Ruan Kruger

Associations between reactive oxygen species, blood pressure and arterial stiffness in black South Africans: the SABPA study

Many mechanisms, including oxidative stress, contribute to hypertension. This study investigated the possible associations between oxidative stress, blood pressure and arterial stiffness in black South Africans. Ambulatory blood pressure measurements were taken for 101 black South African men and 99 women. The stiffness indices included ambulatory arterial stiffness index (AASI) and pulse pressure (PP). Reactive oxygen species (ROS) levels (P<0.0001) were higher in the African women compared with men. ROS levels were also higher in hypertensive compared with normotensive men. The 24 h systolic blood pressure (SBP; P<0.01), 24 h diastolic blood pressure (DBP; P<0.0001) and pulse wave velocity (PWV; P<0.01) were significantly higher in African men compared with women. There were unadjusted positive associations of 24 h SBP (r=0.33; P=0.001), 24 h DBP (r=0.26; P=0.008) and 24 h PP (r=0.29; P=0.003) with ROS in African men only. A positive association between AASI and ROS existed only in hypertensive men (r=0.27; P=0.035), but became nonsignificant (B=0.0014; P=0.14) after adjustments. Adjusted, positive associations of 24 h SBP (B=0.181; P=0.018) and 24 h PP (B=0.086; P=0.050) with ROS were again only evident in African men. ROS is positively associated with SBP and PP in African men, suggesting that increased ROS levels may contribute to hypertension in this population group.

NT-proBNP is associated with fibulin-1 in Africans: The SAfrEIC study

OBJECTIVES The N-terminal prohormone B-type natriuretic peptide (NT-proBNP) is involved in the regulation of volume load and secreted when systemic cardiac overload occurs. Fibulin-1 on the other hand is a component of many extracellular matrix proteins including those present in atherosclerotic lesions, expressed in elastin-containing fibres of blood vessels, and also in the heart. Due to an alarming prevalence of hypertensive heart disease in black South Africans, we investigated the associations of NT-proBNP with fibulin-1 and markers of arterial stiffness in Africans and Caucasians. METHODS We included 231 Africans and 238 Caucasians from South Africa aged 22-77 years. Serum NT-proBNP and fibulin-1 levels were determined, and arterial compliance and pulse wave velocity were measured. RESULTS Africans had significantly higher blood pressure and NT-proBNP levels than Caucasians and African men had higher fibulin-1 levels than Caucasian men. In single regression analysis, NT-proBNP was significantly associated with fibulin-1 in African men and Caucasian women. NT-proBNP correlated negatively with arterial compliance in all groups except Caucasian women. After partial adjustments, the association between NT-proBNP and fibulin-1 strengthened in African men only. After full adjustment in multiple regression analysis, the association of NT-proBNP with fibulin-1 was confirmed in African men (R(2)=0.41; β=0.26; p<0.01) and also in younger women (R(2)=0.34; β=0.251; p=0.012). CONCLUSIONS Only Africans indicated a significant independent association between NT-proBNP and fibulin-1, suggesting that cardiovascular alterations are already present in this relatively young African population as opposed to Caucasians.

NT-proBNP, C-Reactive Protein and Soluble uPAR in a Bi-Ethnic Male Population: The SAfrEIC Study

Objective and design This cross-sectional study aimed to investigate associations between a marker of cardiac strain, the N-terminal prohormone B-type natriuretic peptide (NT-proBNP), and inflammation as reflected by either a conventional or novel inflammatory marker in a bi-ethnic South African cohort. Methods and subjects We measured NT-proBNP, C-reactive protein (CRP) and plasma-soluble urokinase plasminogen activator receptor (suPAR) levels along with conventional biomarkers in black (n = 117) and white (n = 116) men. Results NT-proBNP, CRP and suPAR levels were higher in black compared to white men. NT-proBNP was significantly associated with both CRP (r = 0.38; p = 0.001) and suPAR (r = 0.42; p<0.001) in black men only. After full adjustment in multiple regression analyses, the above associations of NT-proBNP with CRP (β = 0.199; p = 0.018) and suPAR (β = 0.257; p<0.01) were confirmed in black men. Conclusion These results suggest that a low-grade inflammatory state as reflected by both a conventional and novel marker of inflammation may contribute to higher cardiovascular risk as reflected by the associations obtained with a marker of cardiac strain in black South African men.

Ethnic differences regarding arterial stiffness of 6-8-year-old black and white boys.

