Moritake Iguchi

A novel gain-of-function KCNJ2 mutation associated with short-QT syndrome impairs inward rectification of Kir2.1 currents

AIMS Short-QT syndrome (SQTS) is a recently recognized disorder associated with atrial fibrillation (AF) and sudden death due to ventricular arrhythmias. Mutations in several ion channel genes have been linked to SQTS; however, the mechanism remains unclear. This study describes a novel heterozygous gain-of-function mutation in the inward rectifier potassium channel gene, KCNJ2, identified in SQTS. METHODS AND RESULTS We studied an 8-year-old girl with a markedly short-QT interval (QT = 172 ms, QTc = 194 ms) who suffered from paroxysmal AF. Mutational analysis identified a novel heterozygous KCNJ2 mutation, M301K. Functional assays displayed no Kir2.1 currents when M301K channels were expressed alone. However, co-expression of wild-type (WT) with M301K resulted in larger outward currents than the WT at more than -30 mV. These results suggest a gain-of-function type modulation due to decreased inward rectification. Furthermore, we analysed the functional significance of the amino acid charge at M301 (neutral) by changing the residue. As with M301K, in M301R (positive), the homozygous channels were non-functional, whereas the heterozygous channels demonstrated decreased inward rectification. Meanwhile, the currents recorded in M301A (neutral) showed normal inward rectification under both homo- and heterozygous conditions. Heterozygous overexpression of WT and M301K in neonatal rat ventricular myocytes exhibited markedly shorter action potential durations than the WT alone. CONCLUSION In this study, we identified a novel KCNJ2 gain-of-function mutation, M301K, associated with SQTS. Functional assays revealed no functional currents in the homozygous channels, whereas impaired inward rectification demonstrated under the heterozygous condition resulted in larger outward currents, which is a novel mechanism predisposing SQTS.

Incidence of Stroke or Systemic Embolism in Paroxysmal Versus Sustained Atrial Fibrillation The Fushimi Atrial Fibrillation Registry

Background and Purpose— There is controversy on the relationship of the type of atrial fibrillation (AF) to stroke. Although several studies show that patients with paroxysmal AF (PAF) have a stroke risk similar to those with persistent or permanent AF, recent studies suggest that PAF is associated with a lower rate of stroke. Limited data on stroke risk associated with PAF are evident in Asian populations. Methods— The Registry Study of Atrial Fibrillation Patients in Fushimi-ku (Fushimi AF Registry) is a community-based survey of patients with AF in Fushimi-ku, Kyoto, Japan. Patients were categorized into 2 types of AF: PAF or sustained (persistent or permanent) AF. We compared clinical events between PAF (n=1588) and sustained AF (n=1716). Results— Patients with PAF were younger, had less comorbidities, and received oral anticoagulants (OAC) less commonly. A lower risk of stroke/systemic embolism during follow-up period in the patients with PAF was consistently observed (non-OAC users: hazard ratio, 0.45; 95% confidence intervals, 0.27–0.75; P<0.01 and OAC users: hazard ratio, 0.59; 95% confidence interval, 0.35–0.93; P=0.03). The composite end point of stroke/systemic embolism/all-cause mortality was also lower in PAF, whether among OAC users (hazard ratio, 0.77; 95% confidence interval, 0.59–0.99; P=0.046) or non-OAC users (hazard ratio, 0.59; 95% confidence interval, 0.46–0.75; P<0.01). On multivariate analysis, PAF was an independent predictor of lower stroke/systemic embolism risk. Conclusions— In this large cohort of Japanese patients with AF, PAF was independently associated with lower incidence of stroke/systemic embolism than sustained AF. This may aid decision making for anticoagulation, especially in those patients with AF with few stroke risk factors. Clinical Trial Registration— URL: http://www.umin.ac.jp/ctr/index.htm. Unique identifier: UMIN000005834.

The targeting of cyclophilin D by RNAi as a novel cardioprotective therapy: evidence from two-photon imaging.

