The functional ratio of chymase and angiotensin converting enzyme in angiotensin I-induced vascular contraction in monkeys, dogs and rats

Evaluation of Alacepril Administration in Canine Patent Ductus Arteriosus According to Plasma Chymase Activity

Chymase in the renin-angiotensin system (RAS) actively contributes to cardiac disease progression. Chymase is activated to produce angiotensin II during tissue injury and is involved in hemodynamics. A recent study demonstrated that plasma chymase activity reflects hemodynamic changes and aids in understanding patent ductus arteriosus (PDA) pathophysiology. The present study examined the relationship between plasma chymase activity and the administration of angiotensin-converting enzyme (ACE) inhibitor. Alacepril was administered to 13 puppies with PDA. Conventional echocardiographic parameters and non-invasive blood pressure were measured before and after medication. Plasma chymase activity was calculated using the colorimetric absorbance method. Plasma chymase activity significantly increased, but blood pressure significantly decreased. We detected an increase in plasma chymase activity due to ACE inhibition in PDA cases treated with alacepril. Plasma chymase activity was affected and altered by alacepril. In veterinary medicine, plasma chymase activity may be a novel method for assessing the pathology of and therapy for cardiac diseases.

Effects of Astragalus Polysaccharides on Chymase, Angiotensin-converting Enzyme and Angiotensin II in Diabetic Cardiomyopathy in Hamsters

This study investigated the effects of Astragalus polysaccharides (APS), the main active extract from the traditional Chinese medicinal herb Astragalus membranaceus, on myocardial chymase, angiotensin-converting enzyme (ACE) and angiotensin II (Ang II) in diabetic cardiomyopathic hamsters. Plasma levels of insulin, C-peptide and glycosylated serum protein (GSP), plasma and myocardial levels of Ang II, and myocardial gene expression and activity of chymase and ACE were measured after treatment with APS at a dose of 1 g/kg per day or 1 ml of normal saline per day (controls) for 10 weeks. GSP levels, myocardial Ang II levels, and myocardial gene expression and activity of chymase were significantly decreased in diabetic hamsters after treatment with APS compared with controls. These results suggest that APS can inhibit the local chymase–Ang II system in diabetic cardiomyopathy.

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.

G protein-mediated stretch reception

Mechanosensation and -transduction are important for physiological processes like the senses of touch, hearing, and balance. The mechanisms underlying the translation of mechanical stimuli into biochemical information by activating various signaling pathways play a fundamental role in physiology and pathophysiology but are only poorly understood. Recently, G protein-coupled receptors (GPCRs), which are essential for the conversion of light, olfactory and gustatory stimuli, as well as of primary messengers like hormones and neurotransmitters into cellular signals and which play distinct roles in inflammation, cell growth, and differentiation, have emerged as potential mechanosensors. The first candidate for a mechanosensitive GPCR was the angiotensin-II type-1 (AT(1)) receptor. Agonist-independent mechanical receptor activation of AT(1) receptors induces an active receptor conformation that appears to differ from agonist-induced receptor conformations and entails the activation of G proteins. Mechanically induced AT(1) receptor activation plays an important role for myogenic vasoconstriction and for the initiation of cardiac hypertrophy. A growing body of evidence suggests that other GPCRs are involved in mechanosensation as well. These findings highlight physiologically relevant, ligand-independent functions of GPCRs and add yet another facet to the polymodal activation spectrum of this ubiquitous protein family.

Beneficial effects of astragalus polysaccharides treatment on cardiac chymase activities and cardiomyopathy in diabetic hamsters

Over-activation of the local chymase-angiotensin II (Ang II) system has a dominant role in diabetic cardiomyopathy. Astragalus polysaccharides (APS) are used in traditional Chinese medicine to boost immunity. In this study, we investigated the effects of APS treatment on cardiac function, myocardial collagen expression, cardiac ultrastructure, cardiac matrix metalloproteinase (MMP) activity, levels of plasma glycosylated serum protein (GSP), and myocardial enzymes, and the expression of Ang II, chymase, and angiotensin-converting enzyme (ACE) in the diabetic hamster myocardium. Diabetes was induced by a single injection of streptozotocin (60 mg/kg ip). The experimental groups consisted of normal control (n = 15), diabetic (n = 15), insulin-treated diabetic (n = 15, NPH 1-2 U/day ip), and APS-treated diabetic (n = 30, APS 1-2 g/kg/day orally for 10 weeks) hamsters. Diabetic hamsters treated with insulin or APS exhibited significantly decreased blood glucose, plasma GSP, and myocardial enzymes, as well as improvements in cardiac function and cardiac ultrastructure. Compared with insulin treatment, APS treatment significantly reduced myocardial collagen (type I and III) expression and lowered cardiac MMP-2 activity, myocardial Ang II levels, myocardial chymase expression, and p-ERK1/2 kinase expression. In diabetic hamsters, myocardial ACE expression and plasma Ang II levels was not altered by insulin or APS treatment. These results indicate that treatment of diabetic hamsters with APS inhibited the local chymase-Ang II system and improved markers of diabetic cardiomyopathy.

