Mycophenolate mofetil prevents salt-sensitive hypertension resulting from nitric oxide synthesis inhibition

VEGFC ameliorates salt-sensitive hypertension and hypertensive nephropathy by inhibiting NLRP3 inflammasome via activating VEGFR3-AMPK dependent autophagy pathway

Salt-sensitivity hypertension (SSHTN) is an independent predictor for cardiovascular mortality. VEGFC has been reported to be a protective role in SSHTN and hypertensive kidney injury. However, the underlying mechanisms remain largely unclear. The current study aimed to explore the protective effects and mechanisms of VEGFC against SSHTN and hypertensive nephropathy. Here, we reported that VEGFC attenuated high blood pressure as well as protected against renal inflammation and fibrosis in SSHTN mice. Moreover, VEGFC suppressed the activation of renal NLRP3 inflammasome in SSHTN mice. In vitro, we found VEGFC inhibited NLRP3 inflammasome activation, meanwhile, upregulated autophagy in high-salt-induced macrophages, while these effects were reversed by an autophagy inhibitor 3MA. Furthermore, in vivo, 3MA pretreatment weakened the protective effects of VEGFC on SSHTN and hypertensive nephropathy. Mechanistically, VEGF receptor 3 (VEGFR3) kinase domain activated AMPK by promoting the phosphorylation at Thr183 via binding to AMPK, thus enhancing autophagy activity in the context of high-salt-induced macrophages. These findings indicated that VEGFC inhibited NLRP3 inflammasome activation by promoting VEGFR3-AMPK-dependent autophagy pathway in high-salt-induced macrophages, which provided a mechanistic basis for the therapeutic target in SSHTN and hypertensive kidney injury.

The immunology of heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) now accounts for the majority of new heart failure diagnoses and continues to increase in prevalence in the United States. Importantly, HFpEF is a highly morbid, heterogeneous syndrome lacking effective therapies. Inflammation has emerged as a potential contributor to the pathogenesis of HFpEF. Many of the risk factors for HFpEF are also associated with chronic inflammation, such as obesity, hypertension, aging, and renal dysfunction. A large amount of preclinical evidence suggests that immune cells and their associated cytokines play important roles in mediating fibrosis, oxidative stress, metabolic derangements, and endothelial dysfunction, all potentially important processes in HFpEF. How inflammation contributes to HFpEF pathogenesis, however, remains poorly understood. Recently, a variety of preclinical models have emerged which may yield much needed insights into the causal relationships between risk factors and the development of HFpEF, including the role of specific immune cell subsets or inflammatory pathways. Here, we review evidence in animal models and humans implicating inflammation as a mediator of HFpEF and identify gaps in knowledge requiring further study. As the understanding between inflammation and HFpEF evolves, it is hoped that a better understanding of the mechanisms underlying immune cell activation in HFpEF can open up new therapeutic avenues.

Novel avenues to control blood pressure: targeting the renal lymphatic system

Hypertension is associated with the activation of the immune and lymphatic systems as well as lymphangiogenesis. The changes in the lymphatic system are considered an adaptive response to mitigate the deleterious effects of immune and inflammatory cells on the cardiovascular system. In the article recently published in Clinical Science by Goodlett and collaborators, evidence is shown that inducing renal lymphangiogenesis after the establishment of hypertension in mice is an effective maneuver to reduce systemic arterial blood pressure. In this commentary, we will briefly review what is known about the relationship between the activation of the immune and lymphatic systems, and the resulting effects on systemic blood pressure, summarize the findings published by Goodlett and collaborators, and discuss the impact of their findings on the field.

Androgen-Induced Cardiovascular Risk in Polycystic Ovary Syndrome: The Role of T Lymphocytes

An estimated 15-20% of reproductive-age women are affected by polycystic ovary syndrome (PCOS). PCOS is associated with substantial metabolic and cardiovascular long-term consequences. In young women with PCOS, several cardiovascular risk factors may be found, including chronic inflammation, high blood pressure, and elevated leukocytes. These women are at an increased risk of cardiovascular diseases (CVD), not only during the reproductive years, but also with aging and menopause; therefore, the early prevention and treatment of future cardiovascular adverse effects are necessary. The fundamental characteristic of PCOS is hyperandrogenemia, which is associated with increased pro-inflammatory cytokines and T lymphocytes. Whether these factors play a role in the pathophysiology of hypertension, a risk factor of CVD, due to PCOS is not well established. This review will briefly discuss how a modest increase in androgens in females is linked to the development of hypertension through pro-inflammatory cytokines and T lymphocyte subsets and the promotion of renal injury. Moreover, it reveals a few existing research gaps in this area, including the lack of specific therapy directed at androgen-induced inflammation and immune activation, thus emphasizing the necessity to explore the systemic inflammation in women with PCOS to halt the inevitable inflammatory process targeting the underlying abnormalities of CVD.

HSP70 and Primary Arterial Hypertension

Heat shock protein 70 (HSP70) production is a stress-generated cellular response with high interspecies homology. HSP70 has both chaperone and cytokine functions and may induce, depending on the context, tolerogenic anti-inflammatory reactivity or immunogenic and autoimmune reactivity. Intracellular (chaperoning transit of antigens to MHC in antigen-presenting cells) and extracellular HSP70-related effects are associated with hypertension, which is an inflammatory condition recognized as the most important risk factor for cardiovascular disease mortality. Here, we review (a) the relationship between HSP70, inflammation and immune reactivity, (b) clinical evidence relating to stress, HSP70 and anti-HSP70 reactivity with primary hypertension and (c) experimental data showing that salt-sensitive hypertension is associated with delayed hypersensitivity to HSP70. This is a consequence of anti-HSP70 reactivity in the kidneys and may be prevented and corrected by the T-cell-driven inhibition of kidney inflammation triggered by specific epitopes of HSP70. Finally, we discuss our postulate that lifelong stress signals and danger-associated molecular patterns stimulate HSP-70 and individual genetic and epigenetic characteristics determine whether the HSP70 response would drive inflammatory immune reactivity causing hypertension or, alternatively, would drive immunomodulatory responses that protect against 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.

Genetically inducing renal lymphangiogenesis attenuates hypertension in mice

BACKGROUND

Hypertension (HTN) is associated with renal proinflammatory immune cell infiltration and increased sodium retention. We reported previously that renal lymphatic vessels, which are responsible for trafficking immune cells from the interstitial space to draining lymph nodes, increase in density under hypertensive conditions. We also demonstrated that augmenting renal lymphatic density can prevent HTN in mice. Whether renal lymphangiogenesis can treat HTN in mice is unknown. We hypothesized that genetically inducing renal lymphangiogenesis after the establishment of HTN would attenuate HTN in male and female mice from three different HTN models.

