Strain A mouse pulmonary tumor test results for chemicals previously tested in the National Cancer Institute carcinogenicity tests.

Sixty-five chemicals were coded and examined for their ability to induce lung tumors in strain A/St (laboratory A) or strain A/J (laboratory B) mice. Thirty-five chemicals were tested in laboratory A only, 6 in laboratory B only, and 24 in both laboratories. Two-year carcinogenicity test results as well as genotoxicity test data are available for most of these chemicals. There was poor interlaboratory agreement in strain A test results for the 24 chemicals tested in both laboratories. In addition, there was poor agreement between strain A test results from either laboratory and 2-year carcinogenicity test results or genotoxicity results. Possible explanations for these findings include selection of a large number of aromatic amines in the group of chemicals submitted for strain A testing, differences in strain A testing protocols and in statistical analysis of results from the two laboratories, low sensitivity of the strain A/St mice used in this particular study, and general problems inherent in comparing any relatively short-term animal tumor model with 2-year carcinogenicity tests. Since there is no absolute reference for carcinogenicity, no one test system is better than another. Carcinogenicity test data are relevant only to the test model employed.

Separation of early diffuse alveolar cell proliferation from enhanced tumor development in mouse lung.

A/J mice given urethan (1000 mg/kg) followed by four injections of butylated hydroxytoluene (BHT) (400 mg/kg) developed within 4 mo approximately 40% more lung tumors than mice treated with urethan and given four injections of corn oil. Administration of the metabolic inhibitor piperonyl butoxide prior to BHT injection abolished overall alveolar cell proliferation although it did not completely suppress type II alveolar cell proliferation. Tumor multiplicity in those animals remained significantly higher (29%) than in corresponding controls. In mice treated with 3-methylcholanthrene repeated injections of BHT (300 mg/kg) increased tumor multiplicity by a much larger factor (500-800). Pretreatment of mice with BHT reduced the number of tumors produced by methylcholanthrene and at the same time blocked all cell proliferation following additional injections of BHT; nevertheless, BHT treatment given after methylcholanthrene again increased tumor multiplicity by the same factor (500-800%) seen in animals not made tolerant to BHT. It is concluded that the enhancing effect of BHT on lung tumor development is not due to the production of diffuse alveolar cell hyperplasia.

Inhibition of mouse lung tumor development by hyperoxia.

The hypothesis was tested that continuous hyperoxia would enhance the development of lung tumors in mice. In strain A/J mice treated with a single dose of urethan (1000 mg/kg) and exposed to 70% O2 for 16 wk, an average of 5 tumors per lung developed, whereas in animals kept in air, an average of 20 tumors per lung was found. When the animals were returned to air after oxygen exposure, it was found that a difference of 15 tumors per lung between the two groups persisted up to 1 yr later, indicating that O2 was tumoricidal. The shortest duration of O2 exposure to be effective was 4 wk, and delay of O2 exposure up to 12 wk after urethan still was effective in reducing the number of developing tumors. Histopathology showed that continued exposure to 70% O2 produced some hyperplasia of the bronchiolar epithelium and only very discrete changes in the pulmonary parenchyma. Analysis of cell proliferation patterns with a continuous [3H]thymidine labeling technique showed a persistent high cell labeling in the bronchiolar epithelium and a temporary increase in alveolar wall cell labeling. Chronic hyperoxia failed to alter the activities of pulmonary superoxide dismutase or glucose-6-phosphate dehydrogenase. Ornithine decarboxylase, on the other hand, was increased as long as the animals remained exposed to oxygen. It was concluded that hyperoxia kills developing tumor cells in mouse lung.

Pathobiology of lung tumors induced in hamsters by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and the modulating effect of hyperoxia.

Neuroendocrine lung cancer is among the most common types of lung cancers in smokers. We have recently shown that exposure of hamsters to N-nitrosodiethylamine and hyperoxia causes a high incidence of this tumor type. In this study, we show that the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone also causes neuroendocrine lung tumors in hyperoxic hamsters. Animals maintained in ambient air while being treated with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone developed pulmonary adenomas composed of Clara cells and alveolar type II cells. Pathogenesis experiments provide evidence for the tumors caused by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in ambient air being derived from Clara cells. In the hyperoxic hamsters, the neuroendocrine carcinogenesis appears to involve two stages: (a) transformation of focal alveolar type II cells into neuroendocrine cells and (b) development of neuroendocrine lung tumors from such foci.

