Mechanisms Of8-Ketotrichothecene-Induced Anorexia And Emesis

The8-ketotrichothecenes, sometimes referred to as Type B trichothecenes, are a group of toxic sesquiterpenoid mycotoxins produced by Fusarium, fungus that frequently contaminates cereal staples such as wheat, barley and corn. These mycotoxins have been associated with a spectrum of toxic effects in experimental animals that include anorexia, emesis, nausea, growth retardation, neuroendocrine changes and immunosuppression, especially anorexia and emesis which involve food poisoning.These toxins have been recognized as a severe public health threat for animals and human beings.8-ketotrichothecenes include five toxins:(1) deoxynivalenol (DON),(2)3-acetyldeoxynivalenol (3-ADON),(3)15-acetyldeoxynivalenol (15-ADON),(4) fusarenon X (FX) and (5) nivalenol (NIV). Our lab developed an acute mouse bioassay model for conducting8-ketotrichothecenes-induced anorexia study. We pursued the mechanisms of DON-induced anorexia through vagus nerve and cytokines; We compared the potencies of8-ketotrichothecenes in the mouse anorexia model following intraperitoneal (ip) and oral administration and determined the dose response, duration, no observed adverse effect (NOAEL) and lowest observed adverse effect (LOAEL) of anorexia. Then, our lab developed an acute mink emesis model for conducting8-ketotrichothecenes-induced emesis study. We compared potencies of8-ketotrichothecenes in emetic effects following ip and oral administration and determined the latency, duration, incidence and intensity of emesis.We also established the NOAEL, LOAEL and50%emetic dose (ED5o) of8-ketotrichothecenes-induced emesis; The mechanisms of DON-induced emesis were elucidated through regulation of neurotransmitter serotonin (5-HT), neuropeptide peptide YY(PYY) and Cholecystokinin (CCK).1. Characterization and mechanisms of DON-induced anorexia using mouse bioassayA short-term mouse model was devised to investigate induction of food refusal by the common foodborne trichothecene DON. Mice were dosed DON by either ip or oral exposure at0-5mg-kg-1and food intake were measured in16h post-dosing. Dose response, duration and tolerance of DON-induced anorexia were determined. In order to determine the role of vagus nerve in DON-induced anorexia, we conducted anorexia study using vagotomy mouse. In order to determine the role of cytokines in DON-induced anorexia, we determined the mRNA expressions of interleukin-1β (IL-1β) and interleukin-6(IL-6) in mouse spleen using Real-time PCR at0,2and6h after oral exposure to2.5mg·kg-1DON. The results presented herein indicated that DON dose-dependently induced anorexia within2h of exposure when administered either by ip injection or by oral gavage. The no observed adverse effect and lowest observed adverse effect levels in this assay were0.5and1mg-kg-1for ip exposure and1and2.5mg-kg-1for oral exposure, respectively. DON’s effects on food intake were transient, lasting up to3h at1mg-kg-1and up to6h at5mg-kg"1. Interestingly, a dose-dependent orexigenic response was observed in the14h following the initial2h food intake measurement. Toxin-treated mice exhibited partial resistance to feed refusal when exposed to DON subsequently after2d, but not after7d suggesting that this modest tolerance was reversible. DON-induced feed refusal were not affected after vagotomy suggesting that vagus nerve was not associated with DON induced feed refusal. The mRNA expressions of IL-1β and IL-6were upregulated by DON in mouse spleen and reached peak levels at2h post-dosing, and back to basal levels at6h post-dosing, suggesting that DON-induced anorexia was correlated with mRNA expressions of IL-1β and IL-6in mouse spleen.2. Comparison of murine anorectic responses to the8-ketotrichothecenesThe anorectic effects of structurally related8-ketotrichothecenes,3-acetyldeoxynivalenol (3-ADON),15-acetyldeoxynivalenol (15-ADON), fusarenon X (FX) and nivalenol (NIV) were determined in the mouse model for anorexia induction from last chapter and compared with DON. As previously observed for DON, anorectic responses to3-ADON and15-ADON in the B6C3F1female mouse following both intraperitoneal (ip) and oral exposure were transient, lasting only a few hours, with food intake