Radiation induced cell loss in rat submandibular gland and its relation to gland function

Purpose : To understand early and late radiation-induced loss of function of the submandibular gland, changes in cell number were documented and correlated with data on gland function. Modulation of the radiation effect by sialogogues was used to investigate possible mechanisms of action. Materials and methods : Rats were irradiated with a single dose of 15 Gy of X-rays after pre-treatment with either saline, the muscarinic receptor agonists methacholine or pilocarpine, the adrenergic receptor agonist phenylephrine or methacholine plus phenylephrine. Before and 1-240 days after irradiation, submandibular saliva flow rate was measured. At the same time points and from comparable animals submandibular glands were carefully extirpated, weighed and prepared for light microscopic examination. Results : Soon after irradiation (<30 days) no significant loss of cells was observed, whereas the gland function was severely compromized. Sialogogue pre-treatment attenuated the radiation-induced loss of gland function. At later intervals a considerable loss of acinar cells and to a lesser extent loss of granular convoluted tubule cells were observed. Gland function subsequently declined slowly. Pre-treatment with sialogogues gave transient protection against cell loss and loss of gland function. Conclusions : The lack of cell loss observed soon after irradiation indicates that the observed reduction in gland function was caused by a compromised functioning of the acini. The later loss of cells is probably due to death of cells that normally proliferate, leading to a further reduced secretory capacity. Protection of gland morphology and function by sialogogues at later times must therefore involve resistance of progenitor cells to radiation-induced cell death.     

Evidence for early and persistent impairment of salivary gland excretion after irradiation of head and neck tumours

Salivary gland scintigraphy with technetium-99m pertechnetate was used to follow changes in the excretion and uptake function of the major salivary glands until 1 year after irradiation. Twenty-five patients who received radiotherapy for head and neck tumours were included in the study. Seventy-nine salivary glands (39 parotid and 40 submandibular) were evaluated in relation to the average received radiation dose. Salivary gland scintigraphy was performed before and 1, 6 and 12 months after radiotherapy. For each gland the excretion response to carbachol, evaluated by calculation of the salivary excretion fraction (SEF), the cumulative gland uptake (CGU) and the absolute excreted activity (AEA) at various intervals after radiotherapy were compared with the baseline values. The excretion response decreased in 20 of 25 patients at 1 month after radiotherapy. One month after radiotherapy both SEF and AEA decreased significantly in relation to the radiation dose. These decreases in excretion parameters persisted during the follow-up period. Parotid excretion was affected significantly more than submandibular excretion. CGU values did not change significantly until 6 months after radiotherapy, but at 12 months a significant decrease related to radiation dose was observed. Xerostomia was assessed during radiotherapy and on the days of the scintigraphic tests. The incidence of xerostomia did not correspond to the effects observed in the scintigraphy studies. It is concluded that radiotherapy induces early and persistent impairment of salivary gland excretion, related to the radiation dose. This impairment is stronger in parotid glands than in submandibular glands.     

Influence of dose-rate, post-irradiation incubation time and growth factors on interphase cell death by apoptosis and clonogenic survival of human peripheral lymphocytes.

