Isolated heart models: cardiovascular system studies and technological advances

Electrical remodeling of atrioventricular junction: a study on retrogradely perfused chick embryonic heart

Atrioventricular (AV) accessory pathways (APs) provide additional electrical connections between the atria and ventricles, resulting in severe electrical disturbances. It is generally accepted that APs originate in the altered annulus fibrosus maturation in the late prenatal and perinatal period. However, current experimental methods cannot address their development in specific locations around the annulus fibrosus because of the inaccessibility of late fetal hearts for electrophysiological investigation under physiological conditions. In this study, we describe an approach for optical mapping of the retrogradely perfused chick heart in the last third of the incubation period. This system showed stability for electrophysiological measurement for several hours. This feature allowed analysis of the number and functionality of the APs separately in each clinically relevant position. Under physiological conditions, we also recorded the shortening of the AV delay with annulus fibrosus maturation and analyzed ventricular activation patterns after conduction through APs at specific locations. We observed a gradual regression of AP with an area-specific rate (left-sided APs disappeared first). The results also revealed a sudden drop in the number of active APs between embryonic days 16 and 18. Accessory myocardial AV connections were histologically documented in all positions around the annulus fibrosus even after hatching. The fact that no electrically active AP was present at this stage highlights the necessity of electrophysiological evaluation of accessory atrioventricular connections in studying AP formation.NEW & NOTEWORTHY We present the use of retrograde perfusion and optical mapping to investigate, for the first time, the regression of accessory pathways during annulus fibrosus maturation, separately examining each clinically relevant location. The system enables measurements under physiological conditions and demonstrates long-lasting stability compared with other approaches. This study offers applications of the model to investigate electrical and/or functional development in late embryonic development without concern about heart viability.

Amplification of Cardioprotective Response of Remote Ischemic Preconditioning in Rats by Quercetin: Potential Role of Activation of mTOR-dependent Autophagy and Nrf2

OBJECTIVES

Noninvasive remote ischemic preconditioning (RIPC) is a practical, acceptable, and feasible conditioning technique reported to provide cardioprotection in myocardial ischemia-reperfusion injury (MIRI). It has been well-reported that quercetin possesses antioxidant and anti-inflammatory properties. This study investigates the modification of the cardioprotective response of RIPC by quercetin.

METHODS

Adult Wistar rats were randomized into 12 groups of six animals each. MIRI was induced by subjecting the isolated hearts of Wistar rats to global ischemia for 30 min, succeeded by reperfusion of 120 min after mounting on the Langendorff PowerLab apparatus. Hind limb RIPC was applied in four alternate cycles of ischemia and reperfusion of 5 min each by tying the pressure cuff before isolation of hearts.

RESULTS

MIRI was reflected by significantly increased infarct size, LDH-1, and CK-MB, TNF-α, TBARS, and decreased GSH, catalase, and hemodynamic index, and modulated Nrf2. Pretreatment of quercetin (25 and 50 mg/kg; i.p.) significantly attenuated the MIRI-induced cardiac damage and potentiated the cardioprotective response of RIPC at the low dose. Pretreatment of ketamine (10 mg/kg; i.p.), an mTOR-dependent autophagy inhibitor, significantly abolished the cardioprotective effects of quercetin and RIPC.

CONCLUSIONS

The findings highlight the modification of the cardioprotective effect of RIPC by quercetin and that quercetin protects the heart against MIRI through multiple mechanisms, including mTOR-dependent activation of autophagy and Nrf-2 activation.

Liraglutide Pretreatment Does Not Improve Acute Doxorubicin-Induced Cardiotoxicity in Rats

