Subchronic inhalation by rats of mainstream smoke from a cigarette that primarily heats tobacco compared to a cigarette that burns tobacco

A subchronic, nose-only inhalation study comparing the potential biological activity of mainstream smoke from a cigarette that primarily heats tobacco (Eclipse) to mainstream smoke from a 1R4F reference cigarette was conducted using Sprague-Dawley rats of each gender. Smoke exposures were for 1 h/day, 5 days/wk for 13 wk, at concentrations of 0, 0.16, 0.32, or 0.64 mg wet total particulate matter (WTPM)/L air. Smoke was generated at the Federal Trade Commission standard of a 2-s puff of 35 ml, taken once per minute. Clinical signs, body and organ weights, clinical chemistry, hematology, carboxyhemoglobin, serum nicotine, plethysmography, gross pathology, and histopathology were determined. Plethysmography indicated that respiratory rate was decreased at all concentrations of 1R4F smoke, but only at the high concentration of Eclipse smoke. Tidal volume was depressed and minute volume was lower for all smoke-exposed rats. Rats exposed to Eclipse smoke inhaled more smoke at the low and mid-concentration exposures than rats exposed to equivalent concentrations 1R4F smoke. Carboxyhemoglobin and serum nicotine were directly related to the exposure concentrations of carbon monoxide (CO) and nicotine in an exposure-dependent manner. Body weights were slightly lower in smoke-exposed rats, while no treatment-related effects were seen in clinical signs, clinical chemistry, hematology, or gross changes at necropsy. The only treatment-related effect seen in organ weights was an increase in heart weight in females in the Eclipse high-concentration exposure group, attributed to higher CO in the Eclipse exposure atmosphere. Higher CO resulted from the lower dilution of Eclipse smoke required to maintain WTPM concentrations equal to those of the 1R4F smoke, and not from a higher CO yield from Eclipse cigarettes. Nasal epithelial hyperplasia and ventral laryngeal squamous metaplasia were noted after exposure to either the 1R4F or Eclipse smoke. The degree of change was less in Eclipse smoke-exposed rats. Lung macrophages were increased to a similar extent in the Eclipse and 1R4F smoke-exposed groups. Brown/gold pigmented macrophages were detected in the lungs of rats exposed to 1R4F smoke, but not those exposed to Eclipse smoke. Subsets of rats from each group were maintained for an additional 13 wk without smoke exposures. Most of the changes noted at the end of the smoke exposures had disappeared, while those that remained were regressing toward normal. Evaluation of these findings indicated the overall biological activity of Eclipse smoke was less than 1R4F smoke at comparable exposure concentrations.

Relevant exposure to environmental tobacco smoke surrogate does not produce or modify secretory otitis media in the rat

Parental smoking is a possible risk factor in the development of secretory otitis media (SOM) in children. This experiment was designed to determine, using rats as an experimental model, whether exposures to environmental tobacco smoke (ETS) produce SOM and whether ETS exposure affects the rate of clearance of an experimentally induced effusion. Male Sprague-Dawley rats were exposed to 3 different concentrations of aged and diluted sidestream smoke, a surrogate for ETS, from IR4F research cigarettes for 6 hr per day for 5 days. Experimental SOM was induced bilaterally in subgroups of animals from each group, by cold air exposure to the external auditory canals. Ears of rats were examined during the in-life portion of the study. Histopathologic examination of the middle ear was conducted at the termination of the 5-day period. The production of SOM was not induced by ETS exposure, nor were there differences noted between the groups in the rates of clearance of the experimentally induced SOM. Short-term exposure to ETS did not affect the acquisition or clearance of SOM in the rat.

Induction of short-term biomarkers of tumor promotion in skin of CD-1 mice by petroleum middle distillates: preliminary observations

The induction of sustained epidermal hyperplasia in mouse skin has been shown to be a reliable predictor of tumor promoting activity for chemicals as diverse as phorbol esters, anthralins, n-dodecane and organic peroxides (DiGiovanni, 1992). The results contained herein demonstrate that API 81-07 and API 81-10, petroleum middle distillates that exhibit tumor promoting activity in mouse skin, induce epidermal hyperplasia and ODC activity. Other petroleum middle distillates (odorless light petroleum hydrocarbons, a light vacuum distillate, and a mineral seal oil) were also shown to share these activities. It should be emphasized that the relevance of these observations to human skin remains unresolved; however, the availability of these short-term biomarkers offers the opportunity to address the issue by performing comparative investigations on the effects of petroleum middle distillates on human skin xenografted to athymic (nude) mice. Such studies are being initiated.