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.

Astragalus polysaccharides inhibited diabetic cardiomyopathy in hamsters depending on suppression of heart chymase activation

Diabetic cardiomyopathy is associated with high morbidity and mortality of heart failure. Overactivation of the local chymase-Ang II system plays a dominant role in diabetic cardiomyopathy. Astragalus polysaccharide (APS) is used in traditional Chinese medicine to boost immunity. To study the effect of APS on local system of chymase-Ang II in diabetic cardiomyopathy, we investigated APS/normal saline (NS)-administrated streptozotocin-induced diabetic hamsters. After APS/NS administration at a dose of 1 g/kg per day for 10 weeks, hemodynamic parameters, levels of insulin (INS), C-peptide (C-P), glycosylated serum protein (GSP), lipoproteins, myocardial enzymes, and Ang II (plasma and myocardial) were tested; myocardial collagen (type I and III), myocardial ultrastructure, and activities of matrix metalloproteinase (MMPs) were measured; activities and expression of cardiac chymase and ACE were detected by using quantitative real-time RT-PCR and RIA; protein expression of cardiac phosphoric extracellular signal-regulated kinase 1/2 (p-ERK1/2) was measured by Western blot. AP-administrated diabetic hamsters had lower levels of GSP, lipoproteins, myocardial enzymes, myocardial Ang II, expression of collagen I and I/ III, activities of pro-MMP-2 and MMP-2, activities and expression of chymase, and expression of p-ERK1/2 than NS-administrated diabetic hamsters and could better protect the myocardial ultrastructure. There was no difference in hemodynamic parameters between two groups. These results indicate that APS could inhibit diabetic cardiomyopathy in hamsters depending on the suppression of the local cardiac chymase-Ang II system.

Anti-atherosclerotic effects of dihomo-gamma-linolenic acid in ApoE-deficient mice

AIM

Dihomo-gamma-linolenic acid (DGLA) is an n-6 polyunsaturated fatty acid that is mainly metabolized to an anti-inflammatory eicosanoid, prostaglandin (PG) E1, via the cyclooxygenase (COX) pathway. We evaluated the effect of DGLA on atherosclerosis in apoE-deficient mice and studied the mechanism of the anti-atherosclerotic effect.

METHODS

ApoE-deficient mice were fed a normal diet supplemented with 0.5% DGLA or vehicle for 6 months. ApoE-deficient mice were also fed a high-cholesterol diet supplemented with 0.5% DGLA or vehicle for 1 month. To clarify the influence of a COX inhibitor, naproxen, on the anti-atherosclerotic effect of DGLA, age-matched apoE-deficient mice fed a high-cholesterol diet supplemented with 0.5% DGLA were given oral naproxen for 1 month.

RESULTS

In normal diet-fed mice, acetylcholine-induced vascular relaxation was significantly greater in the DGLA group than in the vehicle group. NADPH oxidase subunits, p22phox and gp91phox, intercellular adhesion molecule-1, and vascular cellular adhesion molecule-1 were significantly lower in the DGLA group than in the vehicle group, and DGLA significantly prevented atherosclerosis. In high-cholesterol diet-fed mice, DGLA also significantly prevented atherosclerosis, but the anti-atherosclerotic effect was attenuated by naproxen.

CONCLUSION

DGLA may have an anti-atherosclerotic effect in apoE-deficient mice via PGE1 formation.

