Dietary essential fatty acids and in vivo prostaglandin production in mammals

The Role of Marine n-3 Polyunsaturated Fatty Acids in Inflammatory-Based Disease: The Case of Rheumatoid Arthritis

Inflammation is a conserved process that involves the activation of immune and non-immune cells aimed at protecting the host from bacteria, viruses, toxins and injury. However, unresolved inflammation and the permanent release of pro-inflammatory mediators are responsible for the promotion of a condition called "low-grade systemic chronic inflammation", which is characterized by tissue and organ damage, metabolic changes and an increased susceptibility to non-communicable diseases. Several studies have demonstrated that different dietary components may influence modifiable risk factors for diverse chronic human pathologies. Marine n-3 polyunsaturated fatty acids (n-3 PUFAs), mainly eicosapentaenoic (EPA) and docosahexaenoic acid (DHA), are well-recognized anti-inflammatory and immunomodulatory agents that are able to influence many aspects of the inflammatory process. The aim of this article is to review the recent literature that relates to the modulation of human disease, such as rheumatoid arthritis, by n-3 PUFAs.

Potent synthetic and endogenous ligands for the adopted orphan nuclear receptor Nurr1

Until recently, Nurr1 (NR4A2) was known as an orphan nuclear receptor without a canonical ligand-binding domain, featuring instead a narrow and tight cavity for small molecular ligands to bind. In-depth characterization of its ligand-binding pocket revealed that it is highly dynamic, with its structural conformation changing more than twice on the microsecond-to-millisecond timescale. This observation suggests the possibility that certain ligands are able to squeeze into this narrow space, inducing a conformational change to create an accessible cavity. The cocrystallographic structure of Nurr1 bound to endogenous ligands such as prostaglandin E1/A1 and 5,6-dihydroxyindole contributed to clarifying the crucial roles of Nurr1 and opening new avenues for therapeutic interventions for neurodegenerative and/or inflammatory diseases related to Nurr1. This review introduces novel endogenous and synthetic Nurr1 agonists and discusses their potential effects in Nurr1-related diseases.

Effect of eicosapentaenoic acid-derived prostaglandin E3 on intestinal epithelial barrier function

Prostaglandins (PG) are inflammatory mediators derived from arachidonic or eicosapentaenoic acid giving rise to the 2-series or the 3-series prostanoids, respectively. Previously, we have observed that PGE2 disrupts epithelial barrier function. Considering the beneficial effect of fish oil consumption in intestinal inflammatory processes, the aim of this study was to assess the role of PGE3 on epithelial barrier function assessed from transepithelial electrical resistance and dextran fluxes in Caco-2 cells. The results indicate that PGE3 increased paracellular permeability (PP) to the same extent as PGE2, through the interaction with EP1 and EP4 receptors and with intracellular Ca(2+) and cAMP as the downstream targets. Moreover, we observed a redistribution of tight junction proteins, occludin and claudin-4. In conclusion, PGE3 is able to increase PP thus leading to reconsider the role of PGE2/PGE3 ratio in the beneficial effects of dietary fish oil supplementation in the disruption of barrier function.

Hemostatic factors and renin in Greenland Eskimos on a high eicosapentaenoic acid intake. Results of the Fifth UmanaK Expedition

The Fifth UmanaK expedition compared the fatty acid composition of platelets, bleeding times before and after ingestion of acetylsalicylic acid, 24-hour urinary tetranorprostanedioate, creatinine and Na output, as well as plasma renin, serum electrolytes and antithrombin III in 20 Greenland Eskimos and 20 Danes. The results indicate that the prostaglandin production was not inhibited in the Eskimos, and that the antiaggregatory prostanoids predominate in Eskimos compared to Danes. Although blood pressure and 24-hour urinary Na output were similar, the plasma renin level was significantly higher in the Eskimos on a high eicosapentaenoic acid intake.

Effects of centrally administered prostaglandin E(3) and thromboxane A(3) on plasma noradrenaline and adrenaline in rats: comparison with prostaglandin E(2) and thromboxane A(2)

Previously, we reported the involvement of brain omega-6 prostanoids, especially prostaglandin E(2) and thromboxane A(2), in the activation of central sympatho-adrenomedullary outflow in rats. omega-3 Prostanoids, including prostaglandin E(3) and thromboxane A(3), are believed to be less bioactive than omega-6 prostanoids, although studies on the functions of omega-3 prostanoids in the central nervous system have not been reported. In the present study, therefore, we compared the effects of centrally administered omega-3 prostanoids, prostaglandin E(3) and thromboxane A(3), with those of omega-6 prostanoids, prostaglandin E(2) and thromboxane A(2), on the plasma catecholamines in anesthetized rats. Intracerebroventricularly (i.c.v.) administered prostaglandin E(2) (0.15, 0.3 and 1.5 nmol/animal) and prostaglandin E(3) (0.3 and 3 nmol/animal) predominantly elevated plasma noradrenaline but not adrenaline, but the latter was less efficient than the former. On the other hand, U-46619 (an analog of thromboxane A(2)) (30, 100 and 300 nmol/animal, i.c.v.) and Delta(17)-U-46619 (an analog of thromboxane A(3)) (100 and 300 nmol/animal, i.c.v.) both elevated plasma catecholamines (adrenaline>>noradrenaline) to the same degree. These results suggest that centrally administered prostaglandin E(3) is less effective than prostaglandin E(2) to elevate plasma noradrenaline, and that thromboxane A(3) is almost as equipotent as thromboxane A(2) to elevate plasma catecholamines in rats.

