Effects of dietary supplementation of different ratios of koumine and gelsemin on the liver immunity of common carp (Cyprinus carpio, FFRC)

Abstract

Gelsemium elegans Benth. (GEB) exhibits immunoregulatory and growth-promoting effects in animals. However, owing to its complex composition, the specific mechanism remains to be explored. Koumine (KM) and gelsemine (GS) are the two alkaloids with the highest content and strongest biological activity in GEB. In this experiment, four ratios (0,0 mg/kg, 2,2 mg/kg, 2,1 mg/kg, and 2:0.67 mg/kg) of KM: GS from natural GEB were incorporated into the diet of common carp (Cyprinus carpio, FFRC). A 10-week breeding experiment was conducted to explore the immune and metabolic effects of these different KM and GS ratios on the liver of C. carpio, analyzing histology, antioxidant enzyme activity, immune gene expression, and transcriptomics. Hepatocyte edema and apoptosis were observed in the treatment groups. Acid phosphatase activity in the treatment group was significantly higher than that in the control group (P < 0.05), and malondialdehyde activity was lower (P < 0.05) in the treatment group, demonstrating a dose effect of GS. Superoxide dismutase and total antioxidant capacity activities increased gradually with a decreasing GS ratio (P < 0.05). Compared to the control group, changes in the GS ratio regulated the expression of immune genes. The relative expression of CYP1B1, TNF-β, and Myd-88 increased with decreasing GS ratio in the combination. Conversely, the relative expression of CYP1A1, TNF-α, GPX, IGF1, GST, and TLR-2 decreased with decreasing GS ratio in the combination. A total of 81.33 GB of clean data, 1370 DEGs, and 9258 co-expressed genes were obtained from the transcriptome data. These coexpressed genes were grouped into 244 KEGG pathways. Non-alcoholic fatty liver disease, Fatty acid degradation, Oxidative phosphorylation, and the PPAR signaling pathway were among the most abundant signaling pathways identified. This information contributes to a better understanding of the underlying mechanisms of KM and GS on liver immunity and lays a theoretical foundation for their application.