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T J Slaga

Publications and source records attributed to T J Slaga.

At least 145 records · Page 8Linked to original sources
PubMed1984

Multistage skin carcinogenesis: a useful model for the study of the chemoprevention of cancer.

Skin carcinogenesis can be operationally and mechanistically divided into at least three stages; tumor initiation, stage I and stage II of promotion. Current information suggests that reactive intermediates of skin tumor initiators are mutagenic and bind convalently to DNA of epidermal stem cells (dark basal keratinocytes) leading to some irreversible alteration in the differentiation capacity of these cells. Inhibitors of skin tumor initiation by polycyclic aromatic hydrocarbons (PAH) decrease the level of the PAH diol-epoxide bound to specific DNA adducts. The tumor promoters have been shown to have many cellular and biochemical effects in the skin. Recent data suggests that free radicals may be important in skin tumor promotion. The first stage of promotion is partially irreversible and can be accomplished by a single treatment of a tumor promoter such as TPA or by non-promoting agents such as 4-0-methyl-TPA, calcium ionophore A23187, and hydrogen peroxide, as well as wounding. These agents increase the number of dark basal keratinocytes, which suggest that these cells are important in the first stage of promotion. Prostaglandin E2 was found to specifically enhance stage I of promotion whereas the protease inhibitor tosyl phenylalanine chloromethylketone (TPCK) specially inhibited stage I of promotion and the TPA-induced dark basal keratinocytes. The second stage of promotion is initially reversible but later becomes irreversible. The weak promoting agent mezerein is an effective stage II promoter. Polyamines and epidermal cell proliferation appear to be important events in stage II of promotion. Putrescine was found to specifically enhance stage II, whereas retinoic acid (RA), diflouromethylornithine (DFMO), and butylated hydroxyanisole (BHA) specially inhibited stage II of promotion and the mezerein-induced polyamine levels. Floucinolone acetonide (FA) was found to inhibit both stages but was more effective in counteracting stage I of promotion. Although, TPA can cause a decrease in the number of glucocorticoid receptors during promotion, FA can effectively prevent this loss. Recent data suggest that skin tumor promotion can be effectively inhibited by a combination of stage I and II inhibitors. Furthermore, skin carcinogenesis can be counteracted by a combination of low and nontoxic doses of BHA, TPCK, DFMO and vitamin E.

Animals↗
PubMed1984

Formation and persistence of DNA, RNA, and protein adducts in mouse skin exposed to pure optical enantiomers of 7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo(a)pyre ne in vivo.

The covalent binding of (+)-anti-benzo(a)pyrene-7,8-diol-9,10-epoxide [(+)-anti-BPDE], the carcinogenic metabolite of benzo(a)pyrene, and its noncarcinogenic (-) enantiomer to macromolecules was investigated in mouse skin in vivo. Levels of the adducts were measured in DNA samples isolated from the epidermis of adult Sencar mice exposed topically to (+)- and (-)-anti-BPDE for 3, 24, and 72 hr. The amount of (+)-anti-BPDE bound to epidermal DNA was approximately 3 times higher than that of the (-) enantiomer at all time points studied, with the highest level of adducts observed after 3 hr exposure. A similar time course of binding was observed in DNA purified from epidermal basal cells which were isolated from mice treated with the two enantiomers. As with the results for isolated DNA samples from whole epidermis, we also observed a 3:1 ratio of binding with (+)- and (-)-anti-BPDE in basal cell DNA. Interestingly, no significant difference in total binding between the (+) and (-) enantiomers could be detected at any time point in RNA and protein isolated from the basal cells. The formation of individual DNA adducts derived from topically applied (+)- or (-)-anti-BPDE was monitored at 3, 24, and 72 hr using high-pressure liquid chromatography. The major DNA adduct (64% of total) formed from (+)-anti-BPDE cochromatographed with marker adducts of N2-[10S-[7R,8S,9R-trihydroxy-7,8,9,10-tetrahydrobenzo(a)pyrene]yl] deoxyguanosine, while other minor adducts also were observed. With the (-)-anti-BPDE, a greater variety of DNA adducts was formed, with only 20 to 30% of the radioactivity present in high-pressure liquid chromatography chromatograms corresponding to the N2-deoxyguanosine adduct. The rate of formation and disappearance of individual adducts derived from both isomers of anti-BPDE was similar over the 72-hr time course. The results suggest that, although differences exist in total binding to DNA between the two enantiomers, they do not appear to be of sufficient magnitude to explain the marked difference in biological activity of (+)- and (-)-anti-BPDE in mouse skin.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1984