AIMS An opening of the mitochondrial permeability transition pore (MPTP), which leads to the loss of mitochondrial membrane potential (DeltaPsi(m)), is the earliest event that commits cells to death, and this process is potentially a prime target for therapeutic intervention against myocardial ischaemia/reperfusion. We aimed to investigate the protective effects of RNA interference (RNAi)-mediated gene silencing of cyclophilin D (CypD), one of the putative components of the MPTP, against myocardial ischaemia/reperfusion using two-photon laser scanning microscopy. METHODS AND RESULTS We created an adenovirus carrying short-interfering RNA (siRNA) that inactivates CypD. Transduction of CypD-siRNA in rat cardiomyocytes achieved a 61% reduction in CypD mRNA and a 63% reduction in protein levels as well as protection against oxidant-induced DeltaPsi(m) loss and cytotoxicity. To further investigate the effects in vivo, we monitored the spatio-temporal changes of DeltaPsi(m) in perfused rat hearts subjected to ischaemia/reperfusion using two-photon imaging. Adult rats received direct intramyocardial injections of the adenovirus. Two to three days after injection, rat hearts were perfused by the Langendorff method and DeltaPsi(m) levels of individual cells were monitored. The progressive loss of DeltaPsi(m) during ischaemia/reperfusion was significantly suppressed in CypD-siRNA-transduced cells compared with non-transduced cells. Furthermore, the protective effect of CypD-siRNA was dose-dependent. CONCLUSION Therapeutic interventions designed to inactivate CypD may be a promising strategy for reducing cardiac injury against myocardial ischaemia/reperfusion. The two-photon imaging technique provides deeper insight into cardioprotective therapy that targets mitochondria.

Low Body Weight Is Associated With the Incidence of Stroke in Atrial Fibrillation Patients – Insight From the Fushimi AF Registry –

BACKGROUND Japanese patients with atrial fibrillation (AF) are generally small and lean, but knowledge of the clinical characteristics of those with low body weight (LBW: ≤50 kg) is limited. METHODS AND RESULTS The Fushimi AF Registry is a community-based prospective survey of AF patients who visited the participating medical institutions in Fushmi-ku, Japan. The BW and follow-up data were available for 2,945 patients. We compared the background and the incidence of clinical events during a median follow-up of 746 days between a LBW and non-LBW group. Patients in the LBW group accounted for 26.8% (788 patients) of the total. The LBW group was more often female, older, and had higher CHADS2score. The incidence of stroke/systemic embolism (SE) during follow-up was higher in the LBW group (hazard ratio (HR): 2.19, 95% confidence interval (CI): 1.57-3.04; P<0.01), whereas that of major bleeding was comparable (HR: 1.05, 95% CI: 0.64-1.68; P=0.84). This trend was consistently observed in the subgroups stratified by age, sex, and oral anticoagulant prescription at baseline. Multivariate analysis as well as propensity-score matching analysis further supported the significance of LBW as a risk of stroke/SE. CONCLUSIONS Patients in the LBW group had high risk profiles and showed a higher incidence of stroke/SE, but the incidence of major bleeding was not particularly high.

Direct monitoring of mitochondrial calcium levels in cultured cardiac myocytes using a novel fluorescent indicator protein, GCaMP2-mt