METHODS

Mice with inducible kidney-specific overexpression of VEGF-D (KidVD) experience renal lymphangiogenesis upon doxycycline administration. HTN was induced in KidVD+ and KidVD- mice by subcutaneous release of angiotensin II, administration of the nitric oxide synthase inhibitor L-NAME, or consumption of a 4% salt diet following a L-NAME priming and washout period. After a week of HTN stimuli treatment, doxycycline was introduced. Systolic blood pressure (SBP) readings were taken weekly. Kidney function was determined from urine and serum measures. Kidneys were processed for RT-qPCR, flow cytometry, and imaging.

RESULTS

Mice that underwent renal-specific lymphangiogenesis had significantly decreased SBP and renal proinflammatory immune cells. Additionally, renal lymphangiogenesis was associated with a decrease in sodium transporter expression and increased fractional excretion of sodium, indicating improved sodium handling efficiency.

CONCLUSIONS

These findings demonstrate that augmenting renal lymphangiogenesis can treat HTN in male and female mice by improving renal immune cell trafficking and sodium handling.

Dendritic Cell Epithelial Sodium Channel in Inflammation, Salt-Sensitive Hypertension, and Kidney Damage

Salt-sensitive hypertension is a major risk factor for cardiovascular morbidity and mortality. The pathophysiologic mechanisms leading to different individual BP responses to changes in dietary salt remain elusive. Research in the last two decades revealed that the immune system plays a critical role in the development of hypertension and related end organ damage. Moreover, sodium accumulates nonosmotically in human tissue, including the skin and muscle, shifting the dogma on body sodium balance and its regulation. Emerging evidence suggests that high concentrations of extracellular sodium can directly trigger an inflammatory response in antigen-presenting cells (APCs), leading to hypertension and vascular and renal injury. Importantly, sodium entry into APCs is mediated by the epithelial sodium channel (ENaC). Although the role of the ENaC in renal regulation of sodium excretion and BP is well established, these new findings imply that the ENaC may also exert BP modulatory effects in extrarenal tissue through an immune-dependent pathway. In this review, we discuss the recent advances in our understanding of the pathophysiology of salt-sensitive hypertension with a particular focus on the roles of APCs and the extrarenal ENaC.

Cardiovascular effects of immunosuppression agents

Immunosuppressive medications are widely used to treat patients with neoplasms, autoimmune conditions and solid organ transplants. Key drug classes, namely calcineurin inhibitors, mammalian target of rapamycin (mTOR) inhibitors, and purine synthesis inhibitors, have direct effects on the structure and function of the heart and vascular system. In the heart, immunosuppressive agents modulate cardiac hypertrophy, mitochondrial function, and arrhythmia risk, while in vasculature, they influence vessel remodeling, circulating lipids, and blood pressure. The aim of this review is to present the preclinical and clinical literature examining the cardiovascular effects of immunosuppressive agents, with a specific focus on cyclosporine, tacrolimus, sirolimus, everolimus, mycophenolate, and azathioprine.

Renal Inflammation Induces Salt Sensitivity in Male db/db Mice through Dysregulation of ENaC

BACKGROUND

Hypertension is considered a major risk factor for the progression of diabetic kidney disease. Type 2 diabetes is associated with increased renal sodium reabsorption and salt-sensitive hypertension. Clinical studies show that men have higher risk than premenopausal women for the development of diabetic kidney disease. However, the renal mechanisms that predispose to salt sensitivity during diabetes and whether sexual dimorphism is associated with these mechanisms remains unknown.

METHODS

Female and male db/db mice exposed to a high-salt diet were used to analyze the progression of diabetic kidney disease and the development of hypertension.

RESULTS

Male, 34-week-old, db/db mice display hypertension when exposed to a 4-week high-salt treatment, whereas equivalently treated female db/db mice remain normotensive. Salt-sensitive hypertension in male mice was associated with no suppression of the epithelial sodium channel (ENaC) in response to a high-salt diet, despite downregulation of several components of the intrarenal renin-angiotensin system. Male db/db mice show higher levels of proinflammatory cytokines and more immune-cell infiltration in the kidney than do female db/db mice. Blocking inflammation, with either mycophenolate mofetil or by reducing IL-6 levels with a neutralizing anti-IL-6 antibody, prevented the development of salt sensitivity in male db/db mice.

CONCLUSIONS

The inflammatory response observed in male, but not in female, db/db mice induces salt-sensitive hypertension by impairing ENaC downregulation in response to high salt. These data provide a mechanistic explanation for the sexual dimorphism associated with the development of diabetic kidney disease and salt sensitivity.

The Redox-Metabolic Couple of T Lymphocytes: Potential Consequences for Hypertension

Significance: T lymphocytes, as part of the adaptive immune system, possess the ability to activate and function in extreme cellular microenvironments, which requires these cells to remain highly malleable. One mechanism in which T lymphocytes achieve this adaptability is by responding to cues from both reactive oxygen and nitrogen species, as well as metabolic flux, which together fine-tune the functional fate of these adaptive immune cells. Recent Advances: To date, examinations of the redox and metabolic effects on T lymphocytes have primarily investigated these biological processes as separate entities. Given that the redox and metabolic environments possess significant overlaps of pathways and molecular species, it is inevitable that perturbations in one environment affect the other. Recent consideration of this redox-metabolic couple has demonstrated the strong link and regulatory consequences of these two systems in T lymphocytes. Critical Issues: The redox and metabolic control of T lymphocytes is essential to prevent dysregulated inflammation, which has been observed in cardiovascular diseases such as hypertension. The role of the adaptive immune system in hypertension has been extensively investigated, but the understanding of how the redox and metabolic environments control T lymphocytes in this disease remains unclear. Future Directions: Herein, we provide a discussion of the redox and metabolic control of T lymphocytes as separate entities, as well as coupled to one another, to regulate adaptive immunity. While investigations examining this pair together in T lymphocytes are sparse, we speculate that T lymphocyte destiny is shaped by the redox-metabolic couple. In contrast, disrupting this duo may have inflammatory consequences such as hypertension.

