INTRODUCTION AND AIM The prevalence of cardiovascular disease (CVD) has increased significantly in the black South African population in recent years. Early in the development of CVD, atherosclerotic plaques form in the vessel wall. When this plaque becomes unstable and ruptures, the coagulation cascade is activated and a blood clot forms. The function of this clot is to stop bleeding. However, it cannot remain in the vasculature indefinitely and has to be lysed again. The ability of the body to lyse clots can be measured with global fibrinolytic potential (GFP) assays and expressed as lysis time. Increased clot lysis time (CLT) has been shown to be significantly associated with various CVD risk factors and CVD events in Caucasian populations while very little information is available for other ethnicities. In this study we investigated plasma GFP and its relation to CVD risk factors in a large black African population. We also determined the effect of three polymorphisms in the promoter area of the plasminogen activator inhibitor-1 (PAI-1) gene on PAI-1act (activity) levels (a main determinant of CLT) and CLT, together with gene-environment interactions and the effect of urbanisation on these interactions. PARTICIPANTS AND METHODS Apparently healthy men and women between the ages of 35 and 65 years were recruited to take part in the South African arm of the Prospective Urban and Rural Epidemiology (PURE) study. Approximately 1000 rural and 1000 urban black African individuals participated. Data and samples were collected during a 12-week collection period in 2005 for cross-sectional analysis. RESULTS Increased PAI-1act levels, body mass index (BMI), glycosylated haemoglobin (HbA1c), triglycerides, fibrinogen concentration, C-reactive protein, female sex, positive HIV-status and the metabolic syndrome were all associated with prolonged CLTs, while increased habitual alcohol consumption was associated with shorter iv CLTs. Urban-rural differences for CLT existed in women only. This is likely due to the larger extent of rural-urban differences in other CVD risk factors observed in women compared to what was observed in men. Of the CVD risk factors measured, PAI-1 explained the largest proportion of the variance in CLT (27%). Owing to the important role PAI-1act plays in CLT, we investigated three polymorphisms in the PAI-1 gene promoter area (the 4G/5G polymorphism, the novel SNP C428T and SNP G429A (previously identified)), and the influence of these polymorphisms on PAI-1act levels and CLT. The frequency of the 5G allele was high (0.85) in comparison with previously reported literature. PAI-1act increased significantly across genotypes in the urban (5G/5G: 3.84 U/ml; 4G/5G: 4.85 U/ml; 4G/4G: 5.96 U/ml p=0.009) but not the rural subgroup, while CLT did not differ. We found significant interactions between the 4G/5G polymorphism and BMI, waist circumference and triglycerides in determining PAI-1act, and between the 4G/5G polymorphism and fibrinogen and fibrinogen gamma prime in determining CLT. Direct relationships with PAI-1act or CLT were not found for the C428T and G429A polymorphisms; they did, however, influence associations of other environmental factors with PAI-1act and CLT. Several of these interactions differed significantly between rural and urban subgroups, particularly in individuals harbouring the mutant alleles. CONCLUSION CLT associated with many of the same CVD risk factors described in the literature for Caucasian populations, but also with other risk factors. Rural-urban differences in CLT are dependent on the association of CLT with other CVD risk factors in the rural-urban setting. Genetic polymorphisms of the PAI-1 gene did not directly influence CLT, despite influencing PAI-1act. The main contributor to PAI-1act variance, however, was (central) obesity. The effect of the 4G/5G polymorphism on PAI-1act, as well as gene–environment interactions for the C428T and G429A genotypes in determining PAI-1act and CLT, were significantly influenced by urbanisation. / Thesis (PhD (Nutrition))--North-West University, Potchefstroom Campus, 2013.

