Klotho Gene in Human Salt-Sensitive Hypertension.

Infiltrating T cells in the kidney amplify salt-sensitive (SS) hypertension and renal damage, but the mechanisms are not known. Genetic deletion of T cells (SSCD247-/-) or of the p67phox subunit of NADPH oxidase 2 (NOX2; SSp67phox-/-) attenuates SS hypertension in the Dahl SS rat. We hypothesized that reactive oxygen species produced by NOX2 in T cells drive the SS phenotype and renal damage. T cells were reconstituted by adoptively transferring splenocytes (∼10 million) from the Dahl SS (SS→CD247) rat, the SSp67phox-/- rat (p67phox→CD247), or only PBS (PBS→CD247) into the SSCD247-/- rat on postnatal day 5. Animals were instrumented with radiotelemeters and studied at 8 wk of age. There were no detectable differences in mean arterial pressure (MAP) or albuminuria between groups when rats were maintained on a low-salt (0.4% NaCl) diet. After 21 days of high-salt diet (4.0% NaCl), MAP and albuminuria were significantly greater in SS→CD247 rats compared with p67phox→CD247 and PBS→CD247 rats. Interestingly, there was no difference between p67phox→CD247 and PBS→CD247 rats in albuminuria or MAP after 21 days. The lack of CD3+ cells in PBS→CD247 rats and the presence of CD3+ cells in rats that received the T cell transfer demonstrated the effectiveness of the adoptive transfer. No differences in the number of CD3+, CD4+, or CD8+ cells were observed in the kidneys of SS→CD247 and p67phox→CD247 rats. These results indicate that reactive oxygen species produced by NOX2 in T cells participates in the amplification of SS hypertension and renal damage.NEW & NOTEWORTHY Our current work used the adoptive transfer of T cells that lack functional NADPH oxidase 2 into a genetically T cell-deficient Dahl salt-sensitive (SS) rat model. The results demonstrated that reactive oxygen species produced by NADPH oxidase 2 in T cells participate in the amplification of SS hypertension and associated renal damage and identifies a potential mechanism that exacerbates the salt-sensitive phenotype.

Previous studies utilizing the SS p67 phox–/– rat have demonstrated the importance of systemic NADPH oxidase NOX2-derived reactive oxygen species (ROS) production in the pathogenesis of Dahl Salt-Sensitive (SS) hypertension and renal damage. Our laboratory has established a key role for renal immune cell infiltration in the development of SS hypertension and observed an enrichment of NOX2 subunits in infiltrating T cells. The contribution of ROS specifically derived from immune cells in SS hypertension remains unknown. To assess the role of ROS in immune cells, SS p67 phox–/– rats underwent total body irradiation and received bone marrow transfer from either SS p67 phox–/– (p67/p67) or SS (p67/SS) donor rats. p67/SS rats would be capable of producing NOX2-derived ROS only in the transferred SS cells of hematopoietic origin while the p67/p67 control group would be unable to produce NOX2-derived ROS globally. Mean arterial pressure (MAP) was not different between the p67/SS and p67/p67 rats when fed a 0.4% NaCl diet (112.6±1.4 vs 110.7±2.4 mmHg, n=4-5). After 3 weeks of high salt, however, there was a significantly greater increase in MAP in the p67/SS rats (176.1±4.7 mmHg) compared to the p67/p67 control rats (147.9±8.4 mmHg), which was accompanied by a significant increase in albuminuria (230.3±13.9 vs 153.1±14.9 mg/day, p67/SS vs p67/p67, n=5-6). Interestingly, upon analysis of the immune cells in the kidney, no differences were detected in the number of CD45+ total leukocytes, CD11b/c+ monocytes/macrophages, CD3+ T cells, and CD45R+ B cells between the p67/SS and p67/p67 (n=4-5), indicating that the recruitment of immune cells into the kidney during hypertension and renal damage is independent of NOX2-derived ROS production from the renal parenchyma. The respiratory burst response to phorbol 12-myristate 13-acetate stimulus (135 μM) in peritoneal macrophages isolated from p67/SS was 4.0-fold greater compared to nonresponsive p67/p67 cells, and was completely inhibited by superoxide dismutase, demonstrating that the reconstituted bone marrow cells in the p67/SS are capable of producing superoxide. In summary, the production of NOX2-derived ROS from immune cells alone is sufficient for the development of Dahl SS hypertension and renal damage.