Objectives: Vascular deterioration is suggested to occur earlier in black than white populations, thereby increasing their risk for developing hypertension. To establish whether this is the case, we compared different estimates of arterial stiffness in black and white children and investigated the links with body composition and advanced glycation end products (AGEs) as potential contributors. Methods: We included 40 black and 41 white boys (aged 6‐8 years) from similar schools and measured arterial stiffness [pulse wave velocity (PWV) in different arterial sections, systemic arterial compliance and carotid stiffness estimates], anthropometry as well as urinary pentosidine as a marker of AGEs. Results: Black boys displayed increased PWV [carotid-to-radial (P = 0.002), carotid-to-femoral (P < 0.0001) and carotid-to-dorsalis pedis (P = 0.008)], DBP (P = 0.001) and carotid intima–media thickness (P = 0.007) than white boys. Despite higher pentosidine in black boys (P = 0.039), arterial stiffness indices did not correlate with pentosidine in any group. However, only in black boys, pentosidine correlated negatively with BMI (P = 0.015), BSA (P = 0.017), weight (P = 0.018), waist (P = 0.022) and hip circumference (P = 0.010). Arterial stiffness indices related inversely to body composition in white boys, but femoral PWV correlated inversely with BMI (r = −0.32; P = 0.049) in black boys. Conclusion: Already at very young ages (6‐8 years), with a high proportion of prehypertension, black boys in our study have increased arterial stiffness in all sections of the arterial tree, along with higher DBP, carotid intima–media thickness and AGEs. This phenotype underlines the increasing trend of early-onset vascular aging among black populations.

8-Oxo-7,8-dihydro-2’-deoxyguanosine, reactive oxygen species and ambulatory blood pressure in African and Caucasian men: The SABPA study

Abstract Various studies indicate a relationship between increased oxidative stress and hypertension, resulting in increased DNA damage and consequent excretion of 8-oxo-7,8-dihydro-2’-deoxyguanosine (8-oxodG). The aim of this study was to compare urinary 8-oxodG levels in African and Caucasian men and to investigate the association between ambulatory blood pressure (BP) and pulse pressure (PP) with 8-oxodG in these groups. We included 98 African and 92 Caucasian men in the study and determined their ambulatory BP and PP. Biochemical analyses included, urinary 8-oxodG, reactive oxygen species (ROS) (measured as serum peroxides), ferric reducing antioxidant power (FRAP), total glutathione (GSH), glutathione peroxidase (GPx) and glutathione reductase (GR) activity. The African men had significantly higher systolic (SBP) and diastolic blood pressure (DBP) (both p < 0.001). Assessment of the oxidative stress markers indicated significantly lower 8-oxodG levels (p < 0.001) in the African group. The African men also had significantly higher ROS (p = 0.002) with concomitant lower FRAP (p < 0.001), while their GSH levels (p = 0.013) and GR activity (p < 0.001) were significantly higher. Single and partial regression analyses indicated a negative association between urinary 8-oxodG levels with SBP, DBP and PP only in African men. These associations were confirmed in multiple regression analyses (SBP: R2 = 0.41; β = −0.25; p = 0.002, DBP: R2 = 0.30; β = −0.21; p = 0.022, PP: R2 = 0.30; β = −0.19; p = 0.03). Our results revealed significantly lower urinary 8-oxodG in African men, accompanied by a negative association with BP and PP. We propose that this may indicate a dose-response relationship in which increased oxidative stress may play a central role in the up-regulation of antioxidant defence and DNA repair mechanisms.

Compromised bioavailable IGF-1 of black men relates favourably to ambulatory blood pressure: The SABPA study.

