Fetal accumulation of long-chain polyunsaturated fatty acids.
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Recent studies have demonstrated that annelids possess front-end desaturases and elongases involved in the biosynthesis of physiologically important long-chain polyunsaturated fatty acids (LC-PUFA). However, methyl-end desaturases (ωx desaturases), enzymes that play a central role in the de novo biosynthesis of polyunsaturated fatty acids and their subsequent conversion into LC-PUFA, have so far been reported in only a limited number of polychaete species. To advance our understanding of ωx desaturases across the phylum Annelida, this study performed a comprehensive molecular and functional characterisation of these enzymes in the major annelid taxa Polychaeta, Clitellata and Sipuncula, encompassing species from diverse taxonomic groups and ecological niches. A total of 110 ωx desaturase sequences were retrieved from available genomes and transcriptomes. The number of ωx desaturase genes varied among species, ranging from zero to four copies. Phylogenetic analyses revealed that annelid ωx desaturases are classified into two major clades, designated Cluster A and Cluster B. Analyses of histidine-box motifs and exon-intron organisation revealed conserved patterns within each clade. Functional characterisation of ωx desaturases from Eisenia fetida (Clitellata) and Sipunculus nudus (Sipuncula), together with previously published data from polychaetes, demonstrated that annelids generally possess two ωx desaturases, one with Δ12 desaturase activity and another with ω3 desaturase activity. Collectively, these results demonstrate that annelids possess a phylogenetically and functionally diverse ωx desaturase repertoire that underpins their LC-PUFA biosynthetic capacity and may reflect adaptation to different ecological and nutritional environments.
Lipids comprised 37% and 22.1%, respectively, of the day weights of brush border- and vesicle-rich fractions separated by differential centrifugation of isolated H. diminuta tegument. Neutral lipids of both fractions were rich in cholesterol, but also contained small amounts of glycerides, sterol esters, and (in brush borders) free fatty acids. Phosphatidyl ethanolamine was the most prevalent polar lipid in both fractions, and was particularly abundant (63.4% of total polar lipids) in vesicles; sphingomyelin, not previously reported from H. diminuta, was also present. Polar lipids of both tegumental fractions resembled each other but differed from whole worm polar lipids in fatty acid composition. Tegumental polar lipids contained lower levels of long-chain, polyunsaturated fatty acids than reported for corresponding lipids of whole worms.
In lactating rats, the dietary essential fatty acids influence the composition of the milk. Feeding gamma-linolenic acid increased not only the level of this acid but also that of the 20 and 22 carbon polyunsaturated fatty acids derived from it, both in the milk and the liver triglyceride lipids of the suckling pups. Maternal nutrition, therefore, would play an important role in providing these long-chain polyunsaturated fatty acids during the active phase of growth in the rat.
The lipid composition of immature rat ovaries was examined after induction of ovulation with pregnant mare serum gonadotrophin and human chorionic gonadotrophin and subsequent (7--8 days later) stimulation with 10 micgogram LH. Two hours after the administration of LH, there was a decrease of approximately 50% in the concentration of cholesteryl esters in the ovary. The percentages (by weight) of sterol esters containing stearate, linoleate, eicosatrienoate and arachidonate were reduced by LH treatment, whereas the percentage of the C24:4 acid increased. No changes were observed in either the concentrations or fatty acid composition of phospholipids and triglycerides. These observations suggest that the metabolism of cholesteryl esters is acutely affected by LH and that sterol esters bearing long-chain polyunsaturated fatty acids are preferentially mobilized. Liberation of these unsaturated fatty acyl moieties may have significant effects on metabolism in the ovarian cell.
1. Essential fatty acid-deficient rats were fed gamma-linolenic acid (18: 3omega6) at 2% dietary energy and alpha-linolenic acid (18: 3omega3) at 0, 1-6, 2-8 and 4-0% of the dietary energy. 2. 18: 3omega3 at 1-6% apparently inhibits the synthesis of the C20 and C22 omega6 long-chain polyunsaturated fatty acids (omega6 LC-PUFA) metabolized from 18: 3omega6. 3. However, increasing the dietary levels of 18: 3omega3 from 1-6 to 4-0% has no further influence. 4. The results suggest that dietary 18: 3omega6 is an efficent precursor for the omega6 LC-PUFA synthesis even in the presence of 18: 3omega3.
