Three-dimensional molecular modeling explains why catalytic function for angiotensin-I is different between human and rat chymases

Chymase inhibitors for the treatment of cardiac diseases: a patent review (2010-2018)

INTRODUCTION

Chymase is primarily found in mast cells (MCs), fibroblasts, and vascular endothelial cells. MC chymase is released into the extracellular interstitium in response to inflammatory signals, tissue injury, and cellular stress. Among many functions, chymase is a major extravascular source for angiotensin II (Ang II) generation. Several recent pre-clinical and a few clinical studies point to the relatively unrecognized fact that chymase inhibition may have significant therapeutic advantages over other treatments in halting progression of cardiac and vascular disease.

AREAS COVERED

The present review covers patent literature on chymase inhibitors for the treatment of cardiac diseases registered between 2010 and 2018.

EXPERT OPINION

Increase in cardiac MC number in various cardiac diseases has been found in pathological tissues of human and experimental animals. Meta-analysis data from large clinical trials employing angiotensin-converting enzyme (ACE) inhibitors show a relatively small risk reduction of clinical cardiovascular endpoints. The disconnect between the expected benefit associated with Ang II blockade of synthesis or activity underscores a greater participation of chymase compared to ACE in forming Ang II in humans. Emerging literature and a reconsideration of previous studies provide lucid arguments to reconsider chymase as a primary Ang II forming enzyme in human heart and vasculature.

Chymase inhibitor prevents the development and progression of non-alcoholic steatohepatitis in rats fed a high-fat and high-cholesterol diet

The effect of the chymase inhibitor TY-51469 on the development and progression of non-alcoholic steatohepatitis (NASH) was evaluated in rats fed a high-fat and high-cholesterol (HFC) diet. To evaluate the preventive effect of TY-51469 on the development of NASH, stroke-prone spontaneously hypertensive rat 5 (SHRSP5)/Dmcr rats were fed either a normal or HFC diet for 8 weeks, and concurrently administered either placebo or TY-51469 (1 mg/kg per day). To evaluate the effect of TY-51469 on the survival rate, TY-51469 was administered either concurrently with HFC diet (pretreated group) or 8 weeks after HFC diet at which point NASH had developed (posttreated group). Eight weeks after HFC diet, significant increases of steatosis, fibrosis and chymase-positive cells were observed in liver from the placebo-treated rats. Significant increases of myeloperoxidase, transforming growth factor-β, matrix metalloproteinase-9, and collagen I mRNA levels were also observed. However, all parameters were significantly attenuated in the TY-51469-treated group. A survival rate of the placebo-treated group fed the HFC diet was 0% at 14 weeks. In comparison, the rates of TY-51469-pretreated and TY-51469-posttreated groups were 100% and 50% at 14 weeks, respectively. Chymase inhibitor may be applicable to preventing the development and progression of NASH.

Chymase inhibition improves vascular dysfunction and survival in stroke-prone spontaneously hypertensive rats

OBJECTIVE

To clarify the role of chymase in hypertension, we evaluated the effect of a chymase inhibitor, TY-51469, on vascular dysfunction and survival in stroke-prone spontaneously hypertensive rats (SHR-SP).

METHODS

SHR-SP were treated with TY-51469 (1 mg/kg per day) or placebo from 4 to 12 weeks old or until death. Wistar-Kyoto rats were used as a normal group.

RESULTS

SBP was significantly higher in both the placebo and TY-51469 groups than in the normal group, but there was no significant difference between the two treatment groups. Plasma renin, angiotensin-converting enzyme activity and angiotensin II levels were not different between the placebo and TY-51469 groups. In contrast, vascular chymase-like activity was significantly higher in the placebo than in the normal group, but it was reduced by TY-51469. Acetylcholine-induced vascular relaxation was significantly higher in the TY-51469 group than in the placebo group. There was significant augmentation of the number of monocytes/macrophages and matrix metalloproteinase-9 activity in aortic tissue from the placebo group compared with the normal group, and these changes were attenuated by TY-51469. There were also significant increases in mRNA levels of monocyte chemoattractant protein-1 and tumor necrosis factor-α in the placebo group that were attenuated by TY-51469. Cumulative survival was significantly prolonged in the TY-51469 group compared with the placebo group.

CONCLUSION

Chymase might play an important role in vascular dysfunction via augmentation both of matrix metalloproteinase-9 activity and monocyte/macrophage accumulation in SHR-SP, and its inhibition may be useful for preventing vascular remodeling and prolonging survival.

