Differential cardiotoxic electrocardiographic response to doxorubicin treatment in conscious versus anesthetized mice

Hydroethanolic extract of Cirsium setidens ameliorates doxorubicin-induced cardiotoxicity by AMPK-PGC-1α-SOD-mediated mitochondrial protection

BACKGROUND

Doxorubicin (DOX) is an effective anticancer agent. However, the clinical outcomes of DOX-based therapies are severely hampered by their significant cardiotoxicity.

PURPOSE

We investigated the beneficial effects of an ethanol extract of Cirsium setidens (CSE) on DOX-induced cardiomyotoxicity (DICT).

METHODS

UPLC-TQ/MS analysis was used to identify CSE metabolite profiles. H9c2 rat cardiomyocytes and MDA-MB-231 human breast cancer cells were used to evaluate the effects of CSE on DICT-induced cell death. To elucidate the mechanism underlying it, AMP-activated protein kinase (AMPK), peroxisome proliferator-activated receptor gamma co-activator l-alpha (PGC1-α), nuclear respiratory factor 1 (NRF1), NRF2, superoxide dismutase (SOD1), and SOD2 expression was detected using western blot analysis. The oxygen consumption rate (OCR), cellular ROS, and mitochondrial membrane potential were measured. Finally, we confirmed the cardioprotective effect of CSE against DICT in both C57BL/6 mice and human induced pluripotent stem cell-derived cardiomyocytes (hiPSCCMs) by observing various parameters, such as electrophysiological changes, cardiac fibrosis, and cardiac cell death.

RESULTS

Chlorogenic acid and nicotiflorin were the major compounds in CSE. Our data demonstrated that CSE blocked DOX-induced cell death of H9c2 cells without hindrance of its apoptotic effects on MDA-MB-231 cells. DOX-induced defects of OCR and mitochondrial membrane potential were recovered in a CSE through upregulation of the AMPK-PGC1-α-NRF1 signaling pathway. CSE accelerated NRF1 translocation to the nucleus, increased SOD activity, and consequently blocked apoptosis in H9c2 cells. In mice treated with 400 mg/kg CSE for 4 weeks, electrocardiogram data, creatine kinase and lactate dehydrogenase levels in the serum, and cardiac fibrosis, were improved. Moreover, various electrophysiological features indicative of cardiac function were significantly enhanced following the CSE treatment of hiPSCCMs.

CONCLUSION

Our findings demonstrate CSE that ameliorates DICT by protecting mitochondrial dysfunction via the AMP- PGC1α-NRF1 axis, underscoring the therapeutic potential of CSE and its underlying molecular pathways, setting the stage for future investigations into its clinical applications.

Moderate Endurance Exercise Increases Arrhythmia Susceptibility and Modulates Cardiac Structure and Function in a Sexually Dimorphic Manner

BACKGROUND

Although moderate endurance exercise has been reported to improve cardiovascular health, its effects on cardiac structure and function are not fully characterized, especially with respect to sexual dimorphism. We aimed to assess the effects of moderate endurance exercise on cardiac physiology in male versus female mice.

METHODS AND RESULTS

C57BL/6J mice of both sexes were run on a treadmill for 6 weeks. ECG and echocardiography were performed every 2 weeks. After 6 weeks of exercise, mice were euthanized, and triple parametric optical mapping was performed on Langendorff perfused hearts to assess cardiac electrophysiology. Arrhythmia inducibility was tested by programmed electrical stimulation. Left ventricular tissue was fixed, and RNA sequencing was performed to determine exercise-induced transcriptional changes. Exercise-induced left ventricular dilatation was observed in female mice alone, as evidenced by increased left ventricular diameter and reduced left ventricular wall thickness. Increased cardiac output was also observed in female exercised mice but not males. Optical mapping revealed further sexual dimorphism in exercise-induced modulation of cardiac electrophysiology. In female mice, exercise prolonged action potential duration and reduced voltage-calcium influx delay. In male mice, exercise reduced the calcium decay constant, suggesting faster calcium reuptake. Exercise increased arrhythmia inducibility in both male and female mice; however, arrhythmia duration was increased only in females. Lastly, exercise-induced transcriptional changes were sex dependent: females and males exhibited the most significant changes in contractile versus metabolism-related genes, respectively.

