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1.
Effect of 18∶1n−9, 20∶5n−3, and 22∶6n−3 on lipid accumulation and secretion by atlantic salmon hepatocytes 总被引:1,自引:0,他引:1
We have studied the effects of dietary FA on the accumulation and secretion of [3H]glycerolipids by salmon hepatocytes in culture. Atlantic salmon were fed diets supplemented with either 100% soybean oil
(SO) or 100% fish oil (FO), and grew from an initial weight of 113±5 g to a final weight of 338 ±19 g. Hepatocytes were isolated
from both dietary groups and incubated with [3H]glycerol in an FA-free medium; a medium supplemented with 0.75 mM of one of three FA—18∶1n−9, 20∶5n−3, or 22∶6n−3—or a medium
supplemented with 0.75 mM of the sulfur-substituted FA analog tetradecylthioacetic acid (TTA), which cannot undergo β-oxidation.
Incubations were allowed to proceed for 1,2,6, or 24 h. The rate of the secretion of radioactive glycerolipids with no FA
added was 36% lower from hepatocytes isolated from fish fed the FO diet than it was from hepatocytes isolated from fish fed
the SO diet. Hepatocytes incubated with 18∶1n−9 secreted more [3H]TAG than when incubated with no FA, whereas hepatocytes incubated with 20∶5n−3 or TTA secreted less labeled TAG than when
incubated with no FA. This observation was independent of the feeding group. Hepatocytes incubated with 22∶6n−3 secreted the
highest amounts of total [3H]glycerolipids compared with the other treatments, owing to increased secretion of phospholipids and mono- and diacylglycerols
(MDG). In contrast, the same amounts of [3H]TAG were secreted from these cells as from cells incubated in an FA-free medium. The lipid-lowering effect of FO is thus
independent of 22∶6n−3, showing that 20∶5n−3 is the FA that is responsible for the lipid-lowering effect. The ratio of TAG
to MDG in lipids secreted from hepatocytes to which 20∶5n−3 or TTA had been added was lower than that in lipids secreted from
hepatocytes incubated with 18∶1n−9 or 22∶6n−3, suggesting that the last step in TAG synthesis was inhibited. Morphometric
measurements revealed that hepatocytes incubated with 20∶5n−3 accumulated significantly more cellular lipid than cells treated
with 18∶1n−9, 22∶6n−3, TTA, or no treatment. The area occupied by mitochondria was also greater in these cells. The present
study shows that dietary FO reduces TAG secretion from salmon hepatocytes and that 20∶5n−3 mediates this effect. 相似文献
2.
In this pulse-chase study, rainbow trout fed a diet containing deuterated (D5) (17,17,18,18,18)-18∶3n−3 ethyl ester accumulated D5-22∶6n−3 in pyloric ceca to a greater extent than in liver 2 d post-dose. The ratio of newly synthesized D5-22∶6n−3 in ceca to that in liver 2 d after feeding D5-18∶3n−3 was 4.7±1.2 when expressed as per mg tissue and 5.2±2.4 when expressed as per mg protein. The amount of D5-22∶6n−3 in ceca then declined whereas that in liver and blood increased, with the ratio of ceca to liver falling to 1.7 and
1.4, respectively, by day 5 and approaching unity by day 9. A crude cecal mucosa fraction contained 123±50 ng D5-22∶6n−3/mg protein/mg D5-18∶3n−3 eaten 2 d after feeding the tracer, compared with 35±21 ng D5-22∶6n−3/mg protein/mg D5-18∶3n−3 eaten in liver. Three days later the amount in cecal mucosa had fallen by one-third and that in liver had increased
threefold. Most of the D5-18∶3n−3 was catabolized very rapidly. The ratio of D5-18∶3n−3 to 21∶4n−6 (a relatively inert FA marker) in the diet was 4.0, but this fell to 0.30 in ceca and ca. 0.8 in liver, blood, and whole carcass one day after feeding. These results indicate that ceca are active in the synthesis
of 22∶6n−3 and the oxidation of 18∶3n−3. 相似文献
3.
