Norgestrel Causes Oxidative Damage to the Digestive Gland of the Clam Mactra Veneriformis: Insights from Proteomics, Ultrastructure, and Biochemical Analyses

Abstract

Increasingly, progestins are being detected in aquatic environments, especially in aquaculture areas, and concern about their adverse effects on aquatic organisms is growing. However, the mechanisms underlying progestin-induced oxidative stress and the antioxidant response of aquatic invertebrates to progestin exposure are unknown. Researchers recently reported that norgestrel (NGT) likely causes oxidative stress in the clam Mactra veneriformis. In this study, we assessed reactive oxygen species (ROS) levels, antioxidant enzyme activity, malonaldehyde content, ultrastructure, and DNA damage in the digestive gland of M. veneriformis exposed to 10 or 1000 ng/L of NGT for 21 days. We also conducted tandem mass tag-based quantitative proteomic analysis to detect the protein response and gain insights into response mechanisms in clams exposed to NGT. We found that NGT enhanced oxidative phosphorylation via the wingless/integrated signaling pathway and triggered ROS generation. The alterations of antioxidant enzyme activities suggested that these enzymes are involved in scavenging NGT-induced ROS. NGT weakened antioxidant defense by suppressing the antioxidant synthesis-related AMP-activated protein kinase/forkhead box O and sirtuin 1/forkhead box O pathways. Additionally, cell membrane dissolution, mitochondrial cristae rupture, DNA damage, elevation of malonaldehyde content, and oxidation of lipid, protein, and glucose occurred due to compromised redox homeostasis. Our results highlight the oxidative stress, antioxidant response, and oxidative damage induced by NGT in M. veneriformis and shed light on ecological risks of progestins to aquatic invertebrates.

Keywords: Antioxidant response, Mollusk, oxidative stress, Progestin, proteome