Telmisartan reduces atrial arrhythmia susceptibility through the regulation of RAS-ERK and PI3K-Akt-eNOS pathways in spontaneously hypertensive rats

Influence of electroacupuncture on ghrelin and the phosphoinositide 3-kinase/protein kinase B/endothelial nitric oxide synthase signaling pathway in spontaneously hypertensive rats

OBJECTIVE

To investigate the influence of electroacupuncture (EA) on ghrelin and the phosphoinositide 3-kinase/protein kinase B/endothelial nitric oxide synthase (PI3K/Akt/eNOS) signaling pathway in spontaneously hypertensive rats (SHRs).

METHODS

Eight Wistar-Kyoto rats were used as the healthy blood pressure (BP) control (normal group), and 32 SHRs were randomized into model group, EA group, EA plus ghrelin group (EA + G group), and EA plus PF04628935 group (a potent ghrelin receptor blocker; EA + P group) using a random number table. Rats in the normal group and model group did not receive treatment, but were immobilized for 20 min per day, 5 times a week, for 4 continuous weeks. SHRs in the EA group, EA + G group and EA + P group were immobilized and given EA treatment in 20 min sessions, 5 times per week, for 4 weeks. Additionally, 1 h before EA, SHRs in the EA + G group and EA + P group were intraperitoneally injected with ghrelin or PF04628935, respectively, for 4 weeks. The tail-cuff method was used to measure BP. After the 4-week intervention, the rats were sacrificed by cervical dislocation, and pathological morphology of the abdominal aorta was observed using hematoxylin-eosin (HE) staining. Enzyme-linked immunosorbent assay (ELISA) was used to detect the levels of ghrelin, nitric oxide (NO), endothelin-1 (ET-1) and thromboxane A2 (TXA2) in the serum. Isolated thoracic aortic ring experiment was performed to evaluate vasorelaxation. Western blot was used to measure the expression of PI3K, Akt, phosphorylated Akt (p-Akt) and eNOS proteins in the abdominal aorta. Further, quantitative real-time polymerase chain reaction (qRT-PCR) was conducted to measure the relative levels of mRNA expression for PI3K, Akt and eNOS in the abdominal aorta.

RESULTS

EA significantly reduced the systolic BP (SBP) and diastolic BP (DBP) (P < 0.05). HE staining showed that EA improved the morphology of the vascular endothelium to some extent. Results of ELISA indicated that higher concentrations of ghrelin and NO, and lower concentrations of ET-1 and TXA2 were presented in the EA group (P < 0.05). The isolated thoracic aortic ring experiment demonstrated that the vasodilation capacity of the thoracic aorta increased in the EA group. Results of Western blot and qRT-PCR showed that EA increased the abundance of PI3K, p-Akt/Akt and eNOS proteins, as well as expression levels of PI3K, Akt and eNOS mRNAs (P < 0.05). In the EA + G group, SBP and DBP decreased (P < 0.05), ghrelin concentrations increased (P < 0.05), and the concentrations of ET-1 and TXA2 decreased (P < 0.05), relative to the EA group. In addition, the levels of PI3K and eNOS proteins, the p-Akt/Akt ratio, and the expression of PI3K, Akt and eNOS mRNAs increased significantly in the EA + G group (P < 0.05), while PF04628935 reversed these effects.

CONCLUSION

EA effectively reduced BP and protected the vascular endothelium, and these effects may be linked to promoting the release of ghrelin and activation of the PI3K/Akt/eNOS signaling pathway.

Functional Analysis of Serum Long Noncoding RNAs in Patients with Atrial Fibrillation

Objectives

Long noncoding RNAs (lncRNAs) are closely related to diverse diseases. However, its role in atrial fibrillation (AF) pathogenesis needs further exploration.

Design

We performed microarray analysis on the serum samples from 70 healthy volunteers and 70 AF patients. This study was aimed at detecting the levels of serum lncRNAs and mRNAs and bioinformatically analyze them to establish potential marker(s) for AF diagnosis. Receiver operating curve (ROC) and area under the curve (AUC) were employed to address the AF diagnostic power of lncRNAs.

Results

In the AF serum samples, 753 lncRNAs and 802 mRNAs (p ≤ 0.05; fold change ≥ 2) were upregulated, and 315 lncRNAs and 153 mRNAs were downregulated, as opposed to healthy serum samples. Using bioinformatic analysis, we analyzed the top 4 differentially expressed (DE) lncRNAs, namely, NR-001587, NR-015407, NR-038455, and NR-038894, and found that the PI3K-AKT cell proliferation signaling pathway was most affected. This was in accordance with our functional analysis of DE mRNAs and adjacent lncRNAs. Notably, the elevated serum NR-001587 levels were strongly associated with AF incidence.

