Evidence that angiotensin II is present in human monocytes

Potential Role of Vitamin D, ACE2 and the Proteases as TMPRSS2 and Furin on SARS-CoV-2 Pathogenesis and COVID-19 Severity

BACKGROUND

COVID-19, the 21^st century pandemic disease caused by SARS-CoV-2, has shown a wide clinical spectrum ranging from asymptomatic to deadly serious pneumonia.

OBJECTIVE

In our study, the relationship between the pathogenesis and clinical severity of COVID-19 and vitamin D, ACE2, Furin and TMPRSS2 was investigated.

METHODS

Serum 25(OH)D, 1,25(OH)₂D and ACE2 protein were measured in 85 COVID-19 cases, divided into 5 groups, according to disease severity, from asymptomatic to severe and including a healthy control group. Expression levels of ACE2, VDR, TMPRSS2 and Furin mRNAs in PBMC were also measured. The relationship of the parameters within each group, the severity of the disease and the effect on the patients' fate were investigated.

RESULTS

Statistically significant differences were found between the severity of COVID-19 and all study parameters, except for serum 25(OH)D. A strong negative correlation was found between serum ACE2 protein, 1,25(OH)₂D, and ACE2 mRNA, and disease severity, length of hospital stay and death/survival rate. Vitamin D deficiency increased the death risk by 5.6-fold (95% CI 0.75-41.47), and the levels of 1,25(OH)₂D lower than 1 ng/mL increased the risk of death by 3.8-fold (95% CI 1.07-13.30).

CONCLUSION

This study suggests that vitamin D supplementation could be beneficial in the treatment and/or prevention of COVID-19.

Neuroendocrine-Immune Regulatory Network of Eucommia ulmoides Oliver

Eucommia ulmoides Oliver (E. ulmoides) is a popular medicinal herb and health supplement in China, Japan, and Korea, and has a variety of pharmaceutical properties. The neuroendocrine-immune (NEI) network is crucial in maintaining homeostasis and physical or psychological functions at a holistic level, consistent with the regulatory theory of natural medicine. This review aims to systematically summarize the chemical compositions, biological roles, and pharmacological properties of E. ulmoides to build a bridge between it and NEI-associated diseases and to provide a perspective for the development of its new clinical applications. After a review of the literature, we found that E. ulmoides has effects on NEI-related diseases including cancer, neurodegenerative disease, hyperlipidemia, osteoporosis, insomnia, hypertension, diabetes mellitus, and obesity. However, clinical studies on E. ulmoides were scarce. In addition, E. ulmoides derivatives are diverse in China, and they are mainly used to enhance immunity, improve hepatic damage, strengthen bones, and lower blood pressure. Through network pharmacological analysis, we uncovered the possibility that E. ulmoides is involved in functional interactions with cancer development, insulin resistance, NAFLD, and various inflammatory pathways associated with NEI diseases. Overall, this review suggests that E. ulmoides has a wide range of applications for NEI-related diseases and provides a direction for its future research and development.

Twenty years of progress in angiotensin converting enzyme 2 and its link to SARS-CoV-2 disease

The virulence of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and the aggressive nature of the disease has transformed the universal pace of research in the desperate attempt to seek effective therapies to halt the morbidity and mortality of this pandemic. The rapid sequencing of the SARS-CoV-2 virus facilitated identification of the receptor for angiotensin converting enzyme 2 (ACE2) as the high affinity binding site that allows virus endocytosis. Parallel evidence that coronavirus disease 2019 (COVID-19) disease evolution shows greater lethality in patients with antecedent cardiovascular disease, diabetes, or even obesity questioned the potential unfavorable contribution of angiotensin converting enzyme (ACE) inhibitors or angiotensin II (Ang II) receptor blockers as facilitators of adverse outcomes due to the ability of these therapies to augment the transcription of Ace2 with consequent increase in protein formation and enzymatic activity. We review, here, the specific studies that support a role of these agents in altering the expression and activity of ACE2 and underscore that the robustness of the experimental data is associated with weak clinical long-term studies of the existence of a similar regulation of tissue or plasma ACE2 in human subjects.

The potential similarities of COVID-19 and autoimmune disease pathogenesis and therapeutic options: new insights approach

Abstract

Cytokine pathways and their signaling disorders can be the cause of onset and pathogenesis of many diseases such as autoimmune diseases and COVID-19 infection. Autoimmune patients may be at higher risk of developing infection due to the impaired immune responses, the use of immunosuppressive drugs, and damage to various organs. Increased secretion of inflammatory cytokines and intolerance of the patient’s immune system to COVID-19 infection are the leading causes of hospitalization of these patients. The content used in this paper has been taken from English language articles (2005–2020) retrieved from the PubMed database and Google Scholar search engine using “COVID-19,” “Autoimmune disease,” “Therapeutic,” “Pathogenesis,” and “Pathway” keywords. The emergence of COVID-19 and its association with autoimmune disorders is a major challenge in the management of these diseases. The results showed that the use of corticosteroids in the treatment of autoimmune diseases can make diagnosis and treatment of COVID-19 more challenging by preventing the fever. Due to the common pathogenesis of COVID-19 and autoimmune diseases, the use of autoimmune drugs as a possible treatment option could help control the virus.

Key Points

• Inflammatory cytokines play an essential role in the pathogenesis of COVID-19

• ACE2 dysfunctions are related to the with COVID-19 and autoimmune diseases

• The use autoimmune diseases drugs can be useful in treating COVID-19

Occult SARS-CoV-2 infection; a possible hypothesis for viral relapse

Coronavirus disease 2019 (COVID‐19) has emerged as a global public health emergency, which is characterized by high infection rate and fatal course. Recent data reported that the test for Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) RNA might become positive again after one or two consecutively negative tests. Many researchers are currently evaluating the clinical characteristics of the SARS-CoV-2 reactivation. In this letter, we proposed a possible mechanism of SARS-CoV-2 reactivation or relapse after negative nasopharyngeal swabs PCR.

Monocytes in Uremia

Monocytes play an important role in both innate immunity and antigen presentation for specific cellular immune defense. In patients with chronic renal failure, as well as those treated with maintenance hemodialysis, these cells are largely dysregulated. There is a large body of literature on monocyte alterations in such patients. However, most of the publications report on small series, there is a vast spectrum of different methods and the heterogeneity of the data prevents any meta-analytic approach. Thus, a narrative review was performed to describe the current knowledge. Monocytes from patients with chronic renal failure differ from those of healthy individuals in the pattern of surface molecule expression, cytokine and mediator production, and function. If these findings can be summarized at all, they might be subsumed as showing chronic inflammation in resting cells together with limited activation upon immunologic challenge. The picture is complicated by the fact that monocytes fall into morphologically and functionally different populations and population shifts interact heavily with dysregulation of the individual cells. Severe complications of chronic renal failure such as impaired immune defense, inflammation, and atherosclerosis can be related to several aspects of monocyte dysfunction. Therefore, this review aims to provide an overview about the impairment and activation of monocytes by uremia and the resulting clinical consequences for renal failure patients.

