Heavy ion induced damage to plasmid DNA: plateau region vs. spread out Bragg-peak

We have investigated the damage of synthetic plasmid pBR322 DNA in dilute aqueous solutions induced by fast carbon ions. The relative contribution of indirect damage and direct damage to the DNA itself is expected to vary with linear energy transfer along the ion track, with the direct damage contribution increasing towards the Bragg peak. Therefore, ¹²C ions at the spread-out Bragg peak (dose averaged LET_∞ = 189 ± 15 keV/μm) and in the plateau region of the Bragg curve (LET = 40 keV/μm) were employed and the radical scavenger concentration in the plasmid solution was varied to quantify the indirect effect. In order to minimize the influence of ¹²C break-up fragments, a relatively low initial energy of 90 MeV/nucleon was employed for the carbon ions. DNA damage has been quantified by subsequent electrophoresis on agarose gels. We find that strand breaks due to both indirect and direct effects are systematically higher in the plateau region as compared to the Bragg peak region with the difference being smallest at high scavenging capacities. In view of the fact that the relative biological effectiveness for many biological endpoints is maximum at the Bragg peak our findings imply that DNA damage at the Bragg peak is qualitatively most severe.     

Radiation removal of lead and cadmium complexed with ethylenediamine tetraacetic ACID from aqueous solutions

The removal of lead (100 mg/L) and cadmium (27 mg/L) complexed with ethylenediamine tetraacetic acid (EDTA) in presence of different scavengers has been investigated. The experiments show that in acidic solutions, the EDTA complexed lead may be reduced at a dose of 40 kGy up to 97% without the addition of typical OH radical scavengers such as Na(K) formate. The addition of OH radical scavengers as 1×10⁻³ mol/L HCOOK, 2×10⁻³ mol/L carbonate or 2×10⁻³ mol/L bicarbonate (wide range of pH) results in no further improvement. The bubbling of the solution with nitrogen or oxygen also exhibits no positive effect. On the contrary, saturation with nitrous oxide in the presence of scavengers has a modest positive influence, whereas in the system which is scavenger-free, high negative effect (30 %) was observed. The presence of nitrate (e _aq ⁻ scavenger) appears to be important for an effective reduction of complexed lead. The efficient removal of cadmium complexed with EDTA proceeds up to 96 % at a dose of 40 kGy with an addition of 5×10⁻³ mol/L of carbonate as the OH radical scavenger and simultaneously pH buffer (pH 10.5). After irradiation, the cadmium is present in the final form of CdCO₃.     

Experimental setup and first measurement of DNA damage induced along and around an antiproton beam

Radiotherapy employs ionizing radiation to induce lethal DNA lesions in cancer cells while minimizing damage to healthy tissues. Due to their pattern of energy deposition, better therapeutic outcomes can, in theory, be achieved with ions compared to photons. Antiprotons have been proposed to offer a further enhancement due to their annihilation at the end of the path. The work presented here aimed to establish and validate an experimental procedure for the quantification of plasmid and genomic DNA damage resulting from antiproton exposure. Immunocytochemistry was used to assess DNA damage in directly and indirectly exposed human fibroblasts irradiated in both plateau and Bragg peak regions of a 126 MeV antiproton beam at CERN. Cells were stained post irradiation with an anti-γ-H2AX antibody. Quantification of the γ-H2AX foci-dose relationship is consistent with a linear increase in the Bragg peak region. A qualitative analysis of the foci detected in the Bragg peak and plateau region indicates significant differences highlighting the different severity of DNA lesions produced along the particle path. Irradiation of desalted plasmid DNA with 5 Gy antiprotons at the Bragg peak resulted in a significant portion of linear plasmid in the resultant solution.     

