Chika Matsumoto

Role of gp91phox-containing NADPH oxidase in left ventricular remodeling induced by intermittent hypoxic stress.

Intermittent hypoxia due to sleep apnea syndrome is associated with cardiovascular diseases. However, the precise mechanisms by which intermittent hypoxic stress accelerates cardiovascular diseases are largely unclear. The aim of this study was to investigate the role of gp91(phox)-containing NADPH oxidase in the development of left ventricular (LV) remodeling induced by intermittent hypoxic stress in mice. Male gp91(phox)-deficient (gp91(-/-)) mice (n = 26) and wild-type (n = 39) mice at 7-12 wk of age were exposed to intermittent hypoxia (30 s of 4.5-5.5% O(2) followed by 30 s of 21% O(2) for 8 h/day during daytime) or normoxia for 10 days. Mean blood pressure and LV systolic and diastolic function were not changed by intermittent hypoxia in wild-type or gp91(-/-) mice, although right ventricular systolic pressure tended to be increased. In wild-type mice, intermittent hypoxic stress significantly increased the diameter of cardiomyocytes and interstitial fibrosis in LV myocardium. Furthermore, intermittent hypoxic stress increased superoxide production, 4-hydroxy-2-nonenal protein, TNF-alpha and transforming growth factor-beta mRNA, and NF-kappaB binding activity in wild-type, but not gp91(-/-), mice. These results suggest that gp91(phox)-containing NADPH oxidase plays a crucial role in the pathophysiology of intermittent hypoxia-induced LV remodeling through an increase of oxidative stress.

Chymase Plays an Important Role in Left Ventricular Remodeling Induced by Intermittent Hypoxia in Mice

Intermittent hypoxia caused by sleep apnea is associated with cardiovascular disease. Chymase has been reported to play an important role in the development of cardiovascular disease, but it is unclear whether chymase is involved in the pathogenesis of left ventricular remodeling induced by intermittent hypoxia. The aim of this study was to evaluate the effect of a novel chymase inhibitor (NK3201) on hypoxia-induced left ventricular remodeling in mice. Male C57BL/6J mice (9 weeks old) were exposed to intermittent hypoxia or normoxia and were treated with NK3201 (10 mg/kg per day) or the vehicle for 10 days. Left ventricular systolic pressure showed no significant differences among all of the experimental groups. Exposure to intermittent hypoxia increased left ventricular chymase activity and angiotensin II expression, which were both suppressed by treatment with NK3201. Intermittent hypoxia also increased the mean cardiomyocyte diameter, perivascular fibrosis, expression of inflammatory cytokines, oxidative stress, and NADPH-dependent superoxide production in the left ventricular myocardium. These changes were all suppressed by NK3201 treatment. Therefore, chymase might play an important role in intermittent hypoxia-induced left ventricular remodeling, which is independent of the systemic blood pressure.

Inhibition of Endothelin ETB Receptor System Aggravates Neointimal Hyperplasia after Balloon Injury of Rat Carotid Artery

