Eiji Yahiro

Mast cell chymase limits the cardiac efficacy of Ang I–converting enzyme inhibitor therapy in rodents

Ang I-converting enzyme (ACE) inhibitors are widely believed to suppress the deleterious cardiac effects of Ang II by inhibiting locally generated Ang II. However, the recent demonstration that chymase, an Ang II-forming enzyme stored in mast cell granules, is present in the heart has added uncertainty to this view. As discussed here, using microdialysis probes tethered to the heart of conscious mice, we have shown that chronic ACE inhibitor treatment did not suppress Ang II levels in the LV interstitial fluid (ISF) despite marked inhibition of ACE. However, chronic ACE inhibition caused a marked bradykinin/B2 receptor-mediated increase in LV ISF chymase activity that was not observed in mast cell-deficient KitW/KitW-v mice. In chronic ACE inhibitor-treated mast cell-sufficient littermates, chymase inhibition decreased LV ISF Ang II levels substantially, indicating the importance of mast cell chymase in regulating cardiac Ang II levels. Chymase-dependent processing of other regulatory peptides also promotes inflammation and tissue remodeling. We found that combined chymase and ACE inhibition, relative to ACE inhibition alone, improved LV function, decreased adverse cardiac remodeling, and improved survival after myocardial infarction in hamsters. These results suggest that chymase inhibitors could be a useful addition to ACE inhibitor therapy in the treatment of heart failure.

c-kit Is Required for Cardiomyocyte Terminal Differentiation

c-kit, the transmembrane tyrosine kinase receptor for stem cell factor, is required for melanocyte and mast cell development, hematopoiesis, and differentiation of spermatogonial stem cells. We show here that in the heart, c-kit is expressed not only by cardiac stem cells but also by cardiomyocytes, commencing immediately after birth and terminating a few days later, coincident with the onset of cardiomyocyte terminal differentiation. To examine the function of c-kit in cardiomyocyte terminal differentiation, we used compound heterozygous mice carrying the W (null) and Wv (dominant negative) mutations of c-kit. In vivo, adult W/Wv cardiomyocytes are phenotypically indistinguishable from their wild-type counterparts. After acute pressure overload adult W/Wv cardiomyocytes reenter the cell cycle and proliferate, leading to left ventricular growth; furthermore in transgenic mice with cardiomyocyte-restricted overexpression of the dominant negative Wv mutant, pressure overload causes cardiomyocytes to reenter the cell cycle. In contrast, in wild-type mice left ventricular growth after pressure overload results mainly from cardiomyocyte hypertrophy. Importantly, W/Wv mice with pressure overload–induced cardiomyocyte hyperplasia had improved left ventricular function and survival. In W/Wv mice, c-kit dysfunction also resulted in an ≈14-fold decrease (P<0.01) in the number of c-kit+/GATA4+ cardiac progenitors. These findings identify novel functions for c-kit: promotion of cardiac stem cell differentiation and regulation of cardiomyocyte terminal differentiation.

FAMP, a Novel ApoA‐I Mimetic Peptide, Suppresses Aortic Plaque Formation Through Promotion of Biological HDL Function in ApoE‐Deficient Mice

Background Apolipoprotein (apo) A‐I is a major high‐density lipoprotein (HDL) protein that causes cholesterol efflux from peripheral cells through the ATP‐binding cassette transporter A1 (ABCA1), thus generating HDL and reversing the macrophage foam cell phenotype. Pre‐β1 HDL is the smallest subfraction of HDL, which is believed to represent newly formed HDL, and it is the most active acceptor of free cholesterol. Furthermore it has a possible protective function against cardiovascular disease (CVD). We developed a novel apoA‐I mimetic peptide without phospholipids (Fukuoka University ApoA‐I Mimetic Peptide, FAMP). Methods and Results FAMP type 5 (FAMP5) had a high capacity for cholesterol efflux from A172 cells and mouse and human macrophages in vitro, and the efflux was mainly dependent on ABCA1 transporter. Incubation of FAMP5 with human HDL or whole plasma generated small HDL particles, and charged apoA‐I‐rich particles migrated as pre‐β HDL on agarose gel electrophoresis. Sixteen weeks of treatment with FAMP5 significantly suppressed aortic plaque formation (scrambled FAMP, 31.3±8.9% versus high‐dose FAMP5, 16.2±5.0%; P<0.01) and plasma C‐reactive protein and monocyte chemoattractant protein‐1 in apoE‐deficient mice fed a high‐fat diet. In addition, it significantly enhanced HDL‐mediated cholesterol efflux capacity from the mice. Conclusions A newly developed apoA‐I mimetic peptide, FAMP, has an antiatherosclerotic effect through the enhancement of the biological function of HDL. FAMP may have significant atheroprotective potential and prove to be a new therapeutic tool for CVD.

