Calcium release channel RyR2 regulates insulin release and glucose homeostasis

Cardiovascular consequences of metabolic syndrome

The metabolic syndrome (MetS) is defined as the concurrence of obesity-associated cardiovascular risk factors including abdominal obesity, impaired glucose tolerance, hypertriglyceridemia, decreased HDL cholesterol, and/or hypertension. Earlier conceptualizations of the MetS focused on insulin resistance as a core feature, and it is clearly coincident with the above list of features. Each component of the MetS is an independent risk factor for cardiovascular disease and the combination of these risk factors elevates rates and severity of cardiovascular disease, related to a spectrum of cardiovascular conditions including microvascular dysfunction, coronary atherosclerosis and calcification, cardiac dysfunction, myocardial infarction, and heart failure. While advances in understanding the etiology and consequences of this complex disorder have been made, the underlying pathophysiological mechanisms remain incompletely understood, and it is unclear how these concurrent risk factors conspire to produce the variety of obesity-associated adverse cardiovascular diseases. In this review, we highlight current knowledge regarding the pathophysiological consequences of obesity and the MetS on cardiovascular function and disease, including considerations of potential physiological and molecular mechanisms that may contribute to these adverse outcomes.

KCNQ1 variants associate with hypertension in type 2 diabetes and affect smooth muscle contractility in vitro

KCNQ1 encodes a potassium voltage-gated channel and represents a susceptibility locus for type 2 diabetes mellitus (T2DM). Here, we explored the association between KCNQ1 polymorphisms and hypertension risk in individuals with T2DM, as well as the role of KCNQ1 in vascular smooth muscle cell contraction in vitro. To investigate the relationship between KCNQ1 and the risk of developing hypertension in patients with T2DM, we divided the T2DM cohort into hypertension (n = 452) and non-hypertension (n = 541) groups. The Mann-Whitney U test, chi-square test, and multivariate regression analyses were used to assess the clinical characteristics and genotypic frequencies. In vitro studies utilized the rat aortic smooth muscle A10 cell line. Patients in the hypertension group were significantly older at the time of enrollment and had higher levels of body mass index, waist-to-hip ratio, and triglyceride than those in the non-hypertension group. The KCNQ1 rs3864884 and rs12576239 genetic variants were associated with hypertension in T2DM. KCNQ1 expression was lower in the individuals with the CC versus the CT and TT genotypes. Smooth muscle cell contractility was inhibited by treatment with a KCNQ1 inhibitor. These results suggest that KCNQ1 might be associated with hypertension in individuals with T2DM.

Cardiac electrophysiological alterations and clinical response in cardiac resynchronization therapy with a defibrillator treated patients affected by metabolic syndrome

Metabolic syndrome (MS) is a multifactorial disease that can affect clinical outcomes in patients treated by Cardiac Resynchronization Therapy with a defibrillator (CRT-d).Ninety-one patients received a CRT-d. According to clinical diagnosis, the study population was divided into 46 MS (cases) versus 45 no MS (controls) patients. These patients were followed by clinical, instrumental assessment, and device telemetric interrogations at follow-up. The design of the study was to evaluate the functionality of the CRT-d leads, the arrhythmic events, the CRT-d response, and the clinical outcomes at follow-up.At follow-up, there was a statistical significant difference, comparing MS versus no MS patients regarding the sensing, pacing, and impedance thresholds of the right atrium, right ventricle, and left ventricle leads. There was a statistically significant difference in the percentage of CRT-d responders comparing MS (n = 16, 51%) versus no MS (n = 40, 77%) patients (P = 0.017). MS may be predictive for hospitalization for heart failure worsening (hazard ratio 0.327, 95% confidence interval 0.096-0.943, P = 0.044) in CRT-d patients.MS is a complex multifactorial disease that may affect the functionality of CRT-d leads, the CRT-d response, and clinical outcomes in failing heart patients. These parameters may be detectable by follow-up monitoring.

Beyond the Electrocardiogram: Mutations in Cardiac Ion Channel Genes Underlie Nonarrhythmic Phenotypes

Cardiac ion channelopathies are an important cause of sudden death in the young and include long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, idiopathic ventricular fibrillation, and short QT syndrome. Genes that encode ion channels have been implicated in all of these conditions, leading to the widespread implementation of genetic testing for suspected channelopathies. Over the past half-century, researchers have also identified systemic pathologies that extend beyond the arrhythmic phenotype in patients with ion channel gene mutations, including deafness, epilepsy, cardiomyopathy, periodic paralysis, and congenital heart disease. A coexisting phenotype, such as cardiomyopathy, can influence evaluation and management. However, prior to recent molecular advances, our understanding and recognition of these overlapping phenotypes were poor. This review highlights the systemic and structural heart manifestations of the cardiac ion channelopathies, including their phenotypic spectrum and molecular basis.

Myricitrin Alleviates Oxidative Stress-induced Inflammation and Apoptosis and Protects Mice against Diabetic Cardiomyopathy

Diabetic cardiomyopathy (DCM) has been increasingly considered as a main cause of heart failure and death in diabetic patients. At present, no effective treatment exists to prevent its development. In the present study, we describe the potential protective effects and mechanisms of myricitrin (Myr) on the cardiac function of streptozotosin-induced diabetic mice and on advanced glycation end products (AGEs)-induced H9c2 cardiomyocytes. In vitro experiments revealed that pretreatment with Myr significantly decreased AGEs-induced inflammatory cytokine expression, limited an increase in ROS levels, and reduced cell apoptosis, fibrosis, and hypertrophy in H9c2 cells. These effects are correlated with Nrf2 activation and NF-κB inhibition. In vivo investigation demonstrated that oral administration of Myr at 300 mg/kg/day for 8 weeks remarkably decreased the expression of enzymes associated with cardiomyopathy, as well as the expression of inflammatory cytokines and apoptotic proteins. Finally, Myr improved diastolic dysfunction and attenuated histological abnormalities. Mechanistically, Myr attenuated diabetes-induced Nrf2 inhibition via the regulation of Akt and ERK phosphorylation in the diabetic heart. Collectively, these results strongly indicate that Myr exerts cardioprotective effects against DCM through the blockage of inflammation, oxidative stress, and apoptosis. This suggests that Myr might be a potential therapeutic agent for the treatment of DCM.

Ethnic Variation in the Association of Hypertension With Type 2 Diabetes

Lifestyle changes occurring with urbanization increase the prevalence of both type 2 diabetes mellitus (T2DM) and hypertension (HTN). Yemenites who have immigrated to Israel have demonstrated a dramatic increase in T2DM but the prevalence of HTN in diabetic Yemenites is unclear. In a cross-sectional study, the authors evaluated the prevalence of HTN and lifestyle patterns in Israelis with T2DM of Yemenite (Y-DM) and non-Yemenite (NY-DM) origin. Y-DM (n=63) and NY-DM (n=120) had similar age (63±7 vs 64±7 years, P=.5), diabetes duration, diet adherence, and exercise patterns. Y-DM had a lower prevalence of HTN (63%) than NY-DM (83%) (P<.01). Furthermore, Yemenite origin was independently associated with lower prevalence of HTN (odds ratio, 0.3; 95% confidence interval, 0.12-0.71). Blood pressure was well controlled with fewer antihypertensive medications in Y-DM than NY-DM (P<.01). Even though lifestyle patterns were similar in the two groups, Y-DM had a lower prevalence of HTN compared with NY-DM and required fewer antihypertensive medications.

Physiology and pathophysiology of excitation-contraction coupling: the functional role of ryanodine receptor

Calcium (Ca2+) release from intracellular stores plays a key role in the regulation of skeletal muscle contraction. The type 1 ryanodine receptors (RyR1) is the major Ca2+ release channel on the sarcoplasmic reticulum (SR) of myocytes in skeletal muscle and is required for excitation-contraction (E-C) coupling. This article explores the role of RyR1 in skeletal muscle physiology and pathophysiology.

