Per Gerde

A model for the uptake of inhaled vapors in the nose of the dog during cyclic breathing.

A model was developed to simulate the uptake of inhaled vapors in the nasal airway of the Beagle dog during cyclic breathing. Input data to the model were morphological and physiological data for the dog, and physiocochemical data for the vapors. The model simulates the nasal airway as a slit-like duct, where air passes between the two airway walls in an ideal plug flow. The thickness of the walls corresponds to the distance between the air interface and the average position where vapor molecules are removed into the capillary blood. All resistance to radial mass transfer is assumed to arise on the liquid side in the diffusion of vapors through the air/blood tissue barrier and in transport by the blood. The model results agreed reasonably well with experimental data. The nasal absorption of vapors on inhalation increased from 1% for a compound with a blood/air partition coefficient of 1 to around 95% uptake for a compound with a partition coefficient of 2000. Desorption from the nasal tissues on exhalation increased from approximately 1% to approximately 30% over the same range of partition coefficients. The nasal uptake over one complete breathing cycle, defined as absorption on inhalation minus desorption on exhalation, was almost zero for low partition coefficient compounds and plateaued at around 65% for high partition coefficient compounds. The model indicates that diffusional resistance and inertia of the nasal tissues result in temporary storage of absorbed vapors upon inhalation, followed by desorption of vapors back into the airstream upon exhalation. An important consequence of this phenomenon is a shift in exposure to inhaled vapors from the lungs to the nasal airway during cyclic flow compared with predictions from experiments and models based on unidirectional flow.

Solution-engineered palladium nanoparticles: model for health effect studies of automotive particulate pollution.

Palladium (Pd) nanoparticles are recognized as components of airborne automotive pollution produced by abrasion of catalyst materials in the car exhaust system. Here we produced dispersions of hydrophilic spherical Pd nanoparticles (Pd-NP) of uniform shape and size (10.4 ± 2.7 nm) in one step by Bradleys reaction (solvothermal decomposition in an alcohol or ketone solvent) as a model particle for experimental studies of the Pd particles in air pollution. The same approach provided mixtures of Pd-NP and nanoparticles of non-redox-active metal oxides, such as Al(2)O(3). Particle aggregation in applied media was studied by DLS and nanoparticle tracking analysis. The putative health effects of the produced Pd nanoparticles and nanocomposite mixtures were evaluated in vitro, using human primary bronchial epithelial cells (PBEC) and a human alveolar carcinoma cell line (A549). Viability of these cells was tracked by vital dye exclusion, and apoptosis was also assessed. In addition, we monitored the release of IL-8 and PGE(2) in response to noncytotoxic doses of the nanoparticles. Our studies demonstrate cellular uptake of Pd nanoparticles only in PBEC, as determined by TEM, with pronounced and dose-dependent effects on cellular secretion of soluble biomarkers in both cell types and a decreased responsiveness of human epithelial cells to the pro-inflammatory cytokine TNF-α. When cells were incubated with higher doses of the Pd nanoparticles, apoptosis induction and caspase activation were apparent in PBEC but not in A549 cells. These studies demonstrate the feasibility of using engineered Pd nanoparticles to assess the health effects of airborne automotive pollution.

SITES FOR UPTAKE OF INHALED VAPORS IN BEAGLE DOGS

The site of uptake of inhaled vapors profoundly influences which respiratory tract tissues receive the highest doses. How the site of uptake depends on the physicochemical properties of inhaled vapors has been the subject of experiment and speculation for decades, but remains undefined. Using techniques that distinguish between vapor uptake in the nose and lung during cyclic breathing by Beagle dogs, we examined uptake of the vapors of 2,4-dimethypentane (DMP), propyl ether, butanone, dioxolane, and ethanol. These compounds have blood/air partition coefficients ranging from 1 to 2000. The effect of altering respiratory rates on vapor uptake was examined for DMP and dioxolane vapors. Deposition of vapors in the nasal cavity during inhalation was highly dependent on the partition coefficient. Vapor deposited in the nasal mucosa during inhalation was desorbed to a substantial extent during exhalation. Lung uptake of total inhaled vapor was limited by the amount available after passage through the nose, but in no case did it exceed 50% of the available amount. The data suggest that the diffusion of vapor molecules through the tissue barrier separating the air/tissue interface from the tissue/blood interface constitutes a significant resistance for both nasal uptake and lung uptake of many inhaled vapors. The data were used to validate a mathematical model describing nasal uptake of vapors. The model is described in the companion paper.

A novel method to aerosolize powder for short inhalation exposures at high concentrations: isolated rat lungs exposed to respirable diesel soot.

