Fatty acid and prostaglandin metabolism in children with diabetes mellitus. II. The effect of evening primrose oil supplementation on serum fatty acid and plasma prostaglandin levels

Our previous study demonstrated that levels of dihomo-gamma-linolenic acid (DGLA) and arachidonic acid in serum total lipids decreased in association with increased plasma levels of prostaglandins E2 (PGE2) and F2 alpha (PGF2 alpha) in patients with insulin-dependent diabetes mellitus. In this study, 11 children with insulin-dependent diabetes mellitus completed a double-blind, placebo-controlled study to assess the effect of dietary supplementation with gamma-linolenic acid (GLA) on serum essential fatty acid and plasma PGE2 and PGF2 alpha levels. GLA was given as the seed oil from the evening primrose (EPO) and all patients received either EPO capsules (containing 45 mg of GLA and 360 mg of linoleic acid) or indistinguishable placebo capsules for 8 months. Initially patients took 2 capsules daily for 4 months then 4 capsules daily for a further 4 months. All patients were assessed at the start of the study, after 4 months and at the end of the study, by measuring serum essential fatty acid and plasma PGE2 and PGF2 alpha levels. After administration of 4 capsules daily the DGLA levels increased and PGE2 levels decreased significantly (p less than 0.01) in the EPO compared with the placebo group. Neither fatty acid nor PGE2 and PGF2 alpha levels were altered by administration of 2 EPO capsules daily. This suggests that the altered essential fatty acid and PG metabolism in diabetes may be reversed by direct GLA supplementation.     

Gammalinolenic acid-enriched diet alters cutaneous eicosanoids

There are reports that vegetable oils containing gammalinolenic acid (GLA) may exert beneficial effects on inflammatory skin disorders. To determine whether or not dietary GLA exerts any modulatory role on cutaneous eicosanoids, guinea pigs were fed either a control diet containing safflower oil (less than 0.5% GLA) or borage oil, a GLA-rich diet containing 25% GLA. After an 8-week feeding period, epidermal samples from both animal groups were analyzed for fatty acid composition and tissue eicosanoids. Analysis of epidermal neutral lipids and phospholipids in borage oil-fed animals showed a marked increase in GLA and its elongase product, dihomogammalinolenic acid (DGLA). Similarly, analysis of epidermal eicosanoids in the borage oil-fed animals revealed significant increases in the amounts of the 15-hydroxy fatty acid (15-OH-20:3n-6) and prostaglandin PGE1, both metabolites of DGLA. Since these metabolites have anti-inflammatory potential, our results suggest that increased dietary GLA could result in the generation of local anti-inflammatory metabolites thus providing a non-toxic approach to suppression of cutaneous inflammatory skin disorders.     

The role of prostaglandins in the inhibition of cultured carcinoma cell growth produced by gamma-linolenic acid

The growth of the cultured human breast carcinoma cell line NUB 1 as well as that of other cultured malignant cells has been shown to be inhibited by addition of gamma-linolenic acid (GLA) to the culture medium. It has previously been suggested that these findings may be attributed to correction of a GLA deficiency in malignant cells, with supplementation of this fatty acid leading to increased prostaglandin (PG) production and consequent growth inhibition. To test this hypothesis the effect of 50 micrograms/ml concentrations of GLA and its sequential metabolite dihomo-gamma-linolenic acid (DGLA) and cell growth, morphology and prostaglandin (PGE and PGF) production by NUB 1 cells was investigated. GLA increased PGE and PGF production, inhibited cell growth and caused accumulation of lipid containing cytoplasmic granules. While treatment with DGLA increased PG production to a significantly greater extent than GLA administration it had no apparent effect on cell growth of morphology and did not inhibit cell growth. These findings suggest that some action other than the ability to increase PG production may be responsible for the inhibitory effects produced by GLA in malignant cells.     