Conclusions

Our work highlights the role of lncRNAs in AF pathogenesis and provides a novel serum biomarker for AF diagnosis.

Molecules linked to Ras signaling as therapeutic targets in cardiac pathologies

Abstract

The Ras family of small Guanosine Triphosphate (GTP)-binding proteins (G proteins) represents one of the main components of intracellular signal transduction required for normal cardiac growth, but is also critically involved in the development of cardiac hypertrophy and heart failure. The present review provides an update on the role of the H-, K- and N-Ras genes and their related pathways in cardiac diseases. We focus on cardiac hypertrophy and heart failure, where Ras has been studied the most. We also review other cardiac diseases, like genetic disorders related to Ras. The scope of the review extends from fundamental concepts to therapeutic applications. Although the three Ras genes have a nearly identical primary structure, there are important functional differences between them: H-Ras mainly regulates cardiomyocyte size, whereas K-Ras regulates cardiomyocyte proliferation. N-Ras is the least studied in cardiac cells and is less associated to cardiac defects. Clinically, oncogenic H-Ras causes Costello syndrome and facio-cutaneous-skeletal syndromes with hypertrophic cardiomyopathy and arrhythmias. On the other hand, oncogenic K-Ras and alterations of other genes of the Ras-Mitogen-Activated Protein Kinase (MAPK) pathway, like Raf, cause Noonan syndrome and cardio-facio-cutaneous syndromes characterized by cardiac hypertrophy and septal defects. We further review the modulation by Ras of key signaling pathways in the cardiomyocyte, including: (i) the classical Ras-Raf-MAPK pathway, which leads to a more physiological form of cardiac hypertrophy; as well as other pathways associated with pathological cardiac hypertrophy, like (ii) The SAPK (stress activated protein kinase) pathways p38 and JNK; and (iii) The alternative pathway Raf-Calcineurin-Nuclear Factor of Activated T cells (NFAT). Genetic alterations of Ras isoforms or of genes in the Ras-MAPK pathway result in Ras-opathies, conditions frequently associated with cardiac hypertrophy or septal defects among other cardiac diseases. Several studies underline the potential role of H- and K-Ras as a hinge between physiological and pathological cardiac hypertrophy, and as potential therapeutic targets in cardiac hypertrophy and failure.

Graphic abstract

The Ras (Rat Sarcoma) gene family is a group of small G proteins

Ras is regulated by growth factors and neurohormones affecting cardiomyocyte growth and hypertrophy

Ras directly affects cardiomyocyte physiological and pathological hypertrophy

Genetic alterations of Ras and its pathways result in various cardiac phenotypes

Ras and its pathway are differentially regulated in acquired heart disease

Ras modulation is a promising therapeutic target in various cardiac conditions.

miR-320a in serum exosomes promotes myocardial fibroblast proliferation via regulating the PIK3CA/Akt/mTOR signaling pathway in HEH2 cells

MicroRNAs (miRNAs/miRs) serve an important role in the pathogenesis of chronic heart failure (CHF). A number of reports have illustrated the regulatory effect of serum exosomal miRNA on myocardial fibrosis. The present study aimed to investigate the expression of miR-320a in serum exosomes, as well as the effect of miR-320a on myocardial fibroblast proliferation. Serum exosome samples from 10 patients with CHF and 5 healthy volunteers were obtained and characterized. mRNA and protein expression levels were measured via reverse transcription-quantitative PCR and western blotting, respectively. The content of soluble growth stimulation expressed gene 2 (sST2) was determined via ELISA. HEH2 cell viability and apoptosis were detected by performing MTT assays and flow cytometry, respectively. The results demonstrated that serum miR-320a expression levels and sST2 content were significantly increased in patients with CHF compared with healthy controls, and the expression of serum miR-320a was significantly correlated with clinical CHF indexes. miR-320a expression levels were significantly increased in exosomes isolated from patients with CHF compared with those isolated from healthy controls. Phosphoinositide-3-kinase catalytic α polypeptide gene (PIK3CA) expression levels and sST2 content were increased in HEH2 cells following transfection with miR-320a mimics compared with NC-mimic, whereas miR-320a inhibitor displayed contrasting effects by reduced the cell viability and apoptosis in myocardial fibroblasts compared with the NC-inhibitor group. The protein expression levels of collagen I, collagen III, α-smooth muscle actin, phosphorylated (p)-mTOR (ser 2448)/mTOR, p-Akt (ser 473)/Akt, p-Akt (thr 308)/Akt and PIK3CA were significantly increased in miR-320a mimic-transfected HEH2 cells compared with the NC-mimics groups. By contrast, miR-320a inhibitor notably downregulated the expression levels of these proteins compared with the NC-inhibitor group. Collectively, the results of the present study demonstrated that miR-320a promoted myocardial fibroblast proliferation via regulating the PIK3CA/Akt/mTOR signaling pathway in HEH2 cells, suggesting that serum exosomal miR-320a may serve as a potential biomarker for the diagnosis of CHF.

