Different distribution of two types of angiotensin II-generating enzymes in the aortic wall

Chymase Dependent Pathway of Angiotensin II Generation and Rapeseed Derived Peptides for Antihypertensive Treatment of Spontaneously Hypertensive Rats

The contribution of chymase, one of the enzymes responsible for angiotensin II generation in non-ACE pathway, remains unclear in the development of hypertension. The aim of the study was to investigate chymase inhibition as potential antihypertensive therapy in spontaneously hypertensive rats (SHR). To block chymase we employed chymostatin, a commercial inhibitor, and new analogues of rapeseed-derived peptides, VWIS and RIY. These simple and easy to obtain peptides not only block chymase, but also possess weak activity to inhibit ACE. This is a first attempt to evaluate the impact of chronic administration of selected inhibitors on blood pressure of SHR in two phases of hypertension. Male SHR (6 or 16 weeks old) were treated daily for two weeks with chymostatin (CH; 2 mg/kg/day), the peptides VWIS (12.5 mg/kg/day) or RIY (7.5 mg/kg/day); control groups received chymostatin solvent (0.15% DMSO in saline) or peptide solvent (saline). The substances were administered intravenously to conscious animals via a chronically cannulated femoral vein. Systolic blood pressure (SBP) was measured by telemetry. Metabolic parameters were measured weekly, and tissue samples were harvested after two weeks of treatment. None of the administered chymase inhibitors affected the development of hypertension in young rats. Only RIY exhibited beneficial properties when administered in the established phase of hypertension: SBP decreased from 165 ± 10 to 157 ± 7 mmHg while the excretion of nitric oxide metabolites increased significantly. The glomerulosclerosis index was lower after RIY treatment in both age groups (significant only in young rats 0.29 ± 0.05 vs 0.48 ± 0.04 in the control group; p < 0.05). Hence, it seems that peptide RIY exhibits some positive effect on renal morphology. The results obtained suggest that the peptide RIY may be a useful tool in the treatment of hypertension, especially in cases when ACE inhibitors are not effective.

Effects of chymostatin, a chymase inhibitor, on blood pressure, plasma and tissue angiotensin II, renal haemodynamics and renal excretion in two models of hypertension in the rat

NEW FINDINGS

What is the central question of this study? We examined, in hypertensive rats, whether the angiotensin-converting enzyme-independent enzymes generating angiotensin II in the tissues modulate blood pressure, peripheral circulation and renal function. What is the main finding and its importance? The results suggest that chymostatin-sensitive enzymes diminish vascular tone in renal and extrarenal vascular beds. Chymase or similar chymostatin-sensitive enzymes have a significant role in the synthesis of angiotensin II in different tissues but do not control blood pressure in the short term, similarly in salt-dependent or Goldblatt-type rat hypertension. In salt-dependent hypertension, chymase blockade protected renal outer medullary perfusion, probably by reducing the angiotensin II content in the kidney. Chymase is presumed to be a crucial enzyme of the non-angiotensin-converting enzyme pathway of angiotensin II (Ang II) generation in tissues, a process involved in vascular remodelling and development of hypertension. We examined the role of chymase in hypertension induced by exposure of uninephrectomized rats to high dietary salt intake (UNX HS) and in the Goldblatt renal artery stenosis (two-kidney, one-clip) model. In acute experiments with anaesthetized rats of either model, chymostatin at 2 mg kg(-1) h(-1) or 0.05% DMSO solvent was infused i.v. Mean arterial blood pressure, heart rate, iliac blood flow (a measure of hindlimb perfusion), total renal blood flow and intrarenal regional perfusion (laser-Doppler technique) were measured continuously, along with the glomerular filtration rate and renal excretion. In both models, chymase blockade distinctly decreased plasma and tissue Ang II without lowering mean blood pressure or consistently altering the other functional parameters measured. Unexpectedly, in Goldblatt hypertensive rats the blockade increased the renal and hindlimb vascular resistances by 51 and 33%, respectively (P < 0.05). In UNX HS hypertensive rats, chymase blockade abolished the solvent-induced decrease in outer medullary blood flow. We conclude that chymase or similar chymostatin-sensitive enzyme(s) has a significant role in the synthesis of Ang II in different tissues but does not participate in short-term control of blood pressure in salt-dependent or Goldblatt-type rat hypertension. In the Goldblatt model, chymase appeared to reduce the renal and hindlimb vascular resistances by an unknown mechanism. In salt-dependent hypertension, chymase blockade protected renal outer medullary perfusion, probably by reducing Ang II content in the kidney.

Involvement of mast cell chymase in burn wound healing in hamsters

Mast cells play a significant role in the late stage of wound healing following burn injuries. In the present study, the possible role of mast cell chymase in burn wound healing was examined using a mast cell membrane stabilizer, ketotifen, in hamsters. A total of 28 hamsters were randomly divided into two groups (n=14), termed as the control and ketotifen groups. A deep partial-thickness burn injury was made on the back skin of the hamsters. The control group was orally administered physiological saline (1 ml) and the ketotifen group was orally administered ketotifen (4 mg/kg) once daily, two days prior to and two days subsequent to the burn. The results showed that concentrations of angiotensin II (Ang II), TGF-β1, collagens I and III and interleukin (IL)-1β were significantly decreased in the ketotifen group compared with those in the control group. However, there was no significant difference in fibroblast apoptosis between the two groups. The release of mast cell chymase was inhibited by the mast cell membrane stabilizer ketotifen. Taken together, these results suggest that mast cell chymase may participate in the process of burn wound healing. Chymase may therefore be a promising therapeutic target for the treatment of burn wounds.

Alternative pathways for angiotensin II generation in the cardiovascular system

The classical renin-angiotensin system (RAS) consists of enzymes and peptides that regulate blood pressure and electrolyte and fluid homeostasis. Angiotensin II (Ang II) is one of the most important and extensively studied components of the RAS. The beneficial effects of angiotensin converting enzyme (ACE) inhibitors in the treatment of hypertension and heart failure, among other diseases, are well known. However, it has been reported that patients chronically treated with effective doses of these inhibitors do not show suppression of Ang II formation, suggesting the involvement of pathways alternative to ACE in the generation of Ang II. Moreover, the finding that the concentration of Ang II is preserved in the kidney, heart and lungs of mice with an ACE deletion indicates the important role of alternative pathways under basal conditions to maintain the levels of Ang II. Our group has characterized the serine protease elastase-2 as an alternative pathway for Ang II generation from Ang I in rats. A role for elastase-2 in the cardiovascular system was suggested by studies performed in heart and conductance and resistance vessels of normotensive and spontaneously hypertensive rats. This mini-review will highlight the pharmacological aspects of the RAS, emphasizing the role of elastase-2, an alternative pathway for Ang II generation.

Contributions of ACE and mast cell chymase to endogenous angiotensin II generation and leucocyte recruitment in vivo

AIMS

In vitro studies suggest that mast cell chymase (MCP) is more important than angiotensin-converting enzyme (ACE) for generating angiotensin II (Ang II) within the cardiovascular system. We investigated in vivo the relative contributions of ACE and MCP to leucocyte recruitment induced by endogenously generated Ang II.

METHODS AND RESULTS

Exposure of the murine cremasteric microcirculation of C57BL/6 mice to Ang I (100 nM for 4 h) induced leucocyte-endothelium interactions. Either losartan (an Ang II receptor-1 antagonist, AT(1)) or enalapril (an ACE inhibitor), but not chymostatin (a chymase inhibitor), inhibited Ang I-induced responses. Mast cell degranulation with compound 48/80 (CMP48/80, 1 μg/mL) also induced leucocyte adhesion but this was only weakly affected by the inhibitors. When Ang I and CMP48/80 were co-administered, AT(1B) receptor expression was increased, MCP-4 was found surrounding the vessel wall, and ACE was detected in the endothelium. Ang I + CMP48/80 induced enhanced leucocyte adhesion that was attenuated by losartan, enalapril, enalapril + chymostatin, and cromolyn (a mast cell stabilizer). The use of male mast cell-deficient WBB6F1/J-Kit(w)/Kit(w-v) mice (C57BL/6 background) confirmed these findings.

CONCLUSION

In vivo, Ang II is primarily generated by ACE under basal conditions, but in inflammatory conditions, the release of MCP amplifies local Ang II concentrations and the associated inflammatory process. Thus, AT(1) receptor antagonists may be more effective than ACE inhibitors for treating ongoing Ang II-mediated vascular inflammation.