Genetic analysis of hyperemesis gravidarum reveals association with intracellular calcium release channel (RYR2)

Hyperemesis Gravidarum (HG), severe nausea/vomiting in pregnancy (NVP), can cause poor maternal/fetal outcomes. Genetic predisposition suggests the genetic component is essential in discovering an etiology. We performed whole-exome sequencing of 5 families followed by analysis of variants in 584 cases/431 controls. Variants in RYR2 segregated with disease in 2 families. The novel variant L3277R was not found in any case/control. The rare variant, G1886S was more common in cases (p = 0.046) and extreme cases (p = 0.023). Replication of G1886S using Norwegian/Australian data was supportive. Common variants rs790899 and rs1891246 were significantly associated with HG and weight loss. Copy-number analysis revealed a deletion in a patient. RYR2 encodes an intracellular calcium release channel involved in vomiting, cyclic-vomiting syndrome, and is a thyroid hormone target gene. Additionally, RYR2 is a downstream drug target of Inderal, used to treat HG and CVS. Thus, herein we provide genetic evidence for a pathway and therapy for HG.

An optimized protocol for purification of functional islets of Langerhans

Islets of Langerhans and β-cell isolation constitute routinely used cell models for diabetic research, and refining islet isolation protocols and cell quality assessment is a high priority. Numerous protocols have been published describing isolate of islets, but often rigorous and systematic assessment of their integrity is lacking. Herein, we propose a new protocol for optimal generation of islets. Pancreases from mice and rats were excised and digested using a low-activity collagenase solution and islets were then purified by a series of sedimentations and a Percoll gradient. Islets were maintained in culture for 5 days, during which viability, pro/antiapoptotic, and islet-specific genes, glucose-stimulated calcium entry, glucose uptake, and insulin secretion were assessed. The commonly used islet isolation technique by collagenase injection through the common bile duct (CBD) was also performed and compared with the present approach. This new protocol produced islets that retained a healthy status as demonstrated by the yield of stable living cells. Furthermore, calcium oscillation, glucose uptake, and insulin secretion remained intact in the islet cultures. This was reproducible when many rodent species were used, and neither sex nor age affected the cells behavior. When compared with the CBD technique, islet physiology was similar. Finally, this approach was used to uncover new ion channel candidates implicated in insulin secretion. In conclusion, this study outlines an efficient protocol for islet preparation that may support research into new therapeutic targets in diabetes research.

The association of serum magnesium and mortality outcomes in heart failure patients: A systematic review and meta-analysis

BACKGROUND

Low serum magnesium (Mg) has been independently shown to increase risk of heart failure (HF), but data on the association between serum Mg concentration and the outcome of patients with HF are conflicting. The purpose of this systematic review and meta-analysis was to estimate the prognostic effects of hypermagnesemia and hypomagnesemia on cardiovascular (CV) mortality and all-cause mortality (ACM) of patients with HF.

METHODS

Relevant studies were identified from Medline and Scopus databases. Included and excluded criteria were defined. Effects (i.e., log [risk ratio [RR]]) of hypomagnesemia and hypermagnesemia versus normomagnesemia were estimated using Poisson regression, and then a multivariate meta-analysis was applied for pooling RRs across studies. Heterogeneity was explored using a meta-regression and subgroup analysis.

RESULTS

On analysis, 7 eligible prospective studies yielded a total of 5172 chronic HF patients with 913 and 1438 deaths from CV and ACM, respectively. Most participants were elderly men with left ventricular (LV) ejection fraction ≤40%. Those patients with baseline hypermagnesemia had a significantly higher risk of CV mortality (RR, 1.38; 95% confidence interval [CI], 1.07-1.78) or ACM (RR, 1.35; 95% CI, 1.18-1.54) than those with baseline normomagnesemia. However, baseline hypomagnesemia was not associated with the risk of CV mortality (RR, 1.11; 95% CI, 0.79-1.57) and ACM (RR, 1.11; 95% CI, 0.87-1.41). A subgroup analysis by Mg cutoff suggested a dose-response trend for hypermagnesemia effects, that is, the pooled RRs for CV mortality were 1.28 (95% CI, 1.05-1.55) and 1.92 (95% CI, 1.00-3.68) for the cutoff of 0.89 to 1.00 and 1.05 to 1.70 mmol/L, respectively.

CONCLUSION

The present systematic review and meta-analysis suggested that, in HF patients, hypermagnesemia with serum Mg ≥ 1.05 mmol/L was associated with an increased risk of CV mortality and ACM but this was not observed for hypomagnesemia. This finding was limited to the elderly patients with chronic HF who had reduced LV systolic function.

Genomic contributors to atrial electroanatomical remodeling and atrial fibrillation progression: Pathway enrichment analysis of GWAS data

In atrial fibrillation (AF), left atrial diameter (LAD) and low voltage area (LVA) are intermediate phenotypes that are associated with AF type and progression. In this study, we tested the hypothesis, that these phenotypes share common, genetically-determined pathways using pathway enrichment analysis of GWAS data. Samples from 660 patients with paroxysmal (n = 370) or persistent AF (n = 290) were genotyped for ~1,000,000 SNPs. SNPs found significantly associated with LAD, LVA or AF type were used for gene-based association tests in a systematic biological Knowledge-based mining system for Genome-wide Genetic studies (KGG). Associated genes were tested for pathway enrichment using two enrichment tools (WebGestalt and GATHER) and the databases provided by Kyoto Encyclopedia of Genes and Genomes. The calcium signaling pathway (hsa04020) was the only pathway that reached statistical significance for LAD and LVA in both enrichment tools and was also significantly associated with AF type. Within this pathway, there were 39 genes (i.e. CACNA1C, RyR2) that were associated with LAD, LVA and AF type. In conclusion, there is a genomic contribution to electroanatomical remodeling (LAD, LVA) and AF type via the calcium signaling pathway. Future and larger studies are necessary to replicate and apply these findings.

Integrative mutation, haplotype and G × G interaction evidence connects ABGL4, LRP8 and PCSK9 genes to cardiometabolic risk

This study is expected to investigate the association of ATP/GTP binding protein-like 4 (AGBL4), LDL receptor related protein 8 (LRP8) and proprotein convertase subtilisin/kexin type 9 (PCSK9) gene single nucleotide variants (SNVs) with lipid metabolism in 2,552 individuals (Jing, 1,272 and Han, 1,280). We identified 12 mutations in this motif. The genotype and allele frequencies of these variants were different between the two populations. Multiple-locus linkage disequilibrium (LD) elucidated the detected sites are not statistically independent. Possible integrative haplotypes and gene-by-gene (G × G) interactions, comprising mutations of the AGBL4, LRP8 and PCSK9 associated with total cholesterol (TC, AGBL4 G-G-A, PCSK9 C-G-A-A and G-G-A-A-C-A-T-T-T-G-G-A), triglyceride (TG, AGBL4 G-G-A, LRP8 G-A-G-C-C, PCSK9 C-A-A-G, A-A-G-G-A-G-C-C-C-A-A-G and A-A-G-G-A-G-C-C-C-G-A-A), HDL cholesterol (HDL-C, AGBL4 A-A-G and A-A-G-A-A-G-T-C-C-A-A-G) and the apolipoprotein(Apo)A1/ApoB ratio (A1/B, PCSK9 C-A-A-G) in Jing minority. However, in the Hans, with TG (AGBL4 G-G-A, LRP8 G-A-G-C-C, PCSK9 C-A-A-G, A-A-G-G-A-G-C-C-C-A-A-G and A-A-G-G-A-G-C-C-C-G-A-A), HDL-C (LRP8 A-A-G-T-C), LDL-C (LRP8 A-A-G-T-C and A-A-G-A-A-G-T-C-C-A-A-G) and A1/B (LRP8 A-C-A-T-T and PCSK9 C-A-A-G). Association analysis based on haplotype clusters and G × G interactions probably increased power over single-locus tests especially for TG.

Adrenergic signaling in heart failure and cardiovascular aging

Both cardiovascular disease and aging are associated with changes in the sympathetic nervous system. Indeed, mounting evidence indicates that adrenergic receptors are functionally involved in numerous processes underlying both aging and cardiovascular disorders, in particular heart failure. This article will review the pathophysiological role of the sympathetic nervous system in heart failure and cardiovascular aging.

