Biomedical subjects

Natsuya Keira

Publications and source records attributed to Natsuya Keira.

14 recordsLinked to original sources

PubMed2006

Nicorandil regulates Bcl-2 family proteins and protects cardiac myocytes against hypoxia-induced apoptosis.

Nicorandil has been shown to inhibit myocyte apoptosis by opening of mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels and nitrate-like effect against oxidative stress. However, the detailed mechanism of nicorandil-mediated cardioprotection under hypoxic conditions remains to be largely unknown. The present study examined whether nicorandil can inhibit apoptosis via regulation of Bcl-2 family proteins in hypoxic myocytes. Neonatal rat cardiac myocytes were exposed to hypoxia for 7 hours. Hypoxia-induced myocyte apoptosis (13.9+/-0.9%) under glucose-rich conditions. Myocyte apoptosis was accompanied by loss of mitochondrial membrane potential (Deltapsi(m)), cytochrome c release from mitochondria into cytosol, and activation of caspase-3. Hypoxia also significantly increased Bax and decreased Bcl-2 mRNA and protein expression, thereby increasing Bax/Bcl-2 ratio. Nicorandil 100 micromol/l significantly decreased the percentage of apoptotic myocytes (7.2+/-0.5%) by inhibiting loss of Deltapsi(m) and translocation of cytochrome c. These effects of nicorandil were partially but significantly inhibited by cotreatment of either 500 micromol/l 5-hydroxydecanoate, a selective mitoK(ATP) channel antagonist, or 10 micromol/l 1H-[1,2,4]oxidazolo[4,3-a]quinoxalin-1-one (ODQ), an inhibitor of soluble guanylate cyclase. Moreover, nicorandil significantly inhibited the hypoxia-induced changes in Bax and Bcl-2 expression, and concomitant increased Bax and decreased Bcl-2 immunoreactivity in mitochondria. These effects of nicorandil in Bax and Bcl-2 expression were significantly blunted by cotreatment of ODQ and 5-HD, respectively. Cotreatment of KT5823, an inhibitor of protein kinase G, significantly blocked the effect of nicorandil on Bax expression and 8-bromo-cyclic guanosine 3',5' monophosphate (8-bromo-cGMP), a cGMP analog, mimicked the effect of nicorandil on Bax expression. The present study demonstrates that nicorandil regulates Bcl-2 family proteins via opening of mitoK(ATP) channels and nitric oxide-cGMP signaling and inhibits hypoxia-induced mitochondrial death pathway.

Animals↗

PubMed2004

Aldosterone directly induces myocyte apoptosis through calcineurin-dependent pathways.

BACKGROUND: Aldosterone has recently attracted considerable attention for its involvement in the pathophysiology of heart failure, in which apoptotic cell loss plays a critical role. This study examined whether aldosterone directly induces myocyte apoptosis via its specific receptors. METHODS AND RESULTS: Neonatal rat cardiac myocytes were exposed to aldosterone (10(-8) to 10(-5) mol/L). Nuclear staining with Hoechst 33258 showed that aldosterone induced myocyte apoptosis in a dose- and time-dependent fashion. Treatment of myocytes with 10(-5) mol/L aldosterone significantly increased the percentage of apoptosis (15.5+/-1.4%) compared with serum-deprived control (7.3+/-0.6%). Radio ligand binding assay revealed the existence of plasma membrane receptor with high affinity (K(d), 0.2 nmol/L) for aldosterone in cardiac myocytes but not in fibroblasts. Aldosterone rapidly (approximately 30 seconds) mobilized [Ca2+]i that was blocked by neomycin. Aldosterone induced dephosphorylation of the proapoptotic protein Bad, enhancement of mitochondrial permeability transition, decrease in mitochondrial membrane potential, and release of cytochrome c from the mitochondria into the cytosol with concomitant activation of caspase-3. These effects of aldosterone were inhibited by concurrent treatment with either an L-type Ca2+ channel antagonist, nifedipine, or inhibitors for the Ca2+-dependent phosphatase calcineurin, cyclosporin A and FK506. CONCLUSIONS: The present study demonstrates for the first time that the specific plasma membrane receptor (coupled with phospholipase C) for aldosterone is present on cardiac myocytes and that aldosterone accelerates the mitochondrial apoptotic pathway through activation of calcineurin and dephosphorylation of Bad, suggesting that the proapoptotic action of aldosterone may directly contribute to the progression of heart failure.

Aldosterone↗

PubMed2004

Rate-dependent QRS prolongation during exercise testing associated with hyperkalemia.