More efficient methods are needed to aerosolize dry powders for short-duration inhalation exposures at high concentrations. There is an increasing need to reach the peripheral lung with dry powder medications as well as with collected ambient aerosol particulates in environmental research projects. In a novel aerosol generator, a fixed volume of compressed air was used to create a short burst of a highly concentrated aerosol in a 300-ml holding chamber. Collected diesel soot was deagglomerated to a fine aerosol with a mass median aerodynamic diameter (MMAD) of 0.55 μm, not much larger than the 0.25 μm MMAD of diesel exhaust particles measured in air. A fine powder such as 3-μm silica particles was completely deagglomerated to an aerosol with a MMAD of 3.5 μm. Immediately after generation, the aerosol was available for exposure at a chosen flow rate by the use of an automated valve system. Tritium-labeled diesel soot was thus used to expose the isolated perfused rat lung at an air concentration of ∼3 mg/L and a flow rate of 370 ml/min in a 1-min-long exposure. The lungs were ventilated at 75 breaths/min and a tidal volume of 1.13 ± 0.11 ml (SD, n = 3). Results showed that 19.8 ± 1.1 μg (SD, n = 3) soot was deposited in the lungs. This amount constitutes 9.5% of the amount inhaled and is close to literature data on deposition of similar sized particles in the rat lung. More than 97% of the deposited soot was located distal to the extrapulmonary bronchi, indicating that the system delivers a highly respirable aerosol. The aerosol system is particularly useful for peripheral lung delivery of collected ambient aerosols or dry powder pharmaceuticals following a minimal effort in formulation of the powder.

Toxicity of lunar dust

The formation, composition and physical properties of lunar dust are incompletely characterised with regard to human health. While the physical and chemical determinants of dust toxicity for materials such as asbestos, quartz, volcanic ashes and urban particulate matter have been the focus of substantial research efforts, lunar dust properties, and therefore lunar dust toxicity may differ substantially. In this contribution, past and ongoing work on dust toxicity is reviewed, and major knowledge gaps that prevent an accurate assessment of lunar dust toxicity are identified. Finally, a range of studies using ground-based, low-gravity, and in situ measurements is recommended to address the identified knowledge gaps. Because none of the curated lunar samples exist in a pristine state that preserves the surface reactive chemical aspects thought to be present on the lunar surface, studies using this material carry with them considerable uncertainty in terms of fidelity. As a consequence, in situ data on lunar dust properties will be required to provide ground truth for ground-based studies quantifying the toxicity of dust exposure and the associated health risks during future manned lunar missions.

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.

Dry powder inhalation exposures of the endotracheally intubated rat lung, ex vivo and in vivo: the pulmonary pharmacokinetics of fluticasone furoate.

BACKGROUND The isolated perfused rat lung (IPL) is a suitable model for studying lung-specific pharmacokinetics (PK) of inhaled drugs. So far, little has been known, however, whether the PK measured in the ex vivo organ corresponds to the PK measured in similarly exposed animals in vivo, in particular the endotracheally intubated rat (EIR). The purpose of the current research was to compare the PK of inhaled corticosteroid fluticasone furoate (FF) in the IPL and the EIR. METHOD Aerosols of FF with mass median aerodynamic diameters ranging from 2.2 to 3.2 μm were generated with the DustGun aerosol generator. The IPL, perfused in the single-pass mode, was exposed via inhalation to 5.6 and 46 μg of FF. Following inhalation, the perfusate was repeatedly sampled for 100 min, after which the lungs were recovered for quantitation of remaining FF. Two groups of EIR were also exposed via inhalation to 7 μg of FF. One group was immediately euthanized for determination of the initial deposition of FF in the lungs. From the second group, four venous blood samples were drawn up to 4 hr after exposure. The animals were then sacrificed for determination of FF remaining in the lungs. RESULTS Following inhalation, FF was slowly disappearing from both the IPL and the lungs of the EIR, with a half-life of pulmonary retention of 4.3-4.9 hr for all three exposure series. For the low exposure levels, the concentration curve of FF in the IPL perfusate was similar in shape to that in venous blood of the EIR, with a Cmax of 1.0 and 0.8 nM for the IPL and the EIR, respectively. CONCLUSIONS The results indicate that the IPL and the EIR, when used jointly in PK studies, can provide a detailed characterization of inhaled drugs or toxicants.

How do we compare dose to cells in vitro with dose to live animals and humans? Some experiences with inhaled substances.

