Model Studies for the Direct Effect of High-energy Irradiation on DNA. Mechanism of Strand Break Formation Induced by Laser Photoionization of Poly U in Aqueous Solution

Summary

Laser flash photolysis of polyuridylic acid (poly U) in anoxic aqueous solutions leads to biphotonic photoionization of the uracil moiety followed by the formation of single strand breaks (ssb). The rate constant for ssb formation (1·0 s^?1, obtained from the slow component of conductivity increase at 23°C and pH 6·8) increases with decreasing pH to 235 s^?1 at pH 3·5. The activation energy (pre-exponential factor) was measured to be 66 kJ mol^?1 (5 × 10¹¹ s^?1) at pH 6·8. Addition of dithiothreitol (DTT) or glutathione (GSH) prevents ssb formation by reacting with a poly U intermediate (rate constant = 1·2 × 10⁶ and 0·16 × 10⁶ dm³ mol^?1 s^?1, respectively). Since with OH radicals as initiators very similar data have been obtained for the kinetics of ssb formation and for the reaction with DTT, we conclude that photoionization of the uracil moiety in poly U leads eventually to the same chemical pathway for ssb formation as that induced by OH radicals. Furthermore, we propose that protection by DTT and GSH occurs via H donation to the C-4′ radicals of the sugar moiety of DNA and to the C-4′ and the C-2′ radicals of poly U.     

Radiation-induced Strand Breakage in Poly(Riboadenylic Acid). A Pulse Radiolysis Study on the Protective Action of Cysteamine Under Anoxic Conditions

Summary

Poly(riboadenylic acid) was irradiated in N₂O-saturated dilute aqueous solution at pH 7·8 with single pulses (50–200 ns) of 16 MeV electrons. With the aid of Rayleigh light scattering measurements both the extent and rate of main-chain scission were measured in the absence and the presence of cysteamine (RSH). In both cases two modes of light scattering intensity (LSI) decrease were detected. From this finding it was concluded that two chemically different radical sites, giving rise to main-chain breakage, were produced by OH attack on the macromolecules. Cysteamine reduced the extent of LSI decrease and accelerated the rate of the slow mode of LSI decrease significantly. The fast mode of the LSI decrease is due to fragment diffusion and therefore the influence of cysteamine on the rate of decay of the short-lived radical could not be studied. The assessment of the relative importance of ·OH scavenging (RSH + ·OH → RS· + H₂O) and of repair (PA· + RSH → PAH + RS·) with respect to protection yielded the following: in the case of the long-lived radical, repair contributes significantly at low RSH concentration (< 10^?4 m); in the case of the short-lived radical, OH scavenging dominates and repair becomes noticeable only at [RSH] > 10^?4 m. The following data were evaluated in this work: 100 eV-yield of main-chain scission, G(sb) = 1·1; lifetimes of radicals: < 50 µs (short-lived), 0·6s (long-lived), k_{pa· + rsh} = 3·4 × 10⁶ m^?1 s^?1 (for long-lived radicals).     

Reactions of OH Radicals with Poly(U) in Deoxygenated Solutions: Sites of OH Radical Attack and the Kinetics of Base Release

Summary

Pulse radiolysis of N₂O-saturated solutions of poly(U) in the presence of tetranitromethane showed that 81 per cent of the radicals formed are reducing in nature. Using data from other sources it has been estimated that 70 per cent of the OH radicals add to the base at C(5) and 23 per cent at C(6) while only 7 per cent abstract an H-atom from the sugar moiety. To a large extent the C(5) OH adduct radicals attack the sugar moiety of poly(U) thereby inducing strand breakage and base release. G (base release) = 2·9 can be subdivided into three components: (a) immediate (20 per cent), (b) fast (50 per cent) and (c) slow (30 per cent). The immediate base release must occur either during the free-radical stage or as a result of the rapid (t_½ < 4 min at 0°C) decomposition of a diamagnetic product. The fast and the slow processes are only readily observable at elevated temperatures, e.g. at 50°C the half lives are 83 min and 26 h, respectively (E_a (fast) = 68 kJ mol^?1, E_a (slow) = 89 kJ mol^?1, A (fast) = 1·5 × 10⁷ s^?1, A (slow) = 1·9 × 10⁹ s^?1. It is concluded that there are three different types of sugar lesions giving rise to base release, structures for which are tentatively proposed.     

Modification of Radiation-induced Intestinal Injury in Rats by Chilling after Irradiation

Summary

Chilling of the small intestine of the rat immediately after x-irradiation postponed depression of the mitotic count and degeneration of the crypt cells. Mitotic depression and cellular degeneration occurred, however, when the tissue was re-warmed. The effects of transient chilling at 18°c were essentially identical to those of chilling at 5°c. The inhibition of colchicine-induced metaphase arrest and of tritiated thymidine uptake in chilled crypt cells suggests that postponement of the signs of radiation injury resulted from suppression of metabolic activity and cell division at low temperature. Although there was some suggestion of reduced injury in the chilled tissues, the protective or recovery-promoting effectiveness of hypothermia remains to be established.     

