Chymase-dependent angiotensin II formation in human vascular tissue

Angiotensin-converting enzyme inhibitor therapy after heart transplant: from molecular basis to clinical effects

The use of angiotensin-converting enzyme inhibitors is an important therapy for various cardiovascular diseases, such as hypertension, ischemic heart disease and heart failure. In heart transplant recipients, angiotensin-converting enzyme inhibitors have been demonstrated to be a keystone for the treatment of hypertension with a wide spectrum of pleiotropic molecular effects ranging from improvement of the peripheral vascular system to regulation of the fluid and sodium balance. In addition, angiotensin-converting enzyme inhibitors may be also useful in the prevention of graft failure, cardiac allograft vasculopathy and chronic kidney disease progression. Further tailored multi-center and randomized studies are warranted to confirm the pleiotropic clinical effects of ACEi therapy in HTRs and to support more extended use in daily clinical practice. Finally in the near future, the use of novel pharmacological agents that inhibit the renin-angiotensin-aldosterone system such as the neprylisin inhibitor sacubitril should be investigated in heart transplant recipients. This article is protected by copyright. All rights reserved.

Mechanism of Albuminuria Reduction by Chymase Inhibition in Diabetic Mice

Chymase has several functions, such as angiotensin II formation, which can promote diabetic kidney disease (DKD). In this study, we evaluated the effect of the chymase inhibitor TY-51469 on DKD in diabetic db/db mice. Diabetic mice were administered TY-51469 (10 mg/kg/day) or placebo for 4 weeks. No significant difference was observed in body weight and fasting blood glucose between TY-51469- and placebo-treated groups. However, a significant reduction in urinary albumin/creatinine ratio was observed in the TY-51469-treated group compared with the placebo-treated group. In the renal extract, chymase activity was significantly higher in placebo-treated mice than in non-diabetic db/m mice, but it was reduced by treatment with TY-51469. Both NADPH oxidase 4 expression and the oxidative stress marker malondialdehyde were significantly augmented in the placebo-treated group, but they were attenuated in the TY-51469-treated group. Significant increases of tumor necrosis factor-α and transforming growth factor-β mRNA levels in the placebo-treated group were significantly reduced by treatment with TY-51469. Furthermore, the expression of nephrin, which is a podocyte-specific protein, was significantly reduced in the placebo-treated group, but it was restored in the TY-51469-treated group. These findings demonstrated that chymase inhibition reduced albuminuria via attenuation of podocyte injury by oxidative stress.

Chymase inhibition retards albuminuria in type 2 diabetes

Chymase released from mast cells produces pro‐fibrotic, inflammatory, and vasoconstrictor agents. Studies were performed to test the hypothesis that chronic chymase inhibition provides a renal protective effect in type 2 diabetes. Diabetic (db/db) and control mice (db/m) were chronically infused with a chymase‐specific inhibitor or vehicle for 8 weeks. Baseline urinary albumin excretion (UalbV) averaged 42 ± 3 and 442 ± 32 microg/d in control (n = 22) and diabetic mice (n = 27), respectively (p < .05). After administration of chymase inhibitor to diabetic mice, the change in UalbV was significantly lower (459 ± 57 microg/d) than in vehicle‐treated diabetic mice (645 ± 108 microg/d). U_NGALV was not different at baseline between diabetic mice that would receive the chymase inhibitor (349 ± 56 ng/d, n = 6) and vehicle (373 ± 99 ng/d, n = 6) infusions, but increased significantly only in the vehicle‐treated diabetic mice (p < .05). Glomeruli of diabetic kidneys treated chronically with chymase inhibition demonstrated reduced mesangial matrix expansion compared to glomeruli from untreated diabetic mice. Plasma angiotensin II levels were not altered by chymase inhibitor treatment. In summary, chronic chymase inhibition slowed the progression of urinary albumin excretion in diabetic mice. In conclusion, renal chymase may contribute to the progression of albuminuria in type 2 diabetes renal disease.

Elevated chymase-dependent angiotensin II-forming activity in circulating mononuclear leukocytes was observed in the patient of atrial fibrillation

Chymase is an angiotensin II-forming serine proteinase and elevation of its tissue activity occurs in various cardiovascular diseases. Several authors have suggested that there is an association between the renin-angiotensin system and atrial fibrillation (AF). Chymase-dependent angiotensin II-forming activity in circulating mononuclear leukocytes (CML chymase dAIIFA) was investigated in patients with AF and patients in sinus rhythm. Consecutive outpatients were recruited at our hospital. CML chymase dAIIFA was measured using a Nma/Dnp-type fluorescence-quenching substrate of modified angiotensin I in the presence or absence of a specific serine proteinase inhibitor. To search the independent contributing factor of existence of AF, the analysis between groups was carried out using multivariate analysis after univariate analysis. The patients were classified into a sinus rhythm (SR) group (n = 459) or an AF group (n = 48). CML chymase dAIIFA was significantly higher in the AF group (622 pmol/min/mg) compared with the SR group (488 pmol/min/mg) (p < 0.001). Logistic regression analysis revealed that high CML chymase dAIIFA was an independent determinant of the existence of AF (p < 0.001). Elevation of CML chymase dAIIFA was associated with AF. Activation of chymase might be linked to atrial structural and electrical remodeling.

High Fib4 index in patients with suspected NASH is associated with elevation of chymase-dependent angiotensin II-forming activity in circulating mononuclear leucocytes

Fatal hepatic disease is closely related to non-alcoholic fatty liver disease, especially non-alcoholic steatohepatitis (NASH). NASH is associated with cardiovascular events because it develops on the background of lifestyle-related diseases. Chymase-dependent angiotensin II-forming activity (dAIIFA) in circulating mononuclear leucocytes (CML) is a marker of local angiotensin II production and inflammation. This study investigated the association between CML chymase dAIIFA and NASH. Cardiovascular outpatients were recruited and the Fib4 index (F4I) was calculated. Patients with an F4I > 2.67 were classified into the high F4I group and these patients were strongly suspected to have NASH, while patients with an F4I < 1.30 were classified into the low F4I group. Patient background factors were compared between these groups. CML chymase dAIIFA was measured by ELISA using Nma/Dnp-modified angiotensin I. Among 499 patients, 16% were classified into the high F4I group. Compared with the low F4I group, the high F4I group had a significantly higher age, pancytopenia, more frequent diabetes mellitus, lower diastolic blood pressure, lower estimated glomerular filtration rate, higher brain natriuretic peptide, lower plasma aldosterone concentration, higher total AIIFA, higher CML chymase dAIIFA, and higher pulse wave velocity. Contrary to expectations, the body mass index, triglycerides, and low-density lipoprotein cholesterol were relatively low in the high F4I group. Many cardiovascular outpatients have a high F4I and can probably be categorized as NASH. The high F4I patients had few features of metabolic syndrome and were suspected to have elevated tissue chymase dAIIFA contributing to inflammation in the liver as well as in cardiovascular organs.

