Study of DOK4 gene expression and promoter methylation in sporadic breast cancer.

The analysis of DNA methylation patterns in circulating cell-free DNA in body fluids is an analyte of great interest in clinical research. Downstream of Kinase (DOK) proteins represent a multigenic family of adaptors that includes negative regulators of immune cell signaling and plays important roles in signaling, cellular growth, and survival. The aim of the present study was to investigate the pattern of promoter methylation and expression of the DOK4 gene in breast cancer, and its possible association with histoclinical characteristics. The mRNA expression of the DOK4 gene was evaluated in 164 breast tissues using Real-Time RT-PCR. The promoter methylation of this gene was evaluated in breast tissues and plasma free nucleic acids by MS-PCR. The associations of gene expression and DNA methylation with histoclinical characteristics of the patients were studied. The data indicated that DOK4 mRNA expression was significantly downregulated in breast tumors compared with normal control in all the stages. About 40% of breast tumors showed DOK4 promoter methylation, which somehow confirms the DOK4 promoter methylation rate in the plasma. The data revealed that the reduction in DOK4 expression in all breast cancer groups could well endorse this gene as a candidate possible marker for future investigations on breast cancer management. The DOK4 methylation pattern in breast tissue was correlated with plasma free nucleic acids but the state of DOK4 promoter methylation alone may not be sufficient to differentiate between the two cancerous and normal groups.

Potent radioprotective effects of combined regimens of famotidine and vitamin C against radiation-induced micronuclei in mouse bone marrow erythrocytes.

To investigate the radioprotective effect of the combination of famotidine and vitamin C against radiation-induced micronucleus formation in mouse bone marrow erythrocytes, various doses of famotidine or vitamin C or combinations thereof were administered intraperitoneally to adult male NMRI mice 2 h before 2 and 4 Gy γ-irradiation. The frequency of micronucleated polychromatic erythrocytes (MnPCEs) was scored in 5,000 polychromatic erythrocytes (PCEs), and the cell proliferation ratio [PCE/(PCE + NCE); NCE = normochromatic erythrocytes] was also calculated for each treatment group. Data were statistically evaluated using one-way ANOVA test. The results show that pretreatment with various doses of famotidine and vitamin C before γ-irradiation significantly reduced the frequency of MnPCEs with a protection factor (PF) of 2 and 1.7, respectively. Pretreatment with vitamin C also significantly increased the cell proliferation ratio, while famotidine had no effect. Combination of famotidine and vitamin C was more effective in reducing MnPCEs than each compound alone, leading to a PF of 4.3 after irradiation. Cell proliferation ratio was also significantly improved by the combination compared with the irradiated control groups. Both famotidine and vitamin C are potent scavengers of free radicals and reactive oxygen species, especially OH(·). The combination of the two compounds probably further enhances this activity, thus leading to high bone marrow protection.

Famotidine as a radioprotector for rectal mucosa in prostate cancer patients treated with radiotherapy: phase I/II randomized placebo-controlled trial.

BACKGROUND AND PURPOSE: Acute bowel toxicity significantly affects the quality of life of patients treated with pelvic radiotherapy. This study was performed to assess whether pretreatment with famotidine can reduce acute radiation toxicities in patients undergoing radiotherapy for prostate cancer. PATIENTS AND METHODS: Between April 2012 and February 2013, 36 patients undergoing radiotherapy for prostate cancer were enrolled to receive either placebo or famotidine. The patients received external-beam radiotherapy up to 70 Gy at daily fractions of 1.8-2 Gy (5 days/week). Oral famotidine 40 mg (80 mg/day) or placebo was administered twice daily (4 and 3 h prior to each radiotherapy fraction). Bowel and bladder acute toxicities were evaluated weekly during radiotherapy and once thereafter according to RTOG grading criteria. RESULTS: Famotidine was well tolerated. No grade III or higher acute toxicities were noted in the two groups. Grade II rectal toxicity developed significantly more often in patients receiving placebo than in patients receiving famotidine (10/18 vs. 2/16, p=0.009). Moreover, no rectal bleeding occurred in the famotidine group, while 5 patients in the placebo group experienced rectal bleeding during treatment (p=0.046). The duration of rectal toxicity in the radiotherapy course was also reduced in the famotidine group (15.7 vs. 25.2 days, p=0.027). No significant difference between the two groups was observed in terms of urinary toxicity. CONCLUSION: We demonstrated for the first time that famotidine significantly reduces radiation-induced injury on rectal mucosa representing a suitable radioprotector for patients treated with radiotherapy for prostate cancer.

