The cytotoxicity of chrysotile asbestos fibers to pulmonary alveolar macrophages I. Effects of inhibitors of ADP-ribosyl transferase

Pulmonary alveoler macrophages exposedto very short chrysotile asbestos fibers present a typical cytotoxic response: extracellular releases of lactate dehydrogenase and -galactosidase, and a decrease in cellular ATP content. The objective of this study was to determine if nicotinamide and 3-aminobenzamide, two inhibitors of the ADP-ribosyl transferase, could modify the in vitro toxicity of chrysotilee fibers. After 30 min of pre-exposure with each of the two inihibitors, pulmonary alveolar macrophage monolayers were concominantly exposed for 18 hours to 50g of fibers. It was observed that, in a dose-effect relationship (5 to 30 mM), nicotinamide was very effective in reducing the extracellular liberation of the marker enzymes. At 30 mM, the enzyme releases in the medium had returned to control values; the restoration of cell viability was confirmed by ATP levels. Up to 5 mM 3-aminobenzamide did not provide any protection against chrysotile cytotoxicity. Nicotinic acid, a structural analogue of nicotinamide, but not an inhibitor of the ADP-ribosyl transferase, also showed no protective effect. Nicotinamide and 3-aminobenzamide increased the intracellular NAD⁺ pools, respectively by 350% and 250%. However, with or without additives, the chrysotile fibers caused a constant and significant decrease in NAD⁺ levels (40–55 pmoles). These results suggest that the inhibition of the nuclear ADP-ribosyl transferase is not the major mechanism by which nicotinamide protects pulmonary alveolar macrophages against the chrysotile asbestos fibers.Abbreviations 3-AB 3-aminobenzamide - ADPRT ADP-ribosyl transferase - -GAL -galactosidase - DTT dithiothreitol - FBS fetal bovine serum - FMN flavin mononucleotide - HEPES N-2-hydroxyethyl piperazine-N-2-ethanesulfonic acid - LDH lactate dehydrogenase - NAD⁺ nicotinamide adenine dinucleotide (oxidized form) - NADH nicotimide adenine dinucleotide (reduced forms) - NADPH nicotimide adenine dinucleotide phosphate (reduced form) - NAM nicotinamide - NIC nicotinic acid - ORS oxygen radical species - PAM pulmonary alveolar macrophages - S.E. standard error of the mean - TAPS tris (hydroxymethyl) methylamino-propane sulfonic acid - TRIS tris (hydroxymethyl) aminomethane - VSF very short chrysotile fibers