Salt-Resistant and Salt-Sensitive Phenotypes Determine the Sensitivity of Blood Pressure to Weight Loss in Overweight/Obese Patients

Erythrocyte glycocalyx sensitivity to sodium is associated with salt sensitivity of blood pressure in women but not men

Background

While salt sensitivity of blood pressure (SSBP) is a risk factor for hypertension, end-organ damage and death, most studies are conducted in western countries and in White people. We previously found that the prevalence of SSBP in Blacks living in Sub-Saharan Africa is as high as 75-80% like what has been reported in the west. Erythrocyte glycocalyx sensitivity to sodium (eGCSS), a marker of sodium-induced damage to the erythrocyte and vascular endothelial glycocalyx is thought to be related to blood pressure perturbations associated with salt intake. We hypothesized that SSBP correlates with eGCSS differently in men and women in Black people.

Methods

We conducted a cross sectional study using data from our recent clinical trial from Livingstone University Teaching Hospital among 117 normotensive young adults. We used a "salt blood test" to determine eGCSS and an immediate pressor response to oral salt (IPROS) for the diagnosis of SSBP.

Results

The proportion of males were equal to females and the median age (interquartile range) of the participants was 29 (22-45) years. The eGCSS scores were higher in salt-resistant females compared to salt-sensitive females and males. eGCSS correlated negatively with SSBP (AOR 0.98, 95% CI 0.97-0.99, p = 0.008), however, this relationship was driven by female sex and abrogated by male sex. Although blood pressure elevations exhibited a sustained bimodal pattern in both sexes, in males, systolic and diastolic blood pressure never returned to baseline during the time course as it did in females.

Conclusion

In this study, eGCSS correlated negatively with SSBP in black women but not in black men and the pressor response to dietary salt was significantly higher in men compared to women. These results suggest that women tend to have a higher disruption of the vascular endothelial glycocalyx by an acute salt load, implying that acute changes in blood pressure may not be driven directly by the endothelial glycocalyx. Our findings suggest a novel mechanism linking eGCSS and SSBP with potential implications for sex differences in salt-induced cardiovascular disease.Clinical trial registration: https://clinicaltrials.gov/, identifier [NCT04844255].

Epigenetics of the blood pressure reactivity to salt: Is the salt sensitive phenotype correctable?

Salt sensitivity defines a state characterized by a highly reactive blood pressure to changes in salt intake. The salt-sensitive phenotype is strongly associated with hypertension, visceral adiposity/metabolic syndrome, and ageing. Obesity accounts for around 70% of hypertension in young adults, and 30% to 50% of adult hypertensives carry the salt-sensitive phenotype. It is estimated that the salt-sensitive phenotype is responsible for high blood pressure in over 600 million adults. But is the salt-sensitive phenotype correctable? Interventional, controlled, clinical trials in obese adolescents and young obese adults, demonstrated that weight-reducing lifestyle modifications revert the salt-sensitive to the salt-resistant phenotype, and restored the faulty production of nitric oxide. Correction of the salt-sensitive phenotype lowers the blood pressure by reducing its reactivity to dietary salt. In a random sample of obese adults subjected to lifestyle modifications, those who were salt-resistant at baseline, were also normotensive and failed to further lower their blood pressure despite a 12% drop in body weight. The salt-resistant phenotype protects the metabolically healthy obese from hypertension, even if their salt consumption is comparable to that of salt-sensitive obese. In summary, at early stages, the elevated blood pressure of obesity, is determined by epigenetic changes leading to a state of salt-sensitivity.

High sodium causes hypertension: evidence from clinical trials and animal experiments

Hypertension is a cardiovascular disease affecting approximately one out of every seven people worldwide. High-sodium consumption has been generally accepted as a risk factor for developing hypertension. Today, global sodium consumption greatly exceeds guidelines recommended by all medical institutions. This review synthesizes the data of landmark mammalian and human studies which investigated the role of sodium in the pathogenesis of hypertension, along with modern studies questioning this relationship. Recent studies concerning the potential pathways by which high-sodium concentration induces hypertension were reviewed. Human trials and population studies revealed a strong correlation between high blood pressure and average dietary sodium; and animal studies found a dramatic reduction in vascular function in a variety of mammals treated with high-sodium diets. In spite of a few contrarian studies, we found overwhelming evidence that elevated sodium consumption could cause hypertension.