Importance of sperm gluthatione treatment in ART.

PURPOSE: The aim of this study was to investigate whether treatment of sperm from infertile patients would gluthatione could reduce sperm premature chromosome condensation (PCC). To reach the goals of this study, the frequency of sperm PCC formation in sperm of normal and sub-fertile men with/without glutathione treatment were compared and analyzed. METHODS: Hamster oocytes were retrieved after super ovulation by PMSG and HCG injection. Following treatment with hyaluronidase, zonae was removed by trypsin digestion. Sperm were classified into 3 groups according to morphology, movement and counts, treated with glutathione(10 µg/ml) and then processed by swim up method. After capacitation, zona-free oocytes were incubated with sperm then transferred to fresh media containing colcemid. Cells were fixed and slides prepared using Tarkowskie's standard air drying technique and after staining in 5% Giemsa, oocytes were analyzed at high magnification. RESULTS: Sperm penetration rate was higher and the rate of intact sperm head and PCC was lower in GSH treated samples compared to non treated groups. Sperm penetration rate was significantly higher in treated astheno sperm samples compared to non-treated ones (66.4% and 50. 97% respectively) (P < 0.001). We observed a significantly higher PCC frequency in infertile patients (P < 0.001). In addition, there was a significantly lower rate of intact sperm head in treated astheno sperm samples (17.49%) compared to non treated ones (26.79%) (P < 0.001). Finally, a significantly lower rate of PCC in treated astheno sperm samples comparing to non treated ones was seen (51.06% and 72.96% respectively) (P < 0. 001). CONCLUSIONS: Our results show that sperm PCC formation could be one of the major causes of failed fertilization in individuals with sperm abnormalities. Also sperm PCC formation may be involved in the etiology of some cases of idiopathic infertility. Given that the susceptibility of sperm to oxidative stress is significantly greater in idiopathic infertile men, our results show that treatment with glutathione could significantly reduce these stress factors and increase ART outcome.

Evaluation of concentration and storage effects of mitomycin C in the diagnosis of Fanconi anemia among idiopatic aplastic anemia patients.

BACKGROUND: Fanconi anemia (FA) is a rare autosomal recessive genetic disorder that shows an increased sensitivity to the intercalating agents such as mytomycin C (MMC), measured as chromosomal aberrations. This study was conducted to differentiate between FA and "idiopathic" aplastic anemia on the basis of induced chromosomal breakage study with MMC. MATERIALS AND METHODS: MMC stress tests in different final concentrations of 20 and 50 ng/ml of MMC were conducted on peripheral blood lymphocytes from 32 patients with aplastic anemia and 13 healthy controls. Fifty nanograms per milliliter of MMC from old, fresh and frozen stocks was used to check the sensitivity of diagnosis on FA-diagnosed patients. Statistical analysis was used for the assessment of aberrations, including chromatid and chromosome breaks and exchanges. RESULTS: Eight patients (25%) with a very high percentage of chromosomal breakage were diagnosed as FA on the basis of the chromosomal breakage study. Six of these patients exhibited congenital anomalies at presentation, while another two lacked such anomalies or had minor physical problems. Freshly made MMC has shown more sensitivity to detect FA patients compared with frozen or 1-week-old MMC stock. CONCLUSIONS: The study indicates that freshly made MMC stress test provides an unequivocal means of differentiation between FA and "idiopathic" aplastic anemia. Further, the study, the first of its kind from Iran, stresses on the need for conducting this test in all aplastic anemia cases, even those without congenital anomalies, for accurate and timely diagnosis of FA to implement appropriate therapy.

Modulation of gamma-ray-induced apoptosis in human peripheral blood leukocytes by famotidine and vitamin C.

