Mechanisms Involved in A/J Mouse Lung Tumorigenesis Induced by Inhalation of an Environmental Tobacco Smoke Surrogate

Lung tumors have been reproducibly induced in A/J mice exposed to a surrogate for experimental environmental tobacco smoke (ETSS) in a 5-mo inhalation period followed by 4 mo without further exposure. In order to increase our mechanistic understanding of this model, male mice were whole-body exposed for 6 h/d, 5 d/wk to ETSS with a particulate matter concentration of 100 mg/m(3). Food restriction regimens were included to model or exceed the ETSS-related impairment of body weight development. Half of the mice were pretreated with a single ip injection of urethane to study the effect of the above treatments on lung tumor development induced by this substance. At 5 mo, the tumor response was statistically the same for all groups of non-pretreated mice; however, the expected urethane-induced lung tumorigenesis was significantly inhibited by approximately 25% by ETSS and food restriction. This inhibition was accompanied by a threefold increase in blood corticosterone as a common stress marker for both ETSS and food restriction. At 9 mo, in mice not pretreated, the lung tumor incidence and multiplicity were significantly increased by twofold in the ETSS group; in the urethane-treated groups, the same high tumor multiplicity was reached regardless of previous treatment. The predominant tumor type in all groups was bronchiolo-alveolar adenoma. There was no induction of a specific K-ras mutation pattern by ETSS exposure. These data suggest a stress-induced inhibition of lung tumorigenesis in this model, explaining the need for the posttreatment period.

Frequency and nature of spontaneous age-related eye lesions observed in a 2-year inhalation toxicity study in rats

A group of 160 Wistar rats (both sexes) from a larger chronic inhalation toxicity study was monitored at baseline and after 1 and 2 years with a photo-slitlamp microscope and a direct ophthalmoscope to record spontaneous age-related eye lesions and treatment-related eye lesions over a period of 24 months. A second group from the same study was monitored at the start and after 5 months of a 6-month posttreatment period immediately following the inhalation period. Rats were nose-only exposed for 6 h/day, 7 days/week, for 2 years to low (3 microg/l) or high (10 microg/l) total particulate matter concentrations of room-aged cigarette sidestream smoke (RASS) or diesel engine exhaust (DEE). Control animals were exposed to filtered fresh air. All ophthalmological examinations were performed in mydriasis, and relevant observations were documented on color slide film. At baseline, all animals with eye lesions were excluded from the study. After 1 year, only minor lesions were found: retrolental opacities (14%) and a few cases of corneal dryness with reddish lid margins. After 2 years, 23% of the animals had unilateral or bilateral retrolental opacities, but the most frequent eye lesions were posterior subcapsular cataracts (PSC, 32%). Water clefts and spokes were found in 11% of the lenses and mature cataracts in 6%. All other eye lesions observed were much less frequent. There were a few cases of glaucoma, corneal dryness and stromal neovascularization. The frequency and type of lesion in animals monitored from the start of the posttreatment period was comparable to what was seen after 2 years. Toward the end of this period the frequency of mature cataracts went up to 9% and that of (secondary) glaucomas to 5%. None of the eye lesions observed showed any association in frequency or severity of expression to the treatment, either RASS or DEE, or to the sex of the animals. In comparison to the (limited) literature data available, far fewer corneal lesions were found in this study, but PSCs and mature cataracts were more frequent. Strain differences may influence these parameters. This study provided valuable information on the nature and frequency of spontaneous age-related eye lesions (0-56%, depending on the tissue) in long-term toxicity studies in Wistar rats.

Age-related light scattering in rat lenses observed in a 2-year inhalation toxicity study

