共查询到20条相似文献,搜索用时 31 毫秒
1.
S. C. Cunnane G. Moine S. S. Likhodii J. Vogt T. N. Corso J. T. Brenna H. Demmelmair B. Koletzko K. -H. Tovar G. Kohn G. Sawatzki R. Muggli 《Lipids》1997,32(2):211-217
Our objective was to develop a suitable probe to study metabolism of polyunsaturated fatty acids by 13C nuclear magnetic resonance (NMR) in the suckling rat pup. [3-13C] γ-Linolenic acid was chemically synthesized, and a 20 mg (Experiment 1) or 5 mg (Experiment 2) dose was injected into the
stomachs of 6–10-day-old suckling rat pups that were then killed over a 192 h (8 d) time course. 13C NMR showed that 13C in γ-linolenate peaked in liver total lipids by 12-h post-dosing and that [5-13C]-arachidonic acid peaked in both brain and liver total lipids 48–96 h post-dosing. 13C enrichment in brain γ-linolenic acid was not detected by NMR, but gas chromatography-combustion-isotope ratio mass spectrometry
showed that its mass enrichment in brain phospholipids at 48–96 h post-dosing was 1–2% of that in brain arachidonic acid.
13C was present in liver and brain cholesterol and in perchloric acid-extractable water-soluble metabolites in the brain, liver
and carcass. We conclude that low but measurable amounts of exogenous γ-linolenic acid do access the suckling rat brain in vivo. The slow time course of [5-13C] arachidonic acid appearance in the brain suggests most of it was probably transported there after synthesis elsewhere,
probably in the liver. Some carbon from γ-linolenic acid is also incorporated into lipid products other than n−6 long-chain
polyunsaturated fatty acids. 相似文献
2.
Stephen C. Cunnane Mary Ann Ryan Kerr S. Craig Steven Brookes Berthold Koletzko Hans Demmelmair Janet Singer David J. Kyle 《Lipids》1995,30(8):781-783
The objective was to determine whether rats could synthesize longer chain polyunsaturates from hexadecadienoate (16∶2n−6)
and hexadecatrienoate (16∶3n−3). Rats were gavaged with uniformly13C-labelled hexadecadienoate or hexadecatrienoate, euthanized 24 h later, and total lipids were extracted from liver and carcass.
Gas chromatogrpahy/combustion/isotope ratio mass spectrometry was used to measure13C levels in individual liver, carcass, and whole body fatty acids.13C Enrichment was present in desaturated and chain-elongated polyunsaturates, including linoleate, arachidonate, α-linolenate,
and docosahexaenoate at 12–13% of the dose of tracer given.13C Enrichment from hexadecatrienoate was highest in carcass and liver α-linolenate, representing 3.5 and 17.9% of the total
α-linolenate pool, respectively. For linoleate, arachidonate, or docosahexaenoate, the contribution of13C did not exceed 0.2% of the total body pool. Green leafy vegetables common in the human diet were shown to contain up to
1.2% of total fatty acids as hexadecadienoate and 11.6% as hexadecatrienoate. Hence, humans consuming green vegetables probably
synthesize a small proportion of their total body content of linoleate and α-linolenate. 相似文献
3.
The distribution of isotopic labels inn-heptadecane enriched from [1,2-13C] and [2-13C, 2-2H3) acetates byAnacystis nidulans has been determined by13C nuclear magnetic resonance (13C NMR). Labeling with [1,2-13C] acetate is consistent with assembly from13C−13C units derived from an acetate “starter” group and 8 malonate units, as in fatty acid biosynthesis, followed by production
of a methyl group through bond cleavage of the terminal13C−13C unit. A comparison of the hydrocarbon with palmitic acid (the only fatty acid produced in sufficient amount for NMR analysis)
enriched from [2-13C,2-2H3]acetate by the same culture shows that they have retained the same fraction of2H at corresponding sites, and have therefore undergone identical biosynthetic and hydrogen-deuterium exchange processes, as
would be expected ifn-heptadecane originates from de novo-synthesized stearic acid.
