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L De Ridder

Publications and source records attributed to L De Ridder.

At least 19 recordsLinked to original sources
PubMed1997

Semi-automated micronucleus scoring in cytokinesis-blocked lymphocytes after irradiation.

A semi-automated scoring procedure for the cytokinesis-block micronucleus assay based on computerized image analysis was validated by comparing results of the automated analysis with those from manual analysis by those experienced scorers of micronuclei. Each object selected by the computer system was also relocated and visually inspected. The validation was based on slides of blood samples after in vitro irradiation with X-rays in the low-dose range up to 2 Gy. Up to 1 Gy a very satisfactory agreement between manual and semi-automated scoring was obtained. At 2 Gy the micronucleus yields obtained by the semi-automated scoring were systematically below the manual data due to a small percentage of false negatives (3%). Using the appropriate dose-response relationship the validation study indicates that the results obtained by computerized image analysis are comparable to manual scoring with respect to accuracy. The computerized assay is superior regarding reproducibility. At present, semi-automated scoring of micronuclei is practically feasible for a limited number of slides for large-scale applications of the semi-automated micronucleus is assay in the field of radiation protection an increase of the speed of the system is necessary.

Adult↗
PubMed1997

Flow cytometry as a quantitative and sensitive method to evaluate low dose radiation induced apoptosis in vitro in human peripheral blood lymphocytes.

Human peripheral blood lymphocytes, irradiated in vitro, die by an apoptotic process. The number of apoptotic cells after in vitro gamma-irradiation (0, 0.1, 0.2, 1, 2 and 5 Gy) was measured by flow cytometry using Annexin V and DiOC6 (a cationic dye) after 24 and 48 h incubation. The mean dose-response curves for apoptosis of six healthy volunteers obtained with both methods were steep below 1 Gy and flatter at higher doses. A slightly higher number of apoptotic cells was observed with DiOC6, compared to Annexin V. This can be assigned to a minor DiOC6-int/PI- population. Forty-eight hour cultures contained higher numbers of apoptotic cells compared with 24 h cultures. For both culture times, DiOC6 and Annexin V detected a statistically significant difference between a control sample and a 0.1 Gy irradiated one, illustrating the high sensitivity of the methods.

Annexin A5↗
PubMed1997

In vitro micronucleus-centromere assay to detect radiation-damage induced by low doses in human lymphocytes.

One of the major drawbacks of the in vitro micronucleus (MN) assay for human lymphocytes is its reduced sensitivity for the detection of damage induced by low radiation doses, due to the high variability among the spontaneous MN frequencies. In this paper we investigated the enhancement of the sensitivity of the MN assay by analysing spontaneous and radiation-induced MN for the presence of centromeres. For this, in situ hybridization (FISH) with the human pancentromeric DNA probe, p82H, was performed. Our results revealed that a high percentage (73%) of the spontaneous MN contain a centromere. These centromere-positive MN indicate the presence of a whole chromosome/chromatid. After in vitro irradiation with low doses (0.1-2 Gy) 60Co gamma-rays mainly centromere-negative MN were induced while only a very small number of additional centromere-positive MN were formed. This demonstrates that radiation-induced MN mainly contain acentric fragments pointing to the clastogenic action of ionizing radiation. Furthermore, our data show that the sensitivity of the MN assay for low dose detection is increased by scoring only centromere-negative MN.

Adult↗
PubMed1997

Generation of a monoclonal antibody directed against a human cell substrate adhesion molecule and the expression of the antigen in human tissues.

