Positional distribution of n-3 fatty acids in triacylglycerols from rat adipose tissue during fish oil feeding

Natural phospholipids: Occurrence, biosynthesis, separation, identification, and beneficial health aspects

During the last years, phospholipids (PLs) have attracted great attention because of their crucial roles in providing nutritional values, technological and medical applications. There are considerable proofs that PLs have unique nutritional benefits on human health, such as reducing cholesterol absorption, improving liver functions, and decreasing the risk of cardiovascular diseases. PLs are the main structural lipid components of cell and organelle membranes in all living organisms, and therefore, they occur in all organisms and the derived food products. PLs are distinguished by the presence of a hydrophilic head and a hydrophobic tail, consequently they possess amphiphilic features. Due to their unique characteristics, the extraction, separation, and identification of PLs are critical issues to be concerned. This review is focused on the content of PLs classes in several sources (including milk, vegetable oils, egg yolk, and mitochondria). As well, it highlights PLs biosynthesis, and the methodologies applied for PLs extraction and separation, such as solvent extraction and solid-phase extraction. In addition, the determination and quantification of PLs classes by using thin layer chromatography, high-performance liquid chromatography coupled with different detectors, and nuclear magnetic resonance spectroscopy techniques.

A simple method for positional analysis of phosphatidylcholine

Simple and fast method of positional analysis of fatty acid composition of phosphatidylcholine (PC) from egg-yolk and soy has been elaborated. The key step of the procedure was complete ethanolysis of PC catalyzed by sn-1,3 specific lipase from Mucor miehei (Lipozyme). 2-Acyl-lysophosphatidylcholine (2-acyl LPC), fatty acids ethyl esters (FAEEs) and free fatty acids (FAs) were formed in this process. No acyl migration was observed during the reaction. The products were entirely separated from the products mixture by simple extraction in water:hexane (2:3 v/v) system. The hexane fraction containing free FAs and FAEEs was treated with BF(3)/Et(2)O in ethanol to obtain only FAEEs. The analysis of FAEEs by GC gave the composition of the FAs in the sn-1 position of the PC. 2-Acyl LPC from water fraction after precipitation in cold (-20°C) acetone was converted into FAEEs and analyzed by gas chromatography (GC) to determine FAs composition in the sn-2 position of the PC.

Selective mobilization of fatty acids from adipose tissue triacylglycerols

Adipose tissue triacylglycerols represent the main storage of a wide spectrum of fatty acids differing by molecular structure. The release of individual fatty acids from adipose tissue is selective according to carbon chain length and unsaturation degree in vitro and in vivo in animal studies and also in humans. The mechanism of selective fatty acid mobilization from white fat cells is not known. Lipolysis is widely reported to work at a lipid-water interface where only small amounts of substrate are available. A preferential hydrolysis of a small triacylglycerol fraction enriched in certain triacylglycerol molecular species at the lipid-water interface and enzymological properties of hormone-sensitive lipase could explain the selective mobilization of fatty acids from fat cells. This selectivity could affect the individual fatty acid supply to tissues.

Analysis of docosahexaenoic acid biosynthesis in Crypthecodinium cohnii by 13C labelling and desaturase inhibitor experiments

The lipids of the heterotrophic microalga Crypthecodinium cohnii contain the omega-3 polyunsaturated fatty acid (PUFA) and docosahexaenoic acid (22:6) to a level of over 30%. The pathway of 22:6 synthesis in C. cohnii is unknown. The ability of C. cohnii to use 13C-labelled externally supplied precursor molecules for 22:6 biosynthesis was tested by 13C NMR analysis. Furthermore, the presence of desaturases (typical for aerobic PUFA synthesis) was studied by the addition of specific desaturase inhibitors in the growth medium. The addition of 1-(13)C acetate or 1-(13)C butyrate in the growth medium resulted in 22:6 with only the odd carbon atoms enriched. Apparently, two-carbon units were used as building blocks for 22:6 synthesis and butyrate was first split into two-carbon units prior to incorporation in 22:6. When 1-(13)C oleic acid was added to the growth medium, 1-(13)C oleic acid was incorporated into the lipids of C. cohnii but was not used as a precursor for the synthesis of 22:6. Specific desaturase inhibitors (norflurazon and propyl gallate) inhibited lipid accumulation in C. cohnii. The fatty acid profile, however, was not altered. In contrast, in the arachidonic acid-producing fungus, Mortierella alpina, these inhibitors not only decreased the lipid content but also altered the fatty acid profile. Our results can be explained by the presence of three tightly regulated separate systems for the fatty acid production by C. cohnii, namely for (1). the biosynthesis of saturated fatty acids, (2). the conversion of saturated fatty acids to monounsaturated fatty acids and (3). the de novo synthesis of 22:6 with desaturases involved.

