Immunosuppression with mycophenolate mofetil attenuates the development of hypertension and albuminuria in deoxycorticosterone acetate-salt hypertensive rats

Hypertensive Heart Disease: A Narrative Review Series-Part 3: Vasculature, Biomarkers and the Matrix of Hypertensive Heart Disease

Over the last few decades, research efforts have resulted in major advances in our understanding of the pathophysiology of hypertensive heart disease (HHD). This is the third part of a three-part review series. Here, we focus on the influence of high blood pressure on the micro- and macroalterations that occur in the vasculature in HHD. We also provide an overview of circulating cardiac biomarkers that may prove useful for a better understanding of the pathophysiology, development and progression of HHD, and may play a unique role in the diagnostic and prognostic evaluation of patients with HHD, taking into account their properties showing as abnormal long before the onset of the disease. In the conclusion, we propose an updated definition of HHD and a matrix for clinical classification, which we suspect will be useful in practice, allowing an individual approach to HHD patients.

Bioactive Peptides from Ruditapes philippinarum Attenuate Hypertension and Cardiorenal Damage in Deoxycorticosterone Acetate-Salt Hypertensive Rats

Hypertension is a common disease that affects human health and can lead to damage to the heart, kidneys, and other important organs. In this study, we investigated the regulatory effects of bioactive peptides derived from Ruditapes philippinarum (RPP) on hypertension and organ protection in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. We found that RPPs exhibited significant blood pressure-lowering properties. Furthermore, the results showed that RPPs positively influenced vascular remodeling and effectively maintained a balanced water-sodium equilibrium. Meanwhile, RPPs demonstrated anti-inflammatory potential by reducing the serum levels of inflammatory cytokines (TNF-α, IL-2, and IL-6). Moreover, we observed the strong antioxidant activity of RPPs, which played a critical role in reducing oxidative stress and alleviating hypertension-induced damage to the aorta, heart, and kidneys. Additionally, our study explored the regulatory effects of RPPs on the gut microbiota, suggesting a possible correlation between their antihypertensive effects and the modulation of gut microbiota. Our previous studies have demonstrated that RPPs can significantly reduce blood pressure in SHR rats. This suggests that RPPs can significantly improve both essential hypertension and DOAC-salt-induced secondary hypertension and can ameliorate cardiorenal damage caused by hypertension. These findings further support the possibility of RPPs as an active ingredient in functional anti-hypertensive foods.

Renal and hypothalamic inflammation in renovascular hypertension: role of afferent renal nerves

Renal denervation (RDN) is a potential therapy for drug-resistant hypertension. However, whether its effects are mediated by ablation of efferent or afferent renal nerves is not clear. Previous studies have implicated that renal inflammation and the sympathetic nervous system are driven by the activation of afferent and efferent renal nerves. RDN attenuated the renal inflammation and sympathetic activity in some animal models of hypertension. In the 2 kidney,1 clip (2K1C) model of renovascular hypertension, RDN also decreased sympathetic activity; however, mechanisms underlying renal and central inflammation are still unclear. We tested the hypothesis that the mechanisms by which total RDN (TRDN; efferent + afferent) and afferent-specific RDN (ARDN) reduce arterial pressure in 2K1C rats are the same. Male Sprague-Dawley rats were instrumented with telemeters to measure mean arterial pressure (MAP), and after 7 days, a clip was placed on the left renal artery. Rats underwent TRDN, ARDN, or sham surgery of the clipped kidney and MAP was measured for 6 wk. Weekly measurements of water intake (WI), urine output (UO), and urinary copeptin were conducted, and urine was analyzed for cytokines/chemokines. Neurogenic pressor activity (NPA) was assessed at the end of the protocol calculated by the depressor response after intraperitoneal injection of hexamethonium. Rats were euthanized and the hypothalamus and kidneys removed for measurement of cytokine content. MAP, NPA, WI, and urinary copeptin were significantly increased in 2K1C-sham rats, and these responses were abolished by both TRDN and ARDN. 2K1C-sham rats presented with renal and hypothalamic inflammation and these responses were largely mitigated by TRDN and ARDN. We conclude that RDN attenuates 2K1C hypertension primarily by ablation of afferent renal nerves which disrupts bidirectional renal neural-immune pathways.NEW & NOTEWORTHY Hypertension resulting from reduced perfusion of the kidney is dependent on renal sensory nerves, which are linked to inflammation in the kidney and hypothalamus. Afferent renal nerves are required for chronic increases in both water intake and vasopressin release observed following renal artery stenosis. Findings from this study suggest an important role of renal sensory nerves that has previously been underestimated in the pathogenesis of 2K1C hypertension.

Inflammation and oxidative stress in salt sensitive hypertension; The role of the NLRP3 inflammasome

Salt-sensitivity of blood pressure is an independent risk factor for cardiovascular disease and affects approximately half of the hypertensive population. While the precise mechanisms of salt-sensitivity remain unclear, recent findings on body sodium homeostasis and salt-induced immune cell activation provide new insights into the relationship between high salt intake, inflammation, and hypertension. The immune system, specifically antigen-presenting cells (APCs) and T cells, are directly implicated in salt-induced renal and vascular injury and hypertension. Emerging evidence suggests that oxidative stress and activation of the NLRP3 inflammasome drive high sodium-mediated activation of APCs and T cells and contribute to the development of renal and vascular inflammation and hypertension. In this review, we summarize the recent insights into our understanding of the mechanisms of salt-sensitive hypertension and discuss the role of inflammasome activation as a potential therapeutic target.

