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D J Brenner

Publications and source records attributed to D J Brenner.

At least 19 recordsLinked to original sources
PubMed2006

Testing the stand-alone microbeam at Columbia University.

The stand-alone microbeam at Columbia University presents a novel approach to biological microbeam irradiation studies. Foregoing a conventional accelerator as a source of energetic ions, a small, high-specific-activity, alpha emitter is used. Alpha particles emitted from this source are focused using a compound magnetic lens consisting of 24 permanent magnets arranged in two quadrupole triplets. Using a 'home made' 6.5 mCi polonium source, a 1 alpha particle s(-1), 10 microm diameter microbeam can, in principle, be realised. As the alpha source energy is constant, once the microbeam has been set up, no further adjustments are necessary apart from a periodic replacement of the source. The use of permanent magnets eliminates the need for bulky power supplies and cooling systems required by other types of ion lenses and greatly simplifies operation. It also makes the microbeam simple and cheap enough to be realised in any large lab. The Microbeam design as well as first tests of its performance, using an accelerator-based beam are presented here.

Cell Culture Techniques↗
PubMed2005

Genetic susceptibility to radiation.

In the context of space radiation, it is important to know whether the human population includes genetically predisposed radiosensitive subsets. One possibility is that haploinsufficiency for ATM confers radiosensitivity, and this defect involves 1-3% of the population. Using knock-out mice we chose to study cataractogenesis in the lens and oncogenic transformation in mouse embryo fibroblasts to assay for effects of ATM deficiency. Radiation induced cataracts appeared earlier in the heterozygous versus wild-type animals following exposure to either gamma rays or 1 GeV/nucleon iron ions. In addition, it was found that embryo fibroblasts of Atm heterozygotes showed an increased incidence of oncogenic transformation compared with their normal litter-matched counterparts. From these data we suggest that Ataxia Telangiectasia heterozygotes could indeed represent a societally significant radio sensitive subpopulation. Knock-out mice are now available for other genes including BRCA1 and 2, and Mrad9. An exciting possibility is the creation of double heterozygotes for pairs of mutated genes that function in the same signal transduction pathway, and consequently confer even greater radiosensitivity.

Aerospace Medicine↗
PubMed2005

Mice heterozygous for the ATM gene are more sensitive to both X-ray and heavy ion exposure than are wildtypes.

Previous studies have shown that the eyes of ATM heterozygous mice exposed to low-LET radiation (X-rays) are significantly more susceptible to the development of cataracts than are those of wildtype mice. The findings, as well as others, run counter to the assumption underpinning current radiation safety guidelines, that individuals are all equally sensitive to the biological effects of radiation. A question, highly relevant to human space activities is whether or not, in similar fashion there may exist a genetic predisposition to high-LET radiation damage. Mice haplodeficient for the ATM gene and wildtypes were exposed to 325 mGy of 1 GeV/amu 56Fe ions at the AGS facility of Brookhaven National Laboratory. The fluence was equivalent to 1 ion per lens epithelial cell nuclear area. Controls consisted of irradiated wildtype as well as unirradiated wildtype and heterozygous mice. Prevalence analyses for stage 0.5-3.0 cataracts indicated that not only cataract onset but also progression were accelerated in the mice haplo-deficient for the ATM gene. The data show that heterozygosity for the ATM gene predisposes the eye to the cataractogenic influence of heavy ions and suggest that ATM heterozygotes in the human population may also be radiosensitive. This may have to be considered in the selection of individuals who will be exposed to both HZE particles and low-LET radiation as they may be predisposed to increased late normal tissue damage.

Animals↗
PubMed2004

Chromosome spatial clustering inferred from radiogenic aberrations.