A morphometric study of dedifferentiated and involutional dark keratinocytes in 12-O-tetradecanoylphorbol-13-acetate-treated mouse epidermis.

The epidermis of mice treated with 12-O-tetradecanoylphorbol-13-acetate (TPA) was investigated using the method of stereological cytology. These procedures were carried out in order to quantify the morphological changes taking place in basal cells, the presumed target cells of TPA in the epidermis. The basal layer of the treated epidermis was composed of TPA-induced dark basal keratinocytes (DC) and clear basal keratinocytes. TPA-induced DC could be divided into two types. Type 1 was characterized by a relatively high volume fraction of ribosome and nonbundled filaments and by a low volume fraction of bundled filaments. These characteristics of type 1 DC were relatively constant over the observation period. Type II DC were characterized by a high volume density of mitochrondria , bundled filaments, and cytoplasmic vacuoles. This type of DC was seldom seen in normal epidermis but constituted approximately 20% of the dark cells in the epidermis 24 and 48 hr after treatment with TPA. In contrast, clear basal keratinocytes exhibited time-dependent changes such as an increase of the relative volume of nuclei; an increase in the volume density of mitochondria, nonbundled filaments, and ribosomes; and a decrease in the volume density of bundled filaments. Both the qualitative and quantitative analyses of TPA-treated and fetal epidermis suggest a close similarity between type 1 DC and DC seen in normal fetal epidermis, thus supporting the view that type 1 DC are poorly differentiated cells or dedifferentiated cells, different from type II or involutional DC.

Animals↗
PubMed1984

Alteration in the distribution of the epidermal protein filaggrin during two-stage chemical carcinogenesis in the SENCAR mouse skin.

The histidine-rich epidermal protein filaggrin was purified from urea extracts of newborn SENCAR mouse epidermis. The protein had a molecular weight of 28,000 and an amino acid composition distinctive for this class of proteins. The purified protein was a phosphate acceptor in an in vitro protein kinase assay. Rabbit antibodies raised against filaggrin were used in an indirect immunofluorescent survey of the distribution of filaggrin in the epidermis after single and multiple 12-O-tetradecanoylphorbol-13-acetate treatments as well as in papillomas and carcinomas. The immunofluorescent pattern of acetone-treated adult SENCAR mouse epidermis showed primarily granular layer fluorescence. A single topical 12-O-tetradecanoylphorbol-13-acetate treatment increased immunofluorescence in basal and suprabasal cells. Large papillomas produced by a dimethylbenz[a]anthracene initiation-12-O-tetradecanoylphorbol-13-acetate promotion protocol showed increased fluorescence in all layers. Exuberant papillomas showed a pleomorphic distribution of filaggrin with alternating positive and negative areas of immunofluorescence. Filaggrin immunofluorescence in invasive carcinomas was negative or only slightly positive. The distribution of filaggrin as detected by indirect immunofluorescence is a good indicator of maturation and differentiation in experimental tumors, and its presence correlates with the absence of aggressive or invasive growth.

Amino Acids↗
PubMed1983

Effects of tumor promoters on the rate and commitment to terminal differentiation of subpopulations of murine keratinocytes.

