Neonatal Persistent Exposure to 6‐Propyl‐2‐thiouracil,a Thyroid‐Disrupting Chemical,Differentially Modulates Expression of Hepatic Catalase and C/EBP‐β in Adult Rats

Persistent exposure of rats to 6‐propyl‐2‐thiouracil (PTU) from birth resulted in decreases in plasma thyroid hormone (TH) levels and hepatic expression of catalase and CCAAT enhancer binding protein β (C/EBP‐β). Catalase promoter region (–185 to +52) that contains binding sites for C/EBP‐β showed an augmentation in the methylation level along with a change in methylation pattern of CpG islands in response to PTU treatment. PTU withdrawal on 30 days of birth restored TH levels and C/EBP‐β to control rats in adulthood. Although catalase expression was restored to some extent in adult rats in response to PTU withdrawal, a permanent change in its promoter CpG methylation pattern was recorded. The results suggest that downregulation of adult hepatic catalase gene in response to persistent neonatal PTU exposure may not solely be attributed to thyroid‐disrupting properties of PTU. It is possible that besides thyroid‐disrupting behavior, PTU may impair expression of hepatic catalase by altering methylation pattern of its promoter.