Takuroh Imamura

Adrenomedullin: a possible autocrine or paracrine inhibitor of hypertrophy of cardiomyocytes.

Adrenomedullin (AM), a potent vasodilator peptide, exists in the cardiac ventricle; however, the role of AM in the ventricular tissue remains unknown. In the present study, we investigated the production and secretion of AM in cultured neonatal rat cardiomyocytes, and we examined the effect of AM on de novo protein synthesis in these cells by measuring [14C]phenylalanine incorporation. The cardiomyocytes cultured with serum-free media secreted AM into the media in a time-dependent manner at the rate of 12.2+/-0.5 fmol/10(5) cells/48 hours (mean+/-SEM). Angiotensin II (1 micromol/L) or 10% fetal bovine serum significantly (P<.01) increased the AM secretion by 115% and 305%, respectively. In addition, Northern blot analysis of total RNA extracted from the myocytes disclosed the expression of prepro-AM mRNA of 1.6 kb. Synthetic AM at 1 micromol/L significantly reduced the 10(-6) mol/L angiotensin II- and 10% fetal bovine serum-stimulated [14C]phenylalanine incorporation into the cells, by 16% (P<.05) and 20% (P<.01), respectively. The inhibitory effect of AM on the angiotensin II-stimulated [14C]phenylalanine incorporation was abolished dose-dependently by a calcitonin gene-related peptide receptor antagonist, CGRP(8-37). Furthermore, blockade of the action of endogenous AM by either 10(-6) mol/L CGRP(8-37) or anti-AM monoclonal antibody significantly enhanced the basal and 10(-6) mol/L angiotensin II-stimulated [14C]phenylalanine incorporation. In summary, cultured neonatal rat cardiomyocytes produce and secrete AM, and the secreted AM inhibits the protein synthesis of these cells. Thus, AM may act on cardiomyocytes as an autocrine or a paracrine factor modulating the cardiac growth.

Increased plasma adrenomedullin in acute myocardial infarction

Adrenomedullin has a potent vasodilating effect comparable to that of calcitonin gene-related peptide. To investigate the pathophysiologic role of endogenous adrenomedullin, we determined sequentially the plasma adrenomedullin level in 15 consecutive patients with acute myocardial infarction (AMI). Plasma adrenomedullin was higher immediately after the onset of AMI and decreased gradually; plasma levels during the 3-week period after the AMI were higher than plasma levels in 15 healthy control subjects (p < 0.001), with higher levels in patients with congestive heart failure than in patients without congestive heart failure throughout the period of the study (p < 0.05). Plasma adrenomedullin was positively correlated with pulmonary capillary wedge pressure, pulmonary arterial pressure, right atrial pressure, and heart rate in the early stage of AMI. These findings suggest that the elevation of plasma adrenomedullin is related to the retention of body fluid volume, the enhancement of sympathetic activity, and/or the elevation of pressure in pulmonary vascular beds. Adrenomedullin may act against excessive vasoconstrictors increased in AMI.

An autocrine or a paracrine role of adrenomedullin in modulating cardiac fibroblast growth.

Objective: The aim of the present study was to determine the role of adrenomedullin (AM) in cardiac fibroblasts. Methods: The production and secretion of AM were examined in cultured neonatal rat cardiac fibroblasts, and the effects of AM on proliferation and protein synthesis of these cells were assessed by [3H]thymidine and [3H]phenylalanine incorporation, respectively. Results: Cultured cardiac fibroblasts secreted AM into the medium time-dependently at a rate of 20.3±3.0 fmol/5×104 cells/48 h, mean±S.D. Northern blot analysis showed expression of preproAM mRNA of 1.6 kb in these cells. In addition, 10−6 mol/l of angiotensin II (Ang II) and endothelin-1 (ET-1) significantly increased the AM secretion by 55 and 48%, respectively. Synthetic AM significantly reduced 10−6 mol/l Ang II- or 10−7 mol/l ET-1-stimulated [3H]thymidine and [3H]phenylalanine incorporation in a dose-dependent manner, and these effects were attenuated by a calcitonin gene-related peptide (CGRP) type 1 receptor antagonist, CGRP(8-37). Synthetic AM also had a dose-dependent stimulatory effect on cAMP accumulation in these cells, which was significantly attenuated by CGRP(8-37). A cAMP analogue, 8-bromo-cAMP, mimicked the AM effects, inhibiting the Ang II-stimulated [3H]thymidine and [3H]phenylalanine incorporation. Blockage of the effect of endogenous AM by anti-AM monoclonal antibody not only significantly reduced the basal level of intracellular cAMP, but also enhanced the [3H]thymidine and [3H]phenylalanine incorporation into the cells. Conclusions: Cultured neonatal rat cardiac fibroblasts produce and secrete AM, and the secreted AM may inhibit proliferation and protein synthesis of these cells. AM may exert these inhibitory effects partly by elevating intracellular cAMP. It is suggested that AM has an important role in modulating the growth of cardiac fibroblasts in an autocrine or a paracrine manner.

Adventitial Mast Cells Contribute to Pathogenesis in the Progression of Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is histologically characterized by medial degeneration and various degrees of chronic adventitial inflammation, although the mechanisms for progression of aneurysm are poorly understood. In the present study, we carried out histological study of AAA tissues of patients, and interventional animal and cell culture experiments to investigate a role of mast cells in the pathogenesis of AAA. The number of mast cells was found to increase in the outer media or adventitia of human AAA, showing a positive correlation between the cell number and the AAA diameter. Aneurysmal dilatation of the aorta was seen in the control (+/+) rats following periaortic application of calcium chloride (CaCl2) treatment but not in the mast cell–deficient mutant Ws/Ws rats. The AAA formation was accompanied by accumulation of mast cells, T lymphocytes and by activated matrix metalloproteinase 9, reduced elastin levels and augmented angiogenesis in the aortic tissue, but these changes were much less in the Ws/Ws rats than in the controls. Similarly, mast cells were accumulated and activated at the adventitia of aneurysmal aorta in the apolipoprotein E–deficient mice. The pharmacological intervention with the tranilast, an inhibitor of mast cell degranulation, attenuated AAA development in these rodent models. In the cell culture experiment, a mast cell directly augmented matrix metalloproteinase 9 activity produced by the monocyte/macrophage. Collectively, these data suggest that adventitial mast cells play a critical role in the progression of AAA.

Increased plasma adrenomedullin levels in chronic congestive heart failure

Adrenomedullin is a potent vasodilator peptide and occurs in circulating blood of human beings and experimental animals. Because it is produced in intact aorta of rats and in cultured vascular endothelial cells, adrenomedullin seems to participate in regulation of local vascular tone. To determine the pathophysiological roles of adrenomedullin, we investigated its plasma concentrations in 49 patients with heart failure. Plasma adrenomedullin levels increased significantly with advancing severity of the disease (New York Heart Association functional class I, 4.1 +/- 1.0; II, 5.6 +/- 1.6; III, 6.4 +/- 0.8; IV, 13.2 +/- 6.8 (fmol/l). Plasma adrenomedullin was correlated with pulmonary artery pressure (r = 0.44, p = 0.0114) and pulmonary capillary wedge pressure (r = 0.53, p = 0.0002). These findings indicate that adrenomedullin may play some important role in the pathophysiologic makeup of heart failure by its vasodilating effects against the concomitant exaggeration of humor pressor agents such as catecholamine and the renin-angiotensin system. Hemodynamic changes in pulmonary circulation may have some influence on the increased synthesis and secretion of plasma adrenomedullin in chronic congestive heart failure.

Involvement of C-reactive protein obtained by directional coronary atherectomy in plaque instability and developing restenosis in patients with stable or unstable angina pectoris

