Increasing Exposure Levels Cause an Abrupt Change in the Absorption and Metabolism of Acutely Inhaled Benzo(a)pyrene in the Isolated, Ventilated, and Perfused Lung of the Rat

Breathing in danger: Unveiling the link between human exposure to outdoor PM2.5-bound polycyclic aromatic hydrocarbons and lung cancer risk in an urban residential area of China

Numerous studies have extensively examined the risk of lung cancer associated with polycyclic aromatic hydrocarbons (PAHs), with particular emphasis on the 16 priority PAHs. However, this may underestimate the actual risk. This study seeks to enhance the current risk assessment framework by integrating four additional parent PAHs such as Dibenzo[a,h]pyrene, Dibenzo[a,l]pyrene, Dibenzo[a,e]pyrene, 7H-benzo[c]fluorene with potentially high risk of causing cancer. By considering their physicochemical properties, metabolism, and bioavailability, the study also examines the relationship between low molecular weight (LMW) - and high molecular weight (HMW)-PAH doses and the risk of developing cancer in the human lungs. The study was conducted in Ningbo, China and identified five PAH sources: natural gas combustion (NGC), vehicular exhaust (VE), coal combustion (CC), biomass burning (BB), and volatilization of unburnt fuel (VUF). This study emphasizes the elevated risk associated with highly carcinogenic PAHs, as they consistently exceed acceptable limits for lung cancer risk throughout the year. Based on the study's estimation, approximately 324 out of every one million individuals exposed to PAHs face an increased cancer risk over their lifetime. This research emphasizes the importance of identifying source specific lung cancer risk in residential areas to protect the exposed population. Moreover, while there is a moderate connection between LMW-PAH doses and lung cancer risk, a strong relationship is observed with HMW-PAHs.

Bioavailability of inhaled or ingested PFOA adsorbed to house dust

Indoor environments may impact human health due to chemical pollutants in the indoor air and house dust. This study aimed at comparing the bioavailability and distribution of PFOA following both an inhalation and an oral exposure to PFOA coated house dust in rats. In addition, extractable organofluorine (EOF) was measured in different tissue samples to assess any potential influence of other organofluorine compounds in the experimental house dust. Blood samples were collected at sequential time points after exposure and at the time of termination; the lungs, liver, and kidney were collected for quantification of PFOA and EOF. The concentration of PFOA in plasma increased rapidly in both exposure groups attaining a C_max at 3 h post exposure. The C_max following inhalation was four times higher compared to oral exposures. At 48 h post exposure, the levels of PFOA in the plasma, liver, and kidney were twice as high from inhalation exposures. This shows that PFOA is readily bioavailable and has a rapid systemic distribution following an inhalation or oral exposure to house dust coated with PFOA. The proportion of PFOA to EOF corresponded to 65-71% and 74-87% in plasma and tissues, respectively. The mass balance between EOF and target PFOA indicates that there might be other unknown PFAS precursor and/or fluorinated compounds that co-existed in the house dust sample that can have accumulated in rats.

A review on analysis methods, source identification, and cancer risk evaluation of atmospheric polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) have gained attention because of their environmental persistence and effects on ecosystems, animals, and human health. They are mutagenic, carcinogenic, and teratogenic. The review provides background knowledge about their sources, metabolism, temporal variations, and size distribution in atmospheric particulate matter. The review article briefly discusses the analytical methods suitable for the extraction, characterization, and quantification of nonpolar and polar PAHs, addressing the challenges. Herein, we discussed the molecular diagnostic ratios (DRs), stable carbon isotopic analysis (SCIA), and receptor models, with much emphasis on the positive matrix factorization (PMF) model, for apportioning PAH sources. Among which, DRs and PCA identified as the most widely employed method, but their accuracy for PAH source identification has received global criticism. Therefore, the review recommends compound-specific isotopic analysis (CSIA) and PMF as the best alternative methods to provide detailed qualitative and quantitative source analysis. The compound-specific isotopic signatures are not affected by environmental degradation and are considered promising for apportioning PAH sources. However, isotopic fractions of co-eluted compounds like polar PAHs and aliphatic hydrocarbons make the PAHs isotopic fractions interpretation difficult. The interference of unresolved complex mixtures is a limitation to the application of CSIA for PAH source apportionment. Hence, for CSIA to further support PAH source apportionment, fast and cost-effective purification techniques with no isotopic fractionation effects are highly desirable. The present review explains the concept of stable carbon isotopic analysis (SCIA) relevant to PAH source analysis, identifying the techniques suitable for sample extract purification. We demonstrate how the source apportioned PAHs can be applied in assessing the health risk of PAHs using the incremental lifetime cancer risk (ILCR) model, and in doing so, we identify the key factors that could undermine the accuracy of the ILCR and research gaps that need further investigation.

