Effect of conjugated linoleic acid on dietary lipids utilization, liver morphology and selected immune parameters in sea bass juveniles (Dicentrarchus labrax)

A combined in vivo and in vitro approach to evaluate the influence of linseed oil or sesame oil and their combination on innate immune competence and eicosanoid metabolism processes in common carp (Cyprinus carpio)

This study aimed to evaluate the influence of dietary pure linseed oil or sesame oil or a mixture on innate immune competence and eicosanoid metabolism in common carp (Cyprinus carpio). Carp of 100.4 ± 4.7 g were fed to satiation twice daily for 6 weeks with four diets prepared from three lipid sources (CLO; LO; SO; SLO). On day 42, plasma was sampled for immune parameter analyses, and kidney and liver tissues were dissected for gene expression analysis. On day 45, HKL and PBMCs from remaining fish were isolated and exposed to E. coli LPS at a dose of 10 μg/mL for 24 h. Results show that the SLO diet enhanced feed utilisation (P = 0.01), while no negative effects on growth or survival were observed in plant oil-fed fish compared to those fed a fish-oil based diet. Plant oil diets did not alter lysozyme and peroxidase activities or gene expression levels. Moreover, the diets did not affect the expression levels of some genes involved in eicosanoid metabolism processes (pla, pge2, lox5). Lys expression in HKL in vitro following exposure to LPS was up-regulated in LO-fed fish, while expression levels of pge2 were higher in SLO fish than in other groups (P < 0.05). The highest value for peroxidase activity in HKL exposed to LPS was found in the SLO-fed group (P < 0.05). In conclusion, our results indicate that dietary plant oils did not induce any negative effects on fish growth, survival, and immune competence status. Moreover, a dietary combination of SO and LO improved the feed utilisation efficiency and seemed more effective in inducing a better immunomodulatory response to LPS through a more active eicosanoid metabolism process.

Antiviral activity of palmitic acid via autophagic flux inhibition in zebrafish (Danio rerio)

Fatty acids (FAs) are key elements that affect not only growth but also different immune functions, and therefore, nutrition is important for growing healthy fish. Zebrafish (Danio rerio) is a good model for assessing the beneficial effects of immunostimulants, including FAs, before applying them in aquaculture. Accordingly, this study evaluated the effects of palmitic acid (PA) treatment on different immune parameters of zebrafish and on the mortality caused by the spring viremia of carp virus (SVCV). The results suggest that PA modulates the infection outcome in vivo, which benefits zebrafish and results in reduced mortality and viral titres. The antiviral protection elicited by this FA seems to be associated with the inhibition of autophagy and is independent of other immune processes, such as neutrophil proliferation or type I interferon (IFN) activity. The use of PA as an immunostimulant at low concentrations showed great potential in the prevention of SVCV infections; therefore, this FA could help to prevent the mortality and morbidity caused by viral agents in aquacultured fish. Nevertheless, the potentially detrimental effects of suppressing autophagy in the organism should be taken into account.

The mechanism of action of a fat regulator: Glycyrrhetinic acid (GA) stimulating fatty acid transmembrane and intracellular transport in blunt snout bream (Megalobrama amblycephala)

High-fat diets are associated with fatty liver and aberrant hepatic lipid metabolism, and glycyrrhetinic acid (GA) has been shown to exert a beneficial effect on lipolysis and fat deposition in fish. In the present study, we evaluated the effect of GA on the growth performance and expression of hepatic lipid transport related genes in blunt snout bream (Megalobrama amblycephala) fed a high fat diet. Two hundred and sixteen fish (average body weight: 45.57 g ± 0.98 g) were fed three experimental diets (6% fat/L6 group, control, 11% fat/L11 group, and 11% fat with 0.3 mg kg^-1 GA/L11GA group) for 8 weeks. Compared to the control group, the weight gain and specific growth rate of high-fat fed group at the end of the trialwere significantly improved (P < .05).However, GA showed no effect on animals' growth performance(P > .05). Dietary supplementation with 0.3 mg kg^-1 GA significantly decreased the hepatosomatic index, viscera/body ratio, and intraperitoneal fat ratio (P < .05), and up-regulated the expression levels of fatty acids transport protein (FATP), fatty acids binding protein (FABP), fatty acid translocase (CD36), carnitine palmitoyl transferase I (CPT1) and peroxisome proliferators-activated receptors α (PPARα) compared to both the L6 group and L11 group (P < .05). However, no significant difference was observed in fatty acid synthetase (FAS), acetyl-CoA carboxylase α (ACCα), or lipoprotein lipase (LPL) between groups (P > .05). In conclusion, GA significantly rescued high-fat diet induced hepatic lipid accumulation and metabolism dysfunction in M. amblycephalaby stimulating hepatic fatty acid transport and β-oxidation. Dietary GA may be used as a promising supplement to alleviate high-fat diet induced side effects on M. amblycephala.

