Possible roles of angiotensin II-forming enzymes, angiotensin converting enzyme and chymase-like enzyme, in the human aneurysmal aorta

Inflammation in Abdominal Aortic Aneurysm: Cause or Comorbidity?

Aortic aneurysm is a potentially deadly disease. It is chronic degeneration of the aortic wall that involves an inflammatory response and the immune system, aberrant remodelling of the extracellular matrix, and maladaptive transformation of the aortic cells. This review article focuses on the role of the inflammatory cells in abdominal aortic aneurysm. Studies in human aneurysmal specimens and animal models have identified various inflammatory cell types that could contribute to formation or expansion of aneurysms. These include the commonly studied leukocytes (neutrophils and macrophages) as well as the less commonly explored natural killer cells, dendritic cells, T cells, and B cells. Despite the well-demonstrated contribution of inflammatory cells and the related signalling pathways to development and expansion of aneurysms, anti-inflammatory therapy approaches have demonstrated limitations and may require additional considerations such as a combinational approach in targeting multiple pathways for significant beneficial outcomes.

Angiotensin II constricts mouse iliac arteries: possible mechanism for aortic aneurysms

Abdominal aortic aneurysms (AAA) result from maladaptive remodeling of the vascular wall and reduces structural integrity. Angiotensin II (AngII) infusion has become a standard laboratory model for studying AAA initiation and progression. We determined the different vasoactive responses of various mouse arteries to Ang II. Ex vivo isometric tension analysis was conducted on 18-week-old male C57BL/6 mice (n = 4) brachiocephalic arteries (BC), iliac arteries (IL), and abdominal (AA) and thoracic aorta (TA). Arterial rings were mounted between organ hooks, gently stretched and an AngII dose response was performed. Rings were placed in 4% paraformaldehyde for immunohistochemistry analysis to quantify peptide expression of angiotensin type 1 (AT1R) and 2 receptors (AT2R) in the endothelium, media, and adventitia. Results from this study demonstrated vasoconstriction responses in IL were significantly higher at all AngII doses when compared to BC, and TA and AA responses (maximum constriction-IL: 68.64 ± 5.47% vs. BC: 1.96 ± 1.00%; TA: 3.13 ± 0.16% and AA: 2.75 ± 1.77%, p < 0.0001). Expression of AT1R was highest in the endothelium of IL (p < 0.05) and in the media and (p < 0.05) adventitia (p < 0.05) of AA. In contrast, AT2R expression was highest in endothelium (p < 0.05), media (p < 0.01, p < 0.05) and adventitia of TA. These results suggest that mouse arteries display different vasoactive responses to AngII, and the exaggerated response in IL arteries may play a role during AAA development.

Mechanical activation of the angiotensin II type 1 receptor contributes to abdominal aortic aneurysm formation

Objective

The angiotensin II type 1 receptor (AT1R) can be activated under conditions of mechanical stretch in some cellular systems. Whether this activity influences signaling within the abdominal aorta to promote to abdominal aortic aneurysm (AAA) development remains unknown. We evaluated the hypothesis that mechanical AT1R activation can occur under conditions of hypertension (HTN) and contribute to AAA formation.

Methods

BPH/2 mice, which demonstrate spontaneous neurogenic, low-renin HTN, and normotensive BPN/3 mice underwent AAA induction via the calcium chloride model, with or without an osmotic minipump delivering 30 mg/kg/d of the AT1R blocker Losartan. Systolic blood pressure (SBP) was measured at baseline and weekly via a tail cuff. The aortic diameter (AoD) was measured at baseline and terminal surgery at 21 days by digital microscopy. Aortic tissue was harvested for immunoblotting (phosphorylated extracellular signal-regulated kinase-1 and -2 [pERK1/2] to ERK1/2 ratio) and expressed as the fold-change from the BPN/3 control mice. Aortic vascular smooth muscle cells (VSMCs) underwent stretch with or without Losartan (1 μM) treatment to assess the mechanical stimulation of ERK1/2 activity. Statistical analysis of the blood pressure, AoD, and VSMC ERK1/2 activity was performed using analysis of variance. However, the data distribution was determined to be log-normal (Shapiro-Wilk test) for ERK1/2 activity. Therefore, it was logarithmically transformed before analysis of variance.

Results

At baseline, the SBP was elevated in the BPH/2 mice relative to the BPN/3 mice (P < .05). Losartan treatment significantly reduced the SBP in both mouse strains (P < .05). AAA induction did not affect the SBP. At 21 days after induction, the percentage of increase in the AoD from baseline was significantly greater in the BPH/2 mice than in the BPN/3 mice (101.28% ± 4.19% vs 75.59% ± 1.67% above baseline; P < .05). Losartan treatment significantly attenuated AAA growth in both BPH/2 and BPN/3 mice (33.88% ± 2.97% and 43.96% ± 3.05% above baseline, respectively; P < .05). ERK1/2 activity was increased approximately fivefold in the BPH/2 control mice relative to the BPN/3 control mice (P < .05). In the BPH/2 and BPN/3 mice with AAA, ERK1/2 activity was significantly increased relative to the respective baseline control (P < .05) and effectively reduced by concomitant Losartan therapy (P < .05). Biaxial stretch of the VSMCs in the absence of angiotensin II demonstrated increased ERK1/2 activation (P < .05 vs static control), which was significantly inhibited by Losartan.

Conclusions

In BPH/2 mice with spontaneous neurogenic, low-renin HTN, AAA growth was amplified compared with the normotensive control and was effectively attenuated using Losartan. ERK1/2 activity was significantly elevated in the BPH/2 mice and after AAA induction in the normotensive and hypertensive mice but was attenuated by Losartan treatment. These data suggest that AT1R activation contributes to AAA development. Therefore, further investigation into this signaling pathway could establish targets for pharmacotherapeutic engineering to slow AAA growth. (JVS-Vascular Science 2021;2:194-206.).

Clinical Relevance

Hypertension (HTN) and abdominal aortic aneurysm (AAA) have been epidemiologically linked for decades; however, a biomechanical link has not yet been identified. Using a murine model of spontaneous neurogenic HTN experimentally demonstrated to have low circulating renin, mechanical activation of the angiotensin II type 1 receptor (AT1R) was identified with elevated blood pressure and AAA induction. HTN amplified AAA growth. However, more importantly, blocking the activation of AT1R with the angiotensin receptor blocker Losartan effectively abrogated AAA development. Although inhibiting the production of angiotensin II has previously been unsuccessful in altering AAA growth, the results from the present study suggest that blocking the activation of AT1R through direct ligand binding or mechanical stimulation might alter aortic wall signaling and warrants further investigation.

