Physiological and immunopathological consequences of active immunization of spontaneously hypertensive and normotensive rats against murine renin

Advances in pathogenesis and treatment of essential hypertension

Hypertension is a significant risk factor for cardiovascular and cerebrovascular diseases and the leading cause of premature death worldwide. However, the pathogenesis of the hypertension, especially essential hypertension, is complex and requires in-depth studies. Recently, new findings about essential hypertension have emerged, and these may provide important theoretical bases and therapeutic tools to break through the existing bottleneck of essential hypertension. In this review, we demonstrated important advances in the different pathogenesis areas of essential hypertension, and highlighted new treatments proposed in these areas, hoping to provide insight for the prevention and treatment of the essential hypertension.

Therapeutic vaccine for chronic diseases after the COVID-19 Era

There is currently a respiratory disease outbreak caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). After rapid development, RNA vaccines and adenoviral vector vaccines were approved within a year, which has demonstrated the strong impact of preventing infectious diseases using gene therapy technology. Furthermore, intensive immunological analysis has been performed to evaluate the efficiency and safety of these vaccines, potentially allowing for rapid progress in vaccine technology. After the coronavirus disease 2019 (COVID-19) era, the novel vaccine technology developed will expand to other vaccines. We have been developing vaccines for chronic diseases, such as hypertension, for >10 years. Regarding the development of vaccines against self-antigens (i.e., angiotensin II), the vaccine should efficiently induce a blocking antibody response against the self-antigen without activating cytotoxic T cells. Therefore, the epitope vaccine approach has been proposed to induce antibody production in response to a combination of a B cell epitope and exogenous T cell epitopes through major histocompatibility complex molecules. When these vaccines are established as therapeutic options for hypertension, their administration regimen, which might be a few times per year, will replace daily medication use. Thus, therapeutic vaccines for hypertension may be a novel option to control the progression of cerebrovascular diseases. Hopefully, the accumulation of immunological findings and vaccine technology advances due to COVID-19 will provide a novel concept for vaccines for chronic diseases.

Vaccines against components of the renin-angiotensin system

Even though effective drugs for treating hypertension are available, a great percentage of patients have inadequate control of their blood pressure. Unwanted side effects and inappropriate oral drug adherence are important factors that contribute to the global problem of uncontrolled hypertension. Vaccination could provide a revolutionary therapy with long-lasting effects, increasing patient compliance and therefore better control of high blood pressure. Nowadays, current immunization approaches against hypertension target renin, angiotensin I, angiotensin II, and angiotensin II type 1 receptor, key elements of the renin–angiotensin system. This article reviews the different vaccination attempts with proteins and peptides against the different molecules of the renin–angiotensin system in the last two decades, safety issues, and other novel prospects biomarkers in hypertension, and summarizes the potential of this immunomodulatory approach in clinical practice.

Future Directions of Therapeutic Vaccines for Chronic Diseases

Vaccines are well-known therapies for infectious disease and cancer; however, recently, we and others have developed vaccines for other chronic diseases, such as hypertension, diabetes and dyslipidemia. Although we have many treatment options for hypertension, including angiotensin II type 1 receptor blockers, calcium-channel blockers, and diuretics, a substantial portion of the hypertensive population has uncontrolled blood pressure due to poor medication adherence. When these vaccines are established in the future as therapeutic options for chronic diseases, their administration regimen, such as several times per year, will replace daily medication use. Thus, therapeutic vaccines might be a novel option to control the progression of cardiovascular diseases. Importantly, regarding the development of vaccines against self-antigens (i.e., angiotensin II), the vaccine should efficiently induce a blocking antibody response against the self-antigen without provoking cytotoxic T cells. Therefore, to address the safety and efficiency of therapeutic vaccines, we have developed an original B-cell vaccine to induce antibody production and used carrier proteins, which include exogenous T-cell epitopes through the major histocompatibility complex. In this review, we will introduce the challenges in developing therapeutic vaccines for chronic diseases and describe the therapeutic potential for cardiovascular diseases.

[Development of therapeutic vaccine for life style-related diseases]

In the 18^th century, Edward Jenner proposed the vaccine for smallpox as a first vaccine therapy based on the legend that a vaccinia prevents the infection with smallpox. Recently, the therapeutic target of vaccine will expand from infectious diseases to various diseases, such as amyloid β or tau vaccine for Alzheimer's disease. We are now going to develop a therapeutic vaccine to lifestyle-related diseases (i.e. high blood pressure), and aim to realize a novel therapy which will be injected once or twice per year from a daily medication. For this purpose, the appropriate choice of an antigen, carrier and adjuvants should be required to activate hormonal immunity by the vaccine, leading to efficient antibody production without toxicity, because the therapeutic target of our vaccine is an endogenous protein (i.e. hormone). The clinical advantage of this therapeutic vaccine is to improve the medical adherence and drug management because the multiple drug users are increased in particular old patients, so called polypharmacy. If the vaccine will take place of a part of medicine in future, it may give us a novel therapeutic option with several social benefits.

