Evaluation of newly developed nose-only inhalation exposure chamber for nanoparticles

In this study, a direct-flow-type nose-only exposure chamber developed for inhalation toxicity experiments using a numerical analysis and experiments is evaluated. Maintaining a uniform flow rate and test article concentration are the critical factors when designing an inhalation exposure chamber. Therefore, this study evaluated whether the flow rate and particle size distribution at the injection nozzles at each port could be maintained with a deviation below 10%. To achieve this requirement, a nose-only exposure chamber flow field was simulated using a numerical analysis method, i.e. computational fluid dynamics (CFD) code FLUENT 6.3.26. Based on the simulation results, a test chamber was built and tested. The flow velocity was measured at the injection nozzle of the chamber and the aerosol particle size distribution was also measured at each port while inserting the test material into the exposure chamber. The results indicated that a uniform flow field distribution at each stage and port, the deviation of the flow velocity, and particle size distribution were all within 10%. Thus, the resulting nose-only exposure chamber could be described as well-designed.     

A simple approach to validation of directed-flow nose-only inhalation chambers

Directed-flow nose-only exposure systems are designed and operated so that the genuine test atmosphere is dynamically delivered to each exposure port and exhaled air from exposed animals is immediately exhausted without the possibility of other animals rebreathing this atmosphere. This technique is particularly useful for preventing uncontrolled changes of exposure atmospheres, stimulating breathing activity due to the rebreathing of exhaled carbon dioxide, and the conserving a test material that is available only in limited quantities. The intricate relationship of the delivered flow of air at each exposure port relative to the respiratory minute volume of the exposed animal appears to be critical for the state-of-the-art performance of directed-flow nose-only exposure systems. This analysis revealed that the determination of carbon dioxide concentrations at different inhalation chamber locations, including exposure ports, is a simple and cost-effective procedure to evaluate whether the rebreathing of atmospheres can be excluded. It has been shown that directed-flow systems need to be operated at an exposure air flow rate greater than 2.5 times the respiratory minute volume of the exposed animal or optimally approximately 0.75 l min(-1) per rat exposure port ( approximately 3.75 times the minute volume of young adult rats) to prevent higher CO(2)-concentrations occurring.     

Characterization of a head-only aerosol exposure system for nonhuman primates

A well-characterized exposure chamber is necessary to generate reproducible atmospheres for inhalation toxicology studies. The aim of the present study was to characterize a head-only exposure chamber for non-human primates. Aerosols containing bovine serum albumin (BSA) were used to characterize a 16-L dynamic airflow head-only exposure chamber. A 250-ml plastic bottle with a respirator attached located inside the chamber was used to simulate a breathing head. Chamber leak rate, mixing, and aerosol spatial distributions were quantified. The chamber concentration profile was measured at the chamber exhaust using an aerodynamic particle sizer. Aerosol spatial distribution was determined by collecting filter samples at several chamber locations. The particle size distribution was determined by collecting cascade impactor samples at several chamber locations. The estimated chamber leak rate was within standards suggested in the literature. The measured average aerosol residence time was similar to theoretical aerosol residence time, suggesting that the chamber was mixing well. Additionally, the average concentration measured at each of the sampling locations within the chamber was similar, and the within-run coefficients of variation (CV) across all sampling locations was similar to those reported in previously published studies, again suggesting that the aerosol concentration throughout the chamber was uniform. The particle size distribution was similar throughout the exposure chamber. Additionally, the BSA concentration and particle size distributions measured in the breathing zone of the simulated head were not significantly different from measurements made elsewhere in the chamber, suggesting that respiration does not affect the average aerosol concentration or particle size distribution at the mouth.     

Depletion of Liver Glutathione Levels in Rats: A Potential Confound of Nose-Only Inhalation