Angiotensin II is a crucial factor in retinal aneurysm formation

Retinal arterial macroaneurysms are characterized by the acquired fusiform or saccular dilatations of the retinal artery. Angiotensin II (Ang II) is a major signal molecule of the renin-angiotensin system, which exerts a range of pathogenic actions that are relevant to retinal vascular abnormalities. We aimed to study the effect of Ang II on retinal vessels and explore its relationship with retinal aneurysmal disease. C57BL/6J male mice were administered Ang II at 1000 ng/kg/min for 28 days, and the mice given saline served as controls. The mice in the treatment group were treated once daily by gastric gavage of candesartan cilexetil (an antagonist of Ang II type 1 (AT1) receptor) at 100 mg/kg/day. The in vivo imaging of murine retinas was performed using fundus photography, optical coherence tomography, fluorescein angiography, and indocyanine green angiography at 7th, 14th, and 28th days of infusion. At the end of the infusion and treatment, the morphological changes were evaluated by histopathological examination and electron microscopy; the levels of related proteins in murine retinas were examined by antibody array and Western blot analyses. We found that Ang II infusion induced aneurysm formation in mice retina, which presented as either solitary aneurysms or retinal arterial beading. The aneurysm formation was often accompanied with vessel leakage. Moreover, Ang II infusion itself may result in increased vascular permeability and ganglion cell and inner plexiform layer thickening. The blockade of AT1 receptors by systemic administration of candesartan cilexetil alleviated the Ang II-induced retinal vasculopathy. The protein level analysis further showed that Ang II upregulated IL-1β, PDGFR-β, and MMP-9 expression, and the expression of IL-1β could be inhibited by AT1 receptor antagonist. Our study provides evidence that Ang II is a crucial factor in retinal aneurysm formation and vessel leakage. It is probably the combined effect of Ang II on vessel inflammatory response, pericyte function, and extracellular matrix remodeling that predisposes the retinal arterial wall to aneurysm formation and blood-retinal barrier breakdown.

Current pharmacological management of aortic aneurysm

ABSTRACT

Aortic aneurysm (AA) remains one of the primary causes of death worldwide. Of the major treatments, prophylactic operative repair is used for AA to avoid potential aortic dissection (AD) or rupture. To halt the development of AA and alleviate its progression into AD, pharmacological treatment has been investigated for years. Currently, β-adrenergic blocking agents, losartan, irbesartan, angiotensin-converting-enzyme inhibitors, statins, antiplatelet agents, doxycycline, and metformin have been investigated as potential candidates for preventing AA progression. However, the paradox between preclinical successes and clinical failures still exists, with no medical therapy currently available for ideally negating the disease progression. This review describes the current drugs used for pharmacological management of AA and their individual potential mechanisms. Preclinical models for drug screening and evaluation are also discussed to gain a better understanding of the underlying pathophysiology and ultimately find new therapeutic targets for AA.

Association of Long-term Use of Antihypertensive Medications With Late Outcomes Among Patients With Aortic Dissection

IMPORTANCE

The associations between long-term treatment of aortic dissection with various medications and late patient outcomes are poorly understood.

OBJECTIVE

To compare late outcomes after long-term use of β-blockers, angiotensin-converting enzyme inhibitors (ACEIs), angiotensin receptor blockers (ARBs), or other antihypertensive medications (controls) among patients treated for aortic dissection.

DESIGN, SETTING, AND PARTICIPANTS

This population-based retrospective cohort study using the National Health Insurance Research Database in Taiwan included 6978 adult patients with a first-ever aortic dissection who survived to hospital discharge during the period between January 1, 2001, and December 31, 2013, and who received during the first 90 days after discharge a prescription for an ACEI, ARB, β-blocker, or at least 1 other antihypertensive medication. Data analysis was conducted from July 2019 to June 2020.

EXPOSURE

Long-term use of β-blockers, ACEIs, or ARBs, with use of other antihypertensive medications as a control.

MAIN OUTCOMES AND MEASURES

The primary outcomes of interest were all-cause mortality, death due to aortic aneurism or dissection, later aortic operation, major adverse cardiac and cerebrovascular events, hospital readmission, and new-onset dialysis.

RESULTS

Of 6978 total participants, 3492 received a β-blocker, 1729 received an ACEI or ARB, and 1757 received another antihypertension drug. Compared with patients in the other 2 groups, those in the β-blocker group were younger (mean [SD] age, 62.1 [13.9] years vs 68.7 [13.5] years for ACEIs or ARBs and 69.9 [13.8] years for controls) and comprised more male patients (2520 [72.2%] vs 1161 [67.1%] for ACEIs or ARBs and 1224 [69.7%] for controls). The prevalence of medicated hypertension was highest in the ACEI or ARB group (1039 patients [60.1%]), followed by the control group (896 patients [51.0%]), and was lowest in the β-blocker group (1577 patients [45.2%]). Patients who underwent surgery for type A aortic dissection were more likely to be prescribed β-blockers (1134 patients [32.5%]) than an ACEI or ARB (309 patients [17.9%]) or another antihypertension medication (376 patients [21.4%]). After adjusting for multiple propensity scores, there were no significant differences in any of the clinical characteristics among the 3 groups. No differences in the risks for all outcomes were observed between the ACEI or ARB and β-blocker groups. The risk of all-cause hospital readmission was significantly lower in the ACEI or ARB group (subdistribution hazard ratio [HR], 0.92; 95% CI, 0.84-0.997) and β-blocker group (subdistribution HR, 0.87; 95% CI, 0.81-0.94) than in the control group. Moreover, the risk of all-cause mortality was lower in the ACEI or ARB group (HR, 0.79; 95% CI, 0.71-0.89) and the β-blocker group (HR, 0.82; 95% CI, 0.73-0.91) than in the control group. In addition, the risk of all-cause mortality was lower in the ARB group than in the ACEI group (HR, 0.85; 95% CI, 0.76-0.95).

CONCLUSIONS AND RELEVANCE

The use of β-blockers, ACEIs, or ARBs was associated with benefits in the long-term treatment of aortic dissection.

ATRQβ-001 Vaccine Prevents Experimental Abdominal Aortic Aneurysms

Background

We have developed a peptide vaccine named ATRQβ‐001, which was proved to retard signal transduction initiated by angiotensin II (Ang II). Ang II was implicated in abdominal aortic aneurysm (AAA) progression, but whether the ATRQβ‐001 vaccine would prevent AAA is unknown.

Methods and Results

Ang II‐infused ApoE^−/− mice and calcium phosphate‐induced AAA in C57BL/6 mice were used to verify the efficiency of ATRQβ‐001 vaccine in AAA. Results demonstrated that the vaccine effectively restrained the aneurysmal dilation and vascular wall destruction of aorta in both animal models, beyond anti‐hypertensive effects. In Ang II‐induced AAA vascular sections, Immunohistochemical staining showed that the vaccine notably constrained vascular inflammation and vascular smooth muscle cell (VSMC) phenotypic transition, concurrently reduced macrophages infiltration. In cultured VSMC, the anti‐ATR‐001 antibody inhibited osteopontin secretion induced by Ang II, thereby impeded macrophage migration while co‐culture. Furthermore, metalloproteinases and other matrix proteolytic enzymes were also found to be limited by the vaccine in vivo and in vitro.