Involvement of premacular mast cells in the pathogenesis of macular diseases

We previously reported on the elevated intravitreal activities of tryptase and chymase in association with idiopathic epiretinal membrane (ERM) and idiopathic macular hole (MH). In this present study, we investigated the potential intraocular production of these serine proteases, and measured and compared tryptase and chymase activities in the vitreous body and serum in ERM, MH, proliferative diabetic retinopathy (PDR), and rhegmatogenous retinal detachment (RRD) patients. In addition, nuclear staining with hematoxylin and eosin (H&E) and mast-cell staining with toluidine blue were performed on samples of the vitreous core and bursa premacularis (BPM) of MH. We also performed immunostaining on the above two regions of vitreous samples for MH with anti-tryptase antibody, anti-chymase antibody, anti-podoplanin antibody, anti-lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1) antibody, and anti-fibroblast antibody. Moreover, we performed immunostaining with anti-tryptase antibody and anti-chymase antibody on ERMs collected intraoperatively. Tryptase activity in the vitreous body was significantly higher in ERM and MH than in PDR. However, no significant differences were observed in the tryptase activity in the serum among these four diseases. Chymase activity in the vitreous body was significantly higher in MH than in the other three diseases, yet chymase activity in the serum was below detection limit in any of the diseases. Nuclear staining with H&E revealed an abundance of nuclei in the BPM region, but few in the surrounding area. Mast-cell staining with toluidine blue revealed that the BPM showed metachromatic staining. In immunostaining with anti-fibroblasts antibody, anti-tryptase antibody, anti-chymase antibody, anti-podoplanin antibody, and anti-LYVE-1 antibody, the BPM stained more strongly than the vitreous core. Tryptase and chymase-positive cells were also observed in ERM. These findings revealed that the presence of mast cells in the BPM potentially represent the source of these serine proteases. Moreover, the BPM, as a lymphatic tissue, may play an important role in the pathogenesis of macular disease.

Increase of chymase-dependent angiotensin II-forming activity in circulating mononuclear leukocytes after acute myocardial infarction chymase activity after acute myocardial infarction

A previous clinical study revealed elevation of chymase- and cathepsin G-dependent angiotensin II-forming activity (AIIFA) in the myocardium after acute myocardial infarction (AMI). This study examined the time course of chymase- and cathepsin G-dependent AIIFA in circulating mononuclear leukocytes (CML) after AMI. Consecutive patients with AMI were recruited. Chymase- and cathepsin G-dependent AIIFA in CML were assayed using a modified angiotensin I substrate with Nma/Dnp fluorescence quenching. The changes of CML AIIFA were monitored over time in the patients. Fifteen consecutive AMI patients admitted to our hospital were recruited. At 1 day after the admission, CML chymase- and cathepsin G-dependent AIIFA were 2.9- and 1.7-fold higher than at discharge, respectively. The ratio of chymase-dependent AIIFA to total AIIFA was significantly increased. AIIFA gradually decreased over time after the admission. The peak value of chymase- and cathepsin G-dependent AIIFA was significantly correlated with the maximum levels of aspartate aminotransferase (r = 0.53, 0.64), lactate dehydrogenase (r = 0.57, 0.62), and creatine kinase (r = 0.60, 0.65). This is the first evidence that chymase- and cathepsin G-dependent AIIFA is elevated in CML after AMI. Our data suggested that chymase-dependent AIIFA is increased in CML as well as in the myocardium after AMI, and that the level of chymase-dependent AIIFA might reflect the severity of infarction.

Long-term effects of a renin inhibitor versus a thiazide diuretic on arterial stiffness and left ventricular diastolic function in elderly hypertensive patients

Arterial stiffness and cardiac function are important predictors of cardiovascular events in patients with hypertension, even with adequate blood pressure (BP) control. We evaluated whether a direct renin inhibitor, aliskiren, reduces arterial stiffness and modulates left ventricular function compared with a diuretic, hydrochlorothiazide, in elderly hypertensive patients. Twenty-one hypertensive patients [67 ± 14 (SD) yr] were randomly assigned to receive 6-mo aliskiren (n = 11) or hydrochlorothiazide (n = 10)-based therapy. We assessed β-stiffness of the local arteries, arterial elastance (E_a), and echocardiographic variables, including early (E) and late (A) mitral inflow velocity, deceleration time of E, early (E') and late (A') diastolic mitral annular velocity, and left ventricular end-systolic elastance (E_es) before and after treatment. BP decreased similarly (P < 0.001) after both therapies. β-Stiffness of the carotid artery decreased after aliskiren but increased after hydrochlorothiazide treatment (aliskiren: 6.42 ± 2.34 pre vs. 5.07 ± 1.29 post; hydrochlorothiazide: 5.05 ± 1.78 vs. 7.25 ± 2.68, P = 0.001 for interaction). β-Stiffness of the femoral and radial arteries were not different after either treatment. Different from aliskiren, E decreased (73 ± 16 vs. 67 ± 14 cm/s, P = 0.026), and the deceleration time was prolonged (218 ± 40 vs. 236 ± 35 ms, P = 0.032) after hydrochlorothiazide therapy, whereas the E/A, and E' remained unchanged after both treatments. E_a and E_es decreased after aliskiren therapy (both P < 0.05), whereas the E_a/E_es (ventricular-arterial coupling) was maintained after both treatments. Thus, aliskiren decreased the stiffness of carotid artery and left ventricular end-systolic elastance with maintenance of ventricular-arterial coupling without any effects on diastolic filling, while hydrochlorothiazide increased carotid arterial stiffness and slowed early diastolic filling in elderly hypertensive patients.

Increased expression of chymase in inflammatory polyps in elderly patients with functional bowel disorder

Chymase, a chymotrypsin-like protease, is a non-angiotensin-converting enzyme (ACE) angiotensin II (Ang II)-generating enzyme. The aim of the present study was to investigate whether chymase activity was increased in inflammatory polyps of elderly patients with functional bowel disorder (FBD). This study enrolled 45 elderly patients with FBD and 44 healthy control individuals. Expression of chymase in intestinal mucosa was assessed using fluorescence quantitative polymerase chain reaction and immunohistochemistry (IHC). IHC showed an increased number of chymase-positive mast cells in inflammatory polyps than in healthy intestinal mucosa (P<0.05). Compared with healthy mucosa, expression of chymase at the mRNA and protein level was significantly higher in inflammatory polyps. The frequencies of the chymase GG genotype and the G allele type were higher in the intestinal mucosa of patients with FBD compared with healthy controls (66.67 versus 40.91%, 81.11 versus 63.63%, both P<0.05). The frequency of the G allele type in the intestinal mucosa of the C4 subgroup of FBD was higher than that in the control group. However, in other FBD subgroups, there was no difference between patients and controls. Based on the fact that enhanced chymase expression was observed in inflammatory polyps of elderly patients with FBD relative to those in healthy controls, it was concluded that chymase has a significant role in the pathogenesis of inflammatory polyps in elderly patients with FBD.

