Gary T. Burger

Histological sectioning of the rodent larynx for inhalation toxicity testing

In rodents, the larynx is a major site of histopathologic alteration following inhalation exposure to particulates, vapors, and aerosols. Specifically, the epithelial lining of a narrowly delineated region on the ventral floor of the larynges of rats and mice appears to be especially vulnerable to inhaled materials, and is recognized as a preferred site for histopathological evaluation in inhalation studies. This site is located at the base of the epiglottis, cranial to the ventral laryngeal diverticulum (ventral pouch). The presence of underlying seromucinous glands is critical for histologic identification of this site. We report a histologic sectioning technique, using the ventral laryngeal diverticulum as the anatomical landmark, to obtain tissue sections from this area of predilection in rats and in mice.

Ninety-day inhalation study in rats, comparing smoke from cigarettes that heat tobacco with those that burn tobacco

Abstract Eight groups of 30 male and 30 female rats were exposed 1 hr per day, 5 days per week for 13 weeks, to smoke from reference (tobacco burned) or test (tobacco only heated) cigarettes, at nicotine concentrations of 5, 15, or 30 μg/liter of air. Similar smoke concentrations of wet total particulate matter and carbon monoxide were produced in each of the test/reference comparisons. There was a pronounced depression of minute ventilation of animals in the reference groups, but not in the test animals. Blood carboxyhemoglobin concentrations were similar in animals exposed to smoke from test and reference cigarettes. Plasma concentrations of nicotine and cotinine in the test groups were higher than in the reference groups. There were no differences between the smoke-exposed groups in terms of body weight or feed consumption. At necropsy, an increase in heart weight was noted in both high exposure groups. There were notable differences in histopathology, with fewer and less-pronounced changes in the test groups than in the reference groups. Many of the histopathological responses induced in the reference groups were absent in the test groups. Overall, the study demonstrated a substantial reduction in the biological activity of smoke from the test cigarette when compared with the reference.

2-Week and 13-Week Inhalation Studies of Aerosolized Glycerol in Rats

AbstractThe potential toxicity of aerosolized glycerol was studied by 2-wk and 13-wk nose-only inhalation exposures in Sprague-Dawley-derived (Cr1:CD) rats. In the first study, 10 ratslsedgroup received 10 nose-only exposures of 6 h/day for 2 wk over a 14-day period to mean aerosol concentrations of 0, 7.00 ± 0.08, 1.93 ± 0.123, or 3.91 ± 0.458 mg glycerol/l of filtered room air: Animals were observed for signs of toxicity twice daily, were weighed at 2– to 3-day intervals, and diet consumption was recorded at weekly intervals. All rats underwent complete necropsy, and designated tissues were weighed and examined histopathologically Blood was collected and analyzed for specific hematological and clinical chemistry parameters. The results of this study showed that rats exposed to 6-h nose-only inhalation for 70 days at all three concentrations of glycerol exhibited minimal to mild squamous metaplasia of the epithelium lining the base of the epiglottis. In a second study, 75 ratslsedgroup were exposed 6 h/d...

Comparative Inhalation Study in Rats, Using a Second Prototype of a Cigarette that Heats Rather than Burns Tobacco

AbstractSprague-Dawley rats were exposed nose-only for 1 h/day on weekdays for 13 weeks to the smoke from test and reference cigarettes. The test cigarette was a new prototype: the tobacco is heated rather than burned. The University of Kentucky 1R4F cigarette was used as a reference. The exposures used were around 25% higher than those used in earlier studies, and for the test cigarette the resulting blood carboxy-hemoglobin concentrations approached those associated with death (62+%). The smoke from the reference cigarette produced substantial reductions in breathing frequency, whereas the smoke from the test cigarette did not. The availability of nicotine from test and reference cigarettes was very similar. The histopathology seen (mucus-secreting cells; nasal, laryngeal, and bronchial hyperplasia and squa-mous metaplasia, pulmonary macrophages) indicated that most of the changes observed in the reference animals were absent in the test animals. When changes were seen in the test groups (primarily in t...

Chemical and Biological Studies of a Cigarette That Heats Rather Than Burns Tobacco

Cigarettes can be developed that heat rather than burn tobacco. Such products would be expected to have less “tar” and other combustion products than cigarettes that burn tobacco. With one product of this type, benzo(a)pyrene, N‐nitrosamines, phenolic compounds, acetaldehyde, acrolein, hydrogen cyanide, and N‐heterocyclic compounds have been reduced 10‐ to 100‐fold compared to the Kentucky reference (1R4F) cigarette, a representative low‐tar cigarette. The yields of nicotine and carbon monoxide from this new cigarette are less than the yields of 95% and 75%, respectively, of the cigarettes sold in the United States during 1988. Nicotine absorption from smoking this new cigarette is not significantly different from that of tobacco‐burning cigarettes yielding equivalent levels of nicotine. The urine mutagenicity of smokers of new cigarettes is significantly less (P < .05) than that of smokers of tobacco‐burning cigarettes and is not significantly different (P > .10) from that of nonsmokers. We conclude that cigarettes which heat rather than burn tobacco can reduce the yield of tobacco combustion products. This simplification of smoke chemistry had no effect on nicotine absorption in smokers and resulted in a reduction of biological activity in smokers as measured by urine mutagenicity.