Long-term angiotensin II blockade may improve not only hyperglycemia but also age-associated cardiac fibrosis

In the present study, the effects of long-term angiotensin (Ang) II antagonism on the development of cardiac and endothelial disorders were examined in Spontaneously Diabetic Torii (SDT) rats. Blood glucose concentration started to increase markedly in the untreated SDT rats from 20 weeks of age, while the blood glucose concentrations of candesartan cilexetil-treated SDT rats were significantly lower until 30 weeks of age. Cardiac function deteriorated in SDT rats and was accompanied by severe cardiac fibrosis, cardiac hypertrophy, and microstructural pathologic change in cardiomyocytes. Cardiac function was very well preserved in the age-matched Sprague Dawley (SD) rats, but cardiac fibrosis developed with aging. Candesartan cilexetil treatment improved cardiac structural remodeling and cardiac function in SDT rats. Surprisingly, the degree of cardiac fibrosis in candesartan cilexetil-treated SDT rats was less than that of SD rats. Immunohistological staining confirmed that in addition to collagen deposition, fibroblasts and myofibroblasts were the main cellular components in the cardiac fibrotic areas. The diabetic hearts showed positive staining for ACE, Ang II, and AT(1) receptors. SDT rats also showed decreased endothelial function, which was improved with candesartan cilexetil treatment. These findings indicate that Ang II is involved in the development of cardiac dysfunction by accelerating cardiac remodeling and cardiomyocyte damage in the presence of hyperglycemia. On the other hand, although the mechanisms responsible for the cardiac fibrosis that occurs under normal conditions may differ greatly from those responsible for cardiac fibrosis with hyperglycemia, Ang II seems to play an important role in both.

Gq-coupled receptors as mechanosensors mediating myogenic vasoconstriction

Despite the central physiological function of the myogenic response, the underlying signalling pathways and the identity of mechanosensors in vascular smooth muscle (VSM) are still elusive. In contrast to present thinking, we show that membrane stretch does not primarily gate mechanosensitive transient receptor potential (TRP) ion channels, but leads to agonist-independent activation of G(q/11)-coupled receptors, which subsequently signal to TRPC channels in a G protein- and phospholipase C-dependent manner. Mechanically activated receptors adopt an active conformation, allowing for productive G protein coupling and recruitment of beta-arrestin. Agonist-independent receptor activation by mechanical stimuli is blocked by specific antagonists and inverse agonists. Increasing the AT(1) angiotensin II receptor density in mechanically unresponsive rat aortic A7r5 cells resulted in mechanosensitivity. Myogenic tone of cerebral and renal arteries is profoundly diminished by the inverse angiotensin II AT(1) receptor agonist losartan independently of angiotensin II (AII) secretion. This inhibitory effect is enhanced in blood vessels of mice deficient in the regulator of G-protein signalling-2. These findings suggest that G(q/11)-coupled receptors function as sensors of membrane stretch in VSM cells.

Species Differences in Angiotensin II Generation and Degradation by Mast Cell Chymases

Although chymases are known to exhibit species differences in regard to angiotensin (Ang) II generation and degradation, their properties have never been compared under the same experimental conditions. We analyzed the processing of Ang I by chymases of a variety of species (human chymase, dog chymase, hamster chymase-1, rat mast cell protease-1 [rMCP-1], mouse mast cell protease-4 [mMCP-4]) at physiological ionic strength and under neutral pH conditions. Human chymase generated Ang II from Ang I without further degradation, whereas the chymases of other species generated Ang II, followed by degradation at the Tyr4-Ile5 site in a time-dependent manner. Kinetic analysis showed that in terms of Ang II generating activity (analyzed by cleavage of the Phe8-His9 bond using the model peptide Ang(5-10), Ile5-His6-Pro7-Phe8-His9-Leu10), the chymases ranked as follows: dog > human > hamster > mouse > rat (kcat/Km: 18, 11, 0.69, 0.059, 0.030 microM-1min-1), and that in terms of Ang II degrading activity (i.e., cleavage of the Tyr4-Ile5 bond of Ang II), the order was hamster > rat > mouse > dog (kcat/Km: 5.4, 4.8, 0.39, 0.29 microM-lmin-1). These results suggest species differences in the contribution of chymases to local Ang II generation and degradation.

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.