Dietary intake of concentrated gamma-linolenic acid (GLA)-enriched oil suppresses cutaneous level of dihomo-gamma-linolenic acid (DGLA): possible in vivo inhibition of microsomal elongation of GLA to DGLA.

The dietary supplementation of normal guinea-pig diet with moderate levels of vegetable oils containing gamma-linolenic acid (GLA) is associated with elevation of epidermal levels of dihomo-gamma-linolenic acid (DGLA) and 15-hydroxyeicosatrienoic acid (15-lipoxygenase product of DGLA). However, supplementation of diet with higher level (70%) of GLA (GLA-70) resulted in marked decrease of epidermal level of DGLA. This nutritional observation prompted us to investigate in vitro the effects of varying concentrations of polyunsaturated fatty acids (PUFAs) on rat liver microsomal chain elongation of GLA into DGLA. Our data revealed that low concentrations of GLA (less than 100 microM) are stimulatory on the chain elongation while higher concentrations (greater than 100 microM) are inhibitory. The 18-carbon linoleic acid (precursor of GLA) was also markedly inhibitory at high concentrations. Interestingly, the longer chain 20-carbon n-3 PUFAs: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) exerted negligible effect. The results suggest that increased systemic presence of free PUFAs, such as may occur in vivo after dietary intake of high n-6 PUFA-containing vegetable oils, may explain the decreased level of DGLA in the epidermal tissue.     

Effects of Triterpenes on the Mutagenicities of Various Mutagens toward Salmonella

The effects of different dietary levels of gamma-linolenic acid (GLA) on lipid metabolism was studied in rats using a combination of evening primrose oil (EPO) and palm oil (PLO). EPO compared to PLO significantly reduced liver cholesterol and triglyceride after 4 weeks of feeding, and the effect remained even when EPO was mixed with PLO at the same weight basis. The serum triglyceride level also tended to be low on feeding EPO. Neither liver Δ6-desaturase and phospholipase A₂ activities nor aortic production of prostacyclin and thromboxane A₂ production by platelets were influenced significantly by the fat type, suggesting a peculiar effect of PLO. The percentage of arachidonic acid in liver, serum, and aortic phosphatidylcholine depended on the dietary level of GLA. A more distinct increase in arachidonic acid was observed in tissue triglycerides of rats fed EPO. GLA appears to exert favorable effects on lipid metabolism even when the P/S ratio was lowered from 13.7 of EPO to 1.8 of the 1:1 mixture of EPO and PLO.     

The effects of evening primrose oil, safflower oil and paraffin on plasma fatty acid levels in humans: Choice of an appropriate placebo for clinical studies on primrose oil

In a number of diseases, plasma levels of linoleic acid are normal or elevated while those of gamma-linolenic acid (18:3n-6, GLA) and further metabolites are below normal. Evening primrose oil (EPO), similar to safflower oil (SFO) except that it contains 8-9% of 18:3n-6, has been proposed as a therapeutic agent in these diseases, such as atopic eczema. There is argument as to whether an appropriate placebo for clinical studies on EPO should be an inert material such as paraffin, or a linoleic acid--containing oil such as SFO. We have therefore compared in normal humans the effects on plasma fatty acids of administering EPO, SFO and paraffin for 10 days. Paraffin had no effect on any fatty acid in any fraction. EPO raised the level of 20:3n-6 (dihomo-gamma-linolenic acid, DGLA) the immediate metabolite of GLA but had no significant effect on arachidonic acid. In surprising contrast, SFO raised the levels of linoleic and of arachidonic acids, without raising those of DGLA. This suggests that linoleic acid may be rapidly converted to arachidonic acid by a tightly linked enzyme sequence: GLA, in contrast, may be rapidly converted to DGLA but then only slowly on to arachidonic acid. These results are consistent with recent in vitro observations by others on rat hepatocytes and human fibroblasts.     