Chronic renin inhibition lowers blood pressure and reduces upright muscle sympathetic nerve activity in hypertensive seniors

Cardiovascular risk remains high in patients with hypertension even with adequate blood pressure (BP) control. One possible mechanism may be sympathetic activation via the baroreflex. We tested the hypothesis that chronic inhibition of renin reduces BP without sympathetic activation, but diuresis augments sympathetic activity in elderly hypertensives. Fourteen patients with stage-I hypertension (66 ± 5 (SD) years) were treated with a direct renin inhibitor, aliskiren (n = 7), or a diuretic, hydrochlorothiazide (n = 7), for 6 months. Muscle sympathetic nerve activity (MSNA), BP, direct renin and aldosterone were measured during supine and a graded head-up tilt (HUT; 5 min 30° and 20 min 60°), before and after treatment. Sympathetic baroreflex sensitivity (BRS) was assessed. Both groups had similar BP reductions after treatment (all P < 0.01), while MSNA responses were different between hydrochlorothiazide and aliskiren (P = 0.006 pre/post × drug). Both supine and upright MSNA became greater after hydrochlorothiazide treatment (supine, 72 ± 18 post vs. 64 ± 15 bursts (100 beats)(-1) pre; 60° HUT, 83 ± 10 vs. 78 ± 13 bursts (100 beats)(-1); P = 0.002). After aliskiren treatment, supine MSNA remained unchanged (69 ± 13 vs. 64 ± 8 bursts (100 beats)(-1)), but upright MSNA was lower (74 ± 15 vs. 85 ± 10 bursts (100 beats)(-1); P = 0.012 for pre/post × posture). Direct renin was greater after both treatments (both P < 0.05), while upright aldosterone was greater after hydrochlorothiazide only (P = 0.002). The change in upright MSNA by the treatment was correlated with the change of aldosterone (r = 0.74, P = 0.002). Upright sympathetic BRS remained unchanged after either treatment. Thus, chronic renin inhibition may reduce upright MSNA through suppressed renin activity, while diuresis may evoke sympathetic activation via the upregulated renin-angiotensin-aldosterone system, without changing intrinsic sympathetic baroreflex function in elderly hypertensive patients.

Can proteomics yield insight into aging aorta?

The aging aorta exhibits structural and physiological changes that are reflected in the proteome of its component cells types. The advance in proteomic technologies has made it possible to analyze the quantity of proteins associated with the natural history of aortic aging. These alterations reflect the molecular and cellular mechanisms of aging and could provide an opportunity to predict vascular health. This paper focuses on whether discoveries stemming from the application of proteomic approaches of the intact aging aorta or vascular smooth muscle cells can provide useful insights. Although there have been limited studies to date, a number of interesting proteins have been identified that are closely associated with aging in the rat aorta. Such proteins, including milk fat globule-EGF factor 8, matrix metalloproteinase type-2, and vitronectin, could be used as indicators of vascular health, or even explored as therapeutic targets for aging-related vascular diseases.

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.

Direct evidence for intrarenal chymase-dependent angiotensin II formation on the diabetic renal microvasculature

Our previous work supports a major role for angiotensin-converting enzyme (ACE)-independent intrarenal angiotensin (ANG) II formation on microvascular function in type 2 diabetes mellitus. We tested the hypothesis that there is a switch from renal vascular ACE-dependent to chymase-dependent ANGII formation in diabetes mellitus. The in vitro juxtamedullary afferent arteriole (AA) contractile responses to the intrarenal conversion of the ACE-specific, chymase-resistant ANGI peptide ([Pro(10)]ANGI) to ANGII were significantly reduced in kidneys of diabetic (db/db) compared with control (db/m) mice. AA responses to the intrarenal conversion of the chymase-specific, ACE-resistant ANGI peptide ([Pro(11), D-Ala(12)]ANGI) to ANGII were significantly enhanced in kidneys of diabetic compared with control mice. AA diameters were significantly reduced by 9 ± 2, 15 ± 3, and 24 ± 3% of baseline in diabetic kidneys in response to 10, 100, and 1000 nmol/L [Pro(11), D-Ala(12)]ANGI, respectively, and the responses were significantly attenuated by angiotensin type 1 receptor or chymase-specific (JNJ-18054478) inhibition. [Pro(11), D-Ala(12)]ANGI did not produce a significant AA vasoconstriction in control kidneys. Chymase inhibition significantly attenuated ANGI-induced AA vasoconstriction in diabetic, but not control kidneys. Renal vascular mouse mast cell protease-4 or chymase/β-actin mRNA expression was significantly augmented by 5.1 ± 1.4 fold; while ACE/β-actin mRNA expression was significantly attenuated by 0.42 ± 0.08 fold in diabetic compared with control tissues. In summary, intrarenal formation of ANGII occurs primarily via ACE in the control, but via chymase in the diabetic vasculature. In conclusion, chymase-dependent mechanisms may contribute to the progression of diabetic kidney disease.

Review article: the pathophysiological roles of the renin-angiotensin system in the gastrointestinal tract

BACKGROUND

The renin-angiotensin system (RAS) is a homeostatic pathway widely known to regulate cardiovascular and renal physiology; however, little is known about its influence in gastrointestinal tissues.

AIM

To elicit the anatomical distribution and physiological significance of the components of the RAS in the gastrointestinal tract.

METHODS

An extensive online literature review including Pubmed and Medline.

RESULTS

There is evidence for RAS involvement in gastrointestinal physiology and pathophysiology, with all the components required for autonomous regulation identified throughout the gastrointestinal tract. The RAS is implicated in the regulation of glucose, amino acid, fluid and electrolyte absorption and secretion, motility, inflammation, blood flow and possibly malignant disease within the gastrointestinal tract. Animal studies investigating the effects of RAS blockade in a range of conditions including inflammatory bowel disease, functional gut disorders, gastrointestinal malignancy and even intestinal ischaemia have been encouraging to date. Given the ready availability of drugs that modify the RAS and their excellent safety profile, an opportunity exists for investigation of their possible therapeutic role in a variety of human gastrointestinal diseases.

CONCLUSIONS

The gastrointestinal renin-angiotensin system appears to be intricately involved in a number of physiological processes, and provides a possible target for novel investigative and therapeutic approaches.

Chymase-dependent generation of angiotensin II from angiotensin-(1-12) in human atrial tissue

Since angiotensin-(1-12) [Ang-(1-12)] is a non-renin dependent alternate precursor for the generation of cardiac Ang peptides in rat tissue, we investigated the metabolism of Ang-(1-12) by plasma membranes (PM) isolated from human atrial appendage tissue from nine patients undergoing cardiac surgery for primary control of atrial fibrillation (MAZE surgical procedure). PM was incubated with highly purified ¹²⁵I-Ang-(1-12) at 37°C for 1 h with or without renin-angiotensin system (RAS) inhibitors [lisinopril for angiotensin converting enzyme (ACE), SCH39370 for neprilysin (NEP), MLN-4760 for ACE2 and chymostatin for chymase; 50 µM each]. ¹²⁵I-Ang peptide fractions were identified by HPLC coupled to an inline γ-detector. In the absence of all RAS inhibitor, ¹²⁵I-Ang-(1-12) was converted into Ang I (2±2%), Ang II (69±21%), Ang-(1-7) (5±2%), and Ang-(1-4) (2±1%). In the absence of all RAS inhibitor, only 22±10% of ¹²⁵I-Ang-(1-12) was unmetabolized, whereas, in the presence of the all RAS inhibitors, 98±7% of ¹²⁵I-Ang-(1-12) remained intact. The relative contribution of selective inhibition of ACE and chymase enzyme showed that ¹²⁵I-Ang-(1-12) was primarily converted into Ang II (65±18%) by chymase while its hydrolysis into Ang II by ACE was significantly lower or undetectable. The activity of individual enzyme was calculated based on the amount of Ang II formation. These results showed very high chymase-mediated Ang II formation (28±3.1 fmol × min⁻¹ × mg⁻¹, n = 9) from ¹²⁵I-Ang-(1-12) and very low or undetectable Ang II formation by ACE (1.1±0.2 fmol×min⁻¹ × mg⁻¹). Paralleling these findings, these tissues showed significant content of chymase protein that by immunocytochemistry were primarily localized in atrial cardiac myocytes. In conclusion, we demonstrate for the first time in human cardiac tissue a dominant role of cardiac chymase in the formation of Ang II from Ang-(1-12).