Polycyclic Aromatic Hydrocarbon Levels in Wistar Rats Exposed to Ambient Air of Port Harcourt, Nigeria: An Indicator for Tissue Toxicity

This study investigated the PAH levels in Wistar rats exposed to ambient air of the Port Harcourt metropolis. Twenty Wistar rats imported from a nonpolluted city (Enugu) were exposed to both indoor and outdoor air. Following the IACUC regulation, baseline data were obtained from 4 randomly selected rats, while the remaining 16 rats (8 each for indoor and outdoor) were left till day 90. Blood samples were obtained by cardiac puncture, and the PAH levels were determined using Gas Chromatography Flame-Ionization Detector (GC-FID). GraphPad Prism (version 8.0.2) Sidak's (for multiple data set) and unpaired t-tests (for two data sets) were used to evaluate the differences in group means. Seven of the PAHs found in indoor and outdoor rats were absent in baseline rats. The mean concentrations of PAH in indoor and outdoor animals were higher than those of baseline animals, except for Benzo(a)pyrene, which was found in baseline animals but absent in other animal groups. Additionally, Dibenz(a,h)anthracene, Indeno(1,2,3-c,d)pyrene, Pyrene, 2-methyl, and other carcinogenic PAHs were all significantly higher (p < 0.05) in outdoor groups. The vulnerable groups in Port Harcourt are at the greatest risk of such pollution. Therefore, urgent environmental and public health measures are necessary to mitigate the looming danger.

Modifying and Integrating in vitro and ex vivo Respiratory Models for Inhalation Drug Screening

For the past 50 years, the route of inhalation has been utilized to administer therapies to treat a variety of respiratory and pulmonary diseases. When compared with other drug administration routes, inhalation offers a targeted, non-invasive approach to deliver rapid onset of drug action to the lung, minimizing systemic drug exposure and subsequent side effects. However, despite advances in inhaled therapies, there is still a need to improve the preclinical screening and the efficacy of inhaled therapeutics. Innovative in vitro models of respiratory physiology to determine therapeutic efficacy of inhaled compounds have included the use of organoids, micro-engineered lung-on-chip systems and sophisticated bench-top platforms to enable a better understanding of pulmonary mechanisms at the molecular level, rapidly progressing inhaled therapeutic candidates to the clinic. Furthermore, the integration of complementary ex vivo models, such as precision-cut lung slices (PCLS) and isolated perfused lung platforms have further advanced preclinical drug screening approaches by providing in vivo relevance. In this review, we address the challenges and advances of in vitro models and discuss the implementation of ex vivo inhaled drug screening models. Specifically, we address the importance of understanding human in vivo pulmonary mechanisms in assessing strategies of the preclinical screening of drug efficacy, toxicity and delivery of inhaled therapeutics.

Bioaccessibilities of metal(loid)s and organic contaminants in particulates measured in simulated human lung fluids: A critical review

Particle-bound pollutants can pose a health risk to humans. Inhalation exposure evaluated by total contaminant concentrations significantly overestimates the potential risk. To assess the risk more accurately, bioavailability, which is the fraction that enters into the systemic circulation, should be considered. Researchers have replaced bioavailability by bioaccessibility due to the rapid and cost-efficient measurement for the latter, especially for assessment by oral ingestion. However, contaminants in particulates have different behavior when inhaled than when orally ingested. Some of the contaminants are exhaled along with exhalation, and others are deposited in the lung with the particulates. In addition, a fraction of the contaminants is released into the lung fluid and absorbed by the lung, and another fraction enters systemic circulation under the action of cell phagocytosis on particulates. Even if the release fraction, i.e., release bioaccessibility, is considered, the measurement faces many challenges. The present study highlights the factors influencing release bioaccessibility and the incorporation of inhalation bioaccessibility into the risk assessment of inhaled contaminants. Currently, there are three types of extraction techniques for simulated human lung fluids, including simple chemical solutions, sequential extraction techniques, and physiologically based techniques. The last technique generally uses three kinds of solution: Gamble's solution, Hatch's solution, and artificial lysosomal fluid, which are the most widely used physiologically based simulated human lung fluids. External factors such as simulated lung fluid composition, pH, extraction time, and sorption sinks can affect release bioaccessibility, whereas particle size and contaminant properties are important internal factors. Overall, release bioaccessibility is less used than bioaccessibility considering the deposition fraction when assessing the risk of contaminants in inhaled particulates. The release bioaccessibility measurement poses two main challenges: developing a unified, accurate, stable, simple, and systematic biologically based method, and validating the method through in-vivo assays.