CONCLUSIONS

Our data suggest that moderate endurance exercise can significantly alter multiple aspects of cardiac physiology in a sex-dependent manner. Although some of these effects are beneficial, like improved cardiac mechanical function, others are potentially proarrhythmic.

Sex Differences in Mouse Cardiac Electrophysiology Revealed by Simultaneous Imaging of Excitation-Contraction Coupling

Males and females differ in the basic anatomy and physiology of the heart. Sex differences are evident in cardiac repolarization in humans; women have longer corrected QT and JT intervals. However, the molecular mechanisms that lead to these differences are incompletely understood. Here, we present that, like in humans, sex differences in QT and JT intervals exist in mouse models; female mice had longer corrected QT and JT intervals compared with age-matched males. To further understand the molecular underpinning of these sex differences, we developed a novel technology using fluorescent confocal microscopy that allows the simultaneous visualization of action potential, Ca2+ transients, and contractions in isolated cardiomyocytes at a high temporal resolution. From this approach, we uncovered that females at baseline have increased action potential duration, decreased Ca2+ release and reuptake rates, and decreased contraction and relaxation velocities compared with males. Additionally, males had a shorter overall time from action potential onset to peak contraction. In aggregate, our studies uncovered male and female differences in excitation-contraction coupling that account for differences observed in the EKG. Overall, a better understanding of sex differences in electrophysiology is essential for equitably treating cardiac disease.

Anthracycline cardiotoxicity is exacerbated by global p38β genetic ablation in a sexually dimorphic manner but unaltered by cardiomyocyte-specific p38α loss

Severe cardiotoxic effects limit the efficacy of doxorubicin (DOX) as a chemotherapeutic agent. Activation of intracellular stress signaling networks, including p38 mitogen-activated protein kinase (MAPK), has been implicated in DOX-induced cardiotoxicity (DIC). However, the roles of the individual p38 isoforms in DIC remain incompletely elucidated. We recently reported that global p38δ deletion protected female but not male mice from DIC, whereas global p38γ deletion did not significantly modulate it. Here we studied the in vivo roles of p38α and p38β in acute DIC. Male and female mice with cardiomyocyte-specific deletion of p38α or global deletion of p38β and their wild-type counterparts were injected with DOX. Survival and health were tracked for 10 days postinjection. Cardiac function was assessed by echocardiography and electrocardiography and fibrosis by Picrosirius red staining. Expression and activation of signaling proteins and inflammatory markers were measured by Western blot, phosphorylation array, and chemokine/cytokine array. Global p38β deletion significantly aggravated DIC and worsened cardiac electrical and mechanical function deterioration in female mice. Mechanistically, DIC in p38β-null female mice correlated with increased autophagy, sustained hyperactivation of proapoptotic JNK signaling, as well as remodeling of a myocardial inflammatory environment. In contrast, cardiomyocyte-specific deletion of p38α improved survival of DOX30-treated male mice 5 days posttreatment but did not influence cardiac function in DOX-treated male or female mice. Our data highlight the sex- and isoform-specific roles of p38α and p38β MAPKs in DOX-induced cardiac injury and suggest a novel in vivo function of p38β in protecting female mice from DIC.NEW & NOTEWORTHY We show that p38α and p38β have distinct in vivo functions in a murine model of acute DIC. Specifically, although conditional cardiomyocyte-specific p38α deletion exhibited mild cardioprotective effects in male mice, p38β deletion exacerbated the DOX cardiotoxicity in female mice. Our findings caution against employing pyridinyl imidazole inhibitors that target both p38α and p38β isoforms as a cardioprotective strategy against DIC. Such an approach could have undesirable sex-dependent effects, including attenuating p38β-dependent cardioprotection in females.

