The Angiotensin-(1-12)/Chymase axis as an alternate component of the tissue renin angiotensin system

Angiotensin-(1-12): Does It Exist? A Critical Evaluation in Humans, Rats, and Mice

BACKGROUND

Angiotensin-(1-12), measured by a self-developed, polyclonal antibody-based radioimmunoassay, has been suggested to act as an alternative precursor of angiotensin II. A more reliable detection method would be liquid chromatography-tandem mass spectrometry.

METHODS

We set up the quantification of human and murine angiotensin-(1-12) by liquid chromatography-tandem mass spectrometry and then used this method to measure angiotensin-(1-12) in human, rat, and mouse blood samples, as well as in mouse brain, mouse kidney, and rat heart. We also verified ex vivo angiotensin-(1-12) generation and metabolism in human blood samples incubated at 37 °C.

RESULTS

Stabilization of blood in guanidine hydrochloride was chosen for sample collection since this allowed full recovery of spiked angiotensin-(1-12). Angiotensin-(1-12) was undetectable in human blood samples when incubating nonstabilized plasma at 37 °C, while angiotensin-(1-12) added to nonstabilized human plasma disappeared within 10 minutes. Stabilized human blood samples contained angiotensin II, while angiotensin-(1-12) was undetectable. Blood, hearts, and kidneys, but not brains, of wild-type mice and rats contained detectable levels of angiotensin II, while angiotensin-(1-12) was undetectable. In renin knockout mice, all angiotensins, including angiotensin-(1-12), were undetectable at all sites, despite a 50% rise in angiotensinogen. Angiotensin-(1-12) metabolism in human blood plasma was not affected by renin inhibition. Yet, blockade of angiotensin-converting enzyme and aminopeptidase A, but not of chymase, neutral endopeptidase, or prolyl oligopeptidase, prolonged the half-life of angiotensin-(1-12), and angiotensin-converting enzyme inhibition prevented the formation of angiotensin II.

CONCLUSIONS

We were unable to detect intact angiotensin-(1-12) in humans, rats, and mice, either in blood or tissue, suggesting that this metabolite is an unlikely source of endogenous angiotensins.

Chymase in Plasma and Urine Extracellular Vesicles: Novel Biomarkers for Primary Hypertension

BACKGROUND

Extracellular vesicles (EVs) have emerged as a promising liquid biopsy for various diseases. For the first time, using plasma and urinary EVs, we assessed the activity of renin-angiotensin system (RAS), a central regulator of renal, cardiac, and vascular physiology, in patients with control (Group I) or uncontrolled (Group II) primary hypertension.

METHODS

EVs were isolated from 34 patients with history of hypertension, and characterized for size and concentration by nanoparticle tracking analyses, exosomal biomarkers by immunogold labeling coupled with transmission electron microscopy, flow cytometry and immunoblotting. EVs were analyzed for the hydrolytic activity of chymase, angiotensin converting enzyme (ACE), ACE2, and neprilysin (NEP) by HPLC.

RESULTS

Plasma and urinary EVs were enriched for small EVs and expressed exosomal markers (CD63, CD9, and CD81). The size of urinary EVs (but not plasma EVs) was significantly larger in Group II compared to Group I. Differential activity of RAS enzymes was observed, with significantly higher chymase activity compared to ACE, ACE2, and NEP in plasma EVs. Similarly, urinary EVs exhibited higher chymase and NEP activity compared to ACE and ACE2 activity. Importantly, compared to Group I, significantly higher chymase activity was observed in urinary EVs (p = 0.03) from Group II, while no significant difference in activity was observed for other RAS enzymes.

CONCLUSIONS

Bioactive RAS enzymes are present in plasma and urinary EVs. Detecting chymase in plasma and urinary EVs uncovers a novel mechanism of angiotensin II-forming enzyme and could also mediate cell-cell communication and modulate signaling pathways in recipient cells.