PURPOSE: To investigate the effects of dose-rate, post-irradiation incubation time and growth factors on radiation-induced interphase cell death by apoptosis and reproductive cell death in human peripheral lymphocytes. MATERIALS AND METHODS: Lymphocytes in G0-phase were exposed in vitro to 1-3Gy 137Cs gamma-radiation at a high- (HDR, 45Gy/h) or a low dose-rate (LDR, 0.024Gy/h). HDR exposures were performed either on day 1 (HDR1) simultaneously with the start of the 3 Gy LDR exposure, or on day 6 (HDR6) when the LDR exposures ended. Apoptosis was studied at different times after irradiation by measuring (1) cellular membrane integrity, (2) morphological changes and (3) cell size reduction. Clonogenic survival was analysed for cells plated directly after irradiation (LDR, HDR6, HDR1 day 1) or after 5 days post-irradiation incubation (HDR1 day 6). RESULTS: A significant decrease in reproductive cell death was observed after 3 Gy LDR exposure as compared with the HDR1 exposure for cells plated day 6. For the lower doses applied, the dose-rate effect could not be statistically verified. A decrease in apoptosis for all three doses applied (i.e. 1, 2 and 3Gy) was observed when the LDR exposures were compared with the HDRI analysed day 6, although not of statistical significance. Radiation-induced apoptosis was efficiently counteracted by growth factors up to 24-48 h after 3 Gy HDR exposure. The prevention of radiation-induced cell death by growth factors was dependent on dose and post-irradiation time in G0. When the growth factors were added after a prolonged post-irradiation incubation in G0 (HDR 1 cells plated day 6), a significant increase in reproductive cell death was found (3 Gy) as compared with HDR protocols where the growth factors were added directly after irradiation (HDR 1 plated day 1 and HDR6). CONCLUSIONS: A dose-rate effect on radiation-induced apoptosis was indicated but not statistically verified. A significant dose-rate effect on reproductive cell death was observed. This dose-rate effect was, however, inverted when growth factors were added directly after the HDR irradiations.     

Influence of dose-rate,post-irradiation incubation time and growth factors on interphase cell death by apoptosis and clonogenic survival of human peripheral lymphocytes

Purpose: To investigate the effects of dose-rate, post-irradiation incubation time and growth factors on radiation-induced interphase cell death by apoptosis and reproductive cell death in human peripheral lymphocytes. Materials and methods : Lymphocytes in G0-phase were exposed in vitro to 1-3Gy 137Cs gamma-radiation at a high- (HDR, 45Gy/h) or a low dose-rate (LDR, 0.024Gy/h). HDR exposures were performed either on day 1 (HDR1) simultaneously with the start of the 3Gy LDR exposure, or on day 6 (HDR6) when the LDR exposures ended. Apoptosis was studied at different times after irradiation by measuring (1) cellular membrane integrity, (2) morphological changes and (3) cell size reduction. Clonogenic survival was analysed for cells plated directly after irradiation (LDR, HDR6, HDR1 day 1) or after 5 days post-irradiation incubation (HDR1 day 6). Results: A significant decrease in reproductive cell death was observed after 3Gy LDR exposure as compared with the HDR1 exposure for cells plated day 6. For the lower doses applied, the dose-rate effect could not be statistically verified. A decrease in apoptosis for all three doses applied (i.e. 1, 2 and 3Gy) was observed when the LDR exposures were compared with the HDR1 analysed day 6, although not of statistical significance. Radiation-induced apoptosis was e fficiently counteracted by growth factors up to 24-48h after 3Gy HDR exposure. The prevention of radiation-induced cell death by growth factors was dependent on dose and post-irradiation time in G0. When the growth factors were added after a prolonged post-irradiation incubation in G0 (HDR1 cells plated day 6), a significant increase in reproductive cell death was found (3Gy) as compared with HDR protocols where the growth factors were added directly after irradiation (HDR1 plated day 1 and HDR6). Conclusions: A dose-rate effect on radiation-induced apoptosis was indicated but not statistically verified. A significant dose-rate effect on reproductive cell death was observed. This dose-rate effect was, however, inverted when growth factors were added directly after the HDR irradiations.     

Histamine prevents functional and morphological alterations of submandibular glands induced by ionising radiation

Purpose:?Xerostomia is a common, disturbing side-effect among patients treated with radiotherapy for head-and-neck cancer. The aim of the present work was to investigate whether histamine could prevent salivary gland dysfunction and histological alterations exerted by ionising radiation.

