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Query: UMLS:C0596263 (carcinogenesis)
 64,820 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The distribution of 4-nitroquinoline 1-oxide (4-NQO) reductase, assumed to be closely related to the carcinogenesis of 4-NQO, was investigated in the mucosa of canine digestive tract, and its results indicated following points. 1) The activity of 4-NQO reductase was highest in the esophagus, next in the stomach, and remarkably low in the small and large intestines. 2) There is no significant difference in the 4-NQO reductase activity between the upper, middle, and lower portion of the esophagus, but its activity was higher in the female than in the male in its upper and middle portions. 3) Among the esophageal tissue, its activity was high only in the mucous epithelium and very low in all other layers. 4) Most of the enzymic activity in the esophageal mucosa existed in the cytosol fraction and activity of the microsome fraction was remarkably low. Even if NADPH or NADH was used as the hydrogen donor, its activity was not different in the cytosol fraction, but the former was a better hydrogen donor in the microsome fraction. 5) In the gastric mucosa, the enzymic activity was equally high in various portions of the corpus ventriculi; the greater and lesser curvatures, anterior and posterior parietes, and fundus. It was remarkably low only in the pyloric antrum.
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PMID:Distribution of 4-nitroquinoline 1-oxide reductase in the mucosa of canine digestive tract. 9 82

Nonimmunological defenses are very diverse in type. Some are directed against already transformed cells and belong to mechanisms of containment. Others exert a surveillance by preventing or inhibiting initial events of carcinogenesis. Chalones and oncolytic factors in sera and exudates are agents of containment. Under appropriate circumstances, the autoxidation of thiols and the formation of mixed disulfides lead to destruction of tumor cells in vitro and in vivo. Both processes involve the generation of superoxide radicals and of hydrogen peroxide which, in turn, activate the peroxide:peroxidase:halide system. Thiol:disulfide ratios and interchange codetermine the antioxidative activity of cellular membranes, thus bearing on carcinogenesis. Many aliphatic and aromatic antioxidants are endowed with anticarcinogenic properties. The fact that they are inhibitors of free radical processes corroborates the increasingly evident role of free radicals in carcinogenesis. Endogenous antioxidants and exogenous ones in foods are agents of surveillance. Antioxidant activity, linked with the ergastoplasm, points to a homeostatic mechanism that prevents self-accelerating chain reactions from leading to membrane damage or to carcinogenesis. Carcinogens can also be inactiviated by microsomal enzymes belonging to an overall mechanism of detoxification. Activity levels of these systems depend on diet and state of nutrition. They may be naturally very low, but they can be increased with various inducers.
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PMID:Nonimmunological host defenses: a review. 17 22

Groups of 30 males Sprague-Dawley rats were given 4-nitrosomorpholine-3,3,5,5-d in their drinking water at concentrations of 0.35 and 0.07 X 10(-3) M for 30 weeks. Two similar groups of rats were simultaneously given unlabeled 4-nitrosomorpholine (NM) at the same malar concentrations; all animals were observed throughout their lives. Those receiving the alpha-deuterium-labeled compound had significantly fewer liver tumors than did the corresponding animals receiving the unlabeled compound. The difference in potency appeared to be at least fivefold, a magnitude consistent with a primary kinetic isotope effect on the carcinogenic action of NM. Thus breakage of a bond linking a hydrogen (deuterium) atom with carbon adjacent to the nitrosamino function may be involved in a rate-limiting step of carcinogenesis by NM.
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PMID:Reduction of rat liver carcinogenicity of 4-nitrosomorpholine by alpha-deuterium substitution. 18

The molecular structure and conformation of the cis-5,6-dihydrodiol of 7,12-dimethylbenz[a]anthracene has been determined by an X-ray crystallographic analysis. The compound crystallizes in the space group P21/a with cell dimensions a equals 17.799(6), b equals 33.211(8), c equals 5.241(1) A, beta equals 91.88(2)degrees. There are two molecules, designated A and B in the asymmetrical unit, that are not related to each other by crystallographic symmetry. Their conformations are almost identical, and there are no significant differences in their bond lengths or angles. In both molecules the 5-hydroxyl group is equatorial while the 6-hydroxyl group is axial. This conformation is probably forced by steric hindrance between the hydroxyl group, 0-6, and the hydrogen atoms of the 7-methyl group. The molecules pack in the crystal by forming hydrogen bonds between the hydroxyl groups of adjacent molecules, A with A, B, with B, and A with B. The ring system of the cis-5,6-dihydrodiol is much more buckled than is that in 7,12-dimethylbenz[a]anthracene itself. The angle between the two outermost rings is 36 degrees, the deviation from planarity being primarily a consequence of the partial saturation in the ring containing the two hydroxyl groups. Extrapolation of these results to other dihydrodiol derivatives of carcinogenic hydrocarbons permits some predictions of preferred molecular geometry. Thus, the 8,9-dihydrodiol-10,11-epoxide of 7,12-dimethylbenz]a[anthracene, analogous to the biologically active 7,8-dihydrodiol-9,10-epoxide of benzo]a[pyrene, a mutagen that is believed to be an active intermediate in carcinogenesis by benzo]a[pyrene, should probably exist preferentially in a conformation bearing the8-hydroxyl group in the axial orientation.
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PMID:Molecular structure of the K-region cis-dihydrodiol of 7,12-dimethylbenz[a]anthracene. 40 8

