PubMed Health⌕ Search

Biomedical subjects

D B Couch

Publications and source records attributed to D B Couch.

At least 19 recordsLinked to original sources
PubMed1996

Carcinogenesis: basic principles.

Many steps are required to convert a normal cell into a cancerous one. The cancer cell must be able to multiply under conditions that a normal cell would not and to invade surrounding tissue and spread throughout the body. Both genetic changes, such as activation of oncogenes or inactivation of tumor suppressor genes, and epigenetic changes, such as stimulation of cell proliferation, contribute to the development of cancers. Chemical agents can increase the probability of malignant transformation by inducing mutations that can ultimately lead to tumor formation, by promoting the development of tumors in cells with preexisting genetic damage, or by increasing the rate of acquisition of malignant traits by benign tumors. Chemical carcinogens are structurally diverse, but all initiating agents are either already electrophiles or can be converted to electrophilic reactants through metabolic activation. Genetic and environmental factors can alter an individual's ability to metabolize carcinogens, to repair DNA damage, and to respond to mitogenic stimuli, all of which can alter susceptibility to chemical carcinogenesis. The incidence and time required for appearance of tumors appear to be dose-related, but the existence of no-effect doses of carcinogens remains controversial.

Animals↗
PubMed1995

Induction of micronuclei in murine lymphocytes by morphine.

Although individuals who abuse drugs are prone to an increased risk of malignancy, the mutagenic and carcinogenic potential of these agents has received relatively little attention. We report here on the potential of morphine to induce micronuclei in murine lymphocytes. Following a single intraperitoneal injection of 20 mg/kg morphine, the frequency of micronucleated binuclear (cytochalasin-blocked) murine T- and B-splenocytes was elevated from 12-36 hr after treatment. The maximum frequencies seen 24 hr after injection were 6.3- and 4.9-fold greater than the respective controls. A dose-dependent induction of micronuclei was observed from 5-20 mg/kg morphine, with no further increases in frequency produced by higher doses. In contrast, incubation of mitogen-stimulated splenocytes with 10(-7)-10(-4) M morphine in vitro produced no change in frequency of micronucleated cells relative to controls. Treatment with the narcotic antagonist naloxone (5 mg/kg) alone had no effect on the frequency of micronuclei, but reduced the clastogenic response of a subsequently administered dose of morphine (20 mg/kg). Thus, in murine lymphocytes morphine indirectly produces genetic damage, which is at least in part opioid receptor-mediated.

Analysis of Variance↗
PubMed1995

The clastogenicity of morphine sulfate in vivo.

An opioid analgesic, morphine, and an opioid peptide, beta-endorphin, have been shown to induce chromosome damage, as indicated by an increased frequency of micronucleated lymphocytes, following acute administration to mice. The genotoxic response is opioid receptor-mediated and is abolished in adrenalectomized animals. Further, plasma from morphine-treated animals also induces micronuclei formation in naive lymphocytes in vitro; this response is blocked by inclusion the steroid antagonist RU 486 in the incubation mixture. In addition to the steroid-mediated production of chromosome damage, morphine acts directly on lymphocytes to enhance the clastogenicity of acutely administered cyclophosphamide in manner consistent with depressed DNA repair capacity.

Adrenalectomy↗
PubMed1987

The effect of biotransformation of 2,4-dinitrotoluene on its mutagenic potential.

