Jennifer J. DuPont

High Dietary Sodium Intake Impairs Endothelium-Dependent Dilation in Healthy Salt-Resistant Humans

Background: Excess dietary sodium has been linked to the development of hypertension and other cardiovascular diseases. In humans, the effects of sodium consumption on endothelial function have not been separated from the effects on blood pressure. The present study was designed to determine if dietary sodium intake affected endothelium-dependent dilation (EDD) independently of changes in blood pressure. Method: Fourteen healthy salt-resistant adults were studied (9M, 5F; age 33 ± 2.4 years) in a controlled feeding study. After a baseline run-in diet, participants were randomized to a 7-day high-sodium (300–350 mmol/day) and 7-day low-sodium (20 mmol/day) diet. Salt resistance, defined as a 5 mmHg or less change in a 24-h mean arterial pressure, was individually assessed while on the low-sodium and high-sodium diets and confirmed in the participants undergoing study (low-sodium: 85 ± 1 mmHg; high-sodium: 85 ± 2 mmHg). EDD was determined in each participant via brachial artery flow-mediated dilation on the last day of each diet. Results: Sodium excretion increased during the high-sodium diet (P < 0.01). EDD was reduced on the high-sodium diet (low: 10.3 ± 0.9%, high: 7.3 ± 0.7%; P < 0.05). The high-sodium diet significantly suppressed plasma renin activity (PRA), plasma angiotensin II, and aldosterone (P < 0.05). Conclusion: These data demonstrate that excess salt intake in humans impairs endothelium-dependent dilation independently of changes in blood pressure.

Dietary sodium loading impairs microvascular function independent of blood pressure in humans: role of oxidative stress.

•  Pre‐clinical studies suggest that acute dietary sodium loading impairs vascular function without alterations in blood pressure; however, human data are lacking. •  In this study, normotensive salt‐resistant adults participated in a controlled feeding study, in which they consumed a low‐sodium diet for 1 week and a high‐sodium diet for 1 week, in random order. During each diet, microvascular function was assessed. •  Here we report the novel finding of sodium‐induced impairments in microvascular function independent of blood pressure in healthy adults. •  We additionally show that function was improved by the administration of the anti‐oxidant ascorbic acid. •  Therefore, in addition to its well‐known importance for blood pressure control, lowering sodium intake may have beneficial effects on microvascular function in healthy normotensive adults.

Ascorbic acid or l-arginine improves cutaneous microvascular function in chronic kidney disease

We sought to determine whether oxidative stress or a relative deficit of l-arginine plays a role in reducing cutaneous vasodilation in response to local heating in chronic kidney disease (CKD). Eight patients with stage 3-4 CKD and eight age- and sex-matched healthy control (HC) subjects were instrumented with four microdialysis (MD) fibers for the local delivery of 1) Ringers solution (R), 2) 20 mM ascorbic acid (AA), 3) 10 mM l-arginine (l-Arg), and 4) 10 mM N(G)-nitro-l-arginine methyl ester (l-NAME). Red blood cell (RBC) flux was measured via laser Doppler flowmetry. A standardized nonpainful local heating protocol (42°C) was used. Cutaneous vascular conductance (CVC) was calculated as RBC flux/MAP and all data were expressed as a percentage of the maximum CVC at each site (28 mM sodium nitroprusside, T(loc) = 43°C). The plateau %CVC(max) was attenuated in CKD (CKD: 76 ± 4 vs. HC: 91 ± 2%CVC(max); P < 0.05) and the NO contribution to the plateau was lower in CKD (CKD: 39 ± 7, HC: 54 ± 5; P < 0.05). The plateau %CVC(max) in the CKD group was significantly greater at the AA and l-Arg sites compared with R (AA: 89 ± 2; l-Arg: 90 ± 1; R: 76 ± 4; P < 0.05) and did not differ from HC. Initial peak %CVC(max) was also significantly attenuated at the R and l-Arg sites in CKD (P < 0.05) but did not differ at the AA site. These results suggest that cutaneous microvascular function is impaired in stage 3-4 CKD and that oxidative stress and a deficit of l-arginine play a role in this impairment.