The influence of different combinations of gamma-linolenic, stearidonic and eicosapentaenoic acids on the fatty acid composition of blood lipids and mononuclear cells in human volunteers

This study set out to identify whether stearidonic acid (18:4n-3; STA) can be used to increase the eicosapentaenoic acid (20:5n-3; EPA) content of plasma lipids and cells in humans and to understand more about the effects of increased consumption of gamma-linolenic acid (18:3n-3; GLA), STA and EPA in humans. Healthy young males were randomised to consume one of seven oil blends for a period of 12 weeks (9g oil/day) (n = 8-12 subjects/group). Palm oil, sunflower oil, an EPA-rich oil, borage oil (rich in GLA), and Echium oil (rich in STA) were blended in various combinations to generate a placebo oil and oils providing approximately 2g GLA + STA + EPA per day, but in different combinations. Blood was collected at 0, 4, 8 and 12 weeks and the fatty acid compositions of plasma triacylglycerols, cholesteryl esters and phospholipids and of peripheral blood mononuclear cells (PBMCs) determined. Significant effects were observed with each lipid fraction. Neither STA nor its derivative 20:4n-3 appeared in any of the lipid fractions studied when STA (up to 1g/day) was consumed. However, STA (1g/day), in combination with GLA (0.9 g/day), increased the proportion of EPA in some lipid fractions, suggesting that STA-rich plant oils may offer a novel means of increasing EPA status. Furthermore, this combination tended to increase the dihomo-gamma-linolenic acid (20:3n-6; DGLA) content of PBMCs, without an increase in arachidonic acid (AA) (20:4n-6) content. EPA consumption increased the EPA content of all lipid fractions studied. Consumption of GLA (2g/day), in the absence of STA or EPA, increased DGLA content with a tendency to increase AA content in some fractions. This effect was prevented by inclusion of EPA in combination with GLA. Thus, this study indicates that STA may be used as a precursor to increase the EPA content of human lipids and that combinations of GLA, STA and EPA can be used to manipulate the fatty acid compositions of lipid pools in subtle ways. Such effects may offer new strategies for manipulation of cell composition in order to influence cellular responses and functions in desirable ways.     

Effect of gamma-linolenic acid on lipid metabolism in laying hens.

1. Single comb white leghorn laying hens were given diets with additional mould, Mucus circineloides, containing gamma-linolenic acid (GLA) at levels of 0, 2.59 and 5.06 g GLA/kg diet ad lib. for 2 weeks and serum lipid contents were determined in experiment 1. 2. Serum low density lipoprotein and chylomicron levels were significantly reduced with the increase of dietary GLA levels. Serum triglyceride and cholesterol tended to be lowered by dietary GLA, but not significantly different. 3. Effects of mould GLA and extracted oil GLA on the egg yolk cholesterol concentration and fatty acid composition were compared in experiment 2. Both mould GLA and extracted oil GLA diets containing 5.32 and 4.71 g GLA/kg diet were given ad lib. for 2 weeks. 4. Yolk cholesterol content was not affected by dietary GLA sources. Content of GLA in the yolk was not altered, although that of arachidonic acid was enhanced by dietary GLA supplementation, particularly by the extracted oil GLA. 5. It is suggested that GLA is rapidly metabolized to arachidonic acid in the body and incorporated into the yolk.     

The relationship between schizophrenia and essential fatty acid and eicosanoid metabolism.

Essential fatty acids (EFAs) and their eicosanoid derivatives are important constituents of the brain and regulators of neuronal function. There is direct and indirect evidence of impaired metabolism of prostaglandin (PG)E1 in schizophrenia. There is also direct evidence of abnormal EFA biochemistry with plasma phospholipids from five populations and brain phospholipids from another all showing reduced levels of linoleic acid and elevated levels of 22-carbon EFAs of both n-6 and n-3 series. Clinical trials of PGE1 and of the PGE1 precursors, gamma-linolenic acid (GLA) and dihomo-gamma-linolenic acid (DGLA) have shown modest therapeutic effects. In view of lack of therapeutic process involving drugs based on the dopamine concept of schizophrenia, it is time for new approaches based on the EFA/PG concept to be evaluated thoroughly.     