SERCA2 Deficiency Impairs Pancreatic β-Cell Function in Response to Diet-Induced Obesity

The sarcoendoplasmic reticulum (ER) Ca(2+) ATPase 2 (SERCA2) pump is a P-type ATPase tasked with the maintenance of ER Ca(2+) stores. Whereas β-cell SERCA2 expression is reduced in diabetes, the role of SERCA2 in the regulation of whole-body glucose homeostasis has remained uncharacterized. To this end, SERCA2 heterozygous mice (S2HET) were challenged with a high-fat diet (HFD) containing 45% of kilocalories from fat. After 16 weeks of the HFD, S2HET mice were hyperglycemic and glucose intolerant, but adiposity and insulin sensitivity were not different between HFD-fed S2HET mice and HFD-fed wild-type controls. Consistent with a defect in β-cell function, insulin secretion, glucose-induced cytosolic Ca(2+) mobilization, and the onset of steady-state glucose-induced Ca(2+) oscillations were impaired in HFD-fed S2HET islets. Moreover, HFD-fed S2HET mice exhibited reduced β-cell mass and proliferation, altered insulin production and proinsulin processing, and increased islet ER stress and death. In contrast, SERCA2 activation with a small molecule allosteric activator increased ER Ca(2+) storage and rescued tunicamycin-induced β-cell death. In aggregate, these data suggest a critical role for SERCA2 and the regulation of ER Ca(2+) homeostasis in the β-cell compensatory response to diet-induced obesity.

Influence of Dapagliflozin on Glycemic Variations in Patients with Newly Diagnosed Type 2 Diabetes Mellitus

Objectives. To observe changes in blood glycemic variations and oxidative stress level before and after dapagliflozin treatment in patients with newly diagnosed T2DM. Methods. This was a randomized, double-blind, placebo-controlled, phase 3 trial. A total of 28 patients with newly diagnosed T2DM with HbA1c levels of 7.5-10.5% were randomly selected to receive dapagliflozin or placebo treatment for 24 weeks. After baseline data were collected, we analyzed glycemic variations and plasma 8-iso PGF2α level at baseline and at the endpoint. Primary outcome was the changes of mean amplitude glycemic excursion (MAGE) within groups. Results. After 24-week dapagliflozin therapy, our data showed the significant improvement of MAGE with dapagliflozin therapy (P = 0.010). Compared with control group, patients in dapagliflozin group exhibited reduction in 24-hour MBG (P = 0.026) and lower mean plasma glucose concentrations, especially during periods from 2400 to 0200 and 1300 to 1800 (P < 0.05, resp.). In addition, plasma 8-iso PGF2α level was notably decreased in the treatment group compared to the control group (P = 0.034). Conclusions. In conclusion, this study shows the ability of dapagliflozin to improve glycemic variations and associate with reduction of oxidative stress in patients with T2DM, which may benefit the cardiovascular system.

New-onset ventricular arrhythmias post radiofrequency catheter ablation for atrial fibrillation

As a new complication, new-onset ventricular arrhythmias (VAs) post atrial fibrillation (AF) ablation have not been well defined. This prospective study aimed to describe the details of new-onset VAs post AF ablation in a large study cohort.One thousand fifty-three consecutive patients who underwent the first radiofrequency catheter ablation for AF were enrolled. All patients had no evidence of pre-ablation VAs. New-onset VAs were defined as new-onset ventricular tachycardia (VT) or premature ventricular contractions (PVC) ≥1000/24 h within 1 month post ablation.There were 46 patients (4.4%) who had 62 different new-onset VAs, among whom 42 were PVC alone, and 4 were PVC coexisting with nonsustained VT. Multivariate analysis showed that increased serum leukocyte counts ≥50% post ablation were independently associated with new-onset VAs (OR: 1.9; 95% CI: 1.0-3.5; P = 0.043). The median number of PVC was 3161 (1001-27,407) times/24 h. Outflow tract VAs were recorded in 35 (76.1%) patients. No significant differences were found in origin of VAs (P = 0.187). VAs disappeared without any treatment in 6 patients (13.0%). No VAs-related adverse cardiac event occurred.The study revealed a noticeable prevalence but relatively benign prognosis of new-onset VAs post AF ablation. Increased serum leukocyte counts ≥50% post ablation appeared to be associated with new-onset VAs, implying that inflammatory response caused by ablation might be the mechanism.

Leaky ryanodine receptors contribute to diaphragmatic weakness during mechanical ventilation

Ventilator-induced diaphragmatic dysfunction (VIDD) refers to the diaphragm muscle weakness that occurs following prolonged controlled mechanical ventilation (MV). The presence of VIDD impedes recovery from respiratory failure. However, the pathophysiological mechanisms accounting for VIDD are still not fully understood. Here, we show in human subjects and a mouse model of VIDD that MV is associated with rapid remodeling of the sarcoplasmic reticulum (SR) Ca(2+) release channel/ryanodine receptor (RyR1) in the diaphragm. The RyR1 macromolecular complex was oxidized, S-nitrosylated, Ser-2844 phosphorylated, and depleted of the stabilizing subunit calstabin1, following MV. These posttranslational modifications of RyR1 were mediated by both oxidative stress mediated by MV and stimulation of adrenergic signaling resulting from the anesthesia. We demonstrate in the murine model that such abnormal resting SR Ca(2+) leak resulted in reduced contractile function and muscle fiber atrophy for longer duration of MV. Treatment with β-adrenergic antagonists or with S107, a small molecule drug that stabilizes the RyR1-calstabin1 interaction, prevented VIDD. Diaphragmatic dysfunction is common in MV patients and is a major cause of failure to wean patients from ventilator support. This study provides the first evidence to our knowledge of RyR1 alterations as a proximal mechanism underlying VIDD (i.e., loss of function, muscle atrophy) and identifies RyR1 as a potential target for therapeutic intervention.

Reactive Oxygen Species, Endoplasmic Reticulum Stress and Mitochondrial Dysfunction: The Link with Cardiac Arrhythmogenesis

BACKGROUND

Cardiac arrhythmias represent a significant problem globally, leading to cerebrovascular accidents, myocardial infarction, and sudden cardiac death. There is increasing evidence to suggest that increased oxidative stress from reactive oxygen species (ROS), which is elevated in conditions such as diabetes and hypertension, can lead to arrhythmogenesis.

METHOD

A literature review was undertaken to screen for articles that investigated the effects of ROS on cardiac ion channel function, remodeling and arrhythmogenesis.

RESULTS

Prolonged endoplasmic reticulum stress is observed in heart failure, leading to increased production of ROS. Mitochondrial ROS, which is elevated in diabetes and hypertension, can stimulate its own production in a positive feedback loop, termed ROS-induced ROS release. Together with activation of mitochondrial inner membrane anion channels, it leads to mitochondrial depolarization. Abnormal function of these organelles can then activate downstream signaling pathways, ultimately culminating in altered function or expression of cardiac ion channels responsible for generating the cardiac action potential (AP). Vascular and cardiac endothelial cells become dysfunctional, leading to altered paracrine signaling to influence the electrophysiology of adjacent cardiomyocytes. All of these changes can in turn produce abnormalities in AP repolarization or conduction, thereby increasing likelihood of triggered activity and reentry.

CONCLUSION

ROS plays a significant role in producing arrhythmic substrate. Therapeutic strategies targeting upstream events include production of a strong reducing environment or the use of pharmacological agents that target organelle-specific proteins and ion channels. These may relieve oxidative stress and in turn prevent arrhythmic complications in patients with diabetes, hypertension, and heart failure.

Maintenance of normal blood pressure is dependent on IP3R1-mediated regulation of eNOS

Endothelial cells (ECs) are critical mediators of blood pressure (BP) regulation, primarily via the generation and release of vasorelaxants, including nitric oxide (NO). NO is produced in ECs by endothelial NO synthase (eNOS), which is activated by both calcium (Ca(2+))-dependent and independent pathways. Here, we report that intracellular Ca(2+) release from the endoplasmic reticulum (ER) via inositol 1,4,5-trisphosphate receptor (IP3R) is required for Ca(2+)-dependent eNOS activation. EC-specific type 1 1,4,5-trisphosphate receptor knockout (IP3R1(-/-)) mice are hypertensive and display blunted vasodilation in response to acetylcholine (ACh). Moreover, eNOS activity is reduced in both isolated IP3R1-deficient murine ECs and human ECs following IP3R1 knockdown. IP3R1 is upstream of calcineurin, a Ca(2+)/calmodulin-activated serine/threonine protein phosphatase. We show here that the calcineurin/nuclear factor of activated T cells (NFAT) pathway is less active and eNOS levels are decreased in IP3R1-deficient ECs. Furthermore, the calcineurin inhibitor cyclosporin A, whose use has been associated with the development of hypertension, reduces eNOS activity and vasodilation following ACh stimulation. Our results demonstrate that IP3R1 plays a crucial role in the EC-mediated vasorelaxation and the maintenance of normal BP.