P129 The aim of the study was to evaluate endothelial function in a group of essential hypertensive patients classified on the basis of their salt sensitivity. Forty hypertensive patients were placed on two 7-day periods of low (50 mmol/day) and high (250 mmol/day) salt intakes. Salt sensitivity was defined as a significant rise (p<0.05) in 24-hour mean blood pressure (MBP), from low to high salt intake, measured by ambulatory blood pressure monitoring. Endothelial function was determined by the increase in the forearm blood flow (FBF) (strain-gauge plethysmography) to intrabrachial infusion of increasing doses of acetylcholine and sodium nitroprusside, before and after the addition of the NO synthase inhibitor, L-NMMA. Nineteen hypertensive patients significantly increased MBP with high salt intake (from 105 ± 2.6 to 112.5 ± 2.5 mmHg)and were considered salt sensitive (SS). In contrast, 21 patients did not modify their MBP after high salt intake (from 102 ± 3 to 100 ± 3 mmHg) and were diagnosed as having salt resistant hypertension (SR). The vasodilation response to acetylcholine was significantly blunted (p=0.001) in SS patients (FBF rose from 4.5 ± 0.2 to 20.6 ± 1.4 mL/100mL of forearm tissue [FT] per minute) when compared to SR (FBF rose to 4.4 ± 0.3 to 28.4 ± 1.7 mL/100mL FT per minute). Maximal acetylcholine-dependent vasodilation was inversely correlated with the MBP increase with high salt intake (r=-0.47; p=0.003). Sodium nitroprusside-related vasodilation was similar in SS and SR patients (from 4.4 ± 0.1 to 22.4 ± 1.1 mL/100mL/min in SS and from 4.5 ± 0.2 to 23.9 ± 1.3 mL/100mL/min in SR; p=0.4). In SS patients, L-NMMA infusion cause a decrease in baseline FBF (4.5 ± 0.2 to 3.2 ± 0.1 mL/100mL/min, whereas the response to acetylcholine was not significatively affected (from 3.2 ± 0.1 to 18.1 ± 1.8 mL/100mL/min) In SR patients, L-NMMA infusion also decreases baseline FBF (from 4.3 ± 0.2 to 3.1 ± 0.1 mL/100mL/min) and the response to acetylcholine was impaired in this group(from 3.1 ± 0.1 to 20.5 ± 1.4 mL/100mL/min). We conclude that salt-sensitive hypertension is associated with a higher degree of endothelial dysfunction. This deficient vasodilation may be secondary to an alteration in the L-arginine-NO pathway.

NOX2-derived reactive oxygen species in immune cells exacerbates salt-sensitive hypertension

Dopaminergic modulation of salt sensitivity in patients with essential hypertension