NRCC No. 18251. 相似文献
4.
The additional mass associated with 13C in metabolic tracers may interfere with their metabolism. The comparative isomerization and biohydrogenation of oleic, [1-13C]oleic, and [U-13C]oleic acids by mixed ruminal microbes was used to evaluate this effect. The percent of stearic, cis-14 and- 15, and trans-9 to-16 18∶1 originating from oleic acid was decreased for [U-13C]oleic acid compared with [1-13C]oleic acid. Conversely, microbial utilization of [U-13C]oleic acid resulted in more of the 13C label in cis-9 18∶1 compared with [1-13C]oleic acid (53.7 vs. 40.1%). The isomerization and biohydrogenation of oleic acid by ruminal microbes is affected by the
mass of the labeled tracer. 相似文献
5.
The suppression of plasma very low density lipoprotein (VLDL) triglyceride levels by dietary fish oils rich in polyunsaturated
n−3 fatty acids has been attributed to decreased hepatic VLDL secretion. To investigate the effect of n−3 fatty acids on lipid
metabolism and VLDL secretion in a tissue culture system, we incubated rabbit hepatocytes with oleic acid and eicosapentaenoic
acid (EPA) and examined [3H]glycerol and [14C]fatty acid incorporation into hepatocyte triglyceride and phospholipid and into media VLDL. Glycerol incorporation studies
showed that EPA failed to stimulate VLDL triglyceride secretion from hepatocytes as occurred with oleic acid (P<0.05). Oleic
acid preferentially enhanced hepatocyte triglyceride synthesis while EPA stimulated significantly phospholipid synthesis (P<0.01).
Varying the relative concentrations of oleic acid and EPA at a constant total fatty acid concentration corroborated preferential
triglyceride synthesis from oleic acid. Synthesis shifted predominantly to phospholipids with increasing concentrations of
EPA and lower levels of oleic acid. Incorporation of the [14C]fatty acids (800 μM) followed similar patterns: 87% of [14C]oleic acid was incorporated into hepatocyte triglyceride and 44% of [14C]EPA was assimilated in hepatocyte phospholipid (p<0.001). Fatty acids at trace concentrations (53 nM) showed a more divergent
pattern of lipid incorporation: 60% of [14C]oleic acid was incorporated into triglyceride while 91% of [14CEPA was incorporated into phospholipid (p<0.001). We conclude that in primary rabbit hepatocyte culture, which appears to
be a useful model to study lipid metabolism and VLDL secretion, EPA is avidly incorporated into phospholipid while oleic acid
predominantly becomes esterified in triglyceride. In addition, EPA, unlike oleic acid, fails to stimulate hepatocyte VLDL
secretion. These divergent effects on hepatocyte lipid metabolism are, at least in part, likely to be responsible for fish
oil induced suppression of plasma triglycerides. 相似文献
6.
Dauglas R. Tocher 《Lipids》1993,28(4):267-272
The origin of docosahexaenoic acid (DHA, 22∶6n−3) that accumulates in turbot brain during development was investigated by
studying the incorporation and metabolismvia the desaturase/elongase pathways of [1-14C]-labelled polyunsaturated fatty acids (PUFA) in primary cultures of brain astrocytic glial cells. There was little specificity
evident in the total incorporation of PUFAs into the turbot astrocytes. However, specificity was apparent in the distribution
of the various PUFAs among the individual lipid classes. In particular, there was very specific incorporation of [14C]arachidonic acid (AA, 20∶4n−6) into phosphatidylinositol balanced by a lower incorporation of this acid into total diradyl
glycerophosphocholines. [14C]-Linolenic acid (LNA, 18∶3n−3) and [14C]eicosapentaenoic acid (EPA, 20∶5n−3) were metabolizedvia the desaturase/elongase pathways to a significantly greater extent than [14C]linoleic acid (18∶2n−6) and [14C]AA. The turbot astrocytes expressed very little Δ5 desaturase activity and only low levels of Δ4 desaturation activity.
