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1.
The desaturation of [1-14C]18:3n-3 to 20:5n-3 and 22:6n-3 is enhanced in an essential fatty acid deficient cell line (EPC-EFAD) in comparison with the parent cell line (EPC) from carp. In the present study, the effects of competing, unlabeled C18 polyunsaturated fatty acids (PUFA), linoleic (18:2n-6), -linolenic (18:3n-3), -linolenic (18:3n-6) and stearidonic (18:4n-3) acids, on the metabolism of [1-14C]18:3n-3 were investigated in EPC-EFAD cells in comparison with EPC cells. The incorporation of [1-14C]18:3n-3 in both cell lines was significantly reduced by competing C18 PUFA, with the rank order being 18:4n-3>18:3n-3 = 18:2n-6>18:3n-6. In the absence of competing PUFA, radioactivity from [1-14C]18:3n-3 in EPC cells was predominantly recovered in phosphatidylethanolamine followed by phosphatidylcholine. This pattern was unaffected by competing n-6PUFA, but n-3PUFA reversed this pattern as did essential fatty acid deficiency in the presence of all competing PUFA. The altered lipid class distribution was most pronounced in cells supplemented with 18:4n-3. Competing C18 PUFA significantly decreased the proportions of radioactivity recovered in 22:6n-3, pentaene and tetraene products, with the proportions of radioactivity recovered in 18:3n-3 and 20:3n-3 increased, in both cell lines. However, the inhibitory effect of competing C18 PUFA on the desaturation of [1-14C]18:3n-3 was significantly greater in EPC-EFAD cells. The magnitude of the inhibitory effects of C18 PUFA on [1-14C]18:3n-3 desaturation was dependent upon the specific fatty acid with the rank order being 18:4n-3>18:3n-3>18:2n-6, with 18:3n-6 having little inhibitory effect on the metabolism of [1-14C]18:3n-3 in EPC cells. The differential effects of the C18 PUFA on [1-14C]18:3n-3 metabolism were consistent with mass competition in combination with increased desaturation activity in EPC-EFAD cells and the known substrate fatty acid specificities of desaturase enzymes. However, the mechanism underpinning the greater efficacy with which the unlabeled C18PUFA competed with [1-14C]18:3n-3 in the desaturation pathway in EPC-EFAD cells was unclear.  相似文献   

2.
Rainbow trout (Oncorhynchus mykiss) skin cell cultures were obtained by trypsinization of the tissue and grown in Leibovitz L-15 medium. Lipid class compositions, and fatty acid profiles of total lipids and individual phospholipid classes were determined at different times of culture. The metabolism of polyunsaturated fatty acids (PUFA) was investigated by incubating primary cultures after 7 and 14 days with [1-14C]18:2n-6 and [1-14C-]18:3n-3. The change in morphology between epithelial-like primary cultures and fibroblastic-like secondary subcultures was accompanied by alterations in the lipid composition. Polar lipids became predominant by 14 days in culture. The relative proportions of phosphatidylcholine (PC), the most abundant phospholipid, phosphatidylinositol and cholesterol increased significantly, while sphingomyelin decreased. Saturated fatty acids, 18:1n-9, n-6 and n-9PUFA were more abundant in total lipid in cultures at 14 days and 4 months than in cells initially isolated which contained higher percentages of longer chain monoenes and n-3PUFA. The changes in fatty acid composition with time in culture were observed in all the major phospholipid classes. Rainbow trout skin cells in culture desaturated and elongated both 18:2n-6 and 18:3n-3, with 20:4n-6 and 20:5n-3 being the most abundant products, respectively. PC presented the highest incorporation of radioactivity, especially following incubation with 18:3n-3. Lipid metabolism in general increased with the age of primary cultures, with both the amount of C18 PUFA incorporated and metabolized by desaturation/elongation significantly increased in 14 day cultures compared to 7 day cultures. Product/precursor ratios calculated for both n-6 and n-3 fatty acids showed that, while 6 desaturase activity was increased significantly with cell age, 5 desaturase activity was more affected by the fatty acid series, with 18:3n-3 being more readily transformed to 20:5n-3 than 18:2n-6 to 20:4n-6. Further desaturation of 20:5n-3 to hexaenes was low. Overall, the data suggested that the trout skin cell cultures were more similar to mammalian skin fibroblasts than mammalian epidermal/keratinocyte cultures.  相似文献   

