Dietary Linoleic Acid Elevates Endogenous 2-AG and Anandamide and Induces Obesity

Suppressing hyperactive endocannabinoid tone is a critical target for reducing obesity. The backbone of both endocannabinoids 2-arachidonoylglycerol (2-AG) and anandamide (AEA) is the ω-6 fatty acid arachidonic acid (AA). Here we posited that excessive dietary intake of linoleic acid (LA), the precursor of AA, would induce endocannabinoid hyperactivity and promote obesity. LA was isolated as an independent variable to reflect the dietary increase in LA from 1 percent of energy (en%) to 8 en% occurring in the United States during the 20th century. Mice were fed diets containing 1 en% LA, 8 en% LA, and 8 en% LA + 1 en% eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA) in medium-fat diets (35 en% fat) and high-fat diets (60 en%) for 14 weeks from weaning. Increasing LA from 1 en% to 8 en% elevated AA-phospholipids (PL) in liver and erythrocytes, tripled 2-AG + 1-AG and AEA associated with increased food intake, feed efficiency, and adiposity in mice. Reducing AA-PL by adding 1 en% long-chain ω-3 fats to 8 en% LA diets resulted in metabolic patterns resembling 1 en% LA diets. Selectively reducing LA to 1 en% reversed the obesogenic properties of a 60 en% fat diet. These animal diets modeled 20th century increases of human LA consumption, changes that closely correlate with increasing prevalence rates of obesity. In summary, dietary LA increased tissue AA, and subsequently elevated 2-AG + 1-AG and AEA resulting in the development of diet-induced obesity. The adipogenic effect of LA can be prevented by consuming sufficient EPA and DHA to reduce the AA-PL pool and normalize endocannabinoid tone.     

Dietary docosahexaenoic acid alters pregnant rat reproductive tissue prostaglandin and matrix metalloproteinase production

Shortened gestation is a major cause of infant mortality and morbidity. Evidence from both human and animal studies suggests that essential fatty acids of the n-6 and n-3 series play important and modifiable roles in gestational duration. We examined the influence of linolenic acid (LnA) vs. docosahexaenoic acid (DHA) on rat reproductive tissue prostaglandin (PG) and matrix metalloproteinase (MMP) indices of gestational duration. By varying the oil source of the diet, AIN-93G diets were constructed to provide either 0.7 energy % (en%) LnA, the current US intake of n-3 fatty acids, or 0.7 en% DHA. In addition, enhanced levels of 2.0 en% LnA or 2.0 e% DHA diets were also constructed. All diets contained approximately 6.0 en% linoleic acid (LA), the current US intake of LA. Four groups of 10 female rats were time-mated and fed the respective diets from conception through Day 20 of gestation. Day 20 uterus and placenta DHA were significantly increased by 160-180% by the 0.7 en% DHA diet, and by 250-350% by the 2.0 en% DHA diets in comparison to 0.7 en% LnA diet. DHA diets also significantly reduced uterus and placenta arachidonic acid content. Day 20 placenta and uterus PGE(2) and placenta PGF(2alpha) production rates were significantly reduced by 27-47% in the 0.7 en% DHA group in comparison to 0.7 en% LnA. Increasing LnA to 2.0 en% was without effect. Providing DHA at the enhanced 2.0 en% did not significantly enhance the suppression of PG production. Placenta active MMP-2 and active MMP-9 (gelatinase) production was suppressed significantly by 30-43% in the 0.7 en% DHA group in comparison to the 0.7 en% LnA group, and 2.0 en% DHA did not enhance this suppression. Placenta collagenase activity comprising the sum of MMP-1, MMP-8 and MMP-13 was also suppressed by 60% in the 0.7 en% DHA diet group with no additional effect with 2.0 en% DHA provision. These results suggest that substituting DHA for LnA even at the current US n-3 fatty acid intake of 0.7 en% is effective in suppressing indices of premature delivery and shortened gestation. Increasing LnA intake by 3-fold to 2.0 en% is not effective. The form of dietary n-3 fatty acid, DHA vs. LnA, appears to be more important than the amount.     