Although the percentages were small, approximately 4–5 times as much labelled DHA was produced from [14C]EPA compared with [14C]LNA. However, it was concluded that very little DHA in the turbot brain could result from the metabolism of LNA and EPA
in astrocytic glial cells. 相似文献
7.
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
8.
Kumar D. Mukherjee 《Lipids》1986,21(5):347-352
Lipids in developing seeds ofSinapis alba contain appreciable proportions of (n−7)octadecenoic (vaccenic) acid besides its (n−9) isomer (oleic acid), whereas the constituent
very long chain (>C18) monounsaturated fatty acids of these lipids are overwhelmingly composed of the (n−9) isomers. Cotyledons of developingSinapis alba seed use [1-14C]acetate, [1-14C]malonate or [1,3-14C]malonyl-CoA for de novo synthesis of palmitic, stearic and oleic acids and for elongation of preformed oleic, vaccenic and
stearic acids to their higher (n−9), (n−7) and saturated homologs, respectively. Moreover, elongation of preformed (n−7)palmitoleic
acid to vaccenic acid is observed. Stepwise C2-additions to preformed oleoyl-CoA by acetyl-CoA or malonyl-CoA yielding (n−9)icosenoyl-CoA, (n−9)docosenoyl-CoA and (n−9)tetracosenoyl-CoA
are by far the most predominant reactions catalyzed by the elongase system, which seems to have a preference for oleoyl-CoA
over vaccenoyl-CoA as the primer. The pattern of14C-labeling of the very long chain fatty acids formed from either acetate or malonate shows a close analogy in the mode of
elongation of monounsaturated and saturated fatty acids. 相似文献
9.
Which cell type is responsible for the high levels of very long chain polyunsaturated fatty acids in testis and whether this
fatty acid pattern is a result of a local synthesis are not presently known. In this study, fatty acid conversion from 20∶4n−6
to 22∶5n−6 and from 20∶5n−3 to 22∶6n−3 was investigated in isolated rat germ cells incubated with [1-14C]-labeled fatty acids. The germ cells elongated the fatty acids from 20- to 22-carbon atoms and from 22- to 24-carbon atoms
but had a low Δ6 desaturation activity. Thus, little [14C]22∶5n−6 and [14C]22∶6n−3 were synthesized. When Sertoli cells were incubated with [1-14C]20∶5n−3 for 24 h, an active fatty acid elongation and desaturation were observed. In vivo germ cells normally have a higher content of 22∶5n−6 or 22∶6n−3 than Sertoli cells. An eventual transport of essential fatty
acids from Sertoli cells to germ cells was thus studied. Different co-culture systems were used in which germ cells were on
one side of a filter and Sertoli cells on the opposite side. When isolated pachytene spermatocytes or round spermatids were
added to the opposite side of a semipermeable filter, approximately 1 nmol [14C]-22∶6n−3 crossed the filter. Little of this was esterified in the germ cells. Similarly, in using [1-14C]20∶4n−6 in identical experiments, very little [14C]22∶5n−6 was esterified in germ cells on the opposite side of the filter. Although the very active synthesis of 22∶5n−6 and
22∶6n−3 observed in Sertoli cells suggests a transport of these compounds to germ cells, this was not experimentally determined. 相似文献
10.
The13C NMR spectrum of the carbonyl carbons of the acyl groups of triacylglycerols of palm oil has been shown to give the composition
of saturated, oleic and linoleic acyl groups at the 1,3-positions and at the 2-position of the glycerol moiety. Except for
the lack of differentiation of the saturated fatty acids, the13C NMR technique provides the same information as the tedious enzymatic hydrolysis cum fatty acid analysis. The carbonyl carbon
of the linolenic acyl group (18∶3,[cis, cis, cis]-9, 12, 15) has a chemical shift which is only 0.005 ppm to low frequency of that of the linoleic acyl group (18∶2,[cis, cis]-9, 12), so that the two resonances may not be distinguishable (or resolved) even at a high magnetic field. 相似文献
11.