Effects of dietary saturated, N-6 and N-3 polyunsaturated fats on blood pressure and prostaglandins outflow from perfused mesenteric vascular bed in rats

Effects of the dietary administration of saturated fat and of n-6 and n-3 polyunsaturates on blood pressure, prostaglandin metabolism in small vessels, tissue fatty acid distribution and urinary PGE2 excretion were compared. Rats were divided into three groups. Diets contained 10% hydrogenated coconut oil (HCO), 10% safflower oil (SFO) or 10% cod liver oil (CLO) added to a basic fat free diet for 10 weeks. Systolic blood pressure was increased in the CLO group animals. Urinary PGE2 excretion was decreased in the HCO and CLO groups as compared to that in the SFO group animals. PGE2, 6-keto-PGF1 alpha and thromboxane (Tx) B2 outflow from isolated perfused mesenteric arterial beds were extremely decreased in the CLO group animals, and to a lesser extent in the HCO group as compared to the SFO animals. In the tissue phospholipid, 20:3n-9/20:4n-6 ratios were increased in the HCO group indicating essential fatty acid deficiency, and n-6 and n-3 polyunsaturates were elevated in the SFO and the CLO group animals respectively. Arachidonic acid concentration was highest in the SFO group, while there was no significant differences between the HCO and the CLO group. These results suggest that dietary fatty acid manipulation affects urinary PGE2 excretion and PGI2, PGE2 and TxA2 synthesis in mesenteric arterial beds and also changes the tissue fatty acid distribution. Furthermore, n-3 polyunsaturates caused an extreme reduction of 2-series PGs synthesis in small resistance vessels.     

On possible different mechanisms subserving the release of arachidonic and di-homo-gamma-linolenic acids for the formation of monoenoic and bisenoic prostaglandins in uteri from ovariectomized rats

The uptake of arachidonic acid (AA) and of di-homo-gamma-linolenic acid (DGLA) and their incorporations into phospholipids (PLs) and into neutral lipids (NLs) of uteri isolated from spayed rats and the effect of inhibiting triglyceride (TG) metabolism with 4-pentenoic acid (4-PEA) on tissue TG levels and the output of prostaglandins (PGs), were explored. Attempts were also made to determine whether the acylation of labelled AA and of labelled DGLA into PLs and TGs is different and to confirm possible correlations between the synthesis of PGE1 and the degradation of TGs. Uterine PLs incorporated significantly less DGLA than AA (P less than 0.05). AA was acylated mainly into the phosphatidylinositol (PI) and into phosphatidylcholine (PC) subfractions of rat uteri, whereas the incorporation of DGLA into these two subfractions was significantly smaller than that of AA. The acylation of labelled DGLA into NL fractions, mainly into triacylglycerol, almost doubled that of labelled AA. The levels of TGs in isolated rat uteri suspended in glucose-free medium during a period of 60 minutes were significantly less than immediately after isolation (P less than 0.001). PGE1 released from uteri into the incubating solution, was significantly higher than that of PGE2. Moreover, the presence of 4-PEA (1.0 mM), added after tissue isolation, prevented the decrement of TGs observed following 60 minutes of incubation and simultaneously diminished significantly (P less than 0.001) the enhanced output of PGE1, without altering that of PGE2. Results presented herein suggest that PLs are not normal precursors for the synthesis of PGE1.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dose-dependent effects of dietary gamma-linolenic acid on rat spleen lymphocyte functions.

