Masatsugu Nozoe

Mitochondria-derived reactive oxygen species mediate sympathoexcitation induced by angiotensin II in the rostral ventrolateral medulla.

Objectives Reactive oxygen species (ROS) in the central nervous system are thought to contribute to sympathoexcitation in cardiovascular diseases such as hypertension and heart failure. Nicotinamide adenine dinucleotide phosphate oxidase is a major source of ROS in the central nervous system, which acts as a key mediator (mediators) of angiotensin II (AngII). It is not clear, however, whether mitochondria-derived ROS in the central nervous system also participate in sympathoexcitation. Methods In an in-vivo study, we investigated whether the AngII-elicited pressor response in the rostral ventrolateral medulla, which controls sympathetic nerve activity, is attenuated by adenovirus-mediated gene transfer of a mitochondria-derived antioxidant (Mn-SOD). In an in-vitro study, using differentiated PC-12 cells with characteristics similar to those of sympathetic neurons, we examined whether AngII increases mitochondrial ROS production. Results Overexpression of Mn-SOD attenuated the AngII-induced pressor response and also suppressed AngII-induced ROS production, as evaluated by microdialysis in the rostral ventrolateral medulla. Using reduced MitoTracker red, we showed that AngII increased mitochondrial ROS production in differentiated PC-12 cells in vitro. Overexpression of Mn-SOD and rotenone, a mitochondrial respiratory complex I inhibitor, suppressed AngII-induced ROS production. Depletion of extracellular Ca2+ with ethylene glycol bis-N,N,N′,N′-tetraacetate (EGTA) and administration of p-trifluoromethoxycarbonylcyanide phenylhydrazone, which prevents further Ca2+ uptake into the mitochondria, blocked AngII-elicited mitochondrial ROS production. Conclusion These results indicate that AngII increases the intracellular Ca2+ concentration and that the increase in mitochondrial Ca2+ uptake leads to mitochondrial ROS production.

Inhibition of Rac1-Derived Reactive Oxygen Species in Nucleus Tractus Solitarius Decreases Blood Pressure and Heart Rate in Stroke-Prone Spontaneously Hypertensive Rats

Reactive oxygen species (ROS) in the brain are thought to contribute to the neuropathogenesis of hypertension by enhancing sympathetic nervous system activity. The nucleus tractus solitarius (NTS), which receives afferent input from baroreceptors, has an important role in cardiovascular regulation. reduced nicotinamide-adenine dinucleotide phosphate oxidase is thought to be a major source of ROS in the NTS. Rac1 is a small G protein and a key component of reduced nicotinamide-adenine dinucleotide phosphate oxidase. The role of Rac1-derived ROS in the NTS in cardiovascular regulation of hypertension is unknown. Therefore, we examined whether inhibition of Rac1 in the NTS decreases ROS generation, thereby reducing blood pressure in stroke-prone spontaneously hypertensive rats (SHRSPs). The basal Rac1 activity level in the NTS was greater in SHRSPs than in Wistar-Kyoto rats. Inhibition of Rac1, induced by transfecting adenovirus vectors encoding dominant-negative Rac1 into the NTS, decreased blood pressure, heart rate, and urinary norepinephrine excretion in SHRSPs but not in Wistar-Kyoto rats. Inhibition of Rac1 also reduced nicotinamide-adenine dinucleotide phosphate oxidase activity and ROS generation. In addition, Cu/Zn-superoxide dismutase activity in the NTS of SHRSPs was decreased compared with that of Wistar-Kyoto rats, despite the increased ROS generation. Overexpression of Cu/Zn-superoxide dismutase in the NTS decreased blood pressure and heart rate in SHRSPs. These results indicate that the activation of Rac1 in the NTS generates ROS via reduced nicotinamide-adenine dinucleotide phosphate oxidase in SHRSPs, and this mechanism might be important for the neuropathogenesis of hypertension in SHRSPs.

