Effects of dietary plant meal and soya-saponin supplementation on intestinal and hepatic lipid droplet accumulation and lipoprotein and sterol metabolism in Atlantic salmon (Salmo salarL.)

Abstract

Altered lipid metabolism has been shown in fish fed plant protein sources. The present study aimed to gain further insights into how intestinal and hepatic lipid absorption and metabolism are modulated by plant meal (PM) and soya-saponin (SA) inclusion in salmon feed. Post-smolt Atlantic salmon were fed for 10 weeks one of four diets based on fishmeal or PM, with or without 10 g/kg SA. PM inclusion resulted in decreased growth performance, excessive lipid droplet accumulation in the pyloric caeca and liver, and reduced plasma cholesterol levels. Intestinal and hepatic gene expression profiling revealed an up-regulation of the expression of genes involved in lipid absorption and lipoprotein (LP) synthesis (apo, fatty acid transporters, microsomal TAG transfer protein, acyl-CoA cholesterol acyltransferase, choline kinase and choline-phosphate cytidylyltransferase A), cholesterol synthesis (3-hydroxy-3-methylglutaryl-CoA reductase) and associated transcription factors (sterol regulatory element-binding protein 2 and PPARg). SA inclusion resulted in reduced body pools of cholesterol and bile salts. The hepatic gene expression of the rate-limiting enzyme in bile acid biosynthesis (cytochrome P450 7A1 (cyp7a1)) as well as the transcription factor liver X receptor and the bile acid transporter abcb11 (ATP-binding cassette B11) was down-regulated by SA inclusion. A significant interaction was observed between PM inclusion and SA inclusion for plasma cholesterol levels. In conclusion, gene expression profiling suggested that the capacity for LP assembly and cholesterol synthesis was up-regulated by PM exposure, probably as a compensatory mechanism for excessive lipid droplet accumulation and reduced plasma cholesterol levels. SA inclusion had hypocholesterolaemic effects on Atlantic salmon, accompanied by decreased bile salt metabolism.

Use of Potato Starch in Diets of Tropical Gar (Atractosteus tropicus, Gill 1863) Larvae

“…Previous studies indicate that the use of carbohydrates in formulations depends on the type and concentration included, the fish species and growing conditions, which can promote greater digestibility, improving the level of food intake and consequently growth and larval survival [4,10]. Prior studies of A. tropicus larvae using diets based on rendered proteins (poultry byproduct and pork), showed higher growth and survival than results of the present study.…”

“…Digestive physiology is important to determine the type and amount of nutrients that the body is able to digest and absorb [10]; thus, digestive and absorptive capabilities play an important role influencing the growth of fish [17]. The activities of digestive enzymes play an important role in determining the ability of an animal to obtain nutrients from a particular food sourced [15].…”

Gene regulation of lipid and phospholipid metabolism in Atlantic cod (Gadus morhua) larvae

“…Gu and co-authors suggested that up-regulation of the capability for lipoprotein assembly acted as a compensatory mechanism to transport excessive lipid droplets that accumulated in pyloric caeca and liver (Gu et al, 2014). In the present study, both apoB and apoAI showed significant up-regulation at 17 dph, and apoAI were also significantly upregulated at 13 dph and 60 dph, suggesting that elevated lipoprotein assembly might have occurred at these stages.…”

“…Another recent study showed that both chk and pcyt1a, together with lipoprotein assembly related genes (mttp, apoB, apoAI and apoAIV), were up-regulated in pyloric caeca of post-smolt Atlantic salmon fed plant (lupin) meal compared to that of fish fed fish meal (Gu et al, 2014). Gu and co-authors suggested that up-regulation of the capability for lipoprotein assembly acted as a compensatory mechanism to transport excessive lipid droplets that accumulated in pyloric caeca and liver (Gu et al, 2014).…”

Evaluation of the distribution of adipose tissues in fish using magnetic resonance imaging (MRI)

“…At present, the technical approaches commonly used to determine fat in fish metabolic studies are: 1) chemical measurement of the quantity of lipid in whole fish or tissues by organic solvent extraction (Folch et al, 1957) and 2) observation or measurement of stained lipid droplets in tissue slices using histological methods (Gu et al, 2014). However, the size, shape, quantities and distribution of adipose tissue vary greatly among fish species and neither of these methods provides overall information of adipose tissues in intact fish, particularly in large fish.…”