To study the radioprotective effects of vitamin C and famotidine against radiation-induced apoptosis in human peripheral blood leukocytes, peripheral blood was obtained from six healthy volunteers including three males and three females. Twelve microlitres of blood sample diluted in 1 ml complete RPMI-1640 medium was irradiated with various doses of gamma-rays (4, 8 and 12 Gy) in the presence or absence of various doses of vitamin C and famotidine. After 48 and 72 h incubation in a 37 degrees C CO(2) incubator, neutral comet assay was performed for all samples. At least 1000 cells were analyzed for each sample for presence of apoptosis. Data were statistically evaluated using Mann-Whitney non-parametric and ANOVA tests. Results show a significant increase in apoptosis induction following gamma-irradiation with a dose dependent manner compared to controls (p<0.001). Presence of famotidine at 200 microg/ml produced a significant protective effect against radiation-induced apoptosis for various doses of radiation. Similar effects were observed for vitamin C at much lower doses (10 microg/ml). Dose reduction factor (DRF) calculated for famotidine treatment was about 1.5, and above 2 for vitamin C treatment. These results suggest that both vitamin C and famotidine suppresses radiation-induced apoptosis when used with various doses of gamma-irradiation (4-12 Gy) probably via *OH radical scavenging and an intracellular antioxidation mechanism.

Combined effect of gamma radiation and Perovskia atriplicifolia for the control of red flour beetle, Tribolium castaneum.

In order to explore an effective and safe pesticide that could be coupled up with irradiation method, the present study was conducted to determine the synergistic effects of gamma radiation with an essential oil from Perovskia atriplicifolia (Benth) on Tribolium castaneum (Herbst) as a main stored-product pest. Adult insects were exposed to sub lethal doses of gamma radiation and P. atriplicifolia oil, and the mortality was assessed in a short time period after treatment. There was a significant synergistic effect of exposure to gamma radiation and essential oil on 1-7 days old adults of T. castaneum. The potential toxicity of the essential oil on irradiated adults at 900 Gy was synergistically increased. When irradiated adults were exposed to LD5, LD25 and LD50 values of the oil the mortality was increased 8.5, 13.0 and 16.0 times respectively. This combination of irradiation would have a low environmental impact and high compatibility with P. atriplicifolia.

Among seven testis-specific molecular markers, SPEM1 appears to have a significant clinical value for prediction of sperm retrieval in azoospermic men.

BACKGROUND: To achieve sperm retrieval in azoospermic men, predicting the success rate seems to be necessary. OBJECTIVES: In the present study we aimed to assess expression of seven molecular markers [ESX1, DAZ, DAZL (pre-meiotic markers), ZMYND15, PRM1, TNP1, and SPEM1 (post-meiotic markers)] to predict the success of sperm retrieval. MATERIALS AND METHODS: In this study, 63 azoospermic men [16 OA (obstructive azoospermia) and 47 NOA (nonobstructive azoospermia)] undergoing testicular tissue microdissection (micro-TESE) for intracytoplasmic sperm injection (ICSI). Expression levels of these target genes were determined by real-time reverse transcription polymerase chain reaction using the DDCt method, and efficacy of each gene was compared by receiver operating characteristic (ROC) curve analysis. RESULTS: Expression of post-meiotic transcripts significantly decreases in NOA and its subgroups (SCOS: Sertoli cell only syndrome, MA: maturation arrest, and HS: hypospermatogenesis) with spermatogenic failure compared to normal spermatogenesis (OA), with an exception of ZMYND15 for the HS group. These findings suggest the differential expression of the post-meiotic ZMYND15 marker is in accordance with histological findings and can discriminate HS from SCOS and MA. Post-meiotic markers were significantly reduced in negative vs. positive sperm retrieval groups. DISCUSSION AND CONCLUSION: Among the seven markers, SPEM1 had the best positive prediction power (96%) and negative prediction power (85%) at a 0.086 cutoff with the area under the curve (AUC) of 0.91 for receiver operating characteristic 4 (ROC) to predict the micro-TESE outcome.

Cytogenetic sensitivity of G0 lymphocytes of Fanconi anemia patients and obligate carriers to mitomycin C and ionizing radiation.

It is well known that Fanconi anemia (FA) patients show a hypersensitivity to the effect of cross-linking agents such as mitomycin C (MMC) and diepoxybutane (DEB), while the sensitivity of these patients to ionizing radiation is still controversial. Fanconi anemia heterozygotes do not show a hypersensitivity to the above mentioned agents compared to normal individuals. To examine the radio-sensitivity of Fanconi anemia patients and heterozygotes, ten patients and 13 heterozygotes were enrolled in this study. Standard metaphase analysis for detection and verification of radio-sensitivity was used to establish the relationship between gamma-ray and chromosome breakages in these groups. Statistical analysis was used for the assessment of aberrations including chromatid and chromosome breaks and exchanges. Results of chromosome aberration yield that: (i) differentiation between obligate carriers and the control group after MMC treatment and gamma irradiation was not possible; (ii) homozygotes were clearly distinguishable from heterozygotes and controls after MMC treatment; (iii) FA patients don't show hypersensitivity to gamma irradiation compared to normal controls and heterozygous carriers.