The IFNγ-PDL1 Pathway Enhances CD8T-DCT Interaction to Promote Hypertension

BACKGROUND

Renal T cells contribute importantly to hypertension, but the underlying mechanism is incompletely understood. We reported that CD8Ts directly stimulate distal convoluted tubule cells (DCTs) to increase sodium chloride co-transporter expression and salt reabsorption. However, the mechanistic basis of this pathogenic pathway that promotes hypertension remains to be elucidated.

METHODS

We used mouse models of DOCA+salt (DOCA) treatment and adoptive transfer of CD8⁺ T cells (CD8T) from hypertensive animals to normotensive animals in in-vivo studies. Co-culture of mouse DCTs and CD8Ts was used as in-vitro model to test the effect of CD8T activation in promoting sodium chloride co-transporter-mediated sodium retention and to identify critical molecular players contributing to the CD8T-DCT interaction. IFNγ (interferon γ)-KO mice and mice receiving renal tubule-specific knockdown of PDL1 were used to verify in-vitro findings. Blood pressure was continuously monitored via radio-biotelemetry, and kidney samples were saved at experimental end points for analysis.

RESULTS

We identified critical molecular players and demonstrated their roles in augmenting the CD8T-DCT interaction leading to salt-sensitive hypertension. We found that activated CD8Ts exhibit enhanced interaction with DCTs via IFN-γ-induced upregulation of MHC-I and PDL1 in DCTs, thereby stimulating higher expression of sodium chloride co-transporter in DCTs to cause excessive salt retention and progressive elevation of blood pressure. Eliminating IFN-γ or renal tubule-specific knockdown of PDL1 prevented T cell homing into the kidney, thereby attenuating hypertension in 2 different mouse models.

CONCLUSIONS

Our results identified the role of activated CD8Ts in contributing to increased sodium retention in DCTS through the IFN-γ-PDL1 pathway. These findings provide a new mechanism for T cell involvement in the pathogenesis of hypertension and reveal novel therapeutic targets.

Therapeutic targeting of inflammation in hypertension: from novel mechanisms to translational perspective

Both animal models and human observational and genetic studies have shown that immune and inflammatory mechanisms play a key role in hypertension and its complications. We review the effects of immunomodulatory interventions on blood pressure, target organ damage, and cardiovascular risk in humans. In experimental and small clinical studies, both non-specific immunomodulatory approaches, such as mycophenolate mofetil and methotrexate, and medications targeting T and B lymphocytes, such as tacrolimus, cyclosporine, everolimus, and rituximab, lower blood pressure and reduce organ damage. Mechanistically targeted immune interventions include isolevuglandin scavengers to prevent neo-antigen formation, co-stimulation blockade (abatacept, belatacept), and anti-cytokine therapies (e.g. secukinumab, tocilizumab, canakinumab, TNF-α inhibitors). In many studies, trial designs have been complicated by a lack of blood pressure-related endpoints, inclusion of largely normotensive study populations, polypharmacy, and established comorbidities. Among a wide range of interventions reviewed, TNF-α inhibitors have provided the most robust evidence of blood pressure lowering. Treatment of periodontitis also appears to deliver non-pharmacological anti-hypertensive effects. Evidence of immunomodulatory drugs influencing hypertension-mediated organ damage are also discussed. The reviewed animal models, observational studies, and trial data in humans, support the therapeutic potential of immune-targeted therapies in blood pressure lowering and in hypertension-mediated organ damage. Targeted studies are now needed to address their effects on blood pressure in hypertensive individuals.

Autoimmune-mediated renal disease and hypertension

Hypertension is a major risk factor for cardiovascular disease, chronic kidney disease (CKD), and mortality. Troublingly, hypertension is highly prevalent in patients with autoimmune renal disease and hastens renal functional decline. Although progress has been made over the past two decades in understanding the inflammatory contributions to essential hypertension more broadly, the mechanisms active in autoimmune-mediated renal diseases remain grossly understudied. This Review provides an overview of the pathogenesis of each of the major autoimmune diseases affecting the kidney that are associated with hypertension, and describes the current state of knowledge regarding hypertension in these diseases and their management. Specifically, discussion focuses on Systemic Lupus Erythematosus (SLE) and Lupus Nephritis (LN), Immunoglobulin A (IgA) Nephropathy, Idiopathic Membranous Nephropathy (IMN), Anti-Neutrophil Cytoplasmic Antibody (ANCA)-associated glomerulonephritis, and Thrombotic Thrombocytopenic Purpura (TTP). A summary of disease-specific animal models found to exhibit hypertension is also included to highlight opportunities for much needed further investigation of underlying mechanisms and novel therapeutic approaches.

