RESUMO
Peripheral blood samples from three donors of different ages were exposed to 300 kVp x-rays or 138 MeV protons (0.2, and 9 Gy dose). After 48 h incubation, CD4 and CD8 T-lymphocytes were labelled with specific monoclonal antibodies and cellular DNA was stained by propidium iodine. Radiation-induced apoptosis was followed by flow cytometry and the data were processed by LYSIS II software. The data analysis revealed an age-dependent sensitivity to radiation-induced apoptosis by 300 kVp x-rays and 138 MeV protons, for both CD4 and CD8 T-lymphocytes. Radiation-induced apoptosis was about 4 times greater in CD4 lymphocytes from the youngest donor than the oldest donor and was about 2 times greater in CD8 T-lymphocytes, both after x-ray and proton exposures. RBE values for CD4 T-lymphocytes ranged from 0.9 to 1.4 and for CD8-positive cells from 0.7 to 0.9. It is concluded that radiation-induced apoptosis of CD4 and CD8 T-lymphocytes, which is already exploited to predict patient response in conventional radiotherapy, may also be used to predict response in proton treatment planning.
Assuntos
Apoptose , Exposição Ambiental/efeitos adversos , Prótons/efeitos adversos , Linfócitos T/patologia , Linfócitos T/efeitos da radiação , Adulto , Fatores Etários , Linfócitos T CD4-Positivos/efeitos da radiação , Linfócitos T CD8-Positivos/efeitos da radiação , Relação Dose-Resposta à Radiação , Citometria de Fluxo , Humanos , Masculino , Pessoa de Meia-Idade , SoftwareRESUMO
5-bromodeoxyuridine (BUdR) provides in vitro measures of tumor cell proliferation. We used positron emission tomography to study tissue and plasma kinetics of [76Br]BUdR in tumor-bearing animals. In order to account for the slow washout of the major plasma metabolite, [76Br]bromide, a mathematical correction for the distribution volume of [76Br]bromide was applied. However, following correction specific tumor tracer retention was low or even zero and did not correlate with independent measures of proliferation. The kinetic characteristics of [76Br]BUdR make this tracer unsuitable for proliferation imaging.
Assuntos
Bromodesoxiuridina/farmacocinética , Neoplasias/metabolismo , Radiossensibilizantes/farmacocinética , Animais , Radioisótopos de Bromo/sangue , Bromodesoxiuridina/sangue , Gatos , Cães , Feminino , Citometria de Fluxo , Meia-Vida , Masculino , Matemática , Neoplasias/diagnóstico por imagem , Neoplasias/patologia , Distribuição Tecidual , Tomografia Computadorizada de EmissãoRESUMO
PURPOSE: To examine whether wortmannin enhances radiation-induced apoptosis in human lymphoid cells. METHODS AND MATERIALS: Different concentrations of wortmannin (0-40 micrOM) were added to TK6 lymphoblastoid cell and whole blood cell cultures 15 min before irradiation (0-6-Gy X-rays). After irradiation, medium was changed and cells were left to incubate for 48 h. In blood samples, CD4, CD8, and CD20 lymphocytes were labeled using FITC-conjugated antibodies. All cell types were fixed in a diethyleneglycol-formaldehyde solution. DNA was stained with propidium iodide. Apoptosis was quantified using flow cytometry and confirmed using fluorescence microscopy. RESULTS: Wortmannin significantly enhances radiation-induced apoptosis in lymphoblastoid cells. Compared to the controls, wortmannin treatment only slightly enhanced radiation-induced apoptosis in quiescent T-lymphocytes and had no effect in quiescent B-lymphocytes. CONCLUSION: Wortmannin enhances radiation-induced apoptosis in a cell-type dependent manner. If the selective effect of wortmannin on proliferative tissues also exists in nonlymphoid tissues, it should enhance the therapeutic ratio of treatments for tumors located in poorly proliferative healthy tissues. Further studies are needed to compare the effects of wortmannin in human tumor cells and various normal cells including proliferative and quiescent cells.
