Alginate oligosaccharide improves fat metabolism and antioxidant capacity in the liver of grass carp (Ctenopharyngodon idellus)

Abstract

The aim of the current study was to investigate the potentially beneficial effects of alginate oligosaccharide (AOS) on the modulation of growth, fatty acid metabolism, and antioxidant capacity in grass carp (Ctenopharyngodon idellus), and the fundamental mechanisms involved. AOS enhanced the growth performance of grass carp in a dose-dependent manner. Histopathological analysis revealed that AOS had a protective effect in the liver and head kidney when changed by Aeromonas hydrophila, and that it could also reduce fat accumulation in the liver. In order to identify the mechanisms of action of AOS, transcriptomic profiling was performed in control fish fed a normal diet, and groups of fish fed 5 g/kg, 10 g/kg, or 20 g/kg of AOS. A total of 21,836 known genes and 818 novel genes were obtained, and higher dosages of AOS were associated with more differentially expressed genes (DEGs). Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated that all three dosages of AOS activated fatty metabolism-related pathways. To further elucidate the transcriptomic data, expression levels of the six fatty metabolism-related genes Apoa 1, Apoa 4, Agpat 1, DGAT, MGAT, and ABCG 5 were determined. All six genes were activated by AOS. Antioxidant capacities were detected after 6 weeks on a diet containing AOS, including superoxide dismutase, glutathione peroxidase, and catalase. These results suggested that dietary AOS improves the liver's antioxidant capacity. Lastly, lipase, triglyceride, and malondialdehyde data showed that AOS could enhance lipase activity and reduce fat accumulation in the liver, lower residual malondialdehyde in the liver, and reduce apoptosis in the liver. The present study suggests that AOS can enhance growth performance, promote fat metabolism, and improve antioxidant capacity in the liver in grass carp. AOS can be beneficial as a dietary supplement in grass carp, particularly within the aquaculture industry.