Genetic susceptibility to thymic lymphomas and K‐ras gene mutation in mice after exposure to X‐rays and N‐ethyl‐N‐nitrosourea

Purpose: Ras activation is one of the major mechanisms for the development of murine thymic lymphomas by radiation and chemical carcinogens. To gain insight into the relationship between genetic susceptibility and ras gene mutation, the frequency and spectrum of ras gene mutation was examined in thymic lymphomas from susceptible and resistant mice.

Materials and methods: K‐ and N‐ras mutations in thymic lymphomas that arose in X‐ray‐irradiated and N‐ethyl‐N‐nitrosourea (ENU)‐treated mice of susceptible C57BL/6, rather resistant C3H and their hybrid B6C3F1 were analysed by polymerase chain reaction‐single‐strand conformation polymorphism and subsequent DNA sequencing.

Results: C57BL/6 exhibited a higher incidence of thymic lymphomas after exposure to X‐rays and ENU than C3H, with B6C3F1 being intermediate. K‐ras gene mutations occurred frequently in the pathogenesis of ENU‐induced thymic lymphomas in susceptible C57BL/6 as opposed to resistant C3H. The ras mutations were more frequent in ENU‐induced thymic lymphomas than X‐ray‐induced thymic lymphomas, and with the latter, there was no clear evidence for strain differences, suggesting that the genetic susceptibility to X‐rays was independent of ras activation. The mutations of K‐ras in thymic lymphomas from C57BL/6 were predominantly GGT to GAT in codon 12, whereas this mutation type was never found in those from C3H. No strain difference was observed in the nucleotide sequence or expression levels of O⁶‐alkylguanine alkyltransferase, indicating that this enzyme did not account for the genetic susceptibility to ras activation.

Conclusions: The results indicate that there is a clear strain and carcinogen dependency of K‐ras mutation and that the frequency of ras mutation might determine the genetic susceptibility to ENU‐induced lymphomagenesis, whereas pathways independent of ras activation might determine the susceptibility to X‐ray‐induced lymphomagenesis.     

Decreased c‐Myc expression and its involvement in X‐ray‐induced apoptotic cell death of human T‐cell leukaemia cell line MOLT‐4

Purpose: To investigate the possible involvement of c‐Myc and ceramide‐c‐Jun N‐terminal kinase (JNK) pathway in X‐ray‐induced apoptotic cell death of MOLT‐4 cells.

Materials and methods: The expressions of c‐Myc protein and c‐myc mRNA after X‐irradiation were analysed by Western blotting and RT‐PCR between radiosensitive MOLT‐4 and radioresistant variant Rh‐1a cells with less JNK activation than the parental cells. Apoptotic cell death was determined by a dye exclusion test, the appearance of chromatin condensation and DNA fragmentation. The effect of a JNK activator anisomycin or c‐Myc inhibitor peptides (Int‐H1‐S6A, F8A) on the amount of c‐Myc protein and on the induction of apoptosis was investigated, respectively.

Results: In X‐irradiated MOLT‐4 cells, amounts of both c‐myc mRNA and c‐Myc protein rapidly decreased, which was followed by apoptotic cell death, while little change or limited reduction of c‐Myc protein was observed in X‐irradiated Rh‐1a cells with accompanying higher cell viability. Exposure of MOLT‐4 and Rh‐1a cells to c‐Myc inhibitor peptides similarly induced apoptotic cell death with decreases of c‐Myc protein. Anisomycin rapidly induced JNK activation and a subsequent decrease of c‐Myc protein, causing cell death in MOLT‐4 cells. On the other hand, Rh‐1a cells were more resistant to anisomycin than parental MOLT‐4 cells, showing less JNK activation and a delayed decrease of c‐Myc protein.

Conclusion: A decrease of c‐Myc protein was considered important in X‐ray‐induced apoptotic cell death of MOLT‐4 cells; activation of the JNK pathway caused reduction in the amounts of c‐myc mRNA and c‐Myc protein, and finally induced apoptotic cell death.     

Assessment of DNA damage produced by 125I‐triplex‐forming oligonucleotides in cells

Purpose: Triplex‐forming oligodeoxyribonucleotides (TFOs) bind specifically to their target sequences by forming hydrogen bonds within the major groove of the target duplex. When labeled with Auger‐electron‐emitting radioisotopes, TFOs are able to damage the target gene in a process named antigene radiotherapy. We compared radiotoxicity and the amount of DNA damage produced within cultured cells by two ¹²⁵I‐labeled TFOs, one with a single target in the genome and another with multiple targets.

Materials and methods: Radiotoxicity was measured by clonogenic assay while DNA damage was assessed by the number of histone γ‐H2AX foci formed at the sites of DNA double strand breaks (DSBs).

Results: The TFO with multiple nuclear targets was 1.7 fold more radiotoxic and produced on average 1.9 fold more γ‐H2AX foci per cell than the TFO with a single target.

Conclusion: Since the two methods gave comparable results, measuring the number of γ‐H2AX foci per decay may be a useful procedure for the assessment of cytotoxic effects and the intranuclear localization of radionuclides when they produce DSBs.     

Chromosomal Radiosensitivity in Secondary‐Progressive Multiple Sclerosis Patients

Purpose: To investigate chromosomal radiosensitivity of secondary progressive (SP) multiple sclerosis (MS) patients in comparison to a group of healthy individuals.

Material and methods: Chromosomal radiosensitivity was assessed in vitro with the G2 assay and the G0‐micronucleus (MN) assay. For the G2 assay phytohaemagglutinin (PHA) stimulated blood cultures were irradiated with a dose of 0.4?Gy ⁶⁰Co γ rays in the G2 phase of the cell cycle. For the MN assay unstimulated diluted blood samples were exposed to 3.5?Gy ⁶⁰Co γ rays delivered at a high dose‐rate (HDR=1?Gy/min) or low dose‐rate (LDR=4 mGy/min).

Results: No significant differences in the number of chromatid breaks were observed between MS patients and healthy individuals. With the G0‐MN assay a higher spontaneous MN yield was found in MS patients. At HDR irradiation no significant differences were shown, while at LDR irradiation, MS patients were found less sensitive than healthy controls. The dose‐rate sparing index was higher for MS patients, pointing to a better repair capacity.

Conclusions: MS patients are not characterised by an enhanced in vitro chromosomal radiosensitivity. The radioresistant response, which was only observed with the MN assay after LDR irradiation, may point to an adaptive response induced by in vivo oxidative stress in SPMS patients.     

Role of Ca2+ in radiation‐induced damage in murine splenocytes

Purpose: To address the links between calcium, peroxidation, cell damage and death and the response of the enzymes involved in free radical metabolism, in splenocytes of mice irradiated with gamma‐rays.

Materials and methods: Splenocytes of Swiss albino mice were irradiated with various doses (0–7?Gy) of gamma‐rays (⁶⁰Co) at a dose‐rate of 0.0575?Gy?s^?1. Membrane peroxidation and fluidity were determined by the thiobarbituric acid‐reactive substances (TBARS) method, and fluorescence polarization of 1,6‐diphenyl‐1,3,5‐hexatriene (DPH), respectively. Apoptosis was analysed by nucleosomal ladder formation and activity of NF‐κB by electrophoretic mobility shift assay (EMSA). The specific activities of the antioxidant enzymes, lactate dehydrogenase (LDH), levels of nitric oxide (NO^?) and glutathione were determined spectrophotometrically. Modulatory effects of Ca²⁺ were examined at 3?Gy using different concentrations (1, 3 and 5?mM) in the presence or absence of the ionophore A23187.

Results: Irradiation of splenocytes resulted in enhanced peroxidative damage, membrane fluidity, apoptosis and DNA binding activity of NF‐κB. The specific activities of LDH and antioxidant enzymes superoxide dismutase (SOD), DT‐diaphorase (DTD), glutathione S‐transferase (GST) and levels of glutathione (GSH) and NO^? were increased with radiation dose up to 4?Gy. Ca²⁺ augmented the radiation‐induced responses. The presence of ionophore A23187 potentiated the modulatory effects of Ca²⁺.

Conclusions: These findings show that Ca²⁺ augments radiation damage and is more effective intracellularly. Ca²⁺, peroxidation, cellular damage and apoptosis are possibly interlinked through signals, as is evident from the increased activity of NF‐κB and generation of NO^?. The enhanced antioxidant status suggests an attempt made by the irradiated cells to maintain their normal functions.     

Repeated exposure to low‐level extremely low frequency‐modulated microwaves affects baseline and scopolamine‐modified electroencephalograms in freely moving rats

Purpose: To compare in the electroencephalogram of rats the effects of scopolamine (an acetylcholine receptor antagonist) alone and after repeated exposure to low‐level microwaves modulated at extremely low frequency.

Materials and methods: Averaged frequency spectra (0.5–30?Hz) of the electroencephalogram were studied in freely moving rats with carbon electrodes implanted into the somatosensory cortex. The rats were repeatedly (3 days, 30?min?day^?1) exposed to low‐intensity (?0.3?mW?cm^?2) microwaves (915?MHz, 20‐ms pulse duration), amplitude modulated (square‐wave) at extremely low frequency (4?Hz).

Results: The exposure to extremely low frequency microwaves alone significantly enhanced the fast electroencephalographic rhythms (18–30?Hz). This effect was observed neither in subsequent sham‐exposure experiment nor in radiation‐naïve animals. In the microwave‐exposed rats, scopolamine (0.1?mg?kg^?1, subcutaneously) did not cause a slowing in the electroencephalogram that was shown in non‐exposed rats. A similarity between the scopolamine‐induced electroencephalogram effect in the microwave‐exposed rats and that of physostigmine (enhancing the acetylcholine level in the brain) in radiation‐naïve animals was noted. This paradoxical phenomenon stimulates new experimentation for understanding its mechanism(s).

Conclusions: The data obtained provide additional evidence that repeated low‐level exposure to extremely low frequency microwaves can modify an activity of cholinergic system in the brain.     

Persistence of altered 5‐hydroxytryptamine turnover following hemibody X‐irradiation in the rat distal colon

Purpose: Acute gastrointestinal responses to ionizing radiation exposure include a role for 5‐hydroxytryptamine (5‐HT), but it is not known whether involvement of 5‐HT persists and contributes to late effects. The aim was to investigate the acute and later effects of lower hemibody irradiation on 5‐HT turnover and the biological effect in the rat distal colon.

Materials and methods: Rats were exposed to 10?Gy lower hemibody X‐radiation. 5‐HT and 5‐hydroxyindole acetic acid tissue levels were measured in the distal colon along with the serotonin re‐uptake transporter and tryptophan hydroxylase mRNA. 5‐HT‐containing cells and crypt cell numbers were estimated in addition to 5‐HT‐stimulated short‐circuit current responses in isolated mucosa. Studies were performed from 3 days to 3 months post‐exposure.

Results: During the acute phase, at 3 days post‐irradiation, reductions in cell number, tissue resistance, serotonin re‐uptake transporter expression and secretory responses to 5‐HT were observed. However, at later times when secretory responses were normal, 5‐HT tissue levels and enterochromaffin cell numbers were increased.

Conclusions: The results provide evidence that after 10?Gy hemibody irradiation, modifications persist past the acute phase. In particular, 5‐HT turnover in the distal colon is altered during a longer period.     

Androgen and the blocking of radiation‐induced sensitization to Fas‐mediated apoptosis through c‐jun induction in prostate cancer cells

Purpose: To clarify the key mechanism by which androgen makes prostate cancer cells highly resistant to Fas‐mediated apoptosis.

Materials and methods: The role of c‐jun induction by 10?nM dihydrotestosterone (DHT) in 5?Gy radiation‐induced up‐regulation of Fas and sensitization to the apoptosis was studied by using the human prostate cancer cell line LNCaP.

Results: On exposure to 5?Gy radiation, LNCaP cells demonstrated high sensitization to Fas‐mediated apoptosis through increased Fas expression, stabilized p53 expression and binding to p53 response elements within the promoter and first intronic region of the Fas gene. Following treatment with DHT, in vivo binding of p53 to its response elements was strongly inhibited. In addition, DHT significantly up‐regulated c‐jun expression through extracellular stress‐regulated kinase (ERK) activation, and transfection of an antisense oligonucleotide for c‐jun or ERK inhibition by PD98059 cancelled DHT‐mediated suppression of radiation‐induced transactivation of Fas gene and sensitization to Fas‐mediated apoptosis.

Conclusions: Radiation‐induced Fas sensitization in prostate cancer cell was mediated through p53‐dependent transactivation of the Fas gene, which can be blocked by androgen stimulation mainly through induction of c‐jun.     

Radiation‐induced fragmentation of cardiolipin in a model membrane

Purpose: To obtain evidence for the possibility of free‐radical fragmentation of cardiolipin under the action of ionizing radiation as measured by its aqueous dispersion from liposomes.

Materials and methods: Liposomes of tetramyristoylcardiolipin (TMCL) were exposed to γ‐rays from ⁶⁰Co or ¹³⁷Cs sources at doses between 1 and 24?kGy. Fragmentation products were identified using thin‐layer chromatography and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS).

Results: Using MALDI‐TOF MS and thin‐layer chromatography, it was shown that γ‐irradiation of liposomes consisting of TMCL was accompanied by free‐radical fragmentation of the lipid to form dimiristoylphosphatidic acid and dimiristoylphosphatidyl hydroxyacetone. The yields of dimiristoylphosphatidic acid were greater than those of dimiristoylphosphatidyl hydroxyacetone, and formation of the named compounds was inhibited by dissolved oxygen.

Conclusion: It is shown for the first time that on γ‐irradiation, cardiolipin can undergo free‐radical fragmentation in its polar component.     

Therapeutic potential of 5‐[125I]iodo‐2′‐deoxyuridine and methotrexate in the treatment of advanced neoplastic meningitis

Purpose: To assess the therapeutic potential of methotrexate (MTX) and 5‐[¹²⁵I]iodo‐2′‐deoxyuridine (¹²⁵IdUrd) administered sequentially in rats bearing advanced (ten‐day‐old) intrathecal (i.t.) TE671 human rhabdomyosarcoma tumours.

Materials and methods: Nude rats were injected with TE671 cells through an i.t. placed catheter. Ten days later, the animals were injected i.t. over a 12‐day period with (i) saline daily, (ii) MTX every other day, (iii) ¹²⁵IdUrd every other day, or (iv) MTX and ¹²⁵IdUrd on alternating days. Onset of paralysis was determined as a function of time, and the medians for onset (M), percentage of cells killed (% kill), and log cell kill were calculated.

Results: The data show that (i) injection of MTX leads to a moderate delay in the onset of paralysis (M_MTX=29?d versus M_saline=20?d), (ii) administration of ¹²⁵IdUrd is more effective (M_IdUrd=36?d), and (iii) sequential administration of MTX–¹²⁵IdUrd further increases the therapeutic efficacy of ¹²⁵IdUrd (M_MTX–IdUrd=47?d).

Conclusions: Intrathecal injection of MTX–¹²⁵IdUrd is efficacious in the therapy of advanced intrathecal tumours.     

Difference in the induction,but not in the repair,of X‐ray‐ and nitrogen ion‐induced DNA single‐strand breaks as measured using human cell extracts

Purpose: To compare the repair efficiency of X‐ray (low linear energy transfer [LET]) and nitrogen ion (high LET)‐induced single‐strand breaks (SSB) in a human cell‐free end‐joining system.

Materials and methods: SSB were introduced into a bacterial plasmid, pBR322, by X‐rays (4?MeV photons) and nitrogen ions with an LET=125?keV?µm^?1. Repair efficiency was studied under incubation with the protein extracts from human squamous carcinoma cells, UT‐SCC‐5.

Results: A several fold higher dose of nitrogen ion radiation compared with X‐ray radiation was needed to induce a similar loss of supercoiled plasmid DNA. There was no difference in the repair efficiency of SSB induced by these two types of radiation.

Conclusion: The data indicate that X‐rays at 25?Gy and nitroging ions at 100?Gy radiation doses, under condition of low scavenging capacity (10?mM Tris), induce SSB of similar complexity or, alternatively, differences in SSB complexity do not alter the repair rate.     

Time benefit in the assessment of recurrences following fractionated radiotherapy in an experimental tumour system using positron‐emission tomography with 18F‐fluorodeoxyglucose

Purpose: To determine the sensitivity and specificity of ¹⁸F‐fluorodeoxyglucose‐positron‐emission tomography (FDG‐PET) in the diagnosis of R1H tumours after fractionated radiotherapy, and the dependency of sensitivity and specificity on time after therapy. In addition, the time benefit of FDG‐PET concerning early recognition of recurrences after fractionated radiotherapy was assessed.

Material and methods: Subcutaneously growing rat rhabdomyosarcoma R1H tumours were irradiated by applying total doses of 80 or 85?Gy after reaching a start volume of 0.8?cm³. Twenty animals were treated. Tumour volume was determined twice a week. FDG‐PET was performed weekly before, during and for 6 months after therapy using a conventional full‐ring whole‐body PET scanner. In total, 600 PET results were evaluated qualitatively using a six‐scale score. PET results and actual tumour volumes were compared. The sensitivity and specificity of tumour detection by PET was calculated for different times after the onset of therapy. The optimal score for tumour detection and the influence of time after therapy on the quality of PET (time benefit) was evaluated using receiver‐operating characteristics.

Results: After irradiation, 8/20 tumours (40%) were locally controlled, while 12/20 recurred. In this tumour model, evidence of relapse is assured when a volume of 0.1?cm³ is reached. Sensitivity of tumour diagnosis by PET increases with time, i.e. with the volume of recurrent tumours after the onset of therapy, mounting to >0.95 after 100 days. Specificities of 0.95–1.0 were determined after therapy, showing no increase with time. Tumour diagnosis by PET is highly accurate when performed 80 days after the start of treatment. On average, tumours were recognized by PET on 31, 62, 74 and 81 days (median) before approaching volumes of 0.2, 0.5, 0.8 or 1.0?cm³, respectively.

Conclusion: An experimental system was implemented that allows reproducible detection of recurrent R1H tumours after radiotherapy using FDG‐PET. The usefulness of PET as a diagnostic test for R1H tumours is very good and a reliable resolution for PET is demonstrated for volumes<1?cm³. The results indicate that FDG‐PET enables early recognition of recurrences after fractionated radiotherapy.     

IL‐1β, TNFα and IL‐6 induction in the rat brain after partial‐body irradiation: role of vagal afferents

Purpose: To evaluate the central nervous system neuroimmune and inflammatory responses during the prodromal phase of the acute irradiation syndrome in rat brains after partial‐body exposure (head‐protected) and to investigate the potential neural signalling pathways from the irradiated periphery to the non‐irradiated brain.

Material and methods: The study included four groups of rats: one irradiated group and one sham irradiated group, each containing non‐vagotomized and vagotomized rats. In vagotomized rat groups, the subdiaphragmatic vagal section surgery was carried out 45 days before the irradiation exposure. The rats were partial‐body irradiated with the head shielded with ⁶⁰Co γ‐rays to a dose of 15?Gy. They were sacrificed 6?h after the end of exposure. The hypothalamus, hippocampus, thalamus and cortex were then collected, and the concentrations of IL‐1β, TNFα and IL‐6 in each were measured by ELISA assays.

Results: Six hours after irradiation, IL‐1β levels had increased in the hypothalamus, thalamus and hippocampus, and TNFα and IL‐6 levels had increased significantly in the hypothalamus. Vagotomy before irradiation prevented these responses.

Conclusions: It was concluded that the hypothalamus, hippocampus, thalamus and cortex react rapidly to peripheral irradiation by releasing pro‐inflammatory mediators. The results also show that the vagus nerve is one of the major ascending pathways for rapid signalling to the brain with respect to partial body irradiation.     

Radiation‐induced variations in urothelial expression of intercellular adhesion molecule 1 (ICAM‐1): association with changes in urinary bladder function

Purpose: To assess the effect of single‐dose irradiation on intercellular adhesion molecule 1 (ICAM‐1) expression in the urothelium of mouse urinary bladder and to correlate ICAM‐1 variations with fluctuations in storage capacity during the early and late radiation response.

Materials and methods: Groups of female C3H mice were subjected to irradiation with either 20 or 0?Gy. The intensity of immunohistochemical ICAM‐1 staining in the urothelium was assessed in a semiquantitative way applying an arbitrary score (0–5). Changes in bladder storage function were assessed by transurethral cystometry.

Results: For the early radiation response phase, a reduction in bladder capacity by >50%, i.e. a positive functional radiation response, was seen in 40% of the irradiated animals between days 0 and 15, and in 64% of animals during days 16–30. During the late response phase, 71% of the animals sacrificed after day 180 developed a positive functional response. Urothelial cells were found to express ICAM‐1 constitutively. Irradiation resulted in an early rise in staining signal by day 2, with a maximum on day 4 and a return to control values on day 13. A permanent increase in ICAM‐1 staining signal was observed in the late phase, from day 90 to 360 after irradiation. The expression of ICAM‐1 in animals with a positive late response was 4.2±1.2 (mean±standard deviation), compared with 2.6±1.0 in non‐responders (p=0.0009).

Conclusion: Irradiation induces significant acute and chronic changes in urothelial ICAM‐1 expression indicating that the urothelium contributes to the pathogenesis of both acute and late radiation effects in the urinary bladder.     

Identification of proteins in the hamster DNA end‐binding complex

Purpose: To identify the protein components of the DNA end‐binding complex in hamster cells.

Materials and methods: DNA end‐binding complexes were identified as follows. Nuclear extracts from Chinese hamster ovary cells (0.5–1.0?µg protein/lane) were incubated with 0.5?ng ³²P‐labelled probe (144?bp) for 20?min at room temperature in the presence of 1?µg closed circular pUC18 plasmid, a non‐specific competitor in a final volume of 20?µl. The electrophoretic mobility of the protein–DNA complexes was analysed by electrophoresis in 5% polyacrylamide gels subjected to autoradiography. Antibodies to various DNA repair‐associated proteins were added to the DNA end‐binding complex reaction and a supershift identified DNA end‐binding complex components. These were confirmed by Western analysis of purified DNA end‐binding complex contents.

Results: Using both supershift and Western analysis, the following proteins were identified in the DNA end‐binding complex: Ku70, Ku80, DNA‐dependent protein kinase catalytic subunit, DNA ligase IV, X‐ray cross complementing protein 4, meiotic recombination protein 11 (Mre11), Werner's syndrome protein, Bloom's syndrome protein, p53, poly(ADP‐ribose) polymerase, replication protein A (RPA) 14, and RPA32, ataxia telangiectasia mutant, c‐Abl, Rad50, Nijmegen breakage syndrome protein 1 (NBS1), and DNA ligase III were not detected in the binding complex by any assay. Using a combination of electro‐elution and autoradiography, it was estimated that the single DNA end‐binding complex contains at least 15 proteins whose molecular weights of the DNA end‐binding proteins ranged from 620 to 12?kDa.

Conclusions: A combination of both a supershift assay and Western analysis of the DNA end‐binding complexes has identified 12 of at least 15 proteins present in the DNA end‐binding complex of Chinese hamster ovary cells. This protein complex contains Mre11, but not Rad50 or NBS1, suggesting that under some conditions, Mre11 might function independently of Rad50 and NBS1.     

Distribution of radiation‐induced exchange aberrations in all human chromosomes

Purpose: To investigate the DNA‐proportional distribution of radiation‐induced chromosome aberrations for all chromosomes of a male and a female human karyotype.

Materials and methods: Metaphases were prepared from whole blood cultures obtained from two healthy donors and set up after irradiation with 3?Gy 220?kV X‐rays. Single whole‐chromosome FISH painting simultaneously with pancentromeric DNA painting were performed separately for each chromosome of the human karyotype. One thousand exclusively first‐division metaphases were analysed per chromosome and donor. After statistical analysis, the data obtained were compared with theoretically expected values.

Results: All aberration types (translocations, dicentrics) showed deviations from a DNA‐proportional distribution. For both donors, chromosomes 2 and 3 exhibited significantly less and chromosome 4 more symmetrical translocations than expected. Chromosomes 15 and 22 showed more symmetrical translocations than predicted for one of the two donors. Less dicentrics than expected became apparent for chromosomes 2, 3 and 18, while more dicentrics were seen for chromosomes 15, 16 and 17. Moreover, chromosomes 4, 14 and 22 showed a significant deviation from the theoretically expected 1:1 ratio of the yields of symmetrical translocations to the yields of dicentrics.

Conclusion: The results from the whole‐chromosome complement in two different donors confirmed published data from the analysis of single chromosomes that some human chromosomes were not involved in radiation‐induced dicentrics and symmetrical translocations proportional to their DNA content. This must be taken into account if chromosome subsets for dose reconstruction are selected or if whole genomic frequencies have to be calculated from partial genome analysis.     

Cellular origin of ionizing radiation‐induced NF‐κB activation in vivo and role of NF‐κB in ionizing radiation‐induced lymphocyte apoptosis

Purpose: To investigate the cellular origin of ionizing radiation (IR)‐induced NF‐κB activation in vivo and the role of NF‐κB in IR‐induced lymphocyte apoptosis.

Materials and methods: NF‐κB activities were analysed by gel shift/supershift assay in isolated murine T‐ and B‐cells, macrophages (M?) and tissues from normal and T‐ and B‐cell‐deficient Rag1 mice with or without exposure to IR. IR‐induced lymphocyte apoptosis was determined by analysis of 3,3′‐dihexyloxacarbocyanine iodide (DiOC₆) uptake, annexin‐V staining and the sub‐G0/1 population, or by TUNEL assay.

Results: The results showed that IR activated NF‐κB in lymphocytes, including both T‐ and B‐cells, but failed to do so in M?. Furthermore, T‐ and B‐cell‐deficient Rag1 mice exposed to IR exhibited a significant reduction in NF‐κB activation as compared with normal mice. Although NF‐κB1 (p50) gene knockout or NF‐κB decoy oligonucleotide treatment specifically inhibited IR‐induced lymphocyte NF‐κB activation, they had no significant effect on IR‐induced lymphocyte apoptosis.

Conclusions: This finding suggests that lymphocytes are the main cellular origin of IR‐induced NF‐κB activation in vivo. However, NF‐κB activation has no significant effect on IR‐induced lymphocyte apoptosis.     

A back‐of‐the‐envelope risk assessment of star wars

The risks associated with the deployment of a Star Wars system and from a space‐based conflict have been rapidly evaluated on the basis of known facts about SDI‐like programmes. Back‐of‐the‐envelope evaluations indicate that effects of a space‐based conflict might be lethal for life on Earth.     

‘In‐field’ and ‘out‐of‐field’ functional impairment during subacute and chronic phases of experimental radiation enteropathy in the rat

Purpose: To investigate subacute and chronic functional consequences of localized irradiation of rat small intestine on exposed and shielded segments (proximal and distal).

Materials and methods: The surgical model of a scrotal hernia was used. The ileal loop was exposed to single doses of 18, 21 or 29.6?Gy X‐irradiation. Epithelial structure and transport capacity were followed 2 and 26 weeks post‐exposure.

Results: Irradiated segments showed mucosal ulceration followed by transmural fibrosis. Transport capacity was impaired from 2 to 26 weeks. Subacute functional impairment was noticed in the proximal segment, without either morphological alteration or neutrophil influx. At 26 weeks, both proximal and distal segments showed impaired epithelial transport capacity, with neutrophil influx in the submucosa in cases of 21‐Gy exposure and in the submucosa and muscularis propria after 29.6?Gy.

Conclusions: Radiation enteritis was characterized by functional impairment, within as well as outside, the irradiation field. During the subacute phase, the irradiated segment may be a source of mediators which might influence intestinal function outside the site of injury via the blood stream and/or enteric nervous system. The development of an intestinal occlusion syndrome during the chronic phase might be responsible for intestinal dysfunction but it does not rule out a possible inflammatory process developing in the shielded parts of the small intestine.