Respiratory safety pharmacology: Positive control drug responses in Sprague–Dawley rats, Beagle dogs and cynomolgus monkeys

Practical Considerations in Dose Extrapolation from Animals to Humans

Animal studies are an important component of drug product development and the regulatory review process since modern practices have been in place, for almost a century. A variety of experimental systems are available to generate aerosols for delivery to animals in both liquid and solid forms. The extrapolation of deposited dose in the lungs from laboratory animals to humans is challenging because of genetic, anatomical, physiological, pharmacological, and other biological differences between species. Inhaled drug delivery extrapolation requires scrutiny as the aerodynamic behavior, and its role in lung deposition is influenced not only by the properties of the drug aerosol but also by the anatomy and pulmonary function of the species in which it is being evaluated. Sources of variability between species include the formulation, delivery system, and species-specific biological factors. It is important to acknowledge the underlying variables that contribute to estimates of dose scaling between species.

Increased stress associated with head-out plethysmography testing can exacerbate respiratory effects and lead to mortality in rats

INTRODUCTION

DSM421, a dihydroorotate dehydrogenase inhibitor, was in preclinical development as a potential treatment option for malaria. When tested in a core battery of safety pharmacology assays, DSM421 did not produce any effects at oral doses up to 750 mg/kg in an Irwin test in rats, but a respiratory study in rats using head-out plethysmography resulted in substantial changes in respiratory function as well as moribundity and mortality at that and lower doses. An investigation was performed to determine the source of this discrepancy.

METHODS

Potential testing errors, differences in types of plethysmography testing chambers, effects on stress indicators, and off-target activity were investigated.

RESULTS

Respiratory changes and toxicity (resulting in euthanasia in extremis) were confirmed in a repeat, head-out plethysmography test, but the effects of DSM421 were much less severe overall when the rats were tested in whole-body chambers. Additionally, at the end of the 5-h post-dosing respiratory monitoring periods, levels of stress-related hormones (particularly corticosterone) were higher overall in the head-out, than in the whole-body, tested rats. Furthermore, DSM421 was found to produce changes in cardiovascular function in unrestrained rats, and it was shown to have off-target binding affinity at the adenosine A₃ receptor (which is associated with bronchoconstriction).

DISCUSSION

The generalized stress inherent to head-out plethysmography testing exacerbated the respiratory effects of DSM421 and was possibly compounded by DSM421's cardiovascular effects, thus artifactually resulting in moribundity and mortality in rats. Care should be taken when choosing whether to use head-out versus whole-body plethysmography chambers during respiratory function testing in animals.

Cardiovascular and respiratory safety evaluation of Musca Domestica larvae low molecular weight peptide in beagle dogs

Background: Many studies have demonstrated that the water extracts and low-molecular-weight peptide (LMWP) of the Musca domestica larvae contain significant biological activity. However, the cardiovascular and respiratory safety evaluations of LMWP are yet to be sufficiently investigated. Aim: This study focused on the cardiovascular and respiratory safety evaluations of the M. domestica larvae LMWP in beagle dogs. Methods: Direct cardiovascular and respiratory effects of three different doses of the M. domestica larvae LMWP were investigated following only once oral administration in conscious telemetered dogs, whereby ECG, arterial pressure, and respiratory data were collected using the Data Science International telemetric system. Results: The PR, QT, and QTcf intervals were significantly shortened in the medium-dose LMWP treatment group at 3 h after drug administration. Furthermore, no significant differences were observed in any of the corresponding indexes of other treatment groups at different time points compared to those of the control group. P wave, ST segment, R wave, systolic pressure, diastolic pressure, and mean pressure were significantly different, although these differences had no significant dose-effect relationship. Respiratory frequency significantly increased in the medium-dose LMWP treatment group at 8 h after drug administration compared to that of the control group. Respiratory rate and tidal volume showed no significant differences at varying time points among all LMWP treatment groups. Conclusions: No toxicological effects related to cardiovascular and respiratory safety in beagle dogs were observed at any dose level of the M. domestica larvae LMWP.

Acute inhalation toxicity study of n-heneicosane and its combination with diflubenzuron: An attracticide of Aedes aegypti

Objective:

Combination of an oviposition pheromone and an insect growth regulator for the control of vectors is an effective approach. There is a need for toxicological evaluation before its introduction. The present study evaluates the acute inhalation toxicity of n-heneicosane and its combination with diflubenzuron in a head-only inhalation exposure chamber made of glass.

Materials and methods:

A head-only inhalation exposure chamber made of glass (volume: 3.5 l) was used for exposing four rats at a time. A glass nebulizer was used for aerosolization of n-heneicosane and its combination with diflubenzuron (1:10 w/w). Nebulization pressure was 10 and 15 psi and the air flow of exposure the chamber was adjusted to 30 lpm. Male Wistar rats were acclimatized in whole body plethysmographs that were connected to volumetric flow pressure transducers by silicon tubes. The transducers were connected to an amplifier and a digitized response was recorded through an oscillograph and personal computers. Respiratory variables were recorded online. After inhalation exposure, various other parameters like survival, body weight, organ body weight index and biochemical changes were recorded for analysis.