3.
To examine the ability of pike (Esox lucius L.) to modify exogenous PUFA by desaturation and elongation, 14C-labelled 18:2(n-6), 18:3(n-3), 20:4(n-6) and 20:5(n-3) were injected intraperitoneally and the distribution of radioactivity in tissue lipid classes and liver PUFA measured. In all tissues examined, radioactivity from all 14C-PUFA was recovered in many classes of acyl lipids and the level of recovery generally reflected the relative abundance of the lipid classes. Triacylglycerols, CGP and EGP usually contained high levels of all incorporated 14C-PUFA. PI contained higher levels of radioactivity from 14C-20:4(n-6) than from other injected substrates. In liver lipid, the 6 desaturation products of 14C-18:2(n-6) and 14C-18:3(n-3) contained no measurable radioactivity although the elongation products of the 6 desaturation products were labelled, as were the direct elongation products of these injected substrates. No radioactivity from 14C-18:2(n-6) or 14C-18:3(n-3) was detected in C20 or C22 products of 5 and 4 desaturation. Almost all radioactivity from injected 14C-20:4(n-6) was recovered in this PUFA. Of the total radioactivity from 14C-20:5(n-3) incorporated into liver lipid, 7% was present as 24:5 and 16.4% was recovered in hexaenoic fatty acids. In liver, 24:5(n-3) and 24:6(n-3) each accounted for 1% of the mass of total fatty acids and were located almost exclusively in triacylglycerols. The presence of radioactivity in these C24 PUFA suggests that in pike the synthesis of 22:6(n-3) from 20:5(n-3) may proceed without 4 desaturase via the pathway which involves chain shortening of 24:6(n-3). It is concluded that under the circumstances employed in this study pike, do not exhibit 5 desaturase activity and are unable to synthesize 20:4(n-6) and 20:5(n-3) from 18:2(n-6) and 18:3(n-3), respectively. This suggests that pike may require 20:4(n-6) and 20:5(n-3) preformed in the diet.Abbreviations CGP choline glycerophospholipids - CL cardiolipin - EGP ethanolamine glycerophospholipids - PG phosphatidylglycerol - PI phosphatidylinositol - PS phosphatidylserine - PUFA polyunsaturated fatty acids - SM sphingomyelin - TLC thin-layer chromatography  相似文献   

4.
The effects of sub-lethal doses of dichlorvos and formalin, antimicrobial/parasitic agents used in aquaculture, on lipid composition and metabolism of rainbow trout skin cells in primary culture were investigated. [1-14C]Stearic (18:0), [1-14C]lin 18:2n-6) and [1-14C]linolenic (18:3n-3) acids were used as tracers to determine effects on fatty acid incorporation and metabolism. Formalin increased cell numbers and reduced the lipid content of the cells and the incorporation of radioactive fatty acids. The effects of dichlorvos were qualitatively similar but quantitatively less. Formalin induced relatively small but significant changes in lipid class composition including a decreased proportion of phosphatidycholine with increased proportions of sphatidylethanolamine and phosphatidylserine. Dichlorvos had no significant effect on lipid class compositions. The trout primary skin cells expressed substantial 9, 6 and 5 fatty acyl desaturase activities. Although, as expected, the cells were m active towards [1-14C]18:3n-3, the cells were unusually active towards [1-14C]18:2n-6. Both dichlorvos and, especially, formalin appeared to significantly inhibit 9 and 6 desaturation. Changes in the distribution of radioactivity between individual spholipid classes was also influenced by formalin and dichlorvos, and this may be related to changes in desaturase activity. This study has shown that topically active agents used in aquaculture, formalin and dichlorvos, had a range of effects on the rainbow trout skin cell cultures that may affect cell proliferation and lipid and fatty acid metabolism. Both agents significantly inhibited desaturation of fatty acids, particularly of 18:2n-6 to 20:4n-6 and, as 20:4n-6 is a major eicosanoid precursor ish and considering the importance of eicosanoids in the biochemistry of skin, it is suggested that these agents may have direct effects on fish skin that could have important consequences for fish health in general.  相似文献   