BACKGROUND An opening of the mitochondrial permeability transition pore (MPTP), which leads to loss of mitochondrial membrane potential (ΔΨ(m)), is the earliest event that commits a cell to death. Mitochondrial matrix calcium ([Ca(2+)](m)) is considered to be a critical regulator of MPTP, but direct monitoring of [Ca(2+)](m) is difficult with previously-reported sensors. We developed a novel fluorescent indicator for [Ca(2+)](m), GCaMP2-mt, by adding a mitochondrial targeting sequence to a high signal-to-noise Ca(2+) sensor protein GCaMP2, and monitored dynamic changes in oxidant-induced cardiac myocyte death. METHODS AND RESULTS GCaMP2-mt was transduced into neonatal rat cardiac myocytes using a recombinant adenovirus. We confirmed that GCaMP2-mt colocalized with tetramethylrhodamine ethyl-ester, a fluorescent indicator of ΔΨ(m). We monitored oxidant-induced responses of [Ca(2+)](m) and ΔΨ(m) using time-lapse confocal microscopy. The response of [Ca(2+)](m) was synchronous with that of cytosolic calcium and was divided into three kinetically-distinct phases; the first phase, during which [Ca(2+)](m) maintained its baseline level; the second phase, during which [Ca(2+)](m) showed a rapid and sudden increase; and the third phase, during which [Ca(2+)](m) continued to increase at a slower rate until the collapse of ΔΨ(m). The third phase was likely to be mediated through a mitochondrial Ca(2+) uniporter, because it was modulated by uniporter-acting drugs. Importantly, there was a remarkable cellular heterogeneity in the third phase, and ΔΨ(m) loss occurred in an all-or-none manner depending on the cellular [Ca(2+)](m) level with a clear cut-off value. CONCLUSIONS Direct monitoring of [Ca(2+)](m) using GCaMP2-mt provides deeper insight into the mechanism of cardiac myocyte death.

Thyroid Storm with Heart Failure Treated with a Short-acting Beta-adrenoreceptor Blocker, Landiolol Hydrochloride.

Beta-adrenoreceptor blockers are essential in controlling the peripheral actions of thyroid hormones and a rapid heart rate in patients with thyroid storm, although they should be used with great caution when there is the potential for heart failure. A 67-year-old woman was diagnosed as having thyroid storm in addition to marked tachycardia with atrial fibrillation and heart failure associated with a reduced left ventricular function. The administration of an oral beta blocker, bisoprolol fumarate, induced hypotension and was not tolerable for the patient, whereas landiolol hydrochloride, a short-acting intravenous beta-adrenoreceptor blocker with high cardioselectivity and a short elimination half-life, was useful for controlling the patients tachycardia and heart failure without causing hemodynamic deterioration.

Adaptive servoventilation versus oxygen therapy for sleep disordered breathing in patients with heart failure: a randomised trial

Background Both adaptive servoventilation (ASV) and nocturnal oxygen therapy improve sleep disordered breathing (SDB), but their effects on cardiac parameters have not been compared systematically. Methods and results 43 patients with chronic heart failure (CHF; left ventricular ejection fraction (LVEF) ≤50%) with SDB were randomly assigned to undergo ASV (n=19, apnoea hypopnoea index (AHI)=34.2±12.1/h) or oxygen therapy (n=24, 36.9±9.9/h) for 3 months. More than 70% of SDB events in both groups were central apnoeas or hypopnoeas. Although nightly adherence was less for the ASV group than for the oxygen group (4.4±2.0 vs 6.2±1.8 h/day, p<0.01), the improvement in AHI was larger in the ASV group than in the oxygen group (−27.0±11.5 vs −16.5±10.2/h, p<0.01). The N-terminal pro-brain natriuretic peptide (NT-proBNP) level in the ASV group improved significantly after titration (1535±2224 to 1251±2003 pg/mL, p=0.01), but increased slightly at follow-up and this improvement was not sustained (1311±1592 pg/mL, p=0.08). Meanwhile, the level of plasma NT-proBNP in the oxygen group did not show a significant change throughout the study (baseline 1071±1887, titration 980±1913, follow-up 1101±1888 pg/mL, p=0.19). The significant difference in the changes in the NT-proBNP level throughout the study between the 2 groups was not found (p=0.30). Neither group showed significant changes in echocardiographic parameters. Conclusions Although ASV produced better resolution of SDB in patients with CHF as compared with oxygen therapy, neither treatment produced a significant improvement in cardiac function in the short term. Although we could not draw a definite conclusion because of the small number of participants, our data do not seem to support the routine use of ASV or oxygen therapy to improve cardiac function in patients with CHF with SDB. Trial registration number NCT01187823 (http://www.clinicaltrials.gov).

