Integrated physiological, energy metabolism, and metabonomic responses indicate the stress response in the hepatopancreas of Litopenaeus vannamei to nitrite stress.

Nitrite is a toxic substance found in rearing water that affects shrimp health. The hepatopancreas is an important digestive, immune, and metabolic organ in the shrimp. In this study, shrimps (Litopenaeus vannamei) were separately exposed to 1 and 5 mg/L nitrite stress for 48 h, and the toxicity of nitrite in the hepatopancreas was explored by integrating histology, physiological indicators, energy metabolism, and metabolomics. Nitrite stress induced morphological changes and stress responses in the hepatopancreas. Specifically, physiology-related indices, such as the relative gene expression levels of antioxidants (ROMO1, Nrf2, GPx), endoplasmic reticulum stress (Bip, IRE1 and XBP1), and immune genes (ALF, Pen-3, Lys) were decreased, whereas the gene expression of apoptosis (Casp-3), detoxification (CYP450), and glutamic oxaloacetic transaminase (GOT) activity were increased. The activities of osmotic adjustment-related enzymes (NKA, CMA, and ATPase) also decreased. Energy metabolism-related indices, such as pyruvate and hepatic glycogen contents, increased, whereas glucose, lactic acid, triglyceride, and ATP contents and ATPase activity decreased, and the relative gene expression levels of carbohydrate metabolism (PDH, HK, and LDH) and electron-transport chain genes (CytC, COI and CCO) decreased, and the expressions of lipid metabolism (AMPK, SREBP, and FAS), tricarboxylic acid cycle (MDH, CS, IDH and FH) genes were also disturbed. The metabolic pattern of the hepatopancreas was affected by nitrite stress. Glycine, serine, and threonine metabolism were highly affected, and more functional amino acids varied in the 5 mg/L nitrite stress group. These results reveal the toxic effects of nitrite stress on the stress response, physiology, energy metabolism, and metabolite homeostasis in the hepatopancreas of shrimp. Several potential metabolite biomarker candidates were identified for toxicological evaluation.