Doxorubicin is an effective drug for cancer treatment; however, cardiotoxicity limits its use. Cardiotoxicity pathophysiology is multifactorial. GLP-1 analogues have been shown to reduce oxidative stress and inflammation. In this study, we evaluated the effect of pretreatment with liraglutide on doxorubicin-induced acute cardiotoxicity. A total of 60 male Wistar rats were allocated into four groups: Control (C), Doxorubicin (D), Liraglutide (L), and Doxorubicin + Liraglutide (DL). L and DL received subcutaneous injection of liraglutide 0.6 mg/kg daily, while C and D received saline for 2 weeks. Afterwards, D and DL received a single intraperitoneal injection of doxorubicin 20 mg/kg; C and L received an injection of saline. Forty-eight hours after doxorubicin administration, the rats were subjected to echocardiogram, isolated heart functional study, and euthanasia. Liraglutide-treated rats ingested significantly less food and gained less body weight than animals that did not receive the drug. Rats lost weight after doxorubicin injection. At echocardiogram and isolated heart study, doxorubicin-treated rats had systolic and diastolic function impairment. Myocardial catalase activity was statistically higher in doxorubicin-treated rats. Myocardial protein expression of tumor necrosis factor alpha (TNF-α), phosphorylated nuclear factor-κB (p-NFκB), troponin T, and B-cell lymphoma 2 (Bcl-2) was significantly lower, and the total NFκB/p-NFκB ratio and TLR-4 higher in doxorubicin-treated rats. Myocardial expression of OPA-1, MFN-2, DRP-1, and topoisomerase 2β did not differ between groups (p > 0.05). In conclusion, doxorubicin-induced cardiotoxicity is accompanied by decreased Bcl-2 and phosphorylated NFκB and increased catalase activity and TLR-4 expression. Liraglutide failed to improve acute doxorubicin-induced cardiotoxicity in rats.

Penigrines A-E: Five undescribed azepine-indole alkaloids from Penicillium griseofulvum

Penigrines A-E (1-5), five undescribed azepine-indole alkaloids, were isolated from the fungus Penicillium griseofulvum. Their structures with absolute configurations were determined by NMR, HRESIMS, ECD calculation, and X-ray diffraction experiments. Penigrine C (3) possesses an undescribed 6-oxa-8-azabicyclo[3.2.2]nonane-7,9-dione moiety that fused to an indole core, and penigrines D and E (4 and 5) are a pair of epimers. The plausible biosynthetic pathways of 1-5 are proposed. Penigrine A (1) shows the potential for heart failure treatment.

Middle-age abolishes cardioprotection conferred by thioredoxin-1 in mice

Thioredoxin-1 (Trx1) has cardioprotective effects on ischemia/reperfusion (I/R) injury, although its role in ischemic postconditioning (PostC) in middle-aged mice is not understood. This study aimed to evaluate if combining two cardioprotective strategies, such as Trx1 overexpression and PostC, could exert a synergistic effect in reducing infarct size in middle-aged mice. Young or middle-aged wild-type mice (Wt), transgenic mice overexpressing Trx1, and dominant negative (DN-Trx1) mutant of Trx1 mice were used. Mice hearts were subjected to I/R or PostC protocol. Infarct size, hydrogen peroxide (H2O2) production, protein nitration, Trx1 activity, mitochondrial function, and Trx1, pAkt and pGSK3β expression were measured. PostC could not reduce infarct size even in the presence of Trx1 overexpression in middle-aged mice. This finding was accompanied by a lack of Akt and GSK3β phosphorylation, and Trx1 expression (in Wt group). Trx1 activity was diminished and H2O2 production and protein nitration were increased in middle-age. The respiratory control rate dropped after I/R in Wt-Young and PostC restored this value, but not in middle-aged groups. Our results showed that Trx1 plays a key role in the PostC protection mechanism in young but not middle-aged mice, even in the presence of Trx1 overexpression.

Long-term Xenopus laevis tadpole -heart-organ-culture: Physiological changes in cholinergic and adrenergic sensitivities of tadpole heart with thyroxine-treatment

The present study clarified changes in physiological sensitivities of cultured Nieuwkoop and Faber stage 57 Xenopus laevis tadpole-organ-heart exposed to thyroxine (T4) using acetylcholine (ACh), norepinephrine (NE) and atropine. For preliminary life span and the chemical tests, 60% minimum essential medium (MEM), two types of modified Hank's balanced salt-solution-culture-media (MHBSS-CM) I and II containing relatively lower concentrations of amino acids and collagen were prepared. In preliminary lifespan-test of cultured tadpole hearts, the hearts maintained in 60% MEM was 50 days on average, whereas that of the tadpole-hearts in MHBSS-CMs was extended by 109 days on average, showing superior effectiveness of MHBSS-CMs. 4 min-stimulation by 5 × 10-9 M T4 tended to increase the tadpole heartbeat. 10-9 M ACh decreased the tadpole heartbeat. Frog-heart at 2-4 weeks after metamorphosis completion and tadpole heart treated with 5 × 10-10 M T4 for 45 h also responded to 10-9 M ACh, and low-resting hearts were restored to the control level with the competitive muscarinic antagonist 10-8 M atropine, whereas excessive exposure of 10-5 M atropine to T4-treated tadpole heart did not increase heartbeat in spite of the increased frog heartbeat over the control. 10-14 -10-12 M NE increase the tadpole heartbeat in a concentration-dependent manner, however, 10-12 M NE did not act to stimulate adrenergic receptors on both T4-treated tadpole- and the frog-hearts. These results suggest that T4 induces the desensitization of atropine-sensitive muscarinic and adrenergic receptors in organ-cultured tadpole-heart.

