Cigarette smoke inhalation decreases alpha 1-antitrypsin activity in rat lung.

Brief inhalation exposure of rats to three or six puffs of cigarette smoke significantly decreases elastase inhibitory capacity per milligram of alpha 1-antitrypsin in lung lavage fluid. This effect is not observed in ozone-tolerant rats and can be reversed by treating the lung lavage fluid from smoke-exposed rats with reducing agents. Samples of human serum obtained immediately after smoking also show decreased elastase inhibitory capacity per milligram of alpha 1-antitrypsin. Again, elastase inhibitory capacity can be restored by treatment with a reducing agent. Cigarette smoking may cause emphysema by inactivating alpha 1-antitrypsin through oxidation.

Experimental approaches for exposure to sized glass fibers.

A number of studies have shown that glass fibers induce both malignant mesothelioma and fibrosis in rats and that these reactions may be primarily a function of the physical properties of the fiber. However, these studies were carried out with fibers having broad size distributions and used methods of administration which bear little resemblance to the way man is exposed. To better characterize the health effects of glass fibers, techniques have been developed to expose rats to glass fibers of defined sizes by intratracheal instillation of aqueous suspensions and by "nose only" inhalation exposure, and to determine the deposition, translocation, and ultimate fate of these fibers in the rat. The fibers have known size distributions with geometric mean diameters of 1.5 micrometers (sigma g = 1.1) and lengths of either 5 micrometers (sigma g = 1.49) or 60 micrometers (sigma g = 3.76). The fibers have been activated with neutron irradiation. Of the several resulting radionuclides, 65Zn appeared to be the most suitable for long-term clearance studies by use of in vivo whole body radioassay techniques. A fluidized bed aerosol generator has been developed to expose rats by "nose only" inhalation to approximately 500 fibers/cm3. The generator and exposure system permits reuse of fibers which pass through the exposure chamber and produces no significant alteration of the fiber size distribution. Rats were exposed by intratracheal instillations to 20 mg of the longer fibers and to equal numbers (2 mg) and equal mass (20 mg) of the shorter fibers. Through approximately 19 weeks little difference was observed in the whole rat clearance rate of long versus short fibers in the initial exposure group. Histopathology, however, showed differences at this time with the short fibers apparently successfully phagocytized by alveolar macrophages and cleared to the lymph nodes, while the long fibers were not.

Effects of vinyl chloride exposures to rats pretreated with phenobarbital.

Male rats were exposed to 10 consecutive days, 6 hr/day, to vinyl chloride vapors at an average concentration of 13,500 ppm. The exposed rats were divided into three groups of eight rats each: one group was pretreated with 3-methylcholanthrene, one group was pretreated with phenobarbital, and the third group received no treatment. Half the animals in each group were sacrificed 18 hr after the last exposure and half were sacrificed 4 days later. In a second experiment, four rats pretreated with phenobarbital were exposed to vinyl chloride vapors at a concentration of 17,300 ppm for 2 days and sacrificed about 9 A.M. on the third day. In both experiments control animals, also treated with phenobarbital or 3-methylcholanthrene, were exposed to air only. At the time of sacrifice, lungs, kidneys, spleen, heart, and a small piece of liver from each animal were preserved for histological examination. The remainder of the liver was processed for assay of microsomal enzyme activity. The following parameters were investigated: growth rate, organ weights, morphological changes, and both benzphetamine-N-demethylase activity and cytochrome P-450 content of microsomes prepared from the livers. In both experiments the only marked difference noted in any group was a decrease in the growth rate of the animals exposed to vinyl chloride and treated with phenobarbital. This decreased growth rate was particularly apparent on the third day of the vinyl chloride exposures. Occasional morphological changes were also seen in the livers of the animals treated with phenobarbital and exposed to vinyl chloride.

Inhalation exposure methodology.

Modern man is being confronted with an ever-increasing inventory of potentially toxic airborne substances. Exposures to these atmospheric contaminants occur in residential and commercial settings, as well as in the workplace. In order to study the toxicity of such materials, a special technology relating to inhalation exposure systems has evolved. The purpose of this paper is to provide a description of the techniques which are used in exposing laboratory subjects to airborne particles and gases. The various modes of inhalation exposure (whole body, head only, nose or mouth only, etc.) are described at length, including the advantages and disadvantages inherent to each mode. Numerous literature citations are included for further reading. Among the topics briefly discussed are the selection of appropriate animal species for toxicological testing, and the types of inhalation studies performed (acute, chronic, etc.).