Vaccine Development against the Renin-Angiotensin System for the Treatment of Hypertension

Hypertension is a global public health issue and the most important preventable cause of cardiovascular diseases. Despite the clinical availability of many antihypertensive drugs, many hypertensive patients have poor medication adherence and blood pressure control due, at least partially, to the asymptomatic and chronic characteristics of hypertension. Immunotherapeutic approaches have the potential to improve medication adherence in hypertension because they induce prolonged therapeutic effects and need a low frequency of administration. The first attempts to reduce blood pressure by using vaccines targeting the renin-angiotensin system were made more than half a century ago; however, at the time, a poor understanding of immunology and the mechanisms of hypertension and a lack of optimal vaccine technologies such as suitable antigen design, proper adjuvants, and effective antigen delivery systems meant that attempts to develop antihypertensive vaccines failed. Recent advances in immunology and vaccinology have provided potential therapeutic immunologic approaches to treat not only infectious diseases but also cancers and other noncommunicable diseases. One important biotechnology that has had a major impact on modern vaccinology is virus-like particle technology, which can efficiently deliver vaccine antigens without the need for artificial adjuvants. A human clinical trial that indicated the effectiveness and safety of a virus-like particle-based antiangiotensin II vaccine marked a turning point in the field of therapeutic antihypertensive vaccines. Here, we review the history of the development of immunotherapies for the treatment of hypertension and discuss the current perspectives in the field.

Therapeutic Vaccines for Hypertension: a New Option for Clinical Practice

PURPOSE OF REVIEW

Vaccines are commonly used as preventive methods, primarily against infectious diseases. The goal of our study is to develop the therapeutic vaccine for hypertension.

RECENT FINDINGS

We and others recently reported that an angiotensin II (AngII) vaccine for hypertension successfully attenuated elevated blood pressures in an animal model without any immunogenic side effects. In this system, an immunogenic molecule (i.e., KLH) with adjuvants provides an antigen that supports the activation of helper T cells. In addition, pretreatment with the AngII vaccine exerts neuroprotective effects in a cerebral ischemia model and cardioprotective effects in a myocardial infarction model. In the early phase of clinical trial, the administration of an AngII vaccine (AngQb-Cyt006) successfully decreased blood pressure in hypertensive patients with the increase of anti-AngII antibody titer. Increasing the effectiveness of drug adherence interventions in the clinical setting may have a large impact on the health of the population, which can be improved by using successful therapeutic vaccines. In this review, we describe the concept of therapeutic vaccines for hypertension and future directions for therapeutic vaccines.

Development of DNA vaccines as an anti-hypertensive therapy or for anti-angiogenesis

INTRODUCTION

Vaccines are used as preventive medicine for infectious diseases worldwide; however, several recent studies have indicated the potential of therapeutic vaccines for managing Alzheimer's disease or hypertension.

AREAS COVERED

The concept and history of therapeutic vaccines for hypertension are introduced. The improvement of drug compliance associated with vaccines in hypertensive patients may assist in better control of blood pressure, leading to reduced complications. Recently, groups have attempted to develop a therapeutic vaccine against hypertension. The vaccine-induced anti-angiotensin II antibodies can efficiently ameliorate high blood pressure. DNA vaccines have also been designed via a similar strategy using a plasmid vector encoding a hepatitis B core (HBc)-angiotensin II fusion protein. The immunogenic molecule (i.e., HBc) is used to provide an antigen that supports the activation of T cells in this DNA vaccine system. The platform technology can also be applied to generate a VEGF vaccine for cancer.

EXPERT OPINION

To date, several clinical studies of DNA vaccines have been conducted, but their effectiveness has not been determined. We hope that the novel concept of DNA vaccines will contribute to promoting health and medicine in the future.

Peptide Vaccines for Hypertension and Diabetes Mellitus

Vaccines are commonly used as a preventive medicine for infectious diseases worldwide; however, the trial for an amyloid beta vaccine against Alzheimer’s disease will open a new concept in vaccination. In case of therapeutic vaccines for cancer, their targets are usually specific antigens in cancer cells, allowing activated cytotoxic T cells (CTLs) to attach and remove the antigen-presenting cancer cells. In our therapeutic vaccines against hypertension, the target is angiotensin II (Ang II) and induced anti-Ang II antibodies could efficiently ameliorate high blood pressure. Similarly, we developed the therapeutic vaccine against DPP4 for diabetes mellitus. However, because Ang II or DPP4 is an endogenous hormone, we must avoid autoimmune disease induced by these vaccines. Therefore, our system was used to design a therapeutic vaccine that elicits anti-Ang II or DPP4 antibodies without CTL activation against Ang II or DPP4. In this review, we will describe our concept of therapeutic vaccines for hypertension and diabetes mellitus.