The present case showed gradual increase of QRS duration from 100 ms up to 180 msec during an ergometer exercise test along with the heart rate increase. After exercise, QRS duration shortened and normalized. Laboratory test showed hyperkalemia (K = 8.0 mEq/l). T1 myocardial scintigraphy revealed exercise-induced transient ischemia in posterolateral region of left ventricle. Coronary angiography showed significant stenosis in the distal portion of left circumflex coronary artery. The increase of QRS duration was possibly due to the combination of hyperkalemia and the effect of mexiletine. The rate dependent blocking effect on sodium channel of mexiletine might be intensified under hyperkalemia.

Aged↗

PubMed2004

Cytokine-induced nitric oxide inhibits mitochondrial energy production and induces myocardial dysfunction in endotoxin-treated rat hearts.

The mechanism responsible for cardiac depression in septic shock remains unknown. The present study examined whether nitric oxide (NO) overproduced by inducible NO synthase (iNOS) can inhibit aerobic energy metabolism and impair the myocardial function in endotoxin-treated rat hearts. Lipopolysaccharide (LPS) significantly decreased systolic blood pressure (BP) to 44% of control during the 48 h treatment. Hearts from control and LPS-treated rats were perfused in a Langendorff apparatus. After LPS injection, left ventricular (LV) developed pressure (LVDP) was significantly depressed, plasma NO2-/NO3- (NO(x)) concentration was markedly increased, and myocardial adenosine 5'-triphosphate (ATP), creatine phosphate (CrP), and the ratio of ATP/adenosine 5'-diphosphate were progressively decreased with time. Immunological examination showed a significant expression of iNOS protein in the LPS-treated myocytes. Aminoguanidine, an inhibitor of iNOS, significantly attenuated these LPS-induced functional and metabolic changes. Myocardial cyclic guanosine 3',5'-monophosphate (cGMP) content was significantly increased after LPS injection. Methylene blue, an inhibitor of soluble guanylate cyclase, blunted this increase in cGMP and significantly restored the LPS-induced contractile dysfunction 6 h after LPS injection. In addition, there was a significant negative correlation between LVDP and myocardial cGMP levels as well as a significant negative correlation between LVDP and plasma NO(x) levels. In contrast, 48 h after LPS injection, methylene blue no longer affected cardiac performance, and there was a significant positive correlation between LVDP and myocardial ATP content. Furthermore, the normalized activities (as a ratio of the citrate synthase activity) of mitochondrial NADH-CoQ reductase, succinate-CoQ reductase, and ATPase, were significantly inhibited, and the swelling or disruption of mitochondria cristae was seen in the 48 h LPS treatment. These LPS-induced functional and morphological disorders in the mitochondria were significantly improved by aminoguanidine. The findings suggest that sustained production of NO by iNOS leads to contractile dysfunction via cGMP in the early stage, but that it can directly impair the mitochondrial function, lower myocardial energy production, and contribute significantly to the myocardial dysfunction in the later stage of septic shock.

Adenosine Diphosphate↗

PubMed2004

Idiopathic long QT syndrome with early afterdepolarization induced by epinephrine. Acase report.

A patient with idiopathic long QT syndrome had repeated syncopal episodes. The QTc interval on the electrocardiogram at rest was 530 ms and was prolonged by exercise up to 740 ms with T wave alternation. Intravenous epinephrine (0.1 microg/kg weight per min), but not isoproterenol (0.7 microg/min), produced early after depolarization of the monophasic action potential recorded at the right ventricular apex. Epinephrine prolonged the QTc interval to 710 ms. After the addition of propranolol to the epinephrine, the QTc (580 ms) was longer than at baseline. Methoxamine also prolonged the QTc to 580 ms. The QT interval in long QT syndrome is generally considered to be prolonged by a beta-adrenergic effect, but in the present case alpha-adrenergic stimulation had an additional effect on the prolongation of the QT interval.

Adrenergic alpha-Agonists↗

PubMed2003

Nitric oxide-cGMP pathway is involved in endotoxin-induced contractile dysfunction in rat hearts.