Assuntos
Androstadienos/farmacologia , Apoptose/efeitos dos fármacos , Linfócitos B/efeitos dos fármacos , Radiossensibilizantes/farmacologia , Linfócitos T/efeitos dos fármacos , Androstadienos/administração & dosagem , Linfócitos B/citologia , Linfócitos B/efeitos da radiação , Divisão Celular , Células Cultivadas/efeitos dos fármacos , Ensaios de Seleção de Medicamentos Antitumorais , Citometria de Fluxo , Humanos , Microscopia de Fluorescência , Radiossensibilizantes/administração & dosagem , Linfócitos T/citologia , Linfócitos T/efeitos da radiação , WortmaninaRESUMO
PURPOSE: To investigate sources of variation in radiosensitivity displayed by cancer patients and blood donors using the leukocyte apoptosis assay. METHODS AND MATERIALS: Probes were obtained from 105 healthy blood donors, 48 cancer patients displaying normal sensitivity to radiotherapy, 12 cancer patients displaying hypersensitivity to radiotherapy, 12 Ataxia telangiectasia blood donors, and 4 additional individuals with genetic diseases of potentially modified radiosensitivity; 2 neurofibromatosis (NF) donors, a Nijmegen breakage syndrome (NBS) donor, and an Immunodeficiency, Chromosome fragility, Facial anomaly syndrome (ICF) donor. Heparinized blood was diluted in medium, irradiated, and left to incubate for 48 h. CD4 and CD8 T-lymphocyte DNA was stained with propidium iodide and the cells were analyzed by flow cytometry. RESULTS: Radiation-induced apoptosis depended on age and cell type. Cohorts of hypersensitive cancer patients, NBS and AT donors displayed compromised apoptotic response. An asymmetric apoptotic response of T-lymphocytes was observed in an ICF donor and a cryptic hypersensitivity donor. Two NF donors displayed no abnormal sensitivity to radiotherapy but compromised apoptotic T-cell response to X-rays. CONCLUSION: Our studies reveal 4 physiologic sources of variation in radiation response-2 are genetic: cryptic hypersensitivity and hereditary disease, and 2 are epigenetic: cell type and donor age. They emphasize the important role of proteins involved in the recognition and repair of DNA double-strand breaks in determining the response of individuals to radiotherapy.
Assuntos
Apoptose/fisiologia , Linfócitos T CD4-Positivos/efeitos da radiação , Linfócitos T CD8-Positivos/efeitos da radiação , Neoplasias/radioterapia , Tolerância a Radiação/fisiologia , Adolescente , Adulto , Fatores Etários , Idoso , Idoso de 80 Anos ou mais , Ataxia Telangiectasia/genética , Doadores de Sangue , Criança , Pré-Escolar , Estudos de Coortes , Humanos , Pessoa de Meia-Idade , Neoplasias/genética , Neoplasias/patologia , Tolerância a Radiação/genéticaRESUMO
PURPOSE: Cells from ataxia-telangiectasia (A-T) patients are extremely sensitive to radiation but display decreased apoptosis, as measured during the first 3 days following radiation. To explain this apparent contradiction, we examined apoptosis in normal and A-T cells at late time points following radiation, under the assumption that radiation-induced apoptosis is delayed in the A-T cells. METHODS AND MATERIALS: Blood cells and lymphoblastoid cell lines from A-T patients, as well as healthy donors, were irradiated with X-rays. Apoptosis was measured at different time points (up to 7 and 30 days for lymphocytes and lymphoblastoid cells, respectively) using a flow cytometric method based on the reduction of intracellular DNA content (sub-G1 population). RESULTS: Compared to normal cells, CD4 and CD8 A-T lymphocytes displayed constantly reduced levels of radiation-induced apoptosis for up to 7 days after treatment. A-T lymphoblastoid cells, however, displayed a delayed and prolonged apoptosis. CONCLUSION: A-T lymphoblastoid cells show high levels of delayed radiation-induced apoptosis, which may contribute to the high cellular radiosensitivity displayed by the A-T phenotype. ATM (the gene mutated in A-T) plays different roles in the apoptotic response to ionizing radiation in quiescent lymphocytes and proliferative lymphoblastoid cells.