Angiotensin-converting enzyme inhibition augments the expression of rat elastase-2, an angiotensin II-forming enzyme

Mounting evidence suggest that tissue levels of angiotensin (ANG) II are maintained in animals submitted to chronic angiotensin-converting enzyme (ACE) inhibitor treatment. We examined the expression levels of transcripts for elastase-2, a chymostatin-sensitive serine protease identified as the alternative pathway for ANG II generation from ANG I in the rat vascular tissue and the relative role of ACE-dependent and -independent pathways in generating ANG II in the rat isolated carotid artery rings of spontaneously hypertensive rats (SHR) and Wistar normotensive rats (WNR) treated with enalapril for 7 days. Enalapril treatment decreased blood pressure of SHR only and resulted in significantly more elastase-2 mRNA expression in carotid artery of both enalapril-treated WNR and SHR. Captopril induced a comparable rightward shift of concentration-response curves to ANG I in vehicle and enalapril-treated rats, although this effect was of lesser magnitude in SHR group. Chymostatin induced a rightward shift of the dose response to ANG I in vehicle-treated and a decrease in maximal effect of 22% in enalapril-treated WNR group. Maximal response induced by ANG I was remarkably reduced by chymostatin in enalapril-treated SHR carotid artery (by 80%) compared with controls (by 23%). Our data show that chronic ACE inhibition was associated with augmented functional role of non-ACE pathway in generating ANG II and increased elastase-2 gene expression, suggesting that this protease may contribute as an alternative pathway for ANG II generation when ACE is inhibited in the rat vascular tissue.

Angiotensin III stimulates aldosterone secretion from adrenal gland partially via angiotensin II type 2 receptor but not angiotensin II type 1 receptor

Angiotensin II (Ang II) and Ang III stimulate aldosterone secretion by adrenal glomerulosa, but the angiotensin receptor subtypes involved and the effects of Ang IV and Ang (1-7) are not clear. In vitro, different angiotensins were added to rat adrenal glomerulosa, and aldosterone concentration in the medium was measured. Ang II-induced aldosterone release was blocked (30.3 ± 7.1%) by an Ang II type 2 receptor (AT2R) antagonist, PD123319. Candesartan, an Ang II type 1 receptor (AT1R) antagonist, also blocked Ang II-induced aldosterone release (42.9 ± 4.8%). Coadministration of candesartan and PD123319 almost abolished the Ang II-induced aldosterone release. A selective AT2R agonist, CGP42112, was used to confirm the effects of AT2R. CGP42112 increased aldosterone secretion, which was almost completely inhibited by PD123319. In addition to Ang II, Ang III also induced aldosterone release, which was not blocked by candesartan. However, PD123319 blocked 22.4 ± 10.5% of the Ang III-induced aldosterone secretion. Ang IV and Ang (1-7) did not induce adrenal aldosterone secretion. In vivo, both Ang II and Ang III infusion increased plasma aldosterone concentration, but only Ang II elevated blood pressure. Ang IV and Ang (1-7) infusion did not affect blood pressure or aldosterone concentration. In conclusion, this report showed for the first time that AT2R partially mediates Ang III-induced aldosterone release, but not AT1R. Also, over 60% of Ang III-induced aldosterone release may be independent of both AT1R and AT2R. Ang III and AT2R signaling may have a role in the pathophysiology of aldosterone breakthrough.

Design and Synthesis of Indole and Tetrahydroisoquinoline Hydantoin Derivatives as Human Chymase Inhibitors

The synthesis of new potential inhibitors of human chymase is described. Treatment of dihydroimidazo[1,5-a]indole and [1,5-b]isoquinoline-dione with thioaryl followed by oxidation gave the N-arylsulfonylmethyl of polycyclic hydantoin derivatives 3, 5 and 6.

Does the renin-angiotensin system also regulate intra-ocular pressure?

The renin-angiotensin-aldosterone system is known to play an essential role in controlling sodium balance and body fluid volumes, and thus blood pressure. In addition to the circulating system which regulates urgent cardiovascular responses, a tissue-localized renin-angiotensin system (RAS) regulates long-term changes in various organs. Many recognized RAS components have also been identified in the human eye. The highly vasoconstrictive angiotensin II (Ang II) is considered the key peptide in the circulatory RAS. However, the ultimate effect of RAS activation at tissue level is more complex, being based not only on the biological activity of Ang II but also on the activities of other products of angiotensinogen metabolism, often exerting opposite effects to Ang II action. In recent studies, orally administered angiotensin II type 1 receptor blockers and angiotensin-converting enzyme inhibitors lower intra-ocular pressure (IOP), likewise topical application of these compounds, the effect being more prominent in ocular hypertensive eyes. Based on previous findings and our own experimental data, it can strongly be suggested that the RAS not only regulates blood pressure but is also involved in the regulation of IOP.

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.

cDNA cloning of hamster angiotensin-converting enzyme and mRNA expression

Angiotensin-converting enzyme (ACE; EC 3.4.15.1), a dipeptidyl carboxypeptidase, converts angiotensin I to angiotensin II, the central product of the renin-angiotensin system. We here report molecular cloning of the complete open reading frame (ORF) of hamster somatic-type ACE and its expression in hamster organs. The cloned cDNA comprises an ORF of 3942 bp, which encodes 1314 amino acids of the precursor protein of hamster somatic ACE. On the deduced amino acid sequence a putative signal peptide and a transmembrane segment are predicted at the N-terminus and near the C-terminus, respectively. Two homologous domains, referred to as N- and C-domains, are present within somatic ACE, and within each of the homologous domains a putative active center is found, as has been the case in human, mouse, rat and rabbit. The similarity of the hamster sequence with the sequences of these other mammals at both the nucleotide and amino acid levels is high (above 83%). mRNA expression analysis by conventional polymerase chain reaction (PCR) shows wide distribution of the transcript, with dominant expression in lung and kidney. Quantitative analysis of mRNA expression demonstrates that levels in lung and kidney are 100-1000 times higher than in the other organs, suggesting that these organs are important in the hamster renin-angiotensin system, as they are for other mammals.

Application of novel tissue microarrays to investigate expression of tryptase, chymase and KIT protein in placental mast cells

INTRODUCTION

Tissue microarrays comprise numerous small representative tissue samples from hundreds of different cases assembled on a single histologic slide, and therefore allow high throughput analysis of multiple specimens at the same time. Mast cells are paracrine cells found ubiquitously in connective tissue. Expression of the serine proteases tryptase and chymase, as well as KIT protein, the receptor for stem cell factor (SCF), has been demonstrated in mast cells. Because little is known about the role of mast cells in the placenta, we investigated the number and expression of chymase, tryptase, and KIT protein in placental mast cells using newly developed tissue microarrays.

MATERIALS AND METHODS

Tissue microarrays were prepared from archival paraffin tissue blocks of 90 placentae, including 15 normal ones as a control group. Gestational age of the placentae ranged from 7 to 42 weeks. Sections of formalin-fixed paraffin-embedded material were prepared on chemically activated cover-slides. The slides were cut in 4-mm(2) squares containing representative areas, and transferred to a tissue microarray. Hematoxylin and eosin (H&E), chloroacetate esterase (CAE), toluidine blue, periodic acid--Schiff (PAS), and immunohistochemical staining were performed. The number of mast cells and expression of chymase, tryptase, and KIT protein were evaluated in each case.

RESULTS

Mast cell numbers in placentae with inflammation/abortion exceeded that of normal placentae. Although statistically not significant, we furthermore observed an increase in chymase-positive mast cells in the group of placentae associated with fetal malformations/chromosomal aberrations compared with normal placentae.

DISCUSSION

Novel tissue microarray technique has been introduced into placental research, and allows multiple placental tissue samples to be effectively analyzed simultaneously. This study indicated an increased number of chymase-positive mast cells in placentae with fetal malformation/chromosomal aberration. Activation of angiotensin II by chymase may play a role in fetal malformation. Moreover, it has been speculated that mast cells may only express chymase (MC(C)). Our findings denote the presence of placental MC(C). However, further studies are needed to elucidate more precisely the role of mast cell chymase in the placenta.

Pre-procedural ACE-activity does not predict symptomatic in-stent restenosis

BACKGROUND

Several studies indicate that ACE-activity is related to atherosclerosis. We investigated the correlation between ACE-activity, in plasma as well as in the atherosclerotic plaque, and in-stent restenosis.

METHODS AND RESULTS

ACE-activity was measured in blood samples from 178 patients who underwent a percutaneous coronary intervention with stent placement. During 8 months follow-up, 51 of these patients had an adverse clinical event. ACE-activity did not differ between patients with or without adverse events (21.5 vs. 23.1 nM/ml/min; P=0.36). Tissue samples were obtained with an atherectomy catheter before elective stent placement in another group of 13 patients with de novo stenosis. In this tissue, we determined the ACE-content immunohistologically. These patients were scheduled for follow-up quantitative coronary angiography after 12 months. In this group, the quantity of ACE was not correlated to the late luminal loss (0.31 vs. 0.38 mm; P=0.76).

CONCLUSION

In this study, pre-procedural ACE-activity, in plasma as well as in the atherosclerotic plaque, does not predict the occurrence of in-stent restenosis.

