8-Hydroxyguanine: From its discovery in 1983 to the present status

8-Hydroxyguanine (8-OH-G) was discovered in 1983 in our laboratory at the National Cancer Center Research Institute, Tokyo. Since it could be formed in DNA not only in vitro but also in vivo by oxygen radical forming agents, we immediately hypothesized the importance of this discovery in connection with its biological consequence. Further intensive efforts by us from 1983 to 1990 confirmed that 8-OH-G is a highly significant oxidated DNA lesion involved in mutation and/or carcinogenesis in mammals, including humans. With the subsequent entry of many investigators to this research field the number of publications on 8-OH-G increased exponentially, reaching more than several thousands by the end of 2005. In this article, a summary is given of the important works carried out in the early days, and further notable contributions by many investigators are reviewed, focusing on 8-OH-G in the mammalian system. A special emphasis is given to research on knockout mice that are deficient in genes involved in the repair systems of the 8-OH-G lesion. Lastly, our own recent work is summarized involving a one-year carcinogenesis study of Ogg1 (the gene for 8-OH-G specific glycosylase/AP lyase^*1) knockout mice that have been exposed to oxidative stress.     

Renal Clearable Luminescent WSe2 for Radioprotection of Nontargeted Tissues during Radiotherapy

High‐energy ionizing radiation is widely used in medical diagnosis and cancer radiation therapy. However, high‐energy radiation can also impose significant damages in healthy tissues during medical treatments via direct DNA damages and indirect damages from production of reactive oxygen species (ROS). Therefore, it is urgent to develop highly effective radioprotectants with low toxicities that can meet the increasing needs for alleviating the adverse effects from cancer radiation therapy and nuclear emergency. In this work, strongly catalytic ultrasmall (sub‐5 nm) cysteine‐protected WSe₂ dots are employed to protect healthy tissues against radiation via diminishing radiation‐induced free radicals. The WSe₂ dots with high surface activities can recover radiation‐induced DNA damages and eliminate the excessive ROS generated from radiation. In vivo experiments confirm that the survival rate of mice treated with WSe₂ dots is significantly elevated with radiation damages postponed under exposure to high‐dose ionizing radiation. Furthermore, the free radicals in major organs and hematological system can be appreciably omitted, suggesting their unique role as free radical scavengers. These WSe₂ dots in ultrasmall size show rapid renal clearance of ≈74% injection dose via urine excretion in 24 h and do not cause any apparent toxicity in vivo for up to 30 d.     

Structural analysis of base mispairing in DNA containing oxidative guanine lesion

Classical molecular dynamics methods were used to analyze the importance of 8-oxoguanine (8-oxoG) pairing with other DNA bases in order to determine the impact of oxidative guanine lesions on DNA structure. Six lesioned molecules, each containing 8-oxoG mispaired with one of the four normal bases on the the opposite strand at the center of 40-mer DNA, and one non-damaged DNA molecule, were simulated for 2 nanoseconds of real time. The 8-oxoG lesioned bases were found to incorporate opposite all normal bases. There are observed conformational and energetical differences among these parings. 8-oxoG in anti-form creates firm hydrogen bonds with cytosine and this bonding has a strong attractive electrostatic interaction energy similar to that of a native base pair-guanine to cytosine. Meanwhile, it does not form a stable base pair with purine bases (adenine and guanine) nor with the pyrimidine base thymine. On the other hand, the 8-oxoG in syn-form was found to pair with adenine.      