A correlation study of the effects of two agents, 2-methyl-2-[p-(1,2,3,4-tetrahydro-1-naphthyl)phenoxy]propionic acid (TPIA) and amiloride, on aldosterone-induced alterations in Na+ transport, lipid synthesis, and phospholipid fatty acid composition has been carried out in the toad urinary bladder. TPIA, an inhibitor of acetyl-CoA carboxylase, inhibits aldosterone-stimulated Na+ transport as well as hormone-induced lipid synthesis and the increase in weight percentage of phospholipid long-chain polyunsaturated fatty acids. Amiloride, a diuretic which blocks sodium entry into the transporting epithelium, does not alter aldosterone's effects on lipid and fatty acid metabolism but prevents the hormone-induced increase in Na+ transport. These results support the conclusion that aldosterone increases Na+ transport in the toad urinary bladder by altering membrane fatty acid metabolism and that the lipid biosynthetic events following aldosterone treatment are a primary response to the hormone and not secondary to increased Na+ transport.
The cholesterol and cholesteryl ester concentration and cholesteryl ester composition were determined in the ovaries of immature rats, sexually mature rats and superovulated immature rats. The immature rat ovary accumulated cholesteryl esters, and long-chain polyunsaturated fatty acids were preferentially incorporated into these esters. The cholesteryl esters decreased in concentration and changed in composition with the onset of the first estrous cycle. Superovulation of immature rats, by injection of 50 I.U. pregnant mare serum gonadotropin, caused a decrease in the cholesteryl ester concentration of the ovary within 24 h and specific depletion of some esters, particularly those of 20 : 1 and 22 : 6 acids. Human choriogonadotropin, administered 54 h later, induced synchronous luteinization of the ovaries and was followed by increases in the concentration of free and esterified cholesterol and preferential accumulation of the esters of 20 : 4, 22 : 4, 4, 22 : 5 and 22 : 6 acids. Acute stimulation of luteinized ovaries by a second injection of the rats with 25 I.U. of human choriogonadotropin resulted in preferential hydrolysis of the esters of 18 : 1, 20 : 4, 22 : 4 and 22 : 5 acids.
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The fetal brain accumulates long-chain (C20 and 22) polyunsaturated fatty acids--arachidonic and docosahexaenoic--during cell division. De-novo synthesis of these acids does not occur and they are thought to be either directly derived from food or by metabolism from linoleic and linolenic acids, respectively. Administration of isotopically labelled linoleic and linolenic acids to pregnant guineapigs showed that only a small proportion of the label was converted to their respective long-chain polyunsaturated derivatives in the maternal liver. The proportion was increased within the phospholipids (structural lipids) by what appeared to be amultiple processing system which increased chain length and degree of polyunsaturation from maternal liver to placenta, fetal liver, and to fetal brain. Observations in man suggest a similar trend. The porportion of long-chain polyunsaturated acids increased in the phospholipids from maternal blood, cord blood, fetal liver, and fetal brain. These data show that the placenta and fetus are radically modifying the maternal phospholipids so as to achieve the high proportions of the C20 and C22 polyunsaturated fatty acids in the structural lipids of the developing brain.
The proportion of long-chain polyunsaturated derivatives of linoleic and linolenic acids in the erythrocyte lipids of infants fed a cow's milk formula was lower than in breast-fed infants. Although th formula provided only 0.55% of the total energy as linoleic acid, essential fatty acid deficiency was not detected; the triene:tetraene ratio was 0.09.
