Using neutrons of 14 MeV generated by 600 kV Cockcroft-Walton accelerator,the DNA samples with or without mannitol or VND3207 were irradiated with various absorbed doses,and the DNA strand breaks were determined by means of gel electrophoresis.The results indicate that neutron can produce the DNA single-and double-strand breaks,and the yields of strand breaks increase with the dose increment,i.e.there is a distinct dose response.Although for the solution system with additive of mannitol or VND3207,there is also a dose response,the yields of DNA strand breaks are much less than that without mannitol or VND3207 solution.It can be suggested that mannitol or VND3207 reduces the yields of DNA single-and double-strand breaks induced by neutron irradiation efficiently,and mannitol or VND3207 has stronger capability of radioprotection against neutron radiation.

The pUC19 plasmid DNA solutions in different DNA concentrations,with or without mannitol,were irradiated by 16 MeV protons to different doses.Changes in the DNA form were observed by means of gel electrophoresis in order to study effects of dose and DNA concentration on yields of DNA strand breaks.The results indicate that the dose and DNA concentration response exist in two solution systems,the forms of DNA changed from intact supercoiled to open circular,in a linear relationship with the dose.The yields of DNA strand breaks in DNA solution without mannitol are much more than that those with mannitol,illuminating that mannitol can scavenge the free radicals and reduce the yields of DNA single and double strand breaks induced by protons efficiently.In addition,the dose effects of DNA damage were investigated at a concentration of 10 or 100 ng/?L.The results show that dilute DNA solution need lower dose than the dense solution in observing similar degree of damage.

To evaluate the influence of the DNA concentra-tion in the aqueous solution on DNA radiation damage, the plasmid DNA in the presence or absence of Mannitol (scavenger of free radical OH-) was irradiated by 7Li ions and γ rays at various DNA concentrations. Gel electrophore-sis analysis revealed that the DNA damage of single and double strand breaks induced by irradiation was dependent on DNA concentra-tion and became more severe at lower DNA concentration in the radiation experiment when all others parameters are the same. In the con-dition of γ-ray irradiation, most of double strand breaks (DSB) damage was neutralized and less associated with DNA concentration in the presence of mannitol. However, under 7Li irradiation, the DSB damage could not be cleared by mannitol but was gradually aggravated with de- creasing DNA concentrations. Our study sheds light on the underlying mechanisms in the DNA radiation damage process. And there are poten-tial significances for the human space flight, cancer therapy by heavy ions as well as the ra-diation security assessment.

To measure the protective effect of salidroside on radiation,the plasmid DNA samples in TE Buffers with different concentrations of salidroside were irradiated by 14.2 MeV protons(linear energy transfer = 3.5 keV/μm) andγrays respectively.The images of gel electrophoresis and the DNA forms distribution showed that DNA lesions became lightened with increasing salidroside concentration for both kinds of radiations.At the same time,there were linear DNA forms come forth in DNA samples after irradiated by protons at lower concentrations of salidroside,and that did not appear after irradiated by 7 rays.It should be correlative with the direct ionizing of protons.

A dynamical model for the p53-Mdm2 feedback loop regulated by Akt is reported in this work. By computational simulation, it reproduces the stable oscillatory pulses in p53- Mdm2 negative feedback loop which is functionally responsible for cell repair or apoptosis in individual cell. With the survival stress, in the tumor suppressor-oncoproteins networks, the model indicates the potential to exhibit the oscillation-stationary state bifurcation for the kinetics of p53, and the death-survival switch in the p53-Akt cross talk which somehow leads cell to either programmed apoptosis or survival. It's found that low Akt activation is speculated to p53 normally holding the response to cellular repair or apoptosis, but large Akt amount keeping a high Akt activation restricts p53 at a low expression level and engenders malfunctions in cellular repair or apoptosis so that the cell survives with potential probability to cancer or mutation.

<正>在长期载人航天中,除失重外,空间辐射对人是一个严重的威胁,其中空间辐射危害,需考虑的关键粒子是质子和重离子。深入了解空间辐射环境特点及危害程度,对保

3-Nitrotyrosine(3-NY) has been reported as a potential source of reactive oxygen species (ROSs). In this work, plasmid pBR322 DNA was irradiated by gamma rays in aqueous solution in presence and absence of 3-NY, DNA strand breaks were analyzed by neutral electrophoresis followed by quantification with image analysis software. It was found that the presence of 3-NY could effectively reduce radiation-induced DNA strand breaks. A side-by-side comparison was performed between 3-NY and tyrosine, the results showed that the protective role 3-NY was comparable with tyrosine, which might imply that protein tyrosine nitration might not significantly decrease its ability as a free radical scavenger.