Antibodies to mouse lung capillary endothelium.

We are interested in developing monoclonal antibodies (MoAbs) that recognize specific cell types in the lung of BALB/c mice. Normal mouse lung homogenate was used to immunize F344 rats and hybridomas were produced by fusion of rat spleen cells with mouse myeloma SP 2/0. Two hybridomas were selected which produced MoAbs active in immunohistochemistry of lung cells. MoAb 273-34A and 411-201B both show extensive peroxidase staining of capillary endothelial cells within alveolar walls of lungs at the light microscopic level. To demonstrate cell specificity, immunoelectron microscopy with gold-labeled antibody was performed. Lightly fixed lungs were frozen and thin-sectioned before staining with MoAb and 5-nm gold particles coupled to secondary antibody. Quantitative analyses of these cryosections show that both antibodies, used at optimal concentrations, are specific for binding to capillary endothelial cells. More than 95% of the gold particles are associated with capillary endothelial cells on the thin side of the alveolar wall. When capillaries adjoined thick septa containing interstitial cells, about two thirds of the gold particles were associated with endothelial cells and about one quarter with interstitial cells. These MoAbs should be useful in studying the role of endothelial cells in toxic lung injury.

Effects of hyperoxia on B16-F10 cells in vivo.

The in vivo effects of hyperoxia were studied in lung colonies formed by B16-F10 melanoma cells in C57BL/6 mice. Several antioxidant defenses were found to change with in vivo exposure: glutathione reductase and glucose-6-phosphate dehydrogenase activities decreased as compared with levels in the cultured cells, glutathione peroxidase activity dramatically increased, and Mn-superoxide dismutase activity and levels of total glutathione were similar in vivo and in vitro. Exposure of tumor-bearing animals to 70%, O2 for 3 weeks did not alter the antioxidant defenses measured in the tumors. One hundred percent O2 exposure did not affect either initial arrest or subsequent retention of radiolabeled B16-F10 cells in the lung. Likewise, hyperoxia did not appear to alter cell division in B16-F10 cells growing in the lung. These results are consistent with our previous studies indicating that the B16-F10 cell line is resistant to levels of O2 in vivo that adversely affect other tumor cell lines.

Promotion of lung tumors in mice.

Several elements of two-stage carcinogenesis apply to the development of lung tumors in Strain A or Swiss-Webster mice. At least three agents which have been identified as promoters in skin, urinary bladder and liver will also enhance tumor formation in lung; phorbol, saccharin and butylated hydroxytoluene (BHT). The antioxidant BHT acts in many respects like a typical promoting agent: it is effective if animals are treated after exposure to an initiating agent, but not if they are treated beforehand. Administration of BHT can be delayed up to 5 months after urethan treatment and still enhance tumor formation. BHT enhances lung tumor formation regardless of its route of administration (IP injection, gavage, or ingestion in the diet). The lowest dose of BHT required to produce an effect has not yet been determined. In at least one mouse strain, BHT also enhances tumor formation in animals initiated with 3-methylcholanthrene or dimethylnitrosamine. On the other hand, no evidence is available yet to show that BHT would enhance tumor development in animals treated with subcarcinogenic doses of an initiating compound. Nor has it been possible to produce more tumors with BHT in mouse strains which have a low spontaneous tumor incidence and respond poorly to urethan. The question has not been resolved whether BHT accelerates growth of preformed tumors only or whether it induces the formation of more tumors. Nevertheless, the data collected on the effects of BHT on mouse lung tumor development have broadened the concept of two-stage carcinogenesis and complement the evidence for initiation- promotion available for other epithelial tissues such as liver, colon, stomach, trachea, urinary bladder and mammary gland.

The role of toxicological interactions in lung injury.