Targets of chymase inhibitors

INTRODUCTION

Chymase converts angiotensin I to angiotensin II and it can also convert precursors of TGF-β and MMP-9 to their active forms. Therefore, diseases related to angiotensin II TGF-β, and MMP-9 could potentially be treated with chymase inhibitors.

AREAS COVERED

This review discusses the appropriate targets and safety of chymase inhibitors. Six diseases with notable mortality or morbidity as targets of chymase inhibitors are focused on; abdominal aortic aneurysms (AAAs), nephropathy and retinopathy, cardiomyopathy, nonalcoholic steatohepatitis (NASH), organ fibrosis and intestinal diseases.

EXPERT OPINION

If chymase inhibition proves to be a useful strategy for the attenuation of angiotensin II, TGF-β and MMP-9 in vivo, the application of chymase inhibitors is likely to become widespread in various diseases in the clinical setting. Chymase inhibitors are anticipated not to interfere with the homeostasis of resting tissues, that is, those not affected by injury or inflammation.

New approaches to blockade of the renin-angiotensin-aldosterone system: chymase as an important target to prevent organ damage

Chymase plays a crucial role in angiotensin II formation in various tissues. Angiotensin II induces gene expression of transforming growth factor (TGF)-beta and matrix metalloproteinase (MMP)-9 precursors, and chymase can convert precursors of TGF-beta and MMP-9 to their active forms. In cultured fibroblasts, significant increases in cell growth and TGF-beta levels were observed after chymase injection; these increases were inhibited by a chymase inhibitor, but not by an angiotensin II-receptor blocker. In apolipoprotein E-deficient mice, abdominal aortic aneurysm (AAA) development depends on an increase in MMP-9 activities induced by angiotensin II infusion, but the inhibition of MMP-9 activation by a chymase inhibitor resulted in attenuation of the angiotensin II-induced AAA development. The upregulation of MMP-9 and TGF-beta levels is involved in damage to various organs, but these gene expressions are not completely induced by angiotensin II alone. Therefore, chymase inhibition may be useful for attenuating MMP-9 and TGF-beta levels, in addition to reducing angiotensin II formation, and this function may provide powerful organ protection. In this review, we propose the possible use of chymase inhibitors as agents to prevent organ damage.

The effect of angiotensin II on the proliferation of human gingival fibroblasts

Angiotensin not only raises blood pressure and modifies body fluids and electrolytes but also induces differentiation and proliferation of fibroblasts in the circulatory system in order to repair damage. The purpose of the present study was to observe the influence of the addition of angiotensin II (AngII) or nifedipine (NIF) alone or both sequentially on proliferative activity, the intracellular Ca(2+) concentration ([Ca(2+)]i), and the inositol-1,4,5-triphosphate (IP3) level in cultivated human gingival fibroblasts. Addition of 10(-8)-10(-4) M NIF or 10(-5)-10(-4) M AngII alone increased the proliferation of cultivated gingival fibroblasts, and the interaction of NIF and AngII suppressed proliferation. Addition of AngII alone increased [Ca(2+)]i, with a peak 60 s afterward and a return to a level slightly higher than the pretreatment level at 120 s. Addition of both AngII and NIF did not increase [Ca(2+)]i as much as the addition of AngII alone. When Ca(2+) was absent from the extracellular environment, the AngII-induced increase in [Ca(2+)]i was suppressed. AngII increased the concentration of IP(3), with a peak at 120 s after its addition. From these results we concluded that AngII increased the proliferation of gingival fibroblasts by causing an influx of Ca(2+), which increased [Ca(2+)]i.

Significance of chymase-dependent angiotensin II formation in the progression of human liver fibrosis

AIM

Angiotensin II may contribute to liver fibrogenesis. In addition to angiotensin-converting enzyme (ACE), chymase, which is expressed by mast cells, is also known to be an angiotensin II-forming enzyme. However, it is unclear which of these two angiotensin II-forming enzymes plays a more important role in liver cirrhosis progression. In the present study, the role of angiotensin II-forming enzymes in the progression of liver cirrhosis was clarified.

METHODS

A total of 77 patients (16 in F0 stage, 10 in F1 stage, 22 in F2 stage, 12 in F3 stage, and 17 in F4 stage) were classified according to the new Inuyama classification into a non-cirrhosis (F0) group, an early cirrhosis (F1 + F2) group, and a chronic cirrhosis (F3 + F4) group.

RESULTS

Both chymase and total angiotensin II-forming activities were significantly higher in chronic cirrhosis patients than in the other two groups. However, there was nodifference among the three groups in ACE activity. On immunohistology, the number of chymase- and angiotensin II-positive cells was significantly higher in the chronic cirrhosis group than in the non-cirrhosis and early cirrhosis groups. There were significant correlations between the number of chymase-positive cells and the number of angiotensin II-positive cells, between the number of chymase-positive cells and the degree of fibrosis, and between the number of angiotensin II-positive cells and the degree of fibrosis.

CONCLUSION

These results suggest that chymase-dependent angiotensin II formation may play an important role in hepatic fibrosis of patients with cirrhosis.

Possible roles of mast cell-derived chymase for skin rejuvenation

The relationships between mast cell-derived chymase, angiotensin II, and extracellular matrix production in the skin after intense pulsed light (IPL) were clarified in hamsters. Dorsal areas of the hamsters were irradiated once or twice a week by IPL. The index of extracellular matrix production in the skin was defined as the depth stained with Azan-Mallory stain from the epidermis to the dermis at the point of maximum thickness. The index had significantly increased 7 days after IPL irradiation in sections treated once or twice with IPL compared with that of untreated control sections. The numbers of mast cells, chymase-positive cells, and angiotensin II-positive cells had also significantly increased in IPL-irradiated areas. Significant increases in chymase and angiotensin II activities were observed in the extracts obtained from IPL-irradiated skin. Mast cell-derived chymase may be involved via angiotensin II formation in the dermal extracellular matrix production that occurs after IPL irradiation.

Inhibiting the renin-angiotensin system with ACE Inhibitors or ARBs after MI

As part of the recommended modern post-myocardial infarction (MI) management, including reperfusion strategies, antiplatelet therapy, and beta-blockers, we may wonder whether the impact of early inhibition of the renin-angiotensin system (RAS) is as important as it was 20 years ago. This review demonstrates that significant clinical benefit can be derived from angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) even when added to other currently recommended treatment strategies in post-MI patients. Moreover, the effects of RAS inhibition extend far beyond the early post-MI neurohormonal activation and left ventricular remodeling phases. The favorable effects of RAS inhibition on important prognostic markers such as atrial fibrillation, renal function, and diabetes have recently been unraveled. Post-MI RAS inhibition also benefits all age groups, including elderly patients.