Effect of exposure route, regimen, and duration on benzene-induced genotoxic and cytotoxic bone marrow damage in mice.

Mice were exposed to benzene for 13 to 14 weeks by inhalation for either 3 or 5 consecutive days per week or by gavage for 5 consecutive days per week. A weekly evaluation of peripheral blood smears for micronucleated (MN) erythrocyte frequencies and for the percentage of polychromatic erythrocytes (PCE) indicated that the induction of MN-PCE by benzene depended on the sex and strain of mice and on the route of exposure, but not on the inhalation regimen or on the exposure duration. The frequency of MN normochromatic erythrocytes (NCE) not only depended on the sex and strain of mice and on the route of exposure, but directly depended on the inhalation regimen and on the exposure duration. Similarly, the extent of erythropoietic depression in benzene-exposed mice was dependent on sex, mouse strain, exposure duration, and route. However, in contrast to the MN-NCE data, the 3 day/week exposure regimen induced a more persistent depression in erythropoiesis than the 5 day/week exposure regimen. Exposure to benzene also induced in mice a significant depression in packed cell volume (PCV) and bone marrow cellularity, the magnitude of which depended on the sex and strain of mice and on the regimen and route of exposure.

Hematotoxicity and carcinogenicity of inhaled benzene.

CBA/Ca male mice have been exposed to benzene in air at 10, 25, 100, 300, 400, and 3000 ppm for variable intervals 6 hr/day, 5 days/week for up to 16 weeks. Two weeks of inhaling 10 ppm produced no hematologic effects; 25 ppm induced a significant lymphopenia. Inhalation of 100, 300, and 400 ppm produced dose-dependent decreases in blood lymphocytes, bone marrow cellularity, marrow content of spleen colony-forming units (CFU-S) and an increased fraction of CFU-S in DNA synthesis. Exposure of mice to 300 ppm for 2, 4, 8, and 16 weeks produced severe lymphopenia and decrease in marrow CFU-S. Recovery was rapid and complete after 2 and 4 weeks of exposure. After 8 and 16 weeks of exposure, recovery of lymphocytes was complete within 8 weeks. It took 16 weeks for the CFU-S to recover to that of the age-matched controls after 8 weeks of exposure and 25 weeks to recover to age-matched after 16 weeks of exposure. Inhalation of 3000 ppm for 8 days was less damaging than inhalation of 300 ppm for 80 days (same integral amount of benzene inhaled). The inhalation of 3000 ppm has not increased the incidence of leukemia or shortened its latency for development. Inhalation of 300 ppm 6 hr/day for 16 weeks significantly increases the incidence of myelogenous neoplasms in male CBA/Ca mice. Inhalation of 100 ppm for same interval does not influence incidence of myelogenous neoplasms but does increase incidence of solid neoplasms particularly in female CBA/Ca mice. Benzene is a potent carcinogen in CBA/Ca mice.

Effect of in vivo exposure to benzene on the characteristics of bone marrow adherent cells.

The effect of benzene on the adherent cell population, cultured from the bone marrow of exposed mice was investigated in the presence and absence of hydrocortisone. The adherent CFUs from exposed animals did not differ either in numbers or self-replicate ability to those derived from shown exposed animals. Adherent layers from mice exposed to 100 or 400 pp-benzene were devoid of fat cells regardless of the presence or absence of hydrocortisone. Hydrocortisone was shown to influence the proportion of acid phosphatase-positive cells derived from benzene-exposed animals. Those results suggest that benzene exposure may influence the bone marrow stromal cells.

Changes in rat lung structure and composition as a result of subchronic exposure to acrolein.

Groups of Fischer-344 rats were exposed to either filtered air, 0.4, 1.4, or 4.0 ppm acrolein for 62 days (6 h/day, 5 days/week). Mortality was observed only in the 4.0 ppm chamber, where 32 of 57 male rats died, but none of the 8 exposed females died. The lungs of the 4.0 ppm group were heavier than those of the larger control animals. Relative to controls, there was a 20% increase in total dry lung weight while the percent dry weight decreased 1.5% in the high dose group. This increased dry weight and the absence of significant changes in the DNA and protein content per unit dry weight indicated that the greater lung weight observed in this group was in part due to increased cellularity. Lung connective tissue content was increased as a result of subchronic acrolein exposure. The amount of elastin per unit dry weight was 173% of control values in the animals exposed to 4.0 ppm acrolein. Collagen levels were elevated in both the 1.4 and 4.0 ppm groups, 113 and 137%, respectively, of control values. Histologically, the 4.0 ppm animals demonstrated bronchiolar epithelial necrosis and sloughing, bronchiolar edema with macrophages, and focal pulmonary edema. Exposure related lesions were observed in only 3 of the 31 rats examined from the 1.4 ppm chamber and in none of the animals exposed to 0.4 ppm acrolein.

