Salt-responsive gut commensal modulates TH17 axis and disease.

The importance of dietary sodium chloride in the regulation of blood pressure has received much attention over the past few years. This area of research and knowledge has been controversial for several reasons. The major reason for controversy is that the science of the relationship is difficult to ascertain. Population science is limited by the narrow range of dietary sodium intake by most populations and individuals and the multiple confounders in those populations at the extremes of intake. Results from clinical trials have been difficult to interpret because of the difficulty in maintaining a given level of sodium intake over a period of time sufficient for study. Furthermore, basic science studies have been challenged by identifying appropriate models that mimic salt-sensitive hypertension in humans. Moreover, a lack of a well-funded proponent in industry complicates the research challenges. Guyton’s concept that the role of the kidney in handling sodium is key to the long-term regulation of blood pressure is now generally accepted.1 However, the exact role that dietary sodium plays in this relationship remains controversial. The relationship between renal handling of sodium and blood pressure is apparently influenced by a complex combination of factors including nutritional, other environmental, genetic, neurohormonal, and metabolic factors. The skepticism of many regarding the role of dietary sodium in blood pressure regulation and control has been tempered by the results of the DASH sodium study.2 Most acknowledge that this study reliably confirmed the benefit of dietary sodium restriction in blood pressure management. The study showed a dose-dependent impact of dietary sodium restriction on blood pressure in older hypertensive and nonhypertensive subjects. For many interested in this area of research, the questions have shifted as a result of the DASH sodium study. Rather than questioning whether dietary sodium is important, many investigators have turned their …

Consumption of fructose as a sweetener has increased in the past three decades. A high-fructose diet has been implicated in the epidemic of diabetes, obesity, and hypertension. A third of the US population consumes 20-40% of their caloric intake from added sugars, with half of those calories from fructose. Little is known about the role of high fructose intake in renal salt handling and blood pressure regulation during high salt intake. In genetic models of salt-sensitive hypertension, the Na/K/2Cl cotransporter NKCC2 plays an important role by reabsorbing NaCl in the thick ascending limb (TAL). We hypothesized that 20% fructose in drinking water stimulates NKCC2 and sensitizes normal rats to high salt induced hypertension. Adult Sprague-Dawley rats were given 20% fructose or 20% glucose in drinking water for 1 week after which a high salt diet (4% Na in chow) was started. Systolic blood pressure (SBP) was measured every other day by tail cuff after 2 weeks of training. After one week of fructose or glucose alone, SBP did not change. In rats fed fructose, adding a 4% NaCl diet increased SBP to 128±6 mmHg by day 2 (p<0.01 vs glucose) and continued to increase up to 144±18 mmHg after 2 weeks on high salt (p<0.01 vs baseline; p<0.01 vs glucose). In glucose-fed rats high salt did not increase SBP (from 122±6 to 116±9 mmHg). 20% fructose alone for 3 weeks, or high salt alone did not change SBP. NKCC2 phosphorylation at Thr96,101 is associated with enhanced TAL NaCl reabsorption. We found that NKCC2 phosphorylation at Thr96,101 (normalized to total NKCC2) was higher in TALs isolated from rats fed fructose plus salt for 2 weeks compared to high salt alone (high-salt: 100%; fructose + high-salt: 250±40%, p<0.05). We concluded that a high fructose but not high glucose diet induces salt-sensitive hypertension in Sprague Dawley rats. This effect occurs within 1 week of a high fructose diet. In addition, a high fructose diet may stimulate NKCC2 activity by enhancing its phosphorylation. These data suggest that high fructose intake may increase blood pressure by preventing appropriate renal NaCl excretion during high dietary salt intake.