Cell substrate adhesion is a prerequisite for invasion and the subsequent formation of metastases. Therefore, we designed monoclonal antibodies (MAbs) against epitopes on the extracellular cell membrane domain of SK-BR-3 cells. One of the antibodies, called MAb 14C5, binds to an extracellular epitope of a plasma membrane antigen of SK-BR-3 and MCF-7 human breast cancer cells. This MAb 14C5 is able to inhibit cell substrate adhesion, not only on culture-treated plastic but also on host tissue, and therefore prevents invasion and metastases. We evaluated the tissue distribution of the 14C5 antigen by immunohistochemistry. The antigen is specifically overexpressed in 64% of invasive ductal adenocarcinomas of the breast (n = 33), in all investigated cases of invasive squamous cell carcinoma (n = 7) and in 40% of basocellular carcinomas of the skin (n = 5). The 14C5 molecule is located on the cell membrane of the carcinoma cells. However, when the tumor is characterized by a highly invasive phenotype, 65% of the cases also show an extensive stromal expression on the fibroblasts between the tumor cells (n = 71). This stromal expression is caused by the presence of the 14C5 antigen on the membrane of the adjacent fibroblasts. In normal tissues as well as in the stroma surrounding in situ carcinomas of the breast (n = 15), no expression of the 14C5 antigen occurred. A 90-kDa protein was purified from lysates of human breast cancer cells using a 14C5 MAb Sepharose column and is considered as the antigen recognized by the MAb 14C5.

Antibodies, Monoclonal↗
PubMed1996

Mechanism of age-dependent involution in embryonic chick notochords.

To study the possible mechanism of the age-dependent involution of the notochord, isolated mesenchyme-free notochords of chick embryos were cultured in vitro and compared with their counterparts in vivo. Two different aspects were evaluated: (1) DNA synthesis measured by [3H]thymidine incorporation and visualized by autoradiography and (2) cell death quantified by counting the number of pyknotic nuclei. The results demonstrate that [3H]thymidine uptake by notochords shows an age-dependent decrease in vitro as well as in vivo. The number of [3H]thymidine-labelled notochord cells, however, is higher in vitro than in vivo. At the same time, there is an age-dependent increase in pyknosis in the notochord in vivo and in vitro. So, during the aging process, the number of both pyknotic nuclei and of [3H]thymidine-labelled nuclei suggest a high turnover of notochord cells in vitro. From these results, we can conclude that the process of involution in aging notochord seems to be controlled by a programmed intrinsic process, which might be influenced partially by the microenvironment in vivo.

Animals↗
PubMed1996

A cytogenetic study of radiological workers: effect of age, smoking and radiation burden on the micronucleus frequency.

A large scale cytogenetic study of the radiation damage in nuclear power plant workers and medical workers handling X-ray machines (269 individuals) was undertaken using the micronucleus assay for peripheral blood lymphocytes. The micronucleus frequency was found to increase systematically with donor age. After correction for the age-dependence, no correlation of the micronucleus frequency with smoking habits, expressed as cigarette-years and cigarette consumption per day, could be observed. Compared to the group of administrative workers receiving doses below 1 mSv/year, limit recommended by the ICRP for public exposure, the micronucleus frequency was slightly increased in the group of radiation workers, exposed occupationally. However, applying the Mann-Whitney test, the observed differences are not statistically significant. After correction of the dose accumulation pattern for the turn-over of the lymphocyte pool, a weak correlation between the micronucleus frequency and the equivalent dose accumulated over the 10 years preceding the study was obtained. For clear-cut conclusions on the radiation damage of low-dose worker cohorts, an increase in the sensitivity of the assay, e.g., by analysis of the micronuclei for the presence of centromeres is necessary.

Adult↗
PubMed1996

Micronucleus induction by 60Co gamma-rays and fast neutrons in ataxia telangiectasia lymphocytes.

Ataxia telangiectasia (AT) is an autosomal recessive disease characterized by a progressive neuronal degeneration, immunodeficiency, cancer proneness and an extreme sensitivity to ionizing radiation. In this work, micronucleus dose-response curves for lymphocytes of normal and AT individuals, exposed in G(zero) to low LET gamma-rays and high LET fast neutrons, are compared. After gamma-irradiation, the micronucleus yields for AT lymphocytes are strongly increased compared with controls. The micronucleus dose-response curve for AT cells shows a linear dependence instead of a linear-quadratic one which is found for normal cells. After neutron irradiation, the increase in micronucleus yield above controls is less pronounced than with gamma-rays and the micronucleus dose-response curves are linear, as expected. The high increase in micronucleus yield compared with controls after gamma-irradiation further suggests the application of the micronucleus assay as a diagnostic tool for ataxia telangiectasia.

