Effects of Dietary Selenium and Oxidized Fish Oils on Intestinal Lipid Metabolism and Antioxidant Responses of Yellow Catfish Pelteobagrus fulvidraco.

Currently, the effect of selenium and oxidized fish oil interactions on the intestinal lipid metabolism and antioxidant responses of fish remains unknown. Herein, yellow catfish Pelteobagrus fulvidraco (weight: 3.99 ± 0.01 g) were used as experimental animals and were fed four diets: an adequate amount of selenium (0.25 mg kg-1) with fresh fish oil (A-Se+FFO), an adequate amount of selenium with oxidized fish oil (A-Se+OFO), a high amount of selenium (0.50 mg kg-1) with fresh fish oil (H-Se+FFO), and a high amount of selenium with oxidized fish oil (H-Se+OFO). The feeding experiment was conducted for 10 weeks. The results showed that selenium supplementation alleviated the intestinal tissue damage and reduced the lipid accumulation that was induced by oxidized fish oils. Meanwhile, we also found that 0.50 mg kg-1 selenium reduced the oxidative stress that is caused by oxidized fish oils through increasing the GSH and the activity and mRNA expression of antioxidant enzymes. Dietary selenium and oxidized fish oils also affected the mRNA expression of intestinal selenoproteins including selenow2a, selenop2, and selenot2. Mechanistically, Se and oxidized eicosapentaenoic acid (oxEPA) influenced the GSH content by affecting the DNA binding ability of activating transcription factor (ATF) 3 to the slc7a11 promoter. For the first time, our results suggested that selenium alleviated the oxidized fish oil-induced intestinal lipid deposition and the oxidative stress of the fish. We also elucidated the novel mechanism of selenium increasing the GSH content by affecting the interaction of ATF3 and the slc7a11 promoter.

Novel insights for SREBP-1 as a key transcription factor in regulating lipogenesis in a freshwater teleost, grass carp Ctenopharyngodon idella.

Disturbances in lipid metabolism are at the core of several health issues facing modern society, including fatty liver and obesity. The sterol regulatory element-binding protein 1 (SREBP-1) is one important transcription factor regulating lipid metabolism, but the relevant mechanism still remains unknown. The present study determined the transcriptional regulation of SREBP-1 and its target genes (including acetyl-CoA carboxylase α (accα), fatty acid synthase (fas) and stearoyl-CoA desaturase 1 (scd1)) in a freshwater teleost, grass carp Ctenopharyngodon idella. We cloned and characterised the 1988 bp, 2043 bp, 1632 bp and 1889 bp sequences of srebp-1, accα, scd1 and fas promoters, respectively. A cluster of putative binding sites of transcription factors, such as specific protein, yin yang 1, nuclear factor Y, sterol response elements (SRE) and enhancer box (E-box) element, were predicted on their promoter regions. Overexpression of nSREBP-1 reduced srebp-1 promoter activity, increased scd1 and fas promoter activity but did not influence accα promoter activity. The site-mutation and electrophoretic mobility shift assay analysis indicated that srebp-1, fas and scd1 promoters, but not accα promoter, possessed SRE. In Ctenopharyngodon idella kidney (CIK) cells of grass carp, nSREBP-1 overexpression significantly reduced srebp-1 mRNA expression and up-regulated miR-29 mRNA expression. The 3'UTR of srebp-1 possessed the potential miR-29 binding site and miR-29 up-regulated the luciferase activity of srebp-1 3'UTR and srebp-1 mRNA expression, implying a self-activating loop of SREBP-1 and miR-29 in grass carp. Based on the above-mentioned results, we found two novel transcriptional mechanisms for SREBP-1 in grass carp: (1) the auto-regulation sited on the SREBP-1 promoter regions was suppressive and (2) there was a self-activating loop of SREBP-1 and miR-29.

In vitro effects of selenium on copper-induced changes in lipid metabolism of grass carp (Ctenopharyngodon idellus) hepatocytes.

