Plasma and tissue concentrations of proangiotensin-12 in rats treated with inhibitors of the renin-angiotensin system

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

Mechanism Underlying Triple VEGFR Inhibitor Tivozanib-Induced Hypertension in Mice Model

Tivozanib is a triple vascular endothelial growth factor receptor inhibitor, recently approved for the treatment of refractory advanced renal cell carcinoma. Clinical studies showed that around 46% of patients who received tivozanib suffer from hypertension in all grades. Thus, the present study was conducted to identify the role of angiotensin-II (AngII) in the mechanism underlying tivozanib-induced vascular toxicity and hypertension. C57BL/6 male mice received tivozanib (1 mg/kg) with or without losartan (10 or 30 mg/kg) for 3 weeks. Blood pressure was recorded every 3 days, and proteinuria was measured every week. On day 21, all mice were euthanized, and samples were harvested for further analysis. Tivozanib elevated blood pressure until systolic blood pressure reached 163 ± 6.6 mmHg on day 21 of treatment with low urination and high proteinuria. AngII and its receptors, endothelin-1, and oxidative stress markers were significantly increased. While nitric oxide (NO) levels were reduced in plasma and aortic tissues. AngII type 1 receptor blockade by losartan prevented these consequences caused by tivozanib and kept blood pressure within normal range. The results showed that AngII and ET-1 might be potential targets in the clinical studies and management of hypertension induced by tivozanib.

Does the Naked Emperor Parable Apply to Current Perceptions of the Contribution of Renin Angiotensin System Inhibition in Hypertension?

PURPOSE OF REVIEW

To address contemporary hypertension challenges, a critical reexamination of therapeutic accomplishments using angiotensin converting enzyme inhibitors and angiotensin II receptor blockers, and a greater appreciation of evidence-based shortcomings from randomized clinical trials are fundamental in accelerating future progress.

RECENT FINDINGS

Medications targeting angiotensin II mechanism of action are essential for managing primary hypertension, type 2 diabetes, heart failure, and chronic kidney disease. While the ability of angiotensin converting enzyme inhibitors and angiotensin II receptor blockers to control blood pressure is undisputed, practitioners, hypertension specialists, and researchers hold low awareness of these drugs' limitations in preventing or reducing the risk of cardiovascular events. Biases in interpreting gained knowledge from data obtained in randomized clinical trials include a pervasive emphasis on using relative risk reduction over absolute risk reduction. Furthermore, recommendations for clinical practice in international hypertension guidelines fail to address the significance of a residual risk several orders of magnitude greater than the benefits. We analyze the limitations of the clinical trials that have led to current recommended treatment guidelines. We define and quantify the magnitude of the residual risk in published hypertension trials and explore how activation of alternate compensatory bioprocessing components within the renin angiotensin system bypass the ability of angiotensin converting enzyme inhibitors and angiotensin II receptor blockers to achieve a significant reduction in total and cardiovascular deaths. We complete this presentation by outlining the current incipient but promising potential of immunotherapy to block angiotensin II pathology alone or possibly in combination with other antihypertensive drugs. A full appreciation of the magnitude of the residual risk associated with current renin angiotensin system-based therapies constitutes a vital underpinning for seeking new molecular approaches to halt or even reverse the cardiovascular complications of primary hypertension and encourage investigating a new generation of ACE inhibitors and ARBs with increased capacity to reach the intracellular compartments at which Ang II can be generated.

