Masahiro Okazaki

Comparison of acute and chronic impact of adaptive servo-ventilation on left chamber geometry and function in patients with chronic heart failure.

The aim of this study was to determine differences in the acute and chronic impact of adaptive servo‐ventilation (ASV) on left chamber geometry and function in patients with chronic heart failure (CHF).

Coexistence of hERG current block and disruption of protein trafficking in ketoconazole-induced long QT syndrome

Many drugs associated with acquired long QT syndrome (LQTS) directly block human ether‐a‐go‐go‐related gene (hERG) K+ channels. Recently, disrupted trafficking of the hERG channel protein was proposed as a new mechanism underlying LQTS, but whether this defect coexists with the hERG current block remains unclear. This study investigated how ketoconazole, a direct hERG current inhibitor, affects the trafficking of hERG channel protein.

Urotensin II-induced activation of extracellular signal-regulated kinase in cultured vascular smooth muscle cells: Involvement of cell adhesion-mediated integrin signaling

Urotensin II (UII), a cyclic dodecapeptide, is a potent mammalian vasoconstrictive substance recently shown to induce proliferation of vascular smooth muscle cells (VSMCs). However, little is known about mechanisms involved in UII-induced mitogenic response such as cell proliferation. To investigate the intracellular signaling pathways involved in this process, we examined the effects of UII on activation of extracellular signal-regulated kinase (ERK) and focal adhesion kinase (FAK) in VSMCs. UII stimulated in time- and dose-dependent manners the phosphorylation level of ERK. In contrast, UII failed to alter the phosphorylation level of FAK. Although angiotensin II-induced ERK phosphorylation was noted even in suspended cells, UII failed to induce an increase in ERK phosphorylation in such cells. On the other hand, UII induced an increase in the phosphorylation level of ERK, but not FAK, in cells adherent to fibronectin. Furthermore, UII-induced proliferation of VSMCs was inhibited by ERK kinase inhibitor PD98059. Our results suggested that activation of integrin-mediated signaling pathways play a critical role in UII-induced phosphorylation of ERK, leading to proliferation of VSMCs, which does not involved increased phosphorylation of FAK.

Clinical Significance of Natriuretic Peptides and Cyclic GMP in Hemodialysis Patients with Coronary Artery Disease

Background: Plasma concentrations of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and cyclic guanosine monophosphate (cGMP) are suitable markers of ’dry body weight’ (DW) in hemodialysis (HD) patients. However, it is still unknown whether these markers can be applied to patients with renal failure and coronary artery disease (CAD). We examined the reliability of these peptides as volume markers in HD patients with CAD. We also assessed the relationship between natriuretic peptides and indices of left ventricular (LV) function. Methods: Plasma concentrations of ANP, BNP and cGMP were determined before and after HD in patients with CAD (group 1, n = 19, mean age 63 ± 12 years) and were compared with those of patients without cardiac disease (group 2, n = 20, age 61 ± 15 years). Using data obtained by cardiac catheterization, we examined the relationship between natriuretic peptides and indices of LV function in HD patients with CAD. Results: Baseline ANP (244 ± 205 pg/ml), BNP (713 ± 928 pg/ml) and cGMP (29.6 ± 21.6 pmol/ml) were significantly higher in group 1 than in 11 healthy volunteers (18.6 ± 9.9 pg/ml, 7.7 ± 7.6 pg/ml, cGMP 8.9 ± 4.9 pmol/ml, respectively). HD significantly reduced plasma ANP (87 ± 75 pg/ml) and BNP (477 ± 702 pg/ml) although they were still above normal control. HD reduced plasma cGMP (7.2 ± 4.5 pmol/ml) to normal values, suggesting the elimination of cGMP across the dialyzers. Baseline levels of ANP, BNP and cGMP in group 2 were less than those of group 1 but higher than the control. HD reduced natriuretic peptides in group 2 to levels lower than those in post-HD group 1. After HD, there was no significant correlation between reductions in body weight and changes in ANP or BNP. Baseline ANP and BNP levels closely correlated with pulmonary artery pressure, pulmonary artery wedge pressure, left ventricular end-diastolic pressure and left ventricular ejection fraction. A significant correlation was observed between BNP levels and the severity of CAD. Conclusion: ANP, BNP and cGMP seem to be a useful markers for fluid overload but not for DW in HD patients with CAD. Plasma ANP and BNP might be useful markers for left ventricular function.