Docosahexaenoic acid synthesis from alpha-linolenic acid is inhibited by diets high in polyunsaturated fatty acids

The conversion of the plant-derived omega-3 (n-3) α-linolenic acid (ALA, 18:3n-3) to the long-chain eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) can be increased by ALA sufficient diets compared to ALA deficient diets. Diets containing ALA above an optimal level result in no further increase in DHA levels in animals and humans. The present study evaluates means of maximizing plasma DHA accumulation by systematically varying both linoleic acid (LA, 18:2n-6) and ALA dietary level. Weanling rats were fed one of 54 diets for three weeks. The diets varied in the percentage of energy (en%) of LA (0.07–17.1 en%) and ALA (0.02–12.1 en%) by manipulating both the fat content and the balance of vegetable oils. The peak of plasma phospholipid DHA (>8% total fatty acids) was attained as a result of feeding a narrow dietary range of 1–3 en% ALA and 1–2 en% LA but was suppressed to basal levels (～2% total fatty acids) at dietary intakes of total polyunsaturated fatty acids (PUFA) above 3 en%. We conclude it is possible to enhance the DHA status of rats fed diets containing ALA as the only source of n-3 fatty acids but only when the level of dietary PUFA is low (<3 en%).     

Fatty acid composition and lipoxygenase metabolism in blood cells of the lesser spotted dogfish, Scyliorhinus canicula.

1. The fatty acid composition of erythrocytes and leucocytes of the elasmobranch, Scyliorhinus canicula, was determined so as to indicate substrate availability for eicosanoid formation. 2. Leucocytes showed a greater degree of fatty acid unsaturation than the erythrocytes, with particularly high levels of docosahexaenoic acid (22:6,n-3). 3. The major eicosanoid precursors, arachidonic acid (20:4,n-6) and eicosapentaenoic acid (20:5,n-3), represented 13.9% and 5.2% of the total fatty acid, respectively, in erythrocytes compared with 10.7% and 6% in leucocytes. 4. Whole blood and isolated leucocytes were stimulated with calcium ionophore, A23187 and the resulting lipoxygenase products separated by reverse phase high performance liquid chromatography. 5. The main lipoxygenase products formed were 6-trans-leukotriene B4, 6-trans-12-epi-leukotriene B4, 5(S),6(R) dihydroxyeicosatetraenoic acid and 5- and 15-hydroxyeicosatetraenoic acid. 6. No leukotriene B4, leukotriene B5, or lipoxins were detected.     

Brugia malayi: microfilarial polyunsaturated fatty acid composition and synthesis

The polyunsaturated fatty acid composition of Brugia malayi microfilariae was analyzed by gas chromatography and compared to that of sera from B. malayi-infected jirds. The essential fatty acid, linoleic acid (18:2 omega 6), was the most abundant fatty acid present in both microfilarial total lipids and phospholipids as well as in jird sera. In contrast, arachidonic acid (20:4 omega 6), as well as the 18:3 omega 6, 20:2 omega 6, and 20:3 omega 6 intermediates that are formed in the enzymatic conversion of linoleic acid to arachidonic acid, were proportionally more abundant in microfilariae than in jird sera. To assess the capacity of microfilariae to transform linoleic acid into arachidonic acid, B. malayi microfilariae were incubated with [14C]linoleic acid. Microfilarial lipids were extracted and resolved by high-pressure liquid chromatography and thin-layer chromatography. A portion of [14C]linoleic acid incorporated by microfilariae was converted to [14C]arachidonic acid. Thus, microfilariae can not only incorporate exogenous arachidonic acid, as previously demonstrated, but can also synthesize arachidonic acid from exogenous linoleic acid. The capacity of microfilariae to utilize specific host polyunsaturated fatty acids raises the possibility that intravascular filarial parasites may synthesize eicosanoid metabolites of arachidonic acid that could mediate filarial-host cell interactions.     

