Beneficial effect of increased dietary linoleate upon in vivo platelet function in man

Significant inverse associations of serum n-6 fatty acids with plasma plasminogen activator inhibitor-1

Epidemiological studies suggested that n-6 fatty acids, especially linoleic acid (LA), have beneficial effects on CHD, whereas some in vitro studies have suggested that n-6 fatty acids, specifically arachidonic acid (AA), may have harmful effects. We examined the association of serum n-6 fatty acids with plasminogen activator inhibitor-1 (PAI-1). A population-based cross-sectional study recruited 926 randomly selected men aged 40-49 years without CVD during 2002-2006 (310 Caucasian, 313 Japanese and 303 Japanese-American men). Plasma PAI-1 was analysed in free form, both active and latent. Serum fatty acids were measured with gas-capillary liquid chromatography. To examine the association between total n-6 fatty acids (including LA and AA) and PAI-1, multivariate regression models were used. After adjusting for confounders, total n-6 fatty acids, LA and AA, were inversely and significantly associated with PAI-1 levels. These associations were consistent across three populations. Among 915 middle-aged men, serum n-6 fatty acids had significant inverse associations with PAI-1.

Effects of dietaryn-3 polyunsaturated fatty acids from plant and marine origin on platelet aggregation in healthy elderly subjects

In the present intervention study we compared the effects of α-linolenic acid with those of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on platelet aggregationin vitroandex vivoin healthy non-institutionalized elderly subjects. We also compared the effects of α-linolenic acid on platelet aggregation in elderly subjects with those in younger volunteers. During a run-in period of 3 weeks all subjects (thirty-eight elderly (> 60 years) and twelve younger volunteers (< 35 years)) received a diet rich in oleic acid. For the next 6 weeks the elderly subjects received a diet rich in oleic acid (n11), α-linolenic acid (n14) (6·8 g/d) or EPA/DHA (n13) (1·05 g EPA plus 0·55 g DHA). The younger subjects were given a diet rich in α-linolenic acid. The diets did not affect ADP- or collagen-induced platelet aggregationin vitroin either platelet-rich plasma or whole blood. Theex vivoplatelet aggregation as measured with filtragometry was significantly decreased in the elderly group that received EPA/DHA compared with the α-linolenic acid (P= 0·006) and the oleic acid (P= 0·005) diet groups. Effects of α-linolenic acid were not age-dependent. Our results suggest that α-linolenic acid and EPA/DHA do not changein vitroplatelet aggregation. Compared with oleic acid, EPA/DHA, but not α-linolenic acid, favourably affectsex vivoplatelet aggregation in healthy elderly subjects.

Stearic, oleic, and linoleic acids have comparable effects on markers of thrombotic tendency in healthy human subjects

Because human studies concerning the effects of stearic acid on thrombotic tendency are inconsistent, we compared the effects of stearic acid with those of its unsaturated derivatives, oleic acid and linoleic acid. In this randomized, crossover study, 45 subjects (27 women and 18 men) consumed, in random order, 3 experimental diets, each for 5 wk. Diets contained approximately 38% of energy as fat. Dietary compositions were the same except for 7% of energy from stearic, oleic, or linoleic acids. At the end of each period, ex vivo and in vitro platelet aggregation, and variables of coagulation, fibrinolysis, and hematology were evaluated. In men, ex vivo platelet aggregation time as measured by filtragometry (P = 0.036 for diet effects) was favorably prolonged during consumption of the linoleic acid diet compared with the stearic acid diet (P = 0.040), but there was no difference with consumption of the oleic acid diet (P = 0.198). In vitro platelet aggregation induced by collagen and ADP, and variables of coagulation (factor VII amidolytic activity and concentrations of fibrinogen and prothrombin fragment 1 and 2) and fibrinolysis [plasminogen activator inhibitor (PAI) activity and concentrations of tissue plasminogen activator (tPA)/PAI-1 complexes] did not differ among the 3 diets. The mean platelet volume of the subjects decreased during consumption of the stearic acid diet by 0.32 fL compared with the oleic acid diet (P < 0.001) and by 0.35 fL compared with the linoleic acid diet (P < 0.001). In conclusion, our results do not suggest that stearic acid is highly thrombogenic compared with oleic and linoleic acids.

