Seabuckthorn amiliated the foodborne pathology in fish gut-liver axis (Image by IHB) 

Fish intestinal mucosa is an active interface between the body and the outside world. The mucosal immune system plays the dual functions of shielding pathogens and assisting nutrient absorption. At immune aspect, liver and intestinal mucosa constitute the gut-liver axis in fish. The enteritis caused by feeds is often accompanied by hepatic inflammation in cultured fish. Therefore, it has been imperative to conduct research into drugs, discovery methods and evaluation systems to treat fish intestinal and hepatic inflammation.   

In a study published online in Frontiers in Physiology, a research team led by Prof. XIA Xiaoqin at Institute of Hydrobiology (IHB), Chinese Academy of Sciences, revealed that dietary seabuckthorn supplementation might be important in mitigating fish foodborne entities through the gut-liver immune axis.    

Based on the grass carp’s intestinal and hepatic transcriptome data during soybean meal induced enteritis (SBMIE), the researchers obtained the potential drug for fish intestinal and hepatic inflammation through bioinformatic prediction via TCMID (traditional Chinese medicines integrated database).    

By comprehensively analyzing the expression level of differentially expressed genes (DEGs) and protein interaction network (PPI), the researchers used gene-rank algorithm to sort the target genes according to their importance, and selected the top 300 genes to construct the list of key genes.    

Then, they matched the target compounds corresponding to the key genes to TCMID to obtain the traditional Chinese medicine with certain corresponding herbal components. Considering the active components of traditional Chinese medicine and its pharmacology, the potential drug, seabuckthorn (Hippophae rhamnoides L), was predicted.    

The researchers subsequently added seabuckthorn to the feed to evaluate its anti-enterohepatitis effect in zebrafish foodborne enteritis model. Methods, such as immune gene expression analysis, immune cell imaging, pathology and growth evaluation, and multi-omics analysis (transcriptome and microbiome), have been applied to reveal the molecular immune mechanism of seabuckthorn against enterohepatitis.   

“In the zebrafish SBMIE model, we found that the addition of seabuckthorn fruit powder could significantly reduce the inflammatory reaction of intestinal mucosa and liver tissue. Pathologically, seabuckthorn fruit powder can improve intestinal villus atrophy caused by soybean meal feed and reduce the deposition of inflammation related fat particles in the liver,” said Dr. WU Nan, the corresponding author.    

On the other hand, the micro-CT data showed that the fat content of fish body increases significantly in seabuckthorn group, suggesting that dietary inclusion of seabuckthorn has reversed the decline of growth performance caused by soybean meal.    

Furthermore, in the SBMIE model of zebrafish larva, immunofluorescence imaging observation revealed seabuckthorn's immunomodulatory effect on innate immune cells (including neutrophils and macrophages) and adaptive immune cells (lymphocytes, especially T cells).    

“The number of neutrophils and macrophages was reduced in the hindgut, and the morphology of macrophages was changed upon the seabuckthorn’s inclusion, but we do not find the inflammatory aggregation of T lymphocytes in the hindgut in the larva,” said Dr. WU Nan. Correspondingly, inclusion of seabuckthorn could reduce the proportion of CD4 positive cells in liver of adult zebrafish SBMIE model.    

The KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway enrichment analysis of DEGs in transcriptomic data suggested that seabuckthorn could block the apoptosis related p53 signal in intestinal mucosa, in addition to activating the PPAR signal pathway in liver to regulate fatty acid metabolism.    

At the same time, the results of microbiome analysis demonstrated that in the seabuckthorn group, the OUT (operational taxonomic unit) richness of intestinal mucosa increased significantly, and the microbial composition was even similar to that in the non-inflammatory fish meal group, suggesting that seabuckthorn can also improve mucosa health by modulating the gut microbiota.   

This study suggests that seabuckthorn fruit powder, as a feed additive for fish, can prevent the intestinal and hepatic inflammation caused by feeds in aquaculture, and thus guarantee fish growth performance. It provides an example of comprehensive bioinformatic prediction of functional additives or drugs for aquatic feeds.  

(Editor: MA Yun)