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- Jutfelt, Fredrik, 1975, et al.
(författare)
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Parr-smolt transformation and dietary vegetable lipids affect intestinal nutrient uptake, barrier function and plasma cortisol levels in Atlantic salmon
- 2007
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Ingår i: Aquaculture. - : Elsevier BV. - 0044-8486. ; 273:2-3, s. 298-311
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Tidskriftsartikel (refereegranskat)abstract
- For Atlantic salmon, the gastrointestinal tract is the site of food digestion and nutrient uptake, a regulatory site for ion and water balance as well as a barrier against invading pathogens. During the parr–smolt transformation and subsequent seawater (SW) transfer, major changes occur in the intestine. A global shortage of fish oils (FO) for feed production is estimated to appear within a few years, and vegetable oils (VO) are being considered as alternatives for FO in fish feed production. However, VO influences the fatty acid composition of the polar lipids of cell membranes in the intestine which can disturb intestinal functions. A VO-based diet during the parr–smolt transformation, which is a sensitive developmental period, may cause adverse effects. Therefore, Atlantic salmon parr were fed either sunflower oil (SO) or FO as the major lipid source during out-of-season light controlled parr–smolt transformation. At three time points gill Na+,K+-ATPase activity and plasma levels of cortisol and growth hormone were assessed. Intestinal epithelia were sampled for assessment of nutrient absorption and bacterial translocation using an Ussing chamber in vitro system. While both dietary groups showed plasma hormone profiles indicative of successful parr–smolt transformation, the SO-fed fish had consistently increased cortisol levels compared to the FO-fed fish. Translocation of pathogenic bacteria increased, probably due to disturbed barrier functions, during the parr–smolt transformation. However, the fish fed the SO-diet maintained a higher barrier function compared to FO-fed fish, an effect that may be beneficial to these fish. Nutrient uptake was less affected by smoltification. Fish fed the SO-diet had higher uptake rates of amino acids and free fatty acids during mid-smoltification than fish fed the FO-diet. The combined effects of barrier function and nutrient uptake may suggest a positive effect of including vegetable lipids in the diet during the parr–smolt transformation. However, the vegetable lipid diet also seemed to act as a stressor and elevated the basal cortisol levels, which may be of concern in the context of general fish health and welfare.
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- Jutfelt, Fredrik, 1975
(författare)
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The intestinal epithelium of salmonids : transepithelial transport, barrier function and bacterial interactions
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The salmonid intestinal epithelium is important for growth and health of the fish. The epithelium is exposed to a multitude of internal and external factors that can influence its function. During the parr-smolt transformation and subsequent seawater transfer, the epithelium adapts for an osmoregulatory role and the fish starts drinking seawater (SW). Endocrine signals increases the intestinal water uptake partly through an up-regulation of Na+,K+-ATPase activity. It is shown that the epithelial paracellular permeability decrease concurrent with the increase in water transport, suggesting that water flow is directed from a paracellular to a more transcellular route. The rational for this could be the increase in epithelial exposure to the environment at SW entrance. Tightening the paracellular route could be a mechanism to reduce paracellular transfer of harmful substances and pathogens. A major salmonid pathogen is the bacterium Aeromonas salmonicida, which cause losses in both aquaculture and in wild populations. It is not known, however, by which route the A. salmonicida enters the fish. A. salmonicida has been positively demonstrated in the intestinal lumen but it has been controversial whether or not the bacteria cross the epithelial barriers. It is demonstrated that A. salmonicida can translocate across the intestinal barrier, indicating the intestine as a functional route for bacterial infection in salmonids. It is concluded that A. salmonicida employs many virulence mechanisms, such as exotoxins, endotoxin and cell bound factors, to disrupts epithelial morphology and function and promote translocation. During the later phases of parr-smolt transformation the epithelial barrier integrity decreased and translocation of pathogens increased. The increased disease susceptibility during this life stage could thus partly be caused by a decreased barrier function. Vegetable lipids are used as replacement for fish oil in salmonid aquaculture, but there are concerns about how the new diets affect the intestinal epithelium. The epithelial functions presently investigated indicate a slight increase in permeability, supporting earlier histological reports of epithelial disruptions but not to the same extent. Nutrient uptake and barrier function during the parr-smolt transformation was significantly improved by a vegetable lipid-containing diet, indicating that this inclusion may be beneficial in the freshwater (FW) stage. The fatty acid profile of the natural diet for salmonids in FW is more similar to a blend of vegetable oils than to the profile of marine feed ingredients, routinely used in salmonid aquaculture. This may be the rationale for the positive effects. Salmon fed sunflower oil, however, showed long term elevation of plasma cortisol levels indicating a chronic stress. As chronic stress is known to depress immune function, specific vegetable lipids potentially stressful to the fish may also affect their health and welfare. Thus, while vegetable lipids at certain life stages are feasible substitutes for fish oil, possible long term stress effects by vegetable oils should be considered. In conclusion, the salmonid intestinal epithelium is a sensitive and dynamic tissue which is affected by external factors, such as pathogen bacteria, environment and diet, but which also can be endogenously regulated to compensate for this disturbance.