Expression, localisation and function of ACE and chymase in normal and atherosclerotic human coronary arteries

The expression, localisation and function of enzymes responsible for the local formation of angiotensin II in atherosclerotic and non-atherosclerotic human coronary arteries were studied. Human epicardial coronary arteries expressed mRNA for both ACE and chymase. Immunohistochemical studies revealed that ACE was localised to the vascular endothelium, and to a lesser extent the medial smooth muscle cells, in both large and small arteries. Chymase was detected in both types of vessel but was shown to be associated with mast cells. The contractions to angiotensin I in large arteries were inhibited only by a combination of quinaprilat and soyabean trypsin inhibitor. In the intramyocardial arteries the response to angiotensin I was markedly inhibited in the presence of chymostatin. These findings demonstrate that a dual pathway for the synthesis of angiotensin II is active in diseased and non-diseased coronary arteries.

Conversion of renin substrate tetradecapeptide to angiotensin II by rat MAB elastase-2

A new approach for the purification of rat mesenteric arterial bed (MAB) elastase-2 has been developed using the chromogenic substrates N-succinyl-Ala-Ala-Pro-Phe-p-nitroanilide and N-succinyl-Ala-Ala-Pro-Leu-p-nitroanilide to monitor the enzymatic activity during various stages of purification. The purified enzyme was evaluated in the presence of various inhibitors and confirmed to have angiotensin (Ang) II-forming ability. The active site-directed inhibitor acetyl-Ala-Ala-Pro-Leu-chloromethylketone (100 µmol·L-1), described for human pancreatic elastase-2, abolished the enzymatic activity, confirming that the enzyme is an elastase-2. Chymostatin (100 µmol·L-1), an inhibitor regarded as selective for chymases, also showed a remarkable inhibitory effect (94%), whereas captopril (100 µmol·L-1) had no effect at all on the Ang II-forming activity. The Ang II precursor renin substrate tetradecapeptide (RS-14P) was converted into Ang II by the rat MAB elastase-2 with the following kinetic constants: Km= 124 ± 21 µmol·L-1; Kcat= 629 min-1; catalytic efficiency (Kcat/Km) = 5.1 min-1µ(mol/L)-1. In conclusion, the strategy for the purification of rat MAB elastase-2 with the chromogenic substrates proved to be simple, rapid, accurate, and highly reproducible; therefore, it can be reliably and conveniently used to routinely purify this enzyme. The kinetic parameters for the formation of Ang II from RS-14P by rat MAB elastase-2 emphasize differences in substrate specificity between this and other Ang II-forming enzymes.Key words: N-succinyl-Ala-Ala-Pro-Phe-p-nitroanilide, N-succinyl-Ala-Ala-Pro-Leu-p-nitroanilide, elastase-2, angiotensin II, renin substrate tetradecapeptide.

Functional role, cellular source, and tissue distribution of rat elastase-2, an angiotensin II-forming enzyme

We recently described a chymostatin-sensitive elastase-2 as the major angiotensin (ANG) II-forming enzyme in the perfusate of the rat mesenteric arterial bed (MAB) with the same cDNA sequence as rat pancreatic elastase-2. The role of this enzyme in generating ANG II was examined in the rat isolated and perfused MAB. The vasoconstrictor effect elicited by ANG I and the renin substrate tetradecapeptide was only partially inhibited by captopril but abolished by the combination of captopril and chymostatin or N-acetyl-Ala-Ala-Pro-Leu-chloromethylketone (Ac-AAPL-CK; inhibitor originally developed for human elastase-2). The effect induced by [Pro11,d-Ala12]-ANG I, an ANG I-converting enzyme (ACE)-resistant biologically inactive precursor of ANG II, was blocked by chymostatin or Ac-AAPL-CK. It was also demonstrated that cultured rat mesenteric endothelial cells synthesize elastase-2 and that mRNA for this enzyme can be detected in different rat tissues such as the pancreas, MAB, lung, heart, kidney, liver, and spleen. In conclusion, the demonstration of a functional alternative pathway to ACE for ANG II generation in the rat MAB and the fact that cultured MAB endothelial cells are capable of producing and secreting elastase-2 represent strong evidence of a physiological role for this enzyme in the rat vasculature.

[Role of chymase in vascular diseases and the efficacy of chymase inhibitor]

In vascular tissues, angiotensin II is cleaved from angiotensin I by chymase and angiotensin converting enzyme (ACE). In the normal state, chymase is stored in mast cells and has no angiotensin II-forming activity, while chymase is activated immediately where mast cells have been activated by local stimuli. A clinical trial of an angiotensin receptor blocker (ARB) for preventing restenosis after percutaneous transluminal coronary angioplasty was successful, but that of an ACE inhibitor was not. After balloon injury in dog vessels, chymase activity was significantly increased in the injured artery, and a chymase inhibitor and an ARB were effective in preventing the vascular proliferation, but an ACE inhibitor was ineffective. In dog grafted veins, intimal area, chymase activity, and angiotensin II concentration were significantly increased after the operation, while they were significantly suppressed by a chymase inhibitor. However, the chymase inhibitor, unlike ACE inhibitor and ARB, did not affect blood pressure. These reports indicate that local angiotensin II production by chymase is involved only in the injured vessels. Therefore, a chymase inhibitor may be useful for preventing vascular disorders without affecting blood pressure.

Effect of chymase inhibitor on vascular proliferation

In vascular tissues, angiotensin II is potentially cleaved from angiotensin I by chymase and angiotensin-converting enzyme (ACE). In the normal state, vascular ACE regulates local angiotensin II formation and plays a crucial role in the regulation of blood pressure, whereas chymase is stored in mast cells and has no enzymatic activity. Chymase is activated immediately upon its release into the extracellular matrix in vascular tissues after mast cells have been activated by stimuli such as vessel injury by grafting or a balloon catheter. In dog grafted veins, chymase activity is increased, and the vascular proliferation is suppressed by either a chymase inhibitor or an angiotensin II receptor blocker. After balloon injury in dog vessels, chymase activity is significantly increased in the injured artery, and a chymase inhibitor is effective in preventing the vascular proliferation, but an ACE inhibitor is ineffective. Chymase plays an important role in the development of vascular proliferation via the induction of local angiotensin II formation in injured vessels.

Chymase and angiotensin converting enzyme activities in a hamster model of glaucoma filtering surgery

PURPOSE

Two pathways for the formation of angiotensin II (Ang II) in local tissues are known to exist, one involving angiotensin-converting enzyme (ACE), and the other in which chymase plays a role. It has been shown that chymase activity is present in monkey, dog, and hamster eyes. Because chymase activates various cytokines by increasing Ang II formation, thereby promoting the production of extracellular matrix, the role of Ang II in wound healing has attracted much interest. In this work, we created sclerocorneal wounds in hamster eyes and measured the levels of ACE and chymase activities in the eye during the wound healing process.

METHODS

Sclerocorneal wounds were made at 6 locations on the corneal limbus of one eye in each of 36 hamsters. Using the contralateral eyes as controls, we measured levels of chymase and ACE activities in the overall eye at 3, 7, and 21 days postoperatively. Histopathological evaluations of the sclerocorneal wounds in the treated eyes were also carried out for samples stained with toluidine blue.

RESULTS

Chymase activity in the treated eyes tended to be higher than that in the control at 21 days. ACE activity in the treated eyes was significantly higher than that in the control at 3, 7, and 21 days postoperatively. Histopathological examination revealed increased mast cells in the subconjunctival tissue and around the tunnel opening in the sclerocornea.

CONCLUSIONS

These findings show that not only ACE but also chymase contributes to the formation of Ang II in the healing of sclerocorneal wounds in hamster eyes. This leads to the suggestion that ACE inhibitors or chymase inhibitors could potentially inhibit scarring in glaucoma filtering surgery.

Molecular cloning and sequencing of the cDNA for rat mesenteric arterial bed elastase-2, an angiotensin II-forming enzyme

A 28.5-kD protein expressed in rat mesenteric arterial bed (MAB) perfusate with angiotensin II-forming ability was previously characterized. This protein, a member of the elastase-2 family of enzymes, seems to be the only representative of this family of proteases to be secreted outside the digestive tract and implicated in the generation of angiotensin II. The cloning and sequencing of the cDNA for the rat MAB elastase-2 by using reverse transcription polymerase chain reaction are reported. The sequence of this cDNA was found to be identical to the sequence of the rat pancreatic elastase-2; the cDNA is 909 nucleotides in length plus a poly (A) tail and encodes a preproenzyme of 271 amino acids. Analysis of the putative amino acids in the extended angiotensin I binding site of the rat MAB elastase-2 reveals features that could explain the dipeptidyl carboxypeptidase-like activity required for efficient conversion of angiotensin I to angiotensin II. Additionally, the sequence reveals structural features that could contribute to the lack of activity of this enzyme toward angiotensin II. Rat MAB elastase-2 was expressed in mesenteric arteries and lung but not in aorta. These results may also indicate that rat MAB elastase-2 is expressed in resistance vessels but not in conduit vessels.

