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

The effect of vitamins A, C and E, butylated hydroxytoluene (BHT) and glutathione (GSH) on gastric carcinogenesis induced by N-methyl-N-nitro-N-nitrosoguanidine (MNNG) was investigated. Male and female BD-VI rats 2-3 months old received a single oral application of MNNG dissolved in corn oil. The male rats were divided into four groups: Group-I: MNNG 250 mg/kg by intubation; Group-II: MNNG + vitamin C daily in the drinking water (400 mg/l); Group-III: MNNG + vitamin C (400 mg/l) + 100 g of milk broth (for each of 10 rats) containing vitamin A (40,000 IU), vitamin E (0.5 g) and BHT (0.1 g) three times a week. The treatment with antioxidants started 7 days before the MNNG administration and continued until the end of experiment. Group-IV rats received MNNG + oxyferriscorbone, i.p. as a single dose of 1.0 mg/kg, daily during the week before and the week after MNNG exposure and than 3 times a week till the end of the experiment. Female rats were divided into two groups: Group-I: MNNG 333 mg/kg by intubation; Group-II: MNNG + GSH orally at a dose of 100 mg/rat 1 h before and 5, 24, 48, and 72 h after MNNG intubation. The incidence of gastric tumors after 15 months of treatment was as follows: male rats, 82.4% in Group-I, 40.0% in Group-II, 40.7% in Group-III, and 50.0% in Group-IV; female rats; 72.7% in Group-I, and 36.0% in Group-II.
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PMID:The effect of antioxidants on MNNG-induced stomach carcinogenesis in rats. 378 64

A large proportion of the metabolites formed from benzo[a]pyrene (BP) in cell cultures from rodents, fish and humans result from conjugation of an oxidized metabolite of BP with sulfate, glucuronic acid or glutathione (GSH). To improve the analysis of these metabolites, a reversed-phase ion-pair h.p.l.c. system using a step gradient of methanol:tetrabutyl-ammonium bromide in ammonium formate buffer has been developed for the separation of these three classes of conjugates. This system separated 3-hydroxy-BP glucuronide and sulfate conjugates and resolved them from GSH conjugates of BP 4,5-oxide, 7,8-oxide and 7,8-diol-9,10-epoxide. Cultures of early passage Syrian hamster, Wistar rat and Sencar mouse embryo cells, a bluegill fry (BF-2) cell line and a human hepatoma cell line (HepG2) were exposed to [3H]BP for 24 h. Medium samples from each were extracted with chloroform: methanol:water, and the water-soluble metabolites were analyzed by ion-pair h.p.l.c. The largest peak of metabolites in the media from cell cultures from rodents and the bluegill fry cell line co-eluted with the glucuronic acid conjugate of 3-hydroxy-BP. These phenol-glucuronides represented 48-62% of the total water-soluble metabolites in the fish and rodent cell cultures. Treatment of this material with beta-glucuronidase released 3-hydroxy-BP and 9-hydroxy-BP in ratios from 3:4 to 13.3:1 in various cultures. Media from the bluegill fry cell line and the mouse embryo cell cultures also contained a peak of BP-diol glucuronides; treatment of these peaks with beta-glucuronidase released mainly BP-7,8-diol. In HepG2 cells, 40% of the water-soluble metabolites were identified as sulfate conjugates of 3-hydroxy-BP and 9-hydroxy-BP. No glucuronic acid conjugates of BP metabolites were detected in HepG2 cells. Only small amounts of the water-soluble metabolites from these cell cultures eluted in the same volumes as the synthetic GSH conjugate of BP-4,5-oxide, BP-7,8-oxide and BP-7,8-diol-9,10-oxide. These studies indicate that conjugation with glucuronic acid represents a major pathway of formation of water-soluble metabolites from BP in cells derived from a number of species and demonstrate the value of this ion-pair h.p.l.c. system for the analysis of conjugates formed from BP.
Carcinogenesis 1987 Jan
PMID:Separation by ion-pair high-performance liquid chromatography of the glucuronide, sulfate and glutathione conjugates formed from benzo[a]pyrene in cell cultures from rodents, fish and humans. 380 96