Nose-only inhalation exposure chambers offer key advantages to whole-body systems, particularly when aerosol or mixed aerosol-vapor exposures are used. Specifically, nose-only chambers provide enhanced control over the route of exposure and dose by minimizing the deposition of particles either on the subjects skin/fur or on surfaces of a whole-body exposure system. In the current series of experiments, liver, brain, and lung total glutathione (GSH) levels were assessed following either nose-only or whole-body exposures to either jet fuel or to clean, filtered air. The data were compared to untreated control subjects. Acute nose-only inhalation exposures of rats resulted in a significant depletion of liver GSH levels both in subjects that were exposed to clean, filtered air as well as those exposed to JP-8 jet fuel and to a synthetic jet fuel. Glutathione levels were not altered in lung or brain tissue. Whole-body inhalation exposure had no effect on GSH levels in any tissue for any of the treatment groups. A second experiment demonstrated that the loss of GSH did not occur if rats were anaesthetized prior to and during nose-only exposure to clean, filtered air or to mixed hydrocarbons. These data appear to be consistent with studies demonstrating depletion in liver GSH levels among rats subjected to restraint stress. Finally, the depletion of GSH that was observed in liver following a single acute exposure was reduced following five daily exposures to clean, filtered air, suggesting the possibility of habituation to restraint in the nose-only exposure chamber. The finding that placement in a nose-only exposure chamber per se yields liver GSH depletion raises the possibility of an interaction between this mode of toxicant exposure and the toxicological effects of certain inhaled test substances.     

Depletion of liver glutathione levels in rats: a potential confound of nose-only inhalation

Nose-only inhalation exposure chambers offer key advantages to whole-body systems, particularly when aerosol or mixed aerosol-vapor exposures are used. Specifically, nose-only chambers provide enhanced control over the route of exposure and dose by minimizing the deposition of particles either on the subjects skin/fur or on surfaces of a whole-body exposure system. In the current series of experiments, liver, brain, and lung total glutathione (GSH) levels were assessed following either nose-only or whole-body exposures to either jet fuel or to clean, filtered air. The data were compared to untreated control subjects. Acute nose-only inhalation exposures of rats resulted in a significant depletion of liver GSH levels both in subjects that were exposed to clean, filtered air as well as those exposed to JP-8 jet fuel and to a synthetic jet fuel. Glutathione levels were not altered in lung or brain tissue. Whole-body inhalation exposure had no effect on GSH levels in any tissue for any of the treatment groups. A second experiment demonstrated that the loss of GSH did not occur if rats were anaesthetized prior to and during nose-only exposure to clean, filtered air or to mixed hydrocarbons. These data appear to be consistent with studies demonstrating depletion in liver GSH levels among rats subjected to restraint stress. Finally, the depletion of GSH that was observed in liver following a single acute exposure was reduced following five daily exposures to clean, filtered air, suggesting the possibility of habituation to restraint in the nose-only exposure chamber. The finding that placement in a nose-only exposure chamber per se yields liver GSH depletion raises the possibility of an interaction between this mode of toxicant exposure and the toxicological effects of certain inhaled test substances.     

Characterization of a microprocessor-controlled tubular multiple metered dose inhaler aerosol generator for inhalation exposures of pharmaceuticals.

A microprocessor-controlled tubular multiple metered dose inhaler (MDI) aerosol generator was constructed for the delivery of pharmaceutical aerosols to inhalation chambers. The MDIs were mounted in four cassettes containing one to four MDIs on a stepped end plate. The MDIs in each cassette were pneumatically activated at intervals that were controlled by the microprocessor. The cassettes permitted easy replacement of each set of MDIs with a fresh set of MDIs whenever necessary. Aerosol concentration was controlled by varying the number of active MDIs in each cassette and the frequency of activations per minute of each row. Aerosol from the MDIs flowed along the long axis of the tube, which provided a path length sufficient to diminish impaction losses. Using a light-scattering device to monitor the aerosol concentration, the pulsatile output from the MDIs in the cassettes was demonstrated to be adequately damped out provided that the dilution/mixing/aging chamber exceeded 3 ft in length. The tube diameter selected was the minimum compatible with mounting the required number of MDIs so that the linear velocity of the aerosol was adequate to efficiently transport the aerosol out of the dilution chamber. Aerosol concentration and particle size data were recorded for a nose-only rodent exposure chamber. Reproducible aerosol concentrations ranging from 0.03 to 0.6 mg/L were generated. Particle sizes ranged from 2- to 3-microm mass median aerodynamic diameter. Thus, the aerosol generated was within the size range suitable for inhalation exposures.     