Conjugated linoleic acid alters growth performance, tissue lipid deposition, and fatty acid composition of darkbarbel catfish (Pelteobagrus vachelli)

Fatty liver syndrome is a prevalent problem of farmed fish. Conjugated linoleic acid (CLA) has received increased attention recently as a fat-reducing fatty acid to control fat deposition in mammals. Therefore, the aim of the present study was to determine whether dietary CLA can reduce tissue lipid content of darkbarbel catfish (Pelteobagrus vachelli) and whether decreased lipid content is partially due to alterations in lipid metabolism enzyme activities and fatty acid profiles. A 76-day feeding trial was conducted to investigate the effect of dietary CLA on the growth, tissue lipid deposition, and fatty acid composition of darkbarbel catfish. Five diets containing 0 % (control), 0.5 % (CLA0.5), 1 % (CLA1), 2 % (CLA2), and 3 % (CLA3) CLA levels were evaluated. Results showed that fish fed with 2-3 % CLA diets showed a significantly lower specific growth rate and feed conversion efficiency than those fed with the control diet. Dietary CLA decreased the lipid contents in the liver and intraperitoneal fat with the CLA levels from 1 to 3 %. Fish fed with 2-3 % CLA diets showed significantly higher lipoprotein lipase and hepatic triacylglycerol lipase activities in liver than those of fish fed with the control, and fish fed with 1-3 % CLA diets had significantly higher pancreatic triacylglycerol lipase activities in liver than those of fish fed with the control. Dietary CLA was incorporated into liver, intraperitoneal fat, and muscle lipids, with higher percentages observed in liver compared with other tissues. Liver CLA deposition was at the expense of monounsaturated fatty acids (MUFA). In contrast, CLA deposition appeared to be primarily at the expense of MUFA and n-3 polyunsaturated fatty acids (PUFA) in the intraperitoneal fat, whereas in muscle it was at the expense of n-3 PUFA. Our results suggested that CLA at a 1 % dose can reduce liver lipid content without eliciting any negative effect on growth rate in darkbarbel catfish. This lipid-lowering effect could be in part due to an increment in the activity of lipid metabolism enzymes and an extensive interconversion of fatty acids. Although CLA deposition in muscle (0.66-3.19 % of total fatty acids) are higher than presented in natural sources of CLA, EPA (C20:5n-3) in fish muscle appears simultaneously expendable, when the fish fed with 2-3 % CLA.

Effects of conjugated linoleic acid on growth, non-specific immunity, antioxidant capacity, lipid deposition and related gene expression in juvenile large yellow croaker (Larmichthys crocea) fed soyabean oil-based diets

The effects of conjugated linoleic acid (CLA) on growth performance, non-specific immunity, antioxidant capacity, lipid deposition and related gene expression were investigated in the large yellow croaker (Larmichthys crocea). Fish (7·56 (sem 0·60) g) were fed soyabean oil-based diets with graded levels of CLA (0, 0·42, 0·83, 1·70 %) for 70 d. Quantitative PCR was used to assess the effects of CLA on the transcription of inflammation- and fatty acid oxidation-related genes. Growth in fish fed the diet with 0·42 % CLA was significantly higher. Also, phagocytic index and respiratory burst activity were significantly higher in fish fed the diets containing 0·42 and 0·83 % CLA, respectively. Hepatic total antioxidative capacity and catalase activities increased significantly when CLA increased from 0 to 0·83 %, and then decreased with further increase of CLA. However, hepatic malondialdehyde content decreased significantly as dietary CLA increased. Lipid concentration in the whole body and muscle increased significantly with increasing dietary CLA. Transcription of genes related to inflammation (cyclo-oxygenase-2 and IL-β) in the liver and kidney and fatty acid oxidation (carnitine palmitoyl transferase I and acyl CoA oxidase) in the kidney decreased significantly as dietary CLA increased. PPARα and acyl CoA oxidase expression in the liver decreased significantly as CLA increased from 0·42 to 1·70 %. These results strongly suggest that dietary CLA could significantly affect growth performance, non-specific immunity, antioxidant capacity, lipid deposition and transcription of inflammation- and fatty acid oxidation-related genes of the large yellow croaker. This may contribute to our understanding of the mechanisms related to the physiological effects of dietary CLA in fish.

trans-10,cis-12 conjugated linoleic acid improved growth performance, reduced lipid deposition and influenced CPT I kinetic constants of juvenile Synechogobius hasta

trans-10,cis-12 (t10c12) Conjugated linoleic acid (CLA) reduced body lipid deposition in various experimental animals, but the mechanisms involved were still emerging. Carnitine palmitoyltransferase I (CPT I) catalyzes an important regulatory step in lipid metabolism. At present, no studies, to our knowledge, have evaluated the kinetic constants influenced by dietary CLA in fish. In the present study, we tested the hypothesis that changes in body lipid content in fish as a response to dietary t10c12 CLA was related to the change of CPT I kinetic constants [Michaelis constant (K m), maximal velocity and catalytic efficiency for carnitine and palmitoyl-CoA]. Juvenile Synechogobius hasta were fed three experimental diets with fish oil replaced with 0 (control), 1, or 2 % t10c12 CLA for 8 weeks. Weight gain, specific growth rate and protein efficiency rate increased with dietary t10c12 CLA level. Dietary t10c12 CLA addition significantly reduced lipid contents both in liver and muscle. Dietary CLA addition also improved CPT I activities in muscle but did not significantly influence hepatic CPT I activity. CPT I kinetic parameters (K m, V max and catalytic efficiency) were significantly influenced by t10c12 CLA. CPT I catalytic efficiencies with carnitine and palmitoyl-CoA as substrates were higher in muscle and liver of fish fed increasing t10c12 CLA. For the first time, the findings demonstrated effect of dietary CLA addition on CPT I kinetics in fish and supported our starting hypothesis that dietary t10c12 CLA addition induced alterations in CPT I kinetic constants of muscle and liver. Increased CPT I catalytic efficiency might be the main reason for reduced lipid deposition in these tissues by dietary t10c12 CLA supplementation.