Chem. Res. Toxicol. 1995, 8, 600-606
600
Physicochemical Mechanism of the Interaction between Cobalt Metal and Carbide Particles To Generate Toxic Activated Oxygen Species Dominique Lison,*>' Philippe Carbonnelle,' Laura Mollo,; Robert Lauwerys,? and Bice Fubini; Industrial Toxicology and Occupational Medicine Unit, Faculty of Medicine, Catholic University of Louvain, Brussels, Belgium, and Department of Inorganic Chemistry, Physical and Materials Chemistry, Faculty of Pharmacy, University of Torino, Italy Received December 16, 1994@ Hard metal alloys (or cemented carbides) are made of a mixture of tungsten carbide particles (WC, more than 80%) cemented in cobalt metal powder (Co, 5-10%). The inhalation of hard metal particles may cause a n interstitial pulmonary disease, the mechanism of which involves a n interaction between Co and WC particles. Some epidemiological data also suggest that hard metal dust can induce lung cancer in workers. In a macrophage culture model, butylated hydroxytoluene (1mM) protected from the cytotoxicity of hard metal particles, suggesting a possible involvement of lipid peroxidation in the toxicity of these powders. In a biochemical system, a mixture of Co and WC particles, but not Co or WC alone, stimulated the production of thiobarbituric acid-reactive substances from arachidonic acid. Using a spin trapping system applied to aqueous particulate suspensions and electrochemical techniques, we present experimental evidence that the association of Co and carbide particles represents a specific toxic entity producing large amounts of activated oxygen species. The mechanism of this interaction proceeds through the oxidation of cobalt metal catalyzed at the surface of carbide particles and resulting in the reduction of dissolved oxygen. This physicochemical property of hard metal particles provides a new basis for interpreting their inflammatory action and their possible carcinogenic effect on the lung.
Introduction Hard metal alloys (or cemented carbides) are made of a mixture of tungsten carbide particles (usually more than 80%) cemented in cobalt metal powder (usually 5-10%) and small amounts of other metallic carbides. After mixing, milling, and sintering, this material acquires remarkable properties of hardness and is used for the manufacturing of different tools requiring high resistance to wear and heat, e.g., saw blades, cutters, drill bits, etc. (11. Different forms of pulmonary diseases have been described among workers exposed to hard metal dust: (i) asthmatic reactions that are similar in presentation to other forms of occupational asthma and (ii) interstitial changes characterized by the presence of a desquamative alveolitis which may progress to end-stage fibrosis (hard metal disease). Recently, an excess of lung cancer has been found among hard metal workers (2). With regard to asthma, there is ample evidence that cobalt alone is the offending compound, and specific bronchial provocation tests with cobalt salts, metal, or hard metal dust are usually positive ( 3 ) . By contrast, epidemiologic ( 4 ) and experimental data (5) strongly suggest that the fibrosing alveolitis is not induced by cobalt alone but requires the simultaneous inhalation of particles of cobalt metal and of other compounds such as tungsten carbide. * Address correspondence to this author at the Industrial Toxicology and Occupational Medicine Unit, Faculty of Medicine, Catholic University of Louvain, Clos Chapelle aux Champs, 30.54, 1200 Brussels, Belgium. Phone: -32.2.764.35.36; FAX: -32.2.764.32.28; E-mail: lison@%oxi.ucl.ac.be. Catholic University of Louvain. University of Torino. e Abstract published in Advance ACS Abstracts, May 1, 1995.
We have previously demonstrated in the rat that the alveolitis produced by hard metal dust cannot be explained by its cobalt content but results from an interaction between cobalt and metallic carbide particles (5). In the present study, we provide experimental evidence that this interactive toxicity is mediated by activated oxygen species (AOS)' produced by the association of cobalt metal and metallic carbide particles, but not by cobalt or tungsten carbide alone. The involvement of AOS was examined in cellular, biochemical, and physicochemical systems.
Materials and Methods Particles and Chemicals. The following powders were used: (1)extrafine cobalt metal obtained from a cobalt refinery (99.87% purity; median particle size (dso),4 ,um), called hereafter Co; (2) tungsten carbide (Johnson Matthey 625655, 99.5% purity, d50,