PURPOSE: Analysing chromosome aberrations induced by low linear energy transfer (LET) radiation in order to characterize systematic spatial clustering among the 22 human autosomes in human lymphocytes and to compare their relative participation in interchanges. MATERIALS AND METHODS: A multicolour fluorescence in situ hybridization (mFISH) data set, specifying colour junctions in metaphases of human peripheral blood lymphocytes 72 h after in vitro exposure to low LET radiation, was analysed separately and in combination with previously published results. Monte Carlo computer simulations and mathematical modelling guided data analysis. RESULTS AND CONCLUSIONS: Statistical tests on aberration data confirmed two clusters of chromosomes, [1, 16, 17, 19, 22] and [13, 14, 15, 21, 22], as having their members being on average closer to each other than randomness would predict. The first set has been reported previously to be near the centre of the interphase nucleus and to be formed mainly by gene-rich chromosomes, while the second set comprises the nucleolus chromosomes. The results suggest a possible interplay between chromosome positioning and transcription. A number of other clusters suggested in the literature were not confirmed and considerable randomness of chromosome-chromosome juxtapositions was present. In addition, and consistent with previous results, it was found that chromosome participation in interchanges is approximately proportional to the two-thirds power of the DNA content.

Chromosome Aberrations↗
PubMed2004

Bystander effect and adaptive response in C3H 10T(1/2) cells.

PURPOSE: To address the relationship between the bystander effect and the adaptive response that can compete to impact on the dose-response curve at low doses. MATERIALS AND METHODS: A novel radiation apparatus, where targeted and non-targeted cells were grown in close proximity, was used to investigate these phenomena in C3H 10T(1/2) cells. It was further examined whether a bystander effect or an adaptive response could be induced by a factor(s) present in the supernatants of cells exposed to a high or low dose of X-rays, respectively. RESULTS: When non-hit cells were co-cultured for 24 h with cells irradiated with 5 Gy alpha-particles, a significant increase in both cell killing and oncogenic transformation frequency was observed. If these cells were treated with 2 cGy X-rays 5 h before co-culture with irradiated cells, approximately 95% of the bystander effect was cancelled out. A 2.5-fold decrease in the oncogenic transformation frequency was also observed. When cells were cultured in medium donated from cells exposed to 5 Gy X-rays, a significant bystander effect was observed for clonogenic survival. When cells were cultured for 5 h with supernatant from donor cells exposed to 2 cGy and were then irradiated with 4 Gy X-rays, they failed to show an increase in survival compared with cells directly irradiated with 4 Gy. However, a twofold reduction in the oncogenic transformation frequency was seen. CONCLUSIONS: An adaptive dose of X-rays cancelled out the majority of the bystander effect produced by alpha-particles. For oncogenic transformation, but not cell survival, radioadaption can occur in unirradiated cells via a transmissible factor(s).

Adaptation, Physiological↗
PubMed2004

The bystander response in C3H 10T1/2 cells: the influence of cell-to-cell contact.

Although radiation-induced heritable damage in mammalian cells was thought to result from the direct interaction of radiation with DNA, it is now accepted that biological effects may occur in cells that were not themselves traversed by ionizing radiation but are close to those that were. However, little is known about the mechanism underlying such a bystander effect, although cell-to-cell communication is thought to be of importance. Previous work using the Columbia microbeam demonstrated a significant bystander effect for clonogenic survival and oncogenic transformation in C3H 10T(1/2) cells. The present study was undertaken to assess the importance of the degree of cell-to-cell contact at the time of irradiation on the magnitude of this bystander effect by varying the cell density. When 10% of cells were exposed to a range of 2-12 alpha particles, a significantly greater number of cells (P < 0.0001) were inactivated when cells were irradiated at high density (>90% in contact with neighbors) than at low density (<10% in contact). In addition, the oncogenic transformation frequency was significantly higher in high-density cultures (P < 0.0004). These results suggest that when a cell is hit by radiation, the transmission of the bystander signal through cell-to-cell contact is an important mediator of the effect, implicating the involvement of intracellular communication through gap junctions.

Alpha Particles↗
PubMed2003

Domestic radon risks may be dominated by bystander effects--but the risks are unlikely to be greater than we thought.