A comparison between track-structure, condensed-history Monte Carlo simulations and MIRD cellular S-values.

The S-value is a standard measure in cellular dosimetry. S-values are calculated by applying analytical methods or by Monte Carlo simulation. In Monte Carlo simulation, particles are either tracked individually event-by-event or close events are condensed and processed collectively in different steps. Both of these methods have been employed for estimation of cellular S-values, but there is no consistency between the published results. In the present paper, we used the Geant4-DNA track-structure physics model as the reference to estimate the cellular S-values. We compared the results with the corresponding values obtained from the following three condensed-history physics models of Geant4: Penelope, Livermore and standard. The geometry and source were exactly the same in all the simulations. We utilized mono-energetic electrons with an initial kinetic energy in the range 1-700 keV as the source of radiation. We also compared our results with the MIRD S-values. We first drew an overall comparison between different data series and then compared the dependence of results on the energy of particles and the size of scoring compartments. The overall comparison indicated a very good linear correlation (R 2 > 91%) and small bias (3%) between the results of the track-structure model and the condensed-history physics model. The bias between MIRD and the results of Monte Carlo track-structure simulation was considerable (-8%). However, the point-by-point comparison revealed differences of up to 28% between the condensed-history and the track-structure MC codes for self-absorption S-values in the 10-50 keV energy range. For the cross-absorption S-values, the difference was up to 34%. In this energy range, the difference between the MIRD S-values and the Geant4-DNA results was up to 68%. Our findings suggest that the consistency/inconsistency of the results obtained with different MC simulations depends on the size of the scoring volumes, the energy of the particles, the step-size in electron tracking and the energy cutoff used in the MC codes.

Radioprotective Effects of Sulfur-containing Mineral Water of Ramsar Hot Spring with High Natural Background Radiation on Mouse Bone Marrow Cells.

BACKGROUND: We intend to study the inhibitory effect of sulfur compound in Ramsar hot spring mineral on tumor-genesis ability of high natural background radiation. OBJECTIVE: The radioprotective effect of sulfur compounds was previously shown on radiation-induced chromosomal aberration, micronuclei in mouse bone marrow cells and human peripheral lymphocyte. Ramsar is known for having the highest level of natural background radiation on Earth. This study was performed to show the radioprotective effect of sulfur-containing Ramsar mineral water on mouse bone marrow cells. METHOD: Mice were fed three types of water (drinking water, Ramsar radioactive water containing sulfur and Ramsar radioactive water whose sulfur was removed). Ten days after feeding, mice were irradiated by gamma rays (0, 2 and 4 Gy). 48 and 72 hours after irradiating, mice were killed and femurs were removed. Frequency of micronuclei was determined in bone marrow erythrocytes. RESULTS: A significant reduction was shown in the rate of micronuclei polychromatic erythrocyte in sulfur-containing hot spring water compared to sulfur-free water in hot spring mineral water. Gamma irradiation induced significant increases in micronuclei polychromatic erythrocyte (MNPCE) and decreases in polychromatic erythrocyte/polychromatic erythrocyte + normochromatic erythrocyte ratio (PCEs/PCEs+NCEs) (P < 0.001) in sulfur-containing hot spring water compared to sulfur-free hot spring mineral water. Also, apparently there was a significant difference between drinking water and sulfur-containing hot spring water in micronuclei polychromatic erythrocyte and polychromatic erythrocyte/polychromatic erythrocyte+ normochromatic erythrocyte ratio. CONCLUSION: The results indicate that sulfur-containing mineral water could result in a significant reduction in radiation-induced micronuclei representing the radioprotective effect of sulfur compounds.

Oral Administration of Vitamin C, Cimetidine and Famotidine on Micronuclei Induced by Low Dose Radiation in Mouse Bone Marrow Cells.