Endocannabinoids and nutrition

The endocannabinoids anandamide (AEA) and 2-arachidonoylglycerol (2-AG) are bioactive lipids derived from the n-6 family of polyunsaturated fatty acids that are essential fatty acids. Symptoms of essential fatty acid deficiency in rats - growth retardation, scaly skin, and increased transepidermal water loss - can mainly be attributed to lack of linoleic acid as a structural element of the epidermis. Arachidonic acid, however, also serve essential functions, particularly in cellular signalling via its precursor role for numerous oxygenated derivatives such as prostaglandins, leukotrienes, hepoxilins and other eicosanoids. Furthermore, arachidonic acid is also a structural part of endocannabinoids that have signalling functions in relation to modulation of neurotransmitter release, which might involve physiological and pathophysiological phenomena such as regulation of appetite, energy metabolism, pain perception, memory and learning. Furthermore, along with AEA formation other acylethanolamides are always formed - e.g., oleoylethanolamide (OEA), that can inhibit food intake, and palmitoylethanolamide, that is anti-inflammatory - possibly through activation of peroxisome proliferator activated receptor alpha (PPAR alpha) and/or GPR119. As all these unsaturated fatty acids are ingested daily in smaller or larger amounts, one can ask whether different dietary fats can affect the levels of these fatty acids in the tissues and thereby the quantitative formation of these bioactive signalling molecules. Generally, in vivo arachidonic-acid-derived eicosanoid production can be increased and decreased by prolonged feeding with pharmacological levels of arachidonic acid and long-chain (n-3) fatty acids (fish oil), respectively. Changes in levels of these two fatty acids within the traditional human diet hardly affects the eicosanoid production, however. Moreover, preliminary data suggest that dietary intake of arachidonic acid and fish oil also doesn't easily affect endocannabinoid formation; however, dietary fat in terms of saturated, polyunsaturated and monounsaturated seems to affect tissue levels of AEA, 2-AG and OEA.

Effect of altering dietary omega-6/omega-3 fatty acid ratios on prostate cancer membrane composition, cyclooxygenase-2, and prostaglandin E2

PURPOSE

To determine whether altering the dietary content of omega-6 (n-6) and omega-3 (n-3) polyunsaturated fatty acids affects the growth of androgen-sensitive prostate cancer xenografts, tumor membrane fatty acid composition, and tumor cyclooxygenase-2 and prostaglandin E(2) (PGE(2)) levels.

EXPERIMENTAL DESIGN

Individually caged male severe combined immunodeficiency mice were fed isocaloric 20% kcal fat diets with the fat derived either primarily from n-6 fatty acids (n-6 group) or with the fat consisting of n-6 and n-3 fatty acids in a ratio of 1:1 (n-3 group), and injected s.c. with Los Angeles Prostate Cancer 4 (LAPC-4) cells. Tumor volumes and mouse weights were measured weekly, caloric intake was measured 3 days per week, and tumors and serum were harvested at 8 weeks postinjection.

RESULTS

Tumor growth rates, final tumor volumes, and serum prostate-specific antigen levels were reduced in the n-3 group relative to the n-6 group. The n-3 group tumors had decreased proliferation (Ki67 staining) and increased apoptosis (terminal nucleotidyl transferase-mediated nick end labeling staining). In vitro proliferation of LAPC-4 cells in medium containing n-3 group serum was reduced by 22% relative to LAPC-4 cells cultured in medium containing serum from the n-6 group. The n-6/n-3 fatty acid ratios in serum and tumor membranes were lower in the n-3 group relative to the n-6 group. In addition, n-3 group tumors had decreased cyclooxygenase-2 protein and mRNA levels, an 83% reduction in PGE(2) levels, and decreased vascular endothelial growth factor expression.

CONCLUSION

These results provide a sound basis for clinical trials evaluating the effect of dietary n-3 fatty acids from fish oil on tumor PGE(2) and membrane fatty acid composition, and serum and tumor biomarkers of progression in men with prostate cancer.

Prostate cancer prevention by nutritional means to alleviate metabolic syndrome

In 1987 when Reaven introduced syndrome X (metabolic syndrome, or MS), we were studying skeletal muscle insulin resistance and found that when rodents were fed a high-fat, refined-sugar (HFS) diet, insulin resistance developed along with aspects of MS, including hyperinsulinemia, hypertension, hypertriglyceridemia, and obesity. MS was controlled in rodents by switching them to a low-fat, starch diet and was controlled in humans with a low-fat starch diet and daily exercise (Pritikin Program). Others reported inverse relations between serum insulin and sex hormone-binding globulin (SHBG). When subjects were placed on the Pritikin Program, insulin fell and SHBG rose and it was suggested that prostate cancer might also be an aspect of MS. A bioassay was developed with tumor cell lines grown in culture and stimulated with serum before and after a diet and exercise intervention. Diet and exercise altered serum factors that slowed the growth rate and induced apoptosis in androgen-dependent prostate cancer cells. Changes in serum with diet and exercise that might be important include reductions in insulin, estradiol, insulin-like growth factor-I (IGF-I), and free testosterone with increases in SHBG and IGF binding protein-1. Hyperinsulinemia stimulates liver production of IGF-I, plays a role in the promotion of prostate cancer, and thus is the cornerstone for both MS and prostate cancer. Adopting a low-fat starch diet with daily exercise controls MS and should reduce the risk of prostate cancer.

Evaluation of the effect of Neptune Krill Oil on chronic inflammation and arthritic symptoms

OBJECTIVES

a) To evaluate the effect of Neptune Krill Oil (NKO) on C-reactive protein (CRP) on patients with chronic inflammation and b) to evaluate the effectiveness of NKO on arthritic symptoms.