KCNN2 polymorphisms and cardiac tachyarrhythmias

Potassium calcium-activated channel subfamily N member 2 (KCNN2) encodes an integral membrane protein that forms small-conductance calcium-activated potassium (SK) channels. Recent studies in animal models show that SK channels are important in atrial and ventricular repolarization and arrhythmogenesis. However, the importance of SK channels in human arrhythmia remains unclear. The purpose of the present study was to test the association between genetic polymorphism of the SK2 channel and the occurrence of cardiac tachyarrhythmias in humans. We enrolled 327 Han Chinese, including 72 with clinically significant ventricular tachyarrhythmias (VTa) who had a history of aborted sudden cardiac death (SCD) or unexplained syncope, 98 with a history of atrial fibrillation (AF), and 144 normal controls. We genotyped 12 representative tag single nucleotide polymorphisms (SNPs) across a 141-kb genetic region containing the KCNN2 gene; these captured the full haplotype information. The rs13184658 and rs10076582 variants of KCNN2 were associated with VTa in both the additive and dominant models (odds ratio [OR] 2.89, 95% confidence interval [CI] = 1.505-5.545, P = 0.001; and OR 2.55, 95% CI = 1.428-4.566, P = 0.002, respectively). After adjustment for potential risk factors, the association remained significant. The population attributable risks of these 2 variants of VTa were 17.3% and 10.6%, respectively. One variant (rs13184658) showed weak but significant association with AF in a dominant model (OR 1.91, CI = 1.025-3.570], P = 0.042). There was a significant association between the KCNN2 variants and clinically significant VTa. These findings suggest an association between KCNN2 and VTa; it also appears that KCNN2 variants may be adjunctive markers for risk stratification in patients susceptible to SCD.

SIRT6 suppresses isoproterenol-induced cardiac hypertrophy through activation of autophagy

Reduction in autophagy has been reported to contribute to the pathogenesis of cardiac hypertrophy. However, the molecular pathways leading to impaired autophagy at the presence of hypertrophic stimuli remain to be elucidated. The present study aimed to investigate the role of sirtuin 6 (SIRT6), a sirtuin family member, in regulating cardiomyocyte autophagy, and its implication in prevention of cardiac hypertrophy. Primary neonatal rat cardiomyocytes (NRCMs) or Sprague-Dawley (SD) rats were submitted to isoproterenol (ISO) treatment, and then the hypertrophic responses and changes in autophagy activity were measured. The influence of SIRT6 on autophagy was observed in cultured NRCMs with gain- and loss-of-function approaches to regulate SIRT6 expression, and further confirmed in vivo by intramyocardial delivery of an adenovirus vector encoding SIRT6 cDNA. In addition, the involvement of SIRT6-mediated autophagy in attenuation of cardiomyocyte hypertrophy induced by ISO was determined basing on genetic or pharmaceutical disruption of autophagy, and the underlying mechanism was preliminarily explored. ISO-caused cardiac hypertrophy accompanying with a significant decrease in autophagy activity. SIRT6 overexpression enhanced autophagy in NRCMs and in rat hearts, whereas knockdown of SIRT6 by RNA interference led to suppression of cardiomyocyte autophagy. Furthermore, the protective effect of SIRT6 against ISO-stimulated hypertrophy was associated with induction of autophagy. SIRT6 promoted nuclear retention of forkhead box O3 transcription factor possibly via attenuating Akt signaling, which was responsible for autophagy activation. Our findings revealed that SIRT6 positively regulates autophagy in cardiomyocytes, which may help to ameliorate ISO-induced cardiac hypertrophy.

Inhibition of autophagy promotes apoptosis and enhances anticancer efficacy of adriamycin via augmented ROS generation in prostate cancer cells

The interplay between autophagy and apoptosis response to chemotherapy is still a subject of intense debate in recent years. More efforts have focused on the regulation effects of apoptosis on autophagy, whereas how autophagy affects apoptosis remains poorly understood. In this study performed on prostate cancer cells, we investigated the role of autophagy in adriamycin-induced apoptosis, as well as the mechanisms mediating the effects of autophagy on apoptosis response to adriamycin (ADM). The results show that ADM not only inhibited cell viability and enhanced apoptosis, but also promoted autophagy via PI3K/Akt(T308)/mTOR signal pathway. Inhibition of autophagy by either pharmacological inhibitor chloroquine (CQ) or RNA interference of Atg5 increased ADM-induced apoptosis and enhanced the chemosensitivity of prostate cancer cells. Moreover, blockade of autophagy augmented reactive oxygen species (ROS) generation induced by ADM. Scavenging of ROS by antioxidant N-acetyl-cysteine (NAC) reversed the strengthened effects of CQ on ADM-induced apoptosis and rescued the cells from apoptosis. The results identified ROS as a potential mediator directing the modulation effects of the protective autophagy on apoptosis response to ADM. Suppression of the protective autophagy might provide a promising strategy to increase the anticancer efficacy of agents in the treatment of prostate cancer.

c-Src tyrosine kinase mediates high glucose-induced endothelin-1 expression

Endothelin-1 (ET-1) plays an important role in the pathophysiology of diabetes-associated cardiovascular disorders. The molecular mechanisms leading to ET-1 upregulation in diabetes are not entirely defined. c-Src tyrosine kinase regulates important pathophysiological aspects of vascular response to insults. In this study, we aimed to elucidate whether high glucose-activated c-Src signaling plays a role in the regulation of ET-1 expression. Human endothelial cells EAhy926 (ECs) were exposed to normal or high levels of glucose for 24h. Male C57BL/6J mice were rendered diabetic with streptozotocin and then treated with a specific c-Src inhibitor (Src I1) or c-Src siRNA. Real-time PCR, Western blot, and ELISA, were used to investigate ET-1 regulation. The c-Src activity and expression were selectively downregulated by pharmacological inhibition and siRNA-mediated gene silencing, respectively. High glucose dose-dependently up-regulated c-Src phosphorylation and ET-1 gene and protein expression levels in human ECs. Chemical inhibition or silencing of c-Src significantly decreased the high-glucose augmented ET-1 expression in cultured ECs. In vivo studies showed significant elevations in the aortic ET-1 mRNA expression and plasma ET-1 concentration in diabetic mice compared to non-diabetic animals. Treatment with Src I1, as well as in vivo silencing of c-Src, significantly reduced the upregulated ET-1 expression in diabetic mice. These data provide new insights into the regulation of ET-1 expression in endothelial cells in diabetes. Pharmacological targeting of c-Src activity and/or expression may represent a potential therapeutic strategy to reduce ET-1 level and to counteract diabetes-induced deleterious vascular effects.

New Features of Electrocardiogram in a Case Report of Arrhythmogenic Right Ventricular Cardiomyopathy: A Care-Compliant Article

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a crucial health problem. With sudden death often being the first presentation, early diagnosis for ARVC is essential. Up to date, electrocardiogram (ECG) is a widely used diagnostic method without invasive harms. To diagnose and treat ARVC as well as possible, we should clearly elucidate its pathophysiological alterations. A 66-year-old farmer presented to the Emergency Department with continuous palpitation, chest tightness, profuse sweating, and nausea with no obvious predisposing causes. An ECG indicated ventricular tachycardia (VT). The patient experienced a sudden drop in blood pressure and acute confusion. After an immediate electrical conversion, his consciousness was gradually restored, and symptoms relieved. The patient was then transferred to the Department of Cardiology to receive ECG, echocardiography, coronary angiogram, biochemical assays, endocardiac tracing, and radiofrequency ablation. In the end, he was diagnosed with ARVC, evidenced by bilateral ventricle dilation and epsilon waves in leads V1-V3. Appropriate therapies were provided for this patient including pharmacological intervention and radiofrequency ablation. Although the diagnosis of ARVC is not difficult, this patient's ECG manifested several interesting features and should be further investigated: T wave inversions were found extensively in the anterior and inferior leads, revealing the involvement of bilateral ventricles; VTs with different morphologies and cycle lengths were found, and some VTs manifested the feature of irregularly irregular rhythm, reminding us to carefully differentiate some special VTs from atrial fibrillation (AF); and epsilon waves gradually appeared in leads V1-V3 and avR since the onset of ARVC. Most importantly, the epsilon waves behind QRS complex appeared in both sinus rhythm and ventricular premature beats/VT originating from cardiac apex, whereas the epsilon waves prior to QRS complex occurred in VT originating from right ventricular outflow tract (RVOT). The features of T wave inversion and epsilon wave in ECGs and the appearance of VTs with different morphologies can reflect the progression of ARVC. The position relationship between epsilon wave and QRS complex in VT depends on ventricular activation sequence, that is, the localization of epsilon wave depends on where VT is originating from.

