Sachiyo Igata

Renal Nerve-Mediated Erythropoietin Release Confers Cardioprotection During Remote Ischemic Preconditioning

BACKGROUND Remote ischemic preconditioning (RIPC) induced by transient limb ischemia is a powerful innate mechanism of cardioprotection against ischemia. Several described mechanisms explain how RIPC may act through neural pathways or humoral factors; however, the mechanistic pathway linking the remote organ to the heart has not yet been fully elucidated. This study aimed to investigate the mechanisms underlying the RIPC-induced production of Janus kinase (JAK)-signal transducer and activator of the transcription (STAT)-activating cytokines and cardioprotection by using mouse and human models of RIPC. METHODS AND RESULTS Screened circulating cardioprotective JAK-STAT-activating cytokines in mice unexpectedly revealed increased serum erythropoietin (EPO) levels after RIP induced by transient ischemia. In mice, RIPC rapidly upregulated EPO mRNA and its main transcriptional factor, hypoxia-inducible factor-1α (HIF1α), in the kidney. Laser Doppler blood flowmetry revealed a prompt reduction of renal blood flow (RBF) after RIPC. RIPC activated cardioprotective signaling pathways and the anti-apoptotic Bcl-xL pathway in the heart, and reduced infarct size. In mice, these effects were abolished by administration of an EPO-neutralizing antibody. Renal nerve denervation also abolished RIPC-induced RBF reduction, EPO production, and cardioprotection. In humans, transient limb ischemia of the upper arm reduced RBF and increased serum EPO levels. CONCLUSIONS Based on the present data, we propose a novel RIPC mechanism in which inhibition of infarct size by RIPC is produced through the renal nerve-mediated reduction of RBF associated with activation of the HIF1α-EPO pathway.

Increased Expression of HCN Channels in the Ventricular Myocardium Contributes to Enhanced Arrhythmicity in Mouse Failing Hearts

Background The efficacy of pharmacological interventions to prevent sudden arrhythmic death in patients with chronic heart failure remains limited. Evidence now suggests increased ventricular expression of hyperpolarization‐activated cation (HCN) channels in hypertrophied and failing hearts contributes to their arrythmicity. Still, the role of induced HCN channel expression in the enhanced arrhythmicity associated with heart failure and the capacity of HCN channel blockade to prevent lethal arrhythmias remains undetermined. Methods and Results We examined the effects of ivabradine, a specific HCN channel blocker, on survival and arrhythmicity in transgenic mice (dnNRSF‐Tg) expressing a cardiac‐specific dominant‐negative form of neuron‐restrictive silencer factor, a useful mouse model of dilated cardiomyopathy leading to sudden death. Ivabradine (7 mg/kg per day orally) significantly reduced ventricular tachyarrhythmias and improved survival among dnNRSF‐Tg mice while having no significant effect on heart rate or cardiac structure or function. Ivabradine most likely prevented the increase in automaticity otherwise seen in dnNRSF‐Tg ventricular myocytes. Moreover, cardiac‐specific overexpression of HCN2 in mice (HCN2‐Tg) made hearts highly susceptible to arrhythmias induced by chronic β‐adrenergic stimulation. Indeed, ventricular myocytes isolated from HCN2‐Tg mice were highly susceptible to β‐adrenergic stimulation‐induced abnormal automaticity, which was inhibited by ivabradine. Conclusions HCN channel blockade by ivabradine reduces lethal arrhythmias associated with dilated cardiomyopathy in mice. Conversely, cardiac‐specific overexpression of HCN2 channels increases arrhythmogenicity of β‐adrenergic stimulation. Our findings demonstrate the contribution of HCN channels to the increased arrhythmicity seen in failing hearts and suggest HCN channel blockade is a potentially useful approach to preventing sudden death in patients with heart failure.

Function and expression pattern of TRPM8 in bladder afferent neurons associated with bladder outlet obstruction in rats