Therapy of Marfan Syndrome

Marfan syndrome is a common inherited disorder of connective tissue caused by deficiency of the matrix protein fibrillin-1. Effective surgical therapy for the most life-threatening manifestation, aortic root aneurysm, has led to a nearly normal lifespan for affected individuals who are appropriately recognized and treated. Traditional medical therapies, such as beta-adrenergic receptor blockade, are used to slow pathologic aortic growth and decrease the risk of aortic dissection by decreasing hemodynamic stress. New insights regarding the pathogenesis of Marfan syndrome have developed from investigation of murine models of this disorder. Fibrillin-1 deficiency is associated with excess signaling by transforming growth factor beta (TGFbeta). TGFbeta antagonists have shown great success in improving or preventing several manifestations of Marfan syndrome in these mice, including aortic aneurysm. These results highlight the potential for development of targeted therapies based on discovery of disease genes and interrogation of pathogenesis in murine models.

The intrarenal renin-angiotensin system: from physiology to the pathobiology of hypertension and kidney disease

In recent years, the focus of interest on the role of the renin-angiotensin system (RAS) in the pathophysiology of hypertension and organ injury has changed to a major emphasis on the role of the local RAS in specific tissues. In the kidney, all of the RAS components are present and intrarenal angiotensin II (Ang II) is formed by independent multiple mechanisms. Proximal tubular angiotensinogen, collecting duct renin, and tubular angiotensin II type 1 (AT1) receptors are positively augmented by intrarenal Ang II. In addition to the classic RAS pathways, prorenin receptors and chymase are also involved in local Ang II formation in the kidney. Moreover, circulating Ang II is actively internalized into proximal tubular cells by AT1 receptor-dependent mechanisms. Consequently, Ang II is compartmentalized in the renal interstitial fluid and the proximal tubular compartments with much higher concentrations than those existing in the circulation. Recent evidence has also revealed that inappropriate activation of the intrarenal RAS is an important contributor to the pathogenesis of hypertension and renal injury. Thus, it is necessary to understand the mechanisms responsible for independent regulation of the intrarenal RAS. In this review, we will briefly summarize our current understanding of independent regulation of the intrarenal RAS and discuss how inappropriate activation of this system contributes to the development and maintenance of hypertension and renal injury. We will also discuss the impact of antihypertensive agents in preventing the progressive increases in the intrarenal RAS during the development of hypertension and renal injury.

Treatment of hypertension with olmesartan medoxomil, alone and in combination with a diuretic: an update

Olmesartan medoxomil is an angiotensin II (Ang II) receptor blocker (ARB) that has been approved by the US Food and Drug Administration (FDA) for the treatment of hypertension. It is a prodrug that is hydrolysed in the gut into its active metabolite, olmesartan (RNH-6270). Olmesartan is highly selective for the Ang II type 1 receptor (AT1) to which it binds completely and insurmountably and has very little affinity for the other receptor subtypes AT2 and AT4. After oral administration, in animals and humans, it achieves a maximal blood drug concentration within a maximal time of approximately 2 h. It is then slowly eliminated in the urine and faeces. His half-life is approximately 13 h, which makes it suitable for once-daily administration. Olmesartan medoxomil given orally in single daily doses of 20-40 mg has demonstrated significant blood pressure (BP) lowering effects in hypertensive patients. A medline search for the preparation of this manuscript was conducted and revealed 128 references, from 2000 to 2007. Of these, only 16 well-designed prospective clinical trials were selected. The remaining were either animal studies, reviews or studies in progress. In well-designed clinical trials, olmesartan medoxomil has demonstrated similar antihypertensive actions to the other antihypertensive drugs, as well as other members of its class given the highest recommended doses. In addition, the BP lowering effect of olmesartan, like the other members of its class, is greatly enhanced in combination with a diuretic. Its safety profile is similar to the other ARBs and no different than placebo.

Endothelin

In humans, the endothelins (ETs) comprise a family of three 21-amino-acid peptides, ET-1, ET-2 and ET-3. ET-1 is synthesised from a biologically inactive precursor, Big ET-1, by an unusual hydrolysis of the Trp21 -Val22 bond by the endothelin converting enzyme (ECE-1). In humans, there are four isoforms (ECE-1a-d) derived from a single gene by the action of alternative promoters. Structurally, they differ only in the amino acid sequence of the extreme N-terminus. A second enzyme, ECE-2, also exists as four isoforms and differs from ECE-1 in requiring an acidic pH for optimal activity. Human chymase can also cleave Big ET-1 to ET-1, which is cleaved, in turn, to the mature peptide as an alternative pathway. ET-1 is the principal isoform in the human cardiovascular system and remains one of the most potent constrictors of human vessels discovered. ET-1 is unusual in being released from a dual secretory pathway. The peptide is continuously released from vascular endothelial cells by the constitutive pathway, producing intense constriction of the underlying smooth muscle and contributing to the maintenance of endogenous vascular tone. ET-1 is also released from endothelial cell-specific storage granules (Weibel-Palade bodies) in response to external stimuli. ETs mediate their action by activating two G protein-coupled receptor sub-types, ETA and ET(B). Two therapeutic strategies have emerged to oppose the actions of ET-1, namely inhibition of the synthetic enzyme by combined ECE/neutral endopeptidase inhibitors such as SLV306, and receptor antagonists such as bosentan. The ET system is up-regulated in atherosclerosis, and ET antagonists may be of benefit in reducing blood pressure in essential hypertension. Bosentan, the first ET antagonist approved for clinical use, represents a significant new therapeutic strategy in the treatment of pulmonary arterial hypertension (PAH).

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.

Chymase inhibition prevents cardiac fibrosis and dysfunction after myocardial infarction in rats

Human chymase activates not only angiotensin II but also transforming growth factor-beta, a major stimulator of myocardial fibrosis, while rat chymase activates transforming growth factor-beta, but not angiotensin II. To clarify the role of chymase-dependent transforming growth factor-beta activation, we evaluated whether chymase inhibition prevents cardiac fibrosis and cardiac dysfunction after myocardial infarction in rats. Myocardial infarction was induced by ligation of the left anterior descending coronary artery. One day after the ligation, rats were randomized into 2 groups: 1) a chymase-treated group that received 10 mg/kg per day of the chymase inhibitor NK3201 orally for 4 weeks; and 2) a vehicle group of non-treated rats with myocardial infarction. We also included a control group who underwent sham-operation and no treatment. Four weeks after ligation, echocardiography revealed that chymase inhibitor treatment reduced the akinetic area and increased fractional area change but did not significantly change left ventricular end-diastolic area. Chymase inhibition significantly reduced left ventricular end-diastolic pressure, increased the maximal end-systolic pressure-volume relationship and decreased the time constant of left ventricular relaxation. Chymase activity in the non-infarcted myocardium was significantly increased in the vehicle group, but it was significantly reduced by chymase inhibitor treatment. The fibrotic area in the cardiac tissues and the mRNA levels of collagen I and collagen III were also significantly lower in the chymase inhibitor-treated group than in the vehicle group. Therefore, the pathway forming chymase-dependent transforming growth factor-beta may play an important role in myocardial fibrosis and cardiac dysfunction rather than left ventricular dilatation after myocardial infarction.