Soluble fms-like tyrosine kinase 1 promotes angiotensin II sensitivity in preeclampsia

Preeclampsia is a hypertensive disorder of pregnancy in which patients develop profound sensitivity to vasopressors, such as angiotensin II, and is associated with substantial morbidity for the mother and fetus. Enhanced vasoconstrictor sensitivity and elevations in soluble fms-like tyrosine kinase 1 (sFLT1), a circulating antiangiogenic protein, precede clinical signs and symptoms of preeclampsia. Here, we report that overexpression of sFlt1 in pregnant mice induced angiotensin II sensitivity and hypertension by impairing endothelial nitric oxide synthase (eNOS) phosphorylation and promoting oxidative stress in the vasculature. Administration of the NOS inhibitor l-NAME to pregnant mice recapitulated the angiotensin sensitivity and oxidative stress observed with sFlt1 overexpression. Sildenafil, an FDA-approved phosphodiesterase 5 inhibitor that enhances NO signaling, reversed sFlt1-induced hypertension and angiotensin II sensitivity in the preeclampsia mouse model. Sildenafil treatment also improved uterine blood flow, decreased uterine vascular resistance, and improved fetal weights in comparison with untreated sFlt1-expressing mice. Finally, sFLT1 protein expression inversely correlated with reductions in eNOS phosphorylation in placental tissue of human preeclampsia patients. These data support the concept that endothelial dysfunction due to high circulating sFLT1 may be the primary event leading to enhanced vasoconstrictor sensitivity that is characteristic of preeclampsia and suggest that targeting sFLT1-induced pathways may be an avenue for treating preeclampsia and improving fetal outcomes.

NADPH oxidase-derived reactive oxygen species contribute to impaired cutaneous microvascular function in chronic kidney disease

Oxidative stress promotes vascular dysfunction in chronic kidney disease (CKD). We utilized the cutaneous circulation to test the hypothesis that reactive oxygen species derived from NADPH oxidase and xanthine oxidase impair nitric oxide (NO)-dependent cutaneous vasodilation in CKD. Twenty subjects, 10 stage 3 and 4 patients with CKD (61 ± 4 yr; 5 men/5 women; eGFR: 39 ± 4 ml·min(-1)·1.73 m(-2)) and 10 healthy controls (55 ± 2 yr; 4 men/6 women; eGFR: >60 ml·min(-1)·1.73 m(-2)) were instrumented with 4 intradermal microdialysis fibers for the delivery of 1) Ringer solution (Control), 2) 10 μM tempol (scavenge superoxide), 3) 100 μM apocynin (NAD(P)H oxidase inhibition), and 4) 10 μM allopurinol (xanthine oxidase inhibition). Skin blood flow was measured via laser-Doppler flowmetry during standardized local heating (42°C). N(g)-nitro-l-arginine methyl ester (L-NAME; 10 mM) was infused to quantify the NO-dependent portion of the response. Cutaneous vascular conductance (CVC) was calculated as a percentage of the maximum CVC achieved during sodium nitroprusside infusion at 43°C. Cutaneous vasodilation was attenuated in patients with CKD (77 ± 3 vs. 88 ± 3%, P = 0.01), but augmented with tempol and apocynin (tempol: 88 ± 2 (P = 0.03), apocynin: 91 ± 2% (P = 0.001). The NO-dependent portion of the response was reduced in patients with CKD (41 ± 4 vs. 58 ± 2%, P = 0.04), but improved with tempol and apocynin (tempol: 58 ± 3 (P = 0.03), apocynin: 58 ± 4% (P = 0.03). Inhibition of xanthine oxidase did not alter cutaneous vasodilation in either group (P > 0.05). These data suggest that NAD(P)H oxidase is a source of reactive oxygen species and contributes to microvascular dysfunction in patients with CKD.

Aldosterone and Vascular Mineralocorticoid Receptors: Regulators of Ion Channels Beyond the Kidney

