Can the synthesis of platelet-activating factor, a potent vasodilator and pro-aggregatory agent, be altered by dietary marine oils?

Fish Oil Supplementation Inhibits Platelet Aggregation and ATP Release Induced by Platelet-activating Factor and Other Agonists

The anti-inflammatory effects of fish oil may partly be due to the inhibition of platelet activation induced by platelet-activating factor (PAF) and other agonists. To investigate this hypothesis, the diets of 12 healthy volunteers were supplemented with 12 fish oil capsules or 12 olive oil capsules daily for 4 weeks in a double blind crossover study. Aggregation induced by PAF (18 and 12.5 nM) and collagen (20 μg/ml)tended to be reduced after fish oil but the effect was statistically significant only in subjects receiving fish oil in the 6rst 4 weeks of the study (P 0.05, n=6). The effect of fish oil supplementation on platelet ATP release was more marked with significant inhibition of ATP release induced by PAF (1200 and 36 nM, P 0.01, n = 12), collagen (20 μg/ml, P 0.005, n = 12) and ADP (15,10 and 5 μM, P 0.05, n = 12). Olive oil supplementation appeared to inhibit ATP release induced by collagen (45 and 30 μg/ml, P> 0.025, n = 12), while aggregation and ATP release induced by arachidonic acid and adrenaline were unaffected by the supplements. Plasma fibrinogen was significantly reduced after olive oil (P 0.01, n = 12) while prothrombin time was reduced after fish oil (P 0.001, n = 12) and olive oil (P 0.0025). Reduced platelet aggregation and more importantly, inhibition of platelet release induced by PAF and other agonists may contribute to the anti-inflammatory effects of fish oil supplementation in a number of disease states but olive oil may also independently affect platelet function and influence the effect offish oil.

Long-chain n-3 polyunsaturated fatty acids: new insights into mechanisms relating to inflammation and coronary heart disease

Evidence from observational studies, prospective cohort studies and randomized clinical intervention studies indicate that moderate doses of long-chain n-3 polyunsaturated fatty acids (LC n-3 PUFA) significantly decrease risk of fatal coronary heart disease (CHD). Higher doses and longer duration of intervention may also protect from non-fatal CHD events. The exact mechanisms through which LC n-3 PUFA has an effect on CHD are not well established but may include a decrease in fasting and postprandial triacylglycerol levels, a decrease in arrhythmias, modulation of platelet aggregation and decreased synthesis of pro-inflammatory agents. The mechanistic relation between LC n-3 PUFA and inflammation has attracted great interest, and in vitro studies have revealed that these fatty acids decrease endothelial activation, affect eicosanoid metabolism (including epoxygenation pathways) and induce inflammatory resolution. However, the effects of LC n-3 PUFA on established biomarkers of inflammation and endothelial activation in vivo are not strong. Consequently we need new and more sensitive and systemic biomarkers to reveal the effects of LC n-3 PUFA on localized inflammatory processes.

Interactions between dietary fat, fish, and fish oils and their effects on platelet function in men at risk of cardiovascular disease

Recent studies have suggested that omega 3-fats of marine origin may have a protective role in heart disease. This study aimed to compare the effects of fish or fish oil, in the setting of a high- or low-fat diet, on platelet aggregation and platelet thromboxane in men with increased risk of cardiovascular disease. One hundred twenty men who were nonsmokers, 30 to 60 years old, with mildly elevated blood pressure and cholesterol were randomly allocated to one of five high-fat (40% of daily energy) or two low-fat (30%) groups for 12 weeks. The five high-fat groups took either 6 or 12 fish oil capsules daily; fish; a combination of fish and fish oil; or placebo capsules. The two low-fat groups took either fish or placebo capsules. Fish meals provided 1.3 g of eicosapentaenoic acid daily, equivalent to 6 fish oil capsules, and contained an average of 3.65 g/d of omega 3-fatty acids. Multiple regression analysis of the combined groups showed that all groups taking omega 3-fatty acids reduced platelet aggregation to both collagen (P < .0001) and platelet-activating factor (PAF) (P < .05) and platelet thromboxane B2 responses (P < .05) to collagen-induced aggregation. The low-fat diet alone had no effect on PAF-induced platelet aggregation and only a small effect on platelet responses to collagen (P < .05). Platelet aggregation responses to PAF were reduced more by fish oil than fish in a high-fat diet, whereas fish had a greater effect when part of a low-fat rather than a high-fat diet. There was no significant difference in collagen-induced platelet aggregation or platelet thromboxane between fish and fish oils on a high or low fat intake. In conjunction with our previous findings of improvements in lipoproteins, blood pressure, and heart rate in this population, these results on platelet function suggest that dietary omega 3-fatty acids incorporated into a low- rather than a high-fat diet have a wider spectrum of more favorable effects on cardiovascular risk factors.