High Salt Intake Enhances Blood Pressure Increase during Development of Hypertension via Oxidative Stress in Rostral Ventrolateral Medulla of Spontaneously Hypertensive Rats

High salt intake increases blood pressure (BP) in spontaneously hypertensive rats (SHR), and central neural mechanisms are suggested to be involved. Increased generation of reactive oxygen species (ROS) in the rostral ventrolateral medulla (RVLM) contributes to the neural mechanism of hypertension in SHR. We sought to examine whether high salt intake increases hypertension in SHR and whether the increased ROS in the RVLM contributes to this mechanism. Male SHR and Wistar-Kyoto rats (WKY) (6 weeks old) were fed a high-salt diet (8%: HS-S; HS-W) or a regular-salt diet (0.5%: RS-S; RS-W) for 6 weeks. Systolic BP was significantly higher in HS-S than in RS-S at 12 weeks of age (244±5 vs. 187±7 mmHg, n=8; p<0.05). Urinary norepinephrine excretion was significantly higher in HS-S than in RS-S. Thiobarbituric acid-reactive substances levels in the RVLM were significantly higher in HS-S than in RS-S (9.9±0.5 vs. 8.1±0.6 μmol/g wet wt, n=5; p<0.05). Microinjection of tempol or valsartan into the RVLM induced significantly greater BP reduction in HS-S than in RS-S. The increase in angiotensin II type 1 receptor (AT1R) expression and the increase in reduced nicotinamide-adenine dinucleotide phosphate (NAD(P)H) oxidase activity in the RVLM were significantly greater in HS-S than in RS-S. These findings indicate that high salt intake exacerbates BP elevation and sympathetic nervous system activity during the development of hypertension in SHR. These responses are mediated by increased ROS generation that is probably due to upregulation of AT1R/NAD(P)H oxidase in the RVLM.

Amlodipine-Induced Reduction of Oxidative Stress in the Brain Is Associated with Sympatho-Inhibitory Effects in Stroke-Prone Spontaneously Hypertensive Rats

Amlodipine is a dihydropyridine calcium channel blocker that is widely used for the treatment of hypertensive patients and has an antioxidant effect on vessels in vitro. The aim of the present study was to examine whether treatment with amlodipine reduced oxidative stress in the brains of stroke-prone spontaneously hypertensive rats (SHRSP). The animals received amlodipine, nicardipine or hydralazine for 30 days in their drinking water. Levels of thiobarbituric acid-reactive substances (TBARS) in the brain (cortex, cerebellum, hypothalamus, and brainstem) were measured before and after each treatment. Systolic blood pressure decreased to similar levels in the amlodipine-, nicardipine-, and hydralazine-treated groups. Urinary norepinephrine excretion was significantly reduced in SHRSP after treatment with amlodipine, but not with nicardipine or hydralazine. Levels of TBARS in the cortex, cerebellum, hypothalamus, and brainstem were significantly higher in SHRSP than in Wistar-Kyoto rats (WKY), and were reduced in amlodipine-treated, but not in nicardipine- or hydralazine-treated, SHRSP. Electron spin resonance spectroscopy revealed increased levels of reactive oxygen species in the brains of SHRSP, which were reduced by treatment with amlodipine. Intracisternal infusion of amlodipine also reduced systolic blood pressure, urinary norepinephrine excretion, and the levels of TBARS in the brain. These results suggested that oxidative stress in the brain was enhanced in SHRSP compared with WKY rats. In addition, antihypertensive treatment with amlodipine reduced oxidative stress in all areas of the brain examined and decreased blood pressure without a reflex increase in sympathetic nerve activity in SHRSP.

Pressor response induced by central angiotensin II is mediated by activation of Rho/Rho-kinase pathway via AT1 receptors.

Objectives The brain renin–angiotensin system plays an important role in cardiovascular regulation and the pathogenesis of hypertension. Angiotensin II activates the Rho/Rho-kinase pathway in vascular smooth muscle cells and cardiomyocytes in vitro. The aim of the present study was to determine whether angiotensin II in the brainstem activates the Rho/Rho-kinase pathway, and, if so, whether this mechanism is involved in the central pressor action of angiotensin II. Methods and results Angiotensin II infused intracisternally for 7 days in Wistar–Kyoto rats (WKY) increased systolic blood pressure (SBP) and urinary norepinephrine excretion. These responses were abolished by the co-infusion of Y-27632, a specific Rho-kinase inhibitor, or valsartan. The intracisternal infusion of Y-27632 or valsartan also reduced SBP and norepinephrine excretion in spontaneously hypertensive rats (SHR). Western blot analysis was performed to examine the expression levels of membranous RhoA and phosphorylated ezrin, radixin, and moesin (p-ERM), which reflects Rho/Rho-kinase activity. The expression levels of membranous RhoA and p-ERM in the brainstem were significantly greater in both angiotensin II-treated WKY and SHR than in vehicle-treated WKY. Valsartan reduced the expression levels of membranous RhoA and p-ERM in angiotensin II-treated WKY and SHR. Y-27632 reduced the expression levels of p-ERM in angiotensin II-treated WKY and SHR. Conclusions These results suggest that the pressor response induced by intracisternally infused angiotensin II is substantially mediated by the activation of the Rho/Rho-kinase pathway via AT1 receptors of the brainstem in WKY, and that this pathway might be involved in the hypertensive mechanisms of SHR.