The present study was designed to examine the effects of EFA deficiency (EFAD) on biochemical, functional, and structural
aspects of the kidney in growing and adult rats fed a normal or EFAD diet for 9 wk after weaning. Food and fluid intake (FI),
urine volume, and Na+ and K+ excretions were measured weekly from weeks 4 to 8 by placing the rats in individual metabolic cages for 24 h. At week 9,
Li+ and a 5% water load, respectively, were administered at 14 and 1.5 h prior to glomerular and proximal tubular function studies,
as assessed by 3-h creatinine (CCr) and Li+ (CLi+) clearances. Hematocrit and urine volume; serum and urine [Cr], [Li+], [Na+], and [K+]; and renal FA distribution were also measured. Data [corrected to 100 g/body weight (bw) and presented as means ±SEM] were
significant, at P<-0.05. Despite a similar ingestion of solids from weeks 4 to 7 (weeks 7 to 10 of life), the rats on the EFAD diet showed
a decreased body weight from week 5. From weeks 4 to 8, Fl and urine volume were similar for both groups, but the Fl increased
at week 6 in the EFAD group; 24-h Na+ and K+ excretions were similar at all weeks, except for an increase in the EFAD group for both ions at week 7. In the EFAD group,
CCr and CLi+ decreased by 27 and 56.3%, respectively (385.7±33.4 vs. 280±21.1, and 21.0±2.1 vs. 9.2±1.1 μL/min/100 g; n=9 vs. 10), the latter result suggesting increased proximal reabsorption. The 3-h Na+ and K+ excretions were similar, but the Li+ decreased (0.78±0.06×10−2 vs. 0.32±0.03×10−2 μeq/min/100 g) in the EFAD group, giving additional support to the suggestion. Renal structure was normal and similar for
both groups, but the EFAD group showed a more prominent proximal tubule brush border, together with heavier periodic acid-Schiff
staining in all specimens from weeks 5 to 9. In the EFAD group, FA of the n−9 and n−7 series were higher, but most of the
n−6 series were lower as a percentage of total lipids in the medulla and cortex. Medullary levels of 20∶4n−6 were maintained,
22∶4n−6 declined twice, arachidonic acid was maintained, and 20∶5n−3 was lower. The EFAD diet affected glomerular function,
proximal tubular structure and function, and FA distribution in the rat kidney. 相似文献
4.
The effects of dietary n−3 and n−6 polyunsaturated fatty acids on the fatty acid composition of phospholipid, Ca++· Mg++ ATPase and Ca++ transport activities of mouse sarcoplasmic reticulum were investigated. Mice were fed a 2 weight percent fat diet containing
either 0.5 weight percent ethyl esters of 18∶3n−3, 20∶5n−3 or 22∶6n−3 as a source of n−3 polyusaturated fatty acid or 0.5
weight percent safflower oil as a cource of n−6 polyunsaturated fatty acid for 10 days. Olive oil (2 weight percent) was used
as a control diet. Although feeding n−6 polyunsaturated fatty acid induced very little modifications of the phospholipid sarcoplasmic
reticulum fatty acid composition, feeding n−3 polyunsaturated fatty acid altered it markedly. Inclusion of 18∶−3, 20∶5n−3
or 22∶6n−3 in the diet caused an accumulation of 22∶6n−3, which replaced 20∶4n−6 and 18∶2n−6 in phospholipid sarcoplasmic
reticulum. The saturated fatty acids were significantly increased with a concurrent reduction of 18∶1n−9. These changes in
the fatty acid composition resulted in a decrease in the values of the n−6/n−3 polyunsaturated fatty acid ratio and a decrease
in the ratio of 20 carbon to 22 carbon fatty acids esterified in the phospholipid sarcoplasmic reticulum. This was associated
with a decrease in Ca++ uptake by n−3 polyunsaturated fatty acid enriched sarcoplasmic reticulum vesicles as compared with n−6 fatty acid and control
diet sarcoplasmic reticulum vesicles. However, neither the affinity for Ca++ nor the maximal velocity of ATP hydrolysis activity of Ca++·MG++ ATPase were altered by the different diets. The data suggest that the incorporation of 22∶6n−3 and/or the decrease of 20∶4n−6
plus 18∶2n−6 in the phospholipid sarcoplasmic reticulum may affect the membrane lipid bilayer structure and make it more permeable
to Ca++. 相似文献
5.