Molecular modeling study for inhibition mechanism of human chymase and its application in inhibitor design

Human chymase catalyzes the hydrolysis of peptide bonds. Three chymase inhibitors with very similar chemical structures but highly different inhibitory profiles towards the hydrolase function of chymase were selected with the aim of elucidating the origin of disparities in their biological activities. As a substrate (angiotensin-I) bound crystal structure is not available, molecular docking was performed to dock the substrate into the active site. Molecular dynamics simulations of chymase complexes with inhibitors and substrate were performed to calculate the binding orientation of inhibitors and substrate as well as to characterize conformational changes in the active site. The results elucidate details of the 3D chymase structure as well as the importance of K40 in hydrolase function. Binding mode analysis showed that substitution of a heavier Cl atom at the phenyl ring of most active inhibitor produced a great deal of variation in its orientation causing the phosphinate group to interact strongly with residue K40. Dynamics simulations revealed the conformational variation in region of V36-F41 upon substrate and inhibitor binding induced a shift in the location of K40 thus changing its interactions with them. Chymase complexes with the most active compound and substrate were used for development of a hybrid pharmacophore model which was applied in databases screening. Finally, hits which bound well at the active site, exhibited key interactions and favorable electronic properties were identified as possible inhibitors for chymase. This study not only elucidates inhibitory mechanism of chymase inhibitors but also provides key structural insights which will aid in the rational design of novel potent inhibitors of the enzyme. In general, the strategy applied in the current study could be a promising computational approach and may be generally applicable to drug design for other enzymes.

Chymase inhibition provides pancreatic islet protection in hamsters with streptozotocin-induced diabetes

Angiotensin II may be involved in pancreatic disorganization, but the involvement of chymase has been unclear. In the present study, we examined whether chymase is involved in pancreatic disorganization in hamsters with streptozotocin (STZ)-induced diabetes. Hamsters were injected with streptozotocin (60 mg/kg), and non-injected hamsters served as controls. To investigate the effect of a chymase inhibitor, TY-51469 (30 mg/kg per day), hamsters in the STZ group were administered TY-51469 or placebo from 2 weeks after STZ injection, for 1 week. A significant increase in blood glucose level was observed at 1 week after STZ injection. This was maintained at 2 weeks, and a further significant increase was observed at 3 weeks. Until 2 weeks after STZ injection, all angiotensin II-related enzyme activities were unchanged, but at 3 weeks pancreatic chymase and total angiotensin II-forming activities, but not angiotensin-converting enzyme activity, were significantly increased. TY-51469 significantly attenuated blood glucose level along with reductions of chymase and total angiotensin II-forming activities and malondialdehyde level. Furthermore, there were significantly more pancreatic islets in the TY-51469 group than in the placebo group. In conclusion, chymase inhibition might protect against pancreatic islet disorganization.

Chymase inhibition reduces the progression to heart failure after autoimmune myocarditis in rats

Chymase has been known as a local angiotensin II-generating enzyme in the cardiovascular system in dogs, monkeys, hamsters, and humans; however, recently it was reported that chymase also has various other functions. Therefore, we decided to examine whether the inhibition of chymase improves disease conditions associated with the pathophysiology of dilated cardiomyopathy in rats and its possible mechanism of action as rat chymase is unable to produce angiotensin II. We examined the effect of TY-51469, a novel chymase inhibitor (0.1 mg/kg/day [group CYI-0.1, n = 15] and 1 mg/kg/day [group CYI-1, n = 15]), in myosin-immunized postmyocarditis rats. Another group of myosin-immunized rats was treated with vehicle (group V, n = 15). Age-matched normal rats without immunization (group N, n = 10) were also included in the study. After 4 weeks of treatment, we evaluated cardiac function; area of fibrosis; fibrogenesis; levels of transforming growth factor (TGF)-beta1 and collagen III; hypertrophy and its marker, atrial natriuretic peptide (ANP); and mast cell activity. Survival rate and myocardial functions improved dose-dependently with chymase inhibitor treatment after myosin immunization. A reduction in the percent area of myocardial fibrosis, fibrogenesis, myocardial hypertrophy, and mast cell activity along with a reduction in TGF-beta1, collagen III, and ANP levels in the myocardium were noted in postmyocarditis rats that received chymase inhibitor treatment. The treatment also decreased myocardial aldosterone synthase levels in those animals. Inhibition of chymase reduces the pathogenesis of postmyocarditis dilated cardiomyopathy and progression to heart failure by preventing the pathological remodeling and residual inflammation in rats.

