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Biomedical subjects

G W Barendsen

Publications and source records attributed to G W Barendsen.

At least 37 records · Page 2Linked to original sources
PubMed1992

RBE for non-stochastic effects.

Evidence is reviewed concerning the variation of RBE values of high-LET radiations for non-stochastic effects, generally impairment of tissue integrity and function. The RBE values are dependent on the type of radiation, the type of tissue effect and the dose rate or fractionation schedule. RBE values depend strongly on the effect considered, with high values for late effects in lung, kidney and central nervous system. RBE values generally increase with decreasing dose rate or dose per fraction. Maximum values can be derived by extrapolation on the basis of a radiobiological model. These values are denoted RBEm to distinguish them from RBEM derived for stochastic effects, e.g. carcinogenesis. Values of RBEm are generally in the range of 2 to 10 and are considerably smaller by a factor of 2 to 5 than values of RBEM for various types of stochastic effects. RBE values for effects from actual exposures to mixtures of high-LET and low-LET radiations can be derived by considering the doses received and the tissue at risk. Applications of RBEm values will yield estimates of maximum values of equivalent doses and these should only be applied for planning medical interventions if the contribution from high-LET radiation is small. The selection of Q values for radiation protection is mostly based on RBE--values and the application of Q values in cases where non-stochastic effects are important might therefore result in an overestimate of the risks of exposure.

Animals↗
PubMed1990

On-line sorting of human chromosomes by centromeric index, and identification of sorted populations by GTG-banding and fluorescent in situ hybridization.

Using slit-scan flow cytometry, the shape of human metaphase chromosomes, as expressed in their centromeric index (CI), and the DNA content of the chromosomes have been used as parameters in bivariate flow karyotyping. The resolution of the DNA vs CI flow karyogram of the larger chromosomes up to chromosome 13 is much higher than the resolution obtained in the DNA-based monovariate flow karyogram. Chromosome length appears to be an important factor in the resolution of the DNA vs CI-based flow karyogram. A method has been developed to obtain chromosomes in suspension that are long enough for adequate analysis. Several chromosomes that cannot be distinguished or are difficult to discriminate in the DNA-based karyogram can now be distinguished as individual peaks, e.g., chromosomes 1 and 2. The peak of chromosomes 9-12 can be separated into two peaks formed by chromosomes 9 and 11, and 10 and 12, respectively. The advantage of the system applied in this study is that the DNA vs CI analysis is performed on-line, allowing chromosomes to be sorted on the bases of their CI. Pulse shapes of the selected chromosomes can be recorded simultaneously with the transmission of the sorting command. The purity of the sorted fraction can be estimated from the off-line inspection of these pulse shapes. Fractions of chromosome 1 have been sorted out on the basis of the CI information, centrifuged on slides, fixed and subsequently banded with trypsin and Giemsa or hybridized with the chromosome 1 specific probe, pUC 1.77. The observed purity under the selected conditions ranges from 80%-99% and is in accordance with the estimates of the purities made on the basis of the simultaneously recorded pulse shapes. Fixation of the chromosome suspension prior to flow cytometric analysis and sorting appears to be essential for the preservation of their morphology and has no adverse influence on the resolution of Giemsa banding or on the quality of in situ hybridization.

Cell Line↗
PubMed1990

Mechanisms of cell reproductive death and shapes of radiation dose--survival curves of mammalian cells.

A 'paired dsb' mechanism of action for cell reproductive death by ionizing radiations is proposed, which allows interpretation of differences in shapes of survival curves caused by variation of linear energy transfer of the radiation, by the stage in the cell cycle, but cell culture conditions and by sensitizing and protecting compounds. It is based on the analysis of shapes of survival curves in terms of S(D)/S(O) = exp - (a1D + a2D2) and the suggestion that paired dsb in DNA, produced within distances of the order of 10 nm, are efficient in initiating the sequence of events causing cell reproductive death by individual particle tracks. Part of the lethality may result from two dsb's produced by single tracks at larger distances, and this might constitute potentially lethal damage which in favourable conditions can be repaired. Thus, the initial slope of a survival curve is not independent of the repair capacity of a cell, but indeed can be modified by cell conditions. The damage causing the quadratic term in the survival equation may be interpreted as a consequence of two dsb produced by two different ionizing particles, although other interactions cannot be excluded. The suggested mechanism of 'paired dsb' damage is consistent with information concerning the LET dependence of different effects in cells and their constituents.