Effect of alpha-linolenic acid in the human diet on linoleic acid metabolism and prostaglandin biosynthesis

The effect of dietary alpha-linolenic acid intake on linoleic acid metabolism and prostaglandin (PG) biosynthesis was investigated in two groups of six healthy females (25-32 yr). They were given isocaloric formula diets (FD) containing linoleic acid at a constant intake (4% of calories), with different amounts of alpha-linolenic acid: 0% (FD4/0), 4% (FD4/4), 8% (FD4/8) (group I) and 12% (FD4/12) or 16% (FD4/16) (group II); the diets were given for 2 weeks each. Comparing diet FD4/0 to FD4/16, enrichment of alpha-linolenic acid was greatest in cholesteryl esters (+6.8% in plasma, +7.1% in low density lipoproteins (LDL), +5.9% in high density lipoproteins (HDL)), less in phosphatidylcholine (+2.5% in plasma, +2.9% in LDL, +2.7% in HDL), and least in platelet lipids (+0.7%). The accumulation of alpha-linolenic acid was compensated by a decrease of oleic acid. Eicosapentaenoic acid (EPA), which was excluded from the diet, increased in all plasma lipids with augmented alpha-linolenic acid intake, indicating a chain elongation and desaturation of alpha-linolenic acid to EPA. However, even at the end of FD4/16, EPA was less than 2% of total fatty acids in all plasma lipids. Plasma linoleic acid levels were constant during all dietary regimes, according to the constant dietary intake of this fatty acid. No replacement of linoleic acid by alpha-linolenic acid could be observed. The percentage of arachidonic acid in all lipids was unaffected by alpha-linolenic acid intake. As arachidonic acid was not provided by the diet, it can be concluded that alpha-linolenic acid does not inhibit chain elongation and desaturation of linoleic acid to arachidonic acid in man.(ABSTRACT TRUNCATED AT 250 WORDS)     

Platelet-neutrophil interactions. (12S)-hydroxyeicosatetraen-1,20-dioic acid: a new eicosanoid synthesized by unstimulated neutrophils from (12S)-20-dihydroxyeicosatetraenoic acid

In the course of a cell-cell interaction, 12-HETE (12-hydroxy-5,8,10,14-eicosatetraenoic acid), the arachidonic acid lipoxygenase product released from stimulated platelets, is metabolized by a cytochrome P-450 enzyme system in unstimulated neutrophils to 12,20-DiHETE (12,20-dihydroxy-5,8,10,14-eicosatetraenoic acid). This report describes time-dependent formation of a new eicosanoid by unstimulated neutrophils exposed to 12-HETE, which is more polar than 12,20-DiHETE (reversed-phase high performance liquid chromatography). Time course studies indicated that the precursor compound of this new eicosanoid was 12,20-DiHETE. This was determined by incubation of purified 12,20-DiHETE with neutrophils, which resulted in a progressive decrease in 12,20-DiHETE as formation of the polar metabolite increased. In the absence of neutrophils, 12,20-DiHETE was quantitatively unchanged. The new metabolite of 12,20-DiHETE was identified as 12-hydroxyeicosatetraen-1,20-dioic acid, based upon its UV spectrum, co-chromatography with a chemically synthesized standard in both high performance liquid chromatography and thin layer chromatography systems, and gas chromatography-mass spectrometry. Formation of 12-HETE-1,20-dioic acid was partially inhibited by 20-hydroxy-LTB4. This indicated that the neutrophil dehydrogenase responsible for further metabolism of 12,20-DiHETE may also be involved in conversion of 20-hydroxy-LTB4 to 20-carboxy-LTB4. The 12,20-DiHETE dehydrogenase enzyme system specifically requires NAD as cofactor and has subcellular components in both cytosolic and microsomal fractions which are synergistic in their activity. These results provide additional evidence for the occurrence of multicellular metabolic events during hemostasis, thrombosis, and the inflammatory response.     

Docosahexaenoic acid is an antihypertensive nutrient that affects aldosterone production in SHR.

