2000 Progress Report: Environmental Endocrine Disruption in Avian WildlifeEPA Grant Number: R826298
Title: Environmental Endocrine Disruption in Avian Wildlife
Investigators: Lasley, Bill L. , Conley, Alan J. , Fry, D. Michael , Overstreet, James W.
Current Investigators: Lasley, Bill L. , Conley, Alan J. , Enan, Essam E. , Fry, D. Michael , Overstreet, James W.
Institution: University of California - Davis
EPA Project Officer: Hahn, Intaek
Project Period: February 1, 1998 through January 31, 2001
Project Period Covered by this Report: February 1, 1999 through January 31, 2000
Project Amount: $437,544
RFA: Endocrine Disruptors (1997) RFA Text | Recipients Lists
Research Category: Economics and Decision Sciences , Endocrine Disruptors , Health , Safer Chemicals
Objective:The overall objective of this project is to characterize the mechanisms by which halogenated aromatic hydrocarbons (HAHs) cause disruption of growth factor and steroid hormone signal transduction in the cells of avian wildlife species. Our general hypothesis is that the primary mechanism of toxic action of HAHs involves the activation of cytoplasmic signal transduction which then interferes with steroid hormone and growth factor functions. This hypothesis was based on results from laboratory mammals that had demonstrated not only an interaction of TCDD with sex steroids but a protective effect of estrogen in terms of the adverse effects of TCDD on most cell types in vivo and in vitro. The first 2 years of this study clearly demonstrated that while an interaction of TCDD and estrogen also was found in avian species, estrogen was not protective, but instead seemed to increase the adverse effects of TCDD in avian species. Therefore, the focus in the third year of funding was directed towards gaining a better understanding of gender differences in toxicity in avian species and specifically on the mechanism(s) of actions of HAHs and their interaction with estrogen.
We tested the hypothesis that 2,3,7,8-tetrachlorodibenzodioxin (TCDD) antagonizes estrogen-induced hepatic lipid synthesis and metabolism in birds. Twenty 7 to 9 week-old male chickens (Gallus domesticus) were divided evenly into four groups: (1) vehicle control, (2) estrogen alone (1.0 mg/kg estradiol cypionate injected on 3 consecutive days), (3) TCDD alone (50 mg/kg injected on the fourth day), and (4) a combination of the estrogen and TCDD treatments. On Day 14, liver samples were collected for quantitative fatty acid analysis by capillary gas chromatography. Birds treated with estrogen alone had increased total triacylglyceride concentrations with specific increases in the 9-desaturase products 16:1n7, 18:1n7, 18:1n9, and 20:1n9. However, these increases did not occur for birds treated with TCDD alone or in combination with estrogen. TCDD and estrogen plus TCDD treatments increased concentrations of total phospholipids and of the diet-derived polyunsaturated fatty acids 18:2n6, 18:3n6, 20:3n6, 18:3n3, and 20:5n3. The antagonism of estrogen-induced triacylglyceride synthesis by TCDD could explain the greater sensitivity of female birds to the wasting syndrome and the reduced or delayed egg production. Finally, birds treated with TCDD or estrogen plus TCDD did not develop fatty livers or accumulate triacylglycerides but instead had increased concentrations of phospholipids. Results from these investigations demonstrate that total concentrations of triacylglycerides were increased in plasma of the TCDD group but the total concentrations of other lipid classes and the total lipid content of the plasma are not significantly different across treatment groups. Although the total plasma concentrations of saturated fatty acids were not different across treatment groups, the triacylglyceride concentrations were higher in the TCDD group. Specifically, concentrations of 14:0, 15:0, 16:0, 18:0, 20:0, 22:0, and 24:0 were all elevated in plasma triacylglycerides of the TCDD group, however, these increases were not seen in the estrogen plus TCDD group. In the free fatty acid fraction, the TCDD group also had higher concentrations of 24:0 compared to all other groups. The cholesterol ester concentrations of 14:0 and 18:0 also were increased in the TCDD group.
The concentrations of long chain fatty acids 20:1n9 and 20:3n9 were consistently higher in cholesterol esters and triacylglycerides of TCDD-treated birds while concentrations of 22:1n9 were higher in those two groups plus free fatty acids. Similarly, the concentration of 22:1n9 was elevated in all plasma lipid classes of the estrogen plus TCDD group, however the triacylglyceride concentration of 22:1n9 and also the cholesterol ester concentration of 20:1n9 were still significantly lower compared to TCDD treatment alone. Compared to the control group, cholesterol ester concentrations of 22:1n9 also were decreased when estrogen was administered alone. These changes in 22:1n9 concentrations in specific lipid classes were reflected in the total plasma pool which was higher in the estrogen plus TCDD and TCDD groups.
The plasma concentration of n-6 fatty acids was increased in phospholipids, triacylglycerides, cholesterol esters and overall in the TCDD group. The phospholipid concentrations of 18:2n6, 20:2n6, and 20:3n6 were increased in the TCDD group, however, the concentration of 20:4n6 was highest in the estrogen group. In free fatty acids, the concentration of 20:2n6 was decreased in the estrogen plus TCDD group, while the concentration of 20:4n6 was increased with estrogen treatment. The triacylglycerides and cholesterol esters of the TCDD group had increased concentrations of 18:2n6, 20:2n6, 20:3n6, whereas the combination of estrogen plus TCDD only increased the cholesterol ester concentration of 20:3n6. Estrogen treatment alone reduced the cholesterol ester concentration of 20:2n6. Finally the total plasma concentrations of 18:2n6, 20:2n6, 20:3n6 were increased in the TCDD group but the concentrations of 20:4n6 were maintained in the TCDD group and increased in the estrogen group. Estrogen treatment alone increased the total plasma and phospholipid concentrations of n-3 fatty acids while TCDD increased concentrations of this fatty acid family, and particularly 18:3n3, in the triacylglyceride fraction. In phospholipids, the concentrations of 20:4n3 and 20:5n3 were increased in the TCDD group, the concentration of 22:5n3 was lower in the estrogen plus TCDD group, and 22:6n3 was highest with estrogen treatment alone. The concentration of 22:6n3 was again elevated in free fatty acids, cholesterol esters and triacylglycerides of the estrogen group. For cholesterol esters, the TCDD group had higher concentrations of 18:3n3 and 20:5n3 while the estrogen plus TCDD group had more 20:4n3. Overall, 20:5n3 concentrations were increased in the TCDD group, 22:5n3 was decreased in the estrogen plus TCDD group, and 22:6n3 was increased in the estrogen group.
Future Activities:We have applied for and been granted a no-cost extension to complete the mechanistic study and extend our observation to wildlife species. We will next determine if the adverse effects of TCDD-like compounds exert their adverse effect on reproduction by altering lipid metabolism. Specifically, we will test the hypothesis that the ability of TCDD to completely block specific key enzymes, prevents yolk formation in mature females. If this hypothesis is true, then a more generalized hypothesis can be generated to explain the difference observed between mammalian and avian species.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
|Other project views:||All 7 publications||4 publications in selected types||All 4 journal articles|
||Stanton B, Watkins S, German JB, Lasley B. Interaction of estrogen and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) with hepatic fatty acid synthesis and metabolism of male chickens (Gallus domesticus). Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology 2001;129(2):137-150.||