Inflammatory response and genotoxicity of seven wood dusts in the human epithelial cell line A549

https://doi.org/10.1016/j.mrgentox.2007.04.016Get rights and content

Abstract

Exposure to wood dust is common in many workplaces. Epidemiological studies indicate that occupational exposure to hardwood dusts is more harmful than to softwood dusts. In this study, human epithelial cell line A549 was incubated with well-characterized dusts from six commonly used wood species and from medium density fibreboard (MDF), at concentrations between 10 and 300 μg/ml. After 3 and 6 h of incubation, genotoxicity was assessed by measurement of DNA damage with the single-cell gel electrophoresis (comet) assay and inflammation was measured by the expression of IL-6 and IL-8 mRNA and by the amount of IL-8 protein. There was a 1.2–1.4-fold increase in DNA strand breaks after incubation with beech, teak, pine and MDF dusts compared with the levels in untreated cells, but after 6 h only the increase induced by the MDF dust remained. Increased expression of cellular IL-6 and IL-8 mRNA was induced by all of the wood dusts at both times. Similar to IL-8 mRNA expression, the amounts of secreted IL-8 protein were elevated, except after incubation with oak dust, where a marginal reduction was seen. On the basis of the effects on IL-8 mRNA expression, the wood dusts could be divided into three groups, with teak dust being the most potent, MDF, birch, spruce and pine being intermediate, and beech and oak being the least potent. The induction of DNA strand breaks did not correlate well with the interleukin response.

In conclusion, all wood dusts induced cytokine responses, and some dusts induced detectable DNA damage. The inflammatory potency seemed intermediate for dusts from the typical softwoods spruce and pine, whereas the dusts from species linked to cancer, beech and oak, were the least inflammatory. The variation of the effects induced by different wood dusts over time indicates that the DNA damage was not secondary to the cytokine response. Although hardwoods are often considered more harmful than softwoods by regulatory agencies, the current experiments do not provide evidence for a clear-cut distinction between toxicities of hardwood and softwood dust.

Introduction

Wood dust is one of the most common occupational dust exposures. Worldwide, approximately 13 million people were occupied in the forestry sector and about 3.5 million people in the furniture industry in year 2000. This means that about 0.4% of the total labour force were occupied in the forestry sector [1]. Recently, Kauppinen et al. [2] reported that 3.6 million workers, i.e. 2.0% of the workforce, were occupationally exposed to wood dusts in the European Union.

Many countries differentiate the regulation between exposures to hardwoods and softwoods (see, e.g. the European Union Directive 1999/38). Hardwoods are usually defined as woods of broad-leaved trees, whereas softwoods are conifers. This categorization is based on the botanical classification system rather than on the physical and chemical properties of the wood species.

Cancer in the sino-nasal cavities is rare, with a worldwide annual standardized incidence rate of 1.05/100,000 persons for men and 0.45 for women [3]. Cancer at this site has been strongly associated with different occupational exposures [4], including exposure to wood dust. Several independent studies have found excess risks among employees working in wood-related industries [5], [6], [7]. When classifying the cancers by histology, adeno-carcinomas are even more strongly associated with wood dust exposure. In a meta-analysis of 12 case–control studies, an odds ratio of 45.5 (28.3–72.9) was calculated for male workers in jobs with high levels of wood dust exposure [5].

In 1995, the International Agency for Research of Cancer [8] evaluated wood dust as being carcinogenic to humans (Group 1). The conclusion was based on a substantial amount of epidemiological evidence, despite the sparse knowledge about the underlying mechanisms and pathways. The studies showed the strongest correlation between nasal cancer and exposure to dust from hardwood, especially oak and beech [9]. However, sino-nasal cancer among employees who worked with other wood types and species has also been reported [8].

In addition to cancer, wood dust exposure is also associated with non-malignant health effects like impaired lung function, occupational asthma, rhinitis and allergic contact dermatitis [10], [11], [12], [13], [14], [15]. We therefore tested whether an indirect pathway involving inflammation and oxidative stress was related to DNA strand break formation, which is a potential indicator of a carcinogenic mechanism [16].

This study was aimed at investigating whether the inflammatory response and the genotoxicity of dusts from common woods differ. Animal models for studying the carcinogenic effects of wood dusts are lacking. Therefore, in vitro data may be an important tool for suggesting preventive measures, such as distinguishing between the toxicity of certain wood types. Dusts made from six wood species and dust from medium density fibreboard (MDF) was tested to encompass common wood materials (i.e. hard, soft, exotic and artificial wood). Beech, birch and oak were selected because of their widespread use in the furniture industry. Teak is a popular exotic hardwood in furniture making. Pine and spruce represent softwoods, and MDF is a manufactured wood material that is commonly used in furniture and for construction.

