Junko Ohashi

Crucial role of nitric oxide synthases system in endothelium-dependent hyperpolarization in mice

The endothelium plays an important role in maintaining vascular homeostasis by synthesizing and releasing several relaxing factors, such as prostacyclin, nitric oxide (NO), and endothelium-derived hyperpolarizing factor (EDHF). We have previously demonstrated in animals and humans that endothelium-derived hydrogen peroxide (H2O2) is an EDHF that is produced in part by endothelial NO synthase (eNOS). In this study, we show that genetic disruption of all three NOS isoforms (neuronal [nNOS], inducible [iNOS], and endothelial [eNOS]) abolishes EDHF responses in mice. The contribution of the NOS system to EDHF-mediated responses was examined in eNOS−/−, n/eNOS−/−, and n/i/eNOS−/− mice. EDHF-mediated relaxation and hyperpolarization in response to acetylcholine of mesenteric arteries were progressively reduced as the number of disrupted NOS genes increased, whereas vascular smooth muscle function was preserved. Loss of eNOS expression alone was compensated for by other NOS genes, and endothelial cell production of H2O2 and EDHF-mediated responses were completely absent in n/i/eNOS−/− mice, even after antihypertensive treatment with hydralazine. NOS uncoupling was not involved, as modulation of tetrahydrobiopterin (BH4) synthesis had no effect on EDHF-mediated relaxation, and the BH4/dihydrobiopterin (BH2) ratio was comparable in mesenteric arteries and the aorta. These results provide the first evidence that EDHF-mediated responses are dependent on the NOSs system in mouse mesenteric arteries.

Roles of Endothelial Oxidases in Endothelium-derived Hyperpolarizing Factor Responses in Mice

The endothelium synthesizes and releases several vasodilator substances, including prostacyclin, nitric oxide (NO), and endothelium-derived hyperpolarizing factor (EDHF). We have demonstrated that endothelium-derived hydrogen peroxide (H2O2) is an EDHF in animals and humans and that superoxide anions derived from endothelial nitric oxide synthases (NOSs) system are an important precursor for EDHF/H2O2 in mice. There are several intracellular sources of superoxide anions other than NOSs, including NAD(P)H oxidase, xanthine oxidase, lipoxygenase, and mitochondrial electron transport chain. In this study, we examined the possible role of endothelial oxidases other than NOSs in the EDHF-mediated responses. In angiotensin II-infused mice, both EDHF-mediated relaxations and hyperpolarizations to acetylcholine were significantly reduced, nitric oxide-mediated relaxations were rather enhanced, and vascular smooth muscle responses were preserved. Antihypertensive treatment normalized blood pressure but failed to improve EDHF-mediated responses in those mice. Acute inhibition of endothelial oxidases other than NOSs, including NAD(P)H oxidase, xanthine oxidase, lipoxygenase, or mitochondrial electron transport chain, had no inhibitory effects on EDHF-mediated responses. Furthermore, in p47phox-knockout mice, EDHF-mediated responses were unaltered. These results suggest that endothelial oxidases other than NOSs are not involved in EDHF/H2O2 responses in mice, suggesting a specific link between endothelial NOSs system and EDHF responses under physiological conditions.

Essential Role of Bone Marrow for Microvascular Endothelial and Metabolic Functions in Mice

