End-organ damage in urbanized Africans with low plasma renin levels: the SABPA study

An Overview of Vascular Dysfunction and Determinants: The Case of Children of African Ancestry

The balance between dilatory and constrictive factors is important as it keeps blood vessels in a homeostatic state. However, altered physiological processes as a result of obesity, hypertension, oxidative stress, and other cardiovascular risk factors may lead to vascular damage, causing an imbalance of vasoactive factors. Over time, the sustained imbalance of these vasoactive factors may lead to vascular dysfunction, which can be assessed by non-invasive methods, such as flow-mediated dilation, pulse wave velocity, flow-mediated slowing, retinal vessel analysis, peripheral vascular reactivity, and carotid intima-media thickness assessment. Although there is increasing prevalence of cardiovascular risk factors (obesity and hypertension) in children in sub-Saharan Africa, little is known about how this may affect vascular function. This review focuses on vasoactive factors implicated in vascular (dys)function, highlighting the determinants and consequences of vascular dysfunction. It further describes the non-invasive methods used for vascular (dys)function assessments and, last, describes the impact of cardiovascular risk factors on vascular dysfunction in children of African ancestry.

The renin-angiotensin-system and left ventricular mass in young adults: the African-PREDICT study

PURPOSE

Raised blood pressure, with the renin-angiotensin system (RAS) as a central regulatory component, is one of the most important contributors to early development of left ventricular hypertrophy. Factors such as increased age, sex, black ethnicity and a low socio-economic status also contribute to left ventricular remodelling. To better understand early contributors to left ventricular mass, we investigated the relationship between left ventricular mass index (LVMi) and the components of the RAS in young healthy adults while considering ethnicity, sex and socio-economic status.

MATERIALS AND METHODS

Black and white women and men (N = 1186) between the ages of 20-30 years were included. By using standard echocardiography, we determined LVMi. Ultra-pressure-liquid chromatography tandem-mass spectrometry (LC-MS/MS) was used to measure the RAS-fingerprint^®.

RESULTS

Components of the RAS such as plasma renin activity (PRA-S), angiotensin I (Ang I), angiotensin II (Ang II) and aldosterone were suppressed in the black compared to the white group (all p < 0.001). No associations between LVMi and the RAS were evident in the total, black or white groups. With additional grouping according to sex and socio-economic status, inverse associations between LVMi and PRA-S (β= -0.168;  p = 0.017), Ang I (β= -0.155; p = 0.028) and Ang II (β= -0.172; p = 0.015) were found only in low socio-economic black women.

CONCLUSION

Despite a suppressed RAS in the black compared to the white group, components of the RAS were not associated with LVMi in this young cohort. The low socio-economic black women of this study population may be vulnerable to future RAS-related increases in left ventricular mass.

Change in renin, cardiovascular and inflammatory markers over three years in a black and white population: the SABPA study

Background

To investigate if percentage change (%∆) in renin over a 3 year follow-up is associated with %∆ in cardiovascular and inflammatory markers in a low renin bi-ethnic group.

Methods

Blood pressure, active renin, C-reactive protein and interleukin-6 levels of 73 black and 81 white teachers were measured at baseline and after 3 years.

Results

In the black group, %∆ renin was inversely associated with %∆ systolic blood pressure (β = −0.27; p = 0.011). In the white group %∆ renin was inversely associated with %∆interleukin-6 (β = −0.24; p = 0.005).

Conclusions

These prospective results indicate that a decrease in renin over time is associated with an increase in blood pressure in a low renin black South African cohort.

Electronic supplementary material

The online version of this article (doi:10.1186/s12872-017-0538-x) contains supplementary material, which is available to authorized users.

Recent advances in understanding hypertension development in sub-Saharan Africa

Consistent reports indicate that hypertension is a particularly common finding in black populations. Hypertension occurs at younger ages and is often more severe in terms of blood pressure levels and organ damage than in whites, resulting in a higher incidence of cardiovascular disease and mortality. This review provides an outline of recent advances in the pathophysiological understanding of blood pressure elevation and the consequences thereof in black populations in Africa. This is set against the backdrop of populations undergoing demanding and rapid demographic transition, where infection with the human immunodeficiency virus predominates, and where under and over-nutrition coexist. Collectively, recent findings from Africa illustrate an increased lifetime risk to hypertension from foetal life onwards. From young ages black populations display early endothelial dysfunction, increased vascular tone and reactivity, microvascular structural adaptions as well as increased aortic stiffness resulting in elevated central and brachial blood pressures during the day and night, when compared to whites. Together with knowledge on the contributions of sympathetic activation and abnormal renal sodium handling, these pathophysiological adaptations result in subclinical and clinical organ damage at younger ages. This overall enhanced understanding on the determinants of blood pressure elevation in blacks encourages (a) novel approaches to assess and manage hypertension in Africa better, (b) further scientific discovery to develop more effective prevention and treatment strategies and

Quantification of systemic renin-angiotensin system peptides of hypertensive black and white African men established from the RAS-Fingerprint®

Objective:

The objective of this study was to make use of a quantitative and qualitative approach comparing the systemic renin-angiotensin system (RAS) of hypertensive black and white African men by using RAS equilibrium analysis.

Materials and methods:

This sub-study involved 23 black (n = 15) and white (n = 8) hypertensive men aged 39.5–41 years, living in the North West Province of South Africa. The RAS-Fingerprinting was determined with LC-MS/MS quantification of angiotensin peptides. Blood pressure and other variables were determined with known methods.

Results:

The main finding of this study was the significant lower Ang I (<5.0 and 45.1 pg/ml; p = 0.005) and Ang II (15.6 and 123.9 pg/ml; p ⩽ 0.001) encountered in the hypertensive black African men compared to their white counterparts. Levels of Ang 1-5 (downstream metabolite of Ang 1-7) (1.8 and 3.0 pg/ml), were detected in black and white hypertensive men, respectively.

Conclusions:

The observed differences between circulating RAS components, which are reflected via equilibrium angiotensin levels, point to a distinctive molecular regulation of the RAAS in the two study cohorts. The increased peripheral resistance observed in hypertensive black individuals might take over a dominant role in control of blood pressure in this study population. A novel highly sensitive LC-MS/MS method resolved the issue of peptide recovery variations during sample preparation by using internal standards for each individual angiotensin metabolite.