Antibody response to COVID-19 vaccination in patients with lymphoma.

Patients with lymphoma are at increased risk for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2); therefore, evaluation of SARS-CoV-2 vaccination efficacy is essential. We conducted a prospective observational study to monitor the antibody response in 500 patients with lymphoma after SARS-CoV-2 vaccination. Antibody levels increased in a stepwise manner after the first and second dose of the vaccine. After completion of the two-dose series, anti-S antibody was negative in 109 patients (21.8%), and below clinically protective levels (anti-S ≥ 264 U/mL) in 236 patients (47.2%). The median anti-S titers at 0-6 months, 7-12 months, 13-24 months, and 24 months after treatment completion were 0.4 U/mL, 3.8 U/mL, 270 U/mL, and 650 U/mL, respectively. Multivariate analysis showed that receiving the vaccine < 6 months since completing treatment, white blood cell count < 5050/µL, percentage of CD19 + cells < 10%, CD4 + cells < 27%, immunoglobulin (Ig) A < 195 mg/dL, IgM < 50 mg/dL, serum soluble interleukin 2 receptor > 600 U/mL, and presence of lymphoma cells in the peripheral blood were significantly correlated with anti-S < 264 U/mL. Lymphoma patients had variably impaired antibody response to the SARS-CoV-2 vaccine. We identified various factors to predict COVID-19 vaccine effectiveness in lymphoma patients that may help tailoring possible vaccine boosters.

Low clinical protective response to SARS-CoV-2 mRNA COVID-19 vaccine in patients with multiple myeloma.

We conducted a prospective, three-center, observational study in Japan to evaluate the prevalence of seropositivity and clinically protective titer after coronavirus disease 2019 vaccination in patients with plasma cell dyscrasia(PCD). Two-hundred sixty-nine patients with PCD [206 symptomatic multiple myeloma (MM)] were evaluated. Seropositivity was observed in 88.7% and a clinically protective titer in 38.3% of MM patients, both of which were significantly lower than those of healthy controls. Patients receiving anti-CD38 antibodies had much lower antibody titers, but antibody titers recovered in those who underwent a wash-out period before vaccine administration. Older age (≥65), anti-CD38 antibody administration, immunomodulatory drugs use, lymphopenia (<1000/µL), and lower polyclonal IgG (<550 mg/dL) had a negative impact for the sufficient antibody production according to multivariate analysis. Patients with clinically protective titer had a significantly higher number of CD19+ lymphocytes than those with lower antibody responses (114 vs. 35/µL, p = 0.016). Our results suggested that patients with PCD should be vaccinated, and that the ideal protocol is to temporarily interrupt anti-CD38 antibody therapy for a "wash-out" period of a few months, followed by a (booster) vaccine after the B-cells have recovery.

Urinary 8-hydroxy-2'-deoxyguanosine as a novel biomarker of inflammatory activity in patients with cardiac sarcoidosis.

BACKGROUND: Inflammation and oxidative stress play a crucial role in the pathogenesis of cardiac sarcoidosis (SAR). We investigated whether urinary (U) 8-hydroxy-2'-deoxyguanosine (8-OHdG)--an oxidative DNA damage marker--was related to SAR inflammatory activity. METHODS: U-8-OHdG levels were measured in 31 SAR patients, classified as active (n=17) or non-active (n=14) based on (18)F-fluorodeoxyglucose positron emission tomography-computed tomography ((18)F-FDG-PET/CT), 28 dilated cardiomyopathy (DCM) patients, and 30 controls. In active SAR patients, U-8-OHdG levels were reexamined and compared with (18)F-FDG-PET/CT results at 6 months after corticosteroid treatment to assess therapeutic response. RESULTS: Immunohistochemical examination of left ventricle (LV) autopsy samples from SAR patients revealed positive 8-OHdG staining in cardiomyocyte nuclei from LV sections showing (18)F-FDG accumulation on PET/CT, while serum 8-OHdG levels were significantly higher in the coronary sinus than in the aortic root only in active SAR patients. U-8-OHdG levels in SAR patients were higher than those in controls, and significantly higher in active SAR patients than in non-active SAR and DCM patients. U-8-OHdG was a powerful predictor of active SAR in receiver operating characteristic curve analysis (AUC, 0.98; 95% CI, 0.94-1.02; optimal cutoff value, 13.1 ng/mg creatinine), with a sensitivity of 88.2% and a specificity of 92.9%. U-8-OHdG levels in responders significantly decreased at 6 months after corticosteroid treatment initiation, in proportion with the decrease in the focal cardiac uptake of (18)F-FDG. CONCLUSIONS: U-8-OHdG is a potentially clinically useful biomarker for evaluating inflammatory activity and monitoring the effectiveness of corticosteroid therapy in SAR patients.

