Induction of squamous metaplasia: requirement for cell multiplication, and competition with lobuloalveolar development in cultured mammary glands

Mouse mammary glands were previously shown to undergo either of two courses of development and differentiation in whole organ culture. The combination of insulin, prolactin, aldosterone, and hydrocortisone induces a structural development of lobuloalveoli, followed by casein production. In the second course, the mixture of dibutyryl cyclic AMP, prostaglandins E1, E2 and B1, and papaverine brings about an extensive squamous metaplasia and excessive keratinization. In the present study, the foci of the metaplastic squamous cells appeared to originate from single or very few cells. A preferential stimulation of squamous cell multiplication was involved in the induction process. Twice the relative number of nuclei incorporated 3H-thymidine in the squamous metaplastic cells than in the surrounding cuboidal epithelium, according to autoradiography. The necessity for cell multiplication was indicated by the reversible and complete inhibitions of both the metaplastic squamous development and 3H-thymidine incorporation by 1 mM hydroxyurea in the culture medium. Simultaneous inductions of both courses of development and differentiation revealed a competitive and reciprocal relationship between the two pathways. The concurrent expressions of both courses were considerably less than those achieved when either pathway was induced alone. Only the combination of the three types of inducers of squamous metaplasia was able to compete effectively with the hormonal induction of lobuloalveolar development and differentiation. The findings suggest that individual metaplastic squamous foci may originate as clones of cells by processes that require cell multiplication, rather than through a direct non- replicative conversion of pre-existent cells of the cuboidal epithelium.(ABSTRACT TRUNCATED AT 250 WORDS)

Carcinogenesis in canine bistomal heterotopic tracheal grafts

Successful canine lung cancer models have required repeated focal bronchial carcinogen exposure under general anesthesia. To simplify serial studies of the respiratory mucosa during carcinogenesis, bistomal autologous heterotopic tracheal pedicle grafts have been made. These grafts can readily be returned to the original orthotopic site, and this has been shown to be a method with which to study reversibility of mucosal changes. Polycyclic aromatic hydrocarbons were applied topically to the mucosa three times a week for 21 to 22 months in 21 grafts. Implants of Silastic polymer from which carcinogen was released in sustained-release fashion were then left in the grafts for 4 to 6 weeks. Serial cytological and histological examinations showed development of atypical squamous metaplasia in the graft mucosa. Mucosal papillomatosis was noted in 4 of 7 grafts surgically excised 17 to 18 months after completion of carcinogen exposure. The heterotopic bistomal tracheal graft provides a useful method for studying respiratory epithelial carcinogenesis without repeated general anesthesia.

Effect of estrogen on the formation of struvite calculi in female rats

The administration of 1 mg estradiol every other week for 12 weeks to female rats resulted in a high incidence (about 50%) of bladder stones. Most calculi were struvite, suggesting the predisposition to urinary tract infection. Enterobacteria, staphylococcus and streptococcus were identified as infecting organisms. Metaplasia of the transitional bladder epithelium by estrogen to a stratified or pseudostratified columnar epithelium may be involved in the underlying cause of urinary tract infection.

Cytologic evidence of extensive keratotic reaction in women exposed to diethylstilbestrol in utero

Squamous mucous membranes and squamous metaplastic epithelium sometimes undergo hypermaturation with the production of a keratin layer. Anucleated keratotic squamous plaques in smears are generally recognized as cytologic evidence of this altered maturation. This keratotic reaction was quantified in cytologic smears from 191 women exposed in utero to diethylstilbestrol (DES). Keratotic reaction was observed in the vaginal smear in 40% of the cases, in the cervical smear in 26% and in the endocervical smear in 19%; overall, a keratotic reaction was observed in at least one specimen from 48% of the women. These frequencies are higher than those reported in other studies. The observed frequency was age related. The significance of the hyperkeratosis, including its possible relationship to a lower dysplasia rate among DES-exposed women, is unclear. No conclusions can be drawn until more is known about behavioral factors in DES-exposed women.

[Benzopyrene (BaP) implants into the glottic mucous membrane of hamsters]

For testing the effect of benzo (a) pyrene (BaP) on glottical epithelium European hamsters were used. With laryngofissure hamsters larynges had been opened and a mixture of tricaprilin, beewax and 1 mg BaP was implanted into a pocket formed by mucous membrane of one vocal fold. Compared to typical histology in smoker's larynx, squamous metaplasia and dysplasia and in one case papillary polyps could be described. No squamous cell carcinomata was found.