Radon risks derive from exposure of bronchio-epithelial cells to alpha particles. Alpha-particle exposure can result in bystander effects when irradiated cells emit signals resulting in damage to nearby unirradiated bystander cells. Bystander effects can cause downwardly-curving dose-response relations and inverse dose-rate effects. We have extended a quantitative mechanistic model of bystander effects to include protracted exposure, with inverse dose-rate effects attributed to replenishment, during exposure, of a subpopulation of cells which are hypersensitive to bystander signals. In this approach, bystander effects and the inverse dose-rate effect are manifestations of the same basic phenomenon. The model was fitted to dose- and dose-rate dependent radon-exposed miner data; the results suggest that one directly-hit target cell can send bystander signals to about 50 neighboring cells and that, in the case of domestic radon exposures, the risk could be dominated by bystander effects. The analysis concludes that a naive linear extrapolation of radon miner data to low doses, without accounting for dose rate/bystander effects, would result in an underestimation of domestic radon risks by about a factor of approximately 4. However, recent domestic radon risk estimates (BEIR VI) have already applied a phenomenological correction factor of approximately 4 for inverse dose-rate effects, and have thus already implicitly taken into account corrections which we here suggest are due to bystander effects. Thus current domestic radon risk estimates are unlikely to be underestimates as a result of bystander effects.

Air Pollution, Indoor↗
PubMed2002

Routine screening mammography: how important is the radiation-risk side of the benefit-risk equation?

The potential radiation hazards associated with routine screening mammography, in terms of breast cancer induction, are discussed in the context of the potential benefits. The very low energy X-rays used in screening mammography (26-30 kVp) are expected to be more hazardous, per unit dose, than high-energy X- or gamma-rays, such as those to which A-bomb survivors (from which radiation risk estimates are derived) were exposed. Based on in vitro studies using oncogenic transformation and chromosome aberration end-points, as well as theoretical estimates, it seems likely that low doses of low-energy X-rays produce an increased risk per unit dose (compared with high energy photons) of about a factor of 2. Because of the low doses involved in screening mammography, the benefit-risk ratio for older women would still be expected to be large, though for younger women the increase in the estimated radiation risk suggests a somewhat later age than currently recommended--by about 5-10 years--at which to commence routine breast screening.

Adult↗
PubMed2002

Do low dose-rate bystander effects influence domestic radon risks?

PURPOSE: Radon risks derive from exposure of bronchio-epithelial cells to high-linear energy transfer (LET) alpha-particles. alpha-particle exposure can result in bystander effects, where irradiated cells emit signals resulting in damage to nearby unirradiated bystander cells. This can result in non-linear dose-response relations, and inverse dose-rate effects. Domestic radon risk estimates are currently extrapolated from miner data, which are at both higher doses and higher dose-rates, so bystander effects on unhit cells could play a large role in the extrapolation of risks from mines to homes. Therefore, we extend an earlier quantitative mechanistic model of bystander effects to include protracted exposure, with the aim of quantifying the significance of the bystander effect for very prolonged exposures. MATERIALS AND METHODS: A model of high-LET bystander effects, originally developed to analyse oncogenic transformation in vitro, is extended to low dose-rates. The model considers radiation response as a superposition of bystander and linear direct e It attributes bystander effects to a small subpopulation of hypersensitive cells, with the bystander contribution dominating the direct contribution at very low acute doses but saturating as the dose increases. Inverse dose-rate effects are attributed to the replenishment of the hypersensitive subpopulation during prolonged irradiation. RESULTS: The model was fitted to dose- and dose-rate-dependent radon-exposed miner data, suggesting that one directly hit target bronchio-epithelial cell can send bystander signals to about 50 neighbouring target cells. The model suggests that a naïve linear extrapolation of radon miner data to low doses, without accounting for dose-rate, would result in an underestimation of domestic radon risks by about a factor of 4, a value comparable with the empirical estimate applied in the recent BEIR-VI report on radon risk estimation. CONCLUSIONS: Bystander effects represent a plausible quantitative and mechanistic explanation of inverse dose-rate effects by high-LET radiation, resulting in non-linear dose-response relations and a complex interplay between the effects of dose and exposure time. The model presented provides a potential mechanistic underpinning for the empirical exposure-time correction factors applied in the recent BEIR-VI for domestic radon risk estimation.