5.
Atlantic salmon (Salmo salar) were fed diets containing fish oil supplemented with 22:6n-3 (FO diet) or linseed oil supplemented with 20:5n-3 (LO diet) for 6 months. The effects of these diets, both containing about 36% n-3 fatty acids, on the esterification, desaturation and elongation of [1-14C] 18:2n-6 and [1-14C] 18:3n-3 were investigated in isolated hepatocytes. The percentages of radioactivity which was esterified from [1-14C] 18:2n-6 or [1-14C]18:3n-3 into total lipids, were approximately 20% lower in hepatocytes from fish fed the FO diet than in hepatocytes from fish fed the LO diet. The percentages of radioactivity esterified in both groups were further reduced when 0.1 mM unlabelled 22:6n-3 was added to the incubation. The percentage of desaturation and elongation products formed from [1-14C] 18:2n-6 was twice as high in hepatocytes from salmon fed the FO diet as it was in hepatocytes from fish fed the LO diet. The ratio of 18:2n-6 to 18:3n-3 was five times higher in the FO diet, and this probably promoted the conversion of 18:2n-6 to longer chain n-6 fatty acids. When 0.1mM unlabelled 22:6n-3 was added to the incubation medium, the percentages of desaturation and elongation products formed were unchanged. Thus, a high level of 22:6n-3 in the diet is apparently not inhibiting the conversion of 18:2n-6 to 20:4n-6, as long as the amount of 18:2n-6 present is substantially higher than that of 18:3n-3. No desaturation and elongation products were recovered from the phospholipids of hepatocytes incubated with [1-14C] 18:3n-3 in any of the groups. However, the `dead end' elongation product 20:3n-3 was found in the triacylglycerol fraction, and the percentage of this fatty acid increased when 22:6n-3 was added to the incubation medium.  相似文献   

6.
The incorporation, and the capacity for desaturation and elongation in vivo, of intraperitoneally-injected,14C-labelled n-3 and n-6 C18 and C20 polyunsaturated fatty acids (PUFA) were investigated in juvenile golden grey mullet,Liza aurata. The results indicate that juvenile mullet have only limited ability to convert C18 polyunsaturated fatty acids to C20 and C22 highly unsaturated fatty acids (HUFA)in vivo. This suggests that juvenile golden grey mullet require the provision of preformed C20/22 HUFA, such as eicosapentaenoic and docosahexaenoic acids, in the diet. The impairment in the desaturase/elongase pathway was similar to that found in turbot,Scophthalmus maximus, and gilthead sea bream,Sparus aurata, being primarily at the level of Δ5-desaturase. The data from the largely herbivorous golden grey mullet juveniles are consistent with the hypothesis that marine fish in general, irrespective of dietary habits, have limited capacity for the desaturation and elongation of C18 PUFA. The defect in Δ5-desaturase activity combined with the consistent finding that arachidonic acid is selectively incorporated and retained in membrane phosphatidylinositol suggests that, like turbot and gilthead sea bream, golden grey mullet may also have a requirement for preformed arachidonic acid in the diet.  相似文献   

7.
Tilapia (Oreochromis) nilotica were fed either a commercial diet containing 2.2% (n-3) and 0.5% (n-6) polyunsaturated fatty acids (PUFA), or a diet containing 1.0% methyl linoleate as the only PUFA. The fatty acid composition of tissue lipids generally reflected that of the diet. Fish from both dietary groups were injected intraperitoneally with 14C-labelled linoleic acid, 18:2 (n-6), or linolenic acid, 18:3 (n-3), and the distribution of radioactivity in tissue lipids examined. The conversion of both 18:2 (n-6) and 18:3 (n-3) to longer chain PUFA was lower in fish fed the commercial diet than in those fed the diet containing only 18:2 (n-6). Half of the radioactivity from both substrates recovered in liver polar lipids was present in C20 and C22 PUFA with fish maintained on the experimental diet. It is concluded that T. nilotica is capable of elongating and desaturating both 18:2 (n-6) and 18:3 (n-3), but that this conversion is suppressed by dietary longer chain PUFA. NERC Unit of Aquatic Biochemistry  相似文献   

8.
The influence of feeding high levels of polyunsaturated fatty acids (PUFA) on muscle fatty acid composition and indices of oxidative damage was examined in Arctic charr, Salvelinus alpinus (L.). All diets contained 100 g kg?1 lipid of dry weight. Two diets contained marine fish oils giving a PUFA level of 250 g kg?1 and 500 g kg?1 of lipid. The remaining two diets contained vegetable oils high in either 18:2n-6 or 18:3n-3, giving a PUFA level of more than 500 g kg?1 of dietary lipid. The charr were maintained at 8°C until their weight doubled, and were then transferred to 0.8°C for 30 days. Growth was similar in all groups. The fatty acid compositions of muscle were influenced by dietary PUFA but were less diverse than those of the diets. The overall pattern of fatty acid compositions indicated preferential desaturation and elongation of n-3 PUFA coupled with selective oxidation of 18:2n-6. Total n-3 PUFA content in TAG was always lowered compared with the diet, suggesting a specific mechanism for the removal of these fatty acids. Subjecting the fish to low temperature increased PUFA content in muscle of charr fed the 250 g kg?1 marine n-3 PUFA diet, but had no effect on the other treatments. For fish at 8°C, no significant differences were found between groups in terms of haematocrit, plasma alanine aminotransferase (ALAT), and plasma and muscle thiobarbituric acid reactive substances (TBARS), although there was a tendency towards increased levels of TBARS in the group receiving 500 g kg?1 marine n-3 PUFA of lipid. Subjecting the muscle to forced oxidative conditions resulted in increases in TBARS in all groups, particularly those fed 500 g kg?1 marine n-3 PUFA. Lowering the environmental temperature corresponded with a further increase in the plasma ALAT and muscle TBARS in this group. It is concluded that feeding diets containing high levels of long-chain n-3 PUFA may be detrimental to the fish's health and flesh quality, particularly at low environmental temperatures.  相似文献   

9.
Arctic charr,Salvelinus alpinus L. were fed five test diets containing 0% or 1% of different polyunsaturated fatty acids (PUFA) for 93 days. The fish were injected intraperitoneally with (1–14C)–18:2(n–6) or (1–14C)–18:3(n–3), and the bioconversion to longer chain PUFA studied. The conversion rate in neutral lipids was slow, with most label found as the fatty acid injected, while extensive modification took place prior to or during incorporation into polar lipids. Linolenic acid was preferred over linoleic acid as substrate for elongation and desaturation regardless of diet. In polar lipids, the predominant products of (1–14C)–18:2(n–6) metabolism were generally 20:3(n–6) and 20:4(n–6), while 18:4(n–3), 20:5(n–3) and 22:6(n–3) were the major products of (1–14C)–18:3(n–3) metabolism. The lack of radioactivity in 22:5(n–6) suggests that 4 desaturation is specific for (n–3) PUFA. Feeding the PUFA deficient diet reduced the 5 desaturation compared to fish maintained on PUFA supplemented diets. The 6 desaturation was only reduced in fish fed C18 PUFA and injected with (1–14C)–18:3(n–3). Longer chain C20 and C22 PUFA, particularly those of the (n–3) family, exerted some inhibition on the elongation and desaturation of injected fatty acids compared to those fed C18 PUFA. The incorporation of radiolabelled fatty acids into polar lipids of fish fed a commercial diet was very low, and the desaturation neglectible in both polar and neutral lipids, showing that Arctic charr under culture conditions do not convert short chain PUFA to longer chain metabolites.  相似文献   

10.
We hypothesized that replacing fish oil with 18:3n-3-rich linseed oil may enable salmon to maintain the levels of tissue n-3HUFA levels through a combination of increased desaturation activity and increased substrate fatty acid provision. To this end we investigated desaturation/elongation of [1-14C18:3n-3 in hepatocytes and intestinal enterocytes, and determined the extent to which 18:3n-3 was oxidized and desaturated by measuring both simultaneously in a combined assay. Salmon smolts were stocked randomly into five seawater pens and fed for 40 weeks on diets in which the fish oil was replaced in a graded manner by linseed oil. At the end of the trial, fatty acyl desaturation/elongation and oxidation activities were determined in isolated hepatocytes and intestinal enterocytes using [1-14C]18:3n-3 as substrate, and samples of liver and intestinal tissue were collected for analysis of lipid and fatty acid composition. The results showed that, despite increased desaturation of [1-14C]18:3n-3 in hepatocytes, provision of dietary 18:3n-3 did not prevent the decrease in tissue n-3HUFA in fish fed linseed oil. Intestinal enterocytes were a site of significant fatty acid desaturation but, in contrast to hepatocytes, the activity was not increased by feeding linseed oil and was generally lower in fish fed linseed oil compared to fish fed only fish oil. In contrast, oxidation of [1-14C]18:3n-3 in enterocytes was generally increased in fish fed linseed oil compared to fish fed the diet containing only fish oil. However, oxidation of [1-14C]18:3n-3 in hepatocytes was 4- to 8-fold lower than in enterocytes and was not affected by diet. Furthermore, oxidation of [1-14C]18:3n-3 in enterocytes exceeded desaturation irrespective of dietary treatment, whereas similar amounts of [1-14C]18:3n-3 were desaturated and oxidized in hepatocytes from fish fed only fish oil and desaturation exceeded oxidation by 3-fold in fish fed the diet containing 100% linseed oil. The molecular mechanisms underpinning these results were discussed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

11.
Cells from a relatively stenohaline marine species, turbot (Scophthalmus maximus) (TF) and an anadromous species, Atlantic salmon (AS) were cultured in media supplemented with NaCl to produce OPs varying from 300 to 500 mOsm kg–1 and the direct effects of OP (salinity) on the fatty acid compositions of the main glycerophospholipid classes were determined. The most dramatic effects of salinity on total lipid fatty acids were observed in polyunsaturated fatty acids (PUFA) in TF cells. There was a graded decrease in the percentage of 18:2n-9, and consequently total n-9 PUFA, and concomitantly increased percentages of both total n-3 and n-6 PUFA with increasing salinity. The increased n-3 and n-6 PUFA was due to significantly increased percentages of the major fatty acids in each of these groups, namely 22:6n-3 and 20:4n-6, respectively. The reciprocal changes in n-9 PUFA and n-3/n-6 PUFA in TF cell total lipid resulted in the percentage of total PUFA not being significantly affected by changes in salinity. The graded decrease in 18:2n-9 with increasing salinity in TF cells was observed in all the major glycerophospholipids but especially PE, PI and PS. Increasing salinity resulted in graded increases in the percentages of 22:6n-3 in PE and PS in TF cells. The quantitatively greatest increase in the percentage of n-6 PUFA in TF cells occurred with 20:4n-6 in PC, PE and PL. There were less significant changes in the fatty acid compositions of glycerophospholipids in AS cells. However, the proportion of total n-3 + n-6 PUFA in PE varied reciprocally with the proportion of dimethylacetals in response to salinity. Similar reciprocal changes between fatty acids in response to salinity were also evident in the quantitatively more minor glycerophospholipids PS and Pl. In PS, the percentage of 22:6n-3 was significantly lower at 400 mOsm kg–1 whereas the proportion of total monoenes was significantly higher at that salinity. A similar inverse relationship between total monoenes and 20:4n-6 (and, to a lesser extent total saturates) in response to salinity was noted in PI. The results show that environmental salinity, without whole-body physiological stimuli, has direct effects on the fatty acid composition of major glycerophospholipid classes in fish cells and that these effects differ in cells from different fish speciesAbbreviations ANOVA analysis of variance - BHT butylated hydroxytoluene - BSA bovine serum albumin - DMA dimethylacetals - EMEM Eagle's minimal essential medium - FCS fetal calf serum - GC gas chromatography - HBSS Hank's balanced salt solution (without Ca2+ and Mg2+) - OP osmotic pressure - PC phosphatidylcholine - PE phosphatidylethanolamine - PI phosphatidylinositol - PS phosphatidylserine - PUFA polyunsaturated fatty acid - TLC thin-layer chromatography  相似文献   

12.
The desaturation and elongation of [1-14C]18:3n-3 was investigated in hepatocytes of the tropical warm freshwater species, zebrafish (Danio rerio) and Nile tilapia (Oreochromis niloticus). The hepatocyte fatty acid desaturation/elongation pathway was assayed before and after the fish were fed two experimental diets, a control diet containing fish oil (FO) and a diet containing vegetable oil (VO; a blend of olive, linseed and high oleic acid sunflower oils) for 10 weeks. The VO diet was formulated to provide 1% each of 18:2n-6 and 18:3n-3, and so satisfy the possible EFA requirements of zebrafish and tilapia. At the end of the dietary trial, the lipid and fatty acid composition was determined in whole zebrafish, and liver, white muscle and brain of tilapia. Both zebrafish and tilapia expressed a hepatocyte fatty acid desaturation/elongation pattern consistent with them being freshwater and planktonivorous fish. The data also showed that hepatic fatty acid desaturation/elongation was nutritionally regulated with the activities being higher in fish fed the VO diet compared to fish fed the FO diet. In zebrafish, the main effect of the VO diet was increased fatty acid Δ6 desaturase activity resulting in the production of significantly more 18:4n-3 compared to fish fed the FO diet. In tilapia, all activities in the pathway were greater in fish fed the VO diet resulting in increased amounts of all fatty acids in the pathway, but primarily eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3). However, the fatty acid compositional data indicated that despite increased activity, desaturation of 18:3n-3 was insufficient to maintain tissue proportions of EPA and DHA in fish fed the VO diet at the same level as in fish fed the FO diet. Practically, these results indicate that manipulation of tilapia diets in commercial culture in response to the declining global fish oil market would have important consequences for fish fatty acid composition and the health of consumers. Scientifically, zebrafish and tilapia, both the subject of active genome mapping projects, could be useful models for studies of lipid and fatty acid metabolism at a molecular biological and genetic level. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