Sorcin Links Pancreatic β-Cell Lipotoxicity to ER Ca2+ Stores

Preserving β-cell function during the development of obesity and insulin resistance would limit the worldwide epidemic of type 2 diabetes. Endoplasmic reticulum (ER) calcium (Ca(2+)) depletion induced by saturated free fatty acids and cytokines causes β-cell ER stress and apoptosis, but the molecular mechanisms behind these phenomena are still poorly understood. Here, we demonstrate that palmitate-induced sorcin downregulation and subsequent increases in glucose-6-phosphatase catalytic subunit-2 (G6PC2) levels contribute to lipotoxicity. Sorcin is a calcium sensor protein involved in maintaining ER Ca(2+) by inhibiting ryanodine receptor activity and playing a role in terminating Ca(2+)-induced Ca(2+) release. G6PC2, a genome-wide association study gene associated with fasting blood glucose, is a negative regulator of glucose-stimulated insulin secretion (GSIS). High-fat feeding in mice and chronic exposure of human islets to palmitate decreases endogenous sorcin expression while levels of G6PC2 mRNA increase. Sorcin-null mice are glucose intolerant, with markedly impaired GSIS and increased expression of G6pc2 Under high-fat diet, mice overexpressing sorcin in the β-cell display improved glucose tolerance, fasting blood glucose, and GSIS, whereas G6PC2 levels are decreased and cytosolic and ER Ca(2+) are increased in transgenic islets. Sorcin may thus provide a target for intervention in type 2 diabetes.

Calstabin 2: An important regulator for learning and memory in mice

Calstabin2, also named FK506 binding protein 12.6 (FKBP12.6), is a subunit of ryanodine receptor subtype 2 (RyR2) macromolecular complex, which is an intracellular calcium channel and abundant in the brain. Previous studies identified a role of leaky neuronal RyR2 in posttraumatic stress disorder (PTSD). However, the functional role of Calstabin2 in the cognitive function remains unclear. Herein, we used a mouse model of genetic deletion of Calstabin2 to investigate the function of Calstabin2 in cognitive dysfunction. We found that Calstabin2 knockout (KO) mice showed significantly reduced performance in Morris Water Maze (MWM), long-term memory (LTM) contextual fear testing, and rotarod test when compared to wild type (WT) littermates. Indeed, genetic deletion of Calstabin2 reduced long-term potentiation (LTP) at the hippocampal CA3-CA1 connection, increased membrane excitability, and induced RyR2 leak. Finally, we demonstrated that the increase in cytoplasmic calcium activated Ca(2+) dependent potassium currents and led to neuronal apoptosis in KO hippocampal neurons. Thus, these results suggest that neuronal RyR2 Ca(2+) leak due to Calstabin2 deletion contributes to learning deficiency and memory impairment.

Dipeptidyl Peptidase-4 Inhibitor Use Is Not Associated With Acute Pancreatitis in High-Risk Type 2 Diabetic Patients: A Nationwide Cohort Study

To analyze the association between use of DPP-4 inhibitors and acute pancreatitis in high-risk type 2 diabetic patients. A retrospective nationwide cohort study was conducted using the Taiwan National Health Insurance claim database. The risk associated with sitagliptin was compared to that with acarbose, a second-line antidiabetic drug prescribed for patients with similar diabetes severity and with a known neutral effect on pancreatitis. Between January 1, 2009 and December 31, 2010, a total of 8526 sitagliptin initiators and 8055 acarbose initiators who had hypertriglyceridemia or prior hospitalization history for acute pancreatitis were analyzed for the risk of hospitalization due to acute pancreatitis stratified for baseline propensity score. In the crude analysis, sitagliptin was associated with a decreased risk of acute pancreatitis (hazard ratio [HR] 0.74; 95% confidence interval [CI]: 0.62-0.88) compared to acarbose in diabetic patients with prior history of hospitalization for pancreatitis or hypertriglyceridemia. The association was abolished after stratification for propensity score quintiles (adjusted HR 0.95; 95% CI: 0.79-1.16). Similar results were found separately in both patients' histories of prior hospitalization of acute pancreatitis (adjusted HR 0.97; 95% CI: 0.76-1.24) and those with hypertriglyceridemia (adjusted HR 0.86; 95% CI: 0.65-1.13). No significant association was found for different durations or accumulative doses of sitagliptin. In the stratified analysis, no significant effect modification was found in relation to patients' characteristics. Use of sitagliptin was not associated with an increased risk of acute pancreatitis in high-risk diabetic patients with hypertriglyceridemia or with history of acute pancreatitis.

Aldosterone-to-Renin Ratio Is Associated With Reduced 24-Hour Heart Rate Variability and QTc Prolongation in Hypertensive Patients

Aldosterone is considered to exert direct effects on the myocardium and the sympathetic nervous system. Both QT time and heart rate (HR) variability (HRV) are considered to be markers of arrhythmic risk and autonomous dysregulation. In this study, we investigated the associations between aldosterone, QT time, and HRV in patients with arterial hypertension.We recruited 477 hypertensive patients (age: 60.2 ± 10.2 years; 52.3% females) with a mean systolic/diastolic 24-hour ambulatory blood pressure monitoring (ABPM) value of 128 ± 12.8/77.1 ± 9.2 mmHg and with a median of 2 (IQR: 1-3) antihypertensive agents. Patients were recruited from the outpatient clinic at the Department of Internal Medicine of the Medical University of Graz, Austria. Blood samples, 24-hour HRV derived from 24-hour blood pressure monitoring (ABPM) and ECG's were obtained. Plasma aldosterone and plasma renin concentrations were measured by means of a radioimmunoassay. Twenty-four-hour urine specimens were collected in parallel with ABPM.Mean QTc was 423.3 ± 42.0 milliseconds for males and 434.7 ± 38.3 milliseconds for females. Mean 24H-HR and 24H-HRV was 71.9 ± 9.8 and 10.0 ± 3.6 bpm, respectively. In linear regression analyses adjusted for age, sex, body mass index, ABPM, and current medication, aldosterone to active renin ratio (AARR) was significantly associated with the QTc interval, a marker for cardiac repolarization abnormalities (mean = 426 ± 42.4 milliseconds; β-coefficient = 0.121; P = 0.03) as well as with the 24-hour heart rate variability a surrogate for autonomic dysfunction (median = 9.67 [IQR = 7.38-12.22 bpm]; β-coefficient = -0.133; P = 0.01).In hypertensive patients, AARR is significantly related to QTc prolongation as well as HRV. Further studies investigating the effects of mineralocorticoid receptor blocker and aldosterone synthase inhibitors on QTc and HRV are warranted.

Molecular and Electrophysiological Mechanisms Underlying Cardiac Arrhythmogenesis in Diabetes Mellitus

Diabetes is a common endocrine disorder with an ever increasing prevalence globally, placing significant burdens on our healthcare systems. It is associated with significant cardiovascular morbidities. One of the mechanisms by which it causes death is increasing the risk of cardiac arrhythmias. The aim of this article is to review the cardiac (ion channel abnormalities, electrophysiological and structural remodelling) and extracardiac factors (neural pathway remodelling) responsible for cardiac arrhythmogenesis in diabetes. It is concluded by an outline of molecular targets for future antiarrhythmic therapy for the diabetic population.

