In vitro genotoxic effects of hard metal particles assessed by alkaline single cell gel and elution assays

Abstract

Hard metals (WC-Co) are made of a mixture of cobalt metal (Co, 5-10%) and tungsten carbide particles (WC, >80%). Excessive inhalation of WC-Co is associated with the occurrence of different lung diseases including an excess of lung cancers. The elective toxicity of hard metal is based on a physico-chemical interaction between cobalt metal and tungsten carbide particles to produce activated oxygen species. The aim of the present study was to assess the genotoxic activity of hard metal particles as compared with Co and WC alone. In human peripheral lymphocytes incubated with Co or WC-Co, a dose- and time-dependent increased production of DNA single strand breaks (ssb) was evidenced by alkaline single cell gel electrophoresis (SCGE) and modified alkaline elution (AE) assays. Addition of 1 M formate, a hydroxyl radical scavenger, had a protective effect against the production of ssb by both WC-Co or Co alone. On the basis of an equivalent cobalt-content, WC-Co produced significantly more ssb than Co. WC alone did not produce DNA ssb detectable by the AE assay, but results obtained with the SCGE assay may suggest that it either allows some uncoiling of the chromatin loops or induces the formation of slowly migrating fragments. Overall, this in vitro study is the first demonstration of the clastogenic property of cobalt metal-containing dusts. The results are consistent with the implication of an increased production of hydroxyl radicals when Co is mixed with WC particles. The SCGE results also suggest that WC may modify the structure of the chromatin, leading to an increased DNA sensitivity to clastogenic effects. Both mechanisms are not mutually exclusive and may concurrently contribute to the greater clastogenic activity of WC-Co dust. This property of WC-Co particles may account for the excess of lung cancers observed in hard metal workers.

Characterization of exposures among cemented tungsten carbide workers. Part I: Size-fractionated exposures to airborne cobalt and tungsten particles

“…Using powder concentrations of 22.5 mg/ml (which is high relative to observed mass concentrations in Table 1) and an electron spin resonance technique, Lison et al ( , 1996 proposed the following precise mechanism for HMD: when both cobalt metal (which is thermodynamically able to reduce ambient oxygen) particles and tungsten carbide (a good electron conductor) particles are associated, electrons provided by the cobalt metal are easily transferred to the surface of the carbide particles, where reduction of oxygen can occur at an increased rate, resulting in the generation of free radicals. Analogous results have been reported for genotoxicity studies (Anard et al, 1997;Van Goethem et al, 1997;Lison et al, 2001;De Boeck et al, 2003a, b;Mateuca et al, 2005): cobalt associated with tungsten carbide particles (mechanical mixture or pre-sintered hard metal powder) produce more free radicals and DNA strand breaks than pure cobalt or tungsten carbide powder alone. Additionally, in vitro cobalt ions (75 mM) can inhibit DNA repair as measured by the alkaline unwinding method (Lison et al, 2001).…”

“…In humans, excess lung cancer has been observed among hard metal workers exposed to CTC dusts (Lasfargues et al, 1994;Moulin et al, 1998;Wild et al, 2000;Lison et al, 2001), but not among cobalt production workers exposed to cobalt alone (Moulin et al, 1993). In vitro and in vivo studies indicate that the genotoxicty of cobalt in the presence of tungsten carbide is greater than either component alone (Anard et al, 1997;Van Goethem et al, 1997;Lison et al, 2001;De Boeck et al, 2003a, b;Mateuca et al, 2005).…”

Nanotoxicity: emerging concerns regarding nanomaterial safety and occupational hard metal (WC-Co) nanoparticle exposure

“…Early data concerning the effects of inhaled WC-Co dusts first emerged in the 1960s and continued through the 1980s, providing researchers the foundation to further explore the toxic effects of hard metal exposure using in vitro [71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87][88] and in vivo 72,[89][90][91][92][93][94][95][96] models. Although cobalt itself was originally considered the causative agent of HMLD, several studies demonstrated that this is not the case and the disease mainly develops due to the simultaneous presence of WC with Co. 71,74,[76][77][78][79]90,91 It is currently understood that the combination of WC-Co is more toxic than Co, W, or WC particles alone, both in vitro and in vivo, 71,72,74,78,79,81,85,90,91,93,94,…”

“…74,75 Nano-WC-Co toxicity has also been reported in rainbow trout gill cells, murine epidermal cells, and fibroblasts at concentrations ,100 μg/mL for 3 h and up to 3 days. 83,84 Nano-WC-Co has been shown to exert genotoxic effects by affecting the expression of genes involved in cellular apoptosis and stress responses. 75 In addition, nano-WC-Co has been found to induce greater cellular toxicity and higher levels of oxidative stress than micro-WC-Co particles of the same composition under identical conditions (Figure 2).…”

The Genotoxic Potential of Novel Materials Used in Modern Hip Replacements for Young Patients

“…The scientists used lead chromate (PbCrO 4 ) and sodium chromate (Na 2 CrO 4 ) as prototypical particulate and soluble Cr VI salts, respectively, to show that the amount of chromosomal damage increased with increasing concentrations after 24h to both compounds (and so did the cytotoxicity levels) (Wise et al, 2002). Other studies have showed that metallic Co particles were able to induce DNA breaks and micronuclei in human peripheral lymphocytes in a dose dependent manner (Anard et al, 1997, Van Goethem et al, 1997. De Boeck et al showed that despite a relatively large interexperimental and interdonor variability, the DNA-damaging potential of the Co-tungsten carbide mixture was higher than that of Co metal and Co chloride which had comparable responses (De Boeck et al, 2003).…”