Because both oxidative and reductive metabolism of the hepatocarcinogen 2,4-dinitrotoluene (2,4-DNT) can occur in vivo, we have examined the mutagenicity of compounds which can be formed from 2,4-DNT in an attempt to establish which metabolic pathways contribute to the formation of genotoxic products. A quantitative reversion assay using Salmonella typhimurium TA98 was used to evaluate the mutagenicity of these compounds. 2,4-Dinitrobenzyl alcohol, 2-amino-4-nitrotoluene and 2-nitroso-4-nitrotoluene were found to be more mutagenic to S. typhimurium than is 2,4-DNT and did not require metabolic activation by post-mitochondrial supernatants of Aroclor-induced rat liver homogenates (S9) for their effect. 2-Amino-4-nitrobenzoic acid was also mutagenic to S. typhimurium TA98 in the absence of S9, but its mutagenicity was enhanced when S9 was included in the incubation mixture. 2,4-Diaminotoluene required S9 for demonstration of mutagenicity and was approximately as effective, on a molar basis, as 2,4-DNT in inducing reversion to histidine prototrophy. These results suggest that both oxidative and reductive metabolism may be involved in production of mutagenic metabolites of 2,4-DNT.

Animals↗
PubMed1987

Genotoxicity of two fecal steroids in murine colonic epithelium assessed by the sister chromatid exchange technique.

Two components of human feces are known to induce nuclear anomalies in mice when applied intrarectally, but to be nonmutagenic in Salmonella. We have tested these two compounds for their ability to induce sister chromatid exchanges in the colonic epithelium of mice, the same tissue in which they induce nuclear anomalies when administered by the same route. One, 4-cholesten-3-one, induced sister chromatid exchanges whereas the other, 5-alpha-cholestan-3-one did not, even at the maximum feasible dose. The results suggest that 4-cholesten-3-one is more likely to be a significant factor in human colon cancer than the 5-alpha analog.

Animals↗
PubMed1986

Induction of sister chromatid exchanges in murine colonic tissue.

As cancers of the large bowel arise primarily in the epithelial cells of the colon, measurement of genetic damage induced in those cells may aid in elucidating contributing factors in the etiology of the disease. Accordingly, procedures for the in vivo measurement of sister chromatid exchanges (SCE) have been adapted for use with colonic cells. Agar-coated 5-bromo-2'-deoxyuridine (BrdUrd) tablets were implanted (s.c.) in mice and colonic tissue prepared for measurement of SCE 48 hr later. When mice were treated by intraperitoneal injection with 20 mg/kg 1,2-dimethylhydrazine (DMH), a colon carcinogen, a significant increase over control SCE frequencies was found when treatment with carcinogen occurred in the interval from 14 hr before to 36 hr following BrdUrd administration. Treatment with DMH 2 hr following implantation of BrdUrd produced a dose-dependent increase in SCE frequencies, with the highest dose (20 mg/kg) resulting in frequencies approximately twice those of controls. Dimethylhydrazine was not found to be effective in inducing SCE in bone marrow cells of mice. As SCE can be induced by carcinogens and mutagens, measurement of SCE in colonic epithelium may be useful in identifying potential colon carcinogens.

1,2-Dimethylhydrazine↗
PubMed1982

The use of primary rat hepatocytes to achieve metabolic activation of promutagens in the Chinese hamster ovary/hypoxanthine-guanine phosphoribosyl transferase mutational assay.

A method is described in which primary rat hepatocytes have been cocultured with Chinese hamster ovary (CHO) cells to provide metabolic activation of promutagens in the Chinese hamster ovary/hypoxanthine-guanine phosphoribosyl transferase (CHO/HGPRT) mutational assay. Single cell hepatocyte suspensions were prepared from male Fischer-344 rats using the in situ collagenase perfusion technique. Hepatocytes were allowed to attach for 1.5 hours in tissue culture dishes containing an approximately equal number of CHO cells in log growth. The cocultures were exposed to promutagens for up to 20 hours in serum-free medium. The survival and 6-thioguanine-resistant fraction of treated CHO cells were then determined as in the standard CHO/HGPRT assay. Aflatoxin B1 (AFB1) 7,12-dimethylbenz(a)anthracene (DMBA) and benzo(a)pyrene (B(A)P) were found to produce increases in the mutant fractions of treated CHO cells as a function of concentration. The time required for optimum expression of the mutant phenotype following exposure to DMBA and AFB1 was approximately 8 days. Primary cell-mediated mutagenesis may be useful in elucidating metabolic pathways important in the production and detoxification of genotoxic products in vivo.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1982

Cytotoxicity and mutagenicity of dinitrotoluenes in Chinese hamster ovary cells.