13.
Eight purified diets were fed to juvenile white sturgeon, Acipenser transmontanus Rick, for 9 weeks to investigate the effect of dietary lipids on the fatty acid composition of phospholipids and triglycerides from muscle, liver and brain. The diets contained 150 g kg?1 of oils from canola, corn, cod liver, lard, linseed, soybean, safflower, or a control mixture (corn oil/cod liver oil/lard, 1:1:1, by wt). Dietary lipids significantly (P≤ 05) affected the composition of tissue triglycerides and phospholipids. Tissue triglyceride fatty acid composition ranged widely, in parallel with the dietary lipids, while phospholipids changes were more conservative. Brain phospholipid fatty acid composition was less responsive to diet compared with that in muscle and liver. Considerable amounts of n-6 and n-3 long chain polyun-saturated fatty acids (> C20) were found in triglycerides and phospholipids with all diets, demonstrating that white sturgeon can desaturate and elongate linoleic acid (18:2n–6) and linolenic acid (18:3n–3). Further, the products of the Δ6 desaturase, i.e. 18:3 n–6 and 18:4n–3, were relatively abundant in triglyceride, suggesting that the Δ6 desaturase might not be a limiting step in the process in white sturgeon. Nevertheless, accumulation of both EPA and DHA was greater in the sturgeon fed fish oil than those fed linseed oil, indicating that muscle triglyceride EPA and DHA levels are best enhanced by diets rich in preformed EPA and DHA.  相似文献   

14.
The effect of long-term culture of fish cells in mammalian serum on the phospholipid fatty acid composition was investigated. All the cell lines studied had much lower levels of polyunsaturated fatty acids (PUFA) than those found in intact fish tissues. In particular (n-3) PUFA were considerably depleted in the cultured cell lines, leading to very low (n-3)/(n-6) ratios in all the phospholipid classes. In general the cells were rich in 18:1, 16:0, 18:0 and 16:1 with 20:4(n-6) and 22:6(n-3) as the major PUFA. The fatty acid composition reflected the composition of the fetal calf serum added to the media rather than their fish tissue origins. The results were discussed in relation to the roles of PUFA in general cell metabolism and more specifically the role of (n-3) PUFA in fish cells.  相似文献   

15.
The static or declining supply of fish oil from industrial fisheries demands the search of alternatives, such as plant (vegetable) oils, for diets in expanding marine aquaculture. Vegetable oils are rich in C18 polyunsaturated fatty acids but devoid of the n-3 highly unsaturated fatty acids in fish oils. Previous studies, primarily with salmonids, have shown that including vegetable oils in their diets increased hepatocyte fatty acid desaturation. In the present study, we have investigated the effects of dietary partial substitution of fish oil (FO) with rapeseed oil (RO), linseed oil (LO) and olive oil (OO) on the desaturation /elongation and, -oxidation capacities of [1-14C]18:3n-3 in isolated hepatocytes from European sea bass (Dicentrarchus labrax L.), in a simultaneous combined assay. Fish were fed during 34 weeks with diets containing 100% FO, or RO, LO and OO, each included at 60% with the balance being met by FO, with no detrimental effect upon growth or survival. The highest total desaturation rates were found in hepatocytes of fish fed FO diet (0.52±0.08 pmol/h/mg protein) and OO diet (0.43±0.09 pmol/h/mg protein), which represented 3.2% and 2.7% of total [1-14C]18:3n-3 incorporated, respectively. In contrast, lowest desaturation rates were presented by hepatocytes of fish fed LO and RO diets (0.23±0.06 and 0.14±0.05 pmol/h/mg protein, respectively) represented 1.4% and 0.9% of total [1-14C]18:3n-3 incorporated, respectively. The rates of [1-14C]18:3n-3 β-oxidized were between 11-fold and 35-fold higher than desaturation. However, no significant differences were observed among β-oxidation activities in hepatocytes of fish fed any of the diets. The present study demonstrated that the European sea bass, as a carnivorous marine fish, presented a ‘marine’ fish pattern in the metabolism of 18:3n-3 to 20:5n-3 and 22:6n-3. This species appeared to have all the enzymic activities necessary to produce 22:6n-3 but presented only extremely low rates of fatty acid bioconversion. Furthermore, nutritional regulation of hepatocyte fatty acid desaturation was minimal, and dietary vegetable oils did not increase desaturase activities, and in RO and LO treatments the activity was significantly lower. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