METHODS

Randomized, double blind, placebo controlled study. Ninety patients were recruited with confirmed diagnosis of cardiovascular disease and/or rheumatoid arthritis and/or osteoarthritis and with increased levels of CRP (>1.0 mg/dl) upon three consecutive weekly blood analysis. Group A received NKO (300 mg daily) and Group B received a placebo. CRP and Western Ontario and McMaster Universities (WOMAC) osteoarthritis score were measured at baseline and days 7, 14 and 30.

RESULTS

After 7 days of treatment NKO reduced CRP by 19.3% compared to an increase by 15.7% observed in the placebo group (p = 0.049). After 14 and 30 days of treatment NKO further decreased CRP by 29.7% and 30.9% respectively (p < 0.001). The CRP levels of the placebo group increased to 32.1% after 14 days and then decreased to 25.1% at day 30. The between group difference was statistically significant; p = 0.004 at day 14 and p = 0.008 at day 30. NKO showed a significant reduction in all three WOMAC scores. After 7 days of treatment, NKO reduced pain scores by 28.9% (p = 0.050), reduced stiffness by 20.3% (p = 0.001) and reduced functional impairment by 22.8% (p = 0.008).

CONCLUSION

The results of the present study clearly indicate that NKO at a daily dose of 300 mg significantly inhibits inflammation and reduces arthritic symptoms within a short treatment period of 7 and 14 days.

Differential effects of prostaglandin derived from omega-6 and omega-3 polyunsaturated fatty acids on COX-2 expression and IL-6 secretion

Omega-6 (omega-6) polyunsaturated fatty acids (PUFA), abundant in the Western diet, are precursors for a number of key mediators of inflammation including the 2-series of prostaglandins (PG). PGE(2), a cyclooxygenase (COX) metabolite of arachidonic acid, a omega-6 PUFA, is a potent mediator of inflammation and cell proliferation. Dietary supplements rich in omega-3 PUFA reduce the concentrations of 2-series PG and increase the synthesis of 3-series PG (e.g., PGE(3)), which are believed to be less inflammatory. However, studies on cellular consequences of increases in 3-series PG in comparison to 2-series PG have not been reported. In this study, we compared the effects of PGE(2) and PGE(3) on (i) cell proliferation in NIH 3T3 fibroblasts, (ii) expression and transcriptional regulation of the COX-2 gene in NIH 3T3 fibroblasts, and (iii) the production of an inflammatory cytokine, IL-6, in RAW 264.7 macrophages. PGE(3), unlike PGE(2), is not mitogenic to NIH 3T3 fibroblasts. PGE(2) and PGE(3) both induce COX-2 mRNA via similar signaling mechanisms; however, compared with PGE(2), PGE(3) is significantly less efficient in inducing COX-2 gene expression. Furthermore, although both PGE(2) and PGE(3) induce IL-6 synthesis in RAW 264.7 macrophages, PGE(3) is substantially less efficient compared with PGE(2). We further show that increasing the omega-3 content of membrane phospholipid results in a decrease in mitogen-induced PGE(2) synthesis. Taken together, our data suggest that successful replacement of omega-6 PUFA with omega-3 PUFA in cell membranes can result in a decreased cellular response to mitogenic and inflammatory stimuli.

Long-chain n-3-to-n-6 polyunsaturated fatty acid ratios in breast adipose tissue from women with and without breast cancer

Animal studies suggest that dietary polyunsaturated fatty acids (PUFAs) of the n-6 class, found in corn and safflower oils, may be precursors of intermediates involved in the development of mammary tumors, whereas long-chain (LC) n-3 PUFAs, found in fish oil, can inhibit these effects. This case-control study was designed to examine the relationship between the PUFA composition of breast adipose tissue and the risk of breast cancer. Using fatty acid levels in breast adipose tissue as a biomarker of past qualitative dietary intake of fatty acids, we examined the hypothesis that breast cancer risk is negatively associated with specific LC n-3 PUFAs (eicosapentaenoic acid and docosahexaenoic acid) and positively associated with n-6 PUFAs (linoleic acid and arachidonic acid). Breast adipose tissue was collected from 73 breast cancer patients and 74 controls with macromastia. The fatty acid levels were determined by gas-liquid chromatography. A logistic regression model was used to obtain odds ratio estimates while adjusting for age. The age-adjusted n-6 PUFA (linoleic acid and arachidonic acid) content was significantly higher in cases than in controls (P = 0.02). There was a trend in the age-adjusted data suggesting that, at a given level of n-6 PUFA, LC n-3 PUFAs (eicosapentaenoic acid and docosahexaenoic acid) may have a protective effect (P = 0.06). A similar inverse relationship was observed with LC n-3-to-n-6 ratio when the data were adjusted for age (P = 0.09). We conclude that total n-6 PUFAs may be contributing to the high risk of breast cancer in the United States and that LC n-3 PUFAs, derived from fish oils, may have a protective effect.

Modulation of omega-3/omega-6 polyunsaturated ratios with dietary fish oils in men with prostate cancer

OBJECTIVES

The results of epidemiologic and animal studies support the role of a low-fat diet supplemented with omega-3 fatty acids contained in fish oil in preventing the development and progression of prostate cancer. As a first step in studying the role of a low-fat, fish oil-supplemented (LF/FOS) diet in a clinical setting, we conducted a prospective study in men with untreated prostate cancer to evaluate whether a 3-month dietary intervention affects the ratio of omega-3 to omega-6 fatty acids in plasma and gluteal fat. In addition, we evaluated the feasibility of studying cyclooxygenase-2 (COX-2) expression in serial prostate needle biopsy specimens before and after the diet.

