High salt intake fails to enhance plasma adiponectin in normotensive salt-sensitive subjects

The role of dietary salt in metabolism and energy balance: Insights beyond cardiovascular disease

Dietary salt (NaCl) is essential to an organism's survival. However, today's diets are dominated by excessive salt intake, which significantly impacts individual and population health. High salt intake is closely linked to cardiovascular disease (CVD), especially hypertension, through a number of well-studied mechanisms. Emerging evidence indicates that salt overconsumption may also be associated with metabolic disorders. In this review, we first summarize recent updates on the mechanisms of salt-induced CVD, the effects of salt reduction and the use of salt substitution as a therapy. Next, we focus on how high salt intake can impact metabolism and energy balance, describing the mechanisms through which this occurs, including leptin resistance, the overproduction of fructose and ghrelin, insulin resistance and altered hormonal factors. A further influence on metabolism worth noting is the reported role of salt in inducing thermogenesis and increasing body temperature, leading to an increase in energy expenditure. While this result could be viewed as a positive metabolic effect because it promotes a negative energy balance to combat obesity, caution must be taken with this frame of thinking given the deleterious consequences of chronic high salt intake on cardiovascular health. Nevertheless, this review highlights the importance of salt as a noncaloric nutrient in regulating whole-body energy homeostasis. Through this review, we hope to provide a scientific framework for future studies to systematically address the metabolic impacts of dietary salt and salt replacement treatments. In addition, we hope to form a foundation for future clinical trials to explore how these salt-induced metabolic changes impact obesity development and progression, and to elucidate the regulatory mechanisms that drive these changes, with the aim of developing novel therapeutics for obesity and CVD.

Innate Immunity System in Patients With Cardiovascular and Kidney Disease

With a global burden of 844 million, chronic kidney disease (CKD) is now considered a public health priority. Cardiovascular risk is pervasive in this population, and low-grade systemic inflammation is an established driver of adverse cardiovascular outcomes in these patients. Accelerated cellular senescence, gut microbiota-dependent immune activation, posttranslational lipoprotein modifications, neuroimmune interactions, osmotic and nonosmotic sodium accumulation, acute kidney injury, and precipitation of crystals in the kidney and the vascular system all concur in determining the unique severity of inflammation in CKD. Cohort studies documented a strong link between various biomarkers of inflammation and the risk of progression to kidney failure and cardiovascular events in patients with CKD. Interventions targeting diverse steps of the innate immune response may reduce the risk of cardiovascular and kidney disease. Among these, inhibition of IL-1β (interleukin-1 beta) signaling by canakinumab reduced the risk for cardiovascular events in patients with coronary heart disease, and this protection was equally strong in patients with and without CKD. Several old (colchicine) and new drugs targeting the innate immune system, like the IL-6 (interleukin 6) antagonist ziltivekimab, are being tested in large randomized clinical trials to thoroughly test the hypothesis that mitigating inflammation may translate into better cardiovascular and kidney outcomes in patients with CKD.

High-salt intake reduces renal tissue levels of inflammatory cytokines in mice

High salt (HS) intake is usually considered as an aggravating factor to induce inflammatory renal injury. However, the changes in the renal levels of inflammatory cytokines during HS intake is not yet clearly defined. We hypothesize that HS increases renal levels of tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) but decreases interleukin-10 (IL-10; anti-inflammatory cytokine) and these responses exacerbate in NO deficient conditions. Both wild-type (WT) and endothelial NO synthase knockout (eNOSKO) mice (~8 weeks old, n = 6 in each group) were given normal-salt (NS; 0.3% NaCl) and HS (4% NaCl) containing diets for 2 weeks. Systolic blood pressure (SBP) was determined by tail-cuff plethysmography and urine collections were made using metabolic cages. Basal SBP was higher in eNOSKO than WT mice (131 ± 7 vs 117 ± 3 mmHg; p < .05). HS intake for 2 weeks increased SBP in eNOSKO (161 ± 5 mmHg) but not in WT mice. In NS groups, the cytokine levels in renal tissues (measured using ELISA kits and expressed in pg/mg protein) were significantly higher in eNOSKO than WT mice (TNF-α, 624 ± 67 vs. 325 ± 73; IL-6, 619 ± 106 vs. 166 ± 61; IL-10, 6,087 ± 567 vs. 3,929 ± 378). Interestingly, these cytokine levels in HS groups were significantly less both in WT (TNF-α, 114 ± 17; IL-6, 81 ± 14; IL-10, 865 ± 130) and eNOSKO (TNF-α, 115 ± 18; IL-6, 56 ± 7; IL-10, 882 ± 141) mice. These findings indicate that HS induces downregulation of cytokines in the kidney. Such HS-induced reduction in cytokines, particularly TNF-α (a natriuretic agent), would facilitate more salt-retention, and thus, leading to salt-sensitive hypertension in NO deficient conditions.