The effects of skin-tumor-promoting and -nonpromoting agents on the kinetics of terminal differentiation of subpopulations of keratinocytes differing in buoyant density isolated from mice (SENCAR) that are very sensitive to 12-O-tetradecanoylphorbol-13-acetate (TPA) promotion were investigated. Topical pretreatment of dorsal skin with complete (TPA), first-stage (calcium ionophore A23187) and second-stage (mezerein) tumor promoters, but not the hyperplastic agent ethylphenylpropiolate, accelerated the rate of terminal differentiation of keratinocytes with densities less than 1.074 g/cm3, but had little effect on cells with a greater density. Within 8.5 hr of TPA treatment, a period preceding mitosis, a large percentage of the most dense basal-cell keratinocytes (greater than or equal to 1.074 g/cm3) were converted to cells with a lower density, with a reduced plating efficiency and with an increased rate of differentiation, suggesting that TPA induces a subpopulation of basal cells to commit to terminal differentiation, and accelerates the rate of differentiation of committed cells.

Calcimycin↗
PubMed1983

The lack of initiating and/or promoting activity of sodium malondialdehyde on SENCAR mouse skin.

Malondialdehyde (MDA), a lipid peroxidation product, has been implicated in carcinogenesis, in part for its reported mutagenic activity. It was of interest therefore, to determine its activity as either a complete carcinogen, a tumor initiator, or a tumor promoter. Using the SENCAR mouse skin model, pure sodium MDA (NaMDA) was found to lack activity in any of these categories. Furthermore, NaMDA was determined to be negative in the Chinese hamster V-79 metabolic cooperation assay for promoters.

Animals↗
PubMed1983

Diazepam inhibition of phorbol ester tumor promotion.

Diazepam (Valium) had previously been shown to enhance the growth rate of some transplantable tumors although studies in other systems have suggested an inhibitory effect. Skin tumor promotion studies were therefore carried out to determine the effect of diazepam on 12-O-tetradecanoyl phorbol-13-acetate (TPA) promotion in SENCAR mice. A sex-independent dose response inhibition occurred over a dose range of 100 g to 5 mg, both in number of papillomas and percent of mice bearing tumors. Furthermore, a dose-response reduction in tumor size was observed. By itself, diazepam had no tumor promoting activity.

Animals↗
PubMed1983

Keratinocyte cell-mediated mutagenesis assay: correlation with in vivo tumor studies.

A murine keratinocyte cell-mediated mutagenesis assay was characterized and examined as an in vitro model system for studying the biotransformation of promutagens/procarcinogens by mouse skin. The assay used living cultured newborn SENCAR keratinocytes for the metabolic activation of promutagens and Chinese hamster lung V-79 fibroblasts for detection of resulting mutagens. Mutations at, or affecting, the hypoxanthine-guanine phosphoribosyltransferase locus were scored by resistance to 6-thioguanine. The relative mutagenicities of several polycyclic aromatic hydrocarbons (PAHs) in the cell-mediated assay correlated with the in vivo skin tumorigenicity of the PAHs determined in a two-stage carcinogenesis protocol. Metabolic activation of the promutagenic PAHs to ultimate mutagens was dependent upon the presence of the cultured keratinocyte feeder layer. 7,8-Benzoflavone, a potent inhibitor of 7,12-dimethylbenz[a]anthracene (DMBA)-dependent initiation in mouse skin, inhibited DMBA-dependent mutagenesis in the cell-mediated assay in a concentration responsive manner. The non-PAH promutagens, dimethylnitrosamine (DMN) and sterigmatocystin (STC) were both activated by cultured keratinocytes to cytotoxic derivatives. DMN was neither mutagenic in the cell-mediated assay nor tumorigenic in mouse skin when tested in a two-stage carcinogenesis protocol. STC was weakly mutagenic and tumorigenic in mouse skin.

Animals↗
PubMed1983

Enhancement of the skin tumor-initiating activity of polycyclic aromatic hydrocarbons by methyl-substitution at non-benzo 'bay-region' positions.

