ISSN:0192-2521    

DOI:10.1002/em.2860070602

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

年代:1985

数据来源: WILEY

摘要:

AbstractIt has been shown that circulating peripheral blood lymphocytes can be used for the enumeration of 6‐thioguanine‐resistant cells that presumably arise by mutation in vivo. This somatic cell mutation test has been studied in lymphocytes from human populations exposed to known mutagens and/or carcinogens. The sensitivity of the test could be further enhanced by including other gene markers, since there is evidence for locus‐specific differences in response to mutagens. Resistance to diphtheria toxin (Dipr) seemed like a potential marker to incorporate into the test because the mutation acts codominantly, can readily be selected in human diploid fibroblasts and Chinese hamster cells with no evidene for cell density or cross‐feeding effects, and can be assayed for in nondividing cells by measuring protein synthesis inhibition. Blood samples were collected from seven individuals, and fresh, cryopreserved, or Epstein‐Barr virus (EBV)‐transformed lymphocytes were tested for continued DNA synthesis (3H‐thymidine, autoradiography) or protein synthesis (35S‐methionine, scintillation counting). Both fresh and cryopreserved lymphocytes, stimulted to divide with phytohemagglutinin (PHA), continued to synthesize DNA in the presence of high doses of diphtheria toxin (DT). Similarly, both dividing (PHA‐stimulated) and nondividing fresh lymphocytes carried on significant levels of protein synthesis even 68 hr after exposure to 100 flocculating units (LF)/ml DT. The findings were confirmed in cord blood lymphocytes, ruling out the possibility that diphtheria immunization could have led to a selection ofDiprlymphocytes. One lymphoblast line (EBV‐transformed lymphocytes) showed a reduction in protein synthesis to 0.2% of controls only at 192 hr after exposure to 100 LF/ml. The results suggest that human T and B lymphocytes may not be as sensitive to DT protein synthesis inhibition as human fibroblast and Chinese hamster cells. For this reason,Diprmay not be a suitable marker for the somatic

ISSN:0192-2521    

DOI:10.1002/em.2860070603

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

年代:1985

数据来源: WILEY

摘要:

AbstractA standard protocol for a micronucleus assay in root tips ofZea mayswas developed and calibrated using137Cs gamma radiation, ethylmethanesulfonate (EMS), and N‐ethyl‐N‐nitrosourea (ENU). The root tips were sampled 1, 3, and 5 days after the treatment period. Primary root tips (sampled 1 day after treatment) were the most responsive with the highest frequencies of micronuclei. The frequencies then decreased to control values after 3 days. By treating the same kernels for this assay and theyellow‐green‐2(yg2) forward mutation assay, it was possible to analyze and compare the induction kinetics of micronuclei formation in root‐tip cells and forward mutation at the yg2 locus in leaf primordial cells. Forward mutation at theyg2locus by gamma rays, EMS, or ENU exhibited one hit kinetics. The induction of micronuclei demonstrated nonlinear kinetics with a significant increase over controls above 200 rads gamma rays, 10 mM EMS, or 250 μM ENU. ENU induced a higher frequency of micronuclei at all treatment concentrations than did gamma radiation or EMS. The data suggest that a higher relative proportion ofyg2mutant sectors induced by ENU may be due to chromosome aberrations than those induced by gamma radi

ISSN:0192-2521    

DOI:10.1002/em.2860070604

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

年代:1985

数据来源: WILEY

摘要:

AbstractCimetidine is widely prescribed as a palliative or cure for gastric disorders in man. It is known to be noncarcinogenic to rodents and has been shown to be inactive in a wide range of in vitro and in vivo genotoxicity assays. It was therefore of concern when an injectable formulation of this drug (Cimetex) was reported to initiate UDS in cultured primary rat hepatocytes [Martelli et al, 1983]. We have confirmed the ability of Cimetex to elicit UDS in primary hepatocytes and established that cimetidine itself is inactive. These data indicate that it is not cimetidineper se, but rather its protonated formulation which is responsible for the activity. These observations pose fundamental questions regarding the validity of the UDS end‐point when testing salts in vitro, rather than presenting a challenge to the nongenotoxic status of cimetidin