16.
Three diets in which the lipid component was supplied either as fish oil (FO), linseed oil (LO) or olive oil (OO) were fed to duplicate groups of juvenile turbot (Scophthalmus maximus) of initial weight 1.2 g for a period of up to 12 weeks. The latter two diets resulted in a significant reduction in specific growth rate and an increased mortality compared to the FO (control) fed fish. A liver histopathology was evident in around half of the fish fed the LO and OO diets but was absent in fish fed FO. The lesion showed indications of cellular alterations consisting of foci of densely basophilic cells but without evidence of inflammatory activity. The total lipid fatty acid composition of the carcass from fish fed LO had increased percentages of 18:2n-6 and 18:3n-3, but decreased percentages of all other polyunsaturated fatty acids (PUFA) including the physiologically important 20:4n-6, 20:5n-3 and 22:6n-3, compared to fish fed FO. Almost 2/3 of the total fatty acids in the carcass of OO-fed fish were monounsaturated while the percentages of total saturated fatty acids and all other PUFA, except 18:2n-6, were significantly reduced compared to fish fed FO. Broadly similar effects on total lipid fatty acid composition were observed in liver. In the liver glycerophospholipid classes of fish fed LO, percentages of 18:2n-6, 18:3n-3 and 20:3n-3 were significantly increased whereas all C20 and C22 PUFA, with the exception of 20:5n-3 in PI, were significantly reduced compared to fish fed FO. The liver glycerophospholipids of fish fed OO all showed significantly increased total monounsaturates, 18:2n-6, 20:2n-6, 18:2n-9 and 20:2n-9 as well as reduced percentages of 20:4n-6 and 22:6n-3, compared to fish fed FO. The brain glycerophospholipids showed broadly similar changes in response to dietary treatment although the magnitude of fatty acid alterations was less than those observed in liver. The greater mortalities in the OO-fed fish compared to the LO-fed fish suggests that incorporation of 18:3n-3 into tissue phospholipids can offset losses of long-chain PUFA more effectively than incorporation of 18:1n-9. However, levels of dietary long-chain PUFA must be optimised to allow normal growth and development. We conclude that the very low flux through the fatty acid desaturase/elongase pathways in turbot is not up-regulated by diets deficient in 20:5n-3 and 22:6n-3.  相似文献   

17.
Lates calcarifer, commonly known as the Asian sea bass or barramundi, is an interesting species that has great aquaculture potential in Asia including Malaysia and also Australia. We have investigated essential fatty acid metabolism in this species, focusing on the endogenous highly unsaturated fatty acid (HUFA) synthesis pathway using both biochemical and molecular biological approaches. Fatty acyl desaturase (Fad) and elongase (Elovl) cDNAs were cloned and functional characterization identified them as ∆6 Fad and Elovl5 elongase enzymes, respectively. The ∆6 Fad was equally active toward 18:3n-3 and 18:2n-6, and Elovl5 exhibited elongation activity for C18–20 and C20–22 elongation and a trace of C22–24 activity. The tissue profile of gene expression for ∆6 fad and elovl5 genes, showed brain to have the highest expression of both genes compared to all other tissues. The results of tissue fatty acid analysis showed that the brain contained more docosahexaenoic acid (DHA, 22:6n-3) than flesh, liver and intestine. The HUFA synthesis activity in isolated hepatocytes and enterocytes using [1-14C]18:3n-3 as substrate was very low with the only desaturated product detected being 18:4n-3. These findings indicate that L. calcarifer display an essential fatty acid pattern similar to other marine fish in that they appear unable to synthesize HUFA from C18 substrates. High expression of ∆6 fad and elovl5 genes in brain may indicate a role for these enzymes in maintaining high DHA levels in neural tissues through conversion of 20:5n-3.  相似文献   

