Vegetable lipid sourcesin vitrobiosyntheis of triacylglycerols and phospholipids in the intestine of sea bream(Sparus aurata)

Abstract

Despite the good growth performance of several fish species when dietary fish oil is partly replaced by vegetable oils, recent studies have reported several types of intestinal morphological alterations in cultured fish fed high contents of vegetable lipid sources. However, the physiological process implied in these morphological changes have not been clarified yet, since alterations in the physiological mechanisms involved in the different processes of lipid absorption could be responsible for such gut morphological features. The objective of the present study was to investigate the activities of reacylation pathways in fish, the glycerol-3-phosphate and the monoacylglycerol pathways, in order to clarify the intestinal triacylglycerol (TAG) and phospholipid biosynthesis to better understand the morphological alterations observed in the intestine of fish fed vegetable oils. Intestinal microsomes of sea bream fed different lipid sources (fish, soyabean and rapeseed oils) at three different inclusion levels were isolated and incubated with L-[ 14 C(U)]glycerol-3-phosphate and [1-14 C]palmitoyl CoA. The results showed that in this fish species the glycerol-3-phosphate pathway is mainly involved in phospholipid synthesis, whereas TAG synthesis is mainly mediated by the monoacylglycerol pathway. Feeding with rapeseed oil reduced the reacylation activity in both pathways, explaining the high accumulation of lipid droplets in the supranuclear portion of the intestinal epithelium, whereas soyabean oil enhanced phosphatidylcholine synthesis, being associated with the increase in VLDL found in previous studies.

Fish larval nutrition and feed formulation: knowledge gaps and bottlenecks for advances in larval rearing

“…Deplano et al. (1991) and Caballero et al. (2002, 2006a) isolating enterocyte microsomes demonstrated that in gilthead seabream, PL synthesis occurs mainly through the glycerol‐3‐phosphate pathway, whose activity is modulated through dietary lipids.…”

Potential of three new krill products for seabream larval production

“…The incorporation of 18:2n-6 into PLs as a substitution of EPA and DHA could produce an insu⁄cient PL synthesis rate or an impaired function of the enterocyte membrane and its integrity (Caballero et al 2003(Caballero et al , 2006a. The physiological signi¢cance of this gut morphological feature could be the result of a reduction in the renovation rate of the enterocytes in ¢sh fed with PLs rich in 18:2n-6 in comparison with the n-3 HUFA-rich enterocytes.…”

Hydrolysis of Acyl‐Homogeneous and Fish Oil Triacylglycerols Using Desalted Midgut Extract from Atlantic Salmon, Salmo salar

“…In order to accomplish this, fish require an efficient system for the intestinal digestion of TAG for absorption across the brush border membrane (BBM) and subsequent resynthesis of hydrolytic products in enterocytes for transportation. The MAG pathway has recently been established as the predominant pathway for TAG resynthesis in the intestine of Atlantic salmon [13,14] and sea bream [15], which challenges the presence of a non-specific bile salt-dependent lipase (BSDL) as the major lipolytic enzyme of the luminal content in fish. There is a general assumption that BSDL does not discriminate towards sn-acyl position on the glycerol 'backbone' of TAG thus yielding glycerol and FFAs that must be resynthesized by the slower and more energetically-consuming glycerol-3-phosphate (G3P) pathway in enterocytes [6].…”

“…Recent reports have however, shown the existence of MGAT in both Atlantic salmon [13,14] and seabream, Sparus aurata [15], which is most likely required for a fast and efficient transfer of absorbed intestinal lipid to the blood as lipoproteins. This again indicates that the hydrolysis of luminal TAG may proceed through sn-1,3-specificity.…”