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G D McCoy

Publications and source records attributed to G D McCoy.

At least 19 recordsLinked to original sources
PubMed1994

Effect of acute administration of N-nitrosopyrrolidine to male Syrian golden hamsters.

A protocol has been developed which decreases the time for administration of N-nitrosopyrrolidine (NPYR) to male Syrian golden hamsters from 25 weeks to a single i.p. injection. Animals were divided into five groups: group I received two 0.5-mmol doses on alternate days; group II was given three 0.33-mmol doses on alternate days; group III received a single dose of 0.5 mmol; group IV was given a single dose of 0.25 mmol and group V served as a control and received saline. Preneoplastic and neoplastic changes in the upper respiratory tract and liver were observed in all carcinogen-treated groups. The number of animals with laryngeal and tracheal tumors in the NPYR-treated groups was dose-dependent. Groups I and II, respectively, had 21 of 26 (81%) and 18 of 24 (75%) animals with either laryngeal or tracheal tumors. Groups III and IV showed 4 of 12 (33%) and 3 of 13 (23%) hamsters with these tumors. No laryngeal or tracheal tumors were observed in control animals. These results indicate that a single dose of NPYR is sufficient to induce respiratory tract tumors in Syrian golden hamsters.

Adrenal Gland Neoplasms↗
PubMed1991

Generation and fate of enamines in the microsomal metabolism of cyclic tertiary amines.

Microsomal oxidation of 1-benzylpiperidine (1-BP) and its cis-2,6-dimethyl analog was studied to assess the involvement of endocyclic enamines, in equilibrium with the initially formed iminiums, in the metabolic activation of cyclic tertiary amines such as phencyclidine. Since the iminiums can be trapped with cyanide, the selective prevention by cyanide of the metabolic production of 1-benzyl-3-piperidone from 1-BP implicates the iminium in equilibrium with enamine as the source of this metabolite. In cases where iminium-enamine coupling is sterically prevented, the iminium in equilibrium with enamine species can be studied independently and are found to be more potent metabolism-dependent inactivators of cytochrome P-450 than are the corresponding parent amines. Possible mechanisms for biological oxidation of cyclic enamines to reactive intermediates are considered.

Amines↗
PubMed1990

Non-mutagenic carcinogens are primarily hydrophobic.

There is no unique mechanism to explain the activity in animals of 'non-genotoxic' carcinogens. In this they differ from 'genotoxic' carcinogens that are DNA reactive. In the present study it is reported that non-mutagenic carcinogens, as a group, have significantly higher computed octanol/water partition coefficients than mutagenic ones. This property of non-mutagenic carcinogens may suggest that their ability to induce tumors is associated with membraneous receptor sites and/or a longer residence time in the animal.

Animals↗
PubMed1988

Reconstitution of rabbit liver microsomal N-nitrosopyrrolidine alpha-hydroxylase activity.

The in vitro alpha-hydroxylation of N-nitrosopyrrolidine (NPYR) by both isolated rabbit liver microsomes and purified cytochrome P-450 isozymes was investigated. Microsomes from untreated rabbits catalyzed the alpha-hydroxylation of NPYR at rates similar to those reported previously for rats, mice, and hamsters. The effect of established inducers of microsomal P-450 caused complex changes in apparent rates of alpha-hydroxylation of NPYR which made interpretation of responses to inducer pretreatment difficult and suggested the participation of multiple cytochrome P-450 isozymes in the metabolism of NPYR. Partial inhibition of alpha-hydroxylase activity by antibodies against rabbit isozymes 2, 3a, and 5 indicated the participation of at least these three isozymes in microsomal catalysis. Reconstitution studies using purified rabbit isozymes 2, 3a, 3b, 3c, 4, and 6 indicated that isozymes 2, 3a, 4, and 6 possessed significant alpha-hydroxylase activity with isozymes 3a and 6 exhibiting the highest activity when assayed at 20 mM NPYR. As NPYR concentrations were decreased, the rates of catalysis for the reconstituted systems were differentially decreased such that isozyme 3a exhibited the highest activity at low NPYR concentrations. These data indicate that isozyme 3a is the preferred catalyst for the alpha-hydroxylation of NPYR at low substrate concentrations and suggest that conditions such as chronic ethanol consumption which lead to the induction of isozyme 3a in rabbits or its orthologue in other species can account for enhanced rates of alpha-hydroxylation and metabolic activation of NPYR.

Acetone↗
PubMed1988

Biochemical and immunochemical evidence for the induction of an ethanol-inducible cytochrome P-450 isozyme in male Syrian golden hamsters.