Mycophenolate Improves Brain-Gut Axis Inducing Remodeling of Gut Microbiota in DOCA-Salt Hypertensive Rats

Microbiota is involved in the host blood pressure (BP) regulation. The immunosuppressive drug mofetil mycophenolate (MMF) ameliorates hypertension. The present study analyzed whether MMF improves dysbiosis in mineralocorticoid-induced hypertension. Male Wistar rats were assigned to three groups: untreated (CTR), deoxycorticosterone acetate (DOCA)-salt, and DOCA treated with MMF for 4 weeks. MMF treatment reduced systolic BP, improved endothelial dysfunction, and reduced oxidative stress and inflammation in aorta. A clear separation in the gut bacterial community between CTR and DOCA groups was found, whereas the cluster belonging to DOCA-MMF group was found to be intermixed. No changes were found at the phylum level among all experimental groups. MMF restored the elevation in lactate-producing bacteria found in DOCA-salt joined to an increase in the acetate-producing bacteria. MMF restored the percentage of anaerobic bacteria in the DOCA-salt group to values similar to control rats. The improvement of gut dysbiosis was associated with an enhanced colonic integrity and a decreased sympathetic drive in the gut. MMF inhibited neuroinflammation in the paraventricular nuclei in the hypothalamus. This study demonstrates for the first time that MMF reduces gut dysbiosis in DOCA-salt hypertension models. This effect seems to be related to its capacity to improve gut integrity due to reduced sympathetic drive in the gut associated with reduced brain neuroinflammation.

Greater T Regulatory Cells in Females Attenuate DOCA-Salt-Induced Increases in Blood Pressure Versus Males

Hypertension is the most common risk factor for cardiovascular disease, causing over 18 million deaths a year. Although the mechanisms controlling blood pressure (BP) in either sex remain largely unknown, T cells play a critical role in the development of hypertension. Further evidence supports a role for the immune system in contributing to sex differences in hypertension. The goal of the current study was to first, determine the impact of sex on the renal T-cell profiles in DOCA-salt hypertensive males and females and second, test the hypothesis that greater numbers of T regulatory cells (Tregs) in females protect against DOCA-salt-induced increases in BP and kidney injury. Male rats displayed greater increases in BP than females following 3 weeks of DOCA-salt treatment, although increases in renal injury were comparable between the sexes. DOCA-salt treatment resulted in an increase in proinflammatory T cells in both sexes; however, females had more anti-inflammatory Tregs than males. Additional male and female DOCA-salt rats were treated with anti-CD25 to decrease Tregs. Decreasing Tregs significantly increased BP only in females, thereby abolishing the sex difference in the BP response to DOCA-salt. This data supports the hypothesis that Tregs protect against the development of hypertension and are particularly important for the control of BP in females.

Hypertension: a new treatment for an old disease? Targeting the immune system

Arterial hypertension represents a serious public health problem, being a major cause of morbidity and mortality worldwide. The availability of many antihypertensive therapeutic strategies still fails to adequately treat around 20% of hypertensive patients, who are considered resistant to conventional treatment. In the pathogenesis of hypertension, immune system mechanisms are activated and both the innate and adaptive immune responses play a crucial role. However, what, when and how the immune system is triggered during hypertension development is still largely undefined. In this context, this review highlights scientific advances in the manipulation of the immune system in order to attenuate hypertension and end-organ damage. Here, we discuss the potential use of immunosuppressants and immunomodulators as pharmacological tools to control the activation of the immune system, by non-specific and specific mechanisms, to treat hypertension and improve end-organ damage. Nevertheless, more clinical trials should be performed with these drugs to establish their therapeutic efficacy, safety and risk-benefit ratio in hypertensive conditions. LINKED ARTICLES: This article is part of a themed section on Immune Targets in Hypertension. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.12/issuetoc.

Arterial Hypertension and Interleukins: Potential Therapeutic Target or Future Diagnostic Marker?

Hypertension as a multifactorial pathology is one of the most important cardiovascular risk factors, affecting up to 30-40% of the general population. Complex immune responses are involved in the inflammatory mechanism of hypertension, with evidence pointing to increased inflammatory mediators even in prehypertensive patients. Increased vascular permeability, thrombogenesis, and fibrosis, effects that are associated with sustained hypertension, could be attributed to chronic inflammation. Chronic inflammation triggers endothelial dysfunction via increased production of ROS through proinflammatory cytokines. Increased serum level of proinflammatory cytokines such as IL-1β, IL-6, IL-8, IL-17, IL-23, TGFβ, and TNFα in hypertensive patients has been associated with either increased blood pressure values and/or end-organ damage. Moreover, some cytokines (i.e., IL-6) seem to determine a hypertensive response to angiotensin II, regardless of blood pressure values. Understanding hypertension as an inflammatory-based pathology gives way to new therapeutic targets. As such, conventional cardiovascular drugs (statins, calcium channels blockers, and ACEIs/ARBs) have shown additional anti-inflammatory effects that could be linked to their blood pressure lowering properties. Moreover, anti-inflammatory drugs (mycophenolate mofetil) have been shown to decrease blood pressure in hypertensive patients or prevent its development in normotensive individuals. Further research is needed to evaluate whether drugs targeting hypertensive-linked proinflammatory cytokines, such as monoclonal antibodies, could become a new therapeutic option in treating arterial hypertension.

T Cells and Hypertension: Solved and Unsolved Mysteries Regarding the Female Rat

T-cell function in female animal models of hypertension is poorly understood since most research is conducted in males. Our findings in Dahl-salt-sensitive and Dahl salt-resistant rats support prior research showing sex-specific T-cell effects in the pathophysiology of hypertension. Further studies are needed to inform clinical studies in both sexes and to provide clues into immune mechanisms underlying susceptibility and resilience to developing hypertension and associated disease.