Endothelin-1 (ET)/ETA receptor system has been known to play an important role in the pathogenesis of neointimal hyperplasia after endothelial injury. However, the pathological role of endothelin ETB receptors on neointimal hyperplasia remains to be elucidated. In the present study, we investigated the pathological role of ETB receptors on neointimal hyperplasia in balloon-injured rat carotid arteries by pharmacological blockade with use of 2R-(4-propoxyphenyl)-4S-(1,3-benzodioxol-5-yl)-1-(N-(2,6-diethylphenyl)aminocarbonyl-methyl)-pyrrolidine-3R-carboxylic acid (A-192621), a selective ETB receptor antagonist, 2R-(4-methoxyphenyl)-4S-(1,3-benzodioxol-5-yl)-1-(N,N-di(n-butyl)aminocarbonyl-methyl)-pyrrolidine-3R-carboxylic acid (ABT-627), a selective ETA receptor antagonist, and (+)-(5S,6R,7R)-2-butyl-7-[2-((2S)-2-carboxypropyl)-4-methoxyphenyl]-5-(3,4-methylenedioxyphenyl)cyclopenteno[1,2-b]pyridine-6-carboxylic acid (J-104132), an ETA/ETB dual receptor antagonist. Moreover, the spotting-lethal rats, which carry a naturally occurring deletion in the endothelin ETB receptor gene, were used to examine the effects of genetic deficiency for this receptor subtype. Two weeks after balloon injury, the ratio of the neointimal to the medial area (neointima/media ratio) was determined. Treatment with A-192621 (30 mg/kg/day) for 2 weeks after injury significantly increased the neointima/media ratio in the injured artery. In contrast, ABT-627 (10 mg/kg/day) and J-104132 (10 mg/kg/day) markedly decreased the neointima/media ratio to the same extent. Furthermore, the neointima/media ratio in the injured artery of the ETB-deficient rat was significantly increased compared with that of the wild-type rat, and this increase was abolished by treatment with J-104132. These findings suggest that the inhibition of the ETB receptor system leads to an aggravation of neointimal hyperplasia after balloon injury, and the augmentation of ETA-mediated actions are responsible for the neointimal hyperplasia aggravated by the pharmacological blockade of ETB receptor or by its genetic deficiency. The antagonism of the ETA receptor system is essential for preventing restenosis after angioplasty.

Pitavastatin reduces oxidative stress and attenuates intermittent hypoxia-induced left ventricular remodeling in lean mice.

We have reported previously that intermittent hypoxia related to sleep apnea induces cardiovascular remodeling secondary to the oxidative stress. The aim of this study was to examine the effect of pitavastatin as an antioxidant to prevent intermittent hypoxia-induced left ventricular (LV) remodeling in mice without hypercholesterolemia. Eight-week-old male C57BL/6J mice (n=35) were exposed to intermittent hypoxia (30 s exposure to 5% oxygen, followed by 30 s exposure to 21% oxygen) for 8 h per day during the daytime or maintained under normoxic conditions; in addition, they were either treated with pitavastatin (3 mg kg−1 per day) or vehicle for 10 days. After cardiac catheterization and blood sampling, the LV myocardium was examined. The systemic blood pressure and plasma level of total cholesterol were similar among the four groups. Intermittent hypoxia significantly increased the expression levels of 4-hydroxy-2-nonenal (4-HNE) proteins, TNF-α and TGF-β mRNA, and also the number of terminal deoxynucleotidyl transferase-mediated dUTP-biotin end labeling (TUNEL)-positive myocardial cells in the LV myocardium. In addition, enhanced hypertrophy of the cardiomyocytes, perivascular fibrosis and histological degeneration were observed in the mice exposed to hypoxic stress. Treatment with pitavastatin significantly suppressed the expression levels of the 4-HNE proteins, cytokines, superoxide production and TUNEL-positive myocardial cells in the LV myocardium, consequently attenuating the hypoxia-induced histological changes. Pitavastatin preserved, at least partially, the morphological structure of the LV myocardium in lean mice exposed to intermittent hypoxia, through its antioxidant effect.

Dietary salt restriction activates mineralocorticoid receptor signaling in volume-overloaded heart failure.