To assess changes in the activity of the brain renin-angiotensin system during (i) the development of salt-sensitive hypertension; and (ii) the prevention of salt-sensitive hypertension by blocking brain 'ouabain'. In protocol I, angiotensin converting enzyme (ACE) mRNA and activity and angiotensin I and II levels were assessed in the hypothalamus and pons of Dahl salt-sensitive (Dahl S) and salt-resistant (Dahl R) rats on regular (120 micromol Na+ per g) or high (1370 micromol Na+ per g) salt diet from 4-6 weeks or 4-9 weeks of age. In protocol II, ACE mRNA and activity were assessed in the hypothalamus and pons in Dahl S on regular or high salt treated with intracerebroventricular (i.c.v.) Fab fragments blocking brain 'ouabain' or gamma-globulins, and in Dahl R on high or regular salt ACE mRNA was assessed by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) assay and angiotensin I and II by radioimmunoassay after high-performance liquid chromatography. In protocol III, effects of i.c.v. angiotensin I and i.c.v. bradykinin on renal sympathetic nerve activity (RSNA), heart rate and blood pressure before and after i.c.v. captopril were assessed in Dahl S and R rats on regular or high salt intake from 4-8 weeks of age. High salt diet caused a gradual, but marked increase in blood pressure in Dahl S but not Dahl R rats. Dahl S rats showed small but significant increases in ACE mRNA in the hypothalamus on regular salt diet. In Dahl S rats on high salt diet for 2 or 5 weeks ACE mRNA levels significantly increased in both hypothalamus and pons, compared with Dahl R rats on either diet or Dahl S rats on regular diet. After 5 weeks of high salt diet, ACE mRNA levels in the hypothalamus in Dahl S rats were almost three-fold higher and in the pons two-fold higher than in Dahl R rats on either diet or Dahl S on regular salt diet. High salt diet also increased ACE activity of the hypothalamus and pons in Dahl S but not Dahl R. Consistent with this increased ACE activity, central responses to angiotensin I were clearly enhanced and to bradykinin markedly diminished in Dahl S on high salt intake. Chronic blockade of brain 'ouabain' by i.c.v. Fab fragments prevented the increases in blood pressure, ACE mRNA and activity in the hypothalamus and pons by high salt intake in Dahl S rats. Angiotensin I levels in the hypothalamus and pons were similar in both groups of rats and there were no significant changes caused by high salt diet in Dahl S and R rats. On regular salt intake angiotensin II levels in the hypothalamus of Dahl S rats showed a significant decrease as compared with Dahl R rats on regular salt diet, and were similar in the pons of the two strains. High salt intake did not affect angiotensin II levels in either hypothalamus or pons in Dahl S and R rats. These results indicate that high salt intake increases blood pressure, ACE expression and activity in the hypothalamus and pons of Dahl S rats without a parallel increase in angiotensin II levels. Effects of high salt intake on ACE mRNA and activity appear to be secondary to activation of brain 'ouabain'.