Modeling the bioaccessibility of inhaled semivolatile organic compounds in the human respiratory tract

The bioaccessibility of semivolatile organic compounds (SVOCs) via inhalation has rarely been studied, as indicated by the literature. There is no model to calculate the SVOC bioaccessibility following inhalation, and measurement data have focused on only a few polycyclic aromatic hydrocarbons (PAHs) in the particle phase. The present work developed a mechanistic model to address the mass transfer of inhaled SVOCs among the gas, particle and mucus phases in the human respiratory tract. The model considers (1) the SVOC partitioning between the gas and particle phases as well as between the gas and mucus phases and (2) the deposition of gas- and particle-phase SVOCs in the mucus of the respiratory tract. Based on the model, the inhalation bioaccessibility for 72 SVOCs was calculated. The SVOCs were measured in French dwellings at the nationwide scale, and their median concentrations in both the gas and particle phases were used for the bioaccessibility calculations. The results show that the inhalation bioaccessibility varies considerably from one compound to another, e.g., between 0.62 and 1.00 for phthalates, between 0.71 and 0.79 for polybrominated diphenyl ethers (PBDEs), between 0.48 and 0.56 for polychlorinated biphenyls (PCBs), between 0.48 and 1.00 for different chemical families of pesticides and between 0.48 and 0.90 for PAHs.

CAR, a Homing Peptide, Prolongs Pulmonary Preferential Vasodilation by Increasing Pulmonary Retention and Reducing Systemic Absorption of Liposomal Fasudil

Here, we sought to elucidate the role of CAR (a cyclic peptide) in the accumulation and distribution of fasudil, a drug for pulmonary arterial hypertension (PAH), in rat lungs and in producing pulmonary specific vasodilation in PAH rats. As such, we prepared liposomes of fasudil and CAR-conjugated liposomal fasudil and assessed the liposomes for CAR conjugation, physical properties, entrapment efficiencies, in vitro release profiles, and stabilities upon incubation in cell culture media, storage, and aerosolization. We also studied the cellular uptake of fasudil in different formulations, quantified heparan sulfate (HS) in pulmonary arterial smooth muscle cells (PASMCs), and investigated the distribution of the liposomes in the lungs of PAH rats. We assessed the drug accumulation in a close and recirculating isolated perfused rat lung model and studied the pharmacokinetics and pharmacological efficacy of the drug and formulations in Sugen/hypoxia-induced PAH rats. The entrapment efficiency of the liposomal fasudil was 95.5 ± 4.5%, and the cumulative release was 93.95 ± 6.22%. The uptake of CAR liposomes by pulmonary arterial cells and their distribution and accumulation in the lungs were much greater than those of no-CAR-liposomes. CAR-induced increase in the cellular uptake was associated with an increase in HS expression by rat PAH-PASMCs. CAR, when conjugated with liposomal fasudil and given via an intratracheal instillation, extended the elimination half-life of the drug by four-fold compared with fasudil-in-no-CAR-liposomes given via the same route. CAR-conjugated liposomal fasudil, as opposed to fasudil-in-no-CAR-liposomes and CAR pretreatment followed by fasudil-in-no-CAR-liposomes, reduced the mean pulmonary arterial pressure by 40-50% for 6 h, without affecting the mean systemic arterial pressure. On the whole, this study suggests that CAR aids in concentrating the drug in the lungs, increasing the cellular uptake, extending the half-life of fasudil, and eliciting a pulmonary-specific vasodilation when the peptide remains conjugated on the liposomal surface, but not when CAR is given as a pretreatment or alone as an admixture with the drug.