Results and discussion:

Particle size determination proved that the aerosol particles were within the respirable range. LC50 of n-heneicosane and its combination with diflubenzuron was found to be more than 5 g/m3. There were minimal changes observed during exposure to n-heneicosane and also its combination with diflubenzuron on the respiratory variables. The changes were not consistent with the dose.

Conclusion:

n-Heneicosane and its combination with diflubenzuron showed low mammalian toxicity.

Overview of Respiratory Studies to Support ICH S7A

Tests of pulmonary function are useful tools for evaluating the potential for compounds to produce toxicity affecting the pulmonary system. Insults to the pulmonary system (i.e., due to drugs, biologics, toxins) can cause detectable dysfunction through multiple mechanisms. Manifestation of the response to insults will depend on the component(s) involved and the compensatory mechanism(s) initiated. The purpose of this chapter is to introduce the concepts of pulmonary testing as it is applied to the preclinical evaluation of pharmaceutical test articles. The topics will include the techniques and methods that have been developed for use in nonclinical (animal) subjects and the parameters that are routinely measured.

Reprint of "Non-invasive measure of respiratory mechanics and conventional respiratory parameters in conscious large animals by high frequency Airwave Oscillometry"

INTRODUCTION

A number of drugs in clinical trials are discontinued due to potentially life-threatening airway obstruction. As some drugs may not cause changes in core battery parameters such as tidal volume (Vt), respiratory rate (RR) or minute ventilation (MV), including measurements of respiratory mechanics in safety pharmacology studies represents an opportunity for design refinement. The present study aimed to test a novel non-invasive methodology to concomitantly measure respiratory system resistance (Rrs) and conventional respiratory parameters (Vt, RR, MV) in conscious Beagle dogs and cynomolgus monkeys.

METHODS

An Airwave Oscillometry system (tremoFlo; THORASYS Inc., Montreal, Canada) was used to concomitantly assess Rrs and conventional respiratory parameters before and after intravenous treatment with a bronchoactive agent. Respiratory mechanics measurements were performed by applying a short (i.e. 16s) single high frequency (19Hz) waveform at the subject's airway opening via a face mask. During measurements, pressure and flow signals were recorded. After collection of baseline measurements, methacholine was administered intravenously to Beagle dogs (n=6) and cynomolgus monkeys (n=4) at 8 and 68μg/kg, respectively.

RESULTS

In dogs, methacholine induced significant increases in Vt, RR and MV while in monkeys, it only augmented RR. A significant increase in Rrs was observed after methacholine administration in both species with mean percentage peak increases from baseline of 88 (53)% for dogs and 28 (16)% for cynomolgus monkeys.

CONCLUSION

Airwave Oscillometry appears to be a promising non-invasive methodology to enable respiratory mechanics measurements in conscious large animals, a valuable refinement in respiratory safety pharmacology.

Respiratory mechanics: comparison of Beagle dogs, Göttingen minipigs and Cynomolgus monkeys

INTRODUCTION

When the no observed adverse effect level (NOAEL) is determined by respiratory safety pharmacology, follow-up studies are warranted and may include airway resistance and compliance. Respiratory mechanics in commonly used large animal species (Beagle dogs, Cynomolgus monkeys, and Göttingen minipigs) were compared.

METHODS

Eighteen animals were used (3/sex/species) in an anesthetized model (propofol infusion) with pancuronium as a neuromuscular blocker. Parameters of respiratory mechanics were evaluated at baseline and at peak drug effect. Resistance (Rrs) and elastance (Ers) were measured by applying a single frequency forced oscillation (0.5 Hz) to the subject's airway opening and fitting the flow, volume and pressure data to the single compartment model of the lung. Increasing doses of intravenous (IV) methacholine were administered in all three species, as well as doubling aerosolized concentrations of the same bronchoconstrictor agent before and after inhaled albuterol.

RESULTS

The slope of the IV methacholine dose-response curve for Rrs was similar in dogs and monkeys and both species differed from minipigs, which showed greater reactivity. At the highest IV dose tested, minipigs also reached higher levels of bronchoconstriction than the other two species. They were followed, in decreasing order, by dogs and monkeys. Albuterol induced a significant decrease in the slope of the dose-response curve only in dogs and monkeys.

DISCUSSION

Scientific literature is available on respiratory mechanics in monkeys and dogs but not in minipigs. Our results suggest that minipigs were more reactive than dogs and monkeys to IV methacholine while less sensitive to inhaled albuterol.