Angiotensin-converting enzyme and vascular remodeling

Vascular remodeling is the result of a close interplay of changes in vascular tone and structure. In this review, the role of angiotension-converting enzyme (ACE) and the impact of ACE inhibition on vascular remodeling processes during vascular injury and restenosis, hypertension, atherosclerosis, and aneurysm formation are discussed. The role of ACE and angiotensin II (Ang II) in neointimal thickening has been firmly established by animal studies and is mediated by Ang II type 1 (AT(1)) receptor signaling events via monocyte chemoattractant protein-1 and NAD(P)H oxidase. ACE and Ang II are involved in the remodeling of large and resistance arteries during hypertension; here, cell proliferation and matrix remodeling are also regulated by signaling events downstream of the AT(1) receptor. In atherosclerosis, Ang II is involved in the inflammatory and tissue response, mediated by various signaling pathways downstream of the AT(1) receptor. Although ACE inhibition has been shown to inhibit atherosclerotic processes in experimental animal models, results of large clinical trials with ACE inhibitors were not conclusive. Remodeling of vessel dimensions and structure during aneurysm formation is counteracted by ACE inhibition. Here, a direct effect of ACE inhibitors on matrix metalloproteinase activity has to be considered as part of the working mechanism. The role of ACE2 in vascular remodeling has yet to be established; however, ACE2 has been shown to be associated with vascular changes in hypertension and atherosclerosis.

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.

Effect of chymase on intraocular pressure in rabbits

Chymase is a chymotrypsin-like serine protease that is stored exclusively in the secretory granules of mast cells and converts big endothelins to endothelin-1 (1-31). The aim of this study was to evaluate the effect of chymase on intraocular pressure in rabbits. Chymase injection (3 and 10 mU) resulted in a trend toward increased intraocular pressure and a significant increase in intraocular pressure at a dose of 10 mU compared with the control. A specific chymase inhibitor, Suc-Val-Pro-Phe(P)(OPh)(2), attenuated the ocular hypertension induced by chymase. Endothelin-1 (1-31) also caused ocular hypertension, which was inhibited by a selective endothelin ET(A) receptor antagonist, cyclo(D-Asp-Pro-D-Val-Leu-D-Trp) (BQ-123). Moreover, chymase-induced ocular hypertension was inhibited by BQ-123. These results suggest that chymase influences the regulation of intraocular pressure, and it is likely that the formation of endothelin-1 (1-31) and subsequent activation of endothelin ET(A) receptors are involved in the development of ocular hypertension induced by chymase.

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-derived angiotensin II and arrhythmias after myocardial infarction

Mast cell-derived chymase seems to be important in the regulation of local angiotensin (A) II formation in cardiovascular tissues. In human heart, chymase accounts for 80% of A II formation. Therefore, the chymase-dependent A II pathway may play an important role in the pathogenesis of A II-related cardiovascular diseases. For example, cardiac chymase was activated earlier than ACE and this activation lasted longer than that of ACE after myocardial infarction (MI) in hamsters. Treatment with a specific chymase inhibitor treatment, but not an ACE inhibitor, improved post-MI survival as well as cardiac function and the extent of the beneficial effects was similar to that observed for an AT1-receptor antagonist treatment in this model. The survival benefit after MI seems to be related to an antiarrhythmic effect of the chymase inhibitor because chymase inhibition reduces the incidence of ventricular arrhythmias during periods of heart ischemia in a dog MI model. Thus, an antiarrhythmic effect of the chymase inhibitor may contribute to a reduction in mortality rate during the acute phase after MI.

An antiarrhythmic effect of a chymase inhibitor after myocardial infarction

Chymase plays an important role in the regulation of local angiotensin (Ang) II formation in the cardiac tissue. We recently found that cardiac chymase was activated significantly and survival rate markedly improved by treatment with chymase inhibitors after myocardial infarction (MI) in hamsters. However, the mechanisms for this effect have not been established. Because lethal arrhythmias are generally believed to contribute to sudden cardiac death, we assessed whether inhibition of cardiac chymase would provide an antiarrhythmic effect during the 8-h ischemic period after 2-[4-(5-fluoro-3-methylbenzo-[b]thiophen-2-yl)sulfonamide-3-methanesulfonylphenyl]oxazole-4-carboxylicacid (TY51184) (a specific chymase inhibitor, 1 mg/kg i.v.) treatment by ligation of left anterior descending coronary artery (LAD) in dogs. Effects of candesartan (an Ang II type 1 receptor antagonist, 1 mg/kg i.v.) in this model were also assessed. Total Ang II-forming activity and chymase activity in the infarcted heart were increased significantly 8 h after LAD ligation. A time-dependent elevation of Ang II in plasma was also observed. A decrease in plasma Ang II levels after TY51184 treatment occurred concomitantly with suppression of cardiac chymase activity. LAD ligation resulted in a large number of ventricular arrhythmias (VAs). TY51184 and candesartan treatments largely suppressed the appearance of VAs, and the efficacy of the two agents was similar. These findings demonstrate that chymase inhibition can provide an antiarrhythmic effect after MI, and the reduction of Ang II by TY51184 may be mainly responsible for this beneficial effect. An antiarrhythmic effect of chymase inhibitors may contribute to reductions in the mortality rate during the acute phase after MI.