Mosquito coil smoke inhalation toxicity. Part I: validation of test approach and acute inhalation toxicity

Burning mosquito coils indoors to repel mosquitoes is a common practice in many households in tropical countries. The evaluation and assessment of the inhalation toxicity of smoke emitted from mosquito coils appear to be particularly challenging due to the complex nature of this type of exposure atmosphere. The potential health implications of the gases, volatile agents and particulate matter emitted from burning coils or incense have frequently been addressed; however, state-of-the-art inhalation toxicity studies are scarce. The focus of this paper was comparatively to evaluate and assess the appropriateness and practical constraints of the whole-body versus the nose-only mode of exposure for inhalation toxicity studies with burning mosquito coils. With regard to the controlled exposure of laboratory animals to complex smoke atmospheres the nose-only mode of exposure had distinct advantages over the whole-body exposure, which included a rapid attainment of the inhalation chamber steady state, minimization of particle coagulation and uncontrolled adsorption of condensate onto the chamber surfaces. While in whole-body chambers a different kinetic behaviour of volatile and particulate constituents was found which caused inhomogeneous, i.e. artificially enriched atmospheres with volatile components at the expense of aerosols, the nose-only mode of exposure provided maximum exposure intensities without losses of the particulate phase of the exposure atmosphere. Collectively, the results obtained support the conclusion that the dynamic nose-only mode of exposure is experimentally superior to the quasistatic whole-body exposure mode which provides the least control over exposure atmospheres and the outcome highly contingent on selected experimental factors. Acute inhalation toxicity studies in rats suggest that the most critical metrics of exposure are apparently related to (semi)volatile upper respiratory tract sensory irritants, whilst the asphyxic component, carbon monoxide, plays a role only at overtly irritant exposure levels. However, this study was conducted at exposure concentrations much higher than encountered by people in residential settings and the effects observed under these conditions may not be relevant to hazards from exposures at common use levels. Neither an acute 8 h exposure of rats nor the 1 h sensory irritation study in mice and rats provided experimental evidence that irritant particle-related effects had occurred in the lower respiratory tract. In summary, the protocols devised evaluate and assess the acute inhalation toxicity of mosquito coil smoke demonstrating that the nose-only mode of exposure of rats to the smoke of mosquito coils is suitable to assess the toxic potency of different coils. The nose-only mode has clear advantages over the whole-body exposure mode. The inhalation studies conducted show unequivocally that acute toxic effects are difficult to produce with this type of product even under rigorous testing conditions.     

Impact of Inhalation Exposure Modality and Particle Size on the Respiratory Deposition of Ricin in BALB/c Mice

Ricin is a toxic lectin derived from the seed of Ricinus communis (castor plant). It is lethal in small quantities when disseminated as an aerosol. We determined the impact of using two types of exposure chambers and different particle sizes on the deposition of ricin aerosols in mice. Initially, two types of inhalation exposure chambers (whole-body [WB] or nose-only [NO]) were compared using the same size aerosol (1 µm) to determine the potential impact upon respiratory deposition and presented dose. We then assessed the role of particle size on deposition by using aerosols with two distinctly sized particle distributions. Selected organs were collected at four time points after exposure and were analyzed by quantitative enyzme-linked immunosorbent assay (ELISA) and epifluorescence microscopy. Results of the exposure chamber comparison, using 1-µm particles only, indicated approximately 50% of the total ricin in the 4 organs was detected in the lung tissue 1 h after exposure. The trachea and nasopharyngeal region of the animals exposed using the WB chamber contained significantly more ricin than those of animals exposed in the NO chamber. Histopathology indicated an accumulation of ricin in both the tracheobronchial and pulmonary regions with pronounced bronchiolar degradation 48 h postexposure. When particles larger than 3 µm were used, results indicated a considerable amount of ricin initially detected in the trachea, although this finding was discounted due to the heterodispersity of the particles generated. Interestingly, no animals died as a result of exposure to the equivalent of 4 LD50s (as determined using a 1-µm particle) when exposed to the larger size distribution of particles. This result indicates a differential lethality that is contingent upon aerosol size.     