Ablation of TRPV1-positive nerves exacerbates salt-induced hypertension and tissue injury in rats after renal ischemia-reperfusion via infiltration of macrophages

Background: High-salt intake after renal ischemia/reperfusion (I/R) injury leads to hypertension and further renal injury, but the mechanisms are largely unknown. This study tested the hypothesis that degeneration of transient receptor potential vanilloid 1 (TRPV1)-positive nerves exacerbates salt-induced hypertension and renal injury after I/R via enhancing renal macrophage infiltration.Methods: Large dose of capsaicin (CAP, 100 mg/kg, subcutaneously) was used to degenerate rat TRPV1-positive nerves. Then, rats were subjected to renal I/R injury and fed with a low-salt (0.4% NaCl) diet for 5 weeks after I/R, followed by a high-salt (4% NaCl) diet for 4 weeks during which macrophages were depleted using liposome-encapsulated clodronate (LC, 1.3 ml/kg/week, intravenously).Results: The protein level of TRPV1 in the kidney was downregulated by renal I/R injury and was further decreased by CAP treatment. LC treatment did not affect the protein levels of renal TRPV1. After renal I/R injury, high-salt diet significantly increased renal macrophage infiltration, inflammatory cytokines (tumor necrosis factor-alpha and interleukin 1 beta), systolic blood pressure, the urine/water intake ratio, plasma creatine and urea levels, urinary 8-isoprostane, and renal collagen deposition. Interestingly, CAP treatment further increased these parameters. These increases were abolished by depleting macrophages with LC treatment.Conclusions: These data suggest that degenerating TRPV1-positive nerves exacerbates salt-induced hypertension and tissue injury in rats after renal I/R injury via macrophages-mediated renal inflammation.

Mycophenolate mediated remodeling of gut microbiota and improvement of gut-brain axis in spontaneously hypertensive rats

Microbiota has a role in the host blood pressure (BP) regulation. The immunosuppressive drug mofetil mycophenolate (MMF) ameliorates hypertension. The present study analyzes whether MMF improves dysbiosis in a genetic model of hypertension. Twenty weeks old male spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY) were randomly divided into three groups: untreated WKY, untreated SHR, and SHR treated with MMF for 5 weeks. MMF treatment restored gut bacteria from the phyla Firmicutes and Bacteroidetes, and acetate- and lactate-producing bacteria to levels similar to those found in WKY, increasing butyrate-producing bacteria. MMF increased the percentage of anaerobic bacteria in the gut. 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. MMF increased the lower regulatory T cells proportion in mesenteric lymph nodes and Th17 and Th1 infiltration in aorta, improved aortic endothelial function and reduced systolic BP. This study demonstrates for the first time that MMF reduces gut dysbiosis in SHR. This effect could be related to its capability to improve gut integrity due to reduced sympathetic drive in the gut associated to the reduced brain neuroinflammation.

Amplification of Salt-Sensitive Hypertension and Kidney Damage by Immune Mechanisms

Humans with salt-sensitive (SS) hypertension demonstrate increased morbidity, increased mortality, and renal end-organ damage when compared with normotensive subjects or those with salt-resistant hypertension. Increasing evidence indicates that immune mechanisms play an important role in the full development of SS hypertension and associated renal damage. Recent experimental advances and studies in animal models have permitted a greater understanding of the mechanisms of activation and action of immunity in this disease process. Evidence favors a role of both innate and adaptive immune mechanisms that are triggered by initial, immune-independent alterations in blood pressure, sympathetic activity, or tissue damage. Activation of immunity, which can be enhanced by a high-salt intake or by alterations in other components of the diet, leads to the release of cytokines, free radicals, or other factors that amplify renal damage and hypertension and mediate malignant disease.

NF-κB blockade during short-term l-NAME and salt overload strongly attenuates the late development of chronic kidney disease

Nitric oxide synthase inhibition by N^ω-nitro-l-arginine methyl ester (l-NAME) plus a high-salt diet (HS) is a model of chronic kidney disease (CKD) characterized by marked hypertension and renal injury. With cessation of treatment, most of these changes subside, but progressive renal injury develops, associated with persistent low-grade renal inflammation. We investigated whether innate immunity, and in particular the NF-κB system, is involved in this process. Male Munich-Wistar rats received HS + l-NAME (32 mg·kg^-1·day^-1), whereas control rats received HS only. Treatment was ceased after week 4 when 30 rats were studied. Additional rats were studied at week 8 (n = 30) and week 28 (n = 30). As expected, HS + l-NAME promoted severe hypertension, albuminuria, and renal injury after 4 wk of treatment, whereas innate immunity activation was evident. After discontinuation of treatments, partial regression of renal injury and inflammation occurred, along with persistence of innate immunity activation at week 8. At week 28, glomerular injury worsened, while renal inflammation persisted and renal innate immunity remained activated. Temporary administration of the NF-κB inhibitor pyrrolidine dithiocarbamate, in concomitancy with the early 4-wk HS + l-NAME treatment, prevented the development of late renal injury and inflammation, an effect that lasted until the end of the study. Early activation of innate immunity may be crucial to the initiation of renal injury in the HS + l-NAME model and to the autonomous progression of chronic nephropathy even after cessation of the original insult. This behavior may be common to other conditions leading to CKD.

Differential effects of low-dose sacubitril and/or valsartan on renal disease in salt-sensitive hypertension

Diuretics and renin-angiotensin system blockers are often insufficient to control the blood pressure (BP) in salt-sensitive (SS) subjects. Abundant data support the proposal that the level of atrial natriuretic peptide may correlate with the pathogenesis of SS hypertension. We hypothesized here that increasing atrial natriuretic peptide levels with sacubitril, combined with renin-angiotensin system blockage by valsartan, can be beneficial for alleviation of renal damage in a model of SS hypertension, the Dahl SS rat. To induce a BP increase, rats were challenged with a high-salt 4% NaCl diet for 21 days, and chronic administration of vehicle or low-dose sacubitril and/or valsartan (75 μg/day each) was performed. Urine flow, Na+ excretion, and water consumption were increased on the high-salt diet compared with the starting point (0.4% NaCl) in all groups but remained similar among the groups at the end of the protocol. Upon salt challenge, we observed a mild decrease in systolic BP and urinary neutrophil gelatinase-associated lipocalin levels (indicative of alleviated tubular damage) in the valsartan-treated groups. Sacubitril, as well as sacubitril/valsartan, attenuated the glomerular filtration rate decline induced by salt. Alleviation of protein cast formation and lower renal medullary fibrosis were observed in the sacubitril/valsartan- and valsartan-treated groups, but not when sacubitril alone was administered. Interestingly, proteinuria was mildly mitigated only in rats that received sacubitril/valsartan. Further studies of the effects of sacubitril/valsartan in the setting of SS hypertension, perhaps involving a higher dose of the drug, are warranted to determine if it can interfere with the progression of the disease.

Kidney-specific lymphangiogenesis increases sodium excretion and lowers blood pressure in mice

OBJECTIVE

Hypertension is associated with renal immune cell accumulation and sodium retention. Lymphatic vessels provide a route for immune cell trafficking and fluid clearance. Whether specifically increasing renal lymphatic density can treat established hypertension, and whether renal lymphatics are involved in mechanisms of blood pressure regulation remain undetermined. Here, we tested the hypothesis that augmenting renal lymphatic density can attenuate blood pressure in established hypertension.

METHODS

Transgenic mice with inducible kidney-specific overexpression of VEGF-D ('KidVD+' mice) and KidVD- controls were administered a nitric oxide synthase inhibitor, L-NAME, for 4 weeks, with doxycycline administration beginning at the end of week 1. To identify mechanisms by which renal lymphatics alter renal Na handling, Na excretion was examined in KidVD+ mice during acute and chronic salt loading conditions.