Potassium supplementation blunts the effects of high salt intake on serum retinol-binding protein 4 levels in healthy individuals

Aims/Introduction

Excessive dietary salt or low potassium intakes are strongly correlated with insulin resistance (IR) and type 2 diabetes mellitus. In epidemiological and experimental studies, increased serum retinol‐binding protein 4 (RBP4) contributes to the pathogenesis of type 2 diabetes mellitus. Herein, we hypothesized that RBP4 might be an adipocyte‐derived “signal” that plays the crucial role in salt‐related insulin resistance or type 2 diabetes mellitus. This study aimed to assess whether salt consumption and potassium supplementation influence serum RBP4 levels in healthy individuals.

Materials and Methods

A total of 42 participants (aged 25–50 years) in a rural area of Northern China were successively provided normal (3 days at baseline), low‐salt (7 days; 3 g/day NaCl) and high‐salt (7 days; 18 g/day) diets, and a high‐salt diet with potassium additive (7 days; 18 g/day NaCl and 4.5 g/day KCl). Urinary sodium and potassium were measured to ensure compliance to dietary intervention. Then, RBP4 levels were evaluated by enzyme‐linked immunosorbent assay.

Results

High salt intake significantly raised serum RBP4 levels in healthy participants (17.5 ± 0.68 vs 28.6 ± 1.02 µg/mL). This phenomenon was abrogated by potassium supplementation (28.6 ± 1.02 vs 17.6 ± 0.88 µg/mL). In addition, RBP4 levels presented positive (r = 0.528, P < 0.01) and negative (r = −0.506, P < 0.01) associations with 24‐h urinary sodium‐ and potassium excretion levels.

Conclusions

RBP4 synthesis is motivated by high salt intake and revoked by potassium supplementation. Our pioneer work has contributed to the present understanding of salt‐induced insulin resistance or type 2 diabetes mellitus.

Effects of Salt Loading on Plasma Osteoprotegerin Levels and Protective Role of Potassium Supplement in Normotensive Subjects

BACKGROUND

Excess dietary salt is strongly correlated with cardiovascular disease, morbidity, and mortality. Conversely, potassium likely elicits favorable effects on cardiovascular disorders. In epidemiological studies, increased plasma osteoprotegerin (OPG) concentrations are associated with atherosclerosis and vascular deaths. Our study was designed to examine the effects of salt intake and potassium supplementation on plasma OPG levels in normotensive subjects.Methods and Results:The 18 normotensive subjects were selected from a rural community in China. They were sequentially maintained on low-salt diet for 7 days (3 g/day, NaCl), high-salt diet for 7 days (18 g/day), and high-salt diet with potassium supplementation for 7 days (18 g/day of NaCl+4.5 g/day of KCl). High-salt intake enhanced plasma OPG levels (252.7±13.9 vs. 293.4±16.1 pg/mL). This phenomenon was abolished through potassium supplementation (293.4±16.1 vs. 235.1±11.3 pg/mL). Further analyses revealed that the OPG concentration positively correlated with 24-h urinary sodium excretion (r=0.497, P<0.01). By contrast, OPG concentration negatively correlated with 24-h urinary potassium excretion (r=0.594, P<0.01).

CONCLUSIONS

Salt loading can enhance the production of circulating OPG. Potassium supplementation can reverse the effects of excessive OPG. Our study results may improve our understanding of the roles of salt and potassium in the risk of cardiovascular disorders.