Successful bipolar ablation for ventricular tachycardia with potential substrate identification by pre-procedural cardiac magnetic resonance imaging

Cardiac magnetic resonance imaging (MRI) is a useful tool for detecting the arrhythmogenic substrate in cardiac sarcoidosis. We herein present a case of bipolar radiofrequency catheter ablation for ventricular tachycardia (VT) complicated with cardiac sarcoidosis, guided by pre-procedural cardiac MRI. Neither echocardiography nor endocardial voltage mapping suggested a septal VT substrate. However, MRI alone detected intramural lesions in the septum. Although application of endocardial energy failed to treat the VT, bipolar ablation targeting the potential substrate identified by MRI successfully eliminated the VT. Even when no abnormalities are depicted on echocardiography and endocardial voltage mapping, intramural scar tissue identified by cardiac MRI could be critical for VT.

Superior Rhythm Discrimination With the SmartShock Technology Algorithm ― Results of the Implantable Defibrillator With Enhanced Features and Settings for Reduction of Inaccurate Detection (DEFENSE) Trial ―

BACKGROUND Shocks delivered by implanted anti-tachyarrhythmia devices, even when appropriate, lower the quality of life and survival. The new SmartShock Technology®(SST) discrimination algorithm was developed to prevent the delivery of inappropriate shock. This prospective, multicenter, observational study compared the rate of inaccurate detection of ventricular tachyarrhythmia using the SST vs. a conventional discrimination algorithm.Methods and Results:Recipients of implantable cardioverter defibrillators (ICD) or cardiac resynchronization therapy defibrillators (CRT-D) equipped with the SST algorithm were enrolled and followed up every 6 months. The tachycardia detection rate was set at ≥150 beats/min with the SST algorithm. The primary endpoint was the time to first inaccurate detection of ventricular tachycardia (VT) with conventional vs. the SST discrimination algorithm, up to 2 years of follow-up. Between March 2012 and September 2013, 185 patients (mean age, 64.0±14.9 years; men, 74%; secondary prevention indication, 49.5%) were enrolled at 14 Japanese medical centers. Inaccurate detection was observed in 32 patients (17.6%) with the conventional, vs. in 19 patients (10.4%) with the SST algorithm. SST significantly lowered the rate of inaccurate detection by dual chamber devices (HR, 0.50; 95% CI: 0.263-0.950; P=0.034). CONCLUSIONS Compared with previous algorithms, the SST discrimination algorithm significantly lowered the rate of inaccurate detection of VT in recipients of dual-chamber ICD or CRT-D.

Very late perforation by a Riata implantable cardioverter-defibrillator lead-A case report

Cardiac perforation by a transvenous lead is an uncommon but serious complication. We herein present a case of very late perforation of a Riata implantable cardioverter‐defibrillator lead, which occurred 8 years after implantation. The patient was successfully treated with percutaneous lead extraction using an excimer laser. Lead perforation should be considered, even after years from implantation.

Successful percutaneous retrieval of a micra transcatheter pacing system at 8 weeks after implantation

An 86‐year‐old woman suffering from repeated methicillin‐resistant Staphylococcus aureus (MRSA) bacteremia underwent percutaneous lead extraction using an excimer laser. Since negative blood cultures were confirmed three times after lead extraction under intravenous infusion of anti‐MRSA drugs, a Micra transcatheter pacing system (Micra TPS) was implanted 7 days after the lead extraction. Although infusion of anti‐MRSA drugs was continued for 5 weeks, MRSA was isolated in four separate samples of blood cultures 3 weeks after the discontinuation of the anti‐MRSA therapy. The micra TPS was successfully retrieved using a steerable sheath and snare at 8 weeks after implantation.