The extended cleavage specificity of the rodent beta-chymases rMCP-1 and mMCP-4 reveal major functional similarities to the human mast cell chymase

In rat and mouse the phylogenetic homologues of the human mast cell alpha-chymase (rMCP-5 and mMCP-5) have lost their chymase activity and instead become elastases. To investigate whether rodents hold enzymes with equivalent function as the primate alpha-chymases, we have determined the extended cleavage specificity of the major connective tissue mast cell beta-chymases in rat and mouse, rMCP-1 and mMCP-4. By using a phage display approach we determined the enzyme/substrate interaction in seven positions, both N- and C-terminal of the cleaved bond. The two proteases were found to display rather similar specificities. Both enzymes prefer Phe in position P1, and aliphatic amino acids are favoured N-terminal of the cleaved bond, i.e. Leu in P2 and Val in P3 and P4. Val and Leu are overrepresented also in positions P1' and P3'. The two enzymes differ clearly only in one position, the P2' residue, where mMCP-4 strongly prefers negatively charged amino acids while rMCP-1 favours Ser. Interestingly, Asp and Glu are often present in position P2' of known substrates for the human chymase. Overall, these two rodent beta-chymases have very similar amino acid preferences as the human chymase, particularly mMCP-4, which most likely have a very similar function as the human chymase. This finding indicates that rodent and primate connective tissue mast cells seem to have relatively similar proteolytic repertoires, although they express different sets of serine proteases.

Expression profile of novel members of the rat mast cell protease (rMCP)-2 and (rMCP)-8 families, and functional analyses of mouse mast cell protease (mMCP)-8

Four hematopoietic serine proteases are common to the mast cell chymase locus of all analyzed mammals: alpha-chymase, cathepsin G, granzyme B, and granzyme C/H. Apart from these common genes, the mouse and rat loci hold additional granzyme-, beta-chymase-, and Mcpt8-like genes. To better understand the functional consequences of these additional enzymes and to be able to compare human and rodent immune functions, we have analyzed the expression of novel beta-chymase- and Mcpt8-like genes in the rat. Four novel genes, i.e., Mcpt2-rs2a, Mcpt2-rs2c, Mcpt8-rs1, and Mcpt8-rs4 were transcribed in tissues holding mucosal mast cells (MMC), where also the classical MMC protease Mcpt2 was expressed. We also found transcripts of rat vascular chymase (rVch) in some of these tissues. RVch is a beta-chymase that converts angiotensin I, like the human chymase. Rat MMC may therefore have similar angiotensin-converting properties as chymase-positive human mast cells, although these are mostly regarded the counterpart of rat connective tissue mast cells. The human mast cells that are considered the counterpart of rat MMC express, however, only tryptase, whereas rat MMC express various proteases, but no tryptase. We further studied the proteolytic activity of mMCP-8 as a first representative for the Mcpt8-subfamily. Based on sequence comparison and molecular modeling, mMCP-8 may prefer aspartic acid in substrate P1 position. However, we could not detect hydrolysis of chromogenic substrates or phage-displayed random nonapeptides despite numerous trials. On the other hand, we have obtained evidence that the function of the Mcpt8-like proteases depends on proteolytic activity. Namely, the expression of the only Mcpt8-family member with a mutation in the catalytic triad, Mcpt8-rs3, was strongly reduced. Thus, the substrate specificity of mMCP-8 may be too narrow to be detected with the employed methods, or the enzyme may require a substrate conformation that is not provided by the analyzed peptides.

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

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

[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.

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.

Effects of ACE inhibition and angiotensin II type 1 receptor blockade on cardiac function and G proteins in rats with chronic heart failure

1. Inhibition of the renin-angiotensin system (RAS) improves symptoms and prognosis in heart failure. The experimental basis for these benefits remains unclear. We examined the effects of inhibition of ACE or blockade of angiotensin II type 1 (AT1) receptor on the haemodynamics, cardiac G-proteins, and collagen synthesis of rats with coronary artery ligation (CAL), a model in which chronic heart failure (CHF) is induced. 2. Rats were orally treated with the ACE inhibitor trandolapril (3 mg kg(-1) day(-1)) or the AT1 receptor blocker L-158809 (1 mg kg(-1) day(-1)) from the 2nd to 8th week after CAL. CAL resulted in decreases in the left ventricular systolic pressure and its positive and negative dP/dt, an increase in the left ventricular end-diastolic pressure, and the rightward shift of the left ventricular pressure-volume curve. Long-term treatment with either drug improved these signs of CHF to a similar degree. 3. Cardiac Gsalpha and Gqalpha protein levels decreased, whereas the level of Gialpha protein increased in the animals with CHF. Long-term treatment with trandolapril or L-158809 attenuated the increase in the level of cardiac Gialpha protein of the animals with CHF without affecting Gsalpha and Gqalpha protein levels. Cardiac collagen content of the failing heart increased, whose increase was blocked by treatment with either drug. 4. Exogenous angiotensin I stimulated collagen synthesis in cultured cardiac fibroblasts, whose stimulation was attenuated by either drug. 5. These results suggest that blockade of the RAS, at either the receptor level or the synthetic enzyme level, may attenuate the cardiac fibrosis that occurs after CAL and thus affect the remodelling of the failing heart.