Gene expression profiling in the lung tissue of cynomolgus monkeys in response to repeated exposure to welding fumes

Many in the welding industry suffer from bronchitis, lung function changes, metal fume fever, and diseases related to respiratory damage. These phenomena are associated with welding fumes; however, the mechanism behind these findings remains to be elucidated. In this study, the lungs of cynomolgus monkeys were exposed to MMA-SS welding fumes for 229 days and allowed to recover for 153 days. After the exposure and recovery period, gene expression profiles were investigated using the Affymetrix GeneChip Human U133 plus 2.0. In total, it was confirmed that 1,116 genes were up-or downregulated (over 2-fold changes, P\0.01) for the T1 (31.4 ± 2.8 mg/m3) and T2 (62.5 ± 2.7 mg/m3) dose groups. Differentially expressed genes in the exposure and recovery groups were analyzed, based on hierarchical clustering, and were imported into Ingenuity Pathways Analysis to analyze the biological and toxicological functions. Functional analysis identified genes involved in immunological disease in both groups. Additionally, differentially expressed genes in common between monkeys and rats following welding fume exposure were compared using microarray data, and the gene expression of selected genes was verified by real-time PCR. Genes such as CHI3L1, RARRES1, and CTSB were up-regulated and genes such as CYP26B1, ID4, and NRGN were down-regulated in both monkeys and rats following welding fume exposure. This is the first comprehensive gene expression profiling conducted for welding fume exposure in monkeys, and these expressed genes are expected to be useful in helping to understand transcriptional changes in monkey lungs after welding fume exposure.

Respiratory safety pharmacology: concurrent validation of volume, rate, time, flow and ratio variables in conscious male Sprague-Dawley rats

This study compares basic respiratory variables (rate, tidal and minute volumes) with time-, flow- and ratio-derived parameters obtained using head-out plethysmography in rats following administration of reference drugs (isotonic saline, 2.0 mL/kg, IV; albuterol, 400 μg/kg, inhalation; methacholine, 136 μg/kg, IV; and remifentanil, 14 μg/kg, IV) to identify respiratory variables with superior sensitivity. Paired t-tests by block-period, and analysis of covariance (ANCOVA) with baseline as covariate and a posteriori pair-wise comparisons using Dunnett's test were used. Variations in respiratory parameters observed over time justify the use of a control group in any respiratory safety pharmacology study for inter-groups comparison. Handling-, and slumbering-, induced perturbations were minimal. The system was sensitive and specific to detect changes in respiratory variables related to pharmacologically-induced bronchodilation, bronchoconstriction and central respiratory depression. The standard variables (respiratory rate, tidal and minute volumes) confirmed to be the cornerstone of respiratory safety pharmacology to detect pharmacological changes. Flow-derived parameters appeared as highly valuable complement for interpretation of respiratory response, whereas time- and ratio-derived parameters presented limited added value during interpretation.

Combined cardiopulmonary assessments with implantable telemetry device in conscious freely moving cynomolgus monkeys

Female cynomolgus monkeys were surgically implanted with telemetry transmitters recording ECG (DII), arterial pressure, physical activity, body temperature, and tidal volume. Respiratory rate (RR) and tidal volume (TV) were monitored simultaneously with the telemetry transmitter using impedance. Impedance-based monitoring of RR and TV by telemetry correlated with controlled TV and with pneumotachometer (>98%) in restrained animals. Control drugs with cardiovascular and respiratory effects, including saline, medetomidine (0.01, 0.02 and 0.04mg/kg) and cocaine (0.5, 1.0 and 1.5mg/kg) were administered intravenously. An averaging epoch of 5min was used for analysis of respiratory data. Medetomidine induced significant respiratory depression with decrease in RR and TV in freely moving animals while cocaine increased TV, RR and minute ventilation (MV) with concomitant increase in heart rate when compared with time matched values from saline-treated animals. The onset, duration and magnitude of cardiovascular and respiratory changes were correlated. This highlights the dependency of the cardiovascular and respiratory systems. The use of cardiopulmonary monitoring can allow continuous monitoring including during night time when variability of respiratory parameters is lower. Monitoring of cardiovascular and respiratory parameters in the same animals could also help to decrease the number of animals used in research.

Pharmacological validation of a telemetric model for the measurement of bronchoconstriction in conscious rats

INTRODUCTION

Telemetric measurement of intra-pleural pressure in conscious animals that are restrained in head-out plethysmography chambers enables determination of airway resistance. Originally proposed over 10 years ago, pharmacological validation of this technique is limited. Here airway resistance in conscious, instrumented rats was compared to measurement in anaesthetised rats via a fluid filled oesophageal catheter following administration of two different pharmacological agents.

METHODS

Male rats were implanted with telemetry devices and were trained to accept the restraint of head-out plethysmography chambers. A separate group of male rats were anaesthetised, placed in a body-enclosed plethysmography chamber and were prepared with a tracheal, oesphageal and jugular vein cannulae. Methacholine or NECA were given intravenously and changes in ventilation and airway resistance were measured.

RESULTS

The pressure signal obtained in the telemetered rats was found to be extremely variable. Variability was confounded by excessive struggling, particularly during the infusion periods. Misplacement of the pressure sensitive catheter tip and prior habituation to the chamber were not factors in signal variability. Consequently, no dose-response relationship to either pharmacological agent was established in this model. Dose-dependent increases in resistance to both methacholine and NECA were measured in anaesthetised rats using body-enclosed plethysmography.

DISCUSSION

Given the variability of the pressure signal within and between rats, the feasibility of a model in conscious rats for the measurement of airway resistance is questioned. Improved restraint methods or alternative models in conscious animals should therefore be explored. In the meantime, assessment of airway resistance is best confined to the anaesthetised rat.