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We evaluated the individual and combined effects of salinity and alkalinity on gill Na+/K+-ATPase enzyme activity, plasma ion concentration, and osmotic pressure in Luciobarbus capito. Increasing salinity concentrations (5, 8, 11, and 14 g/L) were associated with an initial increase and then decrease in L. capito gill Na+/K+-ATPase activity. Activity was affected by the difference between internal and external Na+ ion concentrations and osmotic pressure (P<0.05). Both plasma ion (Na+, K+, and Cl−) concentration and osmotic pressure increased significantly (P<0.05). An increase in alkalinity (15, 30, 45, and 60 mM) caused a significant increase in plasma K+ and urea nitrogen concentrations (P<0.05) but had no effect on either plasma osmotic pressure or gill filament ATPase activity. In the two-factor experiment, the saline-alkaline interaction caused a significant increase in plasma ion (Na+, Cl−, and urea nitrogen) and osmotic pressure (P<0.05). Variance analysis revealed that salinity, alkalinity, and their interaction significantly affected osmotic pressure, with salinity being most affected, followed by alkalinity, and their interaction. Gill filament ATPase activity increased at first and then decreased; peak values were observed in the orthogonal experiment group at a salinity of 8 g/L and alkalinity of 30 mM. [ABSTRACT FROM AUTHOR]

Introduction: High-alkalinity water is a serious health hazard for fish and can cause oxidative stress and metabolic dysregulation in fish livers. However, the molecular mechanism of liver damage caused by high alkalinity in fish is unclear., Methods: In this study, 180 carp were randomly divided into a control (C) group and a high-alkalinity (A25) group and were cultured for 56 days. High-alkalinity-induced liver injury was analysed using histopathological, whole-transcriptome, and metabolomic analyses., Results: Many autophagic bodies and abundant mitochondrial membrane damage were observed in the A25 group. High alkalinity decreased superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) activity and the total antioxidant capacity (T-AOC) and increased the malondialdehyde (MDA) content in liver tissues, causing oxidative stress in the liver. Transcriptome analysis revealed 61 differentially expressed microRNAs (miRNAs) and 4008 differentially expressed mRNAs. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that mammalian target of rapamycin (mTOR), forkhead box O (FoxO), mitogen-activated protein kinase (MAPK), and the autophagy signalling pathway were the molecular mechanisms involved. High alkalinity causes oxidative stress and autophagy and results in autophagic damage in the liver. Bioinformatic predictions indicated that Unc-51 Like Kinase 2 (ULK2) was a potential target gene for miR-140-5p, demonstrating that high alkalinity triggered autophagy through the miR-140-5p-ULK2 axis. Metabolomic analysis revealed that the concentrations of cortisol 21-sulfate and beta-aminopropionitrile were significantly increased, while those of creatine and uracil were significantly decreased., Discussion: The effects of high alkalinity on oxidative stress and autophagy injury in the liver were analysed using whole-transcriptome miRNA-mRNA networks and metabolomics approaches. Our study provides new insights into liver injury caused by highly alkaline water., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Shang, Geng, Wei, Liu, Che, Li, Liu, Shi, Li, Teng and Xu.)