Endotoxin binding to erythrocyte membrane and erythrocyte deformability in human sepsis and in vitro

OBJECTIVE

Several studies have shown that lipopolysaccharide and lipid A impair red blood cell deformability and. However, it is unclear whether impaired red blood cell deformability is associated with binding of lipopolysaccharide to the red blood cell membrane.

DESIGN

Analysis of hydroxymyristic acid content in red blood cell membranes and red blood cell deformation in patients with Gram-negative septicemia and after incubation of red blood cells from healthy adults with 100 microg of lipid A or 1 mg of lipopolysaccharide per milliliter of red blood cell in buffer solution and in whole blood. Hydroxymyristic acid is a fatty acid of the lipid A part of lipopolysaccharide in most Gram-negative bacteria.

SETTING

University research laboratories.

SUBJECTS

Ten healthy adults and four patients with clinical and laboratory signs of septicemia.

INTERVENTIONS

Blood sampling.

MEASUREMENTS AND MAIN RESULTS

Red blood cell deformation was measured with a laser-diffraction shearing device (Rheodyn) and a computerized micropore filtration system (CTA). Lipopolysaccharide and lipid A binding to red blood cell membranes was studied by measuring the amide-linked hydroxymyristic acid by gas chromatography. The detection rates of hydroxymyristic acid were 82% for lipopolysaccharide and 79% for lipid A in buffer solution. In membranes of washed red blood cell, the detection rates of lipopolysaccharide and lipid A were 0.26 +/- 0.03% (2.6 +/- 0.3 microg/mL) and 1.3 +/- 0.5% (1.3 +/- 0.5 microg/mL), and in red blood cell membranes of whole blood the detection rates were 2.6% (25.5 microg/mL) and 4.1% (4.1 microg/mL), respectively. The lipopolysaccharide content in red blood cell membranes of septic patients ranged from 47 to 103 microg/mL of red blood cell. Red blood cell deformation in the Rheodyn and in the CTA were not influenced by lipopolysaccharide incubated with washed red blood cells. In the Rheodyn, red blood cell deformation was significantly decreased by 18% after lipid A incubation in washed red blood cells, by 26% after lipopolysaccharide incubation in whole blood, and by 31% in septic patients. Similar effects were observed when we used the CTA.

CONCLUSIONS

Red blood cell deformation is decreased in septic patients, after incubation of washed red blood cells with lipid A and of whole blood with lipopolysaccharide. Lipopolysaccharide did not influence red blood cell deformation after incubation with washed red blood cells. The decrease of red blood cell deformation was related to the amount of hydroxymyristic acid measured in red blood cell membranes, suggesting that endotoxin binding directly affects mechanical properties of red blood cells.

Stereospecific incorporation of palmitoyl, oleoyl and linoleoyl moieties into adipose tissue triacylglycerols of rats results in constant sn-1:sn-2:sn-3 in rats fed rapeseed, olive, conventional or high oleic sunflower oils, but not in those fed coriander oil