Materials and methods:?Forty-eight rats were divided into four groups. Histamine and histamine-5 Gy groups received a daily subcutaneous histamine injection (0.1 mg/kg) starting 24?h before irradiation. Histamine-5 Gy and untreated-5 Gy groups were irradiated with a single dose of whole-body Cesium-137 irradiation. Control and untreated-5 Gy groups were given daily saline injections. Three days post irradiation metacholine-induced salivary secretion was measured or animals were sacrificed and submandibular gland (SMG) removed, stained and histological characteristics were evaluated. Proliferation and apoptosis markers were studied by immunohistochemistry.

Results:?Radiation decreased salivary secretion by 40% in comparison to untreated rats, which was associated with loss of SMG mass, alteration of epithelial architecture, partial loss of secretor granular material, diminished proliferation and a remarkable apoptotic response. In contrast, histamine completely reversed the reduced salivation induced by radiation, conserved glandular mass with normal appearance and preserved the structural organisation of secretor granules. Radiation-induced toxicity is prevented by histamine essentially by suppressing apoptosis of ductal and acinar cells, reducing the number of apoptotic cells per field (19.0?±?3.8 vs. 106.0?±?12.0 in untreated animals, P?<?0.001), and also by preventing the radiation-induced decrease in cell proliferation.

Conclusions:?Histamine prevents morphological and functional radiation-induced damage on SMG, representing a potential radioprotector for treatment of patients undergoing radiotherapy for head and neck malignancies.     

Delayed cytotoxic and genotoxic effects in a human cell line following X-irradiation

Background: In order to clarify the relationship between delayed reproductive death and radiation-induced genomic instability, the colony-forming efficiency of surviving, irradiated human squamous carcinoma cells and centromere positive as well as centromere negative micronuclei in surviving progeny were examined. Materials and methods: Colony-forming ability and micronucleus (MN) frequency in binucleated cells 24h after the addition of cytochalasin B during 2 weeks of post-irradiation growth were determined in a squamous cell carcinoma cell line (SCL-II) of human origin. In addition, centromeres in micronuclei were detected using FISH. Results: In the human epithelial cell line used for these experiments, delayed reproductive death was pronounced and persisted for at least 2 weeks after irradiation. Although there is evidence for an increased rate of centromere positive micronuclei, but not of centromere negative micronuclei, arising during the first week of post-irradiation proliferation, this decreases later while the rate of delayed reproductive death remains elevated. Conclusion: In the studied cell line, the observed delayed reproductive death is not closely related to the investigated criteria of radiation-induced genomic instability. This casts doubt on the common assumption that delayed reproductive death is a direct manifestation of radiation-induced genomic instability.     

Delayed cytotoxic and genotoxic effects in a human cell line following X-irradiation.

BACKGROUND: In order to clarify the relationship between delayed reproductive death and radiation-induced genomic instability, the colony-forming efficiency of surviving, irradiated human squamous carcinoma cells and centromere positive as well as centromere negative micronuclei in surviving progeny were examined. MATERIALS AND METHODS: Colony-forming ability and micronucleus (MN) frequency in binucleated cells 24 h after the addition of cytochalasin B during 2 weeks of post-irradiation growth were determined in a squamous cell carcinoma cell line (SCL-II) of human origin. In addition, centromeres in micronuclei were detected using FISH. RESULTS: In the human epithelial cell line used for these experiments, delayed reproductive death was pronounced and persisted for at least 2 weeks after irradiation. Although there is evidence for an increased rate of centromere positive micronuclei, but not of centromere negative micronuclei, arising during the first week of post-irradiation proliferation, this decreases later while the rate of delayed reproductive death remains elevated. CONCLUSION: In the studied cell line, the observed delayed reproductive death is not closely related to the investigated criteria of radiation-induced genomic instability. This casts doubt on the common assumption that delayed reproductive death is a direct manifestation of radiation-induced genomic instability.     