Section snippets

Wood dust

Well-characterized wood dusts from beech, birch, MDF, oak, pine, spruce and teak were produced by the Kupio Regional Institute of Occupational Health (Kuopio, Finland) according to methods described by Naarala et al. [17]. Good-quality raw materials were selected that had not been impregnated with wood preservatives. The production and characteristics of the wood dusts have been described by Long et al. [18] and Maatta et al. [19], [20], except for the MDF dust. The MDF dust was produced by the

Cytotoxicity

Cytotoxicity was assessed by measuring the secretion of lactate dehydrogenase into the medium as the fraction of the activity in lysates of Triton-X-lysed cells. In the initial set-up, we measured the LDH content in the media after 3, 6, 24 and 48 h of exposure, and found that the wood dusts were strongly toxic after 24 and 48 h of incubation (data not shown). After 3 and 6 h of exposure, no substantial toxicity was detected (Table 2). For this reason, we decided to focus the study on the 3 and

Discussion

Several epidemiological studies have shown both malignant and non-malignant health effects after occupational exposure to wood dust, especially after exposure to hardwood dusts [5], [12]. However, in most of the epidemiological studies, the employees have worked with several wood species simultaneously, which makes it difficult to estimate the harmful potential of the different wood species. Another problem is that it has not yet been possible to mimic in experimental animals the human wood

Conclusions

We here report that four out of seven wood dusts induce DNA strand-breaks in cultured A549 cells. DNA strand-breaks occurred before the inflammation had reached its maximum, which suggests that wood dusts are genotoxic without involvement of inflammatory responses. Both hardwood and softwood species caused DNA strand-breaks. Cytokine responses were induced by all seven wood dust species, with the lowest and highest responses found among the hardwoods, and the responses of the softwoods between

Acknowledgements

Technical assistance from Lourdes Pedersen and Yonit Bertelsen and the comments from Dr. Corey Cohn are gratefully acknowledged. This study was supported by EU 5th Framework Programme, Key Action 4, Environment and Health, Quality of Life and Management of Living Resources, project no. QLK4-2000-00573 and the Airpolife center of excellence granted by the Danish Research agency.

References (36)

  • J.K. Gøtrik et al.

    National Board of Health. Cancer incidence in Denmark 2000

    (2004)
  • D. Luce et al.

    Sinonasal cancer and occupational exposures: a pooled analysis of 12 case–control studies

    Cancer Causes Control

    (2002)
  • P.A. Demers et al.

    Wood dust and sino-nasal cancer: pooled reanalysis of twelve case-control studies

    Am. J. Ind. Med.

    (1995)
  • J.H. Olsen

    Occupational risks of sinonasal cancer in Denmark

    Br. J. Ind. Med.

    (1988)
  • E.D. Acheson et al.

    Nasal cancer in England and Wales: an occupational survey

    Br. J. Ind. Med.

    (1981)
  • International Agency for Research on Cancer

    IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Wood dust and formaldehyde

    (1995)
  • E. Mohtashamipur et al.

    Cancer epidemiology of woodworking

    J. Cancer Res. Clin. Oncol.

    (1989)
  • V. Schlunssen et al.

    Indices of asthma among atopic and non-atopic woodworkers

    Occup. Environ. Med.

    (2004)
  • Cited by (52)

    • Comet assay and hormesis

      2024, Environmental Pollution
    • New formaldehyde-free adhesives for wood manufacturing: In vitro evaluation of potential toxicity of fine dust collected during wood sawing using a new experimental model to simulate occupational inhalation exposure

      2022, Toxicology
      Citation Excerpt :

      Regarding the potential genotoxic effects, in the cells exposed to natural woods in the present study we found a similar modest dose-dependent DNA damage with a slight oxidative DNA damage induction by spruce that seems to be in accordance with Gaballah et al. (2017) although they investigated the effects on lymphocytes of exposed workers. The findings relative to spruce wood dust could be compared to those found by Bornholdt et al. (2007) who evaluated genotoxic effects of this wood on the same cell line exposed to 10−300 μg/mL for shorter exposure times and did not find significant direct DNA damage by comet assay. The different result in respect to our study could be due to the different size of wood particles (up to 5 μm, therefore also larger than those used in our study) and to the shorter duration of exposure that probably did not allow to damage the membrane with the following entrance of particles and induction of ROS and DNA damage.

    • Leisure time activities related to carcinogen exposure and lung cancer risk in never smokers. A case-control study

      2014, Environmental Research
      Citation Excerpt :

      The use of a variety of potential carcinogens to preserve, manufacture, and finish wood products might also pose implications in the adverse effect of wood dust exposure (Wu et al., 1995). Studies in cell lines have shown that wood dust induces carcinogenic mechanisms such as inflammation, production of reactive oxygen species and DNA damage in human lung epithelial cell line (Bornholdt et al., 2007). Additionally to wood dust, wood related leisure activities potentially involve exposure to glues, formaldehyde, epoxy, methylene chloride, toluene, methyl alcohol and other noxious substances (Zuskin et al., 2007).

    • Genotoxicity but not the AhR-mediated activity of PAHs is inhibited by other components of complex mixtures of ambient air pollutants

      2014, Toxicology Letters
      Citation Excerpt :

      The same set of EOMs from air pollutants was used in the present study to investigate genotoxic effects and modulation of AhR-dependent genes involved in PAH activation in A549 cells, a well-characterized model of human alveolar type II cells (Giard et al., 1973). This cell line has been widely employed in molecular biology studies to analyze the toxic effects of various chemicals (Hansen et al., 2007), dusts (Bornholdt et al., 2007), airborne particulate matter (Gutierrez-Castillo et al., 2006) and engineered nanoparticles (Lanone et al., 2009). Dimethylsulfoxide (DMSO) was purchased from Merck, Darmstadt, Germany.

    • Research progress of occupational hazards in plywood manufacturing

      2023, Chinese Journal of Industrial Hygiene and Occupational Diseases
    View all citing articles on Scopus
    View full text