[Alcohol and epithelial regeneration in the rat stomach following experimental lesions]

In man, chronic consumption of alcohol has been incriminated as a promoting factor in the development of columnar-lined lower esophagus (Barrett's syndrome). To test the effects of alcohol on the regeneration of squamous epithelium, rats were fed a diet containing 2,5 g alcohol daily for 6 weeks after the junctional region between the squamous epithelium of their fore stomach and the columnar epithelium of their glandular chamber had been injured and denuded. Compared to animals fed an isocaloric control diet the alcohol-fed rats showed neither major macroscopical nor histological differences in the regeneration process of the epithelium. Under the influence of alcohol the mucosal border did not move in an orad direction. Thus, these results fail to support the hypothesis of alcohol promoting the replacement of defects in squamous epithelium by columnar epithelium which is thought to be the major pathomechanism in Barrett's syndrome.

Uterine tumors in old female mice exposed prenatally to diethylstilbestrol

Pregnant strain CD-1 mice were treated with diethylstilbestrol (DES) or vehicle. Their female offspring were raised to old age and autopsied when terminally ill. Squamous metaplasia and adenomyosis were more common in uteri of these old mice exposed prenatally to DES than in control mice. Tumors of the uterine horns were seen in 17 of 143 DES-exposed mice and in 3 of 64 control mice. The controls had only leiomyomas, whereas 14 of the DES-exposed mice had adenocarcinomas. There were 5 cervical adenocarcinomas and 1 vaginal adenocarcinoma among treated mice but none in the control mice. Thus the effects of prenatal exposure to DES interacted with the effects of aging to produce a relatively high frequency of uterine adenocarcinoma.

Mutagens: some possible health impacts beyond carcinogenesis

Considerable attention is currently being given to the roles of environmental and endogenous mutagens in tumor induction and in tumor progression through the abilities of mutagens to induce one or another kind of somatic mutation. It is proposed here that mutagens, also through induction of somatic mutations, initiate a spectrum of additional, much more common, focal lesions that are important to the human condition. While individually they are of relative insignificance and thus neglected by many clinicians, the functional attributes of these focal lesions have important impacts on human physiology and thus contribute substantially to the process of aging. Additionally, one individual focus may progress to an extent that it produces clinically recognizable symptoms and may even jeopardize the carrier's life. The ultimate and developed expression of these lesions is heterogeneous, is far removed in time from initial induction, and relies on additional host and environmental factors for expression; therefore, the possible role of somatic mutation is readily overlooked. The focal lesions reviewed are fibrous atherosclerotic plaques, senile cataracts, and metaplasias. Literature that implicates metaplasias as precursor or as predisposing lesions in the ultimate formation of gallstones, duodenal ulcers, and adenocarcinomas is summarized.

Effect of carcinogen release rate on the incidence of preneoplastic and neoplastic lesions of the respiratory tract epithelium in rats

Inbred F34 rat tracheal transplants were exposed to 7,12-dimethylbenz[a]anthracene (DMBA) delivered at different release rates for intraluminal pellets made of various matrices to study the effect of carcinogen dose rate on the induction of lesions in the epithelium. These matrices were beeswax, beeswax-stearyl alcohol, and beeswax-cholesterol. In addition, DMBA absorbed onto carbon particles was dispersed in beeswax-stearyl alcohol. The fastest release was obtained from beeswax pellets from which 99% of the carcinogen (198 micrograms) was released in 4 weeks, and the slowest release was from DMBA absorbed on carbon at a ratio of 1:9 from which only 56% (113 micrograms) was released in 16 weeks. Morphometry of histologic sections showed marked differences in the percentage of luminal surface covered by dysplastic-neoplastic epithelium (i.e., 7.5% in the tracheas exposed to the fastest releasing pellets and 46.3% in the tracheas exposed to the slowest releasing pellets). An inverse linear correlation was found between the cumulative amount of DMBA relased from the different pellet matrices of 2 weeks and the incidence of dysplastic plus neoplastic lesions of tracheal epithelium at 16 weeks. The results indicate that lower doses of carcinogen delivered slowly are more effective in producing dysplastic plus neoplastic lesions than hgher doses delivered rapidly.