The effects of dietary docosahexaenoic acid (DHA), an omega-3 polyunsaturated fatty acid, on blood pressure and some pressure-regulating systems were measured in young spontaneously hypertensive rats (SHR). Plasma aldosterone and corticosterone levels, adrenal aldosterone production in vitro, and characteristics of adrenal angiotensin receptors were measured after 6 weeks of diet. Renal cytochrome P450 (CYP) 4A gene expression and arachidonic acid metabolism by renal microsomes were also investigated. Plasma cholesterol, triglycerides, and high-density lipoprotein cholesterol were measured. Diets contained either corn/soybean oil alone (CSO), or oil enriched with DHA. After 6 weeks, rats fed DHA had systolic blood pressures averaging 34 mmHg less than controls (P < 0.001). Plasma aldosterone levels were 33% lower in the DHA-fed animals than in controls (22 +/- 3 vs. 33 +/- 3.7 ng/dl, P < 0.05). Plasma levels of corticosterone were 18% lower in animals fed DHA than in controls, but this difference was not statistically significant. Adrenal glomerulosa cells from DHA-fed rats produced less aldosterone in vitro in response to angiotensin II, ACTH, or potassium. The difference was less marked when aldosterone production was stimulated by supplying exogenous corticosterone, suggesting an effect of DHA on postreceptor steps in signal transduction or the early pathway of aldosteronogenesis. We found no significant differences in angiotensin receptor subtype, number, or affinity. Production of arachidonic epoxides by renal microsomes was 17% lower in DHA-fed animals than in controls (P < 0.05). Renal cortical mRNA levels of CYP4A genes and formation of 19- and 20-hydroxyeicosatetraenoic acid (HETE) did not differ between dietary groups. Plasma total cholesterol and high-density-lipoprotein (HDL) levels were significantly reduced in SHR fed the DHA supplement, but triglyceride levels were not significantly different. The effects of DHA on steroid and eicosanoid metabolism may be part of the mechanism by which this fatty acid prevents some of the hypertension in growing SHR.     

Long-chain conversion of [13C]linoleic acid and alpha-linolenic acid in response to marked changes in their dietary intake in men

We studied the long-chain conversion of [U-13C]alpha-linolenic acid (ALA) and linoleic acid (LA) and responses of erythrocyte phospholipid composition to variation in the dietary ratios of 18:3n-3 (ALA) and 18:2n-6 (LA) for 12 weeks in 38 moderately hyperlipidemic men. Diets were enriched with either flaxseed oil (FXO; 17 g/day ALA, n=21) or sunflower oil (SO; 17 g/day LA, n=17). The FXO diet induced increases in phospholipid ALA (>3-fold), 20:5n-3 [eicosapentaenoic acid (EPA), >2-fold], and 22:5n-3 [docosapentaenoic acid (DPA), 50%] but no change in 22:6n-3 [docosahexanoic acid (DHA)], LA, or 20:4n-6 [arachidonic acid (AA)]. The increases in EPA and DPA but not DHA were similar to those in subjects given the SO diet enriched with 3 g of EPA plus DHA from fish oil (n=19). The SO diet induced a small increase in LA but no change in AA. Long-chain conversion of [U-13C]ALA and [U-13C]LA, calculated from peak plasma 13C concentrations after simple modeling for tracer dilution in subsets from the FXO (n=6) and SO (n=5) diets, was similar but low for the two tracers (i.e., AA, 0.2%; EPA, 0.3%; and DPA, 0.02%) and varied directly with precursor concentrations and inversely with concentrations of fatty acids of the alternative series. [13C]DHA formation was very low (<0.01%) with no dietary influences.     

The health implications of changing linoleic acid intakes

Linoleic acid is the most prominent polyunsaturated fatty acid (PUFA) in the Western diet. It is virtually found in every food we eat and is the predominant PUFA in land-based meats, dairy, vegetables, vegetable oils, cereals, fruits, nuts, legumes, seeds and breads. Because linoleic acid is the metabolic precursor of arachidonic acid and bioactive eicosanoids derived from arachidonic acid, there is concern that dietary linoleic acid could augment tissue arachidonic acid content, eicosanoid formation and subsequently enhance the risk of and/or exacerbate conditions associated with acute and chronic diseases (i.e., cancers, cardiovascular disease, inflammation, neurological disorders, etc.). The following series of papers examines the impact of modifying dietary levels of linoleic acid on health outcomes. The authors were asked to start with current intakes of linoleic acid (adults) and determine if health outcomes would change if linoleic acid intake increased or decreased. The authors addressed changes in tissue arachidonic acid content and eicosanoid formation, cardiovascular disease, inflammation, and psychiatric disorders.     