We report the stereospecific (sn-1, sn-2, sn-3) distribution of fatty acids in subcutaneous adipose tissue triacylglycerols of male weaned Wistar rats fed either a standard diet or diets containing, in addition to 20 g corn oil/kg feed, 120 g/kg feed, each, of canola-type rapeseed oil, olive oil, conventional or high oleic sunflower oil or high petroselinic coriander oil for 10 wk. The regiospecific distribution of the major acyl moieties in the sn-1 (3) vs. sn-2 positions of the adipose tissue triacylglycerols broadly reflected that of the dietary oils. The saturated palmitoyl and stearoyl moieties were more abundant in the sn-1 and sn-3 positions compared with the sn-2 position of the adipose tissue triacylglycerols, and both occurred at a higher proportion in the sn-1 than in the sn-3 position. Oleoyl moieties were abundant in all the three positions of the adipose tissue triacylglycerols, whereas petroselinoyl moieties were more abundant in the sn-1 and sn-3 positions compared with the sn-2 position. Linoleoyl moieties occurred predominantly in the sn-2 position compared with the sn-1 and sn-3 positions of the adipose tissue triacylglycerols; however, they were more abundant in the sn-3 than in the sn-1 position. Despite widely varying proportions of the palmitoyl, oleoyl and linoleoyl moieties at the three positions of the dietary triacylglycerols, the ratios of each of these acyl moieties at the sn-1, sn-2, and sn-3 positions in adipose tissue triacylglycerols were essentially constant for all groups, with the exception of the group fed coriander oil, indicating a rigid stereospecific incorporation.

The composition of the major molecular species of adipose tissue triacylglycerols of rats reflects those of dietary rapeseed, olive and sunflower oils

We report the composition of constituent fatty acids and molecular species of adipose tissue triacylglycerols of male weaned Wistar rats fed diets containing, in addition to 20 g corn oil/kg feed, 120 g per kg feed canola-type rapeseed oil, olive oil or conventional sunflower oil for 10 wk. The composition of fatty acids and molecular species of the triacylglycerols of subcutaneous, epididymal and perirenal adipose tissues did not differ among groups (P > 0.01), broadly reflecting the corresponding compositions of the dietary oils. The major molecular species of dietary triacylglycerols, especially trioleoylglycerol (OOO) and linoleoyl-dioleoylglycerols (LOO) in the rapeseed oil and olive oil diets, dioleoyl-palmitoylglycerols (OOP) in the olive oil diet, dilinoleoyl-oleoylglycerols (LLO) in the rapeseed oil and sunflower oil diets, and dilinoleoyl-palmitoylglycerols (LLP), linoleoyl-oleoyl-palmitoylglycerols (LOP) as well as trilinoleoylglycerol (LLL) in the sunflower oil diet were also prominent constituents of the corresponding adipose tissue triacylglycerols. On the other hand, predominant molecular species containing alpha-linolenoyl (Ln) moieties, e.g., alpha-linolenoyl-linoleoyl-oleoylglycerols (LnLO) and alpha -linolenoyl-dioleoylglycerols (LnOO) from the rapeseed oil diet were not prominent constituents of rat adipose tissue triacylglycerols, whereas LOP from rapeseed oil and olive oil diets and OOP from rapeseed oil and sunflower oil diets were distinctly enriched in the corresponding adipose tissues. Most of the minor molecular species of the dietary triacylglycerols from all the three diets were distinctly present in the corresponding adipose tissues. Thus, despite numerous biochemical processes involved in the metabolism of dietary triacylglycerols, a substantial proportion of the molecular species of adipose tissue triacylglycerols containing linoleoyl (L), oleoyl (O) and palmitoyl (P) moieties resemble those of dietary triacylglycerols.

Effects of dietary fats on red blood cell membrane insulin receptor in normo- and hypercholesterolemic miniature swine