METHODS

Nine men with untreated prostate cancer consumed an LF/FOS diet for 3 months. Plasma, gluteal adipose tissue, and prostate needle biopsy specimens were obtained from each patient before and after the intervention. The fatty acid compositions of the plasma and gluteal adipose tissue were determined by gas-liquid chromatography, and the COX-2 expression in the prostatic tissue specimens was determined by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

Short-term intervention with an LF/FOS diet caused a significant increase in the omega-3/omega-6 fatty acid ratio in plasma (P = 0.002) and gluteal adipose tissue (P = 0.002) in men with prostate cancer. The COX-2 expression in prostatic tissue was quantitated by RT-PCR in 7 of 9 patients, and COX-2 expression decreased in 4 of these 7 patients.

CONCLUSIONS

A short-term dietary intervention in men with prostate cancer leads to a significant increase in the omega-3/omega-6 fatty acid ratios in plasma and adipose tissue. The potential for this diet to prevent the development and progression of prostate cancer by way of altered COX-2 expression and prostaglandin production in prostatic tissue requires further study.

Formation of N-acyl-phosphatidylethanolamines and N-acetylethanolamines: proposed role in neurotoxicity

The formation of N-acyl-phosphatidylethanolamine (NAPE) and N-acylethanolamine (NAE), including anandamide, in mammals in relation to neurotoxicity is discussed. Data on the characterization of the NAPE-forming N-acyltransferase, the NAPE-hydrolyzing phospholipase D, and the NAE-hydrolyzing amidase are reviewed. We suggest that NAPE and NAE, including anandamide, are formed in neurons in response to the high intracellular calcium concentrations that occur in injured neurons, e.g. due to glutamate excitotoxicity. NAPE may have functions of its own besides being a precursor for NAE. The formation of both of these lipids may serve as a cytoprotective response, whether mediated by physical interactions with membranes or enzymes, or mediated by activation of cannabinoid receptors. This suggestion implies that NAPE and NAE may have pathophysiological roles in the brain. Whether these lipids also have physiological roles is uncertain.

Dietary modulation of omega-3/omega-6 polyunsaturated fatty acid ratios in patients with breast cancer

BACKGROUND

Polyunsaturated fatty acids of the omega-6 (omega-6) class, as found in corn and safflower oils, can act as precursors for intermediates involved in the growth of mammary tumors when fed to animals, whereas polyunsaturated fatty acids of the omega-3 (omega-3) class, as found in fish oil, can inhibit these effects. The effects of dietary intervention on the ratios of these fatty acids in breast and other adipose tissues have not previously been prospectively studied.

PURPOSE

The present investigation was conducted to study the impact on the ratio of omega-3 and omega-6 polyunsaturated fatty acid in plasma and in adipose tissue of the breast and buttocks when women with breast cancer consume a low-fat diet and fish oil supplements.

METHODS

Twenty-five women with high-risk localized breast cancer were enrolled in a dietary intervention program that required them to eat a low-fat diet and take a daily fish oil supplement throughout a 3-month period. Breast and gluteal fat biopsy specimens were obtained from each woman before and after dietary intervention. The fatty acid compositions of specimens of plasma, breast fat, and gluteal fat were determined by gas-liquid chromatography. Statistical analysis involved use of a two-sided paired t test.

RESULTS

After dietary intervention, a reduction in the level of total omega-6 polyunsaturated fatty acids in the plasma was observed (P<.0003); moreover, total omega-3 polyunsaturated fatty acids increased approximately three-fold (P<.0001) and the omega-3/omega-6 polyunsaturated fatty acids ratio increased approximately fourfold (i.e., mean values increased from 0.09 to 0.41; P = .0001). An increase in total omega-3 polyunsaturated fatty acids in breast adipose tissue was observed following dietary intervention (P = .04); the omega-3/omega-6 polyunsaturated fatty acid ratio increased from a mean value of 0.05 to 0.07 (P = .0001). An increase in total omega-3 polyunsaturated fatty acids was observed in gluteal adipose tissue following the intervention (P = .05); however, the ratio of omega-3 to omega-6 polyunsaturated fatty acids (mean ratio values of 0.036-0.045; P = .06) was unchanged.

CONCLUSION

Short-term dietary intervention can lead to statistically significant increases in omega-3/omega-6 polyunsaturated fatty acid ratios in plasma and breast adipose tissue. Breast adipose tissue changed more rapidly than gluteal adipose tissue in response to the dietary modification tested in this study. Therefore, gluteal adipose tissue may not be a useful surrogate to study the effect of diet on breast adipose tissue.

Molecular species of phosphoglycerides in liver microsomes of rats fed a fat-free diet

The influence of a fat-free diet on the molecular species composition of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylinositol (PI) of rat liver microsomes was studied by using reversed-phase high-pressure liquid chromatography. In the three phosphoglyceride classes analyzed, the fat-free diet produced a large decrease in the 18:0/20:4n-6 species but less important changes were found in the 16:0/20:4n-6 species. In PC, the most abundant phosphoglyceride class of rat liver microsomes, the fall in the 18:0/20:4n-6 species was counterbalanced mainly by an enhancement in the 16:0/18:1n-9 species although it was not evident in PE. In PI, the decrease in the 18:0/20:4n-6 species was counterbalanced by an increase in the 18:0/20:3n-9 species. Fluorescence polarization measurements of 1,7-diphenyl-1,3,5-hexatriene in liposomes of 16:0/18:1n-9, 18:0/18:1n-9-, 16:0/20:4n-6-, and 18:0/20:4n-6-PC indicated that the change in the saturated fatty acid in the sn-1 position accompanying the replacement of 20:4n-6 by 18:1n-9 could be very important for a homeoviscous compensation, maintaining the membrane physical properties without large alterations in spite of the essential fatty acid deficiency due to the fat-free diet.