The pleiotropic effects of angiotensin receptor blockers

The angiotensin receptor blockers (ARBs) are very effective and safe antihypertensive drugs. They exert their antihypertensive effect through blockage of the angiotensin II, type 1 receptor and quite possibly through stimulation by angiotensin II of the unoccupied type 2 receptor. Besides hypertension, the ARBs have been found recently to be of value in the treatment of heart failure and diabetic nephropathy. In addition, ARBs have emerged lately as being very effective and perhaps superior to other antihypertensive drugs in the prevention of de novo or recurrent strokes. Other actions that may account for their stroke-protective effects include their antiatherogenic, antidiabetic, antiplatelet aggregating, hypouricemic, and atrial antifibrillatory actions. All these actions make the ARBs a true pleiotropic class of drugs. Each of the foregoing effects will be discussed briefly in this concise review.

Advanced glycation end products activate a chymase-dependent angiotensin II-generating pathway in diabetic complications

BACKGROUND

Angiotensin II is a key mediator of diabetes-related vascular disease. It is now recognized that in addition to angiotensin-converting enzyme, chymase is an important alternative angiotensin II-generating enzyme in hypertension and diabetes. However, the mechanism of induction of chymase in diabetes remains unknown.

METHODS AND RESULTS

Here, we report that chymase is upregulated in coronary and renal arteries in patients with diabetes by immunohistochemistry. Upregulation of vascular chymase is associated with deposition of advanced glycation end products (AGEs), an increase in expression of the receptor for AGEs (RAGE), and activation of ERK1/2 MAP kinase. In vitro, AGEs can induce chymase expression and chymase-dependent angiotensin II generation in human vascular smooth muscle cells via the RAGE-ERK1/2 MAP kinase-dependent mechanism. This is confirmed by blockade of AGE-induced vascular chymase expression with a neutralizing RAGE antibody and an inhibitor to ERK1/2 and by overexpression of the dominant negative ERK1/2. Compared with angiotensin-converting enzyme, chymase contributes to the majority of angiotensin II production (>70%, P<0.01) in response to AGEs. Furthermore, AGE-induced angiotensin II production is blocked by the anti-RAGE antibody and by inhibition of ERK1/2 MAP kinase activities.

CONCLUSIONS

AGEs, a hallmark of diabetes, induce chymase via the RAGE-ERK1/2 MAP kinase pathway. Chymase initiates an important alternative angiotensin II-generating pathway in diabetes and may play a critical role in diabetic vascular disease.

The effects of ACE inhibition on serum angiotensin II concentration following cardiac transplantation

AIMS

ANGII mediates vascular neointimal formation through smooth muscle cell stimulation and enhanced production of growth factors leading to increased arterial medial layer thickness, which is a characteristic of transplant arteriosclerosis. ACE inhibition is known to be of benefit to patients with cardiovascular risk factors. We aimed to determine the effect of ACE inhibitor therapy on ACE enzymatic activity and serum ANGII levels following cardiac transplantation.

METHODS

A total of 43 serum samples from eight transplant recipients were used for analysis. Samples were taken monthly from the date of transplant for the initial 6 months. ANGII was measured using sandwich ELISA. ACE enzymatic activity was measured using spectrophotometric kinetic analysis.

RESULTS

There was a significant reduction in ACE enzymatic activity among individuals treated with ACE inhibitor therapy (18.0 +/- 16.6 vs 31.8 +/- 23.4, P = .008). We found significantly higher ANGII serum levels in patients receiving ACE inhibitor therapy compared to those not (2.4 +/- 2.1 vs 8.0 +/- 7.4, P = .002). There was also a significant positive correlation between ACE enzymatic activity and ANGII serum level (coefficient 0.332, P = .03).

CONCLUSIONS

Our results suggest an effective ACE independent pathway for ANGII conversion. Chymase can convert ANGI with higher affinity than ACE. Also, chymase is stored in mast cells, which infiltrate the myocardium following transplantation. This data indicate that pharmacological chymase inhibition may be a possible therapeutic strategy following transplantation.

Tissue-specific renin-angiotensin system in pulmonary lymphangioleiomyomatosis

Lymphangioleiomyomatosis (LAM), a multisystem disease found in middle-aged women, is characterized by cystic lung destruction and abdominal tumors (e.g., angiomyolipomas, lymphangioleimyomas), resulting from proliferation of abnormal-appearing, smooth muscle-like cells (LAM cells). The LAM cells, in combination with other cells, form nodular structures within the lung interstitium and in the walls of the cysts. LAM cells contain mutations in the tuberous sclerosis complex TSC1 and/or TSC2 genes, which lead to dysregulation of the mammalian target of rapamycin, affecting cell growth and proliferation. Proliferation and migration of vascular smooth muscle cells and production of angiogenic factors are regulated, in part, by angiotensin II. To determine whether a LAM-specific renin-angiotensin system might play a role in the pathogenesis of LAM, we investigated the expression of genes and gene products of this system in LAM nodules. mRNA for angiotensinogen was present in RNA isolated by laser-captured microdissection from LAM nodules. Angiotensin I-converting enzyme and chymase-producing mast cells were present within the LAM nodules. We detected renin in LAM cells, as determined by the presence of mRNA and immunohistochemistry. Angiotensin II type 1 and type II receptors were identified in LAM cells by immunohistochemistry and immunoblotting of microdissected LAM nodules. Angiotensin II is localized in cells containing alpha-smooth muscle actin (LAM cells). A LAM-specific renin-angiotensin system appears to function within the LAM nodule as an autocrine system that could promote LAM cell proliferation and migration, and could represent a pharmacologic target.

Inhibition of intimal/medial hyperplasia by perindopril in canine vein grafts

We used a canine model to assess the efficacy of an angiotensin-converting enzyme inhibitor (perindopril) at modulating intimal/medial hyperplasia in vein bypass grafts. Fourteen beagle dogs were divided into medicated and control groups and underwent bilateral grafting of external jugular veins into the common carotid artery. Samples of normal veins were obtained from the control group during vein grafting. Vein grafts were harvested 1 week and 4 weeks after surgery in both groups. Subsequently, intimal/medial thickness was measured by staining with hematoxylin and eosin; antibodies for proliferating cell nuclear antigen were employed to determine the degree of cellular proliferation; apoptotic cells were detected using the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling method. In the medicated group, the intimal/medial cross-sectional area was significantly smaller and increased 8- to 9-fold in comparison to the control group, which increased 12- to 20-fold. There was a significantly higher rate of cell proliferation in the control group, whereas the medicated group showed a significantly higher rate of apoptotic cells. These data support the efficacy of perindopril at reducing intimal/medial hyperplasia in arterialized vein grafts during a short postoperative period.

Angiotensin receptor blockers suppress antigen-specific T cell responses and ameliorate collagen-induced arthritis in mice

OBJECTIVE

The renin-angiotensin system plays an important role in the regulation of cardiovascular, renal, and endocrine functions. Recent studies have demonstrated that angiotensin II has proinflammatory effects that may contribute to the pathogenesis of immune-mediated diseases. We used the collagen-induced arthritis (CIA) model to investigate the influence of angiotensin II receptor blockers (ARBs) on antigen-specific immune responses and determine whether ARBs have preventive or therapeutic effects on the development of arthritis.