Sacubitril/Valsartan Decreases Atrial Fibrillation Susceptibility by Inhibiting Angiotensin II-Induced Atrial Fibrosis Through p-Smad2/3, p-JNK, and p-p38 Signaling Pathways

Sacubitril/valsartan (SAC/VAL) prevents angiotensin II (AngII) from binding AT1-R and blocks degradation of natriuretic peptides. Despite its efficacy in reducing ventricular fibrosis and preserving cardiac functions, which has been extensively demonstrated in myocardial infarction or pressure overload models, few studies have been conducted to determine whether SAC/VAL could attenuate atrial fibrosis and decrease atrial fibrillation (AF) susceptibility. Our study provided evidence for the inhibition of atrial fibrosis and reduced susceptibility to AF by SAC/VAL. After 28 days of AngII continuous subcutaneous stimulation, rats in SAC/VAL group exhibited reduced extent of atrial fibrosis, inhibited proliferation, migration, and differentiation of atrial fibroblasts, and decreased susceptibility to AF. We further found that inhibition of p-Smad2/3, p-JNK, and p-p38MAPK pathways is involved in the role of SAC/VAL on AngII-induced atrial fibrosis in vivo. These results emphasize the importance of SAC/VAL in the prevention of AngII-induced atrial fibrosis and may help to enrich the options for AF pharmacotherapy.

Left atrial fibrosis in atrial fibrillation: Mechanisms, clinical evaluation and management

Atrial fibrillation (AF), the commonest arrhythmia, shows associations with various disease conditions. Mounting evidence indicates that atrial fibrosis is an important part of the arrhythmogenic substrate, with an essential function in the generation of conduction abnormalities that underlie the transition from paroxysmal to persistent AF, which in turn contributes to AF perpetuation. Left atrial (LA) fibrosis is considered a possible major factor and predictor in AF treatment. The present review provides insights into LA fibrosis’ association with AF. The information is focused on clinical aspects and mechanisms, clinical evaluating methods that evaluate fibrosis changes and examining possible options for the prevention of atrial fibrosis.

Signal Transduction Profiling of Angiotensin II Type 1 Receptor With Mutations Associated to Atrial Fibrillation in Humans

The AT1 receptor (AT1R) has a major role in the Renin-Angiotensin System, being involved in several physiological events including blood pressure control and electrolyte balance. The AT1R is a member of the G protein coupled receptors (GPCR) family, classically known to couple G_αq and engage β-arrestin recruitment. Both G protein and arrestin signaling pathways are involved in modulation of different downstream kinases. A previous study reported that mutations in the AT1R (A244S and I103T-A244S) were positively correlated with higher risk of atrial fibrillation in men. Based on that report, we aimed to investigate if these mutations, including I103T only, could affect AT1R signal transduction profile, and consequently, implicate in atrial fibrillation outcome. To address that, we engineered an AT1R carrying the above-mentioned mutations, and functionally evaluated different signaling pathways. Phosphokinase profiler array to assess the mutations downstream effects on kinases and kinase substrates phosphorylation levels was used. Our results show that the I103T-A244S mutant receptor presents decreased β-arrestin 2 recruitment, which could lead to a harmful condition of sustained G_αq signaling. Moreover, the phosphokinase profiler array revealed that the same mutation led to downstream modulation of kinase pathways that are linked to physiological responses such as fibrous tissue formation, apoptosis and cell proliferation.

Left heart function evaluation of patients with essential hypertension and paroxysmal atrial fibrillation by two-dimensional speckle tracking imaging combined with real-time three-dimensional ultrasound imaging

Background

This study aims to assess the value of two-dimensional speckle tracking imaging (2D-STI) combined with real-time 3-dimensional echocardiography (RT-3DE) in evaluating left heart function in patients with combined ETH and PAF.