α-Linolenate reduces the dietary requirement for linoleate in the growing rat

Background: We hypothesized that due to the absence of a dietary source of omega-3 fatty acids, the essential fatty acid (EFA) deficiency model leads to an overestimate of linoleic acid (LA) requirements. Methods: over 7 wk, young rats consumed an EFA diet containing either 0 en% linoleate (0LA) and 0 en% α-linolenate (0LNA) or a diet containing 0.5 en% LNA plus one of seven levels of added LA (0.12–4.0 en%; n=6/group).Results: Rats consuming the 0LA–0LNA diet had the lowest final body weight, 34–68% lower LA and arachidonate in plasma and liver, 87% lower LA in epididymal fat, and an 8–20 fold higher eicosatrienoate in plasma, liver and muscle lipids. 0.5LNA completely prevented the lower growth and partly prevented the rise in eicosatrienoate seen in the 0LA–0LNA group.Conclusion: Providing dietary LNA at 0.5 en% reduces the rat's physiological requirement for LA by an estimated factor of at least four (0.5 en% instead of 2 en%). Since LA requirements in humans are also based on the same flawed model of EFA deficiency, it is plausible that they too have been overestimated and should therefore be reinvestigated.     

Linoleic and α-linolenic acid as precursor and inhibitor for the synthesis of long-chain polyunsaturated fatty acids in liver and brain of growing pigs

Studies suggested that in human adults, linoleic acid (LA) inhibits the biosynthesis of n-3 long-chain polyunsaturated fatty acids (LC-PUFA), but their effects in growing subjects are largely unknown. We used growing pigs as a model to investigate whether high LA intake affects the conversion of n-3 LC-PUFA by determining fatty acid composition and mRNA levels of Δ5- and Δ6 desaturase and elongase 2 and -5 in liver and brain. In a 2 × 2 factorial arrangement, 32 gilts from eight litters were assigned to one of the four dietary treatments, varying in LA and α-linolenic acid (ALA) intakes. Low ALA and LA intakes were 0.15 and 1.31, and high ALA and LA intakes were 1.48 and 2.65 g/kg BW0.75 per day, respectively. LA intake increased arachidonic acid (ARA) in liver. ALA intake increased eicosapentaenoic acid (EPA) concentrations, but decreased docosahexaenoic acid (DHA) (all P < 0.01) in liver. Competition between the n-3 and n-6 LC-PUFA biosynthetic pathways was evidenced by reductions of ARA (>40%) at high ALA intakes. Concentration of EPA (>35%) and DHA (>20%) was decreased by high LA intake (all P < 0.001). Liver mRNA levels of Δ5- and Δ6 desaturase were increased by LA, and that of elongase 2 by both ALA and LA intakes. In contrast, brain DHA was virtually unaffected by dietary LA and ALA. Generally, dietary LA inhibited the biosynthesis of n-3 LC-PUFA in liver. ALA strongly affects the conversion of both hepatic n-3 and n-6 LC-PUFA. DHA levels in brain were irresponsive to these diets. Apart from Δ6 desaturase, elongase 2 may be a rate-limiting enzyme in the formation of DHA.     

Subchronic exposure of cardiomyocytes to low concentrations of tumor necrosis factor α attenuates the positive inotropic response not only to catecholamines but also to cardiac glycosides and high calcium concentrations

The study investigated the changes in individual molecular species in PE and the effects of a variety of dietary fats with varying proportions of saturated and unsaturated fatty acids on membrane composition, eicosanoid production and cytokine production in thioglycollate-elicited rat macrophages.The data obtained indicates that the greatest degree of modulation by dietary fats on cytokine production was observed after 8 weeks feeding and at this time, the total diacyl species containing linoleic acid (18:2 n-6) and arachidonic acid (20:4 n-6) at the sn-2 position related in a curvilinear fashion to total 18:2 n-6 intake and that IL1 and IL6 production related in a curvilinear fashion to the total diacyl species with 20:4 and 18:2 at the sn-2 position.After 4 weeks of feeding, fish and olive oils enhanced production of IL6 and LTB₄, however, while IL1 production, after 8 weeks of dietary treatment, was greatest from macrophages of animals fed corn and olive oils, PGE₂ production was greatest in the former group and LTB₄ production in the latter. Thus an eicosanoid effect may explain the modulatory influence of olive oil and IL1 production but, cannot explain the effect of corn oil on production of the cytokine. The data from the present study provides some insight into how dietary fats could provide therapy for conditions in which inflammatory cytokines are implicated.     