Animals↗
PubMed1989

Flow cytometric analysis of experimental parameters for the immunofluorescent labeling of BrdUrd in various tumour cell lines.

This report describes the results of the comparison of three different methods and three monoclonal antibodies to stain cells in suspension for incorporated bromodeoxyuridine and total DNA content. The procedures were tested in three different experimental tumour cell lines. The sensitivity of the different procedures was expressed as the ratio of the anti-BrdUrd fluorescence intensities of the S and G1 phase cells (FS/FG1 ratio). There were remarkable differences in sensitivity between the different procedures. With the heat denaturation the most favourable FS/FG1 ratio's were obtained but substantial cell loss occurred during this procedure which is a disadvantage for clinical application. With the pepsin digestion + acid denaturation procedure cell loss was negligible. The standard acid denaturation procedure was inferior to the other two methods. Using the pepsin digestion + acid denaturation procedure we examined the variations in sensitivity for the different monoclonal antibodies and cell lines and the influence of BrdUrd concentration, labelingtime and cell concentration. The binding characteristics for the various antibodies differed considerably in our hands. Only with the IU4 antibody we obtained FS/FG1 ratio's comparable with those described in the literature. No difference was observed between the cell lines. Variation in cell concentration between 1 x 10(4) to 1 x 10(6) ml nor BrdUrd concentration appeared to influence the sensitivity of the procedure. A labelingtime of 1 h or even 30 min seems to be more than sufficient for an optimal FS/FG1 ratio. Our results indicate that using the appropriate antibody and immunofluorescence BrdUrd can be detected by flow cytometry, after incorporation into the DNA of tumour cells under a wide range of culture conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies, Monoclonal↗
PubMed1987

Radiosensitivity of cells in recurrent experimental tumours and the effectiveness of tumour retreatment.

Two experimental tumour models, a rat rhabdomyosarcoma (R-1) and a rat urether carcinoma (RUC-2) have been employed to evaluate the X-ray sensitivity of tumours recurrent after primary treatments with various doses of X-rays and to correlate changes in volume responses with the cellular radiosensitivity. The responsiveness of R-1 tumours, assessed from the volume reduction as a function of the time after treatment, was less for recurrent tumours, but their growth delay was slightly increased, while the X-ray sensitivity of the tumour cells, assessed by cell survival, was equal to that of the controls. For RUC-2 tumours, however, the reduction in volume after irradiation of the recurrent tumour was larger than after primary treatment, the growth delay was increased, but cell survival curves were not significantly different from those of the controls. It is concluded that differences in volume responses between untreated tumours and recurrent tumours are largely determined by a tumour bed effect (TBE) and that changes in cellular radiosensitivity in these tumours do not play a significant part.

Animals↗
PubMed1987

Klaas Breur memorial lecture 1986. Differences in radiosensitivity among cells in culture and in experimental tumours: significance for the effectiveness of human cancer therapy.

Problems in the application of radiobiological data on various types of models, cell in vitro, experimental tumours, and clinical models, to the prediction of tumour radiocurability are discussed. On the basis of observations on cells in culture and experimental tumours it is suggested that heterogeneity in responsiveness of tumours in patients is caused in a large part by differences in intrinsic cellular radiosensitivity. Methods and developments are reviewed, which may yield better assays for the prediction of tumour responsiveness to treatments.

Cells, Cultured↗
PubMed1987

X-ray- and neutron-induced chromosome damage detected by flow cytometry compared to cell lethality and chromosome structural changes.