Production of human mast cell chymase in human myometrium and placenta in cases of normal pregnancy and preeclampsia

OBJECTIVE

To investigate whether the human mast cell chymase-endothelin-1(1-31) system was present in human myometrium, chorion and umbilical cord in normal pregnancy.

METHODS

Myometrium, placenta and umbilical cord were obtained from five normal pregnant women and 10 with preeclampsia. Each tissue was stained with antibodies against hMC and ET-1(1-31).

RESULTS

Routine cells were located mainly around vessels. The number of hMC-positive cells and production of ET-1(1-31) were significantly higher in myometrium from patients with severe preeclampsia compared to those from normal pregnant women. In contrast, their numbers were significantly lower in placenta and umbilical cord in patients with severe preeclampsia.

CONCLUSIONS

These results suggest that the hMC-ET-1(1-31) system is active in normal pregnancy. Overproduction of hMC and ET-1(1-31) in the myometrium may be involved in the pathogenesis of severe preeclampsia, and in such cases some defense mechanism may operate in the fetus to cope with the pathological effect of the hMC-ET-1(1-31) system.

Inhibitory effect of a novel angiotensin II type 1 receptor antagonist RNH-6270 on growth of vascular smooth muscle cells from spontaneously hypertensive rats: different anti-proliferative effect to angiotensin-converting enzyme inhibitor

The current study was undertaken to evaluate the anti-proliferative effect of a novel angiotensin II type 1 (AT1) receptor antagonist, RNH-6270, on exaggerated growth of vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR), in comparison with the effects of an angiotensin-converting enzyme (ACE) inhibitor. RNH-6270 and temocapril significantly inhibited basal DNA synthesis in VSMCs from SHRs in a dose-dependent manner, but not in cells from Wistar-Kyoto (WKY) rats. SHR-derived VSMC showed a hyperresponse of DNA synthesis to serum and angiotensin II compared with that of WKY rats-derived VSMC. RNH-6270 did not affect serum-stimulated DNA synthesis in VSMCs from both rat strains. RNH-6270 abolished angiotensin II-stimulated DNA synthesis in VSMC from both rat strains. RNH-6270 significantly inhibited proliferation of VSMC from both rat strains, but the ACE inhibitor temocapril did not exert such an effect. RNH-6270 decreased the specific binding of angiotensin II to VSMC in a competitive manner for angiotensin II receptors in both rat strains. RNH-6270 and temocapril significantly decreased the expression of growth factor mRNAs and proteins in VSMC from SHR, but not in cells from WKY rats. These results suggest that RNH-6270 is a potent AT1 receptor antagonist and has anti-proliferative effects on VSMCs from SHR, which was not seen with an ACE inhibitor. The growth inhibitory effect of RNH-6270 may be associated with the inhibition of growth factors via antagonism to AT1 receptors.

Altered expression of prostacyclin synthase in a subset of the thick ascending limb cells and mesangial cells in 5/6-nephrectomized rats

The aim of this study was to evaluate the possible role of prostacyclin (PGl2) in the onset and development of hypertension and chronic renal failure in 5/6-nephrectomized rats (5/6NX). We measured the systolic blood pressure, 24-h urinary excretion levels of 6-keto-PGF1alpha, which was a stable metabolite of PGI2, and levels of PGI2 synthase (PCS) mRNA in the kidneys. Immunostaining for PCS in the kidneys was also evaluated. Systolic blood pressure was higher in 5/6NX than in sham-operated rats. The 24-h urinary excretion levels of 6-keto-PGF1alpha in 5/6NX at 1 week postsurgery were lower than in sham-operated rats. In renal morphology, tubulointerstitial injury was observed at 2 weeks postsurgery, and glomerulosclerosis at 4 weeks. Levels of PCS mRNA in 5/6NX decreased significantly at 1 and 2 weeks postsurgery compared with those in sham-operated rats, but at 8 weeks these levels showed a tendency to increase. Immunostaining for PCS was positive in a subset of the cortical thick ascending limb of Henle's loop cells, including macula densa in both groups. Moreover, in 5/6NX at 8 weeks postsurgery, mesangial cells also stained positive for PCS. In conclusion, our findings suggest that PCS might play an important role in mitigating glomerular hemodynamic changes associated with reduction of renal mass.

Local angiotensin II-generating system in vascular tissues: the roles of chymase

Roles of each angiotensin II producing enzymes of each of the angiotensin II-producing enzymes were reviewed based on experimental models. In vascular tissues, angiotensin II is potentially cleaved from angiotensin I by angiotensin converting enzyme (ACE) and chymase. It has been confirmed that vascular tissues of humans, monkeys, dogs and hamsters have a chymase-dependent angiotensin II-forming pathway. Much like other hypertensive models, hamster hypertensive models show high levels of vascular ACE activity, but not chymase activity. In hypertensive hamsters, administration of either an ACE inhibitor or an angiotensin II type 1 (AT1) receptor antagonist resulted in similar reductions in blood pressure, suggesting that chymase is not involved in the maintenance of high blood pressure in this model. In monkeys fed a high-cholesterol diet, ACE activity was increased in the atherosclerotic lesions, and an ACE inhibitor and an AT1 receptor antagonist prevented atherosclerosis to a similar degree, suggesting that ACE may be mainly involved in the development of atherosclerosis. After balloon injury in dog vessels, both ACE and chymase activities were locally increased about 3-fold in the injured arteries, and an AT1 receptor antagonist was effective in preventing the intimal formation, but an ACE inhibitor was ineffective. In dog grafted veins, the activities of chymase were increased 15-fold, but those of ACE were increased only 2-fold, and the intimal formation was suppressed by either an AT1 receptor antagonist or a chymase inhibitor. In the normal vascular tissues, ACE plays a crucial role for angiotensin II production, whereas chymase is stored in mast cells in an inactive form. Chymase acquires the ability to form angiotensin II following mast cells activation followed by mast cells activation by a strong stimulus such as occurs in catheter-injury or grafting. Together, these results indicate that chymase plays a major role in the vascular angiotensin II-generating system, particularly in cases of vascular injury.

Chymase-dependent angiotensin II formation in the saphenous vein versus the internal thoracic artery

OBJECTIVES

The great saphenous vein graft is known to be less patent than the internal thoracic artery graft. Recently, we reported that chymase-dependent angiotensin II formation plays an important role in the development of intimal hyperplasia in dog grafted veins. In this study we investigated the levels of angiotensin II-forming enzymes, angiotensin-converting enzyme, and chymase in human saphenous veins and internal thoracic arteries.

METHODS

The saphenous vein and internal thoracic artery specimens were obtained from coronary artery bypass grafts of patients during surgical procedures (saphenous vein, n = 16; internal thoracic artery, n = 16). Activities of angiotensin-converting enzyme and chymase were determined by using the extract from the saphenous vein or internal thoracic artery. Sections of the saphenous vein or internal thoracic artery were stained with van Gieson's elastin stain and were immunostained with anti-human chymase antibody.

RESULTS

The activities of angiotensin-converting enzyme in the saphenous vein and internal thoracic artery were 0.34 +/- 0.12 and 0.32 +/- 0.17 mU/mg protein, respectively, and the difference was not significant. The chymase activity in the saphenous vein was significantly higher than that in the internal thoracic artery (saphenous vein, 10.1 +/- 0.81 mU/mg protein; internal thoracic artery, 6.21 +/- 1.86 mU/mg protein). Chymase-positive cells in the saphenous vein were located in both the media and adventitia, and those in the internal thoracic artery were located only in the adventitia. The number of chymase-positive cells in the saphenous vein was about 2.6 times that in the internal thoracic artery.

CONCLUSION

The chymase activity, but not the angiotensin-converting enzyme activity, was significantly higher in the saphenous vein, suggesting that the high levels of chymase activity may be related to the poorer performance of the saphenous vein for use as a bypass conduit.

Salt intake and non-ACE pathways for intrarenal angiotensin II generation in man

Angiotensin-converting enzyme (ACE) plays a crucial role in the generation of angiotensin II (Ang II) via conversion from angiotensin I (Ang I). There has been substantial recent interest in non-ACE pathways of Ang II generation in the heart, large arteries, and the kidney. In the case of the human kidney, studied when in balance on a low-salt diet, the renal haemodynamic response to Ang II antagonists substantially exceeds the renal response to ACE inhibitors (ACE-I), suggesting that about 30-40% of Ang II-generation occurs via non-ACE pathways. In this study, we examined the relative contribution of non-ACE pathways, by comparing the response to candesartan and to captopril at the top of the dose-response in normal humans when in balance on a low-salt, as well as a high-salt, diet. As anticipated on a low-salt diet, the increase in renal plasma flow (RPF) in response to candesartan (165+/-14 mL/min/1.73 m2) significantly exceeded the response to captopril (118+/-12 mL/min/1.73 m2; p<0.01). In subjects studied on a high-salt diet, the response to candesartan (97+/-20 mL/min/1.73 m2) also significantly exceeded the response to captopril on the same diet(30+/-15 mL/min/1.73 m2; p<0.01). This remarkable response to candesartan in subjects on a high-salt diet,when compared with the response to captopril,suggests that non-ACE-dependent Ang II generation was influenced less than the classical renal pathway with an increase in salt intake, so that the percentage of Ang II generated via the non-ACE pathway rose to the 60-70% range.