Impact of inhalation exposure modality and particle size on the respiratory deposition of ricin in BALB/c mice

Ricin is a toxic lectin derived from the seed of Ricinus communis (castor plant). It is lethal in small quantities when disseminated as an aerosol. We determined the impact of using two types of exposure chambers and different particle sizes on the deposition of ricin aerosols in mice. Initially, two types of inhalation exposure chambers (whole-body [WB] or nose-only [NO]) were compared using the same size aerosol (1 micro m) to determine the potential impact upon respiratory deposition and presented dose. We then assessed the role of particle size on deposition by using aerosols with two distinctly sized particle distributions. Selected organs were collected at four time points after exposure and were analyzed by quantitative enyzme-linked immunosorbent assay (ELISA) and epifluorescence microscopy. Results of the exposure chamber comparison, using 1- micro m particles only, indicated approximately 50% of the total ricin in the 4 organs was detected in the lung tissue 1 h after exposure. The trachea and nasopharyngeal region of the animals exposed using the WB chamber contained significantly more ricin than those of animals exposed in the NO chamber. Histopathology indicated an accumulation of ricin in both the tracheobronchial and pulmonary regions with pronounced bronchiolar degradation 48 h postexposure. When particles larger than 3 micro m were used, results indicated a considerable amount of ricin initially detected in the trachea, although this finding was discounted due to the heterodispersity of the particles generated. Interestingly, no animals died as a result of exposure to the equivalent of 4 LD50s (as determined using a 1- micro m particle) when exposed to the larger size distribution of particles. This result indicates a differential lethality that is contingent upon aerosol size.     

A computer-controlled whole-body inhalation exposure system for the oil dispersant COREXIT EC9500A

An automated whole-body inhalation exposure system capable of exposing 12 individually housed rats was designed to examine the potential adverse health effects of the oil dispersant COREXIT EC9500A, used extensively during the Deepwater Horizon oil spill. A computer-controlled syringe pump injected the COREXIT EC9500A into an atomizer where droplets and vapor were formed and mixed with diluent air. The aerosolized COREXIT EC9500A was passed into a customized exposure chamber where a calibrated light-scattering instrument estimated the real-time particle mass concentration of the aerosol in the chamber. Software feedback loops controlled the chamber aerosol concentration and pressure throughout each exposure. The particle size distribution of the dispersant aerosol was measured and shown to have a count median aerodynamic diameter of 285 nm with a geometric standard deviation of 1.7. The total chamber concentration (particulate + vapor) was determined using a modification of the acidified methylene blue spectrophotometric assay for anionic surfactants. Tests were conducted to show the effectiveness of closed loop control of chamber concentration and to verify chamber concentration homogeneity. Five automated 5-h animal exposures were performed that produced controlled and consistent COREXIT EC9500A concentrations (27.1 ± 2.9 mg/m(3), mean ± SD).     

Comparison of delivery characteristics from a combination metered-dose inhaler using the Andersen cascade impactor and the next generation pharmaceutical impactor

The purpose of this research was to compare two cascade impaction devices for the aerodynamic particle size assessment of a combination metered-dose inhaler (MDI) product, Combivent. Particle size analysis was performed using an Anderson Mark II cascade impactor (ACI) and a Next Generation Pharmaceutical Impactor (NGI), both fitted with a preseparator and either a 1 L glass chamber or USP throat, and operated at various flow rates. Particle size distributions (PSDs) and dose delivery profiles were assessed by means of the mass median aerodynamic diameter (MMAD), geometric standard deviation (GSD), fine particle fraction <5 micron aerodynamic diameter (FPF(<5 microm)), and induction port deposition fraction (IPF). Under their normal operating conditions, the ACI (28.3 L/min) and the NGI (30 L/min) yield similar PSDs and dose delivery profiles. However, this equivalent performance for the ACI and the NGI no longer exists at a higher flow rate of 60 L/min. Furthermore, changes in PSD results may also be obtained between different operators and/or when different induction port designs were employed. Thus, it is strongly recommended that special care be taken to eliminate variation in experimental parameters and/or selection of ancillary devices such as the preseparator, induction port or throat, to insure good repeatability and reproducibility when testing inhalation drugs.     

A LOW-SAMPLE-CONSUMPTION DRY-PARTICULATE AEROSOL GENERATOR FOR USE IN NOSE-ONLY INHALATION EXPOSURES

Generation of stable, low concentrations of dry particulates in nose-only chambers can be difficult, and if the supply of particulate is limited, the problems can be greatly increased. One problem is that many dry-particulate aerosol generators have higher aerosol output or airflow than can be accommodated by a nose-only inhalation chamber, requiring much of the aerosol generated to be diverted to waste. Another problem is that mixing vessels used to modulate the fluctuating output from aerosol generators can cause substantial wall losses, consuming much of the aerosol generated. To overcome these problems, a low-consumption dry-particulate aerosol generator was designed to deliver stable concentrations in the range of 1-50 mg/m 3 to a nose-only chamber without the need for diverting any of the generator output. The generator air flow of 10-15 L/min supplies all the air to the exposure chamber, with a 6-h exposure at 10-15 mg/m 3 consuming as little as 200-300 mg of particulate. The generator uses the principle of a carpenter's chalk line to pick up particles from a small reservoir, carry them out through an orifice, and past an air jet, where the particles are blown off the string.     