Stimulatory effects of brain natriuretic peptide on cyclic GMP accumulation and tyrosine hydroxylase activity in cultured bovine adrenal medullary cells

SummaryWe studied the effect of brain natriuretic peptide (BNP) on the accumulation of cyclic GMP and the phosphorylation and activity of tyrosine hydroxylase, compared with that of atrial natriuretic peptide (ANP), in cultured bovine adrenal medullary cells. 1. BNP as well as ANP increased cellular cyclic GMP accumulation in a concentration-dependent manner (10–1000 nmol/1). BNP (1 μmol/1) and ANP (1 μmol/1) produced a 60-fold and 30-fold increase in cyclic GMP accumulation, respectively. 2. The stimulatory effects of BNP and ANP on cyclic GMP accumulation were observed even when Ca2+ or Na+ was removed from the incubation medium. 3. 12-O-Tetradecanoylphorbol 13-acetate (TPA), an activator of protein kinase C, inhibited the stimulatory effect of BNP on cyclic GMP accumulation in a concentration-dependent manner (1–100 nmol/1). Furthermore, the BNP-induced accumulation of cyclic GMP was attenuated by forskolin (1 μmol/1), an activator of adenylate cyclase. 4. BNP (1 μmol/1) and ANP (1 μ mol/1) caused a significant increase in phosphorylation and activity of tyrosine hydroxylase in the cells. 5. In digitonin-permeabilized cells, cyclic GMP (1–100 μmol/1) activated tyrosine hydroxylase in the presence of ATP and Mg2+.These results suggest that BNP stimulates the accumulation of cyclic GMP in a manner similar to that of ANP. The increased accumulation of cyclic GMP by these peptides may be negatively modulated by protein kinase C and cyclic AMP and may cause the phosphorylation and activation of tyrosine hydroxylase-in cultured bovine adrenal medullary cells.

Upregulation of Vascular Extracellular Superoxide Dismutase in Patients With Acute Coronary Syndromes

Objective—We examined the vascular expression levels of extracellular superoxide dismutase (EC-SOD), a major antioxidant enzyme in the cardiovascular system, in patients with acute coronary syndromes. Methods and Results—Twenty-one consecutive patients with acute myocardial infarction (AMI), 14 patients with unstable angina, 11 patients with stable angina, and 20 control subjects were studied. The levels of vascular EC-SOD expression were assessed by the difference in plasma EC-SOD concentrations before and after intravenous heparan injection. In the patients with AMI, vascular EC-SOD expression (ng/mL) was significantly higher on day 1 after the onset of AMI (148±10) as compared with the control subjects (116±6, P <0.05). The vascular EC-SOD expression returned to the normal range on day 7 (104±8), and that level persisted thereafter. The vascular EC-SOD expression was also significantly higher in the patients with unstable angina (160±13) than in those with stable angina (122±10) or in the controls (116±6) (P <0.05 each). Moreover, in the patients with AMI, higher levels of vascular EC-SOD expression on day 1 were significantly associated with smaller myocardial infarct size (P <0.05). Conclusions—This is the first clinical demonstration showing that vascular EC-SOD may be upregulated in acute coronary syndromes in humans in vivo. EC-SOD may play an important protective role against increased oxidative stress during acute ischemic coronary events.

Involvement of PDGF in pressure-induced mesangial cell proliferation through PKC and tyrosine kinase pathways.

In glomerular hypertension, mesangial cells (MC) are subjected to at least two physical forces: mechanical stretch and high transmural pressure. Increased transmural pressure, as well as mechanical stretch, promotes MC proliferation, which may enhance glomerulosclerosis. The exact mechanism of this effect is not fully understood. We examined the effects of transmural pressure alone on cell proliferation and DNA synthesis and investigated the role of platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF), candidates for mediation of glomerular diseases, in the pressure-induced events. Pressure was applied to cultured MC placed in a sealed chamber using compressed helium gas. Application of pressure resulted in a time-dependent ( approximately 2 h) and pressure level-dependent (approximately 80 mmHg) increase in cell number (1.4-fold) and [(3)H]thymidine incorporation (2.7-fold). Pressure-induced DNA synthesis was significantly suppressed by inhibitors of phospholipase C (2-nitro-4-carboxyphenyl-N, N-diphenylcarbamate), protein kinase C [1-(5-isoquinolinylsulfonyl)-2-methylpiperazine and chelerythrine], or tyrosine kinases (genistein). Pressure caused a rapid but transient formation of inositol 1,4,5-trisphosphate, which was blocked by the phospholipase C inhibitor. Pressure also promoted a rapid increase in tyrosine kinase activity. Pressure increased mRNA levels of PDGF-B, with a peak at 6 h, but not those of PDGF-A or bFGF. Pressure-induced DNA synthesis was partially inhibited by a neutralizing anti-PDGF antibody but not by an antibody against bFGF or nonimmune IgG. Our results indicated that pressure by itself increases DNA synthesis and proliferation of cultured rat MC possibly through activation of protein kinase C and tyrosine kinases, and PDGF-B could be partially involved in these pathways.