Cardioprotective action of aprepitant in a rat model of ischemia-reperfusioninduced myocardial injury: role of PI3K-AkT-GSK-3β-HIF-1α signaling pathway

PURPOSE

The present study explored the role and mechanism involved in aprepitant-induced cardioprotective effects in rat model of ischemia-reperfusion injury.

METHODS

The isolated hearts of Wistar male albino rats were subjected to ischemia-reperfusion injury on Langendorff apparatus. The extent of myocardial injury was assessed by measuring lactate dehydrogenase 1 and CK-MB release in the coronary effluent. The rats were treated with aprepitant (5, 10 and 20 mg/kg) before isolating hearts. After injury, the levels of HIF-1α, p-AkT, p-GSK-3β/GSK-3β were measured in heart homogenates. LY294002 was employed as PI3K inhibitor.

RESULTS

Ischemia-reperfusion led to significant myocardial injury and decreased the levels of HIF-1α, p-AkT and ratio of p-GSK-3β/GSK-3β. Aprepitant attenuated myocardial injury and restored the biochemical changes in a dose-dependent manner. Pre-treatment with LY294002 (10 and 20 mg/kg) abolished aprepitant-mediated cardioprotective effects and restored the biochemical parameters in the heart homogenate.

CONCLUSIONS

Aprepitant may be effective in preventing ischemia-reperfusion-induced myocardial injury, which may be due to activation of PI3K-AkT-GSK-3β and HIF-1α signaling pathway.

Assessment of Cardiac Toxicity of Manganese Chloride for Cardiovascular Magnetic Resonance

MRI is widely used in cardiology to characterize the structure and function of the heart. Currently, gadolinium-based contrast agents are widely used to improve sensitivity and specificity of diagnostic images. Recently, Manganese, a calcium analogue, has emerged as a complementary contrast agent with the potential to reveal remaining viable cells within altered tissue. Imaging applications may be limited by substantial toxicity of manganese. Indeed, cardiac safety of manganese is not yet comprehensively assessed. In this study we investigated the effect of MnCl2 (1–100 µM) on cardiac function. Hemodynamic function was determined ex vivo using an isolated working rat heart preparation. HL-1 cardiac myocytes were used to investigate cell viability (calcein AM) and calcium cycling (Cal-520 a.m.). Rat ventricular cardiomyocytes were dissociated by enzymatic digestion. Action potentials and calcium currents were recorded using the patch clamp technique. MRI experiments were performed at 1.5T on formalin-fixed rat hearts, previously perfused with MnCl2. MnCl2 perfusion from 1 up to 100 µM in isolated working hearts did not alter left ventricular hemodynamic parameters. Contractility and relaxation index were not altered up to 50 µM MnCl2. In HL-1 cardiac myocytes, incubation with increasing concentrations of MnCl2 did not impact cell viability. The amplitude of the calcium transients were significantly reduced at 50 and 100 µM MnCl2. In freshly isolated ventricular myocytes, action potential duration at 20, 50 and 90% of repolarization were not modified up to 10 µM of MnCl2. L-type calcium current amplitude was significantly decreased by 50 and 100 µM of MnCl2. MRI on heart perfused with 25 and 100 µM of MnCl2 showed a dose dependent decrease in the T1 relaxation time. In conclusion, our results show that low concentrations of MnCl2 (up to 25 µM) can be used as a contrast agent in MRI, without significant impact on cardiac hemodynamic or electrophysiology parameters.