RESULTS

Renal VEGF-D induction for 3 weeks enhanced lymphatic density and significantly attenuated blood pressure in KidVD+ mice whereas KidVD- mice remained hypertensive. No differences were identified in renal immune cells, however, the urinary Na excretion was increased significantly in KidVD+ mice. KidVD+ mice demonstrated normal basal sodium handling, but following chronic high salt loading, KidVD+ mice had a significantly lower blood pressure along with increased urinary fractional excretion of Na. Mechanistically, KidVD+ mice demonstrated decreased renal abundance of total NCC and cleaved ENaCα Na transporters, increased renal tissue fluid volume, and increased plasma ANP.

CONCLUSION

Our findings demonstrate that therapeutically augmenting renal lymphatics increases natriuresis and reduces blood pressure under sodium retention conditions.

Immune mechanisms of hypertension

Hypertension affects 30% of adults and is the leading risk factor for heart attack and stroke. Traditionally, hypertension has been regarded as a disorder of two systems that are involved in the regulation of salt-water balance and cardiovascular function: the renin-angiotensin-aldosterone system (RAAS) and the sympathetic nervous system (SNS). However, current treatments that aim to limit the influence of the RAAS or SNS on blood pressure fail in ~40% of cases, which suggests that other mechanisms must be involved. This Review summarizes the clinical and experimental evidence supporting a contribution of immune mechanisms to the development of hypertension. In this context, we highlight the immune cell subsets that are postulated to either promote or protect against hypertension through modulation of cardiac output and/or peripheral vascular resistance. We conclude with an appraisal of knowledge gaps still to be addressed before immunomodulatory therapies might be applied to at least a subset of patients with hypertension.

Senecio serratuloides extract prevents the development of hypertension, oxidative stress and dyslipidemia in nitric oxide-deficient rats

Background Hypertension is a silent killer with no obvious signs and symptoms; thus, it is crucial to prevent its development. Oxidative stress and hyperlipidemia are associated risk factors for developing hypertension. This study aimed at investigating the role of a crude extract of Senecio serratuloides in preventing the development of hypertension, oxidative stress and hyperlipidemia in a rat model of nitric oxide deficiency. Methods Female Wistar rats were co-treated with Nω-Nitro L-arginine methyl ester (L-NAME) (40 mg/kg) and the hydroethanolic extract of S. Serratuloides (HESS150 or HESS300 mg/kg) for 4 weeks. Twenty-hour urine samples were collected weekly during the study. At the end of the study serum, heart and kidneys were harvested for biochemical and histopathological analysis. Results The higher dose (300 mg/kg) of the extract was more effective in preventing increase in systolic (p<0.001) and diastolic (p<0.05) blood pressure. At the end of the treatment period HESS300 treated rats had significantly (p<0.01) higher concentration of creatinine (91.24 ± 6 mg/dL) in urine and significantly (6.36 ± 0.4 mg/24 h; 0.001) lower proteinuria compared to L-NAME control rats (55.75 ± 8 mg/dL and 18.92 ± 2 mg/24 h, respectively). Creatinine clearance and glomerular filtration rate were lower in the L-NAME control group compared to all treatment groups. HESS300 prevented L-NAME-induced decrease in serum angiotensin II concentration, significantly decreased malondialdehyde concentration in serum (p<0.05) and kidneys (p<0.001). It also significantly (p<0.001) decreased low-density lipoprotein concentration while increasing the concentration of high-density lipoprotein cholesterol. It showed cardio- and reno-protective effects and significantly (p<0.01) prevented collagen deposition in these target organs. Conclusion These findings demonstrate the potential of S. Serratuloides in protecting rats from developing hypertension, hyperlipidemia and oxidative stress.

Pathogenic role of innate immunity in a model of chronic NO inhibition associated with salt overload

Nitric oxide inhibition with N^ω-nitro-l-arginine methyl ester (l-NAME), along with salt overload, leads to hypertension, albuminuria, glomerulosclerosis, glomerular ischemia, and interstitial fibrosis, characterizing a chronic kidney disease (CKD) model. Previous findings of this laboratory and elsewhere have suggested that activation of at least two pathways of innate immunity, Toll-like receptor 4 (TLR4)/NF-κB and nucleotide-binding oligomerization domain, leucine-rich repeat, and pyrin domain containing 3 (NLRP3) inflammasome/IL-1β, occurs in several experimental models of CKD and that progression of renal injury can be slowed with inhibition of these pathways. In the present study, we investigated whether activation of innate immunity, through either the TLR4/NF-κB or NLRP3/IL-1β pathway, is involved in the pathogenesis of renal injury in chronic nitric oxide inhibition with the salt-overload model. Adult male Munich-Wistar rats that received l-NAME in drinking water with salt overload (HS + N group) were treated with allopurinol (ALLO) as an NLRP3 inhibitor (HS + N + ALLO group) or pyrrolidine dithiocarbamate (PDTC) as an NF-κB inhibitor (HS + N + PDTC group). After 4 wk, HS + N rats developed hypertension, albuminuria, and renal injury along with renal inflammation, oxidative stress, and activation of both the NLRP3/IL-1β and TLR4/NF-κB pathways. ALLO lowered renal uric acid and inhibited the NLRP3 pathway. These effects were associated with amelioration of hypertension, albuminuria, and interstitial inflammation/fibrosis but not glomerular injury. PDTC inhibited the renal NF-κB system and lowered the number of interstitial cells staining positively for NLRP3. PDTC also reduced renal xanthine oxidase activity and uric acid. Overall, PDTC promoted a more efficient anti-inflammatory and nephroprotective effect than ALLO. The NLRP3/IL-1β and TLR4/NF-κB pathways act in parallel to promote renal injury/inflammation and must be simultaneously inhibited for best nephroprotection.

Intrarenal Renin–Angiotensin System Involvement in the Pathogenesis of Chronic Progressive Nephropathy—Bridging the Informational Gap Between Disciplines

Chronic progressive nephropathy (CPN) is the most commonly encountered spontaneous background finding in laboratory rodents. Various theories on its pathogenesis have been proposed, but there is a paucity of data regarding specific mechanisms or physiologic pathways involved in early CPN development. The current CPN mechanism of action for tumorigenesis is largely based on its associated increase in tubular cell proliferation without regard to preceding subcellular degenerative changes. Combing through the published literature from multiple biology disciplines provided insight into the preceding cellular events. Mechanistic pathways involved in the progressive age-related decline in rodent kidney function and several key inflexion points have been identified. These critical pathway factors were then connected using data from renal models from multiple rodent strains, other species, and mechanistic work in humans to form a cohesive picture of pathways and protein interactions. Abundant data linked similar renal pathologies to local events involving hypoxia (hypoxia-inducible factor 1α), altered intrarenal renin–angiotensin system (RAS), oxidative stress (nitric oxide), and pro-inflammatory pathways (transforming growth factor β), with positive feedback loops and downstream effectors amplifying the injury and promoting scarring. Intrarenal RAS alterations seem to be central to all these events and may be critical to CPN development and progression.

