In ovo effects of perfluorohexane sulfonate and perfluorohexanoate on pipping success, development, mRNA expression, and thyroid hormone levels in chicken embryos.

Perfluoroalkyl acids (PFAAs), specifically perfluorinated sulfonates and carboxylates, are synthetic substances known for their chemical stability, resistance to degradation, and potential to biomagnify in food chains. The toxicological and biological effects of PFAAs in avian species are not well characterized, although there is some evidence to suggest that they can impact neurodevelopment and hatching success. Our laboratory recently reported significant effects of perfluorohexane sulfonate (PFHxS) and perfluorohexanoate (PFHxA) on messenger RNA (mRNA) levels of thyroid hormone (TH)-responsive genes in chicken embryonic neuronal cells. In this study, we determined in ovo effects of PFHxS and PFHxA exposure (maximum dose = 38,000 and 9700 ng/g egg, respectively) on embryonic death, developmental endpoints, tissue accumulation, mRNA expression in liver and cerebral cortex, and plasma TH levels. Pipping success was reduced to 63% at the highest dose of PFHxS; no effects were observed for PFHxA. PFHxS exposure (38,000 ng/g) decreased tarsus length and embryo mass. PFHxS and PFHxA accumulated in the three tissue compartments analyzed as follows: yolk sac > liver > cerebral cortex. Type II and type III 5'-deiodinases (D2 and D3) and cytochrome P450 3A37 mRNA levels were induced in liver tissue of chicken embryos exposed to PFHxS, whereas D2, neurogranin (RC3), and octamer motif binding factor 1 mRNA levels were upregulated in cerebral cortex. Plasma TH levels were reduced in a concentration-dependent manner following PFHxS exposure; PFHxA had no effect. This in ovo study successfully validated previous in vitro results concerning the modulation of TH-responsive genes and identified adverse effects associated with TH homeostasis in response to PFHxS treatment.