Bioaccessibility and bioavailability of environmental semi-volatile organic compounds via inhalation: A review of methods and models

Semi-volatile organic compounds (SVOCs) present in indoor environments are known to cause adverse health effects through multiple routes of exposure. To assess the aggregate exposure, the bioaccessibility and bioavailability of SVOCs need to be determined. In this review, we discussed measurements of the bioaccessibility and bioavailability of SVOCs after inhalation. Published literature related to this issue is available for 2,3,7,8-tetrachlorodibenzo-p-dioxin and a few polycyclic aromatic hydrocarbons, such as benzo[a]pyrene and phenanthrene. Then, we reviewed common modeling approaches for the characterization of the gas- and particle-phase partitioning of SVOCs during inhalation. The models are based on mass transfer mechanisms as well as the structure of the respiratory system, using common computational techniques, such as computational fluid dynamics. However, the existing models are restricted to special conditions and cannot predict SVOC bioaccessibility and bioavailability in the whole respiratory system. The present review notes two main challenges for the estimation of SVOC bioaccessibility and bioavailability via inhalation in humans. First, in vitro and in vivo methods need to be developed and validated for a wide range of SVOCs. The in vitro methods should be validated with in vivo tests to evaluate human exposures to SVOCs in airborne particles. Second, modeling approaches for SVOCs need to consider the whole respiratory system. Alterations of the respiratory cycle period and human biological variability may be considered in future studies.

Predicting lung dosimetry of inhaled particleborne benzo[a]pyrene using physiologically based pharmacokinetic modeling

Benzo[a]pyrene (BaP) is a by-product of incomplete combustion of fossil fuels and plant/wood products, including tobacco. A physiologically based pharmacokinetic (PBPK) model for BaP for the rat was extended to simulate inhalation exposures to BaP in rats and humans including particle deposition and dissolution of absorbed BaP and renal elimination of 3-hydroxy benzo[a]pyrene (3-OH BaP) in humans. The clearance of particle-associated BaP from lung based on existing data in rats and dogs suggest that the process is bi-phasic. An initial rapid clearance was represented by BaP released from particles followed by a slower first-order clearance that follows particle kinetics. Parameter values for BaP-particle dissociation were estimated using inhalation data from isolated/ventilated/perfused rat lungs and optimized in the extended inhalation model using available rat data. Simulations of acute inhalation exposures in rats identified specific data needs including systemic elimination of BaP metabolites, diffusion-limited transfer rates of BaP from lung tissue to blood and the quantitative role of macrophage-mediated and ciliated clearance mechanisms. The updated BaP model provides very good prediction of the urinary 3-OH BaP concentrations and the relative difference between measured 3-OH BaP in nonsmokers versus smokers. This PBPK model for inhaled BaP is a preliminary tool for quantifying lung BaP dosimetry in rat and humans and was used to prioritize data needs that would provide significant model refinement and robust internal dosimetry capabilities.

Influence of amine-modified poly(vinyl alcohol)s on vibrating-membrane nebulizer performance and lung toxicity

A suitable aerosol droplet size and formulation output rate is essential for the therapy of lung diseases under application of nebulizers. The current study investigated the potential of amine-modified poly(vinyl alcohol)s as excipients for inhalation delivery. A change of conductivity (effective at <0.1mg/ml) and viscosity (effective at >0.1mg/ml) of samples that were supplemented with charge-modified polymers had a significant influence on the generated droplet size (shift from ~8 to ~4 μm) and formulation throughput rate (shift from ~0.2 to ~1.0 g/min), where polymers with a higher amine density (and molecular weight) showed an elevated activity. Biocompatibility assessment of polymers in A549 cells and an isolated lung model resulted in cell lysis and lung edema formation dependent on the type (degree of amine substitution) and dose of polymer applied. Suitable compositions and concentrations of amine-modified poly(vinyl alcohol)s were identified with respect to an optimized nebulizer performance and acceptable biocompatibility. Charge-modified polymers represent novel excipients with potential to improve inhalation therapy.

Polycyclic Aromatic Hydrocarbons: Part I. Exposure

Polycyclic aromatic hydrocarbons (PAH) comprise the largest class of cancer-causing chemicals and are ranked ninth among chemical compounds threatening to humans. Although interest in PAH has been mainly due to their carcinogenic property, many of these compounds are genotoxic, mutagenic, teratogenic, and carcinogenic. They tend to bioaccumulate in the soft tissues of living organisms. Interestingly, many are not directly carcinogenic, but act like synergists. PAH carcinogenicity is related to their ability to bind DNA thereby causing a series of disruptive effects that can result in tumor initiation. Thus, any structural attribute or modification of a PAH molecule that enhances DNA cross linking can cause carcinogenicity. In part I, we review exposure to these dangerous chemicals across a spectrum of use in the community and industry.