Rationale: We have previously demonstrated that the importance of endothelium-derived hyperpolarizing factor (EDHF) increases as the vessel size decreases and that endothelium-derived hydrogen peroxide (H2O2) is an EDHF in animals and humans, for which endothelial nitric oxide synthase (eNOS) is the major source. Recent studies have suggested the important role of the bone marrow (BM) in modulating cardiovascular and metabolic functions. Objective: We aimed to examine whether BM plays a role in modulating microvascular endothelial and metabolic functions in mice, and if so, to elucidate the mechanisms involved. Methods and Results: Male eNOS−/− mice were transplanted with BM cells from wild-type (WT) or eNOS−/− mice and were maintained for 6 weeks. Endothelium-dependent relaxations and hyperpolarizations of mesenteric arteries to acetylcholine were reduced in eNOS−/− mice and were markedly improved when transplanted with WT-BM but not with eNOS−/−-BM. The enhanced component of endothelium-dependent relaxations was abolished by catalase, indicating that the improved responses were mediated by H2O2. In contrast, no such beneficial effect was noted in the aorta. Reduced plasma adiponectin levels and impaired glucose tolerance in eNOS−/− mice were also improved by WT-BM transplantation. Neuronal nitric oxide synthase (nNOS) in mesenteric arteries of eNOS−/− mice was significantly upregulated only when transplanted with WT-BM. Importantly, the beneficial effects of WT-BM transplantation were absent in eNOS−/−/adiponectin−/− or eNOS−/−/nNOS−/− mice. Conclusions: These results provide the first evidence that BM plays an important role in modulating microvascular endothelial and metabolic functions, for which adiponectin and nNOS may be involved.

Prevention of life-threatening ventricular tachyarrhythmia by a novel and pure class-III agent, nifekalant hydrochloride.

Abstract: Nifekalant hydrochloride (NIF) is a novel intravenous class-III antiarrhythmic agent with a pirimidinedione structure that purely blocks the K+channel without inhibiting β-adrenergic receptors. The authors investigated the efficacy of NIF for refractory ventricular tachycardia/fibrillation (VT/VF). They studied 30 patients treated with an intravenous infusion of NIF [ 26 men, 4 women; age: 63 ± 17 (mean ± SD) years] at a dose of 0.19 ± 0.14 mg/kg body weight per hour. Sixteen were patients with acute coronary syndrome (ACS), and 14 were patients with chronic structural heart disease (Chr-HD). Amiodarone and sotalol had already been administered to 9 patients with Chr-HD before the administration of NIF. The QT and T peak-end (Tp-e) intervals were measured and corrected by Bazetts method (QTc, cTp-e). The left ventricular ejection fraction was depressed (28 ± 9%). NIF was effective for preventing VT/VF without proarrhythmia and hemodynamic deterioration in 21 patients (70%; 12 with ACS; 9 with Chr-HD), but ineffective in 4 patients (all with Chr-HD). The QTc prolongation in the responders was more pronounced than in the nonresponders (25% ± 15% versus 5% ± 7% increase; P < 0.05). Proarrhythmic torsade de pointes (TdP) developed transiently in the remaining 5 patients in whom the cTp-e was markedly increased compared with that in the responders (93% ± 49% versus 37% ± 41% increase; P < 0.05). In conclusion, these findings indicate that the intravenous administration of NIF is useful in the emergent treatment of inhibiting drug-refractory VT/VF, although proarrhythmic TdP owing to an enhancement of transmural dispersion of repolarization needs to be taken into account.

Percutaneous Transcatheter Balloon Valvuloplasty for Bioprosthetic Tricuspid Valve Stenosis

A 59-year-old woman was admitted to our hospital because of exertional dyspnea, abdominal distension, and leg edema over the past 2 weeks. She had a history of rheumatic fever at the age of 12 years. In 1983, at the age of 37, she had undergone tricuspid valve replacement with a Carpentier-Edwards bioprosthesis for tricuspid stenosis and mitral valve replacement with a mechanical valve for mitral stenosis. The physical examination on admission revealed marked edema in both legs. There was also presystolic pulsation of the liver, which was palpable 4 cm below the right costal margin. A Levine grade III/VI, rough, diastolic rumble at the lower left sternal border was accentuated during inspiration. Echocardiography revealed severe tricuspid stenosis and a large amount of ascites. The leaflets were thickened, …

Hereditary Hemorrhagic Telangiectasia With Pulmonary Arteriovenous Fistulas

A 65-year-old woman presented with exertional dyspnea and general fatigue that began 1 week ago. She had a family history of hereditary hemorrhagic telangiectasia manifesting as telangiectasia of gastrointestinal (GI) tract and nasal mucosa and of pulmonary arteriovenous fistulas (PAVFs). Her first PAVF was diagnosed in 1999 but was untreated at that time. Her medical history was significant for multiple GI bleeds, mild to moderate nosebleeds, and a minor cerebral stroke probably due …