Analysis of sterilization effect by pulsed dielectric barrier discharge

Atmospheric pressure (AP) plasmas can sterilize against almost all kinds of bacteria because many ions and reactive species, such as oxygen atoms and ozone, etc., are generated during AP plasmas. So AP plasmas are proper processes for application to air cleaners and sterilizers. The aim of this paper is to evaluate a germicidal effect caused by pulsed plasma system in air utilizing a dielectric barrier discharge (DBD) type reactor incorporating alumina, glass, etc. Escherichia coli, Bacillus subtilis and Pseudomonas aeruginosa bacteria were used for this sterilization experiment. For analysis of the relationship between sterilization results and chemical species generated in the discharge, we used optical emission spectroscopy and we checked emission spectra by atomic oxygen (394.2 and 436.8 nm) and second positive system of nitrogen (337.1 nm). Experimental results showed that DBD treatment during 70 s sterilized E. coli with 99.99% effectively and ozone molecules were the dominant germicidal species. From these results we concluded that the pulsed DBD system is very effective for sterilization.     

Dynamics of energy release in a low-voltage pulsed arc in air

The influence of the discharge conditions on the dynamics of energy release is considered for pulsed arcs in air at initial pressures from 10⁵ to 8×10⁵ Pa and a low-voltage capacitor voltage of up to 400 V. A novel method for determining the resistance of the discharge channel in the final stage of a spark discharge is proposed. The method is applied to estimating the discharge channel parameters.     

Application of silica–magnetite nanocomposites to the isolation of ultrapure plasmid DNA from bacterial cells

The aim of this study was to develop a simple and rapid method for purification of ultrapure plasmid DNA with high yields from bacterial cultures. Nanosized superparamagnetic nanoparticles (Fe₃O₄) were prepared by chemical precipitation method using Fe²⁺, Fe³⁺ salt, and ammonium hydroxide under a nitrogen atmosphere. Silica–magnetite nanocomposites were prepared by the method of acid hydrolysis of tetraethoxysilane (TEOS) to coat the silica onto magnetite nanoparticles. DNA was adsorbed to the support under high salt conditions, and recovered directly in water for immediate downstream application, without the need for precipitation. We demonstrated that a useful plasmid, pRSETB-EGFP, encoding for the green fluorescent protein with T7 promoter, could be amplified in Escherichia coli of DE3 strain. Up to approximately 43 μg of high-purity (A₂₆₀/A₂₈₀ ratio=1.75) plasmid DNA was isolated from 3 ml of an overnight bacterial culture. The eluted plasmid DNA was used directly for restriction enzyme digestion, bacterial cell transformation and polymerase chain reaction (PCR) amplification with success. The protocol, starting from the preparation of bacterial lysate and ending with purified plasmid takes less than 8 min. The silica–magnetite nanocomposites deliver significant time-savings, overall higher yields, lower RNA contamination, and better PCR amplification compared to commercial available silica-based and other methods.     

Excitation dependence of the bending mode temperature in pulsed TE CO2 lasers

The observation of “steps” which appear in the gain immediately after excitation in pulsed TE CO₂ discharges is reported. It is shown that the measurement of the step size relative to the peak gain serves to determine the population of the lower laser level and thereby, the initial vibrational temperature (T₁) of the bending mode. This technique is applied to a study of T₁ as a function of the discharge input energy.     

Application of femtosecond‐pulsed lasers for direct optical manipulation of biological functions

Absorption of photon energy by cells or tissue can evoke photothermal, photomechanical, and photochemical effects, depending on the density of the deposited energy. Photochemical effects require a low energy density and can be used for reversible modulation of biological functions. Ultrashort‐pulsed lasers have a high intensity due to the short pulse duration, despite its low average energy. Through nonlinear absorption, these lasers can deliver very high peak energy into the submicrometer focus area without causing collateral damage. Absorbed energy delivered by ultrashort‐pulsed laser irradiation induces free electrons, which can be readily converted to reactive oxygen species (ROS) and related free radicals in the localized region. Free radicals are best known to induce irreversible biological effects via oxidative modification; however, they have also been proposed to modulate biological functions by releasing calcium ions from intracellular organelles. Calcium can evoke variable biological effects in both excitable and nonexcitable cell types. Controlled stimulation by ultrashort laser pulses generate intracellular calcium waves that can modulate many biological functions, such as cardiomyocyte beat rate, muscle contractility, and blood–brain barrier (BBB) permeability. This article presents optical methods that are useful therapeutic and research tools in the biomedical field and discuss the possible mechanisms responsible for biological modulation by ultrashort‐pulsed lasers, especially femtosecond‐pulsed lasers.     