Zu Jun Zhang Henry G. Wilcox Marshall B. Elam Lawrence W. Castellani Murray Helmberg 《Lipids》1991,26(7):504-511
The hepatic metabolism of oleic acid and n−3 fatty acids (eicosapentaenoic acid, EPA and docosahexaenoic acid, DHA), and secretion
of very low density lipoprotein (VLDL) were studied in isolated perfused rat livers from normal chow fed male rats. The basal
perfusion medium contained 30% bovine erythrocytes, 6% bovine serum albumin (BSA), and 100 mg/dL glucose, in Krebs-Henseleit
bicarbonate buffer (pH 7.4) which was recycled through the liver for 2 hr. Individual fatty acids (EPA, DHA or oleic acid),
as complexes with 6% BSA, or albumin alone, were infused at a rate of 70 μmol/hr. When any of these fatty acids was infused
at this rate, the ambient concentration in the medium was maintained at 0.3–0.4 μmol/mL, indicative of similar hepatic rates
of uptake for each fatty acid (i.e., approximately 6 μmol/g liver/hr). When fatty acid was not infused, the ambient free fatty acid level was 0.16 μmol/mL. The
concentrations of infused free fatty acids increased appropriately in the perfusion medium; however, with infusion of EPA,
DHA, or oleate, the concentrations of perfusate palmitate and linoleate were the same as when fatty acid was not infused.
Additionally, the perfusate concentration of oleate in the free fatty acid fraction was not affected by infusion of EPA and
DHA. These data indicate a constant outflow of endogenous fatty acid unaffected by the presence of the exogenously supplied
fatty acid.
The net secretion rate of VLDL lipids and protein was stimulated by infusion of oleate, whereas when EPA was infused, secretion
rates were lower and similar [except for VLDL cholesterol (C), which was greater] to those occuring when fatty acid was not
provided. DHA stimulated the secretion of VLDL triacylglycerol (TG), phospholipid (PL) and C to a similar rate, as did oleate,
but secretion of VLDL cholesteryl ester (CE) and protein was lower and similar to that with EPA. VLDL and hepatic TG and CE
were enriched with the infused fatty acids, compared to experiments without fatty acids, as determined by gas chromatography.
Enrichment of PL, however, was significant only in liver upon infusion of EPA. The formation of14CO2 and perchloric acid soluble products from [1-14C]EPA, considered separately, did not differ statistically from that obtained with [1-14C]oleate, although the mean values were higher with [1-14C]EPA. However, the sum of oxidation products derived from EPA was significantly greater than that from oleate. Incorporation
of [1-14C]EPA into TG and CE, but not into PL, was lower as compared to that from [1-14C]oleate. These lower rates of incorporation of [1-14C]EPA into VLDL lipids therefore paralleled the mass fatty acid enrichment-patterns. It may be concluded that EPA is used
to a similar extent as oleate for synthesis of PL, but is a poorer substrate for synthesis of TG. The reduced output of newly
synthesized (radioactive) PL reflected the lower hepatic output of VLDL. Since hepatic uptake of EPA, DHA or oleate was identical,
utilization of EPA for TG synthesis was less than that of oleate or DHA. Further-more, utilization of endogenous fatty acids
for TG synthesis and secretion of the VLDL was reduced in the presence of EPA. The decreased TG synthesis resulted in reduced
formation of VLDL for transport of TG from the liver. These effects taken together with an apparently increased oxidation
of EPA provide substantial evidence for a decrease in formation of VLDL and transport of TG, PL, C and CE into the circulation
in response to EPA. DHA, however, appears to be an adequate substrate for TG synthesis and stimulates VLDL secretion. The
reduced transport of CE may reflect lower selectivity of DHA by acyl-CoA; cholesterol acyltransferase for CE formation. 相似文献
12.