Noncanonical Mechanisms for Direct Bone Marrow Generating Ang II (Angiotensin II) Predominate in CD68 Positive Myeloid Lineage Cells

Bone marrow (BM) Ang II (angiotensin II) is a major participant in the regulation of hematopoiesis and immunity. The novel tissue substrate Ang-(1-12) [angiotensin-(1-12)] and its cleaving enzyme chymase are an essential source of Ang II production in cardiac tissue. We hypothesized this noncanonical chymase-mediated Ang II-producing mechanism exists in the BM tissue. Immunohistostaining and flow cytometry confirmed the presence of Ang-(1-12) immunoreaction in the BM of SD (Sprague Dawley) rats. Chymase-mediated Ang II-producing activity in BM was ≈1000-fold higher than ACE (angiotensin-converting enzyme)-mediated Ang II-producing activity (4531±137 and 4.2±0.3 fmol/min per mg, respectively; n=6; P<0.001) and 280-fold higher than chymase activity in the left ventricle of 16.3±1.7 fmol/min per mg (P<0.001). Adding a selective chymase inhibitor, TEI-F00806, eliminated almost all ¹²⁵I-Ang II production. Flow cytometry demonstrated that delta median fluorescence intensity of chymase in cluster of differentiation 68 positive cells was significantly higher than that in cluster of differentiation 68 negative cells (1546±157 and 222±48 arbitrary units, respectively; P=0.0021). Cluster of differentiation 68 positive and side scatter low subsets, considered to be myeloid progenitors, express the highest chymase fluorescence intensity in rat BM. Chymase activity and cellular expression was similar in both male and female rats. In conclusion, myeloid lineage cells, especially myeloid progenitors, have an extraordinary Ang II-producing activity by chymase in the BM.

Monocytic angiotensin-converting enzyme 2 relates to atherosclerosis in patients with chronic kidney disease

Background: Increased levels of monocytic angiotensin-converting enzyme (ACE) found in haemodialysis (HD) patients may directly participate in the pathogenesis of atherosclerosis. We demonstrated recently that uremia triggers the development of highly pro-atherogenic monocytes via an angiotensin II (AngII)–dependent mechanism. Opposing actions of the AngII-degrading ACE2 remain largely unknown. We examined the status of both ACEs and related receptors in circulating leukocytes of HD, not-dialyzed CKD and healthy individuals. Furthermore, we tested the possible impact of monocytic ACEs on atherogenesis and behaviour of the cells under conditions mimicking chronic renal failure.

Methods: Expression of ACE, ACE2, AT1R, AT2R and MASR was investigated on circulating leukocytes from 71 HD (62 ± 14 years), 24 CKD stage 3–5 (74 ± 10 years) patients and 37 healthy control subjects (53 ± 6 years) and isolated healthy monocytes treated with normal and uremic serum. Analyses of ACE, ACE2, ICAM-1, VCAM-1, MCSF and endothelial adhesion were tested on ACE-overexpressing THP-1 monocytes treated with captopril or losartan. ACE2-overexpressing monocytes were subjected to transmigration and adhesion assays and investigated for MCP-1, ICAM-1, VCAM-1, MCSF, AT1R and AT2R expression.

Results: The ACE mRNA level was significantly increased in HD and CKD stage 3–5 leukocytes. Correspondingly, ACE2 was downregulated and AngII as well as MAS receptor expression was upregulated in these cells. Healthy monocytes preconditioned with uremic serum reflected the same expressional regulation of ACE/ACE2, MAS and AngII receptors as those observed in HD and CKD stage 3–5 leukocytes. Overexpression of monocytic ACE dramatically decreased levels of ACE2 and induced a pro-atherogenic phenotype, partly reversed by AngII-modifying treatments, leading to an increase in ACE2. Overexpression of ACE2 in monocytes led to reduced endothelial adhesion, transmigration and downregulation of adhesion-related molecules.

Conclusions: HD and not-dialyzed CKD stage 3–5 patients show enhanced ACE and decreased ACE2 expression on monocytes. This constellation renders the cells endothelial adhesive and likely supports the development of atherosclerosis.

Deriving vascular smooth muscle cells from mesenchymal stromal cells: Evolving differentiation strategies and current understanding of their mechanisms

Vascular smooth muscle cells (VSMCs) play essential roles in regulating blood vessel form and function. Regeneration of functional vascular smooth muscle tissue to repair vascular diseases is an area of intense research in tissue engineering and regenerative medicine. For functional vascular smooth muscle tissue regeneration to become a practical therapy over the next decade, the field will need to have access to VSMC sources that are effective, robust and safe. While pluripotent stem cells hold good future promise to this end, more immediate translation is expected to come from approaches that generate functional VSMCs from adult sources of multipotent adipose-derived and bone marrow-derived mesenchymal stromal cells (ASCs and BMSCs). The research to this end is extensive and is dominated by studies relating to classical biochemical signalling molecules used to induce differentiation of ASCs and BMSCs. However, prolonged use of the biochemical induction factors is costly and can cause potential endotoxin contamination in the culture. Over recent years several non-traditional differentiation approaches have been devised to mimic defined aspects of the native micro-environment in which VSMCs reside to contribute to the differentiation of VSMC-like cells from ASCs and BMSCs. In this review, the promises and limitations of several non-traditional culture approaches (e.g., co-culture, biomechanical, and biomaterial stimuli) targeting VSMC differentiation are discussed. The extensive crosstalk between the underlying signalling cascades are delineated and put into a translational context. It is expected that this review will not only provide significant insight into VSMC differentiation strategies for vascular smooth muscle tissue engineering applications, but will also highlight the fundamental importance of engineering the cellular microenvironment on multiple scales (with consideration of different combinatorial pathways) in order to direct cell differentiation fate and obtain cells of a desired and stable phenotype. These strategies may ultimately be applied to different sources of stem cells in the future for a range of biomaterial and tissue engineering disciplines.

Persistent and selective upregulation of renin-angiotensin system in circulating T lymphocytes in unstable angina

Introduction:

Unstable angina is associated with an acute systemic inflammatory reaction and circulating T lymphocytes are activated. We investigated whether in unstable angina with marked immune system activation a selective upregulation of the circulating T-cell renin–angiotensin system, modulated by angiotensin II, could occur.

Methods:

We studied 13 unstable angina patients, 10 patients with stable angina and 10 healthy subjects. After T-lymphocyte isolation, mRNAs for angiotensin-converting enzyme (ACE) and angiotensin type 1 receptor (AT1-R) were quantified at baseline and after angiotensin II stimulation. ACE activity in cell pellet and supernatant and angiotensin II cell content were measured.

Results:

Plasma renin activity was similar in controls, stable and unstable angina patients. At baseline ACE and AT1-R mRNA levels were higher (P<0.05) in T cells from unstable angina patients than in T cells from stable angina patients and controls, and further increased after angiotensin II addition to cultured T cells. ACE activity of unstable angina T cells was significantly higher than that of T cells from controls and stable angina patients. Only in T cells from unstable angina patients did angiotensin II stimulation cause the almost complete release of ACE activity in the supernatant.

Conclusions:

The circulating T-cell-based renin–angiotensin system from unstable angina patients was selectively upregulated. In vivo unstable angina T cells could locally increase angiotensin II concentration in tissues where they migrate independently of the circulating renin–angiotensin system.