A low-dose ß1-blocker in combination with milrinone improves intracellular Ca2+ handling in failing cardiomyocytes by inhibition of milrinone-induced diastolic Ca2+ leakage from the sarcoplasmic reticulum.

OBJECTIVES: The purpose of this study was to investigate whether adding a low-dose ß1-blocker to milrinone improves cardiac function in failing cardiomyocytes and the underlying cardioprotective mechanism. BACKGROUND: The molecular mechanism underlying how the combination of low-dose ß1-blocker and milrinone affects intracellular Ca(2+) handling in heart failure remains unclear. METHODS: We investigated the effect of milrinone plus landiolol on intracellular Ca(2+) transient (CaT), cell shortening (CS), the frequency of diastolic Ca(2+) sparks (CaSF), and sarcoplasmic reticulum Ca(2+) concentration ({Ca(2+)}SR) in normal and failing canine cardiomyocytes and used immunoblotting to determine the phosphorylation level of ryanodine receptor (RyR2) and phospholamban (PLB). RESULTS: In failing cardiomyocytes, CaSF significantly increased, and peak CaT and CS markedly decreased compared with normal myocytes. Administration of milrinone alone slightly increased peak CaT and CS, while CaSF greatly increased with a slight increase in {Ca(2+)}SR. Co-administration of ß1-blocker landiolol to failing cardiomyocytes at a dose that does not inhibit cardiomyocyte function significantly decreased CaSF with a further increase in {Ca(2+)}SR, and peak CaT and CS improved compared with milrinone alone. Landiolol suppressed the hyperphosphorylation of RyR2 (Ser2808) in failing cardiomyocytes but had no effect on levels of phosphorylated PLB (Ser16 and Thr17). Low-dose landiolol significantly inhibited the alternans of CaT and CS under a fixed pacing rate (0.5 Hz) in failing cardiomyocytes. CONCLUSION: A low-dose ß1-blocker in combination with milrinone improved cardiac function in failing cardiomyocytes, apparently by inhibiting the phosphorylation of RyR2, not PLB, and subsequent diastolic Ca(2+) leak.

A low-dose ß1-blocker effectively and safely slows the heart rate in patients with acute decompensated heart failure and rapid atrial fibrillation.

OBJECTIVE: Recently, we reported that low-dose landiolol (1.5 µg·kg(-1)·min(-1)), an ultra-short-acting ß-blocker, safely decreased the heart rate (HR) in patients with acute decompensated heart failure (ADHF) and sinus tachycardia, thereby improving cardiac function. We investigated whether low-dose landiolol effectively decreased the HR in ADHF patients with rapid atrial fibrillation (AF). METHODS: We enrolled 23 ADHF patients with rapid AF (HR ≥120 beats·min(-1) and New York Heart Association class III-IV) and systolic heart failure (SHF: n = 12) or diastolic heart failure (DHF: n = 11) who received conventional therapy with diuretics, vasodilators, and/or low-dose inotropes. They were administered continuous intravenous infusion of low-dose landiolol (1.0-2.0 µg·kg(-1)·min(-1)), and their electrocardiograms and blood pressures were monitored for 24 h thereafter. RESULTS: Two hours after starting landiolol, the HR was reduced significantly (22%), without a reduction in blood pressure, and remained constant thereafter. The HR reduction 2 h after landiolol administration was significantly greater in the DHF group than in the SHF group. No incidence of hypotension was recorded. CONCLUSIONS: Digitalis or amiodarone is currently recommended for HR control in ADHF patients with rapid AF. Our results showed that continuous infusion of low-dose landiolol may also be useful as first-line therapy in these patients.

Enhanced binding of calmodulin to the ryanodine receptor corrects contractile dysfunction in failing hearts.

