Haemostatic markers and cardiovascular function in black and white South Africans : the SABPA study
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Motivation - In the black population of South Africa, cardiovascular disease (CVD) is rapidly increasing due to urbanisation. Stroke is usually accompanied by a pro-thrombotic haemostatic profile. Changing lifestyle factors that accompany the urbanisation process could have a negative impact on the haemostatic profile of black South Africans. Elevated levels of pro-coagulant factors, von Willebrand factor (vWF), fibrinogen and fibrin D-dimer have been reported in the black population, which could increase the black population’s susceptibility to CVD. However, low levels of plasminogen activator inhibitor-1 (PAI-1) previously reported in the black population could contribute towards a pro-fibrinolytic state, which may counteract the hypercoagulant state. This may have a beneficial effect on the haemostatic profile of the black population. More investigation into the haemostatic profile of black South Africans is therefore needed to determine if an altered haemostatic profile exists in this group, and if so, to what extent these alterations may relate to cardiovascular dysfunction. This study included markers of both the coagulation (vWF, fibrinogen, fibrin D-dimer) and fibrinolytic (PAI-1, fibrin D-dimer and fibrinolytic potential) systems in an attempt to investigate the haemostatic profile of the black population of South Africa, and for comparison purposes that of the white population as well. The relationship of these markers’ with selected markers of cardiovascular function was also examined to determine if they could possibly contribute to an increase in cardiovascular risk, especially in the black population. Aims - The aims of this study were to first compare coagulation and fibrinolysis markers in the black and white populations of South Africa. Furthermore, to determine if associations exist between the selected components of the haemostatic system and markers of cardiovascular function, especially in the black population of South Africa, who tends to be at a higher cardiovascular risk due to altered metabolic and haemostatic profiles. Methodology - The Sympathetic activity and Ambulatory Blood Pressure in Africans (SABPA) study was a prospective cohort study that consisted of 409 participants at baseline (2008-2009) that were equally distributed according to both ethnicity (200 black; 209 white) and gender (black, 101 men, 99 women; white, 101 men, 108 women). At follow-up (2011/2012) the cohort totaled 359 participants (170 black, 88 men and 82 women; 189 white, 93 men and 96 women). Data from baseline measurements were used for the first two manuscripts (chapters 2 and 3), while followup data was used for the third manuscript (chapter 4). vWF, fibrinogen, PAI-1, fibrin D-dimer, CLT, serum peroxides, glutathione, glutathione per-oxidase and reductase activity were determined, and ambulatory blood pressure and the retinal vessel calibres were measured. The groups were stratified by ethnicity as specified by statistical interaction terms. T-tests and chi-square tests were used to compare means and proportions, respectively. Pearson and partial regression analyses were used to determine correlations between the components of the haemostatic system and cardiovascular function markers. This was followed by multiple linear regression analyses to investigate whether independent associations exist between the variables in both ethnic groups. P-values ≤0.050 were deemed significant. Results and conclusion of each manuscript The first manuscript (chapter 2) compares the haemostatic profiles of the black and white population to determine whether ambulatory blood pressure is related to components of the haemostatic system. The black participants displayed a pro-thrombotic profile with significantly higher vWF, fibrinogen, PAI-1, fibrin D-dimer and a longer CLT than their white counterparts. Furthermore, partial and multiple linear regression analyses showed a positive association of systolic and diastolic blood pressure with fibrin D-dimer in the black population, while a negative association existed between ambulatory blood pressure and CLT in the white population. These associations suggest that fibrin D-dimer may contribute, at least in part, to the high prevalence of hypertension in the black population. The second manuscript (chapter 3) determined associations between markers of the haemostatic and oxidant-antioxidant systems in the black and white populations. In addition to the pro-thrombotic profile that exists in the black population, this group also had significantly higher serum peroxides (oxidative stress) and lower glutathione per-oxidase activity (antioxidant) levels. Multiple linear regression analyses indicated positive associations between fibrinogen and serum peroxides in both populations. In the white population, an additional positive association was found between serum peroxide and CLT. In the black population, vWF and CLT were negatively associated with GPx activity. The results suggest that there are ethnic-specific relationships between the haemostatic and oxidant-antioxidant systems. The third manuscript (chapter 4) investigated the relationships between the retinal vessel calibres and components of the haemostatic system in the black and white population. The investigation focussed specifically on arteriolar diameters in the lower median, since a narrow arteriolar diameter is known to be associated with elevated blood pressure. In both ethnic groups, a narrower arteriolar calibre was accompanied by narrower venular calibres. Independent positive associations were found between the central retinal vein equivalent (CRVE) and fibrinogen in the black population, as well as vWF and CLT in the white population. In addition, independent negative associations were found between the central retinal artery equivalent and CLT in the black population and with vWF in the white population. The results suggest that haemostatic alterations are linked to early vascular changes that may differ between ethnicities. General conclusion - Ethnic-specific relationships between the components of the haemostatic system and measures of cardiovascular function are evident. The pro-thrombotic profile that is observed in the black population, together with the adverse associations of the haemostatic components with blood pressure, a compromised oxidant-antioxidant profile, and retinal vessel calibres may contribute, at least in part, to the high cardiovascular and cerebrovascular risk evident in this population group.
- Health Sciences