Na+-Cl- cotransporter-mediated chloride uptake contributes to hypertension and renal damage in aldosterone-infused rats

Recently, in addition to epithelial sodium channel alpha-subunit (αENaC), the thiazide-sensitive sodium-chloride cotransporter (NCC) and pendrin, also known as sodium-independent chloride/iodide transporter, were reported to be activated by aldosterone. Here, we investigated whether chloride (Cl^-) is responsible for hypertension, inflammation, and renal damage in aldosterone-infused rats. Following left nephrectomy, 8-wk-old male Sprague-Dawley rats were allocated into four groups: 1) drinking 1.0% sodium chloride solution with aldosterone infusion (Aldo/NaCl rats); 2) drinking 1.44% sodium bicarbonate solution with aldosterone infusion (Aldo/NaHCO₃ rats); 3) drinking distilled water with aldosterone infusion (Aldo/water rats); and 4) drinking distilled water without aldosterone infusion (sham rats). Additionally, heminephrectomized rats with aldosterone infusion were fed a 0.26% NaCl diet (control); 8.0% NaCl diet (high-Na/high-Cl); or a 4.0% NaCl 6.67% sodium citrate diet (high-Na/half-Cl). Last, Aldo/NaCl rats were treated with or without hydrochlorothiazide. Blood pressure in the Aldo/NaCl rats was significantly higher than in the Aldo/NaHCO₃ rats, which was associated with the increased expression of NCC. Expression of markers of inflammation (CD3, CD68, interleukin-17A) and fibrosis (α-smooth muscle actin, collagen 1) were also increased in Aldo/NaCl rats. Similarly, aldosterone-infused rats fed a high-Na/half-Cl diet had lower blood pressure than those fed a high-Na/high-Cl diet, with a reduction of phosphorylated NCC, but not αENaC and pendrin. NCC inhibition with hydrochlorothiazide attenuated interleukin-17A protein expression along with the phosphorylation of NCC in Aldo/NaCl rats. These findings suggest that NCC-mediated Cl^- uptake plays important roles in the development of aldosterone-induced hypertension and renal injury.

Mycophenolate Mofetil Attenuates DOCA-Salt Hypertension: Effects on Vascular Tone

Inflammation is increasingly recognized as a driver of hypertension. Both genetic and pharmacological inhibition of B and T cells attenuates most forms of experimental hypertension. Accordingly, the immunosuppressive drug mycophenolate mofetil (MMF) reduces blood pressure in the deoxycorticosterone acetate (DOCA-) salt model. However, the mechanisms by which MMF prevent hypertension in the DOCA-salt model remain unclear. Recent studies indicate that immunosuppression can inhibit sodium transporter activity in the kidney, but its effect on vascular tone is not well characterized. Therefore, the aim of the present study was to analyze the vascular and renal tubular effects of MMF in the DOCA-salt model in rats (4 weeks without uninephrectomy). Co-treatment with MMF attenuated the rise in blood pressure from day 11 onward resulting in a significantly lower telemetric mean arterial pressure after 4 weeks of treatment (108 ± 7 vs. 130 ± 9 mmHg, P < 0.001 by two-way analysis of variance). MMF significantly reduced the number of CD3⁺ cells in kidney cortex and inner medulla, but not in outer medulla. In addition, MMF significantly reduced urinary interferon-γ excretion. Vascular tone was studied ex vivo using wire myographs. An angiotensin II type 2 (AT₂) receptor antagonist blocked the effects of angiotensin II (Ang II) only in the vehicle group. Conversely, L-NAME significantly increased the Ang II response only in the MMF group. An endothelin A receptor blocker prevented vasoconstriction by endothelin-1 in the MMF but not in the vehicle group. MMF did not reduce the abundances of the kidney sodium transporters NHE3, NKCC2, NCC, or ENaC. Together, our ex vivo results suggest that DOCA-salt induces AT₂ receptor-mediated vasoconstriction. MMF prevents this response and increases nitric oxide availability. These data provide insight in the antihypertensive mechanism of MMF and the role of inflammation in dysregulating vascular tone.

Anti-CD3 antibody therapy attenuates the progression of hypertension in female mice with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic inflammatory autoimmune disorder with prevalent hypertension that significantly contributes to the mortality in this patient population. Pre-clinical and clinical evidence suggests that anti-CD3 antibody therapy may attenuate the development of autoimmune diseases like SLE. However, it is unclear whether this treatment impacts the development of the prevalent hypertension associated with SLE. The present study was designed to determine whether anti-CD3 antibody treatment attenuates the progression of hypertension in female SLE mice with already established renal disease (albuminuria ≥100mg/dL). Female SLE (NZBWF1) and control (NZW) mice were administered either an antibody to CD3ε, a component of the T cell receptor complex expressed on all T cells, or IgG antibody (isotype control) for up to 4 weeks (intranasal; 25μg/week). Spleen weight was lower in SLE mice treated with anti-CD3 antibody than in IgG-treated SLE mice, suggesting that immune system hyperactivity is decreased. Circulating anti-dsDNA autoantibodies were increased in SLE mice compared to controls and were blunted in the anti-CD3-treated SLE mice. The development of hypertension was attenuated in anti-CD3 treated mice with SLE independently of changes in renal injury (assessed by urinary albumin). These data suggest anti-CD3 therapy during autoimmune disease may have added clinical benefit to attenuate cardiovascular risk factors like hypertension.