Effects of postnatal age and diet on the fatty acid composition of plasma lipid fractions in preterm infants

Diet and postnatal age effect the fatty acid composition of plasma and tissue lipids. This work was designed as a transversal study to evaluate the changes in the fatty acid composition of plasma phospholipids, cholesteryl esters, triglycerides and free fatty acids in preterm infants (28-35 weeks gestational age), fed human milk (HM) and milk formula (MF) from birth to 1 month of life. Sixteen blood samples were obtained from cord, and 19 at 6-8 h after birth, 14 at 1 week and 9 at 4 weeks from HM-fed infants and 18 at 1 week and 14 at 4 weeks from MF-fed ones. Groups had similar mean birth weight, gestational age and sex ratio. The MF provided 69 kcal/dl and contained 16% of linoleic acid and 1.3% of alpha-linolenic acid on the total fat. Plasma lipid fractions were extracted and separated by thin-layer chromatography and fatty acid methyl esters were quantitated by gas liquid chromatography. In plasma phospholipids, linoleic acid (18:2 omega 6) continuously increased from birth to 1 month of age, but no changes were seen as related to type of diet; polyunsaturated fatty acids greater than 18 carbon atoms of both the omega 6 and omega 3 series (PUFA omega 6 greater than 18 C and omega 3 greater than 18 C) dropped from birth to 1 week and continued to decrease in MF-fed infants until 1 month; eicosatrienoic (20:3 omega 6), arachidonic (20:4 omega 6) and docosahexaenoic (22:6 omega 3) were the fatty acids implicated. In cholesteryl esters palmitoleic (16:1 omega 7) and oleic (18:1 omega 9) acids decreased from birth to 1 month and linoleic acid increased and arachidonic acid dropped, especially in MF fed infants. In triglycerides, palmitic, palmitoleic and stearic acid (18:0) decreased during the first month of life; oleic acid remained constant and linoleic acid increased in all infants, but arachidonic acid decreased only in those fed formula. Free fatty acids showed a similar behavior in fatty acids and in plasma triglycerides. Preterm neonates seem to have special requirements of long-chain PUFA and adapted MF should contain these fatty acids in similar amounts to those of HM to allow the maintenance of an adequate tissue structure and physiology.     

The effect of dietary linoleic acid on rat platelet sialic acid

The total sialic acid content of blood platelets from rats raised for 8 weeks or 12 months on a diet containing 1% linoleic acid (1LA) was significantly lower (by over 30%) than that from those raised on an isocalorific diet containing 6% linoleic acid (6LA). The transfer of sialic acid to endogenous glycoprotein acceptor was also significantly lower (up to almost 4-fold) in 1LA platelet and megakaryocyte-rich preparations but the transfer to exogenous glycoprotein acceptor was similar in both 1LA and 6LA platelets. The megakaryocyte-rich fraction of 1LA animals showed a reduced phosphodolichol-sensitive N-acetylglucosaminyl (but not mannosyl) transfer to endogenous glycoprotein compared with 6LA animals. No significant difference was found between the megakaryocytes of 1LA and 6LA animals in the incorporation of radioactive mannose and glucosamine into the glycoprotein of the whole cells. It was concluded that the decreased transfer of sialic acid to glycoproteins of platelets and megakaryocyte of animals on the 1LA diet was due to the decreased availability of sialyl acceptor. The formation of N-linked oligosaccharide was the same in both 1LA and 6LA megakaryocytes, and thus any differences in phosphodolichol-mediated N-glycosylation did not account for this decreased availability of sialyl acceptor.     

