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R J Preston

Publications and source records attributed to R J Preston.

At least 37 records · Page 2Linked to original sources
PubMed1995

Ethylene oxide: evaluation of genotoxicity data and an exploratory assessment of genetic risk.

A risk estimate of the heritable effects of ethylene oxide exposure, using the parallelogram approach, as suggested by Frits Sobels, is described. The approach is based on available data on the ethylene oxide-induced responses for the same genetic endpoint in somatic cells of both laboratory animals and humans, and for germ cell mutations in the same laboratory animal. Human germ cell effects are estimated. The available data sets for this approach were evaluated. We consider this as complementary to the genetic risk assessment carried out by U.S. EPA scientists, in which the risk from heritable (reciprocal) translocations induced by ethylene oxide was estimated. In the present study we restricted our assessment to dominant mutations. The sensitivity factor relating mouse to man was based on ethylene oxide-induced HPRT mutant frequencies in lymphocytes in vivo. From this comparison, it could be concluded that occupational exposure for 1 year to 1 ppm ethylene oxide would lead to a risk of a dominantly inherited disease in the offspring of 4 x 10(-4) above the background level. The uncertainty interval of this figure is quite large (0.6-28) x 10(-4). The values are compatible with the existing estimates of the corresponding risk from exposure to low LET radiation when the genotoxic potency ratio of ethylene oxide and radiation is considered. This risk estimation approach has allowed us to identify additional data that are required for a more complete risk estimation of the heritable effects of ethylene oxide, or indeed any mutagenic chemical.

Animals↗
PubMed1994

Future of germ cell cytogenetics.

The celebration of the 25th Anniversary of the Environmental Mutagen Society provides an excellent opportunity to assess the status of research in a broad range of areas, with an emphasis on the directions in which they are going. This chapter concentrates on the analysis of chromosomal alterations in mammalian germ cells. The future developments in germ cell cytogenetics research will build heavily upon techniques developed over the past 25 years. With these it is possible to assess numerical and structural alterations in the male in differentiating spermatogonia, spermatocytes, and post-meiotic cells (at the first cleavage division) and for the female in oocytes and the zygote. The most predictable advances will be in the identification of specific alterations through FISH of interphase spermatozoa in humans and further improvements with the human sperm/hamster egg in vitro fertilization technique. Of particular importance is the fact that this will allow for the study of effects in human germ cells. From a more speculative viewpoint it might be possible to assess the role of particular genomic organization on genetic outcomes by direct observation; these might include genomic imprinting and the visual separation of male and female genomes. The overall aim of germ cell cytogenetic studies will remain as improving our ability to identify and estimate the true genetic risk in humans.

Animals↗
PubMed1994

A re-evaluation of the cytogenetic effects of styrene.

Results from new chromosome studies in laboratory animals, comparative investigations of styrene metabolism and pharmacokinetics in humans and animals, and several recent cytogenetic surveys of styrene-exposed workers have necessitated a comprehensive re-evaluation of the chromosome-damaging effects of this chemical. Both styrene and its genotoxic metabolite, styrene oxide, can induce chromosome aberrations (CA) and sister chromatid exchanges (SCE) in vitro, but the chromosome-damaging ability of styrene is only manifested if test conditions favour its metabolic activation over inactivation. There is no convincing evidence of styrene clastogenicity in experimental animals. Styrene oxide is clastogenic only at lethal concentrations via i.p. injection in Chinese hamsters (but not via inhalation) or after oral treatment of mice, a route considered inappropriate for investigating the chromosome-damaging potential of inhaled styrene in man. Styrene and styrene oxide can induce SCE in animals at very high concentrations. Eighteen of 52 cytogenetic studies (CA, micronuclei, SCE) on peripheral blood lymphocytes of styrene workers have reported increases in chromosome damage. The positive findings are not compatible with the conclusion that styrene is responsible for the cytogenetic effects for the following reasons. (a) The positive or negative outcome of the various investigations bears no relationship to the degree of exposure of the workers. (b) There is no convincing evidence of a positive dose response relationship. (c) The relative induction of CA and SCE in worker studies are the opposite of observations of styrene effects in cultured lymphocytes and in laboratory animals. (d) The reports of chromosome-type exchanges in some studies of styrene workers is inconsistent with observations of styrene clastogenicity in cultured lymphocytes. (e) Reports of SCE induction in workers exposed to low concentrations of styrene are not compatible with results of animal inhalation studies, particularly in view of the differences in styrene metabolism and pharmacokinetics between humans and rodents. The increases in cytogenetic effects reported in some studies on styrene workers are probably attributable to the presence of other chromosome-damaging agents in the workplace and/or to inadequate investigations.

Animals↗
PubMed1994

Report from the working group on the in vivo mammalian bone marrow chromosomal aberration test.

