bluuebunny/crossref_metadata_2025_split huggingface dataset:
Caffeine toxicity is inversely related to DNA repair in simian virus 40‐transformed xeroderma pigmentosum cells irradiated with ultraviolet light
Authors: Cleaver J. E. 
Published: February 2006

AbstractHuman cells transformed by simian virus 40 (SV40) are more sensitive to killing by ultraviolet light when grown in caffeine after irradiation. The degree of sensitization at 2 mM caffeine (expressed as the ratio of the 37% survival dose for control cells divided by the 37% survival dose for cells grown in caffeine, i.e., the dose modification factor) was approximately 1.9 in transformed normal cells and 3.8–5.8 in excision‐defective xeroderma pigmentosum (XP) groups A, C, and D cells. A large dose modification factor of 12 was observed in a transformed XP variant cell line. Chinese hamster ovary cells were not significantly different from transformed normal human cells, with a maximum dose modification factor of 1.5. Two radioresistant XP revertants that do not excise cyclobutane dimers gave different responses; one resembled its group A parent in being sensitized by caffeine, and one did not. These results can be interpreted on the basis of a single hypothesis that cells are killed as a result of attempts to replicate damaged DNA. Increased replication rates caused by transformation, increased numbers of replication forks in DNA caused by caffeine, and increased numbers of damaged sites ahead of replication forks in excision‐defective cells are all processes that will consequently increase killing according to this hypothesis. A corollary is that the XP variant may be highly sensitized to caffeine because of excision defects at the DNA replication forks, an idea that may be important in designing cloning strategies for the XP variant gene.
Benzamide prevention of ultraviolet radiation‐induced transformation as measured by anchorage‐independent growth and the absence of correlation with thymidine dimer formation and DNA repair
Authors: Milo George E. , D'Ambrosio Steven , Kun Ernest 
Published: February 2006

AbstractSynchronized human fibroblasts were exposed in early S phase to increasing doses of ultraviolet (UV) irradiation in the presence and absence of an antitrans‐forming drug, benzamide. Cellular survival, initial thymidine dimer formation and its repair, and cellular phenotypic transformation were simultaneously monitored in the presence and absence of 1 mM externally added benzamide that reaches 8 to 15 μM intracellular levels. Cellular transformation as measured by an expression of anchorage‐independent growth was inhibited by nontoxic doses of benzamide. Antitransforming action of benzamide is confined to low intracellular drug concentrations, which in the case of benzamide is in the 4–9 μM range. Because of the lack of effect of benzamide on the formation of UV‐induced thymidine dimers and the specific repair of these dimers, these results suggest that the processes of thymidine dimer formation and its repair are not involved in the mode of action of benzamide that influences the expression of a transformed phenotype with low malignant vigor.
Deletion screening at the hypoxanthine‐guanine phosphoribosyltransferase locus in chinese hamster cells using the polymerase chain reaction
Authors: Xu Zhidong , Yu Yongjia , Hsie Abraham W. , Thomas Caskey C. , Rossiter Belinda , Gibbs Richard A. 
Published: February 2006

AbstractWe have developed a rapid screening method using the polymerase chain reaction (PCR) for detecting deletion mutations at the hypoxanthine‐guanine phosphoribosyltransferase (hprt) locus in Chinese hamster cells. DNA was extracted from spontaneous and ultraviolet (UV) light‐ and X‐ray‐induced hprt‐deficient mutants. Two primer sets were used to amplify 276 bp and 344 bp fragments containing the entire exon 3 and exon 9 coding sequence, respectively. The PCR was performed using Taq DNA polymerase for 40 cycles, and the PCR product was directly analyzed for the presence of the respective amplified DNA using electrophoresis on agarose gels stained with ethidium bromide. With this assay, we have analyzed 39 independently derived hprt‐deficient mutants. Four of ten spontaneous mutants were found to have deletions in exon 9. UV light produced mutants with predominantly wild‐type amplification patterns (10/14). X‐ray induced mostly deletion patterns (11/15); six of these occurred only in exon 9, and five occurred in both exons 3 and 9. These observations are consistent with the classical notion that UV light induces predominantly missense mutations and X‐ray produces a high proportion of deletion mutations. Deletion mutations occurred most frequently at the 3° end of the hprt gene, suggesting the possible existence of hot spots for deletions in this region. The PCR assay for deletion detection has the advantage that it can be completed in less than 4 hr without using radioisotopes. This assay should be useful for routine deletion screening.
Induction of sister chromatid exchange in multiple murine tissues in vivo by various methylating agents
Authors: Neft Robin E. , Conner Mary K. 
Published: February 2006