Prevalence of obesity and overweight and associated nutritional factors in a population-based Swiss sample: an opportunity to analyze the impact of three different European cultural roots

PURPOSE

Obesity represents a growing public health concern worldwide. The latest data in Switzerland rely on self-reported body mass index (BMI), leading to underestimation of prevalence. We reassessed the prevalence of obesity and overweight in a sample of the Swiss population using measured BMI and waist circumference (WC) and explored the association with nutritional factors and living in different linguistic-cultural regions.

METHODS

Data of 1,505 participants of a cross-sectional population-based survey in the three linguistic regions of Switzerland were analyzed. BMI and WC were measured, and a 24-h urine collection was performed to evaluate dietary sodium, potassium and protein intake.

RESULTS

The prevalence of overweight, obesity and abdominal obesity was 32.2, 14.2 and 33.6%, respectively. Significant differences were observed in the regional distribution, with a lower prevalence in the Italian-speaking population. Low educational level, current smoking, scarce physical activity and being migrant were associated with an higher prevalence of obesity. Sodium, potassium and protein intake increased significantly across BMI categories.

CONCLUSIONS

Obesity and overweight affect almost half of the Swiss adolescents and adults, and the prevalence appears to increase. Using BMI and WC to define obesity led to different prevalences. Differences were furthermore observed across Swiss linguistic-cultural regions, despite a common socio-economic and governmental framework. We found a positive association between obesity and salt intake, with a potential deleterious synergistic effect on cardiovascular risk.

Insulin resistance and the relationship between urinary Na(+)/K(+) and ambulatory blood pressure in a community of African ancestry

BACKGROUND

Although groups of African descent are particularly sensitive to blood pressure (BP) effects of salt intake, the role of obesity and insulin resistance in mediating this effect is uncertain. We determined whether obesity or insulin resistance is independently associated with urinary Na(+)/K(+)-BP relationships in a community sample of African ancestry.

METHODS

We measured 24-hour urinary Na(+)/K(+), homeostasis model assessment of insulin resistance (HOMA-IR), and nurse-derived conventional and 24-hour ambulatory BP in 331 participants from a South African community sample of black African descent not receiving treatment for hypertension.

RESULTS

With adjustments for diabetes mellitus and the individual terms, an interaction between waist circumference and urinary Na(+)/K(+) was associated with day diastolic BP (P < 0.05) and an interaction between log HOMA-IR and urinary Na(+)/K(+) was associated with 24-hour and day systolic (P < 0.05) and 24-hour, day, and night diastolic (P < 0.002; P < 0.001) BP. The multivariable-adjusted relationship between urinary Na(+)/K(+) and night diastolic BP increased across tertiles of HOMA-IR (tertile 1: β-coefficient = -0.79 ± 0.47; tertile 2: β-coefficient = 0.65 ± 0.35; tertile 3: β-coefficient = 1.03 ± 0.46; P < 0.05 tertiles 3 and 2 vs. 1). The partial correlation coefficients for relationships between urinary Na(+)/K(+) and 24-hour (partial r = 0.19; P < 0.02), day (partial r = 0.17; P < 0.05), and night (partial r = 0.18; P < 0.02) diastolic BP in participants with log HOMA-IR greater than or equal to the median were greater than those for relationships between urinary Na(+)/K(+) and 24-hour (partial r = -0.08; P = 0.29), day (partial r = -0.10; P < 0.22), and night (partial r = -0.06; P = 0.40) diastolic BP in participants with log HOMA-IR less than the median (comparisons of r values: P < 0.05).

CONCLUSIONS

Insulin resistance may modify the relationship between salt intake, indexed by urinary Na(+)/K(+), and ambulatory BP in groups of African descent.

Association of dietary sodium and potassium intakes with albuminuria in normal-weight, overweight, and obese participants in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) Study

BACKGROUND

Among obese adults, sodium intake has been associated with cardiovascular disease. Few data are available on sodium intake and albuminuria, a marker of kidney damage and risk factor for cardiovascular disease.

OBJECTIVE

We examined the relation between dietary sodium and potassium intakes and the ratio of sodium to potassium (Na/K) with albuminuria by BMI in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) Study (n = 30,239 adults aged ≥45 y).