Technical grade dinitrotoluene (DNT), a mixture composed predominantly of 2,4- and 2,6-DNT but containing lesser amounts of 2,3-, 2,5-, 3,4- and 3,5-DNT, has been shown to be a hepatocarcinogen in rats, The mutagenicity of these compounds has been evaluated using the CHO/HGPRT system, a quantitative mammalian somatic cell mutational assay. Dinitrotoluenes were tested for their ability to induce mutation to 6-thioguanine (TG) resistance in the presence and absence of microsomal preparations (PMS) from rats pretreated with the mixed function oxidase inducer Aroclor 1254. A marked difference in cytotoxicity of the isomers was observed. However, neither technical grade DNT nor any of the purified isomers resulted in a significant increase in the TG-resistant fraction of surviving cells, with or without added PMS.

Animals↗
PubMed1982

A critical review of the literature on nitrobenzene toxicity.

This literature review encompassing information available through 1980 and limited coverage in 1981, emphasizes results useful in assessing the potential toxic effects of nitrobenzene to man. Nitrobenzene exposure in man or experimental animals is most often associated with methemoglobinemia. Histopathologic changes also are observed in the hemato-lymphoreticular system, central nervous system, and liver. In addition, lesions have been reported in adrenals and testes. No information was found on carcinogenic or teratogenic potential, fertility, or reproductive effects of nitrobenzene. Results from Ames Salmonella assay are negative but test procedures are questionable; metabolites give positive results. Metabolism of nitrobenzene involves either oxidation or reduction yielding p-aminophenol and p-nitrophenol, and other reduced intermediates. From the foregoing, several aspects of nitrobenzene toxicity have been identified which warrant further study. Recommendations are made for chronic and subchronic exposure of test animals via inhalation to assess various toxicological endpoints. In addition, the relationship of nitrobenzene metabolism to its toxicity needs to be established. Genotoxic effects of nitrobenzene also need study.

Abnormalities, Drug-Induced↗
PubMed1981

Stability of activating systems for in vitro mutagenesis assays: enzyme activity and activating ability following long-term storage at - 85 degrees C.

Activating systems for in vitro mutagenesis assays are commonly prepared and stored at low temperature until required. The objective of the studies reported here was to determine the long-term stability of activating systems stored at - 85 degrees C. A broad range of microsomal enzymes in the postmitochondrial supernatant (PMS) and the microsomal fraction of livers from Aroclor 1254 treated rats were studied in conjunction with the ability of these fractions to catalyse the conversion of dimethylnitrosamine (DMN) and benzo(a)pyrene (B(a)P) to products mutagenic to Chinese hamster ovary (CHO) cells and Salmonella typhimurium TM677. Biphenyl-2- and biphenyl-4-hydroxylase showed a rapid decline in activity on storage, epoxide hydratase activity increased with storage and other enzyme activities studied were relatively stable for up to 32 weeks. No consistent trends in the ability of either the microsomes or the PMS to catalyze DMN or B(a)P induced mutation were observed for up to 12 weeks with CHO cells and 24 weeks with bacteria. It is concluded that low temperature storage of activating systems is an acceptable procedure. However, the results also indicate that certain enzyme activities change during storage, suggesting that aberrant results may be obtained when stored activating systems are used in in vitro tests to screen for mutagens.

Animals↗
PubMed1981

The mutagenicity of dinitrotoluenes in Salmonella typhimurium.