AbstractIn order to study the reliability of in vivo sister chromatid exchange (SCE) assays for predicting carcinogenicity, several known animal carcinogens were tested in a multicellular in vivo SCE assay and an in vivo/in vitro murine lymphocyte assay. The methylating agents 1,2‐dimethylhydrazine · 2 HCl (DMH), dimethylnitrosamine (DMN), methylnitrosourea (MNU), methyl methane‐sulphonate (MMS), and methylazoxymethanol acetate (MAM) were tested for SCE induction in several murine tissues in vivo, including bone marrow, alveolar macrophages, regenerating and intact liver, and kidney from B6D2F1 mice. In all cell types, clear dose‐responses were observed following exposure of mice to subcytotoxic fractions of the LD50 dose of DMH, MNU, or MMS. DMN (0.03–0.27 mmol/kg) produced small, although not dose‐related, increases in SCE in all cell types. At the doses tested (0.06 and 0.08 mmol/kg), MAM did not induce elevated SCE in the various cell types.Following a series of multiple i.p. injections of low, non‐toxic doses of DMH (0.15 mmol/kg, once a week, for 10 weeks), significant differences were observed in intact vs. regenerating liver and in single vs. multiple injections in regenerating liver.Following exposure of B6D2F1 mice to a single i.p. injection of 0.25 mmol/kg DMN, DMH, or MMS or 0.19 mmol/kg MNU, SCE responses were evaluated in Concanavalin A (Con A)‐ and LPS‐stimulated blood and spleen lymphocytes. Considerable cytotoxicity was observed in blood lymphocytes. In Con A‐ and LPS‐stimulated spleen lymphocytes, DMH‐, and DMN‐ and MMS‐induced SCE frequencies were approximately 1.5–2 × baseline levels and MNU‐induced SCE were approximately three‐ to fourfold higher than baseline values in cultures initiated at 1 and 24 h postexposure.At 48 and 72 h after an i.p. injection of 0.131 mmol/kg MNU, SCE responses in lymphocytes were approximately 2 × baseline levels. At 24 h following one, two, or four injections (one/week) of 0.075 mmol/kg MNU dose‐related increases in SCE were observed in spleen lymphocytes. These studies illustrate that carefully designed in vivo SCE assays may have the capacity to predict the tumorigenic potential of chemical agents.
Embryotoxic and teratogenic studies of phosphamidon in Swiss albino mice
Authors: Soni I. , Bhatnagar P. 
Published: February 2006

AbstractPhosphamidon, an organophosphate pesticide, is little known for its possible effects on mammalian conceptus. The present investigation was carried out to evaluate its embryotoxic and teratogenic effects on Swiss albino mice. Female mice of similar age and weight were divided into four experimental groups. The animals of groups I and II received 15 and 35 ppm phosphamidon ad libitum, respectively, during the entire gestational period, that is, from days 1 to 18. Groups III and IV were treated before mating with 35 ppm phosphamidon for 30 and 60 days, respectively, and the treatment was continued during pregnancy up to the 18th day. The autopsies were performed on the 18th day of gestation, and routine teratological observations were made. The lower dose did not produce significant effects. The higher dose reduced the number of implants, litter size, and foetal weight and increased the resorption of embryos when administered for 30 days prior to mating. Exposure to the pesticide for 60 days prior to mating and during gestation, however, did not produce significant effects. It appears that the mice probably developed some resistance to the pesticide, when exposed for such a long duration.
Absence of DNA damage‐mediated induction of human methyltransferase specific for precarcinogenic O6‐methylguanine
Authors: Wani Gulzar , Wani Altaf A. , Gibson‐D'Ambrosio Ruth , Samuel Mervyn , Lowder Elizabeth , D'Ambrosio Steven M. 
Published: February 2006