GRAPHICAL ABSTRACT

The Renin-Angiotensin System: The Challenge behind Autoimmune Dermatological Diseases

Autoimmune dermatological diseases (AIDD) encompass a diverse group of disorders characterized by aberrant immune responses targeting the skin and its associated structures. In recent years, emerging evidence suggests a potential involvement of the renin-angiotensin system (RAS) in the pathogenesis and progression of these conditions. RAS is a multicomponent cascade, primarily known for its role in regulating blood pressure and fluid balance. All of the RAS components play an important role in controlling inflammation and other immune responses. Angiotensin II, the main effector, acts on two essential receptors: Angiotensin Receptor 1 and 2 (AT1R and AT2R). A disturbance in the axis can lead to many pathological processes, including autoimmune (AI) diseases. AT1R activation triggers diverse signaling cascades involved in inflammation, fibrosis and tissue remodeling. Experimental studies have demonstrated the presence of AT1R in various cutaneous cells and immune cells, further emphasizing its potential contribution to the AI processes in the skin. Furthermore, recent investigations have highlighted the role of other RAS components, beyond angiotensin-converting enzyme (ACE) and Ang II, that may contribute to the pathophysiology of AIDD. Alternative pathways involving ACE2, Ang receptors and Ang-(1-7) have been implicated in regulating immune responses and tissue homeostasis within the skin microenvironment. Understanding the intricate involvement of the RAS in AIDD may provide novel therapeutic opportunities. Targeting specific components of the RAS, such as angiotensin receptor blockers (ARBs), ACE inhibitors (ACEIs) or alternative RAS pathway modulators, could potentially ameliorate inflammatory responses, reduce tissue damage and lessen disease manifestations. Further research is warranted to outline the exact mechanisms underlying RAS-mediated immune dysregulation in AIDD. This abstract aims to provide a concise overview of the intricate interplay between the RAS and AIDD. Therefore, we elaborate a systematic review of the potential challenge of RAS in the AIDD, including psoriasis, systemic sclerosis, vitiligo, lupus erythematosus and many more.

Immunomodulation of Myocardial Fibrosis

Immunotherapy is a potential cornerstone in the treatment of myocardial fibrosis. During a myocardial insult or heart failure, danger signals stimulate innate immune cells to produce chemokines and profibrotic cytokines, which initiate self-escalating inflammatory processes by attracting and stimulating adaptive immune cells. Stimulation of fibroblasts by inflammatory processes and the need to replace damaged cardiomyocytes fosters reshaping of the cardiac fibroblast landscape. In this review, we discuss new immunomodulatory strategies that manipulate and direct cardiac fibroblast activation and differentiation. In particular, we highlight immunomodulatory strategies that target fibroblasts such as chimeric antigen receptor T cells, interleukin-11, and invariant natural killer T-cells. Moreover, we discuss the potential of manipulating both innate and adaptive immune system components for the translation into clinical validation. Clearly, multiple pathways should be considered to develop innovative approaches to ameliorate myocardial fibrosis and hence to reduce the risk of heart failure.

Internalization of Angiotensin-(1-12) in Adult Retinal Pigment Epithelial-19 Cells

Purpose: Angiotensin-(1-12) [Ang-(1-12)] serves as a primary substrate to generate angiotensin II (Ang II) by angiotensin-converting enzyme and/or chymase suggests it may be an unrecognized source of Ang II-mediated microvascular complication in hypertension-mediated retinopathy. We investigated Ang-(1-12) expression and internalization in adult retinal pigment epithelial-19 (ARPE-19) cultured cells. We performed the internalization of Ang-(1-12) in ARPE-19 cells in the presence of a highly specific monoclonal antibody (mAb) developed against the C-terminal end of the Ang-(1-12) sequence. Methods: All experiments were performed in confluent ARPE-19 cells (passage 28-35). We employed high-performance liquid chromatography to purify radiolabeled, 125I-Ang-(1-12) and immuno-neutralization with Ang-(1-12) mAb to demonstrate Ang-(1-12)'s internalization in ARPE-19 cells. Internalization was also demonstrated by immunofluorescence (IF) method. Results: These procedures revealed internalization of an intact 125I-Ang-(1-12) in ARPE-19 cells. A significant reduction (∼53%, P < 0.0001) in 125I-Ang-(1-12) internalization was detected in APRE-19 cells in the presence of the mAb. IF staining experiments further confirms internalization of Ang-(1-12) into the cells from the extracellular culture medium. No endogenous expression was detected in the ARPE-19 cells. An increased intensity of IF staining was detected in cells exposed to 1.0 μM Ang-(1-12) compared with 0.1 μM. Furthermore, we found hydrolysis of Ang-(1-12) into Ang II by ARPE-19 cells' plasma membranes. Conclusions: Intact Ang-(1-12) peptide is internalized from the extracellular spaces in ARPE-19 cells and metabolized into Ang II. The finding that a selective mAb blocks cellular internalization of Ang-(1-12) suggests alternate therapeutic approaches to prevent/reduce the RPE cells Ang II burden.

