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

Hypoxia preconditioning of adipose stem cell-derived exosomes loaded in gelatin methacryloyl (GelMA) promote type H angiogenesis and osteoporotic fracture repair

The challenges posed by delayed atrophic healing and nonunion stand as formidable obstacles in osteoporotic fracture treatment. The processes of type H angiogenesis and osteogenesis emerge as pivotal mechanisms during bone regeneration. Notably, the preconditioning of adipose-derived stem cell (ADSC) exosomes under hypoxic conditions has garnered attention for its potential to augment the secretion and functionality of these exosomes. In the present investigation, we embarked upon a comprehensive elucidation of the underlying mechanisms of hypo-ADSC-Exos within the milieu of osteoporotic bone regeneration. Our findings revealed that hypo-ADSC-Exos harboured a preeminent miRNA, namely, miR-21-5p, which emerged as the principal orchestrator of angiogenic effects. Through in vitro experiments, we demonstrated the capacity of hypo-ADSC-Exos to stimulate the proliferation, migration, and angiogenic potential of human umbilical vein endothelial cells (HUVECs) via the mediation of miR-21-5p. The inhibition of miR-21-5p effectively attenuated the proangiogenic effects mediated by hypo-ADSC-Exos. Mechanistically, our investigation revealed that exosomal miR-21-5p emanating from hypo-ADSCs exerts its regulatory influence by targeting sprouly1 (SPRY1) within HUVECs, thereby facilitating the activation of the PI3K/AKT signalling pathway. Notably, knockdown of SPRY1 in HUVECs was found to potentiate PI3K/AKT activation and, concomitantly, HUVEC proliferation, migration, and angiogenesis. The culminating stage of our study involved a compelling in vivo demonstration wherein GelMA loaded with hypo-ADSC-Exos was validated to substantially enhance local type H angiogenesis and concomitant bone regeneration. This enhancement was unequivocally attributed to the exosomal modulation of SPRY1. In summary, our investigation offers a pioneering perspective on the potential utility of hypo-ADSC-Exos as readily available for osteoporotic fracture treatment.

Mechanisms of Atrial Fibrillation in Obstructive Sleep Apnoea

Obstructive sleep apnoea (OSA) is a strong independent risk factor for atrial fibrillation (AF). Emerging clinical data cite adverse effects of OSA on AF induction, maintenance, disease severity, and responsiveness to treatment. Prevention using continuous positive airway pressure (CPAP) is effective in some groups but is limited by its poor compliance. Thus, an improved understanding of the underlying arrhythmogenic mechanisms will facilitate the development of novel therapies and/or better selection of those currently available to complement CPAP in alleviating the burden of AF in OSA. Arrhythmogenesis in OSA is a multifactorial process characterised by a combination of acute atrial stimulation on a background of chronic electrical, structural, and autonomic remodelling. Chronic intermittent hypoxia (CIH), a key feature of OSA, is associated with long-term adaptive changes in myocyte ion channel currents, sensitising the atria to episodic bursts of autonomic reflex activity. CIH is also a potent driver of inflammatory and hypoxic stress, leading to fibrosis, connexin downregulation, and conduction slowing. Atrial stretch is brought about by negative thoracic pressure (NTP) swings during apnoea, promoting further chronic structural remodelling, as well as acutely dysregulating calcium handling and electrical function. Here, we provide an up-to-date review of these topical mechanistic insights and their roles in arrhythmia.