The present study was performed to evaluate the in vitro effects of selenium (Se) supplementation to prevent copper (Cu)-induced changes in lipid metabolism of hepatocytes from grass carp (Ctenopharyngodon idellus). Four groups (control and 100 µM Cu in combination with 0, 5, and 10 µM Se, respectively) were chosen. Compared with the control, activities of glucose 6-phosphatedehydrogenase, 6-phosphogluconate dehydrogenase, malic enzyme, and carnitine palmitoyltransferase I (CPT I) of all three Cu-exposed groups at 24 and 48 h were significantly greater. However, among three Cu-exposed groups, increasing Se concentration tended to increase activities of G6PD and ME at 24 h and 6PGD activity at 24 and 48 h but decreased CPT I activity at 24 h. Compared with the control, Cu exposure alone, or in combination with Se, downregulated mRNA levels of sterol regulatory element-binding protein-1 (SREBP-1c), fatty acid synthase (FAS), acetyl-CoA carboxylase, peroxisome proliferator activated receptor alpha (PPARα), CPT I, and hormone-sensitive lipase (HSL) at 24 h as well as SREBP-1c, FAS, and ACC mRNA levels at 48 h. However, upregulated mRNA levels of PPARα, CPT I, and HSL, as well as decreased triglyceride content, were recorded at 48 h. Thus, although toxic at greater levels, lower levels of Se provided significant protection against Cu-induced changes in lipid metabolism. For the first time, our study indicates the dose- and time-dependent effects of Se addition on changes in lipid metabolism induced by Cu in fish hepatocytes and provides new insights into Se-Cu interaction at both enzymatic and molecular levels.

Kinetics of carnitine palmitoyltransferase I (CPT I) in Chinese sucker (Myxocyprinus asiaticus) change with its development.

The present study was conducted to evaluate the ontogeny and kinetic of CPT I in several tissues of the Chinese sucker Myxocyprinus asiaticus. To this end, liver, muscle and intestine tissues were examined at five various developmental stages of Chinese sucker: newly-hatched larvae, 68-day-old, 4-month-old, 1- and 2-year-old Chinese sucker, respectively. The total carnitine (TC) content in the liver increased from birth to 1-year-old Chinese sucker and then declined in the 2-year-old Chinese sucker. From the 68-day-old to the 1-year-old Chinese sucker, both free and total concentrations in muscle increased. Both acyl carnitine (AC) and TC concentrations in intestine were very variable at different stages. The ratio of AC to free carnitine (FC) in liver progressively increased from hatching to 4 months, and declined at the age of 1 year, and then increased by 2 years. In muscle, the highest and lowest ratios of AC/FC were observed at 68-days-old and 4 month-old Chinese sucker. The highest proportion of AC/FC in intestine was also observed at 68-day-old Chinese sucker. All the Chinese sucker larvae at hatching had a high value of the Michaelis constant (K(m)) for carnitine. Maximal velocity (V(max)) in intestine increased with age. V(max) in liver and muscle increased with age except a decrease at 4 months in liver and at 2 years in muscle. The FC concentration in the examined tissues at all developmental stages were less than the respective K(m), indicating that Chinese suckers require supplemental carnitine in their food to ensure that CPT I activity is not constrained by carnitine availability.

Differential effects of acute and chronic zinc (Zn) exposure on hepatic lipid deposition and metabolism in yellow catfish Pelteobagrus fulvidraco.

The present study is conducted to determine the potential mechanisms of Zn on hepatic lipid deposition and metabolism for yellow catfish Pelteobagrus fulvidraco with 8-week chronic exposure to low Zn levels (Zn levels: 0.05, 0.35 and 0.86mg/l Zn, respectively) and 96-h acute exposure to a high Zn level (Zn level: 4.71mg/l Zn, respectively). For that purpose, hepatic lipid deposition and Zn accumulation, hepatic carnitine palmitoyltransferase I (CPT I) and lipoprotein lipase (LPL) activities, and the hepatic mRNA expression of ten genes involved in lipid metabolism are determined. Chronic (8 weeks) exposure to low Zn levels apparently increases hepatic lipid content, hepatosomatic index (HSI) (P<0.05) and LPL activity, and reduces hepatic CPT I activity. In contrast, the acute (96h) exposure to high Zn level reduces hepatic lipid content, HSI and LPL activity, and increases CPT I activity. The change of mRNA levels of genes related to lipid metabolism is Zn concentration-dependent. Pearson correlations among mRNA expression levels, lipid content, CPT I and LPL activities in liver are also observed in yellow catfish with the 8-week chronic Zn exposure. For the first time, our study demonstrates the effect of waterborne Zn exposure on lipid metabolism at the molecular levels in fish, which may contribute to understanding the mechanism of Zn-induced hepatic toxicity 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.