18.
Arctic charr (Salvelinus alpinus L.) were fed either a commercial diet or six experimental test diets containing coconut oil and different polyunsaturated fatty acids (PUFA) at a level of 1% by dry weight. Best growth rates were observed with the commercial diet, worst with diet containing coconut oil with no PUFA. An increase in hepatic lipid, hepatic sterol esters and muscular moisture content, and a decrease in muscular lipid was generally found in fish fed the test diets compared to those maintained on the commercial diet.Phosphatidylcholine was the dominant polar lipid (PL) class in all tissues examined. Extensive modification of dietary saturated fatty acids into 18:1 (n-9) was observed in tissue triacylglycerols (TAG) of fish fed test diets. No changes occurred with the commercial diet.Dietary PUFA were essentially incorporated unchanged into tissue TAG of all fish in the present study. PUFA composition of hepatic phospholipids was significantly influenced by that contained in the diets. However both 18:2 (n-6) and 18:3 (n-3) in the test diets were extensively elongated and desaturated prior to incorporation into PL. The (n-9) PUFA content was always higher in liver of fish fed the test diets. When 18:2 (n-6) and 18:3 (n-3) were supplied together, the level of (n-3) PUFA exceeded those of (n-6) PUFA. Muscle PL were less influenced by diet than liver. In muscle (n-3) PUFA were always the predominant PUFA irrespective of diet. Only low amounts of (n-9) PUFA were found. It is suggested that (n-3) PUFA are the prime essential fatty acids for Arctic charr, and that they are used in preference to (n-6) PUFA for elongation, desaturation and incorporation into PL. The results suggest that the quantitative requirement of Arctic charr for EFA is may be higher than that of other salmonids.  相似文献   

19.
The aim of this work was to study the fatty acid (FA) bioconversion ability in Eurasian perch fed with diets differing in their polyunsaturated fatty acids (PUFA) from n‐3 and n‐6 series content at two development stages: adults in exogenous vitellogenesis, and juveniles during the on‐growing phase. Duplicate groups of adults and juveniles were fed for 12 weeks with four diets: D1 and D2, two diets prepared with fish oil partially or totally as the lipid source, and so containing long‐chain PUFA (LC‐PUFA). Those two diets differed by their n‐3/n‐6 FA dietary ratio (0.2 and 7.0, respectively), D1 being characterized by a high n‐6 LC‐PUFA level, while D2 had a high level of n‐3 LC‐PUFA. D3 and D4 were constituted only with vegetable oils, and were therefore devoid of LC‐PUFA. D3 was characterized by a high level of 18:2 n‐6 (n‐6/n‐3 ratio of 0.3), while D4 was characterized by a high level of 18:3 n‐3 (n‐3/n‐6 ratio of 1.9). Both groups of fish were able to elongate and desaturate the 18:3 n‐3 precursor into eicosapentaenoic acid and docosahexaenoic acid, regarding the FA profile of livers. Furthermore, total elongation/desaturation from [1‐14C]18:3 n‐3 of LC‐PUFA was higher in fish fed with the high dietary 18:3 n‐3 level compared to the diet rich in n‐3 LC‐PUFA. By opposition, the bioconversion of 18:2 n‐6 into LC‐PUFA was limited, regarding the elongation/desaturation activity of LC‐PUFA from [1‐14C]18:2 n‐6. In view of the great ability for bioconversion of n‐3 FA, linseed oil is a promising alternative to fish oil in formulating feed for juveniles perch as there were no differences in terms of specific growth rate between the treatments, but adults undergoing maturation should have at least partially LC‐PUFA in their diet, particularly arachidonic acid (ARA) which is important during maturation, as breeders are not able to bioconvert 18:2 n‐6 into ARA.  相似文献   

20.
Atlantic salmon fry (4 g) were fed a semi-synthetic diet devoid of n-3 and n-6 polyunsaturated fatty acids (PUFA) for 4 months. External signs of nutritional imbalance during the period were slow growth rate and increased mortality. Some symptoms of essential fatty acid deficiency appeared in the fatty acid composition of the blood and liver during the fourth month. At that time, the percentages of n-3 and n-6 PUFA of triacylglycerols (TAG) were nearly exhausted, and the percentages of 22:6 n-3 and of 20:5 n-3 in phospholipids (PL) showed a marked decrease. This decrease in the PUFA level of the PL was paralleled by the appearance of 20:3 n-9, whereas in the TAG an increase in the percentage of 18:1 n-9 was observed. After 4 months the monounsaturated fatty acid 18:1 n-9 constituted nearly 50% of the fatty acids in the TAG fraction of the liver. The time course of the changes in fatty acid composition of liver and blood lipids was quite similar, whereas the carcass lipid composition appeared to respond slowly to a diet devoid of essential fatty acids.  相似文献   

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