LAUSR

Progestins, such as norethindrone (NET), have been increasingly detected in aquatic environments due to their extensive use for medical applications. While NET is notorious for its endocrine disrupting effects, it has been recently shown to cause cellular damage, suggesting its potential impacts on the body defence of organisms. Hence, we examined the histological features and antioxidant defence of zebrafish (Danio rerio) after exposing to NET (50 ng/L and 500 ng/L) for 72 days, followed by analysing its metabolome to explore whether NET disturbs the metabolic processes responsible for antioxidant defence. While acute mortality was not triggered, we found that antioxidant defence was substantially weakened by NET at 500 ng/L (i.e. reduced SOD and GSH levels) and hence liver injury was inflicted (i.e. elevated ALT and MDA levels), as manifested by vacuolization of liver tissues and reduced number of normal cells in the liver. Metabolomic analysis showed that the metabolic processes responsible for antioxidant defence were disrupted by NET (e.g. upregulation of nervonyl carnitine and chenodeoxycholic acid 3-sulfate; downregulation of homolanthionine and acevaltrate) and these changes can undermine antioxidant defence by suppressing Nrf2-ARE and NF-κB pathways that contribute to the synthesis of SOD and GSH. This study demonstrates how NET can compromise the body defence of aquatic organisms via metabolic disruption, suggesting that the impacts of progestins on their fitness are more detrimental than previously thought.