Differential analysis of transient increases of serum cTnI in response to handling in rats.

Serum cardiac troponins are the key biomarkers of myocardial necrosis in humans and in preclinical species. The use of ultrasensitive assays for serum cardiac troponin I (cTnI) as a biomarker in safety studies is hampered by interindividual differences. In this study, we investigated the effect of handling procedures on serum cTnI and explored modeling and simulation approaches to mitigate the impact of these interindividual differences. Femoral-catheterized male Crl:WI(Han) rats (n = 16/group) were left undisturbed in their cages with no handling; subjected to 5 min of isoflurane/O2 anesthesia (A); or placed into a rodent restrainer followed by simulated tail vein injection (RR). Serum cTnI concentrations were assessed over a 24-h period using an ultrasensitive assay, and the study was repeated for confirmation. The mean serum cTnI concentration pre-procedure was 4.2 pg/mL, and remained stable throughout the duration of the study in the rats submitted to the A procedure. Serum cTnI concentrations increased transiently after the RR procedure with a median time to maximum concentration (T max), of 1 and 2 h and a mean maximum value concentration (C max), of 53.0 and 7.2 pg/mL in the initial and repeat studies, respectively. A population pharmacodynamic model identified interindividual, procedure- and study-specific effects on serum cTnI concentrations in rats. It is concluded that a modeling and simulation approach more appropriately describes and statistically analyzes the data obtained with this ultrasensitive assays.

Myocardial mononuclear cell infiltrates are not associated with increased serum cardiac troponin I in cynomolgus monkeys.

Myocardial mononuclear cell infiltrate is a spontaneous cardiac finding commonly identified in laboratory cynomolgus monkeys. The infiltrates are predominantly composed of macrophages with lesser lymphocytes and are not typically associated with histologically detectable cardiomyocyte degeneration. These infiltrates are of concern because they confound interpretation of test article-related histopathology findings in nonclinical safety toxicology studies. The interpretation of safety studies would be simplified by a biomarker that could identify myocardial infiltrates prior to animal placement on study. We hypothesized that monkeys with myocardial mononuclear cell infiltrates could be identified before necropsy using an ultrasensitive immunoassay for cardiac troponin I (cTnI). Serum cTnI concentrations in monkeys with myocardial infiltrates were not higher than those in monkeys without infiltrates at any of the sampling times before and on the day of necropsy. Increased serum cTnI levels are not suitable for screening monkeys with myocardial mononuclear cell infiltrates before placement in the study.

The complete pharmacokinetic profile of serum cardiac troponin I in the rat and the dog.

Recent improvements in assays have allowed serum cardiac troponin I (cTnI) to be measured at previously undetectable concentrations, which may have implications for cardiotoxicity studies. We characterized the pharmacokinetics of cTnI after a single iv administration of purified cTnI in rats at doses of 0.005, 0.05, and 0.5 µg/kg and in beagle dogs at doses of 0.05, 0.1, and 0.2 µg/kg. Serum cTnI concentration-time profiles were well described by a two-compartment pharmacokinetic model with first-order elimination in both species. The estimated mean (SD) values of total serum clearance, volume of distribution of the central compartment, and terminal half-life were 318 ml/h/kg, 52.9 ml/kg, and 0.8 h in rats and 481 (135) ml/h/kg, 230 (70) ml/kg, and 1.85 (0.5) h in dogs, respectively. In both species, a fast distribution phase was followed by a relatively slow elimination phase. These data indicate that the current practice in cardiotoxicity studies of unguided blood sampling should be revised. A targeted case-by-case approach is required whereby samples are collected not only relative to the kinetics of the test article but also in relation to the kinetics of the biomarker in the test species and the type and severity of anticipated cardiovascular perturbation. This approach is essential for the identification of subtle increases of serum cTnI concentrations in the low dynamic range.

A pharmacokinetic-pharmacodynamic model for cardiovascular safety assessment of R1551.

INTRODUCTION: Pharmacokinetic-pharmacodynamic relationships are crucial in understanding a drug's arrhythmogenic potential. Models assist to quantitatively relate parent and metabolite concentrations to adverse electrocardiographic effects, including an apparent delay between effect and circulating parent species concentration. Here, we used an effect compartment model to investigate PR and QRS prolongation previously observed in preclinical studies with the NK1-NK3 antagonist R1551. METHOD: Using a cross-over design, beagle dogs received a single oral dose of R1551 (0-100mg/kg), and cynomolgus monkeys received oral doses of 0-30 mg/kg once daily for 5 days. PR and QRS intervals and heart rate were measured by telemetry, for ≥ 24h after each dose in dogs, and on treatment days 1, 3, and 5 in monkeys. Pharmacokinetic parameters were estimated by fitting a two-compartment model to the data. For each species, a linear effect compartment model was used to relate PR and QRS intervals to effect compartment concentrations. RESULTS: The effect compartment model provided a good fit to the observed data for both ECG parameters in dogs, and for QRS interval in monkeys (PR(0)=95.1 ms ± 2.74 and 64.9 ms ± 1.46, QRS(0)=42.5 ms ± 1.24 and 46.5 ms ± 1.11 in dog and monkey, respectively). For PR interval in monkeys, the fit was improved by adding a placebo effect compartment to the linear model. R1551 effects on intervals in dogs suggested the presence of responder and non-responder sub-populations. In monkeys, only the highest R1551 dose prolonged PR intervals. Effect slope factors were similar between dog and monkey for both intervals (S(PR)=0.00930 ms mg(-1)kg(-1)l(-1) ± 0.00133 in dog and 0.00934 ms mg(-1)kg(-1)l(-1) ± 0.00141 in monkey; S(QRS)=0.00274 ms mg(-1)kg(-1)l(-1) ± 0.00101 in dog and 0.00200 ms mg(-1)kg(-1)l(-1) ± 0.000552 in monkey). DISCUSSION: Our results indicate a non-linear relationship between R1551 plasma kinetics and electrophysiological effects and suggest that the parent was not responsible for the observed ECG effects. In addition, the population based approach allows exploitation of sparse PK data in dog and monkey, analysis throughout the complete effect time course, and assessment of inter-individual variability, all in a single comprehensive model.

Assessment of the toxicity of hydralazine in the rat using an ultrasensitive flow-based cardiac troponin I immunoassay.

The purpose of this study was to correlate the histologic changes in the heart to serum cardiac troponin I (cTnI) concentrations assayed with the Erenna Immunoassay System in Wistar rats (Crl:Wi[Han]) using the hydralazine model of cardiotoxicity. A single dose of hydralazine caused an increase of cTnI concentrations at six hours post-dose, followed by a sharp decrease at twenty-four hours and a return to baseline at forty-eight hours. The second dose of hydralazine caused a smaller magnitude increase in cTnI concentrations at six hours as compared to the first dose. Also, cTnI concentrations returned to baseline at twenty-four hours after the second dose. The increased cTnI concentrations coincided with acute myocardial necrosis at histology. However, increased cTnI concentrations in the absence of microscopic lesions were identified in several rats. As cTnI concentrations decreased, microscopic changes in the heart matured to cardiomyophagy. In conclusion, the increases in cTnI concentrations six hours after the administration of hydralazine were indicative of a myocardial damage that did not consistently have a microscopic correlate. However, the window of increased cTnI concentrations was short, and only microscopic evaluation of the heart detected the damage at twenty-four to forty-eight hours after the episode of acute myocardial necrosis.