Elevated levels of the steroid hormone aldosterone have been reported in populations at risk for cardiovascular disease and are associated with adverse cardiovascular events, such as myocardial infarction, stroke, and death.1–3 Clinical trials demonstrate that either inhibition of aldosterone production or antagonism of its receptor, the mineralocorticoid receptor (MR), significantly reduces cardiovascular ischemic events and mortality.4–8 Classically, aldosterone regulates blood pressure by binding to the MR in renal epithelial cells and increasing expression and activity of ion channels in the distal nephron resulting in sodium retention and blood pressure elevation.9 Accordingly, clinical trials of MR antagonists report decreases in blood pressure.4,5 However, the modest reductions in BP do not fully account for the cardioprotective effects of MR antagonism nor do renal electrolyte changes fully explain the antihypertensive effects of MR antagonists.10 For the past 2 decades, it has become clear that aldosterone and MR have extrarenal actions that may contribute to alterations in vascular function leading to the development and progression of cardiovascular disease. Exploration of the precise mechanisms by which aldosterone/MR regulates vascular function and promotes cardiovascular diseases remains a very active area of investigation and a potential avenue for novel pharmacological interventions. Because MR is a critical regulator of renal ion channels,9 and more recently has been implicated in ion channel regulation in the heart,11 we propose that MR may also regulate vascular ion channel expression and function, thereby contributing to aldosterone/MR-induced vascular dysfunction and cardiovascular disease. Vascular ion channels are critical to generation of vascular tone, vessel contraction and relaxation, and vascular stiffness (reviewed elsewhere)12–15 and contribute to vascular dysfunction associated with diseases, including atherosclerosis,16 diabetes mellitus,17–19 and hypertension.20,21 This review focuses on new …

Effect of moderate-to-severe chronic kidney disease on flow-mediated dilation and progenitor cells.

A reduction in progenitor cell populations that help preserve vascular continuity and induce vascularization may accentuate endothelial cell apoptosis and dysfunction, ultimately contributing to organ failure and increased cardiovascular disease in chronic kidney disease (CKD). We hypothesized that CD45+ myeloid and CD34+ hematopoietic circulating progenitor cell (CPC) subpopulations would be reduced, peripheral blood mononuclear cell (PBMNC) colony-forming units (CFU) would be impaired, and flow-mediated dilation (FMD) would be impaired in patients with moderate-to-severe CKD as compared with healthy controls. Eleven moderate-to-severe CKD patients (mean estimated glomerular filtration rate [eGFR]: 36 ± 5) and 14 healthy controls were studied; blood was drawn and FMD was assessed by brachial artery FMD. CPCs were quantified via flow cytometry, and isolated PBMNCs were cultured for the colony-forming assay. CKD patients had significantly impaired FMD; lower CD34+, CD34+/KDR+, CD34+/CD45− and CD34+/KDR+/CD45− hematopoietic CPCs; lower CD45+, CD45+/KDR+, CD34+/CD45+ and CD34+/KDR+/CD45+ myeloid CPCs; and impaired CFUs as compared with healthy controls. Regression analysis revealed that CD34+, CD34+/KDR+ and CD34+/CD45− hematopoietic CPCs were associated positively with eGFR and negatively with blood urea nitrogen and serum creatinine. The CD45+/KDR+ myeloid CPCs also were associated positively with eGFR and negatively with serum creatinine. CD34+ hematopoietic CPCs and CD45+/KDR+ as well as CD34+/CD45+ myeloid CPCs were associated positively with FMD. In conclusion, myeloid and hematopoietic CPCs are reduced and associated with renal function as well as FMD in CKD. Therefore, reductions in CPCs may be a potential mechanism by which vascular integrity is compromised, increasing cardiovascular disease risk and contributing to renal disease progression in CKD.

Vascular mineralocorticoid receptor regulates microRNA-155 to promote vasoconstriction and rising blood pressure with aging

Hypertension is nearly universal yet poorly controlled in the elderly despite proven benefits of intensive treatment. Mice lacking mineralocorticoid receptors in smooth muscle cells (SMC-MR-KO) are protected from rising blood pressure (BP) with aging, despite normal renal function. Vasoconstriction is attenuated in aged SMC-MR-KO mice, thus they were used to explore vascular mechanisms that may contribute to hypertension with aging. MicroRNA (miR) profiling identified miR-155 as the most down-regulated miR with vascular aging in MR-intact but not SMC-MR-KO mice. The aging-associated decrease in miR-155 in mesenteric resistance vessels was associated with increased mRNA abundance of MR and of predicted miR-155 targets Cav1.2 (L-type calcium channel (LTCC) subunit) and angiotensin type-1 receptor (AgtR1). SMC-MR-KO mice lacked these aging-associated vascular gene expression changes. In HEK293 cells, MR repressed miR-155 promoter activity. In cultured SMCs, miR-155 decreased Cav1.2 and AgtR1 mRNA. Compared to MR-intact littermates, aged SMC-MR-KO mice had decreased systolic BP, myogenic tone, SMC LTCC current, mesenteric vessel calcium influx, LTCC-induced vasoconstriction and angiotensin II-induced vasoconstriction and oxidative stress. Restoration of miR-155 specifically in SMCs of aged MR-intact mice decreased Cav1.2 and AgtR1 mRNA and attenuated LTCC-mediated and angiotensin II-induced vasoconstriction and oxidative stress. Finally, in a trial of MR blockade in elderly humans, changes in serum miR-155 predicted the BP treatment response. Thus, SMC-MR regulation of miR-155, Cav1.2 and AgtR1 impacts vasoconstriction with aging. This novel mechanism identifies potential new treatment strategies and biomarkers to improve and individualize antihypertensive therapy in the elderly.