High salt intake as a multifaceted cardiovascular disease: new support from cellular and molecular evidence

Scientists worldwide have disseminated the idea that increased dietary salt increases blood pressure. Currently, salt intake in the general population is ten times higher than that consumed in the past and at least two times higher than the current recommendation. Indeed, a salt-rich diet increases cardiovascular morbidity and mortality. For a long time, however, the deleterious effects associated with high salt consumption were only related to the effect of salt on blood pressure. Currently, several other effects have been reported. In some cases, the deleterious effects of high salt consumption are independently associated with other common risk factors. In this article, we gather data on the effects of increased salt intake on the cardiovascular system, from infancy to adulthood, to describe the route by which increased salt intake leads to cardiovascular diseases. We have reviewed the cellular and molecular mechanisms through which a high intake of salt acts on the cardiovascular system to lead to the progressive failure of a healthy heart.

Genetic variants in adiponectin and blood pressure responses to dietary sodium or potassium interventions: a family-based association study

Previous studies have shown that genetic factors might have an important role in blood pressure (BP) responses to dietary salt or potassium intake. The aim of this study was to assess the association of common genetic variants of the adiponectin gene with BP responses to controlled dietary sodium or potassium interventions. Subjects (n=334) from 124 families in rural areas of Northern China were recruited. After a 3-day baseline observation, participants sequentially maintained a 7-day low-sodium diet (NaCl, 3 g per day; or sodium, 51.3 mmol per day), followed by a 7-day high-sodium diet (NaCl, 18 g per day; or sodium, 307.8 mmol per day) and a 7-day high-sodium plus potassium supplementation intervention (KCl, 4.5 g per day; or potassium, 60 mmol per day). A total of seven single nucleotide polymorphisms (SNPs) in the adiponectin gene were selected as the study sites. After adjustment for multiple testing, the adiponectin SNP rs16861205 was significantly associated with the diastolic BP (DBP) response to low-salt intervention, and the DBP and mean arterial pressure (MAP) responses to high-salt intervention (P=0.028, 0.023 and 0.027, respectively). SNP rs822394 was associated with the DBP and MAP responses to low-salt intervention and the DBP response to high-salt intervention (P=0.023, 0.030 and 0.033 respectively). Meanwhile, significant association also existed between SNP rs16861194 and the systolic BP response to potassium supplementation intervention (P=0.026). In addition, SNP rs822394 was significantly associated with basal DBP after adjustment for multiple testing (P=0.033). Our study indicated that the genetic polymorphisms in the adiponectin gene are significantly associated with BP responses to dietary sodium and potassium intake.

Low Response of Renin-Angiotensin System to Sodium Intake Intervention in Chinese Hypertensive Patients

The interactions of sodium balance and response of renin-angiotensin-aldosterone system are important for maintaining the hemodynamic stability in physiological conditions. However, the influence of short-term sodium intake intervention in the response of renin-angiotensin system (RAS) on hypertensive patients is still unclear. Thus, we conducted a clinical trial to investigate the effects of short-term sodium intake intervention on the response of RAS in hypertensive patients.One hundred twenty-five primary Chinese hypertensive patients were divided into high, moderate, and low sodium groups by 24-hour urinary sodium excretion (UNa). All the patients received a 10-day dietary sodium intake intervention with standardized sodium (173.91mmol/day) and potassium (61.53mmol/day). Blood pressure, urinary sodium, urinary potassium, plasma sodium, potassium, creatinine, the levels of plasma renin activity, plasma angiotensin II concentrations (AT-II), and plasma aldosterone concentrations were detected before and after the intervention.Before the intervention, no differences were found in blood pressure and RAS among 3 groups. After standardized dietary sodium intake intervention, both UNa excretion and systolic pressure decreased in high-sodium group, while they increased in moderate and low-sodium groups. Intriguingly, there were no changes in the levels of plasma renin activity, AT-II, and plasma aldosterone concentrations among 3 groups during the intervention.The present study demonstrated that the influenced sodium excretion and blood pressure by short-term sodium intake intervention were independent of RAS quick response in Chinese hypertensive patients.

