Gender differences in animal bioassays for carcinogenicity.

Animal bioassays for carcinogenicity are essential components of occupational health studies. Animal data that have been collected under controlled experimental conditions provide definitive information about the carcinogenic activities of individual substances or defined mixtures and their relative potencies in the test species. Such information serves as a frame of reference for clinical and epidemiologic studies, pointing to potential adverse health effects and to the types of substances that might produce them. This article alerts the occupational and environmental health communities to 20 substances that produced breast tumors, 13 substances that produced uterine tumors, and 8 substances that produced ovarian tumors in long-term National Toxicology Program animal studies. Each of the substances also produced neoplasms at other body sites. Follow-up studies of molecular measures of exposure and response in people and in animals will reduce the uncertainties of transspecies extrapolations.

Two-dimensional polyacrylamide gel electrophoretic characterization of proteins from organs of C3H mice expressing the scurfy (sf) genetic mutation during early and late stages of disease progression.

Scurfy (sf), is an X-linked recessive lethal mutation that occurs spontaneously in the C3H mouse. The disease is characterized by lymphoid and hematopoietic dysfunction. Affected males are of small stature and exhibit scaliness and crusting of the eyelids, ears, tail, and feet, marked splenomegaly, moderate hepatomegaly, enlarged lymph nodes, and atrophy of the thymus. The average lifespan of the affected hemizygous males (sf/y) is 24 +/- 0.7 days. Total cellular proteins were extracted from pooled samples of thymus and spleen obtained from combined litters of mice. Tissue-specific protein profiles characteristic of either sf mutant or normal mice were analyzed by two dimensional polyacrylamide gel electrophoresis (2DPAGE) at different stages of the phenotypic expression of the sf mutation, to identify changes in protein patterns that might be associated with the progression of the disease. The resultant gels were silver stained, digitized, and analyzed, by image analysis utilizing a pipelined image processor connected to a host computer. At 14 +/- 1 days of age, protein patterns from sf mutant and normal mice control organs showed considerable homogeneity, although there were proteins identified unique to the sf mutant and to the normal controls. At 20 +/- 1 days of age, the pattern differences between the sf mutant and normal control increased markedly. Differences were expressed as the percent of proteins that were unique to either the sf mutant or the normal control from the total number of each type. The percent of proteins that increased or decreased in the three organs utilized in this study ranged between 21%-39% at 14 days and were between 25%-54% at 20 days. Differences in protein expression between the normal and sf mutant as the disorder progressed for each of the three tissues examined. In addition, thymus protein profiles from 9 day old littermates that were phenotypically normal but genotypically unknown were evaluated to determine if marker proteins could be identified for the sf mutation. Limited protein changes were noted at relative molecular weights of 66, 60, 54, 39, 37, 33, 25, 23, 27, and 11 kDa. These data suggest that the sf mutation follows a trackable pattern of protein expression and repression different than the normal control C3H mouse. Several potential marker proteins associated with the sf mutation were identified in 9 day thymus prior to the phenotypic expression of the disease. These putative biomarkers may be useful for characterizing the sf mutation and the mutant may act a possible model the Wiskott-Aldrich syndrome (WAS).

Transgenic mice in carcinogenicity testing.

The biological effects of the expression of single genes can be evaluated in transgenic animals. Transgenic techniques have been used to investigate a wide variety of biomedical topics, including the consequences of oncogene expression, but their use in carcinogenicity testing is just beginning. Probable future developments involving transgenic animals are new short-term assays for carcinogenicity in vivo and methods for detecting and characterizing the critical genotoxic events in carcinogenesis.

Evidence that toxic injury is not always associated with induction of chemical carcinogenesis.

