摘要:

AbstractFETAX (frog embryo teratogenesis assay:Xenopus) is a 96‐hr teratogenesis screening assay using embryos of the South African clawed frog,Xenopus laevis.SinceXenopusembryos have limited xenobiotic metabolism through 96 hr of development, we have developed an in vitro metabolic activation system employing Aroclor 1254‐induced rat liver microsomes. By adding an exogenous source of mixed functional oxidase (MFO) activity, we may more accurately assess the teratogenic risk of proteratogenic compounds.Xenopusembryos were cocultured with varying concentrations of cyclophosphamide (CP), Aroclor 1254‐induced microsomal protein, an NADPH‐generating system, and antibiotics in a static renewal fashion for 96 hr. Residual Aroclor 1254 remaining in the microsomes was successfully reduced during purification to levels that had no significant effect on embryo survival and development. The results of three definitive dose‐response tests performed with CP revealed that activation reduced the 96 hr LC50from 8.0 to 1.4 mg/ml (5.7‐fold). The 96‐hr EC50(malformation) was reduced from 6.2 to 0.4 mg/ml (15.5‐fold). Activation also increased the types and severity of malformation and reduced embryonic growth. Aroclor 1254‐induced rat liver microsomes may be used as an acceptable in vitro metabolic activation

ISSN:0270-3211    

DOI:10.1002/tcm.1770080502

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractIn vitro microassay for the screening of teratogens was investigated on cancer chemotherapeutic agents sterigmatocystins and benzimidazoles using human embryonic palatal mesenchymal (HEPM) cells. Five thousand cells were inoculated into each well of 96‐well microtiter plates, and cultivated for 24 hr, after which the media were changed with new ones that contained various amounts of chemicals; after cultivation for an additional 72 hr, the media were discarded, and cells attached to the tissue plate were fixed and stained with Giemsa's solution; the cell number then was counted by colony counter with three readings for each well. For the metabolic activation, the liver S9 obtained from rats pretreated with phenobarbital and 5,6‐benzoflavone and cofactors (S9 mix) were added directly to the HEPM cell cultures along with chemicals. After 6 hr, the cultures were exchanged with a fresh medium and incubated for a further 72 hr. The final IC50(the concentration that inhibits growth 50%) concentration‐finding run had 7 to 11 concentration points (mean, three to four wells).Concentrations of the cancer chemotherapeutic agents that inhibited growth by 50% ranged from 0.001 to 10 μg/ml. Sterigmatocystins indicated strong inhibition; among three derivatives, O‐acetyl sterigmatocystin was the most potent inhibitor. Benzimidazoles also exhibited an inhibitoy action on HEPM cell growth; nitro and chloro groups at the 5 position in 2‐(2‐pyridyl)benzimidazole were found to be potent substituents. As for the activation of cyclophosphamide in the HEPM cell culture, IC50was decreased to 1.0 ug/ml by the incubation with S9 mix for 6 hr under our experimental conditions, and sterigmatocystin was found to be activated by S9 mix. This system was simple and useful for the detection of teratogens that inhibit HEPM cell growth with or without metabolic activ

ISSN:0270-3211    

DOI:10.1002/tcm.1770080503

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractSister chromatid exchange (SCE) frequencies in peripheral lymphocytes are a frequently used endpoint to indicate exposures to genotoxins in groups of humans. The aim of this study was to ascertain, in an experimental design, whether or not SCE rates have any association with the risk of cancer at the individual level in rats exposed to a known carcinogen. Individual SCE rates were determined in three consecutive analyses in cultured blood lymphocytes of 50 adult male Wistar rats. Analyses were done before as well as 24 hr and 7 days after a single intraperitoneal administration of 0, 25, 50, or 75 mg/kg ofN‐ethyl‐N‐nitrosourea (ENU). The animals were followed until death; also, the relationship between SCEs and carcinogenic outcome, i.e., the presence or absence of tumors, and their latency period were examined. ENU significantly decreased the life expectancy of the rats. The tumor types most clearly associated with ENU treatment were various gliomas and thyroid‐gland and testicular tumors. ENU induced a moderate (maximally 1.6‐fold) increase in the mean frequency of SCEs/cell at both sampling times after treatment. The effect was somewhat more pronounced 1 day rather than 1 week after treatment. The mean SCE rates in rats with ENU‐specific cancers or in animals with early or multiple tumors did not differ from those in animals that survived no less than 65 weeks or longer without developing tumors. In ENU‐treated animals with tumors, no relationship was found between the mean SCE rate and survival time. It is concluded that in outbred Wistar rats the SCE response in cultured lymphocytes does not indicate individual susceptibility to the carcinogenic action of ENU. On a group basis, however, animals with high SCE rates were shown to have increased r