We investigated whether positive immunohistochemical staining of C-reactive protein (CRP) in initial culprit lesions is related to coronary plaque instability and whether it could affect the outcome of directional coronary atherectomy (DCA). The plasma level of CRP is a reliable marker of the risk of coronary events and restenosis after percutaneous coronary intervention. However, the influence of tissue CRP in atheromatous plaque on plaque vulnerability and restenosis remains unknown. Samples of DCA obtained from 12 patients with stable angina pectoris and 15 patients with unstable angina pectoris were immunohistochemically stained with a monoclonal antibody against CRP. We performed follow-up coronary angiography on 22 of 27 patients to evaluate the presence of restenosis after DCA. Immunoreactivity to CRP was localized to macrophages, smooth muscle cells, and necrotic areas. The ratio of CRP positive cells to total cells was significantly higher in DCA samples from patients with unstable (17.9 +/- 2.0%) than with stable angina (11.0 +/- 2.5%) (p <0.05). Follow-up coronary angiography showed that 12 of 22 patients developed restenosis after DCA. The ratio was also significantly higher in DCA specimens from patients with restenosis (19.3 +/- 2.8%) compared with those without restenosis (11.0 +/- 2.0%) (p <0.05). In addition, the ratio significantly correlated with late luminal loss (r = 0.428, p <0.05) and loss index (r = 0.636, p = 0.0011) after DCA. Immunoreactivity to CRP in coronary atheromatous plaque increases in culprit lesions of unstable angina, and it affects restenosis after DCA. These findings suggest that CRP in atheromatous plaque plays an important role in the pathogenesis of unstable angina and restenosis after coronary intervention.

Factor XI contributes to thrombus propagation on injured neointima of the rabbit iliac artery

Summary.  Background: Thrombus formation through the activation of tissue factor (TF) and factor (F) XI is a critical event in the onset of cardiovascular disease. TF expressed in atherosclerotic plaques and circulating blood is an important determinant of thrombogenicity that contributes to fibrin‐rich thrombus formation after plaque disruption. However, the contribution of FXI to thrombus formation on disrupted plaques remains unclear. Methods: A mouse monoclonal antibody against FXI and activated FXI (FXIa) (XI‐5108) was generated by immunization with activated human FXI. Prothrombin time (PT), activated partial thromboplastin time (APTT), bleeding time, and ex vivo platelet aggregation in rabbits were measured before and after an intravenous bolus injection of XI‐5108. We investigated the role of FXI upon arterial thrombus growth in the rabbit iliac artery in the presence of repeated balloon injury. Results: The XI‐5108 antibody reacted to the light chain of human and rabbit FXI/FXIa, and inhibited FXIa‐initiated FXa and FXIa generation. Fibrin‐rich thrombi developed on the injured neointima that was obviously immunopositive for glycoprotein IIb‐IIIa, fibrin, TF, and FXI. Intravenous administration of XI‐5108 (3.0 mg kg−1) remarkably reduced thrombus growth, and the APTT was significantly prolonged. However, PT, bleeding time and platelet aggregation were not affected. Conclusions: These results indicate that plasma FXI plays a potent role in thrombus growth on the injured neointima. Inhibition of plasma FXI activity might help to reduce thrombus growth on ruptured plaques without prolonging bleeding time.

Enhanced Adrenomedullin Production by Mechanical Stretching in Cultured Rat Cardiomyocytes

Adrenomedullin (AM) is secreted from cultured cardiac myocytes. In this study, we examined whether mechanical stretching stimulates AM production in cardiac myocytes, and if so, whether angiotensin II (Ang II) is involved in that mechanism. Neonatal rat cardiac myocytes cultured in serum-free medium were stretched 10% or 20% on flexible silicone rubber culture dishes, and AM mRNA expression was examined by quantitative polymerase chain reaction. The AM mRNA levels in the myocytes stretched 10% and 20% for 24 hours significantly increased by 56% (P<0.05) and 88% (P<0.01), respectively, when compared with the levels in nonstretched cells. AM secretion into the medium after the myocytes were stretched 10% and 20% increased by 22% (P<0.05) and 45% (P<0.01), respectively. In nonstretched myocytes incubated with 10(-6) mol/L Ang II for 24 hours, AM mRNA and secretion increased by 86% (P<0.05) and 36% (P<0. 01), respectively. These effects of Ang II were abolished by 10(-6) mol/L CV-11974, an Ang II type I (AT(1)) receptor antagonist, but not by 10(-6) mol/L PD-123319, an Ang II type II antagonist. Stretch-induced increases of AM gene expression and secretion were significantly inhibited (P<0.05) in the presence of 10(-6) mol/L CV-11974 by 46% and 52%, respectively; however, they were not affected by 10(-6) mol/L PD-123319. These findings indicate that AM production from cardiac myocytes is augmented by mechanical stretching, partially through the AT(1) receptors, which suggests a local interaction between AM and the renin-angiotensin system in stretched cardiac myocytes.