Air Pollution, Indoor↗
PubMed2002

Microbeams: a potent mix of physics and biology. Summary of the 5th International Workshop on Microbeam Probes of Cellular Radiation Response.

Single-cell microbeam irradiators are of increasing interest to the biological community. The 5th International Workshop on Microbeam Probes of Cellular Radiation Response, which took place in Stresa, Italy, in May 2001, was attended by about 120 registrants, roughly evenly divided between physicists and biologists. Many new microbeam devices are now under development, and there has been a significant diversification of the biological questions addressed. Most current uses of microbeams have been to address radiobiological questions, but the advent of sub-micrometre targeting capabilities, and the development of new single-cell assays, point to the potential for microbeams to make an important contribution to biological, and not just radiobiological, studies.

Animals↗
PubMed2001

Modest increased sensitivity to radiation oncogenesis in ATM heterozygous versus wild-type mammalian cells.

Subpopulations that are genetically predisposed to radiation-induced cancer could have significant public health consequences. Individuals homozygous for null mutations at the ataxia telangiectasia gene are indeed highly radiosensitive, but their numbers are very small. Ataxia Telangiectasia heterozygotes (1-2% of the population) have been associated with somewhat increased radiosensitivity for some end points, but none directly related to carcinogenesis. Here, intralitter comparisons between wild-type mouse embryo fibroblasts and mouse embryo fibroblasts carrying ataxia telangiectasia mutated (ATM) null mutation indicate that the heterozygous cells are more sensitive to radiation oncogenesis than their normal, litter-matched, counterparts. From these data we suggest that Ataxia Telangiectasia heterozygotes could indeed represent a societally-significant radiosensitive human subpopulation.

Animals↗
PubMed2001

Long-term efficacy of intracoronary irradiation in inhibiting in-stent restenosis.

BACKGROUND: Intracoronary irradiation is a promising modality for inhibition of in-stent restenosis. Results of randomized clinical trials at 6 months after gamma ray irradiation are highly encouraging. The first results at 3 years after irradiation, while still showing benefit, have shown significant late loss. The probable mechanism of the radiation is to inactivate (prevent from dividing) most cells that otherwise could proliferate to produce neointimal formation. We measured the proportion of cells that survive with their clonogenic potential intact after the doses and dose rates used in the randomized trials, and we then modeled the subsequent repopulation of the surviving cells that might cause late restenosis. METHODS AND RESULTS: Human aortic smooth muscle cells were irradiated with gamma rays, including the doses and dose rates used in current trials, and clonogenic surviving fractions were measured. The subsequent repopulation of the surviving cells was modeled with the assumption that the repopulation kinetics were similar to those in unirradiated cells. The radiation is expected to delay the time to restenosis by factors of approximately 6 to 8, depending on the dose, shifting the delay from a median of 6 months (for no irradiation) to median values from 36 months (for a nominal 13 Gy) to 43 months (for a nominal 15 Gy). CONCLUSIONS: These results and predictions are quantitatively consistent with clinical results and suggest that clonogenic inactivation (prevention of cellular division) is the dominant mechanism of radiation action in the delay of restenosis. Intracoronary radiotherapy is a very promising modality for significantly delaying, although probably not preventing, in-stent restenosis.

Cell Survival↗
PubMed2001

Biomarkers specific to densely-ionising (high LET) radiations.