Isolation of chymase complexed with physiological inhibitor similar to secretory leukocyte protease inhibitor (SLPI) from hamster cheek pouch tissues

A low molecular weight protein complexed with chymase was isolated from hamster cheek pouch tissues. This protein had an apparent molecular mass of about 10 kDa on SDS-PAGE and the N-terminal sequence showed some homology to secretory leukocyte protease inhibitor (SLPI), which is known as the predominant inhibitor of neutrophil elastase and cathepsin G. Remarkably enhanced inhibition of chymase activity was achieved in the presence of heparin, indicating that the functional property was also similar to SLPI. These findings suggest that this SLPI-like protein is a candidate for a physiological inhibitor of chymase.

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

Recently, a chymase-dependent angiotensin (Ang) II-forming pathway was found in human cardiovascular tissues, and the significance of this pathway in the pathogenesis of some cardiovascular diseases was suggested. The present study examined the ratio of angiotensin converting enzyme (ACE) to chymase-dependent Ang II formation in various isolated vessels from monkeys, dogs and rats. In all of the examined vessels, the addition of KCl at a concentration of 50 mM could induce a maximal contraction. Except for monkey coronary artery and rat renal and femoral artery, the addition of Ang I could induce transitory contractions, whereas the force of contractions in these vessels was quite different. The sensitivity to Ang II in these vessels was similar to that for Ang I. In monkey gastroepiploic and mesenteric arteries, about 70% of the Ang I-induced contraction was suppressed by chymase inhibition, while it was suppressed about 50% in monkey renal, femoral and carotid arteries. In dog renal arteries, about 65% of the Ang I-induced contraction was suppressed by chymase inhibition, while it was suppressed by about 30% in other dog arteries. In contrast, in all rat arteries, Ang I-induced contractions were completely suppressed by treatment with ACE inhibitor alone. We concluded that regional differences in the response to Ang I exist in vascular tissues, and the ratio of ACE- to chymase-dependent Ang II formation is different in the various vessels.

Expression and function of angiotensin converting enzyme, chymase, and angiotensin II in the human radial artery and internal thoracic artery

BACKGROUND

The potential role of the local renin-angiotensin system to differentially affect radial artery and internal thoracic artery graft performance has not been examined.

METHODS

Contractile responses to angiotensin I and II in the radial artery and the internal thoracic artery were examined in vitro. The expression function, and localization of angiotensin receptors, angiotensin converting enzyme, and chymase were studied in radial artery and internal thoracic artery segments.

RESULTS

Angiotensin I and II contractions were significantly greater (p < 0.05) in the radial artery compared to the internal thoracic artery. In both arteries, angiotensin II responses were mediated via the AT1 receptor. Messenger RNA transcripts for angiotensin-converting enzyme and chymase were detected in both arteries. Angiotensin-converting enzyme was localized to luminal and vaso vasorum endothelial cells and smooth muscle cells in both vessels, while chymase was colocalized with mast cells in adventitial and medial layers. An angiotensin converting enzyme or a chymase inhibitor singularly had no effect on angiotensin I contractions, however, when combined, a marked inhibition of the angiotensin I response was observed in both vessels.

CONCLUSIONS

Our results illustrate the complexities which exist within the local renin angiotensin system and suggest that clinical trials which may modulate the system are warranted.

The renin angiotensin system in bypass graft surgery

The renin angiotensin system is implicated in the development of vein graft disease after coronary artery bypass surgery. Components of this system have been shown to play important roles in determining the short-term and long-term performance of coronary artery bypass grafts. Significant differences exist in the commonly used arterial and venous grafts in angiotensin converting enzyme activity and angiotensin responses. The existence of a dual enzyme pathway in angiotensin II formation has also been demonstrated. Such findings have implications for the use of AT1-receptor antagonists over enzyme inhibitors to improve graft performance and prevent the development of coronary artery bypass graft disease.

Impact of angiotensin II on the kidney: does an angiotensin II receptor blocker make sense?

The renin-angiotensin system (RAS) regulates blood pressure, volume, and electrolyte balance. Derangements of the RAS may contribute to hypertension and renal injury, particularly in patients with types 1 or 2 diabetes. Angiotensin-converting enzyme (ACE) inhibitors have been proven to be beneficial in patients with hypertension and diabetes by preventing or delaying the development and progression of proteinuria and glomerulosclerosis. Comparisons with other drug classes demonstrate renoprotective effects for ACE inhibitors that are independent of-and additive to-their systemic antihypertensive actions. These renal effects may derive from their preferential dilation of renal efferent arterioles, which further reduces intraglomerular pressure. Inhibition of angiotensin II (Ang II) synthesis is subtotal, however, because local non-ACE enzymes also convert Ang I to Ang II. The existence of alternative pathways for Ang II generation that are unaffected by ACE inhibitors raises questions about whether ACE is the optimal target for RAS suppression. Ang II receptor blockers (ARBs), which interrupt the RAS at the target-organ receptor level, will block the effect of angiotensin whether its production involved ACE or a non-ACE pathway. ARBs are currently undergoing clinical trials to assess their efficacy in hypertensive patients with nephropathy.

Chymase mediates mast cell-induced angiogenesis in hamster sponge granulomas

We investigated the contribution of mast cell chymase in mast cell-dependent angiogenesis using the hamster sponge-implant model, where angiogenesis in the granulation tissue surrounding the subcutaneously implanted sponge was evaluated by measuring the hemoglobin content. Daily local injection of compound 48/80 (3-100 microg/site/day), a potent mast cell activator, induced formation of granulomas and angiogenesis in time- and dose-dependent manners. This angiogenic response was inhibited by chymase inhibitors including chymostatin (> or = 1 nmol/site/day), soybean trypsin inhibitor (SBTI; > or = 1.4 nmol/site/day) and lima bean trypsin inhibitor (LBTI; > or = 3.3 nmol/site/day), but not by a tryptase inhibitor like leupeptin (> or = 700 nmol/site/day). Although pyrilamine (> or = 2,580 nmol/site/day), a histamine H1 receptor antagonist, and protamine (300 microg/site/day) also inhibited angiogenesis, these effects were much less pronounced than those by chymase inhibitors. Furthermore, antigen-induced angiogenesis in hamsters pre-sensitized with ovalbumin was also inhibited by the chymase inhibitors by 60-70%. Our results suggest that chymase is a major mediator in mast cell-mediated angiogenesis.

Dissociation between ACE activity and autonomic response to ACE inhibition in patients with heart failure

BACKGROUND

Administration of angiotensin-converting enzyme (ACE) inhibitors to patients with congestive heart failure has been shown to increase parasympathetic tone as indicated by increases in high-frequency heart rate variability. The mechanism for this effect, including its relation to changes in baroreflex activity, blood pressure variability, and suppression of ACE activity, remains undefined. This study was designed to test the relation of these variables, which may govern changes in autonomic activity, to the previously described increase in parasympathetic tone.

METHODS

Seven patients with heart failure received a 3-hour infusion of the ACE inhibitor enalaprilat. Hemodynamic variables and parameters of heart rate and blood pressure variability, baroreflex gain derived from the interaction of heart rate and blood pressure variability, and serum ACE activity were measured during and after the infusion. Measures of heart rate and blood pressure variability were also compared against a historic control group.

RESULTS

Serum ACE activity was significantly suppressed throughout and after enalaprilat infusion. Hemodynamic measures did not change other than a small decline in right atrial and pulmonary capillary wedge pressures. Parasympathetic tone showed an initial significant increase with a peak at 2 hours but then declined below baseline 8 hours after initiation of enalaprilat infusion. Sympathetically influenced low-frequency heart rate variability was significantly increased above baseline in the enalaprilat treatment group 8 hours after initiation of the infusion. Baroreflex gain showed a significant trend to an increase with the maximum value coinciding with the peak in parasympathetic tone. There was no change in blood pressure variability in the enalaprilat group and no change in baroreflex gain, heart rate variability, or blood pressure variability in the control group.