Association of Traditional Chinese Medicine Therapy and the Risk of Vascular Complications in Patients With Type II Diabetes Mellitus: A Nationwide, Retrospective, Taiwanese-Registry, Cohort Study

With an increasing use of traditional Chinese medicine (TCM) in type 2 diabetes mellitus (T2DM), evidence of long-term benefit with adjunctive TCM treatment is limited. This study investigated whether the concurrent TCM treatment reduces the risk of vascular complications in T2DM patients by using a large population from National Health Insurance Research Database (NHIRD).We identified 33,457 adult patients with newly diagnosed T2DM using anti-diabetic agents from a random sample of one million beneficiaries in the NHIRD between January 1, 2000 and December 31, 2011. We recruited 1049 TCM users (received TCM over 30 days with a diagnosis of T2DM) and randomly selected 4092 controls as the non-TCM cohort at a ratio of 1:4 frequency-matched by age, sex, hypertension, hyperlipidemia, and index year. We investigated the prescription pattern of TCM and conducted a Cox proportional hazards regression to calculate the hazard ratios (HRs) of stroke, chronic kidney diseases (CKD), and diabetic foot between the 2 cohorts.In the TCM cohort, the prescription pattern of TCM was different between insulin and noninsulin patients. The most common herbs were Dan-Shen (Radix Salviae Miltiorrhizae) in noninsulin group and Da-Huang (Radix et Rhizoma Rhei) in insulin group. The most common formulae were Liu-Wei-Di-Huang-Wan in noninsulin group and Yu-Quan-Wan in insulin group. Although no significant reduction in the hazard ratio of CKD and diabetic foot, the incidence rate of stroke was 7.19 per 1000 person-years in the TCM cohort and 10.66 per 1000 person-years in the control cohort, respectively. After adjustment of age, sex, hypertension, hyperlipidemia, and antidiabetes agent use (including sulfonylureas, α-glucosidase, metformin, meglitinide, thiazolidinediones, and insulin), TCM cohorts were found to have a 33% decreased risk of stroke (95% CI = 0.46-0.97; P < 0.05).This population-based retrospective study showed that the complementary TCM therapy might associate with the decreased risk of stroke in T2DM, suggesting TCM as an adjunctive therapy for T2DM to prevent subsequent stroke.

Bidirectional Relationship Between Diabetes and Acute Pancreatitis: A Population-Based Cohort Study in Taiwan

The proposed bidirectional relationship between acute pancreatitis (AP) and diabetes has never been examined with the same source of data. Furthermore, the effects of disease severity on this relationship have not been fully evaluated. The present study employed the findings from a single database to measure the strength of the association between AP and diabetes.Findings from 1 million National Health Insurance beneficiaries were utilized. Two cohort studies with this database were selected to evaluate the linkage between diabetes and AP. The first cohort analysis addressed the risk of AP among diabetic patients and was comprised of 42,080 diabetic patients and 672,146 unexposed subjects. The second cohort analysis considered the risk of diabetes among patients with AP and enrolled 3187 patients with AP and 709259 unexposed subjects. All adult beneficiaries were followed from January 1, 2005 to December 31, 2012 to identify outcomes of interest. Cox regression models were applied to compare hazards adjusted for potential confounders.For the first cohort, the adjusted hazard ratio (HR) of AP was significantly increased by the presence of diabetes (1.72; 95% confidence interval [CI], 1.52-1.96). In diabetic patients with a history of hyperglycemic crisis episodes (HCEs), the HR was even higher (6.32; 95% CI, 4.54-8.81). For the second cohort, the adjusted HR of diabetes in patients with AP was increased compared to the general population (2.15; 95% CI, 1.92-2.41). For patients with severe AP, the HR was also higher (2.22; 95% CI, 1.50-3.29) but did not differ significantly from that for patients with nonsevere AP.The 2 cohort studies provided evidence for the bidirectional relationship between diabetes and AP. Moreover, diabetic patients with history of HCEs may be associated with higher risk of AP.

Ameliorating Endothelial Mitochondrial Dysfunction Restores Coronary Function via Transient Receptor Potential Vanilloid 1-Mediated Protein Kinase A/Uncoupling Protein 2 Pathway

Coronary heart disease arising from atherosclerosis is a leading cause of cardiogenic death worldwide. Mitochondria are the principal source of reactive oxygen species (ROS), and defective oxidative phosphorylation by the mitochondrial respiratory chain contributes to ROS generation. Uncoupling protein 2 (UCP2), an adaptive antioxidant defense factor, protects against mitochondrial ROS-induced endothelial dysfunction in atherosclerosis. The activation of transient receptor potential vanilloid 1 (TRPV1) attenuates vascular dysfunction. Therefore, whether TRPV1 activation antagonizes coronary lesions by alleviating endothelial mitochondrial dysfunction and enhancing the activity of the protein kinase A/UCP2 pathway warrants examination. ApoE(-/-), ApoE(-/-)/TRPV1(-/-), and ApoE(-/-)/UCP2(-/-) mice were fed standard chow, a high-fat diet (HFD), or the HFD plus 0.01% capsaicin. HFD intake profoundly impaired coronary vasodilatation and myocardial perfusion and shortened the survival duration of ApoE(-/-) mice. TRPV1 or UCP2 deficiency exacerbated HFD-induced coronary dysfunction and was associated with increased ROS generation and reduced nitric oxide production in the endothelium. The activation of TRPV1 by capsaicin upregulated UCP2 expression via protein kinase A phosphorylation, thereby alleviating endothelial mitochondrial dysfunction and inhibiting mitochondrial ROS generation. In vivo, dietary capsaicin supplementation enhanced coronary relaxation and prolonged the survival duration of HFD-fed ApoE(-/-) mice. These effects were not observed in ApoE(-/-) mice lacking the TRPV1 or UCP2 gene. The upregulation of protein kinase A /UCP2 via TRPV1 activation ameliorates coronary dysfunction and prolongs the lifespan of atherosclerotic mice by ameliorating endothelial mitochondrial dysfunction. Dietary capsaicin supplementation may represent a promising intervention for the primary prevention of coronary heart disease.

Naringin Reverses Hepatocyte Apoptosis and Oxidative Stress Associated with HIV-1 Nucleotide Reverse Transcriptase Inhibitors-Induced Metabolic Complications

Nucleoside Reverse Transcriptase Inhibitors (NRTIs) have not only improved therapeutic outcomes in the treatment of HIV infection but have also led to an increase in associated metabolic complications of NRTIs. Naringin’s effects in mitigating NRTI-induced complications were investigated in this study. Wistar rats, randomly allotted into seven groups (n = 7) were orally treated daily for 56 days with 100 mg/kg zidovudine (AZT) (groups I, II III), 50 mg/kg stavudine (d4T) (groups IV, V, VI) and 3 mL/kg of distilled water (group VII). Additionally, rats in groups II and V were similarly treated with 50 mg/kg naringin, while groups III and VI were treated with 45 mg/kg vitamin E. AZT or d4T treatment significantly reduced body weight and plasma high density lipoprotein concentrations but increased liver weights, plasma triglycerides and total cholesterol compared to controls, respectively. Furthermore, AZT or d4T treatment significantly increased oxidative stress, adiposity index and expression of Bax protein, but reduced Bcl-2 protein expression compared to controls, respectively. However, either naringin or vitamin E significantly mitigated AZT- or d4T-induced weight loss, dyslipidemia, oxidative stress and hepatocyte apoptosis compared to AZT- or d4T-only treated rats. Our results suggest that naringin reverses metabolic complications associated with NRTIs by ameliorating oxidative stress and apoptosis. This implies that naringin supplements could mitigate lipodystrophy and dyslipidemia associated with NRTI therapy.

