Thyroid endocrine system disruption by pentachlorophenol: An in vitro and in vivo assay

• T-Screen assay was performed to test the thyroid endocrine disrupting activity of PCP in vitro.
• PCP exhibited T3-antagonist activity in the T-Screen assay.
• Zebrafish larvae from embryos exposed to PCP showed changes in T4 and T3 levels.
• Modulation of gene transcription in the hypothalamic–pituitary–thyroid-axis was examined.
• PCP disrupted the thyroid endocrine system in vitro and in vivo.

The present study aimed to evaluate the disruption caused to the thyroid endocrine system by pentachlorophenol (PCP) using in vitro and in vivo assays. In the in vitro assay, rat pituitary GH3 cells were exposed to 0, 0.1, 0.3, and 1.0 μM PCP. PCP exposure significantly downregulated basal and triiodothyronine (T3)-induced Dio 1 transcription, indicating the antagonistic activity of PCP in vitro. In the in vivo assay, zebrafish embryos were exposed to 0, 1, 3, and 10 μg/L of PCP until 14 days post-fertilization. PCP exposure resulted in decreased thyroxine (T4) levels, but elevated contents of whole-body T3. PCP exposure significantly upregulated the mRNA expression of genes along hypothalamic–pituitary–thyroid (HPT) axis, including those encoding thyroid-stimulating hormone, sodium/iodide symporter, thyroglobulin, Dio 1 and Dio 2, alpha and beta thyroid hormone receptor, and uridinediphosphate-glucuronosyl-transferase. PCP exposure did not influence the transcription of the transthyretin (TTR) gene. The results indicate that PCP potentially disrupts the thyroid endocrine system both in vitro and in vivo.