Long-term rodent bioassays with chemicals administered at maximum tolerated doses identify noncarcinogens as well as carcinogens. Thirty-one chemicals recently evaluated for carcinogenic potential by the National Toxicology Program provide unique data on the relationships between mutagenicity, toxicity, and carcinogenicity. Twenty-two substances were classified as carcinogens, and nine showed no evidence of carcinogenicity. Although cellular proliferation does play an intrinsic role in neoplastic processes, the responses associated with chronic toxicity in these studies were not always sufficient to induce neoplasia. Regardless of their mutagenic potential, 19 carcinogens induced toxic effects at sites that did not show neoplastic changes; similar toxic lesions were also seen among the mutagenic and nonmutagenic noncarcinogens. Although many nonmutagens induced neoplasia at sites that showed toxic effects, some of the same chemicals also exhibited toxicity at other sites that showed no neoplastic effect. These results suggest that for some chemicals, properties other than mutagenicity or toxicity may be responsible for their carcinogenic potential.

Cardiac transplantation: a prospective comparison of ketamine and sufentanil for anesthetic induction.

The hemodynamic effects of ketamine, 1.5 mg/kg, or sufentanil, 3.4 +/- 0.3 micrograms/kg, were studied prospectively for the anesthetic induction of 20 patients with cardiomyopathies undergoing cardiac transplantation. Plasma epinephrine (EPI), norepinephrine (NE), and sufentanil levels were also obtained. Measurements were taken at various times before induction and following intubation. Following ketamine, progressive increases (P less than 0.05) in mean arterial pressure (28%, MAP), mean pulmonary artery pressure (56%, PAP), central venous pressure (109%, CVP), and pulmonary capillary wedge pressure (84%, PCWP) occurred over time, whereas the cardiac index (CI), stroke volume index (SVI), and stroke work index (SWI) remained unchanged or decreased. The use of sufentanil was associated with no significant changes in MAP, PAP, CVP, PCWP, CI, SVI, or SWI. The heart rate (HR) did not significantly change in either group. Plasma NE significantly increased (31%) in the ketamine group, peaking at 10 minutes; whereas EPI levels did not significantly change in either group. Plasma sufentanil did not reflect the microgram/kg or microgram/BSA administered dose, suggesting individualized distribution kinetics. Since perioperative morbidity and mortality did not differ between groups, both ketamine and sufentanil are acceptable drugs for the anesthetic induction for cardiac transplantation. However, the dissimilar hemodynamic effects caused by ketamine and sufentanil suggest that this conclusion may not be applicable to the patient with a cardiomyopathy undergoing noncardiac surgery.

Contribution of formaldehyde to respiratory cancer.

This article reviews the available data on the carcinogenicity of formaldehyde from experimental and epidemiologic studies and makes recommendations for further research. Two definitive chronic inhalation bioassays on rodents have demonstrated that formaldehyde produces nasal cancer in rats and mice at 14 ppm and in rats at 6 ppm, which is within the domain of present permissible human exposure (8-hr time-weighted average of 3 ppm, a 5 ppm ceiling, and a 10 ppm short-term exposure limit). Biochemical and physiologic studies in rats have shown that inhaled formaldehyde can depress respiration, inhibit mucociliary clearance, stimulate cell proliferation, and crosslink DNA and protein in the nasal mucosa. No deaths from nasal cancer have been reported in epidemiologic studies of cohorts exposed to formaldehyde, but three case-control studies suggest the possibility of increased risk. Although excesses of lung cancer deaths have been observed in some studies at industrial plants with formaldehyde exposure, uncertainties in interpretation limit the evaluation of these findings. Excess cancers of the brain and of lymphatic and hematopoietic tissues have been reported in certain studies of industrial groups and in most studies of formaldehyde-exposed professionals, but whether these excesses are related to formaldehyde exposure is not known. Several properties of formaldehyde pose unique problems for future research: the mechanisms responsible for its nonlinear response; its probable mechanism of carcinogenic action as a cross-linking agent; its formation in tissues as a normal metabolite; its possible action as a promoter and/or a cocarcinogen; and the importance of glutathione as a host defense at low exposure.

Modification of lung tumor growth by hyperoxia.