Salivary gland scintigraphy: the use of semiquantitative analysis for uptake and clearance

OBJECTIVE: Quantitative analysis of (99m)Tc-pertechnetate salivary gland scintigraphy has been used in the evaluation of salivary gland function, but so far no one method can be considered optimal for this task. In this study, a semiquantitative method providing 2 functional parameters for objective assessment of salivary gland function by scintillation camera imaging was tested. METHODS: Twenty-one patients referred for (99m)Tc-pertechnetate thyroid scanning were studied. Two patients with salivary complaints were also included. Dynamic imaging of the anterior head using a scintillation camera was started after a bolus intravenous injection of 185 MBq (5 mCi) (99m)Tc-pertechnetate at 1 frame per 30 s for 30 min. At 15 min after injection, diluted lemon juice was administered orally. Analysis of the dynamic study included time-activity curves of 4 salivary glands (right and left parotid and right and left submandibular). Two parameters of function were defined: uptake rate, taken as the value of the initial slope of the time-activity curve, and washout fraction, which was the relative mobilizable radioactivity from each salivary gland after ingestion of the sialogogue. A parametric image of the washout fraction was also generated. RESULTS: The images showed gradual uptake in the parotid and submandibular glands. Washout was noted immediately after ingestion of the lemon juice. The pattern of the time-activity curve in all glands showed an early fast-rising part followed by a slow-rising component to nearly a plateau within 6-10 min after injection. The mean value of the uptake rate parameter was 0.10 +/- 0.09 cps/s. There was no significant difference between the parotid and submandibular glands or the right and left sides. Uptake in the parotid gland was 1.5-2 times that in the submandibular gland. The washout fraction was 1.40 +/- 1.60 for the parotid glands and 0.77 +/- 0.41 for the submandibular glands (P = 0.005). CONCLUSION: The quantitative analysis method including the uptake rate and the washout fraction parameters would enable objective assessment of salivary function and provide a reproducible means for follow-up of functional impairment in certain diseases.     

Effects of cycloheximide and actinomycin D on radiation-induced apoptotic cell death in the developing mouse cerebellum.

Effects of cycloheximide and actinomycin D on radiation-induced cell death in the external granular layer (EGL) of the cerebellum were studied in vivo. Newborn mice were exposed to 0.24 Gy gamma-radiation, and dying cells which exhibited pyknosis of nuclei in the EGL were examined at various post-irradiation periods. The number of pyknotic cells began to increase 3 h after irradiation, reached a peak incidence at 6 h, and then gradually fell to the sham-irradiated level by 18 h. When pups were injected with cycloheximide 1 h after irradiation, cell death was suppressed for 6 h, but a peak mortality as high as in the case of radiation alone was attained at 15 h after irradiation. When pups were treated with cycloheximide twice, at 1 and 6 h after irradiation, cell death did not occur for 15 h, but then the incidence rose to a level similar to that after irradiation alone. These findings showed that radiation-induced cell death in the EGL is suppressed by cycloheximide until the chemical is metabolized. Hence, death is by apoptosis which is known to require macromolecular synthesis, and the 'signal' for apoptosis in the cell persists for at least 15 h after irradiation. On the other hand, actinomycin D injected immediately before or after irradiation did not affect the initiation of cell death; actinomycin D alone induced cell death.     

Semi-quantitative assessment of salivary gland function in patients with differentiated thyroid carcinoma after radioiodine-131 treatment