We investigated the function and expression pattern of the transient receptor potential melastatin-8 (TRPM8) in urinary bladder afferent neurons from control and bladder outlet obstruction (BOO) rats. BOO was produced and, after six weeks, the effects of intravesical infusion of menthol, the agonist of TRPM8, were investigated using unanesthetized cystometry. The intravesical infusion of menthol produced an increase in the micturition pressure in both sham surgery and BOO rats. In BOO rats, increased basal and threshold pressure and a decreased micturition interval were observed. Next, the population of TRPM8-positive and the co-expression proportion of TRPM8 with neurochemical markers (NF200 or TRPV1) in the bladder afferent neurons were each compared between the control and BOO rats using retrograde tracing and immunohistochemistry. The population of TRPM8-immunoreactive bladder afferent neurons was larger in BOO rats (3.28±0.43%) than in the control rats (1.33±0.18%). However, there were no statistical differences between the control and BOO rats in the co-expression proportion of neither TRPM8-NF200 (84.1±4.3% vs 79.7±2.7%, p=0.41) nor TRPM8-TRPV1 (33.3±3.6% vs 40.8±2.6%, p=0.08) in the bladder afferent neurons. The present results suggest that the neuronal input through TRPM8-positive bladder afferent neurons are augmented after BOO, however, the neurochemical phenotype of the up-regulated TRPM8-positive bladder afferent neurons is not changed after BOO.

Clinical and Biochemical Factors Associated With Area and Metabolic Activity in the Visceral and Subcutaneous Adipose Tissues by FDG-PET/CT

CONTEXT Body fat distribution and inflammation may play a role in metabolic derangements and cardiovascular disease in obesity. OBJECTIVE The aim of this study is to investigate clinical and biochemical factors associated with area and metabolic activity in the visceral and subcutaneous adipose tissues (VAT and SAT). PARTICIPANTS (18)F-fluorodeoxyglucose-positron emission tomography and computed tomography imaging was performed in 251 consecutive subjects (62.6 ± 9.3 y) for risk screening. MAIN OUTCOME MEASURES We examined which clinical, anthropometric, metabolic, and inflammatory variables including advanced glycation end products (AGEs) and pigment epithelium-derived factor (PEDF) were independently associated with area and metabolic activity in VAT and SAT. Adipose tissue area was determined with computed tomography, whereas metabolic activity was assessed by (18)F-fluorodeoxyglucose uptake expressed as a target to background ratio (TBR) of blood-normalized standardized uptake. RESULTS Serum levels of AGEs and PEDF were 9.81 ± 3.21 U/mL and 14.0 (range 10.8-17.7) μg/mL, respectively. Although the area in VAT and SAT was associated with waist circumference and sex, each adipose tissue area and TBR had different metabolic risk profiles. The TBR value in VAT was higher than that in SAT. In a multiple stepwise regression analysis, AGEs and medication for hypertension were independently associated with VAT TBR (R(2) = 0.102), whereas medication for diabetes, mean intima-media thickness, AGEs, and PEDF were the independent correlates of SAT TBR (R(2) = 0.132). CONCLUSIONS The present study demonstrated that area and metabolic activity in VAT and SAT could be differently regulated, suggesting the involvement of AGEs and PEDF in adipose tissue inflammation.

Disturbance of cardiac gene expression and cardiomyocyte structure predisposes Mecp2 -null mice to arrhythmias

Methyl-CpG-binding protein 2 (MeCP2) is an epigenetic regulator of gene expression that is essential for normal brain development. Mutations in MeCP2 lead to disrupted neuronal function and can cause Rett syndrome (RTT), a neurodevelopmental disorder. Previous studies reported cardiac dysfunction, including arrhythmias in both RTT patients and animal models of RTT. In addition, recent studies indicate that MeCP2 may be involved in cardiac development and dysfunction, but its role in the developing and adult heart remains unknown. In this study, we found that Mecp2-null ESCs could differentiate into cardiomyocytes, but the development and further differentiation of cardiovascular progenitors were significantly affected in MeCP2 deficiency. In addition, we revealed that loss of MeCP2 led to dysregulation of endogenous cardiac genes and myocardial structural alterations, although Mecp2-null mice did not exhibit obvious cardiac functional abnormalities. Furthermore, we detected methylation of the CpG islands in the Tbx5 locus, and showed that MeCP2 could target these sequences. Taken together, these results suggest that MeCP2 is an important regulator of the gene-expression program responsible for maintaining normal cardiac development and cardiomyocyte structure.

Persistent α1-adrenergic receptor function in the nucleus locus coeruleus causes hyperexcitability in AD/HD model rats.