Mycophenolate mofetil prevents cerebrovascular injury in stroke-prone spontaneously hypertensive rats

Stroke-prone spontaneously hypertensive rats (SHR-A3) develop strokes and progressive kidney disease as a result of naturally occurring genetic variations. We recently identified genetic variants in immune signaling pathways that contribute to end-organ injury. The present study was designed to test the hypothesis that a dysregulated immune response promotes stroke susceptibility. We salt-loaded 20 wk old male SHR-A3 rats and treated them with the immunosuppressant mycophenolate mofetil (MMF, 25 mg/kg/day po) (n = 8) or vehicle (saline) (n = 9) for 8 wk. Blood pressure (BP) was measured weekly by telemetry. Compared with vehicle-treated controls, MMF-treated SHR-A3 rats had improved survival and lower neurological deficit scores (1.44 vs. 0.125; P < 0.02). Gross morphology of the brain revealed cerebral edema in 8 of 9, and microbleeds and hemorrhages in 5 of 9 vehicle-treated rats. These lesions were absent in MMF-treated rats. Brain CD68 expression, indicating macrophage/microglial activation, was upregulated in vehicle-treated rats with microbleeds and hemorrhages but was undetectable in the brains of MMF-treated rats. MMF also prevented renal injury in SHR-A3 rats, evidenced by reduced proteinuria (albumin:creatinine) from 7.52 to 1.05 mg/mg (P < 0.03) and lower tubulointerstitial injury scores (2.46 vs. 1.43; P < 0.01). Salt loading resulted in a progressive increase in BP, which was blunted in rats receiving MMF. Our findings provide evidence that abnormal immune activation predisposes to cerebrovascular and renal injury in stroke-prone SHR-A3 rats.

IL-17 mediates neutrophil infiltration and renal fibrosis following recovery from ischemia reperfusion: compensatory role of natural killer cells in athymic rats

T cells have been implicated in the pathogenesis of acute kidney injury (AKI) and its progression to chronic kidney disease (CKD). Previous studies suggest that Th17 cells participate during the AKI-to-CKD transition, and inhibition of T cell activity by mycophenolate mofetil (MMF) or losartan attenuates the development of fibrosis following AKI. We hypothesized that T cell-deficient rats may have reduced levels of IL-17 cytokine leading to decreased fibrosis following AKI. Renal ischemis-reperfusion (I/R) was performed on T cell-deficient athymic rats (Foxn1^rnu-/rnu-) and control euthymic rats (Foxn1^rnu-/+), and CKD progression was hastened by unilateral nephrectomy at day 33 and subsequent exposure to 4.0% sodium diet. Renal fibrosis developed in euthymic rats and was reduced by MMF treatment. Athymic rats exhibited a similar degree of fibrosis, but this was unaffected by MMF treatment. FACS analysis demonstrated that the number of IL-17⁺ cells was similar between postischemic athymic vs. euthymic rats. The source of IL-17 production in euthymic rats was predominately from conventional T cells (CD3⁺/CD161^-). In the absence of conventional T cells in athymic rats, a compensatory pathway involving natural killer cells (CD3^-/CD161⁺) was the primary source of IL-17. Blockade of IL-17 activity using IL-17Rc receptor significantly decreased fibrosis and neutrophil recruitment in both euthymic and athymic rats compared with vehicle-treated controls. Taken together, these data suggest that IL-17 secretion participates in the pathogenesis of AKI-induced fibrosis possibly via the recruitment of neutrophils and that the source of IL-17 may be from either conventional T cells or NK cells.

Recent advances in central cardiovascular control: sex, ROS, gas and inflammation

The central nervous system (CNS) in concert with the heart and vasculature is essential to maintaining cardiovascular (CV) homeostasis. In recent years, our understanding of CNS control of blood pressure regulation (and dysregulation leading to hypertension) has evolved substantially to include (i) the actions of signaling molecules that are not classically viewed as CV signaling molecules, some of which exert effects at CNS targets in a non-traditional manner, and (ii) CNS locations not traditionally viewed as central autonomic cardiovascular centers. This review summarizes recent work implicating immune signals and reproductive hormones, as well as gasotransmitters and reactive oxygen species in the pathogenesis of hypertension at traditional CV control centers. Additionally, recent work implicating non-conventional CNS structures in CV regulation is discussed.

Pentosan polysulfate preserves renal microvascular P2X1 receptor reactivity and autoregulatory behavior in DOCA-salt hypertensive rats

Inflammation contributes to ANG II-associated impairment of renal autoregulation and microvascular P2X1 receptor signaling, but its role in renal autoregulation in mineralocorticoid-induced hypertension is unknown. Autoregulatory behavior was assessed using the blood-perfused juxtamedullary nephron preparation. Hypertension was induced in uninephrectomized control rats (UNx) by subcutaneous implantation of a DOCA pellet plus administration of 1% NaCl in the drinking water (DOCA-salt) for 3 wk. DOCA-salt rats developed hypertension that was unaltered by anti-inflammatory treatment with pentosan polysulfate (DOCA-salt+PPS) but was suppressed with "triple therapy" (hydrochlorothiazide, hydralazine, and reserpine; DOCA-salt+TTx). Baseline arteriolar diameters were similar across all groups. UNx rats exhibited pressure-dependent vasoconstriction with diameters declining to 69 ± 2% of control at 170 mmHg, indicating intact autoregulation. DOCA-salt treatment significantly blunted this pressure-mediated vasoconstriction. Diameters remained between 91 ± 4 and 98 ± 3% of control over 65-170 mmHg, indicating impaired autoregulation. In contrast, pressure-mediated vasoconstriction was preserved in DOCA-salt+PPS and DOCA-salt+TTx rats, reaching 77 ± 7 and 75 ± 3% of control at 170 mmHg, respectively. ATP is required for autoregulation via P2X1 receptor activation. ATP- and β,γ-methylene ATP (P2X1 receptor agonist)-mediated vasoconstriction were markedly attenuated in DOCA-salt rats compared with UNx (P < 0.05), but significantly improved by PPS or TTx (P < 0.05 vs. DOCA-salt) treatment. Arteriolar responses to adenosine and UTP (P2Y2 receptor agonist) were unaffected by DOCA-salt treatment. PPS and TTx significantly reduced MCP-1 and protein excretion in DOCA-salt rats. These results support the hypothesis that hypertension triggers inflammatory cascades but anti-inflammatory treatment preserves renal autoregulation in DOCA-salt rats, most likely by normalizing renal microvascular reactivity to P2X1 receptor activation.