Hypertension Vaccine may be a boon to millions in developing world

Hypertension affects around 40% adults aged 25 years and more worldwide, and accounts for 7% of total disability-adjusted life-years. A simple algorithmic program is required to manage hypertension consisting of screening, life style measures, treatment and follow-up, a reliable drug supply and distribution system, and a credible health information system. Despite availability of effective antihypertensive drugs, long term treatment is still costly, tedious, and at the population level rather unsuccessful. Hypertension leaves patients and families with an avoidable heavy economic burden due to failure to control blood pressure. Health policy needs to address gross imbalance between prevention and management by increasing contribution to the preventive programs. During 21st century, the risk factors for morbidity and mortality have been changed, and researchers have started to work upon vaccines against lifestyle diseases like hypertension, diabetes etc. Researchers began experimenting with vaccines against the renin-angiotensin system to control hypertension around six decades ago. The vaccine candidates against hypertension namely ATR12181, pHAV-4Ang IIs, CYT006-AngQb, AngI-R, ATRQβ-001 have shown promising results. A candidate vaccine, CYT006-AngQb, has crossed initial phase and moved into phase 2 trials. However, more human studies in subsequent phases of trials are required to establish the safety and efficacy of anti-hypertensive vaccine. If proved safe and cost effective, a vaccine even with 50% efficacy against hypertension may protect about 90 million people from hypertension and its heavy economic burden. It can be an appropriate solution for low compliance to antihypertensive drug therapy as well as an avalanche to induce efforts on various chronic disease vaccine development programs.

Therapeutic vaccines against human and rat renin in spontaneously hypertensive rats

Vaccination provides a promising approach for treatment of hypertension and improvement in compliance. As the initiation factor of renin-angiotensin system, renin plays a critical role in hypertension. In this study, we selected six peptides (rR32, rR72, rR215, hR32, hR72, and hR215) belonging to potential epitopes of rat and human renin. The main criteria were as follows: (1) include one of renin catalytic sites or the flap sequence; (2) low/no-similarity when matched with the host proteome; (3) ideal antigenicity and hydrophilicity. The peptides were coupled to keyhole limpet hemocyanin and injected into SpragueDawley (SD) rats, spontaneously hypertensive rats (SHRs) and Wistar-Kyoto rats. The antisera titers and the binding capacity with renin were detected. The effects of the anti-peptides antibodies on plasma renin activity (PRA) and blood pressure were also determined. All peptides elicited strong antibody responses. The antisera titers ranged from 1:32,000 to 1:80,000 in SD rats on day 63. All antisera could bind to renin in vitro. Compared with the control antibody, the antibodies against the rR32, hR32, rR72 and hR72 peptides inhibited PRA level by up to about 50%. Complete cross-reactivity of the anti-rR32 antibody and the anti-hR32 antibody was confirmed. The epitopes rR32 and hR32 vaccines significantly decreased systolic blood pressure (SBP) of SHRs up to 15mmHg (175±2 vesus 190±3 mmHg, P = 0.035; 180±2 vesus 195±3 mmHg, P = 0.039), while no obvious effect on SD rats. Additionally, no significant immune-mediated damage was detected in the vaccinated animals. In conclusion, the antigenic peptide hR32 vaccine mimicking the ³²Asp catalytic site of human renin may constitute a novel tool for the development of a renin vaccine.

Decrease in blood pressure and regression of cardiovascular complications by angiotensin II vaccine in mice

Vaccines have been recently developed to treat various diseases such as cancer, rheumatoid arthritis and Alzheimer’s disease in addition to infectious diseases. However, before use in the clinical setting, vaccines targeting self-antigens must be demonstrated to be effective and safe, evoking an adequate humoral immune response from B cells while avoiding T cell activation in response to self. Although the vaccine targeting angiotensin II (Ang II) is efficient in rodents and humans, little is known regarding the immunological activation and safety of the vaccine. In this study, we evaluated the efficiency and safety of an Ang II peptide vaccine in mice. Immunization with Ang II conjugated to keyhole limpet hemocyanin (KLH) successfully induced the production of anti-Ang II antibody, which blocked Ang II signaling in human aortic smooth muscle cells. However, Ang II itself did not activate T cells, as assessed by the proliferation and lymphokine production of T cells in immunized mice, whereas KLH activated T cells. In an Ang II-infused model, the non-immunized mice showed high blood pressure (BP), whereas the immunized mice (Ang II-KLH) showed a significant decrease in systolic BP, accompanied by significant reductions in cardiac hypertrophy and fibrosis. Importantly, anti-Ang II antibody titer was not elevated even after the administration of large amounts of Ang II, indicating that Ang II itself boosted antibody production, most likely due to less activation of T cells. In addition, no accumulation of inflammatory cells was observed in immunized mice, because endogenous Ang II would not activate T cells after immunization with Ang II-KLH. Taken together, these data indicate that vaccines targeting Ang II might be effective to decrease high BP and prevent cardiovascular complications without severe side effects.