Plasma lipid levels and platelet and neutrophil function in patients with vascular disease following fish oil and olive oil supplementation

This double-blind study was designed to examine and compare the effects of supplementing the existing diet with fish oil or olive oil on lipids and cell function in patients with peripheral vascular disease. Thirty-two patients with symptomatic and angiographically demonstrated peripheral vascular disease were screened, matched, and randomly allocated to take either 15 g/d fish oil or olive oil for 4 weeks. Fish oil reduced serum triglyceride levels by 26%, but increased total cholesterol levels due to a significant increase in both low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein-2 cholesterol (HDL2-C). There was a nonsignificant decrease in HDL3-C levels. Olive oil reduced total cholesterol levels, accountable to a significantly decrease in LDL-C levels. Serum thromboxane B2 (TXB2) levels remained unchanged following fish oil, but were significantly increased by olive oil. Urinary excretion of TXB2 and 6-keto-PGF1 alpha was unaffected by either oil supplement. Platelet aggregation, which was measured in platelet-rich plasma in response to two doses of collagen or platelet-activating factor (PAF), was significantly reduced after fish oil, but was increased by olive oil. Following fish oil, there was a significant increase in eicosapentaenoic acid (EPA, 20:5) and docosahexaenoic acid (DHA, 22:6) levels and a decrease in arachidonic acid content of platelet phospholipids. The platelet fatty acid composition after olive oil was unchanged. Fish oil decreased neutrophil leukotriene B4 (LTB4) generation following calcium ionophore stimulation by 33%, while leukotriene B5 levels increased significantly. Neutrophil PAF production and plasma lyso-PAF were unaffected by either oil.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppression by ingested eicosapentaenoic acid of the increases in nasal mucosal blood flow and eosinophilia of ryegrass-allergic reactions

Nasal mucosal blood flow, assessed by a laser Doppler probe technique, and the concentration of eosinophils in nasal secretions were quantified during challenge of one nostril with ryegrass-pollen antigen and the other nostril with diluent alone in seven patients with ryegrass-allergic rhinitis. The identical studies were repeated after an 8-week course of 3.5 gm/day of eicosapentaenoic acid (EPA). Ryegrass antigen evoked mean rises in nasal blood flow of 30% to 100% after 10 and 30 minutes that were significant, relative to prechallenge levels and to levels after diluent challenge, both before and after EPA. Antigen-induced increases in nasal blood flow were significantly less after than before EPA at 10 minutes, and at 180 minutes increases were significant only before EPA. In ryegrass-allergic patients with rhinitis who did not take EPA between the two studies, the increases in blood flow after antigen challenge were the same on both occasions. Similarly, the nasal eosinophilia elicited by antigen was significant at 180 minutes only before EPA. Both a composite index of signs and symptoms and the constituent variables, reflecting the clinical response to antigen challenge, were unaffected by EPA. The suppression by EPA of responses of nasal blood flow and nasal eosinophils to antigen challenge supports a role for fatty acid and phospholipid mediators in allergic rhinitis, but the clinical assessment did not provide evidence for any symptomatic benefit from EPA.

The effect of fish oil consumption on platelet aggregation responses in washed human platelet suspensions

Although the biochemical mechanisms relating to the inhibitory action of eicosapentaenoic acid on platelet function have previously been investigated in washed platelet suspensions, there is little existing evidence in washed platelet suspensions to indicate that dietary fish oil consumption reduces platelet aggregation responses. In the present work, eight healthy male volunteers consumed 20 fish oil capsules (MaxEPA) per day for a period of six weeks followed by a six week "dry-out" period during which no fish oil was consumed. Washed platelet suspensions were prepared and aggregation responses to collagen, platelet activating factor (PAF), and thrombin were assessed initially at week 0 and subsequently at 3, 6, 9, and 12 weeks of the experimental period. Three weeks of fish oil consumption did not produce any marked alterations in aggregation responses; however, six weeks of dietary fish oil supplementation resulted in decreased maximum aggregation responses to collagen and PAF by 50.1% and 27.2%, respectively. These results provide evidence, in washed platelet suspensions, that dietary fish oil consumption significantly diminishes platelet responses to collagen and PAF. The significance of these observations remains to be explored and interpreted.