Renal autoregulation in health and disease

Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltage-operated Ca(2+) channels (VOCC). Increased [Ca(2+)]i activates inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) to mobilize Ca(2+) from sarcoplasmic reticular stores. Myogenic vasoconstriction is sustained by increased Ca(2+) sensitivity, mediated by protein kinase C and Rho/Rho-kinase that favors a positive balance between myosin light-chain kinase and phosphatase. Increased RPP activates MD-TGF by transducing a signal of epithelial MD salt reabsorption to adjust afferent arteriolar vasoconstriction. A combination of vascular and tubular mechanisms, novel to the kidney, provides for high autoregulatory efficiency that maintains RBF and GFR, stabilizes sodium excretion, and buffers transmission of RPP to sensitive glomerular capillaries, thereby protecting against hypertensive barotrauma. A unique aspect of the myogenic response in the renal vasculature is modulation of its strength and speed by the MD-TGF and by a connecting tubule glomerular feedback (CT-GF) mechanism. Reactive oxygen species and nitric oxide are modulators of myogenic and MD-TGF mechanisms. Attenuated renal autoregulation contributes to renal damage in many, but not all, models of renal, diabetic, and hypertensive diseases. This review provides a summary of our current knowledge regarding underlying mechanisms enabling renal autoregulation in health and disease and methods used for its study.

The immunological basis of hypertension

A large number of investigations have demonstrated the participation of the immune system in the pathogenesis of hypertension. Studies focusing on macrophages and Toll-like receptors have documented involvement of the innate immunity. The requirements of antigen presentation and co-stimulation, the critical importance of T cell-driven inflammation, and the demonstration, in specific conditions, of agonistic antibodies directed to angiotensin II type 1 receptors and adrenergic receptors support the role of acquired immunity. Experimental findings support the concept that the balance between T cell-induced inflammation and T cell suppressor responses is critical for the regulation of blood pressure levels. Expression of neoantigens in response to inflammation, as well as surfacing of intracellular immunogenic proteins, such as heat shock proteins, could be responsible for autoimmune reactivity in the kidney, arteries, and central nervous system. Persisting, low-grade inflammation in these target organs may lead to impaired pressure natriuresis, an increase in sympathetic activity, and vascular endothelial dysfunction that may be the cause of chronic elevation of blood pressure in essential hypertension.

Endothelin ET(B) receptors contribute to sex differences in blood pressure elevation in angiotensin II hypertensive rats on a high-salt diet

Female rats are more resistant to blood pressure increases induced by high salt (HS) intake or angiotensin (Ang) II infusion. Because endothelin ET(B) receptors on endothelial and epithelial cells mediate tonic vasodilation and sodium excretion, we hypothesized that ET(B) receptors limit the hypertensive response and renal injury induced by HS diet alone or with chronic AngII infusion (AngII/HS) in female compared with male rats. A 4 week HS diet (4% NaCl) did not significantly change blood pressure (measured by telemetry) in either male or female Sprague-Dawley rats. Administration of the ET(B) receptor antagonist A-192621 (1, 3 and 10 mg/kg per day in food) during HS feeding caused a dose-dependent increase in blood pressure in both sexes. In AngII/HS rats, males had a larger increase in blood pressure than females. The increase in blood pressure produced by ET(B) receptor blockade in male AngII/HS rats was not significant. However, A-192621 treatment resulted in a significant further increase in blood pressure in female AngII/HS rats. Male rats had consistently higher protein excretion rates before and during AngII/HS, but this was not significantly affected by ET(B) receptor blockade in either sex. In conclusion, ET(B) receptors play a significantly greater beneficial role in protecting female compared with male rats against AngII-induced hypertension and may contribute to the sex differences in AngII-induced hypertension.

Dual opposing roles of adaptive immunity in hypertension

Hypertension involves remodelling and inflammation of the arterial wall. Interactions between vascular and inflammatory cells play a critical role in disease initiation and progression. T effector and regulatory lymphocytes, members of the adaptive immune system, play contrasting roles in hypertension. Signals from the central nervous system and the innate immune system antigen-presenting cells activate T effector lymphocytes and promote their differentiation towards pro-inflammatory T helper (Th) 1 and Th17 phenotypes. Th1 and Th17 effector cells, via production of pro-inflammatory mediators, participate in the low-grade inflammation that leads to blood pressure elevation and end-organ damage. T regulatory lymphocytes, on the other hand, counteract hypertensive effects by suppressing innate and adaptive immune responses. The present review summarizes and discusses the adaptive immune mechanisms that participate in the pathophysiology in hypertension.