CONCLUSIONS

Parasympathetic tone and baroreflex gain increased with parenteral administration of an ACE inhibitor but subsequently decreased below baseline values despite continued suppression of serum ACE activity. The dissociation between ACE suppression and autonomic response to ACE inhibition indicates that enzyme systems not reflected by plasma ACE activity or independent from the classic pathways of angiotensin formation contribute to the regulation of the autonomic response to ACE inhibition in patients with heart failure. The absence of significant change in hemodynamic variables or in blood pressure variability indicates that these autonomic changes are not an indirect reflex response to ACE inhibitor-induced vasodilation or hemodynamic baroreceptor stimulation.

Role of chymase on vascular proliferation

In the normal state, vascular ACE regulates local angiotensin II formation and plays a crucial role in the regulation of blood pressure, whereas chymase is stored in secretory granules in mast cells and has no enzymatic effects such as angiotensin II-forming activity. Chymase has a maximal activity immediately upon release into the extracellular matrix in vascular tissues after mast cells have been activated by a strong stimulus such as experienced by catheter-injured and grafted vessels. Therefore, chymase plays an important role in forming local angiotensin II when vascular tissues are injured, and inhibition of chymase may be useful for preventing vascular proliferation in grafted vessels and after PTCA (Figure 6).

The inhibitory effect of KT3-671, a nonpeptide angiotensin-receptor antagonist, on rabbit and rat isolate vascular smooth muscles: a possible involvement of K(ATP) channels

The vasoinhibitory effect of KT3-671, a recently synthesized nonpeptide angiotensin II (Ang II), AT1-receptor antagonist, and the factors affecting insurmountable antagonism of Ang II were examined in rabbit and rat isolated vascular smooth muscle preparations. In rabbit and rat aortic rings, KT3-671 caused insurmountable antagonism of Ang II. In addition, KT3-671 inhibited contractile responses to angiotensin III (Ang III). In rabbit isolated smooth muscles, KT3-671 was most effective in reducing the maximal contraction induced by Ang II in the renal artery followed by the basilar artery and the aorta. In rat renal arterial rings, KT3-671 (10(-5) M) inhibited the concentration-response curves of prostaglandin F2alpha and STA2. In rabbit and rat aortic rings without endothelium, the insurmountable antagonisms of Ang II by KT3-671 and EXP 3174 were changed to surmountable antagonism by pretreatment with DuP 753 and KT3-671, respectively. In addition, KT3-671 abolished the inhibitory effect of CV- 11974 in the rat aorta but not in the rabbit aorta. Indomethacin (10(-5) M) or the removal of endothelium did not affect the inhibitory effect of Ang II by CV-11974 or EXP 3174 but enhanced the insurmountable antagonism by KT3-671. ODQ (3 x 10(-6) M), N(G)-nitro-L-arginine (3 x 10(-4) M), 4-aminopyridine (3 x 10(-3) M), tetraethylammonium (TEA; 10(-3) M), or iberiotoxin (10(-7) M) did not affect the inhibitory action of KT3-671 or CV-11974. Methylene blue (3 x 10(-6) M), KCl (10(2) M), TEA (10(-2) M), or BaC12 (10(-4) M) changed the insurmountable antagonism by KT3-671 to surmountable antagonism and abolished the inhibitory effect of CV-11974. However, glibenclamide (3 x 10(-6) M) did not affect the inhibitory action of KT3-671 but reduced the insurmountable antagonism by CV- 11974. These results indicate that KT3-671 is an insurmountable antagonist of Ang II in the rabbit and rat aorta. The results in the rat aorta also suggest that K(ATP) channels may be involved in insurmountable antagonism of Ang II by KT3-671 and CV-11974. Key Words: KT3-671-Rabbit-Rat-Vascular smooth muscle-Angiotensin II-Insurmountable antagonist-K(TP)channels.

Chymase as a proangiogenic factor. A possible involvement of chymase-angiotensin-dependent pathway in the hamster sponge angiogenesis model

We investigated the profound involvement of chymase, an alternative angiotensin II-generating enzyme, in angiogenesis using a hamster sponge implant model. In vivo transfection of human pro-chymase cDNA or a direct injection of purified chymase into the sponges implanted resulted in marked increment of hemoglobin contents in the sponge granuloma tissues, demonstrating that chymase has an ability to elicit angiogenesis and is a potent angiogenic factor. Daily injection of basic fibroblast growth factor into the sponges implanted also induced angiogenesis, which was suppressed by the treatment with chymostatin, an inhibitor of chymase, or TCV-116, an antagonist of angiotensin II (Ang II) type 1 receptor. Expression of chymase mRNA and production of Ang II in the granuloma tissues were enhanced by the stimulation with basic fibroblast growth factor. Chymase activity in the sponge granulomas increased in parallel with the rise in hemoglobin contents, and mast cells observed in the granuloma tissues were positively stained with anti-chymase antibody. Exogenous administration not only of Ang II but of angiotensin I (Ang I) directly into the sponges could enhance angiogenesis. Chymostatin inhibited the angiogenesis induced by Ang I but not Ang II, suggesting the presence of a chymase-like Ang II-generating activity in the sponge granulomas. Our results may suggest a potential ability of chymase to promote angiogenesis through the local chymase-dependent and angiotensin-converting enzyme-dependent Ang II generating system in pathophysiological angiogenesis.

Characterization of recombinant human chymase expressed in Escherichia coli

We compared recombinant human chymase expressed in Escherichia coli with human chymase purified from vascular tissues. The recombinant chymase, the structure of which was NH2-enterokinase cleavage site-chymase-COOH, was expressed in Escherichia coli and then was solubilized and renatured. The protein did not have a chymase activity, but gained this activity after the cleavage of the N-terminal site by enterokinase. The enzyme was purified by heparin affinity and gel filtration columns. The N-terminal sequence of the protein was identical to the sequence for human chymase. The molecular weights of the recombinant chymase and chymase purified from human vascular tissues were 26 and 30 kDa, respectively, and the 4 kDa difference was thought to be due to the presence or absence of glycan. The optimum pH of the recombinant enzyme activity was between 7.5 and 9.0. The activity of the recombinant enzyme was inhibited by chymostatin, soybean trypsin inhibitor and phenylmethylsulfonyl fluoride, but not by ethylenediaminetetraacetic acid and aprotinin. This enzyme cleaved specifically the Phe8-His9 bond of angiotensin (Ang) I to form Ang II and that of big endothelin (ET)-1 to form ET-1-(1-31). These findings demonstrated that the enzymatic characteristics of the recombinant enzyme were identical to that of native human chymase.

Implications of species difference for clinical investigation: studies on the renin-angiotensin system

The justification for clinical investigation has its roots in the fact that physiological mechanisms and disease pathogenesis in animal models replicate mechanisms and pathogenesis in humans only in part. In the case of the renin-angiotensin system, there is species variation in the anatomic distribution of the renin-angiotensin system, in the active site of the renin enzyme, and in the structure of angiotensin and the AT(1) receptor. The conversion of angiotensin I (Ang I) to angiotensin II (Ang II) may prove to be the most important aspect of species variation. In plasma, all the conversion occurs through a single enzyme, angiotensin-converting enzyme (ACE), and species variation in structure and function have not been reported. Non-ACE-dependent pathways, which occur only at the tissue level, show unambiguous, striking species variation. Specifically, chymase, the most important enzyme responsible for non-ACE conversion of Ang I to Ang II, shows striking species variation. In humans and a number of species, including the hamster, quantitatively important chymase-independent Ang II formation from Ang I occurs in the heart, arteries, and kidney. In rats and rabbits, on the other hand, chymase differs, is not active in the conversion of Ang I to Ang II, and indeed is involved in Ang II degradation. Consequently, one would anticipate that blockade of the system at the ACE step would be equivalent to that at the Ang II receptor in the rat. This has been widely reported. In humans, on the other hand, one would anticipate that the AT(1) receptor blockers will be more effective than ACE inhibitors. Again, preliminary evidence favors this possibility. The implications for therapeutics are clear.

Participation of angiotensin II and bradykinin in contractile function in dog stunned myocardium

We examined the effects of enalapril and 4'-[(1, 4'-dimethyl-2'-propyl-[2,6'-bi-1H-enzimidazole]-1'-yl)methyl]-[1, 1'-biphenyl]-2-carboxylic acid (BIBR-277), an angiotensin II receptor antagonist, on contractile dysfunction in the stunned myocardium. Dogs were subjected to 20-min ligation of the coronary artery, followed by 60-min reperfusion. Saline, enalapril (1 mg/kg or 3 mg/kg), or BIBR-277 (3 mg/kg) was injected i.v. 10 min before ligation. D-Arginyl-L-arginlyl-L-prolyl-trans-4-hydroxy-L-prolylglycyl -3-(2-thi enyl)-L-alanyl-L-seryl-D-1,2,3, 4-tetrahydro-3-isoquinolinecarbonyl-L-(2alpha, 3beta, 7abeta)-octahydro-1H-indole-2-carbonyl-L-arginine (Hoe-140), a bradykinin B(2) receptor antagonist, at 300 microg/kg was injected i. v. 10 min before drug injection. Contractile function was assessed on the basis of percentage segment shortening (%SS). ATP levels were measured in 60-min reperfused hearts. %SS significantly decreased during ischemia, and recovered during reperfusion, although the %SS was significantly less than the pre-ischemic level. Both enalapril at either dose and BIBR-277 significantly enhanced %SS recovery during reperfusion, an effect which was associated with a tendency toward energy preservation. Hoe-140 completely abolished the effect of enalapril at either dose, while it did not modify that of BIBR-277. Inhibition of angiotensin II formation and bradykinin breakdown may be separately related to the improvement of myocardial stunning.