Feeding rodents a diet rich in evening primrose oil (EPO), which contains 5-10 g gamma-linolenic acid (GLA)/100 g total fatty acids, has been shown to decrease lymphocyte proliferation and natural killer cell activity. However, EPO contains a very high level of linoleic acid which itself can affect lymphocyte functions and it is not clear to what extent the effects of EPO can be attributed to GLA. The current study investigated the effect of two levels of GLA in the rat diet upon immune cell functions; the level of linoleic acid was maintained below 30 g/100 g total fatty acids. Weanling rats were fed on high fat (178 g/kg) diets which contained 4.4 g or 10 g GLA/100 g total fatty acids in place of a proportion of linoleic acid. The total polyunsaturated fatty acid content and the n-6 to n-3 polyunsaturated fatty acid ratio of the diet were maintained at 35 g/100 g total fatty acids and 7, respectively. The fatty acid compositions of the serum and of spleen leukocytes were markedly influenced by that of the diet, with an increase in the proportions of GLA and dihomo-gamma-linolenic acid when the diets containing GLA were fed; these diets also increased the proportion of arachidonic acid in spleen leukocytes. Spleen lymphocyte proliferation in response to concanavalin A was significantly reduced (by 60%) by feeding the diet containing the higher level of GLA, but not by the diet containing the lower level of GLA. Spleen natural killer cell activity and prostaglandin E (PGE) production by spleen leukocytes were not significantly affected by inclusion of GLA in the diet, although there was a tendency towards decreased natural killer cell activity by cells from rats fed the high GLA diet. Thus, this study shows that dietary GLA is capable of altering the fatty acid composition of cells of the immune system and of exerting some immunomodulatory effects, but that the level of GLA in the diet must exceed 4.4 g/100 g total fatty acids for these effects to become apparent.     

Influence of an increased intake of linoleic acid on the incorporation of dietary (n-3) fatty acids in phospholipids and on prostanoid synthesis in rat tissues.

We investigated whether the amount of dietary linoleic acid (LA) (as corn oil) influences the incorporation of dietary eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) in tissue phospholipids and the prostanoid biosynthesis. Rats were fed four different levels of corn oil (at a total dietary fat level of either 2.5%, 5%, 10% or 20%); at each corn oil level, two groups of rats were supplemented with either EPA and DHA (200 mg/day) during 6 weeks, and compared with a group receiving oleic acid. The phospholipid fatty acid composition of liver, kidney and aorta showed, as expected, that the incorporation of EPA was highly suppressed by increasing the content of dietary linoleic acid in the diets. On the other hand, DHA was almost unaffected by the amounts of (n - 6) fatty acids in the diets. These results indicate that EPA levels but not DHA levels in tissue phospholipids were influenced by the competing dietary (n - 6) fatty acids. The tissue arachidonate content was similar under the various dietary linoleic acid conditions, but feeding EPA or DHA lowers the AA content. Moreover, the amount of dietary linoleic acid did not significantly influence the prostaglandin E2 (PGE2) production in stimulated aortic rings. However, PGE2 synthesis was significantly decreased in the groups treated with either EPA or DHA. Thromboxane B2 levels in serum followed a similar pattern. It is suggested that an increase of dietary (n - 3) PUFAs is more efficient to reduce (n - 6) eicosanoid formation than a decrease of dietary (n - 6) fatty acids.     

Effect of L-arginine-nitric oxide system on the metabolism of essential fatty acids in chemical-induced diabetes mellitus