Conclusions

ATRQβ‐001 vaccine prevented AAA initiation and progression in both Ang II and calcium phosphate‐induced AAA models. And the beneficial effects were played beyond decrease of blood pressure, which provided a novel and promising method to take precautions against AAA.

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.

Potential Medication Treatment According to Pathological Mechanisms in Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a vascular disease with high mortality. Because of the lack of effective medications to stop or reverse the progression of AAA, surgical operation has become the most predominant recommendation of treatment for patients. There are many potential mechanisms, including inflammation, smooth muscle cell apoptosis, extracellular matrix degradation, oxidative stress, and so on, involving in AAA pathogenesis. According to those mechanisms, some potential therapeutic drugs have been proposed and tested in animal models and even in clinical trials. This review focuses on recent advances in both pathogenic mechanisms and potential pharmacologic therapies of AAA.

Sex differences in abdominal aortic aneurysms

Abdominal aortic aneurysm (AAA) is a vascular disorder with a high case fatality rate in the instance of rupture. AAA is a multifactorial disease, and the etiology is still not fully understood. AAA is more likely to occur in men, but women have a greater risk of rupture and worse prognosis. Women are reportedly protected against AAA possibly by premenopausal levels of estrogen and are, on average, diagnosed at older ages than men. Here, we review the present body of research on AAA pathophysiology in humans, animal models, and cultured cells, with an emphasis on sex differences and sex steroid hormone signaling.

The Abdominal Aortic Aneurysm and Intraluminal Thrombus: Current Concepts of Development and Treatment

The pathogenesis of the abdominal aortic aneurysm (AAA) shows several hallmarks of atherosclerotic and atherothrombotic disease, but comprises an additional, predominant feature of proteolysis resulting in the degradation and destabilization of the aortic wall. This review aims to summarize the current knowledge on AAA development, involving the accumulation of neutrophils in the intraluminal thrombus and their central role in creating an oxidative and proteolytic environment. Particular focus is placed on the controversial role of heme oxygenase 1/carbon monoxide and nitric oxide synthase/peroxynitrite, which may exert both protective and damaging effects in the development of the aneurysm. Treatment indications as well as surgical and pharmacological options for AAA therapy are discussed in light of recent reports.

Mast cells in human health and disease

Mast cells are primarily known for their role in defense against pathogens, particularly bacteria; neutralization of venom toxins; and for triggering allergic responses and anaphylaxis. In addition to these direct effector functions, activated mast cells rapidly recruit other innate and adaptive immune cells and can participate in "tuning" the immune response. In this review we touch briefly on these important functions and then focus on some of the less-appreciated roles of mast cells in human disease including cancer, autoimmune inflammation, organ transplant, and fibrosis. Although it is difficult to formally assign causal roles to mast cells in human disease, we offer a general review of data that correlate the presence and activation of mast cells with exacerbated inflammation and disease progression. Conversely, in some restricted contexts, mast cells may offer protective roles. For example, the presence of mast cells in some malignant or cardiovascular diseases is associated with favorable prognosis. In these cases, specific localization of mast cells within the tissue and whether they express chymase or tryptase (or both) are diagnostically important considerations. Finally, we review experimental animal models that imply a causal role for mast cells in disease and discuss important caveats and controversies of these findings.

Mast cell chymase and tryptase as targets for cardiovascular and metabolic diseases

Mast cells are critical effectors in inflammatory diseases, including cardiovascular and metabolic diseases and their associated complications. These cells exert their physiological and pathological activities by releasing granules containing histamine, cytokines, chemokines, and proteases, including mast cell-specific chymases and tryptases. Several recent human and animal studies have shown direct or indirect participation of mast cell-specific proteases in atherosclerosis, abdominal aortic aneurysms, obesity, diabetes, and their complications. Animal studies have demonstrated the beneficial effects of highly selective and potent chymase and tryptase inhibitors in several experimental cardiovascular and metabolic diseases. In this review, we summarize recent discoveries from in vitro cell-based studies to experimental animal disease models, from protease knockout mice to treatments with recently developed selective and potent protease inhibitors, and from patients with preclinical disorders to those affected by complications. We hypothesize that inhibition of chymases and tryptases would benefit patients suffering from cardiovascular and metabolic diseases.

Chemokine (C-C motif) receptor 2 mediates mast cell migration to abdominal aortic aneurysm lesions in mice

AIMS

Mast cells participate importantly in abdominal aortic aneurysms (AAAs) by releasing inflammatory cytokines to promote vascular cell protease expression and arterial wall remodelling. Mast cells accumulate in AAA lesions during disease progression, but the exact chemokines by which mast cells migrate to the site of vascular inflammation remain unknown. This study tested the hypothesis that mast cells use chemokine (C-C motif) receptor 2 (CCR2) for their accumulation in experimental mouse AAA lesions.

METHODS AND RESULTS

We generated mast cell and apolipoprotein E double-deficient (Apoe(-/-)Kit(W-sh/W-sh)) mice and found that they were protected from angiotensin II (Ang II) chronic infusion-induced AAAs compared with Apoe(-/-) littermates. Using bone-marrow derived mast cells (BMMC) from Apoe(-/-) mice and CCR2 double-deficient (Apoe(-/-)Ccr2(-/-)) mice, we demonstrated that Apoe(-/-)Kit(W-sh/W-sh) mice receiving BMMC from Apoe(-/-)Ccr2(-/-) mice, but not those from Apoe(-/-) mice, remained protected from AAA formation. Adoptive transfer of BMMC from Apoe(-/-) mice into Apoe(-/-)Kit(W-sh/W-sh) mice also increased lesion content of macrophages, T cells, and MHC class II-positive cells; there was also increased apoptosis, angiogenesis, cell proliferation, elastin fragmentation, and medial smooth muscle cell loss. In contrast, adoptive transfer of BMMC from Apoe(-/-)Ccr2(-/-) mice into Apoe(-/-)Kit(W-sh/W-sh) mice did not affect these variables.

CONCLUSIONS

The increased AAA formation and associated lesion characteristics in Apoe(-/-)Kit(W-sh/W-sh) mice after receiving BMMC from Apoe(-/-) mice, but not from Apoe(-/-)Ccr2(-/-) mice, suggests that mast cells use CCR2 as the chemokine receptor for their recruitment in Ang II-induced mouse AAA lesions.

Emerging role of mast cells and macrophages in cardiovascular and metabolic diseases

Mast cells are essential in allergic immune responses. Recent discoveries have revealed their direct participation in cardiovascular diseases and metabolic disorders. Although more sophisticated mechanisms are still unknown, data from animal studies suggest that mast cells act similarly to macrophages and other inflammatory cells and contribute to human diseases through cell-cell interactions and the release of proinflammatory cytokines, chemokines, and proteases to induce inflammatory cell recruitment, cell apoptosis, angiogenesis, and matrix protein remodeling. Reduced cardiovascular complications and improved metabolic symptoms in animals receiving over-the-counter antiallergy medications that stabilize mast cells open another era of mast cell biology and bring new hope to human patients suffering from these conditions.