The effect of conjugated linoleic acid on platelet function, platelet fatty acid composition, and blood coagulation in humans

Despite extensive research on conjugated linoleic acid (CLA) showing multiple beneficial effects in animal models, little is known about the role of dietary CLA in human health. To investigate if the beneficial effects of CLA seen in animal models are relevant to humans, we conducted a study with 17 healthy female volunteers who lived in the Metabolic Research Unit of the Western Human Nutrition Research Center for 93 d. This paper reports only the results from this study that are related to the effects of CLA supplementation on blood coagulation, platelet function, and platelet fatty acid composition. Throughout the study, the subjects were fed a low-fat diet (30 en% fat, 19 en% protein, and 51 en% carbohydrate) consisting of natural foods with the recommended dietary allowances for all known nutrients. After a 30-d stabilization period, subjects were randomly assigned to either an intervention group (n = 10) whose diet was supplemented with 3.9 g/d of CLA or a control group (n = 7) who received an equivalent amount of sunflower oil consisting of 72.6% linoleic acid with no detectable CLA. Platelet aggregation was measured in platelet-rich plasma using adenosine diphosphate, collagen, and arachidonic acid agonists. No statistical difference was detected between the amount of agonist required to produce 50% aggregation of platelet-rich plasma before and after the subjects consumed the CLA, with the exception of a decrease in response to collagen. This decrease was found in both control and intervention groups with no significant difference between the groups, suggesting that both linoleic acid (sunflower oil) and CLA might have similar effects on platelet function. The prothrombin time, activated partial thromboplastin time, and the antithrombin III levels in the subjects were determined. Again, there was no statistically significant difference in these three parameters when pre- and post-CLA consumption values were compared. The in vivo bleeding times were also unaffected by CLA supplementation (10.4 + 2.8 min pre- and 10.2 + 1.6 min postconsumption). Platelet fatty acid composition was not markedly influenced by the consumption of dietary CLA, although there was a small increase in the amount of the 9 cis,11 trans-18:2 isomer normally present in platelets after feeding CLA for 63 days. In addition, small amounts of the 8 trans,10 cis-18:2 and the 10 trans,12 cis-18:2 isomers were detected in the platelets along with traces of some of the other isomers. Thus, when compared to sunflower oil, the blood-clotting parameters and in vitro platelet aggregation showed that adding 3.9 g/d of dietary CLA to a typical Western diet for 63 d produces no observable physiological change in blood coagulation and platelet function in healthy adult females. Short-term consumption of CLA does not seem to exhibit antithrombotic properties in humans.

Lipids and thrombosis

There is extensive evidence of important interactions between plasma lipoproteins and platelet function. Some population groups, particularly hypercholesterolaemic patients, have strong evidence of abnormal platelet function which is mediated by the binding of lipoproteins, especially oxidized LDL, to surface receptors. Additionally, abnormal plasma lipid levels precipitate membrane composition changes by increasing the cholesterol:phospholipid ratio. The resulting changes in microviscosity seem to affect transmembrane signalling and might in some cases influence receptor binding. This not only has important therapeutic implications with regard to lipid-lowering drug therapy but also with regard to the potential beneficial effects of dietary therapy.

Dietary fats and platelet function among Finnish men

The aim of this study was to elucidate the role of platelet aggregation as a risk factor for ischemic heart disease (IHD) and the relationship between fatty acids and platelet function. Platelet aggregation upon adenosine diphosphate (ADP), adrenaline and thrombin were measured in middle aged men in east and west, two regions of Finland with a nearly twofold difference in IHD mortality. Platelet aggregation results were correlated with the fatty acid compositions of plasma lipid fractions, adipose tissue triglycerides and platelet phospholipids. There was no significant east-west difference in platelet reactivity to ADP, adrenaline and thrombin. ADP-induced platelet aggregation showed significant negative correlations with all the platelet C20-C22 n-3 polyunsaturated fatty acids (PUFA), but significant positive correlations with the percentage of 18:2n-6 in adipose tissue and plasma cholesterol esters (CE) and triglycerides (TG). Adrenaline-induced aggregation correlated negatively with the percentage of 20:5n-3 in plasma CE and TG, and positively with the total percentage of saturated fatty acids in platelets. Aggregation upon thrombin had a negative correlation with the 20:3n-6/20: 4n-6 ratio in plasma CE and a positive correlation with 18:2n-6 in adipose tissue. The percentages of the major PUFA in platelets correlated significantly with the same fatty acids in plasma CE and phospholipids PL. Platelet 20: 5n-3 had a highly significant negative correlation with the percentage of 18: 2n-6 in plasma and adipose tissue lipids. Platelet 20: 4n-6 was unrelated to its precursors in plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum fatty acids and coronary heart disease in Finnish populations

