A sham-exposed control group was treated the same way except for MS inhalation. A post-inhalation period of
2 days was added for a ERK animal study satellite group of mice exposed for 18 months that were allocated to the investigation of gene expression patterns in lung tumor tissue. This short post-inhalation period was expected to down-regulate most of the acute MS exposure related induction of gene expression in order to allow a characterization of longer-term effects that may be characteristic for the tumorigenic process. In Study 1, MS was generated using the standard reference cigarette 2R4F. Due to the diminishing stock of 2R4F cigarettes, 3R4F cigarettes were used in Study 2 for MS generation (University of Kentucky, Lexington, KY) (for specifications see http://www.ca.uky.edu/refcig/). Both reference cigarette types display equivalent MS composition as well as in vitro
and in vivo toxicity (Roemer et al., 2012). MS generation was performed in basic accordance with international standards (International Organization for Standardization, 1991 and International Organization for Standardization, 2000). Analytical characterization of the MS was performed as previously reported (Stinn et al., 2012). The approval for the performance for both studies was obtained according to the Belgium Law on Animal Protection (Belgian Federal Public Service, 2004). The studies were performed in an AAALAC-accredited facility (Association for the Assessment and Accreditation of Laboratory Animal Care International, 1991), where care and for use of the mice Selleckchem MK0683 were in accordance with the American Association for Laboratory Animal Science (AALAS) Policy on the Humane Care and Use of Laboratory Animals (http://www.aalas.org). Male and female A/J mice bred under specified pathogen-free conditions (The Jackson Laboratory, Bar Harbor,
Maine, USA) were obtained through Charles River France (L’Arbresle, France). The age of the mice was between 6 and 10 weeks at arrival and between 8 and 12 weeks at start of the inhalation, as in Study 1. The health status of six male and six female mice was confirmed serologically (Bioreliance, Rockville, MA), bacteriologically, parasitologically (Harlan, UK), and histopathologically. Eight of 12 mice were positive for Klebsiella oxytoca, which was not considered to impact the study quality since there was no pattern of characteristic lesions that might have been associated with Klebsiella infections. Within 1 week after arrival, the mice were individually identified with subcutaneous transponders (Triple A Trading, Tiel, the Netherlands). After random allocation to groups, the mean body weight per group at the start of exposure was approximately 22 g for the male and 18 g for the female mice, with relative standard deviations (SD) of less than 11%.