Interactions between two or more toxic agents can produce lung damage by chemical-chemical interactions, chemical-receptor interactions or by modification, by a first agent, of the cell and tissue response to a second agent. Interactions may occur by simultaneous exposure and if exposure to the two agents is separated in time. Chemical-chemical interactions have been mostly studied in the toxicology of air pollutants, where it was shown that the untoward effect of certain oxidants may be enhanced in the presence of other aerosols. Interactions at the receptor site have been found in isolated perfused lung experiments. Oxygen tolerance may be an example, when pre-exposure to one concentration of oxygen mitigates later exposure to 100% oxygen by modifying cellular and enzymatic composition of the lung. Damage of the alveolar zone by the antioxidant butylated hydroxytoluene (BHT) can be greatly enhanced by subsequent exposure to oxygen concentration which, otherwise, would have little if any demonstrable effect. The synergistic interaction between BHT and oxygen results in a resulting interstitial pulmonary fibrosis. Acute or chronic lung disease may then be caused not only by one agent, but very likely in many instances by the interaction of several agents.

Enhancement of tumor formation in mouse lung by dietary butylated hydroxytoluene.

Male A/J mice were injected i.p. with a single dose of urethan and fed 0.75% butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA) or ethoxyquin in the diet. All animals were killed 4 months after urethan and the number of lung tumors counted. Exposure to BHT, but not to BHA or ethoxyquin significantly enhanced formation of lung tumors if animals were given the BHT-containing diet once a week for 8 consecutive weeks or were kept on it continuously for 8 weeks. Prefeeding mice with BHT had no effect on tumor formation but prefeeding BHA reduced the number of tumors formed by urethan. It is concluded from this and previous work that in mouse lung BHT enhances tumor formation regardless of route of administration and over a 100-fold dose range.

A new monoclonal antibody to study mouse macrophage antigen during BHT-induced lung injury and repair.

A rat monoclonal antibody 133-13A to a mouse lung carcinoma cell line was found to react with macrophages in mouse lung [1]. This monoclonal antibody is different from previously described antibodies to macrophages. Immunogold electron-microscopy and immunoperoxidase light microscopy have been used to show that MoAb 133-13A binds specifically to macrophages in normal and in BHT treated mouse lungs. This MoAb recognizes a protein of approximately 100 kDa (P100) on cultured lung carcinoma cells and a 87 kDa protein on macrophages from lung or the peritoneal cavity which is different from other macrophage antigens. The surface glycoprotein has been purified from cultured cells using immunoaffinity chromatography. The purified protein was radioiodinated and MoAb 133-13A was used to develop a competition radioimmunoassay to quantitate P100. Spleen, intestines, lung, skin and uterus all have high levels of P100. P100 on peritoneal macrophages has been determined to be about 94,000 molecules/cell. Analyses of lung lavage and whole lung homogenates from mice treated with BHT, BHT plus 70% O2, and 70% O2 alone show that treated animals have elevated P100 content compared to corn oil treated mice.

Modification of lung tumor development in A/J mice.

Strain A mice were injected with urethan, 3-methylcholanthrene or dimethylnitrosamine and given repeated injections of butylated hydroxytoluene (BHT). This treatment significantly increased multiplicity of lung tumors induced by all 3 carcinogens. Two other antioxidants, butylated hydroxyanisole (BHA) or alpha-tocopherol (vitamin E) did not enhance tumor formation, nor did methylcyclopentadienyl manganese tricarbonyl (MMT), an agent capable of producing cell proliferation in lung. Lungs were more susceptible to the carcinogenic action of urethan 2 weeks following BHT-induced injury, but not during the phase of acute cell proliferation in lung. It is concluded that the effects of BHT on lung tumor development in mice are not related to its properties as an antioxidant or to its capability to produce extensive cell proliferation in lung.

The effects of dietary butylated hydroxytoluene on liver and colon tumor development in mice.

Male and female C3H mice were fed a diet containing 0.5% or 0.05% of the antioxidant butylated hydroxytoluene (BHT). After 10 months, male but not female animals had a significantly increased incidence of liver tumors compared to animals kept on a BHT-free control diet. In a second experiment, male BALB/c mice were treated subcutaneously with the carcinogens dimethylhydrazine (DMH) or intrarectally with methylnitrosourea (MNU). A diet containing 0.5% BHT significantly increased the incidence of colon tumors in DMH treated animals but had no effect in mice given MNU. It is concluded that the effect of BHT on tumor development depends on strain and target organ examined and possibly also on the chemical carcinogen used.

Protection by parenteral iron administration against the inhalation toxicity of beryllium sulfate.