Radiobiological response of human hepatoma and normal liver cells exposed to carbon ions generated by Heavy Ion Research Facility in Lanzhou

Human hepatoma and normal liver cells were irradiated with ¹²C⁶⁺ ion beams (LET = 96.05 keV/μm) and γ-rays at Heavy Ion Research Facility in Lanzhou (HIRFL). The chromatid breaks and break types were detected using the premature chromosome condensation technique. Our experimental results showed that chromatid breaks seem to have a good relation with ¹²C⁶⁺ absorbed dose and ¹²C⁶⁺ are more effective to induce chromatid breaks as compared to the γ-rays. For ¹²C⁶⁺ ion irradiation the major break was isochromatid break, while chromatid breaks were dominant for γ-ray irradiation. We also observed that the Relative Biology Effectiveness (RBE) of ¹²C⁶⁺ ion is about 2.5 times higher than that of γ-rays.     

Effect of intense, ultrashort laser pulses on DNA plasmids in their native state: strand breakages induced by in situ electrons and radicals

Single strand breaks are induced in DNA plasmids, pBR322 and pUC19, in aqueous media exposed to strong fields generated using ultrashort laser pulses (820 nm wavelength, 45 fs pulse duration, 1 kHz repetition rate) at intensities of 1-12 TW?cm(-2). The strong fields generate, in situ, electrons and radicals that induce transformation of supercoiled DNA into relaxed DNA, the extent of which is quantified. Introduction of electron and radical scavengers inhibits DNA damage; results indicate that OH radicals are the primary (but not sole) cause of DNA damage.     

7Li和12C离子致DNA链断裂的研究

选用HI-13串列加速器产生的不同传能线密度的⁷Li和¹²C重离子,以不同的剂量对纯化的质粒DNA水溶液进行了辐照.利用原子力显微镜对这两种重离子诱发的DNA损伤进行了纳米水平的结构分析,并用ScionImage分析软件完成了DNA碎片长度的测量.得到了DNA分子超螺旋、开环和线性三种形态随剂量的变化情况以及DNA碎片长度的分布函数,并用Tsallis熵统计理论对实验结果进行了拟合.     

Effective scavenging at cryotemperatures: further increasing the dose tolerance of protein crystals

The rate of radiation damage to macromolecular crystals at both room temperature and 100 K has previously been shown to be reduced by the use of certain radical scavengers. Here the effects of sodium nitrate, an electron scavenger, are investigated at 100 K. For sodium nitrate at a concentration of 0.5 M in chicken egg‐white lysozyme crystals, the dose tolerance is increased by a factor of two as judged from the global damage parameters, and no specific structural damage to the disulfide bonds is seen until the dose is greatly in excess (more than a factor of five) of the value at which damage appears in electron density maps derived from a scavenger‐free crystal. In the electron density maps, ordered nitrate ions adjacent to the disulfide bonds are seen to lose an O atom, and appear to protect the disulfide bonds. In addition, results reinforcing previous reports on the effectiveness of ascorbate are presented. The mechanisms of action of both scavengers in the crystalline environment are elucidated.     

