Inhalation toxicity studies on cigarette smoke (VI). 6-week comparative experiments using modified flue-cured cigarettes: histopathology of the lung

Cigarette smoke induced genotoxicity and respiratory tract pathology: evidence to support reduced exposure time and animal numbers in tobacco product testing

Many laboratories are working to develop in vitro models that will replace in vivo tests, but occasionally there remains a regulatory expectation of some in vivo testing. Historically, cigarettes have been tested in vivo for 90 days. Recently, methods to reduce and refine animal use have been explored. This study investigated the potential of reducing animal cigarette smoke (CS) exposure to 3 or 6 weeks, and the feasibility of separate lung lobes for histopathology or the Comet assay. Rats were exposed to sham air or CS (1 or 2 h) for 3 or 6 weeks. Respiratory tissues were processed for histopathological evaluation, and Alveolar type II cells (AEC II) isolated for the Comet assay. Blood was collected for Pig-a and micronucleus quantification. Histopathological analyses demonstrated exposure effects, which were generally dependent on CS dose (1 or 2 h, 5 days/week). Comet analysis identified that DNA damage increased in AEC II following 3 or 6 weeks CS exposure, and the level at 6 weeks was higher than 3 weeks. Pig-a mutation or micronucleus levels were not increased. In conclusion, this study showed that 3 weeks of CS exposure was sufficient to observe respiratory tract pathology and DNA damage in isolated AEC II. Differences between the 3 and 6 week data imply that DNA damage in the lung is cumulative. Reducing exposure time, plus analyzing separate lung lobes for DNA damage or histopathology, supports a strategy to reduce and refine animal use in tobacco product testing and is aligned to the 3Rs (replacement, reduction and refinement).

A comprehensive evaluation of the toxicology of experimental cigarettes manufactured with banded papers

CONTEXT

To comply with state requirements, cigarette manufacturers have added low-permeability bands to the cigarette paper. These bands can extinguish the cigarette when it is no longer being puffed by a smoker.

OBJECTIVE

This study was conducted to evaluate the toxicology resulting from the addition of different types of bands to experimental cigarettes.

MATERIALS AND METHODS

A battery of assays that are typically used in toxicology studies with cigarette smoke, namely smoke chemistry, in vitro mutagenicity and cytotoxicity, and inhalation studies with rats, were used to evaluate different band characteristics added to cigarette paper.

RESULTS

Although differences in the amount of band material was associated with an increase in some metals measured in mainstream tobacco smoke, it was not dose responsive to any band design parameter (base paper permeability, band width, band spacing, band chalk amount, or citrate). Occasional, minor differences were produced by the different types of bands; overall, there was no increased toxicity.

CONCLUSION

Although there were increases and decreases in some mainstream smoke constituents, the in vitro and in vivo testing performed demonstrated that low-permeability bands on cigarettes do not modify the toxicity of smoke inhaled by smokers.

Toxicological evaluation of an electrically heated cigarette. Part 4: Subchronic inhalation toxicology

The biological activity of mainstream smoke from an electrically heated cigarette (EHC) with controlled combustion and from the University of Kentucky Reference Cigarette 1R4F was determined in Sprague Dawley rats exposed nose-only for 90 days, 6 h a day, 7 days per week. For an equivalent response comparison between the two cigarette types, two doses were chosen for the EHC where the anticipated results were in the dynamic range of the 1R4F dose-response curve (four concentrations) for most end points. The number of cigarettes smoked per m(3) of diluted smoke resulted in total particulate matter concentrations of 40 and 90 microg l (-1) for the EHC and 40-170 microg l (-1) for the 1R4F. Biomonitoring indicated achievement of target doses. Mainstream smoke yields were lower for the EHC, with the exception of formaldehyde. No smoke-related mortality, remarkable in-life observations or abnormal gross pathological findings were observed. Smoke- and dose-related clinical pathology and organ weight changes included: increases in segmented neutrophils, some liver parameters and lung and adrenal weight relative to body weight; and decreases in lymphocytes, glucose concentration and spleen weight. Smoke-related histopathological findings in the respiratory tract included epithelial cell hyperplasia, squamous metaplasia, atrophy and accumulation of pigmented alveolar macrophages; they were mostly dose-dependent, more pronounced in the upper than lower respiratory tract and completely or partially reversed by 6 weeks post-inhalation. Qualitatively, the biological effects seen for the EHC and the 1R4F were comparable and similar to those observed in other mainstream smoke inhalation studies. Quantitatively, the biological activity of the EHC mainstream smoke was, on average, 65% lower than that of the 1R4F mainstream smoke on an equal cigarette basis and equivalent activity on an equal TPM basis.