The mechanisms by which endotoxemia causes cardiac depression have not been fully elucidated. The present study examined the involvement of nitric oxide (NO) in this pathology. Rats were infused with lipopolysaccharide (LPS) or saline, and the plasma and myocardial NO(2)(-) and NO(3)(-) (NOx) concentrations were measured before or 3, 6, and 24 h after treatment. The hearts were then immediately isolated and mounted in a Langendorff apparatus, and left ventricular developed pressure (LVDP) was determined before biochemical analysis of the myocardium. LPS injection effected the expression of inducible NO synthase (iNOS) in the myocardium, a marked increase in plasma and myocardial NOx levels, and a significant decline in LVDP compared with saline controls. The LPS-induced NO production and concomitant cardiac depression were most pronounced 6 h after LPS injection and were accompanied by a significant increase in myocardial cGMP content. Myocardial ATP levels were not significantly altered after LPS injection. Significant negative correlation was observed between LVDP and myocardial cGMP content, as well as between LVDP and plasma NOx levels. Aminoguanidine, an inhibitor of iNOS, significantly attenuated the LPS-induced NOx production and contractile dysfunction. Furthermore, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, an inhibitor of soluble guanylate cyclase, significantly decreased myocardial cGMP content and attenuated the contractile depression, although aminoguanidine or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one was not able to completely reverse myocardial dysfunction. Our data suggest that endotoxin-induced contractile dysfunction in rat hearts is associated with NO production by myocardial iNOS and a concomitant increase in myocardial cGMP.

Animals↗

PubMed2003

Intracellular ATP is required for mitochondrial apoptotic pathways in isolated hypoxic rat cardiac myocytes.

OBJECTIVES: The present study examined the possibility that intracellular ATP levels dictate whether hypoxic cardiac myocytes die by apoptosis or necrosis. BACKGROUND: Although apoptosis and necrosis may appear to be distinct forms of cell death, recent studies suggest that the two may represent different outcomes of a common pathway. In ischemic myocardium, apoptosis appears early, while energy stores are presumably still available, followed only later by necrosis. METHODS: Neonatal rat cardiac myocytes were exposed to continuous hypoxia, during which the intracellular ATP concentration was modulated by varying the glucose content in the medium. The form of cell death was determined at the end of the hypoxic exposure. RESULTS: Under total glucose deprivation, ATP dropped precipitously and cell death occurred exclusively by necrosis as determined by nuclear staining with ethidium homodimer-1 and smearing on DNA agarose gels. However, with increasing glucose concentrations (10, 20, 50, 100 mg/dl) cellular ATP increased correspondingly, and apoptosis progressively replaced necrosis until it became the sole form of cell death, as determined by nuclear morphology, DNA fragmentation on agarose gels, and caspase-3 activation. The data showed a significantly positive correlation between myocyte ATP content and the percentage of apoptotic cells. Hypoxia resulted in lactate production and cellular acidification which stimulates apoptosis. However, acidification-induced apoptosis was also increased in an ATP-dependent fashion. Loss of mitochondrial membrane potential and cytochrome c release from the mitochondria was observed in both the apoptotic and necrotic cells. Furthermore, translocation of Bax from cytosol into mitochondria preceded these events associated with mitochondrial permeability transition. Increased lactate production and a lack of effect by the mitochondrial inhibitor oligomycin indicated that ATP was generated exclusively through glycolysis. CONCLUSIONS: We demonstrate that ATP, generated through glycolysis, is a critical determinant of the form of cell death in hypoxic myocytes, independently of cellular acidification. Our data suggest that necrosis and apoptosis represent different outcomes of the same pathway. In the absence of ATP, necrosis prevails. However, the presence of ATP favors and promotes apoptosis.

Adenosine Triphosphate↗

PubMed2003

The dual effects of nitric oxide synthase inhibitors on ischemia-reperfusion injury in rat hearts.

OBJECTIVE: Nitric oxide (NO) is known to act as a mediator of tissue injury as well as being a potent endogenous vasodilator. The functional and metabolic effects of NO on ischemia-reperfusion injury are still controversial. The aim of this study was to clarify the relationship between the degree of NO synthase (NOS) inhibition and the effects on ischemia-reperfusion injury. METHODS AND RESULTS: Langendorff-perfused rat hearts were subjected to 30 minutes of global ischemia followed by 30 minutes of reperfusion. The recovery of left ventricular developed pressure (LVDP), creatine kinase (CK) release, and myocardial high energy phosphates were measured in hearts perfused with or without NOS inhibitors, L-N(G)-monomethyl arginine (L-NMMA) or N(G)nitro-L-arginine methylester (L-NAME). NOS inhibitors exerted different effects on the recovery of LVDP and CK release depending on the concentration. The low dose of L-NMMA improved the recovery of LVDP, decreased the CK release during reperfusion, and preserved the myocardial adenosine triphosphate content after reperfusion. In contrast, the high dose of L-NMMA had adverse effects. L-NMMA reduced NO release in coronary effluent in a dose-dependent fashion. Both effects of L-NMMA were abolished by excessive co-administration of L-arginine and the same doses of D-N(G)-monomethyl arginine (D-NMMA) showed no effect on ischemia-reperfusion injury. Therefore, both effects were due to NOS inhibition. In addition, L-NMMA suppressed the myocardial malondialdehyde accumulation, an indicator of oxidative stress, which might be attributed to the beneficial effects by partial NOS inhibition. On the other hand, the high dose L-NMMA significantly decreased coronary fl ow during aerobic perfusion and reperfusion. Therefore, it is conceivable that the vasoactive NOS inhibition contributes to the harmful effects, which might exceed the beneficial effects due to a decrease in oxidative stress. CONCLUSION: The present results showed that NO inhibitors had dual effects on mechanical function and energy metabolism depending on the concentration. Non-vasoactive inhibition of NOS had beneficial effects due to the suppression of oxidative injury. However, strong vasoactive inhibition of NOS exacerbated the ischemia-reperfusion injury.