The following summary represents a consensus of the working group, except where noted. The goal of this working group was to identify the minimal requirements needed to conduct a scientifically valid and practical in vivo chromosomal aberration assay. For easy reference, the items discussed are listed in the order in which they appear in OECD guideline 475. Specific disagreement with the current and/or proposed OECD guideline is presented in the text. Introduction, purpose, scope, relevance, application, and limits of test: This test would not be appropriate in situations where there was sufficient evidence to indicate that the test article or reactive metabolites could not reach the bone marrow. Test substances: Solid and liquid test substances should be dissolved, if possible, in water or isotonic saline. If insoluble in water/saline, the test substance should be dissolved or homogeneously suspended in an appropriate vehicle (e.g., vegetable oil). A suspension was not considered suitable for an intravenous injection. The use of dimethyl sulfoxide as an organic solvent was not recommended. The use of any uncommonly used solvent/vehicle should be justified. Freshly prepared solutions or suspensions of the test substance should be employed unless stability data demonstrate the acceptability of storage. Selection of species: Any commonly used rodent species was deemed acceptable but rats or mice were preferred, with no strain preference. Number and sex: A consensus could not be reached as to the requirement for both sexes versus one sex in this assay. It was suggested that a single sex should be used unless pharmacokinetic and/or toxicity data indicated a difference in metabolism and/or sensitivity between males and females. The size of the experiment (i.e., number of cells per animal, number of animals per treatment group) should be based on statistical considerations. Lacking a formal analysis, it was agreed that at least 100 metaphase cells should be scored per animal while at least five animals of any one sex should be evaluated per treatment group. Recently, a formal analysis of the numbers of cells to score per animal and numbers of animals to score per treatment group was conducted at a workshop on statistics for in vivo mutagenicity tests (Adler et al., 1994). The conclusion of this workshop was that, based on a type I error of 0.05 and a power of 80% to detect at least a doubling in the control frequency, the minimal number of cells to score per animal was 200 and the minimal number of animals to score per sex per treatment group was four.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Studies of the induction of chromosomal aberration and sister chromatid exchange in rats exposed to styrene by inhalation.

A large number of studies have been reported on the genotoxicity of styrene in vitro and in vivo and the potential effects on humans of occupational exposure. Because of a variety of technical problems and difficulties in data interpretation, it has not been clearly established whether styrene can induce chromosomal aberrations and/or sister chromatid exchange (SCE) in vivo in animals or humans. The importance of clarifying this situation led to the development of the study described in this paper. Male Fischer 344 rats were exposed to styrene at concentrations of 150, 500 or 1000 ppm for 6 h/day on 5 days/week for 4 weeks. A negative control (air) was included. An additional control (ethylene oxide, 150 ppm) group was included in an attempt to establish the usefulness of rat lymphocytes for cytogenetic analysis in this protocol of long-term exposure by inhalation. The choice of agent and of exposure was based on the expectation that they would produce a positive response for SCE and/or chromosomal aberrations under the assay conditions used. Peripheral blood samples were drawn at 1, 2, 3 and 4 weeks of exposure and at 4 weeks after the end of exposure. Cultures were established, and SCE (second mitosis) and chromosomal aberrations (first mitosis) were analysed. The frequency of chromosomal aberrations was not increased over that in the air controls in the animals exposed to styrene or ethylene oxide at any of the sampling times. Styrene did not induce SCE at any of the concentrations or sampling times; however, the frequency of SCE was increased following exposure to ethylene oxide at all sampling times, with a positive exposure-response relationship with time of exposure as the variable. The data are compared with other, similar sets reported in the literature, and their significance for predicting responses in people occupationally exposed to styrene is discussed.

Administration, Inhalation↗
PubMed1992

Isolation and characterization of a 1-beta-D-arabinofuranosylcytosine-resistant Chinese hamster ovary cell mutant that is also X-ray sensitive and is noncomplementary with ataxia telangiectasia cells.

In order to study the mechanism of induction of mutations and chromosome aberrations by ionizing radiations, it is particularly useful to have available radiation-sensitive mutants. While several X-ray-sensitive rodent cell lines are available, they have been selected rather nonspecifically. It was determined that selection for resistance to the DNA replication/repair inhibitor, 1-beta-D-arabinofuranosylcytosine (ara-C), would permit production of a set of X-ray-sensitive mutant cell lines that would be defective in the resynthesis step of excision or recombination repair. Such mutant cells could also be used for the isolation and characterization of human DNA repair genes. In particular, it was predicted that the repair gene defective in individuals with ataxia telangiectasia (AT) might be amenable to study with ara-C-resistant (X-ray-sensitive) mutants, since additional studies, presented here, have shown that AT cells are resistant to ara-C. In the long term, it is hoped that determining the specific defect in AT might lead to an understanding of the possible role of defective repair in tumor induction and/or progression. The general approach used to isolate ara-C-resistant Chinese hamster ovary cell mutants was to treat cells with ethyl methanesulfonate and select in increasing concentrations of ara-C. Although several mutants were isolated, one in particular, Ara-CR213, has been studied most extensively. It was selected largely because it shows the greatest sensitivity to X-rays. Ara-CR213 cells were hypersensitive to the killing effect of X-rays with an LD10 of 2.5 Gy as compared to the wild-type cells that had an LD10 of 6 Gy. The mutant showed an increased frequency of X-ray-induced chromosomal aberrations in the G1 and G2 stages of the cell cycle compared to wild-type frequencies. There was no increase in sister chromatid exchange levels. All of these observations in Ara-CR213 are very similar to those made with AT cells in our and other laboratories. Even more important, complementation analysis of Ara-CR213 x AT hybrid cells indicated that the gene responsible for X-ray sensitivity of AT is also mutated in Ara-CR213 cells. Thus, Ara-CR213 appears to have a mutant phenotype and probably genotype that is very similar to, if not exactly the same as, those of AT. This makes it quite different from other X-ray-sensitive cells that have been isolated in other laboratories.

Animals↗
PubMed1991

The role of O6-alkylguanine in cell killing and mutagenesis in Chinese hamster ovary cells.

Chinese hamster ovary cells with no detectable (less than 200 molecules/cell) O6-methylguanine-DNA methyltransferase (EC 2.1.1.63) were transfected with human cell DNA and pSV2neo plasmid by electroporation. Two stable transformant clones, GC-1 and GC-2, containing 4 X 10(4) and 4-6 X 10(3) methyltransferase molecules/cell respectively were isolated by successive screening in the presence of G418 and 2-chloroethyl-N-nitrosourea (CNU). Only three or four copies of pSV2neo DNA and no repetitive human DNA sequence were detected in these isolates. Secondary transfection of parent cells with GC-1 DNA yielded several clones containing 2-10 X 10(3) methyltransferase molecules/cell. The rate of removal of O6-methylguanine in GC-1, GC-2 and parent cells in vivo reflected their methyltransferase levels, while the N-methylpurines were removed at similar rates in all three cell lines. The differential sensitivity of these cells to several alkylating agents, namely CNU, N-methyl-N-nitrosourea, N-methyl-N'-nitro-N-nitrosoguanidine and methyl-methane sulfonate (MMS), known to yield different proportions of O6-alkylguanine among the alkyl adducts in DNA, varied widely. The largest and smallest differences in toxic response were observed with CNU and MMS respectively. These cell lines showed no difference in sensitivity to the DNA cross-linking agent psoralen. These data strongly suggest that alkylating agents produce two classes of lethal lesions, one of which is O6-alkylguanine. Induction of mutations at the hypoxanthine-phosphoribosyltransferase locus in these cells lines suggests that, regardless of its relative yield, O6-methylguanine is the major mutagenic lesion for all alkylating agents.

Alkylating Agents↗
PubMed1991

Modulation of restriction enzyme-induced damage by chemicals that interfere with cellular responses to DNA damage: a cytogenetic and pulsed-field gel analysis.

The electroporation of restriction enzymes into mammalian cells results in DNA double-strand breaks that can lead to chromosome aberrations. Four chemicals known to interfere with cellular responses to DNA damage were investigated for their effects on chromosome aberrations induced by AluI and Sau3AI; in addition, the number of DNA double-strand breaks at various times after enzyme treatment was determined by pulsed-field gel electrophoresis (PFGE). The poly(ADP-ribose) polymerase inhibitor 3-aminobenzamide (3AB) dramatically increased the yield of exchanges and deletions and caused a small but transitory increase in the yield of double-strand breaks induced by the enzymes. 1-beta-D-Arabinofuranosylcytosine, which can inhibit DNA repair either by direct action on DNA polymerases alpha and delta or by incorporation into DNA, potentiated aberration induction but to a lesser extent than 3AB and did not affect the amount of DNA double-strand breakage. Aphidicolin, which inhibits polymerases alpha and delta, had no effect on AluI-induced aberrations but did increase the aberration yield induced by Sau3AI. The postreplication repair inhibitor caffeine had no effect on aberration yields induced by either enzyme. Neither aphidicolin nor caffeine modulated the amount of DNA double-strand breakage as measured by PFGE. These data implicate poly(ADP-ribosyl)ation and polymerases alpha and delta as important components of the cellular processes required for the normal repair of DNA double-strand breaks with blunt or cohesive ends. Comparison of these data with the effect of inhibitors on the frequency of X-ray-induced aberrations leads us to the conclusion that X-ray-induced aberrations can result from the misjoining or nonrejoining of double-strand breaks, particularly breaks with cohesive ends, but that this process accounts for only a portion of the induced aberrations.