Reproductive tract abnormalities in rats treated neonatally with DES

Neonatal female Sprague-Dawley rats were given daily injections of 3 micrograms diethylstilbestrol (DES) for 5 days beginning within 24 hours of birth. Some of these rats were ovariectomized between the 15th and 18th postnatal days, and on the 60th postnatal day were given daily injections of 3 micrograms estradiol for 1, 3, or 5 weeks. Intact rats were sacrificed at 60, 95, or 130 days. The morphology of the upper vagina, cervix, and lower uterus was examined by light and scanning electron microscopy. Two abnormalities resulting from neonatal DES exposure were found. The first was squamous metaplasia observed in the uteri of rats given DES and later exposed to exogenous or endogenous estrogen. Metaplasia was seen in both the luminal and glandular epithelium. The longer the rats were exposed to exogenous or endogenous estrogen, the more extensive was the metaplasia. The second was a gross morphologic abnormality seen in all rats given DES regardless of any later treatment. That part of the cervix that protrudes into the cranial limit of the vagina was absent and, thus, a vaginal fornix was nonexistent. Previous investigations have emphasized abnormalities of the lower reproductive tract. The present study indicates that the upper reproductive tract also must be considered in investigations of the effects of hormones administered to neonates.

Vaginal adenosis and adenocarcinoma in mice exposed prenatally or neonatally to diethylstilbestrol

The association of intrauterine exposure to diethylstilbestrol (DES) and the subsequent development of reproductive tract abnormalities in young women has been well documented. Although the incidence of vaginal adenocarcinoma was low in the exposed population, vaginal adenosis, a nonmalignant abnormality, was quite common. In order to study the pathogenesis of adenocarcinoma and to determine the frequency of adenosis following prenatal exposure to DES, timed pregnant CD-1 mice were treated s.c. with DES (dose range, 5 to 100 micrograms/kg/day) on Days 9 though 16 of gestation. This period corresponds to major organogenesis of the reproductive tract in the mouse. Female offspring were sacrificed between 1 and 18 months of age. In addition to nonmalignant abnormalities, some of which have been described in women exposed prenatally to DES, two cases of vaginal adenocarcinoma (2%) were observed in 91 prenatally DES-treated animals. No comparable epithelial lesions were seen in 158 control female mice. One other case of adenocarcinoma of the vagina was reported previously by this laboratory using the prenatally exposed animal model. In another series of mice treated prenatally with DES, 100 micrograms/kg/day, 3 of 20 (15%) 1-month-old animals and one of 10 (10%) 18-month-old treated offspring had glandular epithelium abnormally located in the vaginal fornices (adenosis). Other cervicovaginal abnormalities observed after prenatal DES exposure included structural alterations, cervical enlargement, squamous metaplasia in the endocervical canal, excess keratinization of the ectocervix and vagina, transverse folds and basal cell hyperplasia in the upper vagina, and prominent Wolffian duct remnants. Thus, vaginal adenosis in the mouse does not appear to be a common abnormality following treatment with DES in utero. Neonatal exposure to DES on Days 1 to 5, on the other hand, resulted in six of eight (75%) animals with adenosis at 35 days of age. Since perinatal mouse studies have reported high incidences of vaginal adenosis, but, to our knowledge, no cases of vaginal adenocarcinoma, the results presented in this report suggest that the stage of cellular differentiation at the time of DES exposure may be critical in the final expression of these abnormalities.

Bleomycin pulmonary toxicity: production of fibrosis by bithiazole-terminal amine and terminal amine moieties of bleomycin A2

We have previously demonstrated that endotracheal administration of the terminal amines of several bleomycins, when administered as the free amines, produce pulmonary fibrosis of severity comparable to the intact drug. In the present report, bleomycin A2 and its sulfonium ion-containing terminal substituents, with and without the bithiazole rings, were administered to mice endotracheally. The incidence and severity of epithelial metaplasia was greater with the intact drug in comparison to the terminal substituents. In contrast, the terminal substituents and intact drug produced similar degrees of fibrosis. These results underscore the importance of the variable bleomycin terminal substituents in the pathogenesis of pulmonary fibrosis.

