Comparative Biochemistry and Physiology Part C 136 (2003) 47–62 1532-0456/03/$ - see front matter  2003 Elsevier Science Inc. All rights reserved. doi:10.1016/S1532-0456(03)00166-2 Mechanisms of TCDD-induced abnormalities and embryo lethality in white leghorn chickens A.L. Blankenship *, K. Hilscherova , M. Nie , K.K. Coady , S.A. Villalobos , K. Kannan , a,b, a,c a a a a D.C. Powell , S.J. Bursian , J.P. Giesy d d a National Food Safety and Toxicology Center, Department of Zoology, Institute for Environmental Toxicology, a Michigan State University, East Lansing, MI, USA ENTRIX, Inc., 4295 Okemos Road, Suite 101, Okemos, MI 48864, USA b Department of Environmental Chemistry and Ecotoxicology, Faculty of Science, Masaryk University, Brno, Czech Republic c Department of Animal Science, Michigan State University, East Lansing, MI, USA d Received 18 March 2003; received in revised form 11 July 2003; accepted 12 July 2003 Abstract The toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds in birds has been well-established in laboratory and field studies. Observed effects of TCDD and related chemicals in birds include developmental deformities, reproductive failure, liver damage, wasting syndrome and death. The mechanism of action of TCDD at the cellular level is primarily mediated through the aryl hydrocarbon receptor (AhR). However, the mechanism of toxic action at the organism level is poorly understood. In this study, the role of radical oxygen species and mixed function oxidize (MFO; cytochrome P4501A) in the mechanism of TCDD-induced abnormalities and lethality were examined by co-injecting radical scavengers and an MFO inhibitor (piperonyl butoxide). Egg injection studies were conducted to determine if in ovo TCDD exposure can cause oxidative stress in white leghorn chicken eggs. Test agents were injected into the yolk prior to incubation. Treatments included TCDD (150 ngykg), triolein (vehicle control), and various co- treatments including MnTBAP (a mimetic of superoxide dismutase), piperonyl butoxide, piroxicam, vitamin A acetate, and vitamin E succinate. Phenytoin, which is known to cause teratogenesis through oxidative stress was used as a positive control. Eggs were incubated until hatch and then the following parameters were assessed: mortality, hatching success, abnormalities, weights for whole body, liver, heart and brain, and biochemical endpoints for oxidative stress. As a measure of exposure, concentrations of TCDD and ethoxyresorufin-O-deethylase (EROD) activities were measured in tissues of hatchlings. While greater mortality and abnormalities were observed in the TCDD treatment groups, the number of the replicates were not great enough to detect statistically significant differences in abnormality rates for the co-treatments. Some of the observed developmental abnormalities included edema, liver necrosis and bill, eye and limb deformities with TCDD treatments, bill and brain deformities with phenytoin treatments, eye abnormalities with Vitamin E treatments, and abnormal feather pigmentation with piperonyl butoxide treatments.  2003 Elsevier Science Inc. All rights reserved. Keywords: Ah Receptor; Avian; Chick; Dioxin; Deformities *Corresponding author. Tel.: q1-517-381-1434; fax: q1-517-381-1435. E-mail address: ablankenship@entrix.com (A.L. Blankenship).