Golden Standard or Obsolete Method? Review of ECG Applications in Clinical and Experimental Context

Cardiovascular system and its functions under both physiological and pathophysiological conditions have been studied for centuries. One of the most important steps in the cardiovascular research was the possibility to record cardiac electrical activity. Since then, numerous modifications and improvements have been introduced; however, an electrocardiogram still represents a golden standard in this field. This paper overviews possibilities of ECG recordings in research and clinical practice, deals with advantages and disadvantages of various approaches, and summarizes possibilities of advanced data analysis. Special emphasis is given to state-of-the-art deep learning techniques intensely expanded in a wide range of clinical applications and offering promising prospects in experimental branches. Since, according to the World Health Organization, cardiovascular diseases are the main cause of death worldwide, studying electrical activity of the heart is still of high importance for both experimental and clinical cardiology.

Basic Research Approaches to Evaluate Cardiac Arrhythmia in Heart Failure and Beyond

Patients with heart failure often develop cardiac arrhythmias. The mechanisms and interrelations linking heart failure and arrhythmias are not fully understood. Historically, research into arrhythmias has been performed on affected individuals or in vivo (animal) models. The latter however is constrained by interspecies variation, demands to reduce animal experiments and cost. Recent developments in in vitro induced pluripotent stem cell technology and in silico modelling have expanded the number of models available for the evaluation of heart failure and arrhythmia. An agnostic approach, combining the modalities discussed here, has the potential to improve our understanding for appraising the pathology and interactions between heart failure and arrhythmia and can provide robust and validated outcomes in a variety of research settings. This review discusses the state of the art models, methodologies and techniques used in the evaluation of heart failure and arrhythmia and will highlight the benefits of using them in combination. Special consideration is paid to assessing the pivotal role calcium handling has in the development of heart failure and arrhythmia.

Model Systems for Addressing Mechanism of Arrhythmogenesis in Cardiac Repair

PURPOSE OF REVIEW

Cardiac cell-based therapy represents a promising approach for cardiac repair. However, one of the main challenges is cardiac arrhythmias associated with stem cell transplantation. The current review summarizes the recent progress in model systems for addressing mechanisms of arrhythmogenesis in cardiac repair.

RECENT FINDINGS

Animal models have been extensively developed for mechanistic studies of cardiac arrhythmogenesis. Advances in human induced pluripotent stem cells (hiPSCs), patient-specific disease models, tissue engineering, and gene editing have greatly enhanced our ability to probe the mechanistic bases of cardiac arrhythmias. Additionally, recent development in multiscale computational studies and machine learning provides yet another powerful tool to quantitatively decipher the mechanisms of cardiac arrhythmias. Advancing efforts towards the integrations of experimental and computational studies are critical to gain insights into novel mitigation strategies for cardiac arrhythmias in cell-based therapy.

Endogenous Cardiotonics: Search And Problems

Medicinal preparations currently used for the treatment of patients with chronic cardiac failure involve those that reduce the heart load (vasodilators, diuretics, beta-blockers, and angiotensin-converting enzyme (ACE) inhibitors). Cardiotonic drugs with the cAMP-dependent mechanism are unsuitable for long-term administration due to the intensification of metabolic processes and an increase in the oxygen demand of the myocardium and all tissues of the body. For many years, digoxin has remained the only preparation enhancing the efficiency of myocardial performance. The detection of digoxin and ouabain in intact animals has initiated a search for other compounds with cardiotonic activity. The review summarizes current data on the effect exerted on the heart performance by endogenous compounds, from simple, such as NO and CO, to steroids, fatty acids, polypeptides, and proteins. Controversial questions and problems with the introduction of scientific achievements into clinical practice are discussed. The results obtained by the authors and their colleagues after many years of studies on the cardiotropic properties of serum lipoproteins are also reported. The experimentally established cardiotonic activity of apoprotein A-1, which is accompanied by a decrease in the relative consumption of oxygen, maybe of great interest.