Vaccination against the angiotensin type 1 receptor for the prevention of L-NAME-induced nephropathy

Previous studies have shown that renin-angiotensin (Ang) system vaccines may be effective for the treatment of hypertension, but their efficacy for the prevention of renal disease is unclear. The aim of this study was to compare the effects of an Ang II type 1 (AT1) receptor vaccine with an Ang II receptor blocker (ARB) and a vasodilator on blood pressure (BP) and renal injury in the L-NAME nephropathy model. Male spontaneously hypertensive rats (SHRs) were divided into six groups and treated transiently with three injections of vehicle or AT1 receptor vaccine (0.1 mg) at age 4, 6 and 8 weeks, or continuously with candesartan cilexetil (0.1 mg kg(-1) per day) or hydralazine hydrochloride (5 mg kg(-1) per day), then administered NG-nitro-L-arginine methyl ester (L-NAME) from age 18 to 21 weeks to induce renal injury. Vaccination against the AT1 receptor caused a significant increase in AT1 receptor titers, and a sustained decrease in BP. L-NAME treatment resulted in a marked increase in proteinuria in the control groups, which was completely suppressed in the AT1 vaccine-treated group, and glomerular injury scores were also significantly decreased. Real-time RT-PCR and immunofluorescence studies revealed increased renin mRNA, and increased glomerular expression of nephrin. Comparable results were seen in rats treated continuously with the ARB candesartan, but not with hydralazine. These results suggest that transient AT1 vaccination is as effective as continuous treatment with ARB, not only for the attenuation of hypertension, but also for the prevention of L-NAME-induced nephropathy in SHR.

Therapeutic perspectives in hypertension: novel means for renin-angiotensin-aldosterone system modulation and emerging device-based approaches

The conventional antihypertensive therapies including renin–angiotensin–aldosterone system antagonists (converting enzyme inhibitors, receptor blockers, renin inhibitors, and mineralocorticoid receptor blockers), diuretics, β-blockers, and calcium channel blockers are variably successful in achieving the challenging target blood pressure values in hypertensive patients. Difficult to treat hypertension is still a commonly observed problem world-wide. A number of drugs are considered to be used as novel therapies for hypertension. Renalase supplementation, vasopeptidase inhibitors, endothelin antagonists, and especially aldosterone antagonists (aldosterone synthase inhibitors and novel selective mineralocorticoid receptor blockers) are considered an option in resistant hypertension. In addition, the aldosterone antagonists as well as (pro)renin receptor blockers or AT₂ receptor agonists might attenuate end-organ damage. This array of medications has now been complemented by a number of new approaches of non-pharmacological strategies including vaccination, genomic interference, controlled breathing, baroreflex activation, and probably most successfully renal denervation techniques. However, the progress on innovative therapies seems to be slow and the problem of resistant hypertension and proper blood pressure control appears to be still persisting. Therefore the regimens of currently available drugs are being fine-tuned, resulting in the establishment of several novel fixed-dose combinations including triple combinations with the aim to facilitate proper blood pressure control. It remains an exciting question which approach will confer the best blood pressure control and risk reduction in this tricky disease.

Vaccines against non-communicable diseases

Chronic non-communicable diseases (NCDs) are increasingly recognized as the major cause of morbidity and mortality worldwide. Effective, affordable and broadly accessible medicines for their treatment are much sought after. Therapeutic B-cell vaccines aim at inducing neutralizing auto-reactive antibodies against important mediators of such diseases. Numerous animal models have demonstrated that active immunotherapy can induce disease-modifying levels of auto-antibodies. Recent findings from clinical trials have indicated that self-reactive antibodies can also be readily induced in humans; therapeutic efficacy, however, has not always been achieved. To date, clinical experience with vaccines against self-molecules is limited. Choice of the right target, proper vaccine design, optimal vaccine dose and regimen remain the major challenges to achieve clinical efficacy and safety for this novel class of biotherapeutics.

Vaccine for hypertension: modulating the renin-angiotensin system

Hypertension, which is one of the most common diseases afflicting mankind, is associated to increased morbidity, mortality and cost to society. Cardiovascular disease is the leading cause of death all around the world and hypertension is the most common reversible risk factor for cardiovascular diseases. The renin-angiotensin system (RAS) commands an important role in the regulation of blood pressure, and so, at present, has been a target for clinical control by drugs acting on the system. Despite the fact that effective drugs are available, only about one out of three people has their blood pressure successfully controlled, and the blame goes to the undesirable side effects and the poor oral drug compliance. Keeping in mind the increasing incidence of hypertension and the patients' inconsistency for the polypharmacy, immunization against renin and the angiotensins, although with less success, had been attempted in the past. More recently, immunization against angiotensin-I with PMD-3117 vaccine, angiotensin-II with CYT006-AngQb vaccine and targeting angiotensin-II type 1A receptor with ATR12181 vaccine have provided optimism in the development of a hypertension vaccine. AngQb vaccine has proved to become the first vaccine ever to lower (-9/-4 mm Hg) blood pressure in human beings. Vaccine could induce long lasting effects with a dosing interval of months, increasing patient acceptability and compliance and thus a better control of high blood pressure. Our objective will be to focus on the importance of the RAS and to explore the extent of safety, efficacy and the future implications of vaccine against the RAS.

