THE EFFECTS OF TRICHLOROETHYLENE ON HEART DEVELOPMENT

Abstract

Trichloroethylene (TCE; TRI; C2HCl3) is an organic solvent used as an industrial degreasing agent. Due to its widespread use and volatile nature, TCE is a common environmental contaminant. Trichloroethylene exposure has been implicated in the etiology of heart defects in human populations and animal models. Recent data suggest misregulation of Ca2+ homeostasis in a cardiomyocyte cell line after TCE exposure (Caldwell, Thorne et al. 2008). We hypothesized that misregulation of Ca2+ homeostasis alters myocyte function and leads to changes in embryonic blood flow. In turn, changes in cardiac flow are known to cause cardiac malformations. To investigate this hypothesis we dosed developing chick embryos in ovo with environmentally relevant doses of TCE (8 ppb and 800 ppb). We then isolated RNA from embryos at crucial time points in development for real-time PCR analysis of markers for altered blood flow. Based on this analysis, we observed effects on ET-1 (Endothelin-1), NOS-3 (Nitric Oxide Synthase-3) and Krüppel-Like Factor 2 (KLF2) expression relative to TCE exposure. Additionally, we assessed cardiomyocyte function by isolating chick E18 cardiomyocytes from embryos exposed to TCE in ovo. Cells were measured for rate of contraction after pulsing with extracellular Ca2+ and electrical stimulation at a frequency of 1.0 Hz. These functional data showed an effect on Ca2+ handling in cardiomyocytes exposed to TCE. To investigate an apparent non-monotypic effect in the heart where 8 ppb produced a stronger effect than 800 ppb, we isolated RNA from the developing heart and AV Canal to investigate the expression of several candidate Cytochrome P450s (CYPs) related to TCE metabolism. We observed a significant induction of multiple CYP2 family members in the developing heart after low dose TCE exposure. Together, these data suggest cardio-specificity of TCE as a teratogen and may reflect a requirement for normal calcium regulation of contractile function during organ development.