Computerized equipment for the delivery of inhaled doses of solid particles in specific bronchial challenge.

An apparatus to generate solid particles was tested for use in diagnosing occupational asthma. This equipment measures the inhaled dose of dry particles during specific inhalation challenge. It includes an aerosol generator, a cyclone type particle size selector, and an inhalation chamber to which a patient breathing at tidal volume can be connected for the test. It is fully controlled by a standard personal computer in automatic mode, acting on the flow rate and the aerosol generator to maintain the concentration at a fixed value, usually 3 mg/m3. The dose of aerosol delivered to the patient was calculated from the aerosol concentration, and the inhaled volume was calculated by integration of the corresponding signals. The coefficient of variation for this measurement was estimated to be 12%. The mass median aerodynamic diameter (MMAD) of aerosol inside the inhalation chamber was measured for three substances: lactose, wheat flour, and buckwheat flour. The MMAD of the aerosol inside the chamber was also estimated from the particle size distribution of the raw powder. The relative difference between the measured MMAD and the calculated value was less than 15%. The corresponding relative difference between the measured geometrical SD and the calculated value was found to be less than 26%.     

Development of a Mouse Whole-Body Exposure System from a Directed-Flow,Rat Nose-Only System

Abstract

In many inhalation exposure experiments, such as pharmacokinetic studies in unrestrained pregnant animals, it is desirable to expose unrestrained animals and to remove animals from the exposure system at intermediate time points. A two-tiered, 32-port, directed-flow, nose-only exposure system was modified with extended 0.635-mm stainless steel inlet tubes to create a whole-body, modified nose-only (WB-MNO) exposure system. Individual pregnant CD-1 mice held within a rat nose-only tube were exposed to a well-mixed methanol (MeOH) atmosphere. The volume of an individual mouse (～30 ml) constituted approximately 5% of the 600-ml tube volume. Maternal MeOH pharmacokinetics were obtained on gestational day 8 following 6-h WB-MNO MeOH exposures at either 10,000 or 15,000 ppm. Results from these WB-MNO exposures were compared with a 6-h, 15,000 ppm MeOH exposure using a Hinners-type 1-m³ whole-body inhalation chamber (WB-H). The WB-MNO exposure atmosphere was produced using a wick generator heated to 29-35°C and a fluid-metering pump. The vapor was mixed with the total air supply (12-15 Umin). Atmospheric MeOH concentrations (mean ± SEM) achieved were 10,224 ± 35 and 15,210 ± 39 ppm for the WB-MNO and 14,980 ± 70 ppm for the WB-H exposures. End-of-exposure maternal plasma MeOH concentrations were 65 ± 25 (10,000 ppm, WB-MNO), 223 ± 23 (15,000 ppm, WB-MNO), and 194 ± 13 mM (15,000 ppm, WB-H). These findings suggest that the WB-MNO system results in maternal MeOH pharmacokinetics that are similar to those observed using more conventional WB-H exposure systems. The WB-MNO should lend itself to numerous additional applications for pharmacokinetic and toxicity studies.     

Computer controlled multi-walled carbon nanotube inhalation exposure system

Inhalation exposure systems are necessary tools for determining the dose–response relationship of inhaled toxicants under a variety of exposure conditions. The objective of this project was to develop an automated computer controlled system to expose small laboratory animals to precise concentrations of airborne multi-walled carbon nanotubes (MWCNT). An aerosol generator was developed which was capable of suspending a respirable fraction of multi-walled carbon nanotubes from bulk material. The output of the generator was used to expose small laboratory animals to constant aerosol concentrations up to 12?mg/m³. Particle distribution and morphology of the MWCNT aerosol delivered to the exposure chamber were measured and compared to samples previously taken from air inside a facility that produces MWCNT. The comparison showed the MWCNT generator was producing particles similar in size and shape to those found in a work environment. The inhalation exposure system combined air flow controllers, particle monitors, data acquisition devices, and custom software with automatic feedback control to achieve constant and repeatable exposure chamber temperature, relative humidity, pressure, aerosol concentration, and particle size distribution. The automatic control algorithm was capable of maintaining the mean aerosol concentration to within 0.1?mg/m³ of the selected target value, and it could reach 95% of the target value in less than 10?minutes during the start-up of an inhalation exposure. One of the major advantages of this system was that once the exposure parameters were selected, a minimum amount of operator intervention was required over the exposure period.     

