Modification of upper gastrointestinal prostaglandin synthesis by dietary fatty acids

The effects of dietary iols on gastric, duodenal mucosa and liver were investigated ina rat model. Unsaturated fatty acid profles and in vitro prostaglandin (PG) synthesis (PGE₂, PGF_2α, 6-oxo-PGF_1α and thromboxane B₂). were measured after 14 days of dietary oil supplements.There were no significant differences in prostanoid synthesis between rats fed coconut oil (high saturated fat content) and standard diet. After fish oil supplement, tissue eicosapentaenoic acid and docosahexaenoic acid levels were higher, arachidonic acid levels were lower, and prostanoid synthesis was reduced in both stomach and duodenum. After corn oil and evening primrose oil, linoleic acid levels were variaby increased, bt there were no significant differences in arachidonic acid or prostanoid synthesis. Dihomogamma-linolenic acid levels were slightly increased after evening primrose oil.Dietary incorporation of fatty acids into gastroduodenal tissue is not uniform. When incorporated, fatty acids can modify prostaglandin synthesis.     

The prostaglandin outflow from perfused mesenteric vasculature of rats fed different fats

The effects of dietary n-6 polyunsaturated fatty acids and replacement with saturated fat or fish oil on the prostaglandin outflow from perfused mesenteric vasculature in rats were studied. Seventy-two weanling male rats were fed ad libitum a semi-synthetic diet supplemented with 10% by weight of oil, composed wholly of n-6 fatty acid-rich evening primrose oil, or replaced partly or completely (25, 50, 75 or 100%) by n-6 fatty acid-deficient fish oil or hydrogenated coconut oil for 8 weeks. The outflows of 6-keto-PGF1 alpha, thromboxane B2, and prostaglandin E from the perfused mesenteric vasculature were measured at 60 min-time point after starting the perfusion. In general, the release of prostanoids from the mesenteric vasculature was significantly reduced in rats fed a diet in which evening primrose oil was partly or completely replaced by either hydrogenated coconut or fish oil. This was probably due to the insufficient conversion of linoleic acid to arachidonic acid. The extent of reduction was greater in fish oil-fed than in hydrogenated coconut oil-fed rats, while the levels of arachidonic acid in aortic phospholipids were similar between these two groups. This result implies that the greater reduction of prostaglandin synthesis in rats fed fish oil was due to the inhibitory effect of eicosapentaenoic and docosahexaenoic acids in fish oil on the conversion of arachidonate to eicosanoids.     

Attempts at dietary alteration of prostaglandin pathways in the management of pre-eclampsia

It has been suggested that dietary supplementation with prostaglandin precursors may enhance the synthesis of PGE which lowers vascular sensitivity to increased levels of angiotensin II in pregnancy. Therefore the effect of dietary supplementation with evening primrose oil (linoleic acid and gamma-linoleic acid) in African primigravidae with established pre-eclampsia was studied. Patients were randomly allocated to one of two groups. Group A (23 patients) received 8 capsules/day of evening primrose oil and group B (24 patients) received 8 capsules of placebo. No significant differences were found between the groups in respect to perinatal outcome, blood pressure lowering effect and haematological indices.     

Studies on the cultivation and uses of evening primrose (Oenothera spp.) in China

Evening primrose originated in North America and became naturalized in the north-east of China about one hundred years ago, where it has been used as famine food and animal feed. New uses for the seed oil, which contains γ-linolenic acid (GLA), that have been developed in China and overseas since 1980 have created a much larger commercial demand for the seed. There are eight species of Oenothera L. growing wild in China, of which Oenothera biennis L. is preferred. The maximum annual production of wild evening primrose seed is estimated to be about 3000 tons but, since 1986, evening primrose has also been cultivated for its seed and oil using O. biennis (primarily in the provinces of Jilin, Liaoning, Hebei, and Shandong) to meet the increasing demand. New production techniques have been developed and disseminated, and reported seed yields range from 750 to 3000 kg ha^-1. Commercial production follows a cyclical pattern, with the largest harvest to date, in 1999, estimated at 16 000-19 000 tons of seed. During 20 years of research on a wide range of wild oilseed plants, Chinese scientists found that evening primrose oil was antiatherosclerotic, lowered hyperlipidemia and was antithrombotic. The oil was developed and licensed as a drug (which required work on processing technology, physicochemical characteristics, pharmacology, formulation, and clinical studies) and it has since been widely used in clinical practice. Further research work has been done on other bioactive properties of evening primrose oil, alternative sources of GLA, the concentration of GLA, the synthesis of prostaglandin E1, and the development of health care drugs and cosmetics containing evening primrose oil. We believe that the prospects for the future development of evening primrose are good.     

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.     