Ex situ heart perfusion: The past, the present, and the future

Despite the advancements in medical treatment, mechanical support, and stem cell therapy, heart transplantation remains the most effective treatment for selected patients with advanced heart failure. However, with an increase in heart failure prevalence worldwide, the gap between donor hearts and patients on the transplant waiting list keeps widening. Ex situ machine perfusion has played a key role in augmenting heart transplant activities in recent years by enabling the usage of donation after circulatory death hearts, allowing longer interval between procurement and implantation, and permitting the safe use of some extended-criteria donation after brainstem death hearts. This exciting field is at a hinge point, with 1 commercially available heart perfusion machine, which has been used in hundreds of heart transplantations, and a number of devices being tested in the pre-clinical and Phase 1 clinical trial stage. However, no consensus has been reached over the optimal preservation temperature, perfusate composition, and perfusion parameters. In addition, there is a lack of objective measurement for allograft quality and viability. This review aims to comprehensively summarize the lessons about ex situ heart perfusion as a platform to preserve, assess, and repair donor hearts, which we have learned from the pre-clinical studies and clinical applications, and explore its exciting potential of revolutionizing heart transplantation.

An isolated retrograde-perfused newborn mouse heart preparation

The Langendorff-perfused model is a powerful tool to study biological responses in the isolated heart in the absence of confounders. The model has been adapted recently to enable study of the isolated mouse heart and the effects of genetic manipulation. Unfortunately, the small size and fragility of the mouse heart pose significant challenges, limiting application of the Langendorff model to the study of adult mice. Cardiac development is a complex and dynamic process that is incompletely understood. Thus, establishing an isolated-perfused heart model in the newborn mouse would be an important and necessary advance. Here we present a method to successfully cannulate and perfuse the isolated newborn murine heart. We describe the basic and fundamental physiological characteristics of the ex-vivo retrograde-perfused beating neonatal heart in wild-type C57Bl/6 male mice. Our approach will enable future study of the physiological and pharmacological responses of the isolated immature murine heart to enhance knowledge of how developmental cardiac biology impacts health and disease.•

The Langendorff model is a powerful tool to study the heart without confounders.

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An isolated-perfused newborn murine heart model has yet to be established.

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We demonstrate the first successful isolated neonatal murine heart preparation.

Experimental models of cardiac physiology and pathology

Experimental models of cardiac disease play a key role in understanding the pathophysiology of the disease and developing new therapies. The features of the experimental models should reflect the clinical phenotype, which can have a wide spectrum of underlying mechanisms. We review characteristics of commonly used experimental models of cardiac physiology and pathophysiology in all translational steps including in vitro, small animal, and large animal models. Understanding their characteristics and relevance to clinical disease is the key for successful translation to effective therapies.

Strategies for targeting the cardiac sarcomere: avenues for novel drug discovery

Introduction: Heart failure remains one of the largest clinical challenges in the United States. Researchers have continually searched for more effective heart failure treatments that target the cardiac sarcomere but have found few successes despite numerous expensive cardiovascular clinical trials. Among many reasons, the high failure rate of cardiovascular clinical trials may be partly due to incomplete characterization of a drug candidate's complex interaction with cardiac physiology.Areas covered: In this review, the authors address the issue of preclinical cardiovascular studies of sarcomere-targeting heart failure therapies. The authors consider inherent tradeoffs made between mechanistic transparency and physiological fidelity for several relevant preclinical techniques at the atomic, molecular, heart muscle fiber, whole heart, and whole-organism levels. Thus, the authors suggest a comprehensive, bottom-up approach to preclinical cardiovascular studies that fosters scientific rigor and hypothesis-driven drug discovery.Expert opinion: In the authors' opinion, the implementation of hypothesis-driven drug discovery practices, such as the bottom-up approach to preclinical cardiovascular studies, will be imperative for the successful development of novel heart failure treatments. However, additional changes to clinical definitions of heart failure and current drug discovery culture must accompany the bottom-up approach to maximize the effectiveness of hypothesis-driven drug discovery.