Novel Association Between the Reverse-Dipper Pattern of Ambulatory Blood Pressure Monitoring and Metabolic Syndrome in Men But Not in Women

The aim of this study was to investigate the relationships between nocturnal variations in blood pressure (BP) and metabolic syndrome (MetS) in different gender.This cross-sectional study involved 509 hypertensive patients (254 males and 255 females, 45 to 75 years old) from September 2013 to March 2014. BP values were acquired from ambulatory BP monitoring (ABPM). The dipper pattern of BP was defined as 10% to 20% reduction of the mean systolic BP (SBP) values at night compared with the daytime values. The diagnosis of MetS was made according to NCEP ATP-III definition. Multivariate logistic regression analyses were used to explore the relationships between ABPM results and MetS.In our study, MetS were observed in 29.1% of male and 18.4% of female participants. The prevalence of MetS was higher in the patients with reverse-dipper pattern than in others. After multivariate logistic regression analysis, the reverse-dipper pattern of BP (odds ratio 2.298; P = 0.006) and 24-SBP (odds ratio 1.063; P = 0.021) were independently correlated with MetS in males. However, there was no association between MetS and BP reverse dipping in females.Our cross-sectional study showed that the reverse-dipper pattern of BP is associated with MetS in male, while the underlying mechanism deserves further investigation.

Evaluation of low doses BPA-induced perturbation of glycemia by toxicogenomics points to a primary role of pancreatic islets and to the mechanism of toxicity

Epidemiologic and experimental studies have associated changes of blood glucose homeostasis to Bisphenol A (BPA) exposure. We took a toxicogenomic approach to investigate the mechanisms of low-dose (1 × 10⁻⁹M) BPA toxicity in ex vivo cultures of primary murine pancreatic islets and hepatocytes. Twenty-nine inhibited genes were identified in islets and none in exposed hepatocytes. Although their expression was slightly altered, their impaired cellular level, as a whole, resulted in specific phenotypic changes. Damage of mitochondrial function and metabolism, as predicted by bioinformatics analyses, was observed: BPA exposure led to a time-dependent decrease in mitochondrial membrane potential, to an increase of ROS cellular levels and, finally, to an induction of apoptosis, attributable to the bigger Bax/Bcl-2 ratio owing to activation of NF-κB pathway. Our data suggest a multifactorial mechanism for BPA toxicity in pancreatic islets with emphasis to mitochondria dysfunction and NF-κB activation. Finally, we assessed in vitro the viability of BPA-treated islets in stressing condition, as exposure to high glucose, evidencing a reduced ability of the exposed islets to respond to further damages. The result was confirmed in vivo evaluating the reduction of glycemia in hyperglycemic mice transplanted with control and BPA-treated pancreatic islets. The reported findings identify the pancreatic islet as the main target of BPA toxicity in impairing the glycemia. They suggest that the BPA exposure can weaken the response of the pancreatic islets to damages. The last observation could represent a broader concept whose consideration should lead to the development of experimental plans better reproducing the multiple exposure conditions.

Store-operated Ca2+ Entry Mediated by Orai1 and TRPC1 Participates to Insulin Secretion in Rat β-Cells

Store-operated Ca(2+) channels (SOCs) are voltage-independent Ca(2+) channels activated upon depletion of the endoplasmic reticulum Ca(2+) stores. Early studies suggest the contribution of such channels to Ca(2+) homeostasis in insulin-secreting pancreatic β-cells. However, their composition and contribution to glucose-stimulated insulin secretion (GSIS) remains unclear. In this study, endoplasmic reticulum Ca(2+) depletion triggered by acetylcholine (ACh) or thapsigargin stimulated the formation of a ternary complex composed of Orai1, TRPC1, and STIM1, the key proteins involved in the formation of SOCs. Ca(2+) imaging further revealed that Orai1 and TRPC1 are required to form functional SOCs and that these channels are activated by STIM1 in response to thapsigargin or ACh. Pharmacological SOCs inhibition or dominant negative blockade of Orai1 or TRPC1 using the specific pore mutants Orai1-E106D and TRPC1-F562A impaired GSIS in rat β-cells and fully blocked the potentiating effect of ACh on secretion. In contrast, pharmacological or dominant negative blockade of TRPC3 had no effect on extracellular Ca(2+) entry and GSIS. Finally, we observed that prolonged exposure to supraphysiological glucose concentration impaired SOCs function without altering the expression levels of STIM1, Orai1, and TRPC1. We conclude that Orai1 and TRPC1, which form SOCs regulated by STIM1, play a key role in the effect of ACh on GSIS, a process that may be impaired in type 2 diabetes.

Irisin protects against endothelial injury and ameliorates atherosclerosis in apolipoprotein E-Null diabetic mice

OBJECTIVE

The circulating irisin increases energy expenditure and improves insulin resistance in mice and humans. The improvement of insulin resistance ameliorates atherosclerosis. Therefore, we hypothesized that irisin alleviates atherosclerosis in diabetes.

METHODS

Endothelial function was measured by acetylcholine-induced endothelium-dependent vasodilation using aortic rings in apolipoprotein E-Null (apoE(-/-)) streptozotocin-induced diabetic mice. Atherosclerotic lesion was evaluated by plaque area and inflammatory response in aortas. In addition, the endothelium-protective effects of irisin were also further investigated in primary human umbilical vein endothelial cells (HUVECs) in vitro.

RESULTS

The in vivo experiments showed that irisin treatment significantly improved endothelial dysfunction, decreased endothelial apoptosis, and predominantly decreased atherosclerotic plaque area of both en face and cross sections when compared with normal saline-treated diabetic mice. Moreover, the infiltrating macrophages and T lymphocytes within plaque and the mRNA expression levels of inflammatory cytokines in aortas were also significantly reduced by irisin treatment in mice. The in vitro experiments revealed that irisin inhibited high glucose-induced apoptosis, oxidative stress and increased antioxidant enzymes expression in HUVECs, and pretreatment with LY294002, l-NAME, AMPK-siRNA or eNOS-siRNA, attenuated the protection of irisin on HUVECs apoptosis induced by high glucose. In addition, the in vivo and in vitro experiments showed that irisin increased the phosphorylation of AMPK, Akt and eNOS in aortas and cultured HUVECs.

CONCLUSIONS

The present study indicates that systemic administration of irisin may be protected against endothelial injury and ameliorated atherosclerosis in apoE(-/-) diabetic mice. The endothelium-protective action of irisin was through activation of AMPK-PI3K-Akt-eNOS signaling pathway. Irisin could be therapeutic for atherosclerotic vascular diseases in diabetes.

Relationship Between Myo-Inositol Supplementary and Gestational Diabetes Mellitus: A Meta-Analysis

To determine whether myo-inositol supplement will increase the action of endogenous insulin, which is mainly measured by markers of insulin resistance such as homeostasis model assessment of insulin resistance.PubMed, Cochrane Library, Embase, and web of science were comprehensively searched using "gestational diabetes mellitus" and "myo-inositol" to identify relevant studies. Both subject headings and free texts were adopted. The methodological quality of the included studies were assessed and pooled analyzed by the methods recommended by the Cochrane collaboration.A total of 5 trials containing 513 participants were included. There was a significant reduction in aspects of gestational diabetes incidence (risk ratio [RR], 0.29; 95% confidence interval (95% CI), 0.19-0.44), birth weight (mean difference [MD], -116.98; 95% CI, -208.87 to -25.09), fasting glucose oral glucose tolerance test (OGTT) (MD, -0.36; 95% CI, -0.51 to -0.21), 1-h glucose OGTT (MD, -0.63; 95% CI, -1.01 to -0.26), 2-h glucose OGTT (MD, -0.45; 95% CI, -0.75 to -0.16), and related complications (odds ratio [OR], 0.28; 95% CI 0.14-0.58).On the basis of current evidence, myo-inositol supplementation reduces the development of gestational diabetes mellitus (GDM), although this conclusion requires further evaluation in large-scale, multicenter, blinded randomized controlled trials.

Rutin Increases Muscle Mitochondrial Biogenesis with AMPK Activation in High-Fat Diet-Induced Obese Rats

Decreased mitochondrial number and dysfunction in skeletal muscle are associated with obesity and the progression of obesity-associated metabolic disorders. The specific aim of the current study was to investigate the effects of rutin on mitochondrial biogenesis in skeletal muscle of high-fat diet-induced obese rats. Supplementation with rutin reduced body weight and adipose tissue mass, despite equivalent energy intake (p < 0.05). Rutin significantly increased mitochondrial size and mitochondrial DNA (mtDNA) content as well as gene expression related to mitochondrial biogenesis, such as peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), nuclear respiratory factor-1 (NRF-1), transcription factor A (Tfam), and nicotinamide adenine dinucleotide (NAD)-dependent deacetylase, sirtulin1 (SIRT1) in skeletal muscle (p < 0.05). Moreover, rutin consumption increased muscle adenosine monophosphate-activated protein kinase (AMPK) activity by 40% (p < 0.05). Taken together, these results suggested at least partial involvement of muscle mitochondria and AMPK activation in the rutin-mediated beneficial effect on obesity.