AIMS: The channel function of the cardiac ryanodine receptor (RyR2) is modulated by calmodulin (CaM). However, the involvement of CaM in aberrant Ca(2+) release in diseased hearts remains unclear. Here, we investigated the pathogenic role of defective CaM binding to the RyR2 in the channel dysfunction associated with heart failure. METHODS AND RESULTS: The involvement of CaM in aberrant Ca(2+) release was assessed in normal and pacing-induced failing canine hearts. The apparent affinity of CaM for RyR2 was considerably lower in failing sarcoplasmic reticulum (SR) compared with normal SR. Thus, the amount of CaM bound to RyR2 was markedly decreased in failing myocytes. Expression of the CaM isoform Gly-Ser-His-CaM (GSH-CaM), which has much higher binding affinity than wild-type CaM for RyR1, restored normal CaM binding to RyR2 in both SR and myocytes of failing hearts. The Ca(2+) spark frequency (SpF) was markedly higher and the SR Ca(2+) content was lower in failing myocytes compared with normal myocytes. The incorporation of GSH-CaM into the failing myocytes corrected the aberrant SpF and SR Ca(2+) content to normal levels. CONCLUSION: Reduced CaM binding to RyR2 seems to play a critical role in the pathogenesis of aberrant Ca(2+) release in failing hearts. Correction of the reduced CaM binding to RyR2 stabilizes the RyR2 channel function and thereby restores normal Ca(2+) handling and contractile function to failing hearts.

Low-dose ß-blocker in combination with milrinone safely improves cardiac function and eliminates pulsus alternans in patients with acute decompensated heart failure.

BACKGROUND: The purpose of this study was to determine whether a low-dose ß-blocker, in combination with milrinone, improves cardiac function in acute decompensated heart failure (ADHF) with tachycardia. METHODS AND RESULTS: Twenty ADHF patients (New York Heart Association classification III, n=1, and IV, n=19; heart rate [HR], 107±12 beats/min; left ventricular ejection fraction, 24±7%; cardiac index [CI], 2.2±0.6 L·min(-1)·m(-2); pulmonary capillary wedge pressure [PCWP], 26±8 mmHg) were enrolled in this study. The patients first underwent conventional therapy with milrinone, vasodilators and diuretics; landiolol (1.5-6.0 µg·kg(-1)·min(-1); i.v.), which is an ultra-short-acting ß(1)-selective blocker, was then added to the treatment regimen to study its effect on hemodynamics. Low-dose landiolol (1.5 µg·kg(-1)·min(-1)) significantly reduced HR by 11% without changing blood pressure (BP) and CI, whereas higher doses (≥3.0 µg·kg(-1)·min(-1)) tended to decrease BP and CI while increasing PCWP and systemic vascular resistance. After treatment with landiolol (1.5 µg·kg(-1)·min(-1)), hemodynamic parameters such as PCWP, stroke volume index, SvO(2), rate pressure product, filling time/RR, E/e', and Tei index were significantly improved. CONCLUSIONS: A low-dose ß-blocker in combination with milrinone improved cardiac function in ADHF patients with tachycardia; therefore, it may be considered as an adjunct therapy for use when standard therapy with milrinone is not effective at slowing HR.

Effects of isoproterenol and propranolol on the inducibility and frequency of ventricular fibrillation in patients with Brugada syndrome.

BACKGROUND: Isoproterenol (ISP), a beta-adrenergic agonist, suppresses arrhythmic storm in patients with sporadic Brugada syndrome (BS). However, the influence of ISP and the beta-adrenergic antagonist propranolol (PRO) on the inducibility and frequency of ventricular fibrillation (VF) in BS patients remains unclear. METHODS AND RESULTS: Twenty-seven BS patients with induced VF>10s in a control state were enrolled. Electrophysiological stimulation (EPS) testing was performed during ISP and after PRO in selected patients. The inducibility and frequency of VF were compared. Dominant frequency (DF) was obtained by Fast Fourier transform from 4-s data (phase) and sequentially every 2s up to phase 5. ISP prevented induction of VF in 20 of 25 patients (80%). During ISP, 5 patients experienced induction of VF. ISP significantly influenced DF transition compared with the control state. DF gradually increased but was unchanged after the middle phase. PRO had no effect on incidence of induced VF in 5 patients; increased PRO induced VF in 5 (83.3%) of 6 patients who tested negative during ISP. After PRO, 10 patients experienced induction of VF. Thus, PRO significantly influenced DF transition. DF after PRO was higher than that in the corresponding phase in the control state. CONCLUSION: ISP suppressed induction of VF and the increase of DF with time. PRO aggravated VF and accelerated DF.