Relative extents of base-catalyzed, hydrogen-deuterium exchange have been determined for a number of nitrosamines. Observed trends in the exchanges are discussed in terms of substitution, ring size and conformation. The relevance of the exchanges to deuterium isotope effects in carcinogenesis tests is discussed. Those compounds which give pronounced biological isotope effects undergo exchange only to a small extent. No biological isotope effect is found for compounds which undergo extensive exchange.
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PMID:Relative extents of hydrogen-deuterium exchange of nitrosamines: relevance to biological isotope effect studies. 50 16

Whereas the radiotoxicity of tritium has been extensively studied, comparatively little information exists on its long-term effects as a potential environmental pollutant, particularly at small dosage. This investigation was primarily aimed at assessing comparatively a possible carcinogenic potency of tritiated water versus radioactive precursors of DNA, RNA and proteins, namely tritiated thymidine, uridine and leucine in C57 Black mice. Tritium is largely released in the environment in the form of tritiated water. There are many uncertainties, however, as to how tritium is incorporated from tritiated water into cell constituents quantitively and qualitatively. In 1965, we reported on the carcinogenic effect of tritium in the form of tritiated thymidine on newborn C57 BL mice in the dose range of 0.3--1.5 muCi/g [Mewissen. 1965]. Hence the selection of tritiated water, and of tritiated precursors, in an attempt to evaluate their respective role in the tritium transfer process and to correlate their possible late effects with their specific patterns or sites of incorporation. This study deals with tritium incorporation from tritiated water and various precursors at the 1 or 10 muCi level. RSA values, i.e., the ratio of organically bound tritium per hydrogen content of dry tissue over aqueous tritium per hydrogen content of water, were estimated for newborn, juvenile and adult mice, at various time intervals (1, 8, 15, 22 and 29 days) following single administration of tritiated water, tritiated thymidine, uridine or leucine. The data available at this time show that administration of tritiated water (or precursors) result in a complex time dependent and age dependent residual activity dynamics both in the organic component and in the aqueous fraction of tissue. A few preliminary conclusions can be made. Following a single acute or brief exposure to tritiated water, values of activity become exceedingly small after a relatively short time period. In a steady state equilibrium, resulting from chronic exposure to tritiated drinking water, RSA values tend to stabilize. However, wide variations between various organs are to be expected, as suggested by their respective RSA values following a single exposure. In view of these observations, it would seem that a realistic estimate of the internal dose to the radiosensitive nucleus must take into consideration the age dependent incorporation of tritium from tritiated water, as well as the variation between organs. The carcinogenic risk has often been estimated from a uniform dose dependency model. The influence of time and space microdistribution of dose within tissues and more particularly at specific sites (such as DNA, RNA or protein) has received, as yet, little attention, as well as the relative contributions of the time sequence of dose absorption during the usually long latency period. Such factors, among others, may be critical in carcinogenesis from internal irradiation...
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PMID:Comparative incorporation of tritium from tritiated water versus tritiated thymidine, uridine or leucine. 63 49

The gastric mucosal barrier to hydrogen ion (H+) after the administration of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) on the rat stomach was studied. Increased H+ back-diffusion was observed 3 hr after oral doses of 1 mg of MNNG over a 3-day period. MNNG in concentrations of 250 microgram/ml, 167 microgram/ml, 86 microgram/ml, and 50 microgram/ml in the presence of acid caused increased H+ back-diffusion across the gastric mucosa within 1 hr. Gastric mucosal barrier disruption by MNNG may play a pathogenic role in gastric carcinogenesis.
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PMID:Effect of N-methyl-N'-nitro-N-nitrosoguanidine on the gastric mucosal barrier in rats. 67 5