Kyoto Congestive Heart Failure (KCHF) Study: Rationale and Design.

Over the last decade, major developments in medicine have led to significant changes in the clinical management of heart failure patients. This study was designed to evaluate the recent trends in clinical characteristics, management, and short‐term and long‐term prognosis of patients with acute decompensated heart failure (ADHF) in Japan.

Relationship of Hypertension and Systolic Blood Pressure With the Risk of Stroke or Bleeding in Patients With Atrial Fibrillation: The Fushimi AF Registry

BACKGROUND Hypertension is considered a major risk factor of stroke and systemic embolism (SE) as well as bleeding in patients with atrial fibrillation (AF). The purpose of this study was to investigate the relationship of hypertension and systolic blood pressure (SBP) with the risk of stroke/SE or bleeding in AF patients. METHODS The Fushimi AF Registry, a community-based prospective survey, was designed to enroll all of the AF patients in Fushimi-ku, Kyoto. Fushimi-ku is densely populated with a total population of 283,000. Follow-up data were available for 3,713 patients (follow-up rate 90.0%) as of August 2015, and the median follow-up period was 1,035 days. RESULTS We compared the clinical backgrounds at baseline, and follow-up outcomes of AF patients between those with hypertension (HTN; n = 2,304, 62.1% of total) and those without (non-HTN; n = 1,409). History of hypertension was neither associated with the incidence of stroke/SE, ischemic stroke, hemorrhagic stroke nor major bleeding. However, when we divided the HTN group by baseline SBP ≥150 mm Hg (HTN-high blood pressure [HBP]: n = 305, 13.3% of HTN group) or <150 mm Hg (HTN-low blood pressure [LBP]: n = 1,983), HTN-HBP group was significantly associated with a higher incidence of both stroke/SE (hazard ratio [HR]: 1.74, 95% confidence interval [CI]: 1.08-2.72) and major bleeding (HR: 2.01, 95% CI: 1.21-3.23) compared with the non-HTN group. In contrast, HTN-LBP group was not associated with the risk of stroke/SE or major bleeding, compared with the non-HTN group. CONCLUSION The incidences of stroke/SE and bleeding were higher in AF and hypertension patients with elevated SBP. UMIN Clinical Trials Registry: UMIN000005834.

Causes of death in Japanese patients with atrial fibrillation: The Fushimi Atrial Fibrillation Registry

Aims To investigate the causes of death and the associated clinical factors in patients with atrial fibrillation (AF) in the contemporary clinical practice. Methods and results The Fushimi AF Registry is a community-based prospective survey of AF patients since March 2011 in Fushimi-ku, Kyoto. We investigated causes of death and the clinical indicators of cardiovascular (CV) and non-CV death in 4045 patients with available follow-up data by the end of November 2016. The mean age was 73.6 ± 10.9 years and the mean CHA2DS2-VASc score was 3.38 ± 1.69. Oral anticoagulants were prescribed in 55% of patients. During a median follow-up of 1105 days, there were 705 all-cause deaths (5.5%/year); 180 CV (26% of total deaths), 381 non-CV (54%), and 144 undetermined causes (20%). The most common causes of CV and non-CV death were heart failure (14.5%), malignancy (23.1%), and infection/sepsis (17.3%), while mortality due to stroke was only 6.5%. Mortality due to infection/sepsis and undetermined causes increased with aging. On multivariate analysis, the strongest indicator of CV death was pre-existing heart failure [hazard ratio (HR) 2.42, 95% confidence interval (CI) 1.66-3.54; P < 0.001] and that of non-CV death was anaemia (HR 2.84, 95% CI 2.22-3.65; P < 0.001). Conclusion In a Japanese community-based AF cohort, CV death was not mainly related to stroke but to heart failure. Non-CV death, mainly malignancy and infection, comprised more than a half of all deaths, which increased substantially in accordance with aging. Clinical factors that were associated with CV and non-CV death were distinct.