Effect of Chymase Inhibition on the Arteriovenous Fistula Stenosis in Dogs

A snapshot of early venous remodeling in a 7-day-old arteriovenous fistula

Early remodeling of the arteriovenous fistula (AVF) determines maturation outcomes. However, the cellular response of the venous wall early after AVF creation remains largely enigmatic because of the lack of venous biopsies obtained shortly after anastomosis. This report presents a detailed immunohistochemistry analysis of a pre-access cephalic vein and the resulting seven-day-old AVF that required ligation due to steal syndrome. We test for markers of mature and progenitor endothelial cells (CD31, CD34, VWF), contractile smooth muscle cells and myofibroblasts (MYH11, SMA), and immune cell populations (CEACAM8, CD3, CD20, CD11b, CD45, CD68, CD163, tryptase). We demonstrated near complete endothelial coverage of the fistula at 7 days, a high degree of wall neovascularization, pronounced loss of myofibroblasts and smooth muscle cells, and significant infiltration of mast cells, neutrophils, monocytes, and macrophages. Of interest, the presence of CD163+ macrophages in the AVF suggests a reactive response to increased intramural oxygenation. In conclusion, these images provide for the first time a glimpse of early remodeling in a human AVF by immunohistochemistry. This case demonstrates the possibility to obtain additional precious samples of this early stage through future multicenter collaborative efforts.

Tryptase-Positive Mast Cells Promote Adipose Fibrosis in Secondary Lymphedema through PDGF

Lymphedema is a chronic and progressive condition that causes physical disfigurement and psychological trauma due to the accumulation of lymphatic fluid in the interstitial space. Once it develops, lymphedema is difficult to treat because it leads to the fibrosis of adipose tissue. However, the mechanism behind this remains unclear. The purpose of this study was to investigate the involvement of mast cells (MCs) in the adipose tissues of patients with lymphedema. We found that fibrosis spread through blood vessels in the adipose tissues of lymphedema patients, and the expression of the collagen I and III genes was significantly increased compared to that of those in normal adipose tissue. Immunostaining of vimentin and α-smooth muscle actin showed that fibroblasts were the main cellular components in severely fibrotic regions. Toluidine blue staining confirmed a significant increase in the number of MCs in the adipose tissues of lymphedema patients, and immunostaining of serial sections of adipose tissue showed a significant increase in the number of tryptase-positive cells in lymphedema tissues compared with those in normal adipose tissues. Linear regression analyses revealed significant positive correlations between tryptase and the expressions of the TNF-α, platelet-derived growth factor (PDGF)-A, and PDGFR-α genes. PDGF-A-positive staining was observed in both fibroblasts and granules of tryptase-positive MCs. These results suggest that MC-derived tryptase plays a role in the fibrosis of adipose tissue due to lymphedema directly or in cooperation with other mediators.

Increased Chymase-Positive Mast Cells in High-Grade Mucoepidermoid Carcinoma of the Parotid Gland

It has long been known that high-grade mucoepidermoid carcinoma (MEC) has a poor prognosis, but the detailed molecular and biological mechanisms underlying this are not fully understood. In the present study, the pattern of chymase-positive mast cells, as well as chymase gene expression, in high-grade MEC was compared to that of low-grade and intermediate-grade MEC by using 44 resected tumor samples of MEC of the parotid gland. Chymase expression, as well as chymase-positive mast cells, was found to be markedly increased in high-grade MEC. Significant increases in PCNA-positive cells and VEGF gene expression, as well as lymphangiogenesis, were also confirmed in high-grade MEC. Chymase substrates, such as the latent transforming growth factor-beta (TGF-β) 1 and pro-matrix metalloproteinase (MMP)-9, were also detected immunohistologically in high-grade MEC. These findings suggested that the increased chymase activity may increase proliferative activity, as well as metastasis in the malignant condition, and the inhibition of chymase may be a strategy to improve the poor prognosis of high-grade MEC of the parotid gland.