Vaccines in development to prevent and treat atherosclerotic disease

Coronary heart disease (CHD) remains the leading cause of death in the United States. Immune mechanisms have been recently proposed to play an important role in the development of atherosclerotic plaques in CHD. Heat shock proteins and oxidized low-density lipoprotein are proinflammatory substances that have been shown to have an important role in the pathogenesis of atherosclerosis, and are now targets for clinical vaccine development. In addition, a vaccine has been developed to inhibit cholesteryl ester transfer protein. It is now recognized that many medications used to combat plaque development and rupture have significant anti-inflammatory effects and these effects are critical for drug efficacy. The influenza vaccine is associated with an atheroprotective effect. In addition, a nicotine vaccine, an antiangiotensin vaccine, and an anti-obesity vaccine may play a therapeutic role in modifying known risk factors for the development of atherosclerosis and its complications. This article reviews these vaccines as possible additions to the armamentarium of atheroprotective treatment modalities.

Role of naofen, a novel WD repeat-containing protein, in reducing nitric oxide-induced relaxation

1. Naofen, a novel WD40 repeat domain-containing protein, has recently been found in the intracellular compartment. The aim of the present study was to determine whether naofen affects thoracic aortic vascular reactivity in normotensive and hypertensive rats and whether naofen is present in the thoracic aorta. In addition, we examined whether naofen modulates acetylcholine (ACh)-stimulated nitric oxide (NO) release from the endothelium. 2. Immunohistochemistry showed greater naofen expression in endothelial cells in the DOCA-salt group compared with controls. There was increased naofen mRNA expression in deoxycorticosterone acetate (DOCA)-salt hypertensive rats compared with normotensive rats. 3. Acetylcholine-induced relaxation of rat aortic strips was decreased in DOCA-salt hypertensive rats compared with normotensive rats. Naofen-N- but not naofen-C-terminal protein caused a significant decrease in ACh-induced relaxation of aortic strips from normotensive rats. 4. Using a nitrite assay in a murine aortic endothelial cell line demonstrated that naofen-N-terminal protein, but not naofen-C-terminal protein, significantly reduced ACh-induced NO production, suggesting that naofen interferes with NO production. 5. Administration of naofen-N-terminal protein, but not naofen-C-terminal protein, significantly inhibited cyclohydrolase (GCH) I mRNA expression in a murine aortic endothelial cell line, suggesting that naofen-N-terminal protein interferes with NO synthesis by inhibiting GCH I mRNA expression. 6. The results of the present study suggest that naofen is present in vascular endothelial cells and has an inhibitory effect on ACh-induced relaxation under normotensive conditions. The findings reinforce the functional significance of naofen-N-terminal protein on rat vascular reactivity.

Long-term, high-dosage candesartan suppresses inflammation and injury in chronic kidney disease: nonhemodynamic renal protection

Recent evidence suggests that higher-than-usual antihypertensive dosages of renin-angiotensin-aldosterone system blockers may provide additional protection from progression of chronic renal disease; however, there have been few long-term studies, and the underlying mechanisms remain uncertain. This study examined the effects of long-term (14 mo) administration of ultrahigh dosages of the angiotensin receptor blocker candesartan on the progression of renal injury in spontaneously hypertensive rats (SHR). Beginning 8 wk after birth, SHR underwent unilateral nephrectomy and were given vehicle (control), or candesartan at a standard 5 mg/kg per d (T5), high 25 mg/kg per d (T25), or ultrahigh 75 mg/kg per d dosage (T75). After 2 wk, BP was reduced in all treated groups; however, it was better controlled in the high-dosage groups (T25 and T75). Urinary protein was significantly reduced in T75 after 2 wk of treatment and was also declined in the other two treatment groups but only after 2 mo. Exogenous angiotensin II test showed that complete angiotensin receptor blockade was achieved only in the high-dosage groups. Renal inflammation and macrophage (ED-1) infiltration were significantly ameliorated in both T25 and T75 but not in T5 rats. This was associated with the changes of tubular expression of monocyte chemoattractant protein-1, RANTES (regulated upon expression normal T cell expressed and secreted), and the phosphorylated NF-kappaB, a marker for activation. Suppression of ED-1, monocyte chemoattractant protein-1, and RANTES expression and NF-kappaB activation were greater in T75 as compared with T25. These findings suggest that candesartan has dosage-dependent, anti-inflammatory effects that are mediated by suppression of NF-kappaB activation and chemokine expression. Renal protection with high-dosage therapy may depend on these nonhemodynamic effects.

Th1 inflammatory response with altered expression of profibrotic and vasoactive mediators in AT1A and AT1B double-knockout mice