Structure of a kallikrein-like enzyme and its tissue localization in the dog

We previously purified a kallikrein-like enzyme from the dog heart and demonstrated that it is not only able to form kinins but can also convert angiotensin (Ang) I to Ang II. The aim of the present study was to clarify the structure and tissue localization of this enzyme. Western blot analysis of various canine tissues was performed with antiserum against the purified dog heart enzyme. The purified enzyme was subjected to a determination of its amino acid composition and a sequence analysis. Western blotting indicated that this enzyme was present in the heart, aorta, kidney, pancreas, lung, liver, spleen, small intestine, and skeletal muscle. The amino acid composition of the enzyme was different from that of dog urinary kallikrein. Amino acid sequence analysis indicated that it is likely to be N-terminally blocked. The present study showed that this kallikrein-like enzyme is different from previously reported kallikrein and is distributed not only in the heart, but also in other tissues such as the aorta, kidney, lung, liver, spleen, small intestine, and skeletal muscle. This enzyme may exert local effects by generating kinins and Ang II.

Increased expression of mast cell chymase in the lungs of patients with congenital heart disease associated with early pulmonary vascular disease

The molecular mechanism involved in pulmonary vascular disease (PVD) associated with congenital heart disease (CHD) remains uncertain. Evidence suggesting that angiotensin converting enzyme plays an important role in pulmonary vascular pathology led us to hypothesize that mast cell chymase, another angiotensin I converting enzyme, also had the potential to contribute to the development of PVD in CHD. Twenty-three patients 3 mo to 45 yr of age with atrial or ventricular or both septal defects with increased pulmonary arterial blood flow and pressure, with pulmonary vascular resistance ranging from 1.3 to 8.1 units/m(2), were studied. Mast cells and mast cell chymase were immunohistochemically identified in the lung biopsy tissues obtained during corrective surgery. There was a significant difference in numbers of total mast cells between patients (n = 23) and control subjects (n = 10) with normal pulmonary circulation (p < 0.01). Moreover, chymase-containing mast cells in the lung tissues of patients with CHD showed striking differences from those of control subjects. In the patients, 72% of lung mast cells contained chymase, compared with only 15% in control subjects (p < 0.0001). Chymase-containing mast cells predominantly appeared in the media and adventitia of vessel walls. Importantly, angiotensin II was immunohistochemically detected in perivascular lesions where chymase was present, but not in the lesions where chymase was sparsely seen. Furthermore, the number of chymase-containing mast cells was correlated with pulmonary vascular resistance (r = 0.64). These findings suggest a possible role of mast cell chymase in the development of early-stage PVD in patients with CHD.

A new experimental approach in endothelium-dependent pharmacological investigations on isolated porcine coronary arteries mounted for impedance planimetry

1. The aim of this study was to investigate whether the balloon-based impedance planimetry technique could be a useful tool in endothelium-dependent investigations. 2. Porcine large coronary arteries contracted with prostaglandin F2alpha (PGF2alpha, 10 microM) did not relax to bradykinin (0.1 nM - 0.1 microM), but did relax to sodium nitroprusside (SNP, 10 microM). However, after eversion of the segments, bradykinin induced relaxations with pD2 values and maximal responses of 8.78+/-0.09 and 75+/-2% (n=6), respectively. 3. Incubation with captopril (1 microM) did not reveal a relaxation to bradykinin in the normal vessel configuration and had no influence on the concentration-relaxation relationship in everted segments. 4. Lowering the luminal pressure in contracted segments from 131+/-5 mmHg (isometric, n=5) to 60 mmHg (isobaric, n=5) did not facilitate the action of bradykinin. 5. Eversion of segments did not influence the concentration-response relationship for K+ (4.7 - 125 mM), PGF2alpha (0.3 - 30 microM), and SNP (30 nM - 30 microM), although the time-courses of responses were faster when the agents were added from the intimal compared to the adventitial side of the preparation. 6. In the same everted segment contracted with PGF2alpha, the concentration-response relationship for bradykinin was not different under isometric and isobaric conditions. 7. These results indicate that, (1) reduced endothelium-dependent relaxations to adventitially administered substances can be ascribed to a diffusion barrier in the vessel wall, while enzymatic degradation, luminal pressure and precontractile responses seem not to play a role, (2) impedance planimetry applied to everted cylindrical segments could be a useful experimental approach in pharmacological studies of endothelium-dependent responses under isobaric and isometric conditions.

Alternative angiotensin II formation in rat arteries occurs only at very high concentrations of angiotensin I

Contrary to previous reports, recent enzymatic assays showed the predominance of chymase-like activity in rat arteries. We determined the existence and significance of such alternative pathways in rat carotid arteries by measuring contraction of arterial rings in organ baths and blood pressure in conscious rats. Hamster aorta served as a positive control for chymase. Temocapril (30 micromol/L) inhibited the contractions to angiotensin (Ang) I (10(-9) to 10(-5) mol/L) except at high concentrations of Ang I (>10(-7) mol/L). Addition of chymostatin (100 micromol/L) to temocapril exerted a synergistic inhibitory effect. Hamster aorta gave similar results, except that temocapril was 30-fold less effective than in rat arteries. [Pro(11), D-Ala(12)]Ang I (10(-8) to 10(-5) mol/L), a chymase-specific substrate, provoked similar responses in rat and hamster arteries; chymostatin, but not temocapril, attenuated the responses. CV 11974 (30 micromol/L), an Ang II type 1 receptor antagonist, abolished the responses to both peptides. In conscious rats, Ang I (0.03 to 30 microg/kg) and [Pro(11),D-Ala(12)]Ang I (7 to 700 microg/kg) produced similar pressor responses. Not only CV 11974 (1 mg/kg) but also temocapril (2 mg/kg) abolished Ang I-induced responses in vivo. CV 11974, but not temocapril, inhibited responses to [Pro(11), D-Ala(12)]Ang I. Our results showed the presence of the alternative pathway in rat arteries, but it did not play a major role. Arteries with the opposing characteristics of chymase responded equally to [Pro(11),D-Ala(12)]Ang I. These findings suggest that biochemical and [Pro(11),D-Ala(12)]Ang I-derived results may not reflect the functional significance of chymase.

Role of mast cell chymase in angiotensin-induced vascular contraction of hamster cheek pouch microvessels

We investigated the contribution of chymase-dependent conversion of angiotensin I to angiotensin II in hamster cheek pouch. To investigate the converting activities in intact tissues, angiotensin I or II was applied to microvessels of the intact cheek pouch, and the vascular contractile response was recorded. Angiotensin I or angiotensin II (20 nM) induced a rapid contraction of arterioles, irrespective of their diameter. In the presence of I mM captopril, there was no contraction in response to angiotensin I in arterioles < 25 microm in diameter, whereas contraction was still observed in larger arterioles. Chymostatin (100 microM) treatment also reduced the response to angiotensin I in arterioles > 40 microm in diameter. Treatment with 1 mM captopril and 100 microM chymostatin resulted in the loss of response to angiotensin I, but not to angiotensin II, in all arterioles. Treatment of microvessels with 100 microg/ml compound 48/80 enhanced angiotensin I-induced vascular contraction response, suggesting the significance of mast cells as a source of cheek pouch chymase.

Chymase-dependent angiotensin II formation in human vascular tissue

BACKGROUND

Some reports have suggested that, in vitro, human heart chymase in homogenates contributes little to angiotensin (Ang) II formation in the presence of natural protease inhibitors such as alpha-antitrypsin. We studied whether chymase bound to heparin, resembling an in vivo form, could contribute to Ang II formation in the presence of natural protease inhibitors.