The effect of exposure regimen and duration on benzene-induced bone-marrow damage in mice. I. Sex comparison in DBA/2 mice.

In the mouse, the concurrent evaluation of micronuclei frequencies in peripheral blood polychromatic erythrocytes (PCE) and normochromatic erythrocytes (NCE) permits an assessment of both recently-induced and chronically-accumulated bone-marrow damage. This assay system was used to evaluate on a weekly basis the effect of exposure duration (1-13 weeks, 6 h per day) and exposure regimen (Regimen 1:5 exposure days per week; Regimen 2:3 exposure days per week) on the ability of 300 ppm benzene to induce genotoxic damage in the bone marrow of male and female DBA/2 mice. In addition, an analysis of the percentage of PCE in peripheral blood was used to evaluate benzene-induced alterations in the rate of erythropoiesis. Exposure to benzene induced a marked increase in the frequency of micronucleated PCE (MN-PCE), an effect which was considerably greater in male mice than in female mice. In both sexes, the induction of MN-PCE was independent of exposure regiment and of exposure duration. Exposure to benzene also resulted in an exposure duration-dependent increase in the frequency of MN-NCE. The frequency of MN-NCE increased more slowly in female than in male mice and, within each sex, more slowly in Regimen 2 animals. Apparent steady-state conditions for MN-NCE frequencies were attained by about the fifth week of exposure in female mice exposed by either regimen and in male mice exposed by Regimen 2. Steady-state conditions for MN-NCE frequencies in male mice exposed to benzene by Regimen 1 did not occur during the duration of the study. An analysis of %PCE data revealed an initial severe depression in the rate of erythropoiesis in both sexes, with the return in the production of PCE to control levels being dependent on both sex and exposure regimen. Suppression of PCE production occurred throughout the course of the study in Regimen 2 males, while the percentage of PCE returned to control levels sporadically after 5 weeks in Regimen 1 males and within 5 weeks in females, regardless of regimen. Thus, while the sex-dependent induction of genotoxic damage by multiple exposures to benzene over a 13-week period was independent of exposure regimen and duration, the induction of cytotoxic damage was both sex- and regimen-dependent. The most severe depression of erythropoiesis occurred in male DBA/2 mice exposed to benzene by the more intermittent regimen (i.e., 3 days/week versus 5 days/week).(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of exposure regimen and duration on benzene-induced bone marrow damage in mice. II. Strain comparisons involving B6C3F1, C57B1/6 and DBA/2 male mice.

In a companion paper (Luke et al., 1988), the effect of exposure duration and regimen on benzene induced-bone marrow damage was evaluated in male and female DBA/2 mice using the peripheral blood micronucleus assay. To assess the general applicability of the findings obtained for DBA/2 mice to other strains, similar studies were conducted using B6C3F1 and C57B1/6 male mice. An analysis of peripheral blood smears taken weekly from these mice exposed to 300 ppm benzene for 13 weeks (6 h per day) for either 5 days per week (Regimen 1) or for 3 days per week (Regimen 2) revealed: (i) a highly significant increase in the frequency of micronucleated polychromatic erythrocytes (MN-PCE), the magnitude of which was strain specific (DBA/2 greater than C57B1/6 = B6C3F1), but independent of exposure regimen and, except for Regimen 2 B6C3F1 mice, of exposure duration. In male B6C3F1 mice, MN-PCE frequencies increased slightly with increasing exposure duration; (ii) a strain- (C57B1/6 = B6C3F1 greater than DBA/2) and regimen- (Regimen 1 greater than Regimen 2) dependent increase across time in the frequency of micronucleated normochromatic erythrocytes (MN-NCE). Apparent steady-state conditions for MN-NCE frequencies were attained by about 5 weeks of exposure in male mice of all three strains exposed to benzene by Regimen 2. Steady-state conditions for MN-NCE frequencies in male mice exposed to benzene by Regimen 1 did not occur during the duration of the study, with strain-dependent differences in the kinetics of MN-NCE accumulation being present; and (iii) in all 3 strains, an initial severe depression in the rate of erythropoiesis, the return of which to normal levels was both strain- (C57B1/6 = B6C3F1 greater than DBA/2) and regimen- (Regimen 1 greater than Regimen 2) dependent. These data indicate that the induction of genotoxic and cytotoxic damage in the bone marrow of male mice exposed to benzene for 13 weeks can be highly dependent on strain, exposure regimen and exposure duration but that under no circumstance did the level of genotoxic damage induced by benzene decrease under multiple exposure conditions.