The effects of ethanol and of phenobarbital pretreatment on hamster microsomal metabolism of aniline and p-nitrophenol have been investigated. Hydroxylation of both compounds was increased over 2-fold by ethanol pretreatment, whereas phenobarbital pretreatment had little effect on either activity. Ethanol pretreatment had no effect on the specific content of total cytochrome P-450, while phenobarbital pretreatment increased the specific content 1.6-fold. Comparison of the specific activities for aniline hydroxylation and p-nitrophenol hydroxylation of individual microsomal samples from control, ethanol-pretreated and phenobarbital-pretreated animals showed a high degree of correlation (r2 = 0.98) consistent with the involvement of the same site for catalysis of these two compounds. Antibody to rabbit ethanol-inducible cytochrome P-450 (isozyme 3a) inhibited over 80% of the aniline (high affinity) and p-nitrophenol hydroxylase activities of microsomes from ethanol-treated hamsters. A comparison of the antibody-inhibitable rates for both hydroxylase activities with microsomes from untreated, ethanol- or phenobarbital-pretreated hamsters suggested that an isozyme homologous to rabbit isozyme 3a (hamster cytochrome P-450alc) was induced in hamsters about 3.5-fold by ethanol and was unaffected by phenobarbital. The induction of hamster cytochrome P-450alc was confirmed by immunoblot analysis of hamster microsomes. A single protein with a molecular weight of approximately 54,000 was recognized by antibody to the rabbit isozyme. Quantification of the immunoblots demonstrated that the hamster isozyme was increased about 3-fold, in good agreement with the induction determined by a comparison of the antibody-inhibitable rates. The results indicated that, although there was no change in the total spectrally observable cytochrome P-450, there was a marked change in the distribution of the isozymes of cytochrome P-450, with an increase in the alcohol-inducible form after 28-day ethanol consumption by chow-fed hamsters. This isozyme can be readily monitored by either high-affinity aniline or p-nitrophenol hydroxylation or by Western immunoblot analysis and appears to be the ethanol-inducible form of cytochrome P-450 in hamsters.

Aniline Hydroxylase↗
PubMed1987

Mutagenicity, unscheduled DNA synthesis, and metabolism of 1-nitropyrene in the human hepatoma cell line HepG2.

The cell line HepG2 is derived from a well differentiated human hepatoblastoma, which retains many of the morphological characteristics of liver parenchymal cells. These cells at passages greater than 95 were found to metabolically activate carcinogens to genotoxic metabolites. The addition of 6.8 microM 1-methyl-3-nitro-1-nitrosoguanidine, 5.3 microM 4-nitroquinoline-N-oxide, and 4-20.3 microM 1-nitropyrene resulted in the induction of mutations at the HGPRT locus as determined by 6-thioguanine resistance. This is the first description of the induction of mutations in these cells. Additionally, unscheduled DNA synthesis in the presence of 4 mM hydroxyurea was increased by 9% with 5.3 microM 4-nitroquinoline-N-oxide, 57% with 13.6 microM 1-methyl-3-nitro-1-nitrosoguanidine, and 300% with 8.2 microM 1-nitropyrene. High performance liquid chromatographic analysis of metabolites formed following incubation of HepG2 with either [3H]-1-nitropyrene or [14C]benzo(a)pyrene demonstrate the occurrence of arene oxidation as well as nitroreduction.

4-Nitroquinoline-1-oxide↗
PubMed1986

Characterization of hamster liver nicotine metabolism. I. Relative rates of microsomal C and N oxidation.

A high pressure liquid chromatographic procedure has been developed for the determination of the two principal N- and C-oxidation products of nicotine in hamster liver subcellular fractions. Advantage was taken of the fact that cyanide ion forms a stable adduct with the microsomal metabolite that is the precursor of cotinine. The rate and extent as well as the sensitivity of inhibition were similar for cotinine, the 5'-cyanonicotine adduct, and an as yet unidentified microsomal metabolite which is presumed to be the initial microsomal metabolite on the pathway to cotinine formation. The rates of nicotine-N'-oxidase and nicotine-5'-hydroxylase activities exhibited differential response to inhibitors as well as differential susceptibility to proteolytic digestion. Data are presented which indicate that low levels of nornicotine contamination in stock nicotine resulted in the artifactual formation of methylcyanonornicotine adduct. No evidence consistent with the formation of nornicotine by isolated microsomes was obtained.

Animals↗
PubMed1986

Comparative effects of topically applied nitrated arenes and their nonnitrated parent arenes on cutaneous and hepatic drug and carcinogen metabolism in neonatal rats.