Pathophysiological mechanisms and therapeutic approaches in obstructive sleep apnea syndrome

Obstructive sleep apnea syndrome (OSAS) is a common breathing disorder in sleep in which the airways narrow or collapse during sleep, causing obstructive sleep apnea. The prevalence of OSAS continues to rise worldwide, particularly in middle-aged and elderly individuals. The mechanism of upper airway collapse is incompletely understood but is associated with several factors, including obesity, craniofacial changes, altered muscle function in the upper airway, pharyngeal neuropathy, and fluid shifts to the neck. The main characteristics of OSAS are recurrent pauses in respiration, which lead to intermittent hypoxia (IH) and hypercapnia, accompanied by blood oxygen desaturation and arousal during sleep, which sharply increases the risk of several diseases. This paper first briefly describes the epidemiology, incidence, and pathophysiological mechanisms of OSAS. Next, the alterations in relevant signaling pathways induced by IH are systematically reviewed and discussed. For example, IH can induce gut microbiota (GM) dysbiosis, impair the intestinal barrier, and alter intestinal metabolites. These mechanisms ultimately lead to secondary oxidative stress, systemic inflammation, and sympathetic activation. We then summarize the effects of IH on disease pathogenesis, including cardiocerebrovascular disorders, neurological disorders, metabolic diseases, cancer, reproductive disorders, and COVID-19. Finally, different therapeutic strategies for OSAS caused by different causes are proposed. Multidisciplinary approaches and shared decision-making are necessary for the successful treatment of OSAS in the future, but more randomized controlled trials are needed for further evaluation to define what treatments are best for specific OSAS patients.

Role of epigenetic abnormalities and intervention in obstructive sleep apnea target organs

ABSTRACT

Obstructive sleep apnea (OSA) is a common condition that has considerable impacts on human health. Epigenetics has become a rapidly developing and exciting area in biology, and it is defined as heritable alterations in gene expression and has regulatory effects on disease progression. However, the published literature that is integrating both of them is not sufficient. The purpose of this article is to explore the relationship between OSA and epigenetics and to offer better diagnostic methods and treatment options. Epigenetic modifications mainly manifest as post-translational modifications in DNA and histone proteins and regulation of non-coding RNAs. Chronic intermittent hypoxia-mediated epigenetic alterations are involved in the progression of OSA and diverse multiorgan injuries, including cardiovascular disease, metabolic disorders, pulmonary hypertension, neural dysfunction, and even tumors. This article provides deeper insights into the disease mechanism of OSA and potential applications of targeted diagnosis, treatment, and prognosis in OSA complications.

Ameliorative Impact of Liraglutide on Chronic Intermittent Hypoxia-Induced Atrial Remodeling

Atrial fibrillation (AF) is the most frequent form of clinical cardiac arrhythmias. Previous evidence proved that atrial anatomical remodeling (AAR) and atrial electrical remodeling (AER) are crucial for the progression and maintenance of AF. This study is aimed at investigating the impact of the glucagon-like peptide-1 (GLP-1) receptor agonist, Liraglutide (Lir), on atrial remodeling (AR) mouse model induced by chronic intermittent hypoxia (CIH). C57BL/6 mice were categorized randomly into the control, Lir, CIH, and CIH+Lir groups. CIH was performed in CIH and CIH+Lir groups for 12 weeks. Lir (0.3 mg/kg/day, s.c) was administered to the Lir and CIH+Lir groups for four weeks, beginning from the ninth week of CIH. Meanwhile, echocardiography and right atrial endocardial electrophysiology via jugular vein, as well as induction rate and duration of AF, were evaluated. Masson and Sirius red staining assays were utilized to assess the extent of fibrosis in the atrial tissue of the mice. Immunohistochemical staining, RT-qPCR, and Western blotting were performed to evaluate the marker levels of AAR and AER and the expression of genes and proteins of the miR-21/PTEN/PI3K/AKT signaling pathway, respectively. ELISA was also performed to evaluate the changes of serum inflammatory factor levels. The CIH group exhibited significant AR, increased atrial fibrosis, and a higher incidence rate of AF compared to the control group. Lir could significantly downregulate the protein expression level in the PI3K/p-AKT pathway and upregulated that of phosphatase and tensin homolog deleted on chromosome ten (PTEN). Moreover, Lir downregulated the expression of miR-21. However, the protein expressions of CACNA1C and KCNA5 in atrial tissue were not changed significantly. In addition, Lir significantly attenuated the levels of markers of inflammation (TNF-α and IL-6) in the serum. In the mouse model of CIH, Lir treatment could ameliorate AR by the miR-21/PTEN/PI3K/AKT signaling pathway and modulation of inflammatory responses.