Comparison of Plasma levels of mature adrenomedullin and natriuretic peptide as markers of cardiac function in hemodialysis patients with coronary artery disease

Background: It has been suggested that, like ANP and BNP, high plasma levels of mature adrenomedullin (mAM) indirectly reflect the severity of heart failure or renal failure. However, the relationship between mAM levels and hemodynamics and cardiac function has not been examined in hemodialysis (HD) patients with coronary artery disease (CAD). The best marker, among mAM, ANP and BNP, for left-ventricular function in those patients is also unclear. Patients and Methods: Plasma levels of mAM, total AM (tAM), ANP and BNP were determined before HD in chronic HD patients with CAD (group 1; n = 17) and were compared with those of HD patients without cardiac disease (group 2; n = 22). We examined their relationship to hemodynamics and cardiac function in group 1 using data obtained by cardiac catheterization. Results: Plasma levels of ANP and BNP were significantly higher in group 1 than in group 2, but there was no significant difference in plasma levels of mAM and tAM between the two patient groups. Plasma levels of both mAM and tAM significantly correlated with right atrial pressure (RAP), and only plasma tAM levels correlated with pulmonary artery pressure (PAP) and pulmonary artery wedge pressure (PAWP). However, no correlations were found between levels of the two forms of AM and ejection fraction (EF). In contrast, plasma ANP and BNP levels significantly correlated with both PAP and PAWP, and also with EF, although they did not correlate with RAP. The correlation of PAP and PAWP with ANP and BNP levels was closer than that with tAM levels. The most significant correlation was between BNP levels and EF (r = –0.756, p < 0.0001). Conclusions: Our results suggest that the mAM level may be less useful than natriuretic peptide levels as a marker of cardiac function in HD patients with CAD, and that the BNP level might be the best indicator of left-ventricular function. In addition, cardiac disease such as CAD may have a minor impact on mAM levels compared to renal failure.

Adrenomedullin inhibits transmural pressure induced mesangial cell proliferation through activation of protein kinase A.

Adrenomedullin (AM), a hypotensive peptide isolated from human pheochromocytoma, inhibits the proliferation of mesangial cells (MC) induced by mitogens such as platelet-derived growth factor. Quite recently, we have demonstrated that transmural pressure applied to cultured MC increased DNA synthesis and cell proliferation through protein kinase C and tyrosine kinase pathways. However, the modulatory effect of AM on pressure-induced cell proliferation is as yet unknown. In the present study, we examined the effect of AM on transmural pressure-induced DNA synthesis in cultured rat MC. Pressure was applied to cells placed in a sealed chamber using compressed helium. Application of pressure resulted in an increase in [3H]thymidine incorporation (approximately 2.0-fold). AM clearly inhibited pressure-induced DNA synthesis in a concentration-dependent manner. This inhibition was paralleled by an increase in cellular cAMP levels evoked by AM. Forskolin and dibutyryl cAMP mimicked the inhibitory effect of AM. The protein kinase A inhibitor H-89 significantly attenuated the effect of AM. Human AM(22–52)-NH2, a putative AM receptor antagonist, reversed the inhibitory effects of AM more potently than did human CGRP(8–37), a calcitonin gene related peptide receptor antagonist. Our results suggest that AM, by acting mainly on AM-sensitive receptors, inhibits pressure-induced DNA synthesis in cultured rat MC through activation of protein kinase A. AM may play a protective role against MC proliferation in certain pathological conditions.

Evidence of a Vicious Cycle in Mitral Regurgitation With Prolapse Secondary Tethering Attributed to Primary Prolapse Demonstrated by Three-Dimensional Echocardiography Exacerbates Regurgitation

Background— In patients with mitral valve prolapse, nonprolapsed leaflets are often apically tented. We hypothesized that secondary left ventricular dilatation attributed to primary mitral regurgitation (MR) causes papillary muscle (PM) displacement, resulting in this leaflet tenting/tethering, and that secondary tethering further exacerbates malcoaptation and contributes to MR severity. Methods and Results— Three-dimensional transesophageal echocardiography was performed in 25 patients with posterior mitral leaflet prolapse with an intact anterior mitral leaflet (AML) and 20 controls. From 3D zoom data sets, 11 equidistant antero-posterior cut planes of the mitral valve at midsystole were obtained. In each plane, tenting area of nonprolapsed leaflet and prolapse area of prolapsed leaflet were measured. Prolapse/tenting volume of each region was obtained as the product of interslice distance and the prolapse/tenting area. AML tenting volume and whole leaflet prolapse/tenting volume were then obtained. The PM tethering distance between PM tips and anterior mitral annulus was measured from 3D full-volume data sets. The severity of MR was quantified by vena contracta area extracted from color 3D transesophageal echocardiography data sets. AML tenting volume was significantly larger in patients with posterior mitral leaflet prolapse compared with that in controls (1.2±0.5 versus 0.6±0.2 mL/m2; P<0.001). Multivariate regression analysis identified independent contribution to AML tenting volume from an increase in PM tethering distance. Multivariate regression analysis identified independent contributions to MR severity (vena contracta area) from both whole leaflet tenting volume (r=0.44; P<0.05) and prolapse volume (r=0.44; P<0.05). AML tenting volume decreased along with left ventricular volume and PM tethering distance postrepair (n=8; P<0.01). Conclusions— These results suggest that primary mitral valve prolapse with MR causes secondary mitral leaflet tethering with PM displacement by left ventricular dilatation, which further exacerbates valve leakage, constituting a vicious cycle that would suggest a pathophysiologic rationale for early surgical repair.