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Biomedical subjects

J Ashby

Publications and source records attributed to J Ashby.

At least 145 records · Page 8Linked to original sources
PubMed1995

Chemicals for evaluating the sensitivity and specificity of reduced/transgenic rodent cancer bioassay protocols.

The standard two-species/two-gender lifetime carcinogenicity bioassay protocol is not practical when assessing the possible carcinogenicity of a large number of chemicals. This has led to consideration of reduced cancer bioassay protocols (e.g., male rat/female mouse), or to the use of genetically altered rodents that succumb to chemically induced cancer in a fraction of their lifespans. Two uncertainties accompany these endeavours. First, that use of reduced protocols may lead to the non-detection of some weak or tissue-specific carcinogens. Second, that genetically altered rodents may be so sensitive to chemical disturbance of homoeostasis that their carcinogen specificity may be low. Such uncertainties lead to the requirement that the modified test protocols should be validated using appropriate carcinogens and non-carcinogens. Given that several such studies may take place over the coming years it seems appropriate that a common pool of chemicals should be agreed upon for this purpose. To this end a selection of human carcinogens, and rodent carcinogens/non-carcinogens defined by the US National Toxicology Program (NTP), have been collected together. Six categories of chemicals are listed: (1) representative human carcinogens; (2) representative trans-species genotoxic carcinogens; (3) all two-species non-carcinogens reported to be negative in the Salmonella mutation assay and lacking structural alerts to electrophilicity; (4) representative single-species/presumed non-genotoxic carcinogens; (5) all two-species non-carcinogens that are mutagens in the Salmonella mutation assay and which are structurally alerting; (6) all chemicals possessing equivocal evidence of carcinogenicity and which are both structurally alerting and mutagenic to Salmonella. Chemicals in the first four groups provide robust calibrants for determining the sensitivity and specificity of reduced/accelerated rodent carcinogenicity bioassay protocols. Chemicals in the last two groups may be of value when studying the interface between the sensitivity and the specificity of modified rodent carcinogenicity bioassay protocols.

Animals↗
PubMed1995

Genetic toxicity in relation to receptor-mediated carcinogenesis.

There is growing agreement on the types and number of assays required to assess the ability of a chemical to mutate or to affect in a heritable manner the expressional integrity of DNA. This usually involves measurement of the ability of a chemical to induce chromosomal aberrations or gene mutations in cultured cells, coupled to confirmation of genetic toxicity in rodents. The results of such assays, coupled to assessment of the chemical structure of the agent for sites of actual or potential electrophilicity, provide a major and primary input to estimation of whether a rodent carcinogen is operating by a genotoxic or a non-genotoxic mechanism. The extent and sites of carcinogenesis also contribute to this decision. In cases where the mechanism of action of a carcinogen is to be studied in detail, additional assessments of genetic toxicity can be made in the species/gender/tissue subject to carcinogenesis. Suitable assays include measurements of DNA adducts (e.g., 32P post-labelling), assessment of DNA damage using, for example, the single-cell gel electrophoresis (Comet) assay, or the determination of transgenic mutation frequencies in appropriate rodent model systems. The genetic toxicity of o-anisidine, methyl clophenipate, etoposide and taxol are discussed to illustrate these concepts. The present need is for high quality genetic toxicity data to be derived and integrated with other relevant toxicological data on a new carcinogen in order to provide an informed estimate its most likely mechanisms of carcinogenic action.

Aniline Compounds↗
PubMed1995

A sequential approach to testing with the rodent bone marrow micronucleus assay--obviation of the need for statistical analyses of data.

The 'sequential' protocol we use for the conduct of mouse bone marrow micronucleus assays is described. The most important criterion for activity in the assay is the reproducibility of any induced effects. The frequencies of micronucleated polychromatic erythrocytes among 239 male CBA control mice are displayed and discussed. Our decision to avoid statistical analysis when assessing mouse bone marrow micronucleus data is explained.

Animals↗
PubMed1995

Comparison of lacI and lacZ transgenic mouse mutation assays: an EU-sponsored interlaboratory study.

As part of an EU Environment Programme sponsored study, the performance of two transgenic mouse mutation assays has been evaluated in three laboratories using common liver samples. The systems studied were the lacI-(Big Blue) mutation assay, and the GalE- positive selection modified lacZ- (Muta Mouse) assay. The liver samples compared were derived from mice treated with either saline or dimethylnitrosamine (DMN; 14 day recovery). Each assay gave an increased mutation frequency (MF) for the DMN-treated livers when compared to the saline control MFs. Sources of variability in the assays are discussed, and it is concluded that whole liver should be homogenised before DNA extraction, and that concurrent controls should be processed in parallel with test samples.