On the Relationship between Diabetes and Obstructive Sleep Apnea: Evolution and Epigenetics

This review offers an overview of the relationship between diabetes, obstructive sleep apnea (OSA), obesity, and heart disease. It then addresses evidence that the traditional understanding of this relationship is incomplete or misleading. In the process, there is a brief discussion of the evolutionary rationale for the development and retention of OSA in light of blood sugar dysregulation, as an adaptive mechanism in response to environmental stressors, followed by a brief overview of the general concepts of epigenetics. Finally, this paper presents the results of a literature search on the epigenetic marks and changes in gene expression found in OSA and diabetes. (While some of these marks will also correlate with obesity and heart disease, that is beyond the scope of this project). We conclude with an exploration of alternative explanations for the etiology of these interlinking diseases.

The effect of adaptation to hypoxia on cardiac tolerance to ischemia/reperfusion

The acute myocardial infarction (AMI) and sudden cardiac death (SCD), both associated with acute cardiac ischemia, are one of the leading causes of adult death in economically developed countries. The development of new approaches for the treatment and prevention of AMI and SCD remains the highest priority for medicine. A study on the cardiovascular effects of chronic hypoxia (CH) may contribute to the development of these methods. Chronic hypoxia exerts both positive and adverse effects. The positive effects are the infarct-reducing, vasoprotective, and antiarrhythmic effects, which can lead to the improvement of cardiac contractility in reperfusion. The adverse effects are pulmonary hypertension and right ventricular hypertrophy. This review presents a comprehensive overview of how CH enhances cardiac tolerance to ischemia/reperfusion. It is an in-depth analysis of the published data on the underlying mechanisms, which can lead to future development of the cardioprotective effect of CH. A better understanding of the CH-activated protective signaling pathways may contribute to new therapeutic approaches in an increase of cardiac tolerance to ischemia/reperfusion.

Long-Term High-Altitude Exposure Does Not Increase the Incidence of Atrial Fibrillation Associated with Organic Heart Diseases

Wang, Man, Mengxue Liu, Jia Huang, Dan Fan, Shengzhong Liu, Tao Yu, Keli Huang, Xinchuan Wei, and Qian Lei. Long-term high-altitude exposure does not increase the incidence of atrial fibrillation associated with organic heart diseases. High Alt Med Biol. 00:000-000, 2021.- Background: Atrial fibrillation (AF) is one of the most common arrhythmias and is associated with several complications following cardiac surgery. However, the differences in the incidence of AF associated with organic heart diseases between highland and lowland populations have not been comprehensively studied. Methods: In this retrospective study, a total of 2,316 highland and lowland patients who underwent cardiac surgery between January 2013 and December 2018 in a single center were enrolled. According to the altitude of residence, patients were divided into high-altitude (>1,500 m) and low-altitude (<1,500 m) groups. A propensity score matching analysis was performed to estimate the association of lifetime high-altitude exposure with AF. Results: Among the enrolled patients, 239 (10.9%) were from a high-altitude plateau, while 1,946 (89.1%) were from a low-altitude area. There were statistical differences in age, gender, European System for Cardiac Operative Risk Evaluation, and other factors, between the two groups (p < 0.05). According to the propensity score, 237 patients in the high-altitude group were successfully matched to 237 patients in the low-altitude group without significant difference in baseline data (p > 0.05). Among the matched patients, 125 patients (26.4%) suffered from AF, with 66 (27.8%) in the high-altitude group and 59 (24.9%) in the low-altitude group. The incidence of AF was statistically similar between the two groups and not significantly influenced by long-term high-altitude exposure (odds ratio 1.07; 95% confidence interval 0.71-1.60, p > 0.05). Conclusion: Long-term high-altitude exposure did not significantly increase the occurrence of AF in patients with organic heart diseases. Clinical Trial No. ChiCTR1900028612.