Integration of purinergic and angiotensin II receptor function in renal vascular responses and renal injury in angiotensin II-dependent hypertension

Glomerular arteriolar vasoconstriction and tubulointerstitial injury are observed before glomerular damage occurs in models of hypertension. High interstitial ATP concentrations, caused by the increase in arterial pressure, alter renal mechanisms involved in the long-term control of blood pressure, autoregulation of glomerular filtration rate and blood flow, tubuloglomerular feedback (TGF) responses, and sodium excretion. Elevated ATP concentrations and augmented expression of P2X receptors have been demonstrated under a genetic background or induction of hypertension with vasoconstrictor peptides. In addition to the alterations of the microcirculation in the hypertensive kidney, the vascular actions of elevated intrarenal angiotensin II levels may be mitigated by the administration of broad purinergic P2 antagonists or specific P2Y12, P2X1, and P2X7 receptor antagonists. Furthermore, the prevention of tubulointerstitial infiltration with immunosuppressor compounds reduces the development of salt-sensitive hypertension, indicating that tubulointerstitial inflammation is essential for the development and maintenance of hypertension. Inflammatory cells also express abundant purinergic receptors, and their activation by ATP induces cytokine and growth factor release that in turn contributes to augment tubulointerstitial inflammation. Collectively, the evidence suggests a pathophysiological activation of purinergic P2 receptors in angiotensin-dependent hypertension. Coexistent increases in intrarenal angiotensin II and activates Ang II AT1 receptors, which interacts with over-activated purinergic receptors in a complex manner, suggesting convergence of their post-receptor signaling processes.

Antihypertensive effects of the hydro-ethanol extract of Senecio serratuloides DC in rats

BACKGROUND

Senecio serratuloides DC is used in folk medicine for treating hypertension, skin disorders, internal and external sores, rashes, burns and wounds. This study aimed at investigating the antihypertensive effects of the hydroethanol extract of S. serratuloides (HESS) in N-Nitro-L-arginine methyl ester (L-NAME) induced hypertension in rats.

METHODS

Acute toxicity of HESS was first determined to provide guidance on doses to be used in this study. Lorke's method was used to determine safety of the extract in mice. Female Wistar rats were treated orally once daily with L-NAME (40 mg/kg) for 4 weeks and then concomitantly with L-NAME (20 mg/kg) and plant extract (150 and 300 mg/kg), captopril (20 mg/kg) or saline as per assigned group for 2 weeks followed by a 2-week period of assigned treatments only. Blood pressure was monitored weekly. Lipid profile, nitric oxide, renin and angiotensin II concentrations were determined in serum while mineralocorticoid receptor concentration was quantified in the kidney homogenate. Nitric oxide (NO) concentration was determined in serum and cardiac histology performed.

RESULTS

HESS was found to be non-toxic, having a LD50 greater than 5000 mg/kg. Blood pressure increased progressively in all animals from the second week of L-NAME treatment. HESS treatment significantly and dose-dependently lowered systolic blood pressure (p < 0.001), diastolic blood pressure (p < 0.01), low density lipoprotein cholesterol (p < 0.01) and triglycerides (p < 0.01). It significantly prevented L-NAME induced decrease in serum angiotensin II (p < 0.01), high density lipoprotein cholesterol (p < 0.001) and serum nitric oxide concentrations (p < 0.001). HESS also significantly (p < 0.01) prevented collagen deposition in cardiac tissue.

CONCLUSION

The hydro-ethanol extract of Senecio serratuloides showed antihypertensive, antihyperlipidemic and cardioprotective effects in rats thus confirming its usefulness in traditional antihypertensive therapy and potential for antihypertensive drug development.

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.

Immune cell trafficking, lymphatics and hypertension

Activated immune cell infiltration into organs contributes to the development and maintenance of hypertension. Studies targeting specific immune cell populations or reducing their inflammatory signalling have demonstrated a reduction in BP. Lymphatic vessels play a key role in immune cell trafficking and in resolving inflammation, but little is known about their role in hypertension. Studies from our laboratory and others suggest that inflammation-associated or induction of lymphangiogenesis is organ protective and anti-hypertensive. This review provides the basis for hypertension as a disease of chronic inflammation in various tissues and highlights how renal lymphangiogenesis is a novel regulator of kidney health and BP. 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.

Enhancing Renal Lymphatic Expansion Prevents Hypertension in Mice

RATIONALE

Hypertension is associated with renal infiltration of activated immune cells; however, the role of renal lymphatics and immune cell exfiltration is unknown.

OBJECTIVE

We tested the hypotheses that increased renal lymphatic density is associated with 2 different forms of hypertension in mice and that further augmenting renal lymphatic vessel expansion prevents hypertension by reducing renal immune cell accumulation.

METHODS AND RESULTS

Mice with salt-sensitive hypertension or nitric oxide synthase inhibition-induced hypertension exhibited significant increases in renal lymphatic vessel density and immune cell infiltration associated with inflammation. Genetic induction of enhanced lymphangiogenesis only in the kidney, however, reduced renal immune cell accumulation and prevented hypertension.

CONCLUSIONS

These data demonstrate that renal lymphatics play a key role in immune cell trafficking in the kidney and blood pressure regulation in hypertension.

Role of the Immune System in Hypertension

High blood pressure is present in more than one billion adults worldwide and is the most important modifiable risk factor of death resulting from cardiovascular disease. While many factors contribute to the pathogenesis of hypertension, a role of the immune system has been firmly established by a large number of investigations from many laboratories around the world. Immunosuppressive drugs and inhibition of individual cytokines prevent or ameliorate experimental hypertension, and studies in genetically-modified mouse strains have demonstrated that lymphocytes are necessary participants in the development of hypertension and in hypertensive organ injury. Furthermore, immune reactivity may be the driving force of hypertension in autoimmune diseases. Infiltration of immune cells, oxidative stress, and stimulation of the intrarenal angiotensin system are induced by activation of the innate and adaptive immunity. High blood pressure results from the combined effects of inflammation-induced impairment in the pressure natriuresis relationship, dysfunctional vascular relaxation, and overactivity of the sympathetic nervous system. Imbalances between proinflammatory effector responses and anti-inflammatory responses of regulatory T cells to a large extent determine the severity of inflammation. Experimental and human studies have uncovered autoantigens (isoketal-modified proteins and heat shock protein 70) of potential clinical relevance. Further investigations on the immune reactivity in hypertension may result in the identification of new strategies for the treatment of the disease.