It has been demonstrated that the type of dietary fat affects insulin receptors in various tissues in normal humans and animals by altering membrane fluidity. This study compares the effects of n-3 fatty acids from fish oil and n-6 fatty acids from corn oil on red blood cell membrane insulin receptors in normal and hypercholesterolemic minipigs. A group of minipigs were made hypercholesterolemic by feeding cholesterol and lard for 2 months; the other group served as controls and was fed stock diet. Both groups were then fed experimental diets containing either corn oil or menhaden oil or a mixture of the two for 23 additional weeks. Blood was collected at 0, 2, 12 and 23 weeks after the start of the experimental diets and membranes were prepared from the red blood cells. Insulin binding to red blood cell membranes was measured by radioreceptor assay. Plasma insulin was measured by radioimmunoassay. Insulin binding to red blood cell membrane was compared with the fluidity of the membrane measured and reported earlier. There was no significant effect of cholesterol feeding on plasma insulin concentrations. After 23 weeks on experimental diet plasma insulin was significantly higher in minipigs fed menhaden oil compared to those fed corn oil. No such effect was observed in hypercholesterolemic minipigs. No significant effect of either hypercholesterolemia or fish oil was observed on red blood cell insulin binding. A significant negative relationship was observed between insulin binding and anisotropy at 4°C for all probes but at 37°C significant negative relationship was observed only with polar probes. The data suggest that n-3 fatty acids from fish oil significantly increases plasma insulin in minipigs compared to n-6 fatty acids from corn oil. However, the unsaturation has no significant effect on insulin receptors on erythrocytes. Similarly, prior hypercholesterolemic state also has no effect on plasma insulin levels or the insulin binding to red blood cell membranes.

Incorporation of eicosapentaenoic and docosahexaenoic acids by a yeast (FO726A)

An eicosapentaenoic acid (EPA)- and docosahexaenoic acid (DHA)-incorporating yeast, FO726A, was putatively identified as Candida guilliermondii on the basis of morphological, physiological and biochemical characteristics. Culture conditions for FO726A were investigated with respect to cell mass productivity, cellular accumulation of total lipid, triglyceride (TG), EPA and DHA. When grown at 20 degrees C for 24 h in an optimal medium containing 1 g scrap fish oil, the yeast yielded 820 mg dry cells which consisted of 40.7% lipid, 40.2% protein and 14.1% carbohydrate. The lipid (334mg) consisted of 300 mg TG (36.6% of dry cells), 23.2 mg EPA (2.8%) and 54.8 mg DHA (6.7%), and the recovery rates of EPA and DHA from the fish oil were 27.1 and 43.6%, respectively. The positional distributions of fatty acids in the TG from the yeast were then investigated and compared with those in the TG from the fish oil. The EPA and DHA in the fish oil were concentrated more in the sn-1,3 positions (8.8 and 13.7%, respectively) than in the sn-2 position (3.7 and 10.8%, respectively). In the case of the TG from the yeast, EPA was present to a greater extent in the sn-1,3 positions than in the sn-2 position. In contrast, DHA was preferentially present in the sn-2 position, approximately twice that in the sn-1,3 positions.

Effects of altering dietary fatty acid composition on prostaglandin synthesis and fertility

Several studies over the past 20 years have demonstrated that subjects on diets composed of substances with high levels of n-3 polyunsaturated fatty acids (PUFAs) (e.g. fish) have a decreased incidence of heart disease. On this basis, a recent report from the Department of Health has advised UK consumers to decrease the proportion of saturated as opposed to unsaturated fats in their diet and to increase the ratio of n-3 to n-6 PUFAs. This could be achieved by altering the amounts of these constituents in milk and meat. n-3 Fatty acids can most easily be added to animal feed as either fish oil or linseed oil and can be increased in the blood and milk of ruminants following protection to avoid hydrogenation in the rumen. In western countries the ratio of consumption of n-6 to n-3 PUFAs is greater than 10 and current evidence tends to suggest that a ratio nearer 5 would be more desirable and compatible with cardiovascular well being. As fertility in the UK dairy herd is already poor, it is important to establish whether alterations in dietary n-3 and n-6 PUFAs affects herd fertility before widespread changes in animal diets are recommended. Therefore, this review considers the role played by PUFAs and eicosanoids in fertility, with particular reference to the implications for farm livestock production. The evidence reviewed shows that alteration of the concentration and ratio of n-6 and n-3 PUFAs in feeds can influence prostaglandin synthesis/metabolism in a number of mammalian systems. The changed patterns of prostaglandin synthesis can as a consequence, affect the diverse functions (e.g. hormone secretion) that are normally mediated via prostaglandins. Similarly, changes in prostaglandin synthesis effected through manipulation of PUFAs has a major bearing on fertility (as PGs affect many reproductive parameters, e.g. ovulation). Several studies in cattle and other mammals, show that feeding or infusing different types of fat with varying PUFA content to females can alter: the number and size of ovarian follicles, the ovulation rate, progesterone production by the corpus luteum, the timing of luteolysis and gestational length. In the male most recent work has focussed on sperm production and experiments in fowl have demonstrated clear effects of dietary PUFAs on both the sperm membrane phospholipid composition and on fertilizing ability.