Spontaneously hypertensive rats (SHR) are widely used as a model of attention deficit hyperactivity disorder (ADHD) as their ADHD-like behaviors are restored by methylphenidate. However, a postnatal neural development in SHR is unknown. We performed whole cell patch clamp recordings from locus coeruleus (LC) neurons in neonatal [postnatal day (P) 3-5], juvenile (P21-28), and adult (P 49-56) SHR and age-matched Wistar rats to evaluate α1- and α2-adrenergic receptor (ARs) activities at each developmental period. LC neurons in neonatal Wistar rats and SHR showed no difference in resting membrane potential and spontaneous firing rate, while juvenile and adult SHR LC neurons showed depolarized resting membrane potential and faster spontaneous firing rate than in Wistar rats. Blockade of α1-AR activity by prazosin hyperpolarized the membrane and abolished spontaneous firings in all developmental periods in SHR LC neurons, but not in juvenile and adult Wistar rats. α1-AR stimulation by phenylephrine evoked an inward current in juvenile LC neurons in SHR, but not in juvenile Wistar rats. This phenylephrine-induced inward current was abolished by nonselective cation channel blockers. By contrast, α2-AR stimulation-induced outward currents in the presence of an α1-AR antagonist were equivalent in SHR and Wistar LC neurons. These data suggest that Wistar LC neurons lose α1-AR function during development, whereas α1-ARs remain functional in SHR LC neurons. Thus persistent intrinsic activity of α1-ARs may be a neural mechanism contributing to developmental disorders in juvenile SHRs.

Vascular Inflammation Evaluated by [18F]-Fluorodeoxyglucose-Positron Emission Tomography/Computed Tomography Is Associated With Endothelial Dysfunction

Objective—Endothelial dysfunction is an initial step in atherosclerotic cardiovascular disease. However, involvement of vascular inflammation in endothelial dysfunction is not fully investigated in humans because of the lack of diagnostic modality to noninvasively evaluate vascular inflammation. We assessed the relationship between endothelial function and vascular inflammation evaluated by [18F]-fluorodeoxyglucose-positron emission tomography/computed tomographic imaging. Approach and Results—We examined endothelial function and vascular inflammation by flow-mediated dilation (FMD) of the brachial artery and [18F]-fluorodeoxyglucose-positron emission tomography/computed tomographic imaging of carotid arteries, respectively, in 145 subjects (95 men and 50 women; mean age, 61.8±9.5 years) who underwent a risk-screening test for cardiovascular disease in Kurume University Hospital. Vascular inflammation was measured by blood-normalized standardized uptake value, known as a target:background ratio (TBR). We investigated whether absolute changes from baseline of %FMD after antihypertensive treatment for 6 months (&Dgr;%FMD) were correlated with those of TBR in 33 drug-naive patients with essential hypertension. Multiple logistic regression analysis revealed that age (odds ratio, 1.767 for 10-year increase), male sex (odds ratio, 0.434), low-density lipoprotein-cholesterol (odds ratio, 1.630 for 26-mg/dL increase), and TBR values (odds ratio, 1.759 for 0.2 increase) were independently associated with %FMD in 145 patients. There was an inverse correlation between &Dgr;%FMD and &Dgr;TBR; &Dgr;TBR was a sole independent associate of &Dgr;%FMD in hypertensive patients (r=−0.558; P<0.001). Conclusions—The present study showed that vascular inflammation in the carotid arteries evaluated by [18F]-fluorodeoxyglucose-positron emission tomography/computed tomography was one of the independent correlates of decreased %FMD, thus suggesting the association of vascular inflammation with endothelial dysfunction in humans.

Positive correlation between malondialdehyde-modified low-density lipoprotein cholesterol and vascular inflammation evaluated by 18F-FDG PET/CT

OBJECTIVE The purpose of this study was to investigate the relationship between serum levels of malondialdehyde-modified low-density lipoprotein cholesterol (MDA-LDL) and vascular inflammation evaluated by fluorine-18 fluorodeoxyglucose ((18)F-FDG) positron emission tomography/computed tomography (PET/CT). METHODS/RESULTS The study involved 106 consecutive patients (75 males and 31 female, mean age 62.5 ± 7.7 years) who visited our hospital for cardiovascular risk screening and underwent carotid ultrasonography, (18)F-FDG PET/CT, complete history, physical examinations, and determination of blood chemistry including high-sensitivity C-reactive protein (hsCRP), asymmetric dimethylarginine (ADMA), and MDA-LDL. Vascular inflammation, was measured as blood-normalized standardized (18)F-FDG uptake value, known as the target-to-background ratio (TBR) of carotid arteries. Univariate and multiple stepwise regression analyses were performed for determining independent correlates of carotid TBR values. Median MDA-LDL, mean carotid TBR values and carotid intima-media thickness (IMT) were 127.5 (IQR 92.0-147.8) U/l, 1.55 ± 0.22, and 0.72 ± 0.15 mm, respectively. Univariate analysis revealed that carotid TBR values positively correlated with MDA-LDL (p = 0.043) and carotid IMT (p = 0.049). Multiple stepwise regression analysis demonstrated that MDA-LDL (p = 0.043) and carotid IMT (p = 0.038) were independently associated with carotid TBR values. CONCLUSION The present study reveals that serum levels of MDA-LDL are independently associated with vascular inflammation evaluated by (18)F-FDG PET/CT. Circulating MDA-LDL may be a more useful clinical biomarker for vascular inflammation within the atherosclerotic plaques than hsCRP or ADMA.

