It is difficult to correlate in vitro toxin concentration with in vivo exposure, however, the concentration of toxin used in both models are similar as 2.3 mg DON/kg of feed corresponds to 7.7 μM ( Sergent et al., 2006; Pinton et al., 2009). It is interesting to observe that in both models, there is a good correlation in the increase of expression of phosphorylated MAPK. The extent of MAPK activation, lower in samples obtained from the in vivo experiment than in explants, could be explained by the mode of exposure to the toxin, in the culture medium

or in ingested feed. A significant increase was observed only for ERK and p38. Following the same signaling arrangement, each individual MAPK pathway responds Ku0059436 to specific stimuli and then regulates their specific substrates ( Cui et al., 2007), which can explain the selective activation of MAPK. JNK and ERK are involved in regulation of both cell survival and death depending on cell types and stimulus, whereas p38 can promote apoptosis via p53 activation (Bae and Pestka, 2008). ERK 1/2 is of particular Bcl-2 pathway importance because it can be involved in intestinal epithelial cell morphology and in the structure of tight junctions that regulate the barrier function of the intestinal tract (Oshima et al., 2008). Increase in MAPK phosphorylation was described in in vitro assays when the intestinal cell

line IPEC-1 was exposed to DON, resulting in a decreased expression of tight junction proteins ( Pinton et al., 2010). In a previous study, we have also observed that piglets fed a diet contaminated with 3 mg/kg of DON, showed a significant decrease expression of occludin and E-cadherin in jejunum and ileum ( Bracarense et al., 2012). Explants exposed to 10 μM of DON showed a decreased expression of E-cadherin in immunohistochemical assay (data not shown). All these data reinforce the role of DON in the activation of ERK which in turn induces changes in the expression of adherens and occludens junctions

proteins. In DON-stimulated RAW 264.7 cells competing apoptotic and survival cell pathway are induced by p38 and ERK activation, Ribonucleotide reductase respectively (Zhou et al., 2005b). In the present study, both in vivo and ex vivo exposure to DON induced a significant decrease in the total intestinal score in comparison to the control group. In addition, when immunohistochemical analysis for caspase-3 was performed in jejunal explants, a significant increase in immunostaining was verified in samples exposed to 10 μM of DON (data not shown). Probably, apoptosis of enterocytes was mediated by an activation of p38. DON and trichothecenes-related mycotoxins have shown to induce apoptotic changes in vitro and in vivo in several organs. In vitro, these changes were correlated to MAPKinases activation ( Yang et al., 2000; Pinton et al., 2010). This correlation was also demonstrated with other stressors than trichothecenes, for example heat stress in intestinal cells ICE-6 ( Yu et al., 2010).