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.

Renal tubular angiotensin converting enzyme is responsible for nitro-L-arginine methyl ester (L-NAME)-induced salt sensitivity

Renal parenchymal injury predisposes to salt-sensitive hypertension, but how this occurs is not known. Here we tested whether renal tubular angiotensin converting enzyme (ACE), the main site of kidney ACE expression, is central to the development of salt sensitivity in this setting. Two mouse models were used: it-ACE mice in which ACE expression is selectively eliminated from renal tubular epithelial cells; and ACE 3/9 mice, a compound heterozygous mouse model that makes ACE only in renal tubular epithelium from the ACE 9 allele, and in liver hepatocytes from the ACE 3 allele. Salt sensitivity was induced using a post L-NAME salt challenge. While both wild-type and ACE 3/9 mice developed arterial hypertension following three weeks of high salt administration, it-ACE mice remained normotensive with low levels of renal angiotensin II. These mice displayed increased sodium excretion, lower sodium accumulation, and an exaggerated reduction in distal sodium transporters. Thus, in mice with renal injury induced by L-NAME pretreatment, renal tubular epithelial ACE, and not ACE expression by renal endothelium, lung, brain, or plasma, is essential for renal angiotensin II accumulation and salt-sensitive hypertension.

Anti-Inflammatory Effects and Prediction of Blood Pressure Response by Baseline Inflammatory State in Catheter-Based Renal Denervation

This retrospective analysis aimed to examine off-target effects on inflammatory and renal function parameters in n=78 subsequent patients treated with renal denervation (RDN) for resistant hypertension. Ambulatory and office blood pressure (ABP/OBP), serum creatinine, glomerular filtration rate (GFR), cystatin C, C-reactive protein (CRP), interleukin-6 (IL-6), and white blood cell count (WBC) were assessed before, 6 and 12 months after RDN. ABP was significantly reduced by -8.2/-3.8 mm Hg (P=.002/.021) at 1 year after RDN, while an initial OBP reduction was not sustained during follow-up. IL-6 levels significantly decreased by -0.5 pg/mL (P=.042) and by -1.7 pg/mL (P<.001) at 6 and 12 months, baseline IL-6 levels possibly predicting ABP response to RDN (r=-0.295; P=.020). Concurrently, leukocyte count was reduced by -0.5 × 103 /μL (P=.017) and -0.8 × 103 /μL (P<.001), respectively. Serum creatinine and GFR remained unchanged, but we observed a significant increase in cystatin C by 0.04 mg/L (P=.026) and 0.14 mg/L (P<.001) at 6 and 12 months after the intervention.

Hypertension as an autoimmune and inflammatory disease

Hypertension that is considered idiopathic is called essential hypertension and accordingly has no clear culprit for its cause. However, basic research and clinical studies in recent years have expanded our understanding of the mechanisms underlying the development of essential hypertension. Of these, increased oxidative stress, both in the kidney and arterial wall, closely coupled with inflammatory infiltration now appear to have a prominent role. Discovery of regulatory and interleukin-17-producing T cells has enabled us to better understand the mechanism by which inflammation and autoimmunity, or autoinflammation, lead to the development of hypertension. Despite achieving considerable progress, the intricate interactions between oxidative stress, the immune system and the development of hypertension remain to be fully elucidated. In this review, we summarize recent developments in the pathophysiology of hypertension with a focus on the oxidant stress-autoimmunity-inflammation interaction.

Myeloid Suppressor Cells Accumulate and Regulate Blood Pressure in Hypertension

RATIONALE

Chronic inflammation is a major contributor to the progressive pathology of hypertension, and T-cell activation is required for the genesis of hypertension. However, the precise role of myeloid cells in this process is unclear.

OBJECTIVE

To characterize and understand the role of peripheral myeloid cells in the development of hypertension.

METHODS AND RESULTS

We examined myeloid cells in the periphery of hypertensive mice and found that increased numbers of CD11b(+)Gr1(+) myeloid cells in blood and the spleen are a characteristic of 3 murine models of experimental hypertension (angiotensin II, L-NG-nitroarginine methyl ester, and high salt). These cells express surface markers and transcription factors associated with immaturity and immunosuppression. Also, they produce hydrogen peroxide to suppress T-cell activation. These are characteristics of myeloid-derived suppressor cells (MDSCs). Depletion of hypertensive MDSCs increased blood pressure and renal inflammation. In contrast, adoptive transfer of wild-type MDSCs to hypertensive mice reduced blood pressure, whereas the transfer of nicotinamide adenine dinucleotide phosphate oxidase 2-deficient MDSCs did not.

CONCLUSION

The accumulation of MDSCs is a characteristic of experimental models of hypertension. MDSCs limit inflammation and the increase of blood pressure through the production of hydrogen peroxide.

Salt Sensitivity in Response to Renal Injury Requires Renal Angiotensin-Converting Enzyme

Recent evidence indicates that salt-sensitive hypertension can result from a subclinical injury that impairs the kidneys' capacity to properly respond to a high-salt diet. However, how this occurs is not well understood. Here, we showed that although previously salt-resistant wild-type mice became salt sensitive after the induction of renal injury with the nitric oxide synthase inhibitor Nω-nitro-l-arginine methyl ester hydrochloride; mice lacking renal angiotensin-converting enzyme, exposed to the same insult, did not become hypertensive when faced with a sodium load. This is because the activity of renal angiotensin-converting enzyme plays a critical role in (1) augmenting the local pool of angiotensin II and (2) the establishment of the antinatriuretic state via modulation of glomerular filtration rate and sodium tubular transport. Thus, this study demonstrates that the presence of renal angiotensin-converting enzyme plays a pivotal role in the development of salt sensitivity in response to renal injury.

Purinergic receptors in tubulointerstitial inflammatory cells: a pathophysiological mechanism of salt-sensitive hypertension

Recent studies have suggested that both the tubulointerstitial inflammatory cells and the activation of purinergic receptors integrate common mechanisms that result in salt-sensitive hypertension. The basis of this hypothesis is that renal endothelial cells release ATP in response to shear stress in the setting of hypertension. It has been demonstrated that the over-expression and activation of the P2X7, P2Y12 and P2X1 receptors favour the elevation of blood pressure induced by high-salt intake. In addition, the release of interleukins and inflammatory mediators in the tubulointerstitial area appears to be related to the activation of these receptors. Renal vasoconstriction and tubulointerstitial injury develop as a result, which increase sodium reabsorption by epithelial cells. Consistent with these effects, the reduction of tubulointerstitial inflammation caused by immunosuppressants, such as mycophenolate mofetil, prevents the development of salt-sensitive hypertension. Also, P2X7-receptor knockout mice develop minor renal injury when hypertension is induced via the administration of deoxycorticosterone acetate and a high-salt diet. In the setting of angiotensin II-induced hypertension, which is an early stage in the development of salt-sensitive hypertension, an acute blockade with the specific, non-selective P2 antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid prevented the renal vasoconstriction induced by angiotensin II. In addition, it normalized glomerular haemodynamics and restored sodium excretion to control values. These findings suggest that chronic administration of P2 purinergic antagonists may prevent the deleterious effects of purinergic receptors during the development of salt-sensitive hypertension.

Crosstalk between the unfolded protein response and NF-κB-mediated inflammation in the progression of chronic kidney disease

The chronic inflammatory response is emerging as an important therapeutic target in progressive chronic kidney disease. A key transcription factor in the induction of chronic inflammation is NF-κB. Recent studies have demonstrated that sustained activation of the unfolded protein response (UPR) can initiate this NF-κB signaling phenomenon and thereby induce chronic kidney disease progression. A key factor influencing chronic kidney disease progression is proteinuria and this condition has now been demonstrated to induce sustained UPR activation. This review details the crosstalk between the UPR and NF-κB pathways as pertinent to chronic kidney disease. We present potential tools to study this phenomenon as well as potential therapeutics that are emerging to regulate the UPR. These therapeutics may prevent inflammation specifically induced in the kidney due to proteinuria-induced sustained UPR activation.

Role of Angiotensin II type 1 receptor on renal NAD(P)H oxidase, oxidative stress and inflammation in nitric oxide inhibition induced-hypertension

AIMS

Activation of the renin-angiotensin system (RAS), renal oxidative stress and inflammation are constantly present in experimental hypertension. Nitric oxide (NO) inhibition with N(w)-nitro-L-arginine methyl ester (L-NAME) has previously been reported to produce hypertension, increased expression of Angiotensin II (Ang II) and renal dysfunction. The use of Losartan, an Ang II type 1 receptor (AT1R) antagonist has proven to be effective reducing hypertension and renal damage; however, the mechanism by which AT1R blockade reduced kidney injury and normalizes blood pressure in this experimental model is still complete unknown. The current study was designed to test the hypothesis that AT1R activation promotes renal NAD(P)H oxidase up-regulation, oxidative stress and cytokine production during L-NAME induced-hypertension.

MAIN METHODS

Male Sprague-Dawley rats were distributed in three groups: L-NAME, receiving 70 mg/100ml of L-NAME, L-NAME+Los, receiving 70 mg/100ml of L-NAME and 40 mg/kg/day of Losartan; and Controls, receiving water instead of L-NAME or L-NAME and Losartan.

KEY FINDINGS

After two weeks, L-NAME induced high blood pressure, renal overexpression of AT1R, NAD(P)H oxidase sub-units gp91, p22 and p47, increased levels of oxidative stress, interleukin-6 (IL-6) and interleukin-17 (IL-17). Also, we found increased renal accumulation of lymphocytes and macrophages. Losartan treatment abolished the renal expression of gp91, p22, p47, oxidative stress and reduced NF-κB activation and IL-6 expression.

SIGNIFICANCE

These findings indicate that NO induced-hypertension is associated with up-regulation of NADPH oxidase, oxidative stress production and overexpression of key inflammatory mediators. These events are associated with up-regulation of AT1R, as evidenced by their reversal with AT1R blocker treatment.

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.

Reactive oxygen species as important determinants of medullary flow, sodium excretion, and hypertension

The physiological evidence linking the production of superoxide, hydrogen peroxide, and nitric oxide in the renal medullary thick ascending limb of Henle (mTAL) to regulation of medullary blood flow, sodium homeostasis, and long-term control of blood pressure is summarized in this review. Data obtained largely from rats indicate that experimentally induced elevations of either superoxide or hydrogen peroxide in the renal medulla result in reduction of medullary blood flow, enhanced Na(+) reabsorption, and hypertension. A shift in the redox balance between nitric oxide and reactive oxygen species (ROS) is found to occur naturally in the Dahl salt-sensitive (SS) rat model, where selective reduction of ROS production in the renal medulla reduces salt-induced hypertension. Excess medullary production of ROS in SS rats emanates from the medullary thick ascending limbs of Henle [from both the mitochondria and membrane NAD(P)H oxidases] in response to increased delivery and reabsorption of excess sodium and water. There is evidence that ROS and perhaps other mediators such as ATP diffuse from the mTAL to surrounding vasa recta capillaries, resulting in medullary ischemia, which thereby contributes to hypertension.

Uric acid, hypertension, and cardiovascular and renal complications

Over the last decade, the biologic interference of uric acid with the cardiovascular (CV) system and the kidney has been intensively investigated, and several experimental studies in animal models and in vitro documented that hyperuricemia may trigger hypertension and incite endothelial dysfunction, vascular damage and renal disease. A substantial proportion of epidemiological studies are compatible with the hypothesis that hyperuricemia may be noxious to the CV system and the kidney as well. However, there are still no well-powered trials testing whether uric acid-lowering interventions may reduce BP or attenuate the risk for adverse CV and renal outcomes. Evidence still remains largely insufficient to recommend changes in the current policy of not prescribing uric acid-lowering drugs to individuals with asymptomatic hyperuricemia.

Sex differences in T cells in hypertension

PURPOSE

Hypertension is a major risk factor for cardiovascular disease, stroke, and end-organ damage. There is a sex difference in blood pressure (BP) that begins in adolescence and continues into adulthood, in which men have a higher prevalence of hypertension compared with women until the sixth decade of life. Less than 50% of hypertensive adults in the United States manage to control their BP to recommended levels using current therapeutic options, and women are more likely than are men to have uncontrolled high BP. This, is despite the facts that more women compared with men are aware that they have hypertension and that women are more likely to seek treatment for the disease. Novel therapeutic targets need to be identified in both sexes to increase the percentage of hypertensive individuals with controlled BP. The purpose of this article was to review the available literature on the role of T cells in BP control in both sexes, and the potential therapeutic application/implications of targeting immune cells in hypertension.

METHODS

A search of PubMed was conducted to determine the impact of sex on T cell-mediated control of BP. The search terms included sex, gender, estrogen, testosterone, inflammation, T cells, T regulatory cells, Th17 cells, hypertension, and blood pressure. Additional data were included from our laboratory examinations of cytokine expression in the kidneys of male and female spontaneously hypertensive rats (SHRs) and differential gene expression in both the renal cortex and mesenteric arterial bed of male and female SHRs.

FINDINGS

There is a growing scientific literature base regarding the role of T cells in the pathogenesis of hypertension and BP control; however, the majority of these studies have been performed exclusively in males, despite the fact that both men and women develop hypertension. There is increasing evidence that although T cells also mediate BP in females, there are distinct differences in both the T-cell profile and the functional impact of sex differences in T cells on cardiovascular health, although more work is needed to better define the relative impact of different T-cell subtypes on BP in both sexes.