Activation of Mast-Cell-Derived Chymase in the Lacrimal Glands of Patients with IgG4-Related Ophthalmic Disease

The purpose of this present study was to investigate the distribution and expression of chymase in the lacrimal glands (LGs) of patients afflicted with IgG4-related ophthalmic disease (IgG4-ROD). LGs from patients with severe canalicular obstruction were considered the control group. Toluidine blue staining confirmed a significant increase in the number of mast cells in the LGs obtained from the IgG4-ROD patients. In addition, immunostaining of serial sections from the LGs showed a significant increase in the number of chymase-positive cells and tryptase-positive cells in the IgG4-ROD LGs compared to the normal control LGs. The mRNA expression of chymase, tryptase, TGF-β1, and collagen-I tended to increase in the IgG4-ROD LGs. Immunostaining of vimentin and α-smooth muscle actin (α-SMA) showed that myofibroblasts were the main cellular components in severely fibrotic regions of LGs in patients with IgG4-ROD. Linear regression analyses on the number of mast cells, chymase-positive cells, and tryptase-positive cells revealed significant positive correlations between those respective cells. Our findings suggest that chymase may play a role in the fibrotic disorder of IgG4-ROD LGs through the regulation of TGF-β1 activation and collagen-I deposition, and that it may be a therapeutic target for patients afflicted with IgG4-ROD.

Increase in Chymase-Positive Mast Cells in Recurrent Pleomorphic Adenoma and Carcinoma Ex Pleomorphic Adenoma of the Parotid Gland

Incomplete excision of pleomorphic adenoma (PA) may result in recurrent pleomorphic adenoma (RPA). Furthermore, long-term neglected PA may become carcinoma ex pleomorphic adenoma (CXPA). In the present study, the relationships between mast cell-derived chymase and these tumors were examined. The tumor tissues of PA consisted of either or both glandular and fibrotic structures. Histological features of RPA were almost similar to those of PA, except that they showed multinodular structures. CXPA is composed of a mixture of PA and carcinoma. The main stromal cells in PA were myofibroblasts, whereas fibroblasts constituted the main cellular portion in the stromal tissue of RPA. Cancer-associated fibroblasts (CAFs) were present abundantly in CXPA. With increased VEGF expression, neovascularization tended to increase in RPA or CXPA. Compared with PA, chymase-positive mast cells, as well as chymase gene expression, were increased in the tumor tissues from patients with RPA or CXPA. SCF, TGFβ1, and PCNA-positive staining was widely observed in these tumor tissues. The above results suggest that mast cell-derived chymase through its direct or cooperative effects with other mediators may participate in the pathophysiology of RPA and CXPA.

Possible Roles of Periostin in the Formation of Hemodialysis Vascular Access Stenosis after Polytetrafluoroethylene Graft Implantation in Dogs

Periostin, a recently found matricellular protein, has been implicated in neointima formation after balloon injury. However, the relationship between periostin and hyperplastic intima formation after PTFE graft implantation is unclear. Under mixed anesthesia, PTFE grafts were implanted between the canine carotid artery and jugular vein, and PTFE graft samples were harvested 1, 2, and 4 months after implantation. Intima formation started on the luminal surface of PTFE grafts at the venous anastomotic region 1 month after implantation. Thereafter, the increase in intimal volume was not only observed in the venous and arterial anastomotic regions, but also in the middle region of the PTFE grafts. In accordance with the increased intimal formation, time-dependent increases in mRNA expressions of periostin and transforming growth factor beta 1 (TGF-β1), as well as a strong positive correlation between periostin and TGF-β1, were observed. These findings suggest that periostin may play a very important role in the pathogenesis of hemodialysis vascular access stenosis through the acceleration of intimal formation. Thus, periostin may be a very important therapeutic target for the treatment of vascular access graft dysfunction in hemodialysis patients.

Decrease in number of mast cells in resected nasal polyps as an indicator for postoperative recurrence of chronic rhinosinusitis

Background

In the clinical setting, chronic rhinosinusitis with nasal polyps (CRSwNP) is usually divided into eosinophilic‐CRS (ECRS) and non‐ECRS (NECRS) in Japan. Patients with the former are believed to be at risk for postoperative recurrence of CRS. However, some patients have been missed according to these phenotypic classifications due to the low number of infiltrating eosinophils in polyp tissues.

Objective

In the present study, we attempted to identify cellular or molecular candidate markers to predict nasal polyp recurrence.

Methods

Nasal polyps were collected from 32 patients with CRSwNP who had undergone an endoscopic sinus surgery. These patients were divided into ECRS and NECRS groups in accordance with the Japanese Epidemiological Survey of Refractory Eosinophilic Chronic Rhinosinusitis (JESREC) scoring system and the number of eosinophils in polyp tissues. Unclassifiable patients were referred to as the unknown group.

