Development and application of an improved in vitro model for aerosol toxicology

Abstract

In vitro cellular studies offer an economical and rapid screening tool for assessing aerosol toxicity. Traditional submerged in vitro cell models and exposure techniques are often criticized for their inability to (1) simulate in vivo cellular morphology (2) maintain the chemical and physical characteristics of sampled aerosol and (3) estimate 'delivered' exposure levels. Further, the exposure levels applied in traditional submerged in vitro systems are often orders of magnitude above inhalational exposures that occur in vivo. Improved airway cell culture models and direct air-to-cell exposure systems have been developed over the last few decades; these improvements offer greater 'real-world' significance to in vitro aerosol toxicology. Air-liquid interfaced airway cell cultures offer greater physiological relevance than previous, submerged cell cultures. Further, direct air-to-cell exposure systems offer the ability to (1) better maintain the chemical and physical characteristics of test aerosols and (2) more closely control and approximate exposure levels. Presented here, are two improved direct air-to-cell aerosol exposure systems that rely upon electrostatic deposition or gravitational settling to directly expose well-differentiated airway cell cultures to three different aerosols of interest, with regard to occupational and environmental health. The first and second study presented here used electrostatic deposition to expose well-differentiated normal human bronchial epithelial cells to diesel particulate matter and complete diesel exhaust. Cells were exposed to either (1) diesel particulate matter or (2) complete diesel exhaust from an engine run on either petro- or biodiesel, and with and without a diesel particulate filter. Cellular response was assessed by measuring transcripts associated with inflammation, oxidative stress, aromatic hydrocarbon response and overall cellular dysfunction at 1, 3, 6, 9, and 24 hours after exposure to diesel particulate matter. Cellular response to complete diesel exhaust was assessed by measuring transcripts associated with oxidative stress and aromatic hydrocarbon response at two hours after exposure. The main aims of these two studies were to (1) characterize the time course of the proinflammatory response of normal human bronchial epithelial cells after exposure to diesel particulate matter and (2) screen for the effects of exposure to petro- and biodiesel exhaust, with and without a diesel particulate filter. The third study presented here used gravitational settling to expose well-differentiated human bronchial or nasal epithelial cells to two different particle size fractions from inhalable dust collected at a local dairy parlor. Cellular response was assessed by measuring transcripts associated with inflammation at two hours after exposure. Cell compromise was also measured in all three studies by measuring percent lactate dehydrogenase release. Significant airway cellular responses were observed in all three studies, at levels of exposure far lower than reported in previous traditional in vitro studies. Results from the work presented here strongly support the use of improved airway cell models and direct air-to-cell exposure systems in future in vitro studies in aerosol toxicology.