The mutagenicity of technical grade 2,4-dinitrotoluene (DNT), a mixture composed predominantly of 2,4-DNT (76.5%) and 2,6-DNT (18.8%) but containing 3,4-, 2,3-, 2,5- and 3,5-DNT, and the 6 isomers of DNT has been determined in 3 assays with Salmonella typhimurium. The mixture and the individual isomers of DNT were found to be mutagenic in the Ames' Salmonella/microsome test, particularly in strains responding to frame-shift mutagens; 3,5-DNT was found to be the most effective isomer in inducing reversion to histidine prototrophy in S. typhimurium strains TA98 and TA1538. Similar results were obtained with a quantitative reversion assay using strain TA98; 3,5-DNT was the most mutagenic of the compounds examined, particularly in the absence of post-mitochondrial supernants of rat-liver homogenates. While all isomers and the mixture of DNTs increased the 8-azaguanine-resistant fraction of S. typhimurium TM677 to some degree, the greater mutagenicity of 3,5-DNT compared to other isomers was not evident in the forward mutational assay.

Animals↗
PubMed1978

Mutagenicity of dimethylnitrosamine and ethyl methanesulfonate as determined by the host-mediated CHO/HGPRT assay.

Host-mediated assays have been developed to allow determination of the mutagenic potential of promutagens and procarcinogens which require metabolic activation to exert their effects on indicator organisms. We report here the development of the host-(mouse)-mediated CHO/HGPRT system using the procarcinogen dimethylnitrosamine (DMN) as a model agent. Using a 2--h treatment time, we observed a linear dose-response relationship up to 250 mg of DMN per kg body weight. At 100 and 500 mg/kg DMN, mutation induction increased with time up to at least 6 h. DMN was not mutagenic when tested in vitro. Athymic (nude) mice, their phenotypically normal littermates, or BALB/c mice of both sexes were found to be suitable as hosts. A time- and dose-dependency of induced mutation frequency by a direct-acting agent, ethyl methanesulfonate (EMS), was observed in both the in vitro and the host-mediated assays.

Animals↗
PubMed1978

Mutagenicity and cytotoxicity of congeners of two classes of nitroso compounds in Chinese hamster ovary cells.

The induction of mutation by certain nitrosamidines and nitrosamides has been quantitated utilizing the hypoxanthine--guanine phosphoribosyl transferase (HGPRT) locus in Chinese hamster ovary cells. Dose--response relationships for cytotoxicity and mutagenicity are presented for N-methyl-N-nitrosourea (MNU), N-ethyl-N-nitrosourea (ENU), N-butyl-N-nitrosourea (BNU), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), and N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG). Based on the concentration of each agent required to kill 90% of the cells, the following order of cytotoxicity was observed: MNNG greater than ENNG greater than MNU greater than ENU greater than BNU. This is the same order of potency as observed for mutation induction per unit concentration of mutagen.

Cell Line↗
PubMed1978

Comparative mutagenicity of alkylsulfate and alkanesulfonate derivatives in Chinese hamster ovary cells.

Mutation induction and cell killing produced by selected alkylsulfates and alkanesulfonates have been quantitated using the Chinese hamster ovary/hypoxanthine--guanine phosphoribosyl transferase (CHO/HGPRT) system. Dose--response relationships of cytotoxicity and mutagenicity are presented for two alkylsulfates [dimethylsulfate (DMS), diethylsulfate (DES)] and three alkyl alkanesulfonates [methyl methanesulfonate (MMS), ethyl methanesulfonate (EMS), and isopropyl methanesulfonate (iPMS)]. Under the experimental conditions employed, cytotoxicity decreased with the size of the alkyl group. DMS was more toxic than DES, and MMS was more toxic than EMS and iPMS. All agents produced linear dose--response of mutation induction: DMS was more mutagenic than DES, and MMS was more mutagenic than EMS and iPMS based on mutants induced per unit mutagen concentration. However, the following relative mutagenic potency was observed when comparisons were made at 10% survival: DES greater than DMS; EMS greater than MMS greater than iPMS.

Cell Line↗