Development of a novel AlphaLISA ImmunoAssay for Big angiotensin-25

We previously described the discovery of Big angiotensin-25 (Bang-25), an angiotensin-related peptide isolated from human urine. Bang-25 consists of the first 25 amino acids of the N-terminus of angiotensinogen (Aogen), with N-linked glycosylation on the 14th amino acid and a cysteine conjugated to the 18th amino acid. Bang-25 is rapidly converted into angiotensin II (Ang II) by chymase. Because Bang-25 is widely distributed in human tissues, including islet cells in the pancreas and podocytes in the kidney, we hypothesized that it may participate in the Ang II production system in these tissues. To test this hypothesis, we developed a specific assay for Bang-25 and used it to examine the urinary concentrations of Bang-25 in patients with diabetes mellitus (DM). The assay used the Amplified Luminescent Proximity Homogeneous Assay (Alpha)-based ELISA method (AlphaLISA) of PerkinElmer Japan and included antibodies specific to the N-terminus of Ang II and the C-terminus of Bang-25. The AlphaLISA ImmunoAssay specifically recognized Bang-25 and had no cross-reactivity with Aogen or Ang I. Bang-25 was detected in healthy volunteers' urine samples but not in their plasma samples. In patients with DM, the urinary Bang-25 concentration was significantly higher than in healthy volunteers. Moreover, the results indicated that the Bang-25 concentration in the urine may offer a different perspective on disease status from that provided by urinary albumin. This assay could provide a useful tool for determining urinary Bang-25, which may prove an important biomarker for diabetic kidney disease.

Multifunctional Role of Chymase in Acute and Chronic Tissue Injury and Remodeling

Chymase is the most efficient Ang II (angiotensin II)-forming enzyme in the human body and has been implicated in a wide variety of human diseases that also implicate its many other protease actions. Largely thought to be the product of mast cells, the identification of other cellular sources including cardiac fibroblasts and vascular endothelial cells demonstrates a more widely dispersed production and distribution system in various tissues. Furthermore, newly emerging evidence for its intracellular presence in cardiomyocytes and smooth muscle cells opens an entirely new compartment of chymase-mediated actions that were previously thought to be limited to the extracellular space. This review illustrates how these multiple chymase-mediated mechanisms of action can explain the residual risk in clinical trials of cardiovascular disease using conventional renin-angiotensin system blockade.

Estrogen modulates the differential expression of cardiac myocyte chymase isoforms and diastolic function

Chymases, a family of serine proteases with chymotryptic activity, play a significant role in cardiac angiotensin II (Ang II) formation from its substrate Ang-(1-12) in both human and rodent models. No studies, to date, have assessed the differences in enzymatic activity among these isoforms in Ang II formation, particularly in the cardiomyocyte (CM). Using PCR and DNA sequencing, we demonstrated that MCP-1, MCP-2, MCP-4, and MCP-5 mRNAs are expressed in the CM of both spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). While rMCP-1 and rMCP-5 gene transcripts were higher than that of other isoforms in both rat strains, WKY CM exhibits higher levels of rMCP-1 and rMCP-5 mRNAs compared to the SHR CM. Ovariectomy (OVX) increased the expression of rMCP-1 and rMCP-5 mRNAs in WKY. In SHR, OVX was associated with a blunted increase in rMCP-1 mRNA compared to OVX normotensive WKY. Chymase activity, measured as Ang II formation from Ang-(1-12), significantly correlated with rMCP-1 and rMCP-5 mRNA expression in both rat strains. Both rMCP-1 and rMCP-5 mRNA expressions were positively correlated with progressive diastolic dysfunction (increasing the ratio of early mitral inflow velocity-to-early mitral annular velocity, E/e') and expanding chamber dimensions or increasing left ventricular internal diameter end diastole. These data show rMCP-1 and rMCP-5 as the Ang II forming chymase isoforms participating in the loss of normal cardiac function due to OVX in rodents.

Novel Cardiac Intracrine Mechanisms Based on Ang-(1-12)/Chymase Axis Require a Revision of Therapeutic Approaches in Human Heart Disease

PURPOSE OF THE REVIEW

Drugs targeting the renin-angiotensin system (RAS), namely angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers, are the most commonly prescribed drugs for patients with or at risk for cardiovascular events. However, new treatment strategies aimed at mitigating the rise of the heart failure pandemic are warranted because clinical trials show that RAS blockers have limited benefits in halting disease progression. The main goal of this review is to put forward the concept of an intracrine RAS signaling through the novel angiotensin-(1-12)/chymase axis as the main source of deleterious angiotensin II (Ang II) in cardiac maladaptive remodeling leading to heart failure (HF).