AbstractThe ability of cultured normal human fetal liver and kidney epithelial cells to repair the premutagenic and precarcinogenic O6‐methylguanine (O6‐MeGua) DNA adduct was determined by directly monitoring its loss in cellular DNA and quantitating the number of O6‐MeGua‐DNA‐methyltransferase (O6‐MT) molecules per cell. Following treatment of the epithelial cells with the direct acting carcinogen N‐methyl‐N‐nitrosourea (MNU), the loss of the O6‐MeGua adduct was biphasic, exhibiting a half‐life of 2.0 and 1.5 h in the liver and kidney cells, respectively. The activity of O6‐MT in the liver and kidney epithelial cells in culture was 0.19 pmol/mg protein or 18,500 molecules/cell. The activity of O6‐MT was maintained throughout the life of the cultures, i.e., 20 subpassages or 50 cumulative population doublings for the liver and kidney. In order to ascertain whether human fetal epithelial cells exhibit an induction of O6‐MT, the cell cultures were treated with single and multiple conditioning doses of N‐methyl‐N‐nitro‐N‐nitroso‐guanidine (MNNG) or γ‐irradiated and assayed for the amount of O6‐MT. A 1 h exposure of cells to 2, 4, and 8 μM MNNG resulted in an 80–100% decrease of the initial O6‐MT activity which was restored to the constitutive levels within 48 and 72 h post‐treatment. Rat hepatoma cells, used as a positive control, increased their levels of O6‐MT to 2.8‐fold the constitutive levels following treatment with MNNG. Treatment of the human liver and kidney epithelial cells with chronic low doses of MNNG exhibited O6‐MT levels identical to untreated cells. The O6‐MT activity in epithelial cells remained unaffected upon pre‐irradiation with 1.2 or 2.5 Gy of γ‐irradiation. These result indicate that (i) the normal human fetal liver and kideny epithelial cells in culture actively repair O6 MeGua; (ii) resynthesis of O6 ‐MT in cultured cell and recovery to the basal constitutive levels occurs followinggonotoxin exposure; and (iii) O6‐MT is not induced following the chllenge does of physical and chemical agents.
Cytotoxicity and effect on mutagenicity of buffers in a microsuspension assay
Authors: Demarini David M. , Dallas Mary M. , Lewtas Joellen 
Published: February 2006

AbstractWe have examined the effects of three buffers–‐Vogel‐Bonner minimal E (VBM) and 0.15 and 0.015 M sodium phosphate, pH 7.4–‐and two concentrations of overnight cells (5× and 10×) on the mutagenicity of two pure compounds and two complex mixtures in strain TA98 using a modification of a microsuspension assay developed by Kado et al. (Mutation Research 121:25–32, 1983). The assay was performed by adding 50 μ1 of cell concentrate of an overnight culture of TA98 resuspended in the appropriate buffer; 50 μ1 of the same buffer or S9 mix; and 2 μ1 of mutagen or dimethyl sulfoxide to a 1‐dram vial or 13 × 150‐mm test tube. The suspension was incubated for 90 min at 37°C, top agar was added, and the contents poured onto a bottom agar of minimal medium. Cell concentration (5× vs. 10×) had little effect on the mutagenic potencies of the agents tested. The mutagenic potencies of the direct‐acting agents (1‐nitropyrene and diesel exhaust) were consistently lower with 0.15 M buffer compared to the mutagenic potencies of these agents with the other two buffers. The three buffers gave similar results for the indirect‐acting agents (2‐aminoanthracene and environmental tobacco smoke). The 0.15 M buffer was considerably cytotoxic in the absence of S9, which may explain why the direct‐acting agents were less potent with this buffer compared to the other buffers. VBM was also somewhat cytotoxic, but this did not appear to affect the mutagenic potencies of the agents studied. Thus, other factors in addition to cytotoxicity may account for the effects of the different buffers on the mutagenic potencies of the direct‐acting mutagens. Based on these results, we recommend the use of 0.015 M sodium phosphate buffer or VBM and either 5× or 10× cells for use with the microsuspension assay described here.
Thioethers, mutagens, and D‐glucaric acid in urine of operating room personnel exposed to anesthetics
Authors: Pasquini R. , Monarca S. , Sforzolini G. Scassellati , Bauleo F. A. , Angeli G. , Cerami F. 
Published: February 2006