High frequency of adventitious shoot regeneration from commercial cultivars of evening primrose (Oenothera spp.) using thidiazuron

Evening primrose (Oenothera spp.) is grown commercially for its seed oil that contains gamma linolenic acid (GLA), a valuable food supplement and pharmaceutical. There is considerable interest in the potential of genetic engineering to improve yields of GLA in evening primrose, and attention has focused on the current state of tissue‐culture knowledge in this species which is a prerequisite for genetic transformation. Published protocols for the regeneration of plants from leaf or cotyledon material of Oenothera spp. are available, but these prove unsatisfactory when applied to commercial cultivars used in this study. An efficient method for regenerating three commercial cultivars of evening primrose Rigel, Merlin and Vulcan was developed using thidiazuron (TDZ) as a growth regulator. Explants from one month old seedlings were cultivated in vitro; a large number of buds were induced directly from strips of leaves, cotyledons and stems when cultured on Murashige and Skoog (MS) basal medium containing TDZ and indole‐butyric acid (IBA). Shoots that were excised and placed onto MS basal medium, supplemented with IBA, rooted with 85–90% efficiency. Plantlets were transferred to soil after 6–8 wk. TDZ stimulated the regeneration process, and its effects were enhanced when combined with IBA or indole‐3‐acetic acid (IAA). The methods developed may be a useful advance toward improvement of this oil seed crop through genetic modification.     

Effect of Temperature on the Fatty Acid Composition and Yield of Evening Primrose (Oenothera lamarckiana) Seeds

The oil content and yield of evening primrose (Oenothera lamarckianaL.) seeds decreased significantly at high temperatures (32 ?C)compared with lower ones (25 ?C and below), under controlledgrowing conditions. Moreover, the fatty acid composition ofthe seed oils was also affected by the temperature regime. Higheroleic acid levels and lower linoleic and -linolenic acid (GLA)levels were characteristic of the seeds developed at highertemperatures. The opposite trend was observed at lower temperatures.In field experiments, seeds of O. lamarckiana plants sown inautumn contained lower oleic acid levels, and higher linoleicacid and GLA levels than seeds of spring plantings. This effectwas also demonstrated for seeds developed on the same stem inflorescenceunder increasing temperatures during the season in the field.Changes in fatty acid composition during various stages of seeddevelopment were observed. Key words: Evening primrose, oil, fatty acids, Oenothera spp., gamma linolenic acid     

Dissociation of Large and Small Bovine Casein Micelles by Dialysis

The effects of dietary fat types on the thermogenic activity of brown adipocytes isolated from rat were examined. When beef tallow (saturated fatty acids + oleic) and safflower oil (linoleic) were the dietary fats, the respiration rates of brown adipocytes activated either by norepinephrine or an uncoupler of mitochondrial respiration (carbonylcyanide-m-chlorophenylhydrazone) were both slightly higher in rats fed the polyunsaturated fat. When the effects of safflower oil and evening primrose oil (linoleīc + γ-linolenic) were compared, the activated respiration rate tended to be higher in the latter. The respiratory responses to varying concentrations of norepinephrine were apparently dependent on the dietary fat types. Triglyceride stored in interscapular brown adipose tissue appeared to be modified by dietary fat types. Dietary fat also characteristically modified the fatty acid compositions of interscapular brown and epididymal white adipose tissues. Thus, the type of dietary fat caused an alteration to the thermogenesis of brown adipose tissue at the cellular level.     

Physiological effects of γ-linolenic acid and sesamin on hepatic fatty acid synthesis and oxidation

Interrelated effects of γ-linolenic acid (GLA) and sesamin, a sesame lignan, on hepatic fatty acid synthesis and oxidation were examined. Rats were fed experimental diets supplemented with 0 or 2 g/kg sesamin (1:1 mixture of sesamin and episesamin) and containing 100 g/kg of palm oil (saturated fat), safflower oil rich in linoleic acid, or oil of evening primrose origin containing 43% GLA (GLA oil) for 18 days. In rats fed sesamin-free diets, GLA oil, compared with other oils, increased the activity and mRNA levels of various enzymes involved in fatty acid oxidation, except for some instances. Sesamin greatly increased these parameters, and the enhancing effects of sesamin on peroxisomal fatty acid oxidation rate and acyl-CoA oxidase, enoyl-CoA hydratase and acyl-CoA thioesterase activities were more exaggerated in rats fed GLA oil than in the animals fed other oils. The combination of sesamin and GLA oil also synergistically increased the mRNA levels of some peroxisomal fatty acid oxidation enzymes and of several enzymes involved in fatty acid metabolism located in other cell organelles. In the groups fed sesamin-free diets, GLA oil, compared with other oils, markedly reduced the activity and mRNA levels of various lipogenic enzymes. Sesamin reduced all these parameters, except for malic enzyme, in rats fed palm and safflower oils, but the effects were attenuated in the animals fed GLA oil. These changes by sesamin and fat type accompanied profound alterations in serum lipid levels. This may be ascribable to the changes in apolipoprotein-B-containing lipoproteins.     