N-acetylcysteine (NAC) was administered to rats in various combinations with an enzyme inducer (Aroclor 1254) and with depletors of reduced glutathione (GSH), i.e., diethyl maleate (DEM) and buthionine sulfoximine (BSO). NAC increased intracellular glutathione levels in erythrocytes and in liver and lung cells, and replenished its stores following depletion. It did not affect the concentrations nor the spectral properties of cytochromes P-450 in hepatic and pulmonary microsomes, whereas it stimulated, especially in Aroclor-pre-treated animals, cytosolic enzyme activities involved in NADP reduction (glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase), in glutathione reduction (GSSG-reductase) and in the reductive detoxication of xenobiotics by-passing formation of reactive oxygen species (DT-diaphorase). In vivo treatment with the drug enhanced detoxication by liver and lung S-12 fractions of direct-acting mutagens (ICR 191, epichlorohydrin, 4-nitroquinolino-N-oxide and dichromate) and counteracted opposite effects triggered by administration of GSH depletors. The metabolic activation of procarcinogens (aflatoxin B1, 2-aminofluorene, cyclophosphamide, benzo[a]pyrene, a tryptophan pyrolysate product and cigarette smoke condensate) was inhibited by NAC in uninduced rats, while it was further stimulated in Aroclor-pre-treated animals. Additional assays, performed also with other enzyme inducers (phenobarbital and 3-methylcholanthrene) suggested that the effect of NAC on the metabolic activation of procarcinogens depends on the balance between an increased production of mutagenic metabolites (prevailing in induced animals) and their binding by intracellular thiols (prevailing under normal conditions). Thus, due to its dual role as a nucleophile and as a SH donor, NAC appears to exert protective effects by modulating glutathione metabolism and the biotransformation of mutagenic/carcinogenic compounds. This may have clinical relevance, since NAC is administered to individuals, such as cigarette smokers, who are more heavily exposed to GSH depletors and to carcinogenic agents.
Carcinogenesis 1985 Dec
PMID:In vivo effects of N-acetylcysteine on glutathione metabolism and on the biotransformation of carcinogenic and/or mutagenic compounds. 390 42

The kinetics of the enzyme-catalyzed conjugation of (+/-)-7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-oxy-7,8,9,10-tetrahydrobenzo[a]-pyrene [(+/-)-anti-BPDE] with glutathione (GSH) by the following purified soluble rat liver GSH transferases: 1-1, 1-2, 2-2, 3-3, 3-4 and 4-4 have been studied. When BPDE concentration was varied while GSH concentration remained constant (1 mM), linear Lineweaver-Burk plots were obtained: maximum rates of conjugation mediated by GSH transferases 1-1, 1-2, 2-2, 3-3, 3-4 and 4-4 were 105, 72, 83, 35, 179 and 357 nmol/min/mg protein, respectively. When GSH concentration was varied while BPDE concentration remained constant (40 microM), biphasic Lineweaver-Burk plots were obtained in each case with a break point of 0.2 mM GSH below which the affinity of these enzymes for GSH was apparently greater. These results are discussed with respect to the detoxication of benzo[a]pyrene (BP) in vivo.
Carcinogenesis 1985 Jan
PMID:Glutathione conjugation of the carcinogenic and mutagenic electrophile (+/-)-7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-oxy-7,8,9,10-tetra hydrobenzo[a]pyrene catalyzed by purified rat liver glutathione transferases. 391 72

The effect of long-term GSH administration on aflatoxin B1 (AFB1)-induced carcinogenesis in the livers of male Wistar II rats was evaluated. No significant effect of an 11 months period of reduced glutathione (GSH) administration was observed concerning both the survival curve and the incidence of liver tumors. Liver tissues of all animals were bearing tumors or nodular lesions 24 months after AFB1 treatment, regardless of GSH treatment. The capacity of the GSH conjugation system was elevated in the liver tissue of AFB1-treated animals both by an increase of GSH content and an increase of the specific activities of several GSH S-transferase isoenzymes. Likewise the specific activities of GSH related enzymes as GSSG reductase and gamma-glutamyltransferase (gamma-GT) and the activity of the GSH independent detoxication system NAD(P)H:quinone oxidoreductase were increased in the AFB1-treated livers, there was no significant effect of GSH treatment. These results demonstrate that long-term GSH treatment has no effect on the survival of AFB1-pretreated male rats on the incidence of liver tumors and on the activities of drug metabolizing systems. The hepatic detoxication capacity 24 months after AFB1 treatment is elevated.
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PMID:Lack of effect of long-term glutathione administration on aflatoxin B1-induced hepatoma in male rats. 392 36

Aflatoxin B1 (AFB1)-8,9-oxide, the proposed ultimate carcinogen is conjugated enzymically with glutathione (GSH) to give 8-(S-glutathionyl)-9-hydroxy-8,9-dihydro AFB1 (AFB1-SG). The GSH conjugate isolated from rat bile was shown, on the basis of 1H n.m.r. to be identical to AFB1-SG. Of the seven soluble rat liver GSH transferases tested, namely GSH transferases 1-1, 1-2, 2-2, 3-3, 3-4, 4-4 and 5-5 (see reference 1 for the new system of nomenclature), only the first three were active with microsomally generated AFB1-8,9-oxide, their rates of conjugation being 1.1, 0.61 and 0.64 nmol/min/mg enzyme, respectively. AFB1-SG is a thioacetal, but it was not formed from the incubation of the hemiacetal, AFB1-8,9-dihydrodiol, with GSH or GSH plus GSH transferase 1-1 plus 1-2. The covalent binding of in vitro microsomally activated AFB1 to DNA and the formation of AFB1-SG were linearly related to AFB1 concentration in the range of 0.2-2 micrograms/ml. DNA binding was decreased by 38% by the competing formation of AFB1-SG throughout this range of concentrations. These results are in accord with the observation of Scott Appleton et al. (Cancer Res., 42, 3659-3662) that, in the rat in vivo, there is no evident threshold for the binding of AFB1 to DNA. These findings are also consistent with the further observation, reported in this paper that GSH and GSH transferases have no effect on the mutagenicity of microsomally activated AFB1 to Salmonella typhimurium TA 100.
Carcinogenesis 1985 May
PMID:Studies on the detoxication of microsomally-activated aflatoxin B1 by glutathione and glutathione transferases in vitro. 392 29

Cellular pro-oxidant states appear to play role in the promotion phase, presumably because tumor promoter-treated cells overproduce activated forms of oxygen and/or deficient in their ability to destroy them. Since one of the earliest responses to the potent tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA) may be the generation of reactive oxygen species, we have determined the effects of this compound on the natural glutathione-dependent antioxidant protective system of the epidermal cells. Here we report that eight (chemically different) tumor promoters (including the phorbol esters, hydrogen peroxide, benzoyl peroxide, anthralin and mezerein) decreases to various degrees the intracellular ratio of reduced (GSH)/oxidized (GSSG) glutathione in isolated mouse epidermal cells. TPA leads to a rapid, transient increase in GSH peroxidase activity within 20 min, concomitant with a marked decrease in the ratio of GSH/GSSG. Beyond 1 h, while the GSH/GSSG ratio remains low, the GSH peroxidase activity declines below the control level in TPA-treated epidermal cells. This sequence suggests that the GSH-dependent detoxifying system of the cell is initially turned on but then rapidly overwhelmed by the oxidative challenge linked to the tumor-promoting activity of TPA. Since free radical scavengers, GSH level-raising agents and selenium-containing compounds all inhibit the effects of TPA on both GSH metabolism and tumor promotion, it is proposed that the enhancement of the GSH-dependent antioxidant protective system of the epidermal cells during TPA treatment might inhibit skin tumor promotion.
Carcinogenesis 1986 Mar
PMID:Decreased ratio of reduced/oxidized glutathione in mouse epidermal cells treated with tumor promoters. 394 35

Chromatography of benzo[a]pyrene (BaP) sulfate, glucuronide and glutathione (GSH) conjugate standards were examined by h.p.l.c. on a C8 column as modified by various organic acids and solvents. Sulfate and glucuronide standards were positional isomers derived from BaP-1,3,6,7,9 phenols and BaP-GSH conjugates consisted of a racemic mixture of BaP-4,5-GSH. In the absence of acid, BaP conjugates appeared as rapidly eluting, unresolved peaks in aqueous-methanol or acetonitrile gradients or coeluted as broad peaks in a water-propanol gradient, with the exception of BaP-7-OH sulfate which eluted as a distinct symmetrical peak. Addition of acetic or trifluoroacetic (TFA) acids enhanced column retention of BaP conjugates in each solvent system. Upon acidification of mobile phases, BaP-GSH isomers were partially resolved, isomers of BaP sulfates or of BaP glucuronides coeluted, and BaP-7-OH sulfate was resolved from all conjugates. BaP-GSH conjugates were most resolved and preceded elution of other conjugates when TFA was added to mobile phases. BaP sulfates and glucuronides generally coeluted but were partially resolved at 0.1% TFA in a water-methanol gradient. Water-soluble metabolites from cultured hamster embryo fibroblasts (HEF) incubated with [3H]BaP for 24 h were chromatographed by h.p.l.c. in a water-methanol gradient with TFA. BaP glucuronides, consisting of tetraols, triols, quinones, dihydrodiols and phenols eluted as a single peak which could be removed by beta-glucuronidase treatment and organic extraction. BaP sulfates were not detected. The remaining BaP metabolites which were resistant to enzymatic hydrolysis, generally eluted prior to BaP glucuronides suggesting they constitute a family of BaP-GSH derivatives.
Carcinogenesis 1985 Sep
PMID:H.p.l.c. of benzo[a]pyrene glucuronide, sulfate and glutathione conjugates and water-soluble metabolites from hamster embryo fibroblasts. 402 29