Effects of mainstream and environmental tobacco smoke on the immune system in animals and humans: a review

This review evaluates the available information on the effects of mainstream and environmental tobacco smoke on the immune system in animals and humans. The primary emphasis is on mainstream smoke since little information is available on the effects of environmental smoke. The effects of mainstream tobacco smoke on the immune system in humans and animals are similar. Animals exposed to mainstream tobacco smoke for periods of a few weeks generally exhibit a slight immunostimulation. However, subchronic and chronic exposure studies indicate that immunosuppressive changes develop. Lymphocyte proliferation in response to the mitogens PHA and LPS is decreased, suggesting compromise of cell function. Antibody production can be suppressed. Smoke-exposed animals that are challenged with metastasizing tumors or viruses have been shown to exhibit a higher incidence of tumorigenic and infectious diseases, respectively. Localized immunological changes in the lung can include reduction of bronchus-associated lymphoid tissue and immunoglobulin levels. Smoking-related changes in the peripheral immune system of humans have included elevated WBC counts, increased cytotoxic/suppressor and decreased inducer/helper T-cell numbers, slightly suppressed T-lymphocyte activity, significantly decreased natural killer cell activity, lowered circulating immunoglobin titers, except for IgE which is elevated, and increased susceptibility to infection. The effects of environmental tobacco smoke on the immune system, in contrast to mainstream tobacco smoke, have just begun to be investigated and information available in the literature, to date, is limited. Immunoreactive substances are known to be present in environmental tobacco smoke, but to date, environmental tobacco smoke has been more closely associated with irritation than sensitization. A few studies have indicated a potential for environmental smoke-induced hypersensitivity and suppression of immunoregulatory substances. In contrast, other investigators have failed to detect immunological or other biological changes associated with environmental smoke. Clearly, more research is needed to resolve these differences.

Cigarette smoking and inorganic dust in human lungs

Whole left lungs from 18 smokers and 16 nonsmokers were obtained at autopsy and studied to determine the severity of subclinical emphysema and elemental dust loads of aluminum and silicon. Lungs selected were from individuals with work histories in non-dusty occupations and were sex- and age-matched by decade. Whole lung Gough sections were studied and emphysema was graded on a 0 to 100 score. Concentrations of aluminum and silicon were determined in homogenized-lyophilized lung of all 34 cases by plasma emission spectrometry. In addition, histological sections from 9 pairs of age-matched smokers and nonsmokers were studied by light microscopy and scanning electron microscopy in concert with semiquantitative x-ray spectrometric analysis of aluminum and silicon content in specific anatomical regions. The results of these studies indicate that aluminum and silicon concentrations increase in smokers with increased cigarette smoking. As expected, severity of pulmonary emphysema was associated with heavy cigarette smoking.

Cell proliferation in lung following acute fly ash exposure

Cell proliferation was examined in the lung parenchyma, the ciliated airway epithelium and the lymph nodes of Fischer-344 rats following a 6-h exposure to fly ash obtained from the baghouse of an experimental fluidized bed combustor. The fly ash concentration was 142 mg/m3 with a mass median aerodynamic diameter (MMAD) of approximately 3.0 micron and a geometric standard deviation (sigma g) of approximately 2.6. Lung deposition of fly ash was measured in the right lung to be 90 +/- 20 and 80 +/- 30 mg for male and female rats, respectively, resulting in a calculated value for male rats of (140 +/- 30 micrograms/animal) and for female rats of 130 +/- 50 micrograms/animal). Autoradiographic methods were used to detect cells that incorporated [3H] thymidine. About a 10-fold increase in labeling of the lung epithelial type II cells was observed following the 6-h fly ash exposure. There was also an increase in [3H] thymidine incorporation into DNA of alveolar macrophages. Labeling activity of macrophages within the lung was increased for up to 4 days following fly ash exposure; however, the size of the macrophage population was not altered. Following exposure, a higher labeling index was also observed in the epithelial cells of the airways. Labeling in the trachea reached a peak at 4 days after exposure while in the bronchi and in small airways (inside diameter of less than 0.35 mm) the highest level of labeling was observed at 1 day after exposure. Labeling in airway epithelial cells was increased 2-4 times above that of sham-exposed animals. Lung-associated lymph nodes accumulated particulate material and had variable amounts of [3H]thymidine incorporation. These results demonstrate that acute inhalation exposure to fly ash initiated cell division or DNA synthesis in several cell populations of lung parenchyma and airways.