Adenine Nucleotides↗

PubMed2003

Amlodipine inhibits doxorubicin-induced apoptosis in neonatal rat cardiac myocytes.

OBJECTIVES: We examined whether amlodipine, a calcium channel antagonist with potent antioxidant activity, inhibits doxorubicin-induced apoptosis in cultured neonatal rat cardiac myocytes. BACKGROUND: Recent studies have shown that doxorubicin induces apoptosis as well as necrosis in myocytes through generation of reactive oxygen species. METHODS: The effects of amlodipine and several other antioxidants on doxorubicin-induced oxidative stress and mitochondria-mediated apoptosis were examined. RESULTS: Treatment of myocytes with doxorubicin (10(-6) mol/l) for 14 h increased the number of cells with elevated peroxides, as histochemically estimated by 2',7'-dichlorofluorescin (DCF) diacetate, and the percentage of apoptotic myocytes, as estimated by Hoechst 33258 nuclear staining, compared with control myocytes (25.0 +/- 1.6% vs. 5.2 +/- 1.2%). Moreover, doxorubicin-induced myocyte apoptosis was also confirmed by annexin V-fluorescein isothiocyanate binding assay. Doxorubicin induced a reduction in myocyte adenosine 5'-triphosphate content, a loss of mitochondrial membrane potential, cytochrome c release from the mitochondria into the cytosol, and caspase-3 activation to 1.9-fold of control. Amlodipine significantly attenuated increased DCF fluorescence, inhibited the mitochondria-mediated apoptotic responses described earlier, and decreased apoptosis in the doxorubicin-treated myocytes in a dose-dependent fashion. Amlodipine at 10(-6) mol/l significantly decreased apoptosis to 15.4 +/- 0.7%, and this antiapoptotic action was more effective than that seen with other antioxidants, including probucol, ascorbic acid, and alpha-tocopherol. In contrast, the calcium channel antagonist nifedipine (10(-6) mol/l) did not inhibit apoptosis. Catalase, glutathione, and N-acetylcysteine, but not mannitol or superoxide dismutase, significantly decreased DCF fluorescence and attenuated myocyte apoptosis induced by doxorubicin to 18.7 +/- 1.2%, 19.1 +/- 1.7%, and 18.7 +/- 0.6%, respectively. CONCLUSIONS: Amlodipine significantly inhibits doxorubicin-induced myocyte apoptosis by suppressing the mitochondrial apoptotic pathway. This effect is attributed to the antioxidant properties of amlodipine, affecting mainly hydrogen peroxide.

Amlodipine↗

PubMed2003

Effects of ACE inhibition on myocardial apoptosis in an ischemia-reperfusion rat heart model.