The effect of substituting a methyl group at the non-benzo 'bay-region' site of several polycyclic aromatic hydrocarbons on skin tumor-initiating activity was determined. A methyl group at this position enhanced the tumor-initiating activity of dibenz[a,h]anthracene, 3-methylcholanthrene and 7-methyldibenz[a,j]anthracene, but not of dibenz[a,c]anthracene. 2,3,7,8-Tetrachlorodibenzo-p-dioxin was an effective inhibitor of skin tumor initiation by 7,14-dimethyldibenz-[a,h]anthracene and 3,6-dimethylcholanthrene. There appears to be a general rule regarding methyl-substituted hydrocarbons: where a 'bay-region' exists in a polycyclic aromatic hydrocarbon molecule, methyl-substitution at the non-benzo 'bay-region' site results in enhanced tumor-initiating activity. The effect of methyl substitution in this position can be most simply explained as due to enhancement of the reactivity of the benzo ring through distortion of the aromatic ring system from planarity. The consequences of this effect are discussed.

Animals↗
PubMed1983

Mouse skin tumor initiation-promotion and complete carcinogenesis bioassays: mechanisms and biological activities of emission samples.

Extracts of soots obtained from various sources were applied to the skin of mice in an effort to identify carcinogens in these mixtures and to link these materials to the etiology of human cancer. Samples of coal chimney soot, coke oven materials, industrial carbon black, oil shale soot, and gasoline vehicle exhaust materials have been examined by this method. The studies reported here have been constructed to compare the carcinogenic and tumorigenic potency of extracts from various particulate emissions: coke ovens, diesel and gasoline vehicles and a roofing tar pot. Automobile emission samples were obtained by collecting the diluted and cooled exhaust on Teflon-coated glass fiber filters. Coke oven and roofing tar samples were particulate emission samples collected by impaction and filtration. The organic components associated with each of the particles were extracted with dichloromethane and dermally applied to SENCAR mice. All agents were applied as tumor initiators by using a five-dose protocol. Selected extracts were also applied as complete carcinogens and as tumor promotors. Statistical analyses of the resulting tumor data were performed by using nonlinear Poisson and probit models. The results from these experiments provide a suitable data base for comparative potency estimation of complex mixtures.

Air Pollutants↗
PubMed1983

Overview of tumor promotion in animals.

Our present understanding of two-stage carcinogenesis encompasses almost four decades of research. Evidence for chemical promotion or cocarcinogenesis was first provided by Berenblum, who reported that a regimen of croton oil (weak or noncarcinogenic) applied alternately with small doses of benzo(a)pyrene (BP) to mouse skin induced a larger number of tumors than BP alone. Subsequently, Moltram found that a single subcarcinogenic dose of BP followed by multiple applications of croton oil could induce a large number of skin tumors. These investigations as well as a number of others, such as Boutwell, Van Duuren and Hecker, were responsible in defining many important aspects of the initiation and promotion of two-stage carcinogenesis. The initiation stage in mouse skin requires only a single application of either a direct-acting carcinogen or a procarcinogen and is essentially an irreversible step which as data suggests probably involves a somatic cell mutation. The promotion stage in mouse skin can be accomplished by a wide variety of weak or noncarcinogenic agents and is initially reversible later becoming irreversible. Current information suggests that skin tumor promoters are not mutagenic but bring about a number of important epigenetic changes, such as epidermal hyperplasia, and an increase in polyamines, prostaglandins and dark basal keratinocytes as well as other embryonic conditions. Recently, tumor promotion in mouse skin was shown to consist of at least two stages, in which each stage can be accomplished by either a known promoter or a weak or nonpromoting agent. Some of the important characteristics of the first stage of promotion are: (1) only one application of a first-stage promoter, such as phorbol ester tumor promoters, calcium ionophore A23187, hydrogen peroxide and wounding is needed; (2) the action is partially irreversible; (3) an increase in dark basal keratinocytes and prostaglandins is important; and (4) such an increase can be inhibited by antiinflammatory steroids and protease inhibitors. The second stage of promotion is initially reversible but later becomes irreversible. Polyamines and epidermal cell proliferation are important events in the second stage of promotion. A number of weak or nonpromoting agents, such as mezerein, are effective second-stage promoters which can be counteracted by retinoic acid, antiinflammatory steroids and polyamine synthesis inhibitors. Although skin tumor promotion has been extensively studied in mice, not all strains and stocks of mice are susceptible to phorbol ester tumor promoters. In this regard, the C57BL/6 mice appear to be fairly resistant to phorbol ester tumor promoters. In addition, not all species are equally susceptible to phorbol ester tumor promotion. Recently the generality of the two-stage system of inducing tumors has been shown to exist in a number of experimental carcinogenesis systems, such as the liver, bladder, lung, colon, esophagus, stomach, mammary gland, pancreas and cells in culture. In these systems, a wide variety of promoting agents such as diet, bile acids, hormones, saccharin, tryptophan, phenobarbital, polychlorinated biphenyls, polybrominated biphenyls and butylated hydroxytoluene have been used to accomplish the tumor promotion stage. It is not presently known if other experimental carcinogenesis systems and the induction of human cancer involves a series of stages similar to that in the mouse skin.