AbstractMutagenic hazards related to occupational exposure to nitrous oxide and enflurane was studied in the personnel of five operating rooms using a coupled environmental and biological monitoring approach. The environmental monitoring revealed air concentrations of the two anesthetics exceedings the TLVs by 10–15‐fold. These values were correlated individually with the concentrations of the two anesthetics in the expired air of the exposed subjects. The biological monitoring was carried out by determining two parameters associated with mutagen exposure (urinary mutagenicity and thioethers) and a parameter associated with the enzymatic induction (D‐glucaric acid) in the urine of exposed and unexposed subjects (N = 64 and N = 37, respectively). The results showed no difference in the two groups for urine mutagenicity and D‐glucaric acid, but urine thioethers were significantly increased among highly exposed subjects.
Methotrexate resistance in NIH3T3 cells expressing polyoma virus oncogenes
Authors: Wani Maqsood , Snapka Robert M. 
Published: February 2006

AbstractNIH3T3 cell lines expressing different polyoma virus oncogenes were found to differ by almost three orders of magnitude in frequencies of methotrexate‐resistant (MTXr) cells in single‐step selections. Cells expressing the polyoma small T antigen showed the highest frequencies of MTX resistance, whereas cells expressing the polyoma middle T antigen showed the lowest frequencies of MTX resistance. Amplification of the dihydrofolate reductase (dhfr) gene was not a mechanism of MTX resistance in these cell lines. Cells expressing large T antigen also showed a high frequency of MTXr colonies with only two of 20 such colonies showing evidence of marginal (less than threefold) dhfr gene amplification. Cells carrying the cloning vector without an oncogene showed intermediate frequencies of MTX resistance, and in contrast to the oncogene expressing lines, two‐thirds of these MTXr colonies showed marked dhfr gene amplification. The results suggest that the plasticity of the genome as measured by frequency or extent of dhfr gene amplification is not increased by expression of either immortalizing or transforming polyoma oncogenes. These oncogenes may, however, influence MTX resistance through epigenetic mechanisms. In addition, there appears to be no relationship between frequency of methotrexate resistance and frequency of dhfr gene amplification. It is clear that mechanisms of resistance other than dhfr gene amplification can be exclusively associated with either very high or very low frequencies of resistance.
Clastogenic effects of benzo[a]pyrene in postimplantation embryos with different genetic background
Authors: Adler I.‐D. , Kliesch U. , Kiefer F. 
Published: February 2006

AbstractCertain strains of mice vary in their enzyme inducibility by polycyclic hydrocarbons, i.e., the strain C57 shows high and the strain DBA shows low inducibility of aryl hydrocarbon hydroxylase (AHH) by benzo[a]pyrene (BaP). The effect of this genetically determined difference on the clastogenic response to BaP was studied in 11 day old embryos after transplacental treatment. The four possible crosses, C57 and DBA inter se, C57 × DBA and DBA × C57, were used to determine the influence of the genetic background on the aberration yields in the embryos. Constitutive and induced AHH levels were measured in liver, bone marrow, and placenta of the pregnant females and in their embryos.Enzyme inducibility was high in tissues of C57 dams and in their homozygous or heterozygous embryos. In contrast, induction of AHH activity was low in tissues of DBA females and their homozygous embryos. The high BaP‐induced AHH activity found in heterozygous embryos of DBA dams is in agreement with the dominant mode of inheritance for high AHH inducibility. The cytogenetic results showed that the clastogenic response was lowest in homozygous C57 embryos and highest in hybrid embryos independent of the genetic constitution of the dams. Homozygous DBA embryos showed an intermediate abberation yield.The AHH inducibility by BaP did not correlate quantitatively with the induced aberration rates. However, the data suggest that BaP activation in embryonic tissue on day 11 of pregnancy is sufficient to account for the clastogenicity in the fetuses. It is concluded that the genetic endpoint chromosomal breakage is not only determined by the formation of active BaP metabolites but also by genetically controlled detoxification of BaP, repair process, and the rate of transformation of primary DNA lesions into true DNA discontinuities.
Comparative in vivo sister chromatid exchange induction by ethyl carbamate in maternal and fetal tissues of tumor‐susceptible and ‐resistant murine strains
Authors: Neeper‐Bradley T. L. , Conner Mary K. 
Published: February 2006