ISSN:0192-2521    

DOI:10.1002/em.2860070605

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe metabolism and growth effects of benzo(a)pyrene (BaP) were studied using a freshwater green alga,Selenastrum capricomutum. Algal cultures were incubated under gold light with BaP added at concentrations of 40, 160, 400, and 1,200 μ liter for the periods of 1–4 days. The metabolites and BaP were identified and quantified from ethyl acetate extracts of both algal cells and incubation medium. The ethyl acetate extracts were evaluated for genotoxicity using a micro‐volumeSalmonella typhimuriumforward mutation assay with resistance to 8‐azaguanine for selection. This assay detected the presence of small quantities of BaP and was particularly sensitive to the mutagenicity of BaP diols. Of those extracts prepared from algae and medium from cultures exposed to 400 μ BaP/liter (10 μ/25 ml culture), only algal cell extracts from one day's growth were mutagenic. In cultures exposed to 1,200 μ BaP/liter (30 μ /25 ml culture), mutagenic materials were produced or persisted in both algae and media throughout the 4‐day incubation. The observed mutagenic response can be attributed in part to the presence of unmetabolized BaP or

ISSN:0192-2521    

DOI:10.1002/em.2860070606

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

年代:1985

数据来源: WILEY

摘要:

AbstractInducers of liver mixed function oxidase (MFO) activities have profound effects on the genotoxicity of substances that undergo metabolic activation by the MFO system. The polychlorinated biphenyl mixture Aroclor 1254 is a broad‐spectrum inducer of liver MFO activities that has been employed as a pretreatment to augment the metabolic activation capabilities of rat liver fractions used in a number of short‐term tests for genotoxicity, including the AmesSalmonella/bacterial mutagenicity assay. The present study was designed to characterize the effects of Aroclor pretreatment of rats on the DNA repair responses elicited by various chemicals in the in vitro hepatocyte primary culture/DNA repair (HPC/DR) assay as well as the in vivo/in vitro HPC/DR assay. The amount of DNA repair produced in vitro by diethylnitrosamine (DEN), benzo(a)pyrene (B(a)P), 3‐meth‐ylcholanthrene (3‐MC), 2‐acetylaminofluorene (2‐AAF), o‐aminoazotoluene (o‐AT), and aflatoxin B1(AFB1) was significantly greater in hepatocytes derived from Aroclor‐pretreated rats than in control rat hepatocytes; in vitro responses to dimethylnitrosamine (DMN), 7,12‐dimethylbenzanthracene (DMBA), benzidine (BZ), and 2‐naphthylamine (2‐NA) were not significantly affected by Aroclor pretreatment. DNA repair elicited by the direct‐acting alkylating agents methyl methanesulfonate and N‐methyl‐N′‐nitro‐N‐nitrosoguanidine was also not increased by Aroclor pretreatment, which indicated that Aroclor does not exert a general stimulatory effect on the hepatocellular DNA repair capacity. Therefore, the pretreatment‐related potentiation of DNA repair observed for 6 out of 12 compounds tested in vitro was considered to be due to enhanced metabolic activation. These results suggested that pretreatment with Aroclor may increase the sensitivity of the in vitro HPC/DR assay to certain compounds. In contrast, Aroclor pretreatment had little effect on the amount of hepatocellular DNA repair elicited by in vivo administration of DMN, DEN, o‐AT, 2‐AAF, 3‐MC, or AFB1, which indicated that this pretreatment regimen may have little utility for improving the s

ISSN:0192-2521    

DOI:10.1002/em.2860070607

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

年代:1985

数据来源: WILEY

摘要:

AbstractA technique was developed to measure rapidly DNA strand breaks in soft tissues. This method measured the rate of alkaline unwinding of DNA, which was proportional to strand breakage. Alkaline unwinding of DNA was done by treating tissue homogenates with NaOH. Single‐stranded DNA was removed by extraction with aqueous phenol. DNA unwinding was quantitated by measuring the remaining double‐stranded DNA. Using the described technique, a dose‐effect relationship was observed between N‐nitrosodimethylamine (NDMA) and alkaline unwinding of mouse li