The effect of high glucose on the inhibitory action of C21, a selective AT2R agonist, of LPS-stimulated tissue factor expression in human mononuclear cells

Background

Intimate links connect tissue factor (TF), the principal initiator of the clotting cascade, to inflammation, a cross-talk amplified by locally generated Angiotensin (AT) II, the effector arm of the Renin Angiotensin System (RAS). C21, a selective AT2R agonist, downregulates the transcriptional expression of TF in LPS-activated peripheral blood mononuclear cell(PBMC)s implying the existence of ATII type 2 receptor (AT2R)s whose stimulation attenuates inflammation-mediated procoagulant responses. High glucose, by activating key signalling pathways and increasing the cellular content of RAS components, augments TF expression and potentiates the inhibitory effect of AT1R antagonists. It is unknown, however, the impact of that stimulus on AT2R-mediated TF inhibition, an information useful to understand more precisely the role of that signal transduction pathway in the inflammation-mediated coagulation process. TF antigen (ELISA), procoagulant activity (PCA, 1-stage clotting assay) and TF-mRNA (real-time polymerase chain reaction) were assessed in PBMCs activated by LPS, a pro-inflammatory and procoagulant stimulus, exposed to either normal (N) or HG concentrations (5.5 and 50 mM respectively).

Results

HG upregulated TF expression, an effect abolished by BAY 11-7082, a NFκB inhibitor. C21 inhibited LPS-stimulated PCA, TFAg and mRNA to an extent independent of glucose concentration but the response to Olmesartan, an AT1R antagonist, was quite evidently potentiated by HG.

Conclusions

HG stimulates LPS-induced TF expression through mechanisms completely dependent upon NFkB activation. Both AT2R-stimulation and AT1R-blockade downregulate inflammation-mediated procoagulant response in PBMCs but HG impacts differently on the two different signal transduction pathways.

Angiotensin converting enzyme inhibitors and angiotensin II receptor antagonist attenuate tumor growth via polarization of neutrophils toward an antitumor phenotype

Tumor microenvironments polarize neutrophils to protumoral phenotypes. Here, we demonstrate that the angiotensin converting enzyme inhibitors (ACEis) and angiotensin II type 1 receptor (AGTR1) antagonist attenuate tumor growth via polarization of neutrophils toward an antitumoral phenotype. The ACEis or AGTR1 antagonist enhanced hypersegmentation of human neutrophils and increased neutrophil cytotoxicity against tumor cells. This neutrophil hypersegmentation was dependent on the mTOR pathway. In a murine tumor model, ACEis and AGTR1 antagonist attenuated tumor growth and enhanced neutrophil hypersegmentation. ACEis inhibited tumor-induced polarization of neutrophils to a protumoral phenotype. Neutrophil depletion reduced the antitumor effect of ACEi. Together, these data suggest that the modulation of Ang II pathway attenuates tumor growth via polarization of neutrophils to an antitumoral phenotype.

Compound 21, a selective angiotensin II type 2 receptor agonist, downregulates lipopolysaccharide-stimulated tissue factor expression in human peripheral blood mononuclear cells

Intricate interrelationships connect tissue factor (TF), the principal initiator of the clotting cascade, to inflammation, a cross-talk amplified by locally active angiotensin II, a proinflammatory agent with direct TF-stimulating properties mediated by the angiotensin II type 1 receptor (AT1R)s. However, angiotensin II also stimulates angiotensin II type 2 receptor (AT2R)s and they may as well contribute to TF expression, a possibility in need of further evaluation. We investigated the effect of C21, a highly specific AT2R agonist, on TF antigen (ELISA), procoagulant activity (PCA, one-stage clotting assay) and TF-mRNA (real-time PCR) in peripheral blood mononuclear cell (PBMC)s activated by lipopolysaccharide (LPS), a pro-inflammatory and procoagulant stimulus. C21 downregulated LPS-stimulated TF antigen, PCA and TF mRNA, an effect abolished by PD123 319, a selective AT2R antagonist, and left unchanged by omesartan, a selective AT1R antagonist. PD123 319 per se did not affect LPS-induced TF expression while omesartan inhibited and BAY 11-7082, a specific NFκB inhibitor, abolished endotoxin-activated procoagulant activity (PCA). C21, a selective AT2R agonist, downregulates the transcriptional expression of TF in LPS-activated PBMCs, a finding consistent with the existence in PBMCs of AT2Rs whose stimulation attenuates inflammation-mediated procoagulant responses. The data open insofar unexplored and potentially relevant facets to our understanding of the complex links connecting angiotensin II to inflammation and coagulation.

Investigation of the effect of telmisartan on experimentally induced peripheral nerve injury in rats

AIM

The aim of this study was to investigate the effects of telmisartan on nerve healing in a rat peripheral nerve injury model.

MATERIAL AND METHOD

Thirty adult male Wistar albino rats were divided into five groups: healthy, axonotmesis, anastomosis, axonotmesis+10 mg/kg telmisartan and anastomosis+10 mg/kg telmisartan. Walking track analyses were performed 4 weeks after the surgery. The right sciatic nerves of all the animals were examined histopathologically, stereologically and molecularly.

RESULTS

Many badly damaged axons were detected in the axonotmesis group, in addition to enlarged spaces between the axons. In the anastomosis group, both ir- regular and degenerated axons at different severities were observed. The sections of the telmisartan group after the axonotmesis were similar to those of the healthy group. The sections of the telmisartan group after the anastomosis were similar to those of the healthy group and the telmisartan group after the axonotmesis. Interleukin-1 beta (IL-1β) gene expression increased in both the axonotmesis and the anastomosis groups when compared with the healthy group. Telmisartan had a significant down-regulatory effect on IL-1β expression. Caspase-3 mRNA expression was significantly increased in the anastomosis group, and the administration of telmisartan in this group significantly decreased this rise in caspase-3 mRNA expression. As a functional outcome, telmisartan also increased the walking distance of the rats after axonotmesis and anastomosis.

CONCLUSION

The histopathological, stereological, functional and molecular data suggest that telmisartan improves nerve regeneration in peripheral nerve injuries by inhibiting inflammatory cytokine IL-1β and apoptotic caspase-3.

Angiotensin II: immunohistochemical study in Sardinian pterygium

The Angiotensin II (Ang II) is the principal effector peptide of the RAS system. It has a pleiotropic effect and, beside its physiological role, it has the property to stimulate angiogenesis and activate multiple signalling pathways related to cell proliferation. The purpose of the study was to determinate the Ang II expression and localization in Sardinian pterygium and normal conjunctiva by immunohistochemistry, and its possible involvement in the development and progression of the disease. Twenty-three pterygiums and eleven normal conjunctiva specimens obtained from Sardinian patients, were processed for paraffin embedding and assessed for the immunohistochemi-cal revelation of Ang II. Significant Ang II expression was identified in pterygium and conjunctiva. Particularly, thirteen pterygium specimens (n=13) displayed exclusively moderate to strong nuclear staining; some specimens (n=5) showed exclusively a moderate cytoplasmic immunoreactivity, and few specimens (n=2) displayed moderate to strong immunoreactivity in both cytoplasm and nucleus. Only 3 specimens were negative. Statistical significance difference in respect of nuclear and cytoplasmic localization was observed between normal conjunctiva and pterygium (P=0.020). The results showed a predominant intranuclear localization of Ang II in pterygium epithelial cells, in spite of conjunctiva that mainly showed cytoplasmic localization. These findings suggest a possible role for Ang II in the development and/or progression of pterygium mediated by the activation of local RAS system.

Uremic conditions drive human monocytes to pro-atherogenic differentiation via an angiotensin-dependent mechanism

Aims

Elevated expression levels of monocytic-ACE have been found in haemodialysis patients. They are not only epidemiologically linked with increased mortality and cardiovascular disease, but may also directly participate in the initial steps of atherosclerosis. To further address this question we tested the role of monocytic-ACE in promotion of atherosclerotic events in vitro under conditions mimicking those of chronic renal failure.

