Methodological validation of an existing telemetry system for QT evaluation in conscious guinea pigs

A novel whole-body thermal stress test for monitoring cardiovascular responses in Guinea pigs

Cardiovascular disease is a leading cause of morbidity and mortality worldwide. Stress tests are frequently employed to expose early signs of cardiovascular dysfunction or disease and can be employed, for example, in the context of preterm birth. We aimed to establish a safe and effective thermal stress test to examine cardiovascular function. Guinea pigs were anaesthetized using a 0.8% isoflurane, 70% N₂O mix. ECG, non-invasive blood pressure, laser Doppler flowmetry, respiratory rate, and an array of skin and rectal thermistors were applied. A physiologically relevant heating and a cooling thermal stress test was developed. Upper and lower thermal limits for core body temperature were set at 41.5 ^OC and 34 ^OC, for the safe recovery of animals. This protocol therefore presents a viable thermal stress test for use in guinea pig models of health and disease that facilitates exploration of whole-system cardiovascular function.

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.

Pharmacological characterisation of electrocardiogram J-Tpeak interval in conscious Guinea pigs

Drug-induced human ether-à-go-go-related gene (hERG) channel block and QT interval prolongation increase torsade de pointes (TdP) risk. However, some drugs block hERG channels and prolong QT interval with low TdP risk, likely because they block additional inward currents. We investigated the utility of J-T_peak interval, a novel biomarker of inward current block and TdP risk, in conscious telemetered guinea pigs. Electrocardiogram parameters were analysed in Hartley guinea pigs orally administered one of eight test compounds (dofetilide, flecainide, nifedipine, quinidine, quinine, ranolazine, sotalol, verapamil) or vehicle alone as controls. Heart rate-corrected QT (QTcX) and J-T_peak (J-T_peakcX) were calculated to evaluate the relations of QT-RR and J-T_peak-RR. Dofetilide and sotalol significantly increased ΔQTcX and ΔJ-T_peakcX intervals to similar degrees. Quinidine, quinine and flecainide also increased ΔQTcX and ΔJ-T_peakcX intervals, but the degrees of ΔJ-T_peakcX interval prolongation were shorter than those of ΔQTcX interval prolongation. Ranolazine showed slight increasing trends in ΔQTcX and ΔJ-T_peakcX intervals, but the differences were not significant. Verapamil and nifedipine did not increase the ΔQTcX or ΔJ-T_peakcX intervals. Based on the relations of ΔΔJ-T_peakcX and ΔΔQTcX intervals, dofetilide, sotalol and quinidine were classified as high risk for TdP, quinine, flecainide and ranolazine were classified as intermediate risk and verapamil and nifedipine were classified as low risk. These results supported the usefulness of J-T_peak interval assessment in conscious guinea pigs for predicting drug-induced balanced block of inward currents and TdP risk in early-stage preclinical studies.

Differential effects of four intramuscular sedatives on cardiorespiratory stability in juvenile guinea pigs (Cavia porcellus)

BACKGROUND

Non-invasive physiological monitoring can induce stress in laboratory animals. Sedation reduces the level of restraint required, thereby improving the validity of physiological signals measured. However, sedatives may alter physiological equilibrium introducing unintended bias and/or, masking the experimental outcomes of interest. We aimed to investigate the cardiorespiratory effects of four short-acting sedatives in juvenile guinea pigs.

METHOD

12 healthy, 38 (26-46) day-old Dunkin Hartley guinea pigs were included in this blinded, randomised, crossover design study. Animals were sedated by intramuscular injection using pre-established minimum effective doses of either alfaxalone (5 mg/kg), diazepam (5 mg/kg), ketamine (30 mg/kg), or midazolam (2 mg/kg) administered in random order with a minimum washout period of 48 hours between agents. Sedative depth, a composite score comprised of five assessment criteria, was observed every 5-min from dosing until arousal. Physiological monitoring of cardiorespiratory status included measures of heart rate, blood pressure, respiratory rate, and peripheral microvascular perfusion.

RESULTS

Ketamine and alfaxalone were most effective in inducing stable sedation suitable for physiological monitoring, and diazepam less-so. Midazolam was unsuitable due to excessive hypersensitivity. All sedatives significantly increased heart rate above non-sedated control rates (P<0.0001), without altering blood pressure or microvascular perfusion. Alfaxalone and ketamine reduced respiratory rate relative to their control condition (P<0.0001, P = 0.05, respectively), but within normative ranges.

