Cytotoxicity of ambient air particles to rat lung macrophages: Comparison of cellular and functional assays.

The biological reactivity of ambient air particles was studied in five in vitro lung macrophage assays, involving the release of cytoplasmic and lysosomal enzymes, cellular ATP, neutral red uptake, tetrazolium reduction, and chemiluminescence. Macrophages from rat lungs (2 x 10(5) cells; 1 cm(2) attachment surface; 1 ml culture medium) were exposed for 18 hr to 0-100 mug of (1) the urban dust SRM 1649, (2) titanium dioxide (TiO(2)) or (3) DQ-12 quartz. On the basis of the depressions of neutral red uptake and cellular ATP, and the extracellular releases of lactate dehydrogenase, acid phosphatase and beta-glucuronidase, the ranking of cytotoxicity was as follows: quartz (EC(50) = 20-60 mug/ml) > > SRM 1649 approximately TiO(2) (EC(50) > 100mug/ml). The decrease in 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) reduction was more sensitive to effects of the urban dust, with an EC(50) value for SRM 1649 (35mug/ml) intermediate between those for quartz (15mug/ml) and TiO(2) (82mug/ml). Although SRM 1649 could affect mitochondrial function, the impact of the urban dust on cellular integrity after 18 hr was comparable to that of TiO(2) particles. In contrast, SRM 1649 had profound effects on phagocytosis-related chemiluminescence values measured during a 5-hr exposure period. Quartz and TiO(2) particles induced an oxidative burst from the macrophages. However, whereas a low dose of SRM 1649 (25mug) induced an oxidative burst, a further increase of the dose of particles (100-250mug) resulted in a decrease of the luminol-dependent luminescence (P < 0.05) and, to a lesser extent, of the lucigenin-dependent luminescence. The data imply an early adverse effect of ambient air particles on the bactericidal activity of macrophages with minimal alterations in the structural integrity of the cells.