Mutagenic effect of accelerated heavy ions on bacterial cells

The heavy ion accelerators of the Joint Institute for Nuclear Research were used to study the regularities and mechanisms of formation of different types of mutations in prokaryote cells. The induction of direct (lac⁻, ton B⁻, col B) mutations for Esherichia coli cells and reverse his⁻ → His⁺ mutations of Salmonella typhimurium, Bacillus subtilis cells under the action of radiation in a wide range of linear energy transfer (LET) was studied. The regularities of formation of gene and structural (tonB trp-) mutations for Esherichia coli bacteria under the action of accelerated heavy ions were studied. It was demonstrated that the rate of gene mutations as a function of the dose under the action of Γ rays and accelerated heavy ions is described by linear-quadratic functions. For structural mutations, linear “dose-effect” dependences are typical. The quadratic character of mutagenesis dose curves is determined by the “interaction” of two independent “hitting” events in the course of SOS repair of genetic structures. The conclusion made was that gene mutations under the action of accelerated heavy ions are induced by δ electron regions of charged particle tracks. The methods of SOS chromotest, SOS lux test, and λ prophage induction were used to study the regularities of SOS response of cells under the action of radiations in a wide LET range. The following proposition was substantiated: the molecular basis for formation of gene mutations are cluster single-strand DNA breaks, and that for structural mutations, double-strand DNA breaks. It was found out that the LET dependence of the relative biological efficiency of accelerated ions is described by curves with a local maximum. It was demonstrated that the biological efficiency of ionizing radiations with different physical characteristics on cells with different genotype, estimated by the lethal action, induction of gene and deletion mutations, precision excision of transposons, is determined by the specific features of energy transfer of the radiations that affect the character of induced DNA damage, and the efficiency inducible and constitutive cell repair systems. The growth of relative biological efficiency of heavy charged particles is determined by the growth of the damage yield of the DNA participating in the formation of radiation-induced effects, and higher efficiency of inducible repair systems. It was established that the LET value (L _max) for which the maximum (according to the applied irradiation criteria) coefficients of relative biological efficiency are observed varies depending on the character of the registered radiation induced effect. It was demonstrated that for gene mutations and induction of precision excision of mobile elements the values of L _max are realized in a LET range of ≈20 keV/μm. For lethal effects of irradiation and induction of deletion mutations the value of L _max is ≈ 100 and 50 keV/μm, respectively. The differences in the L _max for the studied radiation gene effectis are determined by the different type of DNA damage participating in the mutation process. A molecular model of the formation of gene mutations in Escherichia coli cells under the action of ionizing radiation was proposed. Basic DNA radiation damage and main repair ways were considered in the framework of this model. The basis is the idea of the decisive role of mutagenic, error-prone, branch of SOS repair in fixing premutation DNA damage into point mutations. It was demonstrated that the central mechanism in this process is the formation of an inducible multi-enzymatic complex including the DNA polymerase V (Umu C), RecA-protease, SSB proteins, subunits of DNA polymerase III, performing erroneous DNA synthesis on the damaged matrix. A mathematical model of induction of gene mutations under ultraviolet cell irradiation was developed based on the molecular model.     

Biological effects induced by swift heavy ions of lithium on aqueous solution of plasmid pMTa4

Biological samples exposed to swift heavy ions sustain damage on different components. Damage to DNA, a critical component of a living system, has considerable biological implications. In this study aqueous solution of plasmid pMTa4 was exposed to varying fluence of swift ⁷Li ions and its different topological forms were analysed by agarose gel electrophoresis to study the induced damage. To monitor radiation labile nucleotide sequence the ⁷Li ions exposed plasmid was degraded by three different restriction endonucleases and also analysed by agarose gel electrophoresis. The results show that ⁷Li ions predominantly induced double strand breaks in the plasmid DNA in a dose-dependent manner and affected preferentially the GC-rich motifs of the DNA. The results suggest that ⁷Li ions induce premutagenic lesions at an enhanced frequency in segments of the DNA which are rich in CG content as compared to GC-poor segments.     

γ -ray spectroscopy study of 11 ΛB and 12 ΛC

In this paper, a preliminary result from the latest hypernuclear γ -ray spectroscopy experiment (KEK-E566) is presented together with a short discussion. The experiment was performed at the KEK-PS K6 beam line in 2005. In this experiment, the ¹²C(π⁺, K ⁺)¹² _ΛC reaction was employed to populate ¹² _ΛC/¹¹ _ΛB hypernuclei. A germanium detector array, Hyperball2, was constructed to detect γ -rays emitted from the hypernuclei produced. Three hypernuclear γ -ray peaks were observed and assigned.     