The reactive intermediate of aflatoxin B1 (AFB1) forms a glutathione conjugate (AFB1-GSH) and this has been shown to be a substrate for gamma-glutamyl transpeptidase (GGT) in vitro. This study describes the biliary excretion of AFB1-GSH and the product of GGT activity, the cysteinylglycyl conjugate (AFB1-Cys-Gly), following i.v. injection of AFB1 (5 mumol kg-1) in control male rats and in rats that had been maintained on a toxic diet containing 4 p.p.m. AFB1 for 10-12 weeks prior to the experiment. AFB1 metabolites in the bile were analyzed by reverse phase h.p.l.c. and GGT activity in the liver was assessed histochemically and by quantitative fluorimetric assay. In the control male rats (n = 6) AFB1-GSH and AFB1-Cys-Gly together were detected as 4.2 +/- 2.3% of the i.v. dose over the first two hours of bile collection (AFB1-GSH:AFB1-Cys-Gly, 5.5:1). GGT activity (38.2 +/- 7.9 nmol product formed/g liver) was located in the bile duct epithelium. The group maintained on a toxic diet (n = 2) showed higher levels of AFB1-Cys-Gly (AFB1-GSH:AFB1-Cys-Gly, 1:1). GGT activity was elevated (5-10 x control levels) and located in numerous foci throughout the liver. The involvement of GGT in the biliary excretion of AFB1-Cys-Gly was demonstrated by in vivo inhibition of GGT by administering AT125 to a group of animals (n = 3) 15 min prior to the injection of AFB1. Histochemical and quantitative estimation of GGT confirmed total inhibition throughout the liver and conversion of AFB1-GSH to AFB1-Cys-Gly was almost completely blocked. Female Fischer 344 rats (n = 3) showed slightly elevated AFB1-Cys-Gly excretion and higher GGT activity (79.3 +/- 26.3 nmol/min/g liver) compared to control male rats.
Carcinogenesis 1984 Jul
PMID:Effect of manipulation of gamma-glutamyl transpeptidase levels on biliary excretion of aflatoxin B1 conjugates. 614 25

The binding to DNA of reactive metabolites of trans-7,8-dihydro-7,8-dihydroxybenzo[a]pyrene (BP-7,8-diol) was studied following the incubation of tritiated benzo[a]pyrene (BP) and BP-7,8-diol with nuclei from livers of 3-methylcholanthrene-treated rats. Binding was inhibited to a small extent by glutathione (GSH) alone and to a much greater extent by GSH and cytosol or purified GSH-transferases B and E. In this respect GSH-transferases A and C were also active, but less so. Inhibition of binding of BP-7,8-diol metabolites to DNA mediated by GSH-transferases was associated with the formation of GSH conjugates. The extent of inhibition of binding was similar in incubations of nuclei alone, nuclei and rat liver microsomes, and calf thymus DNA and rat liver microsomes. This indicates that reactive metabolites of BP-7,8-diol, formed either by nuclei or microsomes, are readily accessible to soluble GSH-transferases. GSH and cytosol were also active in inhibiting DNA-binding of reactive metabolites from 9-hydroxybenzo[a]pyrene (9-OH-BP). Thus, in the rat hepatocyte GSH and GSH-transferases may be important in protecting DNA from electrophilic attack by reactive BP-7,8-diol and 9-OH-BP species.
Carcinogenesis 1982
PMID:Inactivation of DNA-binding metabolites of benzo[a]pyrene and benzo[a]pyrene-7,8-dihydrodiol by glutathione and glutathione S-transferases. 628 83


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