ISSN:0192-2521    

DOI:10.1002/em.2860070608

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

年代:1985

数据来源: WILEY

摘要:

AbstractVanillin, capsaicin and chili extracts were tested for mutagenicity in Salmonella typhimurium histidine‐deficient tester strains TA 98, TA 100, TA 1535. TA 1537, and TA 1538. Vanillin was nonmutagenic, whereas chili extract and capsaicin were mutagenic with metabolic activation. Capsaicin, an active component of chili extract, was the more potent mutagen. The positive samples were also tested in two mammalian test systems: the micronucleus test and the 8‐azaguanine‐resistant mutagenesis assay that used V79 Chinese hamster cells. It was observed that both were negative for the latter test at the dose level tested, whereas in the micronucleus test, only capsaicin was positive near the LD50dose. Capsaicin also inhibited DNA synthesis in the testes of Swiss mice injected at two dose l

ISSN:0192-2521    

DOI:10.1002/em.2860070609

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe kidney is a key target tissue in animal and human carcinogenesis, yet there are no established short‐term tests for studying the genotoxicity of chemicals in the kidney. We have developed an assay for the measurement of chemically induced DNA repair as unscheduled DNA synthesis (UDS) in isolated rat kidney cells following in vivo treatment. Male Fischer‐344 rats were injected intraperitoneally with chemicals dissolved in saline or corn oil. After various treatment times, the kidneys were perfused with a collagenase/trypsin solution (CTS), minced into small pieces, and stirred in CTS at 37°C for 1 hr to dissociate cells. Cultures contain a high proportion of epithelial cells from the proximal and distal tubules. Cultures were incubated for 16–18 hr with 3H‐thymidine in Williams' Medium E supplemented with 20% fetal bovine serum. UDS was measured by quantitative autoradiography as net grains/nucleus (NG). The percentage of cells in repair (% IR) was defined as the percentage of cells with ⩾ 3 NG. Saline‐ or corn oil‐injected controls consistently produced −3 to −5 NG with<1 % IR. The time course of DNA repair following treatment with the direct‐acting mutagen methylmethane sulfonate (MMS) or the renal carcinogen azaserine showed a peak response at 2 hr after treatment. Azaserine showed a rapid decline in UDS at 12 and 24 hr, whereas MMS exhibited a relatively high UDS level at 24 hr. The renal carcinogens methylazoxymethanol acetate, N‐methyl‐N‐nitrosourea, and streptozotocin all yielded strong positive UDS responses. The liver and intestinal carcinogen 1, 1‐dimethylhydrazine at doses up to 50 mg/kg was cytotoxic to kidney cells, but induced<0 NG. Treatment with 1,2‐dimethylhydrazine, which induces kidney tumors in mice but not rats, also induced<0 NG. Treatment with o‐anisidine, a weak renal carcinogen, did not induce UDS in the kidney, suggesting that it may be acting as a tumor promotor. These results demonstrate the usefulness of this assay for the detection and study of a variety

ISSN:0192-2521    

DOI:10.1002/em.2860070610

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

年代:1985

数据来源: WILEY

摘要:

AbstractAn extensive Salmonella assay database was analyzed in order to develop strategies to reduce costs of screening chemicals for mutagenicity. This database was obtained from testing 941 samples (representing 799 chemicals), 36% of which were judged mutagenic. Strains TA98, TA100, TA1535, and TA1537 without activation, with rat liver S‐9, and with hamster liver S‐9, make up the 12 strain/ activation combinations considered here. The testing strategies examined consist of two or three stages; a positive result at any stage is regarded as definitive and stops the testing. Sequential testing improves efficiency by eliminating the need for further experimentation once a chemical has been found to be mutagenic. Consequently, costs and effort are reduced. For screening chemicals in the Salmonella assay, it is our recommendation that a sequential testing scheme be adopted whose initial stage consists of TA

ISSN:0192-2521    

DOI:10.1002/em.2860070611

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

年代:1985

数据来源: WILEY