Results

Eosinophil infiltration in resected nasal polyps was most evident in the ECRS group. However, the number of mast cells and tryptase‐positive cells in nasal polyps were significantly lower in ECRS and unknown groups compared with the NECRS group. A significant positive correlation was detected between the JESREC score and number of eosinophils. The numbers of mast cells and tryptase‐positive cells were negatively correlated with the JESREC score in all included samples. Significant positive correlations were detected between the number of transforming growth factor β1‐positive cells and the number of mast cells, tryptase‐positive cells, and chymase‐positive cells mast cells.

Conclusions and clinical relevance

These findings indicated that the enumeration of mast cells in resected polyps may be another approach to predict postoperative polyp recurrence in CRSwNP patients.

Interleukin-9 mediates chronic kidney disease-dependent vein graft disease: a role for mast cells

Aims

Chronic kidney disease (CKD) is a powerful independent risk factor for cardiovascular events, including vein graft failure. Because CKD impairs the clearance of small proteins, we tested the hypothesis that CKD exacerbates vein graft disease by elevating serum levels of critical cytokines that promote vein graft neointimal hyperplasia.

Methods and results

We modelled CKD in C57BL/6 mice with 5/6ths nephrectomy, which reduced glomerular filtration rate by 60%, and we modelled vein grafting with inferior-vena-cava-to-carotid interposition grafting. CKD increased vein graft neointimal hyperplasia four-fold, decreased vein graft re-endothelialization two-fold, and increased serum levels of interleukin-9 (IL-9) five-fold. By quantitative immunofluorescence and histochemical staining, vein grafts from CKD mice demonstrated a ∼two-fold higher prevalence of mast cells, and a six-fold higher prevalence of activated mast cells. Concordantly, vein grafts from CKD mice showed higher levels of TNF and NFκB activation, as judged by phosphorylation of NFκB p65 on Ser536 and by expression of VCAM-1. Arteriovenous fistula veins from humans with CKD also showed up-regulation of mast cells and IL-9. Treating CKD mice with IL-9-neutralizing IgG reduced vein graft neointimal area four-fold, increased vein graft re-endothelialization ∼two-fold, and reduced vein graft total and activated mast cell levels two- and four-fold, respectively. Treating CKD mice with the mast cell stabilizer cromolyn reduced neointimal hyperplasia and increased re-endothelialization in vein grafts. In vitro, IL-9 promoted endothelial cell apoptosis but had no effect on smooth muscle cell proliferation.

Conclusion

CKD aggravates vein graft disease through mechanisms involving IL-9 and mast cell activation.

Perivascular mast cells regulate vein graft neointimal formation and remodeling

Objective. Emerging evidence suggests an important role for mast cells in vein graft failure. This study addressed the hypothesis that perivascular mast cells regulate in situ vascular inflammatory and proliferative responses and subsequent vein graft neointimal lesion formation, using an optimized local mast cell reconstitution method.

Methods and Results. Neointimal hyperplasia was induced by insertion of a vein graft into the right carotid artery in wild type and mast cell deficient Kit^{W−sh/W−sh} mice. In some experiments, mast cells were reconstituted systemically (tail vein injection of bone marrow-derived mast cells) or locally (directly into the right neck area) prior to vein grafting. Vein graft neointimal lesion formation was significantly (P < 0.05) reduced in Kit^{W−sh/W−sh} mice. Mast cell deficiency reduced the number of proliferating cells, and inhibited L-selectin, CCL2, M-CSF and MIP-3α expression in the vein grafts. Local but not systemic mast cell reconstitution restored a perivascular mast cell population that subsequently promoted neointimal formation in mast cell deficient mice.

Conclusion. Our data demonstrate that perivascular mast cells play a key role in promoting neointima formation by inducing local acute inflammatory and proliferative responses. These results suggest that ex vivo intraoperative targeting of mast cells may have therapeutic potential for the prevention of pathological vein graft remodeling.

Mast cells and vascular diseases

Mast cells are increasingly being recognized as effector cells in many cardiovascular conditions. Many mast-cell-derived products such as tryptase and chymase can, through their enzymic action, have detrimental effects on blood vessel structure while mast cell-derived mediators such as cytokines and chemokines can perpetuate vascular inflammation. Mice lacking mast cells have been developed and these are providing an insight into how mast cells are involved in cardiovascular diseases and, as knowledge increase, mast cells may become a viable therapeutic target to slow progression of cardiovascular disease.