Normal light scattering in the eye is determined primarily by the size of alpha-crystalline molecules. Ageing effects appear as an increase in normal lens light scattering in distinct layers. Subliminal effects of toxins on lens transparency can also cause an increase in light scattering due to protein molecule aggregation before visible opacities appear. Scheimpflug photography of the anterior eye segment with subsequent densitometric image analysis is the method of choice to evaluate such effects. To gain more insight into normal ageing and the potential effects of complex aerosols, a subset of Wistar rats (both sexes) belonging to a larger chronic inhalation toxicity study was documented at baseline and after 2 years with a Topcon SL-45 Scheimpflug camera on Kodak T(max) 400 ISO film. The recording procedure, film development, and microdensitometric image analysis were all performed according to standard protocol. A second group from the same study was documented at the start and after 5 months of a 6-month posttreatment period immediately following the inhalation period. Rats were nose-only exposed for 6 h/day, 7 days/week, for 2 years to low (3 microg/l) or high (10 microg/l) concentrations of room-aged cigarette sidestream smoke or diesel engine exhaust. Control animals were exposed to filtered fresh air. At the baseline examination, there were no relevant differences between groups with respect to corneal density or density of defined layers in the lens capsule (1), epithelium and superficial cortex (2), deep cortex (3), supranuclear layer (4) and nucleus (5). At the 2-year examination, mean corneal density was significantly lower in females than in males. This same trend, although not significant, was also found in most layers of the lens. The most prominent differences in density over time were measured in lens layers 3 and 4, but neither corneal density nor lenticular density showed any consistent treatment-related effects in any of the layers. The data from the posttreatment period confirmed the results of the 2-year study. The depth of the anterior chamber increased constantly over the 2.5-year period, but again, treatment did not affect this. This study provided completely new data on age-related light scattering in the cornea and in defined layers of the lens in long-term toxicity studies in Wistar rats.

Comparison of fresh and room-aged cigarette sidestream smoke in a subchronic inhalation study on rats

Two experimental types of cigarette sidestream smoke (SS) were compared in a subchronic inhalation study on rats. Fresh SS (FSS) was generated continuously from the reference cigarette 2R1. Room-aged SS (RASS) was generated by aging FSS for 1.5 h in a room with noninert surfaces with materials typically found in residences or offices. Male Sprague-Dawley rats were head-only exposed to three dose levels of each SS type and to filtered, conditioned fresh air (sham-exposure) for 6 h/day, 7 days/week, for 90 days. Room-aging resulted in decreased concentrations of various SS components, e.g., total participate matter (TPM) and nicotine, while other components, such as carbon monoxide (CO), were not affected. The CO concentrations were 6, 13, and 28 ppm for both SS types. TPM concentrations were between 0.6 and 8.7 (μg/liter and thus up to 100-fold above the maximum of average concentrations of respiratory suspended particles reported for environmental tobacco smoke. Slight reserve cell hyperplasia in the anterior part of the nose as well as hyperplastic and metaplastic epithelial changes in the larynx were the only observed dose-dependent findings. The metabolism of benzo(a)-pyrene-as a proxy for polycyclic aromatic hydrocarbon metabolism-was induced in the nasal respiratory epithelium and in the lungs while no effect was seen in the nasal olfactory epithelium. The lowest-observed effect level was 6 ppm CO or 0.6 μg TPM/liter. Most of the effects seen were less expressed in RASS- than in FSS-exposed rats when compared on the basis of the CO concentrations. When compared on the basis of TPM, these effects were equally pronounced for both SS types, suggesting a major role of particulate matter-associated compounds. All findings reverted to sham control levels following a 42-day postinhalation period.

Comparison of fresh and room-aged cigarette sidestream smoke in a subchronic inhalation study on rats

Two experimental types of cigarette sidestream smoke (SS) were compared in a subchronic inhalation study on rats. Fresh SS (FSS) was generated continuously from the reference cigarette 2R1. Room-aged SS (RASS) was generated by aging FSS for 1.5 h in a room with noninert surfaces with materials typically found in residences or offices. Male Sprague-Dawley rats were head-only exposed to three dose levels of each SS type and to filtered, conditioned fresh air (sham-exposure) for 6 h/day, 7 days/week, for 90 days. Room-aging resulted in decreased concentrations of various SS components, e.g., total particulate matter (TPM) and nicotine, while other components, such as carbon monoxide (CO), were not affected. The CO concentrations were 6, 13, and 28 ppm for both SS types. TPM concentrations were between 0.6 and 8.7 micrograms/liter and thus up to 100-fold above the maximum of average concentrations of respiratory suspended particles reported for environmental tobacco smoke. Slight reserve cell hyperplasia in the anterior part of the nose as well as hyperplastic and metaplastic epithelial changes in the larynx were the only observed dose-dependent findings. The metabolism of benzo(a)-pyrene--as a proxy for polycyclic aromatic hydrocarbon metabolism--was induced in the nasal respiratory epithelium and in the lungs while no effect was seen in the nasal olfactory epithelium. The lowest-observed effect level was 6 ppm CO or 0.6 microgram TPM/liter. Most of the effects seen were less expressed in RASS-than in FSS-exposed rats when compared on the basis of the CO concentrations. When compared on the basis of TPM, these effects were equally pronounced for both SS types, suggesting a major role of particulate matter-associated compounds. All findings reverted to sham control levels following a 42-day postinhalation period.