The oxygen and glucose uptake, lactate formation, ATP/ADP and NADH/NAD ratios and incorporation of [14C]acetate and [14C]linolenic acid into lipids of early fatty streaks and more advanced complicated atherosclerotic lesions of human aorta were determined during aerobic and hypoxic incubation. Compared with grossly normal appearing sections of the aorta in intima and media preparations of early fatty streaks the oxygen uptake was increased while that in further developed atheroma was slightly diminished. Under aerobic incubation conditions the metabolic state of fatty streaks and atheroma was characterized by increased lactate formation, NADH/NAD ratio and incorporation of [14C]acetate and [14C]linolenic acid into the lipids, but by a lowered ATP/ADP ratio. More pronounced changes in these metabolic parameters were observed when the aortic tissue segments were incubated under hypoxic conditions. The analysis by argentation TLC of fatty acid methylesters derived from total lipids of aerobically incubated fatty streaks revealed an increased incorporation of [14C]acetate into the highly unsaturated long-chain fatty acids. In developed atherosclerotic lesions and in hypoxia the incorporation of radioacetate into the polyunsaturated fatty acids and the formation of 20:4 fatty acid from [14C]linolenic acid were, in contrast to the above finding, decreased while the synthesis of eicosatrienoic acid was increased. This finding suggests a block in the desaturation step of linoleic into 20:4 fatty acid in further developed atheroma and in hypoxia. In aerobically incubated atherosclerotic lesions and in hypoxia the palmitic acid was synthesized mainly by chain elongation while in grossly normal areas of the aorta at least part of this acid was synthesized de novo.
3H-alpha-tocopherol intestinal absorption was studied in the unanesthetized rat. The rate of alpha-tocopherol absorption remained linear over a wide range of concentrations (4 nM to 400 micrometer). Increasing the sodium taurocholate concentration in the micellar infusate up to 15 mM did not increase the rate of absorption of the vitamin. Addition of long-chain fatty acids to the micellar infusate decreased the absorption rate of the vitamin (p less than 0.05). The decrease was most significant (p less than 0.01) following the addition of the polyunsaturated linolenic (C18:3) acid. Increasing the hydrogen ion concentration in the perfusate increased the absorption rate of alpha-tocopherol. The present experiments in vivo support the conclusions drawn from in vitro uptake experiments which indicated that alpha-tocopherol is absorbed by a passive diffusion process. These experiments indicate that micellar expansion with polyunsaturated fatty acids interferes with the absorption of alpha-tocopherol and may result in deficiency of the vitamin.
As a part of an investigations on the lipid metabolism in Platyhelminthes, the acoel Convoluta roscoffensis, which harbors the green alga Platymonas convoluta as a symbiont, was studied. Isotopic tracer experiments established that the acoel lacks the ability to synthesize de novo long-chain saturated and unsaturated fatty acids and depends on its algal symbiont for these compounds. The acoel's fatty acid composition closely resembles that of the alga but differs from those of other animals; the acoel's polyunsaturated fatty acids are of the plant type (omega 3 family) rather than of the animal type (omega 6 family). The acoel also lacks the ability to synthesize sterols de novo. It contains 24-methylenecholesterol synthesized by the algae and, in addition, significant amounts of cholesterol, which is probably a host modification product of the algal sterol. With fatty acids provided by the symbiont, the acoel has the ability to synthesize its own complex lipids. The acoel contains relatively large amounts of triglyceride, phosphatidylcholine, and ethanolamine plasmalogen. These compounds are either not present at all or present only in minute amounts in the symbiotic alga. Since acoels belong to the most primitive forms of the present-day flatworms, the observed metabolic defects in this organism suggest that mechanisms for the biosynthesis of fatty acids and sterols were lost early during the evolution of the Platyhelminthes, and that this phenomenon is widespread within the phylum.
The fatty acids middle-chain triglycerides (FAMCT) may be considered as a possible component of alimentary mixtures intended to lower the energy-giving efficiency of the nutritional ration. They do not join the tissue lipids, whereas their reconstruction into long-chain fatty acids requires an additional expenditure of energy. These facts were confirmed by the results obtained in tests on rats. Feeding of growing rats for 5 weeks on a ration containing 12 per cent of the FAMCT on condition of a sufficient administration of polyunsaturated fatty acids (PUFA) through addition of sunflower seed oil led to a significant fall of the body mass gain by comparison with that in rats receiving a ration whose main source of fat was lard. An increased tryglycerides synthesis in the liver was not accompanied by their accumulation in the organ. The triglycerides level in the serum was up. An analysis of the fatty acids composition in the epididymitic fatty tissue, plasma and erythrocytes confirmed that the FAMCT C2-fragments developing during metabolization are used up chiefly in lipogenesis, one of the basic products of which is palmitic acid. The metabolization of FAMC with sufficient PUFA proportion in the ration does not derange the plastic function of fat in the organism, i.e, securing biosynthesis of lipid components of the membranes.