Angiotensin-converting enzyme insertion/deletion polymorphism is a risk factor for thoracic aortic aneurysm in patients with bicuspid or tricuspid aortic valves

OBJECTIVE

The angiotensin-converting enzyme (ACE) is highly expressed in the aneurysmal vascular wall, in both animal models and human disease. Genetic variations in ACE could be crucial in determining the risk of thoracic aortic aneurysm (TAA). The aim of the present study was to examine the role of ACE insertion/deletion polymorphism on the risk of TAA in patients with bicuspid aortic valves or tricuspid aortic valves.

METHODS

We enrolled 216 patients (158 men; age, 58.9±14.9 years) with TAA, associated with bicuspid aortic valves (n=105) and tricuspid aortic valves (n=111) compared with 312 patients (252 men; age, 54.6±11.0 years) with angiographically proven coronary artery disease and 300 healthy controls (91 men; age, 40.4±10.5 years).

RESULTS

The genotype distribution of ACE insertion/deletion was significantly different between the patients with TAA compared with both the control group (P=.0005) and the coronary artery disease group (P=.03). The genotypes were not different between the control group and the coronary artery disease group (P=.3). Compared with the controls, both the bicuspid aortic valve patients (P=.0008) and tricuspid aortic valve patients (P<.0001) had a greater frequency of allele D. The aortic diameters were significantly different among the three genotypes (48.3±6.6, 45.3±8.9, 39.9±8.7 for the DD, DI, and II genotypes, respectively; P=.0002). A synergistic effect between the ACE D allele and hypertension was found for both an increased aortic diameter (P=.003) and the risk of TAA (P<.001). On multivariate logistic regression analysis, D allele (odds ratio, 3.0; 95% confidence interval, 1.1-8.1; P=.03) was a significant predictor of TAA.

CONCLUSIONS

ACE insertion/deletion polymorphism represents a genetic biomarker for TAA. These findings could have a significant effect on both the early detection and effective pharmacologic treatment of aortic disease.

Effects of angiotensin receptor blocker and calcium channel blocker on experimental abdominal aortic aneurysms in a hamster model

Remodeling in the abdominal aortic wall results in abdominal aortic aneurysm (AAA) formation. Many patients with AAA are prescribed antihypertensive drugs. However, the effects of antihypertensive drugs other than their effects on blood pressure control are rarely reported. In this study, we investigated the effects of these drugs on changes in the levels of matrix metalloproteinases (MMPs) and on AAA formation. Experimental AAAs were created in a hamster model by wrapping the abdominal aorta with elastase gauze. Olmesartan medoxomil (angiotensin II receptor antagonist) or azelnidipine (calcium channel antagonist) was administered to the hamsters and then we evaluated the aortic diameter, performed histological analysis, and analyzed the production of MMP-2 and MMP-9 by gelatin zymography. The expansion rate of the aortic diameter was smaller in both treatment groups than in the control group. Elastica van Gieson (EVG) staining showed structural preservation of elastin lamellae in both treatment groups. The active MMP-9 level decreased in both the olmesartan group and the azelnidipine group. Reducing MMP-9 production is important for suppression of AAA formation. Both olmesartan medoxomil and azelnidipine decreased MMP-9 activity, which suppressed degradation of the MMPs and inhibited AAA formation. There are different cascades that determine the production of MMP-9.

Mast cells: pivotal players in cardiovascular diseases

The clinical outcome of cardiovascular diseases as myocardial infarction and stroke are generally caused by rupture of an atherosclerotic plaque. However, the actual cause of a plaque to rupture is not yet established. Interestingly, pathology studies have shown an increased presence of the mast cell, an important inflammatory effector cell in allergy and host defense, in (peri)vascular tissue during plaque progression, which may point towards a causal role for mast cells. Very recent data in mouse models show that mast cells and derived mediators indeed can profoundly impact plaque progression, plaque stability and acute cardiovascular syndromes such as vascular aneurysm or myocardial infarction. In this review, we discuss recent evidence on the role of mast cells in the progression of cardiovascular disorders and give insight in the therapeutic potential of modulation of mast cell function in these processes to improve the resilience of a plaque to rupture.

Cysteinyl cathepsins and mast cell proteases in the pathogenesis and therapeutics of cardiovascular diseases

The initiation and progression of cardiovascular diseases involve extensive arterial wall matrix protein degradation. Proteases are essential to these pathological events. Recent discoveries suggest that proteases do more than catabolize matrix proteins. During the pathogenesis of atherosclerosis, abdominal aortic aneuryms, and associated complications, cysteinyl cathepsins and mast cell tryptases and chymases participate importantly in vascular cell apoptosis, foam cell formation, matrix protein gene expression, and pro-enzyme, latent cytokine, chemokine, and growth factor activation. Experimental animal disease models have been invaluable in examining each of these protease functions. Deficiency and pharmacological inhibition of cathepsins or mast cell proteases have allowed their in vivo evaluation in the setting of pathological conditions. Recent discoveries of highly selective and potent inhibitors of cathepsins, chymase, and tryptase, and their applications in vascular diseases in animal models and non-vascular diseases in human trials, have led to the hypothesis that selective inhibition of cathepsins, chymases, and tryptase will benefit patients suffering from cardiovascular diseases. This review highlights recent discoveries from in vitro cell-based studies to experimental animal cardiovascular disease models, from protease knockout mice to treatments with recently developed selective and potent protease inhibitors, and from patients with cathepsin-associated non-vascular diseases to those affected by cardiovascular complications.

Pathophysiology of abdominal aortic aneurysm relevant to improvements in patients' management

PURPOSE OF REVIEW

Abdominal aortic aneurysm (AAA) is being diagnosed more frequently in older patients due to the increased use of abdominal imaging and the rising average age of western populations. Currently the management of this condition has two important deficiencies: inadequate methods to identify AAAs at risk of progression and rupture and the current lack of effective nonsurgical therapies. In this review recent developments in identifying new diagnostic, prognostic and therapeutic strategies for AAA are discussed.

RECENT FINDINGS

There are growing number of animal and human association studies which have identified markers and strategies of potential value in improving identification, monitoring and treatment of AAA.

SUMMARY

Selective large prospective imaging, biomarker and intervention studies are now required to clearly demonstrate the value of new management pathways for AAA.