Methods

A prospective study was designed, and the research period was from January 2017 to January 2020. A PAF observation group comprised of patients with ETH and PAF, a PAF control group of patients with ETH but without PAF, and a healthy volunteer group referred to as the healthy group, each comprised of 50 patients was established. All patients underwent routine ultrasound imaging examination using 2D-STI and RT-3DE. The interventricular septum thickness (IVST), left and right atrioventricular diameter (LAD), left ventricular posterior wall thickness (PWT), left ventricular ejection fraction (LVEF), the mean left atrium peak strain (mSs, mSe, mSa), strain rate (mSRs, mSRe, mSRa), the left ventricular mass (LVM), left ventricular mass index (LVMI), and left atrial total emptying volume (LATEV), the left atrial volume index (LAVI), left atrial total emptying fraction (LATEF), left atrium expansion index (LAEI), left atrium passive ejection fraction (LAPEF), and left atrial active ejection fraction (LAAEF) were calculated. Patients in the PAF observation group received telmisartan combined with rosuvastatin after diagnosis and 12- and 24-month-follow up visits were conducted. During these visits, 2D-STI combined with RT-3DE was used to evaluate cardiac function and each patient's blood pressure was monitored.

Results

Patients in the PAF observation group had a significantly longer course of ETH than patients in the PAF control group (13.5±4.4 vs. 10.32±5.6, P=0.002). The comparison of routine 2D-STI and RT-3DE ultrasound indexes among the three groups also showed significant differences (P<0.01). During the 2-year follow-up period, the IVST, LAD, PWT, and LVEF of remaining patients significantly improved as treatment progressed (P<0.05). The LAVI, LATEF, and LAEI also improved significantly as the treatment progressed (P<0.05). After 12 months of treatment, the recurrence rate of atrial fibrillation was 16.33% (8/45) and after 24 months this was 34.21% (13/38).

Conclusions

Cardiac function could be evaluated comprehensively by 2D-STI combined with RT-3DE in patients with ETH combined with PAF at initial diagnosis and follow-up.

Targeting peroxisome proliferator-activated receptors: A new strategy for the treatment of cardiac fibrosis

Cardiac fibrosis is a pathogenic factor of many cardiovascular diseases (CVD), which seriously affects people's life, and health and causes huge economic losses. Increasing evidence has shown that peroxisome proliferator-activated receptors (PPARs) can regulate the progression of cardiac fibrosis. For the first time, this review systematically summarizes the literature on cardiac fibrosis from the perspective of PPARs from 2010 to 2020. Moreover, the role of each PPARs in cardiac fibrosis was clarified in this scientific revision from the perspectives of pharmacologically active substances, known agonists, natural extract compounds, and nucleic-acid-based drugs in different CVD models. Furthermore, the combination of multiple PPARs on the treatment of cardiac fibrosis is discussed. This scientific review provides new ideas for targeting PPARs in the treatment of cardiac fibrosis and provides strategies for the development of new, safe, and effective pharmacological antagonists against cardiac fibrosis based on PPAR activity.

A Novel Approach Based on Metabolomics Coupled With Intestinal Flora Analysis and Network Pharmacology to Explain the Mechanisms of Action of Bekhogainsam Decoction in the Improvement of Symptoms of Streptozotocin-Induced Diabetic Nephropathy in Mice

Bekhogainsam decoction (BHID), a representative prescription for the treatment of diabetes mellitus (DM) and diabetic complications in both traditional Korean and Chinese medicine, was examined for its ability to ameliorate diabetic nephropathy (DN), and its mechanism of action was evaluated by metabolomics, gut microbiota, and network pharmacology. In this study, male specific pathogen-free C57BL/6 mice were intraperitoneally injected with streptozotocin (STZ, 100 mg/kg) once per day for 3 days consecutively, and were then orally administered BHID at 100 and 500 mg/kg, and metformin at 250 mg/kg once per day for 4 weeks. Our results showed that the administration of BHID to mice with STZ-induced DN prevented physiological and serological changes, structural damage, and kidney dysfunction. Based on a metabolomics test with serum, the profoundly altered metabolites in the BHID treatment group were identified. Thirty-six BHID-related proteins and four signaling pathways, including valine, leucine, and isoleucine biosynthesis, nicotinate and nicotinamide metabolism, tryptophan metabolism, and alanine, aspartate, and glutamate metabolism pathways, were explored. Principal coordinates analysis (PCoA) of the gut microbiota revealed that BHID treatment significantly affected the flora composition. In addition, the network pharmacology analysis revealed that BHID acted through phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt) and MAPK-related protein targets. Our findings on the anti-DN effects of BHID and its mechanism of action, from the perspective of systems biology, have provided scientific evidence to support the clinical treatment of patients with diabetes, and implied that BHID has the potential to prevent the progression of DN.