Methods and Results

Treatment of human primary monocytes or THP-1 cells with uremic serum as well as PMA-induced differentiation led to significantly up-regulated expression of ACE, further increased by additional treatment with LPS. Functionally, these monocytes revealed significantly increased adhesion and transmigration through endothelial monolayers. Overexpression of ACE in transfected monocytes or THP-1 cells led to development of more differentiated, macrophage-like phenotype with up-regulated expression of Arg1, MCSF, MCP-1 and CCR2. Expression of pro-inflammatory cytokines TNFa and IL-6 were also noticeably up-regulated. ACE overexpression resulted in significantly increased adhesion and transmigration properties. Transcriptional screening of ACE-overexpressing monocytes revealed noticeably increased expression of Angiotensin II receptors and adhesion- as well as atherosclerosis-related ICAM-1 and VCAM1. Inhibition of monocyte ACE or AngII-receptor signalling led to decreased adhesion potential of ACE-overexpressing cells.

Conclusions

Taken together, these data demonstrate that uremia induced expression of monocytic-ACE mediates the development of highly pro-atherogenic cells via an AngII-dependent mechanism.

Renal denervation has blood pressure-independent protective effects on kidney and heart in a rat model of chronic kidney disease

We elucidate the underlying mechanisms of bidirectional cardiorenal interaction, focusing on the sympathetic nerve driving disruption of the local renin-angiotensin system (RAS). A rat model of N(ω)-nitro-L-arginine methyl ester (L-NAME; a nitric oxide synthase inhibitor) administration was used to induce damage in the heart and kidney, similar to cardiorenal syndrome. L-NAME induced sympathetic nerve-RAS overactivity and cardiorenal injury accompanied by local RAS elevations. These were suppressed by bilateral renal denervation, but not by hydralazine treatment, despite the blood pressure being kept the same between the two groups. Although L-NAME induced angiotensinogen (AGT) protein augmentation in both organs, AGT mRNA decreased in the kidney and increased in the heart in a contradictory manner. Immunostaining for AGT suggested that renal denervation suppressed AGT onsite generation from activated resident macrophages of the heart and circulating AGT excretion from glomeruli of the kidney. We also examined rats treated with L-NAME plus unilateral denervation to confirm direct sympathetic regulation of intrarenal RAS. The levels of urinary AGT and renal angiotensin II content and the degrees of renal injury from denervated kidneys were less than those from contralateral innervated kidneys within the same rats. Thus, renal denervation has blood pressure-independent beneficial effects associated with local RAS inhibition.

Neuropathic pain-attenuating potential of aliskiren in chronic constriction injury model in rats

The present study was designed to investigate the potential of aliskiren, a direct renin inhibitor, in chronic constriction injury (CCI)-induced neuropathic pain in rats. Neuropathic pain was induced by placing four loose ligatures around the sciatic nerve. Acetone drop, von Frey hair, pin-prick and hot plate tests were performed to assess cold allodynia, mechanical allodynia, mechanical and heat hyperalgesia, respectively. The levels of Tumor necrosis factor-alpha (TNF-α) were measured in the sciatic nerve as an inflammatory marker. CCI was associated with the development of cold allodynia, mechanical allodynia, mechanical and heat hyperalgesia along with a rise in the levels of Tumor necrosis factor-alpha (TNF-α). Administration of aliskiren (25 or 50 mg/kg intraperitoneal (i.p.)) for 14 days in CCI-subjected rats significantly attenuated CCI-induced pain-related behavior and rise in TNF-α level. It may be concluded that aliskiren-mediated anti-inflammatory actions may be responsible for its beneficial effects in neuropathic pain in rats.

Losartan prevents the development of the pro-inflammatory monocytes CD14+CD16+ in haemodialysis patients

BACKGROUND

The principal cause of mortality in haemodialysis (HD) patients is cardiovascular disease, which is linked to chronic inflammation. Recent studies have demonstrated that angiotensin II receptor AT1 antagonists have anti-inflammatory properties. In this study, we evaluated the effect of losartan on CD14+CD16+ monocytes in HD patients. In addition, we developed an in vitro model to study the mechanisms by which losartan modulates these cells.

METHODS

We divided 18 HD patients into two groups, based on anti-hypertensive treatment: 9 patients were treated with losartan (losartan group) and 9 received other anti-hypertensive drugs that did not affect the renin-angiotensin axis (no-losartan group). Losartan was withdrawn in five patients from the losartan group for 2 months. Ten healthy subjects were included as controls. Invitro, we studied the differentiation of monocytes from healthy donors on stimulation with interleukin (IL)-10, IL-4 and granulocyte monocytes colony-stimulating factor with or without losartan in the culture medium.

RESULTS

In patients who were taking losartan, the percentage of monocytes that expressed CD14+CD16+ was lower compared with patients in the no-losartan group. The percentage of CD14+CD16+ was similar in the losartan group and healthy subjects. When losartan was withdrawn from five patients in the losartan group, the percentage of CD14+CD16+ monocytes increased compared with before withdrawal. In vitro, when we added losartan to the culture medium, CD14++CD16- monocytes failed to differentiate into CD14+CD16+ cells.

CONCLUSION

Losartan acts as an immunomodulator that prevents the development of CD14+CD16+ pro-inflammatory monocytes in HD patients.

Calcific aortic valve stenosis: methods, models, and mechanisms

Calcific aortic valve stenosis (CAVS) is a major health problem facing aging societies. The identification of osteoblast-like and osteoclast-like cells in human tissue has led to a major paradigm shift in the field. CAVS was thought to be a passive, degenerative process, whereas now the progression of calcification in CAVS is considered to be actively regulated. Mechanistic studies examining the contributions of true ectopic osteogenesis, nonosseous calcification, and ectopic osteoblast-like cells (that appear to function differently from skeletal osteoblasts) to valvular dysfunction have been facilitated by the development of mouse models of CAVS. Recent studies also suggest that valvular fibrosis, as well as calcification, may play an important role in restricting cusp movement, and CAVS may be more appropriately viewed as a fibrocalcific disease. High-resolution echocardiography and magnetic resonance imaging have emerged as useful tools for testing the efficacy of pharmacological and genetic interventions in vivo. Key studies in humans and animals are reviewed that have shaped current paradigms in the field of CAVS, and suggest promising future areas for research.

T lymphocytes mediate hypertension and kidney damage in Dahl salt-sensitive rats

This study examined mechanisms by which immune cells participate in the development of hypertension and renal disease in Dahl salt-sensitive (SS) rats. Increasing dietary salt from 0.4% to 4.0% NaCl significantly increased renal infiltration of T lymphocytes from 8.8 +/- 1.2 x 10(5) to 14.4 +/- 2.0 x 10(5) cells/2 kidneys, increased arterial blood pressure from 131 +/- 2 to 165 +/- 6 mmHg, increased albumin excretion rate from 17 +/- 3 to 129 +/- 20 mg/day, and resulted in renal glomerular and tubular damage. Furthermore, renal tissue ANG II was not suppressed in the kidneys of SS rats fed 4.0% NaCl. Administration of the immunosuppressive agent mycophenolate mofetil (MMF; 20 mg.kg(-1).day(-1)) prevented the infiltration of T lymphocytes and attenuated Dahl SS hypertension and renal disease. In contrast to vehicle-treated rats, Dahl SS rats administered MMF demonstrated a suppression of renal tissue ANG II from 163 +/- 26 to 88 +/- 9 pg/g of tissue when fed high salt. Finally, it was demonstrated that the T lymphocytes isolated from the kidney possess renin and angiotensin-converting enzyme activity. These data indicate that infiltrating T cells are capable of participating in the production of ANG II and are associated with increased intrarenal ANG II, hypertension, and renal disease. The suppression of T-cell infiltration decreased intrarenal ANG II and prevented Dahl SS hypertension and kidney damage. As such, infiltrating cells are capable of participating in the established phase of Dahl SS hypertension.