Gamma-linolenic acid provides additional protection against ventricular fibrillation in aged rats fed linoleic acid rich diets

Ligation of the coronary artery in rats produces severe ventricular fibrillation (VF) and malignant cardiac arrhythmia. Mortality increases with the age of the animal. Diets rich in saturated fatty acids (SF) but low in linoleic acid (LA) increase, but diets high in LA and low in SF decrease the severity of VF and mortality in older animals. The effects of an LA enriched diet can be blocked by inhibition of cyclooxygenase suggesting that conversion of LA to eicosanoids is central to the development of VF. Conversion of LA to gamma-linolenic acid (GLA) via delta-6 desaturase is the first step in the process. The activity of delta-6 desaturase declines with age. Thus inclusion of GLA in the diet of older animals may provide an additional benefit over LA alone. Dietary supplements of evening primrose oil (EPO) to one year old rats reduced ischaemic VF more than a supplement of sunflower seed oil (SSO) without GLA. Substitution of borage oil (more GLA than EPO but less LA than either EPO or SSO) was without additional benefit.     

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.     

Effect of n-6 and n-3 polyunsaturated fatty acids ingestion on rat liver membrane-associated enzymes and fluidity

The influences of diets having different fatty acid compositions on the fatty-acid content, desaturase activities, and membrane fluidity of rat liver microsomes have been analyzed. Weanling male rats (35–45 g) were fed a fat-free semisynthetic diet supplemented with 10% (by weight) marine fish oil (FO, 12.7% docosahexaenoic acid and 13.8% eicosapentaenoic acid), evening primrose oil (EPO, 7.8% γ-linolenic acid and 70.8% linoleic acid) or a mixture of 5% FO-5% EPO. After 12 weeks on the respective diets, animals fed higher proportions of (n-3) polyunsaturated fatty acids (FO group) consistently contained higher levels of 20:3(n-6), 20:5(n-3), 22:5(n-3), and 22:6(n-3), and lower levels of 18:2(n-6) and 20:4(n-6), than those of the EPO (a rich source of (n-6) polyunsaturated fatty acids) or the FO + EPO groups. Membrane fluidity, as estimated by the reciprocal of the order parameter S_DPH, was higher in the FO than in the EPO or the FO + EPO groups, and the n-6 fatty-acid desaturation system was markedly affected.     

Effect of oral gamolenic acid from evening primrose oil on menopausal flushing.

OBJECTIVE--To evaluate the efficacy of gamolenic acid provided by evening primrose oil in treating hot flushes and sweating associated with the menopause. DESIGN--Randomised, double blind, placebo controlled study. SETTING--District general hospital and teaching hospital. SUBJECTS--56 menopausal women suffering hot flushes at least three times a day. INTERVENTION--Four capsules twice a day of 500 mg evening primrose oil with 10 mg natural vitamin E or 500 mg liquid paraffin for six months. MAIN OUTCOME MEASURES--Change in the number of hot flushes or sweating episodes a month. RESULTS--56 diaries were analysed, 28 from women taking gamolenic acid and 28 from those taking placebo. Only 18 women given gamolenic acid and 17 given placebo completed the trial. The mean (SE) improvement in the number of flushes in the last available treatment cycle compared with the control cycle was 1.9 (0.4) (P < 0.001) for daytime flushes and 0.7 (0.3) (P < 0.05) for night time flushes in women taking placebo; the corresponding values for women taking gamolenic acid were 0.5 (0.4) and 0.5 (0.3). In women taking gamolenic acid the only significant improvement was a reduction in the maximum number of night time flushes (1.4 (0.6); P < 0.05). CONCLUSION--Gamolenic acid offers no benefit over placebo in treating menopausal flushing.     

Enzymatic fractionation of evening primrose oil by rape lipase: Enrichment of gamma-linolenic acid

Summary Rape lipase discriminates strongly against -linolenic acid (allcis-6, 9, 12–183; GLA). GLA in the fatty acids from evening primrose oil was concentrated from 9.5% to 62% with a 95% yield during esterification of these fatty acids with butanol catalyzed by rape lipase. Hydrolysis of evening primrose oil catalyzed by the rape lipase raised the GLA content in unhydrolyzed acylglycerols to 28%.     

Fatty acid composition and properties of the liver microsomal membrane of rats fed diets enriched with cholesterol.