Characteristics of induced ventricular fibrillation cycle length in symptomatic Brugada syndrome patients.

BACKGROUND: Limited information is available on the ventricular fibrillation (VF) spectrum in Brugada syndrome (BS) patients. We clarified differences in the VF cycle length (CL) using fast-Fourier transformation (FFT) analysis in symptomatic and asymptomatic BS patients. METHODS AND RESULTS: VF was induced by pacing from the right ventricular (RV) apex and/or RV outflow tract (RVOT) for >8s. A 4096-point FFT analysis of results from 28 male BS patients (51.1 ± 13.7 years old) was performed. Dominant frequency (DF) from phases 1 (4s) to 6 was obtained at 2-s intervals. The average DF from surface and intracardiac electrograms (ECG: DF(ECG); ICE: DF(ICE,), respectively) was compared between symptomatic and asymptomatic patients. Symptomatic patients had a significantly shorter effective refractory period at a CL of 600 ms at the RVOT than asymptomatic patients. DF(ECG) significantly increased with phase (5.64 ± 0.32 Hz in phase 1 to 6.16 ± 0.52 Hz in phase 6) and was significantly higher in symptomatic patients than in asymptomatic patients. DF(ICE) had the same characteristics as DF(ECG). CONCLUSIONS: Induced VF in BS patients can be characterized using FFT analysis. Our data support the hypothesis that symptomatic patients have a significantly shorter VF CL than asymptomatic patients.

Urinary 8-hydroxy-2'-deoxyguanosine as a novel biomarker for predicting cardiac events and evaluating the effectiveness of carvedilol treatment in patients with chronic systolic heart failure.

BACKGROUND: The authors recently reported that urinary 8-hydroxy-2'-deoxyguanosine (U8-OHdG) derived from cardiac tissue reflects clinical status and cardiac dysfunction severity in patients with chronic heart failure (CHF). The aim of the present study was to investigate whether U8-OHdG levels can accurately predict cardiac events in CHF patients and their response to ß-blocker treatment. METHODS AND RESULTS: Plasma brain natriuretic peptide (BNP) and U8-OHdG levels were measured in 186 consecutive CHF patients before discharge. Patients were then prospectively followed (median follow-up, 649 days) with endpoints of cardiac death or hospitalization due to progressive heart failure. From receiver operating characteristic curve analysis, cut-offs were 12.4ng/mg creatinine (Cr) for U8-OHdG and 207pg/ml for BNP. On multivariate Cox analysis, U8-OHdG and BNP were independent predictors of cardiac events. Patients were classified into 4 groups according to U8-OHdG and BNP cut-offs. The hazard ratio for cardiac events in patients with BNP ≥207pg/ml and U8-OHdG ≥12.4ng/mg Cr was 16.2 compared with approximately 4 for patients with only 1 indicator above its respective cut-off. Furthermore, carvedilol therapy was initiated in 30 CHF patients. In responders (≥10% increase in left ventricular ejection fraction [LVEF] or ≥1 class decrease in New York Heart Association [NYHA] class), U8-OHdG levels decreased significantly along with improved NYHA class, LVEF, and BNP levels after treatment. CONCLUSIONS: U8-OHdG may be a useful biomarker for predicting cardiac events and evaluating ß-blocker therapy effectiveness in CHF patients.

Mutation-linked defective interdomain interactions within ryanodine receptor cause aberrant Ca²âºrelease leading to catecholaminergic polymorphic ventricular tachycardia.