There have been several suggestions of biomarkers that are specific to high LET radiation. Such a biomarker could significantly increase the power of epidemiological studies of individuals exposed to densely-ionising radiations such as alpha particles (e.g. radon, plutonium workers, individuals exposed to depleted uranium) or neutrons (e.g. radiation workers, airline personnel. We discuss here a potentially powerful high LET biomarker (the H value) which is the ratio of induced inter-chromosomal aberrations to intra-arm aberrations. Both theoretical and experimental studies have suggested that this ratio should differ by a factor of about three between high LET radiation and any other likely clastogen, and will yield more discrimination than the previously suggested F value (ratio of inter-chromosomal aberrations to intra-chromosomal inter-arm aberrations). Evidence of the long-term stability of such chromosomal biomarkers has also been generated. Because these stable intra-arm anld inter-chromosomal aberrations are (1) frequent and (2) measurable at long times after exposure, this H value appears to be a practical biomarker of high LET exposure, and several in vitro studies have confirmed the approach for unstable aberrations. The approach is currently being tested in a population of Russian radiation workers exposed several decades ago to high- or low LET radiation.

Biomarkers↗
PubMed2001

Enterococcus porcinus sp. nov. and Enterococcus ratti sp. nov., associated with enteric disorders in animals.

Recent insights have been brought to the taxonomy of the genus Enterococcus by studies applying whole-cell protein analysis and DNA-DNA reassociation experiments, in addition to conventional physiological tests. Using these techniques, a group of 10 strains resembling the physiological group III of enterococcal species was characterized. Five strains were recovered from pigs and five from rats with enteric disorders. On the basis of the results of conventional physiological tests, the most likely identity of these strains was Enterococcus durans or Enterococcus hirae. Analysis of the electrophoretic whole-cell protein profiles showed two distinct clusters of virtually indistinguishable profiles: one composed of strains isolated from pigs, and one composed of strains isolated from rats. These protein profiles were not similar to the profiles of any previously described Enterococcus species. The results of DNA-DNA relatedness experiments were consistent with the results of the protein-profile analysis. The high levels of DNA relatedness found for pig isolates demonstrated that they belong to a new enterococcal species, for which the designation Enterococcus porcinus sp. nov. is proposed (type strain =DS 1390-83T =ATCC 700913T =CCUG 43229T =NCIMB 13634T). Strains isolated from rats were found to comprise another new species, for which the designation Enterococcus ratti sp. nov. is proposed (type strain =DS 2705-87T =ATCC 700914T =CCUG 43228T =NCIMB 13635T). This report provides data on the phenotypic and genotypic characterization of these two new enterococcal species, which may represent diarrhoeagenic pathogens for animals.

Animals↗
PubMed2001

Legionella gresilensis sp. nov. and Legionella beliardensis sp. nov., isolated from water in France.

Novel Legionella-like isolates, strains Montbéliard A1T and Gréoux 11 D13T, isolated from two different French water sources, were studied taxonomically and phylogenetically. Morphological and biochemical characterization revealed that they were Gram-negative, aerobic, non-spore-forming bacilli with a cut-glass appearance that grew only on L-cysteine-supplemented buffered charcoal yeast extract agar. Phenotypic characterization using fatty acid and ubiquinone profiles and SDS-PAGE analysis confirmed that they were closely related, but distinct from, other species of the genus Legionella, since serotyping could not relate them to any existing serogroup. Genotypic profiles generated by randomly amplified polymorphic DNA and 16S-23S rDNA spacer region PCR analyses were unique for each of these isolates. DNA-DNA relatedness values of strains Montbéliard A1T and Gréoux 11 D13T to each other and to other Legionella type strains were less than 25%. Phylogenetic affiliation of these organisms obtained by 16S rDNA sequence comparisons confirmed that they were distinct from any other known Legionella species. All the above results confirm that these strains constitute two novel species for which the names Legionella gresilensis sp. nov. (type strain Gréoux 11 D13T = ATCC 700509T = CIP 106631T) and Legionella beliardensis sp. nov. (type strain Montbéliard A1T = ATCC 700512T = CIP 106632T) are proposed.

Bacterial Proteins↗