Sialadenitis and xerostomia are well-known side effects of high-dose radioactive iodine ((131)Iota) treatment in patients with differentiated thyroid carcinoma (DTC). This study was undertaken to determine salivary gland function semi-quantitatively in patients with DTC given (131)I for the treatment of the thyroid remnant and/or metastases. Thirty-six patients, 11 males and 25 females, mean age 53.5 years, range 22-73 years, were studied. Scintigraphy of the salivary glands was performed with (99m)Tc-pertechnetate and the salivary excretion fraction (SEF) of the parotid and the submandibular glands was calculated as a measure of their function. Measurements were performed before (131)I treatment as a baseline study, and three weeks and three months later. The patients were clinically evaluated by a standardized subjective questionnaire. Results were as follows: Mean SEF at three weeks and three months after (131)I treatment was reduced as compared to baseline measurements. The total mean baseline measurements, those of three weeks and those of three months later were: 54.9%, 47.2% and 46% respectively; P<0.05 for both measurements (Table 1). The SEF decrease of the parotid glands was greater than that of the submandibular glands (P<0.05 as compared for both salivary glands before and three weeks and three months after (131)I treatment). This confirmed the higher radiosensitivity of the parotid glands as compared to the submandibular glands. In 12 patients (33%) there was no significant decrease of SEF in the salivary glands after (131)I treatment. The relation between the decrease of SEF after three weeks and after three months and the dose of (131)I administered, was for the right and left submandibular glands significant (P=0.016 and P=0.002), while for the parotid glands it was insignificant (P=0.22 and P=0.27 respectively) (Table 4). Reduction of SEF in the parotid glands three months after (131)I treatment was greater than after three weeks. This difference, as regards the submandibular glands, was not significant. Our results show that high dose (131)I treatment in DTC patients induces a significant effect on salivary gland function, which is dose-related in the submandibular glands, and more prominent in the parotid glands.     

Radiation effects on submandibular gland of the rat. Stereological and ultrastructural study

The chronic effect of 2000 rd (20 Gy) of X-rays locally applied to the submandibular gland of Wistar young-adult male rats, was studied by stereology, and light and electron microscopic observations. They demonstrated that degenerative changes were observed during the first months after irradiation. Atrophic processes developed from 6 months onwards. In the acinar compartment, atrophy was progressive from the first months post-irradiation up to 9 months post-irradiation. Ductal cell membranes and mitochondrial damage were clearly detected at ultrastructural level. Nuclear fragmentation and secretory granules alterations were also frequently seen in the acinar compartment.     

小鼠下颌下腺细胞培养及其生物学特性研究

目的：建立和完善小鼠下颌下腺细胞培养方法,并进行生物学特性研究,为涎腺疾病治疗奠定理论基础,并为组织工程涎腺再生提供技术支持。方法无菌环境下切取小鼠下颌下腺,胶原酶消化,接种于含有胎牛血清、表皮生长因子、胰岛素、氢化可的松及转铁蛋白的低糖 DMEM 培养基中培养,倒置相差显微镜及 HE 染色进行形态学观察,透射电镜观察特异性酶原颗粒,生长曲线评估细胞生长特性,特异性α-淀粉酶免疫荧光鉴定细胞来源。结果下颌下腺原代细胞为圆形或多边形,呈铺路石样排列,其生长缓慢,12 d 左右汇合至80％。传代细胞与原代形态相同。HE 染色显示胞核胞浆对比明显。生长曲线大致呈“S”型,与其他细胞增殖特点相似。特异性α-淀粉酶免疫荧光染色阳性,表明细胞为具有功能的涎腺细胞。结论成功地建立了小鼠下颌下腺细胞原代及传代培养,将为涎腺疾病的治疗和涎腺再生提供实验基础。     

Effects of Cycloheximide and Actinomycin D on Radiation-induced Apoptotic Cell Death in the Developing Mouse Cerebellum

Effects of cycloheximide and actinomycin D on radiation-induced cell death in the external granular layer (EGL) of the cerebellum were studied in vivo. Newborn mice were exposed to 0·24 Gy γ-radiation, and dying cells which exhibited pyknosis of nuclei in the EGL were examined at various post-irradiation periods. The number of pyknotic cells began to increase 3 h after irradiation, reached a peak incidence at 6 h, and then gradually fell to the sham-irradiated level by 18 h. When pups were injected with cycloheximide 1 h after irradiation, cell death was suppressed for 6 h, but a peak mortality as high as in the case of radiation alone was attained at 15 h after irradiation. When pups were treated with cycloheximide twice, at 1 and 6 h after irradiation, cell death did not occur for 15 h, but then the incidence rose to a level similar to that after irradiation alone. These findings showed that radiation-induced cell death in the EGL is suppressed by cycloheximide until the chemical is metabolized. Hence, death is by apoptosis which is known to require macromolecular synthesis, and the ‘signal’ for apoptosis in the cell persists for at least 15 h after irradiation. On the other hand, actinomycin D injected immediately before or after irradiation did not affect the initiation of cell death; actinomycin D alone induced cell death.     