Dietary omega-6 fatty acid lowering increases bioavailability of omega-3 polyunsaturated fatty acids in human plasma lipid pools

BackgroundDietary linoleic acid (LA, 18:2n-6) lowering in rats reduces n-6 polyunsaturated fatty acid (PUFA) plasma concentrations and increases n-3 PUFA (eicosapentaenoic (EPA) and docosahexaenoic acid (DHA)) concentrations.ObjectiveTo evaluate the extent to which 12 weeks of dietary n-6 PUFA lowering, with or without increased dietary n-3 PUFAs, alters unesterified and esterified plasma n-6 and n-3 PUFA concentrations in subjects with chronic headache.DesignSecondary analysis of a randomized trial. Subjects with chronic headache were randomized for 12 weeks to (1) average n-3, low n-6 (L6) diet; or (2) high n-3, low n-6 LA (H3–L6) diet. Esterified and unesterified plasma fatty acids were quantified at baseline (0 weeks) and after 12 weeks on a diet.ResultsCompared to baseline, the L6 diet reduced esterified plasma LA and increased esterified n-3 PUFA concentrations (nmol/ml), but did not significantly change plasma arachidonic acid (AA, 20:4n-6) concentration. In addition, unesterified EPA concentration was increased significantly among unesterified fatty acids. The H3–L6 diet decreased esterified LA and AA concentrations, and produced more marked increases in esterified and unesterified n-3 PUFA concentrations.ConclusionDietary n-6 PUFA lowering for 12 weeks significantly reduces LA and increases n-3 PUFA concentrations in plasma, without altering plasma AA concentration. A concurrent increase in dietary n-3 PUFAs for 12 weeks further increases n-3 PUFA plasma concentrations and reduces AA.     

Dietary alpha-linolenic acid suppresses the formation of lysophosphatidic acid,a lipid mediator,in rat platelets compared with linoleic acid

Rats fed a high linoleic acid (LA, 18:2n-6) diet or a high alpha-linolenic acid (ALA, 18:3n-3) diet for 4 months after weaning. Platelets from the high-LA group contained more arachidonic acid (AA, 20:4n-6) and less eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) compared with those from the high-ALA group. Incorporation of [32P]orthophosphate into platelet phospholipids was increased by thrombin-treatment, and was greater by ca. 30% in the high-LA group than in the high-ALA group both in the presence and absence of thrombin. The formation of [32P]lysophosphatidic acid (LPA), a lipid messenger, in [32P]orthophosphate-labeled platelets was increased 6.6-fold in the high-LA group and 4.1-fold in the high-ALA-group by thrombin-treatment. The formation of [32P] LPA in activated platelets was reduced by 35% in the high-ALA group.     

Keloids in rural black South Africans. Part 2: dietary fatty acid intake and total phospholipid fatty acid profile in the blood of keloid patients

In the second part of this study, emphasis is placed on nutritional intakes (fatty acids and micronutrients) and fatty acid intake and metabolism in the blood, respectively, according to a combined 24 h recall and standardized food frequency questionnaire analyses of keloid prone patients (n=10), compared with normal black South Africans (n=80), and total phospholipid blood (plasma and red blood cell ) analyses of keloid patients (n=20), compared with normal individuals (n=20). Lipid extraction and fractionation by standard procedures, total phospholipid (TPL) separation with thin layer chromatography, and fatty acid methyl ester analyses with gas liquid chromatography techniques were used. Since nutrition may play a role in several disease disorders, the purpose of this study was to confirm or refute a role for essential fatty acids (EFAs) in the hypothesis of keloid formations stated in part 1 of this study. (1)According to the Canadian recommendation (1991), we observed that in keloid patients linoleic acid (LA) and arachidonic acid (AA) dietary intakes, as EFAs of the omega-6-series, are higher than the recommended 7-11 g/d. However, the a-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) dietary intakes, as EFAs of the omega-3 series, are lower than the recommendation of 1.1-1.5 g/d. This was also the case in the control group, where a higher dietary intake of the omega-6 fatty acids and a slightly lower dietary intake of the omega-3 fatty acids occurred. Thus, we confirm a high dietary intake of LA (as a product of organ meats, diary products and many vegetable oils) and AA (as a product of meats and egg yolks), as well as lower dietary intakes of ALA (as a product of grains, green leafy vegetables, soy oil, rapeseed oil and linseed), and EPA and DHA (as products of marine oils). Lower micronutrient intakes than the recommended dietary allowances were observed in the keloid group that may influence EFA metabolism and/or collagen synthesis. Of cardinal importance may be the lower intake of calcium in the keloid patients that may contribute to abnormal cell signal transduction in fibroblasts and consequent collagen overproduction, and the lower copper intake that may influence the immune system, or perhaps even the high magnesium intake that stimulates metabolic activity. Micronutrient deficiencies also occurred in the diets of the normal black South Africans that served as a control group. In the case of plasma TPLs, deficiency of the omega-3 EFA series (ALA, EPA and DHA) occurred, and this is in accordance with the apparent lower omega-3 EFA intake in the diets of these patients. In the case of the red blood cell TPLs, as a true and reliable source of dietary fatty acid intake and metabolism, sufficient EFAs of the omega-6 series (LA and AA) and the omega-3 series (ALA, EPA and DHA) occurred. For this study group a relative deficiency of nutritional omega-3 EFA intake apparently did occur, but was probably compensated for by blood fatty acid metabolism.     