Acute reduction of salt intake causes an increase in serum lipid and insulin levels in healthy volunteers and patients with essential hypertension, suggesting induction of insulin resistance by salt restriction. Direct measurements of insulin sensitivity using the euglycaemic clamp showed no significant change after 7 days of salt restriction. Our previous study showed a time dependent course of dyslipidaemia after institution of a low salt diet. We therefore assessed insulin sensitivity (M-value) under euglycaemic conditions (clamp technique) at discrete time points using a parallel group design. Two groups of healthy males were examined on high (200 mmol d-1) and low (20 mmol d-1) salt intake. One group (n = 7, 25 +/- 3 years, BMI 22.4 +/- 2.1 kg m-2) received high and low salt diet in random order each for 7 days. The other group (n = 7, 26 +/- 3 years, 22.1 +/- 1.9 kg m-2) received the respective diet in random order for 3 days. A significantly (P < 0.01) different mean M-value was noted in the group receiving the diets for 3 days, i.e. after low salt intake it was 7.4 +/- 1.2 mg kg-1 min-1 and after high salt intake 8.6 +/- 1.1 mg kg-1 min-1. In contrast, the mean M-value was similar after low and high salt periods in the group of individuals who had been studied after 7 days on either salt take (7.8 +/- 1.8 on low salt vs. 7.6 +/- 1.3 mg kg-1 min-1 on high salt).(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in the osmolality and level of angiotensin II (ANG II) are important peripheral signals modulating appropriate central sympathetic output and maintaining a normal arterial pressure during high salt intake. The median preoptic nucleus (MnPO) receives reciprocal inputs from the subfornical organ (SFO) and organum vasculosum of the lamina terminalis (OVLT), the circumventricular organs that have been shown to be necessary in multiple central effects of changes in the osmolality and circulating ANG II directed toward the maintenance of sodium and water homeostasis. We, therefore, hypothesized that the MnPO is a crucial part of the central neuronal mechanisms mediating the blood pressure control by altered osmolality and/or ANG II signaling during chronic high dietary salt intake. Male Sprague-Dawley rats were randomly assigned to either sham (operation), or electrolytic lesion of the MnPO. After a 7-day recovery, rats were instrumented with radiotelemetric transducers and aortic flow probes for the measurement of the mean arterial pressure + heart rate (HR) and cardiac output (CO), respectively. Femoral venous catheters were also implanted to collect blood for the measurements of plasma osmolality and sodium concentration, as well as plasma renin activity. Rats were given another 10 days to recover and then were subjected to a 28-day-long study protocol that included a 7-day control period (1.0% NaCl diet), followed by 14 days of high salt (4.0% NaCl), and a 7-day recovery period (1.0% NaCl). The data showed, that despite a slight increase in the MAP observed in both MnPO- (n = 12) and sham-lesioned (n = 8) rats during the high-salt period, there were no significant differences between the MAP, HR, and CO in the two groups throughout the study protocol. These findings do not support the hypothesis that the MnPO is necessary to maintain normal blood pressure during high dietary salt intake. However, MnPO-lesioned rats showed less sodium balance than sham-lesioned rats during the first 4 days of high salt intake. Although, these results may be explained partly by the plasma hyperosmolarity and hypernatremia observed in MnPO-lesioned rats; they also shed light on the role of the MnPO in central neuronal control of renal sodium handling during chronic high dietary salt intake.

In Black populations excessive salt intake may exacerbate the genetic predisposition to hypertension and promote the early onset of cardiovascular disease. Ethnic differences in the interaction between sodium intake and the metabolome may play a part in hypertension and cardiovascular disease development. We determined (1) urinary amino acid and acylcarnitine profiles of young Black and White adults according to low, moderate, and high dietary salt intake, and (2) investigated the triad of salt intake, systolic blood pressure (SBP), and the associated metabolomics profile. This study included 447 White and 380 Black adults aged 20-30 years from the African-PREDICT study. Estimated salt intake was determined from 24-hour urinary sodium levels. Urinary amino acids and acylcarnitines were measured using liquid chromatography-tandem mass spectrometry. Black adults exhibited no significant differences in SBP, amino acids, or acylcarnitines across low (<5g/day), moderate (5-10g/day), and high (>10g/day) salt intake. White adults with a high salt intake had elevated SBP compared to those with low or moderate intakes (p < 0.001). Furthermore, gamma-aminobutyric acid (GABA) (q = 0.020), citrulline (q = 0.020), glutamic acid (q = 0.046), serine (q = 0.054) and proline (q = 0.054) were lowest in those with higher salt intake. Only in White and not Black adults did we observe inverse associations of clinic SBP with GABA (Adj. R2 = 0.34; Std. β = -0.133; p = 0.003), serine (Adj. R2 = 0.33; Std. β = -0.109; p = 0.014) and proline (Adj. R2 = 0.33; Std. β = -0.109; p = 0.014). High salt intake in White, but not in black adults, were related to metabolomic changes and may contribute to pathophysiological mechanisms associated with increased BP.

in a previous issue of this journal, Elise Gomez-Sanchez et al. ([4][1]) presented unequivocal evidence that intracerebroventricular (ICV) infusion of the 3β-hydroxy steroid dehydrogenase inhibitor trilostane prevented the development of hypertension in response to high-salt intake in Dahl salt-