The activities of several flavonoids and the related nonflavonoid compound epicatechin were compared with respect to Cu(II)-induced strand scission of DNA by using two different assays. The same series of compounds was used to study the stoichiometry of Cu(II) reduction in the absence of DNA. The compounds were compared for their ability to generate superoxide, hydrogen peroxide and the Cu(II)-dependent production of hydroxyl radicals. Flavonoids were examined to assess the production of a charge-transfer complex with Cu and the rate of decay of the complexes were compared. All the compounds tested had some ability to cause DNA strand scission in the presence of Cu(II), with myricetin being the most active and galangin the least active. The ability to cause such scission correlated with the rate of decay of the charge-transfer complex, the ability to generate active oxygen species and with the stoichiometry of Cu(II) binding. Analysis of the data in the light of the structural differences between the flavonoids led to a discussion of alternative Cu(II)-sequestering mechanisms.
Carcinogenesis 1992 Apr
PMID:Activities of flavonoids for the cleavage of DNA in the presence of Cu(II): correlation with generation of active oxygen species. 131 26

To determine if asbestos exposure could contribute to mesothelial cell carcinogenesis by selection and/or expansion of an initiated cell population, we compared normal human pleural mesothelial cells to either human mesothelioma cell lines or mesothelial cells transfected with cancer-related genes for sensitivity to amosite fibers in vitro. Neither normal nor mesothelioma cells were directly stimulated to replicate or increase DNA synthesis by any of the asbestos exposure conditions tested. The potential selective effect of asbestos exposure was demonstrated by a differential sensitivity of normal mesothelial cells and mesothelioma cells to amosite: for example, up to 20-fold higher concentrations of amosite fibers were required to inhibit replication of mesothelioma cell lines than normal mesothelial cells. In addition, a significant resistance (4-fold) to amosite toxicity was observed for SV40 immortalized mesothelial cell lines that had previously been selected in vitro for resistance to asbestos. SV40 immortalized cells that have become tumorigenic after transfection with either Ha-ras or PDGF A-chain genes were not significantly more resistant to the cytotoxic effects of amosite than primary normal cells, and the primary cells were equally sensitive to amosite as mesothelial cells that were only immortalized by SV40. The sensitivity of normal mesothelial cells to asbestos does not appear to be simply a result of general fragility of the mesothelial cells, since similar levels of hydrogen peroxide and silica were cytotoxic for normal mesothelial cells and mesothelioma cell lines. Because mesothelioma cells have a greater resistance to asbestos cytotoxicity than normal mesothelial cells, we hypothesize that a differential resistance to cell killing by asbestos fibers in vivo may result in a selective expansion of an initiated or transformed cell population and thus contribute to the carcinogenesis process. Since tumorigenicity and asbestos resistance occur independently of one another in genetically altered mesothelial cell lines, genotypic and phenotypic alterations that lead to tumorigenic conversion may not be the same changes that provide resistance to cell killing by asbestos.
Carcinogenesis 1992 Aug
PMID:Human mesothelioma cells and asbestos-exposed mesothelial cells are selectively resistant to amosite toxicity: a possible mechanism for tumor promotion by asbestos. 132 25

As part of a program to study the effects of inhaled fibers, we characterized the capacity of various fibers to initiate hydroxyl radical (.OH) formation from hydrogen peroxide in a non-cellular system. We studied five natural fibers (erionite, crocidolite, amosite, anthophyllite and chrysotile) and two man-made fibers (JM code 100 glass fibers and glass wool). The fibers were incubated for 5 min at 37 degrees C with hydrogen peroxide and salicylic acid in pH 7.0 aqueous solutions. The salicylate reacted with any .OH formed in these mixtures to produce stable addition products. The amount of .OH addition products formed during the incubations was determined by the salicylate assay which uses HPLC with electrochemical detection. Erionite, JM code 100 and glass wool were the most effective initiators of .OH formation, followed, in order, by crocidolite, amosite and chrysotile. When the capacity of the natural fibers to initiate .OH formation was plotted versus either the values for tumor rates of rats that received pleural inoculations of fibers or the literature values for the human mesothelioma mortality rates, positive correlations (r2 > or = 0.896) were found. Similar correlations with man-made fibers were not found. No positive correlation could be made between .OH formation capacity versus the tumor rates of rats that received peritoneal injections of either type of fibers.
Carcinogenesis 1992 Nov
PMID:Fiber-induced hydroxyl radical formation: correlation with mesothelioma induction in rats and humans. 133 Mar 49


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