Supplementation with omega-3 polyunsaturated fatty acids in the management of dysmenorrhea in adolescents

OBJECTIVES

The purpose of the study was to examine whether dietary supplementation with omega-3 fatty acids can relieve symptoms of dysmenorrhea in adolescents.

STUDY DESIGN

Forty-two adolescents with dysmenorrhea were randomly allocated to two groups. In the first group 21 girls received fish oil (1080 mg icosapentaenoic acid, 720 mg docosahexaenoic acid, and 1.5 mg vitamin E) daily for 2 months followed by a placebo for an additional 2 months. In the second group 21 girls received placebo for the first 2 months, followed by fish oil for 2 more months. The Cox Menstrual Symptom Scale was used to assess response to treatment.

RESULTS

There were no significant differences in the Cox Menstrual Symptom Scale between the two groups at baseline after 2 months of placebo administration. After 2 months of treatment with fish oil there was a marked reduction in the Cox Menstrual Symptom Scale from a baseline mean value of 69.9 to 44.0 (p < 0.0004).

CONCLUSIONS

This study suggests that dietary supplementation with omega-3 fatty acids has a beneficial effect on symptoms of dysmenorrhea in adolescents.

Modulation of the endogenous leukotriene production by fish oil and vitamin E

We investigated the effects of fish oil and vitamin E on the endogenous leukotriene production. 10 healthy volunteers were supplemented for 1 week with fish oil (containing 40 mg/kg body weight per day of eicosapentaenoic and docosahexaenoic acid), vitamin E (540 mg, i.e., 800 IU of D-alpha-tocopherol per day), or with both agents. Treatment resulted in a significant increase in the eicosapentaenoate concentration in red blood cell membranes and/or in the vitamin E concentration in serum. In addition, nine obese patients were investigated who were on a hypocaloric diet including 10 mg vitamin E/day for 8 weeks. This diet was associated with a significant decrease in serum vitamin E concentration. The urinary concentration of leukotriene E4 plus N-acetylleukotriene E4 served as a measure for the endogenous leukotriene production. Fish oil reduced leukotriene production in eight of the 10 healthy individuals. After vitamin E supplementation, urinary leukotrienes were significantly reduced in all of the healthy volunteers. The combination of vitamin E plus fish oil had no synergistic effect on leukotriene production in the individuals tested. The decrease in serum vitamin E concentration during the hypocaloric, 10 mg vitamin E/day diet was associated with an increase in urinary leukotrienes in 8 of the 9 obese patients. Urinary prostaglandin metabolites, determined as tetranorprostanedioic acid, increased or decreased in parallel with urinary leukotrienes in most individuals; however, changes were less pronounced than those observed with leukotrienes. We conclude that the endogenous leukotriene production can be reduced effectively by high doses of fish oil or vitamin E, whereas vitamin E depletion is associated with an increase in leukotriene generation.

New biological and clinical roles for the n-6 and n-3 fatty acids

Four new findings of the biochemistry and biology of the essential n-6 and n-3 fatty acids have recently been demonstrated. These findings will augment current knowledge as to the role of the essential fatty acids in human health.

Inhibition of fatty acid synthesis in rat hepatocytes by exogenous polyunsaturated fatty acids is caused by lipid peroxidation

Rat hepatocyte long-term cultures were utilized to investigate the impact of different polyunsaturated fatty acids (PUFA) on the insulin-induced de novo fatty acid synthesis in vitro. The addition of 0.5 mM albumin-complexed oleic, linoleic, columbinic, arachidonic, eicosapentaenoic or docosahexaenoic acid resulted in a marked suppression of fatty acid synthesis. By evaluation of cell viability (determined as the leakage of lactate dehydrogenase (LDH) it turned out, that the antioxidant used (50 microM alpha-tocopherol phosphate) had a low antioxidant activity, resulting in cytotoxic effects by the peroxidized PUFA. Arachidonic acid and eicosapentaenoic acid showed a dose- and time-dependent cytotoxicity. Two other antioxidants: 50 microM alpha-tocopherol acid succinate and 1 microM N,N'-diphenyl-1,4-phenylenediamine, both proved more efficient than alpha-tocopherol phosphate. There was a significant correlation between LDH-leakage and inhibition of fatty acid synthesis. Lipid peroxidation, measured as thiobarbituric acid-reactive substances, also showed a significant correlation with the degree of inhibition of fatty acid synthesis. Furthermore, PUFA had no inhibitory effect on fatty acid synthesis when peroxidation was minimized by the use of proper antioxidants. These data indicate that PUFA in vitro inhibit the insulin-induced de novo fatty acid synthesis in hepatocytes from starved rats, due to cytotoxic effects caused by lipid peroxidation.

The effect of ascorbic acid on arachidonic acid and prostaglandin E2 metabolism in B16 murine melanoma cells