A study on carcinogenesis induced by degraded carrageenan arising from squamous metaplasia of the rat colorectum

We have undertaken studies on carcinogenesis arising from precancerous lesions, such as squamous metaplasia and ulcerative lesions of the rat colorectum, after termination of degraded carrageenan administration. Rates of tumor incidence in groups that were given a 10% diet of degraded carrageenan for 2, 6 and 9 months were 5 rats out of 39 (12.8%), 8 out of 42 (19.0%) and 17 out of 42 (40.5%), respectively. The colorectal squamous metaplasia persisted in all rats and progressed irreversibly. Degraded carrageenan was deposited not only in the colorectal propria mucosa, but also in the other reticuloendothelial organs. These results show that, even with short-term degraded carrageenan administration, degraded carrageenan is carcinogenic to the colorectum of the rat after a prolonged period.

Dysplasia and cytologic findings in 4,589 young women enrolled in diethylstilbestrol-adenosis (DESAD) project

This report presents the cytologic findings and the rates of dysplasia for 4,589 young women enrolled in the National Cooperative Diethylstilbestrol-Adenosis (DESAD) Project. Mucinous columnar cells and/or metaplastic squamous cells with or without mucinous droplets were encountered in 22% of vaginal scrape smears from all diethylstilbestrol (DES)-exposed participants identified by review of prenatal records and in 43% of women in whom vaginal epithelial changes (VEC) were observed by colposcopy or by iodine staining. The frequency of cellular findings in the vaginal scrape smears was closely related to the timing of the administration of the DES to the mother. With increasing age of the daughters, the overall frequencies of both the mucinous and metaplastic cells decreased; relative to each other, an increasing proportion was metaplastic squamous cells. These data suggest that, as the women grow older, vaginal adenosis regresses by the process of squamous metaplasia. Endometrial type cells were found in 2% of vaginal scrape smears. Their cyclical occurrence during the menstrual cycle and lack of correlation with the presence of VEC indicated an origin from the uterine corpus rather than the tuboendometrial type of adenosis. Squamous cell dysplasia of the vagina and cervix was detected by biopsy or scrape smear specimens in 1.8% of DES-exposed women in the record review group. The rate of unexposed women was twice as high. In general, the rates of dysplasia were higher in the cervix than vagina, and the more severe degrees of dysplasia were encountered only in those women who were referred to the DESAD Project or who themselves requested entry. Four patients who were referred or who themselves requested entry were found to have clear cell adenocarcinoma of the vagina. The vaginal smear provided the first clue to the presence of an abnormality in three of them.

Sustained release of benzo(a)pyrene from silicone polymer into the tracheobronchial tree of hamsters and dogs

A method was developed to expose specific sites of the hamster and canine tracheobronchial tree to benzo(a)pyrene (BP) at quantitatively sustained rates. Implants for sustained release were formed by incorporating BP in a silicone rubber matrix at concentrations of 9.05 to 12%. Forty-nine hamsters and 12 dogs had a total of 86 implants surgically adhered to the tracheobronchial mucosa for up to 200 days. BP was released from the implants in hamsters and dogs as a first-order exponential function with a half-time of 54.8 and 44.5 days, respectively. Pathogenesis was progressively time and dose dependent. Squamous metaplasia with atypia regularly occurred in dogs within 150 days or after 7.17 mg BP and in hamsters after 50 days or 288 microgram BP. Bronchogenic cancers occurred in 93% of our hamsters after 100 days and 467 microgram BP. This method has applicability potentially as a bioassay for evaluating carcinogens in hamsters and currently as a means of producing a model of lung cancer in which neoplasia is induced at precise, selected sites.

Induction of atypical squamous metaplasia with benzo[a]pyrene in cultured hamster tracheas

Areas of hyperplasia were produced in hamster tracheal epithelium maintained in vitro by exposure to a suspension of benzo[a]pyrene (BP) in gelatin. Typical and atypical epiodermoid metaplasia were seen by 2 weeks. In atypical areas, cell nuclei were enlarged with prominent nucleoli, the cytoplasm contained dense bundles of tonofilaments and the cells were joined by numerous desmosomes. The peak response to the carcinogen was reached 4 weeks after the application of BP and consisted of extensive atypical epidermoid metaplasia. Tracheas treated with gelatin alone maintained a columnar epithelium for 6 weeks of culture. The characteristics of the metaplastic changes in vitro are essentially identical to those described after exposure of the hamster tracheobronchial epithelium to benzo[a]pyrene-ferric oxide in vivo.