<正>在空间辐射环境中,辐射源主要是银河宇宙射线(GCR)和随机发生的太阳粒子辐射(质子事件)。其中以质子含量最为丰富,其次为α粒子和少量其它更重的离子。已有的模型计算结果表明,

To evaluate the influence of the DNA concentration in the aqueous solution on DNA radiation damage, the plasmid DNA in the presence or absence of Mannitol (scavenger of free radical OH•) was irradiated by 7Li ions and γ rays at various DNA concentrations. Gel electrophoresis analysis revealed that the DNA damage of single and double strand breaks induced by irradiation became more severe at lower DNA concentration. In the condition of γ-ray irradiation, most of double strand breaks (DSB) damage was neutralized and less associated with DNA concentration in the presence of mannitol. However, under 7Li irradiation, DSB damage could not be cleared by mannitol but was gradually aggravated with decreasing DNA concentrations. These findings imply that under low-LET irradiation, most of the DSB damage is generated by free radical OH• diffusion, and thus may be counteracted by scavengers, while at higher-LET irradiation, quite a fraction of DSB induction is caused by direct ionizing energy deposition of heavy ions, which cannot be eliminated. This work also indicates that the proportion between free radical damage and direct ionizing damage is a constant which is independent of DNA concentration when the DNA concentration is under a certain value (50 ng/μL). Our study sheds light on the underlying mechanisms in the DNA radiation damage process.

<正>电离辐射致DNA损伤的程度受到很多因素的影响,如剂量、剂量率、射线种类、DNA浓度等。北京师范大学周宏余课题组利用电子顺磁共振谱仪测量了不同电荷态的低能C离子辐照丙氨酸薄

Ionizing radiation-induced bystander effects have been documented for a multitude of endpoints such as mutations, chromosome aberrations and cell death, which arise in nonirradiated bystander cells having received signals from directly irradiated cells; however, energetic heavy ion-induced bystander response is incompletely characterized. To address this, we employed precise microbeams of carbon and neon ions for targeting only a very small fraction of cells in confluent fibroblast cultures. Conventional broadfield irradiation was conducted in parallel to see the effects in irradiated cells. Exposure of 0.00026% of cells led to nearly 10% reductions in the clonogenic survival and twofold rises in the apoptotic incidence regardless of ion species. Whilst apoptotic frequency increased with time up to 72 h postirradiation in irradiated cells, its frequency escalated up to 24h postirradiation but declined at 48 h postirradiation in bystander cells, indicating that bystander cells exhibit transient commitment to apoptosis. Carbon- and neon-ion microbeam irradiation similarly caused almost twofold increments in the levels of serine 15-phosphorylated p53 proteins, irrespective of whether 0.00026, 0.0013 or 0.0066% of cells were targeted. Whereas the levels of phosphorylated p53 were elevated and remained unchanged at 2h and 6h postirradiation in irradiated cells, its levels rose at 6h postirradiation but not at 2h postirradiation in bystander cells, suggesting that bystander cells manifest delayed p53 phosphorylation. Collectively, our results indicate that heavy ions inactivate clonogenic potential of bystander cells, and that the time course of the response to heavy ions differs between irradiated and bystander cells. These induced bystander responses could be a defensive mechanism that minimizes further expansion of aberrant cells.

Biological effectiveness varies with the linear energy transfer (LET) of ionizing radiation. Plentiful evidence has been presented demonstrating that at physically equivalent doses, high-LET energetic heavy ions are more cytotoxic and genotoxic than low-LET photons like X-rays and γ-rays. Notwithstanding, its potential impact at isosurvival doses is yet to be characterized. Here we investigated the cell-killing effectiveness of γ-rays (0.2 keV/μm) and five different beams of heavy ions with LET ranging from 16.2 to 1610 keV/μm in confluent cultures of normal human fibroblasts. The relative biological effectiveness based on the dose giving 10% clonogenic survival peaked at 108 keV/μm. In cultures exposed to the 10% survival doses, the yield of apoptotic cells escalated with time postirradiation but declined with LET. Our results imply that the cell death mode differs with LET at isosurvival levels.