Increased Levels of Atherosclerosis Markers in Salt-Sensitive Hypertension

Infiltration of T cells into the kidney of the Dahl Salt Sensitive (SS) rat model of human disease accompanies the development of salt-sensitive hypertension and renal damage. Deletion of T cells on the Dahl SS genetic background (SSCD247−/−) attenuates hypertension and renal damage, and subsequent replacement of T cells by splenocyte transfer restores the disease phenotype. The present studies were performed to assess if the T cell subtype (CD4+ vs CD8+) is important in Dahl SS hypertension and interrogate the mechanism of action. In initial experiments, adoptive transfer of purified CD4+ or CD8+ T cells (~5 million) from splenocytes isolated from the Dahl SS (CD4+ SS→CD247 or CD8+ SS→CD247) or PBS vehicle (PBS→CD247) into the SSCD247−/− rat was performed on postnatal day 5. Animals were recovered and instrumented with radiotelemeters at 7 weeks of age. After a week of recovery, baseline measurements of blood pressure and albumin excretion were obtained while rats were fed a low salt (LS, 0.4% NaCl) diet. Rats were then switched to a high salt (HS, 4.0% NaCl) diet for 21 days, with continuous blood pressure measurements and urine collections every 7 days. On day 21, the rats were euthanized, and their kidneys were perfused and collected for immune cell analysis by flow cytometry. During the LS baseline period there was no significant difference observed in mean arterial pressure (MAP) between the CD4+ SS→CD247, CD8+ SS→CD247, or PBS→CD247 groups (113±1, 115±1, 114±1 mmHg; n=21, 10, 24, respectively). After three weeks of HS, rats receiving CD4+ T cells from the SS (CD4+ SS→CD247) demonstrated an amplified salt-sensitive hypertension (154±3 mmHg) and albuminuria (184±22 mg/day) compared to blood pressure (140±3 and 145±3 mmHg) and albuminuria (82±9 and 85±8 mg/day) in the CD8+ SS→CD247 or PBS→CD247 groups, respectively. Since the deletion of the p67phox subunit of NADPH oxidase 2 (NOX2) in adoptively transferred splenocytes attenuated Dahl SS hypertension and kidney damage, parallel studies examined the influence of deletion of p67phox in CD4+ (n=14) and CD8+ T cells (n=8). The adoptive transfer of either CD4+ or CD8+ T cells lacking functional NOX2 did not alter the LS or HS blood pressure or albuminuria when compared to the PBS control group. Finally, a flow cytometric analysis at the end of the experiment confirmed the absence of CD3+ T cells in the PBS→CD247 and documented the reconstitution of equal numbers of CD4+ cells in the blood and kidney of the rats receiving CD4+ cells with intact or deficient NOX2. Interestingly, no difference was observed in CD8+ T cells in the kidney and blood of rats receiving CD8+ cells with intact or deficient NOX2, but a significant number of CD4+ T cells were also observed in the SSCD247−/− rats receiving the purified CD8+ T cells. In summary, these studies demonstrate that CD4+ T cells amplify salt-sensitive hypertension and renal damage in the Dahl SS via a NOX2-dependent mechanism while CD8+ T cells do not alter disease phenotypes when compared to PBS control. GRANTS: HL161231, HL166458, Georgia Research Alliance. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Salt sensitive hypertension is characterized by increases in blood pressure in response to increases in dietary salt intake and is associated with an enhanced risk of cardiovascular and renal morbidity. Although researchers have sought for decades to understand how salt sensitivity develops in humans, the mechanisms responsible for the increases in blood pressure in response to high salt intake are complex and only partially understood. Until now, scientists have been unable to explain why some individuals are salt sensitive and others are salt resistant. Although a central role for the kidneys in the development of salt sensitivity and hypertension has been generally accepted, it is also recognized that hypertension is of multifactorial origin and a variety of factors can induce, or prevent, blood pressure responsiveness to the manipulation of salt intake. Excess salt intake in susceptible persons may also induce inappropriate central and sympathetic nervous system responses and increase the production of intrarenal angiotensin II, catecholamines and other factors such as oxidative stress and inflammatory cytokines. One key factor is the concomitant inappropriate or paradoxical activation of the intrarenal renin-angiotensin system, by high salt intake. This is reflected by the increases in urinary angiotensinogen during high salt intake in salt sensitive models. A complex interaction between neuroendocrine factors and the kidney may underlie the propensity for some individuals to retain salt and develop salt-dependent hypertension. In this review, we focus mainly on the renal contributions that provide the mechanistic links between chronic salt intake and the development of hypertension.