Identification of Pivotal MicroRNAs and Target Genes Associated with Persistent Atrial Fibrillation Based on Bioinformatics Analysis

Atrial fibrillation (AF) is one of the most common supraventricular arrhythmias worldwide. However, the specific molecular mechanism underlying AF remains unclear. Our study is aimed at identifying pivotal microRNAs (miRNAs) and targeting genes associated with persistent AF (pAF) using bioinformatics analysis. Three gene expression array datasets (GSE31821, GSE41177, and GSE79768) and an miRNA expression array dataset (GSE68475) associated with pAF were downloaded. Differentially expressed genes (DEGs) were identified using the LIMMA package, and differentially expressed miRNAs (DEMs) were screened from GSE68475. Target genes for DEMs were predicted using the miRTarBase database, and intersections between these target genes and DEGs were selected for further analysis, including the generation of protein–protein interaction (PPI) network, miRNA–transcription factor–target regulatory network, and drug–gene network. A total of 264 DEGs and 40 DEMs were identified between the pAF and control groups. Functional and pathway enrichment analyses of up- and downregulated DEGs were performed. The common genes (CGs) were primarily enriched in the phosphoinositide 3-kinase- (PI3K-) protein kinase B (Akt) signaling pathway, negative regulation of cell division, and response to hypoxia. The PPI network, miRNA–transcription factor–target regulatory network, and drug–gene network were constructed using Cytoscape. The present study revealed several novel miRNAs and genes involved in pAF. We speculated that miR-4298, miR-3125, miR-4306, and miR-671-5p could represent significant miRNAs that act on the target gene superoxide dismutase 2 (SOD2) during the development of pAF and may serve as essential biomarkers for pAF diagnosis and treatment. Moreover, MYC might function in pAF pathogenesis through the PI3K–Akt signaling pathway.

The involvement of protein kinases in the cardioprotective effect of chronic hypoxia

The purpose of this review is to analyze the involvement of protein kinases in the cardioprotective mechanism induced by chronic hypoxia. It has been reported that chronic intermittent hypoxia contributes to increased expression of the following kinases in the myocardium: PKCdelta, PKCalpha, p-PKCepsilon, p-PKCalpha, AMPK, p-AMPK, CaMKII, p-ERK1/2, p-Akt, PI3-kinase, p-p38, HK-1, and HK-2; whereas, chronic normobaric hypoxia promotes increased expression of the following kinases in the myocardium: PKCepsilon, PKCbetaII, PKCeta, CaMKII, p-ERK1/2, p-Akt, p-p38, HK-1, and HK-2. However, CNH does not promote enhanced expression of the AMPK and JNK kinases. Adaptation to hypoxia enhances HK-2 association with mitochondria and causes translocation of PKCdelta, PKCbetaII, and PKCeta to the mitochondria. It has been shown that PKCdelta, PKCepsilon, ERK1/2, and MEK1/2 are involved in the cardioprotective effect of chronic hypoxia. The role of other kinases in the cardioprotective effect of adaptation to hypoxia requires further research.

The Potential Effects of Aliskiren on Atrial Remodeling Induced by Chronic Intermittent Hypoxia in Rats

Purpose

Atrial remodeling takes part in the pathogenesis of atrial fibrillation (AF). Aliskiren, as a direct renin inhibitor, has been shown to exert protective effects against arrhythmia. The aim of this study was to investigate the potential role of aliskiren in atrial remodeling in a chronic intermittent hypoxia (CIH) rat model.