V79 Chinese hamster cells were irradiated in G0 phase with 200 kV X rays or 14 MeV neutrons, and dose-response curves were determined for three end points: chromosome damage detected by flow cytometric analysis of chromosomes isolated from metaphase cells in irradiated cultures; loss of clonogenic capacity; and induction of dicentric, tricentric, and ring chromosomes. The changes observed in the flow karyotypes from irradiated cultures were quantitatively evaluated by computer analysis. Estimates of the frequencies of chromosome lesions were derived from an analysis of the flow cytometric measurements by means of a comparison with model calculations simulating the effect of chromosome changes on flow karyotypes. The results indicate that lesions assayed by flow cytometry occur three times more frequently than lethal lesions, while the chromosomal structural changes detected by microscopic analysis were about 10 times less frequent than the lesions detected by flow cytometry. Dose-response curves for X rays and neutrons show that cell reproductive death and changes in flow karyotypes result from damage, induced with a similar relative biological effectiveness. Dose-effect relations derived from changes in flow karyotypes, which can be obtained within 24 h after irradiation, might be of value as a predictive test for the sensitivity of cells for loss of clonogenic capacity.

Animals↗
PubMed1985

Comparison of transformation, chromosome aberrations, and reproductive death induced in cultured mammalian cells by neutrons of different energies.

Dose-effect relations for cell transformation and reproductive death induced in C3H/10T1/2 cells, NBCH-3 cells, and WAGR-2 cells by 300 kV X rays and monoenergetic fast neutrons of 0.5, 4.2, and 15 MeV energy have been analyzed on the basis of the relations F(D) = t1D + t2D2 and S(D)/S(0) = exp - (a1D + a2D2), respectively. Values of a1 are a factor of about 10(3) larger than corresponding values of t1, while the dependence on neutron energy is similar for both effects. RBE values and relations between the a1 and t1 values are compared with characteristics, derived from corresponding parameters for chromosome aberrations and reproductive death, induced in other cell lines after irradiation with the same neutron beams. A hypothesis is developed assuming that nonrandom structural changes at a restricted number of sites on one or more chromosomes are the primary causes of transformation of cultured mammalian cells by ionizing radiations, whereas similar but randomly distributed chromosomal changes, which are induced at many sites on all chromosomes, cause observable aberrations and reproductive death. Flow cytometry of chromosome suspensions has been used to demonstrate nonrandom changes of chromosomes in selected clones of transformed cells and of random changes of chromosomes in cells inactivated by X rays and neutrons.

Animals↗
PubMed1984

Preparation of chromosome suspensions from cells of a solid experimental tumour for measurement by flow cytometry.

A method is described by which metaphase chromosomes are isolated from cells of a transplantable rat sarcoma. The chromosomes are derived from cells in a suspension prepared by trypsinisation of tumours from rats that have been treated with vindesine 24 h before excision in order to accumulate cells in mitosis. Histograms obtained for the chromosomes of the solid tumour are compared with flow karyotypes of cells cultured for 20 h or for several generations in vitro.

Animals↗
PubMed1984

Proliferation kinetics of cultured cells after irradiation with X-rays and 14 MeV neutrons studied by time-lapse cinematography.

Exponentially growing cells of an established line derived from a mouse osteosarcoma (MOS) have been studied by time-lapse cinematography after irradiation with 3 Gy of 200 kV X-rays or 1.5 Gy of 14 MeV neutrons. Cell cycle times (Tc) of individual cells and their progeny in three subsequent generations as well as the occurrence of aberrant mitosis have been determined to evaluate the variation in expression of damage in relation to the stage in the intermitotic cycle and the radiation quality. The results show that the radiation doses applied cause an equal elongation of the mean Tc, which is largest in the irradiated cells but persists in the three subsequent generations. After 3 Gy of X-rays, mitotic delay is largest in cells irradiated in later stages of the cycle, but this difference is not observed after 1.5 Gy of 14 MeV neutrons. In subsequent generations the Tc values show larger variations among descendents of cells treated in the same stage of the cycle as compared to controls but this variation is equal for the doses of X-rays and neutrons applied. Division probability was significantly reduced in irradiated cells as well as in subsequent generations, whereby with neutrons as compared to X-rays the damage is expressed in earlier generations, with less variation as a function of the cell cycle.

Animals↗