The cytotoxicity and genotoxicity of soluble and particulate cobalt in human lung fibroblast cells

https://doi.org/10.1016/j.taap.2014.05.002Get rights and content

Highlights

  • Particulate and soluble cobalt are cytotoxic and genotoxic to human lung cells.

  • Soluble cobalt induces more cytotoxicity compared to particulate cobalt.

  • Soluble and particulate cobalt induce similar levels of genotoxicity.

  • Particle-cell contact is required for particulate cobalt-induced toxicity.

Abstract

Cobalt exposure is increasing as cobalt demand rises worldwide due to its use in enhancing rechargeable battery efficiency, super-alloys, and magnetic products. Cobalt is considered a possible human carcinogen with the lung being a primary target. However, few studies have considered cobalt-induced toxicity in human lung cells. Therefore, in this study, we sought to determine the cytotoxicity and genotoxicity of particulate and soluble cobalt in human lung cells. Cobalt oxide and cobalt chloride were used as representative particulate and soluble cobalt compounds, respectively. Exposure to both particulate and soluble cobalt induced a concentration-dependent increase in cytotoxicity, genotoxicity, and intracellular cobalt ion levels. Based on intracellular cobalt ion levels, we found that soluble cobalt was more cytotoxic than particulate cobalt while particulate and soluble cobalt induced similar levels of genotoxicity. However, soluble cobalt induced cell cycle arrest indicated by the lack of metaphases at much lower intracellular cobalt concentrations compared to cobalt oxide. Accordingly, we investigated the role of particle internalization in cobalt oxide-induced toxicity and found that particle-cell contact was necessary to induce cytotoxicity and genotoxicity after cobalt exposure. These data indicate that cobalt compounds are cytotoxic and genotoxic to human lung fibroblasts, and solubility plays a key role in cobalt-induced lung toxicity.

Introduction

The demand for cobalt is rising worldwide. Cobalt is increasingly being used in the production of rechargeable batteries, super-alloys and magnetic products due to its enhanced electrode conductivity, anti-corrosive, high melting point and magnetic properties, (CDI, 2013). Based on World Bureau of Metal Statistics, the demand for cobalt has increased by 15% worldwide from 2010 to 2011 alone (CDI, 2013). As cobalt is increasingly used in manufacturing, the potential for exposure of both industrial workers and the general population is also rising.

The International Agency for Research on Cancer (IARC) has classified cobalt as a Group 2B possible human carcinogen (IARC, 2006). Epidemiological studies on the carcinogenicity of cobalt are limited and inconclusive, partially due to co-exposure with established carcinogens, such as nickel and chromium (IARC, 2006). However, human studies do suggest a correlation between cobalt exposure and lung diseases, including lung cancer, asthma and alveotitis (Mur et al., 1987, Sauni et al., 2010, Van Cutsem et al., 1987). Additionally, animal studies conducted by the National Toxicology Program (1998) demonstrated an increased incidence of alveolar/bronchiolar neoplasms in murine models as a result of cobalt inhalation exposure (Agency for Toxic Substances, Disease Registry (ATSDR), 2004, International Agency for Research on Cancer (IARC), 2006, National Toxicology Program (NTP), 1998).

The potential mechanisms of cobalt-induced lung carcinogenesis remain unknown. Studies indicate that cobalt is genotoxic to human and rodent cells, inducing chromosome aberrations, single and double strand breaks, sister chromatid exchanges and micronuclei (reviewed in Agency for Toxic Substances, Disease Registry (ATSDR), 2004, Beyersmann and Hartwig, 2008, Lison et al., 2001). However, despite the fact that the lung is the major target organ, little is known about the genotoxic effects of cobalt in human lung cells. Only one study has investigated the genotoxicity of cobalt in human lung cells and found that exposure to soluble cobalt ions induces DNA double strand breaks in the cancer-derived H460 human lung epithelial cell line (Pastel et al., 2012). Thus far, no studies have investigated cobalt-induced genotoxicity in a non-cancerous human lung cell model.

Both soluble and particulate cobalt compounds are used in industry, but the role of solubility in cobalt-induced genotoxicity remains unknown. Studies with other metals, such as nickel and chromium, indicate that solubility can play an important role in the potency of metal-induced genotoxicity and carcinogenicity. To date, no studies have compared the potency of soluble and particulate cobalt compounds in human lung cells. Accordingly, the objective of this study was to determine the cytotoxicity and genotoxicity of soluble and particulate cobalt in human lung fibroblast cells and to investigate the role of solubility in cobalt-induced toxicity.

Section snippets

Chemicals and reagents

A 50:50 mixture of Dulbecco's minimal essential medium and Ham's F-12 (DMEM/F-12) was purchased from Mediatech Inc. (Herndon, VA). Sodium pyruvate, penicillin/streptomycin, Gluta-Gro, trypsin/EDTA, phosphate buffered saline (PBS), propidium iodide (PI), and Gurr's buffer were purchased from Life Technologies Corp (Carlsbad, CA). Acetic acid, crystal violet, and methanol were purchased from J.T. Baker (Phillipsburg, NJ). Cosmic calf serum (CCS) was purchased from Hyclone (Logan, UT). Cobalt (II)

Soluble cobalt is more cytotoxic to human lung cells than particulate cobalt

Exposure to particulate or soluble cobalt induced a concentration-dependent increase in cytotoxicity in human lung fibroblasts (Fig. 1). For particulate cobalt, exposure to 0.1, 0.5, 1, and 5 μg/cm2 cobalt oxide for 24 h reduced relative survival to 85, 61, 55, and 8%, respectively (Fig. 1A). For soluble cobalt, exposure to 100, 175, 250, and 500 μM cobalt chloride reduced relative survival to 76, 49, 29, and 4% (Fig. 1B).

Since soluble and particulate cobalt cannot be directly compared based on

Discussion

With the advancement of cobalt mining in the United States and the growing demand for cobalt in general, cobalt inhalation is a growing health concern. Due to lack of conclusive human epidemiological studies, cobalt is listed as a possible carcinogen by IARC, but animal and cell culture studies indicate that cobalt is carcinogenic (Abbracchio et al., 1982, Agency for Toxic Substances, Disease Registry (ATSDR), 2004, Costa et al., 1982, Doran et al., 1998, International Agency for Research on

Conflict of interest

The authors declare that there are no conflicts of interest.

Acknowledgments

We would like to thank Shouping Huang and Chris Gianios for the administrative and technical support and Kellie Joyce for the scientific support. This work was supported by ARO Grant #W911NF-09-1-0296 (J.P.W.), and the Maine Center for Toxicology and Environmental Health.

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