Ataxia Telangiectasia↗
PubMed1995

Micronucleus induction in peripheral blood lymphocytes of patients under radiotherapy treatment for cervical cancer or Hodgkin's disease.

The genetic damage present in peripheral blood lymphocytes of patients treated with fractionated partial-body radiation therapy for cervical cancer or Hodgkin's disease was followed during treatment by means of the cytokinesis-block micronucleus assay. For each patient a dose-response relationship with respect to the number of micronuclei after in vitro irradiation of blood samples pretreatment was also determined. Comparing the individual in vivo-in vitro data, the micronucleus yields after the equivalent whole-body dose during radiotherapy were found to differ substantially from the in vitro dose-response. Contrary to the linear-quadratic dose dependence after in vitro irradiation the initial increase in the micronucleus yield during radiotherapy levelled off at elevated doses. The observed differences cannot be attributed only to the effects of interphase death and the partial irradiation of the lymphocyte pool. The correlation between the micronucleus yield and the equivalent whole-body dose for values up to 2 Gy, observed for the pooled data of the first part of the radiotherapy treatment, demonstrates the suitability of the cytokinesis-block micronucleus assay as a biological dosemeter after accidents involving partial-body irradiation.

Adult↗
PubMed1994

Micronuclei induced by fast neutrons versus 60Co gamma-rays in human peripheral blood lymphocytes.

Here we compared the effectiveness of neutrons ( = 5.5 MeV) versus 60Co gamma-rays in producing micronuclei (MN) in human lymphocytes. To obtain dose-response data, blood samples of six donors were irradiated with doses ranging from 0.1 to 5 Gy for gamma-rays and 0.1-3 Gy for neutrons. A linear dependence of MN yield with dose was found for fast neutrons while for gamma-rays a nonlinear dependence existed. For both radiation qualities no significant interindividual differences were found. Derived relative biological effectiveness values decreased with increasing dose. The MN frequency distributions were overdispersed with respect to the Poisson distribution, with neutrons showing higher dispersion values than with gamma-rays. To compare the repair kinetics of both radiation qualities split-dose experiments were performed. A dose of 4 Gy gamma-rays (3 Gy neutrons) was delivered either as a single exposure or in two equal fractions separated by time intervals ranging from 30 min to 10 h (30 min to 7 h for neutrons). The data showed for gamma-rays a significant decline (30% +/- 10%) in MN yield with interfraction time due to repair of DNA damage. This repair is a continuous process starting almost immediately after the first of the two doses and lasting 3-5 h. For fast neutrons no decline was observed indicating irreparable damage.

Cells, Cultured↗
PubMed1994

[Relationship between endocrinology and craniofacial growth. I: Puberty and craniofacial growth. II: Growth of the craniofacial skeleton].

In this literature, a review is given of the endocrinology and morphology of the craniofacial complex. This article reviews in a first part the endocrinology of puberty and general growth aspects. Afterwards the adolescence growth spurt of the face and the hormonal regulation will be focused. In a second part the morphogenetic aspects together with growth area's and growth theories of the craniofacial complex will be discussed. At last a detailed description of the maxillary and mandibular growth is given.

Adolescent↗
PubMed1994

Comparative and combined effects of interleukin 6, interleukin 1 beta, and tumor necrosis factor alpha on proteoglycan metabolism of human articular chondrocytes cultured in agarose.

