Effects of butyrate feed supplementation on gilthead sea bream (Sparus aurata) growth performance and intestinal health: A transcriptomic approach

Abstract

The aim of the present study was to evaluate the effects of a short fatty acid, the commercial butyrate product (BP-70, ®Norel), on gilthead sea bream performance and intestinal health. Juvenile fish of 25 g initial body weight were distributed in 90-L triplicate tanks/group (15 fish/tank). Fish were fed plant protein-based diets with 20% fish meal and 35% plant oil at the expense of fish oil, and with increasing levels of BP-70 (0%, 0.2%, 0.4%, 0.8%) for 9 weeks. No significant effects of butyrate supplementation were found on growth rates, feed conversion ratio, or retention of N and lipids. No effects were found on hepatosomatic index or viscerosomatic index, but the gut index (fish weight/intestine length) was progressively and significantly increased with butyrate supplementation. Butyrate also increased plasma glucose levels and liver glycogen depots, which highly supports a sparing effect of butyrate on the utilization of glucose as a metabolic fuel. A PCR-array of 90 genes was used to characterize the intestinal gene expression pattern of the two extreme groups (0%, 0.8% diets). Genes were selected as markers of intestine cell proliferation and differentiation, intestinal architecture and permeability, enterocyte mass and epithelia damage, intestinal immune-surveillance and mitochondria activity. The differentially expressed genes of all these categories showed that butyrate supplementation clearly induced a healthy intestine condition. In particular, components of the Hedgehog, bone morphogenic protein and Notch signalling pathways were up-regulated in butyrate treated fish, which would orchestrate a complex regulatory network promoting intestine cell differentiation rather than stem cell proliferation. This agrees with the lowered expression of the proliferating cell nuclear antigen (PCNA), as evidenced by RT-PCR and immunocytochemistry. Butyrate also improved the intestine barrier function, up-regulating the expression of several components of tight junctions (occludin, claudin 12, claudin 15, tight junction protein ZO-1, and coxsackievirus and adenovirus receptor homolog), and altered the expression of nuclear-encoded mitochondrial genes, up regulating the expression of master transcription factors, mitochondrial protein translocases and oxidative enzymes of the tricarboxylic acid cycle, and down-regulated the expression of mitochondrial molecular chaperones of the Hsp 10 family. This expression pattern is indicative of a mitochondrial phenotype with a ¿high power¿ activity and a low risk of oxidative stress. In addition, butyrate supplementation altered the expression of interleukin 7, nucleotide-binding protein oligomerization domain-containing protein 1, vimentin, macrophage mannose receptor 1 and C-C motif chemokine 20, leading to an anti-inflammatory gene expression pattern. Therefore, butyrate supplementation as a whole is a very promising approach to improve the health condition of gilthead sea bream intestine.