Increased plasma chymase concentration and mast cell chymase expression in venous neointimal lesions of patients with CKD and ESRD

The underlying inflammatory component of chronic kidney disease may predispose blood vessels to intimal hyperplasia (IH), which is the primary cause of dialysis access failure. We hypothesize that vascular pathology and markers of IH formation are antecedent to arteriovenous (AV) fistula creation. Blood, cephalic, and basilic vein segments were collected from predialysis chronic kidney disease (CKD) patients with no previous AV access and patients with end-stage renal disease (ESRD). Immunohistochemistry was performed with antibodies against mast cell chymase, transforming growth factor-beta (TGF-β) and interleukin-6 (IL-6), which cause IH. Plasma chymase was measured by ELISA. IH was present in 91% of CKD and 75% of ESRD vein segments. Chymase was abundant in vessels with IH, with the greatest expression in intima and medial layers, and virtually absent in the controls. Chymase colocalized with TGF-β1 and IL-6. Plasma chymase concentration was elevated up to 33-fold in patients with CKD versus controls and was associated with increased chymase in vessels with IH. We show that chymase expression in vessels with IH corresponds with plasma chymase concentrations. As chymase inhibition attenuates IH in animal models, and we find chymase is highly expressed in IH lesions of patients with CKD and ESRD, we speculate that chymase inhibition could have therapeutic value in humans.

"Venopathy" at work: recasting neointimal hyperplasia in a new light

Hemodialysis vascular access is a unique form of vascular anastomosis. Although it is created in a unique disease state, it has much to offer in terms of insights into venous endothelial and anastomotic biology. The development of neointimal hyperplasia (NH) has been identified as a pathologic entity, decreasing the lifespan and effectiveness of hemodialysis vascular access. Subtle hints and new data suggest a contrary idea-that NH, to some extent an expected response, if controlled properly, may play a beneficial role in the promotion of maturation to a functional access. This review attempts to recast our understanding of NH and redefine research goals for an evolving discipline that focuses on a life-sustaining connection between an artery and vein.

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

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

Chymase inhibitor prevents the nonalcoholic steatohepatitis in hamsters fed a methionine- and choline-deficient diet

AIM

Mast cells may be involved in the pathogenesis of nonalcoholic steatohepatitis (NASH). The mast cell protease chymase contributes to the formation of angiotensin II and matrix metalloproteinase (MMP)-9, both of which are intimately involved in liver fibrosis. Therefore, we hypothesized that chymase plays an important role in the development of NASH.

METHODS

Hamsters were fed a methionine- and choline-deficient (MCD) diet for 8 weeks. These animals were divided into two groups and received either TY-51469 (1 mg/kg per day) or placebo. A third group was fed a normal diet as a control.

RESULTS

Total plasma bilirubin, triglycerides, and hyaluronic acid levels were significantly higher in the MCD diet-fed hamsters than in the normal diet-fed hamsters, but the levels were significantly lower in chymase inhibitor-treated MCD diet-fed hamsters than in placebo-treated MCD diet-fed hamsters. Using histological analysis, marked steatosis and fibrosis were observed in MCD diet-fed hamsters, but these changes were significantly attenuated by treatment with the chymase inhibitor. Increases in mast cells and chymase-positive cells were observed in the liver after the MCD diet, but the increases disappeared in the chymase inhibitor-treated group. The significant increase observed in chymase activity in liver tissue extract from the MCD diet-fed group was also reduced by treatment with the chymase inhibitor. Chymase inhibition significantly reduced not only angiotensin II expression but also matrix metallopeptidase 9 activity in MCD diet-fed hamsters.

CONCLUSION

These findings demonstrate that the mast cell protease chymase may play a crucial role in the development of NASH in hamsters.

The extended substrate recognition profile of the dog mast cell chymase reveals similarities and differences to the human chymase

Human chymase (HC) constitutes a major granule protease in one of the two human mast cell (MC) types. The main biological role of this haematopoietic serine protease is probably not yet known, although it has been implicated in a large number of functions. Dogs, like humans, have only one chymase. This enzyme is closely related to its human homologue, and the MC subtypes of human and dog appear to be similar as well. Therefore, the functions of the dog chymase (DC) may closely reflect the functions of the HC. Moreover, dogs may serve as good models for studies of human MC functions and MC-related diseases. To reveal functional similarities and differences between the DC and HC, we have determined the extended cleavage specificity of the DC by substrate phage display. This method allows the simultaneous permutation of primed and unprimed substrate positions. The DC was found to have very similar preferences to its human counterpart for substrate positions P1, P3, P4 and P3', whereas their preferences differ at positions P2, P1' and P2'. Therefore, the HC and DC may have co-evolved with a substrate where positions P1, P3, P4 and P3' are conserved between dogs and humans, whereas positions P2 and P1' are not and P2'differs to a minor extent. The differences observed between these two enzymes suggest that results obtained from dog models cannot be directly extrapolated to human clinical settings but need to be evaluated carefully concerning potential differences in substrate preferences.