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。     

Matching of an extended high-current Z-discharge to a pulsed power system

Conditions for matching an extended high-current Z-discharge to a pulsed power system are numerically investigated. The power system consists of a pulsed voltage generator and a long transmission line. Experiments are aimed at generating a highly ionized dense plasma as an active medium for an extreme ultraviolet laser on hydrogen-like ions of nitrogen (λ = 13.4 nm). Emphasis is on the distribution of the energy transmitted from a storage ring to a load among its components and on the reduction of the energy that remains in the electrical circuit by the end of the pump pulse and will inevitably dissipate in the discharge tube. The solution of this problem will make it possible to diminish the load on the walls of the discharge chamber and extend its service life. It is shown that energy deposition into the load is effective when the timeaveraged sum of the ohmic and dynamic components of the discharge resistance is roughly equal to the wave impedance of the transmission line. In this case, the wave reflected from the load carries away a minimal energy, which allows for optimization of the energy deposited into the load. The input and output energy balances for different matching conditions are calculated with an eye to designing an efficient short-wavelength extreme ultraviolet laser with a long service life of the discharge tube.     

Features of direct cluster stripping in primary fragments from quasielastic20Ne-induced reactions

The primary yield distribution of projectile-like fragments from the²⁰Ne+¹⁹⁷Au reaction has been reconstructed and was found to be similar when the bombarding energy is increased from 150 to 290 MeV. Alternative to theQ _gg-systematics where the relative yields are ruled by exit channel properties, the Friedman model for projectile-fragmentation is successfully applied to the data. It relates the fragment yields essentially to the separation energyQ _F of the clusters removed from the projectile (and transferred to the target) i.e. to entrance channel properties and was successful in describing the relative yields at very high bombarding energy (2 GeV/N). For a good reproduction of the relative yields at the bombarding energy and the heavy target of this experiment it is necessary to make a correction for neutron pick-up which accompanies the cluster stripping process with a certain probability. The predicted momentum widths of the fragment spectra, too, are consistent with the data.     

Low-temperature photoluminescence of ion-implanted SiO2:Sn+ films and glasses

Low-temperature photoluminescence spectroscopy with pulsed synchrotron excitation is applied to study the regularities of excitation and relaxation of both point defects and nanoparticles formed by tin implantation into SiO₂ films and glasses. It has been found that tin implantation followed by air and nitrogen annealing yields the formation of α-Sn nanoclusters and nonstoichiometric SnO _x nanoparticles, while a stable phase of SnO₂ does not appear. Alternative channels of luminescence excitation are revealed for nanoclusters, including energy transfer from excitons and electron-hole pairs of the host SiO₂ matrix.     

Antioxidant systems in supporting environmental and programmed adaptations to low temperatures

Hetero and endothermic adaptive responses arising as a result of natural responses to environmental cues include antioxidant systems that support adaptations to environmental low temperatures in the broadest sense. These temperatures induce phase changes in energy production and consequently changes in the concentration of reactive oxygen species (ROS). The latter may lead to oxidative stress and the impairment of cellular homeostasis and antioxidant defence systems (ADS) scavenge the ROS so generated. In endotherms the ADS responds to oxidative pressure during acute cold stress conditions, this response is tissue specific and does not extend to prevent other oxidative damage. The early acute phase of cold exposure is accompanied by a significant depletion in redox equivalents. Under such conditions it is questionable if ADS has the capacity to neutralize elevated levels of ROS since there is also an increased energy demand and enhanced ATP consumption. Prolonged exposure to cold leads to ADS adaptation. Hibernators and freeze-tolerant species elevate their ADS before hibernation or freezing in order to prepare for and cope with re-awakening. The involvement of ROS and the role of the ADS in organisms subjected to low temperatures are features intercalated into physiological mechanisms of homestasis. The exact mechanisms for ADS regulation have not been fully defined and are the subject of many ongoing intriguing scientific investigations.     