METHODS

We administered ARBs (olmesartan, candesartan, and telmisartan) to mice and evaluated antigen-specific T cell proliferation and cytokine production following immunization with ovalbumin (OVA) or type II collagen in Freund's complete adjuvant (CFA) or aluminum hydroxide (alum). Next, we induced CIA in DBA/1 mice and administered olmesartan. The severity and incidence of arthritis were scored according to clinical manifestations, and joint tissue sections were examined histopathologically.

RESULTS

ARBs severely suppressed lymphocyte proliferation and interferon-gamma production in mice immunized with OVA or type II collagen in CFA. Olmesartan also suppressed lymphocyte proliferation in mice immunized with ovalbumin in alum. In the CIA model, olmesartan reduced the mean arthritis score and the incidence of severe arthritis, even when it was administered only after disease onset. Histopathologic findings for joint destruction were improved in olmesartan-treated mice.

CONCLUSION

ARBs suppressed antigen-specific immune responses for Th1 and Th2 in vivo. Furthermore, olmesartan suppressed the development of severe arthritis and joint destruction in the CIA model. These findings suggest that ARBs may have therapeutic potential in rheumatoid arthritis.

Effect of Chymase Inhibition on the Arteriovenous Fistula Stenosis in Dogs

It was hypothesized that chymase may participate in hemodialysis vascular access dysfunction, as chymase has been known to be an effective enzyme in the conversion of angiotensin I (Ang I) to Ang II and in the latent TGF-beta1 to the active form. An arteriovenous (AV) fistula was created between the brachial artery and vein in dogs. In the AV anastomosis, when the walls of the venous and arterial sides were compared, the eccentric neointimal formation was most evident in the venous wall. Compared with the venous side downstream of the AV anastomosis, a severe neointimal hyperplasia was found in the venous side upstream of the AV anastomosis (intima/media, 153 +/- 25%). The chymase- and TGF-beta-positive mast cells were markedly accumulated in the proliferous neointima and media. In association with the reduction of chymase expression, a marked decrease in Ang II-, AT(1) receptor-, and TGF-beta-positive areas was achieved by NK3201 (a chymase inhibitor) treatment, and the neointima formation (intima/media: region A, 53 +/- 9%, P < 0.001; region B, 54 +/- 14%, P < 0.001) was also significantly suppressed in this group. Although lisinopril treatment also provided some beneficial effects with regard to the prevention of neointimal formation, the degree was less than that seen with chymase inhibition. These findings indicate that mast cell-derived chymase plays an essential role in the pathogenesis of the AV fistula access failure and that chymase inhibition may be a therapeutic target for the treatment of hemodialysis vascular access dysfunction in clinic settings.

Antihypertensive efficacy of olmesartan medoxomil alone and in combination with hydrochlorothiazide

Angiotensin receptor blockers (ARBs) are highly effective antihypertensive agents with excellent safety profiles. ARBs have been shown to improve cardiovascular morbidity and mortality in hypertensive patients with heart failure or diabetic nephropathy. For this later class of patients, the American Diabetes Association recommends ARBs as the primary treatment option. The ARBs function by blocking the binding of angiotensin-II (A-II) to its receptor, thereby inhibiting the action of A-II. Unlike the angiotensin-converting enzyme (ACE) inhibitors, which block the production of A-II through the ACE pathway, the ARBs effectively inhibit A-II regardless of whether it is produced through ACE or some alternate enzyme pathway. This difference in action offers a distinct advantage of ARBs over ACE inhibitors. Olmesartan medoxomil, the latest addition to the ARB class, is a long-acting, safe and well-tolerated antihypertensive drug. The combination of olmesartan medoxomil with a low-dose diuretic, potentiates the blood pressure lowering effect of either agent alone and is highly effective in achieving the recommended blood pressure goals in the majority of patients treated.

Current status of angiotensin receptor blockers for the treatment of cardiovascular diseases: focus on telmisartan

Poorly controlled hypertension is a major risk for cardiovascular morbidity and mortality, strokes, heart failure and renal failure. Despite these devastating complications, blood pressure control of </=140/90 mmHg, which is above the current standard, is very poor worldwide, accounting for 34% of hypertensive patients in the United States, and 6% in other countries. The reasons for this poor control of blood pressure include lack of aggressive treatment by physicians, especially for the systolic blood pressure, drug selection and patient compliance. The blood pressure follows a circadian rhythm and is the highest between 0600 to 1200 h, when most complications occur. Long-acting drugs that extend their action to cover this vulnerable period are preferable, especially those that block the renin-angiotensin-aldosterone system, such as ACE inhibitors and angiotensin receptor blockers, and are the most effective in controlling blood pressure and preventing or reducing its cardiovascular and renal complications. With respect to the angiotensin receptor blockers, telmisartan has been demonstrated by several studies to be the longest acting among its class of drugs and to effectively prevent the early morning rise of blood pressure.

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.

Detection of tryptase-, chymase+ cells in human CD34+ bone marrow progenitors

BACKGROUND

Mast cells (MCs) arise from haematopoietic stem cells. We have recently reported that CD34(+) progenitors derived from human bone marrow (BM) develop into tryptase+, chymase+ MCs when cultured in the presence of recombinant human stem cell factor (rhSCF) and recombinant human IL-6 (rhIL-6). In an experiment for the expression of chymase during differentiation, chymase+ cells were detected in human BM, but tryptase+ cells were not found.

OBJECTIVE

The purpose of this study was to show the appearance of chymase+ cells in CD34(+) cells with an origin different from MC differentiation.

METHODS

CD34(+) cells from human BM were sorted with anti-CD117 monoclonal antibody (mAb), and cytospins of CD34(+), CD34(+)CD117(+), or CD34(+)CD117(-) were prepared. These cells were cultured with rhSCF+rhIL-6 for 12 weeks. Some of the cells were subjected to either histological stain with Wright-Giemsa or immunocytochemistry with anti-chymase mAb. Real-time RT-PCR was also performed to compare the transcriptional level of chymase from each cell preparation.

RESULTS

Chymase was expressed in CD34(+) cells as well as human MCs by immunocytochemistry. Substantial CD34(+)CD117(-) cells, but not CD34(+)CD117(+) cells, were stained immunocytochemically with anti-chymase mAb. For 1 week culture with rhSCF+rhIL-6, no cells expressed chymase in any preparation. Real-time RT-PCR revealed positivity for chymase mRNA in CD34(+) cells, but it reduced at 1 week of culture, and increased as cells developed into MCs. Chymase mRNA in CD34(+)CD117(+) cells was negligible compared with that in CD34(+)CD117(-). Tryptase mRNA was below the detectable level in CD34(+) cells, and increased along with MC differentiation. After 12 weeks of culture, CD34(+)CD117(+) developed predominantly into MCs, whereas CD34(+)CD117(-) developed into monocytes/macrophages.

CONCLUSION

Our findings suggested that chymase is present not only in MCs but also in CD34(+)CD117(-) BM progenitors, but that its origin is different from the MC lineage.

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.