Assuntos
Apoptose/fisiologia , Ataxia Telangiectasia/radioterapia , Linfócitos T CD4-Positivos/efeitos da radiação , Linfócitos T CD8-Positivos/efeitos da radiação , Adolescente , Adulto , Idoso , Ataxia Telangiectasia/fisiopatologia , Linfócitos T CD4-Positivos/fisiologia , Linfócitos T CD8-Positivos/fisiologia , Linhagem Celular , Criança , Pré-Escolar , Citometria de Fluxo , Humanos , Pessoa de Meia-Idade , Tolerância a Radiação/fisiologia , Fatores de TempoRESUMO
The tumour suppressor gene p53 and the intracellular signalling molecule ceramide have both been shown to play crucial roles in the induction of apoptosis by ionising radiation. In this study we examined whether p53 and ceramide are involved in independent signal pathways, inducing different types of apoptosis. TK6 (p53wt/wt) and WTK1 (p53mut/mut) lymphoblastoid cells were treated with ionising radiation or N-acetyl-D-sphingosine (C2-ceramide). Flow cytometry and fluorescence microscopy studies were performed to characterise the time kinetics and morphological features of induced apoptosis. Ceramide- and radiation-induced apoptotic cells display characteristic differences in morphology and DNA staining and ceramide-induced apoptosis is expressed much faster than radiation-induced apoptosis. Radiation-induced apoptosis is p53-dependent and ceramide-induced apoptosis is p53-independent. The p53 pathway and the ceramide pathway are two independent signal pathways leading to distinct types of apoptosis. Since p53 is very often dysfunctional in tumour cells, modifying the ceramide pathway is a promising strategy to increase tumour sensitivity to radiation and other anticancer agents.
Assuntos
Apoptose , Genes p53/genética , Linfoma de Células B/genética , Mutação , Apoptose/efeitos da radiação , Ceramidas/farmacologia , Relação Dose-Resposta à Radiação , Citometria de Fluxo , Humanos , Linfoma de Células B/radioterapia , Microscopia de Fluorescência , Fenótipo , Espalhamento de Radiação , Transdução de Sinais , Fatores de Tempo , Células Tumorais CultivadasRESUMO
Iododeoxyuridine (IUdR) uptake and retention was imaged by positron emission tomography (PET) at 0-48 min and 24 h after administration of 28.0-64.4 MBq (0.76-1.74 mCi) of [124I]IUdR in 20 patients with brain tumors, including meningiomas and gliomas. The PET images were directly compared with gadolinium contrast-enhanced or T2-weighted magnetic resonance images. Estimates for IUdR-DNA incorporation in tumor tissue (Ki) required pharmacokinetic modeling and fitting of the 0-48 min dynamically acquired data to correct the 24-h image data for residual, nonincorporated radioactivity that did not clear from the tissue during the 24-h period after IUdR injection. Standard uptake values (SUVs) and tumor:brain activity ratios (Tm:Br) were also calculated from the 24-h image data. The Ki, SUV, and Tm/Br values were related to tumor type and grade, tumor labeling index, and survival after the PET scan. The plasma half-life of [124I]IUdR was short (2-3 min), and the arterial plasma input function was similar between patients (48 +/- 12 SUV*min). Plasma clearance of the major radiolabeled metabolite ([124I]iodide) varied somewhat between patients and was markedly prolonged in one patient with renal insufficiency. It was apparent from our analysis that a sizable fraction (15-93%) of residual nonincorporated radioactivity (largely [124I]iodide) remained in the tumors after the 24-h washout period, and this fraction varied between the different tumor groups. Because the SUV and Tm:Br ratio values reflect both IUdR-DNA incorporated and exchangeable nonincorporated radioactivity, any residual nonincorporated radioactivity will amplify their values and distort their significance and interpretation. This was particularly apparent in the meningioma and glioblastoma multiforme groups of tumors. Mean tumor Ki values ranged between 0.5 +/- 0.9 (meningiomas) and 3.9 +/- 2.3 microl/min/g (peak value for glioblastoma multiforme, GBM). Comparable SUV and Tm:Br values at 24 h ranged from 0.13 +/- 0.03 to 0.29 +/- 0.19 and from 2.0 +/- 0.6 to 6.1 +/- 1.5 for meningiomas and peak GBMs, respectively. Thus, the range of values was much greater for Ki (approximately 8-fold) compared with that for SUV (approximately 2.2-fold) and Tm:Br (approximately 3-fold). The expected relationships between Ki, SUV, and Tm:Br and other measures of tumor proliferation (tumor type and grade, labeling index, and patient survival) were observed. However, greater image specificity and significance of the SUV and Tm:Br values would be obtained by achieving greater washout and clearance of the exchangeable fraction of residual (background) radioactivity in the tumors, i.e., by increased hydration and urinary clearance and possibly by imaging later than 24 h after [124I]IUdR administration.