Animals↗
PubMed1995

Interleukin-2 (IL-2) augments host cellular immune reactivity in the perioperative period in patients with malignant disease.

Major surgery impairs cellular and humoral immunity, in particular natural cytotoxicity, and this may facilitate the dissemination of tumour cells in the peri-operative period. Recombinant interleukin-2 (rIL-2) has been used to modulate peri-operative immune function. Eighteen patients were randomized to receive either rIL-2 or placebo for three days, as a subcutaneous injection, prior to surgical resection for colorectal cancer. Natural cytotoxicity (natural killer (NK) and lymphokine-activated killer (LAK) cell activity), monocyte phagocytosis and immune cell surface activation marker (CD14+HLA-DR) expression were assessed during therapy and for up to 21 days after surgery. rIL-2 therapy enhanced both NK and LAK cell-mediated cytotoxicity and augmented circulating lymphocyte CD16+ and CD56+ cell subset populations. Circulating monocyte phagocytosis was also increased. Hence, rIL-2 may be used to enhance immune function in the peri-operative period in patients undergoing curative cancer surgery.

Adult↗
PubMed1995

Effect of essential fatty acids on natural cytotoxicity in patients with colorectal cancer.

Essential fatty acids (EFAs), have been shown to modulate lymphocyte reactivity and destroy various tumour cells in vitro. Natural cytotoxicity, mediated by NK and LAK cells, is believed to play an important anti-cancer role in vivo. The effect of EFAs, given orally as dietary supplementation, on NK and LAK cell cytotoxic activity in patients with localized (n = 10) and advanced (n = 20) colorectal cancer has been studied, using in-vitro 51Cr release cytotoxicity assays with K562 (NK) and DAUDI (LAK) cells. The activity of effector cells was expressed as lytic units. NK cell activity showed no significant change following 15 days ingestion of EFAs in the group with localized cancer, but was significantly reduced in the group with advanced disease and continued to decline, reaching minimal levels following 6 months supplementation (P = 0.017). LAK cell activity showed no overall alteration after 15 days ingestion of EFAs in patients with localized cancer, but in the group with advanced disease, the reduction in the activity occurred at day 15 and steadily declined on prolonged intake, reaching significant minimal levels after 6 months of supplementation (P = 0.05). Cell surface marker analysis (FACS-CD MABs) revealed reduced absolute numbers of CD16+, CD56+ and CD57+ lymphocytes (P < 0.05) in the patients with advanced colorectal cancer. More importantly, the cytotoxicity of NK and LAK cells returned to the pre-supplementation values, 3 months after cessation of EFA intake. Furthermore, there was no alteration in the cytotoxic activity of NK and LAK cells in the control group (advanced colorectal cancer without EFA supplementation) during the 6 months period of evaluation. These results suggest that prolonged EFA supplementation, in the doses used in this study, may have detrimental effects on natural anti-cancer cytotoxic mechanisms in patients with malignant disease.

Aged↗
PubMed1995

High resolution rodent bone marrow micronucleus assays of 1,2-dimethylhydrazine: implication of systemic toxicity and individual responders.

1,2-Dimethylhydrazine (DMH) is confirmed as active in male CBA mouse bone marrow micronucleus (MN) assays conducted at non-toxic dose-levels between 25 and 45 mg/kg. Previous reports of the activity of DMH in rodent bone marrow MN assays are reviewed. By the design of the present experiments it has been possible to confirm the advice offered by the United Kingdom Environmental Mutagen Society (UKEMS) that once 2000 polychromatic erythrocytes have been assessed per animal, the use of larger animal group sizes becomes the critical means to increase assay sensitivity. Also, the use of historical control data is shown to enhance assay sensitivity at low dose-levels by enabling recognition of individual animals responding to the test chemical. These outliers are seen before the group mean MPE value has been increased enough to attain group statistical significance. It is concluded that careful consideration of test data, within the context of concurrent and historical control data, is sufficient to discern activity in the assay.

1,2-Dimethylhydrazine↗
PubMed1995

The single cell gel electrophoresis assay for induced DNA damage (comet assay): measurement of tail length and moment.

