Neoplastic transformation of human osteoblast cells to the tumorigenic phenotype by heavy metal–tungsten alloy particles: induction of genotoxic effects

large DU fragments (~2–20 mm), has focused attention on the Heavy metal–tungsten alloys (HMTAs) are dense heavy potential health effects of internalized heavy metals like metal composite materials used primarily in military tungsten and DU used in military applications. applications. HMTAs are composed of a mixture of tungsten Several recent studies have investigated the potential health (91–93%), nickel (3–5%) and either cobalt (2–4%) or iron effects of militarily relevant heavy metals (1–5). These investi(2–4%) particles. Like the heavy metal depleted uranium gations have not only demonstrated the transforming ability (DU), the use of HMTAs in military munitions could result (1) and mutagenicity (2) of DU, but also its neurotoxicity (5). in their internalization in humans. Limited data exist, In contrast, there is no information regarding the health effects however, regarding the long-term health effects of internal- of imbedded HMTAs. Studies have shown that occupational ized HMTAs in humans. We used an immortalized, non- exposure to hard metal dust, a mixture of cobalt- and tungsten tumorigenic, human osteoblast-like cell line (HOS) to study carbide-containing particles, is associated with development the tumorigenic transforming potential of reconstituted of different pulmonary diseases, including fibrosing alveolitis mixtures of tungsten, nickel and cobalt (rWNiCo) and and lung cancer (6,7). The toxic properties of hard metal tungsten, nickel and iron (rWNiFe). We report the ability particles are not only attributed to an interaction between of rWNiCo and rWNiFe to transform immortalized HOS cobalt metal and carbide particles (8), but also to the production cells to the tumorigenic phenotype. These HMTA trans- of hydroxyl radicals, which have been implicated in their formants are characterized by anchorage-independent genotoxic effects (9). The HMTAs used in military applications, growth, tumor formation in nude mice and high level however, are somewhat different from conventional hard metal. expression of the K-ras oncogene. Cellular exposure to HMTA penetrators consist of a combination of tungsten, nickel rWNiCo and rWNiFe resulted in 8.90 0.93- and 9.50 and either cobalt or iron (tungsten 90%, nickel 1–6%, iron 0.91-fold increases in transformation frequency, respect- 1–6% or cobalt ~1–6%), in contrast to hard metal dust, which ively, compared with the frequency in untreated cells. In is a mixture of cobalt metal (5–10%) and tungsten carbide comparison, an equivalent dose of crystalline NiS resulted particles (80%) (10). The differences in metal composition in a 7.7 0.73-fold increase in transformation frequency. and percentages of hard metal particles and tungsten alloys The inert metal tantalum oxide did not enhance HOS used in military applications preclude the assumption that the transformation frequency above untreated levels. The biological effects of hard metal particles and tungsten alloy mechanism by which rWNiCo and rWNiFe induce cell particles would be the same. transformation in vitro appears to involve, at least partially, There are no studies that address the potential health effects direct damage to the genetic material, manifested as of internalized tungsten or HMTAs in terms of genotoxicity, increased DNA breakage or chromosomal aberrations mutagenicity or carcinogenicity. The long-term health risks (i.e. micronuclei). This is the first report showing that associated with internal chronic exposure to HMTA particles HMTA mixtures of W, Ni and Co or Fe cause human are not defined but are crucial to developing carcinogenesis cell transformation to the neoplastic phenotype. While risk standards for personnel who could be injured by HMTA additional studies are needed to determine if protracted shrapnel. Therefore, in view of carcinogenesis risk estimates HMTA exposure produces tumors in vivo, the implication and medical management questions relevant to possible future from these in vitro results is that the risk of cancer induction incidents of tungsten internalization, an examination of molecufrom internalized HMTAs exposure may be comparable lar and cellular effects, including the potential transforming with the risk from other biologically reactive and insoluble ability of tungsten and tungsten alloys, are necessary to carcinogenic heavy metal compounds (e.g. nickel subsulfide understanding the potential carcinogenic effects of this matand nickel oxide). erial. The use of cell culture models to investigate potential or known carcinogens can provide important insights into the cellular and molecular mechanisms of carcinogenesis.