Assuntos
Neoplasias Encefálicas/diagnóstico por imagem , Idoxuridina , Radioisótopos do Iodo , Adulto , Idoso , Encéfalo/diagnóstico por imagem , Neoplasias Encefálicas/patologia , Divisão Celular , Feminino , Fluordesoxiglucose F18 , Humanos , Rim/metabolismo , Masculino , Pessoa de Meia-Idade , CintilografiaRESUMO
PURPOSE: A retrospective study of radiation-induced apoptosis in CD4 and CD8 T-lymphocytes, from 12 cancer patients who displayed enhanced toxicity to radiation therapy and 9 ataxia telangiectasia patients, was performed to test for altered response compared to healthy blood-donors and normal cancer patients. METHODS AND MATERIALS: Three milliliters of heparinized blood from each donor was sent via express post to the Paul Scherrer Institute (PSI) for subsequent examination. The blood was diluted 1:10 in RPMI medium, irradiated with 0-, 2-, or 9-Gy X-rays, and incubated for 48 h. CD4 and CD8 T-lymphocytes were then labeled using FITC-conjugated antibodies, erythrocytes were lysed, and the DNA stained with propidium iodide. Subsequently, cells were analyzed using a Becton Dickinson FACScan flow cytometer. Radiation-induced apoptosis was recognized in leukocytes as reduced DNA content attributed to apoptosis-associated changes in chromatin structure. Apoptosis was confirmed by light microscopy, electron microscopy, and by the use of commercially available apoptosis detection kits (in situ nick translation and Annexin V). Data from hypersensitive individuals were compared to a standard database of 105 healthy blood-donors, and a database of 48 cancer patient blood donors who displayed normal toxicity to radiation therapy. To integrate radiosensitivity results from CD4 and CD8 T-lymphocytes after 2 and 9 Gy, z-score analyses were performed. RESULTS: A cohort of 12 hypersensitive patients was evaluated; 8 showed enhanced early toxicity, 3 showed enhanced late toxicity, and 1 showed both. The cohort displayed less radiation-induced apoptosis (-1.8 sigma) than average age-matched donors. A cohort of 9 ataxia telangiectasia homozygotes displayed even less apoptosis (-3.6 sigma). CONCLUSION: The leukocyte apoptosis assay appears to be a useful predictor of individuals likely to display increased toxicity to radiation therapy; however, validation of this requires a prospective study.
Assuntos
Apoptose , Linfócitos T CD4-Positivos/efeitos da radiação , Linfócitos T CD8-Positivos/efeitos da radiação , Tolerância a Radiação , Adulto , Idoso , Idoso de 80 Anos ou mais , Apoptose/genética , Ataxia Telangiectasia/sangue , Ataxia Telangiectasia/genética , Linfócitos T CD4-Positivos/fisiologia , Linfócitos T CD8-Positivos/fisiologia , Estudos de Coortes , DNA/efeitos da radiação , Fragmentação do DNA , Homozigoto , Humanos , Pessoa de Meia-Idade , Estudos RetrospectivosRESUMO
Mismatch recognition in human cells is mediated primarily by a heterodimer of hMSH2 and hMSH6. Cells mutated in both alleles of the hMSH6 gene are deficient in the correction of base/base mispairs and insertion/deletion loops of one nucleotide and thus exhibit a strong mutator phenotype, evidenced by elevated mutation rates and microsatellite instability, as well as by tolerance to methylating agents. The decrease in replication fidelity associated with a loss of mismatch correction implies that with each division, these cells are likely to acquire new mutations throughout their genomes. Should such secondary mutations occur in genes linked to replication fidelity or involved in the maintenance of genomic stability, they might contribute to the observed mutator phenotype. The human colon tumour line HCT15 represents one such case. Although it carries inactivating mutations in both hMSH6 alleles, it has also been shown to contain a missense mutation in the coding sequence of the proofreading domain of the polymerase-delta gene. In an attempt to find out whether the phenotype of HCT15 cells was indeed brought about solely by the lack of hMSH6, we stably transfected them with a vector carrying the wild-type hMSH6 cDNA. Our results show that although the levels of transgenic hMSH6 were low, expression of the wild-type protein resulted in a substantial restoration of mismatch binding, mismatch repair capacity and the stability of mononucleotide repeats, as well as in the reduction of mutation rates. Although methylation tolerance of the hMSH6-expressing cells was not markedly affected, the G2 cell cycle checkpoint, absent in N-methyl-N'-nitro-N-nitrosoguanidine-treated control cells, was restored.