Finland has one of the highest coronary heart disease (CHD) rates in the whole world, and within the country, the rates are higher in men and eastern Finland than in women and western Finland, respectively. The differences are not wholly explained by the 3 classical risk factors. Several cross-sectional and longitudinal studies suggest that the intake of dietary linoleate (18:2), as reflected in the composition of serum and tissue fatty acids, has an inverse association with CHD, although there are also studies with negative results. Our own retrospective study failed to show any differences in the fatty acid composition of serum CE, TG or PL between men who had died of CHD and age- and risk factor-matched controls, but the negative finding may be due to changes in the fatty acids during storage. Among Finnish populations, most serum CE fatty acids had highly significant correlations with those in other serum lipid fractions, adipose tissue and platelets, and they had good "tracking" for up to 4 yr. Serum CE and TG 18:2, and total omega 6 polyunsaturated fatty acids (PUFA) had strong correlations with dietary 18:2 and PUFA, and can thus be used in the evaluation of population differences in the intake of PUFA. CE fatty acids were analyzed in a total of 2820 free-living 1- to 85-yr-old males and females. The percentages of serum fatty acids were age-dependent. West-Finnish populations had higher contents of 18:2 than those in eastern Finland, and middle-aged women had higher proportions of 18:2 than men. The content of 18:2 in adipose tissue and/or serum CE of middle-aged men was comparable to that in Scotland and lower than those in Italy and Sweden. These findings are compatible with the idea that 18:2 is a negative risk factor of CHD, but the evidence is only circumstantial. Possible mechanisms whereby 18:2 could affect CHD have been discussed. The contents of omega 3 fatty acids in CE were opposite to those of omega 6 fatty acids in that eastern Finnish and male populations had higher contents of 18:3 omega 3 and 20:5 omega 3 than western Finns and females, respectively. This finding is apparently due to substitution of vegetable fat for milk fat in the diet, resulting in a relative deficiency of the omega 3 fatty acids at the expense of 18:2. Experimental evidence for such a mechanism was obtained in an intervention study.(ABSTRACT TRUNCATED AT 400 WORDS)

Self-selected vs. controlled diet as a baseline for human studies: effects of nutrient intakes on blood pressure and on constituents of blood and urine

This study demonstrates that a three-week stabilization period, in which all subjects eat an identical diet, produced a more uniform but different baseline of metabolic parameters than the subject's self-selected or "habitual" diets. Subjects required more food energy to maintain initial body weights during the stabilization period than when they ate their reported self-selected diets; average intakes of almost all nutrients were higher from the stabilization than from the self-selected diet. The switch to the stabilization diet produced small but significant reductions in blood pressure, in some serum enzymes, urine volume, and sodium; and statistically significant increases in serum LDL cholesterol, potassium, aldosterone, protein, albumin, phosphorus, BUN, and in urine potassium. The findings indicate that results must be interpreted with caution from studies in which the baseline for measuring metabolic variables is established by feeding subjects a standardized diet that differed markedly from their regular, self-selected diets.