Telmisartan and thiorphan combination treatment attenuates fibrosis and apoptosis in preventing diabetic cardiomyopathy

Aims

LCZ696, a first-generation dual angiotensin receptor-neprilysin inhibitor (ARNi), is effective in treating heart failure patients. However, the role of ARNis in treating diabetic cardiomyopathy is poorly understood. This study evaluates the efficacy of a novel combination of telmisartan [angiotensin receptor blocker (ARB)] and thiorphan [neprilysin inhibitor (NEPi)] in ameliorating diabetic cardiomyopathy while, at the same time, exploring the relevant underlying molecular mechanism(s).

Methods and results

Diabetes was induced by administration of streptozotocin (55 mg/kg, i.p.) in male Wistar rats. After 4 weeks, diabetic rats were subjected to either thiorphan (0.1 mg/kg/day, p.o.) or telmisartan (10 mg/kg/day, p.o.) monotherapy, or their combination, for a period of 4 weeks. Metabolic and morphometric alterations, failing ventricular functions, and diminished baroreflex indicated development of diabetic cardiac complications. Apart from morphometric alterations, all pathological consequences were prevented by telmisartan and thiorphan combination therapy. Diabetic rats exhibited significant modulation of the natriuretic peptide system, a key haemodynamic regulator; this was normalized by combination therapy. Histopathological studies showed augmented myocardial fibrosis, demonstrated by increased % PSR-positive area, with combination therapy giving the best improvement in these indices. More importantly, the combination of thiorphan and telmisartan was superior in attenuating inflammatory (NF-κB/MCP-1), profibrotic (TGF-β/Smad7) and apoptotic (PARP/Caspase-3) cascades compared to respective monotherapies when treating rats with diabetic cardiomyopathy. In addition, diabetic heart chromatin was in a state of active transcription, indicated by increased histone acetylation (H2AK5Ac, H2BK5Ac, H3K9Ac, and H4K8Ac) and histone acetyltransferase (PCAF and Ac-CBP) levels. Interestingly, combination treatment was sufficiently potent to normalize these alterations.

Conclusion

The protective effect of novel ARB and NEPi combination against diabetic cardiomyopathy can be attributed to inhibition of inflammatory, profibrotic, and apoptotic cascades. Moreover, reversal of histone acetylation assists its protective effect.

Identifying the key microRNAs implicated in atrial fibrillation

OBJECTIVE

This study investigated the potential microRNAs (miRNAs) having a diagnostic value in atrial fibrillation (AF).

METHODS

The miRNA and mRNA expression profiles of atrial tissue from healthy individuals and patients with AF were downloaded from the Gene Expression Omnibus database. Differentially expressed miRNAs/mRNAs (DEMis/DEMs) were identified in patients with AF. Furthermore, an interaction network between DEMis and DMEs was constructed. The biological processes, molecular functions, and signaling pathways of DEMs were enriched. Then, the diagnostic values of candidate DECs among healthy individuals and patients with AF were preliminarily evaluated in the GSE101586, GSEE101684, and GSE112214 datasets.

RESULTS

Twenty DEMis were identified in patients with AF, including seven upregulated and 13 downregulated DEMis. Furthermore, 2,307 DEMs were identified in patients with AF. In the DEMi-DEM interaction network, downregulated miR-193b and upregulated miR-16 interacted with the most targeted DEMs, which interacted with 72 and 65 targeted DEMs, respectively. The targeted DEMs were significantly enriched in biological functions including apoptosis and the PI3K-Akt, mTOR, Hippo, HIF-1, and ErbB signaling pathways. Four of the 20 DEMis (i.e., miR-490-3p, miR-630, miR-146b-5p, and miR-367) had a potential value to distinguish patients with AF from healthy individuals in the GSE68475, GSE70887, and GSE28954 datasets. The area under the curve values for those four DEMis were 0.751, 0.719, 0.709, and 0.7, respectively.

CONCLUSION

DEMis might play key roles in AF progression through the mTOR and Hippo signaling pathways. miR-409-3p, miR-630, miR-146b-5p, and miR-367 had a potential diagnostic value to discriminate patients with AF from healthy controls in this study.