Atlantic salmon were fed fish meal-based diets supplemented with either 100% fish oil (FO) or 100% rapeseed oil (RO) from
an initial weight of 85 g to a final average weight of 280 g. The effects of these diets on the capacity of Atlantic salmon
hepatocytes to elogate, desaturate, and esterify [1-14C]18∶1n−9 and the immediate substrates for the Δ5 desaturase, [1-14C]20∶3 n−6 and [1-14C]20∶4n−3, were investigated. Radiolabeled 18∶1n−9 was mainly esterified into cellular TAG, whereas the more polyunsaturated
FA, [1-14C]20∶3n−6 and [1-14C]20∶4n−3, were primarily esterified into cellular PL. More of the elongation product, [1-14C]20∶1n−9, was produced from 18∶1n−9 and more of the desaturation and elongation products, 22∶5n−6 and 22∶6n−3, were produced
from [1-14C]20∶3n−6 and [1-14C]20∶4n−3, respectively, in RO hepatocytes than in FO hepatocytes. Further, we studied whether increased addition of [1-14C]18∶1n−9 to the hepatocyte culture media would affect the capacity of hepatocytes to oxidize 18∶1n−9 to acid-soluble products
and CO2. An increase in exogenous concentration of 18∶1n−9 from 7 to 100 μM resulted in a nearly twofold increase in the amount of
18∶1n−9 that was oxidized. The conversion of 20∶4n−3 and 20∶3n−6 to the longer-chain 22∶6n−3 and 22∶5n−6 was enhanced by RO
feeding in Atlantic salmon hepatocytes. The increased capacity of RO hepatocytes to produce 22∶6n−3 was, however, not enought
to achieve the levels found in FO hepatocytes. Our data further showed that there were no differences in the hepatocyte FA
oxidation capacity and the lipid deposition of carcass and liver between the two groups. 相似文献
6.
The esterification, desaturation, and elongation of [1-14C]18∶3n−3, [1-14C]18∶2n−6, and [1-14C]20∶5n−3 at 5 and at 12°C were studied using cultivated hepatocytes from Atlantic salmon. The salmon were fed diets, in which
0, 50, or 100% of the supplementary fish oil had been replaced by soybean oil, for 950 day-degrees at 5 and 12°C. The endogenous
percentage of 18∶2n−6 in hepatocyte lipids was 2% in cells from fish fed a diet with 100% of the supplemental lipid from fish
oil, and it was slightly less than 25% in cells from fish fed the diet with 100% of the supplemental lipid from soybean oil.
Furthermore, the percentages of 20∶3n−6 and 20∶4n−6 were significantly higher in hepatocytes from fish fed on soybean oil
than they were in those of fish fed on fish oil. The percentages of 20∶5n−3 and 22∶6n−3, on the other hand, were lower. The
endogenous levels of n−6 FA were not significantly correlated with the total amounts of radiolabeled FA esterified in hepatocyte
lipids. The main radiolabeled products formed from 18∶2n−6 were 20∶2n−6 and 20∶3n−6. The level of the important eicosanoid
precursor 20∶4n−6 was twice as high in hepatocyte phospholipids from fish fed the 100% soybean oil diet as it was in hepatocytes
from fish fed the diet with 100% of supplemental lipid from fish oil. The main products formed from 18∶3n−3 were 20∶4n−3,
20∶5n−3, and 22∶6n−3. High levels of dietary 18∶2n−6 do allow, or even seem to increase, the production of 22∶6n−3 from 18∶3n−3
in hepatocytes. The main products formed from 20∶5n−3 were 22∶5n−3 and 22∶6n−3. The production of 22∶6n−3 from 20∶5n−3 was
higher at 5°C than at 12°C. The percentage of 24∶5n−3 was higher at 5°C than it was at 12°C, as was the ratio of 24∶5 to 22∶5.
These results suggest that the elongation rate of 22∶5n−3 to 24∶5n−3 is higher at the lower temperature. 相似文献
7.
Oxidation, esterification, desaturation, and elongation of [1-14C]18∶2n−6 and [1-14C]18∶3n−3 were studied using hepatocytes from Atlantic salmon (Salmo salar I.) maintained on diets deficient in n−3 and n−6 polyunsaturated fatty acids (PUFA) or supplemented with n−3 PUFA. For both
dietary groups, radioactivity from 18∶3n−3 was incoporated into lipid fractions two to three times faster than from 18∶2n−6,
and essential fatty acids (FFA) deficiency doubled the incorporation. Oxidation to CO2 was very low and was independent of substrate or diet, whereas oxidation to acid-soluble products was stimulated by EFA deficiency.
Products from 18∶2n−6 were mainly 18∶3n−6, 20∶3n−6, and 20∶4n−6, with minor amounts of 20∶2n−6 and 22∶5n−6. Products from
18∶3n−3 were mainly 18∶4n−3, 20∶5n−3, and 22∶6n−3, with small amounts of 20∶3n−3. The percentage of 22∶6n−3 in the polar lipid
fraction of EFA-deficient hepatocytes was fourfold higher than in n−3 PUFA-supplemented cells. This correlated well with our
other results obtained after abdominal injection of [1-14C]18∶3n−3 and [1-14C]18∶2n−6. In hepatocytes incubated with [4,5-3H]-22∶6n−3, 20∶5n−3 was the main product. This retrocon-version was increased by EFA deficiency, as was peroxisomal β-oxidation
activity. This study shows that 18∶2n−6 and 18∶3n−3 can be elongated and desaturated in Atlantic salmon liver, and that this
conversion and the activity of retroconversion of very long chain PUFA is markedly enhanced by FFA deficiency. 相似文献
8.
