Comparative analysis of Seabuckthorn and its significant component in enhancing fish mucosal immunity

Abstract

Seabuckthorn and its significant component, gallic acid, were found to alleviate foodborne enteritis in zebrafish, a model species. To investigate the protective effects on mucosal immunity in cultured fish, seabuckthorn or gallic acid was added to soybean meal feed in a study conducted on juvenile grass carp. After a 5-week feeding trial, histopathology, enteritis-related gene expression, transcriptomics, and 16S rRNA gene sequencing were performed on the hindgut and liver tissues. The results showed that dietary inclusion of seabuckthorn (9.5 g/kg) or gallic acid (1.2 g/kg) prevented enteritis, evidenced by an increase in intestinal villi length and a decrease in goblet cell numbers. The gallic acid group showed benefits in preserving villi length, while seabuckthorn was advantageous in controlling goblet cells. On the molecular level, downregulation of pro-inflammatory genes and upregulation of anti-inflammatory genes were observed. Specifically, seabuckthorn was more effective in controlling cytokine expression, while gallic acid better protected the epithelial barrier function. Omics analysis revealed an upregulated hepatic “PPAR signaling pathway” in the seabuckthorn group and downregulated intestinal “platelet activation” in the gallic acid group, suggesting reduced inflammation and improved immune homeostasis. Regarding intestinal microbiota, both groups showed reduced pathogenic Campilobacterota and Aeromonas, and increased Bacteroides and Cetobacteria, potentially enhancing mucosal immunity. For anti-inflammatory processes, hepatic “fatty acid degradation”, “tryptophan metabolism”, and “FoxO signaling pathway” were elevated only in the seabuckthorn group. Gallic acid was advantaged with more “mitophagy” and “autophagy”. Fish-fed seabuckthorn or gallic acid were challenged with Aeromonas hydrophila to assess impacts on other mucosal surfaces. In the gill, compared to the soybean meal group, significantly higher survival rates, reduced CD4 inflammatory signals, and increased filament space were observed. Comparing seabuckthorn with its active component, seabuckthorn performed better in lipid metabolism, resistance to A. hydrophila, anti-inflammation, and probiotic abundance, while gallic acid mainly showed benefits for mucosal barrier protection, such as increased gill filament space. In summary, seabuckthorn and gallic acid improved mucosal immunity in fish, particularly in the gut and gills, enhancing resistance to bacterial infection and foodborne inflammation. Thus, gallic acid and seabuckthorn may be optimal phytotherapy choices in aquaculture.