The effects of hyperoxia on lung tumor development were examined in mice and rats. In mice, exposure to 70% O2 prevented the development of urethan- or 3-methylcholanthrene-induced lung tumors. Dietary antioxidants [butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA)] were unable to prevent the inhibition of tumor development by oxygen, although BHT retained its capability to enhance tumor development in mouse lung. In visible-size tumors, oxygen did not depress DNA synthesis. Oxygen also reduced the number of pulmonary metastatic nodules after i.v. injection of mammary gland-derived carcinoma cells, but failed to inhibit growth of murine lung carcinoma or murine melanoma-derived cell lines. Rats treated with one single intratracheal instillation of 3-methylcholanthrene developed multiple lung lesions; their growth could be prevented by exposure of the animals to 40 or 70% O2. It is concluded that hyperoxia prevents development of transformed cells in vivo in the lung and may affect adversely the growth of selected cell lines metastatic to the lung.

Chronic inhalation of cigarette smoke by F344 rats.

Specific-pathogen-free female F344 rats were exposed by inhalation to what was considered a maximal tolerated dose of cigarette smoke. Total pulmonary deposition of smoke particulates from a single cigarette was 0.25 mg in young rats. Rats were exposed to smoke from 7 cigarettes/day for as long as 2.5 years, at which time 30% of the rats remained alive. Mortality of smoke-exposed animals was not different from that of untreated or sham-exposed controls. Hyperplastic and metaplastic areas in the epithelium of the nasal turbinates, larynges, and tracheae of exposed animals were observed at death. The lungs of exposed rats contained areas of focal alveolitis consisting of accumulated pigmented macrophages, epithelial hyperplasia, fibrosis, and disrupted alveolar structure. Smoke exposure did not change the total number of tumor-bearing animals relative to controls; however, exposed rats had significantly fewer tumors in the hypophyses, hematopoietic-lymphoid systems, uteri, and ovaries but an increased number of tumors in the respiratory tracts and dermes. Only 1 of 93 (1%) control rats had a tumor (an alveologenic carcinoma) in the respiratory tract as opposed to 7 of 80 (9%) exposed animals (nasal tumors: 1 adenocarcinoma and 1 squamous cell carcinoma; pulmonary tumors: 5 adenomas, 2 alveologenic carcinomas, and 1 squamous carcinoma).

Toward a classification scheme for degrees of experimental evidence for the carcinogenicity of chemicals for animals.

A classification scheme is proposed for degrees of experimental evidence for the carcinogenicity of chemicals for animals. The classification stems from the suggestions of an IARC Working Group that the evaluation of bioassays include consideration of whether an increase in malignant tumours occurred and whether it occurred to an unusual degree or in multiple experiments. We extended the evaluative process to chemical experiments with no evidence of carcinogenicity and gave increased emphasis to results from more than one animal species. Although the proposed classification was developed for a group of NCI bioassays which were similar in design and conduct, it may provide a general framework for the evaluation of carcinogenesis bioassays and stimulate development and application of evaluative methods.

Quantitative assessment of generalized epithelial changes in tracheal mucosa following exposure to 7,12-dimethylbenz(a)anthracene.

Sequential morphological changes occurring after brief carcinogen exposures of heterotopic tracheal transplants in rats were semiquantitatively studied. Tracheas were exposed to 7,12-dimethylbenz(a)anthracene for 1, 2, or 4 weeks, during which time means of 138, 152, and 160 microgram 7,12-dimethylbenz(a)anthracene, respectively, were delivered. The first two types of exposures resulted only in generalized epithelial changes; these included hyperplasia and early metaplasia, both of which regressed rapidly, and persistent atrophic alterations. No focal epithelial lesions or tumors developed. The third type of exposure (160 microgram 7,12-dimethylbenz(a)anthracene delivered in 4 weeks) resulted in the appearance of generalized mucosal changes with long-lasting, severe inhibition of mucus production. In addition, focal metaplastic lesions reappeared at 4 to 8 months after exposure, and invasive carcinomas developed after 1 year with an incidence of 9%. Overall carcinoma incidence, including carcinoma in situ, was 15%. The studies emphasize the importance of the duration of carcinogen exposure, and they demonstrate the emergence of focal lesions when effective carcinogenic exposures are being used. The possible significance of epithelial atrophy in the pathogenesis of cancer in this experimental model is discussed.