SummaryBackgroundThe mechanisms of salt sensitivity as an important intermediate phenotype of essential hypertension remain elusive. A novel theory proposes that lymphatic vessels regulate sodium and fluid homeostasis. Since vascular endothelial growth factor C (VEGF-C) plays a vital role in lymphatic capillary hyperplasia, we hypothesized that VEGF-C was involved in salt-sensitive hypertension. We therefore investigated its plasma concentration in salt-sensitive subjects.Material/MethodsTwenty-seven subjects (BP ≤160/100 mmHg; age range 25–50 years) from a rural community of northern China were enrolled in this study. The baseline BP of volunteers was monitored for 3 days, followed by a low-salt diet for 7 days (3 g/day, NaCl) and a high-salt diet for 7 days (18 g/day, NaCl). Those who exhibited a BP increase of 10% from low-salt period to high-salt period were diagnosed as salt-sensitive subjects. The concentration of plasma VEGF-C was measured by an immunoenzyme method (ELISA).ResultHigh salt intake significantly increased the plasma VEGF-C level. It was higher in the salt-sensitive subjects (3642.2±406.1 pg/ml) than in the salt-resistant subjects (2249.8±214.6 pg/ml). The comparison of VEGF-C levels between the 2 groups had significant statistical difference (P<0.01).ConclusionsThe VEGF-C level increases significantly in the salt-sensitive subjects after high salt intake. VEGF-C could be used as a biomarker of salt sensitivity.

Salt-sensitive hypertension is a complex disease associated with genetic factors. This study aimed to identify the association between 29 candidate single-nucleotide polymorphisms and salt-sensitive hypertension in a Han Chinese population. Sixty-three participants with salt-sensitive hypertension and 279 controls with salt-resistant hypertension were recruited. A modified Sullivan's acute oral saline load and diuresis shrinkage test was used to detect blood pressure salt sensitivity. Lifestyle risk factors were obtained via a questionnaire. We used the Sequenom Mass ARRAY Platform to genotype the 29 candidate single-nucleotide polymorphisms, and the cumulative genetic risk score was used to evaluate the joint genetic effect. The frequencies of eight genotypes and five alleles in CYP11B2, PRKG1, ADRB2, FGF5, SLC8A1 and BCAT1 genes differed significantly between the salt-sensitive and salt-resistant hypertension groups. Multiple logistic regression adjusted for age and sex showed that subjects carrying rs7897633-A (PRKG1), rs434082-A (SLC8A1) and rs1042714-G (ADRB2) risk alleles had 1.83-, 2.84- and 2.40-fold increased risk for salt-sensitive hypertension, respectively. Combined risk allele analysis using the cumulative genetic risk score showed that subjects carrying one risk had 2.30-fold increased risk, and those carrying 2-4 risks had 3.32-fold increased risk for salt-sensitive hypertension. Among 29 candidate single-nucleotide polymorphisms, rs7897633-A in PRKG1, rs434082-A in SLC8A1 and rs1042714-G in ADRB2 were significantly associated with salt-sensitive hypertension. A joint effect of single-nucleotide polymorphisms from different pathways contributed to a high risk of salt-sensitive hypertension.

The mechanisms of salt-sensitive (SS) hypertension are complex and far from clear. Available medications are insufficient to control blood pressure (BP) in the SS subjects, and there is a need for the development of novel effective therapies. SS hypertension is accompanied with an early onset of proteinuria, which results from the loss of podocytes. Many reports highlight that in this disease ultrastructural abnormalities and deficient metabolism in the renal mitochondria may precede histological injury. We hypothesized that podocyte damage occurs in part due to mitochondria dysfunction. Dahl SS rats were used here as an established animal model of SS hypertension. All rats were fed a 0.4% NaCl (normal salt, NS) diet until 8 weeks of age when they were challenged with a high salt (HS) 4% NaCl diet for 21 days. At the end of the protocol BP was measured, kidneys were cleared from blood, tissues were collected, and cortical glomeruli were isolated and subjected to imaging, WB and other applications. Systolic BP was elevated in the HS diet fed rats (171±9 vs 148±6 mmHg in HS vs NS diet fed rats). HS diet fed rats exhibited renal lesions, kidney hypertrophy, decreased GFR and exacerbated glomeruli damage compared to the NS group. We did not observe changes in the renal cortical expression of PGC1α; cortical mtDNA content (ND1 and ND6 gene expression vs genomic DNA) was not affected by a HS diet. Seahorse assay performed on freshly isolated glomeruli revealed that basal mitochondria respiration, maximal respiration, and spare respiratory capacity were lower in the HS group (28 ± 14%, 47 ± 15% and 37 ± 9% lower, respectively, vs NS group). No difference was observed in ATP production, or mitochondrial Complex V (ATPase) activity (expressed as oxidation rate of NADH and measured in glomerular pellets). Using confocal imaging and mitoPY1 staining we detected higher baseline H 2 O 2 level, lower antioxidant capacity, and fragmented mitochondria in the podocytes of the glomeruli isolated from HS diet fed group. EM analysis showed that HS mitochondria have structural abnormalities (swelling, enlargement, less defined cristae, and reduced number). We conclude that glomerular mitochondria in SS hypertension are functionally and structurally impaired.

