Pyrethroids interfere with voltage-gated sodium channels essential for nervous system and cardiac muscle function. Further, they are suggested thyroid hormones (TH) disruptors with structural resemblance to triiodothyronine (T3) and thyroxine (T4). Previously, we found pyrethroid exposure in pregnancy to be associated with ADHD symptoms at 2-4 years-of-age in the large prospective Odense Child Cohort (OCC).
The objectives in the present study were to investigate if pyrethroids bind to the TH transporter protein transthyretin (TTR) and/or affect cardiomyocytes in vitro, and if maternal pregnancy THs was related to pyrethroid exposure, and whether prenatal and/or childhood exposure associate with neurodevelopment and blood pressure (BP) during childhood.
The results suggested that 3-PBA, but none of the parent compounds, bound to TTR at low concentrations (>1.6 µM). All three tested pyrethroids, but not 3-PBA, impaired cardiomyocyte differentiation in the low micromolar range. 3-PBA was detectable in most OCC-samples and associated with higher non-protein bound T3 (fT3) in early pregnancy. No associations between maternal 3-PBA and risk of autism symptoms at age 2-4 years, ADHD symptoms at 5 years, or reduced cognitive function (IQ) at 7 years were seen. Further, child 3-PBA was not associated with ADHD symptoms at 5 years or IQ-scores at 7 years. No associations between 3-PBA and BP were seen.
The results support that pyrethroids have TH disruptive and cardiotoxic properties. The association between 3-PBA and fT3 among pregnant women is of concern. Lack of associations between 3-PBA and child health outcomes might be attributable to a widespread low exposure.