Liver Microsomal Activation System Research Articles

Effect of Oxymetholone on SCE frequency in human lymphocyte chromosomes in vitro

Genotoxicity evaluation of a commonly used synthetic androgen, Oxymetholone, was carried out in human peripheral blood lymphocytes in vitro. Sister chromatid exchange (SCE) was used as genetic end point. The concentrations of the drug were determined after observing its effects on the mitotic index. A wide range of concentrations, i.e., 25, 50, and 100 micro g/ml of the drug, were used to determine the genotoxic effects in the absence as well as in the presence of rat liver microsomal activation system (S9 mix). The drug did not induce any significant increase in the SCE frequency at any of the concentrations either in the presence or in the absence of S9 mix. The maximum value of SCE was observed in the absence of S9 mix at 100 microg/ml concentration (i.e., 1.38+/-0.080/cell), which was not significant statistically. Moreover, the drug was not effective in increasing the SCE frequency even in the presence of S9 mix. The maximum value of SCE (i.e., 1.78+/-0.103/cell) was observed at 50 microg/ml of concentration in the presence of S9 mix. A dose relationship was also not observed. It was concluded that Oxymetholone does not affect the genetic material in human lymphocytes at a wide range of concentrations in the SCE assay.

Effect of cruciferous vegetable consumption on heterocyclic aromatic amine metabolism in man.

The consumption of cooked meat appears to predispose individuals to colonic cancer and heterocyclic aromatic amines (HA), formed during the cooking of meat, have been suggested as aetiological agents. Consumption of cruciferous vegetables is thought to protect against cancer. To study the effect of cruciferous vegetables on heterocyclic aromatic amine metabolism in man, a three-period, dietary intervention study has been carried out with 20 non-smoking Caucasian male subjects consuming cooked meat meals containing known amounts of these carcinogens. A high cruciferous vegetable diet (250 g each of Brussels sprouts and broccoli per day) was maintained during period 2 but such vegetables were excluded from periods 1 and 3. At the end of each period, subjects consumed a cooked meat meal and urinary excretion of the HA 2-amino-3,8-dimethylimidazo(4,5-f)quinoxaline (MeIQx) and 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP) was measured. Following a 12 day period of cruciferous vegetable consumption (period 2), induction of hepatic CYP1A2 activity was apparent from changes in the kinetics of caffeine metabolism. Excretion of MeIQx and PhIP in urine at the end of this period of the study was reduced by 23 and 21%, respectively, compared with period 1. This reduction in excretion is probably due to an increase in amine metabolism that might be expected given the observed increase in CYP1A2 activity, since this enzyme has been shown to be primarily responsible for the oxidative activation of MeIQx and PhIP in man. In period 2, urinary mutagenicity was increased relative to period 1 by 52 and 64% in the absence and presence, respectively, of a human liver microsomal activation system, yet no evidence was found of PhIP adduction to lymphocyte DNA, a potential biomarker of the activation process. After another 12 days without cruciferous vegetables (period 3 of the study), the kinetics of caffeine metabolism had returned to original values but excretion of MeIQx and PhIP was still reduced by 17 and 30%, respectively, and urinary mutagenicity (with metabolic activation) was still elevated compared with period 1. This prolonged response of amine metabolism to the cruciferous vegetable diet, shown especially with PhIP, suggests that enzyme systems other than CYP1A2 are involved and affected by a cruciferous vegetable diet.

Estimation of selected phenols in drinking water with In situ acetylation and study on the DNA damaging properties of polychlorinated phenols

Gas chromatography/mass spectrometry with selected-ion monitoring (GC/MS-SIM) method were used to analyze 23 selected phenols in natural and drinking waters by an in situ acetylation technique. This method was suitable for determining phenol concentrations at the ng/L level because of less background interference and better recoveries. The application range for all these phenols was from 0.01 or 0.04 to 10 micrograms/L, using a 800 ml water sample. The levels of trace phenols in four Taiwan water treatment plants were in the range of 12-312 ng/L. The polychlorinated phenols, namely 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, and pentachlorophenol, were evaluated for their ability to induce deoxyribonucleic acid (DNA) damage using a DNA precipitation assay employing mouse embryonic fibroblast cells (C3H10T1/2) with or without a liver microsomal activation system. These agents exhibited a weak positive response when microsomal activation enzymes were present in this assay. When the tetrachlorohydroquinone, a toxic metabolite of pentachlorophenol, was measured by the same method without the activation system, a significant and dose-dependent DNA damage was found. This result indicates that in the evaluation of the carcinogenic potential of these agents, their corresponding metabolites should be taken into consideration. DNA strand breakage caused by these active metabolites may play an important role in the tumorigenetic process of polychlorinated phenols.

Mutagenic evaluation of primaquine, pentaquine and pamaquine in the Salmonella/mammalian microsome assay

The 8-aminoquinolines, primaquine, pentaquine and pamaquine, were investigated for mutagenic activity in Salmonella typhimurium strains TA100, TA98, TA97 and TA102 in the rat liver microsomal activation system. Primaquine and pentaquine induced mutations in TA97 in the presence and absence of S9 mix. Pamaquine was mutagenic to TA98 only in the absence of S9 mix.

Antimutagenic Activity of Water Extracts of Black Tea and Oolong Tea

Water extracts of leaves of black tea, oolong tea, and green tea, were examined for antimutagenic activity with Salmonella typhimurium test strains, TA 98 and TA 100. These water extracts significantly decreased the reverse mutation induced by crude dimethyl sulfoxide extracts of grilled beef and, by Trp-P-1, Glu-P-1, and B[a]P in the presence of a rat liver microsomal activation system. They also decreased the mutagenicity of AF-2 and 4-NQO requiring no metabolic activation to cause the mutation. Removal of caffeine from tea extracts did not influence the DEGB-induced mutation, but ethyl acetate extraction abolished the effect.

Modifying role of dietary factors on the mutagenicity of aflatoxin B 1: In vitro effect of trace elements

Using Salmonella typhimurium strains TA100 and TA98 tests have been carried out to detect the inhibitory activity of various trace elements on mutagenesis induced by aflatoxin B 1 (AFB 1) in the presence of a rat liver microsomal activation system. Several trace elements have shown significant modulating activity in both the strains, while a few show inhibition only in a particular strain. Among the most effective elements are copper, manganese, zinc and selenium, all of which exhibit an inhibition pattern which is dose-dependent. Copper, in particular, shows exceptional activity, since the molar excess dose of this element required to inhibit AFB 1 mutagenicity by 50% has been observed to be very low. The action of trace elements is possibly mediated through interaction with microsomal enzymes, thereby modulating the formation of the reactive metabolite before modification of DNA. These results suggest that certain trace elements notably copper may have potential anticarcinogenic activity against AFB 1.

Modifying role of dietary factors on the mutagenicity of aflatoxin B 1: In vitro effect of trace elements

Using Salmonella typhimurium strains TA100 and TA98 tests have been carried out to detect the inhibitory activity of various trace elements on mutagenesis induced by aflatoxin B 1 (AFB 1) in the presence of a rat liver microsomal activation system. Several trace elements have shown significant modulating activity in both the strains, while a few show inhibition only in a particular strain. Among the most effective elements are copper, manganese, zinc and selenium, all of which exhibit an inhibition pattern which is dose-dependent. Copper, in particular, shows exceptional activity, since the molar excess dose of this element required to inhibit AFB 1 mutagenecity by 50% ahs been observed to be very low. The action of trace elements is possibly mediated through interaction with microsomal enzymes, thereby modulating the formation of the reactive metabolite before modification of DNA. These results suggest that certain trace elements notably copper may have potential anticarcinogenic activity against AFB 1.

In vitro DNA-binding of microsomally-activated fluoranthene: evidence that the major product is a fluoranthene N2-deoxyguanosine adduct.

Incubation of 3-[3H]fluoranthene with a rat liver microsomal activation system in the presence of calf thymus DNA resulted in radioactivity bound to the DNA. The fluoranthene-modified DNA was enzymatically digested and a DNA adduct elution profile developed using h.p.l.c. The fraction containing the major fluoranthene--DNA adduct was further purified by h.p.l.c. and separated into two subfractions. Treatment of these with perchloric acid liberated guanine in both cases. Evidence that both were N-2 guanine derivatives was based on the pK values of these adducts determined before and after treatment with nitrous acid. The major adduct (70% of total modified deoxyribonucleosides) was further characterized by high resolution, fast atom bombardment mass spectroscopy which yielded a molecular ion consistent with a fluoranthene triol bound to the N-2 position of deoxyguanosine. Synthetic syn and anti 3-[3H]2,3-dihydroxy-1,10b-epoxy-1,2,3-trihydrofluoranthene were reacted directly with DNA and the 8-[3H]-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrofluoranthene was incubated with DNA and microsomes. The DNA from each of these reactions was enzymatically hydrolyzed and h.p.l.c. adduct profiles were developed. The major adduct formed from reaction of the anti 2,3-dihydroxy-1,10b-epoxy-1,2,3-trihydrofluoranthene with DNA and the major N-2 fluoranthene derived adduct had identical elution times on two different h.p.l.c. systems, similar pK values (before and after nitrous acid treatment) and the same u.v. spectra. In addition, derivatization of both adducts with ethyl methanesulfonate yielded identical products, as determined by h.p.l.c. analysis.

Induction of sister chromatid exchanges by the peroxisome proliferators 2,4-D, MCPA, and clofibrate in vivo and in vitro.

Phenoxy acid herbicides 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-methylphenoxyacetic acid (MCPA) have been found to induce proliferation of peroxisomes in the liver cells of rodents in the same manner as the hypolipidemic drug clofibrate. Both phenoxy acid herbicides and clofibrate (ethyl-alpha-p- chlorophenoxyisobutyrate ) are suspected carcinogens. The present study reports the effect of these agents on the induction of sister chromatid exchange (SCE) in the blood lymphocytes of exposed rats (100 mg/kg with 2,4-D and MCPA, 200 mg/kg with clofibrate for 2 weeks in one intragastric dose/day), in the bone marrow cells of exposed Chinese hamsters (100 mg/kg, treatments as above), and in Chinese hamster ovary (CHO) cells in vitro (10(-5), 10(-4), and 10(-3) M, for 1 h). In the experiments in vitro, the effects of purified 2,4-D and MCPA phenoxy acids were studied, in addition to those of the commercial herbicide formulations and clofibrate. No increase of SCE frequency was observed in the blood lymphocytes of the exposed rats in comparison with the controls. In the bone marrow cells of the exposed Chinese hamsters, a slight increase of SCE was found in the group treated with MCPA but not in the groups treated with 2,4-D or clofibrate. A slight increase in the number of SCEs was characteristic of all the treated CHO cell cultures, both with and without a rat liver microsomal activation system (S9 mix). No clear dose-related effects, however, could be discerned with any of the compounds, and no differences in the SCE induction were observed between the commercial herbicide products and the purified phenoxy acetic acids. The present results support the data which indicate that 2,4-D, MCPA, and clofibrate do not act as direct DNA-damaging agents.

Genotoxicity studies with a blend of zinc dialkyldithiophosphate lubricant additives

The mutagenic activity of a blend of primary zinc dialkyldithiophosphate lubricant additives suspended in process oils and a blend of the process oils alone was investigated in agar layer cultures of Salmonella typhimurium TA1535, TA1537, TA1538, TA98 and TA100, both with and without the incorporation of a rat liver microsomal activation system (S9). Zinc dimethyldithiocarbamate was tested as a structurally-related model bacterial mutagen, and, in additional control experiments, the mutagenic activity of zinc dimethyldithiocarbamate and benzo[ a]pyrene was investigated in combination with the blend of process oils in selected bacterial tester strains. Transformation frequencies of BHK cells were determined by colony growth in soft agar culture following treatment with a blend of the zinc dialkyldithiophosphate lubricant additives suspended in process oils, a blend of the process oils, 7,12-dimethylbenzanthracene, both in the presence and in the absence of a blend of the process oils, or zinc dimethyldithiocarbamate. All experiments incorporated a rat liver microsomal activation system (S9). Application of a blend of the zinc dialkyldithiophosphate additives or a blend of the process oils used in their manufacture did not increase the reverse mutation frequencies of Salmonella typhimurium TA1535, TA1537, TA1538, TA98 or TA100, or significantly increase the transformation frequency of BHK cells under the experimental conditions described. Zinc dimethyldithiocarbamate increased the reverse mutation frequency in some bacterial tester strains, but did not significantly increase the transformation frequency of BHK cells under the described experimental conditions. The addition of the blend of the process oils in combination with the control materials, zinc dimethyldithiocarbamate or benzo[ a]pyrene had an inhibitory effect on the mutagenic activity at high doses of each in the bacterial assays, and in the BHK assay the transforming ability of 7,12-Dimethylbenzanthracene was suppressed in the presence of the blend of the process oils. Thus, the additive materials showed on evidence of genotoxic activity in the bacterial mutation assays, or in the BHK transformation assay under the experimental conditions describe.