AbstractMurine susceptibility to ethyl carbamate‐induced carcinogenesis is strain dependent. In vivo sister chromatid exchange (SCE) responses to ethyl carbamate were evaluated in bone marrow cells of gravid adenoma‐susceptible (ICR/Jcl), and resistant (C57Bl/6J) and (DBA/2J) murine dams, as well as in liver cells of their respective ICR/Jcl, C57Bl/6J × DBA/2J (BDF1), and DBA/2J × C57Bl/6J (BDF), fetuses following a single intravenous injection of 1.1, 2.2, or 3.3 mmol/kg of ethyl carbamate on gestation day 13/14. Bone marrow tissues of C57Bl/6J and DBA/2J, but not ICR/Jcl dams, demonstrated greater sensitivity to SCE induction than liver cells of their respective fetuses. Furthermore, relative SCE responses in bone marrow among dams indicated greater sensitivity of the more tumor‐susceptible ICR/Jcl and C57Bl/6J strains to SCE induction by ethyl carbamate relative to the more tumor‐resistant DBA/2J strain. In addition, concurrent alterations (stimulation or inhibition) of bone marrow cell cycle kinetics by ethyl carbamate were consistent with hormone‐related, strain‐dependent hematopoietic stress during pregnancy.
Effect of Ambient Temperature and Running Wheel Activity on the Outcome of Pregnancy in CD‐1 Mice
Authors: Berman Ezra , House Dennis , Carter Hershell B. 
Published: February 2006

AbstractThe effect of ambient temperature and running activity on fetal outcome was studied in CD‐1 mice. Pregnant mice were allowed to be active in a running wheel at various ambient temperatures (26, 30, 32, 34, or 36°C) for 100 min a day. The dams were killed near term, and various maternal and fetal measures made. Mean deep body temperature (measured using radio‐telethermometers implanted in the abdomen) of pregnant dams was raised to 39.5°C while running at an ambient temperature of 36°C. Bred mice, pregnant or not, continued to increase their running activity, but pregnant mice exercised less from mid‐pregnancy on. Running up to 1 km/hr had no effect on maternal weight gain, number of implantations, number of live fetuses, fetal body weight, and fetal relative brain weight. However, increasing ambient temperature was effective in decreasing maternal weight gain and fetal body weight and increasing fetal relative brain weight. Even though body temperature can be increased significantly by increasing either running rate or ambient temperature, the body temperature increase caused by running appears to have no significant influence on the outcome of pregnancy. At levels in this study, body temperature per se does not appear to be the variable on which to predict fetal effects. This is because only body temperature raised by higher ambient temperature, and not body temperature raised by increased running, was shown to effect a fetal change.
Preparation for Human Study of Pesticide Applicators: Sister Chromatid Exchanges and Chromosome Aberrations in Cultured Human Lymphocytes Exposed to Selected Fumigants
Authors: Garry V. F. , Nelson R. L. , Griffith J. , Harkins M. 
Published: February 2006

AbstractIn preparation for a human study of worker exposure to grain fumigants and pesticides, we decided to screen commonly used fumigants for genotoxic effects in vitro. This research strategy was employed to test the possibility that structurally simple chemicals might have similar genotoxic properties in vivo and in vitro. As a first step, we designed our in vitro protocol to mimic to the extent possible, a single in vivo exposure of lymphocytes to fumigants. Go lymphocytes were treated with different doses of carbon tetrachloride, carbon disulfide, methyl bromide, chloropicrin, and melathion with and without addition of rat liver homogenate for 1/2 hour, washed free of toxicant, and stimulated with PHA. After culture, the prepared slides were studied for chromosome aberrations and SCEs. Malathion, methyl bromide, and chloropicrin significantly induced SCEs without S‐9. Carbon disulfide alone required S‐9 for significant SCE induction. Chromosome aberrations were significantly increased by malathion and methyl bromide. Carbon tetrachloride failed to induce SCEs or chromosome aberrations with or without S‐9. We concluded from these preliminary studies and other comparable work that the fumigants studied here may be less likely to express genotoxicity in terms of SCEs or chromosome aberrations than ethylene oxide or phosphine given a single short‐term in vivo exposure. The final design of our human study was altered to focus on seasonal worker exposure rather than on a single exposure event.