OBJECTIVE: To study the effects of recombinant tumor necrosis factor alpha (TNF-alpha), interleukin 1 beta (IL-1 beta) and interleukin 6 (IL-6) on proteoglycan metabolism of isolated chondrocytes. METHODS: Human articular cartilage cells were cultured in agarose gel. In these culture conditions, chondrocytes keep their phenotypic stability. They release cartilage specific proteoglycans into the surrounding artificial matrix. Proteoglycan synthesis was measured by the incorporation of 35sulfate (35S). RESULTS: TNF-alpha and IL-1 beta depressed proteoglycan synthesis and induced proteoglycan degradation. The effects of both cytokines were additive, when used in submaximal doses. No mutual induction of TNF-alpha and IL-1 beta was shown, but both cytokines stimulated the chondrocytes to release IL-6, up to 100,000 pg/ml. Equal amounts of human recombinant IL-6 did not affect proteoglycan synthesis. IL-6 did not alter proteoglycan quality, nor did it modulate the IL-1 beta activities on proteoglycan metabolism. CONCLUSION: These findings illustrate the role of IL-1 beta and TNF-alpha in cartilage degradation and suggest that the role of the large amounts of IL-6 released in response to IL-1 in chronic arthritis is not directly protective with regard to proteoglycan metabolism.

Arthritis↗
PubMed1993

Radiation effects on the matrix synthesis in non-ossifying embryonic cartilage in vitro: a functional and morphological study.

Radiation effects on collagen and glycosaminoglycan (GAG) synthesis were studied in non-ossifying embryonic chick cartilage, in vitro. Fragments of the non-calcifying region of 15-day-old chick sterna were irradiated with 20, 50 and 100 Gy. The counterparts served as controls. Fragments were cultured up to 14 days. Pulse labeling experiments with 3H-proline and 3H-glucosamine started immediately after irradiation and on day 3, 6 and 13 post-irradiation. Fragments for morphological evaluation were fixed on day 1, 4, 7 and 14, simultaneously with the end of the labeling period. The same dose- and time-dependent inhibition was observed for the collagen and GAG synthesis. Radiation doses of 20, 50 and 100 Gy cause respectively and inhibition of about 20, 35 and 60% at the end of the culture period. Morphological alterations were observed after radiation doses of 50 and 100 Gy. Dose- and time-dependent necrosis all over the sternum was observed. A restricted number of cells showed an increased GAG synthesis after irradiation (50 Gy). This could explain the levelling off of the radiation effect on the incorporation of the labeled precursors towards the end of the culture period for radiation doses up to 50 Gy.

Animals↗
PubMed1993

Radiation damage to endothelial cells in vitro, as judged by the micronucleus assay.

The aim of our study was to optimize the cytokinesis-blocked (CB) micronucleus (MN) assay for the evaluation of radiation induced chromosomal damage in endothelial cells (EC) in vitro. After irradiation of confluent monolayers of rat and bovine aortic EC, with various doses of 250 kV X rays (0-3 Gy), the cells were trypsinized, resuspended in medium with cytochalasin B and then replated. After 3 days of growth they were again trypsinized and after fixing and staining of the cells, 1000 CB cells were scored for MN. The MN dose-response curves showed a rapid increase in the MN yield after low doses (< 0.25 Gy) of irradiation. This points to the high radiosensitivity of EC, with rat EC being more radiosensitive than bovine EC. A further slow increase (< 1 Gy) was observed after the initial fast increase. The occurrence of a fast and a slow component can be attributed to differences in radiosensitivity of EC in different stages of the cell cycle. For doses higher than 1 Gy, no further increase occurred due to severe damage at the spindle apparatus, as a result of which the division of many cells was inhibited.

Animals↗
PubMed1992

Study of dose-rate and split-dose effects on the in vitro micronucleus yield in human lymphocytes exposed to X-rays.

This paper reports the effects of changes in dose-rate and dose-fractionation on the micronucleus (MN) yield in human lymphocytes exposed to 250 kV X-rays. For the investigation of dose-rate effects whole blood samples of four healthy donors were irradiated with doses ranging from 1 to 4 Gy given at various dose-rates between 0.2 and 40 Gy/h. For the higher doses (3 and 4 Gy) a decline in the MN yield became apparent when the dose-rate was reduced below 1.6 Gy/h. This effect was enhanced systematically by a further lowering of the dose-rate. For lower doses (1 and 2 Gy) the reduction in the MN yield was less pronounced: only a small effect was observed for two donors when a dose of 2 Gy was administered at a dose-rate of 0.2 Gy/h. In the split-dose experiment a dose of 4 Gy was delivered either as a single exposure or in two fractions of 2 Gy, separated by time intervals ranging from 30 min to 10 h. A continuous decrease of the MN yield with increasing interfraction time is observed: after an initial fast decline a further slight reduction in the MN yield occurs. The observed dose-rate and split-dose effects on the MN yield can be attributed to repair of sublethal damage.