RECENT FINDINGS

Expanding traditional knowledge, Ang II can be produced in tissues independently from the circulatory renin-angiotensin system. In the heart, angiotensin-(1-12) [Ang-(1-12)], a recently discovered derivative of angiotensinogen, is a precursor of Ang II, and chymase rather than ACE is the main enzyme contributing to the direct production of Ang II from Ang-(1-12). The Ang-(1-12)/chymase axis is an independent intracrine pathway accounting for the trophic, contractile, and pro-arrhythmic Ang II actions in the human heart. Ang-(1-12) expression and chymase activity have been found elevated in the left atrial appendage of heart disease subjects, suggesting a pivotal role of this axis in the progression of HF. Recent meta-analysis of large clinical trials on the use of ACE inhibitors and angiotensin receptor blockers in cardiovascular disease has demonstrated an imbalance between patients that significantly benefit from these therapeutic agents and those that remain at risk for heart disease progression. Looking to find an explanation, detailed investigation on the RAS has unveiled a previously unrecognized complexity of substrates and enzymes in tissues ultimately associated with the production of Ang II that may explain the shortcomings of ACE inhibition and angiotensin receptor blockade. Discovery of the Ang-(1-12)/chymase axis in human hearts, capable of producing Ang II independently from the circulatory RAS, has led to the notion that a tissue-delimited RAS signaling in an intracrine fashion may account for the deleterious effects of Ang II in the heart, contributing to the transition from maladaptive cardiac remodeling to heart failure. Targeting intracellular RAS signaling may improve current therapies aimed at reducing the burden of heart failure.

Intracrine angiotensin II functions originate from noncanonical pathways in the human heart

Although it is well-known that excess renin angiotensin system (RAS) activity contributes to the pathophysiology of cardiac and vascular disease, tissue-based expression of RAS genes has given rise to the possibility that intracellularly produced angiotensin II (Ang II) may be a critical contributor to disease processes. An extended form of angiotensin I (Ang I), the dodecapeptide angiotensin-(1-12) [Ang-(1-12)], that generates Ang II directly from chymase, particularly in the human heart, reinforces the possibility that an alternative noncanonical renin independent pathway for Ang II formation may be important in explaining the mechanisms by which the hormone contributes to adverse cardiac and vascular remodeling. This review summarizes the work that has been done in evaluating the functional significance of Ang-(1-12) and how this substrate generated from angiotensinogen by a yet to be identified enzyme enhances knowledge about Ang II pathological actions.

Primacy of cardiac chymase over angiotensin converting enzyme as an angiotensin-(1-12) metabolizing enzyme

We showed previously that rat angiotensin-(1-12) [Ang-(1-12)] is metabolized by chymase and angiotensin converting enzyme (ACE) to generate Angiotensin II (Ang II). Here, we investigated the affinity of cardiac chymase and ACE enzymes for Ang-(1-12) and Angiotensin I (Ang I) substrates. Native plasma membranes (PMs) isolated from heart and lung tissues of adult spontaneously hypertensive rats (SHR) were incubated with radiolabeled (125)I-Ang-(1-12) or (125)I-Ang I, in the absence or presence of a chymase or ACE inhibitor (chymostatin and lisinopril, respectively). Products were quantitated by HPLC connected to an in-line flow-through gamma detector. The rate of (125)I-Ang II formation from (125)I-Ang-(1-12) by chymase was significantly higher (heart: 7.0 ± 0.6 fmol/min/mg; lung: 33 ± 1.2 fmol/min/mg, P < 0.001) when compared to (125)I-Ang I substrate (heart: 0.8 ± 0.1 fmol/min/mg; lung: 2.1 ± 0.1 fmol/min/mg). Substrate affinity of (125)I-Ang-(1-12) for rat cardiac chymase was also confirmed using excess unlabeled Ang-(1-12) or Ang I (0-250 μM). The rate of (125)I-Ang II formation was significantly lower using unlabeled Ang-(1-12) compared to unlabeled Ang I substrate. Kinetic data showed that rat chymase has a lower Km (64 ± 6.3 μM vs 142 ± 17 μM), higher Vmax (13.2 ± 1.3 μM/min/mg vs 1.9 ± 0.2 μM/min/mg) and more than 15-fold higher catalytic efficiency (ratio of Vmax/Km) for Ang-(1-12) compared to Ang I substrate, respectively. We also investigated ACE mediated hydrolysis of (125)I-Ang-(1-12) and (125)I-Ang I in solubilized membrane fractions of the SHR heart and lung. Interestingly, no significant difference in (125)I-Ang II formation by ACE was detected using either substrate, (125)I-Ang-(1-12) or (125)I-Ang I, both in the heart (1.8 ± 0.2 fmol/min/mg and 1.8 ± 0.3 fmol/min/mg, respectively) and in the lungs (239 ± 25 fmol/min/mg and 248 ± 34 fmol/min/mg, respectively). Compared to chymase, ACE-mediated Ang-(1-12) metabolism in the heart was several fold lower. Overall our findings suggest that Ang-(1-12), not Ang I, is the better substrate for Ang II formation by chymase in adult rats. In addition, this confirms our previous observation that chymase (rather than ACE) is the main hydrolyzing enzyme responsible for Ang II generation from Ang-(1-12) in the adult rat heart.