Whether a high plasma aldosterone concentration induced by strict salt restriction promotes cardiac remodeling remains controversial. Male Sprague-Dawley rats at 10weeks of age were given normal salt (NS) (1.5% NaCl) or low salt (LS) (0.05% NaCl) diets. Each animal underwent aortocaval fistula creation for volume-overloaded heart failure or sham surgery. All rats with a fistula received either vehicle or a non-hypotensive dose of spironolactone (200mg/kg/day) by gavage. Two weeks later, the LS diet significantly increased the plasma aldosterone level in the sham-operated and fistula-created rats (2677+/-662pg/ml and 2406+/-422pg/ml) compared with that in rats given the NS diet (518+/-18pg/ml and 362+/-45pg/ml, respectively). In sham-operated rats, the difference in plasma aldosterone level did not affect the extent of myocardial fibrosis (1.8+/-0.1% with LS diet vs. 1.5+/-0.3% with NS diet). However, the increase in myocardial fibrosis in fistula-created rats was more prominent with the LS diet than with the NS diet (4.7+/-0.3% vs. 3.4+/-0.1%). In addition, the fistula-created rats on the LS diet expressed significantly increased oxidative stress and transforming growth factor-beta compared with those on the NS diets (P<0.05). These increases in the fistula-created rats on the LS diet were significantly suppressed by the non-hypotensive dose of spironolactone (P<0.05). These results suggest that increased plasma aldosterone level with strict salt restriction activated the mineralocorticoid receptor signaling in volume-overloaded condition, resulting in increased myocardial fibrosis.

Ca2+-activated outward-rectifier K+ channels and histamine release by rat gastric enterochromaffin-like cells

Gastric enterochromaffin-like (ECL) cells were isolated from rat gastric fundic mucosa by Percoll density-gradient centrifugation and counter-flow elutriation. About 67% of cells in the purified cell suspension were ECL cells, which were reacted with anti-histidine decarboxylase antibody. A23187, a calcium ionophore, at 0.1-10 microM induced histamine release from ECL cell-rich suspension, indicating that the Ca2+ pathway is involved in the mechanism of histamine release from the ECL cells. A23187 at 5 microM significantly increased outward-rectifier cationic current in 62% of cells in the ECL cell-rich factions. A23187-sensitive cells showed acridine orange uptake. In single-channel recordings, a Ca(2+)-dependent outward-rectifier K+ channel of large conductance (146 +/- 22 picosiemens) was found in the cell that showed acridine orange uptake. The channel opened in a voltage-dependent manner at 0.1 microM of intracellular free Ca2+ concentration. These results may suggest that opening of the Ca(2+)-activated K+ channel is one of the steps involved in the mechanism of histamine release in ECL cells.

Efficacy of olmesartan and nifedipine on recurrent hypoxia-induced left ventricular remodeling in diabetic mice

AIMS Recurrent hypoxia due to sleep apnea syndrome is implicated in cardiovascular events, especially in diabetic patients, but the underlying mechanisms remain controversial. We previously reported that angiotensin II receptor blockers can improve hypoxia-induced left ventricular remodeling. The aim of this study was to examine the effect on left ventricular remodeling of adding a calcium channel blocker to angiotensin II receptor blocker therapy in diabetic mice exposed to recurrent hypoxia. MAIN METHODS Male db/db mice (8-week-old) and age-matched control db/+ mice were fed a Western diet and subjected to recurrent hypoxia (oxygen at 10+/-0.5% for 8h daily during the daytime) or normoxia for 3weeks. Hypoxic db/db mice were treated with the vehicle, olmesartan (3mg/kg/day), nifedipine (10mg/kg/day), or both drugs. KEY FINDINGS Recurrent hypoxia caused hypertrophy of cardiomyocytes, interstitial fibrosis, and a significant increase in expression of the oxidative stress marker 4-hydroxy-2-nonenal (4-HNE) in the left ventricular myocardium. Treatment with olmesartan, nifedipine, or both drugs had no effect on systolic blood pressure, and each treatment achieved similar suppression of 4-HNE expression. Olmesartan and the combination with olmesartan and nifedipine significantly prevented cardiomyocyte hypertrophy more than treatment with nifedipine alone. On the other hand, olmesartan combined with nifedipine significantly reduced cytokine expression, superoxide production and matrix metalloproteinase (MMP)-9 activity, and significantly suppressed interstitial fibrosis in the left ventricular myocardium. SIGNIFICANCE The combination with olmesartan and nifedipine, as well as a monotherapy with olmesartan, exerts preferable cardioprotection in diabetic mice exposed to recurrent hypoxia.