The ACE inhibitors enalapril and captopril modulate cytokine responses in Balb/c and C57Bl/6 normal mice and increase CD4(+)CD103(+)CD25(negative) splenic T cell numbers

Increasing evidence implies beneficial effects of angiotensin-converting enzyme (ACE) inhibitors beyond those of their original indications to control hypertension. One of the most attractive non-hemodynamic properties of ACE inhibitors is their ability to regulate cytokine production. The mechanism(s) underlying the role of ACE inhibitors on cytokine synthesis are not well understood but they have traditionally been attributed to the inhibition of angiotensin (Ang) II formation. In fact, it has been extensively demonstrated that ACE inhibitors decrease Ang II-induced production of proinflammatory cytokines and chemokines. However, it is not well described if inhibition of endogenous Ang II generation by ACE inhibitors modulates systemic cytokine production in mice. To verify that, in this work, we investigated the effects of treatment with the ACE inhibitors enalapril and captopril on cytokine synthesis in C57Bl/6 and Balb/c mice. Our results show that enalapril up regulates IL-10 produced by splenocytes from Balb/c and C57Bl/6 mice and captopril increased it only in Balb/c mice. Furthermore, CD4(+)CD103(+) presented increased IL-10 production after enalapril treatment. Enalapril as well as captopril short-term treatment enhanced IL-2 synthesis in Balb/c mice. Besides, enhanced IL-2 and IL-10 levels correlates with increased CD4(+)CD103(+)CD25(negative) T cells numbers in spleens from enalapril-treated mice.

Role of angiotensin II in endothelial dysfunction induced by lipopolysaccharide in mice

Endotoxin [or lipopolysaccharide (LPS)] increases levels of superoxide in blood vessels and impairs vasomotor function. Angiotensin II plays an important role in the generation of superoxide in several disease states, including hypertension and heart failure. The goal of this study was to determine whether the activation of the renin-angiotensin system contributes to oxidative stress and endothelial dysfunction after endotoxin. We examined the effects of enalapril (an angiotensin-converting enzyme inhibitor) or L-158809 (an angiotensin receptor blocker) on increases of superoxide and vasomotor dysfunction in mice treated with LPS. C57BL/6 mice were treated with either enalapril (60 mg.kg(-1).day(-1)) or L-158809 (30 mg.kg(-1).day(-1)) for 4 days. After the third day, LPS (10-20 mg/kg) or vehicle was injected intraperitoneally, and one day later, vasomotor function of the aorta was examined in vitro. After precontraction with PGF(2alpha), the maximal responses to sodium nitroprusside were similar in the aorta from normal and LPS-treated mice. In contrast, the relaxation to acetylcholine was impaired after LPS (54 +/- 5% at 10(-5), mean +/- SE) compared with vessels treated with vehicle (88 +/- 1%; P < 0.05). Enalapril improved (P < 0.05) relaxation in response to acetylcholine to 81 +/- 6% after LPS. L-158809 also improved relaxation in response to acetylcholine to 77 +/- 4% after LPS. Superoxide (measured with lucigenin and hydroethidine) was increased (P < 0.05) in aorta after LPS, and levels were reduced (P < 0.05) following enalapril and L-158809. Thus, after LPS, enalapril and L-158809 reduce superoxide levels and improve relaxation to acetylcholine in the aorta. The findings suggest that activation of the renin-angiotensin system contributes importantly to oxidative stress and endothelial dysfunction after endotoxin.

CX3CR1 receptor is up-regulated in monocytes of coronary artery diseased patients: Impact of pre-inflammatory stimuli and renin–angiotensin system modulators

Fractalkine/CX3CR1 pathway is considered a major modulator of atherosclerosis. In the present study, expression of CX3CR1 on PBMCs/monocytes of healthy individuals and coronary artery diseased patients was initially assessed by flow cytometry. Effects of pre-inflammatory cytokines interferon (INF)-gamma and tumor necrosis factor (TNF)-alpha on expression of CX3CR1 and a single representative of each major chemokine family (CCR5 and CXCR4) were further assessed in three cell models: THP-1 monocytes, Jurkat T lymphocytes and primary monocytes isolated from healthy donors. Finally, effects of angiotensin-converting enzyme (ACE) inhibitors captopril, lisinopril and angiotensin receptor blocker (ARB) losartan on chemokine receptor expression were evaluated in the same cell models either in a naive or stimulated state. INF-gamma significantly affected the chemokine receptor phenotype of THP-1 cells by increasing the rate of CX3CR1-positive cells. Pre-treatment with the ACE inhibitors, captopril and lisinopril, and the ARB, losartan, did not influence these effects. Captopril and lisinopril similarly had no effect on either stimulated or naive primary monocytes. Yet, a small but repeatable increase in CX3CR1 expression after treatment with losartan was noted. Nevertheless, the latter observation did not retain statistical significance after applying the Bonferroni correction. In conclusion, our data did not indicate any significant effect of the ACE inhibitors on the chemokine receptor phenotype of monocytes.

Physiology of Local Renin-Angiotensin Systems

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

LPS induces permeability injury in lung microvascular endothelium via AT1 receptor

Lipopolysaccharide (LPS) is known to stimulate the circulation and local production of angiotensin II (Ang II). To assess whether Ang II plays a role in LPS-induced acute lung injury, rats were injected with LPS, the microvascular endothelial permeability injury was evaluated by histological changes, increased pulmonary wet/dry weight ratio, and pulmonary microvascular protein leak. Besides, increased rat pulmonary microvascular endothelial cell monolayer permeability coefficient (K(f)) was measured after treatment with LPS and/or Ang II, respectively. LPS/Ang II, treatment resulted in a significant increase in K(f). Ang II cooperates with LPS to further increase K(f). Hence, LPS increases pulmonary microvascular endothelial permeability both in vitro and in vivo. Local lung Ang II was increased in response to LPS challenge, and elevated Ang II ulteriorly exacerbates LPS-induced endothelium injury. [Sar(1),Ile(8)]Ang II, a selective block of Ang II type 1 (AT(1)) receptors, eliminated these changes significantly. Our conclusion is that the LPS-induced lung injury may be mediated by the AT(1) receptor.

Preformed angiotensin II is present in human mast cells

PURPOSE

The density of mast cells increases in the myocardium of patients suffering from heart failure. However, their function remains unclear. In this study, preformed angiotensin II (ANG II), a potent growth factor, was found to be contained in, and released by, human mast cells.

METHODS

The human mast cell line (HMC-1) was incubated with 0 to 10(-6) M calcitonin gene-related peptide (CGRP) or culture medium. The expression of renin-angiotensin system mRNA was examined using RT-PCR analysis. ELISA and immunohistochemistry with monoclonal antibody against human ANG II were performed to detect the presence of ANG II in HMC-1. The effect of CGRP on the expression of angiotensinogen mRNA was examined by quantitative RT-PCR analysis.