The implications of angiotensin-converting enzymes and their modulators in neurodegenerative disorders: current and future perspectives

Angiotensin converting enzyme (ACE) is a dipeptidyl peptidase transmembrane bound enzyme. Generally, ACE inhibitors are used for the cardiovascular disorders. ACE inhibitors are primary agents for the management of hypertension, so these cannot be avoided for further use. The present Review focuses on the implications of angiotensin converting enzyme inhibitors in neurodegenerative disorders such as dementia, Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, stroke, and diabetic neuropathy. ACE inhibitors such as ramipril, captopril, perindopril, quinapril, lisinopril, enalapril, and trandolapril have been documented to ameliorate the above neurodegenerative disorders. Neurodegeneration occurs not only by angiotensin II, but also by other endogenous factors, such as the formation of free radicals, amyloid beta, immune reactions, and activation of calcium dependent enzymes. ACE inhibitors interact with the above cellular mechanisms. Thus, these may act as a promising factor for future medicine for neurological disorders beyond the cardiovascular actions. Central acting ACE inhibitors can be useful in the future for the management of neuropathic pain due to following actions: (i) ACE-2 converts angiotensinogen to angiotensin(1-7) (hepatapeptide) which produces neuroprotective action; (ii) ACE inhibitors downregulate kinin B1 receptors in the peripheral nervous system which is responsible for neuropathic pain. However, more extensive research is required in the field of neuropathic pain for the utilization of ACE inhibitors in human.

An evolving story of angiotensin-II-forming pathways in rodents and humans

Lessons learned from the characterization of the biological roles of Ang-(1-7) [angiotensin-(1-7)] in opposing the vasoconstrictor, proliferative and prothrombotic actions of AngII (angiotensin II) created an underpinning for a more comprehensive exploration of the multiple pathways by which the RAS (renin-angiotensin system) of blood and tissues regulates homoeostasis and its altered state in disease processes. The present review summarizes the progress that has been made in the novel exploration of intermediate shorter forms of angiotensinogen through the characterization of the expression and functions of the dodecapeptide Ang-(1-12) [angiotensin-(1-12)] in the cardiac production of AngII. The studies reveal significant differences in humans compared with rodents regarding the enzymatic pathway by which Ang-(1-12) undergoes metabolism. Highlights of the research include the demonstration of chymase-directed formation of AngII from Ang-(1-12) in human left atrial myocytes and left ventricular tissue, the presence of robust expression of Ang-(1-12) and chymase in the atrial appendage of subjects with resistant atrial fibrillation, and the preliminary observation of significantly higher Ang-(1-12) expression in human left atrial appendages.