The effect of a single topical application of several nitroarenes (1-nitropyrene, nitropyrenes mixture, nitrobenzo(ghi)perylene mixture, 3-nitrofluoranthene, nitrofluoranthene mixture, and nitroperylene mixture) and their corresponding parent arenes to neonatal rats on hepatic and cutaneous drug and carcinogen metabolism was studied. Topical application of each nitroarene (10 mg/kg) resulted in significant induction of aryl hydrocarbon hydroxylase (AHH), 7-ethoxyresorufin O-deethylase (ERD), and 7-ethoxycoumarin O-deethylase (ECD) activities in both skin (1.5- to 14.6-fold) and liver (1.3- to 41.9-fold). The induction of these enzymes by each of the nitroarenes was significant when compared to control or to their corresponding parent arenes. Among the nitroarenes studied, 1-nitropyrene was the least effective in inducing enzyme activities. The inducibility in both skin and liver by different nitroarenes tested was in the following order: nitrofluoranthenes mixture greater than 3-nitrofluoranthene greater than nitroperylenes mixture greater than nitrobenzo(ghi)perylenes mixture greater than nitropyrenes mixture greater than 1-nitropyrene. The nitrofluoranthenes mixture and the nitroperylenes mixture were almost as effective as 3-methylcholanthrene (3-MC). Parent arenes were either ineffective or significantly less effective than nitrated arenes in inducing hepatic and/or cutaneous monooxygenase activities. Hepatic and/or cutaneous benzphetamine N-demethylase (BPD), NADPH cytochrome c reductase, NADH ferricyanide reductase activities, and the levels of cytochrome P-450 and cytochrome b5, remained unchanged following treatment with either topically applied nitroarenes or arenes. However, a shift of approximately 1 nm to the blue region in the absorption maximum of hepatic cytochrome P-450 was observed in animals treated with nitroarenes. This shift was not evident in the case of 1-nitropyrene. Analysis of benzo(a)pyrene metabolites by high-pressure liquid chromatography revealed a significant enhancement in the production of metabolites by nitroarene-treated rat skin and liver microsomes. Our studies suggest that nitroarenes are inducers of hepatic and cutaneous monooxygenases in neonatal rats after topical administration and that they resemble the 3-MC type of inducers in this regard.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1986

The effect of chronic ethanol consumption on the tumorigenicity of N-nitrosopyrrolidine in male Syrian golden hamsters.

The effect of oral administration of ethanol on the tumorigenicity of N-nitrosopyrrolidine (NPYR) in chow-fed male Syrian golden hamsters has been investigated. Groups of hamsters were given tap water, 7.4% ethanol or 18.5% ethanol-water mixtures 4 weeks prior to and throughout the carcinogen administration period. A total dose of 1 mmol NPYR was administered by intraperitoneal injection to both tap water and ethanol-consuming animals over a 25-week period. Twenty-four hours after the last injection, ethanol-consuming animals were returned to tap water. In control animals treated with NPYR we observed 3/26 animals with tracheal papillomas, and 6/26 animals with hepatic neoplastic nodules. In animals receiving 7.4% ethanol-water mixtures, we observed 6/26 tracheal papillomas, and 17/26 hepatic neoplastic nodules. Similar results were observed in animals receiving 18.5% ethanol. These data indicate that chronic administration of ethanol to chow-fed hamsters increases the incidence of hepatic neoplastic nodules although no differences in the two levels of ethanol were observed.

Alcoholism↗
PubMed1985

Influence of chronic ethanol consumption on hamster liver microsomal O-dealkylase activities and cytochrome b5 content.

The effects of two different methods of administering ethanol to hamsters on liver microsomal cytochrome levels and the activities of ethoxyresorufin O-deethylase and p-nitroanisole O-demethylase have been examined. Administration of ethanol in liquid diets resulted in enhanced levels of cytochrome P-450, NADPH-supported aniline hydroxylase (Form I), and both NADPH- and NADH-supported p-nitroanisole O-demethylase. NADH-ferricyanide reductase was also increased. No change in NADPH-cytochrome c reductase or in the NADPH-supported rate of ethoxyresorufin O-deethylase was observed. In contrast, both NADH-supported ethoxyresorufin O-deethylase and cytochrome b5 levels were decreased. Administration of ethanol in the drinking water to chow-fed animals had no effect on total cytochrome P-450 levels; however, the rates of NADPH-supported aniline hydroxylase (Form I) and p-nitroanisole O-demethylase activity were increased. No changes in NADPH-cytochrome c reductase, NADH-ferricyanide reductase, or NADH-supported p-nitroanisole O-demethylase activity were noted. Cytochrome b5 levels were decreased as were both the NADPH- and NADH-supported rates of ethoxyresorufin O-deethylase. These data suggest that chronic consumption of ethanol by hamsters either in liquid diet form or as ethanol-water solutions to chow-fed animals lowers cytochrome b5 levels. When cytochrome b5 levels are lowered and total chromosome P-450 levels remain unchanged, the NADPH-supported rate of microsomal O-dealkylation of ethoxyresorufin is decreased. These data suggest that cytochrome b5 participates in the NADPH-supported microsomal O-dealkylation of ethoxyresorufin.