CONCLUSION

Ketamine and alfaxalone are the most effective sedatives for inducing short duration, stable sedation with minimal cardiorespiratory depression in guinea pigs, while diazepam is less-so. However, alfaxalone is the most appropriate sedative for longitudinal studies requiring multiple physiological timepoints.

Pluripotent Stem Cells for Cardiac Regeneration - Current Status, Challenges, and Future Perspectives

Loss of myocardium permanently impairs cardiac function because the adult mammalian heart has limited regenerative capacity. Strategies to regenerate injured heart tissue include the transplantation of multiple types of stem cells. Among them, pluripotent stem cells (PSCs) are a promising option because of their unlimited self-renewal and unequivocal cardiomyogenic ability. To date, advances in stem cell biology allow generation of relatively homogeneous human PSC-derived cardiomyocytes (CMs). In this regard, preclinical studies of PSC-CM transplantation in rodents and larger animal models have provided convincing proof-of-concept results, triggering clinical studies in multiple countries. However, a few important uncertainties are yet to be addressed, warranting further investigation before clinical implementation of this novel therapy. An overview of the potential of stem cell therapy to provide new CMs for cardiac regeneration is presented.

T-Helper Type 1-T-Helper Type 2 Shift and Nasal Remodeling after Fine Particulate Matter Exposure in a Rat Model of Allergic Rhinitis

Background

Exposure to fine particulate matter (particulate matter ≤2.5 μm [PM2.5]) increases the risk of allergic rhinitis (AR), but the underlying mechanisms remains unclear. Thus, we investigated the roles of T-helper (Th)1–Th2 cytokines and nasal remodeling after ambient PM2.5 exposure in a rat model of AR.

Methods

Female Sprague-Dawley rats were randomized into six groups: a negative control group, a group of healthy rats exposed to 3000 μg/m3 PM2.5, an ovalbumin (OVA) induced AR model, and three PM2.5-exacerbated AR groups exposed to three different concentrations (200, 1000, and 3000 μg/m3) of PM2.5 for 30 days via inhalation. Nasal symptoms, levels of Th1–Th2 cytokines, the degree of eosinophilia in nasal lavage fluid (NLF), and the messenger RNA (mRNA) expressions of transcription factors GATA-3 and T-bet in the nasal mucosa were measured in each individual rat. Hyperplasia of globet cells and collagen deposition were examined by histology.

Results

PM2.5 significantly increased the number of sneezes and nasal rubs in rats with AR. PM2.5 also significantly decreased interferon gamma and increased interleukin (IL) 4 and IL-13 expressions as well as the number of eosinophils in NLF. The mRNA expression of GATA-3 in the nasal mucosa of rats with AR was upregulated by PM2.5, whereas T-bet was significantly downregulated. Statistically significant differences in OVA-specific serum immunoglobulin E, goblet cell hyperplasia, collagen deposition, and transforming growth factor beta 1 levels were observed between the PM2.5-exacerbated AR groups and the AR model group.

Conclusion

Analysis of our data indicated that an increase in the immune response with Th2 polarization and the development of nasal remodeling may be the immunotoxic mechanisms behind the exacerbation of AR after exposure to PM2.5.

Rat cardiovascular telemetry: Marginal distribution applied to positive control drugs

Cardiovascular effects are considered frequent during drug safety testing. This investigation aimed to characterize the pharmacological response of the conscious telemetered rat in vivo model to known cardiovascular active agents. These effects were analyzed using statistical analysis and cloud representation with marginal distribution curves for the contractility index and heart rate as to assess the effect relationship between cardiac variables. Arterial blood pressure, left ventricular pressure, electrocardiogram and body temperature were monitored. The application of data cloud with marginal distribution curves to heart rate and contractility index provided an interesting tactic during the interpretation of drug-induced changes particularly during selective time resolution (i.e. marginal distribution curves restricted to Tmax). Taken together, the present data suggests that marginal distribution curves can be a valuable interpretation strategy when using the rat cardiovascular telemetry model to detect drug-induced cardiovascular effects. Marginal distribution curves could also be considered during the interpretation of other inter-dependent parameters in safety pharmacology studies.

Electrical Integration of Human Embryonic Stem Cell-Derived Cardiomyocytes in a Guinea Pig Chronic Infarct Model

BACKGROUND

Human embryonic stem cell-derived cardiomyocytes (hESC-CMs) were recently shown to be capable of electromechanical integration following direct injection into intact or recently injured guinea pig hearts, and hESC-CM transplantation in recently injured hearts correlated with improvements in contractile function and a reduction in the incidence of arrhythmias. The present study was aimed at determining the ability of hESC-CMs to integrate and modulate electrical stability following transplantation in a chronic model of cardiac injury.