Deposition and clearance of labeled cigarette smoke particles in rat respiratory and digestive tract

In this investigation 160 8-wk-old Sprague-Dawley rats inhaled smoke from 14C-labeled cigarettes in a Hamburg II smoking machine. The research cigarettes were labeled with [16,17-14C]dotriacontane. Eighty of the rats were acclimatized to smoke from nonlabeled research cigarettes for 21 d before inhaling labeled cigarette smoke. The investigation was divided into four experiments. In experiment I all rats were killed immediately after exposure to the 14C-labeled smoke from 30 cigarettes (10 muCi per cigarette) and the organs of the respiratory and digestive tracts were measured for 14C activity. These animals showed high activity in the apex nasi, fundus nasi, and larynx. The highest activity was found in the lobus dexter caudalis and the lobus sinister of the lung. The lungs contained four-fifths of the condensate inhaled into the respiratory tract. In experiment II three animals were killed immediately after smoking, three after 6 h, and four after 24 h. No activity was found after 6 h in apex, fundus nasi, larynx, and trachea. The lungs showed no clearance at all. The activity in the digestive tract was highest in the stomach and the esophagus immediately after cessation of smoking. These values decreased rapidly after 6 h. In experiment III the animals were killed after 7, 21, and 42 d. Clearance from the upper respiratory tract was fast, whereas clearance from the lungs was slow. Clearance from all lung lobes was faster in the nonacclimatized animals. In experiment IV the rats inhaled the smoke from 14C-labeled cigarettes (2 muCi per cigarette) on 5 successive days. The animals were killed 7, 14, and 21 d after the last smoke inhalation. Clearance from the lungs was slower in acclimatized and non-acclimatized animals than in experiment III.

Cigarette smoke induced pathology of the rat respiratory tract: a comparison of the effects of the particulate and vapour phases

Changes in the rat respiratory tract produced by a 12-week exposure to the particulate or vapour phases of cigarette smoke are described and compared with the changes produced by combined exposure to both phases. The most extensive changge in the upper respiratory tract was a pronounced squamous metaplasia of the laryngeal epithelium, along with extensive deciliation and squame cell production. In the lung, smoke exposure produced marked increase in the numbers of bronchial goblet cells and intra-alveolar brown-gold macrophages. None of the above changes could be directly attributed to exposure to vapour phase alone, and in many cases the lesions produced by whole smoke and by carbon filtered smoke were directly comparable. For lesions to occur in some ciliated areas of the tract both phases of the smoke were required.

Inhalation toxicity studies on cigarette smoke (VIII). 6-week comparative experiments using modified flue-cured cigarettes: general toxicology

Details are given of studies carried out to compare the inhalation toxicity to rats of smoke from cigarettes modified to give a range of deliveries of particulate matter. Dosimetry work showed that under conditions similar to those used for subsequent toxicity experiments, smoke particulates deposited in the lower respiratory system within the approximate dose range of 500--700 microgram TPM/g lung tissue. Respiratory monitoring showed that the response of animals to a range of smoke exposure conditions was similar and did not change during the course of the experiments. This observation was confirmed by monitoring of blood carboxyhaemoglobin levels after exposure to smoke. During exposure to smoke the rate of respiration decreased to approximately 40% of the pre-exposure rate. Tidal volume, after an initial slight decrease, showed a progressive increase throughout the smoke exposure period. Bodyweight gain was reduced in those animals subjected to smoke exposures. True sham-smoked animals showed a body weight gain intermediate between that of smoke and cage control rats. The clear indications of such between-group differences in response to treatment, coupled with the indicators of consistent dosing of animals under the defined exposure conditions, form a sound basis for the interpretation of terminal pathology.

Inhalation toxicity studies on cigarette smoke (VII). 6-week comparative experiments using modified flue-cured cigarettes: histopathology of the conducting airways

Rats were exposed twice daily for 6 weeks to diluted smoke derived from cigarettes with a range of deliveries of particulate matter. The inhaled smoke caused squamous metaplasia and keratinising hyperplasia in the larynx and goblet cell hyperplasia in the nasal cavity, trachea and intrapulmonary bronchus. Squamous metaplasia occurred in the larynx of almost all rats exposed to smoke but never in their tracheas or bronchi. The degree of reaction observed for the other responses, except goblet cell hyperplasia in the trachea, was positively related, by quantitative microscopy, to the particulate delivery of cigarettes. These findings, together with other smoke-induced changes which occur in the pulmonary alveoli, provide a basis for the short-term bioassay of inhalation toxicity of cigarette smoke.