Dietary linoleic acid has no effect on arachidonic acid,but increases n-6 eicosadienoic acid,and lowers dihomo-γ-linolenic and eicosapentaenoic acid in plasma of adult men

High intakes of linoleic acid (LA,18:2n-6) have raised concern due to possible increase in arachidonic acid (ARA, 20:4n-6) synthesis, and inhibition of alpha linolenic acid (ALA, 18:3n-3) desaturation to eicosapentaenoic (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3). In healthy men, 10.5% energy compared to 3.8% energy LA with 1% energy ALA increased plasma phospholipid LA and 20:2n-6, the elongation product of LA, and decreased EPA, with no change in ARA. However, LA was inversely related to ARA at both 10.5% energy and 3.8% energy LA, (r=?0.761, r=?0.817, p<0.001, respectively). A two-fold variability in ARA among individuals was not explained by the dietary LA, ARA, ALA, or fish intake. Our results confirm LA requirements for ARA synthesis is low, <3.8% energy, and they suggest current LA intakes saturate Δ-6 desaturation and adversely affect n-3 fatty acid metabolism. Factors other than n-6 fatty acid intake are important modifiers of plasma ARA.     

Effect of cyclooxygenase genotype and dietary fish oil on colonic eicosanoids in mice

Dietary ω3 fatty acids can modulate substrate availability for cyclooxygenases (COXs) and lipoxygenases, thus modulating downstream eicosanoid formation. This could be an alternative approach to using nonsteroidal anti-inflammatory drugs and other COX inhibitors for limiting Prostaglandin E(2) (PGE(2)) synthesis in colon cancer prevention. The aims of this study were to evaluate to what extent COX- and lipoxygenase-derived products could be modulated by dietary fish oil in normal colonic mucosa and to evaluate the role of COX-1 and COX-2 in the formation of these products. Mice (wild-type, COX-1 null or COX-2 null) were fed a diet supplying a broad mixture of fatty acids present in European/American diets, supplemented with either olive oil (oleate control diet) or menhaden (fish) oil ad libitum for 9-11 weeks. Colonic eicosanoid levels were measured by liquid chromatography tandem mass spectroscopy (LC-MS/MS), and proliferation was assessed by Ki67 immunohistochemistry. For the dietary alteration of colonic arachidonic acid: eicosapentaenoic ratios resulted in large shifts in formation of COX and lipoxygenase metabolites. COX-1 knockout virtually abolished PGE(2) formation, but interestingly, 12-hydroxyeicosatetraenoic (12-HETE) acid and 15-HETE formation was increased. The large changes in eicosanoid profiles were accompanied by relatively small changes in colonic crypt proliferation, but such changes in eicosanoid formation might have greater biological impact upon carcinogen challenge. These results indicate that in normal colon, inhibition of COX-2 would have little effect on reducing PGE(2) levels.