The emperor penguin (Aptenodytes forsteri) is an Antarctic seabird feeding mainly on fish and therefore has a high dietary intake of n-3 polyunsaturated fatty acids.
The yolk is accumulated in the developing oocyte while the females are fasting, and a large proportion of the fatty acid components
of the yolk lipids are derived by mobilization from the female's adipose tissue. The fatty acid composition of the total lipid
of the yolk was characterized by high levels of n-3 polyunsaturated fatty acids. However, it differed in several respects
from that of the maternal adipose tissue. For example, the proportions of 14∶0, 16∶1n−7, 20∶1n−9, 22∶1n−9, 20∶5n−3, and 22∶6n−3
were significantly greater in adipose tissue than in yolk. Thus adipose tissue lipids contained 7.6±0.3% and 8.0±0.3% (wt%
of total fatty acids; mean ±SE; n=5) of 20∶5n−3 and 22∶6n−3, respectively, whereas the yolk total lipid contained 1.6±0.1 and 5.5±0.3% of these respective
fatty acids. The proportions of 16∶0, 18∶0, 18∶1n−9, 18∶2n−6, and 20∶4n−6 were significantly lower in the adipose tissue than
in the yolk lipids. The proportions of triacylglycerol, phospholipid, free cholesterol, and cholesteryl ester in the yolk
lipid were, respectively, 67.0±0.2, 25.4±0.3, 5.3±0.2, and 1.8±0.2% (wt% of total yolk lipid). The proportions of 20∶4n−6,
20∶5n−3, 22∶5n−3, and 22∶6n−3 were, respectively, 5.7±0.3, 2.8±0.2, 1.4±0.1, and 11.7±0.5% in phospholipid and 0.4±0.0, 1.2±0.1,
0.8±0.1 and 3.6±0.3% in triacylglycerol. About 95% of the total vitamin E in the yolks was in the form of α-tocopherol with
γ-tocopherol forming the remainder. Two species of carotenoids, one identified as lutein, were present. 相似文献
9.
The incorporation of 18∶2n−6, 18∶3n−3, 20∶4n−6 and 20∶5n−3 was greater at 10°C than at 22°C in Atlantic salmon (AS), rainbow
trout (RTG-2) and turbot (TF) cells. However, there were generally no significant differences between the amount of incorporation
of all four polyunsaturated fatty acids (PUFA) into total lipid within a cell type at either 22°C or 10°C. The distributions
of the PUFA between individual phospholipid classes at 22°C was essentially the same in AS and TF cells—with the C18 PUFA the order of incorporation in these cells was phosphatidylcholine (PC) > phosphatidylethanolamine (PE) > phosphatidic
acid/cardiolipin (PA/CL); with 20∶4n−6 the order was PE and phosphatidylinositol (PI)>PC; with 20∶5n−3, PE>PC. In RTG-2 cells
at 22°C the distributions of the C18 PUFA were similar to the other cell lines, but with 20∶4n−6 the order was PC>PI>PE, and with 20∶5n−3 it was PC>PE. At 10°C
the incorporation of C18 PUFA into PC increased and into PE and PA/CL decreased, in general, in all cell lines. Incorporation of 20∶5n−3 into PC and
PE was increased and decreased at 10°C, respectively, in AS and TF cells, whereas in RTG-2 cells the changes at 10°C were
opposite i.e., increased in PE and decreased in PC. With 20∶4n−6, incorporation into PC at 10°C was increased in all cell
lines with decreased incorporation into PI in AS and RTG-2 cells and into PE in AS and TF cells, whereas incorporation of
20∶4n−6 into PE increased in RTG-2 cells. The metabolismvia desaturation and elongation of the n−3 PUFA was greater than that of the equivalent n−6 PUFA in all cell lines, irrespective
of temperature. There was less conversion of the C18 PUFA at 10°C than at 22°C in RTG-2 and TF cells, but the conversion of 18∶3n−3 by AS cells was increased at 10°C. Temperature
had no effect on the conversion of the C20 PUFA. 相似文献
10.