Correlation of the neutron yield from the plasma focus upon variations in the magnetic field energy of the discharge circuit

The relation between neutron yield Y and magnetic field energy variations ΔW in the discharge circuit has been studied for a Mather-type plasma-focus camera. The activation technique (activation of silver isotopes) has been used to measure the integral yield of DD neutrons from the source. The time dependence of the neutron yield has been recorded by scintillation detectors. For the device used in the investigations, the neutron yield exhibits a linear dependence on variations in the magnetic field energy ΔW in the discharge circuit at the instant of neutron generation. It is also found that this dependence is related to the initial deuteron pressure in the discharge chamber.     

Ion-induced secondary electron emission from ZnS thin films deposited by closed-spaced sublimation

ZnS thin films were deposited on soda lime glass and aluminum substrates by close-spaced sublimation technique. The change in composition, structural and optical properties of the films was investigated as a function of the substrate temperature. The deposited films were stoichiometric and crystalline in nature having cubic structure oriented only along (1 1 1) plane. The energy band gap of the films deposited at the substrate temperature of 150, 250 and 350 °C was 3.52, 3.58 and 3.63 eV respectively. These films were then bombarded with 2-10 keV energy pulsed Ar⁺ beam and their electron yield was determined from impinging ion and emitted electron currents. The electron yield of ZnS films was much high as compared to the metals. The electron yield of ZnS films increased with energy of the incident ion and got saturated at about 8 keV. The most important result of this study was that the electron yield of ZnS films having same composition was different. Monte Carlo simulations performed to interpret these experimental findings showed that the dissimilar electron yields of ZnS films is due to the combined effect of energy band gap, surface barrier potential and density of the films.     

DD reaction enhancement and X-ray generation in a high-current pulsed glow discharge in deuterium with titanium cathode at 0.8–2.45 kV

The DD reaction yield (3-MeV protons) and the soft X-ray emission from a titanium (Ti) cathode surface in a periodic pulsed glow discharge in deuterium were studied at a discharge voltage of 0.8–2.45 kV and a discharge current density of 300–600 mA/cm². The electron screening potential U_e = 610 ± 150 eV was estimated in the range of deuteron energies 0.8 keV < E_d < 2.45 keV from an analysis of the DD reaction yield as a function of the accelerating voltage. The obtained data show evidence for a significant enhancement of the DD reaction yield in Ti in comparison to both theoretical estimates (based on the extrapolation of the known DD reaction cross section for E_d ≥ 5 keV to low deuteron energies in the Bosch-Halle approximation) and the results of experiments using accelerators at the deuteron energies E_lab ≥ 2.5 keV and current densities 50–500 μ A/cm². Intense emission of soft X-ray quanta (10¹³–10¹⁴ s^?1 cm^?2) was observed at an average energy of 1.2–1.5 keV. The X-ray emission intensity and the DD reaction yield enhancement strongly depend on the rate of deuterium diffusion in a thin subsurface layer of Ti cathode.     

脉冲放电脱硫反应器中高能电子密度分布的光谱研究

脉冲流光放电产生的大于等于11.2 eV的高能电子能将处于基态的氮分子激发到N₂(C3Π_u)态,测试脉冲流光放电时的N₂(C3Π_u→B3Πg)发射光谱相对强度可以得出脉冲流光放电产生的高能电子的密度。实验在室温常压下研究了空气中线-板式脉冲流光放电脱硫反应器内高能电子密度分布情况,并研究了脉冲电压、反应器的线线间距对反应器内高能电子密度分布的影响。实验结果表明,反应器内的高能电子主要集中在放电线附近高电场区内,随着离放电线的距离增大,高能电子密度减小;脉冲电压对高能电子密度有很大影响,随着电压的升高,高能电子密度基本呈线性增大;线板间距固定,线线间距为线板间距的0.6～1倍时,反应器内高能电子密度分布较为均匀。     

