GENOTOXICITY Anne T. Saber Æ Jette Bornholdt Æ Marianne Dybdahl Anoop K. Sharma Æ Steffen Loft Æ Ulla Vogel Ha˚kan Wallin Tumor necrosis factor is not required for particle-induced genotoxicity and pulmonary inflammation Received: 5 May 2004 / Accepted: 16 September 2004 / Published online: 11 November 2004 Ó Springer-Verlag 2004 Abstract Particle-induced carcinogenicity is not well understood,z but might involve inflammation. The proinflammatory cytokine tumor necrosis factor (TNF) is considered to be an important mediator in inflam- mation. We investigated its role in particle-induced inflammation and DNA damage in mice with and without TNF signaling. TNFÀ/À mice and TNF+/+ mice were exposed by inhalation to 20 mg m À3 carbon black (CB), 20 mg m À3 diesel exhaust particles (DEP), or filtered air for 90 min on each of four consecutive days. DEP, but not CB particles, induced infiltration of neutrophilic granulocutes into the lung lining fluid (by the cellular fraction in the bronchoalveolar lavage fluid), and both particle types induced interleukin-6 mRNA in the lung tissue. Surprisingly, TNFÀ/À mice were intact in these inflammatory responses. There were more DNA strand breaks in the BAL cells of DEP-exposed TNFÀ/ À mice and CB-exposed mice compared with the air- exposed mice. Thus, the CB-induced DNA damage in BAL-cells was independent of neutrophil infiltration. The data indicate that an inflammatory response was not a prerequisite for DNA damage, and TNF was not required for the induction of inflammation by DEP and CB particles. Keywords TNF knock-out mice Æ Lung inflammation Æ DNA damage Æ Carbon black Æ Diesel exhaust particles Introduction Exposure to particulate matter (PM) in urban air is associated with increased mortality and morbidity due to respiratory and cardiovascular disease and cancer (Brunekreef and Holgate 2002). Long-term inhalation studies have demonstrated that two important groups of particles, carbon black (CB) (IARC 1996) and diesel exhaust particles (DEP) (IARC 1989), cause lung cancer in rats. Carbon blacks are manufactured under con- trolled conditions for commercial use primarily as rein- forcing agents in rubber and as black pigments in paints and printing inks. CB particles consist of amorphous carbon with only a small fraction of extractable organic material. In contrast with CB, DEP are unwanted by- products from the incomplete combustion of diesel. DEP are coated with PAHs, nitro-PAHs, and transition metals to a much greater extent than CB. The mechanisms of action of particles are thought to involve inflammation (Driscoll 2000; Oberdo¨rster 2001). A common denominator for DEP and CB par- ticles is that the deposited particles induce inflamma- tory reactions in the lung. This suggests a relationship between inflammation and carcinogenesis. The charac- teristics of PM, in particular the size distribution and chemical composition, are thought to be important for health effects. Thus, experiments with rodents have shown that ultrafine particles (<100 nm) cause more inflammation than the same mass of larger particles (Oberdo¨rster 2001). In addition, the ultrafine particles are able to transport a greater amount of toxic material adsorbed on the surface and react to a greater extent with the cells of the airways than bigger particles do. Particles are genotoxic by induction of oxidative DNA adducts. There are several mechanisms by which par- ticle-induced oxidative damage is generated. The oxi- dative damage may either be mediated by oxidative stress induced by the inflammatory response or by the metabolism of PAHs, in particular PAH quinones, or by free radical groups or transition metals on the A. T. Saber Æ J. Bornholdt Æ M. Dybdahl Æ A. K. Sharma U. Vogel Æ H. Wallin (&) National Institute of Occupational Health, Lersø Parkalle´ 105, 2100 Copenhagen, Denmark E-mail: hwa@ami.dk Fax: +45-39-16-52-01 S. Loft Institute of Public Health, Copenhagen University, 2200 Copenhagen, Denmark Arch Toxicol (2005) 79: 177–182 DOI 10.1007/s00204-004-0613-9