BACKGROUND: The molecular mechanism by which catecholaminergic polymorphic ventricular tachycardia is induced by single amino acid mutations within the cardiac ryanodine receptor (RyR2) remains elusive. In the present study, we investigated mutation-induced conformational defects of RyR2 using a knockin mouse model expressing the human catecholaminergic polymorphic ventricular tachycardia-associated RyR2 mutant (S2246L; serine to leucine mutation at the residue 2246). METHODS AND RESULTS: All knockin mice we examined produced ventricular tachycardia after exercise on a treadmill. cAMP-dependent increase in the frequency of Ca²âº sparks was more pronounced in saponin-permeabilized knockin cardiomyocytes than in wild-type cardiomyocytes. Site-directed fluorescent labeling and quartz microbalance assays of the specific binding of DP2246 (a peptide corresponding to the 2232 to 2266 region: the 2246 domain) showed that DP2246 binds with the K201-binding sequence of RyR2 (1741 to 2270). Introduction of S2246L mutation into the DP2246 increased the affinity of peptide binding. Fluorescence quench assays of interdomain interactions within RyR2 showed that tight interaction of the 2246 domain/K201-binding domain is coupled with domain unzipping of the N-terminal (1 to 600)/central (2000 to 2500) domain pair in an allosteric manner. Dantrolene corrected the mutation-caused domain unzipping of the domain switch and stopped the exercise-induced ventricular tachycardia. CONCLUSIONS: The catecholaminergic polymorphic ventricular tachycardia-linked mutation of RyR2, S2246L, causes an abnormally tight local subdomain-subdomain interaction within the central domain involving the mutation site, which induces defective interaction between the N-terminal and central domains. This results in an erroneous activation of Ca²âº channel in a diastolic state reflecting on the increased Ca²âº spark frequency, which then leads to lethal arrhythmia.

Environmental protection: researches in National Institute of Radiological Sciences.

Some studies for radiological protection of the environment have been made at the National Institute of Radiological Sciences (NIRS). Transfer of radionuclides and related elements has been investigated for dose estimation of non-human biota. A parameter database and radionuclide transfer models have been also developed for the Japanese environments. Dose (rate)-effect relationships for survival, growth and reproduction have been investigated in conifers, Arabidopsis, fungi, earthworms, springtails, algae, duckweeds, daphnia and medaka. Also genome-wide gene expression analysis has been carried out by high coverage expression profiling (HiCEP). Effects on aquatic microbial communities have been studied in experimental ecosystem models, i.e., microcosms. Some effects were detected at a dose rate of 1 Gy day(-1) and were likely to arise from interspecies interactions. The results obtained at NIRS have been used in development of frameworks for environmental protection by some international bodies, and will contribute to environmental protection in Japan and other Asian countries.

Urinary 8-hydroxy-2'-deoxyguanosine reflects symptomatic status and severity of systolic dysfunction in patients with chronic heart failure.

AIMS: Oxidative stress is known to play a crucial role in the pathogenesis of heart failure (HF). We investigated whether urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG), a product of oxidative DNA damage, is a clinically useful biomarker of the severity of chronic heart failure (CHF) and oxidative stress levels in failing hearts. METHODS AND RESULTS: We measured 8-OHdG in the serum obtained from the coronary sinus (CS) and aortic root (Ao) in small groups of control subjects and CHF patients. We then measured urinary 8-OHdG and other biomarkers (brain natriuretic peptide, 8-isoplastane, high-sensitivity C-reactive protein, interleukin-6, and tumour necrosis factor-α) in 31 control subjects and 194 patients with CHF [left-ventricular ejection fraction (LVEF): 28.3 ± 8.1%]. Serum 8-OHdG was significantly higher in the CS than the Ao in CHF patients only. Urinary 8-OHdG was also significantly higher in CHF patients than in control subjects, and urinary 8-OHdG became higher as New York Heart Association class increased. Moreover, there was a significant correlation between urinary 8-OHdG and LVEF (r = -0.27), pulmonary capillary wedge pressure (r = 0.31), or left-ventricular end-diastolic volume index (r = 0.22). In contrast, there was poor correlation between the severity of CHF and the other neurohumoral biomarkers. CONCLUSION: In HF, urinary 8-OHdG seems to reflect the level of oxidative stress and various parameters related to symptomatic status and functional severity of CHF.

Dantrolene, a therapeutic agent for malignant hyperthermia, inhibits catecholaminergic polymorphic ventricular tachycardia in a RyR2(R2474S/+) knock-in mouse model.