Assuntos
Pareamento Incorreto de Bases , Neoplasias do Colo/genética , Reparo do DNA , Proteínas de Ligação a DNA/genética , Sequência de Bases , Neoplasias do Colo/patologia , Primers do DNA , DNA Complementar , Fase G2 , Guanina/análogos & derivados , Guanina/farmacologia , Humanos , Metilnitronitrosoguanidina/farmacologia , Metilnitrosoureia/farmacologia , Repetições de Microssatélites , Mutação , Fenótipo , Transfecção , Células Tumorais CultivadasRESUMO
X-linked chronic granulomatous disease (X-CGD) is a primary immunodeficiency with complete absence or malfunction of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase in the phagocytic cells. Life-threatening infections especially with aspergillus are common despite optimal antimicrobial therapy. Bone marrow transplantation (BMT) is contraindicated during invasive aspergillosis in any disease setting. We report an 8-year-old patient with CGD who underwent HLA-genoidentical BMT during invasive multifocal aspergillus nidulans infection, nonresponsive to treatment with amphotericin-B and gamma-interferon. During the first 10 days post-BMT, the patient received granulocyte colony-stimulating factor (G-CSF)-mobilized, 25 Gy irradiated granulocytes from healthy volunteers plus G-CSF beginning on day 3 to prolong the viability of the transfused granulocytes. This was confirmed in vitro by apoptosis assays and in vivo by finding nitroblue tetrazolium (NBT)-positive granulocytes in peripheral blood 12 and 36 hours after the transfusions. Clinical and biological signs of infection began to disappear on day 7 post-BMT. Positron emission tomography with F18-fluorodeoxyglucose (FDG-PET) and computed tomography (CT) scans at 3 months post-BMT showed complete disappearance of infectious foci. At 2 years post-BMT, the patient is well with full immune reconstitution and no sign of aspergillus infection. Our results show that HLA-identical BMT may be successful during invasive, noncontrollable aspergillus infection, provided that supportive therapy is optimal.
Assuntos
Anfotericina B/uso terapêutico , Antifúngicos/uso terapêutico , Aspergilose/terapia , Aspergillus nidulans , Transplante de Medula Óssea , Fator Estimulador de Colônias de Granulócitos/uso terapêutico , Doença Granulomatosa Crônica/terapia , Transfusão de Leucócitos , Anfotericina B/administração & dosagem , Antifúngicos/administração & dosagem , Apoptose , Aspergilose/diagnóstico por imagem , Aspergilose/tratamento farmacológico , Aspergilose/prevenção & controle , Criança , Terapia Combinada , Portadores de Fármacos , Sobrevivência de Enxerto/efeitos dos fármacos , Granulócitos/fisiologia , Doença Granulomatosa Crônica/complicações , Humanos , Itraconazol/uso terapêutico , Contagem de Leucócitos , Lipossomos , Pneumopatias Fúngicas/tratamento farmacológico , Masculino , Tomografia Computadorizada de Emissão , Resultado do TratamentoRESUMO
Photodynamic therapy (PDT) uses laser light to activate a photosensitizer that has been absorbed preferentially by cancer cells after systemic administration. A phototoxic reaction ensues resulting in cell death and tissue necrosis. Some cells, however, may survive PDT. This study was performed to determine if surviving human breast cancer cells (MCF-7) can become resistant to PDT, chemotherapy or radiotherapy. The MCF-7 cells were cultured under standard conditions prior to being exposed to the photosensitizer, 5,10,15,20-meta-tetra(hydroxyphenyl)chlorin (m-THPC), for 24 h and then irradiated with laser light (652 nm). Surviving cells were allowed to regrow by allowing a 2 week interval between each additional PDT. After the third and final treatment, colony formation assays were used to evaluate the sensitivity of cultured cells to ionizing radiation and PDT and the ATP cell viability assay tested in vitro chemosensitivity. Flow cytometry was used to analyze the cell cycle. No alterations in the cell cycle were observed after three cycles of PDT with m-THPC. Similar responses to chemotherapy and ionizing radiation were seen in control and treatment groups. The m-THPC-sensitized PDT did not induce resistance to subsequent cycles of PDT, chemo- or radiotherapy. Photodynamic therapy with m-THPC may represent a novel adjunctive treatment of breast cancer that may be combined with surgery, chemotherapy or ionizing radiation.