Animals↗
PubMed1983

Initiation-promotion versus complete skin carcinogenesis in mice: importance of dark basal keratinocytes (stem cells).

Tumor promotion research has accelerated at an explosive level during the past decade and continues to do so because of its importance to the understanding of the induction of human cancer. Furthermore, the promotion process, being mostly reversible allows one to find very effective ways to prevent cancer. The extensive data available as well as the multistage nature of tumor promotion suggests that this process, which is thought to occur in most tissues where cancer can be induced or occurs spontaneously, may involve the interaction of a number of environmental factors such as chemical, radiation, viruses and diet and nutrition, thus unifying all of the current areas of cancer research. In terms of human cancer, smoking, asbestos, radiation, alcohol and diet, and nutrition just to mention a few, are not thought to have more than a promotional influence in the carcinogenesis process. Here and in later papers we will discuss some important aspects of promotion as well as discuss the possible controversial nature of this process. In this review we present data which suggest that carcinogenesis can be operatively and mechanistically divided into various stages.

Animals↗
PubMed1983

Simultaneous appearance of keratin modifications and gamma-glutamyltransferase activity as indicators of tumor progression in mouse skin papillomas.

gamma-Glutamyltransferase (GGT), an enzyme not found in normal adult epidermis, was detected in most skin papillomas larger than 13 mm in diameter and in all squamous carcinomas induced by 7,12-dimethylbenz[a]anthracene initiation and 12-O-tetradecanoylphorbol 13-acetate promotion in noninbred Sencar mice. Furthermore, these GGT-positive lesions were also characterized by a marked decrease or absence of high-molecular-weight components of epidermal keratin. Since these characteristics are common to both carcinomas and large papillomas but are practically undetectable in normal epidermis and small papillomas, GGT activity and lack of high-molecular-weight keratin components seem to be good indicators of tumor progression, i.e., from papilloma to squamous carcinoma.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1983

Formation of benzo(a)pyrene/DNA adducts and their relationship to tumor initiation in mouse epidermis.

The tumorigenicity of benzo(a)pyrene [B(a)P] applied topically as a skin tumor initiator in Sencar mice and the formation of epidermal B(a)P/deoxyribonucleoside adducts were compared over a similar range of doses (50 to 1600 nmol). The tumor-initiating activity of B(a)P, its covalent binding to mouse epidermal DNA, and the formation of the major hydrocarbon/deoxyribonucleoside adduct showed approximately parallel dose-response curves. The major hydrocarbon/deoxyribonucleoside adduct formed cochromatographed with marker adducts of (N2-(10S-[7R,8S,9R-trihydroxy-7,8,9,10-tetrahydrobenzo(a)pyrene]y) deoxyguanosine while other minor adducts also were observed. The disappearance of DNA-bound products in the epidermis was followed for 21 days after an initiating dose of B(a)P (100 nmol) was applied topically to the mice. The half-lives of the B(a)P/deoxyribonucleoside adducts and the total radioactivity bound to the DNA were 4.5 and 5.5 days, respectively. However, in spite of the loss of measurable DNA-bound material, the tumor yield was unchanged regardless of whether promotion was begun 7 or 21 days after initiation. The results suggest a possible causal relationship between B(a)P/deoxyribonucleoside adduct formation and papilloma formation in mouse skin.

Animals↗