Uncovering Synergistic Mechanism of Chinese Herbal Medicine in the Treatment of Atrial Fibrillation with Obstructive Sleep Apnea Hypopnea Syndrome by Network Pharmacology

Paroxysmal atrial fibrillation (AF) combined with obstructive sleep apnea hypopnea syndrome (OSAHS) is very common in clinical practice. Traditional Chinese medicine (TCM) rule of regulating the liver based on psycho-cardiology shows satisfactory effectiveness in the treatment of paroxysmal AF combined with OSAHS. However, its underlying pharmacological mechanism has not yet been elucidated. This study applied network pharmacology to identify 94 active components in the six TCM liver-regulating herbs and 182 corresponding targets from several databases and comprehensive literature studies, as well as retrieved AF combined with OSAHS-related targets. Cytoscape software was adopted to construct the component-component target network and component-putative target-AF combined with OSAHS target network. Then, we obtained 38 putative therapeutic targets against AF combined with OSAHS. After the production of a putative therapeutic target interaction network, topological analysis was adopted to determine the core targets of TCM liver-regulating herbs in the treatment of paroxysmal AF combined with OSAHS. For all putative therapeutic targets, biological process analysis and pathway enrichment analysis were utilized to investigate the possible mechanism of TCM liver-regulating herbs in the treatment of paroxysmal AF combined with OSAHS. Mechanistically, it included positive regulation of nitric oxide biosynthetic process, aging, response to hypoxia, TNF signaling pathway, HIF-1 signaling pathway, PI3K-Akt signaling pathway, neuroactive ligand-receptor interaction, and calcium signaling pathway. Especially, six core targets of TCM liver-regulating herbs, namely, TNF, STAT3, AKT1, IL-6, TP53, and INS, were significant in the regulation of the above biological processes and pathways. This study demonstrates the multicomponent, multitarget, and multipathway feature of TCM liver-regulating herbs, provides an extensional foundation for further research, and facilitates the reasonable application of TCM liver-regulating herbs in treating paroxysmal AF combined with OSAHS.

Intrinsic Adaptation of SHR Right Atrium Reduces Heart Rate

Hypertension represents an autonomic dysfunction, characterized by increased sympathetic and decreased parasympathetic cardiovascular tone leading to resting tachycardia. Therefore, studies assessing hypertension-associated changes in isolated cardiac tissues were conducted under electric field stimulation to stimulate the neurons. Herein, we characterize the influence of the autonomic neurotransmitter on the baseline atrial chronotropism of unpaced isolated right atria of normotensive Wistar rats (NWR) and spontaneously hypertensive rats (SHR). Our results revealed a resting bradycardia in tissues from SHR in comparison to NWR. The release of autonomic neurotransmitters, acetylcholine or norepinephrine, still occurs in the electrically unstimulated right atrium, after excision of the sympathetic nerve, which could explain differences in basal heart rate between NWR and SHR. Nicotine and the acetylcholinesterase inhibitor physostigmine reduced the chronotropism of right atria from either NWR or SHR. Conversely, the muscarinic receptor antagonist atropine did not affect the basal chronotropism of tissues from both strains. Furthermore, tyramine increased the chronotropism of NWR and SHR atria indicating availability of the neuronal stocks of noradrenaline. Although the monoamine uptake inhibitor cocaine increased right atrium chronotropism in both strains, the basal heart rate was not affected by the β-adrenoceptor antagonist propranolol. In summary, after acute section of the sympathetic nerve, autonomic neurotransmitters are still released either in resting conditions or upon pharmacological stimulation of right atria from both strains. Nevertheless, autonomic neurotransmission does not affect resting chronotropism, nor is the responsible for reduced basal heart rate of the isolated right atrium of hypertensive rats.

Beneficial effects of tolvaptan on atrial remodeling induced by chronic intermittent hypoxia in rats

INTRODUCTION

Atrial remodeling in the form of fibrosis is considered as the substrate for the development of atrial fibrillation (AF). The aim of this study was to investigate the effects of tolvaptan on chronic intermittent hypoxia (CIH) induced atrial remodeling and the mechanisms underlying such changes.

METHODS

A total of 45 Sprague-Dawley rats were randomized into three groups: Control group, CIH group, CIH with tolvaptan treatment (CIH-T) group (n = 15). CIH rats were subjected to CIH 6 hour/d for 30 days, and CIH-T rats were administrated tolvaptan while they received CIH. After the echocardiography examination, rats were sacrificed in the 31 days. In each group, 5 rats were randomly selected for isolated heart electrophysiology testing, for other 10 rats, the tissues of atria were sampled for histological and molecular biological experiments, Masson's trichrome staining was used to evaluate the extent of atrial fibrosis, expression levels of microRNA-21 (miR-21), Sprouty-1 (Spry1), phosphatase, and tensin homolog (PTEN), extracellular regulated protein kinase (ERK), phospho-extracellular regulated protein kinase (p-ERK), matrix metalloprotein 9 (MMP-9), phosphoinositide 3-kinase (PI3K), protein kinase B (AKT), phospho-protein kinase B (p-AKT), nuclear factor-k-gene binding (NF-κB), phosphor-nuclear factor-k-gene binding (p-NF-κB) were measured.