Mechanism of the hypoxia inducible factor 1/hypoxic response element pathway in rat myocardial ischemia/diazoxide post‑conditioning

Ischemic post-conditioning (IPO) and diazoxide post-conditioning (DPO) has been proven to reduce myocardial ischemia reperfusion injury (MIRI); however, the mechanisms of IPO/DPO are still not clear. The present study aimed to investigate whether mitochondrial ATP-sensitive potassium channels (mitoK_ATP) channels are activated by IPO/DPO, which may further activate the hypoxia inducible factor 1/hypoxic response element (HIF-1/HRE) pathway to mitigate MIRI. Using a Langendorff perfusion device, healthy male (250–300 g) Sprague Dawley rat hearts were randomly divided into the following groups. Group N was aerobically perfused with K-H solution for 120 min. Group ischaemia/reperfusion (I/R) was aerobically perfused for 20 min, then subjected to 40 min hypoxia plus 60 min reperfusion. Group IPO was treated like the I/R group, but with 10 sec of hypoxia plus 10 sec of reperfusion for six rounds before reperfusion. Group DPO was exposed to 50 µM diazoxide for 5 min before reperfusion and otherwise treated the same as group I/R. In groups IPO+5-hydroxydecanoic acid (5HD), DPO+5HD and I/R+5HD, exposure to 100 µM 5HD (a mitoK_ATP channel specific blocker) for 5 min before reperfusion as described for groups IPO, DPO and I/R, respectively. In groups IPO+2-methoxyestradiol (2ME2), DPO+2ME2 and I/R+2ME2, exposure to 2 µM 2ME2 (a HIF-1α specific blocker) for 10 min before reperfusion as described for groups IPO, DPO and I/R respectively. Cardiac hemodynamics, myocardial injury and the expression of HIF-1/HRE pathway [HIF-1α, heme oxygenase (HO-1), inducible nitric oxide synthase (iNOS) and vascular endothelial growth factor (VEGF)] were detected in each group. The infarct size and mitochondrial Flameng scores of groups IPO/DPO were significantly decreased compared with the I/R group (P<0.05), but the myocardial protective effects of IPO/DPO could be eliminated by 5HD or 2ME2 (P<0.05). In addition, IPO/DPO could increase the mRNA expression of HIF-1α and the downstream factors of the HIF-1/HRE pathway (the mRNA and protein expression of HO-1, iNOS and VEGF; P<0.05). However, the myocardial protective effects and the activation the HIF-1/HRE pathway mediated by IPO/DPO could be eliminated by 5HD or 2ME2 (P<0.05). Therefore, the activation of the HIF-1/HRE pathway by opening mitoK_ATP channels may work with the mechanism of IPO/DPO in reducing MIRI.

A Model of Blood Component-Heart Interaction in Cardiac Ischemia-Reperfusion Injury using a Langendorff-Based Ex Vivo Assay

INTRODUCTION

Myocardial infarction is one of the leading causes of morbidity and mortality worldwide. Cellular interactions of red blood cells (RBCs) and platelets with endothelial cells and cardiomyocytes play a crucial role in cardiac ischemia/reperfusion (I/R) injury. However, addressing the specific impact of such cell-to-cell interactions in commonly employed in vivo models of cardiac I/R injury is challenging due to overlap of neuronal, hormonal, and immunological pathways. This study aimed to refine a Langendorff-based ex vivo transfer model to evaluate the impact of specific blood components on cardiac I/R injury.

MATERIAL AND METHODS

Murine whole blood, defined murine blood components (RBCs, platelet-rich plasma [PRP], and platelet-poor plasma [PPP], respectively) as well as human RBCs were loaded to the coronary system of isolated murine hearts in a Langendorff system before initiating global ischemia for 40 minutes. Following 60 minutes of reperfusion with Krebs Henseleit Buffer, left ventricular function and coronary flow were assessed. Infarct size was determined by specific histological staining following 120 minutes of reperfusion.

RESULTS

Loading of murine whole blood to the coronary system of isolated murine hearts at the beginning of 40 minutes of global ischemia improved left ventricular function after 60 minutes of reperfusion and reduced the infarct size in comparison to buffer-treated controls. Similarly, isolated murine RBCs, PRP, and PPP mediated a protective effect in the cardiac I/R model. Furthermore, human RBCs showed a comparable protective capacity as murine RBCs.

CONCLUSION

This Langendorff-based transfer model of cardiac I/R injury is a feasible, time-, and cost-effective model to evaluate the impact of blood components on myocardial infarction. The presented method facilitates loading of blood components of genetically modified mice to murine hearts of a different mouse strain, thus complementing time- and cost-intensive chimeric models and contributing to the development of novel targeted therapies.

