Release of platelet factor 4 (PF4) measured by a polybrene assay in response to in vitro platelet damage

Further observations on the effects of dietary fatty acid composition on platelet reactivity and blood coagulation in man and the influence of methodology on findings

Eight human subjects were fed diets enriched in saturated fat (SF), or polyunsaturated fat (PUF) and after each dietary regimen the plasma heparinthrombin clotting time (HTCT) was determined. The HTCT of citrated plasma indicated reduced heparin-neutralizing activity (HNA) after PUF feeding compared with SF feeding. Platelet factor 4 (PF4) levels in the citrated plasma samples demonstrated an inverse correlation with the HTCT (r = 0.62). Experiments with purified PF4 indicated that the PF4 present in citrated plasma could only account for approximately 10% of the HNA. Plasma prepared in a manner which minimized in vitro release of platelet constituents contained significantly less PF4 after PUF feeding and indicated that most of the PF4 found in citrated plasma resulted from in vitro release. The factor Xa inhibitory activity of citrated plasma was not significantly altered by either of the dietary regimens.

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.

Platelet factor 4: an inhibitor of collagenase

Human platelet factor 4 (PF4) is known to bind to heparin and inhibit its anticoagulant effect. This factor also inhibits the enzyme collagenase derived from cultured human skin and collagenase extracted from human granulocytes. The addition of heparin to the PF4-collagenase assay system has no effect on the observed inhibition of collagenase. Thus PF4 inhibits collagenase, in addition to neutralizing heparin.