Positional analysis of triglycerides and phospholipids rich in long-chain polyunsaturated fatty acids

Four sources of long-chain polyunsaturated fatty acids (LCP) differing in their chemical structure (triglycerides or phospholipids) and in their origin (tuna triglycerides, fungal triglycerides, egg phospholipids, and pig brain phospholipids) were analyzed to determine the distribution of the component fatty acids within the molecule. Lipase and phospholipase A2 hydrolysis was performed to obtain 2-monoacylglycerols and lysophospholipids, respectively, which allowed us to determine the distribution of fatty acids between the sn-2 and sn-1,3 positions of triglycerides or between the sn-1 and sn-2 position of phospholipids. Fatty acids in the LCP sources analyzed were not randomly distributed. In tuna triglycerides, half of the total amount of 22:6n-3 was located at the sn-2 position (49.52%). In fungal triglycerides, 16:0 and 18:0 were esterified to the sn-1,3 (92.22% and 91.91%, respectively)18:1 and 18:2 to the sn-2 position (59.77% and 62.62%, respectively), and 45% of 20:3n-6 and only 21.64% of 20:4n-6 were found at the sn-2 position. In the lipid sources containing phospholipids, LCP were mainly esterified to the phosphatidylethanolamine fraction. In egg phospholipids, most of 20:4n-6 (5.50%, sn-2 vs. 0.91%, sn-1) and 22:6n-3 (2.89 vs. 0.28%) were located at the sn-2 position. In pig brain phospholipids, 22:6n-3 was also esterified to the sn-2 (13.20 vs. 0.27%), whereas 20:4n-6 was distributed between the two positions (12.35 vs. 5.86%). These results show a different fatty acid composition and distribution of dietary LCP sources, which may affect the absorption, distribution, and tissue uptake of LCP, and should be taken into account when supplementing infant formulas.

Dietary menhaden and corn oils and the red blood cell membrane lipid composition and fluidity in hyper- and normocholesterolemic miniature swine

Fatty acids in the diet are readily incorporated into lipids in various tissues. However, it is not clear whether all tissues have the same level of incorporation. Second, (n-6) unsaturated fatty acids increase the fluidity of membranes, but this has not been shown for (n-3) fatty acids. In this study, we measured the incorporation of (n-6) and (n-3) fatty acids into erythrocyte membrane lipids and studied their effects on the fluidity of erythrocyte membranes. One group of female miniature swine was made hypercholesterolemic by feeding the swine cholesterol and lard for 2 mo; the other group served as controls and was fed a stock diet. Both groups were then fed either corn oil or menhaden oil or a mixture of the two for 23 additional weeks. Blood was collected at 0, 2, 4, 12 and 23 wk after initialization of the experimental diets, and fatty acid composition of phospholipids was assessed. Membrane phospholipids of pigs fed menhaden oil had elevated (n-3) fatty acids (20:5 and 22:6), and lower 18:2 than those fed corn oil. There was no difference in 20:4 content. The fatty acid changes occurred as early as 2 wk after consumption of the corn oil or menhaden oil in pigs previously fed a stock diet, but it took longer in pigs previously fed lard + cholesterol, indicating residual effects of pretreatment. Menhaden oil increased anisotropy (indicating decreased fluidity) more than corn oil for the nonpolar probe diphenylhexatriene (DPH) at earlier time points, but not at 23 wk. Erythrocyte membrane fluidity was significantly related to membrane polyunsaturate content, with (n-6) fatty acids having a greater influence than (n-3) fatty acids. A comparison of the present red blood cell fatty acid compositions with brain synaptosome fatty acid compositions for the same animals showed poor correlations for some of the fatty acids. There was no significant direct relationship between docosahexaenoate (DHA) concentrations in erythrocyte membranes with DHA concentrations in brain synaptosomes from cerebellum, forebrain and caudate nucleus.