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

AIM

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

METHODS

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

RESULTS

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

CONCLUSION

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

Significance of angiotensin II receptor blockers with high affinity to angiotensin II type 1 receptors for vascular protection in rats

Angiotensin II receptor blockers (ARBs) vary in their binding affinities to angiotensin II type 1 (AT(1)) receptors in in vitro experiments. We compared a high-affinity ARB, olmesartan, and a low-affinity ARB, valsartan, in terms of their vascular protective effects in stroke-prone spontaneously hypertensive rats (SHR-SP). Blood pressure was equally reduced by placebo, olmesartan (1 mg kg(-1)) and valsartan (3 mg kg(-1)) daily for 2 weeks. In another experiment, 12-week-old SHR-SP were fed 8% salt, and olmesartan (1 mg kg(-1)), valsartan (3 mg kg(-1)) or placebo were administered daily until a survival rate of 60% was reached. In the experiment using SHR-SP, the reduction of acetylcholine-induced vascular relaxation and the increase of p22(phox) expression in the placebo-treated group were significantly attenuated by olmesartan and valsartan, but this attenuation was significantly greater for olmesartan. In immunohistological analysis, all areas positive for angiotensin II, p22(phox) and 4-hydroxy-2-nonenal were significantly reduced by olmesartan and valsartan, but again this reduction was significantly greater for olmesartan. In salt-loaded SHR-SP, the number of days to reach a 60% survival rate was 25 and 42 in placebo and valsartan-treated rats, respectively, and this represented a significant difference. The survival rate in olmesartan-treated rats was 95% at day 42, when valsartan-treated rats reached 60% survival, and this difference was also significant. In the surviving rats, olmesartan, but not valsartan, augmented acetylcholine-induced vascular relaxation and attenuated vascular p22(phox) expression. Thus, heterogeneity in binding affinity to AT(1) receptors among ARBs may result in different degrees of vascular protection and lifespan extension.

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

AIM

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

METHODS

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

RESULTS

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

CONCLUSION

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

Possible roles of mast cell-derived chymase for skin rejuvenation

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

Mast Cell Proteases

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

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

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

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.

Significance of Angiotensin II Receptor Blocker Lipophilicities and Their Protective Effect against Vascular Remodeling

Although the lipophilicities of the various angiotensin II receptor blockers (ARBs) are very different, the relationship between lipophilicity and the protective effect against vascular remodeling is unclear. In this study, we compared the protective effects of a highly lipophilic ARB, telmisartan, and an ARB with low lipophilicity, losartan, on vascular function and oxidative stress in stroke-prone spontaneously hypertensive rats (SHR-SP). SHR-SP received oral placebo, 1 mg/kg telmisartan, or 10 mg/kg losartan for 2 weeks. The blood pressure (BP) in SHR-SP was significantly higher than that in Wistar-Kyoto (WKY) rats before treatment, and the BP was reduced equally in telmisartan- and losartan-treated SHR-SP compared to placebo-treated SHR-SP. Acetylcholine-induced vasorelaxation in isolated carotid arteries was significantly weaker in SHR-SP than in WKY rats, but in both telmisartan- and losartan-treated SHR-SP, acetylcholine-induced vasorelaxation was significantly higher than in placebo-treated SHR-SP. Moreover, acetylcholine-induced vasorelaxation in telmisartan-treated rats was significantly stronger than in losartan-treated SHR-SP. The expression of the endothelial nitric oxide synthase gene was significantly higher in telmisartan- and losartan-treated rats than in placebo-treated SHR-SP, and was significantly higher in telmisartan-treated rats than in losartan-treated rats. In contrast, the expression of the NAD(P)H oxidase subunit p22phox gene in telmisartan-treated SHR-SP was significantly lower than that in losartan-treated SHR-SP. Immunohistochemistry showed that angiotensin II expression in the aorta was significantly lower in telmisartan-treated SHR-SP than in losartan-treated SHR-SP. In conclusion, a highly lipophilic ARB, telmisartan, may be useful for preventing NAD(P)H oxidase activity, and thereby for conferring vascular protection.