Epithelial sodium channels (ENaCs) play critical roles in the maintenance of fluid and electrolyte homeostasis, and their genetic abnormalities cause one type of hereditary salt-sensitive hypertension, Liddle syndrome. As we reported previously, both human and rodent Nedd4L/Nedd4-2 showed molecular diversity, with and without a C2 domain in their N-terminal. Nedd4L/Nedd4-2 isoforms with a C2 domain are hypothesized to be related closely to ubiquitination of ENaCs. We generated Nedd4-2 C2 domain knockout mice. We demonstrate here that loss of Nedd4-2 C2 isoform causes salt-sensitive hypertension under conditions of a high dietary salt intake in vivo. The knockout mice had reduced urinary sodium excretion, osmotic pressure and increased water intake and urine volume with marked dilatation of cortical tubules while receiving a high salt diet. To the contrary, there was no difference in metabolic data between wild-type and knockout mice receiving a normal control diet. In the absence of Nedd4-2 C2 domain, a high salt intake accelerated ENaC expression. Coimmunoprecipitation studies revealed suppressed ubiquitination for ENaC with a high salt intake. Taken together, our findings demonstrate that during a high oral salt intake the Nedd4-2 C2 protein plays a pivotal role in maintaining adaptive salt handling in the kidney.

Insulin-dependent diabetes mellitus (IDDM) patients may have an increased intrarenal angiotensin II activity. In diabetic patients, captopril increases the renal hemodynamic response to an amino acid infusion. We investigated the effects of two salt diets on arterial pressure and renal response to a protein load in 10 normotensive (blood pressure < 140/90 mm Hg) IDDM patients (aged 30 +/- 3 years) who had diabetes for 7 +/- 4 years and normoalbuminuria levels [albumin excretion rate 4.8 (2.5-19.1) microg/min]. After 1 week of normal (approximately 100 mmol/day; approximately 100 mEq/l) and 1 week of high (approximately 300 mmol/day; approximately 300 mEq/l) salt intake, renal hemodynamic studies were performed at baseline and after a protein load (meat meal) of 100 g/1.73 m2. The mean 24-hour urinary sodium excretion levels were 99 +/- 27 and 293 +/- 80 mmol (mEq) with normal and high salt intake, respectively. No significant changes were seen in plasma sodium and glucose control with the normal and high salt diets, respectively: plasma sodium 135 +/- 3 vs. 137 +/- 1 mmol/l (mEq/l), (p = 0.08) and glycated hemoglobin 9.1 +/- 1.9 vs. 9.4 +/- 2.1% (p = 0.36). The body weight (70.9 +/- 12 vs. 71.8 +/- 13 kg; p = 0.015) was significantly higher with a high salt diet. The mean arterial pressure was similar with both diets (normal vs. high salt diet 91 +/- 9 vs. 89 +/- 6 mm Hg, p = 0.25). The plasma renin concentration [28 +/- 15 vs. 16 +/- 6 microU/ml(168 +/- 90 vs. 96 +/- 36 pmol/l), p = 0.013] and angiotensin II [8.8 +/- 4.4 vs. 6.4 +/- 3.5 pg/ml (0.052 +/- 0.025 vs. 0.038 +/- 0.021 nmol/l), p = 0.016] were significantly lower with the high salt diet. Following protein loading, the glomerular filtration rate increased with both diets: normal salt diet 114 +/- 26 vs. 128 +/- 30 ml/min/1.73 m2(1.9 +/- 0.43 vs. 2.13 +/- 0.50 ml/s/1.73 m2), p = 0.04; high salt diet 118 +/- 23 vs. 127 +/- 29 ml/min/1.73 m2 (1.97 +/- 0.38 vs. 2.12 +/- 0.48 ml/s/1.73 m2), p = 0.13. The change in renal plasma flow was similar to that of the glomerular filtration rate with normal and high salt intake, respectively: 566 +/- 94 vs. 617 +/- 142 ml/min/1.73 m2 (9.44 +/- 1.57 vs. 10.29 +/- 2.37 ml/s/173 m2), p = 0.0017; 572 +/- 125 vs. 600 +/- 110 ml/min/1.73 m2 (9.54 +/- 2.08 vs. 10.00 +/- 1.83 ml/s/1.73 m2), p = 0.057. In this subset of normotensive normoalbuminuric IDDM patients, a high salt intake did not promote an exaggerated renal response to the protein load despite inhibition of the renin-angiotensin system.