RESULTS

Compared to the Control rats, CIH rats showed higher atrial interstitial collagen deposition and AF inducibility, mRNA levels of miR-21, MMP-9, PI3K, AKT, and protein levels of ERK, p-ERK, MMP-9, NF-κB, p-NF-κB were significantly increased, whereas mRNA levels of Spry1, ERK, and protein levels of Spry1, PTEN, PI3K, AKT, p-AKT were significantly decreased. Treatment with tolvaptan attenuated CIH-induced atrial fibrosis, reduced AF inducibility, expression levels of miR-21 and its downstream factors were also improved.

CONCLUSIONS

CIH-induced significant atrial remodeling in our rat model, which was attenuated by tolvaptan. These changes may be explained due to alterations in miR-21/Spry1/ERK/MMP-9, miR-21/PTEN/PI3K/AKT, and NF-κB pathways by tolvaptan.

QiDiTangShen Granules Reduced Diabetic Kidney Injury by Regulating the Phosphorylation Balance of the Tyrosine and Serine Residues of Insulin Receptor Substrate 1

Background

Diabetic nephropathy (DN) is a microvascular complication induced by diabetes mellitus (DM), which can affect life quality and long-term prognosis of patients with DM. Angiotensin-converting-enzyme inhibitors (ACEI)/angiotensin receptor blockers (ARB) are currently recommended for treating DN proteinuria, but patients receiving ACEI/ARB are at risk of elevated serum creatinine or potassium levels. Based on the “yin-yang” theory of traditional Chinese medicine, the present study explored the effect of QiDiTangShen (QDTS) granules on DN and the phosphorylation balance of tyrosine and serine residues of IRS-1.

Methods

In this experiment, db/db mice were used as an animal model for type 2 diabetic nephropathy. The intervention (QDTS granules and valsartan) started when the mice were 12 weeks old. C57BL/6 mice were used as normal control. The urine albumin excretion ratio (UAER) was measured by enzyme-linked immunosorbent assay (ELISA) before and after the intervention. The IRS-1, PI3K, Akt, and MAPK proteins expression and the phosphorylation levels were detected by western blot.

Results

QDTS granules reduced the 24-h urinary albumin excretion rate (UAE) in db/db mice with type 2 DM and attenuated the pathological changes of the kidney. QDTS granules also increased the activation level of the PI3K/Akt signaling pathway and reduced insulin resistance. In addition, QDTS granules inhibited the activation of ERK and p38MAPK and decreased the phosphorylation ratio of Ser307/Tyr896 of IRS-1 in renal tissue.

Conclusions

QDTS granules reduced DM-induced renal injury by improving insulin sensitivity via suppressing MAPK signaling and restoring the phosphorylation balance of tyrosine/serine of IRS-1.

Activation of voltage-gated sodium current and inhibition of erg-mediated potassium current caused by telmisartan, an antagonist of angiotensin II type-1 receptor, in HL-1 atrial cardiomyocytes

Telmisartan (TEL) is a non-peptide blocker of angiotensin II type-1 (AT₁ ) receptor. However, the mechanisms through which this drug interacts directly with ion currents in hearts remain largely unclear. Herein, we aim to investigate the effects of TEL the on ionic currents and membrane potential of murine HL-1 cardiomyocytes. In whole-cell recordings, addition of TEL stimulated the peak and late components of voltage-gated Na⁺ currents (I_Na ) with different potencies. The EC₅₀ values required to achieve the stimulatory effect of this drug on peak and late I_Na were 0.2 and 1.2 μmol/L, respectively, and the current-voltage relationship of peak I_Na shifted toward less-depolarized potentials during exposure to TEL. Telmisartan not only increased peak I_Na but also prolonged the inactivation time course of late I_Na . Amiodarone (Amio) or ranolazine (Ran), but not angiotensin II, could reverse TEL-mediated effects. The drug enhanced the recovery rate of I_Na inactivation and exerted an inhibitory effect on erg-mediated K⁺ and L-type Ca²⁺ currents. In whole-cell current-clamp recordings, addition of the drug resulted in prolongation of the duration of action potentials (APs) in a dose-dependent manner in HL-1 cells; Amio or Ran could reverse this increase in AP durations. Telmisartan-mediated prolongation of AP was attenuated in KCNH2 siRNA-transfected HL-1 cells. In cultured smooth muscle cells of the human coronary artery, TEL enhanced I_Na amplitudes and slowed current inactivation. Stimulation by TEL of I_Na in HL-1 cells did not simply increase current magnitude but altered current kinetics, thereby suggesting state-dependent activation. Telmisartan may have greater affinity to the open/inactivated state than to the resting state residing in Na_V channels. Collectively, TEL-mediated stimulation of I_Na and inhibition of I_K(erg) could be an important ionic mechanism underlying the increased cell excitability of HL-1 cells; these actions, however, cannot be entirely explained by its blockade of AT₁ receptor.