The objective of this study was to determine the effect of 2,2-diphenyl-5-(4-{[(1E)-pyridin-3-yl-methylidene]-amino}piperazin-1-yl)pentanenitrile (SC-26196), a Δ6-desaturase inhibitor, on PUFA metabolism in human cells. SC-26196 inhibited the desaturation of 2 μM [1-14C] 18∶2n−6 by 87–95% in cultured human skin fibroblasts, coronary artery smooth muscle cells, and astrocytes. By contrast,
SC-26196 did not affect the conversion of [1-14C]20∶3n−6 to 20∶4 in the fibroblasts, demonstrating that it is selective for Δ6-desaturase. The IC50 values for inhibition of the desaturation of 2 μM [1-14C] 18∶3n−3 and [3-14C]24∶5n−3 in the fibroblasts, 0.2–0.4 μM, were similar to those for the inhibition of [1-14C] 18∶2n−6 desaturation, and the rates of recovery of [1-14C] 18∶2n−6 and [3-14C] 24∶5n−3 desaturation after removal of SC-26196 from the culture medium also were similar. SC-26196 reduced the conversion
of [3-14C] 22∶5n−3 and [3-14C] 24∶5n−3 to DHA by 75 and 84%, respectively, but it had no effect on the retroconversion of [3-14C] 24∶6n−3 to DHA. These results demonstrate that SC-26196 effectively inhibits the desaturation of 18- and 24-carbon PUFA
and, therefore, decreases the synthesis of arachidonic acid, EPA, and DHA in human cells. Furthermore, they provide additional
evidence that the conversion of 22∶5n−3 to DHA involves Δ6-desaturation. 相似文献
11.
To study whether Atlantic salmon β-oxidation was affected by dietary FA composition, an in vitro study with primary hepatocytes was undertaken. Isolated hepatocyte cultures were stimulated with either 16∶0, 18∶1n−9, 18∶2n−6,
18∶3n−3, 20∶5n−3, or 22∶6n−3 in triplicate for 24 h. In addition, a control was included where no FA stimulation was performed,
also in triplicate. After stimulation, radiolabeled [1-14C]18∶3n−3 was added and the cells were incubated for 2 h at 20°C. The cells were then harvested, and radioactivity was determined
in the acid-soluble part of the cells and medium, i.e., the end products of the β-oxidation pathway. Specific β-oxidation
activity was significantly higher in hepatocytes stimulated with 18∶3n−3. Further, when taking into account the amount of
radiolabeled [1-14C]18∶3n−3 taken up by the cells—the relative amount of β-oxidized [1-14C]18∶3n−3 of the total FA taken up by the hepatocytes—no significant differences were found. Thus, the regulation of β-oxidation
activity in the primary Atlantic salmon hepatocytes seems to be at the level of FA uptake and transport into the cell. This
in vitro study shows that the catabolism processes in salmon hepatocytes are affected by the FA available and probably already regulated
at the level of FA uptake. 相似文献
12.
Atlantic salmon post-smolts were fed diets rich in linoleic acid (sunflower oil, SO), α-linolenic acid (linseed oil, LO) or
long-chain polyunsaturated fatty acids (fish oil, FO) for a period of 12 wk. In the liver phospholipids of fish fed SO, the
levels of 18∶2n−6, 20∶2n−6, 20∶3n−6 and 20∶4n−6 were significantly elevated compared to both other treatment. In choline phospholipids
(CPL), ethanolamine phospholipids (EPL) and phosphatidylserine (PS) the levels of 22∶4n−6 and 22∶5n−6 were significantly elevated
in fish fed SO. In liver phospholipids from fish fed LO, 18∶2n−6, 20∶2n−6 and 20∶3n−6 were significantly elevated but 20∶4n−6,
22∶4n−6 and 22∶5n−6 were similar or significantly decreased compared to fish fed FO. Liver phospholipids from fish fed LO
had increased 18∶3n−3 and 20∶4n−3 compared to both other treatments while EPL and phosphatidylinositol (PI) also had increased
20∶5n−3. In fish fed LO, 22∶6n−3 was significantly reduced in CPL, PS and PI compared to fish fed FO. Broadly similar changes
occurred in gill phospholipids. Production of 12-lipoxygenase metabolites in isolated gill cells stimulated with the Ca2+-ionophore A23187 were significantly reduced in fish fed either SO or LO compared to those fed FO. However, the ratio 12-hydroxy-5,8,10,14-eicosatetraenoic
acid (12-HETE)/12-hydroxy-5,8,10,14,17-eicosapentaenoic acid (12-HEPE) was significantly elevated in stimulated gill cells
from SO-fed fish. Although mean values of thromboxane B2 (TXB2) and prostaglandin E2 (PGE2) were increased in fish fed SO, they were not significantly different from those of the other two treatments. 相似文献
13.