Anagliptin, A Dipeptidyl Peptidase-4 Inhibitor Ameliorates Arterial Stiffness in Association with Reduction of Remnant-Like Particle Cholesterol and Alanine Transaminase Levels in Type 2 Diabetic Patients

BACKGROUND Inhibition of dipeptidyl peptidase-4 (DPP-4) has been proposed as a therapeutic target for type 2 diabetes (T2DM). Arterial stiffness, a predictor of future cardiovascular events and all-cause mortality, is augmented in these patients. However, effects of DPP-4 inhibitors on arterial stiffness remain unknown. In this study, we compared effects of anagliptin, an inhibitor of DPP-4 on arterial stiffness evaluated by cardio-ankle vascular index (CAVI) with those of an equipotent glucose-lowering agent, glimepiride in patients with T2DM. METHODS The study involved 50 consecutive outpatients (33 males and 17 females; mean age of 72.5±9.5 years) who visited our hospitals for a risk-screening test or treatment for T2DM. They underwent complete history and physical examination, and determination of blood chemistry and anthropometric variables, and then were randomized to receive either anagliptin (n=26) or glimepiride (n=24) for 6 months. RESULTS After 6-months treatment, fasting plasma glucose and HbA1c values were comparably reduced in both groups. Anagliptin, but not glimepiride treatment significantly decreased low-density lipoprotein cholesterol, malondialdehyde-modified LDL, remnant-like particle (RLP) cholesterol, CAVI, alanine transaminase (ALT), γ-glutamyl transferase and visceral fat volume. In multiple regression analysis, absolute changes from baseline of RLP cholesterol and ALT after anagliptin treatment for 6 months (ΔRLP cholesterol and ΔALT) were independently correlated with ΔCAVI (R2=0.445). CONCLUSION The present study suggests that anagliptin may exert a beneficial effect on arterial stiffness in patients with T2DM, which is independent of its blood glucose-lowering property. Anagliptin may ameliorate arterial stiffness partly via reduction of RLP cholesterol and improvement of liver function.

Switching Dipeptidyl Peptidase-4 Inhibitors to Tofogliflozin, a Selective Inhibitor of Sodium-Glucose Cotransporter 2 Improves Arterial Stiffness Evaluated by Cardio-Ankle Vascular Index in Patients with Type 2 Diabetes: A Pilot Study

BACKGROUND We have found that anagliptin, a dipeptidyl peptidase-4 inhibitor (DPP-4) significantly ameliorates arterial stiffness in Type 2 Diabetes Mellitus (T2DM) patients compared with an equivalent hypoglycaemic agent, glimepiride. However, it remains unclear whether switching DPP-4 inhibitors to tofogliflozin, a selective inhibitor of Sodium-Glucose Cotransporter 2 (SGLT2) improves arterial stiffness in T2DM patients. METHODS Nineteen T2DM patients who had received DPP-4 inhibitors for at least 1 year were enrolled in this study. Clinical parameters and arterial stiffness evaluated by cardio-ankle vascular index (CAVI) were measured at baseline and after 6-months treatment with tofogliflozin. RESULTS At 6 months after switching to tofogliflozin, CAVI, waist circumference, body weight, body mass index, subcutaneous and visceral fat volume, white blood cell number, fasting plasma insulin, uric acid, aspartate transaminase (AST), γ-glutamyl transferase (GTP), and advanced glycation end products (AGEs) were significantly reduced, while red blood cell number, haemoglobin, and HbA1c values were increased. When stratified by median values of change in CAVI after switching to tofogliflozin (ΔCAVI), baseline serum levels of AGEs were significantly higher in the low ΔCAVI group (high responder) than in the high one (low responder). ΔAST and ΔGTP were positively correlated with ΔCAVI. CONCLUSION The present study suggests that switching DPP-4 inhibitors to tofogliflozin ameliorates arterial stiffness in T2DM patients partly via improvement of liver function. Baseline serum levels of AGEs may identify patients who improve arterial stiffness more after treatment with tofogliflozin.