A novel chymase inhibitor, 2-(5-formylamino-6-oxo-2-phenyl-1,6-dihydropyrimidine-1-yl)-N-[[,4-dioxo-1-phenyl-7-(2-pyridyloxy)]2-heptyl]acetamide (NK3201), suppressed intimal hyperplasia after balloon injury

In this study, we investigated whether an orally active 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), prevents intimal hyperplasia in carotid arteries injured by a balloon catheter in dog. Each dog was administered NK3201 (1 mg/kg per day, p.o.) or placebo beginning 5 days before balloon injury and continuing through the experiments. Four weeks after balloon injury, NK3201 did not affect the plasma renin and angiotensin-converting enzyme activities. The chymase activity was significantly increased in the injured arteries, whereas the angiotensin-converting enzyme activity was not. NK3201 significantly reduced the chymase activity in the injured arteries. The intimal area in the placebo- and NK3201-treated group and was 0.46 +/- 0.06 and 0.24 +/- 0.04 mm2, respectively, and this difference was significant. In this study, we demonstrated for the first time that a chymase inhibitor prevented the development of intimal hyperplasia in the balloon-injured arteries.

Rodent alpha-chymases are elastase-like proteases

Although the alpha-chymases of primates and dogs are known as chymotrypsin-like proteases, the enzymatic properties of rodent alpha-chymases (rat mast cell protease 5/rMCP-5 and mouse mast cell protease 5/mMCP-5) have not been fully understood. We report that recombinant rMCP-5 and mMCP-5 are elastase-like proteases, not chymotrypsin-like proteases. An enzyme assay using chromogenic peptidyl substrates showed that mast cell protease-5s (MCP-5s) have a clear preference for small aliphatic amino acids (e.g. alanine, isoleucine, valine) in the P1 site of substrates. We used site-directed mutagenesis and computer modeling approaches to define the determinant residue for the substrate specificity of mMCP-5, and found that the mutant possessing a Gly substitution of the Val at position 216 (V216G) lost elastase-like activity but acquired chymase activity, suggesting that the Val216 dominantly restricts the substrate specificity of mMCP-5. Structural models of mMCP-5 and the V216G mutant based on the crystal structures of serine proteases (rMCP-2, human cathepsin G, and human chymase) revealed the active site differences that can account for the marked differences in substrate specificity of the two enzymes between elastase and chymase. These findings suggest that rodent alpha-chymases have unique biological activity different from the chymases of other species.

Beneficial effects of cardiac chymase inhibition during the acute phase of myocardial infarction

Recently, the presence of the chymase-dependent angiotensin (Ang) II-generating system in hamsters, dogs, monkeys, as well as human cardiovascular tissues has been identified. We have reported that the activation of cardiac chymase was more prominent than that of angiotensin converting enzyme (ACE) and that AT1 receptor antagonist treatment rather than ACE inhibitor treatment alone provided significant beneficial effects on cardiac function and survival after MI in hamsters. The aim of the present study was to determine whether this different effects between AT1 receptor antagonist and ACE inhibitor were due to the activation of cardiac chymase after MI in hamsters by using 4-[1-[[bis-(4-methyl-pheny)-methyl]-carbamoyl]-3-(2-ethoxy-benzyl)-4-oxo-azetidine-2-yloxy]-benzoic acid (BCEAB), a novel, orally active and specific chymase inhibitor. The ACE and chymase activities in the infarcted left ventricle were significantly increased 3 days after MI. BCEAB (100 mg/kg/day, p.o.) treatment starting 3 days before MI significantly suppressed the cardiac chymase activity, while it did not affect the plasma and cardiac ACE activities 3 days after MI. A significant improvement in hemodynamics (maximal negative and positive rates of pressure development; left ventricular systolic pressure) was observed for the treatment with BCEAB 3 days after MI. BCEAB (100 mg/kg/day, p.o.) treatment starting 3 days before MI significantly reduced the mortality rate during 14 days of observation following MI (vehicle, 61.1%, n = 18; BCEAB, 27.8%, n = 18; P < 0.05). These findings demonstrated for the first time that cardiac chymase participates directly in the pathophysiologic state after MI in hamsters.