High salt consumption has since long been associated with elevated blood pressure and cardiovascular disease. Recently, mouse studies suggested that a high dietary salt intake exacerbates the clinical manifestations of autoimmunity. Using naïve cells ex vivo after pre-exposure of mice to high salt intake, we showed that increased salt exposure affects the viability and effector functions of immune cells. CD4+ T-cells evidenced a pro-inflammatory phenotype characterized by increased secretion of IFNγ and IL-17A, when exposed to high salt concentrations in vitro. Interestingly, this phenotype was associated with osmotic pressure, as replacing salt for d-mannitol resulted in similar observations. However, high salt intake did not alter the development of T-cell-dependent autoimmunity. Instead, recruitment of peritoneal macrophages was increased in mice pre-exposed to high salt concentrations. These cells had an increased production of both TNFα and IL-10, suggesting that salt stimulates expansion and differentiation of different subsets of macrophages. Moreover, mice pre-exposed to high salt intake developed exacerbated symptoms of colitis, when induced by dextran sulphate sodium. The aggravated colitis in salt-exposed animals was associated with a higher frequency of CD4+ T-cells and CD11b+ CD64+ macrophages producing TNFα. These phenotypes correlated with elevated titres of faecal IgA and higher lymphocytic cellularity in the colon, mesenteric lymph nodes and spleen. In conclusion, we report here that high salt intake affects both lymphoid and myeloid cells ex vivo. However, the effects of high salt intake in vivo seem less pronounced in terms of CD4+ T-cell responses, whereas macrophage-dependent pathologies are significantly influenced.

High salt intake in pregnancy alters maturation of glomeruli in the rat offspring

The effects of combined behavioral stress and high dietary salt on blood pressure were examined in baboons (N = 4) over the course of 1 year. Either high salt diet (240 mEq Na+/day) or conflict stress were administered for 8 to 16 weeks, followed by high salt intake and stress combined. Mean arterial pressure (MAP) increased by 8 mmHg during high dietary salt alone, by 4 mmHg during stress alone, and increased further to 14 mmHg above baseline during combined salt and stress. Control baboons (N = 2) had no change in MAP across 47 weeks. The data indicate additive effects of chronic high dietary salt intake and behavioral stress on blood pressure in non-human primates.

The relationship between sodium (salt) intake and blood pressure has been convincingly established by epidemiological, observational, interventional, physiological, and some genetic evidence for some time. Yet the interaction remains the subject of passionate and heated debate. Even among those who are convinced of the salt–blood pressure interaction, some advocate a population-wide attempt to reduce dietary salt intake, arguing on the basis of epidemiological and interventional evidence, and others who suggest that such interventions should be targeted toward those most likely to benefit: the “salt-sensitive” subpopulation. Studies have characterized such subgroups on the basis of higher blood pressure, increased age or African-American ethnicity.1 The issue is rendered even more compelling by the findings that salt sensitivity can be identified among “normotensive” subjects (ie, those with blood pressure <140/90) as well as those with hypertension1 and the designation of those with blood pressure levels between 120 and 139 mm Hg systolic and 80 and 89 diastolic as prehypertensive2 and at increased risk for development of fixed hypertension and for cardiovascular events compared with those with lower blood pressure.3 Observational data have provided a starting point for the quantitative considerations of dietary salt intake. The most recent (1999–2000) NHANES survey provides an estimated dietary sodium intake based on food records, excluding discretionary sodium, of 135 to 204 mmol per day for men and 100 to 135 mmol per day for women in the United States.4 Questionnaires are acknowledged to underestimate actual intake, and urinary sodium excretion has been shown to provide a more accurate index of total sodium intake because it represents ≈93% of intake at steady-state conditions.5 A recent British survey reported that urinary sodium excretion averaged 187 mmol per day for men and 139 mmol per day for women.5 This was very similar to …