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- Jutfelt, Fredrik, 1975, et al.
(författare)
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The involvement of Aeromonas salmonicida virulence factors in bacterial translocation across the rainbow trout, Oncorhynchus mykiss (Walbaum), intestine.
- 2008
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Ingår i: Journal of fish diseases. - : Wiley. - 0140-7775. ; 31:2, s. 141-51
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Tidskriftsartikel (refereegranskat)abstract
- The pathogenic bacterium Aeromonas salmonicida is the causative agent of furunculosis, a lethal disease in salmonids. The mode of lateral transmission has not been conclusively defined, but A. salmonicida is able to translocate across the intestinal epithelium of salmonids, making the intestinal route a probable candidate. This study investigated some of the virulence mechanisms used by the bacteria to promote translocation. Intestinal segments were placed in modified Ussing chambers to investigate epithelial functions during exposure to bacterial factors. The factors were: extracellular products (ECP), lipopolysaccharide (LPS) or live or heat-inactivated A. salmonicida. Fluorescein isothiocynate (FITC)-labelling enabled detection of translocated bacteria by fluorometry. Live A. salmonicida translocated to a greater degree than heat-inactivated bacteria, suggesting that the bacteria utilize a heat sensitive surface-bound virulence factor which promotes translocation. The epithelium was negatively affected by ECP, manifested as decreased net ion transport, indicating a disturbance in ion channels or cell metabolism. LPS did not affect the epithelium in vitro when administered on the luminal side of the intestinal segment, but significantly increased epithelial translocation of fluorescent bacterial-sized microspheres when administered on the serosal side. This is suggested to be caused by increased transcellular transport, as the paracellular permeability was unaffected indicating maintained epithelial integrity.
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- Jutfelt, Fredrik, 1975, et al.
(författare)
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Translocation of viable Aeromonas salmonicida across the intestine of rainbow trout, Oncorhynchus mykiss (Walbaum)
- 2006
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Ingår i: Journal of Fish Diseases. - : Wiley. - 0140-7775 .- 1365-2761. ; 29:5, s. 255-262
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Tidskriftsartikel (refereegranskat)abstract
- The pathogenic bacterium Aeromonas salmonicida is the causative agent of the destructive disease furunculosis in salmonids. Horizontal transmission in salmonids has been suggested to occur via the skin, gills and/or intestine. Previous reports are contradictory regarding the role of the intestine as a route of infection. The present study therefore investigates the possibility of bacterial translocation across intestinal epithelia using Ussing chamber technology, in vitro. Intestinal segments were exposed for 90 min to fluorescein isothiocyanate-labelled pathogenic A. salmonicida. Sampling from the serosal side of the Ussing chambers showed that bacteria were able to translocate across the intestinal epithelium in both the proximal and distal regions. Plating and subsequent colony counting showed that the bacteria were viable after translocation. During the 90 min exposure to A. salmonicida, the intestinal segments maintained high viability as measured by electrical parameters. The distal region responded to bacterial exposure by increasing the electrical resistance, indicating an increased mucus secretion. This study thus demonstrates translocation of live A. salmonicida through the intestinal epithelium of rainbow trout, suggesting that the intestine is a possible route of infection in salmonids.
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- Knudsen, David, et al.
(författare)
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Dietary soya saponins increase gut permeability and play a key role in the onset of soyabean-induced enteritis in Atlantic salmon ( Salmo salar L.).