Effects of Subchronic Exposures to Concentrated Ambient Particles (CAPs) in Mice: II. The Design of a CAPs Exposure System for Biometric Telemetry Monitoring

Abstract

We modified, assembled, tested, and validated the versatile aerosol concentration enrichment system (VACES) developed by for use in a subchronic experiment that involved exposures of mice in vivo and of respiratory epithelial cells in vitro to concentrated ambient particles (CAPs). Since the labor-intensive nose-only exposure regimen is not an option in a long-term experiment, a whole-body exposure mouse chamber was designed specifically for use with the VACES. The exposure system consists of a stainless-steel (SS) tub with 32 cubicles (1 mouse per cubicle) separated by perforated SS sheets. The tops of these cubicles are covered with perforated plastic sheets to allow telemetry monitoring during the exposure. In each exposure chamber, perforated aluminum tubes are used to distribute CAPs evenly (within 2% difference) throughout the exposure chamber. The exhaust consists of perforated aluminum tubes covered with a urine shield. The modification to the original design of the VACES facilitated the operation of the system in a subchronic study. Mass flow controllers maintain a constant flow rate into the exposure chambers. For a sham control exposure, the identical system is used, except that a HEPA filter at the inlet to the VACES removes 98% of ambient particles. The entire system allows for simultaneous exposure of 64 mice to CAPs, with an equal number of sham-exposed mice as controls. Telemetry receivers have been modified so that 16 mice per group with electrocardiograph (EKG) transmitters can be monitored during exposure. Furthermore, a BioSampler is used to collect CAPs (one sample per day) for the in vitro exposures. In this article, the assessments of flow and particle distribution of the exposure chamber as well as the performance of the system during the subchronic exposure experiment are described.     

Effects of subchronic exposures to concentrated ambient particles (CAPs) in mice. II. The design of a CAPs exposure system for biometric telemetry monitoring

We modified, assembled, tested, and validated the versatile aerosol concentration enrichment system (VACES) developed by Sioutas et al. (1999) for use in a subchronic experiment that involved exposure of mice in vivo and of respiratory epithelial cells in vitro to concentrated ambient particles (CAPs). Since the labor-intensive nose-only exposure regimen is not an option in a long-term experiment, a whole-body exposure mouse chamber was designed specifically for use with the VACES. The exposure system concsists of a stainless-steel (SS) tub with 32 cubicles (1 mouse per cubicle) separated by perforated SS sheets. The tops of these cubicles are covered with perforated plastic sheets to allow telemetry monitoring during the exposure. In each exposure chamber, perforated aluminum tubes are used to distribute CAPs evenly (within 2% difference) throughout the exposure chamber. The exhaust consists of perforated aluminum tubes covered with a urine shield. The modification to the original design of the VACES facilitated the operation of the system in a subchronic study. Mass flow controllers maintain a constant flow rate into the exposure chambers. For a sham control exposure, the identical system is used, except that a HEPA filter at the inlet to the VACES removes 98% of ambient particles. The entire system allow for simultaneous exposure of 64 mice to CAPs, with an equal number of sham-expose mice as controls. Telemetry receives have been modified so that 16 mice per group with electrocardiograph (EKG) transmitters can be monitored during exposure. Furthermore, a BioSampler is used to collect CAPs (one sample per day) for the in vitro exposures. In this article, the assessments of flow and particle distribution of the exposure chamber as well as the performance of the system during the subchronic exposure experiment are described.     