Autoimmunity: an underlying factor in the pathogenesis of hypertension

One in every three adults in the United States has hypertension, and the underlying cause of most of these cases is unknown. Therefore, it is imperative to continue the study of mechanisms involved in the pathogenesis of hypertension. Decades ago, studies speculated that elements of an autoimmune response were associated with the development of hypertension based, in part, on the presence of circulating autoantibodies in hypertensive patients. In the past decade, a growing number of studies have been published supporting the concept that self-antigens and the subsequent activation of the adaptive immune system promote the development of hypertension. This manuscript will provide a brief review of the evidence supporting a role for the immune system in the development of hypertension, studies that implicate both cell-mediated and humoral immunity, and the relevance of understanding blood pressure control in an autoimmune disease model with hypertension.

Mycophenolate mofetil prevents high-fat diet-induced hypertension and renal glomerular injury in Dahl SS rats

We designed experiments to test the hypothesis that Dahl salt-sensitive (SS) rats are sensitive to high-fat diet (HFD)–induced hypertension and renal injury via an inflammatory mechanism. Twelve-week-old Dahl SS rats were maintained on a normal diet (ND; 14% fat), HFD (59% fat), or HFD supplemented with the lymphocyte immunosuppressive agent, mycophenolate mofetil (HFD + MMF; 30 mg/kg/day orally in diet), for a period of 4 weeks. Mean arterial pressure (MAP), metabolic parameters, T lymphocyte (CD3⁺) localization, and renal structural damage were assessed during the studies. Four weeks of HFD significantly elevated MAP and visceral adiposity without changing circulating levels of lipids or adipokines. Immunohistochemical analysis demonstrated that SS rats on HFD had significantly greater numbers of CD3⁺ cells in renal glomerular and medullary areas compared to ND SS rats. Additionally, HFD led to increased glomerular injury, but did not alter renal medullary injury. Chronic MMF treatment in HFD-fed Dahl SS rats reduced MAP, visceral adiposity, infiltration of CD3⁺ cells in the glomerulus, as well as glomerular injury. However, MMF treatment did not alter HFD-induced infiltration of CD3⁺ cells in the renal medulla. In conclusion, Dahl SS rats are sensitized to HFD-induced hypertension and renal glomerular injury via infiltration of T lymphocytes.

Immune and inflammatory role in renal disease

Chronic and acute renal diseases, irrespective of the initiating cause, have inflammation and immune system activation as a common underlying mechanism. The purpose of this review is to provide a broad overview of immune cells and inflammatory proteins that contribute to the pathogenesis of renal disease, and to discuss some of the physiological changes that occur in the kidney as a result of immune system activation. An overview of common forms of acute and chronic renal disease is provided, followed by a discussion of common therapies that have anti-inflammatory or immunosuppressive effects in the treatment of renal disease.

Immunosuppression preserves renal autoregulatory function and microvascular P2X(1) receptor reactivity in ANG II-hypertensive rats

Autoregulation is critical for protecting the kidney against arterial pressure elevation and is compromised in some forms of hypertension. Evidence indicates that activated lymphocytes contribute importantly to cardiovascular injury in hypertension. We hypothesized that activated lymphocytes contribute to renal vascular dysfunction by impairing autoregulation and P2X(1) receptor signaling in ANG II-infused hypertensive rats. Male Sprague-Dawley rats receiving ANG II infusion were treated with a lymphocyte proliferation inhibitor, mycophenolate mofetil (MMF) for 2 wk. Autoregulation was assessed in vitro and in vivo using the blood-perfused juxtamedullary nephron preparation and anesthetized rats, respectively. ANG II-treated rats exhibited impaired autoregulation. At the single vessel level, pressure-mediated afferent arteriolar vasoconstriction was significantly blunted (P < 0.05 vs. control rats). At the whole kidney level, renal blood flow passively decreased as renal perfusion pressure was reduced. MMF treatment did not alter the ANG II-induced hypertensive state; however, MMF did preserve autoregulation. The autoregulatory profiles in both in vitro or in vivo settings were similar to the responses from control rats despite persistent hypertension. Autoregulatory responses are linked to P2X(1) receptor activation. Accordingly, afferent arteriolar responses to ATP and the P2X(1) receptor agonist β,γ-methylene ATP were assessed. ATP- or β,γ-methylene ATP-induced vasoconstriction was significantly attenuated in ANG II-infused hypertensive rats but was normalized by MMF treatment. Moreover, MMF prevented elevation of plasma transforming growth factor-β1 concentration and lymphocyte and macrophage infiltration in ANG II-infused kidneys. These results suggest that anti-inflammatory treatment with MMF prevents lymphocyte infiltration and preserves autoregulation in ANG II-infused hypertensive rats, likely by normalizing P2X(1) receptor activation.

Role of the immune system in hypertension: modulation by dietary antioxidants

Hypertension is a major health problem worldwide. Individuals with hypertension are at an increased risk for stroke, heart disease, and kidney failure. Although the etiology of essential hypertension has a genetic component, lifestyle factors such as diet play an important role. Insulin resistance is a common feature of hypertension in both humans and animal models affecting glucose and lipid metabolism producing excess aldehydes including methylglyoxal. These aldehydes react with proteins to form conjugates called advanced glycation end products (AGEs). This alters protein structure and function and can affect vascular and immune cells leading to their activation and secretion of inflammatory cytokines. AGEs also act via receptors for advanced glycation end products on these cells altering the function of antioxidant and metabolic enzymes, and ion channels. This results in an increase in cytosolic free calcium, decrease in nitric oxide, endothelial dysfunction, oxidative stress, peripheral vascular resistance, and infiltration of vascular and kidney tissue with inflammatory cells leading to hypertension. Supplementation with dietary antioxidants including vitamins C, E, or B(6), thiols such as cysteine and lipoic acid, have been shown to lower blood pressure and plasma inflammatory cytokines in animal models and humans with essential hypertension. A well-balanced diet rich in antioxidants that includes vegetables, fruits, low fat dairy products, low salt, and includes whole grains, poultry, fish and nuts, lowers blood pressure and vascular inflammation. These antioxidants may achieve their antihypertensive and anti-inflammatory/immunomodulatory effects by reducing AGEs and improving insulin resistance and associated alterations. Dietary supplementation with antioxidants may be a beneficial, inexpensive, front-line alterative treatment modality for hypertension.