Cytogenetic effects of inhaled ozone.

We have repeated as closely as possible the experiments of Zelac et al., who observed significantly elevated levels of chromosome aberrations in short-term cultures of peripheral lymphocytes from Chinese hamsters that had inhaled ozone. Unlike Zelac et al., we observed no increase in chromosome-type aberration levels, though a small increase in chromatid-aberration levels similar to that reported for exposed human subjects by Merz et al. was seen. No increase in the levels of any chromosomal aberration type was seen in parallel direct bone-marrow preparations. Sister-chromatid exchange (SCE) levels and cell-replication rates, which were determined in the Chinese hamster peripheral lymphocyte cultures and also in bone-marrow samples from similarly treated mice, failed to show any ozone-induced changes.

Inhalation carcinogenicity of alpha halo ethers. I. The acute inhalation toxicity of chloromethyl methyl ether and bis(chloromethyl)ether.

A range of acute studies were performed with chloromethyl methyl either (CMME) and bis(chloromethyl)ether (BCME), including 14-day LC50's following single seven-hour inhalation exposures. The LC50's for CMME were 55 ppm for rats and 65 ppm for hamsters. The LC50's for BCME were 7 ppm for both species. All animals showed characteristic changes of acute irritation of the respiratory tract manifested by congestion, edema, and hemorrhage. Severe shortening of life span was seen in 30-day exposures of rats to CMME and in all studies with BCME. Incidences of mucosal changes, including atypia, were generally increased in a dose-related manner in both species. The carcinogenicity of BCME in these range finding experiments was demonstrated by a skin cancer in a rat after three exposures and a nasal tumor in a hamster after one exposure to 1 ppm BCME.

Inhalation carcinogenicity of alpha halo ethers. II. Chronic inhalation studies with chloromethyl methyl ether.

Rats and hamsters were exposed to 1 ppm of chloromethyl methyl ether six hours per day, five days per week, throughout their lifetime. Mortality and weight gain of the exposed animals paralleled that of the control animals. Malignant tumors of the respiratory tract were found in two rats. These were a squamous cell carcinoma of the lung with blood vessel invasion and an esthesloneuroepithelioma originating in the olfactory epithelium and invading the forebrain. One hamster was found to have an adenocarcinoma of the lung and another, a squamous papilloma of the trachea. A single exposed rat had a pituitary tumor of primitive cell type that may well have been coincidental.

Inhalation carcinogenicity of alpha halo ethers. III. Lifetime and limited period inhalation studies with bis(chloromethyl)ether at 0.1 ppm.

Rats and hamsters were exposed to 0.1 ppm bis(chloromethyl)ether (BCME) six hours per day, five days per week throughout their lifetime. Additional groups of rats were given 10, 20, 40, 60, 80, and 100 exposures to 0.1 ppm BCME and then held until death. Forty cancers originating in the respiratory tract were found in the 200 rats involved in these studies. These included 14 cancers of the lung and 26 cancers of the nasal cavity. They occurred in dose-related fashion. A single undifferentiated carcinoma of the lung was seen in a hamster.

Role of exposure databases in risk management.

Despite the development of numerous national exposure-related databases, exposure assessment remains a weak link in the chain of risk assessment and risk-management activities. Most databases include measures of environmental releases or concentrations of pollutants in specific media, but do not include actual measures of exposure. If accurate estimates of exposure experienced by populations or individuals are absent, it is impossible to judge the effectiveness of risk-management strategies. The Risk Management Work Group evaluation identified the following needs: refinement of measurements of total exposure experienced by individuals, improved characterization of the distribution of exposures in the population, longitudinal monitoring of exposure trends, and improved information about the public health implications of exposure. Recommendations are presented with the hope that the utility of existing databases will be improved and that future initiatives will be developed that meet the needs of risk management.