Recent research in various biological systems has revived interest in interactions between the (n−6) and (n−3) essential fatty
acids. We have utilized cultured glioma cells to show that linolenic acid, 18∶3(n−3), is rapidly desaturated and chain elongated;
20∶5(n−3) is the major product and accumulates almost exclusively in phospholipids. We examined effects of various (n−6),
(n−3), (n−9) and (n−7) fatty acids at 40 μM concentration on desaturation and chain elongation processes using [1-14C]18∶3(n−3) as substrate. In general, monoenoic fatty acids were without effect. The (n−6) fatty acids (18∶2, 18∶3, 20∶3,
20∶4 and 22∶4) had little effect on total product formed. There was a shift of labeled product to triacylglycerol, and in
phospholipids, slightly enhanced conversion of 20∶5 to 22∶5 was evident. In contrast, 22∶6(n−3) was inhibitory, whereas 20∶3(n−3)
and 20∶5(n−3) had much less effect. At concentrations <75 μM, all acids were inhibitory. Most products were esterified to
phosphatidylcholine, but phosphatidylethanolamine also contained a major portion of 20∶5 and 22∶5. We provide a condensed
overview of how the (n−6) and (n−3) fatty acids interact to modify relative rates of desaturation and chain elongation, depending
on the essential fatty acid precursor. Thus, the balance between these dietary acids can markedly influence enzymes providing
crucial membrane components and substrates for biologically active oxygenated derivatives. 相似文献
14.
This study has utilized radiolabeled analogues of arachidonic acid to study the substrate specificity of elongation of long-chain
polyunsaturated fatty acids. Human umbilical vein endothelial cells were incubated for 2–72 hr in medium supplemented with
0.9–2.6 μM [14C]fatty acid, and cellular glycerolipids were analyzed by gas-liquid chromatography with radioactivity detection. Elongation
of naturally occurring C20 polyunsaturated fatty acids occurred with eicosapentaenoate (20∶5(n−3))>Mead acid (20∶3(n−9))>arachidonate (20∶4(n−6)). Chain
length markedly influenced the extent of elongation of 5,8,11,14-tetraenoates (18∶4>19∶4>20∶4>21∶4); effects of initial double
bond position were also observed (6,9,12,15–20∶4>4,7,10,13–20∶4. Neither 5,8,14- nor 5,11,14–20∶3 was elongated to the extent
of 5,8,11–20∶3. Differences between polyunsaturated fatty acids were observed both in the initial rates and in the maximal
percentages of elongation, suggesting that the content of cellular C20 and C22 fatty acids may represent a balance between chain elongation and retroconversion.
Umbilical vein endothelial cells do not exhibit significant desaturation of either 22∶4(n−6) or 22∶5(n−3). By contrast, incubation
with 5,8,11,14-[14C]18∶4(n−4) resulted in formation of both [14C]20∶5(n−4) and [14C]22∶5(n−4). The respective time courses for the appearances of [14C]22∶5(n−4) and [14C]20∶5(n−5) suggests Δ6 desaturation of [14C]22∶4(n−4) rather than Δ4 desaturation of [14C]20∶4(n−4). 相似文献
15.
Marine fish have an absolute dietary requirement for C20 and C22 highly unsaturated fatty acids. Previous studies using cultured cell lines indicated that underlying this requirement in
marine fish was either a deficiency in fatty acyl Δ5 desaturase or C18–20 elongase activity. Recent research in turbot cells found low C18–20 elongase but high Δ5 desaturase activity. In the present study, the fatty acid desaturase/elongase pathway was investigated
in a cell line (SAF-1) from another carnivorous marine fish, sea bream. The metabolic conversions of a range of radiolabeled
polyunsaturated fatty acids that comprised the direct substrates for Δ6 desaturase ([1-14C]18∶2n−6 and [1-14C]18∶3n−3), C18–20 elongase ([U-14C]18∶4n−3), Δ5 desaturase ([1-14C]20∶3n−6 and [1-14C]20∶5n−3), and C20–22 elongase ([1-14C]20∶4n−6 and [1-14C]20∶5n−3) were utilized. The results showed that fatty acyl Δ6 desaturase in SAF-1 cells was highly active and that C18–20 elongase and C20–22 elongase activities were substantial. A deficiency in the desaturation/elongation pathway was clearly identified at the level
of the fatty acyl Δ5 desaturase, which was very low, particularly with 20∶4n−3 as substrate. In comparison, the apparent activities
of Δ6 desaturase, C18–20 elongase, and C20–22 elongase were approximately 94-, 27-, and 16-fold greater than that for Δ5 desaturase toward their respective n−3 polyunsaturated
fatty acid substrates. The evidence obtained in the SAF-1 cell line is consistent with the dietary requirement for C20 and C22 highly unsaturated fatty acids in the marine fish the sea bream, being primarily due to a deficiency in fatty acid Δ5 desaturase
activity. 相似文献
16.