Several studies have shown that the activities of delta-6-desaturase and delta-5-desaturase are depressed in experimental diabetes and in humans with insulin- and non-insulin-dependent diabetes mellitus (type I and type II diabetes mellitus respectively). Furthermore, treatment with insulin is known to correct the defects in desaturases in rats and humans with diabetes, especially in type I. In a recent study, we demonstrated that L-arginine and nitric oxide can prevent alloxan-induced beta cell damage, and the severity of diabetes, and restore the antioxidant status to near normal levels. But, no information is available as to the relationship between L-arginine-nitric oxide system and the metabolism of essential fatty acids in diabetes mellitus. In the present study, it was noted that the plasma levels of saturated fatty acids: stearic and palmitic were increased where as unsaturated fatty acids such as oleic, linoleic, gamma-linolenic and eicosapentaenoic acids (OA, LA, GLA and EPA respectively) were decreased in alloxan-induced diabetic rats. In the liver phospholipid (PL) fraction, GLA, DGLA (dihomo-GLA) and alpha-linolenic acid (ALA) were decreased in the alloxan-treated group; in the muscle PL fraction, LA, GLA and DGLA were low, whereas an increase in the saturated fatty acid content was noted. L-arginine (the precursor of nitric oxide) and sodium nitroprusside (a nitric oxide donor) treatment of alloxan-induced diabetic rats enhanced the levels of LA, GLA and DGLA. Further, nitric oxide synthase inhibitor, L-NMMA, prevented this beneficial action of L-arginine-nitric oxide system on essential fatty acid metabolism. The abnormalities in the essential fatty acid metabolism observed also reverted to normalcy following control of diabetes with insulin. These results indicate that nitric oxide can enhance the activities of delta-6- and delta-5 desaturases, which are depressed in diabetes, and suggests that there is a close interaction between L-arginine-nitric oxide system and the metabolism of essential fatty acids.     

Gamma-linolenic acid dietary supplementation can reverse the aging influence on rat liver microsome delta 6-desaturase activity.

We have recently demonstrated that in rats the process of delta 6-desaturation of linoleic and alpha-linolenic acids slows with aging. One method of counteracting the effect of slowed desaturation of linoleic acid would be to provide the 6-desaturated metabolite, gamma-linolenic acid (18:3(n-6) GLA) directly. We have here investigated the 6-desaturation of both linoleic and alpha-linolenic acids in liver microsomes of young and old rats given GLA in the form of evening primrose oil (EPO) (B diet) in comparison to animals given soy bean oil alone (A diet), monitoring also the fatty acid composition of liver microsomes and relating this to the microviscosity of the membranes. In young rats the different experimental diets did not produce any difference in delta 6-desaturase (D6D) activity on either substrate suggesting that, when D6D activity is at or near its peak, the variations in diet tested are unable to influence it. In the old animals the rate of 6-desaturation of linoleic and particularly of alpha-linolenic acid was significantly greater in the B diet fed animals than in the A diet fed. The effects of the diets on the fatty acid composition of liver microsomes were consistent with the findings with regard to 6-desaturation. Administration of GLA partially corrected the abnormalities of n-6 essential fatty acid (EFA) metabolism by raising the concentration of 20:4(n-6) and other 6-desaturated EFAs. Furthermore, the GLA rich diet also increased the levels of dihomo-gamma-linolenic acid and of 6-desaturated n-3 EFAs in the liver microsomes. The microviscosity of microsomal membranes as indicated by DPH polarization was correlated with the unsaturation index of the same membranes. There was a very strong correlation between the two. In both young and old rats the B diet reduced the microviscosity and increased the unsaturation index. However, the effect was much greater in the old animals.     