A male sterile mutant named 39I_3-2 was selected from the M_3 generation of Nongda 108(a maize variety) which dry seeds were irradiated with 30Gy 7Li,and combinations between male sterile plants and other fertile plants were also obtained through bagging cross.The characteristics of the male sterile mutant and its fertilities of combinations were studied,and the fertilities of the F_2 generation were surveyed.The results showed that the sterile material was thoroughly abortive,and the sterile trail was stable,which indicated a genetic feature of single recessive gene controlled nucleus sterility.The appearance of male sterile mutant was caused through gene mutation by heavy ion irradiation.

To measure the DNA lesions and the form of transformation in plasmid DNA irradiated with protons,the plasmid DNA samples were irradiated with 16.4 MeV proton(linear energy transfer=3.12 keV/μm) in aqueous solution containing 0 mmol/L or 600 mmol/L mannitol.DNA were measured by gel electrophoresis and Alpha Innotech digital imaging system.For proton without mannitol,DNA lesions were very evident at the dose of 50 Gy.The fractions of SC form and OC form decreased till they disappeared with increasing doses.The short fragments of DNA came forth at the dose of 300 Gy.In the presence of 600 mmol/L mannitol,DNA lesions were restrained.However the fraction of OC form increased obviously with increasing doses,which showed that there are some direct damages with the proton irradiation.These provide important experimental data for the dangerous assessment of space radiation and proton therapy.

Significant evidence indicates that ionizing radiation causes biological effects in nonirradiated bystander cells having received signals from directly irradiated cells. There is little information available hitherto as to the bystander effect of energetic heavy ions; however, our previous work has shown that in confluent cultures of normal human fibroblast AG01522 cells, targeted exposure of 0.0003% of cells to microbeams of 18.3 MeV/u 12C (103 keV/μm) and 13.0 MeV/u 20Ne (375 keV/μm) ions can similarly cause almost 10% decreases in the clonogenic survival, and twofold increments in the incidence of apoptosis whose temporal kinetics varies between irradiated and bystander cells. Using this experimental system, here we further report that bystander responses of AG01522 cells to 17.5 MeV/u 20Ne ions (294 keV/μm) are consistent with those to 18.3 MeV/u 12C and 13.0 MeV/u 20Ne ions. We also demonstrate that such bystander-induced reductions in the survival are less pronounced and occur independently of Bcl-2 overexpression in human cervical cancer HeLa cells.

To evaluate the effect of free radicals on DNA damage induced by heavy ions,pUC19 plasmid DNA solution with different kinds of scavengers(Mannitol,Vitamin C and Tea Polyphenols) is irradiated by γ rays. The DNA damages are analysed by gel electrophoresis and Alpha Innotech digital imaging system. The results show that all of the three kinds of scavengers can significantly protect DNA;mannitol is more effective than Vitamin C under the same condition;and their capacity of scavenging free radicals induced by γ rays is more remarkable than those induced by heavy ions.

In order to investigate the direct and indirect interaction of DNA damage induced by high LET heavy ions as well as the protective function of scavenger by means of atomic force microscopy, samples of pUC19 plasmid DNA aqueous solution, pUC19 plasmid DNA aqueous solution with scavenger (mannitol) and dry DNA are irradiated by 7Li ions from the HI-13 tandem accelerator in China Institute of Atomic Energy (CIAE). Results show that the indirect interaction of free radical plays an important role in DNA strand break induced by 7Li ions and mannitol can protect the DNA molecules effectively.

As two factors, the changes of concentration of DNA and dose rate are of significance in the study of DNA damage induced by irradiation. The influence of DNA damage induced by γ ray at different concentration of DNA under different dose rate was investigated. The result of gel electrophoresis indicate that DNA molecules were damaged severely as the concentration of DNA decreasing. The number of double strand breakages per DNA were obtained by the software of Alpha Innotech and theoretical analysis. It shows that the numbers of double strand breakages per DNA presented nonlinear feature as the concentration of DNA decreasing, and the dose rate had little influence on DNA damage.

<正>质子作为一种高传能线密度(LET)的辐射,具有能量沉积与局部剂量远大于低LET辐射(如X射线、γ射线和电子束等)的特点,通过物质时有完全不同的径迹结构,能够更有效的诱发DNA发生双链断裂,产生更多的不能修复性损伤,引起细胞的转化和死亡以及癌的发生等较高的相对生物效应(RBE)。在DNA分子水平上研究质子致生物损伤的机理,深入了解其辐射特点及危害程度,并研究相应的防护途径十分重要,其研究结果可为太空辐射环境中质子辐射的危害评估与防护以及