Timp-3 deficiency impairs cognitive function in mice

Extracellular matrix (ECM) degradation is performed primarily by matrix metalloproteinases (MMPs). MMPs have recently been shown to regulate synaptic activity in the hippocampus and to affect memory and learning. The tissue inhibitor of metalloproteinase (Timp) is an endogenous factor that controls MMP activity by binding to the catalytic site of MMPs. At present, four Timp isotypes have been reported (Timp-1 through Timp-4) with 35-50% amino-acid sequence homology. Timp-3 is a unique member of Timp proteins in that it is bound to the ECM. In this study, we used the passive avoidance test, active avoidance test, and water maze test to examine the cognitive function in Timp-3 knockout (KO) mice. Habituation was evaluated using the open-field test. The water maze test showed that Timp-3 KO mice exhibit deterioration in cognitive function compared with wild-type (WT) mice. The open-field test showed decreased habituation of Timp-3 KO mice. Immunostaining of brain slices revealed the expression of Timp-3 in the hippocampus. In situ zymography of the hippocampus showed increased gelatinolytic activity in Timp-3 KO mice compared with WT mice. These results present the first evidence of Timp-3 involvement in cognitive function and hippocampal MMP activity in mice. Moreover, our findings suggest a novel therapeutic target to be explored for improvement of cognitive function in humans.

Critical role of mast cell chymase in mouse abdominal aortic aneurysm formation

BACKGROUND

Mast cell chymase may participate in the pathogenesis of human abdominal aortic aneurysm (AAA), yet a direct contribution of this serine protease to AAA formation remains unknown.

METHODS AND RESULTS

Human AAA lesions had high numbers of chymase-immunoreactive mast cells. Serum chymase level correlated with AAA growth rate (P=0.009) in a prospective clinical study. In experimental AAA produced by aortic elastase perfusion in wild-type (WT) mice or those deficient in the chymase ortholog mouse mast cell protease-4 (mMCP-4) or deficient in mMCP-5 (Mcpt4(-/-), Mcpt5(-/-)), Mcpt4(-/-) but not Mcpt5(-/-) had reduced AAA formation 14 days after elastase perfusion. Even 8 weeks after perfusion, aortic expansion in Mcpt4(-/-) mice fell by 50% compared with that of the WT mice (P=0.0003). AAA lesions in Mcpt4(-/-) mice had fewer inflammatory cells and less apoptosis, angiogenesis, and elastin fragmentation than those of WT mice. Although Kit(W-sh/W-sh) mice had protection from AAA formation, reconstitution with mast cells from WT mice, but not those from Mcpt4(-/-) mice, partially restored the AAA phenotype. Mechanistic studies suggested that mMCP-4 regulates expression and activation of cysteine protease cathepsins, elastin degradation, angiogenesis, and vascular cell apoptosis.

CONCLUSIONS

High chymase-positive mast cell content in human AAA lesions, greatly reduced AAA formation in Mcpt4(-/-) mice, and significant correlation of serum chymase levels with human AAA expansion rate suggests participation of mast cell chymase in the progression of human and mouse AAA.

Interferon-gamma and the interferon-inducible chemokine CXCL10 protect against aneurysm formation and rupture

BACKGROUND

Vascular disease can manifest as stenotic plaques or ectatic aneurysms, although the mechanisms culminating in these divergent disease manifestations remain poorly understood. T-helper type 1 cytokines, including interferon-gamma and CXCL10, have been strongly implicated in atherosclerotic plaque development.

METHODS AND RESULTS

Here, we specifically examined their role in the formation of abdominal aortic aneurysms in the angiotensin II-induced murine model. Unexpectedly, we found increased suprarenal aortic diameters, abdominal aortic aneurysm incidence, and aneurysmal death in apolipoprotein E- and interferon-gamma-deficient (Apoe(-/-)/Ifng(-/-)) mice compared with Apoe(-/-) controls, although atherosclerotic luminal plaque formation was attenuated. The interferon-gamma-inducible T-cell chemoattractant CXCL10 was highly induced by angiotensin II infusion in Apoe(-/-) mice, but this induction was markedly attenuated in Apoe(-/-)/Ifng(-/-) mice. Apoe(-/-)/Cxcl10(-/-) mice had decreased luminal plaque but also increased aortic size, worse morphological grades of aneurysms, and a higher incidence of death due to aortic rupture than Apoe(-/-) controls. Furthermore, abdominal aortic aneurysms in Apoe(-/-)/Cxcl10(-/-) mice were enriched for non-T-helper type 1-related signals, including transforming growth factor-beta1. Treatment of Apoe(-/-)/Cxcl10(-/-) mice with anti-transforming growth factor-beta neutralizing antibody diminished angiotensin II-induced aortic dilation.

CONCLUSIONS

The present study defines a novel pathway in which interferon-gamma and its effector, CXCL10, contribute to divergent pathways in abdominal aortic aneurysm versus plaque formation, inhibiting the former pathology but promoting the latter. Thus, efforts to develop antiinflammatory strategies for atherosclerosis must carefully consider potential effects on all manifestations of vascular disease.

Mast Cell Proteases

Mast cells (MCs) are traditionally thought of as a nuisance for its host, for example, by causing many of the symptoms associated with allergic reactions. In addition, recent research has put focus on MCs for displaying harmful effects during various autoimmune disorders. On the other hand, MCs can also be beneficial for its host, for example, by contributing to the defense against insults such as bacteria, parasites, and snake venom toxins. When the MC is challenged by an external stimulus, it may respond by degranulation. In this process, a number of powerful preformed inflammatory "mediators" are released, including cytokines, histamine, serglycin proteoglycans, and several MC-specific proteases: chymases, tryptases, and carboxypeptidase A. Although the exact effector mechanism(s) by which MCs carry out their either beneficial or harmful effects in vivo are in large parts unknown, it is reasonable to assume that these mediators may contribute in profound ways. Among the various MC mediators, the exact biological function of the MC proteases has for a long time been relatively obscure. However, recent progress involving successful genetic targeting of several MC protease genes has generated powerful tools, which will enable us to unravel the role of the MC proteases both in normal physiology as well as in pathological settings. This chapter summarizes the current knowledge of the biology of the MC proteases.

The Significance of Chymase in the Progression of Abdominal Aortic Aneurysms in Dogs

In this study, we investigated the effect of a specific chymase inhibitor, NK3201, in the progression of abdominal aortic aneurysm in a dog experimental model. Abdominal aortic aneurysms were induced in dogs by injecting elastase into the abdominal aorta. NK3201 (1 mg/kg per day, p.o.) or a placebo was started 3 days before elastase injection and continued for 8 weeks after the injection. On abdominal ultrasound, the aortic diameter was seen to gradually expand in the placebo-treated group, but not in the NK3201-treated group. Eight weeks after elastase injection, the ratio of the medial area to the total area in the placebo-treated group was significantly smaller than that in the normal group, but it was significantly larger than that in the NK3201-treated group. In addition to chymase activity, angiotensin II-forming and matrix metalloproteinase-9 activities were significantly higher in the placebo-treated group than in the normal group; in the NK3201-treated group, all of these activities were significantly decreased. On immunohistochemical analyses, there was a significantly greater number of chymase-positive cells in the placebo-treated group than in the normal group, but the number was significantly smaller in the NK3201-treated group than in the placebo-treated group. Thus, chymase inhibition may become a useful strategy for preventing abdominal aortic aneurysms.