Evaluation of nose-only aerosol inhalation chamber and comparison of experimental results with mathematical simulation of aerosol deposition in mouse lungs

In vivo small rodent efficacy testing of new synthetic and biological molecules for the pulmonary route requires an efficient delivery device. For this purpose, a nose-only inhalation chamber was used to deliver aerosolized aqueous compounds to the respiratory tract of mice. The aim of the study was to determine the efficiency of dose delivery and deposition in the lungs of the mice using this chamber. A secondary goal was to compare the experimental lung deposition results with values predicted from mathematical simulation. Experimental tests were conducted by generating aerosols of a radiolabeled formulation of human serum albumin (HSA) with a mass median aerodynamic diameter (MMAD) of 3.9 +/- 0.5 microm and a geometric standard deviation (GSD) of 1.43 +/- 0.05 using PARI LC STAR jet nebulizers. Based on the total activity placed in the nebulizer, the chamber delivered 0.108 +/- 0.027% to the mice and 0.0087 +/- 0.0021% to the lungs of the mice. In vivo lung deposition was found to be 8.19 +/- 3.56% of total activity deposited in the mouse. Mathematical simulation predictions ranged between 5.89 and 4.40% for various breathing patterns, and did not differ significantly from the in vivo results (p > 0.10). These results provide important quantitative information relevant to aerosol delivery experiments in mouse models. Our results also suggest that the nose-only inhalation chamber would benefit from significant changes to increase the efficiency of deposition in mice such that it can be used for nebulization of expensive therapeutic drugs.     

A new method for long-term inhalation toxicity studies for bronchospasmolytic aerosol formulations in dogs

In routine inhalation toxicity studies laboratory animals are exposed under dynamic exposure conditions to different steady-state concentrations of a test compound. The relevant exposure concentration is the analytically determined time-weighted average concentration in the vicinity of the breathing zone of the animals. If the intended use of a bronchospasmolytic aerosol is taken into account, a non-steady-state exposure regimen might be more appropriate. Using this approach local effects of high aerosol concentrations on the respiratory tract were investigated in dogs by daily head/nose-only exposure for 1 h for 4 weeks. Four groups of four dogs were exposed to 20, 40 and 80 bursts of a bronchodilator formulation using a modified metered dose inhaler. The analytically determined mean concentration of the active ingredient (prostaglandin) in the breathing zone was 43.1, 92.2 and 193.9 micrograms l-1 air, respectively. Maximum concentrations were determined by simulation. The aerosol was in the respirable range (mass median aerodynamic diameter approximately 1.2 microns, geometric standard deviation approximately 1.4). A kinetic model was developed to simulate the mean and maximum non-steady-state concentration for an exposure regimen of 20, 40 and 80 bursts per hour under dynamic exposure conditions. The model was based on first-order inhalation chamber kinetics. The kinetic model was validated experimentally by comparing measured mean and simulated mean concentrations. In all exposure groups the simulated maximum concentrations were ca. 80 mg of test compound (formulation) per litre of air. Plasma levels were elevated in a dose-dependent manner as evidence of the validity of the test model employed.     

A head-only exposure system for controlled exposures of small rodents

We have designed a low-cost, compact, head-only exposure system which is easy to use and allows exposure of up to 8 or 16 small rodents depending on the chamber used with the system. Animals are exposed without anesthesia or extreme restraint. Deflection tubes at the chamber inlet and outlet serve to provide turbulent flow within the chamber. Performance of the exposure system was evaluated by analyzing data which was collected during investigations of the kinetics of respirable nickel chloride (NiCl2) and cobalt chloride (CoCl2) aerosols in Sprague-Dawley rats. Acute 2 h exposure to NiCl2 at concentrations ranging from 129 to 1208 micrograms Ni/m3 (MMAD 0.7-0.9 micron, sigma g 1.2-1.5) had a mean run-to-run coefficient of variation (cv) in chamber concentration of 11.6%, and a mean within-run cv of 8.5%. A 26-day repeated exposure of 3 groups of rats to 18.4 micrograms Ni/m3 gave a mean run-to-run cv of 20.9%, mean within-run cv of 10.2%, and within-day cv of 14.5%. Acute exposure studies with CoCl2 at concentrations ranging from 298 to 1371 micrograms Co/m3 (MMAD 0.9, sigma g 1.4) produced a mean run-to-run cv of 8.4% and a mean within-run cv of 7.8%. The repeated exposure of 2 groups of rats for 5 days to CoCl2 at a concentration of 583 micrograms Co/m3 had a mean run-to-run cv of 10.1%, a within-run cv of 7.4% and a within-day cv of 6.8%. The distribution of aerosol within the chamber is shown to have been uniform, and chamber performance was linear over the range tested. This system provides an inexpensive and uniform means of conducting inhalation exposure studies with selected airborne contaminants that might represent a potential health hazard.