BACKGROUND: Dantrolene, a specific agent for the treatment of malignant hyperthermia, was found to inhibit Ca(2+) leak through not only the skeletal ryanodine receptor (RyR1), but also the cardiac ryanodine receptor (RyR2) by correcting the defective inter-domain interaction between N-terminal (1-619 amino acid) and central (2,000-2,500 amino acid) domains of RyRs. Here, the in vivo anti-arrhythmic effect of dantrolene in a human catecholaminergic polymorphic ventricular tachycardia (CPVT)-associated RyR2(R2474S/+) knock-in (KI) mouse model was investigated. METHODS AND RESULTS: ECG was monitored in KI mice (n=6) and wild-type (WT) mice (n=6), before and after an injection of epinephrine (1.0mg/kg) or on exercise using a treadmill. In all KI (but not WT) mice, bi-directional ventricular tachycardia (VT) was induced after an injection of epinephrine or on exercise. Pre-treatment with dantrolene (for 7-10 days) significantly inhibited the inducible VT (P<0.01). In KI cardiomyocytes, Ca(2+) spark frequency (SpF; s(-1)·100µm(-1): 5.8±0.3, P<0.01) was much more increased after the addition of isoproterenol than in WT cardiomyocytes (SpF: 3.6±0.2). The increase in SpF seen in KI cardiomyocytes was attenuated by 1.0µmol/L dantrolene (SpF: 3.6±0.5, P<0.01). CONCLUSIONS: Dantrolene prevents CPVT, presumably by inhibiting Ca(2+) leak through the RyR2.

Dissociation of calmodulin from cardiac ryanodine receptor causes aberrant Ca(2+) release in heart failure.

AIMS: Calmodulin (CaM) is well known to modulate the channel function of the cardiac ryanodine receptor (RyR2). However, the possible role of CaM on the aberrant Ca(2+) release in diseased hearts remains unclear. In this study, we investigated the state of RyR2-bound CaM and channel dysfunctions in pacing-induced failing hearts. METHODS AND RESULTS: The characteristics of CaM binding to RyR2 and the role of CaM on the aberrant Ca(2+) release were assessed in normal and failing canine hearts. The affinity of CaM binding to RyR2 was lower in failing sarcoplasmic reticulum (SR) than in normal SR. Addition of FK506, which dissociates FKBP12.6 from RyR2, to normal SR reduced the CaM-binding affinity. Dantrolene restored a normal level of the CaM-binding affinity in either FK506-treated (normal) SR or failing SR, suggesting that the defective inter-domain interaction between the N-terminal domain and the central domain of RyR2 (the therapeutic target of dantrolene) is involved in the reduction of the CaM-binding affinity in failing hearts. In saponin-permeabilized cardiomyocytes, the frequency of spontaneous Ca(2+) sparks was much more increased in failing cardiomyocytes than in normal cardiomyocytes, whereas the addition of a high concentration of CaM attenuated the aberrant increase of Ca(2+) sparks. CONCLUSION: The defective inter-domain interaction between N-terminal and central domains within RyR2 reduces the binding affinity of CaM to RyR2, thereby causing the spontaneous Ca(2+) release events in failing hearts. Correction of the defective CaM binding may be a new strategy to protect against the aberrant Ca(2+) release in heart failure.

Defective calmodulin binding to the cardiac ryanodine receptor plays a key role in CPVT-associated channel dysfunction.

Calmodulin (CaM), one of the accessory proteins of the cardiac ryanodine receptor (RyR2), is known to play a significant role in the channel regulation of the RyR2. However, the possible involvement of calmodulin in the pathogenic process of catecholaminergic polymorphic ventricular tachycardia (CPVT) has not been investigated. In this study, we investigated the state of RyR2-bound CaM and channel dysfunctions using a knock-in (KI) mouse model with CPVT-linked RyR2 mutation (R2474S). Without added effectors, the affinity of CaM binding to the RyR2 was indistinguishable between KI and WT hearts. In response to cAMP (1 micromol/L), the RyR2 phosphorylation at Ser2808 increased in both WT and KI hearts to the same extent. However, cAMP caused a significant decrease of the CaM-binding affinity in KI hearts, but the affinity was unchanged in WT. Dantrolene restored a normal level of CaM-binding affinity in the cAMP-treated KI hearts, suggesting that defective inter-domain interaction between the N-terminal domain and the central domain of the RyR2 (the target of therapeutic effect of dantrolene) is involved in the cAMP-induced reduction of the CaM-binding affinity. In saponin-permeabilized cardiomyocytes, the addition of cAMP increased the frequency of spontaneous Ca(2+) sparks to a significantly larger extent in KI cardiomyocytes than in WT cardiomyocytes, whereas the addition of a high concentration of CaM attenuated the aberrant increase of Ca(2+) sparks. In conclusion, CPVT mutation causes defective inter-domain interaction, significant reduction in the ability of CaM binding to the RyR2, spontaneous Ca(2+) leak, and then lethal arrhythmia.