A comparison of the influence on plasma lipids and platelet function of supplements of omega 3 and omega 6 polyunsaturated fatty acids

A randomized double-blind crossover trial was carried out to compare the influence on plasma lipid concentrations, platelet thromboxane B2 production and platelet aggregation induced by ADP, collagen and U46619 (a prostaglandin endoperoxide analogue), of a daily 10 g supplement of a fish-oil concentrate (MaxEPA), which provided (g): 1.7 20:5 omega 3, 0.3 22:5 omega 3 and 1.2 22:6 omega 3, taken for 2 weeks by ten healthy subjects, with one of vegetable oil providing 3.4 18:2 omega 6. A lower response to platelet aggregation induced by 0.5 micrograms collagen/ml but not by other aggregating agents was observed following both types of supplement. Platelet thromboxane B2 production induced by collagen also tended to be lower following the supplements. Plasma total cholesterol concentrations were unaffected by the supplements. The MaxEPA but not the vegetable-oil supplement lowered the concentration of plasma triglycerides and increased that of high-density-lipoprotein-cholesterol.

Serum fatty acids in Finnish men

The fatty acid compositions of 4 serum lipid fractions were analysed from 244 randomly selected 30-59-year-old Finnish men from 4 areas involved in a population survey ('Mini-Finland') in 1979-80. Men in eastern Finland had significantly lower mean percentages of linoleate (18:2) in CE, TG, FFA and PL (45.1, 10.3, 9.3 and 18.8%, respectively) than men in the western part of the country (48.4, 12.5, 10.6 and 20.2%, respectively). Very low values of 18:2 were encountered in the North Karelian community of Ilomantsi, especially in men aged 50-59 (40.9, 8.0, 7.5 and 16.8%, respectively). The percentage of alpha-linolenate tended also to be lower and those of saturated and monounsaturated fatty acids higher in the east, but there were no or only inconsistent differences in the contents of the prostaglandin precursors dihomo-gamma-linolenate, arachidonate and eicosapentaenoate. Eighteen men were studied in November and the following April. Only minor changes in the mean composition of serum fatty acids took place during this period and the correlation coefficients between the percentages of 18:2 recorded at the two time points ranged from 0.70 to 0.81. The low concentrations of 18:2 in serum lipids in Finnish men obviously reflect a low dietary P/S ratio and may contribute to the high prevalence of IHD in Finland and to its regional differences.

In vivo platelet aggregation and plasma catecholamines in acute myocardial infarction

In vivo platelet aggregation assessed with the Filtragometer and potential correlates were compared among (1) patients with acute myocardial infarction (AMI), (2) normal controls, (3) patients with acute chest pain in whom AMI was eventually ruled out (ROMI), and (4) chronic outpatients (Cardiac Clinic group) with a history of myocardial infarction and/or angina pectoris. The measure was independent of sex, age, platelet count, immediate food intake, serum cholesterol, and triglyceride levels. The AMI group showed higher in vivo platelet aggregation than any of the other three groups (p less than 0.01). Least in vivo aggregation was seen in the normal group. Despite lack of correlation with the platelet aggregation measure, plasma epinephrine and norepinephrine showed statistically significant differences between the AMI and each of the other three groups. Our data support an association between platelet function and AMI, although not necessarily a cause and effect relationship.

Comparative beneficial effects on platelet functions and atherosclerosis of dietary linoleic and gamma-linolenic acids in the rabbit

Male rabbits (10 weeks old) were fed, for 20 weeks, purified diets rich in fat (45% of calories) containing saturated fats (butter), polyunsaturated fats (evening primrose oil + butter or sunflower oil + butter) for 20 weeks. Linoleic acid represented respectively 3.6, 33 and 34% of the dietary fatty acids, while gamma-linolenic acid was present (4.4%) solely in the second group. A significant increase in di-homo-gamma-linolenic acid in plasma, platelets and aorta was noted only in the animals fed evening primrose oil. Despite this, the results of the platelet aggregation to thrombin and ADP, the recalcification plasma-clotting time (platelet-rich plasma) and the severity of atherosclerosis were not significantly different from those observed in the group fed sunflower oil. In contrast, in comparison to the butter-fed animals, the two groups fed the polyunsaturated fats showed remarkable improvements in the clotting time (P less than 0.01) and in the severity of atherosclerotic lesions (evening primrose oil P less than 0.001; sunflower oil P less than 0.05). However, the response to thrombin-induced aggregation was significantly decreased (P less than 0.05) only in the evening primrose oil-fed animals. In these long-term studies in young rabbits, dietary gamma-linolenic acid did not seem to have marked beneficial effects, additional to those induced by linoleic acid, on platelet functions or on atherosclerosis.