Animals↗
PubMed1985

Involvement of cytochrome b5 in the hepatic microsomal metabolism of benzo(a)pyrene.

Ethanol consumption decreased the specific content of microsomal cytochrome b5 in both chow-and liquid diet-fed hamsters while cytochrome P450 levels were unchanged in chow-fed animals and increased in liquid diet-fed animals. Microsomes from animals receiving ethanol in their drinking water exhibited decreased rates of microsomal aryl hydrocarbon hydroxylase activity and postmitochondrial supernatant mediated mutagenicity of benzo(a)pyrene. In contrast, microsomes from hamsters receiving ethanol in liquid diets showed no changes in either of these two activities. When the observed rates of 7,8 and 9,10 diol formation per nmole P450 for chow-fed animals are plotted vs. the b5/P450 ratio a positive correlation was observed suggesting that cytochrome b5 participates directly in the microsomal metabolism of benzo(a)pyrene.

Alcoholism↗
PubMed1984

Non-alcohol dehydrogenase-mediated metabolism of methylazoxymethanol in the deer mouse, Peromyscus maniculatus.

The concept that alcohol dehydrogenase (ADH) is involved in the metabolism of methylazoxymethanol (MAM) was examined in a model consisting of two strains of the deer mouse, Peromyscus maniculatus, one of which has a normal complement of the enzyme [ADH(+)], and the other, which completely lacks it [ADH(-)]. Both the ADH(+) and the ADH(-) strains rapidly metabolized [14C]MAM, administered in the form of the acetic acid ester, [14C] MAMOAc , to 14CO2, and the rates and extents of metabolism were virtually identical. Determination of O6-methylguanine and 7-methylguanine in liver DNA 6 and 24 hr after MAMOAc (25 mg/kg) administration showed that the levels of DNA methylation induced by the carcinogen were not significantly different in the two strains, indicating that both are capable of the metabolic activation of MAM to methylating species. Pyrazole, a potent inhibitor of ADH, inhibited MAM metabolism as well as liver DNA methylation in the ADH(+) strain; however similar inhibition of these processes also occurred in the ADH(-) strain. 3-Methylpyrazole, a weak or noninhibitor of ADH, also decreased the levels of MAM metabolism in both the ADH(+) and the ADH(-) strains. From these results, we conclude that ADH is not obligatory either in the metabolism or in the metabolic activation of MAM. As a possible alternative to ADH, liver microsomes were examined for their ability to metabolize MAM. In the presence of a NADPH-generating system, liver microsomes from both strains converted [14C]MAM to 14CH3OH and 14CH2O , although liver microsomes from the ADH(-) strain were more active in this respect. The microsomal metabolism was sensitive to inhibition by CO as well as to inhibition by pyrazole and 3-methylpyrazole.

Alcohol Dehydrogenase↗
PubMed1982

Comparison of microsomal inducer pretreatment on the in vitro alpha-hydroxylation and mutagenicity of N-Nitrosopyrrolidine in rat and hamster liver.

The effect of modifiers of liver mixed function oxidase activity on the in vitro alpha-hydroxylation and mutagenicity of N-nitrosopyrrolidine (NPYR) has been examined in rats and hamsters. Hamster post-mitochondrial supernatants were able to convert NPYR to a mutagen more efficiently than rat preparations under all conditions studied. Aroclor 1254 pretreatment caused the greatest increase in mutagenic activity in both species while phenobarbital and 3-methylcholanthrene pretreatment gave intermediate values when compared to uninduced preparations. Microsomal alpha-hydroxylation of NPYR was induced by Aroclor 1254 pretreatment in both species. Pretreatment with 3-methylcholanthrene increased alpha-hydroxylation in hamsters but decreased it in rats. Phenobarbital pretreatment only slightly increased microsomal alpha-hydroxylation in either species. When microsomal alpha-hydroxylation rates were expressed per gram wet weight of liver, better agreement between rates of alpha-hydroxylation and mutagenicity in phenobarbital pretreated animals was obtained since inducer associated changes in total microsomal protein content were taken into account. An example of differential induction of an activation pathway (alpha-hydroxylation) and a degradative pathway (aldehyde dehydrogenase) is presented to illustrate a potential source of error in the interpretation of metabolic data obtained from post-microsomal supernatants and whole animal studies.

Animals↗