Mutagenicity of Extracts of Pickled Vegetables Collected in Linhsien County, a High-Incidence Area for Esophageal Cancer in Northern China<xref ref-type="fn" rid="fn2">2</xref>, <xref ref-type="fn" rid="fn3">3</xref>

Extracts of pickled vegetables commonly consumed in Linhsien County, a high-incidence area for esophageal cancer in Northern China, were studied for mutagenicity. The liquid residue from ethereal extracts produced a dose-dependent increase of mutants in Salmonella typhimurium TA98 and TA100 strains; mutagenicity required the presence of a fortified liver microsomal activation system induced by Aroclor 1254 in adult male BD VI inbred rats. An amount of extract equivalent to 2.8 g fresh pickled vegetables produced sixfold (75 revertants/g) and twofold (45 revertants/g) increases in revertant frequencies in strains TA98 and TA100, respectively. Roussin's red methyl ester, a tetranitroso compound, [(NO)2Fe(CH3S)]2, not previously reported to occur in nature, was isolated and identified from the ethereal extracts. The synthetic compound was mutagenic in strain TA100 in the presence of a liver activation system, producing 25 revertants/mumol. Findings on the presence of mutagenic compounds in pickled vegetables were discussed in relation to their possible etiologic role in cancer of the esophagus in Linhsien County.

Mutagenic evaluation of ronidazole

Ronidazole was evaluated for mutagenic potential using in vitro microbial tests and in vivo studies in mice. The microbial test used the histidine requiring mutants of Salmonella typhimurium with and without a rat liver microsomal activation system (Ames test). The studies in mice included the dominant lethal test, micronucleus test and cytogenetic assays. Ronidazole was given orally in doses of 50, 100 and 200 mg/kg/day in the in vivo studies. In the dominant lethal test, groups of male mice were treated for five consecutive days before being mated with untreated females. In the micronucleus test, the mice were administered the compound for 2 or 5 consecutive days; they were killed 6 h after the last dose and bone marrow was examined for the presence of micronuclei in developing erythrocytes. In the cytogenetic assays, bone marrow cells in metaphase were examined for chromosome aberrations, 6, 24 and 48 h after mice were treated acutely with the test compound. In addition, similar examinations of chromosomes were made on mice given five consecutive dosages of ronidazole and killed 6 h after the last dose. The results of the various in vivo studies did not suggest that ronidazole would be mutagenic for the mammal. Ronidazole at concentrations of 10 and 50 μg/plate was found to increase the number of back mutations of missense mutants in the in vitro bacterial test. This finding confirms the results of Voogd et al. [19]. Incorporation of the microsomal activation system had no effect on the mutagenic capability of the test compound. In conclusion, although ronidazole was shown to be mutagenic in in vitro bacterial systems, the in vivo systems did not suggest that the compound would be mutagenic for the mammal.

In vitro DNA damage/alkaline elution assay for predicting carcinogenic potential

Summary Various noncarcinogens, ultimate, proximate and procarcinogens were evaluated for their ability to induce chromosomal damage using an in vitro /alkaline elution assay employing Chinese hamster V79 cells with or without a liver microsomal activation system. All of the ultimate carcinogens and most of the procarcinogens caused increased elution of DNA. None of the noncarcinogens induced DNA damage. In general, the extent of DNA damage was dose dependent.