Evening primrose oil, a dietary prostaglandin precursor, diminishes vascular reactivity to renin and angiotensin II in rats

Polyunsaturated fatty acids (PUFA) are biosynthetic precursors of prostaglandins (PG). Endogenous biosynthesis of PG in vessel wall and kidney contributes to the regulation of arterial blood pressure. By increasing the fraction of PUFA in the diet systemic blood pressure can be lowered while PUFA deficient diet leads to an increase in blood pressure. To evaluate the effect of an enhanced PG biosynthesis by dietary PG precursors on vascular reactivity and vascular formation of prostacyclin-like activity, the pressor response to intravenous renin and angiotensin II in rats pretreated p.o. for 3 months with evening primrose oil (EPO, 1 ml/day) was determined and the antiaggregatory activity released by aortas of treated rats studied. EPO is unique in that it contains beside linoleic acid (72%), gamma-linolenic acid itself (9%). In contrast to olive oil treated rats EPO pretreatment diminished vascular reactivity to the vasopressor stimuli of renin and angiotensin II and increased the formation of vascular prostacyclin-like activity (p less than 0.05). These studies imply the possibility of a selective modulation of PG production by dietary maneuvers.

Point of view--a role for "nutritional insurance" supplementation in preventive medicine

While macronutrient dietary profile is receiving increasing attention as a determinant of disease risk, the potential of micronutrient supplementation as a public health tool has received little serious attention within orthodox medical circles. In light of the fact that the biochemical effects of many nutrients vary as a function of dose within and beyond "adequate" intake levels, and in light of individual differences in nutrient requirements, it is evident that micronutrient dietary profile--even under the assumption that all nutrient intakes are at least "adequate" or "normal"--plays a major role in determining long-term disease risk. Intelligently planned "nutritional insurance" supplementation could be expected to prevent or delay the onset of many degenerative diseases, while helping to satisfy idiosyncratically high requirements and preventing nutrient deficiency disease.

Effect of polyunsaturate-rich vegetable oils on blood pressure in essential hypertension

A group of essential hypertensives were treated for a period of six weeks with groundnut oil or safflower oil compared with a control group who were given a placebo medication. A significant drop in diastolic pressure occurred in the groups receiving the polyunsaturated fatty acid (PUFA) preparation. In another group of eight patients, who were already receiving traditional antihypertensive therapy, supplementation with PUFA rich oil resulted in a significant reduction in blood pressure. Further, after the end of the treatment period, an increase in diastolic pressure was found six to eight weeks later with return of pressures to approximately the pre-treatment level. These preliminary observations suggest that PUFA rich vegetable oils may be useful in the control of mild-to-moderate hypertension.

Linoleic acid enrichment of serum phosphatidylcholine in humans by low doses of sodium linoleate

Fifteen volunteers were treated daily during a week with 250 mg of sodium linoleate supply as suppository. A day before and a day after treatment venous blood samples were drawn, high density lipoproteins (HDL) fractionated and 3-sn phosphatidylcholine isolated by thin-layer chromatography from total serum and HDL and their fatty acid composition analyzed by gas-liquid chromatography. The positional esterification of linoleic acid in the phosphatidylcholine molecule was determined by enzymatic hydrolysis. Increases of linoleic acid of 1.8--136.3% in the serum phosphatidylcholine were observed in 14 out of 15 volunteers and an increment of 6.3--32.2% was also detected in the lipid fraction from HDL. In both fractions about 98% of the linoleic acid is located in the C2 position of the phosphatidylcholine molecule. The results reported in the present paper show that it is possible to promote the enrichment of linoleic acid in the phosphatidylcholine fractions of both serum and HDL from humans subjected to low doses of sodium linoleate supply as suppository.