The inhalation route provides closer contact between the ambient environment and living cells than the other major routes-of-entry to the body. In addition, the ambient air transporting exogenous agents to the close proximity of living cells can maintain the reactivity of such agents until they deposit in the extracellular lining layer of the lungs at micrometer distances from the airway epithelium. While toxicity may often occur following the systemic distribution of exogenous substances via the respiratory tract, it is the situation when toxicity occurs at the airway portal-of-entry that pose a particular challenge in the mapping of the dosimetry. In such case, the volume of distribution of solutes before they may enter the airway cells is very small. Therefore exposures of the airway epithelium are more variable and can be much higher than exposures of viable cells of the skin or the gastro-intestinal tract at similar concentrations in the ambient environment. Especially with aerosol exposures, local concentrations around deposited particles can be exceedingly high. To simulate these exposures in a cell culture is a difficult task. However, in order to bridge the in vivo-in vitro gap two methods can be used: (1) Specially designed in vitro systems to better mimic the physiology/morphology of cells residing in the respiratory tract. (2) Mathematical models to analyse the toxicokinetics of the in vitro systems and extrapolate to the corresponding in vivo situation. Both strategies will be exemplified and discussed.

Delivering Horseradish Peroxidase as a Respirable Powder to the Isolated, Perfused, and Ventilated Lung of the Rat: The Pulmonary Disposition of an Inhaled Model Biopharmaceutical

BACKGROUND Our aim was to investigate the potential of the DustGun aerosol technology integrated with the isolated, perfused, and ventilated lung of the rat (IPL) to study the pulmonary disposition of an inhaled model biopharmaceutical, the 40-kDa protein horseradish peroxidase (HRP). METHOD The DustGun aerosol technology was used to deliver respirable powder aerosols of HRP (the mass median aerodynamic diameter: 1.7 μm) as an 80-sec bolus to the IPL perfused in a single-pass mode. Lung perfusate was repeatedly sampled for 125 min after the HRP exposure. The amount of active HRP clearing with the perfusate or being retained in the lung was measured enzymatically. RESULTS AND CONCLUSIONS The total amount of HRP deposited in the lungs was 335 ± 100 μg and 568 ± 47 μg for a low- and high-dose exposure, respectively. After inhalation, the initial appearance of HRP in the perfusate was rapid. However, the total amount of HRP that cleared with the perfusate remained below 0.5% of the deposited dose. The effect of opening the tight junctions between the alveolar epithelial cells on HRP absorption was studied by exposing the IPL to nebulized aerosols of either 0.02, 0.2, or 2% poly-L-Arginine (PLA) (MW 42.5 kDa) in phosphate-buffered saline (PBS) for 5 min, at 40 min after the HRP exposure. Subsequent exposure to 0.02% PLA did not affect HRP absorption. However, exposure to 0.2% PLA increased the absorption rate ninefold, and the total amount of HRP clearing with the perfusate increased to approximately 4% of the deposited dose. No further increase was obtained with 2% PLA, indicating a steep dose-response for the enhancer. It was concluded that the pulmonary absorption of HRP is quite slow, and absorption enhancers affecting tight junctions have a distinctive, yet limited efficiency. The presented inhalation technology can be very useful in studying the pulmonary absorption of biopharmaceuticals.

Vasoconstriction after inhalation of budesonide: a study in the isolated and perfused rat lung.

INTRODUCTION Clinical studies have shown that inhaled corticosteroids can induce rapid vasoconstriction in the airways, leading to decreased mucosal blood flow. The aim of this study was to investigate whether vasoconstriction of the pulmonary circulation after short inhalation of a corticosteroid can be detected in the isolated and perfused rat lung (IPL) - a model which could serve as a substitute or a complement to clinical models. METHODS IPLs were briefly exposed to dry powder aerosol of budesonide. The pulmonary perfusate flow rate was assessed during 100min post-exposure. A reduction in perfusion flow rate was interpreted as vasoconstriction. MAIN RESULTS Vasoconstriction was more pronounced after brief inhalation of 10 and 50microg budesonide than 2microg. The onset of vasoconstriction became statistically significant within 10-40min after inhalation. Co-administration of a selective alpha(1)-adrenoceptor antagonist (prazosin 50nM added to the perfusate) reduced vasoconstriction by approximately 50% during 100min of perfusion (p=0.003). CONCLUSIONS Inhaled budesonide rapidly induces pulmonary vasoconstriction suggesting a nongenomic mechanism probably related to disposition of noradrenaline at the neuro-muscular junction. This ex vivo model could serve as a substitute or a complement to clinical models for investigating rapid effects of glucocorticoid receptor agonists on the pulmonary/bronchial circulation.