Dietary (n-3) and (n-6) polyunsaturated fatty acids rapidly modify fatty acid composition and insulin effects in rat adipocytes

The influence of dietary (n-3) compared with (n-6) polyunsatured fatty acids (PUFA) on the lipid composition and metabolism of adipocytes was evaluated in rats over a period of 1 week. Isocaloric diets comprised 16.3 g/100 g protein, 53.8 g/100 g carbohydrate and 21.4 g/100 g lipids, the latter containing either (n-3) PUFA (32.4 mol/100 mol) or (n-6) PUFA (37.8 mol/100 mol) but having identical contents of saturated, monounsaturated and total unsaturated fatty acids and identical polyunsaturated to saturated fatty acid ratios and double bond indexes. Despite comparable food intake, significantly smaller body weight increments and adipocyte size were observed in rats of the (n-3) diet group after feeding for 1 wk. Rats fed the (n-3) diet also had significantly lower concentrations of serum triglycerides, cholesterol and insulin compared with those fed the (n-6) diet, although levels of serum glucose and free fatty acids did not differ in the two dietary groups. In the (n-6) diet group, the (n-6) and (n-3) PUFA contents of plasma triglycerides, free fatty acids and phospholipids were 30-60% higher and 60-80% lower, respectively, than in the (n-3) diet group, whereas adipocyte plasma membrane phospholipids showed a significantly higher unsaturated to saturated fatty acid ratio and greater fluidity. Glycerol release in response to noradrenaline was significantly higher in the adipocytes of rats fed the (n-3) diet, whereas the antilipolytic effect of insulin generally did not differ in the two groups. Finally, insulin stimulated the transport of glucose and its incorporation into fatty acids to a lesser extent in adipocytes of (n-3) diet fed rats compared with (n-6) diet fed rats. This reduction in the metabolic effects of insulin in rats fed a (n-3) diet for 1 wk could be related to smaller numbers and a lower binding capacity of the insulin receptors on adipocytes and/or to a lesser degree of phosphorylation of the 95 kDa beta subunit of the receptor. In conclusion, dietary intake for 1 wk of (n-3) rather than (n-6) PUFA is sufficient to induce significant differences in the lipid composition and metabolic responses to insulin of rat adipocytes.

Selective mobilization of fatty acids from white fat cells: evidence for a relationship to the polarity of triacylglycerols

Fatty acids are selectively released from white fat cells in accordance with well-defined rules relating their molecular structure and their mobilization rate, emphasizing the possible role of their physicochemical properties. Lipolysis is widely reported to work for conditions where only small amounts of substrate are available. We hypothesize that the preferential hydrolysis of a substrate fraction enriched in the most polar triacylglycerols (TAGs) reflects the pattern of selective fatty acid mobilization. Rat adipose tissue was first manipulated by dietary means to obtain a wide spectrum of fatty acids. Fat cell TAGs were separated into eight fractions according to polarity by liquid-liquid partition chromatography and their fatty acid proportions and compositions were determined by GLC. In the most polar TAG fractions, the relative enrichment of fatty acids (percentage in a TAG fraction divided by percentage in total TAGs) increased with the number of double bonds for a given chain length, whereas it decreased with increasing chain length for a given degree of unsaturation. The relative enrichment of highly mobilized fatty acids (16-20 carbon atoms and four or five double bonds) was very high (more than 2.5) in the most polar TAG fractions, whereas that of weakly mobilized fatty acids (20-24 carbon atoms and no or one double bond) was very low (less than 0.5). The relative enrichment of moderately mobilized fatty acids (comprising all the others) was close to unity. Our study shows that the relative enrichment of fatty acids in the most polar adipose tissue TAGs is consistent with their relative mobilization rates. This supports our hypothesis and raises the possibility that the molecular species of TAGs might be one of the regulating factors.