Clinical Experience With Angiotensin Receptor Blockers With Particular Reference to Valsartan

The angiotensin II receptor blockers (ARBs), are highly selective for the AT1 subtype and will block the effects of angiotensin II on peripheral vessels. Several short- and long-term studies have shown these agents to be safe and effective antihypertensive drugs. Since monotherapy of hypertension may be ineffective in lowering the blood pressure to goal, the use of an ARB, especially in combination with a diuretic or another medication, is frequently necessary to bring the blood pressure <140/90 mm Hg (<130/80 mm Hg among people with diabetes mellitus or chronic renal failure), according to JNC 7 guidelines. Besides hypertension, the ARBs have been shown to reduce left ventricular hypertrophy in hypertensive patients. Other benefits of these medications, as well as the angiotensin I converting enzyme inhibitors (ACEIs), include a decrease in cardiovascular morbidity and mortality in patients with heart failure, or hypertensive diabetic nephropathy with proteinuria. Some of the beneficial effects noted with the ACEIs and ARBs (congestive heart failure, left ventricular hypertrophy), have also been demonstrated with the use of b blockers alone and in combination with a diuretic. These drugs, i.e., b blockers, ARBs, and ACEIs, seem to exert their beneficial action through the blockade of the renin-angiotensin-aldosterone system. The role of this system in cardiovascular remodeling and its blockade will be discussed in this review, which will specifically summarize data with the ARB, valsartan.

Losartan, an angiotensin II (AT1) receptor antagonist, preserves cerebral blood flow in hypertensive patients with a history of stroke

In patients with severe hypertension, chronic heart failure or a history of stroke, the lower limit of autoregulation of cerebral blood flow (CBF) is shifted to higher levels of blood pressure (BP) than those observed in healthy subjects. The aim of pharmacotherapy for hypertensive patients with an impaired autoregulation of CBF should be to reduce BP while preserving an appropriate CBF. In the present study, 16 hypertensive patients who had had an episode of stroke more than 4 weeks previously were administered the angiotensin II (AT1) receptor antagonist losartan at daily doses of 25-100 mg for 4 weeks. Systolic and diastolic blood pressures were recorded for 24 h using an ambulatory BP monitoring system. CBF in both hemispheres of the cerebrum and cerebellum was quantified using single photon emission tomography with N-isopropyl-p-[123I]iodoamphetamine. At baseline, CBF was 29.7 +/- 6.7 ml/min/100 g in the cerebrum and 31.5 +/- 7.5 ml/min/100 g in the cerebellum. At the end of treatment, BP was lower, while CBF increased by 7.7% in the cerebrum, and remained at the baseline level in the cerebellum. Thus, CBF was preserved despite the reduction in BP. We consider the use of losartan is advantageous for hypertensive patients with a history of stroke in whom autoregulation of CBF is potentially impaired.

Fixed combination therapy of hypertension: focus on valsartan/hydrochlorothiazide combination (Diovan/HCT)

Hypertension is a major risk factor for cardiovascular morbidity and mortality. Monotherapy of hypertension is often ineffective, since it controls approximately 50% of the blood pressure of hypertensive patients. For lowering blood pressure to less than 140/90 mmHg (or <130/80 mmHg among people with diabetes or chronic renal disease) according to JNC-7 guidelines, combination therapy of two or more drugs is often necessary. The combination of a diuretic with an angiotensin-converting enzyme inhibitor (ACEI) or an angiotensin receptor blocker (ARB) is effective and provides the additional benefit of blocking the effects of angiotensin II, which is responsible for cardiovascular remodeling and its complications. ARBs may have an advantage over the ACEIs because they block the action of all angiotensin II directly, whereas ACEIs are ineffective in blocking angiotensin II generated by nonclassical ACE pathways. Valsartan (Diovan, Novartis) is one of the seven currently approved ARBs in the USA for the treatment of hypertension, and it has been shown to be very effective in controlling blood pressure given once-daily in doses of 80-160 or 320 mg. Its fixed combination with hydrochlorothiazide (HCT) is even more effective in controlling blood pressure in 70% of the cases. The most commonly used combinations are valsartan/HCT (Diovan/HCT), 80/12.5 and 160/12.5 mg given once-daily.

Effects of conjugated oestrogen and droloxifene on the renin-angiotensin system, blood pressure and renal blood flow in postmenopausal women

OBJECTIVE

The aim of this study was to evaluate the effect of conjugated equine oestrogen (CEE), and droloxifene, a selective oestrogen receptor modulator (SERM) on individual components of renin-angiotensin-aldosterone (RAAS) and blood pressure (BP) in postmenopausal women.

DESIGN AND PATIENTS

Twenty-one normotensive (NT) and 10 hypertensive (HT) postmenopausal women received either CEE (0.625 mg/day) or droloxifene (60 mg/day) for 6 weeks and, after a 4-week washout, were restudied on the alternate medication.

MEASUREMENTS

Hormones of the RAAS and supine BP were measured prior to and at the end of each drug treatment in all subjects. In a subgroup of the NT (n = 10), 24 h ambulatory BP was performed and renal blood flow was determined by PAH clearance both basally and in response to 45-min angiotensin II (Ang II) infusion (3 ng/kg/min).

RESULTS

CEE significantly increased angiotensinogen, decreased active renin and angiotensin-converting enzyme (ACE), and maintained plasma immunoreactive (ir) angiotensin I (Ang I) levels compared to baseline. With droloxifene, angiotensinogen, active renin and Ang I remained unchanged. Both CEE and droloxifene significantly increased plasma ir-Ang II levels (pmol/l) in NT (baseline: 25.7 +/- 2.5, CEE: 36.6 +/- 3.4, droloxifene: 33.3 +/- 3.1, P < 0.002) and HT women (baseline: 17.9 +/- 2.3, CEE: 27.9 +/- 3.2, droloxifene: 25.9 +/- 4.9, P < 0.005). Renal blood flow was lower on CEE (P = 0.02) compared with baseline. Systemic BP (supine and 24-h ambulatory) was unchanged during both treatments.

CONCLUSION

This study demonstrates higher circulating levels of ir-Ang II with CEE and droloxifene.

Application of a chymase inhibitor, NK3201, for prevention of vascular proliferation

NK3201 is an orally active chymase inhibitor. Its inhibitory activity leads to formation of acyl-intermediate between active serine residue of the enzyme and di-ketone structure of NK3201. NK3201 inhibits human, dog and hamster chymases with IC(50) of 2.5, 1.2, and 28 nM, respectively. On the other hand, NK3201 does not inhibit other types of serine proteases, tryptase, thrombin, elastase, plasmin, and plasminogen activator. In dogs, at 8 h after oral administration of NK3201, 1 mg/kg, the drug levels in plasma, heart, and aorta reached 470, 195, and 78 nM, respectively. In a dog model NK3201, 5 mg/kg/day, increased chymase activity in grafted veins, and suppressed vascular proliferation. After balloon injury in dog vessels, chymase activity was increased locally, in the injured artery, and NK3201, 1 mg/kg/day was effective in preventing vascular proliferation. On the other hand, NK3201, unlike angiotensin converting enzyme inhibitors or angiotensin II receptor blockers, did not affect blood pressure. These findings indicate that local angiotensin II production by chymase is involved only in vascular proliferation, as seen in the injured vessels. Therefore, NK3201 may be useful for preventing vascular proliferation without affecting blood pressure.