Methods

A total of 45 Sprague–Dawley rats were randomly assigned into three groups (n=15 per group): control group; CIH group; and CIH with aliskiren (CIH-A) group. CIH and CIH-A rats were subjected to CIH for 6 h per day for 4 weeks. Atrial fibrosis was evaluated using Masson’s trichrome staining. Electrophysiological tests were conducted in the isolated perfused hearts to assess the atrial effective refractory period and inducibility of AF. Atrial ionic remodeling was measured using the whole-cell patch-clamp technique, and Western blotting and real-time quantitative polymerase chain reactionwere performed to evaluate changes in ion channels.

Results

CIH induced obvious collagen deposition, and the abnormal fibrosis was significantly attenuated by aliskiren. The inducibility of AF was increased significantly in the CIH group compared with the control and CIH-A groups (23±24.5% vs 2.0±4.2% vs 5.0±7.0%, respectively; P<0.05). Compared with the control group, the densites of the calcium current (I_CaL) and sodium current (I_Na) were reduced significantly in the CIH group (I_CaL: −3.16±0.61 pA/pF vs −7.13±1.98 pA/pF; I_Na: −50.97±8.71 pA/pF vs −132.58±25.34 pA/pF, respectively; all P<0.05). Following intervention with aliskiren, the reductions in I_CaL and I_Na were significantly improved, and the ionic modeling changes assessed at the mRNA and protein levels were also significantly improved.

Conclusion

CIH could alter atrial modeling and subsequently promote the occurrence and development of AF, which could be attenuated by treatment with aliskiren.

Effects of occlusal disharmony on susceptibility to atrial fibrillation in mice

Tooth loss or incorrect positioning causes occlusal disharmony. Furthermore, tooth loss and atrial fibrillation (AF) are both risk factors for ischemic stroke and coronary heart disease. Therefore, we hypothesized that occlusal disharmony-induced stress increases susceptibility to AF, and we designed the present study to test this idea in mice. Bite-opening (BO) was done by cementing a suitable appliance onto the mandibular incisor to cause occlusal disharmony by increasing the vertical height of occlusion by 0.7 mm for a period of 2 weeks. AF susceptibility, evaluated in terms of the duration of AF induced by transesophageal burst pacing, was significantly increased concomitantly with atrial remodeling, including fibrosis, myocyte apoptosis and oxidative DNA damage, in BO mice. The BO-induced atrial remodeling was associated with increased calmodulin kinase II-mediated ryanodine receptor 2 phosphorylation on serine 2814, as well as inhibition of Akt phosphorylation. However, co-treatment with propranolol, a non-selective β-blocker, ameliorated these changes in BO mice. These data suggest that improvement of occlusal disharmony by means of orthodontic treatment might be helpful in the treatment or prevention of AF.

Role of ion channels in chronic intermittent hypoxia-induced atrial remodeling in rats

AIMS

Atrial remodeling, including structural and electrical remodeling, is considered as the substrate in the development of atrial fibrillation (AF). Structural remodeling mainly involves atrial fibrosis, and electrical remodeling is closely related to the changes of ion channels in atrial myocytes. In this study, we aimed to investigate the changes of ion channels in atrial remodeling induced by CIH in rats, which provide the explication for the mechanisms of AF.

MATERIALS AND METHODS

80 male Sprague-Dawley rats were randomized into two groups: Control and CIH group (n = 40). CIH rats were subjected to CIH 8 h/d for 30 days. Atrial epicardial conduction velocity, conduction inhomogeneity and AF inducibility were examined. Masson's trichrome staining was used to evaluate the extent of atrial fibrosis, and the expression levels of ion channel subunits were measured by RT-qPCR, Western blot, and IHC, respectively. The remaining 40 rats were used for whole-cell patch clamp experiments. Action potential, I_Na, I_Ca-L, I_to were recorded and compared between two groups.