In vitro, in vivo and ex vivo models for studying particle deposition and drug absorption of inhaled pharmaceuticals

Delivery of therapeutic agents via the pulmonary route has gained significant attention over the past few decades because this route of administration offers multiple advantages over traditional routes that include localized action, non-invasive nature and favorable lung-to-plasma ratio. However, assessment of post administration behavior of inhaled pharmaceuticals-such as deposition of particles over the respiratory airways, interaction with the respiratory fluid and movement across the air-blood barrier-is challenging because the lung is a very complex organs that is composed of airways with thousands of bifurcations with variable diameters. Thus, much effort has been put forward to develop models that mimic human lungs and allow evaluation of various pharmaceutical and physiological factors that influence the deposition and absorption profiles of inhaled formulations. In this review, we sought to discuss in vitro, in vivo and ex vivo models that have been extensively used to study the behaviors of airborne particles in the lungs and determine the absorption of drugs after pulmonary administration. We have provided a summary of lung cast models, cascade impactors, noninvasive imaging, intact animals, cell culture and isolated perfused lung models as tools to evaluate the distribution and absorption of inhaled particles. We have also outlined the limitations of currently used models and proposed future studies to enhance the reproducibility of these models.

Challenges in inhaled product development and opportunities for open innovation

Dosimetry, safety and the efficacy of drugs in the lungs are critical factors in the development of inhaled medicines. This article considers the challenges in each of these areas with reference to current industry practices for developing inhaled products, and suggests collaborative scientific approaches to address these challenges. The portfolio of molecules requiring delivery by inhalation has expanded rapidly to include novel drugs for lung disease, combination therapies, biopharmaceuticals and candidates for systemic delivery via the lung. For these drugs to be developed as inhaled medicines, a better understanding of their fate in the lungs and how this might be modified is required. Harmonized approaches based on 'best practice' are advocated for dosimetry and safety studies; this would provide coherent data to help product developers and regulatory agencies differentiate new inhaled drug products. To date, there are limited reports describing full temporal relationships between pharmacokinetic (PK) and pharmacodynamic (PD) measurements. A better understanding of pulmonary PK and PK/PD relationships would help mitigate the risk of not engaging successfully or persistently with the drug target as well as identifying the potential for drug accumulation in the lung or excessive systemic exposure. Recommendations are made for (i) better industry-academia-regulatory co-operation, (ii) sharing of pre-competitive data, and (iii) open innovation through collaborative research in key topics such as lung deposition, drug solubility and dissolution in lung fluid, adaptive responses in safety studies, biomarker development and validation, the role of transporters in pulmonary drug disposition, target localisation within the lung and the determinants of local efficacy following inhaled drug administration.

A review and assessment of menthol employed as a cigarette flavoring ingredient

Cigarette smoking is established as a substantial contributor to risks for cancer, cardiovascular and respiratory diseases. Less is known about the potential of cigarette composition to affect smoking risks. The use of cigarette flavoring ingredients such as menthol is currently of worldwide public health and regulatory interest. The unique conditions of menthol inhalation exposure that occur coincident with that of the complex cigarette smoke aerosol require specialized studies to support an assessment of its safety in cigarette flavoring applications. The present state of knowledge is sufficient to support an assessment of the safety of the use of menthol in cigarettes. Scientific, smoking behavioral and epidemiological data available through mid-2009 is critically reviewed and a broad convergence of findings supports a judgment that menthol employed as a cigarette tobacco flavoring ingredient does not meaningfully affect the inherent toxicity of cigarette smoke or the human risks that attend smoking. There remains a need for well-designed studies of the potential of menthol to affect smoking initiation, cessation and addiction in order to differentiate any independent effects of menthol in cigarettes from those imposed by socioeconomic, environmental and peer influences on these complex human behaviors.