METHODS AND RESULTS

The Ang II formation was increased time-dependently after incubation in an extract (1 mg of protein/mL) of human vascular tissues containing Ang I. The concentration of Ang II in the extract after incubation for 30 minutes was 1.67+/-0.06 nmol/mL, and we regarded this quantity of Ang II as 100%. The Ang II formation was inhibited 10%, 95%, and 96% by 1 micromol/L lisinopril, 100 micromol/L chymostatin, and 0.1 g/L alpha-antitrypsin, respectively. The extract was applied to a heparin affinity column. After the column was washed with PBS, the eluted PBS contained a weak Ang II-forming activity, which was completely inhibited by lisinopril. The eluted PBS, to which >0.8 mol/L NaCl had been added, showed a strong Ang II-forming activity which was inhibited by chymostatin and alpha-antitrypsin. After the application of the extract, the column was washed with PBS and then an Ang I solution in PBS was applied to the column. The Ang II formation in the PBS eluted from the incubated column was increased time-dependently. The concentration of Ang II in the PBS (1 mL) eluted from the column after incubation for 30 minutes was 2.56+/-0.28 nmol/mL, and we regarded this quantity of Ang II as 100%. To study the effects of inhibitors, the extract (1 mg of protein/mL) was applied to a heparin affinity column (1 mL) which was preequilibrated with PBS (3 mL); 100 micromol/L chymostatin or 0.1 g/L alpha-antitrypsin in PBS (1 mL) was then applied to the column. After the column was washed with PBS (3 mL), Ang I solution (1 mg/mL) in PBS was applied to the column, and the column was incubated for 30 minutes. The Ang II formation in the PBS eluted from the column was suppressed up to 5% by application of chymostatin, although this was not affected by application of alpha-antitrypsin.

CONCLUSIONS

These findings suggest that human chymase bound to heparin plays a functional role in Ang II formation in the presence of natural protease inhibitors such as alpha-antitrypsin.

Effects of daphnodorin A, daphnodorin B and daphnodorin C on human chymase-dependent angiotensin II formation

We investigated whether daphnodorin A, daphnodorin B and daphnodorin C inhibited human chymase-dependent angiotensin II-forming activity. Although the structures of these compounds are very similar, daphnodorin A completely inhibited angiotensin II formation generated by chymase, while daphnodorin B partially inhibited and daphnodorin C did not. On the other hand, these daphnodorins did not affect angiotensin converting enzyme-dependent angiotensin II formation. Furthermore, these daphnodorins did not inhibit purified human tryptase, which, like chymase, is contained in mast cells. Therefore, daphnodorin A, but not daphnodorin B and daphnodorin C, may specifically inhibit the chymase-dependent angiotensin II formation, and such differences between inhibitory effects of these compounds to human chymase may be useful for the development of human chymase inhibitor.

Relative localization of angiotensin-converting enzyme, chymase and angiotensin II in human coronary atherosclerotic lesions

BACKGROUND

Studies using cell cultures and animal models have indicated an important role for angiotensin II in atherosclerosis. In humans, at least two major enzymes are involved in the conversion of angiotensin I to angiotensin II: so-called angiotensin-converting enzyme (ACE) and chymase. Enhanced activation of chymase in atherosclerotic tissue homogenates has been reported in animal models, but its contribution to the generation of angiotensin II has not been studied.

OBJECTIVE

To clarify the localization of chymase and its pathophysiologic role in the formation of angiotensin II, using human coronary arteries.

DESIGN AND METHODS

Twenty-four coronary artery segments obtained from 14 autopsied patients were characterized histologically into the following categories: normal coronary arteries with diffuse intimal thickening, hypercellular lesions, atheromatous plaques and fibrosclerotic plaques. We compared the cellular localization of chymase, ACE and angiotensin II expression using immunocytochemical techniques.

RESULTS

Chymase was expressed only in the cytosole of mast cells in all segments. On the basis of the histologic study, the number of chymase-positive cells in the intima of atheromatous plaques was significantly higher than that in normal coronary arteries with diffuse intimal thickening. The expression of angiotensin II in the intima was enhanced in hypercellular lesions and atheromatous plaques. Localization of angiotensin II in the intima was associated with that of ACE. Immunodouble staining did not show colocalization of angiotensin II and chymase.

CONCLUSIONS

These results suggest an important role for the production of angiotensin II by ACE in the progression of atherosclerosis in human coronary arteries. Enhanced expression of chymase appears not to be involved in angiotensin II production in the intima.

Angiotensin II type 1 receptor antagonist, TCV-116, prevents neointima formation in injured arteries in the dog

We investigated the effect of an angiotensin (Ang) II antagonist, (+/-)-1-(cyclohexyloxycarbonyloxy)-ethyl 2-ethoxy- 1- [[2'-(1H-tetrazol-5-yl)biphenyl-4-yl]methyl]- 1H-benzimidazole-7-carboxylate (TCV-116), on neointima formation in dog artery injured by a balloon catheter. Dogs were orally treated with 10 mg/kg TCV-116 or placebo twice a day for 5 weeks. After treatment with these drugs for 1 week, the right carotid artery was injured by a balloon catheter. The left carotid artery was regarded as the control. In the group treated with placebo, neointima formation in the injured arteries was observed. The activities of angiotensin converting enzyme (ACE) and chymase in the injured carotid arteries were increased 2.56- and 3.26-fold compared with those in the non-injured arteries, respectively. The neointimal area in dogs treated with placebo and TCV-116 were 0.51 +/-0.07 and 0.21 +/-0.07 mm2, respectively, and this difference was significant. In conclusion, an Ang II antagonist, TCV-116, prevented neointima formation by blocking the action of Ang II generated by both ACE and chymase in the injured arteries.

Tranilast suppresses vascular chymase expression and neointima formation in balloon-injured dog carotid artery

BACKGROUND

Activation of vascular chymase plays a major role in myointimal hypertrophy after vascular injury by augmenting the production of angiotensin (ANG) II. Because chymase is synthesized mainly in mast cells, we assumed that the chymase-dependent ANG II formation could be downregulated by tranilast, a mast cell-stabilizing antiallergic agent. We have assessed inhibitory effects of tranilast on neointima formation after balloon injury in the carotid artery of dogs, which share a similar ANG II-forming chymase with humans, and further explored the pathophysiological significance of vascular chymase.

METHODS AND RESULTS

Either tranilast (50 mg/kg BID) or vehicle was orally administered to beagles for 2 weeks before and 4 weeks after balloon injury. Four weeks after the injury, remarkable neointima was formed in the carotid arteries of vehicle-treated dogs. Chymase mRNA levels and chymaselike activity of vehicle-treated injured arteries were increased 10.2- and 4.8-fold, respectively, those of uninjured arteries. Angiotensin-converting enzyme (ACE) activity was slightly increased in the injured arteries, whereas ACE mRNA levels were not. Tranilast treatment completely prevented the increase in chymaselike activity, reduced the chymase mRNA levels by 43%, and decreased the carotid intima/media ratio by 63%. In vehicle-treated injured arteries, mast cell count in the adventitia showed a great increase, which was completely prevented by the tranilast treatment. Vascular ACE activity and mRNA levels were unaffected by tranilast.

CONCLUSIONS

Tranilast suppressed chymase gene expression, which was specifically activated in the injured arteries, and prevented neointima formation. Suppression of the chymase-dependent ANG II-forming pathway may contribute to the beneficial effects of tranilast.

Characterization of angiotensin II antagonism displayed by SK-1080, a novel nonpeptide AT1-receptor antagonist

The pharmacologic profile of SK-1080, a nonpeptide AT1-selective angiotensin-receptor antagonist, was investigated by receptor-binding studies, functional in vitro assays with rabbit and rat aorta, and in vivo experiments in pithed rats. SK-1080 inhibited the specific binding of [125I]-[Sar1, Ile8]-angiotensin II to human recombinant AT1 receptor with a 12-fold greater potency than losartan [median inhibitory concentration (IC50): 1.01 and 12.3 nM, respectively], but it did not inhibit the binding of [125I]-CGP 42112A to human recombinant AT2 receptor (IC50: >10 microM for both). The Hill coefficient for the competition curve of SK-1080 against AT1 receptor was not significantly different from unity (0.96). Scatchard analysis showed that SK-1080 interacted with human recombinant AT1 receptor in a competitive manner, as with losartan. In functional studies with rat and rabbit aorta, SK-1080 competitively inhibited the contractile response to angiotensin II (pKB values: 9.97 and 9.51, respectively) with 15-25% decrease in the maximal contractile responses, unlike losartan, which showed competitive antagonism without any change in the maximal contractile responses to angiotensin II (pA2 values, 8.02 and 7.59, respectively). In pithed rats, SK-1080 (i.v.) induced a nonparallel right shift in the dose-pressor response curve to angiotensin II (ID50, 0.07 mg/kg) with a dose-dependent reduction in the maximal responses; this antagonistic effect was approximately 25 times more potent than losartan (ID50, 1.74 mg/kg), which showed competitive antagonism. SK-1080 did not alter the responses induced by other agonists such as norepinephrine, KCI, and vasopressin in isolated rabbit aorta and pithed rats. These results suggest that SK-1080 is a highly potent AT1-selective angiotensin II-receptor antagonist with a mode of insurmountable antagonism.