METHODS AND RESULTS

At 28 days following cardiac cryoinjury, guinea pigs underwent intracardiac injection of hESC-CMs, noncardiac hESC derivatives (non-CMs), or vehicle. Histology confirmed partial remuscularization of the infarct zone in hESC-CM recipients while non-CM recipients showed heterogeneous xenografts. The 3 experimental groups showed no significant difference in the left ventricular dimensions or fractional shortening by echocardiography or in the incidence of spontaneous arrhythmias by telemetric monitoring. Although recipients of hESC-CMs and vehicle showed a similar incidence of arrhythmias induced by programmed electrical stimulation at 4 weeks posttransplantation, non-CM recipients proved to be highly inducible, with a ∼3-fold greater incidence of induced arrhythmias. In parallel studies, we investigated the ability of hESC-CMs to couple with host myocardium in chronically injured hearts by the intravital imaging of hESC-CM grafts that stably expressed a fluorescent reporter of graft activation, the genetically encoded calcium sensor GCaMP3. In this work, we found that only ∼38% (5 of 13) of recipients of GCaMP3+ hESC-CMs showed fluorescent transients that were coupled to the host electrocardiogram.

CONCLUSIONS

Human embryonic stem cell-derived cardiomyocytes engraft in chronically injured hearts without increasing the incidence of arrhythmias, but their electromechanical integration is more limited than previously reported following their transplantation in a subacute injury model. Moreover, non-CM grafts may promote arrhythmias under certain conditions, a finding that underscores the need for input preparations of high cardiac purity.

Knockdown of neurokinin-1 receptor expression by small interfering RNA prevents the development of allergic rhinitis in rats

Objective and design

This study is aimed at exploring the role of neurokinin-1 receptor (NK-1R) in the development of allergic rhinitis (AR) in rats.

Methods

Sprague–Dawley rats were sensitized and challenged with ovalbumin to induce AR. The rats were treated intranasally with saline, control, or NK-1R-specific small interfering RNA (siRNA) before and during the challenge period. The numbers of sneezes and nose rubs and amount of nasal secretion in individual rats were measured. The levels of NK-1R expression in the nasal mucosal tissues after the last challenge were determined. The numbers of eosinophils in the collected nasal lavage fluid and the levels of serum interleukin (IL)-5 in individual rats were determined.

Results

The levels of NK-1R expression in the nasal mucosal tissues of the AR rats that had been treated with saline or control siRNA were significantly higher than those in the healthy controls and the rats treated with NK-1R-specific siRNA, demonstrating NK-1R silencing. Furthermore, knockdown of NK-1R expression significantly reduced the amounts of sneezing, nose rubbing, and nasal secretions in AR rats. Knockdown of NK-1R expression also significantly eliminated eosinophil infiltration in the nasal tissues and reduced the levels of serum IL-5 in rats.

Conclusions

Knockdown of NK-1R expression decreased allergic inflammation in nasal mucosal tissues and alleviated the allergic rhinitis symptoms, suggesting that NK-1R may be a critical mediator of the development of AR.

Human ES-cell-derived cardiomyocytes electrically couple and suppress arrhythmias in injured hearts

Transplantation studies in mice and rats have shown that human embryonic stem cell-derived cardiomyocytes (hESC-CMs) can improve the function of infarcted hearts^1–3, but two critical issues related to their electrophysiological behavior in vivo remain unresolved. First, the risk of arrhythmias following hESC-CM transplantation in injured hearts has not been determined. Second, the electromechanical integration of hESC-CMs in injured hearts has not been demonstrated, so it is unclear if these cells improve contractile function directly through addition of new force-generating units. Here we use a guinea pig model to show hESC-CM grafts in injured hearts protect against arrhythmias and can contract synchronously with host muscle. Injured hearts with hESC-CM grafts show improved mechanical function and a significantly reduced incidence of both spontaneous and induced ventricular tachycardia (VT). To assess the activity of hESC-CM grafts in vivo, we transplanted hESC-CMs expressing the genetically-encoded calcium sensor, GCaMP3^{4, 5}. By correlating the GCaMP3 fluorescent signal with the host ECG, we found that grafts in uninjured hearts have consistent 1:1 host-graft coupling. Grafts in injured hearts are more heterogeneous and typically include both coupled and uncoupled regions. Thus, human myocardial grafts meet physiological criteria for true heart regeneration, providing support for the continued development of hESC-based cardiac therapies for both mechanical and electrical repair.