Inhibitory Mechanism of Daphnodorins for Human Chymase

We investigated the inhibitory mechanisms of daphnodorins for human chymase using three-dimensional molecular modeling. In daphnodorin A-human chymase complex, daphnodorin A was fixed to the active site via hydrogen bonds with Ala177, Phe29, and Gly199 in human chymase, and it formed hydrogen bonds with Ser182 and Gly180, and this complex was formed stably. In daphnodorin B-human chymase complex, daphnodorin B formed hydrogen bonds with Lys28 and Phe29 in human chymase, but it could not form hydrogen bonds with Gly199, Ala177, and Lys179. The phenyl group of daphnodorin B shifted from the P1 hole in human chymase in comparison with that of daphnodorin A. For the inhibition of human chymase by daphnodorins, we indicated that it was significant whether daphnodorins formed hydrogen bonds with Ala177 located in the P1 hole, Ser182 located in the active site, Gly180 located in the anion hole, and with Gly199, Phe29, and Lys28 in human chymase.

Functional reconstitution of an active recombinant human chymase from Pichia pastoris cell lysate

We have previously reported efficient production of mature human chymase (h-chymase) using an original system of expression in Pichia pastoris (Nakakubo et al., 2000), whereby recombinant h-chymase (rh-chymase) was secreted as a mature form with the correct N-terminal amino acid sequence and was easily purified. In the course of investigation of secretory rh-chymase, we also found large amounts of chymase to be present in insoluble form in the transformant cell. Although the cellular rh-chymase had no proteolytic activity, its chymotryptic activity was restored in a reconstitution process utilizing guanidine and glutathione. As with secretory rh-chymase, efficient purification was possible by heparin affinity chromatography. The purified cellular rh-chymase showed the same mobility as secretory rh-chymase in sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) before and after deglycosylation. N-terminal amino acid sequence analysis revealed that the signal peptide had been correctly removed. K(m) value (5.93 mM), as well as pH profile and inhibition profile toward protease inhibitors of reconstituted cellular rh-chymase, indicated that the rh-chymase enzymatically closely resembles native h-chymase. Furthermore, it showed a greatly restricted proteolytic activity towards Ang I, and formed Ang II without the further cleavage which is a feature of h-chymase. It was thus found that the insoluble rh-chymase stored in the cells could be solubilized and reconstituted to give the same structure as h-chymase, not only in terms of enzyme active site but also of substrate recognition site.

Angiotensin II generation by mast cell alpha- and beta-chymases

Mast cells secrete alpha- and beta-chymases. Primate alpha-chymases generate angiotensin (AT) II by selectively hydrolyzing AT I's Phe(8)-His(9) bond. This is distinct from the AT converting enzyme (ACE) pathway. In humans, alpha-chymase is the major non-ACE AT II-generator. In rats, beta-chymases destroy AT II by cleaving at Tyr(4)-Ile(5). Past studies predicted that AT II production versus destruction discriminates alpha- from beta-chymases and that Lys(40) in the substrate-binding pocket determines alpha-chymase Phe(8) specificity. This study examines these hypotheses by comparing AT II generation by human alpha-chymase (containing Lys(40)), dog alpha-chymase (lacking Lys(40)), and mouse mMCP-4 (a beta-chymase lacking Lys(40); orthologous to AT II-destroying rat chymase rMCP-1). The results suggest that human and dog alpha-chymase generate AT II exclusively and with comparable efficiency, although dog chymase contains Ala(40) rather than Lys(40). Furthermore, AT II is the major product generated by degranulation supernatants from cultured dog mast cells, which release tryptases and dipeptidylpeptidase as well as alpha-chymase. In contrast to rMCP-1, mMCP-4 beta-chymase readily generates AT II. Although there is competing AT I hydrolysis at Tyr(4), mMCP-4 does not destroy AT II quickly once it is formed. We conclude (1) that chymases are the dominant AT I-hydrolyzing mast cell peptidases, (2) that residues other than Lys(40) are key determinants of alpha-chymase AT I Phe(8) specificity, (3) that beta-chymases can generate AT II, and (4) that alpha- and beta-chymases are not strictly dichotomous regarding AT I cleavage specificity.