Chemical analysis of cigarette smoke particulate generated in the MSB-01 in vitro whole smoke exposure system

Cigarette mainstream smoke (MS) is a dynamic aerosol consisting of a gas-vapor phase and a particulate phase. In recent years, novel in vitro whole smoke exposure systems have been developed to expose cells directly to whole MS. One such system is the Burghart Mimic Smoker-01 (MSB-01). Our previous data using the MSB-01 indicated that a 50 +/- 10% loss of particulate matter occurred prior to MS delivery into the exposure chamber. Additionally, a change in aerosol particle diameter was also measured, suggesting that the chemical composition of MS might be changing within the system. In this study, we have expanded on our previous work and compared the particulate phase chemical composition of undiluted and diluted MS generated by the instrument and that of the MS delivered into the exposure chamber. The average percent delivery of cigarette smoke condensate (CSC) detected for all the measured chemical constituents was 35 +/- 13% for undiluted MS and 23 +/- 8% for 1:1 diluted MS. The data also indicate that under our experimental conditions, incomplete mixing of the freshly generated MS occurs during its dilution by the system. Taken together, the data presented here show that significant chemical changes occur between the generation of MS by the system and its delivery into the exposure chamber. This indicates that due to the dynamic nature of cigarette smoke, it is important to characterize the exposure conditions in order to gain the best insight and accurately correlate exposure with biological endpoints.

Pulmonary drug delivery with aerosolizable nanoparticles in an ex vivo lung model

The use of colloidal carrier systems for pulmonary drug delivery is an emerging field of interest in nanomedicine. The objective of this study was to compare the pulmonary absorption and distribution characteristics of the hydrophilic model drug 5(6)-carboxyfluorescein (CF) after aerosolization as solution or entrapped into nanoparticles in an isolated rabbit lung model (IPL). CF-nanoparticles were prepared from a new class of biocompatible, fast degrading, branched polyesters by a modified solvent displacement method. Physicochemical properties, morphology, encapsulation efficiency, in vitro drug release, stability of nanoparticles to nebulization, aerosol characteristics as well as pulmonary dye absorption and distribution profiles after nebulization in an IPL were investigated. CF-nanoparticles were spherical in shape with a mean particle size of 195.3+/-7.1nm, a polydispersity index of 0.225+/-0.017 and a zeta-potential of -28.3+/-0.3mV. Encapsulation efficiencies of CF were as high as about 60% (drug loading of 3% (w/w)); 90% of the entrapped CF were released during the first 50min in vitro. Nanoparticle characteristics were not significantly affected by the aerosolization process utilizing a vibrating mesh nebulizer. After deposition of equal amounts of CF in the IPL, less CF was detected in the perfusate for CF-nanoparticles (plateau concentration 9.2+/-2.4ng/ml) when compared to CF aerosolized from solution (17.7+/-0.8ng/ml). In conclusion, the data suggest that inhalative delivery of biodegradable nanoparticles may be a viable approach for pulmonary drug delivery. Moreover, a targeting effect to the lung tissue is claimed.

Short inhalation exposures of the isolated and perfused rat lung to respirable dry particle aerosols; the detailed pharmacokinetics of budesonide, formoterol, and terbutaline

There is an increasing interest in using the lung as a route of entry for both local and systemic administration of drugs. However, because adequate technologies have been missing in the preclinical setting, few investigators have addressed the detailed disposition of drugs in the lung following short inhalation exposures to highly concentrated dry powder aerosols. New methods are needed to explore the disposition of drugs after short inhalation exposures, thus mimicking a future clinical use. Our aim was to study the pulmonary disposition of budesonide, formoterol, and terbutaline, which are clinically used for the treatment of bronchial asthma. Using the recently developed DustGun aerosol technology, we exposed by inhalation for approximately 1 min the isolated and perfused rat lung (IPL) to respirable dry particle aerosols of the three drugs at high concentrations. The typical aerosol concentration was 1 mug/mL, and the particle size distribution of the tested substances varied with a MMAD ranging from 2.3 to 5.3 mum. The IPL was perfused in single pass mode and repeated samples of the perfusate were taken for up to 80 min postexposure. The concentration of drug in perfusate and in lung extracts was measured using LC-MS/MS. The deposited dose was determined by adding the amounts of drug collected in perfusate to the amount extracted from the tissues at 80 min. Deposited amounts of budesonide, formoterol fumarate, and terbutaline sulphate were 23 +/- 17, 36 +/- 8, and 60 +/- 3.2 mug (mean +/- SD, n = 3), respectively. Retention in lung tissues at the end of the perfusion period expressed as fraction of deposited dose was 0.19 +/- 0.05, 0.19 +/- 0.06, and 0.04 +/- 0.01 (mean +/- SD, n = 3) for budesonide, formoterol, and terbutaline, respectively. Each short inhalation exposure to the highly concentrated aerosols consumed 1-3 mg powder. Hence, this system can be particularly useful for obtaining a detailed pharmacokinetic characterization of inhaled compounds in drug discovery/development.