OBJECTIVES Insulin-like growth factor-1 (IGF-1) has potent endothelial-protective, anti-platelet and anti-thrombotic activities, and also exerts mitogenic and proliferatory actions on vascular smooth muscle cells. Conflicting reports exist regarding the role of IGF-1 in vascular protection and atherogenesis. We therefore investigated the relationships of ambulatory blood pressure (BP) and carotid intima-media thickness (cIMT) with a range of components of the IGF-1 axis in a bi-ethnic population. METHODS We included black (N = 86) and white (N = 101) men and measured growth hormone, total IGF-1, insulin-like growth factor binding protein-3 (IGFBP-3), and pregnancy-associated plasma protein-A (PAPP-A) levels. RESULTS Ambulatory BP was almost 10 mmHg higher in black men (137/88 mmHg versus 128/80 mmHg; both p < 0.001), accompanied by an adverse profile of the IGF-axis for all measured components (all p < 0.01), including reduced bioavailable IGF-1 (IGF-1/IGFBP-3; p = 0.006) and tissue IGF-1 accessibility index as represented by IGF-1.PAPP-A/IGFBP-3 (p < 0.001). Single, partial and multiple regression analyses confirmed an independent inverse association between ambulatory systolic BP and bioavailable IGF-1 in black men (R(2) = 0.24; β = -0.22; p = 0.035). cIMT was similar in the ethnic groups (p = 0.34), and was negatively associated with bioavailable IGF-1 in white men (R(2) = 0.42; β = -0.17; p = 0.039) prior to adjustment for γ-glutamyl transferase (R(2) = 0.45; β = -0.10; p = 0.25). CONCLUSION Ambulatory systolic BP is inversely related to bioavailable IGF-1 in black men who displayed low IGF-1 concentrations. An inverse relation was found between cIMT and IGF-1 in white men, which disappeared after correction for γ-glutamyl transferase - opposing reports of a detrimental role of IGF-1 in the early stages of atherogenesis.

Estimated carotid-femoral pulse wave velocity has similar predictive value as measured carotid-femoral pulse wave velocity

Background: Carotid–femoral pulse wave velocity (cfPWV) adds significantly to traditional cardiovascular risk prediction, but is not widely available. Therefore, it would be helpful if cfPWV could be replaced by an estimated carotid–femoral pulse wave velocity (ePWV) using age and mean blood pressure, and previously published equations. The aim of this study was to investigate whether ePWV could predict cardiovascular events independently of traditional cardiovascular risk factors and/or cfPWV. Method: cfPWV was measured and ePWV was calculated in 2366 patients from four age groups of the Danish MONICA10 cohort. Additionally, the patients were divided into four cardiovascular risk groups based on Systematic COronary Risk Evaluation (SCORE) or Framingham risk score (FRS). In 2006, the combined cardiovascular endpoint of cardiovascular death, nonfatal myocardial infarction, stroke and hospitalization for ischemic heart disease was registered. Results: Most results were retested in 1045 hypertensive patients from a Paris cohort. Bland–Altman plot demonstrated a relative difference of −0.3% [95% confidence interval (CI) −15 to 17%] between ePWV and cfPWV. In Cox regression models in apparently healthy patients, ePWV and cfPWV (per SD) added independently to SCORE in prediction of combined endpoint [hazard ratio (95%CI) = 1.38(1.09–1.76) and hazard ratio (95%CI) = 1.18(1.01–1.38)] and to FRS [hazard ratio (95%CI) = 1.33(1.06–1.66) and hazard ratio (95%CI) = 1.16(0.99–1.37)]. If healthy patients with ePWV and/or cfPWV at least 10 m/s were reclassified to a higher SCORE risk category, net reclassification index was 10.8%, P less than 0.01. These results were reproduced in the Paris cohort. Conclusion: ePWV predicted major cardiovascular events independently of SCORE, FRS and cfPWV indicating that these traditional risk scores have underestimated the complicated impact of age and blood pressure on arterial stiffness and cardiovascular risk.

Extracellular matrix biomarker, fibulin-1 and its association with soluble uPAR in a bi-ethnic South African population: the SAfrEIC study.

BACKGROUND Fibulin-1 and soluble urokinase-type plasminogen activator receptor (suPAR) emerged as mediators in the development of sclerotic disease. SuPAR along with C-reactive protein (CRP) and albumin delineate inflammatory processes associated with extracellular matrix turnover in atherosclerosis. We explored the independent relationship of fibulin-1 with these inflammatory markers in a bi-ethnic South African population. METHODS This study included 290 Africans (men: n=130 and women: n=160) and 343 sex- and age-matched Caucasians (men: n=160 and women: n=183). Serum fibulin-1, suPAR, CRP and albumin levels were measured along with conventional cardiovascular and metabolic variables. RESULTS In both single and age-adjusted regression analyses, fibulin-1 correlated with both suPAR and albumin in African men and with suPAR in Caucasian men. These findings were absent in women. In multivariate regression analysis, these associations were confirmed in African men (R(2)=0.22; β=0.329; p<0.001) and Caucasian men (R(2)=0.14; β=0.234; p=0.008). Fibulin-1 independently associated positively with suPAR in all men, but inversely with albumin in African men only. CONCLUSIONS These results are indicating the presence of potential subclinical inflammation (suPAR) within the extracellular matrix of endothelial tissue, contributing to the potential onset of cardiac fibrosis or vascular sclerosis among these South African men with lower albumin levels.