Increased carotid artery plaque score is an independent predictor of the presence and severity of coronary artery disease

OBJECTIVES Carotid ultrasonography is noninvasive and effective for the assessment of atherosclerotic lesions. The relationship between carotid ultrasound findings and presence and severity of coronary artery disease (CAD) was examined in Japanese patients. METHODS AND RESULTS Subjects were 116 patients who underwent carotid ultrasonography and coronary angiography. In carotid ultrasonography, mean-intima-media thickness (IMT), common carotid artery max IMT, bifurcation max IMT, plaque number, and plaque score (PS). The coronary angiographic data was obtained in the same period as carotid ultrasonography was performed. Patients were divided into two groups based on the presence or absence of coronary artery stenosis (CAS and non-CAS) and CAS group was further categorized into three groups, 1 vessel disease (1VD), 2VD, and 3VD. Physical findings, biochemical data, and carotid ultrasonogram data between the groups were compared. Items showing a significant difference between CAS and non-CAS were age, gender (male), incidence of diabetes and dyslipidemia, fasting blood sugar (FBS), triglyceride, HDL-cholesterol (HDL-C), high-sensitivity C-reactive protein, and all carotid ultrasound findings. All of the above parameters also showed a significant difference between four different severity groups. Stepwise logistic regression analysis was performed to determine which factors predict the presence and/or severity of CAS. High PS showed the strongest predictive value for both and followed by low HDL-C and high FBS. The cut-off value of PS obtained by receiver operating characteristic curve for predicting the presence of CAS was 1.9. CONCLUSIONS Assessment of PS by carotid ultrasonography together with other risk factor assessment was clinically relevant to predict the presence and severity of CAS.

LCZ696, an angiotensin receptor-neprilysin inhibitor, improves cardiac function with the attenuation of fibrosis in heart failure with reduced ejection fraction in streptozotocin-induced diabetic mice.

Angiotensin receptor–neprilysin inhibitors (ARNis) acts an ARB and neprilysin inhibitor. Diabetes mellitus significantly increases the risk of cardiovascular disease and heart failure (HF). Therefore, we evaluated the effects and mechanisms of ARNi in HF with reduced ejection fraction (HFrEF) in streptozotocin‐induced diabetic mice.

Reperfusion-induced arrhythmias are suppressed by inhibition of the angiotensin II type 1 receptor.

We examined antiarrhythmic effects of drugs, including renin-angiotensin system (RAS) inhibitors, on reperfusion arrhythmias in rats in vivo. Anesthetized rats were subjected to 5 min of coronary occlusion and 30 min of reperfusion. Arrhythmia scores, calculated as the product of the type of arrhythmia (1 for ventricular tachycardia, 2 for ventricular fibrillation) and its duration (in seconds), were adopted to evaluate the severity of arrhythmias. Reperfusion arrhythmias were suppressed by Na+/H+ exchange inhibitor, Na+/Ca2+ exchange inhibitor and L-type Ca channel antagonist by more than 90%. Angiotensin-converting enzyme inhibitor and angiotensin II (Ang II) type 1 receptor (AT1) antagonist also modestly (by 60–70%) but significantly decreased reperfusion arrhythmias. These effects were not reversed by co-administration of bradykinin B2 receptor antagonist or AT2 antagonist, respectively. Effects of superoxide dismutase (SOD) were also examined, but SOD proved ineffective. Effects of Na+/H+ exchange inhibitor, Na+/Ca2+ exchange inhibitor and L-type Ca channel antagonist suggest a causative relationship of Ca overload in reperfusion arrhythmias. These transport systems are known to be activated by Ang II. Thus, the antiarrhythmic action of RAS inhibitors might be attributable to the inhibition of the action of Ang II via AT1.

