflora

The gastrointestinal tract is home to a diverse community of bacteria, fungi, protozoa, and viruses which line the walls of the distal part of the intestine. This microbiota prevents the growth of pathogenic bacteria through competitive exclusion and the secretion of natural antimicrobial compounds, volatile fatty acids and organic acids. Recent studies on the effect of various mycotoxins on the intestinal microbiota show that DON and other trichothecenes favour the colonisation of coliform bacteria in pigs. DON and ochratoxin A also induce a greater invasion of Salmonella and their translocation to the bloodstream and vital organs in birds and pigs – even at non-cytotoxic concentrations. It is known that fumonisin B1 may induce changes in the balance of sphingolipids at the cellular level, including for gastrointestinal cells. This facilitates the adhesion of pathogenic bacteria, population increase and prolongs infections, as has been shown in the case of E. coli. From the perspective of human health, the colonisation of the intestine of food-producing animals with pathogenic strains of E. coli and Salmonella is of particular concern. Mycotoxin exposure may well increase the transmission of these pathogens, posing a risk to human health.

Interaction with bacterial toxins

When mycotoxins induce changes in the intestinal microbiota, this can lead to an increase in the endotoxin concentration in the intestinal lumen. Endotoxins or lipopolysaccharides (LPS) are cell wall fragments of Gram-negative bacteria. They are released during bacterial cell death, growth and division. Hence endotoxins are always present in the intestine, even in healthy animals. Endotoxins promote the release of several cytokines that induce an enhanced immune response, causing inflammation, thus reducing feed consumption and animal performance, damage to the vital organs, sepsis and, in some cases, death.

The synergy between mycotoxins and endotoxins can result in an overstimulation of the immune system. The interaction between endotoxins and oestrogenic agents such as zearalenone, for example, generates chronic inflammation and autoimmune disorders because immune cells have oestrogen receptors which are stimulated by the mycotoxin. While conversely, the combination of DON at low concentrations and endotoxins in the intestine has been shown to engender a decrease in transepithelial resistance and alter the balance of the microbiota.

Proactive toxin risk management

To prevent the detrimental consequences of mycotoxins on animal health and performance, proactive solutions are needed that support the intestinal epithelium’s digestive and immune functionality and help maintain a balanced microbiome in the GIT. Moreover, it is crucial for any anti-mycotoxin product to feature both anti-mycotoxin and anti-bacterial toxin properties and that it supports the organs most targeted by mycotoxins, e.g., the liver. EW Nutrition’s Mastersorb Gold premix is based on a synergistic combination of natural clay minerals, yeast cell walls and phytomolecules. Its efficacy has been extensively tested, including as a means of dealing with E. coli endotoxins.

A field trial
A field trial conducted in Germany on male Ross 308 broilers showed that for broilers receiving a diet contaminated with DON and zearalenone, adding 1 kg of Mastersorb Gold per tonne of feed to their diet led to significant performance enhancements. Not only did they regain the mycotoxin-induced weight loss (6% increase relative to the group receiving only the challenge), but they also gained weight relative to the control group. Feed conversion also improved by 3% relative to the group challenged with mycotoxins.

Effect against mycotoxins and bacterial toxins

Animal feed is often contaminated with 2 or more mycotoxins, making it important for an anti-mycotoxin agent to be effective against a wide range of different mycotoxins. To prevent mycotoxins damaging the GIT, an effective product should ideally adsorb most mycotoxins in the first part of the animal’s intestine (under acidic conditions). In-vitro experiments at an independent research facility in Brazil showed that an application of 0.2% Mastersorb Gold binds all tested mycotoxins at rates of 95-97% at a pH level of 3, using realistic challenges of 1000ppb (Aflatoxin B1 and ZEA) and 2500ppb (Fumonisin B1 and DON). The binding results achieved for Fumonisin and DON, which are often considered outright as ‘non-binding’ under challenging close to neutral conditions (pH 6), are particularly encouraging.

In terms of its efficacy against endotoxins, an in-vitro study conducted at Utrecht University, among other studies, has shown Mastersorb Gold to be an effective tool against the LPS released by E. coli. For the test, 4 premium mycotoxin binders were suspended in a phosphate buffer solution in concentrations of 0.25% and 1%. E. coli LPS were suspended to a final concentration in each sample of 50ng/ml. Against this particularly high challenge, Mastersorb Gold achieved a binding rate of 75% at an inclusion rate of 1%: clearly outperforming competing products which, at best, showed a binding rate of 10%.

Balanced microflora

A healthy gastrointestinal tract is crucial to animals’ overall health: it ensures that nutrients are optimally absorbed, it provides effective protection against pathogens through its immune function and it is key to maintaining a well-balanced microflora. Even at levels considered safe by the European Union, mycotoxins can compromise different intestinal functions, such as absorption, permeability, immunity and microbiota balance, resulting in lower productivity and susceptibility to disease.

To safeguard animal performance, it is important to continually strive for low levels of contamination in feed raw materials. And to stop the unavoidable mycotoxin loads from damaging the intestinal epithelium through the use of an effective anti-mycotoxin agent, which also supports animals against endotoxins and boosts liver function. Research shows that Mastersorb Gold is a powerful tool for proactive producers seeking better animal health, welfare and productivity.