recovering to control levels within16h. For both ADONs, the no observed adverse effect levels (NOAEL) and lowest observed adverse effect levels (LOAEL) were0.5and1mg-kg-1following ip exposure, respectively, and1and2.5mg-kg-1after oral exposure, respectively. In contrast, food refusal persisted from48h to96h following ip and oral exposure to FX and NIV. For both ip and oral FX exposure, the NOAEL was0.025mg-kg-1and LOAEL was0.25mgkg-1, whereas the NOAELs and LOAELs for NIV were0.01and0.1mg·kg-1, respectively, after ip exposure and0.1and1mg-kg-1, respectively following oral exposure. Both these data and a prior DON study suggest that anorectic responses to8-ketotrichothecenes were always greater when administered ip as compared to oral exposure and follow an approximate rank order of NIV>FX>DON≈3-ADON≈15-ADON for ip exposure and FX>NIV>DON≈3-ADON≈15-ADON for oral exposure.3. Characterization and comparison of emetic responses to the8-ketotrichothecenes using mink bioassayA short-term mink model was devised to investigate induction of emesis by the8-ketotrichothecenes. The emetic capacities of the DON,15-ADON,3-ADON, FX and NIV were compared in female mink via ip and oral administration. In this model, the incidence, latency, duration, and intensity of emesis of all compounds were compared. The NOAELs, LOAELs and ED50of emesis were analyzed by SAS and other statistics methods. The results presented herein indicated that all five congeners dose-dependently induced rapid and short term emesis by both administration methods. Emesis was observed in1hour and lasted several hours. With increasing doses, there were marked decreases in latency to emesis with corresponding increases in emesis duration and number of emetic events. Following IP exposure, the NOAELs and LOAELs were0.05and0.1mg·kg-1, respectively, for DON, FX and NIV. For15-ADON and3-ADON, the NOAELs were both0.1mg-kg-1and LOAELs were0.25and0.2mg-kg-1, respectively. Following oral exposure, the NOAELs and LOAELs were0.01and0.05mg-kg-1for both DON and FX. The NOAEL and LOAEL for15-ADON were0.01and0.1mg-kg-1, for3-ADON,0.05and0.25mg-kg-1, and for NIV,0.1and0.25mg-kg-1, respectively. The effective doses resulting in emetic events in50% of the animals (ED50) for ip exposure to DON,15-ADON,3-ADON, FX and NIV were80,170,180,70, and60μg-kg-1respectively, and for oral exposure were30,40,290,30and250μg-kg-1, respectively. Emetic responses to8-ketotrichothecenes follow an approximate rank order of NIV≈FX≈DON>15-ADON≈3-ADON for ip exposure and DON≈FX≈15-ADON>NIV>3-ADON for oral exposure based on NOAELs, LOAELs and ED50.4. Mechanisms of DON-induced emesis using mink bioassayThe mechanisms of DON-induced emesis were explored in mink model from last chapter.5-HT3receptor antagonist granisetron, Y2receptor antagonist JNJ-31020028and CCK1receptor antagonist devezepide were used to block DON-induced emesis. Then, mink were dosed DON at0.1and0.25mg-kg’1via ip exposure and collected blood at15,30,60and120min post-dosing. DON concentration, neurotransmitter5-HT, neuropeptide PYY and CCK in plasma were measured by ELISA kits. Emetic events were monitored during0-120min. The results presented herein indicated that CCK1receptor antagonist devezepide had no obvious effects on DON-induced emesis. While, Y2receptor antagonist JNJ-31020028significantly attenuated DON-induced emesis. However, that5-HT3receptor antagonist granisetron could totally block DON-induced emesis, partially block PYY induced emesis. Plasma DON concentration reached the peak level in15-30min, declined very quickly thereafter and back to basal level at120min. DON dose-dependently upregulated plasma5-HT and PYY. Plasma5-HT and PYY reached the peak level at60min post-dosing and back to basal level at120min. Plasma PYY increased at30min post-dosing, while5-HT had no changes at that time and increased at60min, suggesting that PYY might induce the release of5-HT. Furthermore, plasma CCK had no changes post-dosing. Most of emetic events happened during0-60min and no emetic events were observed after120min, suggesting that DON-induced emesis might correlate with plasma5-HT and PYY. These results indicated that DON-induced emesis might mediate via5-HT and PYY, while PYY-induced emesis might mediate by5-HT.