Ascorbic acid (Asc), arachidonic acid (AA) and prostaglandin E2 (PGE2) are reported to be important in maintaining the stability of the cell matrix. Asc has also been shown to influence fatty acid (FA) and PGE2 synthesis, with the result that effects of Asc on cell growth are suggested to be mediated through the metabolism of these two compounds. This study examined the effect of Asc, supplemented over the concentration range of 0-100 micrograms/ml, on the in vitro cell growth of non-malignant LLCMK (monkey kidney) cells and malignant B16 murine melanoma cells. The effects of Asc supplementation on AA and PGE2 levels in the cell stroma and membrane fractions of the two cell types was also determined. Asc had no significant inhibitory or stimulatory effect on the growth of either the B16 or LLCMK cells. The total percentage AA composition determined in the B16 control cells (combined stroma and membrane fractions), was similar to that determined in the LLCMK control cells. Asc supplementation of the B16 cells, resulted in an inverse relationship between B16 cell growth and total percentage AA composition. PGE2 concentration in the control B16 cells (combined stroma and membrane fractions) was significantly higher than that detected in the control LLCMK cells. No PGE2 was detected in the B16 stroma fraction, with all appearing to be located in the membrane fraction. However, upon the supplementation of the B16 cells with increasing Asc concentrations, PGE2 appeared to be mobilized from the membrane fraction, resulting in increasing PGE2 levels in the stroma fraction relative to the membrane fraction. This was accompanied by a significant decrease in PGE2 concentration, in the membrane fraction. B16 cell growth and total (stroma and membrane fractions) PGE2 concentration in these cells was inversely related, when cultures were supplemented with increasing levels of Asc. Asc supplementation of the LLCMK cells did not appear to have any significant effect on AA or PGE2 metabolism in these cells.

Dietary protein and fatty acid composition of liver lipids in the rat

In order to compare the effects of different sources of dietary protein on the fatty acid composition of phosphatidylcholines (PC), phosphatidylethanolamines (PE), phosphatidylinositols (PI), cholesteryl esters and triacylglycerols, male rats were fed for a 4-week period on cholesterol-free, or cholesterol-containing, diets based on casein, or soybean protein and olive oil. The most conspicuous difference observed was the occurrence of significantly higher levels of 5,8,11-eicosatrienoic acid, 20:3 (n - 9), in the different lipid classes of casein-fed, compared with soybean protein-fed, animals. In the PI fraction of livers from the groups of rats fed casein diet, this fatty acid amounted to between 9.9 and 13.3% by weight of the total fatty acids. Phospholipids from livers of casein-fed rats contained increased levels of oleic acid, 18:1 (n - 9) (in PC and PE) and reduced levels of stearic acid (18:0). Moreover, in this group of rats PI contained a reduced level of arachidonic acid, 20:4 (n - 6). A casein-related decrease in the linoleic acid, 18:2 (n - 6), content of PC and PE was observed only in the rats fed on cholesterol-free diet. Effects on the fatty acid composition were also observed in the triacyglycerol and cholesteryl ester fractions, in which the rats fed casein diet showed higher levels of palmitoleic acid, 16:1 (n - 7) (cholesterol-supplemented diet) and lower values for linoleic acid, than the soybean protein-fed rats.

Polydipsia in rhesus monkeys deficient in omega-3 fatty acids

Omega-3 fatty acids are a major component of neural membranes. They are essential nutrients for normal biochemical development of the brain and retina and may affect behavior. In our studies of long-term dietary omega-3 fatty acid deficiency, we have found a new effect of this deficiency in rhesus monkeys. Deficient monkeys visited the home cage drinking spout more frequently than controls (Experiment 1), and drank more water over 24 hours (Experiment 2). The increase in intake was mirrored by increased combined output of urine + feces over 24 hours (Experiment 3), and was not due to spillage (Experiment 4). The dietary deficiency greatly reduced omega-3 fatty acids in red blood cells but did not affect serum electrolyte levels. The changes in fluid intake and output may be related to direct or indirect effects on central or peripheral control mechanisms for drinking or excretion, which may be mediated by altered composition of neural or other membranes or changes in eicosanoid metabolism.

Nutrition and biomembranes: additional information concerning the incidence of dietary polyunsaturated fatty acids on membrane organization and biological activity

One of the important questions in biomembranes now is: Do the essential fatty acids (polyunsaturated fatty acids of the n-6 and n-3 series) play an original structural role in the arrangement of the lipid matrix capable, in particular, of triggering modifications of intrinsic protein activities? Preliminary results from our laboratories are presented in rat and piglet fed standard or essential fatty acid-deficient diets. The relative amounts of 18:2 (n-6) and 20:4 (n-6) in total fatty acids of hepatic microsome or enterocyte brush border membrane phospholipids are closely dependent on the type of diet (a globally decreasing effect with deficiency), whereas no differences were observed with relative amounts of cholesterol, phospholipids, and proteins. This effect of deficiency on membrane fatty acids has to be compared to the decreasing specific activities of microsome NADPH-cytochrome c reductase or aniline hydroxylase (studied in rat), to the increasing order of the structure of both membrane microsome and brush border lipid matrix (studied in both rat and piglet), and to the increasing mobility (or accessibility) of the membrane-protein surface-bonded spin-label (studied in the piglet brush border membrane), suggesting a probably defective protein-lipid fit in the case of deficiency. These results could favor conformational change in the whole membrane structure (i.e. proteins and lipids). The specificity of these effects remains to be assessed.

Metabolic utilization of linoleic acid from fat emulsion in infants during total parenteral nutrition

The metabolic utilization of linoleic acid (C18:2w6) from intravenous (iv) soybean oil emulsion via its conversion to higher homologues and prostaglandin biosynthesis was studied in 21 infants. The infants were of normal birth weight, in good clinical and metabolic condition, and aged from 1-4 months. They all received total parenteral nutrition after birth for more than 1 month; the only lipid was provided by iv Intralipid 20%, at levels approximating 350 mg/kg/24 h of linoleic acid (2.5% of the infants' total daily energy intake). Study of the fatty acids of plasma and erythrocyte phospholipids in these infants, compared to healthy controls of the same age (N = 26), showed that 350 mg/kg/24 hr of C18:2w6 supply resulted in normalization of erythrocyte phospholipid fatty acid distribution. This was particularly true of the higher homologues of C18:2w6 (C18:3w6, C20:3w6, and C20:4w6). This suggested that delta 6 and delta 5 desaturation activities are normal in these conditions with this C18:2w6 supply. These results were confirmed by the study of 24-hr urinary excretion of prostaglandins PGE1 and PGE2. With 350 mg/kg/24 hr of C18:2w6 supply their urinary levels were not significantly different from those observed in normal children of the same age receiving an equivalent oral C18:2w6 intake.