高+Gx过载对猴颌下腺组织结构与c-jun基因表达的影响

目的观察高 Gx过载作用对猴颌下腺组织结构和c-jun基因表达的影响。方法9只雄性恒河猴,随机分为4组。对照组与实验1、2、3组受 Gx及其作用时间分别为1Gx/300s、 15Gx/200s、 18Gx/165s、 21Gx/140s。使用专用动物离心机,加载后的动物即刻处死、取材、制片、染色。用免疫组织化学方法观察猴颌下腺组织c-jun表达。结果组织病理学观察:对照组和实验组猴颌下腺组织均未见明显病理学改变。免疫组化观察:对照组颌下腺导管上皮细胞c-jun为弱阳性表达;实验组c-jun表达明显增强,阳性产物呈棕黄色颗粒状弥漫分布于颌下腺导管上皮细胞核,作用强度不同的 Gx组之间无明显差别。结论高 Gx环境中可引起猴颌下腺导管上皮细胞c-jun基因表达增强。     

Nd：YAG激光辐射对大白鼠颌下腺及颌下淋巴结的影响

作者研究Nd:YAG激光辐照口腔颌面部软组织,以大白鼠颌下腺及颌下淋巴结为实验对象。激光输出功率17～18瓦,观察组织反应及超微结构变化,结果表现为碳化、汽化、组织凝固坏死,空泡性变及组织液化。颌下腺组织及淋巴结经激光照射后,不仅局部发生变化,在整个腺体内均有不同程度的反应。产生这种变化的原因,有待进一步研究。电镜下观察Nd:YAG激光照射引起颌下腺腺泡的早期损伤主要为细胞膜结构的破坏,如核膜、线粒体膜等。颌下腺及颌下淋巴结对Nd:YAG激光的早期反应不完全相同,颌下腺主要为空泡性变,细胞变性;淋巴结内淋巴细胞主要为细胞液化及淋巴管渗出。     

F-18 FDG PET/CT imaging of submandibular gland oncocytoma

F-18 FDG PET/CT is used to evaluate head and neck malignancies, including salivary gland tumors. We describe the FDG PET/CT features of a submandibular gland oncocytoma. An 85-year-old patient with small cell cancer of the lung and a history of squamous cell carcinoma of the lower lip was evaluated with FDG PET/CT. There was an intensely hypermetabolic left submandibular gland lesion that was suspected for a metastasis. Ultrasound-guided fine needle aspirate of the lesion proved to be a submandibular gland oncocytoma.     

99TcmO4-动态显像在颌下腺移位术中的临床应用

目的探讨颌下腺动态显像在鼻咽癌颌下腺移位术中的临床价值。方法70例鼻咽癌初诊患者，分为试验组36例，非试验组（对照组）34例。对照组直接行常规放疗；试验组于术前1天行颌下腺^99Tc^mO4^-动态显像，根据结果选取功能较好一侧颌下腺于第2天行颌下腺移位术，术后复查颌下腺功能及择期行常规放疗。放疗后皆行颌下腺^99Tc^mO4^-动态显像及记录患者口腔干燥症状的程度，结果采用非参数秩和检验进行统计分析。结果移位侧颌下腺功能于术后、放疗后损伤明显减轻，与非移位侧颌下腺差异有显著性（P〈0．01）；试验组中度以上口腔干燥症率为13．9％，对照组为76．5％，差异有显著性（P〈0．01）。结论^99Tc^mO4^-颌下腺动态显像可准确、灵敏地评估颌下腺功能。     