Assuntos
Antineoplásicos/toxicidade , Sobrevivência Celular/efeitos dos fármacos , Resistencia a Medicamentos Antineoplásicos , Mesoporfirinas/toxicidade , Fotoquimioterapia , Fármacos Fotossensibilizantes/toxicidade , Tolerância a Radiação , Antineoplásicos/sangue , Antineoplásicos/uso terapêutico , Neoplasias da Mama , Sobrevivência Celular/efeitos da radiação , Resistencia a Medicamentos Antineoplásicos/efeitos da radiação , Feminino , Humanos , Necrose , Paclitaxel/toxicidade , Radioterapia , Células Tumorais CultivadasRESUMO
Spontaneous tumours in dogs and cats are an excellent model for clinical human research, such as in developing proton conformation radiotherapy for humans. The kinetics of tumour cells can be used effectively to predict prognosis and response to therapy in patients with tumours. Knowledge of the kinetic parameters in these tumours is therefore important. In the present study the kinetic parameters evaluated included the labelling index (LI), relative movement (RM), mitotic index (MI), and potential doubling time (Tpot). These parameters were determined using in vivo labelling with bromodeoxyuridine, flow cytometry and histological preparation. Samples were obtained and evaluated from 72 dogs and 20 cats, presenting as patients in our clinic. Within the groups of epithelial and mesenchymal tumours from dogs and cats, the kinetic parameters LI, RM and MI were compared with Tpot. Significant correlations were observed for the comparison Tpot and LI. No correlation was found between Tpot and RM.
Assuntos
Doenças do Gato/patologia , Doenças do Cão/patologia , Neoplasias/veterinária , Animais , Biópsia/veterinária , Bromodesoxiuridina/química , Doenças do Gato/terapia , Gatos , Ciclo Celular/fisiologia , DNA de Neoplasias/química , Doenças do Cão/terapia , Cães , Feminino , Citometria de Fluxo/veterinária , Cinética , Masculino , Índice Mitótico , Neoplasias/patologia , Neoplasias/terapia , Prognóstico , Análise de Regressão , Fatores de TempoRESUMO
Three forms of radiation response were investigated to evaluate the hypothesis that cellular radiation response is the result of active molecular signaling and not simply a passive physicochemical process. The decision whether or not a cell should respond to radiation-induced damage either by induction of rescue systems, e.g. mobilization of repair proteins, or induction of suicide mechanisms, e.g. programmed cell death, appears to be the expression of intricate cellular biochemistry. A cell must recognize damage in its genetic material and then activate the appropriate responses. Cell type is important; the response of a fibroblast to radiation damage is both quantitatively and qualitatively different from that of a lymphocyte. The programmed component of radiation response is significant in radiation oncology and predicted to create unique opportunities for enhanced treatment success.
Assuntos
Apoptose/efeitos da radiação , Animais , Cafeína/farmacologia , Ciclo Celular/efeitos da radiação , Células Cultivadas , Cricetinae , Cricetulus , DNA/metabolismo , DNA/efeitos da radiação , Feminino , Humanos , Leucócitos/efeitos da radiação , Masculino , Camundongos , Radiossensibilizantes/farmacologia , Estaurosporina/farmacologiaRESUMO
We investigated various phenotypic characteristics of radiation-induced morphologically transformed C3H 10T1/2 mouse fibroblasts. The cells were treated with 8 Gy x-rays, and type II/III foci were isolated. Cell lines were developed from these foci, and subsequently clones were established from these focal lines. The clones were examined for DNA content, radiosensitivity and inducible cell cycle arrests. Besides the morphological changes associated with the transformed state, the major difference between the isolated focal lines or derived clones and the parental C3H 10T1/2 line was one of ploidy. The transformed cells often displayed aneuploid and multiple polyploid populations. No change in the radiosensitivity of the transformed cells was observed. Furthermore, the two major radiation- and staurosporine-induced G1 and G2 cell cycle arrests observed in the parental cell line were also observed in the morphological transformants, suggesting that checkpoint function was normal.
