Effects of deoxynivalenol (DON) and related compounds on bovine peripheral blood mononuclear cells (PBMC) in vitro and in vivo.

The Fusarium toxin deoxynivalenol (DON) often co-occurs along with the acetylated derivatives 3-acetyl-DON and 15-acetyl-DON in diets for ruminants. De-epoxy-DON is formed by rumen micro-organisms, while the acetylated DON derivatives might also undergo ruminal metabolism with de-epoxy-DON as an end product. However, despite the fact that de-epoxy-DON is the predominant substance finally absorbed, a complete degradation of the mother compounds can not be assumed for all feeding and metabolic situations of the cow, and thus raising the question of their possible post-absorptive effects. Hence, the aim of the study was to examine the effects of all four compounds on the concanavalin A stimulated proliferation of bovine peripheral blood mononuclear cells (PBMC) using MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide) as indicator in vitro and ex vivo. Among the DON-related compounds, DON and 15-acetyl-DON resulted in a similar IC50 (i.e. the concentration where the proliferation was inhibited by 50%) of 0.5 μM, whereas 3-acetyl-DON was less toxic (IC50 = 2.6 μM), while actually no IC50 could be estimated for de-epoxy-DON which was characterized by a maximum inhibition of approximately 24% at the highest tested in vitro concentration of 18.29 μM. For the in vivo experiment, 14 Holstein cows were used and fed either an uncontaminated control diet (CON) or a diet contaminated with Fusarium toxins, with DON being the predominating toxin for 18 weeks when blood was collected for PBMC isolation and subsequent proliferation/viability assay. The complete diets for the CON and FUS group contained 0.4 and 4.6 mg DON/kg DM, respectively, at that time. Exposure of dairy cows to the FUS diet resulted in maximum serum de-epoxy-DON levels of 52 ng/ml (0.19 μM), while levels of the unmetabolized DON reached maximum levels of 9 ng/ml (0.03 μM). The PBMC of these cows were slightly less viable, by approximately 18% (p = 0.057), while stimulation capability was not decreased at the same time. Although de-epoxy-DON was characterized by the lowest in vitro toxicity among the tested DON-related compounds, there appeared to be a lower viability of the PBMC isolated from cows fed the FUS diet, which had nearly exclusively de-epoxy DON in serum beside slight traces of unmetabolized DON. Thus, the factors responsible for these apparent discrepancies need to be clarified.