KEY FINDINGS

CIH rats showed increased AF inducibility, atrial interstitial collagen deposition, APD, expression levels of RyR2, p-RyR2, CaMKII, p-CaMKII, and decreased atrial epicardial conduction velocity, expression levels of Na_v1.5, Ca_v1.2, K_v1.5, K_v4.2, K_v4.3 compared to the Control rats, and the current density of I_Na, I_Ca-L, I_to were significantly decreased in CIH group.

SIGNIFICANCE

We observed significant atrial remodeling induced by CIH in our rat model, which was characterized by changes in ion channels. These changes may be the mechanisms of CIH promoting AF.

Suppression of experimental atrial fibrillation in a canine model of rapid atrial pacing by the phosphodiesterase 3 inhibitor cilostazol

OBJECTIVE

Atrial fibrillation (AF) represents the most common arrhythmia encountered in cardiology department. The purpose of this study was designed to investigate whether cilostazol, an oral phosphodiesterase 3 inhibitor (PDE3) could have protective effects on atrial remodeling in a canine model of AF and explore the potential molecular mechanisms.

METHODS

Dogs were randomly assigned to Sham, Paced, Paced + cilostazol group, 7 dogs in each group. In Sham group, pacemaker was instrumented but without pacing. Rapid atrial pacing (RAP) at 600 or 500 bpm/min was maintained in Paced group and Paced + cilo group for 2 h or 2 weeks in acute or chronic experiment, respectively. The Paced + cilo group of dogs were pretreated with cilostazol orally (10 mg·kg^-1·d^-1, cilo) for 1 h or 2 days prior RAP induction and served as treatment group. Atrial effective refractory periods (AERP) at different basic cycle lengths (BCLs), inducibility, and duration time of AF were measured after pacing for 2 h. The blood sample, echocardiography, histopathology, inflammation and oxidative stress makers, protein and mRNA expression levels of matrix metalloproteinase-2 (MMP-2) and MMP-9 were detected after 2 weeks pacing in each group.

RESULTS

Significant changes in electrophysiological parameters were observed in the acute RAP canine model, the AERPs shortened with increased inducibility and duration of AF, which was attenuated by cilostazol (P < 0.05). The serum inflammation makers as interleukin-8 (IL-8) and toll like receptor 4 (TLR 4) levels and oxidative stress indicators like xanthine oxidative (XO) and reactive oxygen species (ROS) in the Paced group was significantly higher than that in Sham group (P < 0.01), and was significantly reduced by cilostazol treatment (P < 0.01). The level of mean platelet volume (MPV) which is one of the platelet indices was significantly elevated in Paced group (P < 0.01). While after cilostazol treated for 2 weeks, the level of MPV was obviously decreased than Paced group (P < 0.01). Pathology and echocardiography studies showed that cilostazol can also prevent RAP induced cardiac fibrosis and structural remodeling. The MPV level has close correlations with IL-8, TLR4, XO and ROS (all P < 0.01). MMP-2 and MMP-9 expression were significantly increased in Paced group (all P < 0.01), which can be attenuated by cilostazol.

CONCLUSIONS

Cilostazol may have protective effects on RAP-induced atrial remodeling by anti-inflammatory, anti-oxidative stress action and regulate the extracellular collagen matrix in a canine model. Moreover, MPV level is associated with inflammation and oxidative stress response of RAP, which might be an important predictors of new-onset and recurrent AF.

Doxycycline Improves Fibrosis-Induced Abnormalities in Atrial Conduction and Vulnerability to Atrial Fibrillation in Chronic Intermittent Hypoxia Rats

Background

The structural remodeling of atrial architecture, especially increased amounts of fibrosis, is a critical substrate to atrial fibrillation (AF). Doxycycline (Doxy) has recently been shown to exert protective effects against fibrogenic response. This study investigated whether doxycycline (Doxy) can sufficiently ameliorate the fibrosis-induced changes of atrial conduction and AF vulnerability in a chronic intermittent hypoxia (CIH) rat model.