Dietary triacylglycerol structure and saturated fat alter plasma and tissue fatty acids in piglets

Human and pig milk triacylglycerols contain a large proportion of palmitic acid (16:0) which is predominately esterified in the 2-position. Other dietary fats contain variable amounts of 16:0, with unsaturated fatty acids predominantly esterified in the 2-position. These studies determined if the amount or position of 16:0 in dietary fat influences the composition or distribution of liver, adipose tissue, lung, or plasma fatty acids in developing piglets. Piglets were fed to 18 d with sow milk or formula with saturated fat from medium-chain triglyceride (MCT), coconut or palm oil, or synthesized triacylglycerols (synthesized to specifically direct 16:0 to the 2-position) with, in total fatty acids, 30.7, 4.3, 6.5, 27.0, and 29.6% 16:0, and in 2-position fatty acids, 55.3, 0.4, 1.3, 4.4, and 69.9% 16:0, respectively. The percentage of 16:0 in the 2-position of adipose fat from piglets fed sow milk, palm oil, and synthesized triacylglycerols were similar and higher than in piglets fed MCT or coconut oil. Thus, the amount, not the position, of dietary 16:0 determines piglet adipose tissue 16:0 content. The effects of the diets on the plasma and liver triacylglycerols were similar, with significantly lower 16:0 in total and 2-position fatty acids of the MCT and coconut oil groups, and significantly higher 16:0 in the plasma and liver triacylglycerol 2-position of piglets fed the synthesized triacylglycerols rather than sow milk or palm oil. The lung phospholipid total and 2-position 16:0 was significantly lower in the MCT, coconut, and palm oil groups, but similar in the synthesized triacylglycerol group and sow milk group. The lung phospholipid total and 2-position percentage of arachidonic acid (20:4n-6) was significantly lower in all of the formula-fed piglets than in milk-fed piglets. The physiological significance of this is not known.

The selective mobilization of fatty acids is not based on their positional distribution in white-fat-cell triacylglycerols

Fatty acids have been shown to be selectively mobilized from rat white fat-cells, whatever the dietary manipulations. For convenience, fatty acids have been classified as being highly, weakly and moderately mobilizable. The aim of this study was to examine whether the selective mobilization of fatty acids can be explained, even partly, by their positional distribution in adipose-tissue triacylglycerols (TAG) via the known specificity of hormone-sensitive lipase for the sn-1 and sn-3 positions. Adipose tissue was dietarily manipulated in order to obtain a wide spectrum of fatty acids, including large amounts of either very-long-chain polyunsaturated fatty acids (VLC-PUFA) or very-long-chain monounsaturated fatty acids (VLC-MUFA). The determination of fatty acid distribution in adipose tissue TAG was based on random formation of 1,2-diacyl-rac-glycerols by Grignard degradation, followed by synthesis of phosphatidic acids and hydrolysis in the sn-2 position by phospholipase A2. Regardless of the fatty acid composition and location of fat depots, highly (e.g. 18:4n-3 and some of the VLC-PUFA) and weakly (e.g. VLC-MUFA) mobilizable fatty acids were located mainly in the outer (sn-1 and sn-3) positions of the glycerol moiety (79.5% and 92.5% on average, respectively). Other fatty acids, which are rather moderately mobilizable, were more randomly distributed. We conclude that the selective mobilization of white-fat-cell fatty acids is not based on their positional distribution in TAG.

Lymphatic fatty acids from rats fed human milk and formula supplemented with fish oil

Absorption of long-chain polyunsaturated fatty acids from human milk and formula supplemented with fish oil was studied to determine if the distribution route into lymphatic triacylglycerol (TAG) and phospholipid (PL) varies with the dietary source. Rats were intraduodenally infused with human milk or formula containing graded amounts of fish oil (0, 0.5, or 1.0 g/100 mL), and the mesenteric lymph was collected. Arachidonic acid (20:4n-6) levels in lymphatic TAG and PL were highest from animals fed human milk. In the animals infused with formula containing fish oil, as the amount of eicosapentaenoic acid (EPA, 20:5n-3) infused increased, there was essentially an equal increase in EPA associated with both lymphatic TAG and PL. Animals intraduodenally infused with human milk or formula without fish oil had only minor levels (less than 1%) of EPA in the lymph. In the fish oil-treated animals, as the amount of docosahexaenoic acid (DHA, 22:6n-3) infused increased, there was a 16-fold increase in DHA associated with lymphatic TAG, but only a 3-fold increase in DHA associated with lymphatic PL. The highest level of DHA in rats infused with human milk was observed in lymphatic PL. Hence, fish oil can be added to formula as a source of long-chain polyunsaturated fatty acids, but the distribution of fatty acids into lymphatic TAG and PL is not the same as that observed with human milk.

