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Biomedical subjects

J C Barrett

Publications and source records attributed to J C Barrett.

At least 325 records · Page 18Linked to original sources
PubMed1985

Selective effects in potential fertility: a simulation study.

"The effect of various factors on selection for family planning status and for natural fecundability is studied in a Monte Carlo simulation that incorporates heterogeneity of natural fecundability and of risks of foetal loss. Selection depends crucially on the duration of marriage at which contraceptive status is recorded, and on desired family size....The contraceptive status of sterile women is also revealed in the simulation, including users who do not know that they have become sterile. Formulae are developed to allow the estimation of births averted and potential fertility among the users, and results checked by further simulation." The results indicate "that selection for foetal loss is much less important than selection for natural fecundability in its effect on numbers of averted births and potential fertility." (summary in FRE)

Contraception↗
PubMed1985

Evidence for multiple steps in neoplastic transformation of normal and preneoplastic Syrian hamster embryo cells following transfection with Harvey murine sarcoma virus oncogene (v-Ha-ras).

Neoplastic development of Syrian hamster embryo (SHE) cells in culture is a multistep process in which intermediate or preneoplastic cells can be identified and isolated. In an attempt to further characterize normal and preneoplastic cells, we have compared their susceptibilities to neoplastic transformation following transfection with cloned DNA of the oncogenic virus, Harvey murine sarcoma virus (HaMSV). Normal SHE cells, which are stably nontumorigenic when injected in nude mice, are competent to take up and express exogenous DNA as demonstrated by transfection experiments with pSV2-neo DNA and certain viral DNAs. SHE cells treated with 5 micrograms of HaMSV DNA per dish remained nontumorigenic. Colonies of SHE cells, isolated after cotransfection with HaMSV and pSV2-neo DNA and selection for G418 antibiotic resistance, expressed Harvey murine sarcoma virus oncogene (v-Ha-ras) RNA and were initially morphologically altered; however, all colonies senesced when subcultured. In contrast, transfection of the cells with polyoma virus DNA alone or HaMSV DNA plus MC29 viral DNA (pSVv-myc) and then injection of the cells into nude mice resulted in progressively growing tumors of hamster origin within 3 to 5 weeks. A preneoplastic cell line, DES-4, isolated after treatment of SHE cells with the human carcinogen diethylstilbestrol, was chosen for comparative analyses. These immortalized cells are nontumorigenic and excellent recipients for exogenous DNA. In contrast to SHE cells, DES-4 cells were highly susceptible to neoplastic transformation following transfection with HaMSV DNA. To further investigate the role of HaMSV DNA in the neoplastic transformation of DES-4 cells and to determine whether this occurred as a single step, clones of DES-4 cells cotransfected with pSV2-neo and HaMSV DNAs were selected by antibiotic resistance and characterized. There was a good correlation between tumorigenicity and expression of v-Ha-ras DNA; however, the clones were highly variable in terms of their latency periods in vivo and anchorage-independent growth. Neither of these two parameters correlated with the level of expression of v-Ha-ras RNA. All of the cell lines derived from tumors and reinoculated into nude mice had short latency periods in vivo, were highly anchorage independent, and had high levels of v-Ha-ras expression. These results suggest that, in these experiments, v-Ha-ras expression was necessary, but not sufficient, for the tumorigenicity of DES-4 cells and that additional changes in the cells were acquired.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Cell culture models of multistep carcinogenesis.

