2,3,7,8-tetrachlorodibenzo-p-dioxin reduces myocardial hypoxia and vascular endothelial growth factor expression during chick embryo development.
BACKGROUND
Previous research has demonstrated that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces cardiomyocyte growth arrest, thinner ventricle walls, and reduced number and size of coronary arteries during chick embryogenesis. Coronary vascular development is believed to be mediated, in part, by myocardial oxygen gradients and a subsequent increase in hypoxia-inducible factor 1alpha (HIF-1alpha) and vascular endothelial growth factor-A (VEGF-A) expression. We investigated whether TCDD inhibition of coronary development was associated with altered myocardial oxygen status and reduced cardiac HIF-1alpha and VEGF-A.


METHODS
Chick embryos were exposed to 15% or 20% O2 for 24 hr from incubation days 9-10 or were injected with control (corn oil) or 0.24 pmol TCDD/gm egg on day 0. On day 9, embryos were injected with control (0.9% NaCl) or EF5, a tissue hypoxia marker, and cardiac binding of EF5 was determined by immunohistochemistry on day 10. In addition, embryo hearts were analyzed for VEGF-A mRNA by in situ hybridization and quantitative RT-PCR, and for HIF-1alpha mRNA by quantitative RT-PCR.


RESULTS
Cardiac binding of EF5 was significantly increased in embryos exposed to 15% O2, compared to embryos exposed to 20% O2. In contrast, TCDD-exposed embryos exhibited significantly reduced binding of EF5 in the heart, compared to controls. Similarly, cardiac expression of HIF-1alpha and VEGF-A were increased following hypoxia and tended to be decreased following TCDD exposure.


CONCLUSIONS
These results suggest that the myocardium may be a target of TCDD toxicity, resulting in reduced myocardial hypoxia, and HIF-1alpha and VEGF-A expression believed necessary for normal coronary development.
College of Pharmacy, University of New Mexico Health Sciences Center, Albuquerque, New Mexico 87131, USA.
Irena D
ID
Ivnitski-Steele
Andrea
A
Sanchez
Mary K
MK
Walker
D000818:Animals; D015687:Cell Hypoxia / Q000187:drug effects*; D002642:Chick Embryo; D004785:Environmental Pollutants / Q000494:pharmacology / Q000633:toxicity; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000378:metabolism; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology* / Q000633:toxicity; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics*
D004785:Environmental Pollutants; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D014157:Transcription Factors; D042461:Vascular Endothelial Growth Factor A