Evaluation of terfenadine and ketoconazole-induced QT prolongation in conscious telemetered guinea pigs

Terfenadine and ketoconazole are the most widely used positive reference agents in non-clinical cardiac repolarization safety studies. The aim of the present study was to evaluate the effects of terfenadine, ketoconazole and their combination on QT prolongation using conscious guinea pigs. Conscious telemetered guinea pigs were orally administered terfenadine (50 mg/kg), ketoconazole (200 mg/kg) or a combination of the two, and effects on QT were recorded using a telemetry system. The QT correction was carried out with Bazett's formula to eliminate confounding effect of HR. Neither terfenadine nor ketoconazole produced any effect on the RR and QT intervals, QRS complex or heart rate (HR). However, a combination of terfenadine and ketoconazole significantly prolonged the RR and QT intervals and decreased HR in a time-dependent manner. This study demonstrated that the combination of terfenadine and ketoconazole produces QT prolongation in conscious telemetered guinea pigs.

A cardiovascular monitoring system in conscious cynomolgus monkeys for regulatory safety pharmacology

INTRODUCTION

This project addresses the validation study design of a test system using a telemetered non-human primate model for cardiovascular safety pharmacology evaluation.

METHODS

The validation provided by the supplier evaluated installation (IQ) and operation (OQ) qualifications. This protocol was completed with tests evaluating electronic data management and accuracy and precision of transmitter (n=4) measurements for temperature and pressure criteria with a series of tested values. As part of performance qualification, physical activity (for 24 h) as well as cardiovascular, ECG (20 complexes for each animal) and systemic arterial blood pressure (SAP, 10 different measures), data were recorded simultaneously from the same animals (n=4) using certified equipment and the telemetry system. Reliability was evaluated over 60 days.

RESULTS

The IQ and OQ were completed successfully. The electronic data management was performed successfully. The ex-vivo evaluation for temperature and pressure showed high correlation (R(2)>0.99) but with a slight pressure shift, as expected, with this transmitter model. For physical activity, the correlation coefficients were good to excellent with high activity counts but the comparison demonstrated a limited sensitivity of the telemetry system with animal presenting low activity levels. ECG interval measurement using the telemetry software was considered at least equivalent to manual measurement, but with some limitations in the reading of the ECG. The comparison between both methods of SAP measurement showed adequate precision (R(2)=0.969) but no accuracy.

DISCUSSION

Reference monitoring methods are important to ensure proper test system validation. Monitoring with a reference methodology and the telemetry system is important in order to evaluate precision and accuracy of the test system. Computerized analysis may lack the capability to analyze ECG complexes with abnormal morphologies. This reinforces the need to have ECG evaluation prior to telemetry implantation along with visual evaluation of ECG tracing at standard speed (e.g. 50 mm/s) at all time points.

Aging-related changes of QT and RR intervals in conscious guinea pigs

INTRODUCTION

Although guinea pigs are suitable for in vivo QT assessment of newly discovered drugs at the pre-clinical stage because of the similarity of the ion channels between the guinea pig heart and the human, there is limited data available regarding the characteristics of QT interval in conscious guinea pigs. Aging is one of several factors which have been shown to affect the QT interval in humans and animals. In the present study, we examined the influence of age on QT and RR intervals in conscious guinea pigs.

METHODS

Electrocardiograms were recorded from female Hartley guinea pigs at the age of 6 weeks (young; n=6) and 23 months (old; n=4) via a telemetry system. The QT and RR intervals were measured during daytime and nighttime, and following intravenous bolus injection of E-4031 (0.1 mg/kg) or terfenadine (4 mg/kg). Comparisons were made to determine group differences in: (1) the normal values of the QT and RR intervals, (2) the best-fit QT-correction formula, (3) the circadian rhythm of QT and RR intervals, and (4) drug effects on repolarization.

RESULTS

The normal values of QT and RR intervals in the old group were significantly longer than those in the young group. The best-fit formula for correcting QT interval was a modified Bazett's formula for both young and old groups. The old group did not show the nocturnal variation of either QT or RR interval. Terfenadine caused significantly greater QTc prolongation in the old group compared to the young.

DISCUSSION

Aging affects resting QT and RR intervals in conscious female guinea pigs, a factor which should be considered when examining the effects of compounds on cardiac repolarization. Also, the present study suggests a possibility that age can affect QTc prolongation induced by some IKr blockers.