The A142V Polymorphism of the G Protein Coupled Receptor Kinase 4 Gene Predicts Natriuretic Response to Saline Challenge in Young Normotensive Lean Black and White South African Men

Salt-sensitive hypertension: mechanisms and effects of dietary and other lifestyle factors

Salt sensitivity, which is an increase in blood pressure in response to high dietary salt intake, is an independent risk factor for cardiovascular disease and mortality. It is associated with physiological, environmental, demographic, and genetic factors. This review focuses on the physiological mechanisms of salt sensitivity in populations at particular risk, along with the associated dietary factors. The interplay of mechanisms such as the renin-angiotensin aldosterone system, endothelial dysfunction, ion transport, and estrogen decrease in women contributes to development of salt sensitivity. Because of their effects on these mechanisms, higher dietary intakes of potassium, calcium, vitamin D, antioxidant vitamins, and proteins rich in L-arginine, as well as adherence to dietary patterns similar to the DASH (Dietary Approaches to Stop Hypertension) diet, can be beneficial to salt-sensitive populations. In contrast, diets similar to the typical Western diet, which is rich in saturated fats, sucrose, and fructose, together with excessive alcohol consumption, may exacerbate salt-sensitive changes in blood pressure. Identifying potential mechanisms of salt sensitivity in susceptible populations and linking them to protective or harmful dietary and lifestyle factors can lead to more specific guidelines for the prevention of hypertension and cardiovascular disease.

The importance of G protein-coupled receptor kinase 4 (GRK4) in pathogenesis of salt sensitivity, salt sensitive hypertension and response to antihypertensive treatment

Salt sensitivity is probably caused by either a hereditary or acquired defect of salt excretion by the kidney, and it is reasonable to consider that this is the basis for differences in hypertension between black and white people. Dopamine acts in an autocrine/paracrine fashion to promote natriuresis in the proximal tubule and thick ascending loop of Henle. G-protein receptor kinases (or GRKs) are serine and threonine kinases that phosphorylate G protein-coupled receptors in response to agonist stimulation and uncouple the dopamine receptor from its G protein. This results in a desensitisation process that protects the cell from repeated agonist exposure. GRK4 activity is increased in spontaneously hypertensive rats, and infusion of GRK4 antisense oligonucleotides attenuates the increase in blood pressure (BP). This functional defect is replicated in the proximal tubule by expression of GRK4 variants namely p.Arg65Leu, p.Ala142Val and p.Val486Ala, in cell lines, with the p.Ala142Val showing the most activity. In humans, GRK4 polymorphisms were shown to be associated with essential hypertension in Australia, BP regulation in young adults, low renin hypertension in Japan and impaired stress-induced Na excretion in normotensive black men. In South Africa, GRK4 polymorphisms are more common in people of African descent, associated with impaired Na excretion in normotensive African people, and predict blood pressure response to Na restriction in African patients with mild to moderate essential hypertension. The therapeutic importance of the GRK4 single nucleotide polymorphisms (SNPs) was emphasised in the African American Study of Kidney Disease (AASK) where African-Americans with hypertensive nephrosclerosis were randomised to receive amlodipine, ramipril or metoprolol. Men with the p.Ala142Val genotype were less likely to respond to metoprolol, especially if they also had the p.Arg65Leu variant. Furthermore, in the analysis of response to treatment in two major hypertension studies, the 65Leu/142Val heterozygote predicted a significantly decreased response to atenolol treatment, and the 65Leu/142Val heterozygote and 486Val homozygote were associated in an additive fashion with adverse cardiovascular outcomes, independent of BP. In conclusion, there is considerable evidence that GRK4 variants are linked to impaired Na excretion, hypertension in animal models and humans, therapeutic response to dietary Na restriction and response to antihypertensive drugs. It may also underlie the difference in hypertension between different geographically derived population groups, and form a basis for pharmacogenomic approaches to treatment of hypertension.

Recent advances in hypertension in sub-Saharan Africa

BACKGROUND

Hypertension was once considered rare in sub-Saharan Africa (SSA), but currently it has become a widespread problem with immense socioeconomic importance. The purpose of this review is to summarise new information on hypertension in SSA that has been published since the last major review in 2008.

METHODS AND RESULTS

A literature search was performed in Pubmed, Embase, WHO Global Cardiovascular Infobase, African Journal On-Line, and African Index Medicus using the following search criteria: hypertension, high blood pressure, and Africa/SSA. Epidemiological surveys that used the WHO STEPS approach or similar methods were also included. The overall prevalence of hypertension in SSA was estimated at 16.2% (95% CI 14.2% to 20.3%) with an estimated number of hypertensive individuals to be 74.7 million. The prevalence of hypertension varies widely from country to country. It is projected that the number of affected individuals will increase by 68% (125.5 million) by 2025. Mass migration of rural Africans to urban areas and rapid changes in lifestyle and risk factors account for the rising prevalence of hypertension.

CONCLUSIONS

Proactive public health interventions at a population level need to be introduced to control the growing hypertension epidemic, and there needs to be a major improvement in access to hypertensive care for the individual. There is an important need for better epidemiological data and hypertension related outcome trials in SSA.