Angiotensin-(1-9) in hypertension

Angiotensin-(1-9) [Ang-(1-9)] is a peptide of the non-canonical renin-angiotensin system (RAS) synthesized from angiotensin I by the monopeptidase angiotensin-converting enzyme type 2 (ACE2). Using osmotic minipumps, infusion of Ang-(1-9) consistently reduces blood pressure in several rat hypertension models. In these animals, hypertension-induced end-organ damage is also decreased. Several pieces of evidence suggest that Ang-(1-9) is the endogenous ligand that binds and activates the type-2 angiotensin II receptor (AT2R). Activation of AT2R triggers different tissue-specific signaling pathways. This phenomenon could be explained by the ability of AT2R to form different heterodimers with other G protein-coupled receptors. Because of the antihypertensive and protective effects of AT2R activation by Ang-(1-9), associated with a short half-life of RAS peptides, several synthetic AT2R agonists have been synthesized and assayed. Some of them, particularly CGP42112, C21 and novokinin, have demonstrated antihypertensive properties. Only two synthetic AT2R agonists, C21 and LP2-3, have been tested in clinical trials, but none of them like an antihypertensive. Therefore, Ang-(1-9) is a promising antihypertensive drug that reduces hypertension-induced end-organ damage. However, further research is required to translate this finding successfully to the clinic.

Immunoneutralization of human angiotensin-(1-12) with a monoclonal antibody in a humanized model of hypertension

We engineered a monoclonal antibody (mAb) against the human C-terminus of angiotensin-(1-12) [h-Ang-(1-12)] and performed a biochemical characterization in concert with direct in vivo and ex vivo (carotid artery strips) assessments of h-Ang-(1-12) vasoconstrictor activity in 78 (36 females) transgenic rats expressing the human angiotensinogen gene [TGR(hAGT)L1623] and 26 (10 female) Sprague Dawley (SD) controls. The mAb shows high specificity in neutralizing angiotensin II formation from h-Ang-(1-12) and did not cross-react with human and rat angiotensins. Changes in arterial pressure and heart rate in Inactin® hydrate anesthetized rats were measured before and after h-Ang-(1-12) injections [dose range: 75-300 pmol/kg i.v.] prior to and 30-60 minutes after administration of the h-Ang-(1-12) mAb. Neutralization of circulating Ang-(1-12) inhibited the pressor action of h-Ang-(1-12), prevented Ang-(1-12) constrictor responses in carotid artery rings in both SD and TGR(hAGT)L1623 rats, and caused a fall in the arterial pressure of male and female transgenic rats. The Ang-(1-12) mAb did not affect the response of comparable dose-related pressor responses to Ang II, pre-immune IgG, or the rat sequence of Ang-(1-12). This h-Ang-(1-12) mAb can effectively suppress the pressor actions of the substrate in the circulation of hypertensive rats or in carotid artery strips from both SD and transgenic rats. The demonstration that this Ang-(1-12) mAb by itself, induced a fall in arterial pressure in transgenic hypertensive rats supports further exploring the potential abilities of Ang-(1-12) mAb in the treatment of hypertension.

Heart Angiotensin-Converting Enzyme and Angiotensin-Converting Enzyme 2 Gene Expression Associated With Male Sex and Salt-Sensitive Hypertension in the Dahl Rat

Angiotensin-converting enzyme 2 (ACE 2) in the heart including its sex dependency in the hypertensive heart, has not been much studied compared to ACE. In the present study, we used the Dahl salt-sensitive rat exposed to fructose and salt to model a hypertensive phenotype in males, females, and ovariectomized females. Blood pressure was measured by the tale-cuff technique in the conscious state. Expression of RAS-related genes ACE, ACE2, angiotensin II receptor type 1, Mas1, and CMA1 in the heart were quantified. The results revealed small but significant differences between male and female groups. The main results indicate the presence of a male preponderance for an increase in ACE and ACE2 gene expression. The results are in accordance with the role of androgens or male chromosomal complement in controlling the expression of the two ACE genes.