AT(1) double receptor (AT(1A) and AT(1B)) knockout mice have lower blood pressure, impaired growth, and develop early renal microvascular disease and tubulointerstitial injury. We hypothesized that there would be an increased expression of vasoactive, profibrotic, and inflammatory mediators expressed in the kidneys of AT(1) double-knockout mice. We examined the renal expression of various mediator systems in control (n = 6) vs. double-knockout mice (n = 6) at 3-5 mo of age by real-time PCR, immunohistochemistry, and Western blot analysis. AT(1) double-knockout mice show activation of Th1-dependent pathways (with increased expression of IFN-alpha, IL-2 mRNA) with increased expression of both monocyte (MCP-1 mRNA) and T cell (RANTES mRNA) chemokines, infiltration of CD4(+) and CD11b(+) cells, increased fibrosis-associated mediators (CTGF, TGF-beta and TNF-alpha mRNA) and extracellular matrix (collagens I and III mRNA and protein) deposition compared with controls (P < 0.05 for all markers). These changes were associated with increased mRNA expression of endothelin (ET)-1 and ET-A receptor (P < 0.05), cyclooxygenase (COX)-2/TXA2 synthase (P < 0.05), NADPH oxidase (p40-phox, p67-phox, P < 0.05) and iNOS and nNOS (P < 0.05). COX-2 and nNOS protein were also increased in the kidneys of AT(1) double-knockout mice by Western blot analysis (P < 0.05). Although renin and angiotensinogen mRNA expression were increased in the knockout mice, AT(2) receptor mRNA expression was not significantly different from wild-type mice. In conclusion, the absence of the AT(1) receptor is associated with marked renal alterations in vasoactive, profibrotic, and immune mediators with an inflammatory pattern favoring a Th1 phenotype.

AT2 receptors cross talk with AT1 receptors through a nitric oxide- and RhoA-dependent mechanism resulting in decreased phospholipase D activity

ANG II activation of phospholipase D (PLD) is required for ERK and NAD(P)H oxidase activation, both of which are involved in hypertension. Previous findings demonstrate that ANG II stimulates PLD activity through AT(1) receptors in a RhoA-dependent mechanism. Additionally, endogenous AT(2) receptors in preglomerular smooth muscle cells attenuate ANG II-mediated PLD activity. In the present study, we examined the signal transduction mechanisms used by endogenous AT(2) receptors to modulate ANG II-induced PLD activity through either PLA(2) generation of lysophosphatidylethanolamine or Galpha(i)-mediated generation of nitric oxide (NO) and interaction with RhoA. Blockade of AT(2) receptors, Galpha(i) and NO synthase, but not PLA(2), enhanced ANG II-mediated PLD activity in cells rich in, but not poor in, AT(2) receptors. Moreover, NO donors, a direct activator of guanylyl cyclase and a cGMP analog, but not lysophosphatidylethanolamine, inhibited ANG II-mediated PLD activity, whereas an inhibitor of guanylyl cyclase augmented ANG II-induced PLD activity. AT(2) receptor- and NO-mediated attenuation of ANG II-induced PLD activity was completely lost in cells transfected with S188A RhoA, which cannot be phosphorylated on serine 188. Therefore, our data indicate that AT(2) receptors activate Galpha(i), subsequently stimulating NO synthase and leading to increased soluble guanylyl cyclase activity, generation of cGMP, and activation of a protein kinase, resulting in phosphorylation of RhoA on serine 188. Furthermore, because AT(2) receptors inhibit AT(1) receptor signaling to PLD via modulating RhoA activity, AT(2) receptor signaling can potentially regulate multiple vasoconstrictive signaling systems through inactivating RhoA.

Renin-angiotensin vaccine: old story, new project 'efficacy versus safety'

In the present issue of Clinical Science, Brown and co-workers report preliminary results of Ang I (angiotensin I) immunization in humans. They demonstrate the presence of antibodies in human plasma and report that the procedure is well tolerated, but the blood pressure does not fall. The first attempts to actively immunize against components of the renin-angiotensin system were performed by Goldblatt in the 1950s. In our experience, active immunization against renin was associated with a complete inhibition of endogeneous plasma renin activity and a decrease in blood pressure, followed by the progressive development of a juxtaglomerular autoimmune nephritis. In contrast neither blood pressure nor aldosterone secretion were significantly modified by Ang I immunization. Moreover, Ang I-immunized animals continued to respond to the pharmacological inhibition of renin-angiotensin system. These data provide evidence of the inability of antibodies to target Ang I within tissues.

[What progress can be expected in the management of hypertension? Forecast from 1974 to 2034]

THE POSITIVE IMPACT OF TREATMENT: Antihypertensive treatments have clearly demonstrated their capacity to reduce cardiovascular mortality. The limits to the reduction in risk are imputable to insufficient early management, morbidity and poor compleance insufficiency of pharmacological treatments, absence of individualised adaptation to the causal pathology and inappropriate management of other cardiovascular risk factors. TO IMPROVE MANAGEMENT: Rather than creating more cardiovascular prevention Centres which only concern specific cases and research, it is fundamental to provide physicians, nurses and other health care workers with greater competence in hypertension and the management of cardiovascular risks. Conceptual changes are also necessary, particularly in that which concerns the end of the dichotomy between normotension and hypertension, hypercholesterolemia and normocholesterolemia and its individual and populational impact. PROMOTION OF NUTRITIONAL MEANS: Nutritional means should not be forgotten applied to accompany the whole pharmacological treatment of hypertension, they can be used for individual prevention and for reduction of the incidence of high blood pressure in the general population. NEW THERAPEUTIC STRATEGIES: Other than the search for antihypertensive drugs with greater efficacy and improved tolerance, several targets should be envisaged such as optimising the blockage of the renin-angiotensin-aldosterone system, inihibiting aldo-synthase. A CONSERVATIVE ATTITUDE: Although attractive, the individualisation of treatment based on genetic analysis will not be accessible to the majority of hypertensive patients. The attitude to be considered in 2004 consists above all in improving the use of available drugs at appropriate doses and especially in combinations at fixed-doses to allow for an easier therapeutic schedule.