Increased Gi protein signaling potentiates the negative chronotropic effect of adenosine in the SHR right atrium

Hypertension is a risk factor for cardiovascular diseases, which have been associated with dysfunction of sympathetic and purinergic neurotransmission. Therefore, herein, we evaluated whether modifications of adenosine receptor signaling may contribute to the cardiac dysfunction observed in hypertension. Isolated right atria from spontaneously hypertensive (SHR) or normotensive Wistar rats (NWR) were used to investigate the influence of adenosine receptor signaling cascade in the cardiac chronotropism. Our results showed that adenosine, the endogenous agonist of adenosine receptors, and CPA, a selective agonist of A₁ receptor, decreased the atrial chronotropism of NWR and SHR in a concentration- and time-dependent manner, culminating in cardiac arrest (0 bpm). Interestingly, a 3-fold lower concentration of adenosine was required to induce the negative chronotropic effect in SHR atria. Pre-incubation of tissues from both strains with DPCPX, a selective A₁ receptor antagonist, inhibited the negative chronotropic effect of CPA, while simultaneous inhibition of A₂ and A₃ receptors, with ZM241385 and MRS1523, did not change the adenosine chronotropic effects. Moreover, 1 μg/ml pertussis toxin, which inactivates the Gαi protein subunit, reduced by 80% the negative chronotropic effects of adenosine in the NWR atrium, with minor effects in SHR tissue. These data indicate that the negative chronotropic effect of adenosine in right atrium depends exclusively on the activation of A₁ receptors. Moreover, the distinct responsiveness of NWR and SHR atria to pertussis toxin reveals that the enhanced negative chronotropic response of SHR right atrium is probably due to an increased activity of Gαi protein-mediated.

Telmisartan improves cardiac fibrosis in diabetes through peroxisome proliferator activated receptor δ (PPARδ): from bedside to bench

BACKGROUND

Despite the known risk of diabetes-induced cardiac fibrosis, less is known about whether diabetes causes an altered cardiac phenotype independent of coronary atherosclerosis. Peroxisome proliferator-activated receptor δ (PPARδ), a versatile regulator of metabolic homeostasis, may be a potential therapeutic target. Herein we investigated the effectiveness of telmisartan, a unique angiotensin receptor blocker that increases PPARδ expression, in improving left ventricular remodeling in diabetic humans and rats.

METHODS

In this longitudinal, prospective study, we enrolled 15 diabetic patients receiving telmisartan (20 mg/day) for 12 weeks. After treatment, strain was measured and compared with the baseline value. Using streptozotocin to induce type 1 diabetes rat model, we measured PPARδ expression and downstream targets.

RESULTS

After treatment with telmisartan, both longitudinal and circumferential strains improved in diabetic patients. Compared with that of controls, the diabetic rat heart developed significant fibrosis, which markedly decreased after treatment with telmisartan (30 mg/kg/day, orally) for 7 days. After incubation with 30 mM glucose, rat cardiomyocytes showed a significant down-regulation of PPARδ. Interestingly, the increased expression of fibrosis-associated proteins, including signal transducer and activator of transcription 3 (STAT3) was attenuated by the co-incubation of GW0742, a PPARδ agonist. By knockdown or inhibition of STAT3, the hyperglycemia related high expression of fibrosis associated targets was reversed. Independent from the hyperglycemic incubation, STAT3 over-expression led to similar results. Conversely, in the presence of GSK0660, a PPARδ inhibitor, the protective effects of telmisartan were diminished.

CONCLUSION

Telmisartan improved the hyperglycemia-induced cardiac fibrosis through the PPARδ/STAT3 pathway. Graphical abstract Summary of the mechanism of telmisartan's effect on the suppression of hyperglycemia-induced cardiac fibrosis through PPARδ instead of the AMPK pathway. PPARδ peroxisome proliferator-activated receptor δ, STAT3 signal transducer and activator of transcription 3, CTGF connective tissue growth factor, MMP9 matrix metallopeptidase 9.