The cellular and molecular basis for the multistep process of carcinogenesis can be studied in part by the use of cell culture models. A model system for the study of carcinogen-induced neoplastic transformation of cells in culture is described. Different stages in the neoplastic development of Syrian hamster embryo (SHE) fibroblasts can be identified and quantitated. At least two steps are required for the neoplastic progression of these cells. Morphological alterations are observed early after carcinogen treatment; such cells are preneoplastic and, after further growth in culture, acquire the ability to grow in agar and to form tumours in animals. The induction of morphological transformation of SHE cells occurs within one week after carcinogen treatment in a dose-dependent manner consistent with a one-hit mechanism. Furthermore, this change is induced at frequencies (greater than 1% of the surviving cells) that are higher than those of specific locus mutations. Carcinogens that fail to induce measurable gene mutations induce cell transformation (e.g., diethylstilboestrol, asbestos and arsenic). All three of these carcinogens induce chromosomal changes--either numerical and/or structural aberrations--suggesting a role for such changes in the action of these carcinogens. Different preneoplastic cells vary in the rate of their progression to anchorage-independent growth and tumorigenicity. Cells with the ability to grow in agar arise at rates of 10(-4) to 10(-7) variants/cell per generation, depending on the preneoplastic cell line. Different preneoplastic cell lines also vary in their sensitivity to induction of neoplastic transformation by mutagens and by transfection with viral oncogenes. This heterogenicity of response suggests different intermediate states of neoplastic progression.

Age Factors↗
PubMed1985

Quantitation of the rate of spontaneous generation and carcinogen-induced frequency of anchorage-independent variants of rat tracheal epithelial cells in culture.

The rate of spontaneous generation and the frequency of carcinogen-induced anchorage-independent variants of preneoplastic rat tracheal epithelial (RTE) cells in culture were quantitated. Anchorage-independent variants of different RTE cell lines arose spontaneously by a stochastic process at rates of 0.5 X 10(-4) to 5.4 X 10(-4) variants/cell/generation, as determined by fluctuation analyses. These variants were also induced by the mutagen N-methyl-N'-nitro-N-nitrosoguanidine with a frequency of approximately 10(-3) variants/surviving cell. The rates of spontaneous change and the frequencies of induction are the first reported for epithelial cells and are similar to some, although not all, rates and frequencies of change to anchorage independence for fibroblast-like cells in culture. In addition, these rates and frequencies are similar to those for mutations at some known gene loci. The induced frequency of this late change in neoplastic progression is, however, considerably lower than the frequency of induction of the initial, preneoplastic changes in RTE cells in culture (approximately 3 X 10(-2)/surviving cell). These quantitative determinations are useful in defining the mechanisms of late changes occurring during the progression of RTE cells to the neoplastic state.

Animals↗
PubMed1985

Contrasting responses of normal and transformed rat tracheal epithelial cells to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate.

The data presented here are part of an ongoing effort to examine the response of rat tracheal epithelium to tumor promoting agents and to elucidate the mechanisms of tumor promotion in that epithelial tissue (see Steele, this volume). Previous studies indicated that airway epithelium is responsive to the tumor promoter TPA and that TPA can promote the tumor response in rat tracheal epithelium But what are the mechanisms involved? We have divided this question into two main elements: 1) Which stages of neoplastic development are affected by TPA, i.e., which preneoplastic cell populations are targets for TPA action resulting in the acceleration and enhancement of the process of neoplastic development? 2) What effects does TPA have on various preneoplastic cell populations and how do such effects result in promotion? The experiments discussed here relate to the second part of the question. They suggested that TPA elicits a marked cytotoxic response in stably transformed RTE cell variants (see Fig. 1). These preneoplastic cell variants are clearly different from untransformed RTE cells which are triggered into cell cycle as indicated by an increase in CFE. This difference between normal and transformed cells is of considerable interest in itself since it points to a fundamental, biochemical alteration in the transformed cells. Evidence exists that transformed RTE cell lines have TPA receptors and that at least some of the responses elicited by TPA exposure, such as the induction of ornithine decarboxylase activity, are receptor-mediated. Whether the cytotoxic response elicited by TPA is receptor-mediated is presently not known.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Changes in stem cell populations of rat tracheal epithelial cell cultures at an early stage in neoplastic progression.

The development of transformed colonies and concomitant changes in proliferative and nonproliferative cell compartments were studied in rat tracheal epithelial (RTE) cell cultures following exposure to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Primary RTE cells were plated onto 3T3 feeder layers and treated with MNNG (0.25 micrograms/ml) or solvent. Seven days later, the feeder cells were removed to select for enhanced growth variants, which are the transformants of the RTE cell system, usually scored 5 weeks after carcinogen exposure. Most of the RTE cell colonies, which originally formed during the first 7 days of culture, disappeared within 2 weeks after feeder cell removal in control and MNNG-treated cultures. In control cultures, about 3% of the original colonies persisted, while in MNNG-treated cultures, a larger percentage (approximately 9%) of the colonies persisted. These percentages remained constant from 3 to 7 weeks. Based on colony size, cell density, and cell morphology, the persistent colonies were classified into transformed colonies (large colony size, high cell density, high nuclear:cytoplasmic ratio) and untransformed colonies (small size, low cell density, low nuclear:cytoplasmic ratio). In the MNNG-treated cultures, about 50% of all persistent colonies showed transformed morphology. Their frequency remained unchanged between 3 and 7 weeks of culture. In contrast, only 10 to 15% of the persistent colonies in control cultures showed transformed morphology at 3 weeks, but that proportion increased steadily between 3 and 7 weeks. These data suggest that, in control cultures, transformed colonies developed spontaneously as a function of time within untransformed colonies. Autoradiographic studies with [3H]thymidine showed that labeling indices in the early "normal" RTE cell colonies between Days 4 and 7 of culture were very high, ranging between 75 and 90%. In contrast, the labeling indices of persistent colonies, both those without and those with transformed morphology, were low, i.e., between 18 and 25%, indicating that a major proportion of cells was either noncycling or cycling very slowly. The relative compartment sizes of cells with stem cell characteristics and of cells with characteristics of transformed stem cells were estimated before and after transformed colonies appeared.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

In vitro transformation of rat tracheal epithelial cells: a model for the study of multistage carcinogenesis.

A multistage transformation assay has been developed using normal primary rat tracheal epithelial cells as targets for measuring the transforming activity of a variety of test substances. The assay is suited for quantitation of cell transformation and allows the study of effects of promoters as well as inhibitors of transformation at various stages of this multiphasic process. Studies with TPA and retinoic acid have shown that the first stage of neoplastic transformation of RTE cells cannot be enhanced by TPA but is inhibited by retinoic acid. However, TPA can enhance a later stage of transformation, the conversion of the ag- to the ag+ phenotype. The cellular and biochemical mechanism of the inhibitory effects of RA are under investigation.

Animals↗
PubMed1984

Characterization of an unscheduled DNA synthesis assay with Syrian hamster embryo cells.

The Syrian hamster embryo cell transformation assay is widely used for studies of carcinogenesis. The characterization of an unscheduled DNA synthesis (UDS) assay for these cells is reported. Benzo[a]pyrene, aflatoxin B1 and UV light induced UDS in the cells in a dose-dependent manner without exogenous metabolic activity. Nitrosopiperidine induced UDS as well as gene mutations and cell transformation only in the presence of an exogenous metabolic activation system. The utility of this UDS assay with these cells is discussed.

Aflatoxins↗
PubMed1984

Amitrole-induced cell transformation and gene mutations in Syrian hamster embryo cells in culture.

Amitrole, a widely used herbicide, is an animal carcinogen and an inducer of cell transformation. However, it is inactive as a mutagen in bacterial test systems. Thus, it has been suggested that amitrole is a non-mutagenic carcinogen. Over the dose range that induces morphological transformation of Syrian hamster embryo cells in culture, amitrole induced gene mutations at the Na+/K+ ATPase and hypoxanthine phosphoribosyl transferase loci measured concomitantly in the same cells. These results indicate that amitrole may act via a mutational mechanism.

Amitrole↗
PubMed1984

Colcemid-induced neoplastic transformation and aneuploidy in Syrian hamster embryo cells.