DESIGN

A modified Block 98 food-frequency questionnaire was used for dietary assessment in 21,636 participants, and nutritional variables were categorized by sex-specific quintiles. Normal weight, overweight, and obese were defined as BMI (in kg/m(2)) categories of 18.5-24.9, 25-29.9, and ≥30, respectively. Albuminuria was defined as a ratio (mg/g) of urinary albumin to creatinine of ≥30.

RESULTS

The prevalences of albuminuria were 11.5%, 11.6%, and 16.0% in normal-weight, overweight, and obese participants, respectively. The multivariable-adjusted ORs for albuminuria in a comparison of the highest with the lowest quintile of Na/K intake (≥1.12 to <0.70 for men and ≥1.07 to <0.62 for women) were 0.89 (95% CI: 0.65, 1.22), 1.08 (95% CI: 0.85, 1.36), and 1.28 (95% CI: 1.02, 1.61) in normal-weight, overweight, and obese participants, respectively. The highest quintile of dietary sodium was associated with an increased OR for albuminuria in obese participants (OR: 1.44; 95% CI: 1.00, 2.07) but not in normal-weight or overweight participants. Dietary potassium was not associated with albuminuria.

CONCLUSION

In obese adults, higher dietary Na/K and sodium intakes were associated with albuminuria.

Effects of high- and low-sodium diets on ambulatory blood pressure in patients with hypertension receiving aliskiren

Dietary sodium reduction and, as necessary, pharmacologic treatment are recommended for hypertension management. This prospective, randomized, open-label, blinded-end point, multicenter, crossover study investigated the effect of dietary sodium intake on mean ambulatory systolic blood pressure (maSBP) in patients with hypertension receiving aliskiren 300 mg once daily. Following a 2- to 4-week washout period, patients were randomized to a high- (≥ 200 mmol/d) or low- (≤ 100 mmol/d) sodium diet and were started on aliskiren, 300 mg/d. After 4 weeks, patients were crossed over to the alternate diet for an additional 4 weeks. The primary efficacy variable was change in maSBP between diets. During treatment with aliskiren, maSBP was significantly lower with the low-sodium diet compared with the high-sodium diet (least squares mean difference, 9.4 mm Hg; 95% CI, 7.5-11.4; P < .0001). The percentage of patients achieving a maSBP response to aliskiren (<130 mm Hg or a ≥ 20-mm Hg reduction from baseline) was greater with the low- (76.5%) versus the high-sodium diet (42.6%; P < .0001). Overall, 40.9% patients had ≥ 1 adverse event and the rates were similar between groups. In this study, aliskiren was well tolerated and a low-sodium diet accentuated its antihypertensive effect.

Obesity and hypertension: mechanisms, cardio-renal consequences, and therapeutic approaches

The increasing prevalence of obesity in the industrialized world is causing an alarming epidemic. Almost 70% of American adults are overweight or obese. The link between increasing body weight and hypertension is well established. Obesity hypertension through metabolic, endocrinic, and systemic hemodynamic alteration causes structural vascular and cardiac adaptations that trigger concentric, eccentric left ventricular hypertrophy and electrophysiological changes, which may increase the risk for congestive heart failure and sudden cardiac death as a result of arrhythmias. The increased renal blood flow in conjunction with a decreased renal vascular resistance causes renal hyperperfusion and hyperfiltration. Such changes lead to glomerulomegaly, focal segmental glomerulosclerosis, tubulointerstitial inflammation, and fibrosis that characterize the renal damage in obese hypertensive subjects. We propose that weight reduction, with the addition of other nonpharmacological approaches that included exercise and reduction in alcohol intake, should be the first choice to treat obesity hypertension. Salt restriction may be helpful only in salt-sensitive patients. The benefits of diet in obese patients include improvement of insulin sensitivity, reduction in sympathetic nervous and renin angiotensin system activities, and restoration of leptin sensitivity. As a consequence of these and other metabolic changes, the previously described systemic and renal hemodynamic alterations improved and the cardiovascular and renal morphological changes induced by obesity were lessened. After reviewing the medications available, we believe that owing to the cardiovascular and renal morbidity and mortality that characterized obesity hypertension, the ACEI or ARBs offer the best cardio-renal protection and should be the pharmacologic treatment of choice. If these alone do not control BP adequately, then a low-dose diuretic should be added as a second approach. Although we strongly believe in our proposal, more multicenter long-term clinical pharmacological trials are needed to evaluate the efficacy and safety of the antihypertensive approaches in the treatment of obesity hypertension.