Norflurazon is a herbicide known to inhibit carotene biosynthesis and linolenic acid biosynthesis in plants. In the present
work, the effect of norflurazon on the metabolism of essential fatty acids was studied in isolated rat liver cells and in
rat liver microsomes, incubated with [1-14C] labeled linolenic acid (18∶3, n−3), dihomogammalinolenic acid (20∶3, n−6) and eicosapentaenoic acid (20∶5, n−3). Norflurazon
(0.1 mM, 1.0 mM) was found to inhibit essential fatty acid desaturation. The Δ6 desaturation is inhibited more efficiently
than the Δ5 and Δ4 desaturation. The chain elongation of essential C18 fatty acids to their C20 and C22 homoglogs was not inhibited by norflurazon. 相似文献
13.
The effects of different dietary oils on the fatty acid compositions of liver phospholipids and the desaturation and elongation
of [1-14C]18∶3n−3 and [1-14C]18∶2n−6 were investigated in isolated hepatocytes from Atlantic salmon. Atlantic salmon smolts were fed diets containing
either a standard fish oil (FO) as a control diet, a 1∶1 blend of Southern Hemisphere marine oil and tuna orbital oil (MO/TO),
sunflower oil (SO), borage oil (BO), or oliver oil (OO) for 12 wk. The SO and BO diets significantly increased the percentages
of 18:2n−6, 18:3n−6, 20:2n−6, 20:3n−6, and total n-6 polyunsaturated fatty acids (PUFA) in salmon liver lipids in comparison
with the FO diet. The BO diet also increased the percentage of 20:4n−6. Both the SO and BO diets significantly reduced the
percentages of all n−3 PUFA in comparison with the FO diet. The OO diet significantly increased the percentages of 18:1n−9,
18:2n−6, total monoenes, and total n−6 PUFA in liver lipids compared to the FO diet, and the percentages of all n−3 PUFA were
significantly reduced. With [1-14C]18:3n−3, the recovery of radioactivity in the products of Δ6 desaturation was significantly greater in the hepatocytes from
salmon fed SO, BO, and OO in comparison with the FO diet. The BO diet also increased the recovery of radioactivity in the
products of Δ5 desaturation. Only the BO diet significantly affected the desaturation of [1-14C]18:2n−6, increasing recovery of radioactivity in both Δ6- and Δ5-desaturation products. In conclusion, dietary BO, enriched
in γ-linolenic acid (18:3n−6), significantly increased the proportions of both 20:3n−6 and 20:4n−6 in salmon liver phospholipids
and also significantly increased the desaturation of both 18:2n−6 and 18:3n−3 in salmon hepatocytes. The possible relationships
between dietary fatty acid composition, tissue phospholipid fatty acid composition, and desaturation/elongation activities
are discussed. 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.
Effects of an eicosapentaenoic and docosahexaenoic acid concentrate on a human lung carcinoma grown in nude mice 总被引:1,自引:0,他引:1
M. G. de Bravo R. J. de Antueno J. Toledo M. E. De Tomás O. F. Mercuri C. Quintans 《Lipids》1991,26(11):866-870
The effects of the n−3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), on the growth of a human lung
mucoepidermoid carcinoma (HLMC) in athymic mice were studied. The mice were divided into three groups which were given either
a control chow diet (C), a chow diet supplemented with EPA/DHA (P) (25 or 50 mg of free n−3 fatty acids/g of pellet/day),
or chow diet supplemented with palmitic acid (S) (isocaloric with P). Two independent experimental schedules were followed:
i) host mice bearing either tumors that were allowed to reach 4000 mm3, or only 35 mm3, were fed C, P or S for 21 or 41 days; ii) animals were fed C, P and S for 9 days before tumor implant and were maintained
on these diets throughout tumor growth. Food consumption, mouse weight and liver/body weight ratio showed no significant differences
between supplemented diets and chow. Tumor growth was markedly inhibited (45%) in both experiments by the EPA/DHA supplemented
diet. In Experiment 2, only 60% of mice fed diet P had tumors. The fatty acid composition of neutral and polar lipids of host
liver and tumor reflected the dietary intake of n−3 fatty acids; the content of arachidonic acid was reduced by 50%, and EPA/DHA
was increased 3-to 5-fold. Tumor prostaglandin E2 levels were reduced 7.4-fold in the P group. The reduced PGE2 content may be a factor in tumor growth inhibition.