Intradermal microdialysis of hypertonic saline attenuates cutaneous vasodilatation in response to local heating.

We tested the hypothesis that microdialysis of hypertonic saline would attenuate the skin blood flow response to local heating. Seventeen healthy subjects (23 ± 1 years old) were studied. In one group (n= 9), four microdialysis fibres were placed in the forearm skin and infused with the following: (1) Ringer solution; (2) normal saline (0.9% NaCl); (3) hypertonic saline (3% NaCl); and (4) 10 mm l‐NAME. A second group (n= 8) was infused with the following: (1) normal saline; (2) hypertonic saline; (3) normal saline +l‐NAME; and (4) hypertonic saline +l‐NAME. Red blood cell flux was measured via laser Doppler flowmetry during local heating to 42°C. Site‐specific maximal vasodilatation was determined by infusing 28 mm sodium nitroprusside while the skin was heated to 43°C. Data were expressed as the percentage of maximal cutaneous vascular conductance (%CVCmax). The local heating response at the Ringer solution and normal saline sites did not differ (n= 9; initial peak Ringer solution, 69 ± 6 versus normal saline, 66 ± 2%CVCmax; plateau Ringer solution, 89 ± 4 versus normal saline, 89 ± 5%CVCmax). Hypertonic saline reduced the initial peak (n= 9; normal saline, 66 ± 2 versus hypertonic saline, 54 ± 4%CVCmax; P < 0.05) and plateau (normal saline, 89 ± 5 versus hypertonic saline, 78 ± 2%CVCmax; P < 0.05) compared with normal saline. Plateau %CVCmax was attenuated to a similar value at the normal saline +l‐NAME and hypertonic saline +l‐NAME sites (n= 8; normal saline +l‐NAME, 39 ± 6 and hypertonic saline +l‐NAME, 39 ± 5%CVCmax). The nitric oxide contribution (plateau %CVCmax–l‐NAME plateau %CVCmax) was lower at the hypertonic saline site (normal saline, 55 ± 6 versus hypertonic saline, 35 ± 4; P < 0.01). These data suggest an effect of salt on the cutaneous response to local heating, which may be mediated through a decreased production and/or availability of nitric oxide.

Smooth Muscle Cell–Mineralocorticoid Receptor as a Mediator of Cardiovascular Stiffness With Aging

Stiffening of the vasculature with aging is a strong predictor of adverse cardiovascular events, independent of all other risk factors including blood pressure, yet no therapies target this process. MRs (mineralocorticoid receptors) in smooth muscle cells (SMCs) have been implicated in the regulation of vascular fibrosis but have not been explored in vascular aging. Comparing SMC-MR–deleted male mice to MR-intact littermates at 3, 12, and 18 months of age, we demonstrated that aging-associated vascular stiffening and fibrosis are mitigated by MR deletion in SMCs. Progression of cardiac stiffness and fibrosis and the decline in exercise capacity with aging were also mitigated by MR deletion in SMC. Vascular gene expression profiling analysis revealed that MR deletion in SMC is associated with recruitment of a distinct antifibrotic vascular gene expression program with aging. Moreover, long-term pharmacological inhibition of MR in aged mice prevented the progression of vascular fibrosis and stiffness and induced a similar antifibrotic vascular gene program. Finally, in a small trial in elderly male humans, short-term MR antagonism produced an antifibrotic signature of circulating biomarkers similar to that observed in the vasculature of SMC-MR–deleted mice. These findings suggest that SMC-MR contributes to vascular stiffening with aging and is a potential therapeutic target to prevent the progression of aging-associated vascular fibrosis and stiffness.