Exercise and Cardioprotection: A Natural Defense Against Lethal Myocardial Ischemia-Reperfusion Injury and Potential Guide to Cardiovascular Prophylaxis

Similar to ischemic preconditioning, high-intensity exercise has been shown to decrease infarct size following myocardial infarction. In this article, we review the literature on beneficial effects of exercise, exercise requirements for cardioprotection, common methods utilized in laboratories to study this phenomenon, and discuss possible mechanisms for exercise-mediated cardioprotection.

Humanizing Miniature Hearts through 4-Flow Cannulation Perfusion Decellularization and Recellularization

Despite improvements in pre-clinical drug testing models, predictability of clinical outcomes continues to be inadequate and costly due to poor evidence of drug metabolism. Humanized miniature organs integrating decellularized rodent organs with tissue specific cells are translational models that can provide further physiological understanding and evidence. Here, we evaluated 4-Flow cannulated rat hearts as the fundamental humanized organ model for cardiovascular drug validation. Results show clearance of cellular components in all chambers in 4-Flow hearts with efficient perfusion into both coronary arteries and cardiac veins. Furthermore, material characterization depicts preserved organization and content of important matrix proteins such as collagens, laminin, and elastin. With access to the complete vascular network, different human cell types were delivered to show spatial distribution and integration into the matrix under perfusion for up to three weeks. The feature of 4-Flow cannulation is the preservation of whole heart conformity enabling ventricular pacing via the pulmonary vein as demonstrated by noninvasive monitoring with fluid pressure and ultrasound imaging. Consequently, 4-Flow hearts surmounting organ mimicry challenges with intact complexity in vasculature and mechanical compliance of the whole organ providing an ideal platform for improving pre-clinical drug validation in addition to understanding cardiovascular diseases.

Effect of increased left ventricle mass on ischemia assessment in electrocardiographic signals: rabbit isolated heart study

BACKGROUND

Detailed quantitative analysis of the effect of left ventricle (LV) hypertrophy on myocardial ischemia manifestation in ECG is still missing. The associations between both phenomena can be studied in animal models. In this study, rabbit isolated hearts with spontaneously increased LV mass were used to evaluate the effect of such LV alteration on ischemia detection criteria and performance.

METHODS

Electrophysiological effects of increased LV mass were evaluated on sixteen New Zealand rabbit isolated hearts under non-ischemic and ischemic conditions by analysis of various electrogram (EG) parameters. To reveal hearts with increased LV mass, LV weight/heart weight ratio was proposed. Standard paired and unpaired statistical tests and receiver operating characteristics analysis were used to compare data derived from different groups of animals, monitor EG parameters during global ischemia and evaluate their ability to discriminate between unchanged and increased LV as well as non-ischemic and ischemic state.

RESULTS

Successful evaluation of both increased LV mass and ischemia is lead-dependent. Particularly, maximal deviation of QRS and area under QRS associated with anterolateral heart wall respond significantly to even early phase (the 1st-3rd min) of ischemia. Besides ischemia, these parameters reflect increased LV mass as well (with sensitivity reaching approx. 80%). However, the sensitivity of the parameters to both phenomena may lead to misinterpretations, when inappropriate criteria for ischemia detection are selected. Particularly, use of cut-off-based criteria defined from control group for ischemia detection in hearts with increased LV mass may result in dramatic reduction (approx. 15%) of detection specificity due to increased number of false positives. Nevertheless, criteria adjusted to particular experimental group allow achieving ischemia detection sensitivity of 89-100% and specificity of 94-100%, respectively.

CONCLUSIONS

It was shown that response of the heart to myocardial ischemia can be successfully evaluated only when taking into account heart-related factors (such as LV mass) and other methodological aspects (such as recording electrodes position, selected EG parameters, cut-off criteria, etc.). Results of this study might be helpful for developing new clinical diagnostic strategies in order to improve myocardial ischemia detection in patients with LV hypertrophy.

Effects of vesical and perfusion pressure on perfusate flow, and flow on vesical pressure, in the isolated perfused working pig bladder reveal a potential mechanism for the regulation of detrusor compliance

AIMS

Although there is evidence that deficits in bladder blood flow negatively impact bladder function, the effects of vesical, and perfusion pressures on bladder perfusion (perfusate flow), and of perfusate flow on vesical pressure, remain poorly understood. The present study used the isolated perfused working pig bladder model to examine the relationships between blood flow, and vesical and perfusion pressures.