BACKGROUND: In many studies, chemicals and natural materials were tested to reduce the harmful effects of radiation. It is known that Famotidine and vitamin C reduce DNA damage. OBJECTIVE: The aim of this study was to evaluate the radioprotective effect of vitamin C, Cimetidine and Famotidine on gamma-radiation-induced damage on mouse bone marrow. METHODS: Six-to-seven week male NMRI mice (28 g ±3) were randomly divided into fourteen groups: control, 2Gy irradiation, six group drugs without irradition (Famotidine, Cimetidine, vitaminC, Fam-Cim, Fam-Vit, Cim-Vit), six groups received drugs and 2Gy radiation with a 60Co |γ|-ray source at room temperature 22 ± 2 °C. The mice were killed 48 hours after irradiation by cervical dislocation. Slides were prepared from bone marrow cells and stained in May-Granwald and Giemsa. Finally, the cells were counted with microscope, frequencies of polychromatic erythrocyte (PCE), normochoromatic erythrocyte (NCE) and their micronuclated cell were recorded. PCE / PCE + NCE were calculated. RESULTS: There were significant differences of MNPCE/1000PCE, MNNCE/1000NCE and PCE/PCE+NCE among different groups with similar radiation doses (p≤0.01). Moreover, there were significant differences of MNPCE/1000PCE and PCE/PCE+NCE among different doses of radiation (p≤0.01). While considering MNNCE/1000NCE, there were no significant differences among silimar groups with radiation dose (p˃0.05). CONCLUSION: Oral administration of Famotidine, vitamin C and Cimetidine demonstrate reliable and similar radioprotective effects. Additionally, the protective effect of single use of these drugs was similar to the combination form. Thus, the oral use of combination, 48 hours after irradiation cannot induce more radioprotective effect.

Prevalence of Methylenetetrahydrofolate Reductase C677T Polymorphism in women with Polycystic Ovary Syndrome in southeast of Iran.

Background: One of the notable enzymes in the metabolism of folate is Methylenetetrahydrofolate reductase enzyme, this enzyme is necessary for some biological mechanisms. Mutations in the MTHFR gene could reduce the enzyme activity. Aim: The objective of this research was to assess the prevalence of the very general polymorphism, C677T, in females with polycystic ovary syndrome in the southeastern of Iran. Methods: This research was a case-control research and was conducted on 112 PCOS women and 196 healthy controls. Single type nucleotide polymorphisms (SNP) were genotyped by employing the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Results: It noticed that in C677T, the pervasiveness of C/ C, C/ T, and T/ T genotypes was 54.5%, 34%, and 11.5%, respectively. The repetition of TT genotype was notably higher in PCOS women contrasted to controls. Conclusions: the appearance of 677T allele could be a danger agent for PCOS susceptibility in the southeast of Iran.

Lack of spontaneous and radiation-induced chromosome breakage at interstitial telomeric sites in murine scid cells.

Interstitial telomeric sites (ITSs) in chromosomes from DNA repair-proficient mammalian cells are sensitive to both spontaneous and radiation-induced chromosome breakage. Exact mechanisms of this chromosome breakage sensitivity are not known. To investigate factors that predispose ITSs to chromosome breakage we used murine scid cells. These cells lack functional DNA-PKcs, an enzyme involved in the repair of DNA double-strand breaks. Interestingly, our results revealed lack of both spontaneous and radiation-induced chromosome breakage at ITSs found in scid chromosomes. Therefore, it is possible that increased sensitivity of ITSs to chromosome breakage is associated with the functional DNA double-strand break repair machinery. To investigate if this is the case we used scid cells in which DNA-PKcs deficiency was corrected. Our results revealed complete disappearance of ITSs in scid cells with functional DNA-PKcs, presumably through chromosome breakage at ITSs, but their unchanged frequency in positive and negative control cells. Therefore, our results indicate that the functional DNA double-strand break machinery is required for elevated sensitivity of ITSs to chromosome breakage. Interestingly, we observed significant differences in mitotic chromosome condensation between scid cells and their counterparts with restored DNA-PKcs activity suggesting that lack of functional DNA-PKcs may cause a defect in chromatin organization. Increased condensation of mitotic chromosomes in the scid background was also confirmed in vivo. Therefore, our results indicate a previously unanticipated role of DNA-PKcs in chromatin organisation, which could contribute to the lack of ITS sensitivity to chromosome breakage in murine scid cells.

Induction of cytogenetic adaptive response of mouse bone marrow cells to radiation by therapeutic doses of bleomycin sulfate and actinomycin D as assayed by the micronucleus test.

