The Inuit population of Nunavik (Northern Quebec, Canada) is highly exposed to 
persistent organic pollutants (POPs) through their traditional diet. Some POPs, 
i.e., hydroxylated metabolites of polychlorinated biphenyls (OH-PCBs), 
pentachlorophenol (PCP), and perfluorooctane sulfonate (PFOS), compete with 
thyroxin (T4) for binding sites on transthyretin (TTR), a T4 transport protein 
found in plasma and cerebrospinal fluid. We tested the hypothesis that these 
TTR-binding compounds decrease circulating concentrations of T4 bound to TTR 
(T4-TTR) in Inuit women of reproductive age. We measured the concentration of 
T4-TTR in plasma samples obtained from 120 Inuit women (18-39 years old) by 
combining native-polyacrylamide gel electrophoresis and liquid 
chromatography-tandem mass spectrometry (LC-MS/MS) techniques. Total T4, TTR, 
and thyroxin-binding globulin (TBG) concentrations were also determined, while 
POPs levels had been previously measured. The mean T4-TTR concentration was 8.4 
nmol/L (SD = 2.4) with values ranging from 2.9 to 14.4 nmol/L. Linear regression 
analysis revealed that TTR, TBG, and total T4 concentrations were significant 
predictors (p < 0.002) of T4-TTR levels (total adjusted R-squared = 0.26, p < 
0.0001) but not levels of OH-PCBs, chlorophenols, or PFOS. Our results suggest 
that circulating levels of these TTR-binding compounds in Inuit women of 
childbearing age are not high enough to affect TTR-mediated thyroid hormone 
transport. The possibility of increased delivery of these compounds to the 
developing brain requires further investigation.