Prostaglandins and their precursors in tissues from rats fed on trans, trans-linoleate

Feeding trans,trans-9,12-linoleate to rats as 50 and 100% of the dietary fat decreased the concentrations of n-6 fatty acids, i.e. 18:2, 20:3 and 20:4, in heart, kidney, lung, adipose tissue and platelets of rats. The concentrations of prostaglandin products prostaglandins E1, E2 and F2 alpha in serum were significantly decreased in rats receiving high concentrations of dietary trans, trans-linoleate.

The relationship of dietary fats to prostaglandin biosynthesis

The direct and indirect evidence that the fatty acid composition of dietary fat is involved in the regulation of prostaglandin biosynthesis was reviewed. Direct evidence included effects of essential fatty acid deficiencies and excesses on endogenous tissue levels and production rates of prostaglandins by several tissues. Indirect evidence included lipolytic, platelet aggregatory, hypertensive, inflammatory and immune responses. In general, composition of dietary fat did not affect prostaglandin biosynthesis unless a biochemical essential fatty acid deficiency was induced or the linoleate to saturated fatty acids ratio of the dietary fat was greater than 5. Most results were interpreted in light of changing fatty acid composition; however, very few direct measurements have been made.

Modification of human platelet function by a diet enriched in saturated or polyunsaturated fat

Twelve healthy male subjects were maintained on a saturated fat (SF) dietary regimen followed by a polyunsaturated fat (PUF) regimen. At selected intervals a number of tests were carried out to assess the effect of SF or PUF on platelet composition and activation. Concomitant with the fall in serum cholesterol, associated with the PUF diet, there was a decrease in plasma heparin neutralizing activity (as measured by the heparin--thrombin clotting time), and a fall in the number of circulating platelet aggregates was also observed. These two parameters suggest diminished platelet activation. Malondialdehyde production (an index of prostaglandin synthesis) was unchanged throughout the two dietary periods. Changes in the quality of the dietary fat were manifested in the phospholipid fraction of platelet lipids, particularly phosphatidyl choline and sphingomyelin. Platelet counts of whole blood were significantly decreased when subjects were consuming PUF, but not all of these alterations were reflected in platelet-rich plasma. These results indicate that platelets may be activated in apparently normal people consuming a SF diet (the standard diet of developed countries) and that this activation may be decreased by replacement of dietary SF with PUF.

Drug effects on platelet adherence to collagen and damaged vessel walls

The interaction of platelets with damaged vessel walls leads to the formation of platelet-fibrin thrombi and may also contribute to the development of atherosclerotic lesions because platelets adherent to exposed collagen release a mitogen that stimulates smooth muscle cell proliferation. The first step in thrombus formation, platelet adherence to an injured vessel wall, can be studied quantitatively by the use of platelets labeled with 51chromium. In these investigations, rabbit aortas were damaged by passage of a balloon catheter and segments of the aortas were everted on probes that were rotated in platelet suspensions. Collagen-coated glass cylinders were also used. Adherence was measured in a medium containing approximately physiologic concentrations of calcium, magnesium, protein and red blood cells. Conditions of testing influence the effect of non-steroidal anti-inflammatory drugs, sulfinpyrazone, and dipyridamole on platelet adherence. Aspirin and sulfinpyrazone were not inhibitory when tested in a medium with a 40% hematocrit; this indicates that products formed by platelets from arachidonate probably do not play a major part in the adherence of the first layer of platelets to the surface, although they may be involved in thrombus formation. Indomethacin, dipyridamole, prostaglandin E1, methylprednisolone and penicillin G and related antibiotics did inhibit platelet adherence although the concentrations required were higher than would likely be achieved in vivo upon administration to human patients. None of the non-steroidal anti-inflammatory drugs inhibited the release of granule contents from adherent platelets. Pretreatment of the damaged vessel wall with aspirin increased platelet adherence, presumably because it prevented the formation of PGI2 by the vessel wall. Platelet adherence to undamaged or damaged vessel walls was enhanced by prior exposure of the wall to thrombin. Platelet reactions with aggregating agents and platelet survival can be modified by changes in dietary lipids but there is very little evidence concerning the effects of lipids on platelet adherence. If some forms of dietary fat damage the endothelium, platelet interaction with the damaged area and release of the mitogen for smooth muscle cells would contribute to the development of atherosclerotic lesions.