An in vivo micronucleus assay using bone marrow cells of Syrian albino male mice for identifying the possibility of induction of adaptive response to various doses of radiation following treatment with chemotherapeutics is described. Single doses of bleomycin sulfate (BLM-S) at 300 micrograms/kg and actinomycin-D (ACT-D) at 10 micrograms/kg body weight (therapeutic dose range) were injected intravenously 3 h prior to whole body gamma-irradiation. Irradiation at various doses from 1-4 Gy was carried out at a dose rate of 45 cGy/min. Animals were killed at 24, 36 and 48 h post-irradiation. The results obtained in this study clearly indicate a significant difference for radiation induced micronuclei (MN) in polychromatic erythrocytes (PCEs) with P value < 0.001 over the dose range used. When used in combination with radiation, neither ACT-D nor BLM-S caused a synergistic or additive effect. Irradiated animals showed a higher incidence of micronuclei formation in the presence of ACT-D and BLM-S. However, in both cases, the number of MN induced in PCEs was less than the sum of MN induced by radiation and ACT-D or BLM-S alone. The effect of combined treatment was reduced by a factor of 1.5 for BLM-S and greater than 1.5 for ACT-D treated animals. These observations indicate that although a small amount of ACT-D or BLM-S reaches the bone marrow cells via the circulation, these drugs might produce effects which make bone marrow cells resistant to the clastogenic effects of radiation. Therefore, using these agents repeatedly for cancer treatment in combination with radiation might not cause severe adverse biological effects in normal hemopoeitic tissue.

In vivo protection by cimetidine against fast neutron-induced micronuclei in mouse bone marrow cells.

We have previously shown that cimetidine is capable of reducing the clastogenic effect of gamma-rays. In this research the radioprotective property of this drug was examined against low doses of fast neutrons using the micronucleus assay. Swiss albino male mice (12 weeks old) were irradiated by fast neutrons emitted from a 241Am-9Be source. The absorbed doses were 1.5, 2.25, 3.375 and 5.06 cGy at a dose rate of 0.718 cGy/h. Two hours prior to neutron irradiation mice were treated by cimetidine at a concentration of 15 mg/kg body weight injected i.p. Mice were sacrificed by cervical dislocation at different post-irradiation times (24, 48 and 72 h). The results obtained show that the frequency of neutron-induced micronuclei in polychromatic erythrocytes (PCEs) is significantly higher than those of control groups (P < 0.05) at the neutron doses used in these experiments. Moreover, cimetidine effectively reduced (1.5-2-fold) the frequency of micronuclei in PCE (P < 0.05). These results show that cimetidine can protect bone marrow cells against clastogenic effects of low dose fast neutrons and hence high linear energy transfer (LET) radiation. The mechanism by which cimetidine reduces the clastogenic effects of fast neutrons is not fully understood. It might act through a free radical scavenging mechanism associated with the amplification of the glutathione system.

Laserthermia enhances the clastogenic effects of antineoplastic agents in aerobic and chronically hypoxic HeLa cells in vitro.

The interactive clastogenic effects of Nd-YAG laser induced hyperthermia (laserthermia) in combination with antineoplastic agents on normally oxygenated and chronically hypoxic HeLa cells were investigated. Exponentially growing HeLa cells were treated with bleomycin sulfate (BLM) (2-4 microg/ml), adriamycin (ADM) (2-4 microg/ml) and actinomycin D (ACT) (0.2-0.4 microg/ml) alone or in combination with laser at various powers (7-13 W) or different laser induced elevated temperatures (39.5-43.5 degrees C). HeLa cells were incubated with 3 microg/ml cytochlasin B for 36 h after treatments and the frequency of micronuclei (MN) were determined in binucleated cells. Results showed a relatively high frequency of MN formation after drug treatments in normally oxic and chronically hypoxic cells, although there was a decrease in the frequency of MN in hypoxic cells compared to oxygenated cells. Laserthermia at various powers and different induced temperatures produced a slight increase in MN formation both in oxic and hypoxic cells. When drug treatment and laserthermia was combined, a profound synergistic effect in MN formation was observed for all three drugs used in these experiments. ACT at a concentration of ten times lower than ADM and BLM produced similar effect. Also, ADM showed a marked synergistic effect with laserthermia compared to BLM at similar concentrations. This study suggests that laserthermia in combination with ADM, BLM or ACT would have a greater genotoxic effect on hypoxic cell populations. Therefore, Nd-YAG laser induced hyperthermia may be a useful modality for elimination of the radioresistant hypoxic cells.