Dahl salt-sensitive (SS) hypertensive rats exhibit increased expression of renal (pro)renin receptor (PRR) and aberrant activation of the intrarenal renin-angiotensin system (RAS) with unclear functional implication. Recent evidence demonstrates that soluble PRR (sPRR) serves as a potential regulator of tubular transport via activating Wnt/ β-catenin pathway in the distal nephron and is derived from the cleavage by site-1 protease (S1P). The present study attempted to define the role of sPRR during salt-sensitive hypertension in SS rats. The effect of S1P inhibitor PF-429242 (PF at 20 mg/kg/d via mini-pump) on blood pressure, proteinuria, and urinary renin were tested in SS rats during high salt loading. In a separate group, a recombinant sPRR (sPRR-His at 20 μg/kg/d) was infused via catheterization of jugular vein to SS rats during PF treatment. In High sodium (HS)-loaded SS rats, administration of PF attenuated the hypertension development (MAP on day 10, HS+PF group: 124.5 ± 4.6 mmHg vs. HS group: 144.1 ± 8.2 mmHg) as assessed by radiotelemetry and proteinuria (HS+PF group: 50.9 ± 5.5 μg/24h vs. HS group: 105.3 ± 7.4 μg/24h). PF treatment reduced HS-stimulated urinary sPRR excretion by 65% in SS rats. Supplement of sPRR restored HS-induced hypertension during PF treatment (MAP on day 10, HS+PF+sPRR-His group: 138.7 ± 6.1 vs. HS+PF group: 124.5 ± 4.6 mmHg) and proteinuria (HS+PF+sPRR-His group: 79.0 ± 5.8 μg/24h vs. HS+PF group: 50.9 ± 5.5 μg/24h) in SS rats. Concurrently, PF treatment reduced HS-stimulated urinary renin activity (by 80%), aldosterone excretion (by 36%) and renal medullary prorenin and renin (by 60%), which were all restored by sPRR-His infusion (1.5- to 3-fold). Indices of Wnt/β-catenin pathway including protein levels of renal cytosolic Axin-2 and nuclear β-catenin as assessed by immunoblotting were elevated by HS (3.4-fold, 2.2-fold respectively) in SS but not SR rats, which were all suppressed by S1P inhibition (by 80% and 50% respectively) and restored by sPRR-His infusion. Given β-catenin signaling as a known regulator of intrarenal RAS, our results suggest that S1P-derived sPRR plays a pathogenic role in salt-sensitive hypertension in SS rats via β-catenin/intrarenal RAS pathway.