- 2008
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Ingår i: The British journal of nutrition. - 0007-1145. ; 100:1, s. 120-9
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Tidskriftsartikel (refereegranskat)abstract
- Saponins are naturally occurring amphiphilic molecules and have been associated with many biological activities. The aim of the present study was to investigate whether soya saponins trigger the onset of soyabean-induced enteritis in Atlantic salmon (Salmo salar L.), and to examine if dietary soya saponins increase the epithelial permeability of the distal intestine in Atlantic salmon. Seven experimental diets containing different levels of soya saponins were fed to seawater-adapted Atlantic salmon for 53 d. The diets included a fishmeal-based control diet, two fishmeal-based diets with different levels of added soya saponins, one diet containing 25% lupin kernel meal, two diets based on 25% lupin kernel meal with different levels of added soya saponins, and one diet containing 25% defatted soyabean meal. The effect on intestinal morphology, intestinal epithelial permeability and faecal DM content was examined. Fish fed 25% defatted soyabean meal displayed severe enteritis, whereas fish fed 25% lupin kernel meal had normal intestinal morphology. The combination of soya saponins and fishmeal did not induce morphological changes but fish fed soya saponins in combination with lupin kernel meal displayed significant enteritis. Increased epithelial permeability was observed in fish fed 25% defatted soyabean meal and in fish fed soya saponin concentrate independent of the protein source in the feed. The study demonstrates that soya saponins, in combination with one or several unidentified components present in legumes, induce an inflammatory reaction in the distal intestine of Atlantic salmon. Soya saponins increase the intestinal epithelial permeability but do not, per se, induce enteritis.
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| 9. |
- Oxley, A., et al.
(författare)
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Sn-2-monoaglycerol, not glycerol, is preferentially utilized for triacylglycerols and phosphatidylcholine biosynthesis in Atlantic salmon (Salmo salar L.) intestine.
- 2006
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Ingår i: Comparative Biochemistry and Physiology. Part B: Biochemistry & Molecular Biology. - : Elsevier BV. - 1096-4959. ; 146:1, s. 115-123
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Tidskriftsartikel (refereegranskat)abstract
- Pathways of lipid resynthesis in the intestine of fish are relatively unknown. Various reports have suggested the existence of both sn-1,3-specific (pancreatic) and non-specific (bile salt-activated) lipase activity operating on dietary triacylglycerol (TAG) in the intestinal lumen of fish during digestion. Thus, sn-2-monoacylglycerol (2-MAG) and glycerol, respective hydrolytic products of each lipase, are absorbed and utilised for glycerolipid synthesis in enterocytes via two alternative routes: monoacylglycerol (MAG) and glycerol-3-phosphate (G3P) pathways. Despite different precursors, both pathways converge at the production of sn-1,2-diacylglycerol (1,2-DAG) where TAG or phosphatidylcholine (PC) synthesis can occur. To elucidate the relative activities of MAG and G3P pathways in Atlantic salmon enterocytes, intestinal segments were mounted in Ussing chambers where equimolar mixtures of sn-2-oleoyl-[1,2,3-3H]glycerol (2-MAG) and [14C(U)]glycerol, plus unlabelled 16:0 and 18:2n-6 as exogenous fatty acid sources, were delivered in bile salt-containing Ringer solution to the mucosa. The MAG pathway predominated, over the G3P pathway, synthesizing ca. 95% of total TAG and ca. 80% of total PC after a 3 h incubation period at 10 °C. Further, the 1,2-DAG branch point into TAG or PC was polarised towards TAG synthesis (6:1) via the MAG pathway but more evenly distributed between TAG and PC (1:1) via the G3P pathway. Effect of long-chain saturated, monounsaturated and polyunsaturated fatty acids on the synthesized TAG/PC ratio was assessed by individually exchanging 16:0, 18:1n-9 or 18:2n-6, for 16:0 + 18:2n-6, in mucosal solutions. TAG synthesis was influenced considerably more than PC synthesis, via either pathway, by exogenous fatty acids utilised. 18:1n-9 significantly stimulated TAG synthesis via the MAG pathway yielding a TAG/PC ratio of 12:1. Alternatively, 18:2n-6 stimulated TAG synthesis the most via the G3P pathway (TAG/PC = 4:1). 16:0 significantly attenuated TAG synthesis via either pathway. Micellar fatty acid species also significantly affected intestinal active transport mechanisms as shown by decreasing transepithelial potential (TEP) and short-circuit current (SSC) with increasing fatty acid unsaturation. The epithelial integrity was, however, not compromised after 3 h of exposure to any of the fatty acids. The implications of these findings on dietary fatty acid composition and enterocytic lipid droplet accumulation are discussed.
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