Abdominal aortic aneurysm and cerebral aneurysm present different pathological evolutions and responses to pharmacological therapy

Over-degradation of extracellular components by matrix metalloproteinases (MMPs) has been implicated as an important characteristic during the pathological evolution of the abdominal aortic aneurysm (AAA) and cerebral aneurysm (CA), which contribute to progressive dilation of vascular wall. However, mRNA and protein expression of local rennin-angiotensin system (RAS) components are found down-regulated in CA walls, which is contrary to long-holding concept that local RAS will be activated in response to increased hemodynamic stress and contributes to thickening of arterial wall. Similarly, MMPs inhibition by doxycycline effectively ameliorate AAA expansion in basic and clinical researches, but can not reduce the incidence of CA formation in rat. These evidences may suggest that suppression of RAS favors the regression of AAA, but at an increased risk of CA rupture. As the strategies of RAS blockade have became the optimal antihypertensive drugs of choice in clinical arena, the discrepant responses to pharmacologic intervention of AAA and CA should be received considerable attentions, due to their high prevalence in hypertensive population. Here we proposed that AAA and CA, outward remodeling of elastic and muscular arteries respectively, presented with different pathological evolutions and distinct responses to drug intervention, i.e., RAS and MMPs inhibition. It can not be excluded that the potentially deleterious effects of RAS inhibition on CA may be masked by the beneficial action of controlled blood pressure, and the propagation of CA will be exacerbated once suboptimal dose have been prescribed, or under the condition of stress, even drug withdrawal. If the paradoxical outcomes of these two kinds of arterial remodeling were proven true in basic research, clinical use of RAS blockade should be prudent in hypertensive patients, and routine procedures to detect the existence of CA should be considered. Therefore, in depth investigation in their responses to pharmacological approaches will provide us with more insights into the pathogenesis of arterial aneurysm.

Angiotensin-converting enzyme inhibitors and aortic rupture: a population-based case-control study

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitors prevent the expansion and rupture of aortic aneurysms in animals. We investigated the association between ACE inhibitors and rupture in patients with abdominal aortic aneurysms.

METHODS

We did a population-based case-control study of linked administrative databases in Ontario, Canada. The sample included consecutive patients older than 65 (n=15,326) admitted to hospital with a primary diagnosis of ruptured or intact abdominal aortic aneurysm between April 1, 1992, and April 1, 2002.

FINDINGS

Patients who received ACE inhibitors before admission were significantly less likely to present with ruptured aneurysm (odds ratio [OR] 0.82, 95% CI 0.74-0.90) than those who did not receive ACE inhibitors. Adjustment for demographic characteristics, risk factors for rupture, comorbidities, contraindications to ACE inhibitors, measures of health-care use, and aneurysm screening yielded similar results (0.83, 0.73-0.95). Consistent findings were noted in subgroups at high risk of rupture, including patients older than 75 years and those with a history of hypertension. Conversely, such protective associations were not observed for beta blockers (1.02, 0.89-1.17), calcium channel blockers (1.01, 0.89-1.14), alpha blockers (1.15, 0.86-1.54), angiotensin receptor blockers (1.24, 0.71-2.18), or thiazide diuretics (0.91, 0.78-1.07).

INTERPRETATION

ACE inhibitors are associated with a reduced risk of ruptured abdominal aortic aneurysm, unlike other antihypertensive agents. Randomised trials of ACE inhibitors for prevention of aortic rupture might be warranted.

Pharmacological targets in the treatment of abdominal aortic aneurysms

The natural history of an abdominal aortic aneurysm (AAA) is of progressive aortic wall degeneration occurring over the course of many years, ultimately, culminating in loss of structural integrity and fatal aortic rupture. Although surgical exclusion of an aneurysm can effectively prevent aortic rupture in large aneurysms, small aneurysms are generally completely asymptomatic and are very unlikely to rupture. Further, AAA can be easily diagnosed with noninvasive testing; thus, small aneurysms present an excellent opportunity for disease-modifying pharmacological intervention. Research over the past two decades has defined many of the mechanisms which result in aortic matrix degeneration in both human tissue and particularly within animal models. This has resulted in the identification of several potential targets for pharmacological intervention. Drugs directed at inhibition of the inflammatory process and matrix degrading enzymes have been successful in multiple animal models, and early evidence now suggests that disease modification with some of these agents may be successful in slowing AAA growth in humans as well. The future of AAA therapy, however, may belong to agents which can induce aneurysm regression and to delivery methods which specifically target affected arterial tissue.

Pathological roles of angiotensin II produced by mast cell chymase and the effects of chymase inhibition in animal models

The discovery of a new angiotensin II (Ang II) pathway generated by mast cell chymase has highlighted new biological functions for Ang II that is not related to the classic renin-angiotensin system (RAS). The conversion of Ang I to II occurs not only via the plasma angiotensin converting enzyme (ACE) or tissue ACE but also via chymase produced in the mast cells of humans, monkeys, dogs, and hamsters. The conversion by chymase has been especially found in morbid tissues following the migration of mast cells. The newly discovered functions of chymase are discussed in this review. During the vascular narrowing that occurs after vein grafting or balloon injury in dogs, chymase activity and Ang II concentrations along with intimal proliferation are significantly increased and chymase inhibitors completely suppressed these increase, though ACE inhibitors are ineffective. Similar results have also been confirmed in the dog arteriovenous fistula stenosis model. In both human and animal aneurysmal aortas, chymase activity is significantly increased, and chymase inhibitor has been shown to prevent the development of aneurysms in dogs. Chymase is activated in diseased hearts, and chymase inhibitors reduce both the mortality rates after acute myocardial infarction and the cardiac fibrosis that leads to the development of cardiomyopathy in hamsters. Chymase is also a pro-angiogenic factor, since the injection of chymase strongly facilitates angiogenesis in hamsters. We propose that chymase inhibitors are effective in the prevention of multiple cardiovascular disorders, especially at the local event level without any effect on the systemic blood pressure.

Early increased MT1-MMP expression and late MMP-2 and MMP-9 activity during Angiotensin II induced aneurysm formation

BACKGROUND

Angiotensin II (Ang II) is associated with a variety of cardiovascular diseases including aneurysm formation. The aim of this study was to evaluate the temporal changes in MT1-matrix metalloproteinase (MMP) and MMP-2 and -9 expression and activity during the course of Ang II induced experimental aneurysm formation.

METHODS

Apolipoprotein E knockout mice (ApoE null) were infused with either 1000 ng/kg/min of Ang II (n = 20) or saline (n = 20) and then sacrificed at 7, 14, 21, and 28 days of infusion (n = 5/group/strain). Aortic diameters were measured by digital microscopy. Systolic blood pressure (SBP) was measured in the rodent tail. Suprarenal abdominal aortas had MT1-MMP mRNA levels and MMP-2 and MMP-9 mRNA levels and activity quantitated using reverse transcriptase-polymerase chain reaction (rt-PCR) and gelatin zymography, respectively. Statistical analyses included nonpaired t-test, Fisher's exact test, and analysis of variance (ANOVA).