Primacy of angiotensin converting enzyme in angiotensin-(1-12) metabolism

Angiotensin-(1-12) [ANG-(1-12)], a new member of the renin-angiotensin system, is recognized as a renin independent precursor for ANG II. However, the processing of ANG-(1-12) in the circulation in vivo is not fully established. We examined the effect of angiotensin converting enzyme (ACE) and chymase inhibition on angiotensin peptides formation during an intravenous infusion of ANG-(1-12) in normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). WKY and SHR were assigned to a short ANG-(1-12) infusion lasting 5, 15, 30, or 60 min (n = 4-10 each group). In another experiment WKY and SHR were assigned to a continuous 15-min ANG-(1-12) infusion with pretreatment of saline, lisinopril (10 mg/kg), or chymostatin (10 mg/kg) (n = 7-13 each group). Saline or lisinopril were infused intravenously 15 min before the administration of ANG-(1-12) (2 nmol·kg(-1)·min(-1)), whereas chymostatin was given by bolus intraperitoneal injection 30 min before ANG-(1-12). Infusion of ANG-(1-12) increased arterial pressure and plasma ANG-(1-12), ANG I, ANG II, and ANG-(1-7) levels in WKY and SHR. Pretreatment with lisinopril caused increase in ANG-(1-12) and ANG I and large decreases in ANG II compared with the other two groups in both strains. Pretreatment of chymostatin had no effect on ANG-(1-12), ANG I, and ANG II levels in both strains, whereas it increased ANG-(1-7) levels in WKY. We conclude that ACE acts as the primary enzyme for the conversion of ANG-(1-12) to smaller angiotensin peptides in the circulation of WKY and SHR and that chymase may be an ANG-(1-7) degrading enzyme.

Chymase mediates angiotensin-(1-12) metabolism in normal human hearts

Identification of angiotensin-(1-12) [Ang-(1-12)] in forming angiotensin II (Ang II) by a non-renin dependent mechanism has increased knowledge on the paracrine/autocrine mechanisms regulating cardiac expression of Ang peptides. This study now describes in humans the identity of the enzyme accounting for Ang-(1-12) metabolism in the left ventricular (LV) tissue of normal subjects. Reverse phase HPLC characterized the products of (125)I-Ang-(1-12) metabolism in plasma membranes (PMs) from human LV in the absence and presence of inhibitors for chymase (chymostatin), angiotensin-converting enzyme (ACE) 1 (lisinopril) and 2 (MLN-4760), and neprilysin (SHC39370). In the presence of the inhibitor cocktail, ≥ 98% ± 2% of cardiac (125)I-Ang-(1-12) remained intact, whereas exclusion of chymostatin from the inhibitor cocktail led to significant conversion of Ang-(1-12) into Ang II. In addition, chymase-mediated hydrolysis of (125)I-Ang I was higher compared with Ang-(1-12). Negligible Ang-(1-12) hydrolysis occurred by ACE, ACE2, and neprilysin. A high chymase activity was detected for both (125)I-Ang-(1-12) and (125)I-Ang I substrates. Chymase accounts for the conversion of Ang-(1-12) and Ang I to Ang II in normal human LV. These novel findings expand knowledge of the alternate mechanism by which Ang-(1-12) contributes to the production of cardiac angiotensin peptides.

Hemodynamic and hormonal changes to dual renin-angiotensin system inhibition in experimental hypertension

We examined the antihypertensive effects of valsartan, aliskiren, or both drugs combined on circulating, cardiac, and renal components of the renin-angiotensin system in congenic mRen2.Lewis hypertensive rats assigned to: vehicle (n=9), valsartan (via drinking water, 30 mg/kg per day; n=10), aliskiren (SC by osmotic mini-pumps, 50 mg/kg per day; n=10), or valsartan (30 mg/kg per day) combined with aliskiren (50 mg/kg per day; n=10). Arterial pressure and heart rate were measured by telemetry before and during 2 weeks of treatment; trunk blood, heart, urine, and kidneys were collected for measures of renin-angiotensin system components. Arterial pressure and left-ventricular weight/tibia length ratio were reduced by monotherapy of valsartan, aliskiren, and further reduced by the combination therapy. Urinary protein excretion was reduced by valsartan and further reduced by the combination. The increases in plasma angiotensin (Ang) II induced by valsartan were reversed by the treatment of aliskiren and partially suppressed by the combination. The decreases in plasma Ang-(1-7) induced by aliskiren recovered in the combination group. Kidney Ang-(1-12) was increased by the combination therapy whereas the increases in urinary creatinine mediated by valsartan were reversed by addition of aliskiren. The antihypertensive and antiproteinuric actions of the combined therapy were associated with marked worsening of renal parenchymal disease and increased peritubular fibrosis. The data show that despite improvements in the surrogate end points of blood pressure, ventricular mass, and proteinuria, dual blockade of Ang II receptors and renin activity is accompanied by worsening of renal parenchymal disease reflecting a renal homeostatic stress response attributable to loss of tubuloglomerular feedback by Ang II.