Myocardial ischemia-reperfusion injury involves necrosis and apoptosis. The inhibition of angiotensin-converting enzyme (ACE) has been reported to suppress infarct size. In this study, it was investigated whether an ACE inhibitor affected myocardial apoptosis and apoptosis-related proteins in rats with experimental myocardial infarction. Anesthetized Sprague-Dawley rats were divided into four groups. Group I underwent 30 minutes of left coronary artery occlusion followed by 24 hours of reperfusion (control group); Group II underwent oral administration of the ACE inhibitor quinapril (10 mg/kg/day) before coronary occlusion (quinapril group); Group III underwent administration of the bradykinin B(2)-receptor antagonist Hoe 140 (250 microg/kg/day, subcutaneously) with quinapril (quinapril + Hoe 140 group); and Group IV underwent administration of Hoe 140 alone (Hoe 140 group). After reperfusion, myocardial infarct size was determined by triphenyltetrazolium chloride staining. Myocardial apoptosis was detected immunohistologically using terminal deoxynucleotidyl transferase-mediated nick end labeling staining and DNA electrophoresis. Myocardial caspase-3 activation was analyzed by Western blot and the expressions of Bcl-xL and Bax proteins were detected immunohistochemically. Quinapril significantly reduced the ratio of myocardial infarct size in the ischemic area at risk. In addition, quinapril significantly suppressed the incidence of apoptotic myocytes around the necrotic region (from 18.9 +/- 0.8% to 8.6 +/- 1.0%; P < 0.0001), the intensity of DNA ladder formation, and the activation of caspase-3. Hoe 140 attenuated these protective effects of quinapril. In the immunohistochemical study, Bax and Bcl-xL were expressed in myocytes, and ischemia-reperfusion abolished both proteins in the center region of ischemia. The Bax staining was equally observed among all groups. However, Bcl-xL staining remained in the ischemic area widely after quinapril treatment. In addition, Hoe 140 also depleted this effect of quinapril. These results suggest that inhibition of ACE reduces myocardial infarction and apoptosis via the bradykinin B(2) receptor in part. The antiapoptotic effect of the ACE inhibitor is attributed to the changing expression of Bcl-xL.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2003

Subepicardial aneurysm associated with ventricular septal perforation showing a normal coronary angiogram.

Subepicardial aneurysm is a rare complication of acute myocardial infarction and the present case was associated with ventricular septal perforation. Echocardiography showed the subepicardial aneurysm adjoining the true apico-anteroseptal aneurysm, with the former being discontinuous with the myocardium at its neck, which was narrower than the diameter of the aneurysm. In addition, color Doppler imaging showed shunt flow from the aneurysm to the right ventricle. Coronary angiography revealed extension only of the anterior descending artery without any discernible stenosis. The apical aneurysm was excised and the defect closed with an epicardial patch. The myocardial infarction was probably caused by coronary spasm. Echocardiography was useful for diagnosing the anatomy and hemodynamic condition of the subepicardial aneurysm.

Aged↗

PubMed2002

Lethal effect of cytokine-induced nitric oxide and peroxynitrite on cultured rat cardiac myocytes.

We examined the cytotoxic effect of iNOS-generated NO in cultured cardiac myocytes treated with IL-1 beta, IFN- gamma and LPS. Treatment of the myocytes with cytokines for 48 h resulted in a marked NO production, a significant decline in cellular ATP content, and a significant increase in myocyte death with morphological characteristics of necrosis. Moreover, immunohistochemical examination showed that the cytokines caused nitrotyrosine formation in the injured myocytes. Uric acid and L-cysteine which have the ability to quench peroxynitrite significantly attenuated these cytokine-induced effects, although they did not alter NO production or the decline in cellular ATP. These data suggest that NO production induced by cytokines can not only cause deleterious effects in the myocardial energy balance but also induce myocytes necrosis, through the formation of peroxynitrite.

Adenosine Triphosphate↗

PubMed2002

A case of cardiomyopathy induced by premature ventricular complexes.

Tachycardia-induced cardiomyopathy is a well-known and reversible condition, but the left ventricular dysfunction caused by frequent isolated premature ventricular complexes (PVCs) has been rarely reported. Apparent dilated cardiomyopathy was resolved in a patient after the focal source of PVCs was eliminated by radiofrequency catheter ablation. Echocardiography showed progressive improvement of the abnormal wall motion. Frequent PVCs could be the cause of left ventricular dysfunction in a subset of patients with dilated cardiomyopathy and radiofrequency ablation should be the choice of therapy in those patients.

Cardiomyopathy, Dilated↗

PubMed2002

Two cases of polymorphic ventricular tachycardia induced by the administration of verapamil against paroxysmal supraventricular tachycardia.

Verapamil is widely used for the termination of paroxysmal supraventricular tachycardia (PSVT) with little proarrhythmic effect. We describe two cases of PSVT that changed to non-sustained polymorphic ventricular tachycardia after administration of verapamil. Electrophysiological study revealed atrioventricular nodal reentrant tachycardia in the first case, and atrioventricular reentrant tachycardia due to a concealed left lateral accessory pathway in the second case. Catecholamine-induced automaticity was one of the possible mechanisms of VT in the first case, but the mechanism is unknown in the second case.

Anti-Arrhythmia Agents↗