IMPLICATIONS

The challenge now is to fully understand the molecular mechanisms by which the immune system regulates BP and how the different components of the immune system interact so that specific mechanisms can be targeted therapeutically without compromising natural immune defenses.

Renal angiotensin-converting enzyme is essential for the hypertension induced by nitric oxide synthesis inhibition

The kidney is an important source of angiotensin-converting enzyme (ACE) in many species, including humans. However, the specific effects of local ACE on renal function and, by extension, BP control are not completely understood. We previously showed that mice lacking renal ACE, are resistant to the hypertension induced by angiotensin II infusion. Here, we examined the responses of these mice to the low-systemic angiotensin II hypertensive model of nitric oxide synthesis inhibition with L-NAME. In contrast to wild-type mice, mice without renal ACE did not develop hypertension, had lower renal angiotensin II levels, and enhanced natriuresis in response to L-NAME. During L-NAME treatment, the absence of renal ACE was associated with blunted GFR responses; greater reductions in abundance of proximal tubule Na(+)/H(+) exchanger 3, Na(+)/Pi co-transporter 2, phosphorylated Na(+)/K(+)/Cl(-) cotransporter, and phosphorylated Na(+)/Cl(-) cotransporter; and greater reductions in abundance and processing of the γ isoform of the epithelial Na(+) channel. In summary, the presence of ACE in renal tissue facilitates angiotensin II accumulation, GFR reductions, and changes in the expression levels and post-translational modification of sodium transporters that are obligatory for sodium retention and hypertension in response to nitric oxide synthesis inhibition.

Infiltrating immune cells in the kidney in salt-sensitive hypertension and renal injury

The importance of the immune system in hypertension, vascular disease, and renal disease has been appreciated for over 50 years. Recent experimental advances have led to a greater appreciation of the mechanisms whereby inflammation and immunity participate in cardiovascular disease. In addition to the experimental data, multiple studies in patients have demonstrated a strong correlation between the observations made in animals and humans. Of great interest is the development of salt-sensitive hypertension in humans with the concurrent increase in albumin excretion rate. Experiments in our laboratory have demonstrated that feeding a high-NaCl diet to Dahl salt-sensitive (SS) rats results in a significant infiltration of T lymphocytes into the kidney that is accompanied by the development of hypertension and renal disease. The development of disease in the Dahl SS closely resembles observations made in patients; studies were therefore performed to investigate the pathological role of infiltrating immune cells in the kidney in hypertension and renal disease. Pharmacological and genetic studies indicate that immune cell infiltration into the kidney amplifies the disease process. Further experiments demonstrated that infiltrating T cells may accentuate the Dahl SS phenotype by increasing intrarenal ANG II and oxidative stress. From these and other data, we hypothesize that infiltrating immune cells, which surround the blood vessels and tubules, can serve as a local source of bioactive molecules which mediate vascular constriction, increase tubular sodium reabsorption, and mediate the retention of sodium and water to amplify sodium-sensitive hypertension. Multiple experiments remain to be performed to refine and clarify this hypothesis.

Hypertension after kidney transplantation: a pathophysiologic approach

Post-transplant hypertension is associated with decreased graft and patient survival and cardiovascular morbidity. Unfortunately, post-transplant hypertension is often poorly controlled. Important risk factors include immunosuppressive medications, complications of the transplant surgery, delayed graft function, rejection, and donor and recipient risk factors. The effects of immunosuppressive medications are multifactorial including increased vascular and sympathetic tone and salt and fluid retention. The immunosuppressive agents most commonly associated with hypertension are glucocorticoids and calcineurin inhibitors. Drug therapy for hypertension should be based on the comorbidities and pathophysiology. Evidence-based approaches to defining and treating hypertension in renal transplant recipients are predominantly extrapolated from large-scale studies performed in the general population. Thus, there continues to be a need for larger studies examining the pathophysiology, diagnosis and treatment of hypertension in renal transplant recipients.

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.

Maintenance of hypertensive hemodynamics does not depend on ROS in established experimental chronic kidney disease

While the presence of oxidative stress in chronic kidney disease (CKD) is well established, its relation to hypertensive renal hemodynamics remains unclear. We hypothesized that once CKD is established blood pressure and renal vascular resistance (RVR) no longer depend on reactive oxygen species. CKD was induced by bilateral ablation of 2/3 of each kidney. Compared to age-matched, sham-operated controls all ablated rats showed proteinuria, decreased glomerular filtration rate (GFR), more renal damage, higher mean arterial pressure (MAP), RVR and excretion of oxidative stress markers and hydrogen peroxide, while excretion of stable nitric oxide (NO) metabolites tended to decrease. We compared MAP, RVR, GFR and fractional excretion of sodium under baseline and during acute Tempol, PEG-catalase or vehicle infusion in rats with established CKD vs. controls. Tempol caused marked reduction in MAP in controls (96±5 vs.79±4 mmHg, P<0.05) but not in CKD (130±5 vs. 127±6 mmHg). PEG-catalase reduced MAP in both groups (controls: 102±2 vs. 94±4 mmHg, P<0.05; CKD: 118±4 vs. 110±4 mmHg, P<0.05), but did not normalize MAP in CKD rats. Tempol and PEG-catalase slightly decreased RVR in both groups. Fractional excretion of sodium was increased by both Tempol and PEG-catalase in both groups. PEG-catalase decreased TBARS excretion in both groups. In sum, although oxidative stress markers were increased, MAP and RVR did not depend more on oxidative stress in CKD than in controls. Therefore reactive oxygen species appear not to be important direct determinants of hypertensive renal hemodynamics in this model of established CKD.

The cooperative roles of inflammation and oxidative stress in the pathogenesis of hypertension

SIGNIFICANCE

Innate and adaptive immunity play fundamental roles in the development of hypertension and its complications. As effectors of the cell-mediated immune response, myeloid cells and T lymphocytes protect the host organism from infection by attacking foreign intruders with bursts of reactive oxygen species (ROS).

RECENT ADVANCES

While these ROS may help to preserve the vascular tone and thereby protect against circulatory collapse in the face of overwhelming infection, aberrant elaboration of ROS triggered by immune cells in the absence of a hemodynamic insult can lead to pathologic increases in blood pressure. Conversely, misdirected oxidative stress in cardiovascular control organs, including the vasculature, the kidney, and the nervous system potentiates inflammatory responses, augmenting blood pressure elevation and inciting target organ damage.

CRITICAL ISSUES

Inflammation and oxidative stress thereby act as cooperative and synergistic partners in the pathogenesis of hypertension.

FUTURE DIRECTIONS

Pharmacologic interventions for hypertensive patients will need to exploit this robust bidirectional relationship between ROS generation and immune activation in cardiovascular control organs to maximize therapeutic benefit, while limiting off-target side effects.