In vitro cytotoxicity of various forms of cobalt for rat alveolar macrophages and type II pneumocytes

It has been shown that cobalt (Co) and the mixture cobalt-tungsten carbide (CoWC) are cytotoxic for alveolar macrophages (AM) and alveolar type II cel ls (AT-II), but the exact mechanisms of toxicity are not entirely elucidate d. In this study, we exposed primary cultures of AT-II and AM, in vitro, to different forms of Co (Co particles, CoWC particles, CoCl2) and assessed c ell damage using the dimethylthiazol diphenyl tetrazolium bromide test. In some experiments, inserts were used to separate the particles from the cell s. The results show that AT-II are twice as sensitive to the effects of 100 mu g Co particles/well (1.88 cm(2)) than AM. For this latter cell type, th e presence of WC almost doubled (at 25 mu g Co/well) the toxic effects comp ared to pure Co, bur this synergy between Co and WC only occurred if the pa rticles were in close contact with the cells. Lactalbumin an, to a lesser d egree, EDTA were able to reduce the toxicity of Co, CoWC, and CoCl2 for AT- II and AM. CoCl2 showed a similar toxicity for AT-II and AM. The use of Co- conditioned medium revealed that Co particles are "aged" after having been incubated for 24 h in an aqueous medium and are then no longer able to caus e the same degree of cell damage as fresh Co particles (71 versus 15% viabi lity for 100 mu g Co/well). The time course of the toxicity of the differen t forms of Co for AT-II and AM showed different patterns in causing cell da mage, suggesting different action mechanisms. Evaluation of cell damage by electron microscopy was consistent with biochemical indices. Overall, our r esults indicate that the Co ion does play a role in the toxicity of both Co particles and CoWC particles. (C) 2000 Academic Press.