Journal Name:
Am. J. Clin. Nutr.
Article Title:
Effects of diets high in saturated fatty-acids, canola oil, or safflower oil on platelet-function, thromboxane-B2 formation, and fatty-acid composition of platelet phospholipids.
Date Written:
1991
Volume:
54
Number:
2
Page:
351
Author(s):
Kwon, J.S.; Snook, J.T.; Wardlaw, G.M.; Hwang, D .H.
Article:
Populations with lower levels of coronary heart disease also exhibit decreased platelet aggregation in vitro and less thromboxane A2 (TXA2). Platelet aggregation has been implicated in atherosclerotic plaque formation whereas TXA2, the principal metabolite of the omega 6 long chain fatty acid arachidonic acid (AA) in platelets, contributes to platelet activation and irreversible platelet aggregation in physiological hemostasis and thrombosis. TXA3, formed from the long chain omega 3 fatty acid eicosapentaenoic acid (EPA) in platelets, is a weaker proaggregator than TXA2. These physiological characteristics of TXA2 and TXA3 may modulate development of atherosclerosis. Secretion of ADP also occurs in platelets independently of TX synthesis, and secreted ADP induces secondary aggregation, the irreversible phase of platelet aggregation.
The fatty acid pattern in platelet phospholipids reflects the relatively long-term dietary intake coupled with dietary fatty acid metabolism in liver, because platelets do not contain enzymes for desaturation of omega 6 linoleic acid (LA l8:2n-6) or alpha-linolenic acid (ALA l8:3n-3). In this study, platelet fatty acid composition and function in 30 healthy male subjects who initially consumed a baseline diet high in saturated fatty acids and then one of two vegetable-oil-based diets for 8 weeks (with safflower oil or canola oil) was examined. Safflower oil contained 11% of fatty acids as 18:1n-9 (oleic acid, a monounsaturate); 79% as LA; and 0.5% as ALA. Canola oil provided 60% of fatty acids as oleic acid; 21% as LA; and 10% as ALA.
Fatty acid composition of platelet phospholipids reflected changes in dietary fatty acid composition. Compared with baseline, a significant 35% decrease in AA was observed in platelet phospholipids of the canola oil group and long chain n-3 fatty acids rose 17-26%. Platelet phospholipid EPA significantly increased from 2.05% to 2.40% in subjects on the canola oil diet. A significant increase in linoleic acid and a moderate but insignificant decrease in AA composition were observed in the safflower oil diet.
This study showed that both canola- and safflower-oil based diets had an acute effect on the degree of collagen-induced platelet aggregation 3 wk after the initiation of the diets but only when a large amount of collagen (2 mg collagen/L diluted blood) was used. The degree of platelet aggregation returned to baseline values 8 wk after initiation of the oil based diets. This result suggests that the oil-based diets fed in this study produced only an acute effect on collagen-induced platelet aggregation. There was a significant decrease in ATP secretion after 8 wk of canola oil based diet when 1 mg collagen/L was used as an agonist even though that amount of collagen did not affect the degree of aggregation. ADP secretion may be a reliable indicator of the more subtle process of secondary aggregation. Measurement of ATP secretion in whole blood is equivalent to measurement of ADP secretion because platelets maintain a constant ratio of ATP to ADP.
The researchers speculated that lowered ATP secretion observed only in the canola oil group at 8 wk suggests a long-term beneficial effect of canola oil on platelet function. Possibly, longer-term feeding of a diet enriched in ALA might lengthen the turnover time of some structural platelet phospholipids, which might reduce aggregation. No significant difference was observed in thromboxane B2 concentrations between oil-treatment groups at 8 wk. In this study both safflower oil and canola oil diets temporarily reduced platelet aggregation. The canola-oil based diet had a more persistent effect on platelet function ADP secretion and lag time in platelet aggregation was considered. These effects might reduce incidence of thrombogenic atherosclerosis compared with effects of a diet high in saturated fatty acids.
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