The challenge of early life exposure to deoxynivalenol: Intestinal vulnerability and intervention strategies

Abstract

Humans and animals are frequently challenged by mycotoxins which are among the most prevalent contaminants of food and feed. Mycotoxins are low-molecular weight, natural secondary fungal metabolites with diverse chemical and toxicological properties. Worldwide, the prevalence of the mycotoxin deoxynivalenol (DON) is recently rising significantly. Although different strategies have been applied to control the DON contamination at pre- and postharvest steps, human (especially children) and animal exposure to DON is still no entirely avoidable. Following the ingestion of contaminated food and feed, the intestinal epithelial barrier is one of the first targets for mycotoxins. Non-digestible oligosaccharides, including galacto-oligosacchrides (GOS) have been recognized as valuable health-promoting additives for infant formulas, resembling the various human milk oligosaccharides present in breast milk. These oligosaccharides are assumed to act as prebiotic substances supporting the development of a healthy intestinal microbiota and associated immune system. The first part of the thesis aims to gain a closer understanding of the adverse effects induced by DON and DON-metabolites on intestinal barrier and gut health in a well-defined intestinal epithelial cell (Caco-2) model as well in an in vivo piglet model (due to its resemblance to the human gastrointestinal tract). Moreover, GOS were investigated as possible intervention strategy against DON challenge in piglets. It is demonstrated that exposure to DON and acetylated-DON indeed resulted in a loss of epithelial barrier integrity and increase in the release of the pro-inflammatory chemokine interleukine-8 (CXCL8). Additionally, even low-level and short-term DON exposure in growing piglets induced distinct changes associated with disrupted intestinal barrier functions, oxidative stress and inflammation in growing pigs. Both, in vitro as well as in vivo experiments demonstrated the protective effects of GOS in a DON challenge model. In the second part of the thesis the gut health-promoting effects of GOS were investigated more in detail in a neonatal piglet model. GOS exerted beneficial effects such as the development of a healthy intestinal microbiota, improvement of the intestinal architecture and barrier integrity as well as parameters of the innate immune system such as secretory IgA in neonatal piglets. In addition, the direct interaction between the intestinal epithelium and GOS was investigated in a Caco-2 cell model to get more insight into the effects of GOS on the development of the epithelial barrier function. GOS showed distinct effects on the gene expression and localization of tight junction proteins (TJs) claudin1 and claudin3 as well as the marker of proliferation cyclin D1. Finally, mitogen activated protein kinase (MAPK) signaling was identified as an intracellular mechanism in the microbiota-independent effects of GOS. GOS promoted the reassembly of TJs in Caco-cell monolayers in a c-Jun NH2-terminal kinase and extracellular signal-regulated kinase dependent way. In summary, the investigations presented in this thesis not only illustrate the distinct in vitro and in vivo effects of DON on the intestinal epithelial integrity and function, but also demonstrate various microbiota-dependent and microbiota-independent effects of GOS and the protective effects of GOS against gut-associated adverse effects of the mycotoxin DON.