Animals exposed to an aerosol of BeSO4 showed a significant reduction in mortality with iron treatment. Rats were exposed for 2 h in a nose-only inhalation chamber for 14 days to an aerosol of 2.59 micrograms/Be/l. The cumulative mortality of animals concurrently treated with iron salt was significantly reduced (P less than 0.05) compared to animals which had not received iron treatment.

The effect of cyclosporin A on pulmonary fibrosis induced by butylated hydroxytoluene, bleomycin and beryllium sulfate.

Interstitial pulmonary fibrosis is characterized by an abnormal accumulation of fibroblasts with a resultant increase in lung collagen content. Previous research has implied a possible involvement of the T-lymphocyte in this process. We used cyclosporin A (Cy A), a known immunosuppressant, to deplete T-lymphocyte-dependent responses in animals following treatment with agents known to produce fibrosis; butylated hydroxytoluene (BHT), bleomycin and beryllium (Be). BHT-treated mice and bleomycin-treated rats showed significant reduction in total lung hydroxyproline content with Cy A (P less than 0.05). These results suggest a contribution of the T-lymphocyte in the overall process of fibrosis, but do not indicate its role as the sole causative agent.

Surfactant alterations following acute bleomycin and hyperoxia-induced lung damage.

Hamsters treated with 0.5 U/kg intratracheal bleomycin and exposed for 24 h to 80% O2 develop acute respiratory failure 72 h after treatment. To examine indirectly the lung epithelial type II cell changes, alterations in pulmonary surfactant was measured. Presence and amount of dipalmitoyl phosphatidyl choline (DDPC) and sphingomyelin (SM) were measured, and the DPPC/SM ratio was determined in brochoalveolar lavage samples from treated and control animals 24, 48, 72, and 96 h after treatment. Hamsters treated with bleomycin and O2 had a significantly decreased DPPC/SM ratio at 72 h, which is the time of onset of respiratory failure. The decreased DPPC/SM ratio may reflect type II cell damage and inhibition of surfactant function by the edema fluid.

Nonciliated bronchiolar epithelial (Clara) cell necrosis induced by organometallic carbonyl compounds.

The administration of transition metal organometallic compounds such as manganese, chromium, and iron carbonyls by the i.p. route, and nickel by inhalation (mice) or intravenously (rats), resulted in selective necrosis of the nonciliated bronchiolar epithelial (Clara) cells and variable pulmonary parenchymal damage in BALB/c mice and Fischer-derived rats within 24 h of administration. The pulmonary toxicity of methylcyclopentadienyl manganese tricarbonyl (MMT), a representative of this group of compounds, was enhanced by pretreatment with piperonyl butoxide (PB), an inhibitor of the mixed-function oxidase system. This finding suggests that Clara cell necrosis can result from direct toxicity and that the specificity of toxic agents for Clara cells may not be related solely to the presence of the mixed-function oxidase system.

Enhanced tumour development by butylated hydroxytoluene (BHT) in the liver, lung and gastro-intestinal tract.

Continuous feeding of 0.5 or 0.05% butylated hydroxytoluene (BHT) enhances the development of spontaneously occurring liver tumours in C3H mice, but not in BALB/c mice. In mouse lung, the tumour-enhancing effects of BHT vary with the carcinogen used. In the gastro-intestinal tract of mice and rats, BHT enhances the development of dimethylhydrazine-induced tumours, but is without effect on tumours produced by methylnitrosourea. Strain differences, the effect upon various carcinogens, paradoxical dose responses and mechanisms of action remain major questions in the toxicology of BHT.

Enhancement of lung tumor formation in mice.

There is now a great deal of data available that show that BHT enhances the development of lung tumors in mice. In many ways BHT behaves like a promoting agent. Interestingly, it also has tumor enhancing or promoting properties in other organs than mouse lung, such as rat liver, rat bladder, possibly rat GI tract, and in in vitro systems. The development of lung tumors by BHT may be influenced by comparatively low exposure regimens; the minimum dose found so far to be effective is 6 intraperitoneal injections of 50 mg/kg of BHT of feeding a diet containing 500 ppm of BHT for 2 weeks. While these findings seem to require that the continued use of BHT as a food additive needs to be reevaluated, it should be mentioned that other considerations have led to the conclusion that the use of BHT probably has a large margin of safety. This makes it important to establish the mechanism of action of BHT which at this time remains unknown.