基于Kriging模型的水中放电沉积能量优化分析

水中脉冲放电过程较为复杂,放电参数与放电沉积能量之间没有明确的函数关系。为了获得最佳沉积能量,明晰不同放电参数相互作用对沉积能量的影响,获得最佳放电参数组合,本文搭建了水中高压脉冲放电实验平台,结合Kriging代理模型探究了电压、电极间距和电导率三种放电参数对水中放电沉积能量的影响;利用遗传算法进行全局寻优,确定了最佳放电参数组合。研究结果表明：通过交叉验证评估该模型的均方根误差为6.95%,满足精度要求;外加电压一定时,在电极间距和电导率的协同作用下,沉积能量的变化呈现多峰值特性;在电压、电极间距和电导率分别为17 kV、2.28 mm和0.8 mS/cm的条件下产生的沉积能量最大,为最佳参数组合;通过实验验证了在最佳点的预测值和实际值相对偏差在8%以内。     

Increasing the ·OH radical concentration synergistically with plasma electrolysis and ultrasound in aqueous DMSO solution

In recent years, significant increases in waste processing and material engineering have been seen by using advanced oxidation processes. The treatment results and energy yields of these processes are largely determined by the generation and retention of reactive oxygen species (ROS). However, increasing the amount of ROS remains a key challenge because of the unavailability of performance- and energy-efficient techniques. In this study, plasma electrolysis, ultrasound, and plasma electrolysis combined with ultrasound were used to treat dimethyl sulfoxide (DMSO) solutions, and the results showed that the two methods can synergistically convert filament discharge into spark discharge, and the conversion of the discharge mode can significantly increase the concentration of OH radicals and effectively improve the efficiency of DMSO degradation. We verified the rationality of the results by analyzing the mass transfer path of ROS based on the reaction coefficients and found that the ·OH radicals in aqueous solution were mainly derived from the decomposition of hydrogen peroxide. These findings indicated that the synergistic action of plasma electrolysis and ultrasound can enhance the production of chemically reactive species, and provide new insights and guiding principles for the future translation of this combined strategy into real-life applications. Our results demonstrated that the synergistic strategy of ultrasound and plasma electrolysis is feasible in the switching mode and increasing the ROS, and may open new routes for materials engineering and pollutant degradation.     

纳秒脉冲放电处理有机染料废水的实验研究

随着印染行业的快速发展,印染废水的排放与日俱增。由于废水中的有机物具有成分复杂、难以降解的特点,若未经有效处理直接排放,会对生态环境造成严重的污染和危害。试验设计了一种多针-网式反应器循环处理有机组分为酸性红73(AR73)的模拟废水,其采用自行设计的基于TLT(Transmission Line Transformer)的高压重频纳秒脉冲电源驱动。电源可以产生峰值电压为50 kV,脉宽40 ns,上升沿20 ns的纳秒脉冲信号,工作频率可达500 Hz。试验考察了峰值电压、放电频率、染料初始质量浓度及作用时间等因素对AR73降解效果的影响。为评价处理效果,采用紫外分光光度法分别测量了废水中剩余染料浓度、过氧化氢浓度等指标。结果表明,在初始浓度30 mg/L,循环流量3.4 L/min,放电间距30 mm,峰值电压44.26 kV,放电频率200 Hz条件下处理30 min,AR73降解率可以达到83.20%,单次脉冲注入能量为11.73 mJ,过氧化氢浓度为47.36μmol/L,反应器脱色能效(G50)可以达到31.07 g·kW^-1·h^-1。增大放电电压可以进一步提高AR73降解率,溶液中活性物质浓度提高,但是能量效率有所下降。