Extracellular Matrix Biomarker, Fibulin-1, Is Closely Related to NT-proBNP and Soluble Urokinase Plasminogen Activator Receptor in Patients with Aortic Valve Stenosis (The SEAS Study).

Background Fibulin-1, a circulating extracellular matrix glycoprotein, has been associated with arterial disease and elevated N-terminal prohormone B-type natriuretic peptide (NT-proBNP) in diabetes. Soluble urokinase plasminogen activator receptor (suPAR), a marker of inflammation, has been associated with subclinical atherosclerosis. Therefore, we aimed to explore the interplay between these biomarkers and mild to moderate aortic valve stenosis (AS). Methods In 374 patients with mild to moderate AS, we investigated the relationship of fibulin-1 with NT-proBNP, levels of suPAR and the degree of AS at baseline and after one and four years of treatment with Simvastatin 40 mg and Ezetimibe 10 mg or placebo. Results During treatment, fibulin-1 became more closely associated with NT-proBNP (βyear0 = 0.10, p = 0.08, βyear1 = 0.16, p = 0.005, βyear4 = 0.22, p<0.001) and suPAR (βyear0 = 0.05, p = 0.34, βyear1 = 0.16, p = 0.006, βyear4 = 0.13, p = 0.03) at the expense of the association to aortic valve area index (AVAI) (βyear0 = −0.14, p = 0.005, βyear1 = −0.08, p = 0.11, βyear4 = −0.06, p = 0.22) independently of age, gender, creatinine, and serum aspartate aminotransferase (Adj.Ryear0 2 = 0.19, Adj.Ryear1 2 = 0.22, Adj.Ryear4 2 = 0.27). Fibulin-1 was unrelated to aortic regurgitation, left ventricular mass, and ejection fraction. In patients with baseline AVAI<0.58 cm2/m2 (median value), fibulin-1 was more closely associated to NT-proBNP (βyear0 = 0.25, βyear1 = 0.21, βyear4 = 0.22, all p<0.01), and suPAR (βyear0 = 0.09, p = 0.26, βyear1 = 0.23, βyear4 = 0.21, both p<0.01) independently of age, gender, AST and treatment allocation. Conclusions Increased levels of fibulin-1 were independently associated with higher levels of suPAR and NT-proBNP especially in patients with lower AVAI, suggesting that fibulin-1 may be an early marker of AS as well as cardiac fibrosis secondarily to elevated left ventricular hemodynamic load.

Testosterone and acute stress are associated with fibrinogen and von Willebrand factor in African men: the SABPA study.

BACKGROUND Low testosterone, acute and chronic stress and hypercoagulation are all associated with hypertension and hypertension-related diseases. The interaction between these factors and future risk for coronary artery disease in Africans has not been fully elucidated. In this study, associations of testosterone, acute cardiovascular and coagulation stress responses with fibrinogen and von Willebrand factor in African and Caucasian men in a South African cohort were investigated. METHODS Cardiovascular variables were studied by means of beat-to-beat and ambulatory blood pressure monitoring. Fasting serum-, salivary testosterone and citrate coagulation markers were obtained from venous blood samples. Acute mental stress responses were evoked with the Stroop test. RESULTS The African group demonstrated a higher cardiovascular risk compared to Caucasian men with elevated blood pressure, low-grade inflammation, chronic hyperglycemia (HbA1c), lower testosterone levels, and elevated von Willebrand factor (VWF) and fibrinogen levels. Blunted testosterone acute mental stress responses were demonstrated in African males. In multiple regression analyses, higher circulating levels of fibrinogen and VWF in Africans were associated with a low T environment (R(2) 0.24-0.28; p≤0.01), but only circulating fibrinogen in Caucasians. Regarding endothelial function, a low testosterone environment and a profile of augmented α-adrenergic acute mental stress responses (diastolic BP, D-dimer and testosterone) were associated with circulating VWF levels in Africans (Adj R(2) 0.24; p<0.05). CONCLUSIONS An interdependence between acute mental stress, salivary testosterone, D-dimer and vascular responses existed in African males in their association with circulating VWF but no interdependence of the independent variables occurred with fibrinogen levels.