Cultured hepatocytes have been treated with either DMSO or dimethylnitrosamine (NDMA) for either 1 or 2 h and the cells assessed for DNA-damage using the single cell alkaline gel electrophoresis assay (comet assay). A strong positive test response was observed producing comet tails of a length and DNA content not observed in either viable or dead control cells. A stronger test response was observed after a 2 h, as opposed to a 1 h, incubation of hepatocytes with NDMA. The method of processing the image of the comet is discussed and it is proposed that measurement of the length of the comet tail should commence at the estimated trailing edge of the cell, rather than at the leading edge or the estimated centre of the cell. Using this criterion, many control cells have no comet trails thereby enabling chemically induced tails to be more readily assessed. A simplified version of defining the comet tail moment is proposed.

Animals↗
PubMed1995

Streptozotocin: inherent but not expressed skin sensitizing activity.

We have shown previously that the alkylating agent streptozotocin (STZ) fails to induce responses in the murine local lymph node assay, a predictive test for contact sensitizing potential. In the present study, we demonstrate that this same compound when injected intradermally into the ears of mice provokes a dose-dependent induction of draining lymph node cell proliferation. These data indicate that the intrinsic immunogenicity of STZ is not displayed in the local lymph node assay under conditions of conventional topical exposure, secondary to a failure to cross the lipophilic stratum corneum in sufficient quantities. This finding has implications for the discernment of structure-activity relationships in contact sensitization.

Animals↗
PubMed1994

Mutation studies with dimethyl nitrosamine in young and old lac I transgenic mice.

Young adult (approximately 8 w) and old (approximately 72 w) lac I transgenic mice have been exposed to a single oral dose of dimethyl nitrosamine (NDMA). 2.5 h later unscheduled DNA synthesis was observed in the liver of the young animals (19.5 NG; control value -3.4 NG). The frequency of lac I- mutations in the liver of the young animals was elevated 7, 10 and 20 days after dosing. A similar fold-increase in mutant frequency was seen 7 days after dosing the old animals. It is concluded that mutability of the genome of old animals is not significantly different to that of young animals. Aspects of the minimum Big Blue assay protocol are discussed, as are the differing perceptions of the role of the assay in carcinogen hazard assessment.

Age Factors↗
PubMed1994

Response of the Muta mouse lacZ/galE- transgenic mutation assay to DMN: comparisons with the corresponding Big Blue (lacI) responses.

The lacZ Muta mouse transgenic mutation assay was recently adapted into a selective assay based on use of E. coli galE(-) bacteria and phenyl galactoside (p-gal). A preliminary assessment of this selective assay was undertaken using a single oral dose of 10 mg/kg of dimethyl nitrosamine (DMN). The livers of treated male mice were assessed for UDS 2 h after dosing, and for lacZ- mutations 7, 11 and 20 days after dosing. A strong UDS response was recorded and a clear mutagenic response was observed at each of the 3 timepoints. Comparison of these data with earlier data derived using the Big Blue (lacI) mutation assay reveals a marginally greater sensitivity to DMN of the selective Muta mouse assay, an effect probably related to a biochemical difference between the strains of animal, as evidenced by the larger UDS response seen in the Muta mouse system. The original Muta mouse assay protocol was impractical. The galE- adaption makes the assay emminently practical and cost-effective. We are continuing to assess the true role of both the Big Blue assay and the galE- Muta mouse assay in mutagenicity/carcinogenicity prediction. The former assay enables access to B6C3F1 mice and F344 rats, the latter enables the rapid acquisition of data.

Animals↗
PubMed1994

Change the rules for food additives.

The Delaney clause, embodied in US legislation in 1958, prohibits the addition to food of any level of any carcinogen. This position cannot be sustained in the face of progress in understanding chemically induced cancer.

Animals↗
PubMed1994

International Commission for Protection Against Environmental Mutagens and Carcinogens. Two million rodent carcinogens? The role of SAR and QSAR in their detection.

The accurate prediction of chemical carcinogenicity can only be achieved by a balanced consideration of the following factors: the chemistry and metabolism of the test agent, the interaction between toxicity and genetic toxicity, the possibility of non-genotoxic events that trigger subsequent non-targeted mutagenesis, the difference between activities observed in vitro and in vivo, and the possible inadequacy and/or partiality of all datasets and observations. Extrapolation of activities within a series of congeners is usually possible, but predictions across different chemical classes/mechanisms of carcinogenicity are difficult. Artificial intelligence systems can be used to predict one or more of the above parameters given adequate learning sets, but the hope for a single, coherent and self-contained method of predicting all instances of carcinogenicity is unreal. The future of carcinogen/mutagen prediction lies with data-rich artificial intelligence systems based on known mechanistic principles used selectively within the context of chemical and biological human insight. The major current obstacle to progress is the assumption that mutagenicity and carcinogenicity are unitary phenomena that can be learned and predicted by artificial intelligence systems operating in isolation.

Alkylating Agents↗