肿节风在大鼠腮腺放射性损伤中的防护作用研究

目的研究经X射线照射后大鼠腮腺组织的炎症反应和细胞凋亡情况,探讨肿节风对放射性腮腺损伤的防护作用及可能的机制。方法将120只雄性大鼠简单随机分成5组(每组24只):对照组、单纯照射组、低(6.7 g·kg-1·d-1)、中(13.4 g·kg-1·d-1)、高(26.8 g·kg-1·d-1)剂量肿节风加照射组,给予单次15 Gy X射线照射大鼠腮腺组织,各组分别在照射后第10、40、70天将大鼠经2%戊巴比妥钠(0.16 ml/100 g)腹腔麻醉后经腹主动脉取血,检测血清中活性氧簇(ROS)含量,同时取腮腺组织用苏木精-伊红(HE)染色法和透射电镜观察其病理学改变和超微结构变化,应用免疫组织化学法检测腮腺组织中肿瘤坏死因子α(TNF-α)的表达水平,采用TUNEL法检测腮腺细胞的凋亡情况。结果在同一时间点,单纯照射组中ROS的含量和TNF-α的表达较对照组明显升高(t=-24.723、-35.013、-19.515,P<0.05;t=-13.563、43.519、-15.249,P<0.05),而各药物组的上述观察指标介于二者之间,其中高剂量药物组低于低剂量药物组(t=5.295、8.138、6.545,P<0.05;t=10.093、-7.868、10.539,P<0.05);对照组腮腺组织结构完好,无充血、渗出、水肿等;单纯照射组腮腺组织受照射后10 d出现充血、水肿、炎症细胞浸润,之后40 d时组织纤维化加重,各药物组腮腺组织的炎症反应明显减轻,且与药物剂量呈负相关。TUNEL结果同样显示单纯照射组腮腺细胞的凋亡率均较对照组增高(t=-4.639、-3.979,P<0.05)。结论肿节风对放射性腮腺损伤具有一定的防护作用,其可能通过清除辐射产生ROS、减轻炎症反应和抑制细胞凋亡发挥作用,有望成为理想的放射性腮腺损伤防护剂。     

Radiosensitivity in Cultured Human Fibroblasts

Cells exposed to radiation may undergo death through apoptosis or mitotic death. HeLa cells predominantly undergo mitotic death after irradiation. Treatment of these cells with caffeine has been shown to shorten the G 2 delay after irradiation, and to decrease their survival. The kinase inhibitor staurosporine also decreases the radiationinduced G2 delay in HeLa cells. Here we extend these findings to show that the decrease in radiation-induced G 2 delay mediated by caffeine or staurosporine is accompanied by a shift in the pathway of cell death from mitotic death to apoptotic death. The increase in apoptosis is further accompanied by decreased clonogenic survival after irradiation. Based on these findings we propose the hypothesis that one mechanism of enhancing cell killing by radiation is to trigger apoptosis by decreasing the G 2 delay induced by irradiation.     

Radiation-induced genomic instability in repair deficient mutants of Chinese hamster cells

PURPOSE: To determine the role of single (SSB) and double strand break (DSB) repair in the induction and propagation of radiation-induced instability. MATERIALS AND METHODS: Two defined hamster cell lines with known DNA repair deficiencies in DSB repair (XR-C1) and base excision repair (EM-C11) and the parental wild-type line (CHO-9) were used. The rate of micronucleus formation, apoptosis and survival were measured at 0, 7 and 14 days after X-ray radiation. RESULTS: An enhanced rate of production of damaged cells was observed in wild type and the repair deficient mutants after irradiation. This was cell type, dose and time-dependent. All cells demonstrated delayed death up to day 14 after irradiation along with an elevated apoptosis frequency. The yield of micronuclei was not significantly increased in the wild-type cells, but was in the mutant cells, over the dose and time range studied. For all three endpoints the increase in damage was most pronounced in the SSB deficient cell line. CONCLUSIONS: SSB and/or oxidized base damage play a major role, rather than DSB, in radiation induced instability.