Treatment of Syrian hamster embryo cells in culture with 0.01-0.1 micrograms/ml of colcemid for 48 h resulted in morphological and neoplastic transformation of the cells. Cell transformation was observed with doses which were non-cytotoxic and did not cause mitotic inhibition of the cells. Higher dose of colcemid (greater than 0.1 microgram/ml) resulted in mitotic inhibition of the cells and a significant loss of colony forming ability, but no increase in the frequency of morphological transformation. Treatment of the cells with transforming doses of colcemid did not result in any measurable induction of gene mutations or structural chromosome aberrations; however, numerical chromosome changes in the treated cells were observed. A 14-fold increase in the number of aneuploid cells with a near diploid chromosome complement was found in cultures treated with 0.1 micrograms/ml colcemid and both chromosome loss and gain were induced. The dose response curves for colcemid induced morphological transformation and aneuploidy were similar. These results are consistent with a role of carcinogen-induced chromosome non-disjunction in carcinogenesis.

Aneuploidy↗
PubMed1984

The effect of 12-O-tetradecanoylphorbol-13-acetate and other tumor promoters on the colony formation of rat tracheal epithelial cells in culture.

Normal primary rat tracheal epithelial (RTE) cells were isolated and exposed in culture to tumor promoters and irritants of diverse chemical classes. The phorbol derivative class of tumor promoters greatly stimulated colony forming efficiency (CFE) in culture. The efficacies of the agents tested were ranked in the order: mezerein greater than 12-O-tetradecanoyl-phorbol-13-acetate (TPA) greater than phorbol didecanoate greater than phorbol dibutyrate greater than phorbol dibenzoate greater than 4-O-methyl TPA greater than phorbol diacetate. The parent alcohol phorbol did not stimulate CFE under the conditions tested. The indole alkaloid tumor promoter teleocidin stimulated CFE at concentrations at least 10-fold lower than those required for TPA. Other irritants and non-phorbol ester tumor promoters such as anthralin, benzoyl peroxide, calcium ionophore A23187, and ethylphenyl propiolate were either inactive or reduced CFE. Phenobarbital marginally stimulated CFE at one concentration but reduced CFE at higher concentrations. Increases in CFE elicited by TPA and analogs were dependent upon the time of addition of TPA to the cultures. Maximum increases in CFE were observed when the cells were plated into medium containing TPA. If TPA was added 40 h after plating, stimulation of CFE did not occur. This 40 h time interval may represent a crucial period for the commitment of RTE stem cells to proliferation or differentiation. Whether the stimulation of colony formation seen in normal RTE cells exposed to phorbol derivatives also occurs in carcinogen-altered cells, thereby causing their proliferative expansion, remains to be determined.

Animals↗
PubMed1984

Growth and differentiation of hamster tracheal epithelial cells in culture.

The purpose of these studies was to define culture conditions that support growth and differentiation of normal epithelial cells obtained from hamster tracheas. Epithelial cells from tracheas of adult hamsters were collected using enzymatic procedures and cultured under various conditions. The medium used consisted of a 1:1 mixture of medium 199 and Dulbecco's modified Eagle's medium with 2% fetal bovine serum, which was conditioned by mouse 3T3 cells before use. Insulin, transferrin, hydrocortisone, epidermal growth factor, and an extract from bovine hypothalamus were used as supplements. When seeded on uncoated or collagen-coated tissue culture dishes, the hamster cells grew only poorly. When the cells were seeded on collagen gels, however, rapid and prolonged growth ensued. The cultures had a population doubling time of 20 hr and a colony-forming efficiency of 7-10%, and they could be grown for up to three passages. Growth was dependent on the presence of transferrin, insulin, epidermal growth factor, and 3T3 conditioning factors in the medium. The latter could be omitted if the concentration of serum was increased. Less important for growth was the presence of hydrocortisone and bovine hypothalamus extract. In contrast to results with tracheal epithelial cells from adult rabbits, rats, and mice, differentiation into ciliated cells regularly occurred in cultures of cells derived from hamster tracheas. The appearance of ciliated cells in the cultures was dependent on the presence of collagen gel as a substratum and of 3T3 conditioning factors in the medium. In addition, there were numerous cells that contained electron-dense cytoplasmic granules. The granules were not stained by dialyzed iron, which stains acidic glycoproteins, but were stained positively by periodic acid-Schiff reagents and the periodic acid-thiocarbohydrazide-silver proteinate method, suggesting the presence of secretory granules containing neutral glycoproteins. A similar staining pattern was observed for the secretory granules of intact hamster tracheas. The culture system described supports growth and cellular differentiation of normal tracheal epithelial cells of hamsters. We believe therefore that it will be a useful model for studying the regulation of tracheal cell function on the cellular and biochemical level.