Reduction of renal immune cell infiltration results in blood pressure control in genetically hypertensive rats

Immunocompetent cells infiltrate the kidney in several models of experimental hypertension. We have previously shown that reduction of this infiltrate results in prevention of salt-sensitive hypertension induced by short-term angiotensin II infusion and nitric oxide inhibition (Quiroz Y, Pons H, Gordon KI, Rincón J, Chávez M, Parra G, Herrera-Acosta J, Gómez-Garre D, Largo R, Egido J, Johnson RJ, and Rodríguez-Iturbe B. Am J Physiol Renal Physiol 281: F38-F47, 2001; Rodríguez-Iturbe B, Pons H, Quiroz Y, Gordon K, Rincón J, Chávez M, Parra G, Herrera-Acosta J, Gómez-Garre D, Largo R, Egido J, and Johnson RJ. Kidney Int 59: 2222-2232, 2001). We therefore studied whether hypertension could be controlled in genetically hypertensive rats [spontaneously hypertensive rats (SHR)] by the administration of 20 mg x kg(-1) x day(-1) of the immunosuppressive drug mycophenolate mofetil (MMF group; n = 35). Other SHR received vehicle (n = 35), and Wistar-Kyoto rats (n = 20) were used as controls. MMF or vehicle was given in two separate 4-wk periods, separated by a 3-wk interval. Systemic hypertension was reduced to normal levels in both periods of MMF treatment in association with a reduction in lymphocyte, macrophage, and angiotensin II-positive cells infiltrating the kidney. Oxidative stress was also reduced by MMF, as indicated by a reduction in urinary malondialdehyde (MDA), renal MDA content, and superoxide-positive cells, and was highly correlated with blood pressure levels. We conclude that the renal immune infiltrate plays a major role in the hypertension in SHR.

Role of ouabain-like compound in the regulation of plasma aldosterone concentration in rats

A major biologically active Na,K-ATPase inhibitor in the mammalian circulation may be ouabain-like compound(OLC). We developed a population of immunized rats against ouabain to block the actions of circulating OLC. To investigate the roles of OLC in the regulation of aldosterone secretion and/or production, we measured plasma aldosterone concentration after a week of low salt diet. No significant changes in serum Na and K concentrations were observed in immune rats. The plasma aldosterone concentration was significantly decreased by 30% in 17 immune rats as compared with 11 control rats(control: 455 +/- 53, immune: 315 +/- 21 pg/mL, p < 0.05). These data indicate that chronic blockade of the circulating OLC significantly decreases plasma aldosterone concentration during salt depletion and suggest that endogenous OLC may play an important role in the regulation of aldosterone secretion and/or production.

Regulation of renin release is impaired after nitric oxide inhibition

The aim of the present study was dual: first to establish that a preparation of afferent arterioles freshly isolated from the rat kidney is a suitable model to study renin release and synthesis, and second to investigate the effect(s) of nitric oxide (NO) inhibition on renin release in this model. Purification of renal microvessels was based on iron oxide infusion into the kidneys and separation of the afferent arterioles from glomeruli and connective tissue with a magnet. These microvessels express preprorenin mRNA, contain renin granules and release renin as evidenced by RT-PCR, immunocytochemistry and measurement of renin activity, respectively. Renin secretion was increased in isolated afferent arterioles after in vivo treatment with the diuretic furosemide (+300%) or in vitro treatment with the adenylyl cyclase activator forskolin (+50%), indicating that this vascular preparation responds appropriately to regulators of the renin-angiotensin system. Furthermore, in afferent arterioles isolated from control rats, renin release was positively correlated with total renin content (r = 0.85). In afferent arterioles isolated from rats chronically treated with the NO-synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME), forskolin was ineffective in modifying renin release despite stimulation of cAMP levels. In addition, the correlation between renin release and tissue renin content was disrupted. Similar results were obtained when cortical slices were used instead of afferent arterioles, suggesting that this defect in the regulation of renin release is independent of the presence of macula densa cells. To verify that the lack of regulation of renin release after L-NAME treatment was due to NO inhibition, the NO donor 3-morpholino-syndonimin-hydrochloride (SIN-1) was administered in afferent arterioles or cortical slices from kidneys of L-NAME-treated rats. In both preparations, SIN-1 reversed the L-NAME effect and re-established the responsiveness of renin release to forskolin and the relationship between renin release and renin content. These data indicate that the adenylyl cyclase-mediated mechanism regulating renin release is impaired when NO synthesis is inhibited.