Objective: Excessive salt intake is the leading dietary risk factor for cardiovascular disease (CVD). This increased risk may be attributed to alterations in the human metabolome. Salt sensitivity is associated with ethnicity, and ethnic differences in the interaction between sodium intake and the metabolome may play an integral part in CVD development. We therefore investigated 1) the urinary metabolomic profiles of Black and White adults according to low, moderate and high dietary salt intake; and 2) explored the relationships of identified metabolites with blood pressure. Design and Methods: This study included data of White (N = 447) and Black (N = 380) adults aged 20 to 30 years from the African-PREDICT study. Estimated salt intake was determined from 24hr urinary sodium. Urinary amino acids and acylcarnitines were measured using liquid chromatography tandem mass spectrometry. Clinic, 24hr and central systolic blood pressure (SBP) were measured. Results: Whites with a high salt intake (&gt; 10 g/day) had higher SBP (clinic, 24hr and central) compared to those with low (&lt; 5 g/day) or moderate (5 to 10 g/day) salt intakes (all p &lt; 0.05). The metabolites GABA (q = 0.020), citrulline (q = 0.020), glutamic acid (q = 0.046), serine (q = 0.054) and proline (q = 0.054) were lower in those with higher salt intake. In stepwise multivariable adjusted regression analyses, we found that clinic SBP of white adults were inversely associated with GABA (Adj. R2 = 0.35; Std. β=-0.123; p = 0.005), serine (Adj. R2 = 0.35; Std. β=-0.099; p = 0.022) and proline (Adj. R2 = 0.35; Std. β=-0.099; p = 0.021), and central SBP with GABA (Adj. R2 = 0.34; Std. β=-0.094; p = 0.036), glutamic acid (Adj. R2 = 0.34; Std. β=-0.090; p = 0.035) and proline (Adj. R2 = 0.034; Std. β=-0.106; p = 0.015). In Black adults, there were no differences in SBP or metabolites between low, moderate or high salt intake groups, with no relationships between SBP and GABA, glutamic acid, citrulline, serine or proline. Conclusion: In White adults, high salt intake was associated with low levels of GABA, glutamic acid, serine and proline, which in turn were related to high SBP. We hypothesise that metabolomic changes are related to salt intake and may contribute to pathophysiological mechanisms associated with increased blood pressure.

In response to a high salt intake, salt-sensitive hypertensive individuals retain more sodium and manifest a rise in blood pressure greater than that in salt-resistant individuals. In this study, we tested whether salt sensitivity might be related at least in part to reduced secretion of atrial natriuretic peptide (ANP) or to abnormal nitric oxide production. We measured plasma ANP and NO2+NO3 in 7 normotensive individuals and 13 salt-sensitive and 14 salt-resistant blacks with essential hypertension under conditions of low (10 mEq/d) and high (250 mEq/d) salt intake. To evaluate possible racial differences in ANP secretion, we also measured plasma ANP in 6 salt-sensitive and 8 salt-resistant hypertensive whites during low and high salt intakes. Under low salt conditions, plasma ANP levels were not different in normotensive control subjects and salt-sensitive and salt-resistant hypertensive blacks. During high salt intake, plasma ANP levels did not change in control subjects and salt-resistant patients but decreased in salt-sensitive patients. ANP levels after high salt diet were lower (P < .01) in salt-sensitive than salt-resistant blacks. In hypertensive whites, high salt intake caused no significant change in plasma ANP. Under low salt conditions, plasma NO2+NO3 levels were higher (P < .05) in salt-sensitive (189 +/- 7.9 mumol/L) and salt-resistant (195 +/- 13.5 mumol/L) black patients than in control subjects (108 +/- 9.7 mumol/L). During high salt intake, plasma NO2+NO3 decreased significantly (P < .01) in both salt-sensitive (150 +/- 7.0 mumol/L) and salt-resistant (142 +/- 9.0 mumol/L) patients. These studies show that under conditions of high salt intake, salt-sensitive hypertensive blacks manifest a paradoxical decrease in ANP secretion. This abnormality may play a role in the reduced ability of these individuals to excrete a sodium load and in the sodium-induced rise in blood pressure. This study does not support the hypothesis that salt sensitivity depends on a deficit of nitric oxide production, but it suggests that high salt intake may alter the endothelium-dependent adaptation of peripheral resistance vessels.