Animals↗
PubMed1984

Tracheal epithelial cell transformation: a model system for studies on neoplastic progression.

Most in vitro transformation studies have been conducted with fibroblast cultures of various origins. The phenotypic changes known to accompany transformation are therefore primarily those that are typical for transformed fibroblasts. Little information exists concerning phenotypic changes occurring during transformation of epithelial cells in vitro. However, recently a number of transformation studies have been reported with tracheal epithelium as a prototype for epithelium from the conducting airways. The initial studies were carried out with organ culture-cell culture systems. These studies reported the qualitative phenotypic changes developing in primary outgrowth cultures after exposure to the direct acting carcinogen N-methyl-N'-nitrosoguanidine. The phenotypic changes observed are all related to changes of in vitro growth characteristics. Several stages can be observed as the cell cultures progress from a "carcinogen altered" to the neoplastic state. While these studies laid the groundwork for the epithelial transformation field, they did not permit quantitation of transformants, since the size of the exposed cell population is unknown. More recently transformation systems with dispersed primary tracheal epithelial cells have been developed which allow quantitation of transformed phenotypes. These systems are being used for clonal analysis of the process of epithelial cell transformation and to study progression and promotion during development of neoplastic transformation.

Animals↗
PubMed1984

Correlation of asbestos-induced cytogenetic effects with cell transformation of Syrian hamster embryo cells in culture.

The cytogenetic effects of chrysotile asbestos on Syrian hamster embryo cells in vitro were investigated at doses which induced morphological and neoplastic transformation but which failed to induce measurable gene mutations in the cells at two genetic loci. Chrysotile asbestos treatment of the cells significantly induced chromosome changes in a dose-dependent manner. Up to 50% of the cells had chromosome abnormalities in number or structure following treatment with asbestos (2.0 micrograms/sq cm) for 48 hr. Numerical chromosome changes were the most pronounced abnormalities although significant increases in metaphases with other chromosome aberrations (breaks, fragments, exchanges, and/or dicentrics) and cells with binuclei or micronuclei were also observed. A linear relationship was observed between the incidences of cells with tetraploid metaphases and binucleated cells, suggesting that binucleation and tetraploidy are related. Cytogenetic effects of other mineral dusts were also tested 48 hr following treatment at a concentration of 2.0 micrograms/sq cm. Crocidolite asbestos was less potent than chrysotile asbestos in its ability to induce cell transformation and cytogenetic damage. Treatment of the cells with thin glass fibers (Code 100) was also able to induce cell transformation and cytogenetic effects, but thick glass fibers (Code 110) were much less potent for both endpoints. Milling of the thin glass fibers decreased the length of the fibers and abolished their ability to induce cell transformation and cytogenetic effects. Nonfibrous alpha-quartz induced neither cell transformation nor cytogenetic effects at the dose of 2.0 micrograms/sq cm. The results indicate that the physical characteristics of the fibers determine their ability to induce cell transformation and their ability to induce chromosome mutations, suggesting a possible mechanistic relationship.

Animals↗