Assuntos
Ciclo Celular/efeitos da radiação , Aberrações Cromossômicas , DNA/efeitos da radiação , Tolerância a Radiação , Aneuploidia , Animais , Linhagem Celular , Células Clonais , Relação Dose-Resposta à Radiação , Fibroblastos/citologia , Fibroblastos/efeitos da radiação , Camundongos , Ploidias , Poliploidia , Raios XRESUMO
In the inhomogeneous radiation field surrounding small beta-particle sources, nonlethally and heavily damaged cells are in proximity, permitting interaction via extracellular signals. This situation is typical of hot particles such as those released during the accident at Chernobyl. Beta-particle-emitting yttrium-90 wires (average energy 934 keV) were employed to investigate radiation-induced neoplastic transformation under these conditions. Integrated 24-h doses ranging from 0 to 750 Gy across the exposure field were applied. At equal levels of toxicity a 10-fold enhancement of neoplastic transformation frequency in C3H 10T1/2 cells was observed in the presence of heavily damaged cells. Homogeneous fields of low-dose-rate beta-particle radiation produced neoplastic transformation frequencies typical for comparable photon exposures reported in the literature.
Assuntos
Partículas beta , Transformação Celular Neoplásica/efeitos da radiação , Animais , Células Cultivadas , Dano ao DNA , Feminino , Camundongos , Camundongos Endogâmicos C3HRESUMO
An assay for biological dosimetry based on the induction of apoptosis in human T-lymphocytes is described. Radiation-induced apoptosis was assessed by flow cytometric identification of cells displaying apoptosis-associated DNA condensation. CD4 and CD8 T-lymphocytes were analysed. They were recognized on the basis of their cell-surface antigens. Four parameters were measured for both cell types: cell size, granularity, antigen immunofluorescence and DNA content. Apoptosis was quantified as the fraction of CD4-, or CD8-positive cells with a characteristic reduction of cell size and DNA content. At doses below 1 Gy, levels of radiation-induced apoptosis increased for up to 5 days after irradiation. Optimal dose discrimination was observed 4 days after irradiation, at which time the dose-response curves were linear, with a slope of 8% +/- 0.5% per 0.1 Gy. In controlled, dose-response experiments the lowest dose level at which the radiation-induced apoptosis frequency was still significantly above control was 0.05 Gy. After 5 days post-irradiation incubation, intra- and interdonor variations were measured and found to be similar; thus, apoptotic levels depend more on the dose than on the donor. The results demonstrate the potential of this assay as a biological dosimeter.
Assuntos
Apoptose/efeitos da radiação , Linfócitos T CD4-Positivos/efeitos da radiação , Linfócitos T CD8-Positivos/efeitos da radiação , Radiometria , Linfócitos T CD4-Positivos/patologia , Linfócitos T CD8-Positivos/patologia , Humanos , Reprodutibilidade dos TestesRESUMO
Telomeres shield the ends of chromosomes from degradation and end-to-end fusions. They shorten at each cell division and when they reach a critically short length, cells arrest in the G1 phase of the cell cycle and undergo senescence. This effectively limits the proliferative potential of cells. Senescence functions as a tumour suppressor mechanism and appears to contribute to the process of ageing. If senescence is circumvented by tumour viruses, proliferation is re-initiated until cells enter crisis. Activation of telomerase prevents telomere attrition and cells become immortal. Cellular response to ionizing radiation involves induction of cell cycle checkpoint arrests and programmed cell death. Because radiation produces double strand breaks in DNA, which cause telomere-less chromosome ends, radiation response appears to be the result of inappropriate induction of cellular senescence mechanisms.