Catecholaminergic polymorphic ventricular tachycardia is caused by mutation-linked defective conformational regulation of the ryanodine receptor.

RATIONALE: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is caused by a single point mutation in a well-defined region of the cardiac type 2 ryanodine receptor (RyR)2. However, the underlying mechanism by which a single mutation in such a large molecule produces drastic effects on channel function remains unresolved. OBJECTIVE: Using a knock-in (KI) mouse model with a human CPVT-associated RyR2 mutation (R2474S), we investigated the molecular mechanism by which CPVT is induced by a single point mutation within the RyR2. METHODS AND RESULTS: The R2474S/+ KI mice showed no apparent structural or histological abnormalities in the heart, but they showed clear indications of other abnormalities. Bidirectional or polymorphic ventricular tachycardia was induced after exercise on a treadmill. The interaction between the N-terminal (amino acids 1 to 600) and central (amino acids 2000 to 2500) domains of the RyR2 (an intrinsic mechanism to close Ca(2+) channels) was weakened (domain unzipping). On protein kinase A-mediated phosphorylation of the RyR2, this domain unzipping further increased, resulting in a significant increase in the frequency of spontaneous Ca(2+) transients. cAMP-induced aberrant Ca(2+) release events (Ca(2+) sparks/waves) occurred at much lower sarcoplasmic reticulum Ca(2+) content as compared to the wild type. Addition of a domain-unzipping peptide, DPc10 (amino acids 2460 to 2495), to the wild type reproduced the aforementioned abnormalities that are characteristic of the R2474S/+ KI mice. Addition of DPc10 to the (cAMP-treated) KI cardiomyocytes produced no further effect. CONCLUSIONS: A single point mutation within the RyR2 sensitizes the channel to agonists and reduces the threshold of luminal [Ca(2+)] for activation, primarily mediated by defective interdomain interaction within the RyR2.

What variables were associated with the inducibility of ventricular fibrillation during electrophysiologic stimulation test in patients without apparent organic heart disease?

OBJECTIVE: The purpose of our study was to determine what variables were associated with ventricular fibrillation (VF) induced during electrophysiological stimulation test in patients without apparent organic heart disease. METHODS: Our study evaluated 77 patients (51+/-15 years) who underwent electrophysiological stimulation test, signal averaging, and Na+ channel-blocker challenge test (pilsicainide test). The subjects were divided into two groups, the Brugada group and non-Brugada group. Further, the patients were divided into three subgroups on the base of symptoms (8, 7 symptomatic; 9, 13 syncope; 28, 12 asymptomatic group; in the Brugada and non-Brugada groups, respectively). Multivariate analyses evaluated the association between baseline clinical factors and the induction of VF. RESULTS: The inducibility of VF was significantly (p<0.0001) higher in the Brugada group (n=33, 73%) than the non-Brugada group (n=4, 13%). The multivariate analysis demonstrated that symptoms (odds ratio (OR) 31.6; 95% confidence interval (CI): 2.3-430.6; p<0.01), type 1 electrocardiogram after pilsicainide test (OR 21.3; CI: 1.7-272.2; p<0.02), and syncope (OR 13.5; CI: 1.2-158.8; p<0.05) were strongly associated with the inducibility of VF, but not with family history, type 1 electrocardiogram in control, positive in late potential, maxDeltaST elevation (>==200microV) after pilsicainide test. CONCLUSIONS: The symptoms, syncope, and type 1 electrocardiogram after pilsicainide test were independently associated with the electrophysiological substrate of VF in patients without apparent heart disease.