Animals↗
PubMed1991

Mutations induced by ionizing radiation in a plasmid replicated in human cells. I. Similar, nonrandom distribution of mutations in unirradiated and X-irradiated DNA.

The Escherichia coli supF gene encoding the suppressor tyrosine tRNA in a human shuttle plasmid, pZ189, was used as a target for molecular analysis of X-ray-induced mutations in human lymphoblastoid cells. Following replication of the in vitro-irradiated plasmid in human cells, the mutant supF-containing molecules were cloned by phenotypic screening in E. coli and the nature of the mutations was determined by direct sequencing of the tRNA gene. At 160 Gy the mutant frequency was 13 times (0.39%) that observed in unirradiated controls (0.031%). When control plasmid was replicated directly in E. coli, the mutant frequency was 16 times less than that of the plasmid passaged through the human cells. The distribution of mutations was highly nonrandom and remarkably similar in both irradiated and control DNAs. The majority of the mutations were transitions involving G.C pairs and occurred selectively at most 5'-TC (3'-AG) sequences. These mutations at C's were preferentially distributed in the nontranscribed strand. We propose that mutations in the control plasmid result from oxidative damages that occur during and/or after its incorporation into human cells and that these damages are similar to those induced by ionizing radiation. The hot spots for mutations suggest that the proximate nucleotide sequence and the overall conformation of the target DNA are important in the production and/or processing of these damages during repair and replication.

Base Composition↗
PubMed1991

Mutations induced by ionizing radiation in a plasmid replicated in human cells. II. Sequence analysis of alpha-particle-induced point mutations.

The human shuttle plasmid pZ189, containing the Escherichia coli supF gene as the mutational target, was irradiated in vitro with 210Po alpha particles and transfected into human lymphoblastoid cells. Plasmids which were replicated in human cells were recovered and those containing mutant supF genes were isolated by phenotypic screening in E. coli. The mutations were characterized by sequencing the tRNA gene. The mutant frequency increased linearly with the alpha-particle dose and, at 259 Gy, it was 16 times (0.29%) that observed in unirradiated controls (0.018%). The distribution of alpha-particle-induced point mutations was highly nonrandom and similar to that observed in the unirradiated or X-irradiated plasmid DNAs. The majority of the mutations were G.C----A.T transitions and occurred selectively at most 5'-TC (3'-AG) and 5'-CC (3'-GG) sequences. For the unirradiated control DNA, these mutations at C's (G's) were preferentially located in the nontranscribed strand, similar to the observation previously made for mutations in X-irradiated DNA. Such a strand bias was not observed for mutations in the alpha-particle-irradiated DNA. The data suggest that, although similar types of point mutations are induced in unirradiated, X-irradiated, and alpha-particle-irradiated DNAs, the mechanisms of their induction and the exact nature of the lesions involved may be quite different.

Alpha Particles↗
PubMed1990

N-methyl-N-nitrosourea-induced mutations in a shuttle plasmid replicated in human cells.

The supF gene of the recombinant shuttle plasmid pZ190 (modified pZ189) was used as a target to study the nature of mutations induced by N-methyl-N-nitrosourea (MNU) in human cells. Treatment of the intact plasmid with MNU followed by its replication in human lymphoblastoid cells led to extensive inactivation and no detectable mutations of the plasmid. However, exposure of the supF DNA fragment alone, followed by its ligation into the vector, caused a ten-fold increase in mutant frequency when replicated in O6-methylguanine-DNA methyltransferase-deficient cells (from 0.54 x 10(-3) to 5.8 x 10(-3)) and an 80-fold increase when replicated in cells containing normal levels of the enzyme (from 0.047 x 10(-3) to 3.8 x 10(-3)). About 45% of the mutant plasmid molecules recovered from human cells contained deletions and insertions. Sixty to 70% of the mutant molecules of wild-type size contained a single-base substitution. Most of these changes were of the G.C----A.T type, consistent with the hypothesis that O6-methylguanine is the primary mutagenic adduct induced by MNU. However, the distribution of mutation sites was highly nonrandom; more than half of all mutations were localized at the G.C position 123, and the rest were distributed in about a dozen sites. The high yield of mutations induced in the supF DNA in a host cell whose capacity for the removal of O6-methylguanine far exceeded the amount present in the supF suggests that the repair of damages in extrachromosomal DNA may be inefficient. This is supported by the observation that the yield of mutations in supF transfected into lymphoblastoid cells devoid of repair activity for O6-methylguanine was comparable to that observed with repair-proficient host cells. The present data, together with results of mutations induced in pZ189 by other agents, strongly suggest that one major determinant of mutational hot spots is the structure of the target DNA itself.

Bacterial Proteins↗