Male rats were fed diets containing olive (OO) or evening primrose (EPO) oil (10% w/w), with or without added cholesterol (1% w/w). After 6-week feeding, the lipid and fatty acid compositions, fluidity, and fatty acid desaturating and cholesterol biosynthesis/esterification related enzymes of liver microsomes were determined. Both the OO and EPO diets, without added cholesterol, increased the contents of oleic and arachidonic acids, respectively, of rat liver microsomes. The results were consistent with the increases in delta 9 and delta 6 desaturation of n-6 essential fatty acids and the lower microviscosity in the EPO group. Dietary cholesterol led to an increase in the cholesterol content of liver microsomes as well as that of phosphatidylcholine (PC). The cholesterol/phospholipid and PC/PE (phosphatidylethanolamine) ratios were also elevated. Fatty acid composition changes were expressed as the accumulation of monounsaturated fatty acids, with accompanying milder depletion of saturated fatty acids in rat liver microsomes. In addition, the arachidonic acid content was lowered, with a concomitant increase in linoleic acid, which led to a significant decrease in the 20:4/18:2 ratio in comparison to in animals fed the cholesterol-free diets. Cholesterol feeding also increased delta 9 desaturase activity as well as membrane microviscosity, whereas it decreased delta 6 and delta 5 desaturase activities. There was a very strong correlation between fluidity and the unsaturation index reduction in the membrane. Furthermore, the activity of hydroxymethylglutaryl-CoA reductase increased and the activity of acyl-CoA:cholesterol acyltransferase decreased in liver microsomes from both cholesterol-fed groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of Various Polyunsaturated Fatty Acids on Blood Cholesterol and Eicosanoids in Rats

The hypocholesterolemic efficacy of various polyunsaturated fatty acids was compared in rats given cholesterol-enriched diets with (0.004%) or without indomethacin, the cyclooxygenase inhibitor. Evening primrose oil (EPO, linoleic+ γ-linolenic), safflower oil (SFO, linoleic) or soybean oil (SBO, linoleic + α-linolenic) were added to diets at the 10% level. The serum cholesterol level of the EPO group was consistently lower than the other groups and after 3 weeks, it was significantly different from the SFO group without indomethacin and the SBO group with indomethacin. In rats fed EPO, the aorta tended to produce more prostacyclin whereas the concentration of plasma thromboxane B₂ was much lower than in rats fed SFO or SBO. The effects of indomethacin on these eicosanoids were less evident in rats fed EPO. Thus, in addition to the hypocholesterolemic action of β-linolenic acid (GLA) in preference to linoleic and possibly α-linolenic acid, GLA appears to cultivate an environment suitable for the prevention of carbiovascular disease even in the presence of excess cholesterol in the diet.     

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.     

Possible involvement of delta-6-desaturase in control of melanoma growth by gamma-linolenic acid.

This study examined the effects of linoleic acid (LA) and gamma-linolenic acid (GLA) on BL6 melanoma growth in cell culture and of safflower oil (SFO) which contains LA and evening primrose oil (EPO) which contains GLA, on melanoma growth when grown in mice. The delta-6-desaturase activity of the melanoma cells in the two systems was also examined and an attempt made to relate the activity of the enzyme to the effects of GLA on cell and tumour growth. LA and GLA were found to be equipotent in inhibiting growth of the in vitro cultured BL6 cells which were found to contain an appreciable level of delta-6-desaturase activity. EPO was however found to be a more potent promoter of in vivo melanoma growth in mice than SFO. Melanomas grown in mice were found to lack delta-6-desaturase activity suggesting that the EPO diet, by providing GLA, was able to compensate for the loss of enzyme activity in the melanomas. The possibility that melanomas in mice have a requirement for GLA for growth while in in vitro cultured cells excess GLA inhibits the growth of the cells through an increase in lipid peroxidation is discussed.     

Kinetic analysis of delta-6-desaturation in liver microsomes: influence of gamma-linoleic acid dietary supplementation to young and old rats.

Previous experiments demonstrated the ability-of a gamma-linoleic acid (GLA) dietary supplementation (as evening primrose oil--EPO) to counteract the fall off in delta-6-desaturase (D6D) activity of linoleic acid and alpha-linoleic acid in aged rats. Kinetic parameters of the D6D were determined in order to test the possibility that there may be a significant influence of GLA administration to young and aged rats on the Vm and Km values for 6-desaturation of both the substrates. In young rats GLA supplementation did not affect the kinetic parameters, while in old rats it produced an increase of Vm values of 6-desaturation for both the substrates. Thus the administration of small doses of GLA to old rats might offer substantial protection against the loss of D6D affinity observed in aging, enhancing the capacity of the enzyme itself.     

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.