Nose-Only Exposure of Rats to Carbon Monoxide

AbstractAnimals were exposed nose-only to 0, 527, 1091, or 1800 parts per million (ppm) carbon monoxide for 1 h/day, for 74 consecutive days. Blood carboxyhemoglobin (COHb) concentrations in the 1800 ppm group approached those concentrations associated with lethality (62+%). Respiratory minute volume was reduced to 73% of preexposure values in animals exposed to 1800 ppm CO, through changes in respiratory rate. Most of the erythrocyte parameters showed increases that were proportional to the CO concentration. Accumulation half-lives for COHb in the low, medium, and high exposure groups were 17.2, 12.6, and 9.0 min, respectively; the elimination half-lives were 42.3, 32.6, and 29.7 min, respectively Heart weights were increased by up to 32% in males and 47% in females as a result of this very high exposure to 1800 ppm CO. Chronic inflammation was observed in the cardiac muscle of animals exposed to 1800 ppm CO. The inflammation consisted of scattered interstitial aggregates of lymphohistiocytic cells, foun...

Comparative genotoxicity testing of mainstream whole smoke from cigarettes which burn or heat tobacco

The genotoxic potential of mainstream whole smoke (MWS) from cigarettes which heat tobacco (TEST) was compared to the genotoxic potential of MWS from a cigarette which burns tobacco (REFERENCE). MWS was collected from a University of Kentucky 1R4F cigarette (REFERENCE) and two, TEST cigarettes, one with regular flavor and the other with menthol flavor. All cigarettes were smoked on a smoking machine and the particulate phase was collected on Cambridge filter pads. The vapor phase, which passed through the pad, was bubbled into a dimethyl sulfoxide (DMSO) trap. The filter pad was extracted with the DMSO in the trap and additional DMSO to obtain MWS. MWS representing an identical number of cigarettes was tested to make a per-cigarette comparison of their genotoxic potential. REFERENCE MWS was mutagenic and cytotoxic in the Ames assay in the presence of metabolic activation while it was cytotoxic but not mutagenic in the absence of metabolic activation. Statistically significant increases in frequency of both sister-chromatid exchanges and chromosomal aberrations were observed in Chinese hamster ovary cells exposed to REFERENCE MWS with and without metabolic activation. MWS from the TEST cigarettes, with either regular or menthol flavor, was neither cytotoxic nor mutagenic in any of these assays. In summary, MWS from the 2 TEST cigarettes was neither genotoxic nor cytotoxic under conditions where MWS from the REFERENCE cigarettes was genotoxic and/or cytotoxic in a concentration-dependent manner.

Interspecies Variations in the Histology of Toxicologically Important Areas in the Larynges of CRL:CD Rats and Syrian Golden Hamsters*†

Specific regions in the rodent larynx exhibit cellular changes in response to inhaled xenobiotics. These regions include the base of the epiglottis, ventral pouch, and medial surfaces of the vocal processes of the arytenoid cartilages. There are interspecies differences among laboratory rodents in the microscopic anatomy of these sensitive areas of the laryngeal mucosa. In CRL:CD strain Sprague-Dawley rats, the mucosa covering the epiglottis differs from that of Syrian golden hamsters. The epithelium covering the base of the epiglottis is relatively thin in rats and is composed of a mixture of cell types, whereas in hamsters it is much thicker and is made up almost entirely of tall ciliated columnar cells. The cartilage supporting the ventral pouch in the larynges of hamsters is much more prominent than in rats and forms a distinct protrusion into the laryngeal lumen at the base of the epiglottis. The purpose of this paper is to describe and illustrate these and other subtle differences in rat and hamster laryngeal anatomy, which may be of toxicologic significance.

Comparative Subchronic Inhalation Bioassay in Hamsters of a Cicarette that only Heats Tobacco

AbstractThis subchronic inhalation study compared the effects of nose-only exposure in hamsters to the smoke from the University of Kentucky 1R4F reference cigarette, which burns tobacco, and a test cigarette, which only heats tobacco. Thirty-four Syrian golden hamsters per sex per group were exposed to either reference or test smoke at 0, 120, 350, or 640 pg wet total particulate matter (WTPM)/l of air, 1 h/day, 5 days/wk. Of these 34 hamsters, 9 hamsters/sex/group were evaluated for respiratory flow, blood carboxyhemoglobin, and plasma nicotine and coining during the first 12 wk of exposure and then killed. Another 75 of the 34 hamsters/sex/group were killed and evaluated after 13 wk of exposure (Basic Study); the remaining 10 hamsters/sex/group were held without smoke exposure for an additional 6 wk (Recovery Croup). Clinical appearance, mortality body and selected organ weights, and gross and histologic changes were examined in hamsters killed after 13 wk of exposure and 6 wk after cessation of exposu...

Histopathology, Urine Mutacenicity, and Bone Marrow Cytocenetics of Mice Exposed Nose-Only to Smoke from Cigarettes that Burn or Heat Tobacco

AbstractMale and female B6C3F1 mice were exposed nose-only to smoke from a test cigarette that heats tobacco, or from a reference cigarette that burns tobacco. Cigarette smoke was generated by a smoking machine, and the concentrations of wet total particulate matter (WTPM) were adjusted to 0, 0.16, 0.32, or 0.64 mg/l. Exposures were performed 1 h/day for 14 consecutive days. Urine mutagenicity was assessed by a modified Ames bacterial assay Clastogenesis (sister-chromatid exchanges, chromosome aberrations, and micronuclei) was evaluated in bone marrow cells. Respiratory rate was depressed significantly by exposure to smoke from the reference cigarette, but not the test. Blood carboxyhemoglobin, plasma nicotine, and plasma cotinine showed exposure-dependent increases in the smoke-exposed animals. Histopathological changes similar to those noted previously in smoke-exposed rats were noted, with fewer and less pronounced changes in the animals exposed to smoke from the test cigarette when compared with the r...