Phagosomal pH and Glass Fiber Dissolution in Cultured Nasal Epithelial Cells and Alveolar Macrophages: A Preliminary Study

Abstract

The dissolution rate of glass fibers has been shown to be pH sensitive using in vitro lung fluid simulant models. The current study investigated whether there is a difference in phagosomal pH (ppH) between rat alveolar macrophages (AM) and rat nasal epithelial cells (RNEC) and whether such a difference would influence the dissolution of glass fibers. The ppH was measured in cultured AM and RNEC using flow cytometric, fluorescence-emission rationing techniques with fluorescein-labeled, amorphous silica particles. Glass fiber dissolution was determined in AM and RNEC cultured for 3 weeks with fast dissolving glass fibers (GF-A) or slow dissolving ones (GF-B). The mean diameters of GF-A were 2.7 pm and of GF-B, 2.6 pm, the average length of both fibers was approximately 22 to 25 pm. Dissolution was monitored by measuring the length and diameter of intracellular fibers and estimating the volume, assuming a cylindrical morphology. The ppH of AM was 5.2 to 5.8, and the ppH of RNEC was 7.0 to 7.5. The GF-A dissolved more slowly in RNEC than in AM, and no dissolution was evident in either cell type with GF-B. The volume loss with GF-A after a 3-week culture with AM was 66% compared to 45% for cultured RNEC. These results are different from those obtained using in vitro lung fluidsimulant models where dissolution is faster at higher pH. This difference suggests that dissolution rates of glass fibers in AM should not be applied to the dissolution of fibers in epithelial cells. -Environ Health Prospect 1 02(Suppl 5): 97-102 (1994)

Simulated biological fluids – a systematic review of their biological relevance and use in relation to inhalation toxicology of particles and fibres

“…Measurements of lysosomal pH have been previously reported, including rat alveolar macrophages demonstrating lysosomal pH values of between 5.2 and 5.8 (Johnson 1994;Johansson et al 1997), with similar values of pH 5.2 demonstrated in interstitial macrophages of the same species (Johansson et al 1997). In rabbits, after inhalation and subsequent internalisation of silica particles by alveolar macrophages, the pH of the phagolysosome was measured to be 4.9 the day after particle exposure, with further decreases to 4.5 one week after exposure (Nyberg et al 1989b).…”

Erratum

“…We appreciate the opportunity to address the points raised by Ghio and Bennett in their letter. The pH of our cell-free dissolution studies ) was appropriate because the nasal cavity surface is neutral and does not have airway macrophages and the phagolysosomal pH of nasal epithelial cells is neutral (Johnson 1994). Acidic pH, as in the phagolysosome of alveolar macrophages, dissolves manganese oxide, resulting in increased levels of blood-borne nonparticulate Mn.…”