Okamoto model for necrosis and its expansions,CD38-cyclic ADP-ribose signal system for intracellular Ca2+ mobilization and Reg (Regenerating gene protein)-Reg receptor system for cell regeneration

In pancreatic islet cell culture models and animal models, we studied the molecular mechanisms involved in the development of insulin-dependent diabetes. The diabetogenic agents, alloxan and streptozotocin, caused DNA strand breaks, which in turn activated poly(ADP-ribose) polymerase/synthetase (PARP) to deplete NAD⁺, thereby inhibiting islet β-cell functions such as proinsulin synthesis and ultimately leading to β-cell necrosis. Radical scavengers protected against the formation of DNA strand breaks and inhibition of proinsulin synthesis. Inhibitors of PARP prevented the NAD⁺ depletion, inhibition of proinsulin synthesis and β-cell death. These findings led to the proposed unifying concept for β-cell damage and its prevention (the Okamoto model). The model met one proof with PARP knockout animals and was further extended by the discovery of cyclic ADP-ribose as the second messenger for Ca²⁺ mobilization in glucose-induced insulin secretion and by the identification of Reg (Regenerating gene) for β-cell regeneration. Physiological and pathological events found in pancreatic β-cells have been observed in other cells and tissues.     

不同LET辐射致DNA集簇性损伤的研究

利用辐照质粒DNA构象变化的分子模型,以DNA糖苷酶Fpg和AP核酸内切酶EndoIII识别并切割辐射所致DNA碱基损伤,将其转换为DNA断裂损伤,通过电泳分析DNA分子构象变化,研究比较γ射线、质子和7Li离子诱发DNA集簇性损伤。50Gy以上高剂量γ辐射对质粒DNA的损伤主要表现为单链断裂(SSB)和很少比例的双链断裂(DSB),并能产生一定水平的集簇性损伤。相比之下,高能质子束和高LET的7Li离子直接所致DNA的断裂损伤以及所产生的集簇性碱基损伤比γ射线的要严重,质子10Gy照射就可诱发明显的集簇损伤。     

Study of the isobar configurations in the <Superscript>12</Superscript>C and <Superscript>16</Superscript>O ground states

Experimental research on positive-pion photoproduction on the oxygen nucleus in the ¹⁶O(γ, π⁺p) reaction at high recoil momenta of the residual nuclear system was performed. The yield for the ¹⁶O(γ, π⁺p) reaction was analyzed using a model that takes Δ-isobar configurations in nuclei ground states into account, together with the earlier-measured yield of the¹²C(γ, π⁺p) reaction. The estimated number of isobars per nucleon N _Δ = 0.012 ± 0.005 was obtained for the ¹²C nucleus, and ¹⁶O N _Δ = 0.018 ± 0.004 was obtained for the ¹⁶O nucleus.     

Doppler shapes of the γ line in the <Superscript>9</Superscript>Be(α, nγ)<Superscript>12</Superscript>C reaction in plasma at temperatures <Emphasis Type="Italic">T</Emphasis><Subscript>α</Subscript> < 0.6 MeV

A parametrization of the partial cross section of the ⁹Be(α, nγ)¹²C reaction in the α-particle energy range of 0.3–7.9 MeV is presented, along with the count rates of γ quanta. The need to consider subbarrier (Eα < 1.9 MeV) α-particles in plasma for temperatures T _α < 0.2 MeV is substantiated. The shapes of the Doppler-broadened 4.44 MeV γ line and the count rates of γ quanta in the plasma of the JET tokamak are measured for the first time and compared to the calculated values. An estimated T _α ≲ 160 keV is obtained.     

Energy dependence of the n-γ angular correlation in the <Superscript>9</Superscript>Be(α, nγ)<Superscript>12</Superscript>C reaction

A technique for selecting the parameters required for describing the angular correlation function and finding their energy dependence has been developed. Joint analysis of a Doppler-broadened 4.44 MeV γ lineshape from the ⁹Be(α, nγ)¹²C reaction in the range 1.9–4.5 MeV of E _α energies and with n- and γ-angular distributions was performed. The Doppler-broadened lineshapes were modeled and compared using data measured in the JET plasma experiment. Relativistic effects were analyzed.     