Time-course study of adipose tissue fatty acid composition during mammary tumor growth in rats with controlled fat intake

Previous work in breast cancer patients has indicated an inverse relationship between the risk of relapse and the alpha-linolenic acid (18:3n-3) level in adipose breast tissue. To determine whether low alpha-linolenic levels in patients with aggressive breast cancer resulted from lower 18:3n-3 dietary intake and/or increased metabolism of stored 18:3n-3, we analyzed the fatty acid composition of mammary adipose tissue during tumor growth in a rat model of mammary carcinogenesis. Rats were fed a diet containing 10% fat as rapeseed oil (in which 9% of total fatty acids is 18:3n-3). one-half of the rats received an injection of nitrosomethylurea (NMU) to initiate mammary tumors. In control and NMU-treated groups, three to five animals were sacrificed every three weeks during the five-month experimental time. tumor growth was followed by weekly palpation of the animals and by the measure of total tumor mass and number in sacrificed rats. Mammary tumor and adipose tissues were sampled in sacrificed rats. We found that although mammary adipose tissue fatty acid profile changed throughout the experiment, there was no difference in fatty acid profile between control and NMU-treated rats of the same age. In the NMU-treated group, 18:3n-3 level remained identical throughout the experimental period, irrespective of tumor burden. These data show that, in this model, mammary tumor growth does not modify stored fatty acid levels, including 18:3n-3. this suggests that decreased 18:3n-3 level in patients with poor prognosis is not a consequence of tumor burden but more likely depends on decreased dietary intake.

Composition and structure of triacylglycerols in brown adipose tissue of rats fed fish oil

This study examines the incorporation of highly unsaturated n-3 fatty acids (HUFA) into triacylglycerols (TAG) of brown adipose tissue (BAT), and their effect on the positional distribution of saturated (SFA) and of unsaturated (UFA) 16- or 18-carbon fatty acids. To this end, rats were fed a fish oil diet for up to four weeks. The stereospecific analysis of TAG was based on generation of sn-1,2- and sn-2,3-acylglycerols by Grignard degradation, followed by synthesis of phosphatidic acid and specific hydrolysis with phospholipase A2. From the end of the first week of fish oil feeding, a steady-state in the fatty acid composition of TAG in BAT was reached. HUFA concentration increased 30-fold, mainly at the expense of n-9 UFA and of SFA. The amount of SFA decreased selectively at position 3, where these fatty acids were progressively replaced by n-3 HUFA. By contrast, the amount of UFA decreased at all positions, and their positional distribution was not affected. About 60% of HUFA was incorporated at position 3. Nearly twice as much 22:6n-3 was incorporated into TAG than had been previously observed in white adipose tissue (WAT) [Leray, C., Raclot, T., and Groscolas, R. (1993) Lipids 28, 279-284]. At the steady-state, the distribution of HUFA was characterized by high proportions of 22:6n-3 and 20:5n-3 in position 3. Moreover, in each position of TAG, a steady level was reached rapidly (within 1 wk).(ABSTRACT TRUNCATED AT 250 WORDS)

Heart and liver fatty acid composition and vitamin E content in miniature swine fed diets containing corn and menhaden oils

Female miniature swine, 4-11 yr, were fed 15% fat diets containing n-3 and/or n-6 polyunsaturated fat for 6 months, at 1.95 g fat/kg body weight. Liver lipids from menhaden oil-fed minipigs were elevated in the n-3 fatty acids: 20:5, 22:5 and 22:6, but heart lipids only in 20:5 and 22:6. Liver cell plasma membrane was elevated in 20:5, 22:5 and 22:6 and lowered in the n-6 acids 18:2 and 20:4 in menhaden oil-fed animals, to a greater extent than in the total tissue lipids. Liver alpha-tocopherol tended to decrease upon feeding menhaden oil, but heart alpha-tocopherol concentrations were not affected.