It has long been recognized that in some people substantially increasing dietary intake of salt (NaCl) increases blood pressure, whereas in others, “salt loading” has little or no effect on blood pressure.1 Blood pressure so affected by salt has been called salt sensitive and salt resistant, respectively. Although the blood pressure response to salt is a continuous variable and the trait of salt sensitivity, like that of hypertension, is arbitrarily defined,2 it has been estimated that 30% to 50% of hypertensive humans are salt sensitive and ≈25% of normotensive humans are salt sensitive.3,4 Salt sensitivity confers an increased risk for the occurrence of hypertension and cardiovascular disease.5–7 Furthermore, pathophysiological mechanisms mediating salt sensitivity may contribute to the risk for cardiovascular disease beyond their effects on blood pressure.5 Accordingly, the mechanisms of salt sensitivity continue to be studied intensively with the hope that better understanding of those mechanisms could lead to improved approaches to the prevention and treatment of salt-induced increases in blood pressure and cardiovascular disease. Response by Hall on p 893 Prevailing theory holds that an abnormally large increase in renal retention of salt8–16 is an early pathophysiological event in the causation of salt sensitivity and salt-induced hypertension. In accord with this theory, it is held that a substantial increase in dietary salt does not induce a pressor effect in salt-resistant subjects because they excrete a salt load more rapidly and retain less sodium than salt-sensitive individuals.12,17 In the present analysis, we challenge this conventional view of salt sensitivity/salt resistance and make the case for a “vasodysfunction” theory for the initiation of salt-induced hypertension: An abnormal vascular resistance response to increases in salt intake, in the absence of an abnormally large increase in renal …

Cyclooxygenase (COX)-2, an inducible isoform of the major rate-limiting enzymes that regulate the production of prostaglandins is associated with injury, inflammation and proliferation. We sought to examine whether plasma COX-2 levels and its genetic variants is associated with salt sensitivity, BP changes and/or hypertension in humans. Eighty participants (aged 18-65 years) were maintained sequentially either on a usual diet for 3 days, a low-salt diet (3.0 g) for 7 days, and a high-salt diet (18.0 g) for an additional 7 days. In addition, we studied participants of the original Baoji Salt-Sensitive Study, recruited from 124 families from seven Chinese villages in 2004 who received the same salt intake intervention, and evaluated them for the development of hypertension. Plasma COX-2 levels were significantly decreased with reduction of salt intake from the usual to a low-salt diet and decreased further when converting from the low-salt to the high-salt diet. SNPs rs12042763 in the COX-2 gene was significantly associated with SBP responses to both low-salt and high-salt diet. SNPs rs689466 and rs12042763 were significantly associated with longitudinal changes in BPs. In addition, several COX-2 SNPs were significantly associated with incident hypertension over an 8-year follow-up. Gene-based analyses also supported the overall association of COX-2 with longitudinal changes in SBP and hypertension incidence. This study shows that dietary salt intake affects plasma COX-2 levels and that COX-2 may play a role in salt sensitivity, BP progression and development of hypertension in the Chinese populations studied.

Salt sensitivity, a trait characterized by a pressor blood pressure response to increased dietary salt intake, has been associated with higher rates of cardiovascular target organ damage and cardiovascular disease events. Recent experimental studies have highlighted the potential role of the natriuretic peptides and aldosterone in mediating salt sensitivity. Prospective cohort study. We evaluated 1575 non-hypertensive Framingham Offspring cohort participants (mean age 55 ± 9 years, 58% women) who underwent routine measurements of circulating aldosterone and N-terminal proatrial natriuretic peptide (NT-ANP) and assessment of dietary sodium intake. Participants were categorized as potentially 'salt sensitive' if their serum aldosterone was >sex-specific median but plasma NT-ANP was ≤sex-specific median value. Dietary sodium intake was categorized as lower versus higher (dichotomized at the sex-specific median). We used multivariable linear regression to relate presence of salt sensitivity (as defined above) to longitudinal changes (Δ) in systolic and diastolic blood pressure on follow-up (median four years). Participants who were 'salt sensitive' (N = 437) experienced significantly greater increases in blood pressure (Δ systolic, +4.4 and +2.3 mmHg; Δ diastolic, +1.9 and -0.3 mmHg; on a higher versus lower sodium diet, respectively) as compared to the other participants (Δ systolic, +2.8 and +1.0 mmHg; Δ diastolic, +0.5 and -0.2 mmHg; on higher versus lower sodium diet, respectively; P = 0.033 and P = 0.0127 for differences between groups in Δ systolic and Δ diastolic blood pressure, respectively). Our observational data suggest that higher circulating aldosterone and lower NT-ANP concentrations may be markers of salt sensitivity in the community. Additional studies are warranted to confirm these observations.