Radioprotective effects of cimetidine in mouse bone marrow cells exposed to gamma-rays as assayed by the micronucleus test.

An in vivo micronucleus assay using mouse bone marrow for identifying the radioprotective effect of cimetidine is described. The influence of cimetidine, an antagonist to the histamine H2 receptor, on the kinetics of radiation-induced micronuclei was tested in the CD-1 male mouse. Cimetidine was administered at 15 mg/kg i.p. 2 h prior to irradiation of mouse given various doses of gamma-rays from 0.25 to 1 Gy. The frequency of micronucleated polychromatic erythrocytes (PCEs) and normochromatic erythrocytes (NCEs) per 1500 PCEs were determined at 36, 48 and 72 h post-irradiation. The results obtained indicate a linear dose response for three sampling times, and that cimetidine reduces the number of micronuclei in both PCE and NCE at all sampling times, as well as reducing radiation cytotoxicity. When the overall effects of radiation alone or in the presence of cimetidine are compared, a dose reduction factor (DRF) of 1.5 was found for cimetidine in the dose range used in this study, which is statistically highly significant (p < 0.001). This DRF at the low dosage of cimetidine used in this study compared with known radioprotectors is very promising and it might be useful as a potent radioprotector. The mechanism by which cimetidine reduces clastogenic effects of radiation is not well understood. We propose that it might act by a radical scavenging mechanism via enzyme catalysis.

Kinetics of chromatid aberrations in G2 ataxia-telangiectasia cells exposed to X-rays and ara A.

The cytogenetic effects of X-rays alone or in combination with 9-beta-D-arabinofuranosyladenine (ara A) were studied in an immortalized fibroblastic line of ataxia-telangiectasia (A-T) cells. The average length of G2 in this line was determined by autoradiographic labelling (labelled mitoses) to be approximately 5 h. Samples of A-T cells treated with or without ara A, 4 h prior to fixation were irradiated at 1/2-hourly intervals, from 1.5 h to 3.5 h before fixation and then examined for the presence of metaphase chromatid aberrations. It is postulated that the kinetics of disappearance (rejoining) of chromatid deletions with postirradiation incubation time reflects the underlying repair of dsb. This rejoining was found to be inhibited by ara A. Thus the frequency of deletions in the presence of ara A should represent the frequency of deletions in the absence of dsb repair. The rejoining kinetics for deletions in A-T was similar to that found in a previous study of normal human fibroblasts (Mozdarani and Bryant 1987). The number of deletions in X-irradiated A-T cells at 1.5 h before fixation was found to be higher by a factor of approximately 2 than that found previously in normals, indicating that in A-T a higher rate of conversion of dsb into chromatid deletions occurs. The frequency of exchanges induced in G2 A-T cells was similarly enhanced but, unlike the situation in normal cells, ara A was found to cause only a slight increase in this frequency.

The XRCC2 human repair gene influences recombinational rearrangements leading to chromatid breaks.

PURPOSE: To test the possible involvement of the XRCC2 gene in the control of intra- versus interchromatid rearrangements leading to chromatid breaks in G2 cells by studying the colour-switch ratio (CSR) in harlequin-stained Chinese hamster irs1 cells. MATERIALS AND METHODS: The V79-4 mutant cell lines irs1 (XRCC2 mutation) and irs2 (XRCC8 mutation), two WT V79 lines and GT621-1 (irs1 transfected with the XRCC2 gene) were labelled with BrdU through two cell cycles, irradiated and sampled 1.5h after exposure. Metaphase spreads were analysed for chromatid break frequency and frequencies of colour-switch (colour-switch between chromatids at the break point) and non-colour-switch breaks, from which the CSR was calculated. RESULTS: Chromatid breaks were induced linearly with dose in all lines, and frequencies were elevated in irs1 and irs2 mutant cell lines when compared with WT lines. An XRCC2 transfected line (GT621-1) showed full radiosensitivity complementation with respect to frequencies of chromatid breaks. The CSR was significantly higher in irs1 (13.9%) than in the parental V79-4 (7.5%) or irs2 (4.9%) cells. GT621-1 cells showed partial, but significant complementation with respect to CSR (9.2%). CONCLUSIONS: It is concluded that the significantly higher CSR for the irs1 mutant than for the wild-type parental V79-4 line indicates the involvement of the XRCC2 gene product in the control of the rearrangement process leading to chromatid breaks.