Non-ACE pathway-induced angiotensin II production.

For the past century, the renin-angiotensin system (RAS) has been recognized as one of the major blood pressure-regulating systems. Angiotensin II (Ang II) is the final physiologically active product of RAS, and it works not only as a strong vasopressor but also as a promotor of tissue remodeling in various organs such as heart, arteries, and kidneys. RAS is the predominant pathway of Ang II formation in human plasma, but not in the tissues. There are several alternative pathways producing angiotensin II in human tissues, and they are involved in structural remodeling of the cardiovascular system. Proteinases such as chymase, kallikrein, cathepsin G, and elastase-2 are probably responsible for angiotensin-converting enzyme (ACE)-independent Ang II formation in human tissues. In particular, chymase is an important Ang II-generating enzyme in the human heart. It is important to elucidate the mechanisms of the ACE-independent Ang II formation in human tissues; long-term inhibition of the local Ang II formation may become one of the strategies to prevent cardiovascular remodeling.

Class- and molecule-specific differential effects of angiotensin II type 1 receptor blockers.

Angiotensin II (Ang II) type 1 (AT1) receptor is a member of the G protein-coupled receptor superfamily and contains 359 amino acids. AT1 receptor blockers (ARBs, e.g., eprosartan, losartan, candesartan, valsartan, telmisartan, olmesartan, irbesartan, and azilsartan) have been developed and are available for clinical use, and basic and clinical studies have shown that ARBs are useful for preventing the development of cardiovascular disease. While most ARBs have common molecular structures (biphenyl-tetrazol and imidazole groups), they also show slightly different structures. Some of the benefits conferred by ARBs may not be class-specific effects, and instead may be molecule-specific effects. Their common molecular structures are thought to be responsible for their class effects, whereas their slightly different structures may be important for promoting molecule-specific effects. This review focuses on current evidence regarding the class- and molecule-specific differential effects of ARBs from basic experiments to clinical settings.

Insights into the Characteristics of Mammalian Cardiomyocyte Terminal Differentiation Shown Through the Study of Mice with a Dysfunctional c-Kit

Mammalian cardiomyocytes withdraw from the cell cycle soon after birth. This process is called terminal differentiation. The c-kit, a receptor tyrosine kinase, is expressed on cardiomyocytes immediately after birth but for only a few days. In mice with genetic c-kit dysfunction, adult cardiomyocytes are phenotypically indistinguishable from those of wild type mice, except that they are capable of proliferation in vivo after acute pressure overload. This review explores the idea that postnatal cardiomyocyte differentiation and cell cycle withdrawal are distinct processes and that terminal differentiation may not simply be due to altered expression of genes that regulate the cell cycle but could involve c-kit induced epigenetic change.

Successful catheter ablation of ventricular tachycardia originating from the idiopathic saccular apical left ventricular aneurysm

Left ventricular (LV) aneurysm has been recognized to frequently become a substrate of ventricular tachyarrhythmias. We report a case of a 66-year-old woman with symptomatic sustained monomorphic ventricular tachycardia (SMVT) originating from saccular apical LV aneurysm without definite underlying diseases. We performed catheter ablation using electroanatomical and conventional bipolar potential mapping. During SMVT, we found an area of fragmented potential -40 ms preceding the earliest wide QRS complex in the area of the apical LV aneurysm. Radiofrequency applications were delivered to this area. Since then, SMVT was no longer inducible by programmed electrical stimulation. The patient has remained free of VT recurrences during a subsequent 12-month follow-up period.