FIBRIN NETWORK CHARACTERISTICS AND RED PALM OIL IN HYPERFIBRINOGENAEMIC, HYPERCHOLESTEROLAEMIC SUBJECTS

Abstract

Cardiovascular disease (CVD) is one of the leading causes of death world-wide. Extensive research has been done on the many risk factors for CVD in order to prevent and/or treat CVD. A contributing factor that has not received much attention as yet is the structure of the fibrin networks that forms the basis of blood clots. These fibrin fibres that form when coagulation has been activated, have been shown to vary in length and width. These variations lead to alterations in the character of the fibrin network, causing it to be either more atherogenic or more easily lysable. Long, thin fibres are associated with tight, brittle fibrin networks with large amounts of cross-linking and branching, making the clot less permeable to fibrinolytic enzymes, therefore making it more atherogenic. Short, thick fibres on the other hand, form loose, elastic clots with large pores enabling fibrinolytic enzymes to digest the clots more easily resulting in clots with much less atherogenic potential. The fibrin network characteristics (FNC) measured in this thesis included: the permeability of the clot, the mass-length-ratio of the fibres and the compaction of the clot. The fibrin content of the clot itself was also measured in one study. Diet plays an important role in the primary and secondary prevention of CVD. Little is known about the effect of dietary factors on FNC. One of the studies that form part of this thesis was therefore a 4 week dietary intervention, investigating the effect of 25 g of palm oil (PO), red palm oil (RPO) (rich in antioxidants) and sunflower oil ingested daily, on FNC. ·The type of fat in the diet and antioxidants are two dietary factors that have been shown to affect other CVD risk factors. The other study that fo1ms part of this thesis attempted to answer some fundamental, methodological questions. The first fundan1ental question addressed was the effect of freezing on FNC. Currently most plasma samples are stored frozen for different durations until analysis. Therefore it is necessary to know whether the process of freezing and/or frozen storage have any significant effect on FNC. Together with the effects of freezing and frozen storage we also investigated the effect of freeze-drying on FNC since most control plasmas and standards are in lyophilised form. The second fundamental challenge was to incorporate between-day and within-day analytic variation into the interpretation of the results since no commercial standards or control plasmas are available to ensure quality control. We first undertook the methodological study and then incorporated the results into the dietary intervention study. The reader is referred to the abstracts at the beginning of each separate paper (Chapters 3 and 4), for a description of the subjects, study design and analytical methods used in each study. The results of the methodological study showed that: a) Freezedrying was less deleterious on FNC than freezing. The FNC and fibrinogen concentration of the freeze-dried samples compared better with the fresh samples than did the frozen plasma;b) Frozen storage for up to 4 months at - 83 °C resulted in a linear decrease in mass-lengthratio and compaction of the fibrin fibres and a linear increase in the fibrin content of the clot. This indicates that these variables were probably not stable over the 4 month storage period; c) Storage in the freeze-dried form resulted in a significant increase (p < 0.001) in plasma fibrinogen but a significant decrease (p < 0.001) in the fibrin content of the clots. The results of the dietary intervention showed that: a) Changes in plasma fatty acid concentration may influence FNC. It appears as though decreases in plasma saturated fatty acids together withincreases in plasma unsaturated fatty acids significantly increased (p < 0.001) the masslength-ratio of the fibrin fibres. Increased fibre mass-length-ratio is usually associated with less atherogenic fibrin clots; b) Plasma fibrinogen and D-dimer decreased significantly in the sunflower oil group (p = 0.007 and p = 0.04 respectively); c) Significant correlations were found between the FNC and markers of fibrinolysis, indicating that the fibrin clot structuremay play an important role in fibrinolysis. Although the methodology of FNC determination still needs some refinements new methods are currently being developed. These new developments will hopefully establish a clinical role for FNC and help us understand the exact role and importance thereof in the prevention and treatment of CVD.