Dietary Exposure to 2,2′,4,4′-Tetrabromodiphenyl Ether (BDE-47) Causes Inflammation in the Liver of Common Carp (Cyprinus carpio) and Affects Lipid Metabolism by Interfering with Steroid Hormone Biosynthesis Pathways

2,2',4,4'-tetrabromodiphenyl ether (BDE-47) is a common environmental contaminant and widely detected in aquatic surroundings, while only a few reports exist on the hazard mechanism in economic aquatic animals. It has been shown that 40 and 4000 ng/g of BDE-47 dietary exposure over 42 days significantly increased the levels of blood triglycerides, glucose, and liver glycogen in carp (<i>Cyprinus carpio</i>). Tissue observations showed that BDE-47 resulted in vacuolation, atrophy, and fat deposition in hepatocytes. Combined metabolomic and transcriptomic analyses revealed that BDE-47 affected the inflammatory response and the biosynthesis of steroid hormones. This was further confirmed by gene expression related to inflammatory factors (<i>il-10</i>, <i>tnf-α</i>, <i>il-1β,</i> and <i>tgf-β1</i>), lipid metabolism (<i>acc</i>, <i>fas</i>, <i>srebp</i>, <i>rxr</i>, <i>atgl</i>, <i>hsl</i>, and <i>lpl</i>), and the steroid hormone biosynthetic pathway (<i>11bhsd</i>, <i>hsd3b</i>, and <i>star</i>). Thus, BDE-47 affects liver inflammatory response and lipid deposition through steroid hormone biosynthesis in carp. This helps us to understand how BDE-47 dietary exposure impacts inflammation and lipid metabolism in fish, which affects the health of aquaculture and has potential risks to human health.