Impact of Cerium Oxide Nanoparticles on Metabolic, Apoptotic, Autophagic and Antioxidant Changes in Doxorubicin-Induced Cardiomyopathy: Possible Underlying Mechanisms

Background

In the current study, the effects of cerium oxide nanoparticles (nanocerium; NC) on doxorubicin (DOX)-induced cardiomyopathy and its possible underlying mechanisms were addressed.

Methods

32 adult male rats were allocated into 4 groups; i) control group, ii) NC group; rats received NC (0.2 mg/kg, i.p., daily), iii) DOX group; rats received DOX 4 mg/kg (2 injections with a 14-day interval), and iv) DOX+NC group as DOX but rats received NC. At the end of the experiment, ECG and ECHO recordings and assessments of the levels of cardiac enzymes (CK-MB, LDH), and myocardial oxidative stress (MDA, catalase, and GSH), the expression of LC3 and beclin1 (markers of autophagy), caspase3 (marker of apoptosis) by immunohistochemistry, the expression of acetyl-CoA carboxylase alpha (ACCA) by PCR, and 5'adenosine monophosphate-activated protein kinase (AMPK) levels in the heart tissues were performed.

Results

The DOX group displayed a prolonged corrected QT interval, an increase in cardiac enzymes (CK-MB and LDH), myocardial oxidative stress (high MDA with low catalase and GSH), expression of ACCA, caspase-3, beclin1, and LC3 in myocardial tissues, with reduction in myocardial AMPK levels, and myocardial contractility (low ejection fraction, and fractional shortening). On the other hand, administration of NC with DOX resulted in significant improvement of all studied parameters.

Conclusion

NC offers a cardioprotective effect against DOX-induced cardiomyopathy. This effect might be due to its antioxidant and antiapoptotic effects as well as to the modulation of autophagy and metabolic dysfunctions induced by DOX in the heart tissues.

What to consider for ECG in mice-with special emphasis on telemetry

Genetically or surgically altered mice are commonly used as models of human cardiovascular diseases. Electrocardiography (ECG) is the gold standard to assess cardiac electrophysiology as well as to identify cardiac phenotypes and responses to pharmacological and surgical interventions. A variety of methods are used for mouse ECG acquisition under diverse conditions, making it difficult to compare different results. Non-invasive techniques allow only short-term data acquisition and are prone to stress or anesthesia related changes in cardiac activity. Telemetry offers continuous long-term acquisition of ECG data in conscious freely moving mice in their home cage environment. Additionally, it allows acquiring data 24/7 during different activities, can be combined with different challenges and most telemetry systems collect additional physiological parameters simultaneously. However, telemetry transmitters require surgical implantation, the equipment for data acquisition is relatively expensive and analysis of the vast number of ECG data is challenging and time-consuming. This review highlights the limits of non-invasive methods with respect to telemetry. In particular, primary screening using non-invasive methods can give a first hint; however, subtle cardiac phenotypes might be masked or compensated due to anesthesia and stress during these procedures. In addition, we detail the key differences between the mouse and human ECG. It is crucial to consider these differences when analyzing ECG data in order to properly translate the insights gained from murine models to human conditions.

Medetomidine/midazolam/fentanyl narcosis alters cardiac autonomic tone leading to conduction disorders and arrhythmias in mice