Effect of arachidonic acid, fatty acids, prostaglandins, and leukotrienes on volume regulation in Ehrlich ascites tumor cells

Arachidonic acid inhibits the cell shrinkage observed in Ehrlich ascites tumor cells during regulatory volume decrease (RVD) or after addition of the Ca ionophore A23187 plus Ca. In Na-containing media, arachidonic acid increases cellular Na uptake under isotonic as well as under hypotonic conditions. Arachidonic acid also inhibits KCl and water loss following swelling in Na-free, hypotonic media even when a high K conductance has been ensured by addition of gramicidin. In isotonic, Na-free medium arachidonic acid inhibits A23187 + Ca-induced cell shrinkage in the absence but not in the presence of gramicidin. It is proposed that inhibition of RVD in hypotonic media by arachidonic acid is caused by reduction in the volume-induced Cl and K permeabilities as well as by an increase in Na permeability and that reduction in A23187 + Ca-induced cell shrinkage is due to a reduction in K permeability and an increase in Na permeability. The A23187 + Ca-activated Cl permeability in unaffected by arachidonic acid. PGE2 inhibits RVD in Na-containing, hypotonic media but not in Na-free, hypotonic media, indicating a PGE2-induced Na uptake. PGE2 has no effect on the volume-activated K and Cl permeabilities. LTB4, LTC4 and LTE4 inhibit RVD insignificantly in hypotonically swollen cells. LTD4, moreover, induces cell shrinkage in steady-state cells and accelerates the RVD following hypotonic exposure. The effect of LTD4 even reflects a stimulating effect on K and Cl transport pathways. Thus none of the leukotrienes show the inhibitory effect found for arachidonic acid on the K and Cl permeabilities. The RVD response in hypotonic, Na-free media is, on the other hand, also inhibited by addition of the unsaturated oleic, linoleic, linolenic and palmitoleic acid, even in the presence of the cationophor gramicidin. The saturated arachidic and stearic acid had no effect on RVD. It is, therefore, suggested that a minor part of the inhibitory effect of arachidonic acid on RVD in Na-containing media is via an increased synthesis of prostaglandins and that the major part of the arachidonic acid effect on RVD in Na-free media, and most probably also in Na-containing media, is due to the inhibition of the volume-induced K and Cl transport pathways, caused by a nonspecific detergent effect of an unsaturated fatty acid.

Role of prostaglandins and leukotrienes in volume regulation by Ehrlich ascites tumor cells

PGE2 and LTC4 syntheses in Ehrlich ascites cells were measured by radioimmunoassay. Hypotonic swelling results in stimulation of the leukotriene synthesis and a concomitant reduction in the prostaglandin synthesis. If the cells have access to sufficient arachidonic acid there is a parallel increase in the synthesis of both leukotrienes and prostaglandins following hypotonic exposure. PGE2 significantly inhibits regulatory volume decrease (RVD) following hypotonic swelling in Na-containing medium but not in Na-free media, supporting the hypothesis that the effect of PGE2 is on the Na permeability. PGE2 also had no effect on RVD in Na-free media in the presence of the cation ionophore gramicidin. Since the Cl permeability becomes rate limiting for RVD in the presence of gramicidin, whereas the K permeability is rate limiting in its absence, it is concluded that PGE2 neither affects Cl nor K permeability. Addition of LTD4 accelerates RVD and since the K permeability is rate limiting for RVD this shows that LTD4 stimulates the K permeability. Inhibition of the leukotriene synthesis by nordihydroguaiaretic acid inhibits RVD even when a high K conductance has been ensured by the presence of gramicidin. It is, therefore, proposed that an increase in leukotriene synthesis after hypotonic swelling is involved also in the activation of the Cl transport pathway.

Inhibition of arachidonic acid oxidation by beta-carotene, retinol and alpha-tocopherol

Prostaglandin and hydroxyeicosatetraenoic acid (HETE) production from arachidonic acid in bovine seminal vesicles and kidney as influenced by the addition of beta-carotene, retinol or alpha-tocopherol was studied. The major product formed was prostaglandin E2 (approximately 85% prostaglandin E2 of control), and its proportion decreased with increasing concentration of the additives, while the proportion of HETE increased. Prostaglandin and HETE production was considerably inhibited by beta-carotene and retinol, and to a lesser extent by alpha-tocopherol; HETE production was inhibited less than that of prostaglandin. It appears that beta-carotene, retinol and alpha-tocopherol influence both the cyclooxygenase and lipoxygenase pathways; this modulation of arachidonic acid oxidation by physiological compounds may have important in vivo implications.

Changes in the fatty acid composition of plasma and red blood cell membrane during the first hours of life in human neonates

The objective of this work was to examine the changes in the fatty acid profiles of plasma lipid fractions and red blood cell membrane phospholipids in newborn infants during the first 6-8 h of life. Methyl esters of fatty acids from plasma free fatty acids and phospholipids and from membrane phosphatidylethanolamine, phosphatidylcholine and sphingomyelin for cord blood (n = 20) and venous blood (n = 19) were analyzed by GLC. Important changes were observed in plasma fatty acids. Palmitic and palmitoleic acid increased from birth to 6-8 h of age for both free fatty acids and phospholipids. Palmitic acid also increased in membrane phosphatidylcholine and phosphatidylethanolamine. In the former, stearic acid declined whereas oleic and docosatetraenoic acids increased. Phosphatidylethanolamine and sphingomyelin were less affected than phosphatidylcholine probably because the internal location of the two first fractions in erythrocyte membrane. Polyunsaturated fatty acids dropped slightly during the first hours of life in most lipid fractions. This may be a consequence of the interruption of placental fatty acid supply and the limited capacity of the newborn to desaturate their essential fatty acid tissue stores.