RESULTS

Aneurysms occurred in 40, 40, 20, and 80% of ApoE null-Ang II mice at 7, 14, 21, and 28 days, respectively. An early and significant rise in MT1-MMP mRNA occurred in ApoE null mice infused with Ang II mice, while there was no significant change in MMP-2 or MMP-9 mRNA levels. Total MMP-2 and MMP-9 activity increased over time in ApoE null mice infused with Ang II, peaking at 28 days (ANOVA, P < 0.01). SBP was significantly elevated by 7 days in ApoE null mice infused with Ang II compared to ApoE null mice infused with saline (123 +/- 16 versus 102 +/- 6 mm Hg, P < 0.05).

CONCLUSIONS

Angiotensin II induces an early increase in aortic MT1-MMP expression with a subsequent increase in MMP-2 and MMP-9 activity. The process by which these changes cause aneurysm formation warrants further investigation.

Alterations in angiotensin converting enzyme during rodent aortic aneurysm formation

BACKGROUND

The renin-angiotensin system (RAS) has been implicated in vessel wall remodeling. This investigation tested the hypothesis that the RAS is altered during experimental rodent aneurysm formation.

MATERIALS AND METHODS

Rat aortas were perfused with saline (controls, N = 45) or elastase (6 U/ml, N = 45). At 4, 7, and 14 days after aortic perfusion, aortic diameters were measured (n = 15/time point/group) and aortic wall mRNA and protein were extracted. Real time polymerase chain reation (PCR) measured RNA levels of angiotensin, angiotensin converting enzyme (ACE), angiotensin II receptor 1 (AT(1)), and angiotensin II receptor 2 (AT(2)). Western blot analysis measured ACE protein levels. Immunohistochemical studies localized ACE within the aortic wall. Statistical analyses were performed with the unpaired t-test and ANOVA.

RESULTS

Elastase perfusion significantly increased aortic diameter (P < 0.01), with no significant changes in saline control aortic diameters. ACE mRNA did not become elevated in elastase-perfused aortas, yet ACE protein levels were elevated on days 4 and 7 of perfusion (P < 0.01) compared to controls, and ACE staining was noted in these aortas. This difference resolved by 14 days. In neither group were there significant alterations in AT(1), AT(2), or An mRNA levels, although ACE mRNA was elevated in controls after 7 days of perfusion compared to elastase perfused aortas (P < 0.005).

CONCLUSIONS

Experimental aortic aneurysm formation may be associated with increased aortic wall ACE protein levels. The mechanisms by which these proteins contribute to, or serve as markers of, aneurysm formation in vivo requires further intervention.

Enzymatic pathways involved in the generation of endothelin-1(1-31) from exogenous big endothelin-1 in the rabbit aorta

We investigated whether blood vessels contribute to the production of ET-1(1-31) from exogenous big endothelin-1 (BigET-1) in the rabbit and assessed which enzymes are involved in this process. Vascular reactivity experiments, using standard muscle bath procedures, showed that BigET-1 induces contraction in endothelium-intact rabbit aortic rings. Preincubation of the rings with phosphoramidon, CGS35066 or thiorphan reduced BigET-1-induced contraction. Conversely, chymostatin did not affect BigET-1-induced contraction. Thiorphan and phosphoramidon, but not CGS35066 or chymostatin, reduced ET-1(1-31)-induced contraction. None of the enzymatic inhibitors affected the contraction afforded by ET-1.BQ123-, but not BQ788-, selective antagonists for ET(A) and ET(B) receptors, respectively, produced concentration-dependent rightward displacements of the ET-1(1-31) and ET-1 concentration-response curves. By the use of enzymatic assays, we found that the aorta, as well as the heart, lung, kidney and liver, possess a chymase-like activity. Enzyme immunoassays detected significant levels of Ir-ET-1(1-31) in bathing medium of aortas after the addition of BigET-1 (30 nM). Neither thiorphan nor chymostatin altered the levels of Ir-ET-1(1-31). Conversely, the levels of Ir-ET-1(1-31) were increased in the presence of phosphoramidon. This marked increase of the 31-amino-acid peptide was abolished when phosphoramidon and chymostatin were added simultaneously. The major new finding of the present work is that the rabbit aorta generates ET-1(1-31) from exogenously administered BigET-1. Additionally, by measuring the production of ET-1(1-31), we showed that a chymase-like enzyme is involved in this process when ECE and NEP are inhibited by phosphoramidon. Our results also suggest that ET-1(1-31) is an alternate intermediate in the production of ET-1 following BigET-1 administration. Finally, we showed that NEP is the predominant enzymatic pathway involved in the cleavage of ET-1(1-31) to a bioactive metabolite that will act on ET(A) receptors to induce contraction in the rabbit aorta.

Increased Migration of Vascular Adventitial Fibroblasts from Spontaneously Hypertensive Rats

Experimental evidence has suggested that vascular adventitial fibroblasts (AFs) may migrate into the neointima of arteries after balloon injury in various animal models. However, the research on migration of AFs has been limited to the effects of acute vascular injury. The role of AFs in chronic vascular injury and hypertension is not yet known. In this study, the migration of spontaneously hypertensive rat (SHR)-AFs and Wistar-Kyoto rat (WKY)-AFs from the thoracic aorta was determined by a transwell technique. Our results showed that fetal calf serum, angiotensin II (Ang II), phorbol ester, basic fibroblast growth factor and platelet-derived growth factor-BB induced migration in a dose-dependent manner, and the migration of SHR-AFs was always greater than that of WKY-AFs. Ang II-induced migration of AFs was considered to have been mediated by Ang II type 1 receptor (AT1-R), because the AT1-R antagonist losartan (10(-7)-10(-5) mol/l) suppressed Ang II-induced migration. Ang II-induced migration was also blocked by the extracellular-regulated protein kinase 1/2 (ERK1/2) inhibitor PD98059 (10(-5) mol/l) and p38 kinase inhibitor SB202190 (10(-5) mol/l), indicating that ERK1/2 and p38 kinase were involved in Ang II-induced migration. Ang II (10(-7) mol/l)-induced ERK1/2 and p38 kinase phosphorylation, both of which peaked after 5 min, were suppressed by PD98059 and SB202190, respectively. The Ang-II induced phosphorylation of both proteins was suppressed by losartan, whereas no effect was observed with PD123319, a specific inhibitor of Ang II type 2 receptor (AT2-R). Thus, in the present study, various factors stimulated the migration of SHR-AFs and, to a leber extent, WKY-AFs from the thoracic aorta, and the ERK1/2 and p38 kinase pathways are involved in Ang II-stimulated migration of fibroblasts.