Arrhythmias are critical contributors to cardiovascular morbidity and mortality. Therapies are mainly symptomatic and often insufficient, emphasizing the need for basic research to unveil the mechanisms underlying arrhythmias and to enable better and ideally causal therapies. In translational approaches, mice are commonly used to study arrhythmia mechanisms in vivo. Experimental electrophysiology studies in mice are performed under anesthesia with medetomidine/midazolam/fentanyl (MMF) and isoflurane/fentanyl (IF) as commonly used regimens. Despite evidence of adverse effects of individual components on cardiac function, few data are available regarding the specific effects of these regimens on cardiac electrophysiology in mice. Here we present a study investigating the effects of MMF and IF narcosis on cardiac electrophysiology in vivo in C57BL/6N wild-type mice. Telemetry transmitters were implanted in a group of mice, which served as controls for baseline parameters without narcosis. In two other groups of mice, electrocardiogram and invasive electrophysiology studies were performed under narcosis (with either MMF or IF). Basic electrocardiogram parameters, heart rate variability parameters, sinus node and atrioventricular node function, and susceptibility to arrhythmias were assessed. Experimental data suggest a remarkable influence of MMF on cardiac electrophysiology compared with IF and awake animals. While IF only moderately reduced heart rate, MMF led to significant bradycardia, spontaneous arrhythmias, heart rate variability alterations as well as sinus and AV node dysfunction, and increased inducibility of ventricular arrhythmias. On the basis of these observed effects, we suggest avoiding MMF in mice, specifically when studying cardiac electrophysiology, but also whenever a regular heartbeat is required for reliable results, such as in heart failure or imaging research.

Incorrectly corrected? QT interval analysis in rats and mice

QT interval, a surrogate measure for ventricular action potential duration (APD) in the surface ECG, is widely used to identify cardiac abnormalities and drug safety. In humans, cardiac APD and QT interval are prominently affected by heart rate (HR), leading to widely accepted formulas to correct the QT interval for HR changes (QT corrected - QTc). While QTc is widely used in the clinic, the proper way to correct the QT interval in small mammals such as rats and mice is not clear. Over the years, empiric correction formulas were developed for rats and mice, which are widely used in the literature. Recent experimental findings obtained from pharmacological and direct pacing experiments in unanesthetized rodents show that the rate-adaptation properties are markedly different from those in humans and the use of existing QTc formulae can lead to major errors in data interpretation. In the present review, these experimental findings are summarized and discussed.

Demographic and Methodological Heterogeneity in Electrocardiogram Signals From Guinea Pigs

Electrocardiograms (ECG) are universally used to measure the electrical activity of the heart; however, variations in recording techniques and/or subject demographics can affect ECG interpretation. In this study, we investigated variables that are likely to influence ECG metric measurements in cardiovascular research, including recording technique, use of anesthesia, and animal model characteristics. Awake limb lead ECG recordings were collected in vivo from adult guinea pigs using a platform ECG system, while recordings in anesthetized animals were performed using both a platform and needle ECG system. We report significant heterogeneities in ECG metric values that are attributed to methodological differences (e.g., ECG lead configuration, ECG recording platform, presence or absence of anesthesia) that persist even within the same cohort of animals. Further, we report that variability in animal demographics is preserved in vivo ECG recordings—with animal age serving as a significant contributor, while sex-specific influences were less pronounced. Methodological approaches and subject demographics should be fully considered when interpreting ECG values in animal models, comparing datasets between studies, or developing artificial intelligence algorithms that utilize an ECG database.

Doxorubicin nanomedicine based on ginsenoside Rg1 with alleviated cardiotoxicity and enhanced antitumor activity

Aim: The authors aimed to develop Dox@Rg1 nanoparticles with decreased cardiotoxicity to expand their application in cancer. Materials & methods: Dox@Rg1 nanoparticles were developed by encapsulating doxorubicin (Dox) in a self-assembled Rg1. The antitumor effect of the nanoparticles was estimated using 4T1 tumor-bearing mice and the protective effect on the heart was investigated in vitro and in vivo. Results: Different from Dox, the Dox@Rg1 nanoparticles induced increased cytotoxicity to tumor cells, which was decreased in cardiomyocytes by the inhibition of apoptosis. The study in vivo revealed that the Dox@Rg1 nanoparticles presented a perfect tumor-targeting ability and improved antitumor effects. Conclusion: Dox@Rg1 nanoparticles could enhance the antitumor effects and decrease the cardiotoxicity of Dox.