Roberto J. de Antueno Richard C. Cantrill Yung-Sheng Huang Michele Elliot David F. Horrobin 《Lipids》1993,28(4):285-290
This study was undertaken to investigate the total plasma fatty acid composition and the relationship between plasma triacylglycerol
(TG) levels and liver Δ9 desaturase activity in mice fed n−3 and/or n−6 fatty acid or hydrogenated coconut oil (HCO) (maximum
25 mg/g) supplemented diets. Generally, plasma TG levels and Δ9 desaturase activity were inversely correlated with the ratio
of the sum of long chain n−3 fatty acids to 18∶2n−6 and to the ratio of the sum of long chain n−3 fatty acids to 18∶n−3, but
they were positively correlated with the ratio of products and substrates (18∶1/18∶0) of the enzyme in plasma total lipids.
The n−3 fatty acid (mainly 20∶5n−3) enriched diet, when compared to the HCO diet at 21 d, caused a significant reduction in
plasma TG levels but not in Δ9 desaturase activity. However, a marked reduction in plasma TG content (50–60%) and Δ9 desaturase
activity (55–70%) was observed when both 20∶5n−3 and 18∶3n−6 were supplemented in the diet. The plasma TG levels and Δ9 desaturase
activity rose again when the animals were fed the HCO diet or chow. The results suggest that low dose supplementation of a
mixture of n−3 (mainly 20∶5n−3) and n−6 (18∶3n−6) fatty acids modified both plasma TG content and liver Δ9 desaturase activity,
in parallel. 相似文献
17.
In a previous study we showed that intestinal uptake of α-linolenic acid (18∶3n−3) was carrier-mediated and we suggested that
a plasma membrane fatty acid protein was involved in the transport of long-chain fatty acids. To further test this hypothesis,
the mechanism of linoleic acid (18∶2n−6) uptake by isolated intestinal cells was examined using a rapid filtration method
and 20 mM sodium taurocholate as solubilizing agent. Under these experimental conditions transport of [1-14C]linoleic acid monomers in the concentration range of 2 to 2220 nM was saturable with a Vm of 5.1±0.6 nmol/mg protein/min and a Km of 183±7 nM. Experiments carried out in the presence of metabolic inhibitors, such as 2,4-dinitrophenol and antimycin A,
suggested that an active, carriermediated mechanism was involved in the intestinal uptake of this essential fatty acid. The
addition of excess unlabeled linoleic acid to the incubation medium led to a 89% decrease in the uptake of [1-14C]linoleic acid, whiled-glucose did not compete for transport into the cell. Other long-chain polyunsaturated fatty acids added to the incubation
mixture inhibited linoleic acid uptake by more than 80%. The presence of α-linolenic acid (18∶3n−3) in the incubation medium
caused the competitive inhibition (Ki=353 nM) of linoleic acid uptake. The data are compatible with the hypothesis that intestinal uptake of both linoleic, and
α-linolenic acid is mediated by a membrane carrier common to long-chain fatty acids. 相似文献
18.