ISSN:0270-3211    

DOI:10.1002/tcm.1770080504

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractWe examined the influence of nontoxic concentrations of each of two essential (Zn++and Mn++) and one nonessential (Ni++) bivalent metal ions on spontaneous and radiation‐induced neoplastic transformation and specific gene mutations in mammalian cells. All three metals induced low levels of transformation in mouse BALB/3T3 cells but exerted no mutagenic effect in CHO cells (hprt locus) over a broad range of concentrations. Continuous incubation for 8 or 15 days with each of the metal ions did not enhance the frequency of cell killing, transformation, or mutations induced by acute exposure to x‐rays. Zn++, however, had a small but consistent protective effect on the induction of all three endpoints by xirradiat

ISSN:0270-3211    

DOI:10.1002/tcm.1770080505

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractRecently, the antitumor agent 4′‐(9‐acridinylamino)‐methanesulfon‐m‐anisidide (m‐AMSA) was shown to revert a frameshift mutant of T4 (rFCll), and its mutagenicity was shown to be mediated by T4 DNA topoisomerase II [Ripley et al.: J Mol Biol 200: 665–680, 1988]. Here we report dose‐response data on the mutagenicity and toxicity ofm‐AMSA in T4rFCll. We find thatm‐AMSA is among the most potent frameshift mutagens observed in T4, inducing a 10‐fold increase in mutant frequency in the absence of toxicity and a 500‐fold increase in mutant frequency at 31% survival. In addition tom‐AMSA, the topoisomeraseactive agents ellipticine, oxolinic acid, and nalidixic acid also revertedrFCll; however, they required concentrations 10–100 times greater than those required bym‐AMSA in order to be mutagenic, and they did not produce mutant frequencies as high as those produced bym‐AMSA. Unlikem‐AMSA, all three agents were mutagenic only at toxic doses. The other agents evaluated—actinomycin D, adriamycin, 9‐aminoellipticine, 9‐methoxyellipticine, teniposide (VM‐26), and novobiocin—were toxic but not mutagenic to T4rFCll. Thus,m‐AMSA appears to be distinctly different from the other topoisomerase‐active agents in exhibiting such potent mutagenic activity in T4rFCll.BecauseE. coliDNA gyrase may substitute for T4 topoisomerase II, we examined the ability of two inhibitors ofE. coliDNA gyrase, novobiocin and nalidixic acid, to inhihitm‐AMSA's mutagenicity. Both agents substantially reduced the mutagenicity ofm‐AMSA in T4rFCll, further suggesting

ISSN:0270-3211    

DOI:10.1002/tcm.1770080506

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractDuring histogenesis, mouse and rat fetuses were treated transplacentally with mitomycin C (MMC) and 7,12‐dimethylbenz(a)anthracene (DMBA). The micronucleus (MN)‐inducing effects of MMC were analysed in mouse fetal blood and liver; the effects of DMBA were analysed in mouse fetal and rat fetal blood and in maternal bone marrow of both species. Both test substances were clearly clastogenic during the period of development in which the embryos were analysed—i.e., MMC from gestational day 14 until day 18 in mice and DMBA on days 14 and 17 in mice and days 16 and 19 in rats. In mouse fetal liver and blood the MMC‐induced MN frequencies did not vary significantly during the whole period. MMC was more effective in fetal blood than in fetal liver. DMBA‐induced MN frequencies in maternal bone marrow were slightly higher in rats than in mice. Compared to maternal bone marrow, fetal MN frequencies were about four to five time higher in rats but less than two times higher in mice. Thus, rat fetuses were far more susceptible to the clastogenic action of DMBA than mouse fetuses. These results are discussed with respect to fetal development and maternal/fetal m

ISSN:0270-3211    

DOI:10.1002/tcm.1770080507

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

ISSN:0270-3211    

DOI:10.1002/tcm.1770080501

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY