Ionizing radiation-induced cell death

Management of metastatic bone disease of melanoma

One of the most aggressive tumors arising from the skin, mucosa, and uvea is malignant melanoma, which easily metastasizes. Bone tissue is one of the most typical locations for distant metastasis, and around 5%-20% of patients eventually acquired skeletal metastases. For decades, the incidence of bone metastases was higher, bringing greater burden on the family, society, and healthcare system owing to the progress of targeted therapy and immunotherapy, which prolonging the survival time substantially. Moreover, bone metastases result in skeletal-related events, which influence the quality of life, obviously. Appropriate intervention is therefore crucial. To obtain the optimum cost-effectiveness, existing treatment algorithm must be integrated, which is still controversial. We have aimed to throw light on current views concerning the formation, biological and clinical features, and treatment protocol of melanoma bone metastases to guide the decision-making process.

Cell death mechanisms in head and neck cancer cells in response to low and high-LET radiation

Head and neck squamous cell carcinoma (HNSCC) is a common malignancy that develops in or around the throat, larynx, nose, sinuses and mouth, and is mostly treated with a combination of chemo- and radiotherapy (RT). The main goal of RT is to kill enough of the cancer cell population, whilst preserving the surrounding normal and healthy tissue. The mechanisms by which conventional photon RT achieves this have been extensively studied over several decades, but little is known about the cell death pathways that are activated in response to RT of increasing linear energy transfer (LET), including proton beam therapy and heavy ions. Here, we provide an up-to-date review on the observed radiobiological effects of low- versus high-LET RT in HNSCC cell models, particularly in the context of specific cell death mechanisms, including apoptosis, necrosis, autophagy, senescence and mitotic death. We also detail some of the current therapeutic strategies targeting cell death pathways that have been investigated to enhance the radiosensitivity of HNSCC cells in response to RT, including those that may present with clinical opportunities for eventual patient benefit.

Salvianolic acid B, an antioxidant derived from Salvia militarize, protects mice against γ‑radiation‑induced damage through Nrf2/Bach1

Salvianolic acid B (SB) is an antioxidant derived from Salvia militarize, and is one of the most widely used herbs in traditional Chinese medicine. SB is a potent antioxidant that has been well documented as a scavenger of oxygen free radicals, and has been used for the prevention and treatment of atherosclerosis-associated disorders. To explore its potential therapeutic effects in treating radiation damage, in this study, mice were treated with SB at different doses of 5, 12.5 and 20 mg/kg, subsequent to receiving γ-irradiation. The effects of SB on peripheral blood, bone marrow nucleated cells, spleen and thymus indices, and oxidation resistance were evaluated in both radiated mice and control groups. The results indicated that SB significantly increased the counts of peripheral white blood cells, red blood cells and platelets. The number of nucleated cells in the bone marrow and the level of protein increased as well. In addition, improved spleen and thymus indices in the bone marrow were observed. SB treatment additionally reversed the deterioration of both the thymus and spleen indices, which is associated with increased serum superoxide dismutase activity and decreasing malondialdehyde levels via nuclear factor (erythroid-derived 2)-like 2 protein/BTB and CNC homology 1 mediated antioxidant effect. Furthermore, ROS levels and Bax protein expression were also suppressed by SB. The data suggested that SB is effective in protecting mice from γ-radiation injury, and could potentially be applicable for clinical use. Notably, the present study identified a promising candidate drug for enhancing the hematopoietic and immune systems.

The role of gut in type 2 diabetes mellitus during whole body gamma irradiation in high-fat diet Wistar rats

PURPOSE

The effects of a low rate (100 mGy/min) fractionated whole body gamma irradiation (FWBGI) at different doses were assessed using a real-time PCR technique on the expression of some target genes implicated in the development of type 2 diabetes mellitus in high-fat diet (HFD) Wistar rats.

METHOD

HFD Wistar rats were exposed to different doses (12, 24 and 48 Gy) divided into 24 fractions (three times a week for two months), thus, the daily doses were 0.5, 1, 2 Gy, respectively. Total RNA was extracted and the expression of target genes was measured in the four intestinal segments (duodenum, jejunum, ileum and colon).

RESULTS

The pre-diabetic state already induced by HFD was found to be improved by irradiation exposure. This irradiation effect occurs mainly via altered anti-diabetic gene expressions (mRNA and protein levels) of the incretin glucagon-like peptide-1 (GLP-1) overall bowel segments except the colon which has its own specific response to irradiation exposure by the induction of the insulin receptor substrate 4 (IRS-4) and the uncoupling protein 3 (UCP3).

CONCLUSIONS

Results could be of great importance suggesting for the first time, a protective role for FWBGI on HFD animal models by increasing GLP-1 and UCP3 levels.

A detailed characterization of congenital defects and mortality following moderate X-ray doses during neurulation

BACKGROUND

Both epidemiological and animal studies have previously indicated a link between in utero radiation exposure and birth defects such as microphthalmos, anophthalmos, and exencephaly. However, detailed knowledge on embryonic radiosensitivity during different stages of neurulation is limited, especially in terms of neural tube defect and eye defect development.

METHODS

To assess the most radiosensitive stage during neurulation, pregnant C57BL6/J mice were X-irradiated (0.5 Gy or 1.0 Gy) at embryonic days (E)7, E7.5, E8, E8.5, or E9. Next, the fetuses were scored macroscopically for various defects and prenatal resorptions/deaths were counted. In addition, cranial skeletal development was ascertained using the alcian-alizarin method. Furthermore, postnatal/young adult survival was followed until 5 weeks (W5) of age, after X-irradiation at E7.5 (0.1 Gy, 0.5 Gy, or 1.0 Gy). In addition, body and brain weights were registered at adult age (W10) following X-ray exposure at E7.5 (0.1 Gy, 0.5 Gy).

RESULTS

Several malformations, including microphthalmos and exencephaly, were most evident after irradiation at E7.5, with significance starting respectively at 0.5 Gy and 1.0 Gy. Prenatal mortality and weight were significantly affected in all irradiated groups. Long-term follow-up of E7.5 irradiated animals revealed a reduction in survival at 5 weeks of age after high dose exposure (1.0 Gy), while lower doses (0.5 Gy, 0.1 Gy) did not affect brain and body weight at postnatal week 10.

CONCLUSIONS

With this study, we gained more insight in radiosensitivity throughout neurulation, and offered a better defined model to further study radiation-induced malformations and the underlying mechanisms.

Radioprotective Effect of Grape Seed Proanthocyanidins In Vitro and In Vivo

We have demonstrated that grape seed proanthocyanidins (GSPs) could effectively scavenge hydroxyl radical (•OH) in a dose-dependent manner. Since most of the ionizing radiation- (IR-) induced injuries were caused by •OH, this study was to investigate whether GSPs would mitigate IR-induced injuries in vitro and in vivo. We demonstrated that GSPs could significantly reduce IR-induced DNA strand breaks (DSBs) and apoptosis of human lymphocyte AHH-1 cells. This study also showed that GSPs could protect white blood cells (WBC) from IR-induced injuries, speed up the weight of mice back, and decrease plasma malondialdehyde (MDA), thus improving the survival rates of mice after ionizing radiation. It is suggested that GSPs have a potential as an effective and safe radioprotective agent.

The contribution of women to radiobiology: Marie Curie and beyond

Marie Sklodowska-Curie, an extraordinary woman, a Polish scientist who lived and worked in France, led to the development of nuclear energy and the treatment of cancer. She was the laureate of two Nobel Prizes, the first woman in Europe who obtained the degree of Doctor of Science and opened the way for women to enter fields which had been previously reserved for men only. As a result of her determination and her love of freedom, she has become an icon for many female scientists active in radiation sciences. They are successors of Maria Curie and without the results of their work, improvement in radiation oncology will not be possible. Many of them shared some elements of Maria Curie's biography, like high ethical and moral standards, passionate dedication to work, strong family values, and scientific collaboration with their husbands. The significance of Tikvah Alper, Alma Howard, Shirley Hornsey, Juliana Denekamp, Helen Evans, Eleanor Blakely, Elizabeth L. Travis, Fiona Stewart, Andree Dutreix, Catharine West, Peggy Olive, Ingela Turesson, Penny Jeggo, Irena Szumiel, Eleonor Blakely, Sara Rockwell and Carmel Mothersill contribution to radiation oncology is presented. All the above mentioned ladies made significant contribution to the development of radiotherapy (RT) and more efficient cancer treatment. Due to their studies, new schedules of RT and new types of ionizing radiation have been applied, lowering the incidence of normal tissue toxicity. Their achievements herald a future of personalized medicine.

Radioprotective effect of hesperetin against γ-irradiation-induced DNA damage and immune dysfunction in murine splenocytes

This study was conducted to evaluate the preventive effect of hesperetin against radiation-induced DNA damage and immune dysfunction in murine splenocytes. Isolated splenocytes from BALB/c mice were treated with hesperetin (20, 100, and 500 µM), and then irradiated at a dose of 2 and 4 Gy of γ-irradiation. Exposure to ?-radiation resulted in DNA damage and a reduction of cell viability as well as an elevation of the levels of proinflammatory cytokines, intracellular ROS (reactive oxygen species), and NO (nitric oxide). Hesperetin significantly enhanced the cell viability of the splenocytes compared with the irradiated group. In addition, hesperetin was found to be highly effective in preventing DNA damage as identified by comet and DNA ladder assays. Hesperetin also effectively inhibited proinflammatory cytokines, intracellular ROS, and NO in irradiated splenocytes. In conclusion, hesperetin was shown to be radioprotective against irradiation-induced DNA damage and immune dysfunction in murine splenocytes.

Role of genomics in eliminating health disparities

The Texas Center for Health Disparities, a National Institute on Minority Health and Health Disparities Center of Excellence, presents an annual conference to discuss prevention, awareness education, and ongoing research about health disparities both in Texas and among the national population. The 2014 Annual Texas Conference on Health Disparities brought together experts in research, patient care, and community outreach on the “Role of Genomics in Eliminating Health Disparities.” Rapid advances in genomics and pharmacogenomics are leading the field of medicine to use genetics and genetic risk to build personalized or individualized medicine strategies. We are at a critical juncture of ensuring such rapid advances benefit diverse populations. Relatively few forums have been organized around the theme of the role of genomics in eliminating health disparities. The conference consisted of three sessions addressing “Gene-Environment Interactions and Health Disparities,” “Personalized Medicine and Elimination of Health Disparities,” and “Ethics and Public Policy in the Genomic Era.” This article summarizes the basic science, clinical correlates, and public health data presented by the speakers.

Radioprotectors - the evergreen topic

To protect organisms from ionizing radiation (IR), and to reduce morbidity or mortality, various agents, called radioprotectors, have been utilized. Because radiation-induced cellular damage is attributed primarily to the harmful effects of free radicals, molecules with radical-scavenging properties are particularly promising as radioprotectors. Early development of such agents focused on thiol synthetic compounds, known as WR protectors, but only amifostine (WR-2721) has been used in clinical trials as an officially approved radioprotector. Besides thiol compounds, various compounds with different chemical structure were investigated, but an ideal radioprotector has not been found yet. Plants and natural products have been evaluated as promising sources of radioprotectors because of their low toxicity, although they exhibit an inferior protection level compared to synthetic thiol compounds. Active plant constituents seem to exert the radioprotection through antioxidant and free radical-scavenging activities. Our research established that plants containing polyphenolic compounds (raspberry, blueberry, strawberry, grape, etc.) exhibit antioxidative activities and protect genetic material from IR.

Whole-body imaging of high-dose ionizing irradiation-induced tissue injuries using 99mTc-duramycin

High-dose ionizing irradiation can cause extensive injuries in susceptible tissues. A noninvasive imaging technique that detects a surrogate marker of apoptosis may help characterize the dynamics of radiation-induced tissue damage. The goal of this study was to prove the concept of imaging the temporal and spatial distribution of damage in susceptible tissues after high-dose radiation exposure, using (99m)Tc-duramycin as a phosphatidylethanolamine-binding radiopharmaceutical.

METHODS

Rats were subjected to 15 Gy of total-body irradiation with x-rays. Planar whole-body (99m)Tc-duramycin scanning (n = 4 per time point) was conducted at 24, 48, and 72 h using a clinical γ-camera. On the basis of findings from planar imaging, preclinical SPECT data were acquired on control rats and on irradiated rats at 6 and 24 h after irradiation (n = 4 per time point). Imaging data were validated by γ-counting and histology, using harvested tissues in parallel groups of animals (n = 4).

RESULTS

Prominent focal uptake was detected in the thymus as early as 6 h after irradiation, followed by a gradual decline in (99m)Tc-duramycin binding accompanied by extensive thymic atrophy. Early (6-24 h) radioactivity uptake in the gastrointestinal region was detected. Significant signal was seen in major bones in a slightly delayed fashion, at 24 h, which persisted for at least 2 d. This finding was paralleled by an elevation in signal intensity in the kidneys, spleen, and liver. The imaging results were consistent with ex vivo γ-counting results and histology. Relatively high levels of apoptosis were detected from histology in the thymus, guts, and bones, with the thymus undergoing substantial atrophy.

CONCLUSION

As a proof of principle, this study demonstrated a noninvasive imaging technique that allows characterization of the temporal and spatial dynamics of injuries in susceptible tissues during the acute phase after high-dose ionizing irradiation. Such an imaging capability will potentially be useful for global, whole-body, assessment of tissue damage after radiation exposure. These data, in turn, will contribute to our general knowledge of tissue susceptibility to ionizing irradiation, as well as the onset and progression of tissue injuries.

Cyclin D1 overexpression perturbs DNA replication and induces replication-associated DNA double-strand breaks in acquired radioresistant cells

Fractionated radiotherapy (RT) is widely used in cancer treatment, because it preserves normal tissues. However, repopulation of radioresistant tumors during fractionated RT limits the efficacy of RT. We recently demonstrated that a moderate level of long-term fractionated radiation confers acquired radioresistance to tumor cells, which is caused by DNA-PK/AKT/GSK3β-mediated cyclin D1 overexpression. The resulting cyclin D1 overexpression leads to forced progression of the cell cycle to S-phase, concomitant with induction of DNA double-strand breaks (DSBs). In this study, we investigated the molecular mechanisms underlying cyclin D1 overexpression-induced DSBs during DNA replication in acquired radioresistant cells. DNA fiber data demonstrated that replication forks progressed slowly in acquired radioresistant cells compared with corresponding parental cells in HepG2 and HeLa cell lines. Slowly progressing replication forks were also observed in HepG2 and HeLa cells that overexpressed a nondegradable cyclin D1 mutant. We also found that knockdown of Mus81 endonuclease, which is responsible for resolving aberrant replication forks, suppressed DSB formation in acquired radioresistant cells. Consequently, Mus81 created DSBs to remove aberrant replication forks in response to replication perturbation triggered by cyclin D1 overexpression. After treating cells with a specific inhibitor for DNA-PK or ATM, apoptosis rates increased in acquired radioresistant cells but not in parental cells by inhibiting the DNA damage response to cyclin D1-mediated DSBs. This suggested that these inhibitors might eradicate acquired radioresistant cells and improve fractionated RT outcomes.

Differential activation of NF-κB and nitric oxide in lymphocytes regulates in vitro and in vivo radiosensitivity

Lymphocytes are more sensitive to radiation in vivo than in vitro. However, the mechanism of this differential response is poorly understood. In the present study, it was found that the lipid peroxidation and cell death were significantly higher in lymphocytes following whole body irradiation (WBI) as compared to lymphocytes exposed to radiation in vitro. EL-4 cells transplanted in mice were also more sensitive to radiation than EL-4 cells irradiated in vitro. DNA repair, as assessed by comet assay, was significantly faster in lymphocytes exposed to 4Gy radiation in vitro as compared to that in lymphocytes obtained from whole body irradiated mice exposed to the same dose of radiation. This was associated with increased NF-κB activation in response to genotoxic stress and lesser activation of caspase in lymphocytes in vitro compared to in vivo. To explain the differential radiosensitivity, we postulated a role of nitric oxide, an extrinsic diffusible mediator of radiosensitivity that has also been implicated in DNA repair inhibition. Nitric oxide levels were significantly elevated in the plasma of whole body irradiated mice but not in the supernatant of cells irradiated in vitro. Addition of sodium nitroprusside (SNP), a nitric oxide donor to cells irradiated in vitro inhibited the repair of DNA damage and enhanced apoptosis (increased Bax to Bcl-2 ratio). Administration of l-NAME, a nitric oxide synthase inhibitor, to mice significantly protected lymphocytes against WBI-induced DNA damage and inhibited in vivo radiation-induced production of nitric oxide. These results confirm that the observed differential radiosensitivity of lymphocytes was due to slow repair of DNA due to nitric oxide production in vivo.

HDAC inhibitor, valproic acid, induces p53-dependent radiosensitization of colon cancer cells

Agents that inhibit histone deacetylases (HDAC inhibitors) have been shown to enhance radiation response. The aim of this study was to evaluate the effects of low, minimally cytotoxic concentrations of the HDAC inhibitor, valproic acid (VPA), on radiation response of colorectal cancer cells. Cell lines LS174T and an isogenic pair of HCT116, which differed only for the presence of wild-type p53, were exposed to ionizing radiation (IR) alone, VPA alone, or the combination. Clonogenic survival, gamma-H2AX induction, apoptosis, changes in mitochondrial membrane potential, and mitochondrial levels of p53 and Bcl-2 family proteins were assessed. In vivo studies monitored tumor growth suppression after therapy in mice bearing HCT116/p53(+/+) and HCT116/p53(-/-) tumor xenografts. VPA led to radiosensitization, which was dependent on p53 status. A decrease in clonogenic survival, an increase in apoptosis, and an increase in levels of gamma-H2AX were observed after VPA+IR, compared to IR alone, in wild-type p53 cells (LS174T and HCT116/p53(+/+)), as opposed to p53 null cells (HCT116/p53(-/-)). Exposure to VPA resulted in enhancement of IR-induced mitochondrial localizations of Bax and Bcl-xL, mitochondrial membrane potential, and cytochrome c release only in wild-type p53 cell lines. VPA also enhanced tumor growth suppression after IR only in wild-type p53 xenografts. These data suggest that VPA may have an important role in enhancing radiotherapy response in colorectal cancer, particularly in tumors with the wild-type p53 genotype.

Evaluation of the free radical scavenging activity and radioprotective efficacy of Grewia asiatica fruit

The radioprotective effect of Grewia asiatica fruit (GAE) which contains anthocyanin-type cyanidin 3-glucoside, vitamins C and A, minerals, carotenes and dietary fibre was studied. For the study Swiss albino mice were divided into five groups: (1) control (vehicle treated); (2) GAE treated (700 mg kg(-1) day(-1) for 15 days); (3) irradiated (5 Gy); (4) GAE+irradiated and (5) irradiated+GAE treated. The irradiation of animals resulted in a significant elevation of lipid peroxidation in terms of thiobarbituric acid reactive substances (TBARS) content and depletion in glutathione (GSH) and protein levels at all intervals studied, namely 1-30 days, in comparison to the control group. Treatment of mice with GAE before and after irradiation caused a significant depletion in TBARS content followed by a significant elevation in GSH and protein concentration in the intestine and testis of mice at all post-irradiation autopsy intervals in comparison to irradiated mice. Significant protection of DNA and RNA in testis was also noticed. GAE was found to have strong radical scavenging activity in 2,2-diphenyl-1-picrylhydrazyl (DPPH(*)) and O(2)(-) assays and also showed in vitro radioprotective activity in protein carbonyl assay in a dose-dependent manner. The above results prove the radioprotective efficacy of GAE.

Oligonucleotide chip assay for quantification of gamma ray-induced single strand breaks

An oligonucleotide chip assay was designed for direct quantification of single strand breaks (SSBs) induced by gamma-ray irradiation. The oligonucleotides used were 20-mers, which were short enough to produce only a single strand break within a single oligonucleotide. The two ends of the oligonucleotides were labeled with fluorescein and biotin, respectively. The biotinylated ends of the oligonucleotides were immobilized on a silicon wafer chip treated with (3-aminopropyl)triethoxysilane (APTES), glutaraldehyde, and avidin. The DNA fragments cleaved by gamma-ray irradiation were detected by a laser-induced fluorescence (LIF) detection system. The gamma-ray-induced SSBs were quantified using a calibration curve (fluorescence intensity versus gamma-ray dose) without the need for complicated mathematical calculation based on gel-based separation. The experimentally determined gamma-ray-induced SSBs yield was almost equal to the theoretical value derived from gel electrophoresis of plasmid DNAs and DNA surface coverage.

Irradiation leads to apoptosis of Kupffer cells by a Hsp27-dependant pathway followed by release of TNF-alpha

In a previous publication, we were able to show that irradiation of Kupffer cells, the liver resident macrophages, leads to an increased TNF-alpha concentration in the culture medium. The pathomechanisms underlying this phenomenon, however, remained to be elucidated. Here, we show that following irradiation of Kupffer cells, the apoptosis rate increased drastically within 48 h. At the same time, the total TNF-alpha concentration in cell lysates of Kupffer cells attached to the culture plate decreased. However, normalization of the TNF-alpha concentration with respect to cell number revealed that TNF-alpha concentration per attached cell remained constant during the observation period. Western blot analysis showed that heat shock protein 27 (Hsp27) is strongly downregulated and bax is upregulated in irradiated Kupffer cells as compared to sham-irradiated cells. Overexpression of Hsp27 in Kupffer cells was shown to prevent the effect of irradiation on bax expression, apoptosis and, at the same time, on increase of TNF-alpha concentration in the Kupffer cell medium. We conclude that irradiation of Kupffer cells leads to apoptosis because of downregulation of Hsp27 and consecutive upregulation of bax expression. Furthermore, we suggest that apoptosis of Kupffer cells leads to an increase of TNF-alpha concentration in the culture medium which may be due to cell death rather than active release or synthesis.

Properties of grape seed proanthocyanidins and quercetin in human lymphocytes

This study addresses the in vitro protective effects of proanthocyanidins and quercetin on the frequency of micronuclei with reference to the antioxidant status of cultured human lymphocytes also subjected to 2 Gy of ?-radiation. Treatment of lymphocytes with proanthocyanidins induced a significant decrease in the frequency of micronuclei and reduction of malonyldialdehyde production, as well as increased catalase and glutathione S-transferase activity. Quercetin induces a higher incidence of micronuclei and production of malonyldialdehyde. The seven-fold increase of micronuclei frequency induced by a therapeutic dose of ?-radiation was decreased in the presence of proanthocyanidins. These results demonstrate that proanthocyanidins may be important in the prevention of ROS-induced oxidative lymphocyte damage by decreasing DNA damage, lowering membrane lipid peroxidation, and increasing the activity AOP enzymes, as well as by reducing the level of ?-radiation-induced DNA damage. Our results support the potential benefits of proanthocyanidins as efficient antioxidants and radioprotectors.

Gene therapy for carcinoma of the breast

In view of the limited success of available treatment modalities for breast cancer, alternative and complementary strategies need to be developed. The delineation of the molecular basis of breast cancer provides the possibility of specific intervention by gene therapy through the introduction of genetic material for therapeutic purposes. In this regard, several gene therapy approaches for carcinoma of the breast have been developed. These approaches can be divided into six broad categories: (1) mutation compensation, (2) molecular chemotherapy, (3) proapoptotic gene therapy, (4) antiangiogenic gene therapy, (5) genetic immunopotentiation, and (6) genetic modulation of resistance/sensitivity. Clinical trials for breast cancer have been initiated to evaluate safety, toxicity, and efficacy. Combined modality therapy with gene therapy and chemotherapy or radiation therapy has shown promising results. It is expected that as new therapeutic targets and approaches are identified and advances in vector design are realized, gene therapy will play an increasing role in clinical breast cancer treatment.

Radiobiological effect of 99mTechnetium-MIBI in human peripheral blood lymphocytes: ex vivo study using micronucleus/FISH assay

99mTc-MIBI is currently used, for cardiac investigations, for parathyroid thyroid imaging and evaluation of various tumours. It has been demonstrated that 99mTc-MIBI is specifically taken up by the human peripheral blood lymphocytes (HPBL), cells which are known to be highly radiosensitive. To evaluate the possible chromosomal damage induced on HPBL by their in vitro exposure to increasing activities of 99mTc-MIBI and also to establish whether HPBL undergo apoptosis or necrosis after in vitro exposure to 99mTc-MIBI. Blood from two healthy donors were irradiated, incubated in vitro with increasing activities of 99mTc-MIBI corresponding to absorbed doses ranging from 1 microGy, 100 microGy, 1 cGy, 10 cGy, 50 cGy to 1 Gy. The cytokinesis block micronucleus (MN) assay was used and the frequency of binucleated cells (BN) with MN (MNBN) was analyzed in cultured HPBL (in either the G0- or G1- and S1-phase of the cell cycle). The fluorescence in situ hybridization (FISH) with pancentromeric probes was also applied to study the MN regarding whole chromosomes or acentric fragments. Apoptosis induction by 0.1 Gy of 99mTc-MIBI in HPBL was quantified using annexin-V test. The frequencies of MNBC were similar in control cultures and in HBPL cultures exposed to 1 microGy, 100 microGy and 1 cGy. However, they were significantly higher (P<0.05 versus controls and lower doses) after one treatment exposure to 0.25 mCi of 99mTc-MIBI (corresponding to 10 cGy) or more but the percentages of MNBN with 10 cGy, 50 cGy and 1 Gy did not differ significantly. The increase of MNBN was more pronounced (P<0.05) for cells irradiated during G1 phase than for those irradiated during G0 or S1. Using FISH, 80-90% of the MN were centromere negative. Although small, the absolute number of MN positive for centromeric signal and presumably containing whole chromosomes increased with doses. There is a statistically significant (P=0.001 and 0.006) increase of both apoptotic cells and necrosis, respectively, as compared to control cells in two times studied (24 and 36 h). Chromosomic damages can thus be demonstrated in HPBL after in vitro exposure of blood to at least 0.25 mCi of 99mTc-MIBI corresponding to one absorbed dose of 10 cGy, and for this dose, apoptosis and necrosis phenomenons were detected.

Protection of Mouse Bone Marrow against Radiation-Induced Chromosome Damage and Stem Cell Death by the Ocimum Flavonoids Orientin and Vicenin

In a previous study, orientin and vicenin, the water-soluble plant flavonoids, protected mice against radiation lethality (Uma Devi et al., Radiat. Res. 151, 74-78, 1999). To study bone marrow protection, adult Swiss mice were exposed to 0-6 Gy 60Co gamma rays 30 min after an intraperitoneal injection of 50 microg/ kg body weight of orientin/vicenin. Chromosomal aberrations in bone marrow were studied at 24 h postirradiation. Stem cell survival was studied using the exogenous spleen colony (CFU-S) assay. Radiation produced a dose-dependent increase in aberrant cells as well as in the yield of the different types of aberrations (breaks, fragments, rings and dicentrics) and a decrease in CFU-S. Pretreatment with either flavonoid significantly reduced the aberrant cells and different aberrations and increased the number of CFU-S compared to the respective radiation-alone groups. The dose modification factors for 50% reductions in the number of CFU-S were 1.6 for orientin and 1.7 for vicenin. The present finding that very low nontoxic doses of orientin and vicenin provide efficient protection against bone marrow damage at clinically relevant radiation doses suggests their potential for protection of normal tissues in radiotherapy.

Protective effects of puerarin on radiation injury of experimental rats

OBJECTIVE

To observe the protective effects of puerarin on radiation injury of experimental rats and to discuss the possible mechanism of its radiation protection.

METHODS

Wistar rats were divided randomly into 4 groups with 8 rats in each group: physiological saline non-radiation (SN) group, puerarin non-radiation (PN) group, physiological saline radiation (SR) group, puerarin radiation (PR) group. The source of radiation was cobalt-60 gamma rays, and the rats were exposed to radiation (1.2 Gy/min) at a dose of 18 Gy. Following irradiation of the rats, puerarin was injected intravenously at each dose of 30 mg/kg in 6 consecutive days (24 h interval). Samples were collected and assayed one week later.

RESULTS

Puerarin delayed effectively the declines of the quantity of red blood cells and white blood cells in circulation due to ionizing irradiation, improved the index of thymus and spleen in ionizing irradiation rats, increased the activity of superoxide dismutase (SOD) and decreased the level of malondialdehyde (MDA) in the rat myocardial tissue.

CONCLUSION

Puerarin has a marked protective effect on ionizing irradiation injury of experimental rats, and its protective mechanism is probably based on oxidation-resistance.

Effect of the vitamin D3 analog ILX 23-7553 on apoptosis and sensitivity to fractionated radiation in breast tumor cells and normal human fibroblasts

PURPOSE

Previous work from this laboratory has demonstrated that the vitamin D(3) analogs EB 1089 and ILX 23-7553 enhance the response of breast tumor cells to ionizing radiation and promote radiation-induced apoptotic cell death. The current studies were designed to more closely simulate clinical radiotherapy in the treatment of breast cancer by examining the utility of ILX 23-7553 as an adjunct to fractionated ionizing radiation. The potential toxicity to normal tissue of the combination of ILX 23-7553 and fractionated radiation was assessed in a model of BJ human fibroblasts in culture.

METHODS

MCF-7 cells and human fibroblasts were treated with fractionated radiation alone (5x2 Gy over 3 days), ILX 23-7553 alone (50 n M) or ILX 23-7553 followed by 5x2 Gy. Viable cell numbers were determined by trypan blue exclusion and apoptosis by the TUNEL assay. A statistical model of additivity was utilized to assess the nature of the interaction between ILX 23-7553 and fractionated radiation.

RESULTS

Radiation and ILX 23-7553 each alone reduced viable cell numbers by 72+/-3.1% and 62+/-4.8%, respectively. Pretreatment with ILX 23-7553 followed by 5x2 Gy reduced viable cell numbers by 93.2+/-0.7%. The interaction between ILX 23-7553 and fractionated radiation appeared to be additive despite the fact that the combination of ILX 23-7553 and fractionated radiation also promoted a twofold increase in apoptotic cell death. ILX 23-7553 failed to enhance the response to radiation or to promote apoptosis in BJ human foreskin fibroblasts.

CONCLUSIONS

ILX 23-7553 enhanced the antiproliferative and apoptotic effects of fractionated ionizing radiation in MCF-7 breast cancer cells. These effects appeared to be selective in that similar responses were not observed in a model of normal human fibroblasts. Vitamin D(3) analogs such as ILX 23-7553 may prove to have utility in combination with conventional radiotherapy of breast cancer as well as other malignancies which are sensitive to vitamin D(3).

Induction of DNA-protein cross-links by Hippophae rhamnoides: implications in radioprotection and cytotoxicity

Recently Hippophae rhamnoides has been reported to render chromatin compaction and significantly inhibit radiation induced DNA strand breaks. To investigate the mechanism of action of RH-3, a preparation of Hippophae rhamnoides, in this connection, present study was undertaken. Chromatin compaction induced by RH-3 (100 microg/ml or more) was maximum at alkaline pH but was completely negated by acidic pH (< 6) or presence of free radical scavengers like glycerol, DMSO etc. In a concentration dependent manner, RH-3 inhibited the intercalation of ethidium ions from Et Br into calf thymus DNA and also increased the precipitation of DNA-protein cross-links (DPC) in thymocytes. Chromatin compaction caused by RH-3 treatment did not permit the separation of proteins from DNA even after treatment with 2 M NaCl solution. SDS-PAGE profiles also revealed that RH-3 in a dose dependent manner compacted the chromatin organization, induced DPC and inhibited the extraction of both histone and non-histone matrix proteins from chromatin maximally at 80 microg/ml. More than 80 microg/ml of RH-3, though extracted low molecular weight histones but did not separate non-histone proteins. The RH-3 mediated DPCs were resistant even to 1% SDS, 4 M NaCl and 3.8 M hydroxyl amine hydrochloride but were prone to both urea (8 M) and guanidine hydrochloride (6 M) indicating covalent bonding between DNA and proteins (serine/threonine). RH-3 in a concentration dependent manner induced superoxide anions and the phenomenon was dependent upon nature of medium, presence of metal ions and pH. RH-3 at concentrations up to 100 microg/ml in presence of 50 microM copper sulfate inflicted significant damage to extraneously added 2-deoxyribose molecules and maximum TBARS were formed at a concentration of 100 microg/ml. Higher concentrations of RH-3 more than 100 microg/ml quenched free radicals and inhibited 2-deoxyribose degradation. RH-3 also induced strand breaks in plasmid DNA at concentrations lower than 100 microg/ml but completely inhibited at concentrations higher than 250 microg/ml, indicating bimodal function. Strand breaks induced by lower concentrations of RH-3 (up to 100 microg/ml) were inhibited by antioxidants like GSH, DFR etc. RH-3, in a concentration dependent mode also inhibited the relaxation of supercoiled plasmid DNA (PBR322) by topoisomerase I. Present study indicated that RH-3 caused compaction of reversible (< 100 micrpg/ml) and irreversible (> 100 microg/ml) nature which was related to the magnitude of DNA-protein cross-links formed. Maintenance of chromatin organization, induction of hypoxia, hydrogen atom donation, free radical scavenging and blocking of cell cycle at G2-M phase by interfering with topoisomerase I activity seem to contribute towards the radioprotective efficacy of RH-3.

Usefulness of combined treatment with mild temperature hyperthermia and/or tirapazamine in the treatment of solid tumors: its independence of p53 status

Human head and neck squamous cell carcinoma cells transfected with mutant TP53 (SAS/mp53) or with neo vector as a control (SAS/neo) were inoculated subcutaneously into both hind legs of Balb/cA nude mice. Mice bearing the tumors received 5-bromo-2'-deoxyuridine (BrdU) continuously to label all proliferating (P) cells in the tumors. The mice then received tirapazamine (TPZ) with or without mild temperature hyperthermia (40 degrees C, 60 min) (MTH), gamma-ray irradiation with or without MTH and/or TPZ, cisplatin (CDDP) with or without MTH and/or TPZ, or paclitaxel (TXL) with or without MTH and/or TPZ. After each treatment, the tumors were excised, minced and trypsinized. The tumor cell suspensions thus obtained were incubated with a cytokinesis blocker (cytochalasin-B), and the micronucleus (MN) frequency in cells without BrdU labeling (i.e., quiescent (Q) cells) was determined by using immunofluorescence staining for BrdU. Meanwhile, 6 h after gamma-ray irradiation or 24 h after other cytotoxic treatments, tumor cell suspensions obtained in the same manner were used for determining the frequency of apoptosis in Q cells. The MN frequency and apoptosis frequency in total (P+Q) tumor cells were determined from the tumors that were not pretreated with BrdU. On the whole, gamma-ray irradiation and CDDP injection induced a higher frequency of apoptosis and lower frequency of MN in SAS/neo cells than SAS/mp53 cells. There were no apparent differences in the induced frequency of apoptosis and MN between SAS/neo and SAS/mp53 cells after TPZ or TXL treatment. MTH sensitized cells to TPZ-inducing cytotoxicity more markedly in SAS/mp53 and Q cells than in SAS/neo cells and total cells, respectively. In gamma-ray irradiation and CDDP treatment, the enhancement in combination with MTH and/or TPZ was more remarkable in SAS/mp53 cells and Q cells than in SAS/neo and total tumor cells, respectively. Also in the case of TXL treatment, the combination with MTH and/or TPZ induced a slightly greater enhancement effect in SAS/mp53 cells and Q cells. In view of the difficulty in controlling mutated p53 status tumors and intratumor Q cells, combination treatment with MTH and/or TPZ as a cooperative modality in cancer therapy is considered to have potential for controlling solid tumors as a whole.

IFN-gamma and TNF-alpha production in gamma-irradiated blood units by mononuclear cells and GVHD prevention

Gamma-radiation of blood products is considered the mainstay of transfusion-associated graft-versus-host disease prevention. Previous studies have detected lymphocyte inhibition rate in blood components just one time after irradiation but there is evidence of cellular variability with production of cytokines at different storage time which could be related with irradiation activity and cellular damage repair. IFN-gamma, a Th1 cytokine, and TNF-alpha, a pro-inflammatory one, had a central role in the stimulation of cellular and inflammatory reactions. In this study whole blood was collected from five volunteer healthy donors and each donor bag was divided into two satellite bags: one of them was exposed to 137Cs-irradiation with a 2500 cGy dose. Samples for cytokine production, detected by ELISA methods, and proliferative response, evaluated by incorporation of H3 thymidine, were taken at the following storage time: 0, 24, 48, 72 and 96 h. The time-response curve of irradiated mononuclear cells from blood bags (BBMC) in mitogenic activation showed a time-related inhibition of cell proliferation with an enhanced response only after 24 h of storage and about 84% inhibition at 96 h. A similar pattern is follow by IFN-gamma production after OKT3 stimulation. TNF-alpha levels both in lipopolysaccharide stimulated or unstimulated cells were always high. This data suggest that BBMC cells maintain the ability to produce cytokines after gamma-radiation. On the ground of this study seems to be necessary to evaluate hypothetical risk associated with the administration of cytokine via irradiated blood components.

Clearance of radiation-induced apoptotic lymphocytes: ex vivo studies and an in vitro co-culture model

Lymphocytes are very sensitive to radiation. Our aim was to test the possibility of detecting apoptosis in lymphocytes as a potential short-term biomarker of ionizing radiation exposure. Our in vitro data confirmed the dose-time-effect relationships involved in radiation-induced apoptosis. The detection of in vivo induction of apoptosis in circulating lymphocytes after exposure of animals to radiation appears to depend critically on the technique used to measure apoptosis. Among the different techniques we investigated, mitochondrial modification was the most appropriate; they allowed establishment of dose-time-effect relationships when animals were observed for 72 h. A model of in vitro phagocytosis of apoptotic lymphocytes by macrophages was developed to mimic clearance of apoptotic cells occurring in vivo. Together, our data show that mitochondrial labeling may make it possible to detect ex vivo radiation-induced apoptosis of lymphocytes before macrophage ingestion occurs. We propose the measurement of apoptosis in lymphocytes as a potential short-term biomarker of ionizing radiation exposure.

Modulation of chromatin organization by RH-3, a preparation of Hippophae rhamnoides, a possible role in radioprotection

The present study was aimed to understand the mode of action of alcoholic extract of whole berries of Hippophae rhamnoides (RH-3) which has already been reported to render more than 80 % protection against radiation induced mortality in mice. Direct and indirect antioxidant action (free radical scavenging and metal chelating potential) were assayed using 2-deoxy ribose degradation and 2,2'-bipiridyl assays. Effect of RH-3 on radiation and chemical oxidant mediated DNA damage was evaluated using single cell gel electrophoresis (Comet assay) and alkaline halo assay. Ability of RH-3 to bind with calf thymus DNA was assayed through change in melting temperature (Tm) while toxicity was assayed in thymocytes by trypan blue exclusion. RH-3 inhibited 2-deoxy ribose degradation in a dose dependent manner (IC 50 approximately 500 microg/ml). 2,2'-bipiridyl assay revealed the inability of RH-3 to chelate Fe2+ ions. RH-3 inhibited radiation and tertiary butyl hydroperoxide induced DNA strand breaks in a dose dependent manner and at concentrations of 100 and 120 microg/ml the length of comet tail was considerably reduced and became almost similar to that of untreated control. RH-3 at a concentration of 120 pg/ml or more induced a strong compaction of chromatin as was evident from lack of tail and appearance of intensely stained circular bodies. This made the nuclei resistant even to a radiation dose of 1,000 Gy. The compaction of chromatin was not reversed even by relaxation buffer indicating that salt concentration had no role in RH-3 induced chromatin compaction. Alkaline halo assay also corroborated the results of comet assay. Lower DNA-RH-3 concentrations (1:0.5 and 1:1) induced a shift of Tm towards left by 2 and 5 degrees C respectively; however higher concentrations (1:8 and 1:16) shifted the Tm towards right increasing it by 10 and 21 degrees C correspondingly. RH-3, evinced only a mild free radical scavenging activity at concentrations used in the present study, therefore its ability to protect DNA could mainly be attributed to direct modulation of chromatin organization. Further work to unravel these facts would be necessary.

[Mechanisms of radio-induced apoptosis]

A general overview of the activation mechanisms of programmed cell death or apoptosis following an irradiation is given in this review. First, are summarized the main induction pathways of radiation-induced apoptosis by which extracellular (tumor necrosis factor (TNF), Fas ligand, TNF-related apoptosis-inducing ligand (TRAIL)) and intracellular (mitochondria and caspases) signals are integrated. A second part is then devoted to the importance of p53 and of its regulators (ATR, ATM, DNA-PKcs) in the process of radiation-induced apoptosis. Thereafter, signal transduction pathways and more specially the role of some protein kinases (MEKK, SAPK/JNK, p38-MAPK) is treated. At last, a chapter concerns the clinical interest of radiation-induced apoptosis and the implication of apoptosis in the treatment of certain diseases.

200 Gy sterilised Toxoplasma gondii tachyzoites maintain metabolic functions and mammalian cell invasion, eliciting cellular immunity and cytokine response similar to natural infection in mice

200Gy gamma-irradiated Toxoplasma gondii RH tachyzoites failed to reproduce in vitro and in vivo. In short-term cultures, these parasites maintained a respiratory response, the ability to invade cells and preserved protein and nucleic acid synthesis. ELISA and Western blotting techniques demonstrated the similarity in humoral response between mice infected with gamma-irradiated tachyzoites and animals infected with naive parasites and treated with sulfadoxine, higher than mice immunised with formaldehyde-killed tachyzoites. Splenocyte stimulation by T. gondii antigen produced lymphoproliferative response and cytokine profile (IL-10, IL-12, IFN-gamma and TNF-alpha) similar to those produced by chronic natural infection. Mice immunised with irradiated tachyzoites had extended survival times after subsequent tachyzoite challenge, and displayed minimal cerebral pathology after cyst challenge. Irradiated tachyzoites lose their reproductive ability whilst maintaining metabolic function and may provide a novel tool for the study of toxoplasmosis and vaccine development.

Influence of interferon-gamma on radiation-induced apoptosis in normal and ataxia-telangiectasia fibroblast cell lines

Combination of interferon-gamma (IFN-gamma) with radiation, or chemotherapeutic agents, produces different kind of modulatory effects, depending on the cell types and experimental conditions. The objective of the present study was verify the influence of IFN-gamma on the induction of apoptosis by gamma-radiation. Experiments were carried out on human fibroblast cell lines: VH-25 (primary), MRC-5, and AT-5BIVA (SV40-transformed). Exponentially growing cells were irradiated and exposed to IFN-gamma (1,000, 2,000, and 3,000 UI/mL) until in situ cell staining performed at 6, 24, and 48 h. Induction of apoptosis by ionising radiation was not verified in primary VH-25 cells. A significant increase in the frequencies of apoptotic cells was observed in SV-40-transformed cells lines, MRC-5, and AT-5BIVA fibroblasts, which were irradiated with 1.0 Gy, but the frequencies of necrotic cells were similar to the control levels. In MRC-5 cells, combined treatments with radiation and IFN-gamma induced a statistically significant reduction in the frequencies of apoptotic cells detected at 24 and 48 h after cell irradiation, while for AT cells the interaction effect (reduction of apoptosis frequency) was significant even at earlier time collection (6 h) after gamma-irradiation, and higher when compared to MRC-5 cells. The present study demonstrated that IFN-gamma showed an anti-apoptotic activity in SV40-transformed fibroblasts, normal and AT cells, which were irradiated with gamma-rays, thus indicating a mechanism dependent on the cellular type.

E5 protein of human papillomavirus type 16 protects human foreskin keratinocytes from UV B-irradiation-induced apoptosis

The human papillomavirus type 16 (HPV16) E5 protein associates with the epidermal growth factor receptor (EGFR) and enhances the activation of the EGFR after stimulation by EGF in human keratinocytes. Phosphatidylinositol 3-kinase (PI3K) and ERK1/2 mitogen-activated protein kinase (ERK1/2 MAPK), two signal molecules downstream of the EGFR, have been recognized as participants in two survival signal pathways in response to stress. The fact that E5 can enhance EGFR activation suggests that E5 might act as a survival factor. To test this hypothesis, the apoptotic response of UV B-irradiated primary keratinocytes infected with either control retrovirus, LXSN, or HPV16 2E5-expressing recombinant retrovirus was quantitated. Under the same conditions, LXSN-infected cells showed extensive apoptosis, while E5-expressing cells demonstrated a significant reduction in UV B-irradiation-induced apoptosis. The E5-mediated protection against apoptosis was blocked by wortmannin and PD98059, specific inhibitors of the PI3K and ERK1/2 MAPK pathways, respectively, suggesting that the PI3K and ERK1/2 MAPK pathways are involved in this process. Western blot analysis showed that Akt (also named protein kinase B), which is a downstream effector of PI3K, and ERK1/2 MAPK were activated by EGF. When cells were stimulated by EGF and irradiated by UV B, the levels of phospho-Akt and phospho-ERK1/2 activated by EGF in E5-expressing cells were about twofold greater than those in LXSN-infected cells. Two other UV-activated stress pathways, p38 and JNK, were activated to the same level during UV B irradiation in both LXSN-infected cells and E5-expressing cells, indicating that E5 protein did not affect these two pathways. After UV B irradiation, p53 was activated in both LXSN-infected cells and E5-expressing cells, and cell cycle analysis showed that nearly all cells in both cell populations were growth arrested. These data suggest that unlike HPV16 E6, which blocks apoptosis by inactivation of p53, HPV16 E5 protects cells from apoptosis by enhancing the PI3K-Akt and ERK1/2 MAPK signal pathways.

Prospects for viral-based strategies enhancing the anti-tumor effects of ionizing radiation

Ionizing radiation (IR) has been extensively used to treat a variety of solid tumors to improve local control and overall survival in patients. Gene therapy strategies represent one experimental direction to improve radiocurability. These gene therapy strategies include (1) replacement of mutated or deleted tumor-suppressor genes, (2) delivery of prodrugs, (3) transduction of genes under the control of radiation-inducible promoters, and (4) genetically engineered viruses that replicate preferentially in tumor cells after IR. Although any one of these viral-based gene therapy approaches is unlikely to succeed independently, experimental results suggest that clinically important antitumor can be achieved when these strategies are combined with IR. Several of these strategies are currently being or soon will be evaluated in clinical trials. This review focuses on molecular mechanisms and potential clinical application of these viral-based gene therapy strategies to improve the therapeutic index of IR.

Acetoxy-4-methylcoumarins confer differential protection from aflatoxin B(1)-induced micronuclei and apoptosis in lung and bone marrow cells

The ability of various acetoxy derivatives of 4-methylcoumarins to inhibit the genotoxic changes due to aflatoxin B(1) (AFB(1)) is reported here. Several 4-methylcoumarins (test compounds), such as 7,8-diacetoxy-4-methylcoumarin (DAMC), monoacetoxy-4-methylcoumarin (MAC), 5-N-acetyl-6-acetoxy-4-methylcoumarin (NAMC) and 7,8-dihydroxy-4-methylcoumarin (DHMC) were separately administered intraperitoneally (i.p.) to male wistar rats followed by AFB(1) administration i.p. or intratracheally (i.t.) (2-8 mg/kg b.wt.) and another dose of the test compound. The animals were sacrificed 26h after AFB(1) administration. From animals receiving AFB(1) i.p., bone marrow (BM) cells were isolated and stained with Mayer's haematoxylin and eosin. Micronuclei (MN) in BM were scored by light microscopy. From animals receiving AFB(1) i.t., bronchoalveolar lavage (BAL) was obtained, lung cells (LG) were isolated and stained with fluorochrome 6-diamidino-2-phenylindole (DAPI) for the analysis of MN, apoptotic bodies (AP) and cell cycle variations. Rats were separately treated with the vehicle DMSO to serve as the proper control. AFB(1) caused significant dose-dependent induction of MN in BM as well as LG. AP were observed in LG of rats receiving AFB(1) and was found to correlate with MN induction. DAMC injection caused significant decrease in AP due to AFB(1) in LG and MN in both BM and LG. The effectiveness of MAC was approximately half that of DAMC, thereby indicating that number of acetoxy groups on the coumarin molecule determine the efficacy. The fact that NAMC had no effect either on MN or AP indicate that neither acetoxy group at C-6 nor the N-acetyl group at C-5 facilitate the transfer of acetyl group to P-450 required for inhibition of AFB(1)-epoxidation. DHMC, the deacetylated product of DAMC had no normalizing effect on the induction of MN and AP. These findings confirm our earlier hypothesis that DAMC-mediated acetylation of microsomal P-450 (catalysing epoxidation of AFB(1)) through the action of microsomal transacetylase is responsible for the protective action of DAMC. The relative number and position of acetoxy groups on the coumarin nucleus determine the specificity to the transacetylase necessary for the chemopreventive action.

Involvement of the pathway phosphatidylinositol-3-kinase/AKT-1 in the establishment of the survival response to ionizing radiation

Ionizing radiation is one of the agents inducing activation of DNA repair, cell cycle arrest, apoptosis and cell death. Here we report evidence for an enhanced activity of DNA polymerase beta, one of the repair enzymes, concomitant to the activation of the pathway phosphatidylinositol-3-kinase/AKT-1 (PI-3-kinase/AKT-1), which delivers a survival signal in Friend erythroleukemia cells exposed to 15 Gy. Significantly, the preincubation of the cellls with PI-3-kinase inhibitors wortmannin and LY 294002, disactivating this pathway, sensitizes the cells to ionizing radiation by further reducing the rate of proliferation without substantial variations of the number of dead cells. Thus, we suggest a role for these enzymes in maintaining survival programs upon exposure to ionizing radiation and in giving to these cells a chance to recover from this stress.

Wortmannin selectively enhances radiation-induced apoptosis in proliferative but not quiescent cells

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.

Growth arrest and cell death in the breast tumor cell in response to ionizing radiation and chemotherapeutic agents which induce DNA damage

Breast tumor cells are relatively refractory to apoptosis in response to modalities which induce DNA damage such as ionizing radiation and the topoisomerase II inhibitor, adriamycin. Various factors which may modulate the apoptotic response to DNA damage include the p53 status of the cell, levels and activity of the Bax and Bcl-2 families of proteins, activation of NF-kappa B, relative levels of insulin like growth factor and insulin-like growth factor binding proteins, activation of MAP kinases and PI3/Akt kinases, (the absence of) ceramide generation and the CD95 (APO1/Fas) signaling pathway. Prolonged growth arrest associated with replicative senescence may represent an alternative and reciprocal response to DNA-damage induced apoptosis that is p53 and/or p21waf1/cip1 dependent while delayed apoptosis may occur in p53 mutant breast tumor cells which fail to maintain the growth-arrested state. Clearly, the absence of an immediate apoptotic response to DNA damage does not eliminate other avenues leading to cell death and loss of self-renewal capacity in the breast tumor cell. Nevertheless, prolonged growth arrest (even if ultimately succeeded by apoptotic or necrotic cell death) could provide an opportunity for subpopulations of breast tumor cells to recover proliferative capacity and to develop resistance to subsequent clinical intervention.

Radioprotective effects of the thiols GSH and WR-2721 against X-ray-induction of micronuclei in erythroblasts

The frequency of micronucleated polychromatic erythrocytes (MNPCEs) was assessed in the bone marrow and peripheral blood of adult male Swiss mice treated with reduced glutathione (GSH) and S-2-/3-aminopropylamino/ethyl phosphorothioic acid (WR-2721), at a dose of 400 mg/kg body weight, and exposed to 6 Gy X-rays. GSH or WR-2721 was applied alone, or 60 and 30 min, respectively, prior to X-ray-exposure. The number of MNPCEs was determined at 24 h after the thiol treatment and X-irradiation. The radioprotection and toxicity caused in the mouse erythroblasts by GSH and WR-2721, as indicated by the number of MNPCEs were dependent on the thiol applied. The stronger radioprotective effect is obtained following WR-2721 administration than after GSH application. WR-2721 showed greater toxicity than GSH. The combination of GSH and WR-2721 given before X-ray-exposure resulted in the most radioprotective effect as compared to the respective single-drug treatment of mice. Application of the both thiols, without subsequent X-irradiation appeared to be the most toxic, compared with administration of WR-2721 or GSH alone. The effective radioprotection by the combined action of GSH and WR-2721 against genomic instability induced in the mouse erythroblasts by X-rays was shown.

Radiation response of cell organelles

The cellular responses to various form of radiation, including ionizing- and UV-irradiation or exposure to electromagnetic fields is manifested as irreversible and reversible structural and functional changes to cells and cell organelles. Moreover, beside the morphological signs related to cell death, there are several reversible alterations in the structure of different cell organelles. The radiation-induced changes in the supramolecular organization of the membranes, including plasma membrane, and different cell organelle membranes, play a significant role in the development of acute radiation injury. These signs of radiation-induced reversible perturbation biological membranes reflect changes in the organization and/or composition of the glycocalix, modified activity and/or distribution of different membrane domains, including enzymes and binding sites. The observed changes of the cell surface micromorphology and the alteration of intercellular connections are closely related to the reorganization of the cytoskeletal elements in the irradiated cells. The mitochondria, endoplasmic reticulum, Golgi-complex, the lysosomal system have long been considered to be direct intracellular targets of irradiation. The listed morphological alterations of nuclear chromatin (e.g. changes of fine structure, altered number of nucleolar organizing regions and micronuclei, development of chromosome aberrations) may originate from the radiation-induced damage to the supramolecular organization of DNA and/or nucleus specific proteins. These endpoints of radiation effects resulted as direct consequence(s) of absorbed radiation energy, and indirectly altered intra-, intercellular communication or modified signal transduction. Some complementary data suggest that all these effects are not strictly specific to radiation and may be best considered as general stress responses, similar to those observed after application of various injurious agents and treatments to cells. Moreover, they may be equally responsible for direct degradation of supramolecular component of cells, altered signal transduction, or changes in the amount or ratio of any extracellular mediators upon irradiation. Nevertheless, qualitative and/or quantitative evaluation of any changes of chromosomes by different techniques (morphological analysis of metaphase chromosomes, fluorescent in situ hybridization, development of micronuclei etc.) are useful biological indicators as well as "biological dosimeters" of radiation injury. It is suggested, that some modern methods such as immunohistochemical detection of different proteins, specific markers of cell organelles and cytoskeleton, inspection of distribution of cell surface charged sites and different membrane domains and application of tracer substances may all be included into protocols for evaluation of cell alterations induced by different types and intensities of radiation.

Simultaneous analysis of radio-induced membrane alteration and cell viability by flow cytometry

BACKGROUND

Modifications of intracellular transfer, resulting from a loss of membrane integrity may contribute toward setting the cell onto the pathway of apoptosis.

METHODS

We have developed an original technique of measuring simultaneously, with flow cytometry, changes in membrane fluidity and cell death status. Our aim was to assess the extent to which radio-induced cell death and membrane alterations are linked. Investigations were performed on lymphocytes 24 h after whole human blood gamma-irradiation.

RESULTS

Our results confirmed the expected increase in the percentage of apoptotic cells as a function of dose, but revealed that the percentage of necrotic cells appeared stable after irradiation. At the same time, the fluorescence anisotropy of the living lymphocyte subpopulation decreased significantly and dose dependently as measured 24 h post-irradiation. With TMA-DPH, the anisotropy index of apoptotic lymphocytes was always lower than that of the viable lymphocyte subpopulation. On the other hand, 1,6-diphenyl-1,3,5-hexatriene (DPH) anisotropy was similar in apoptotic and viable cells after irradiation. These findings suggest that apoptotic lymphocytes are characterised by a membrane fluidization that mainly occurs on the cell membrane surface.

CONCLUSION

Our study made technical advances in using cytometric fluorescence anisotropy measurement as an early biological indicator of apoptosis after cellular exposure to ionising radiation.

Effects of radiation on cerebral vasculature: a review

Radiation therapy plays a critical role in the treatment of central nervous system neoplasms and cerebral arteriovenous malformations. The deleterious effects of radiation on cerebral arteries may be the primary limitation to these treatment methods, as radiation may cause a variety of cerebrovascular injuries and hemodynamic changes. Radiation-induced changes in the cerebral arterial wall are determined by a number of cellular processes in endothelium and smooth muscle cells that modulate differences in radiosensitivity and phenotypic expression. The histopathological findings in arterial radiation injury include vessel wall thickening, thrombosis, luminal occlusion, and occasional telangiectases. Mechanisms for radiation injury to blood vessels include phenotypic changes in normal vessel wall cells (especially endothelium) manifested by the expression or suppression of specific gene and protein products that affect cell cycle progression or cellular proliferation or demise via cytotoxic injury or apoptosis. This review describes the molecular and cellular events involved in the systemic and cerebral vascular response to radiation and the potential means by which these responses may be influenced to augment the therapeutic effects of radiation while minimizing the untoward consequences.

Gamma irradiation leads to two waves of apoptosis in distinct cell populations of the retina of newborn rats

Gamma radiation induces apoptosis in the proliferative zone (neuroblastic layer) of the developing rat retina. We asked whether sensitivity to apoptosis might be related to distinct phases of the cell cycle. Explants of newborn rat retina or newborn pups were gamma-irradiated and apoptosis was detected by chromatin condensation, DNA fragmentation in situ and DNA electrophoresis. After 6 hours, early appearing apoptotic bodies were located mainly towards the outer tier of the neuroblastic layer. In contrast, after 24 hours, late-appearing apoptotic cells were located towards the inner margin of the neuroblastic layer, a region associated with the S phase of the cell cycle. Labeling of a cohort of cells with the nucleotide analog bromo-deoxyuridine (BrdU) at the time of irradiation, showed that these cells die in the late wave of apoptosis. BrdU given 3 hours before fixation labeled a large number of late apoptotic cells, but no early apoptotic cells. After labeling of all cycling cells with BrdU, 40% of the early apoptotic profiles were unlabeled, and thus post-mitotic. The same schedules of cell death were identified after gamma irradiation in vivo. The results show that irradiation leads to two waves of apoptosis in distinct cell populations. An early wave comprises both post-mitotic cells and proliferating cells out of the S phase. The late wave comprises cells in S phase, which pass through this phase again to die. The antioxidant pyrrolidinedithiocarbamate prevented the early but not the late wave of apoptosis following irradiation, and blocked lipid peroxidation at 6 hours after the insult, suggesting that the two waves of apoptosis are indeed mediated by distinct mechanisms.