P2X7 deficiency attenuates hypertension and renal injury in deoxycorticosterone acetate-salt hypertension

The P2X(7) receptor is a ligand-gated ion channel, and genetic variations in the P2X(7) gene significantly affect blood pressure. P2X(7) receptor expression is associated with renal injury and inflammatory diseases. Uninephrectomized wild-type (WT) and P2X(7)-deficient (P2X(7) KO) mice were subcutaneously implanted with deoxycorticosterone acetate (DOCA) pellets and fed an 8% salt diet for 18 days. Their blood pressure was assessed by a telemetry system. The mice were placed in metabolic cages, and urine was collected for 24 h to assess renal function. After 18 days of DOCA-salt treatment, P2X(7) mRNA and protein expression increased in WT mice. Blood pressure in P2X(7) KO mice was less than that of WT mice (mean systolic blood pressure 133 ± 3 vs. 150 ± 2 mmHg). On day 18, urinary albumin excretion was lower in P2X(7) KO mice than in WT mice (0.11 ± 0.07 vs. 0.28 ± 0.07 mg/day). Creatinine clearance was higher in P2X(7) KO mice than in WT mice (551.53 ± 65.23 vs. 390.85 ± 32.81 μl·min(-1)·g renal weight(-1)). Moreover, renal interstitial fibrosis and infiltration of immune cells (macrophages, T cells, B cells, and leukocytes) were markedly attenuated in P2X(7) KO mice compared with WT mice. The levels of IL-1β, released by macrophages, in P2X(7) KO mice had decreased dramatically compared with that in WT mice. These results strongly suggest that the P2X(7) receptor plays a key role in the development of hypertension and renal disease via increased inflammation, indicating its potential as a novel therapeutic target.

Loss of renal medullary endothelin B receptor function during salt deprivation is regulated by angiotensin II

We have recently demonstrated that chronic infusion of exogenous ANG II, which induces blood pressure elevation, attenuates renal medullary endothelin B (ET(B)) receptor function in rats. Moreover, this was associated with a reduction of ET(B) receptor expression in the renal inner medulla. The aim of this present work was to investigate the effect of a physiological increase in endogenous ANG II (low-salt diet) on the renal ET system, including ET(B) receptor function. We hypothesized that endogenous ANG II reduces renal medullary ET(B) receptor function during low-salt intake. Rats were placed on a low-salt diet (0.01-0.02% NaCl) for 2 wk to allow an increase in endogenous ANG II. In rats on normal-salt chow, the stimulation of renal medullary ET(B) receptor by ET(B) receptor agonist sarafotoxin 6c (S6c) causes an increase in water (3.6 ± 0.4 from baseline vs. 10.5 ± 1.3 μl/min following S6c infusion; P < 0.05) and sodium excretion (0.38 ± 0.06 vs. 1.23 ± 0.17 μmol/min; P < 0.05). The low-salt diet reduced the ET(B)-dependent diuresis (4.5 ± 0.5 vs. 6.1 ± 0.9 μl/min) and natriuresis (0.40 ± 0.11 vs. 0.46 ± 0.12 μmol/min) in response to acute intramedullary infusion of S6c. Chronic treatment with candesartan restored renal medullary ET(B) receptor function; urine flow was 7.1 ± 0.9 vs. 15.9 ± 1.7 μl/min (P < 0.05), and sodium excretion was 0.4 ± 0.1 vs. 1.1 ± 0.1 μmol/min (P < 0.05) before and after intramedullary S6c infusion, respectively. Receptor binding assays determined that the sodium-depleted diet resulted in a similar level of ET(B) receptor binding in renal inner medulla compared with rats on a normal-salt diet. Candesartan reduced renal inner medullary ET(B) receptor binding (1,414 ± 95 vs. 862 ± 50 fmol/mg; P < 0.05). We conclude that endogenous ANG II attenuates renal medullary ET(B) receptor function to conserve sodium during salt deprivation independently of receptor expression.

Metabolic syndrome: is immunosuppression to blame?

1. Metabolic syndrome (MS) is common after liver transplantation and has been associated with increased risks of cardiovascular disease, cardiovascular death, liver-related death, and overall mortality. 2. Immunosuppression may increase the frequency of hyperlipidemia, diabetes, and hypertension and thus increase the risk and prevalence of MS after transplantation. 3. Corticosteroids are associated with increased rates of diabetes, hypertension, and hyperlipidemia in the short term. These agents are now being used perhaps less frequently and certainly for shorter durations; therefore, the long-term effects on metabolic morbidities may be reduced. 4. Calcineurin inhibitors and mammalian target of rapamycin inhibitors affect many MS parameters to various degrees and contribute to long-term morbidity after transplantation.