Exchange interaction between intermediate D13(1520)-hole and S11(1535)-hole states in the near-threshold coherent η photoproduction from nuclei

Coherent η-meson photoproduction from nuclei is considered within an extended analogue of the Δ-hole model taking into account the configuration mixing of baryon-hole excitations of different sorts of baryons. Calculated integrated and differential cross-sections for reactions ¹²C(γ,η)¹²C_g.s. and ¹⁶O(γ,η)¹⁶O_g.s. demonstrate the important role of the exchange interaction between intermediate D ₁₃(1520)-hole and S ₁₁(1535)-hole excitations.     

Photon polarisation asymmetries in (p,p′γ) experiments

The Stokes parameters characterising the polarization of the photon in theγ-decay of¹²C*(1⁺) are examined in correlation with the scattered proton in¹²C(p,p′)¹²C*(1⁺). This opens up the possibility of efficiently determining empirically the six inelastic scattering amplitudes utilizing only 13 measurements. We identify several alternative sets of such measurements to encourage experimental efforts in this direction.     

Gamma-ray spectroscopy of the nucleus 139Ce

Gamma-ray coincidence techniques are used to determine new level structures in the N = 81 nucleus ¹³⁹Ce, at low spins and excitation energies with the ¹³⁹La(p, nγ) reaction at 5.0 and 6.0MeV incident energy, and at high spins with the ¹³⁰Te(¹²C, 3nγ) reaction at 50.5MeV, respectively. Lifetime determinations are also made in the (p, nγ) reaction with the centroid DSA method. The observed level structures are discussed by comparison with existing calculations and with those in the neighbouring nucleus ¹⁴⁰Ce.     

Pre-irradiation with low-dose <Superscript>12</Superscript>C<Superscript>6+</Superscript> beam significantly enhances the efficacy of <Emphasis Type="Italic">AdCMV-p53</Emphasis> gene therapy in human non-small lung cancer

The combination of ionizing radiation and gene therapy has been investigated. However, there are very few reports about the combination of heavy-ion irradiation and gene therapy. To determine if the pre-exposure to low-dose heavy ion beam enhances the suppression of AdCMV-p53 on non-small lung cancer (NSLC), the cells pre-irradiated or non-irradiated were infected with 20, 40 MOl of AdCMV-p53. Survival fraction and the relative biology effect (RBE) were determined by clonogenic assay. The results showed that the proportions of p53 positive cells in 12C6 beam induced AdCMV-p53 infected cells were more than 90%, which were significantly more than those in γ-ray induced AdCMV-p53 infected cells. The pre-exposure to low-dose 12C6 beam significantly prevented the G0/G1 arrest and activated G2/M checkpoints. The pre-exposure to 12C6 beam significantly improved cell to apoptosis. RBEs for the 12C6 AdCMV-p53 infection groups were 30%-60%, 20% -130% and 30%-70% more than those for the 12C6 -irradiated only, AdCMV-p53 infected only, and γ-irradiation induced AdCMVp53 infected groups, respectively. The data suggested that the pre-exposure to low-dose 12C6 beam significantly promotes exogenous p53 expression in NSLC, and the suppression of AdCMV-p53 gene therapy on NSLC.     

New physics contribution to neutral trilinear gauge boson couplings

We study the one-loop new physics effects to the CP even triple neutral gauge boson vertices γ ^⋆ γ Z, γ ^⋆ Z Z, Z ^⋆ Z γ and Z ^⋆ ZZ in the context of Little Higgs models. We compute the contribution of the additional fermions in Little Higgs models in the framework of direct product groups where [SU(2)×U(1)]² gauge symmetry is embedded in SU(5) global symmetry and also in the framework of the simple group where SU(N)×U(1) gauge symmetry breaks down to SU(2) _L ×U(1). We calculate the contribution of the fermions to these couplings when T parity is invoked. In addition, we re-examine the MSSM contribution at the chosen point of SPS1a′ and compare with the SM and Little Higgs models.