Plasma phospholipid fatty acids and urinary excretion of prostaglandins PGE1 and PGE2 in infants during total parenteral nutrition, with continuous or sequential administration of fat emulsion

During total parenteral nutrition, using an identical supply of fat emulsion (350 mg/kg/24 hr) to correct essential fatty acid deficiency in children, the efficacy of two methods of administration was studied: continuous over 24 hr, or discontinuous 3 hr/day. At the beginning of the study, all the infants (1-4 months old) had proven essential fatty acid deficiency. After at least 1 month of one of the two nutritional protocols (continuous or discontinuous), plasma phospholipid fatty acid composition and PGE1 and PGE2 urinary excretion were measured. The results obtained indicate better utilization of the fat emulsion when it is administered almost every day, in continuous infusion over 24 hr (1 g/kg/24 hr of Intralipid 20%).

Intake of marine fat, rich in (n-3)-polyunsaturated fatty acids, may increase birthweight by prolonging gestation

Birthweights in the Faroe Islands are among the highest in the world. Compared with Denmark, the average birthweight of liveborn singleton infants of primiparous mothers is 194 g higher, and a substantial part of this difference seems to be attributable to longer gestation. Prostaglandins play an important part in the timing of parturition in human beings. Dietary (n-3)-polyunsaturated fatty acids (PUFA) in high amounts influence endogenous prostaglandin metabolism. Owing to the large consumption of marine fat, the average intake of (n-3)-PUFA in the Faroes by far exceeds that in Denmark. The hypothesis proposed is that dietary (n-3)-PUFA in high amounts prolong gestation in human beings by interfering with uterine production of prostaglandins, possibly by inhibiting the production of dienoic prostaglandins, primarily PGF2 alpha and PGE2, which are mediators of uterine contractions and cervical ripening.

Cardiovascular actions of dietary polyunsaturates and related mechanisms. A state-of-the-art-review

A survey of the effects of dietary polyunsaturates on the function of the cardiovascular system is given. In isolated hearts of rats dietary linoleate supply increases both coronary flow and heart muscle function. Hearts of rats fed high amounts of linoleic acid are protected against catecholamine (over)-stimulation. Polyunsaturate rich vegetable oils are effective in lowering blood pressure in several murine hypertension models. This effect seems to be closely related to antihypertensive changes in kidney function and in the function of the arterial vessel wall. Dietary polyunsaturates augment the hypotensive effect of antihypertensive drugs. Cardiovascular effects of dietary polyunsaturates are at least partly mediated via changes in the prostanoid metabolism as well as a reduction of the sympathetic activity. Evidence has been accumulated that cardiovascular effects of dietary polyunsaturates in animal and man are comparable. The observed effects are discussed against the background of a reduced risk of cardiovascular disease after a polyunsaturate rich diet in man.

Quantitative relationships between dietary linoleate and prostaglandin (eicosanoid) biosynthesis

Essential fatty acid deficiency consistently depresses eicosanoid (prostaglandin E2, F2, and I2 and thromboxane) biosynthesis independent of sampling protocols. Tissue fatty acid analyses support the hypothesis that the decrease is due in part to depression of arachidonate and accumulation of eicosatrienoate (n-9). Research on the alteration of eicosanoid biosynthesis by dietary linoleate supplementation is reviewed extensively. Responses of whole blood, lung, liver and heart eicosanoid synthesis to feeding eight concentrations of dietary linoleate between 0 and 27 energy percent are reported. It is concluded that stimulation, depression and no change in eicosanoid production could be equally well documented as a response to linoleate supplementation. Evidence for the obvious mechanism that alterations in precursor fatty acid composition are a possible explanation is fragmentary and inconsistent. The appropriate sampling techniques appear not to be established at this time and most likely are species, gender and tissue specific.

Essential function of linoleic acid esterified in acylglucosylceramide and acylceramide in maintaining the epidermal water permeability barrier. Evidence from feeding studies with oleate, linoleate, arachidonate, columbinate and alpha-linolenate

Essential fatty acid-deficient rats were supplemented with 300 mg per day of pure fatty acid esters: oleate (O), linoleate (L), arachidonate (A), and columbinate (C) for 10 days. During this period, the rats in groups L, A, and C all showed a decrease in their initially high trans-epidermal water loss, a classical essential fatty acid-deficiency symptom, to a level seen in non-deficient rats (group N). The trans-epidermal water loss in rats of group O was unaffected by the supplementation. Fatty acid composition of two epidermal sphingolipids, acylglucosylceramide and acylceramide, from the skin were determined. The results indicate that re-establishment of a low trans-epidermal water loss was associated with incorporation of linolenate into the two epidermal sphingolipids. Supplementation with columbinate resulted in relatively high amounts of this fatty acid in the investigated epidermal sphingolipids. Analysis of pooled skin specimens from a previous study in which weanling rats were fed a fat-free diet and supplemented orally with pure alpha-linolenate for 13 weeks (Hansen, H.S. and Jensen, B. (1983) Lipids 18, 682-690) revealed very little polyunsaturated fatty acid in the two sphingolipids. These rats showed increased evaporation which was comparable to that of essential fatty acid-deficient rats. We interpret these results as strong evidence for a very specific and essential function of linoleic acid in maintaining the integrity of the epidermal water permeability barrier. This function of linoleate is independent of its role as precursor for arachidonate and icosanoids.