RESULTS

Preformed ANG II was detected in a human mast cell line (HMC-1) which is a neoplastic cell line of mast cells by ELISA and immunohistochemistry. Presence of mRNA of angiotensinogen and renin was confirmed by polymerase chain reaction in HMC-1, while mRNA of angiotensin converting enzyme (ACE) was undetectable. Since myocardial mast cells are interfaced with nerve fibers and functionally associated with CGRP, the effect of CGRP on ANG II release from HMC-1 was examined. CGRP induced the release of ANG II and increased angiotensinogen mRNA in HMC-1.

CONCLUSIONS

The presence of preformed ANG II and gene expression of the renin-angiotensin system were detected in human mast cells. The release and synthesis of ANG II in mast cells was regulated by CGRP.

Protective Effects of Angiotensin II Interruption: Evidence for Antiinflammatory Actions

Angiotensin II, the major effector molecule produced from the renin-angiotensin-aldosterone axis, is a vasoconstrictor contributing to hypertension. Evidence indicates, however, that angiotensin II also is a potent proinflammatory mediator with growth and remodeling effects. In vitro and in vivo studies have shown that angiotensin II blockade significantly reduces concentrations of proinflammatory mediators and oxidative stress products in numerous inflammatory models. Interruption of angiotensin II activity with angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers has been beneficial for patients with inflammatory diseases. Much of this benefit occurs independent of the antihypertensive effect of angiotensin II interruption, suggesting a distinctive protective mechanism. Angiotensin II receptor blockers may represent a novel class of antiinflammatory drugs with indications far beyond cardiovascular diseases.

Angiotensin II induces the expression of tissue factor and its mechanism in human monocytes

The renin-angiotensin system (RAS) is linked with the vascular motion and the secretion of aldosterone. The purpose of the present study was to elucidate whether angiotensin II (Ang II) induces monocytes (Mo) to express tissue factor (TF) and if Ang II subtype 1 receptor (AT1R) antagonists inhibit the effect of Ang II. The roles of different intracellular signal transduction pathways and IkappaB/NF-kappaB in Ang II-induced TF expression of Mo were also studied to explore the mechanisms involved. Mo were isolated from heparinized human blood by a two-step gradient centrifugation, cultured in RPMI-1640 and exposed to Ang II and other test reagents. Mo TF activity and TF antigen were determined with a one-stage clotting method and ELISA, respectively, after the culture. Reverse transcription-polymerase chain reaction (RT-PCR) was used to detect the TF mRNA levels in Mo. The level of IkappaBalpha in Mo was detected by Western blot analysis. Electrophoresis mobility shift assay (EMSA) was performed to evaluate the binding activity of NF-kappaB in Mo. The experiment results are as follows: (1) Ang II (10(-10)-10(-7) M) induced Mo to express TF activity but had no marked effect on other mononuclear cells. Ang II 10(-10)-10(-7) M) also caused increased TF mRNA expression and TF antigen from Mo in a dose-dependent manner. The TF antigen of Mo was elevated at 4 h after Mo was exposed to Ang II (10(-7) M) in culture, reached the peak at 6 h, and then declined from 12 h. The changes of TF activity were positively correlated with those of TF antigen. TF mRNA expression was elevated at 1 h, peaked at 3 h, and declined after 8 h. (2) Losartan (10(-6)-10(-5) M) significantly inhibited the stimulative effects of Ang II on TF activity, TF antigen and TF mRNA in Mo in a dose-dependent manner. (3) The protein kinase C (PKC) inhibitor, staurosporine, and the protein tyrosine kinase (PTK) inhibitor, genistein, both lowered TF levels in Mo, but the inhibitory effect of staurosporine was stronger than that of genistein. The effect of mitogen-activated protein kinase (MAPK) inhibitor, U0126, on monocytic TF expression was not significant. (4) Western blot analysis revealed that after Ang II (10(-7) M)exposure, levels of IkappaBalpha began to decrease at 15 min, reached a nadir at 60 min (P<.01), and recovered at 180 min. (5) EMSA showed that NF-kappaB binding activity started to increase at 15 min, reached a peak at 60 min, and returned to baseline at 180 min. The present data suggest that Ang II can directly induce TF expression in human Mo and this effect is mediated by AT1R. PKC may play the most important role in Ang II-induced TF expression among the three signal pathways detected. In addition, activation of NF-kappaB is also involved in the TF expression of Mo induced by Ang II.

An ACE inhibitor reduces Th2 cytokines and TGF-beta1 and TGF-beta2 isoforms in murine lupus nephritis

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitors, such as captopril, are used to control hypertension. In patients and animals with primary nephropathies, these agents improve renal function more than that would be expected from their control of hypertension. Here, we examine the effects of treatment with captopril on lupus nephritis and discuss the potential mechanism(s) by which this agent exerts its renoprotective effects.

METHODS

Lupus-prone, NZB/NZW F1 and MRL-lpr/lpr, mice were treated with captopril or with a control antihypertensive agent, verapamil. Mice were monitored for nephritis, and their sera and tissues analyzed for cytokine and transforming growth factor-beta (TGF-beta) expression.

RESULTS

Captopril treatment delayed the onset of proteinuria when administered to prenephritic mice, whereas verapamil did not. Captopril treatment also retarded disease progression when given to lupus mice that had early disease, and even reversed severe proteinuria in at least some older animals with advanced disease. It reduced chronic renal lesions, but had no effect on autoantibody production. The improvement in renal disease correlated with reduced TGF-beta expression, particularly of the TGF-beta1 and TGF-beta2 isoforms, in the kidneys. Interestingly, in vivo or in vitro exposure to captopril reduced splenic levels of type 2 cytokines, interleukin (IL)-4 and IL-10, suggesting a possible role of the immune system in captopril-mediated disease modulation.

CONCLUSION

Since type 2 cytokines are known to promote lupus glomerulosclerosis, decreased IL-4 and IL-10 production in captopril-treated mice may be related to this agent's renoprotective effects. We argue here that ACE inhibitors not only act as selective TGF-beta inhibitors, but also as selective immunomodulators, to improve lupus nephritis.

Insulin stimulates endogenous angiotensin II production via a mitogen-activated protein kinase pathway in vascular smooth muscle cells

OBJECTIVE

The present study was designed to determine the effects of insulin on cytosolic angiotensin II production and proliferation in cultured rat vascular smooth muscle cells.

DESIGN AND METHODS

Vascular smooth muscle cells were incubated with insulin for 48 h. Cytosolic angiotensin I and II were determined by radioimmunoassays of purified cell homogenates. Angiotensin II was also detected by immunohistochemistry of intact cells. Cell proliferation was determined by pulse labeling with radiolabeled thymidine. Angiotensinogen mRNA expression was determined by slot-blot analysis.

RESULTS

Insulin significantly increased cytosolic angiotensin II concentration in vascular smooth muscle cells. Lisinopril, omapatrilat and irbesartan inhibited this increase of angiotensin II, but had no effect on angiotensin I levels. Immunohistochemical staining confirmed the presence of angiotensin II in control and insulin-treated vascular smooth muscle cells. Insulin increased cell proliferation, and addition of lisinopril, omapatrilat or irbesartan inhibited this effect. Insulin also increased expression of angiotensinogen mRNA in cultured vascular smooth muscle cells, but PD98059, a mitogen-activated protein kinase inhibitor, prevented the rise in angiotensinogen expression.