Secretory production of recombinant human chymase as an active form in Pichia pastoris

We succeeded in expressing in a Pichia pastoris (P. pastoris) host a cDNA encoding a mature human chymase (h-chymase) which was secreted directly into the culture medium. Recombinant human heart chymase (rh-chymase) was purified from the culture medium via a single one-step heparin-agarose column chromatography tracing, using succinyl-Ala-Ala-Pro-Phe-para-nitroanilide (Suc-AAPF-pNA) hydrolysing activity. On SDS-polyacrylamide gel electrophoresis (SDS-PAGE), the rh-chymase showed a diffused protein band with molecular weight of 32-37 kDa. After deglycosylation, however, rh-chymase changed to a sharp protein band with molecular weight 28 kDa, which is equal in size to deglycosylated h-chymase. The rh-chymase had an activity to convert one of the natural substrates, angiotensin I, to angiotensin II. Double reciprocal plot analysis revealed that the K(m) value ofrh-chymase against Suc-AAPF-pNA was approximately 5.1 mM, which is close to that of purified h-chymase.

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.

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.

Lack of effect of carbohydrate depletion on some properties of human mast cell chymase

Human chymase from vascular tissues was purified to homogeneity by heparin affinity and gel filtration chromatography. Treatment of human chymase with endoglycosidase F resulted in cleavage of the carbohydrate moiety yielding a deglycosylation product that did not lose its catalytic activity. This enzymatic deglycosylation product was enough to explore possibilities that N-glycan might modify some properties of human chymase. Substrate specificity, optimum pH and the elution profile from the heparin affinity gel were not affected by the deglycosylation. Only a slight but significant difference was observed in the Km value for conversion of angiotensin I to angiotensin II. Other kinetic constants such as kcat were not influenced. The kinetics of conversion of big endothelin-1 to endothelin-1(1-31) were not significantly affected. The deglycosylated human chymase was more susceptible to deactivation under alkaline pH and thermal stress. Even at physiological temperature and pH, the activity of glycosylated human chymase was more stable. From these results, it appears that the N-glycan of human chymase contributes to the stability of this enzyme but not to its functional properties.

Contractile effects by intracellular angiotensin II via receptors with a distinct pharmacological profile in rat aorta

1. We studied the effect of intracellular angiotensin II (Ang II) and related peptides on rat aortic contraction, whether this effect is pharmacologically distinguishable from that induced by extracellular stimulation, and determined the Ca2+ source involved. 2. Compounds were delivered into the cytoplasm of de-endothelized aorta rings using multilamellar liposomes. Contractions were normalized to the maximum obtained with phenylephrine (10(-5) M). 3. Intracellular administration of Ang II (incorporation range: 0.01-300 nmol mg(-1)) resulted in a dose-dependent contraction, insensitive to extracellular administration (10(-6) M) of the AT1 receptor antagonist CV11947, the AT2 receptor antagonist PD 123319, or the non-selective AT receptor antagonist and partial agonist saralasin ([Sar1,Val5,Ala8]-Ang II (P<0.05). 4. Intracellular administration of CV11947 or PD 123319 right shifted the dose-response curve about 1000 fold or 20 fold, respectively. PD 123319 was only effective if less than 30 nmol mg(-1) Ang II was incorporated. 5. Contraction was partially desensitized to a second intracellular Ang II addition after 45 min (P<0.05). 6. Intracellular administration of Ang I and saralasin also induced contraction (P<0.05). Both responses were sensitive to intracellular CV11947 (P<0.05), but insensitive to PD 123319. The response to Ang I was independent of intracellular captopril. 7. Contraction induced by extracellular application of Ang II and of Ang I was abolished by extracellular pre-treatment with saralasin or CV11947 (P<0.05), but not with PD 123319. Extracellular saralasin induced no contraction. 8. Intracellular Ang II induced contraction was not affected by pre-treatment with heparin filled liposomes, but completely abolished in Ca2+-free external medium. 9. These results support the existence of an intracellular binding site for Ang II in rat aorta. Intracellular stimulation induces contraction dependent on Ca2+-influx but not on Ins(1,4,5)P3 mediated release from intracellular Ca2+-stores. Intracellular Ang I and saralasin induce contraction, possibly via the same binding site. Pharmacological properties of this putative intracellular receptor are clearly different from extracellular stimulated AT1 receptors or intracellular angiotensin receptors postulated in other tissue.