Mitochondrial calcium overload is a key determinant in heart failure

Calcium (Ca2+) released from the sarcoplasmic reticulum (SR) is crucial for excitation-contraction (E-C) coupling. Mitochondria, the major source of energy, in the form of ATP, required for cardiac contractility, are closely interconnected with the SR, and Ca2+ is essential for optimal function of these organelles. However, Ca2+ accumulation can impair mitochondrial function, leading to reduced ATP production and increased release of reactive oxygen species (ROS). Oxidative stress contributes to heart failure (HF), but whether mitochondrial Ca2+ plays a mechanistic role in HF remains unresolved. Here, we show for the first time, to our knowledge, that diastolic SR Ca2+ leak causes mitochondrial Ca2+ overload and dysfunction in a murine model of postmyocardial infarction HF. There are two forms of Ca2+ release channels on cardiac SR: type 2 ryanodine receptors (RyR2s) and type 2 inositol 1,4,5-trisphosphate receptors (IP3R2s). Using murine models harboring RyR2 mutations that either cause or inhibit SR Ca2+ leak, we found that leaky RyR2 channels result in mitochondrial Ca2+ overload, dysmorphology, and malfunction. In contrast, cardiac-specific deletion of IP3R2 had no major effect on mitochondrial fitness in HF. Moreover, genetic enhancement of mitochondrial antioxidant activity improved mitochondrial function and reduced posttranslational modifications of RyR2 macromolecular complex. Our data demonstrate that leaky RyR2, but not IP3R2, channels cause mitochondrial Ca2+ overload and dysfunction in HF.

Mitochondrial oxidative stress promotes atrial fibrillation

Oxidative stress has been suggested to play a role in the pathogenesis of atrial fibrillation (AF). Indeed, the prevalence of AF increases with age as does oxidative stress. However, the mechanisms linking redox state to AF are not well understood. In this study we identify a link between oxidative stress and aberrant intracellular Ca²⁺ release via the type 2 ryanodine receptor (RyR2) that promotes AF. We show that RyR2 are oxidized in the atria of patients with chronic AF compared with individuals in sinus rhythm. To dissect the molecular mechanism linking RyR2 oxidation to AF we used two murine models harboring RyR2 mutations that cause intracellular Ca²⁺ leak. Mice with intracellular Ca²⁺ leak exhibited increased atrial RyR2 oxidation, mitochondrial dysfunction, reactive oxygen species (ROS) production and AF susceptibility. Both genetic inhibition of mitochondrial ROS production and pharmacological treatment of RyR2 leakage prevented AF. Collectively, our results indicate that alterations of RyR2 and mitochondrial ROS generation form a vicious cycle in the development of AF. Targeting this previously unrecognized mechanism could be useful in developing effective interventions to prevent and treat AF.

Rats Prone to Obesity Under a High-Carbohydrate Diet have Increased Post-Meal CCK mRNA Expression and Characteristics of Rats Fed a High-Glycemic Index Diet

We previously reported that rats prone to obesity exhibit an exaggerated increase in glucose oxidation and an exaggerated decline in lipid oxidation under a low-fat high-carbohydrate (LF/HC) diet. The aim of the present study was to investigate the mechanisms involved in these metabolic dysregulations. After a 1-week adaptation to laboratory conditions, 48 male Wistar rats were fed a LF/HC diet for 3 weeks. During weeks 2 and 3, glucose tolerance tests (GTT), insulin tolerance tests (ITT), and meal tolerance tests (MTT) were performed to evaluate blood glucose, plasma, and insulin. Glucose and lipid oxidation were also assayed during the GTT. At the end of the study, body composition was measured in all the rats, and they were classified as carbohydrate resistant (CR) or carbohydrate sensitive (CS) according to their adiposity. Before sacrifice, 24 of the 48 rats received a calibrated LF/HC meal. Liver, muscle, and intestine tissue samples were taken to measure mRNA expression of key genes involved in glucose, lipid, and protein metabolism. ITT, GTT, and MTT showed that CS rats were neither insulin resistant nor glucose intolerant, but mRNA expression of cholecystokinin (CCK) in the duodenum was higher and that of CPT1, PPARα, and PGC1α in liver were lower than in CR rats. From these results, we make the hypothesis that in CS rats, CCK increased pancreatic secretion, which may favor a quicker absorption of carbohydrates and consequently induces an enhanced inhibition of lipid oxidation in the liver, leading to a progressive accumulation of fat preferentially in visceral deposits. Such a mechanism may explain why CS rats share many characteristics observed in rats fed a high-glycemic index diet.

Mechanisms for redox-regulation of protein kinase C

Protein kinase C (PKC) is comprised of a family of signal-regulated enzymes that play pleiotropic roles in the control of many physiological and pathological responses. PKC isoforms are traditionally viewed as allosterically activated enzymes that are recruited to membranes by growth factor receptor-generated lipid cofactors. An inherent assumption of this conventional model of PKC isoform activation is that PKCs act exclusively at membrane-delimited substrates and that PKC catalytic activity is an inherent property of each enzyme that is not altered by the activation process. This traditional model of PKC activation does not adequately explain the many well-documented actions of PKC enzymes in mitochondrial, nuclear, and cardiac sarcomeric (non-sarcolemmal) subcellular compartments. Recent studies address this dilemma by identifying stimulus-specific differences in the mechanisms for PKC isoform activation during growth factor activation versus oxidative stress. This review discusses a number of non-canonical redox-triggered mechanisms that can alter the catalytic properties and subcellular compartmentation patterns of PKC enzymes. While some redox-activated mechanisms act at structural determinants that are common to all PKCs, the redox-dependent mechanism for PKCδ activation requires Src-dependent tyrosine phosphorylation of a unique phosphorylation motif on this enzyme and is isoform specific. Since oxidative stress contributes to pathogenesis of a wide range of clinical disorders, these stimulus-specific differences in the controls and consequences of PKC activation have important implications for the design and evaluation of PKC-targeted therapeutics.

Glucose-Dependent Insulin Secretion in Pancreatic β-Cell Islets from Male Rats Requires Ca2+ Release via ROS-Stimulated Ryanodine Receptors

Glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells requires an increase in intracellular free Ca2+ concentration ([Ca2+]). Glucose uptake into β-cells promotes Ca2+ influx and reactive oxygen species (ROS) generation. In other cell types, Ca2+ and ROS jointly induce Ca2+ release mediated by ryanodine receptor (RyR) channels. Therefore, we explored here if RyR-mediated Ca2+ release contributes to GSIS in β-cell islets isolated from male rats. Stimulatory glucose increased islet insulin secretion, and promoted ROS generation in islets and dissociated β-cells. Conventional PCR assays and immunostaining confirmed that β-cells express RyR2, the cardiac RyR isoform. Extended incubation of β-cell islets with inhibitory ryanodine suppressed GSIS; so did the antioxidant N-acetyl cysteine (NAC), which also decreased insulin secretion induced by glucose plus caffeine. Inhibitory ryanodine or NAC did not affect insulin secretion induced by glucose plus carbachol, which engages inositol 1,4,5-trisphosphate receptors. Incubation of islets with H2O2 in basal glucose increased insulin secretion 2-fold. Inhibitory ryanodine significantly decreased H2O2-stimulated insulin secretion and prevented the 4.5-fold increase of cytoplasmic [Ca2+] produced by incubation of dissociated β-cells with H2O2. Addition of stimulatory glucose or H2O2 (in basal glucose) to β-cells disaggregated from islets increased RyR2 S-glutathionylation to similar levels, measured by a proximity ligation assay; in contrast, NAC significantly reduced the RyR2 S-glutathionylation increase produced by stimulatory glucose. We propose that RyR2-mediated Ca2+ release, induced by the concomitant increases in [Ca2+] and ROS produced by stimulatory glucose, is an essential step in GSIS.