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.

Fourteen-day inhalation study in rats, using aged and diluted sidestream smoke from a reference cigarette. I. Inhalation toxicology and histopathology

Sprague-Dawley rats were exposed 6 hr per day for 14 consecutive days to aged and diluted sidestream smoke (ADSS), used as a surrogate for Environmental Tobacco Smoke (ETS), at concentrations of 0.1 (typical), 1 (extreme), or 10 (exaggerated) mg of particulates per cubic meter. Animals were exposed nose-only, inside whole-body chambers, to ADSS from the 1R4F reference cigarette. End-points included histopathology, CO-oximetry, plasma nicotine and cotinine, clinical pathology, and organ and body weights. The only pathological response observed was slight to mild epithelial hyperplasia and inflammation in the most rostral part of the nasal cavity, in the high-exposure group only. No effects were noted at medium or low exposures. The minimal changes noted were reversible, using a subgroup of animals kept without further treatment for an additional 14 days. Overall, the end-points used in the study demonstrated that there was no detectable biological activity of ADSS at typical or even 10-fold ETS concentrations and that the activity was only minimal at very exaggerated concentrations (particle concentrations 100 times higher than typical real-world concentrations).

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.

Histologic changes in the respiratory tract induced by inhalation of xenobiotics: physiologic adaptation or toxicity?

Toxicologists and pathologists are often faced with the dilemma of categorizing changes observed in the respiratory tract of laboratory animals as either "adaptive" or "toxic." However, it is often difficult to interpret the nature of a given change as either "adaptive" or "toxic." Certain lesions or changes in the respiratory tract are to be expected from the concentration of materials given or the experimental design of a study. Careful analysis suggests that some of these changes may be more properly described as adaptive rather than toxic within the context of a given study or situation. Tissue changes discussed in this paper include squamous metaplasia of laryngeal epithelium, goblet cell change in respiratory epithelium, macrophage accumulation within alveoli, and bronchiolization of alveolar epithelium. Examples provided show that some of these changes observed in inhalation studies are similar in severity but slightly increased in frequency over sham control animals. The introduction of exogenous material into the respiratory tract of laboratory animals in an experimental setting should be expected to result in certain changes. The challenge scientists must accept is to interpret these changes so that toxic events may be separated from adaptive changes. In order to meet this challenge, studies incorporating several species and novel technologies may have to be utilized.

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

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 micrograms/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.

Virulence and immunogenicity of a temperature-sensitive dengue-2 virus in lower primates

Clones of dengue-2 virus were tested for virulence by inoculation of rhesus monkeys and chimpanzees. Although primates showed no overt signs of illness, inoculation with the parent virus or a subline of a large-plaque clone resulted in a viremia lasting 1 to 7 days. By these criteria, sublines of a small-plaque clone were significantly less virulent and produced little or no viremia in primate hosts. Although they had a substantially reduced viremia, primates inoculated with the small-plaque sublines showed stimulation of complement-fixing, hemagglutination-inhibiting, and neutralizing antibodies. The protection afforded rhesus monkeys 3 months after inoculation with two of the small-plaque sublines was demonstrated by a lack of viremia and a failure to escalate preexisting antibody levels after challenge with the parent virus. Both the S-1 subline and the parent virus had a limited capacity to produce central nervous system pathology in monkeys inoculated intrathalamically and intrathecally. Evidence thus far accumulated for primates indicates that the S-1 subline of dengue-2 virus has potential value as a candidate vaccine virus.

Diagnosis of human rabies by the cornea test

The second death due to rabies encephalitis occurring among American servicemen stationed in the Republic of Vietnam is reported. The clinical diagnosis was confirmed by performing the direct fluorescent antibody test for rabies on smears of corneal epithelial cells obtained on the second day of hospitalization. The reliability of various laboratory procedures in confirming the diagnosis of human rabies early in the course of clinical illness is discussed. The cornea test is a useful and rapid method of diagnosing human rabies prior to the development of significant serum antibody titers.