Robert A. Gibson Mark A. Neumann Sharon L. Burnard Josephine A. Rinaldi Glen S. Patten Edward J. McMurchie 《Lipids》1992,27(3):169-176
Adult male marmoset monkeys were fed eicosapentaenoic acid (20∶5n−3) as the ethyl ester in diets containing either 32% (reference
diet, no added cholesterol) or 7% (atherogenic diet with 0.2% added cholesterol) linoleic acid (18∶2n−6) for 30 wk. No changes
were seen in the level of phosphatidylcholine (PC) or phosphatidylethanolamine (PE) but minor changes were observed in both
the sphingomyelin (SPM) and phosphatidylinositol plus phosphatidylserine (PI+PS) fractions of erythrocyte lipids. The extent
of total n−3 fatty acid incorporation into membrane lipids was higher in atherogenic diets (polyunsaturated/monounsaturated/saturated
(P/M/S) ratio 0.2∶0.6∶1.0) than reference diets (P/M/S ratio 1∶1∶1) and this was true for both PE (33.4±1.0%vs 24.3±1.1%) and PC (9.3±0.5%vs 4.9±0.3%). Although suitable controls for cholesterol effects were not included in the study, earlier results obtained with
marmosets lead us to believe such effects were probably small. Regardless of basic diet (atherogenic, reference), 20∶5n−3
was preferentially incorporated into PE (10.8±0.2%, 6.0±0.02%) while smaller amounts were incorporated into PC (6.9±0.4%,
3.2±0.2%). The major n−3 polyunsaturated fatty acid found in PE in response to dietary 20∶5n−3 was the elongation metabolite
22∶5n−3 in both the atherogenic (17.7±0.7%) and reference (14.3±1.0%) dietary groups; 22∶6n−3 levels were less affected by
diet (4.7±0.3% and 3.9±0.2%, respectively). The results can be interpreted to indicate an inverse relationship between the
amount of dietary 18∶2n−6 and incorporation of 20∶5n−3 into erythrocyte membrane phospholipids regardless of whether the major
dietary n−3 fatty acid was α-linolenate (18∶3n−3) or 20∶5n−3. This interpretation is supported by theoretical calculations. 相似文献
19.
The effects of various unsaturated fatty acids such as oleic (18∶1n−9), linoleic (18∶2n−6) and arachidonic (20∶4n−6) on the
activities of fatty acid synthetase (FAS), malic enzyme (ME), glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate
dehydrogenase (6PGDH) all were determined in primary cultures of mouse hepatocytes. Activities of FAS and ME were found to
decrease with time in culture regardless of whether hepatocyte donors were fed diets containing polyunsaturated fatty acid-free
hydrogenated cottonseed oil (HCTO) or corn oil (CO). On the other hand, while G6PDH activity also declined in cultured hepatocytes
obtained from HCTO-fed mice, the activity of this enzyme increased in cells cultured from CO-fed mice. 6PGDH activity was
found to increase in hepatocytes obtained from both diet groups. Neither 18∶2 nor 20∶4 when added to media could alter FAS
or ME activities compared with those observed with either 18∶1-containing or fatty acid-free media. Since lactic dehydrogenase
activity and the rate of incorporation of [3H] leucine into FAS protein were unaltered with time in hepatocyte cultures, the decreased activities of FAS and ME cannot
be attributed to a loss in cell viability during culture but rather appear to be specific for those enzymes which respond
to diet hormones in vivo. Examination of the fatty acid contents of the cells after the culture period showed that the values
for the ratios of 16∶0/16∶1 and of 18∶0/18∶1 were elevated when either 18∶2 or 20∶4 was added to the medium even though there
was no evidence for elongation of the added 18∶2 or for 20∶4 being converted to 22∶4. This result suggest that Δ9-desaturase
activity was inhibited by these polyunsaturated fatty acids and that conversion of 18∶2 to 20∶4 was not required for such
action.
The rate of synthesis determined by the relative rate of incorporation of [3H]leucine into FAS was two to five times higher in hepatocytes prepared from mice fed the HCTO diet than in hepatocytes from
mice fed the CO diet. We have concluded that the mechanisms for long-term regulation may not be contained entirely within
the liver. 相似文献
20.
The FA composition of Fasciola hepatica 12 kDA purified native FA-binding protein (nFh12), a candidate vaccine against fascioliasis, is described. The FA chain lengths ranged between 12 and 24 carbons. The
principal FA were 16∶0 18∶1n−9, 18∶0, 20∶4n−6, and 20∶1n−9. The acids 16∶0, 18∶1n−9, and 18∶0 comprised over half the FA that
were bound to the whole FA-binding protein. Small amounts (1.0–2.8%) of isoanteiso methyl-branched FA also were characterized. Forty-one different FA were identified in extracts of the adult flukes, with
the three most abundant FA also being 16∶0, 18∶1n−9, and 18∶0. A similar proportion of saturated vs. unsaturated FA was observed
between the whole extract from F. hepatica and the nFh12 protein. However, the n−3/n−6 ratio of PUFA was significantly different, being 1.2 in the whole extract vs. 9.6 in the
nFh12 protein complex. The nFh12 protein binds more n−5, n−6, and n−7 PUFA and less n−3 and n−9 PUFA than the whole extract. In addition, cholesterol
(56%), sitosterol (36%), and fucosterol (8%) also were bound to the nFh12 protein complex. 相似文献