Preliminary data were presented at the Annual Meeting of the American Oil Chemists' Society, (1990), Baltimore, MD, (de Antueno,
R.J., Bravo, M.G. de, Toledo, J., De Tomas, M.E., Mercuri, O., Quintans, C. (1990)INFORM 1, 328 (Abstract HH1). 相似文献
16.
The incorporation of [1-14C]linoleic acid, and [1-14C]linoleic acid into cellular lipids of cultured human skin fibroblasts was studied. Cultured cells took up both labeled fatty
acids at nearly the same rate and incorporated them into a variety of lipid classes. At the end of 1 hr incubation with [1-14C]linoleic acid, radioactivity was found in the triacylglycerol (TG) and choline phosphoglyceride (CPG) pools preferentially.
Incorporation into the TG fraction decreased rapidly, while the uptake into CPG, serine phosphoglyceride (SPG), and ethanolamine
phosphoglyceride (EPG) fractions increased progressively with longer incubation times. Similar results were obtained with
[1-14C]linoleic acid as precursor. At the end of 24 hr, desaturation and chain elongation of 18∶3 n−3 was more extensive than conversion
of 18∶2 n−6 to higher polyenoic acids. During pulse-chase experiments with either fatty acid precursor, the incorporated radioactivity
was progressively lost from cellular lipids, particularly from the TG and CPG fractions, but continued to increase in the
SPG and EPG pools. The similar labeling pattern of cellular phospholipids with linoleic or linolenic acids, and data from
pulse-chase studies suggest that a direct transfer of fatty acids from CPG to EPG is a likely pathway in fibroblast cultures.
Incorporation into the EPG pool during the pulse-chase experiments paralleled extensive desaturation and elongation of linoleic
acid into 20∶4 n−6, and 22∶4 n−6; and of linolenic acid into 22∶5 n−3 and 22∶6 n−3. 相似文献
17.
Liver nuclear incorporation of stearic (18∶0), linoleic (18∶2n−6), and arachidonic (20∶4n−6) acids was studied by incubation
in vitro of the [1-14C] fatty acids with nuclei, with or without the cytosol fraction at different times. The [1-14C] fatty acids were incorporated into the nuclei as free fatty acids in the following order: 18∶0>20∶4n−6≫18∶2n−6, and esterified
into nuclear lipids by an acyl-CoA pathway. All [1-14C] fatty acids were esterified mainly to phospholipids and triacylglycerols and in a minor proportion to diacylglycerols.
Only [1-14C] 18∶2n−6-CoA was incorporated into cholesterol esters. The incorporation was not modified by cytosol addition. The incorporation
of 20∶4n−6 into nuclear phosphatidylcholine (PC) pools was also studied by incubation of liver nuclei in vitro with [1-14C]20∶4n−6-CoA, and nuclear labeled PC molecular species were determined. From the 15 PC nuclear molecular species determined,
five were labeled with [1-14C]20∶4n−6-CoA: 18∶0–20∶4, 16∶0–20∶4, 18∶1–20∶4, 18∶2–20∶4, and 20∶4–20∶4. The highest specific radioactivity was found in
20∶4–20∶4 PC, which is a minor species. In conclusion, liver cell nuclei possess the necessary enzymes to incorporate exogenous
saturated and unsaturated fatty acids into lipids by an acyl-CoA pathway, showing specificity for each fatty acid. Liver cell
nuclei also utilize exogenous 20∶4n−6-CoA to synthesize the major molecular species of PC with 20∶4n−6 at the sn-2 position. However, the most actively synthesized is 20∶4–20∶4 PC, which is a quantitatively minor component. The labeling
pattern of 20∶4–20∶4 PC would indicate that this molecular species is synthesized mainly by the de novo pathway. 相似文献
18.