Plasma angiotensin in binephrectomised mice

Plasma renin-angiotensin parameters were measured before and 24h after binephrectomy (BNx) in male Swiss (Ren-1, Ren-2) and BALB/c (Ren-1) female mice (representing the extremes of differences in tissue renin expression), together with in vivo inhibition of residual renin. Plasma Ang II increased from 18.9 +/- 7.3 to 48.1 +/- 16.9 pg/ml after BNx in conscious Swiss mice (+/- sd, p < 0.001, n = 11&12), renin activity (PRA) increased 2.76 times, angiotensinogen (aogen) increased 4.57 times and renin concentration (PRC) fell by 65%. In BALB/c, Ang II+Ang III decreased slightly (56.6 +/- 11 to 37.7 +/- 14.7, p < 0.05, n = 5&6), PRA was unchanged, aogen increased 12 times and PRC fell by 93%. Plasma ACE decreased by 26% and 28% respectively. Aogen did not increase further when post BNx plasma renin was inhibited with antirenin in vivo during 20h. Thus plasma angiotensin is maintained or considerably increased following BNx in mice and the change is consistent with first-order kinetics with respect to renin and aogen in the circulation. Whether the strain carries one or two renin genes, high renal and extrarenal renin production combined with a low plasma aogen phenotype yields resting angiotensin levels similar to other mammals. A kinetic regulation of aogen levels is proposed in mice wherein Ang II production is limited by low substrate concentration thereby ensuring normotension in the face of abundant extrarenal renin secretion.

Renin-angiotensin system in neonatal rats: induction of a renal abnormality in response to ACE inhibition or angiotensin II antagonism

In experiments designed to analyze cardiovascular structure in response to antihypertensive therapy with an ACE inhibitor, we decided to start very early in life with the aim to prevent blood pressure increases and the development of vascular structural changes. In these treated groups of rats we unexpectedly observed that after they were weaned, their water consumption and urine volume, respectively, increased substantially. The present study was designed to determine if inhibition of the renin-angiotensin system produced similar effects in different strains of rats, and focused on characterizing the abnormal fluid balance occurring as a consequence to neonatal treatment with ACE inhibitors or angiotensin II blockers. Three-day-old Wistar Kyoto (WKY), Wistar (WR) and spontaneously hypertensive rats (SHR) were given either saline, enalapril, captopril, losartan and the AT2 blocker, PD123319, in the same amount of volume for 20 days. Treatment was stopped and rats were examined with regard to renal morphology at 4, 14 and 30 weeks of age. In addition, water consumption, urine volume, urine electrolytes and osmolality were analyzed at 14 weeks of age, that is, 10 weeks off treatment. Early treatment with the ACE inhibitors, enalapril and captopril, and the AT1 blocker, losartan, but not the AT2 blocker, PD 123319, in the SHR and in the normotensive strains WKY and WR produced persistent, irreversible histopathological renal abnormalities in adult life, long after the rats had been taken off treatment. These abnormalities consisted of mainly cortical tubulointerstitial inflammation, various degrees of papillary atrophy and pelvic dilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacology of renin inhibitors and their application to the treatment of hypertension

Several different strategies have been followed to block the activity of renin, the enzyme catalysing the first and rate-limiting step in the renin-angiotensin cascade. The unique substrate specificity of this enzyme makes it an attractive target for specifically interfering with the renin-angiotensin system. Attempts to block the activity of renin in animals by an immunological approach, with either active or passive immunization against renin, have been successful. This approach has not been considered as a realistic therapy in humans for the treatment of hypertension or heart failure, but has provided useful tools for purifying and quantifying renin. Considerable efforts have been focused on the design of orally active, synthetic inhibitors of renin. This has resulted in the discovery of low molecular weight pseudo-tetrapeptide compounds that are resistant to enzymatic cleavage and are potent and selective inhibitors of renin. Studies in animal models and preliminary studies in humans indicate that renin inhibitors have the same therapeutic potential as angiotensin-converting enzyme inhibitors. However, the generally poor oral bioavailability and rapid elimination of currently available renin inhibitors have prevented their development as useful drugs. Inhibitors with better oral bioavailability and a long duration of action are needed to assess their full therapeutic potential and to determine whether they offer advantages over the angiotensin-converting enzyme inhibitors or the more recently developed angiotensin II-receptor antagonists.

A developmental genetic mechanism involving angiotensin in spontaneously hypertensive rats

1. Certain genes drive the blood pressure of young spontaneously hypertensive rats (SHR) to stable hypertensive levels in adulthood. 2. Relatively brief blockade of the renin-angiotensin system in young SHR can reset the track of SHR pressure to a lower level for the life of the animal. This effect appears to be a characteristic of the SHR strain. 3. It is proposed that the expression of a particular SHR hypertensive gene depends on angiotensin and is limited to young animals. This hypothesis explains some of the phenotypic abnormalities observed in young SHR and the decremental long-term blood pressure effects following ACE inhibitor treatment. 4. The identity of the gene is unclear, but information from biochemical, physiological and pharmacological studies may direct attention to distinct candidate genes within specific chromosomal regions of interest. 5. Understanding these genetic mechanisms may have important implications for future preventive strategies.