The genetic determinants of polyunsaturated fatty acid (PUFA) status during the perinatal window require deeper understanding. We conducted a genome-wide association study of perinatal PUFA patterns in 1352 mother-child pairs from the French EDEN cohort using maternal genotype data. Five perinatal PUFA patterns had been previously derived using PUFA levels measured in maternal blood, cord blood, and colostrum simultaneously. We used linear regression models assuming additive genetic effects to assess the associations between common SNPs and each pattern, adjusting for maternal age, study center, and genetic ancestry. Pattern 1 "High omega-3 Long-chain (LC)-PUFAs, low omega-6 LC-PUFAs" was not associated with any genetic variants. Patterns 2 to 5-"Omega-6 LC-PUFAs," "Colostrum LC-PUFAs," "Omega-6 precursor (LA) and DGLA," and "LA and colostrum ALA"-were strongly associated with variants in the FADS gene cluster. The strongest association was observed between Pattern 4 "Omega-6 precursor (LA) and DGLA," and rs174546 located on FADS1 gene region (β (SE) = 0.80 (0.034), p < 10⁻102). No other robust association was found with other genes. These findings underscore the main contribution of FADS variants to the variability of four specific perinatal PUFA patterns in our cohort. This study should be replicated in larger, ancestrally diverse populations beyond individuals of European descent.
A feeding experiment was carried out in which piglets were fed to a diet enriched with either mackerel oil or olive oil. The oil consumption amounted to about 100 g per animal per day. The aim of this experiment was to study the effect of feeding high amounts of fish oil rich in polyunsaturated and long-chain monoenoic acids in order to determine if any morbid changes occurred in the animals as a result of this addition. The piglets fed olive oil served as controls. After 4 weeks, blood hemoglobin, plasma glucose, and serum triglycerides were significantly lower in the mackerel oil group as compared with the control group. There was no difference in serum cholesterol and serum lipid composition. Very low density lipoproteins were lower in the mackerel oil group. The fatty acid composition of blood serum, heart muscle, and liver showed considerable differences, omega3 acids being higher and both omega6 and omega9 acids being lower in the mackerel oil group than in the control group. Some increase in the amount of triglycerides in the heart muscle was observed in the mackerel oil group. Some characteristics of "yellow fat disease" developed in the mackerel oil group. This type of vitamin E deficiency seems to be the result of the considerable amount of omega3 fatty acids present in the mackerel oil. No clinical symptoms due to ingestion of long-chain monoenoic acids were observed.
A cross-over study was done with 19 male and 23 female volunteers living in a monastery and a convent, respectively. The effect of a fat gish (mackerel) diet on the blood serum lipid composition was studied. As the normal diet of these volunteers was of the lacto-ovo-vegetarian type, a control diet in which the fish was replaced by full-fat cheese was used. Subjects consuming the fish diet had a daily uptake of polyunsaturated acids of the omega3 family of about 8 g; comparable amounts of linoleic acid were ingested with both diets. Both diets were consumed for a period of 3 weeks. Serum cholesterol was slightly but significantly (7.5%) lower and serum triglycerides considerably lower (35%) on the fish diet, whereas high density lipoprotein cholesterol increased slightly. Lipoprotein analysis showed a strong very low density lipoprotein decrease by the fish diet while, in the men, both low and high density lipoproteins increased. The fatty acid composition of serum lipids showed considerable differences; C20:5omega3 increased in all fractions and C22:6omega3 was found in the triglycerides and the phospholipids, but not in the sterol esters. These increases occurred chiefly at the expense of C18:1omega9 and, in particular, C18:2omega6, which indicates a replacement of omega6 by omega3 acids. Long-chain monoenoic acids which are abundant in the mackerel were not detected in any serum lipid fraction.