Uptake of fatty acids by the developing rat brain 总被引:1,自引:0,他引:1
Polyunsaturated fatty acids are avidly taken up by the developing rat brain. To explore the specificity of this process, [1-14C]labeled 16∶0, 18∶2n−6, 18∶3n−3, and 22∶6n−3 each were co-injected with [3H]18∶1n−9 into the jugular vein of two-wk-old functionally hepatectomized and shamoperated control rats. The radioactivities
present in the brain, liver and serum were assessed 30 min after injection. Uptake of labeled fatty acids into brain lipids
steadily increased with increasing degree of unsaturation, with more than twice as much uptake of 22∶6n−3 compared to 16∶0.
Phosphatidylcholine was the principal radioactive species in the brain except for animals injected with [1-14C]22∶6n−3, in which more of the label was incorporated into phosphatidylethanolamine. Determination of watersoluble oxidation
products in the brain and serum revealed that the greater uptake of the more unsatrated fatty acids did not result from differences
in rates of degradation. 相似文献
19.
The aim of this study was to investigate the effect of the oxysterol 5α-cholestane-3β, 5, 6β-triol (triol) on the metabolism
of linoleic acid (18∶2n−6) to arachidonic acid (20∶4n−6) and on the cell membrane fatty acid composition. Porcine kidney cells
were incubated in medium with or without 10 μg/mL of triol for 24 h, then incubated for 1, 6, or 12 h in a medium which contained
50 μM of either [14C]linoleic acid or unlabeled linoleic acid. The cellular uptake of [14C] linoleic acid was significantly higher in the triol-treated cells than in control cells. After 1- and 6-h incubations despite
the increase of [14C]linoleic acid pool size in the triol-treated cells, neither total n−6 polyunsaturated fatty acids (PUFA) metabolites nor
arachidonic acid were increased in the triol-treated cells as compared to the control cells, but trienoic acids accumulated
to a greater extent in the triol-treated cells. Therefore, the ratios of n−6 PUFA metabolites vs. pool size of linoleic acid
and of tetraenoic acids vs. dienoic acids were significantly decreased in triol-treated cells as compared to the control cells.
The cellular fatty acid composition also showed that linoleic acid percentage was significantly increased while arachidonic
acid percentage was significantly decreased in the triol-treated cells, and that the accumulation of trienoic acids (18∶3n−6+20∶3n−6)
observed from the [14C]linoleic acid experiment was due solely to increased 20∶3n−6 content. This latter finding indicates that a decrease of elongase
activity by triol is unlikely. Our results also showed that the triol-treated cells had a lower level of free cholesterol
but higher levels of phospholipid and triol in their membranes, suggesting that triol displaced free cholesterol from the
cell membrane. 相似文献
20.
The incorporation of [1-14C]18∶3n−3, (LNA) and [1-14C]-22∶6n−3 (DHA), and the metabolismvia the desaturase/elongase pathways of [1-14C]LNA, and [1-14C]20∶5n−3 (EPA) were studied in brain cells from newly-weaned (1-month-old) and 4-month-old turbot. The rank order of the
extent of net incorporation of both LNA and DHA into glycerophospholipids was total diradyl glycerophosphocholines (CPL)>
total diradyl glycerophosphoethanolamines (EPL)> phosphatidylserine (PS) and phosphatidylinositol (PI) and was independent
of the polyunsaturated fatty acid added, the age of the fish and the time of incubation. However, the rate of incorporation
of LNA into total lipid, CPL, EPL and PS was significantly greater than the rate of incorporation of DHA, and there was a
significantly greater amount of DHA incorporated into EPL than LNA. There was no significant difference between the amounts
of LNA and DHA incorporated into total lipid, CPL, PS and PI. Therefore, little preferential uptake and incorporation of DHA
into brain cells was apparent. In 24-h incubations, on average 1.1% and 8.5% of radioactivity from [1-14C]LNA and [1-14C]EPA, respectively, were recovered in the DHA fraction. Therefore, LNA cannot contribute significantly to brain DHA levels
in the turbot but EPA can. There were no significant differences between the amounts of radioactivity from either [1-14C]LNA or [1-14C]EPA recovered in the individual products/intermediates of the desaturase pathways in brain cells from 30-day-old and 120-day-old
turbot. 相似文献