Tissue Inhibitor of Metalloproteinase-3 Plays Important Roles in the Kidney Following Unilateral Ureteral Obstruction

Tissue inhibitor of metalloproteinase-3 (Timp-3), an inhibitor of matrix-degrading enzymes, is an important molecule for maintenance of the extracellular matrix. In this study, we generated Timp-3-deficient mice and used them to examine the effect of Timp-3-deficiency on blood pressure and to investigate the role of Timp-3 in the kidney following unilateral ureteral obstruction. The blood pressure and heart rate of Timp-3-deficient mice were not significantly different from those of wild-type mice. On the other hand, the obstructed kidneys of Timp-3-deficient mice developed more severe hydronephrosis than those of wild-type animals. Matrix metalloproteinase activities assessed by in situ zymography and transforming growth factor-beta expression were elevated in Timp-3-deficient mice. The renal tissues were thinner and the ratio of renal medulla to cortex was significantly lower in the obstructed Timp-3-deficient kidneys. These findings indicate that Timp-3-deficiency does not substantially affect the blood pressure in mice, and that Timp-3 plays an important role in the maintenance of renal macrostructure after unilateral ureteral obstruction.

Role of Chymase-Dependent Angiotensin II Formation in Regulating Blood Pressure in Spontaneously Hypertensive Rats

Vascular smooth muscle cells in spontaneously hypertensive rats (SHR) express angiotensin II-forming chymase (rat vascular chymase [RVCH]), which may contribute to blood pressure regulation. In this study, we studied whether chymase-dependent angiotensin II formation contributes to the regulation of blood pressure in SHR. The systolic blood pressure in 16-week-old Wistar-Kyoto (WKY) rats was 113 +/- 9 mmHg, compared to 172 +/- 3 mmHg in SHR. Using synthetic substrates for measuring angiotensin-converting enzyme (ACE) and chymase activities, it was found that both ACE and chymase activities in extracts from SHR aortas were significantly higher than in those from WKY rat aortas. Using angiotensin I as a substrate, angiotensin II formation in SHR was found to be significantly higher than that in WKY rats, and its formation was completely suppressed by an ACE inhibitor, but not by a chymase inhibitor. RVCH mRNA expression could not be detected in aorta extracts from either WKY rats or SHR. In carotid arteries isolated from WKY rats and SHR, angiotensin I-induced vasoconstriction was completely suppressed by an ACE inhibitor, but not by a chymase inhibitor. Angiotensin I-induced pressor responses in both WKY rats and SHR were also completely inhibited by an ACE inhibitor, but they were not affected by a chymase inhibitor. In SHR, an ACE inhibitor and an angiotensin II receptor blocker showed equipotent hypotensive effects, but a chymase inhibitor did not have a hypotensive effect. These results indicated that chymase-dependent angiotensin II did not regulate blood pressure in SHR in the present study.

Chymase as a novel target for the prevention of vascular diseases

In vascular tissues, chymase catalyzes the production of angiotensin II, which plays a crucial role in vascular diseases. Recent clinical studies and animal models of vascular proliferation and atherosclerosis have provided evidence that angiotensin II formed by chymase is involved in these processes. These observations suggest that chymase might promote the development of vascular proliferation and atherosclerosis. Chymase also activates matrix metalloproteinase 9, which promotes aortic aneurysm and angiogenesis, and thus chymase inhibitors might also prevent the progression of abdominal aortic aneurysm and angiogenesis. We propose that chymase is a novel target for preventing vascular diseases.

Therapeutic applications of chymase inhibitors in cardiovascular diseases and fibrosis

Chymase activates not only angiotensin I to angiotensin II but also latent transforming growth factor-beta-binding protein to transforming growth factor-beta. In dog grafted veins, chymase activity and angiotensin II concentration along with vascular proliferation were significantly increased, while they were significantly suppressed by a chymase inhibitor. After balloon injury in dog arteries, chymase activity was significantly increased in the injured artery, and a chymase inhibitor and an angiotensin AT(1) receptor antagonist were effective in preventing the vascular proliferation, but an angiotensin-converting enzyme inhibitor was ineffective. In fibrotic models, the tissue fibrosis was reduced by chymase inhibitors. In adhesion models, the transforming growth factor-beta concentration and adhesion formation were suppressed by chymase inhibitors. Therefore, chymase inhibitors may be useful for preventing cardiovascular diseases and fibrosis via inhibition of angiotensin II formation and transforming growth factor-beta activation.

A Specific Chymase Inhibitor, 2-(5-Formylamino-6-oxo-2-phenyl-1,6-dihydropyrimidine-1-yl)-N-[{3,4-dioxo-1-phenyl-7-(2-pyridyloxy)}-2-heptyl]acetamide (NK3201), Suppresses Development of Abdominal Aortic Aneurysm in Hamsters

In this study, we investigated the effect of a specific chymase inhibitor, 2-(5-formylamino-6-oxo-2-phenyl-1,6-dihydropyrimidine-1-yl)-N-[[3,4-dioxo-1-phenyl-7-(2-pyridyloxy)]-2-heptyl]acetamide (NK3201), in the development of abdominal aortic aneurysm in a hamster experimental model. The abdominal aortic aneurysm was induced by application of elastase onto the abdominal aorta in hamster. Each hamster was administered NK3201 (30 mg/kg/day p.o.) or placebo beginning 4 days before application of elastase and continuing through the experiments. Sham-operated hamsters received saline application onto the abdominal aorta. Two weeks after application of elastase, the aortic diameter in the placebo-treated group was significantly increased to 1.6-fold compared with the value for the sham-operated group, whereas that in the NK3201-treated group was significantly reduced. The chymase activities in the sham-operated and the placebo-treated groups were 0.35 +/- 0.01 and 3.44 +/- 0.62 mU/mg protein, respectively, and this difference was significant. NK3201 significantly reduced the chymase activity in the placebo-treated group. Here, we demonstrated for the first time that a chymase inhibitor prevented the development of abdominal aortic aneurysm in a hamster experimental model.

Role of a decreased expression of the local renin-angiotensin system in the etiology of cerebral aneurysms

BACKGROUND

Local renin-angiotensin systems (RAS) have been implicated as playing an important role in vascular remodeling. The relationship of this system to the etiology of cerebral aneurysm was investigated.

METHODS AND RESULTS

The aneurysmal wall from patients with a ruptured or unruptured cerebral aneurysm and the cortical cerebral artery in control patients with head trauma or a glioma were taken during surgery for study. Local RAS were evaluated by reverse transcription-polymerase chain reaction (RT-PCR) and/or immunohistochemistry. RT-PCR analysis revealed a significantly decreased expression of angiotensin-converting enzyme (ACE), angiotensin type 1 (AT1) receptor, basic fibroblast growth factor, platelet-derived growth factor-AA, and tissue inhibitor of matrix metalloproteinases-1 mRNA in the aneurysmal wall as compared with the control cortical arterial wall. Immunohistochemistry also revealed a decreased expression of ACE, AT1 receptor, and angiotensin II in the aneurysmal wall.

CONCLUSIONS

Expression of local RAS was decreased in the aneurysmal wall, which may induce aneurysm formation caused by a lack of vascular remodeling that prevents the arterial wall from thickening under increased hemodynamic stress. This is the first report that suggests that a decreased expression of local RAS plays a part in the pathogenesis of any disease.