Sex differences in n-3 and n-6 fatty acid metabolism in EFA-depleted rats

We studied the effect of sex on the distribution of long-chain n-3 and n-6 fatty acids in essential fatty acid-deficient rats fed gamma-linolenate (GLA) concentrate and/or eicosapentaenoate and docosahexaenoate-rich fish oil (FO). Male and female weanling rats were rendered essential fatty acid deficient by maintaining them on a fat-free semisynthetic diet for 8 weeks. Thereafter, animals of each sex were separated into three groups (n = 6) and given, for 2 consecutive days by gastric intubation, 4 g/kg body wt per day of GLA concentrate (containing 84% 18:2n-6), n-3 fatty acid-rich FO (containing 18% 20:5n-3 and 52% 22:6n-3), or an equal mixture of the two oil preparations (GLA + FO). The fatty acid distributions in plasma and liver lipids were then examined. GLA treatment increased the levels of C-20 and C-22 n-6 fatty acids in all lipid fractions indicating that GLA was rapidly metabolized. However, the increases in 20:3n-6 were less in females than those in males, while those in 20:4n-6 were greater, suggesting that the conversion of 20:3n-6 to 20:4n-6 was more active in female than in male rats. FO treatment increased the levels of 20:5n-3 and 22:6n-3 and reduced those of 20:4n-6. The increase in n-3 fatty acids was greater in females than that in males and the reduction in 20:4n-6 was smaller. Consequently, the sum of total long-chain EFAs incorporated was greater in females than that in males. The administration of n-3 fatty acids also reduced the ratio of 20:4n-6 to 20:3n-6 in GLA + FO-treated rats indicating that n-3 fatty acids inhibited the activity of delta-5-desaturase. However, this effect was not affected by the sex difference.     

Fatty acid changes in liver choline and ethanolamine glycerophospholipids in aspirin-treated rats fed linoleate, gamma-linolenate and fish oil

The effects of dietary linoleic acid, gamma-linolenic acid and marine fatty acids on the development of aspirin-induced gastric hemorrhage and the distribution of liver glycerophospholipid fatty acids in fat-deficient growing rats were studied. Aspirin (100 mg/day)-treated and nontreated rats were fed for 7 days, a mixed diet of 2.5% safflower oil and 7.5% hydrogenated coconut oil (SFO/HCO) or 7.5% fish oil (SFO/FO), or 2.5% gamma-linolenate concentrate and 7.5% fish oil (GLA/FO). Gastric hemorrhage was induced in animals by aspirin treatment to various extents. It was not affected by FO feeding, but was significantly alleviated by GLA feeding. Aspirin treatment reduced the proportions of 20:4n-6 in liver phosphatidylcholine. FO feeding (in SFO/FO and GLA/FO rats) further reduced the 20:4n-6 level and replaced it by n-3 fatty acids. GLA feeding, on the other hand, elevated the proportion of 20:4n-6. As a result, the reduction of 20:4n-6 by fish oil feeding, was less significant in GLA/FO rats than in SFO/FO rats. The degree of gastric hemorrhage appeared to relate negatively to the levels of 20:4n-6 in liver phosphatidylcholine, and to the sum of 20:4n-6 and 20:5n-3 when FO was included in the diet. It is suggested that long-chain polyunsaturated fatty acids (20:4n-6 and 20:5n-3) per se in addition to being precursors of prostaglandins, may also affect the development of gastric hemorrhage, possibly by modulating the permeability of cell membranes in the gastric mucosa.     

Long chain polyunsaturated fatty acids alter membrane-bound RANK-L expression and osteoprotegerin secretion by MC3T3-E1 osteoblast-like cells