Chromosome Aberrations↗
PubMed1991

Nimodipine decreases resuscitability in a cardiopulmonary arrest model in the rat.

Although calcium has been implicated in ischemia-induced brain death or dysfunction, many animal studies do not show a beneficial effect of calcium-entry blockers given after resuscitation from a cardiopulmonary arrest (CPA). This may be due to the fact that treatment was started too late; we, therefore, evaluated the effect of the calcium-entry blocker nimodipine administered at the earliest feasible postischemic moment, i.e. at the start of the resuscitation attempts. In anesthetized Wistar rats, CPA was induced by an intra-cardiac injection of KCl, and maintained for 7 min by chest restriction. At the start of the resuscitation attempts, 50 rats were blindly and randomly assigned to intravenous treatment with either nimodipine (10 micrograms/kg over 2 min, followed by 1 micrograms/kg per min for 60 min; n = 25) or saline (n = 25). In the nimodipine group, significantly less rats could be resuscitated (11/25 versus 20/25) and the survival rate at the end of the 7 days evaluation period tended to be lower (5/25 versus 11/25). In the rats surviving after 7 days, there was no difference between both groups in incidence of seizures, neurological status and histological lesions in the hippocampus. It is concluded that nimodipine, in the dose tested and given during resuscitation in this rat model, has a detrimental effect on resuscitability and no beneficial effect on the neurological outcome in the surviving animals.

Animals↗
PubMed1991

The healing of cranial defects by demineralized osseous implants: a radiographic, histological and radioisotope-uptake study in rats.

The purpose of this study was to evaluate by different techniques the healing effect of demineralized allogeneic bone in parietal cranial defects in rats. 45Ca incorporation was measured for nine consecutive weeks in groups of control and implanted rats. Repeated 99mTc MDP uptake measurements were performed for nine weeks on the same group of rats. Each measurement was preceded by a cranial radiography. At the end of the study the animals were sacrificed for histologic evaluation. The results of the 45Ca incorporation, 99mTc MDP uptake measurements and the histologic pictures confirmed the osteogenic capacity of demineralized allogenic bone. From the results it can concluded that 99mTc MDP uptake measurements are a powerful tool in the evaluation of the healing process. It can be utilized sequentially in the same animal and gives detailed information about the progress of osteogenic activity over the entire implant area.

Animals↗
PubMed1990

Nimodipine has no beneficial effect on neurological outcome in a cardiopulmonary arrest model in the rat.

Brain damage after resuscitation from cardiac arrest is believed to be related to calcium influx in ischaemic neurons and to postischaemic calcium-dependent vasospasm. We therefore evaluated the potentially protective effects of the calcium-entry blocker nimodipine in a cardiopulmonary arrest model in the rat. Male Wistar rats were anaesthetized with ketamine (group I) or hexobarbital (group II) and subjected to a KCl-induced cardiac arrest during 7 min (group I) or 12 min (group II). Five minutes after resuscitation, the rats were treated intravenously in a randomized and blind fashion. Group I received either saline or 1 microgram.kg-1.min-1 or 5 micrograms.kg-1.min-1 of nimodipine and group II either saline or 1 microgram.kg-1.min-1 of nimodipine. Survival, occurrence of seizures and neurological status were assessed daily during 7 days after resuscitation. On day 7, the brains of the surviving rats were perfusion-fixed and a histopathological evaluation of the hippocampus was performed. Nimodipine, in the doses tested, had no beneficial influence on the 7 day survival rate, nor on the occurrence of seizures and the neurological and histopathological scores in the rats surviving after 7 days. With the highest dose of nimodipine, there was even a trend towards a decrease of the survival rate, probably related to the drug's hypotensive effect. Therefore, our data do not show a protective effect of nimodipine after cardiac arrest.

Animals↗