INTRODUCTION AND AIM The prevalence of cardiovascular disease (CVD) has increased significantly in the black South African population in recent years. Early in the development of CVD, atherosclerotic plaques form in the vessel wall. When this plaque becomes unstable and ruptures, the coagulation cascade is activated and a blood clot forms. The function of this clot is to stop bleeding. However, it cannot remain in the vasculature indefinitely and has to be lysed again. The ability of the body to lyse clots can be measured with global fibrinolytic potential (GFP) assays and expressed as lysis time. Increased clot lysis time (CLT) has been shown to be significantly associated with various CVD risk factors and CVD events in Caucasian populations while very little information is available for other ethnicities. In this study we investigated plasma GFP and its relation to CVD risk factors in a large black African population. We also determined the effect of three polymorphisms in the promoter area of the plasminogen activator inhibitor-1 (PAI-1) gene on PAI-1act (activity) levels (a main determinant of CLT) and CLT, together with gene-environment interactions and the effect of urbanisation on these interactions. PARTICIPANTS AND METHODS Apparently healthy men and women between the ages of 35 and 65 years were recruited to take part in the South African arm of the Prospective Urban and Rural Epidemiology (PURE) study. Approximately 1000 rural and 1000 urban black African individuals participated. Data and samples were collected during a 12-week collection period in 2005 for cross-sectional analysis. RESULTS Increased PAI-1act levels, body mass index (BMI), glycosylated haemoglobin (HbA1c), triglycerides, fibrinogen concentration, C-reactive protein, female sex, positive HIV-status and the metabolic syndrome were all associated with prolonged CLTs, while increased habitual alcohol consumption was associated with shorter iv CLTs. Urban-rural differences for CLT existed in women only. This is likely due to the larger extent of rural-urban differences in other CVD risk factors observed in women compared to what was observed in men. Of the CVD risk factors measured, PAI-1 explained the largest proportion of the variance in CLT (27%). Owing to the important role PAI-1act plays in CLT, we investigated three polymorphisms in the PAI-1 gene promoter area (the 4G/5G polymorphism, the novel SNP C428T and SNP G429A (previously identified)), and the influence of these polymorphisms on PAI-1act levels and CLT. The frequency of the 5G allele was high (0.85) in comparison with previously reported literature. PAI-1act increased significantly across genotypes in the urban (5G/5G: 3.84 U/ml; 4G/5G: 4.85 U/ml; 4G/4G: 5.96 U/ml p=0.009) but not the rural subgroup, while CLT did not differ. We found significant interactions between the 4G/5G polymorphism and BMI, waist circumference and triglycerides in determining PAI-1act, and between the 4G/5G polymorphism and fibrinogen and fibrinogen gamma prime in determining CLT. Direct relationships with PAI-1act or CLT were not found for the C428T and G429A polymorphisms; they did, however, influence associations of other environmental factors with PAI-1act and CLT. Several of these interactions differed significantly between rural and urban subgroups, particularly in individuals harbouring the mutant alleles. CONCLUSION CLT associated with many of the same CVD risk factors described in the literature for Caucasian populations, but also with other risk factors. Rural-urban differences in CLT are dependent on the association of CLT with other CVD risk factors in the rural-urban setting. Genetic polymorphisms of the PAI-1 gene did not directly influence CLT, despite influencing PAI-1act. The main contributor to PAI-1act variance, however, was (central) obesity. The effect of the 4G/5G polymorphism on PAI-1act, as well as gene–environment interactions for the C428T and G429A genotypes in determining PAI-1act and CLT, were significantly influenced by urbanisation. / Thesis (PhD (Nutrition))--North-West University, Potchefstroom Campus, 2013.

Motivation In the black population of South Africa, cardiovascular disease (CVD) is rapidly increasing due to urbanisation. Stroke is usually accompanied by a prothrombotic 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 totalled 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 peroxidase 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 prothrombotic 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 prothrombotic profile that exists in the black population, this group also had significantly higher serum peroxides (oxidative stress) and lower glutathione peroxidase 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 prothrombotic 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. / PhD (Physiology), North-West University, Potchefstroom Campus, 2015

Motivation In the black population of South Africa, cardiovascular disease (CVD) is rapidly increasing due to urbanisation. Stroke is usually accompanied by a prothrombotic 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 totalled 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 peroxidase 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 prothrombotic 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 prothrombotic profile that exists in the black population, this group also had significantly higher serum peroxides (oxidative stress) and lower glutathione peroxidase 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 prothrombotic 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. / PhD (Physiology), North-West University, Potchefstroom Campus, 2015