CONCLUSION

These results support the concept that insulin stimulates angiotensin II production in cultured vascular smooth muscle cells through a mitogen-activated, protein kinase-dependent pathway that might be a factor in the progression of atherosclerosis. Agents that block the renin-angiotensin system have direct protective effects, reducing vascular angiotensin II and growth of vascular smooth muscle cells and are thus of cardiovascular benefit.

Renin-angiotensin system expression in rat bone marrow haematopoietic and stromal cells

The existence of a bone marrow renin-angiotensin system (RAS) is evidenced by the association of renin, angiotensin converting enzyme (ACE), and angiotensin (Ang) II and its AT(1) and AT(2) receptors with both normal and disturbed haematopoiesis. The expression of RAS components by rat unfractionated bone marrow cells (BMC), haematopoietic-lineage BMC and cultured marrow stromal cells (MSC) was investigated to determine which specific cell types may contribute to a local bone marrow RAS. The mRNAs for angiotensinogen, renin, ACE, and AT(1a) and AT(2) receptors were present in BMC and in cultured MSC; ACE2 mRNA was detected only in BMC. Two-colour flow fluorocytometry analysis showed immunodetectable angiotensinogen, ACE, AT(1) and AT(2) receptors, and Ang II, as well as binding of Ang II to AT(1) and AT(2) receptors, in CD4(+), CD11b/c(+), CD45R(+) and CD90(+) BMC and cultured MSC; renin was found in all cell types with the exception of CD4(+) BMC. Furthermore, Ang II was detected by radioimmunoassay in MSC homogenates as well as conditioned culture medium. The presence of Ang II receptors in both haematopoietic-lineage BMC and MSC, and the de novo synthesis of Ang II by MSC suggest a potential autocrine-paracrine mechanism for local RAS-mediated regulation of haematopoiesis.

Tissue renin angiotensin systems

The RAAS is a powerful regulator of vascular tone and intravascular volume and of tissue architecture and a variety of other functions. The recent appreciation of the immunoregulatory role of angiotensin II and its possible involvement in the genesis of atherosclerosis and in plaque rupture all speak to the wide-ranging physiologic and pathophysiologic activities of the peptide. So do its actions in fat cell differentiation and in neuromodulation. The system exists in the circulation, and RAASs, whole or partial, exist in many tissues. These systems are regulated at many levels ranging from the synthesis of renin to the dimerization of angiotensin receptors. Regulation occurs in multiple tissues and, as a result, tissue concentrations of angiotensin II and the concentration of other RAS components and their active metabolites can vary independently of the circulating system in these tissues. An RAS seems also to function within certain cells. Therapeutic interventions involving ACEIs and ARBs seem likely to provide benefit at least in part through the interruption of local systems. It is to be expected that with enhanced understanding of the biology of the multiple RASs, new suggestions for therapeutic interventions will be forthcoming.

Control of dendritic cell differentiation by angiotensin II

Here we analyze the role of the angiotensinergic system in the differentiation of dendritic cells (DC). We found that human monocytes produce angiotensin II (AII) and express AT1 and AT2 receptors for AII. DC differentiated from human monocytes in the presence of AT1 receptor antagonists losartan or candesartan show very low levels of CD1a expression and poor endocytic and allostimulatory activities. By contrast, DC differentiation in the presence of either the AT2 receptor antagonist PD 123319 or exogenous AII results in the development of nonadherent cells with CD1a expression and endocytic and allostimulatory activities higher than control DC. Similar contrasting effects were observed in mouse DC obtained from bone marrow cultures supplemented with granulocyte-monocyte colony-stimulating factor. DC differentiated in the presence of the AT1 receptor antagonist losartan express lower levels of CD11c, CD40, and Ia and display a lower ability to endocyte horseradish peroxidase (HRP) and to induce antibody responses in vivo, compared with controls. By contrast, DC differentiation in the presence of either the AT2 receptor antagonist PD 123319 or exogenous AII results in cells with high levels of CD11c, CD40, and Ia, as well as high ability to endocyte HRP and to induce antibody responses in vivo. Our results support the notion that the differentiation of DC is regulated by AII.

The clinical implication of tissue renin angiotensin systems

The presence, and in many cases the regulated synthesis, of components of the renin-angiotensin system have been demonstrated in multiple tissues, indicating the existence of tissue angiotensin-generating systems. These vary with respect to which renin-angiotensin system components are synthesized locally and which are taken up from plasma. Enzymes unrelated to the classical renin-angiotensin system may also contribute to tissue angiotensin synthesis. However, based on the available data, the prevailing opinion that kidney-derived renin is in all cases the only physiologically relevant renin in tissues must be revised. Also there is evidence indicating a role for tissue angiotensin systems in the pathogenesis of cardiovascular disease and in cardiovascular structural remodeling. The angiotensin-regulated synthesis of aldosterone in cardiac tissue has been described, suggesting the possibility that a renin-angiotensin-aldosterone system exists in the heart. In addition, intracellular (intracrine) sites of angiotensin action have been reported. Some of these findings have implications for therapeutics and, in particular, for the use of angiotensin converting-enzyme inhibitors and angiotensin receptor blockers. Finally, tissue angiotensin systems outside the cardiovascular system also appear to be physiologically relevant.

Elements of angiotensin system are involved in leeches and mollusks immune response modulation

We present immunocytochemical, biochemical and cellular evidences for the presence of a renin-angiotensin system (RAS) in coelomocytes of invertebrates (leech, Theromyzon tessulatum and mollusk Mytilus edulis). Leech coelomocytes are immunoreactive to polyclonal antisera raised against the T. tessulatum angiotensin-converting enzyme (ACE) and leech brain angiotensin II (AII) and a commercial anti-AT1 receptor. Biochemically, renin, ACE- and AT1-like receptor were identified in the leech immune cells. We further demonstrate that leech AII (10(-6) M) alone does not initiate nitric oxide (NO) release in invertebrate immunocytes but does only after pre-exposing the cells to IL-1 (15.9+/-2.6 nM; P<0.005 vs. 1.1 nM when AII is added alone). Similar results were obtained with human leukocytes (14.5+/-2.7 nM; P<0.005 IL-1+AII vs. 0.9 nM when AII is added alone). Then, an immunocytochemical study performed at the structural and ultrastructural levels confirmed the presence in same immune cells all the molecules of the renin-angiotensin system (RAS) in leeches as epitopes to IL-1-like protein and IL-1-like receptor. This is the first report in invertebrates and of a co-action between cytokines like substances and neuropeptides in an immune process and the involvement of the RAS in modulation of the immune response.

The angiotensin system elements in invertebrates

In this review, the different components of the renin-angiotensin system (RAS) in invertebrates are discussed. This system is implicated in osmoregulation, reproduction, memory processes and immune system regulation. As the elements of this hormone-enzymatic system also exist in invertebrates, it appears that the RAS originated very early in evolution.

Expression of renin-angiotensin system genes in immature and mature dendritic cells identified using human cDNA microarray

Using a cDNA glass microarray, the expression of 1081 genes in immature and mature dendritic cells (DCs) of two different individuals has been studied. The upregulation of mRNA transcripts of genes encoding the transcription factor ZFM1, Mos proto-oncogene serine/threonine-protein kinase, B-cell-specific transcription factor, preB-cell growth stimulating factor, ets translocation variant 6, and epidermal growth-factor-like CRIPTO was for the first time detected in DCs. Using semiquantitative RT-PCR analysis the upregulation of the transforming growth factor-alpha, integrin alpha 6 and ZFM 1 transcription factor in mature DCs was confirmed in samples from four different individuals. On the other hand, the downregulation of renin-binding protein transcript was detected in mature DCs using a cDNA microarray. For the first time, the expression of renin-angiotensin system genes was evaluated during maturation of DCs in samples from four donors by semiquantitative RT-PCR. A possible role of the renin-angiotensin system in DCs is discussed.