High sodium intake is associated with short leukocyte telomere length in overweight and obese adolescents

Background/Objectives

Telomere shortening plays an important role in cellular aging. However, the impact of high sodium intake, an important risk factor of age-related diseases, on telomere shortening remains unknown. Therefore, we examined the relationship between high dietary sodium intake and leukocyte telomere length, particularly in the context of obesity since obesity increases salt sensitivity.

Subjects/Methods

Leukocyte telomere length (LTL) was determined by a quantitative polymerase chain reaction method in 766 adolescents aged 14–18 years (50% female, 49% African Americans). Dietary sodium intake was assessed by seven independent 24-h dietary recalls. We divided the sample into low sodium (mean 2388 ± 522 mg/day) or high sodium groups (mean 4142 ± 882 mg/day) based on the median value (3280.9 mg/day).

Results

In the entire cohort, there was no significant association between sodium intake and LTL (r = −0.05, p = 0.24). However, there was a significant interaction between sodium intake and obesity status (p = 0.049). Further multiple linear regression analyses revealed that higher dietary sodium intake was associated with shorter LTL in the overweight/obese group (BMI ≥ 85^th percentile, β = −0.37, p = 0.04), but not in the normal weight group (β = 0.01, p= 0.93) after adjusting for multiple confounding factors. In the overweight/obese group, LTL was significantly shorter in the high sodium intake subjects vs. low sodium intake subjects (1.24 ± 0.22 vs. 1.32 ± 0.20, p = 0.02), but not the normal weight group (1.29 ± 0.24 vs. 1.30 ± 0.24, p = 0.69).

Conclusions

Higher dietary sodium intake is associated with shorter telomere length in overweight and obese adolescents.

A randomized trial of sodium-restriction on kidney function, fluid volume and adipokines in CKD patients

Background

Dietary sodium restriction is a key management strategy in chronic kidney disease (CKD). Recent evidence has demonstrated short-term reduction in blood pressure (BP) and proteinuria with sodium restriction, however the effect on other cardiovascular-related risk factors requires investigation in CKD.

Methods

The LowSALT CKD study involved 20 hypertensive Stage III-IV CKD patients counselled by a dietitian to consume a low-sodium diet (<100 mmol/day). The study was a randomised crossover trial comparing 2 weeks of high-sodium (additional 120 mmol sodium tablets) and low-sodium intake (placebo). Measurements were taken after each crossover arm including BP (peripheral and central), adipokines (inflammation markers and adiponectin), volume markers (extracellular-to-intracellular [E/I] fluid ratio; N-terminal pro-brain natriuretic peptide [NT-proBNP]), kidney function (estimated Glomerular Filtration Rate [eGFR]) and proteinuria (urine protein-creatinine ratio [PCR] and albumin-creatinine ratio [ACR]). Outcomes were compared using paired t-test for each cross-over arm.

Results

BP-lowering benefits of a low-sodium intake (peripheral BP (mean ± SD) 148/82 ± 21/12 mmHg) from high-sodium (159/87 ± 15/10 mmHg) intake were reflected in central BP and a reduction in eGFR, PCR, ACR, NTproBNP and E/I ratio. There was no change in inflammatory markers, total or high molecular weight adiponectin.

Conclusions

Short-term benefits of sodium restriction on BP were reflected in significant change in kidney function and fluid volume parameters. Larger, long-term adequately powered trials in CKD are necessary to confirm these results.

Trial registration

Universal Trial Number U1111-1125-2149 registered on 13/10/2011; Australian New Zealand Clinical Trials Registry Number ACTRN12611001097932 registered on 21/10/2011.

Dietary sodium, adiposity, and inflammation in healthy adolescents

OBJECTIVES

To determine the relationships of sodium intake with adiposity and inflammation in healthy adolescents.

METHODS

A cross-sectional study involved 766 healthy white and African American adolescents aged 14 to 18 years. Dietary sodium intake was estimated by 7-day 24-hour dietary recall. Percent body fat was measured by dual-energy x-ray absorptiometry. Subcutaneous abdominal adipose tissue and visceral adipose tissue were assessed using magnetic resonance imaging. Fasting blood samples were measured for leptin, adiponectin, C-reactive protein, tumor necrosis factor-α, and intercellular adhesion molecule-1.