Inflammation triggers an increase in osteoclast (bone resorbing cell) number and activity. Osteoclastogenesis is largely controlled by a triad of proteins consisting of a receptor (RANK), a ligand (RANK-L) and a decoy receptor (osteoprotegerin, OPG). Whilst RANK is expressed by osteoclasts, RANK-L and OPG are expressed by osteoblasts. The long chain polyunsaturated fatty acid (LCPUFA) arachidonic acid (AA, 20:4n-6) and its metabolite prostaglandin E2 (PGE2), are pro-inflammatory and PGE2 is a potent stimulator of RANKL expression. Various LCPUFAs such as eicosapentaenoic acid (EPA, 20:5n-3), docosahexaenoic acid (DHA, 22:6n-3) and gamma-linolenic acid (GLA, 18:3n-6) have anti-inflammatory activity. We aimed to determine if AA itself can stimulate RANKL expression and whether EPA, DHA and GLA inhibit RANKL expression in osteoblasts. MC3T3-E1/4 osteoblast-like cells were cultured under standard conditions with each of the LCPUFAs (5microg/ml) for 48h. Membrane-bound RANKL expression was measured by flow cytometry and OPG secretion measured by ELISA. In a second experiment, RANKL expression in MC3T3-E1/4 cells was stimulated by PGE2 treatment and the effect of EPA, DHA and GLA on membrane-bound RANKL expression and OPG secretion determined. The percentage of RANKL-positive cells was higher (p<0.05) than controls following treatment with AA or GLA but not after co-treatment with the cyclooxygenase inhibitor, indomethacin. DHA and EPA had no effect on membrane-bound RANKL expression under standard cell culture conditions. Secretion of OPG was lower (p<0.05) in AA-treated cells but not significantly different from controls in GLA, EPA or DHA treated cells. Treatment with prostaglandin E2 (PGE2) resulted in an increase (p<0.05) in the percentage of RANK-L positive cells and a decrease (p<0.05) in mean OPG secretion. The percentage of RANKL positive cells was significantly lower following co-treatment with PGE2 and either DHA or EPA compared to treatment with PGE2 alone. Mean OPG secretion remained lower than controls in cells treated with PGE2 regardless of co-treatment with EPA or DHA. Results from this study suggest COX products of GLA and AA induce membrane-bound RANKL expression in MC3T3-E1/4 cells. EPA and DHA have no effect on membrane-bound RANKL expression in cells cultured under standard conditions however both EPA and DHA inhibit the PGE2-induced increase in RANKL expression in MC3T3-E1/4 cells.     

Effect of increasing amounts of dietary fish oil on brain and liver fatty composition

Increasing dietary fish oil in rat had the following effect on brain lipids: Arachidonic acid regularly decreased; eicosapentanenoic acid, normally nearly undetectable, was present; 22:5(n - 3), dramatically increased but remained below 1% of total fatty acids; cervonic acid was increased by 30% at high fish oil concentration. Saturated and monounsaturated fatty acids were not affected regardless of chain-length. In contrast, in the liver, nearly all fatty acids (saturated, monounsaturated and polyunsaturated) were affected by high dietary content of fish oil, but liver function was normal: serum vitamin A and E, glutathione peroxidase, alkaline phosphatase, transaminases were not affected. Serum total cholesterol, unesterified cholesterol and phosphatidylcholine were slightly affected. In contrast, triacylglycerols were dramatically reduced in proportion to the fish oil content of the diet.     

Uptake of 13C-Tracer Arachidonate and γ-Linolenate by the Brain and Liver of the Suckling Rat Observed Using 13C-NMR

Arachidonic acid (AA; 20:4n-6) is one of the principal components of the phosphoglycerides in neural cell membranes. During the critical period of postnatal development in mammals, AA is supplied preformed, directly from the milk or derived from precursor fatty acids such as gamma-linolenic acid (GLA; 18:3n-6). In this study, 13C-NMR spectroscopy was applied to investigate the incorporation of [1-(13)C]AA and [3-(13)C]GLA into liver and brain lipids of 7-15-day-old rats. The main objective was to establish the importance of dietary GLA for tissue AA accretion relative to the contribution from preformed dietary AA. [1-(13)C]AA and [3-(13)C]GLA were injected into the stomach of 7-day-old rats as a mixture. 13C-NMR spectroscopy of lipid extracts revealed incorporation of [1-(13)C]AA and [5-(13)C]AA (the latter derived from metabolism of the injected [3-(13)C]GLA) into phosphoglycerides and triacylglycerols. Preformed AA was 10 (liver)-17 (brain) times more efficient in contributing to tissue AA than AA derived from precursor GLA. In separate experiments, NMR spectroscopy was used to assess uptake of [1-(13)C]AA directly in living rats and intact organs. Results showed that intact liver and brain contain an appreciable amount of NMR-detectable lipids. The in vivo/in vitro information obtained from organs provided details on the mobility and turnover of tissue lipids.