Control of renin secretion from adrenal gland in transgenic Ren-2 and normal rats

In Ren-2 rats, plasma active renin and prorenin increase following binephrectomy (BNx) related to increasing plasma potassium. Adrenal is the source of the increasing prorenin but active renin comes mainly from thymus and gut. Trophic influences other than potassium were tested in the present work. Angiotensin did not influence the post-BNx increases in plasma active or prorenin but suppressed resting plasma prorenin from non-adrenal, non-renal sources virtually to zero. ACTH and histamine had no discernible effects. Hexamethonium decreased by 50% the post BNx increase in prorenin but not active renin. In Sprague-Dawley and spontaneously hypertensive rats, low levels of active renin secretion were detected from adrenal but no prorenin. Thus, in anesthetized Ren-2 rats, secreted prorenin is from two sources, i.e. extrarenal and extra-adrenal sites readily suppressible with angiotensin and the adrenal that is partly suppressible by autonomic blockage. This may assist in identifying the origin of extra-renal prorenin secreted in man.

Angiotensin II: a regulator of inflammation during renal disease?

It has been recently recognized that besides its vasoactive actions Angiotensin II (Ang II) exerts various immunomodulatory effects that may contribute to renal injury and to the progression of renal disease. Consistent with this concept, Ang II facilitates macrophage recruitment into the kidney either directly or through the-upregulation of different chemotactic molecules such as RANTES (Regulated on Activation Normal T Expressed and Secreted), monocyte chemoattractant protein-1 (MCP-1) and osteopontin. Infiltrating macrophages not only produce a number of cytokines, growth factors and proinflammatory Mediators, but also synthesize Ang II intacellularly which increases tissue levels of the hormone within the kidney. Finally, specific binding sites for Ang II have been demonstrated on macrophages and increasing evidence indicates that Ang II directly modulates many of the cellular functions of these cells during the course of renal disease. Together these data suggest that Ang II plays an important role in modulating inflammatory responses in the kidney.

Renin in thymus, gut, hindlimb, and adrenal of (mRen-2)27 and normal rats: secretion and content studies

Thymic ablation and assay of organ renin revealed that one-third of the increasing plasma level of active renin after removal of kidneys and adrenals from Ren-2 rats originates from the thymus. Splanchnic arteriovenous difference and renin content indicate that gut can account for the remainder. Secretion of active renin from these sites correlated significantly with increasing plasma potassium. Prorenin was not secreted from these sites or from hindlimb in amounts sufficient to raise the plasma level, and yet plasma prorenin remained higher than active renin throughout the 12-h protocol. The source of prorenin that accounts for the high plasma prorenin phenotype of the intact conscious Ren-2 rat was not specifically identified. When sensitive assays were used, a low level of active renin secretion from thymus and gut was also apparent 12 h after removal of kidneys and adrenals in normal Sprague-Dawley rats, and plasma prorenin was at this time higher than active renin. A likely source of this extrarenal, extra-adrenal renin is the macrophage.

Angiotensin II and connective tissue: homeostasis and reciprocal regulation

As a concept traditionally applied to integrative organ physiology, homeostasis likewise applies to self-regulated growth and structure of loose, dense and specialized connective tissues. De novo generation and co-induction of signals, either stimulatory or inhibitory to the formation of these tissues, provide for a reciprocal regulation of their composition; angiotensin (Ang) II is a growth stimulator. Components involved in AngII generation and its biological activity, including angiotensin converting enzyme (ACE) and AngII receptors, are expressed by mesenchymal cells responsible for connective tissue turnover. ACE inhibition or AT1 receptor antagonism attenuate the formation of these connective tissues. The concept of circulatory homeostasis, and the endocrine properties of plasma AngII involved in maintaining same, need each be broadened to encompass auto- and paracrine effects of AngII produced within connective tissues, where it contributes to their homeostatic regulation of structure and composition.

Angiotensin II AT1-receptor blockade inhibits monocyte activation and adherence in transgenic (mRen2)27 rats

This study investigated whether angiotensin II AT1-receptor blockade with losartan inhibits endothelium-monocyte interactions originating from long-term activation of the renin-angiotensin system in hypertensive transgenic rats [TGR(mRen2)27]. The number of circulating activated monocytes, monocytes adhered to thoracic aorta endothelium, and the extent of endothelial cell injury were compared in adult male transgenic (mRen2)27 and age-matched Hannover Sprague-Dawley (SD) rats after 12 days of continuous subcutaneous administration of saline (120 microl/24 h), losartan (10 mg/kg/24 h), or the vasodilator hydralazine (3 mg/kg/24 h). At the doses administered in this experiment, both losartan and hydralazine normalized mRen2 rat blood pressures equal to values in similarly treated SD rats. Compared with saline infusion, administration of either antihypertensive in mRen2 rats reduced (p<0.05) endothelial cell injury, but only losartan significantly (p<0.05) decreased the number of activated circulating and endothelium-adherent monocytes. Infusion of antihypertensives in SD rats had no effect on blood pressures, monocyte activity, or endothelial injury compared with saline administration. These findings suggest that the recruitment and infiltration of leukocytes into the subendothelium associated with renin-angiotensin system-induced hypertension is partly mediated by pressure-independent AT1-receptor pathways.

Angiotensin, LDL peroxidation and atherosclerosis

Hypertension is a known risk factor for the development of atherosclerosis. However, in most of the studies, no effect of blood pressure reduction was demonstrated on the incidence of coronary artery disease, except in the SHEP study in which it was shown that in older persons, with isolated systolic hypertension, antihypertensive stepped-care drug treatment reduced the incidence of total stroke and major cardiovascular event. In hypertensive patients with elevated plasma renin activity, a 5-fold increased incidence of myocardial infarction was demonstrated. As oxidation of low density lipoprotein (LDL) was suggested to be a major risk factor for atherosclerosis, we studied the relationship between hypertension and LDL oxidation. We demonstrated increased propensity of LDL obtained from hypertensive patients to oxidative modification, in comparison with LDL obtained from normotensive subjects and suggested that angiotensin II (Ang-II) may be involved in this effect. Ang-II was shown to enhance macrophage lipid peroxidation both in vivo and in vitro. This effect was dose-dependent and involved the binding of Ang-II to its receptor on the macrophage surface. In addition, these lipid peroxidized Ang-II-treated macrophages could substantially oxidize LDL. Ang-II was shown to possess additional atherogenic properties such as increasing the activity of the macrophage oxidized LDL receptors. It also binds to LDL, thus leading to the formation of a modified lipoprotein, which is taken up by macrophages at enhanced rate through the scavenger receptor. Inhibition of Ang-II formation by angiotensin converting enzyme inhibitors reduced LDL peroxidation in hypertensive patients as well as in the atherosclerotic apo E deficient mice. The reduction in LDL peroxidation in these mice was accompanied by a 70-90% reduction in the atherosclerotic lesion area. A similar effect in these mice was demonstrated with the Ang-II receptor antagonist, Losartan. Thus, we suggest that Ang-II is involved in the development of atherogenesis in hypertensive patients and inhibition of Ang-II formation or prevention of its interaction with its receptor may attenuate the atherosclerotic process.