RESULTS

The average sodium intake was 3280 mg/day. Ninety-seven percent of our adolescents exceeded the American Heart Association recommendation for sodium intake. Multiple linear regressions revealed that dietary sodium intake was independently associated with body weight (β = 0.23), BMI (β = 0.23), waist circumference (β = 0.23), percent body fat (β = 0.17), fat mass (β = 0.23), subcutaneous abdominal adipose tissue (β = 0.25), leptin (β = 0.20), and tumor necrosis factor-α (β = 0.61; all Ps < .05). No relation was found between dietary sodium intake and visceral adipose tissue, skinfold thickness, adiponectin, C-reactive protein, or intercellular adhesion molecule-1. All the significant associations persisted after correction for multiple testing (all false discovery rates < 0.05).

CONCLUSIONS

The mean sodium consumption of our adolescents is as high as that of adults and more than twice the daily intake recommended by the American Heart Association. High sodium intake is positively associated with adiposity and inflammation independent of total energy intake and sugar-sweetened soft drink consumption.

Low sodium diet and adipokine secretion: implications for the cardiovascular system?

The influence of dietary sodium intake on cardiovascular risk factors has been a matter of decade-long discussions. Needed is a clear-cut elucidation of the beneficial mechanisms of action of reduced salt intake. In a recent study, lean and obese mice were subjected to a high or low salt diet for 16 weeks. The low salt diet tremendously reduced fasting insulin in obese animals, and HOMA-IR was improved. Reduced adiponectin expression in the heart and in peritoneal adipose tissue in obese animals was restored or even increased compared to normal levels with the low salt diet. Corresponding with the beneficial effect on adiponectin, inflammatory markers were reduced to lean levels by the low salt diet. Whether the increase in adiponectin would have been larger if the rise in aldosterone had been prevented is one of the questions raised by this study. The data obtained in this animal study are based on a robust methodological basis for two reasons: first, the long-term intervention of 16 weeks clearly represents a strength of the study; second, dietary sodium restriction was modest, as judged by only 2-fold increased plasma renin activity. Overall, the data presented by Baudrand et al. in the current issue of NMCD may path the way to a better understanding of the mode of action of modest sodium restriction. However, a replication of the results in a more human-like diet-induced obesity mouse model is warranted.

Long-term dietary sodium restriction increases adiponectin expression and ameliorates the proinflammatory adipokine profile in obesity

BACKGROUND/AIM

Obesity is associated with changes in adiponectin and pro-inflammatory adipokines. Sodium intake can affect adipokine secretion suggesting a role in cardiovascular dysfunction. We tested if long-term dietary sodium restriction modifies the expression of adiponectin and ameliorates the pro-inflammatory profile of obese, diabetic mice.

METHODS/RESULTS

Db/db mice were randomized to high sodium (HS 1.6% Na+, n = 6) or low sodium (LS 0.03% Na+, n = 8) diet for 16 weeks and compared with lean, db/+ mice on HS diet (n = 8). Insulin levels were 50% lower in the db/db mice on LS diet when compared with HS db/db (p < 0.05). LS diet increased cardiac adiponectin mRNA levels in db/db mice by 5-fold when compared with db/db mice on HS diet and by 2-fold when compared with HS lean mice (both p < 0.01). LS diet increased adiponectin in adipose tissue compared with db/db mice on HS diet, achieving levels similar to those of lean mice. MCP-1, IL-6 and TNF-α expression were reduced more than 50% in adipose tissue of db/db mice on LS diet when compared with HS db/db mice (all p < 0.05), to levels observed in the HS lean mice. Further, LS db/db mice had significantly reduced circulating MCP-1 and IL-6 levels when compared with HS db/db mice (both p < 0.01).

CONCLUSION

In obese-diabetic mice, long-term LS diet increases adiponectin in heart and adipose tissue and reduces pro-inflammatory factors in adipose tissue and plasma. These additive mechanisms may contribute to the potential cardioprotective benefits of LS diet in obesity-related metabolic disorders.