Material/Methods

Sixty rats were randomized into 3 groups: Control, CIH, and CIH with Doxy treatment (DOXY) group. CIH rats were exposed to CIH (6 h/d) and Doxy-treated rats were treated with Doxy during processing CIH. After 6 weeks, echocardiographic and hemodynamic parameters were measured. Isolated atrial epicardial activation mapping and heart electrophysiology were performed. The extent of atrial interstitial fibrosis were estimated by Masson’s trichrome staining. The expression levels of TGF-β1 and downstream factors were determined by real-Time PCR, immunohistochemistry, and Western blot analysis.

Results

Compared to Control rats, the CIH rats showed significant atrial interstitial fibrosis, longer inter-atrial conduction time, and elevated conduction inhomogeneity and AF inducibility, and the expression of TGF-β1, TGF-βRI, TGF-βRII, P-Smad2/3, α-SMA, CTGF, and Collagen I were significantly increased, whereas the velocity of atrial conduction and the expression of miR-30c were dramatically decreased. All of these changes were significantly improved by Doxy treatment.

Conclusions

The findings suggested that Doxy can profoundly mitigate atrial fibrosis, conduction inhomogeneity as well as high AF inducibility secondary to fibrosis in a CIH rat model through suppressing the TGF-β1 signaling pathway.

Epigenetics: A Potential Mechanism Involved in the Pathogenesis of Various Adverse Consequences of Obstructive Sleep Apnea

Epigenetics is defined as the heritable phenotypic changes which do not involve alterations in the DNA sequence, including histone modifications, non-coding RNAs, and DNA methylation. Recently, much attention has been paid to the role of hypoxia-mediated epigenetic regulation in cancer, pulmonary hypertension, adaptation to high altitude, and cardiorenal disease. In contrast to sustained hypoxia, chronic intermittent hypoxia with re-oxygenation (IHR) plays a major role in the pathogenesis of various adverse consequences of obstructive sleep apnea (OSA), resembling ischemia re-perfusion injury. Nevertheless, the role of epigenetics in the pathogenesis of OSA is currently underexplored. This review proposes that epigenetic processes are involved in the development of various adverse consequences of OSA by influencing adaptive potential and phenotypic variability under conditions of chronic IHR. Improved understanding of the interaction between genetic and environmental factors through epigenetic regulations holds great value to give deeper insight into the mechanisms underlying IHR-related low-grade inflammation, oxidative stress, and sympathetic hyperactivity, and clarify their implications for biomedical research.

In Vivo and In Vitro Effects of Vasopressin V2 Receptor Antagonism on Myocardial Fibrosis in Rats

BACKGROUND

Myocardial fibrosis is a major pathophysiologic substrate of heart failure with preserved ejection fraction. Vasopressin is an important therapeutic target in heart failure with preserved ejection fraction since it can modulate fluid balance, and based on a few studies, myocardial matrix deposition. Hence we examined the role of vasopressin antagonism in modulating myocardial matrix metabolism in vivo and in vitro.

MATERIALS AND METHODS

In vivo studies utilized an established model of hyperhomocysteinemia-induced myocardial fibrosis in Sprague-Dawley rats combined with high salt diet; in vivo studies also utilized the same profibrotic stimuli of homocysteine and NaCl in cultured rat cardiac fibroblasts.

RESULTS

Hyperhomocysteinemia combined with high-salt diet promoted myocardial fibrosis, profibrotic and matrix gene expression and tolvaptan attenuated all these in vivo effects. In cultured cardiac fibroblasts, combined treatment with homocysteine and NaCl increased profibrotic and matrix gene expression and activation of PI3/Akt pathway; all these effects were attenuated by tolvaptan Vasopressin levels, gene expression and V2 receptor expression were increased in vivo and in vitro on exposure to profibrotic stimuli, and tolvaptan attenuated these in vivo and in vitro effects.

CONCLUSIONS

Antagonism of vasopressin V2 receptor, via direct actions on cardiac fibroblast, attenuates myocardial matrix deposition.