METHODS

Vesical arteries of pig bladders obtained from a local slaughterhouse were cannulated and perfused with Krebs-Henseleit solution at different pressures, and with carbachol to cause bladder contraction. The urethra of each bladder was cannulated to permit filling (10 mL/min), isovolumetric contraction and emptying. A ureter was cannulated with a pressure sensor to monitor vesical pressure.

RESULTS

When at rest (50 mL vesical volume), bladder vesical pressure was 8.06 ± 1.5 mmHg and perfusate flow driven by a pressure gradient of 105 mmHg was 22.5 ± 2 mL/min (58.9 ± 7.8 mL/min-100 g). During filling, vesical pressure increased and flow decreased, but not necessarily in-parallel. Perfusate flow decreased transiently during isovolumetric contraction, and flow increased during emptying. A reduction in perfusion pressure from ∼105 to ∼40 mmHg reduced flow from ∼70 to ∼20 mL/min-100g, and reduced flow correlated with reduced vesical pressure.

CONCLUSION

Perfusate flow is dependent on bladder perfusion pressure, and not necessarily reciprocally dependent on vesical pressure. Vesical pressure is highly sensitive to the level of perfusate flow, which supports the hypothesis that vesical pressure is dependent on the level of detrusor smooth muscle contractile activity (tone), and that compliance is dependent on bladder perfusion.

DS16570511 is a small-molecule inhibitor of the mitochondrial calcium uniporter

In cardiac myocytes, regulation of mitochondrial Ca²⁺ is important for cellular signaling and cardiac contraction. Ca²⁺ entry into the mitochondria is mediated by a highly selective Ca²⁺ channel called the mitochondrial calcium uniporter, which consists of a pore-forming subunit MCU and regulatory subunits such as MICU1. Although pharmacological regulation of the mitochondrial Ca²⁺ influx is a promising approach to controlling the cellular functions, a cell-permeable and specific inhibitor of the mitochondrial calcium uniporter has not yet been developed. Here, we identify a novel cell-permeable inhibitor of the uniporter by a high-throughput screening of 120 000 small-molecule compounds. In our study, DS16570511 dose-dependently inhibited serum-induced mitochondrial Ca²⁺ influx in HEK293A cells with an IC₅₀ of 7 μM. DS16570511 inhibited Ca²⁺ uptake of isolated mitochondria from human cells, rat heart and pig heart. Overexpression of hMCU or hMICU1 in HEK293A cells increased mitochondrial Ca²⁺ influx, and the increases were completely suppressed by the pretreatment with DS16570511. DS16570511 also blocks mitochondrial Ca²⁺ overload in a Langendorff perfused beating rat heart. Interestingly, DS16570511 increased cardiac contractility without affecting heart rate in the perfused heart. These results show that DS16570511 is a novel cell-permeable inhibitor of the mitochondrial calcium uniporter and applicable for control of the cardiac functions.

Tolerance of isolated rabbit hearts to short ischemic periods is affected by increased LV mass fraction

Hypertrophied hearts are known for increased risk of arrhythmias and are linked with reduced ischemic tolerance. However, still little is known about state characterized only by increased left ventricle (LV) mass fraction. Seventeen isolated rabbit hearts with various LV mass were divided into two groups according to LV weight/heart weight ratio (LVW/HW ratio), namely group H and L (with higher and lower LVW/HW ratio, respectively) and underwent three short cycles of global ischemia and reperfusion. The differences in electrogram (heart rate, QRS(max), mean number, onset and dominant form of ventricular premature beats) and in biochemical markers of myocardial injury (creatine kinase, lactate dehydrogenase - LDH) and lipid peroxidation (4-hydroxy-2-nonenal - 4-HNE) were studied. As compared to group L, hearts in group H exhibited lower tolerance to ischemia expressed as higher incidence and severity of arrhythmias in the first ischemic period as well as increase of LDH and 4-HNE after the first reperfusion. In the third cycle of ischemia-reperfusion, the preconditioning effect was observed in both electrophysiological parameters and LDH release in group H. Our results showed consistent trends when comparing changes in electrograms and biochemical markers. Moreover, 4-HNE seems to be good potential parameter of moderate membrane alteration following ischemia-reperfusion injury.