In Vitro Dissolution of Uniform Cobalt Oxide Particles by Human and Canine Alveolar Macrophages

Abstract

Intracellular dissolution of inhaled particles is an important pathway of clearance of potentially toxic materials. To study this process, monolayers of human and canine alveolar macrophages (AM) were maintained alive and functional in vitro for more than 2 wk. Complete phagocytosis of moderately soluble, monodisperse 57Co3O4 test particles of four different sizes was obtained by optimizing the cell density of the monolayer and the particle-to-cell ratio. The fraction of the initial particle mass that was soluble increased over time when the particles were ingested by AM but remained constant when in culture medium alone. Smaller particle sizes had a faster characteristic intracellular dissolution rate constant than did larger particles. The dissolution rates differed between AM obtained from two human volunteers as compared to those obtained from six mongrel dogs. These in vitro dissolution rates were very similar to in vivo translocation rates previously obtained from human and canine lung clearance studies after inhalation of the same or similar monodisperse, homogeneous 57Co3O4 test particles. We believe an important clearance mechanism for inhaled aerosol particles deposited in the lungs can be simulated in vitro in a cell culture system.

Intracellular Particle Dissolution in Alveolar Macrophages

“…In a more quantitative approach, the intracellular dissolution rates of monodisperse, porous Co304 particles with different specific surface areas were determined in cultured AM from man and dogs (48)(49)(50)(51) and in AM of man, rats, and baboons (52) using slightly different methods. In the latter study, 260-mL culture flasks were used to culture all the AM together, and in the former study, the cells were incubated in 96-well cell culture plates, which allowed additional cell function tests in separate wells to be conducted during the entire incubation time.…”

“…various time points during 2 weeks ofincubation (50). Because the integrity and function of the cultured AM is another essential condition for this assay during the 2 weeks ofincubation, cell viability and phagocytic function were monitored at each sampling time to discard results from malfunctioning cell cultures.…”

“…range of 5 (45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60), it is plausible to conclude that the intracellular mechanism of particle dissolution is controlled by these two parameters. However, at this moment we cannot exclude other mechanisms of IPD resulting from proteolytic enzymes, oxygen radicals, chelators, precipitators, etc., that are contained in the phagolysosomal plasma (20).…”

In Vitro Assessment of Biopersistence Using Mammalian Cell Systems

“…These studies emphasize the difference between the phagosome compartment of macrophages and epithelial cells, in particular their pH. Certain in vitro studies (45,46) have shown a good correlation with in vivo studies. However, in one study, using an acellular dissolution system (45) Certain factors have to be considered for the development of in vitro cell systemsthe particle dimensions, the nature of culture media, and the cell viability.…”

Mechanisms, measurement, and significance of lung macrophage function.

“…Particles are not only ingested but undergo gradual dissolution within the phagolysosomes of macrophages (1). The …”