The present thesis focuses on the inflammatory, genotoxic and carcinogenic effects of exposure to different species of wood dust. The experimental work performed in this thesis consists of two parts. The first part of the study was carried out in an in vitro model with the human lung epithelial cell line A549 measuring inflammatory and DNA damaging effects. The second part consists of a molecular analysis of the K-ras gene for mutations in the hotspots codons in human sinonasal cancers. Design, calibration and validation of the assays were performed.

Cancer at the sinonasal cavities is rare with incidence rates between of 0.3 to 1.4 per 100,000 for men and 0.1 to 0.8 per 100,000 for women in Europe, depending on country. However, cancer at this site is associated with occupational exposures including wood dust. Especially the adenocarcinoma subtype is strongly associated with exposure to wood dust primarily from hard woods. Non-malignant symptoms like allergy, asthma, rhinitis and chronic bronchitis have also been associated with occupational exposure to wood dust in epidemiological studies. In most epidemiological studies hardwoods (e.g. oak and beech wood dust) seems to have greater association to both the malignant and non-malignant symptoms compared to softwoods (e.g. pine and spruce wood dust). Since, well standardized experiments of wood dust exposure are limited and difficult to execute in humans, knowledge of the cellular mechanisms underlying wood dust induced carcinogenicity and non-malignant symptoms are still poorly understood. Particulate induced inflammation as well as extractives are suggested to be involved in the carcinogenesis. In this thesis wood dust potential to induce DNA damage and inflammation was investigated exposing the human lung epithelial cell line A549 to various species of wood dust and endpoints for inflammation and genotoxicity was evaluated. The experiments showed that the different species of wood dust vary in their ability to cause DNA strand breaks and inflammation. There was no apparent correlation between the species potential to initiate inflammation and their potential to cause DNA damage. Contrary to our hypothesis, we showed that pure wood dust is able to cause primary DNA damage, independent of inflammation as well as hardwoods had no higher inflammatory or genotoxic potential than softwoods. To investigate the molecular mechanisms behind the wood dust induced carcinogenesis, we examined human sinonasal tumours for mutations in the ras genes. The mutational spectrum, which is the type, site and frequency of mutations, provides useful clues to etiological factors and identification of exposure related tumours .We examined all incident cases of sinonasal adenocarcinoma and squamous cell carcinoma reported to the Danish Cancer Registry between 1991 and 2001. After a very careful inclusion process in order only to include sinonasal cancer of the nasal cavities and sinuses with correct histology, we included 174 cases. Wood dust exposure was assessed by interview and job/trade codes from the National Pension Fund and self reported job titles in the Central Personal Register. Among the cases wood dust exposure occurred in 21 percent of our patients and was 7 times more frequent in patients with adenocarcinomas than in squamous cell carcinoma (p<0.0001). In the mutational analysis, the K-ras gene was mutated in adenocarcinoma (13%) which is in the range reported in earlier studies, whereas the frequency was very low in the squamous cell carcinoma (1%). By analysis of all published K-ras mutations, the GGTGLY ¿GAT ASP transition was the most common K-ras codon 12 mutation. Despite that 65 percent of these patients had been exposed to wood dust, it was not significantly different from the patients without a G¿A mutation. The main conclusions based on the results obtained in this thesis are: All wood dust species cause inflammation. However, the species vary in their potential to induce the inflammation.

• Wood dust species vary in their potential to cause DNA damage. The DNA damage observed seemed to be caused by a direct genotoxic effect of the dust it selves.
• The current study provides evidence that the distinction between hard and softwoods dust may not be that clear cut in relation to health effects.
• The previously reported association between adenocarcinomas and exposure to wood dust could be confirmed by our study.
• Mutations activation of K-ras was restricted to a small subpopulation of the adenocarcinomas. The predominant mutations among these tumours were GC¿AT transitions.
  • Overall, the study suggests a limited role for K-ras mutations in development of sinonasal cancer.