Inhibition of 5-hydroxytryptamine2A receptor prevents occlusive thrombus formation on neointima of the rabbit femoral artery

Summary.  Background: Thrombus propagation on disrupted plaque is a major cause of acute coronary events and serious complication after coronary intervention. 5‐hydroxytryptamine (5‐HT) is a potent vasoactive and platelet‐aggregating substance that is predominantly mediated by 5‐HT2A receptor. However, the roles of 5‐HT2A receptor in occlusive thrombus formation on disrupted plaque remain obscure. Objective: We investigated the role of 5‐HT2A receptor in thrombus formation using a rabbit model of repeated balloon‐injury. Methods: Three weeks after a first balloon‐injury of the femoral arteries, luminal diameter, neointimal growth, and vasoconstriction by 5‐HT in vitro were examined. Thrombus propagation and the role of 5‐HT2A receptor after a second balloon‐injury were evaluated using sarpogrelate, a selective 5‐HT2A receptor antagonist. Results: Three weeks after the first balloon‐injury, luminal stenosis was evident in the femoral arteries, where the neointima expressed tissue factor and 5‐HT2A receptor. The hypercontractile response of the stenotic arteries to 5‐HT was significantly reduced by sarpogrelate. Balloon‐injury of the neointima with substantially reduced blood flow promoted the formation of occlusive thrombus that was immunoreactive against glycoprotein IIb‐IIIa, 5‐HT2A receptor and fibrin. Intravenous injection of sarpogrelate significantly inhibited ex vivo platelet aggregation induced by adenosine 5′‐diphosphate, thrombin and collagen alone as well as with 5‐HT, and significantly prevented occlusive thrombus formation in vivo. Conclusions: The 5‐HT2A receptor appears to play a crucial role in occlusive thrombus formation in diseased arteries via platelet aggregation and vasoconstriction. Inhibition of 5‐HT2A receptor might help reduce the onset of acute coronary events and of acute coronary occlusion after the intervention.

Soluble Guanylate Cyclase Stimulation on Cardiovascular Remodeling in Angiotensin II–Induced Hypertensive Rats

It is unknown whether long-term pharmacological stimulation of soluble guanylate cyclase (sGC), elevating intracellular cGMP levels, has a beneficial effect on hypertension. The purpose of this study is to investigate the effects of BAY41-2272, an orally available sGC stimulator, on cardiovascular remodeling in hypertensive rats. Eight-week-old male Wistar rats with hypertension induced by angiotensin II infused subcutaneously at 250 ng/kg per minute were treated orally with a low ([L] 2 mg/kg per day) or high ([H] 10 mg/kg per day) dose of BAY41-2272 for 14 days. BAY41-2272-H partially suppressed the rise in blood pressure and reduced the heart weight (4.20±0.34 versus 3.68±0.20 mg/g; P<0.01), whereas BAY41-2272-L had no effect. However, both doses decreased the angiotensin II–induced left ventricular accumulation of collagen in the perivascular area (L, −20%, P<0.05; H, −30%, P<0.01) and myocardial interstitium (L, −21%, P<0.05; H, −38%, P<0.01), reducing the number of activated fibroblasts surrounding coronary arteries (L, −74%; H, −79%; P<0.05). BAY41-2272 downregulated the angiotensin II–induced left ventricular gene expression of type 1 collagen (L, −41%, P<0.05; H, −49%, P<0.01) and transforming growth factor-β1 (L, −49%, P<0.05; H, −65%, P<0.01). cGMP levels were elevated by BAY41-2272 not only in the left ventricle, but also in cultured cardiac fibroblasts, resulting in reduced thymidine incorporation into the cells. Thus, stimulation of sGC by BAY41-2272 attenuates fibrosis of the left ventricle in rats with angiotensin II–induced hypertension partly in a pressure-independent manner, suggesting an important role for sGC generating cGMP in inhibiting cardiovascular remodeling.