Chemical Competition in Target Radical Reactions: Numerical Simulation of the Theory and Comparison with Measured Oxygen Effect on DNA Damage in Cells

Summary

An intracellular radiation-chemical reaction scheme is tested in which solute and solvent radicals R· react with non-target molecules Sa (scavengers) or with target molecules (presumed to be DNA) to produce target radicals T·, which may also be produced by direct ionization of DNA. The rate of target radical decomposition to become ‘uncommitted damage’ that the cell may repair is affected by the concentration of oxygen (O₂), thiols (S) and electronaffinic sensitizers (F), which compete with one another to form, respectively, target products TO₂, TS and TF. This uncommitted damage is then subject to biochemical modification, including molecular repair, by the cell. The rate equations for this competing reaction scheme were written and programmed for computer simulations of changes in oxygen, thiol and electronaffinic sensitizer concentrations. A reaction scheme that also includes some non-radical target damage was also simulated. Simulations were made using available experimental data concerning intranuclear concentrations and reaction rate constants, respectively, k_o, k_s and k₁ for the reactions T· + O₂→TO₂, T· + S→TS and T· + F→TF, which produce uncommitted chemical damage. Experimental data on strand-break induction in glutathione-proficient and glutathione-deficient cells, in cells treated with thiol active agents, and in cells treated with hypoxic sensitizers, along with the computer simulations, generally agree that thiol molecules can react with target radicals to reverse T· in competition with O₂ and/or electronaffinic sensitizers.

Forward reaction rate constants k_o, k_s (dithiothreitol), k_s (glutathione) and k₁ (misonidazole) in the approximate ratio 10 : 0·3 : 0·02 : 0·4 satisfied the above reaction scheme, and approximately 5 per cent non-radical target molecule damage could be included with satisfactory agreement with experimental data.     

Evaluation of cell viability,DNA single-strand breaks,and nitric oxide production in LPS-stimulated macrophage RAW264 exposed to a 50-Hz magnetic field

Purpose: Synergistic effects between cellular oxidative stress and magnetic fields may explain the adverse biological effects of 50/60?Hz magnetic fields. To determine whether this hypothesis holds in macrophage RAW264 cells, we measured DNA single-strand breaks (SSB), cell viability, and nitric oxide (NO) production in cells with or without exposure to 0.5-mT, 50-Hz magnetic fields for 24?h and with or without simultaneous stimulation via the bacterial endotoxin, lipopolysaccharide (LPS).

Materials and methods: Macrophages stimulated with 10?ng/ml LPS for 1?h were exposed to or not exposed to a magnetic field and were then subjected to (1) the alkaline comet assay to measure SSBs, (2) trypan-blue exclusion assay for cell viability, and (3) measurements of NO for evaluation of oxidative stress.

Results: The 50-Hz magnetic field enhanced DNA SSB and decreased cell viability only in the LPS-stimulated macrophages in which NO production was greatly enhanced. The magnetic field alone did not alter NO production.

Conclusion: Co-stimulation of the cell with LPS and a 50-Hz magnetic field promoted SSB and lowered cell viability, but these were not mediated by LPS-induced NO production.     

萃取-紫外分光光度法测定替硝唑微球中药物的含量

目的建立一种测定替硝唑乳酸羟基乙酸共聚物微球中药物含量的方法。方法采用二氯甲烷溶解微球后,以0.1mol/L盐酸提取药物的方法处理样本,运用紫外分光光度法测定药物的含量。结果替硝唑在6~30 mg/L的范围内,浓度与吸收度的线性关系良好,本方法高中低三种浓度的平均回收率为(99.25±0.21)%,RSD为1.03%。结论该方法操作简单、可靠,可用于快速测定微球中的药物的含量。     

Differential Radiosensitization of Human Tumour Cells by 3-aminobenzamide and Benzamide: Inhibitors of Poly(ADP-ribosylation)

Summary

The effect of 3-aminobenzamide (3AB) and benzamide (BZ) (inhibitors of poly(ADP-ribose) synthetase) on radiosensitivity was investigated in normal human fibroblasts and three human cell lines established from tumours with varying degrees of clinical radiocurability. The human tumour cell lines selected were: (1) Ewing's sarcoma, a bone tumour usually considered radiocurable with moderate radiation doses; (2) lung adenocarcinoma, a tumour considered radiocurable with high doses of radiotherapy; and (3) osteosarcoma, a very resistant tumour which is rarely controlled by standard doses of radiotherapy. Poly(ADP-ribose) synthetase inhibitors were added to cultures 2h prior to irradiation and removed 24h after. Inhibitors were used at doses producing little or no toxicity in cells.

In the presence of these inhibitors, a differential radiosensitization was observed. Ewing's sarcoma cells and normal human fibroblasts were sensitized to an equal extent by either 8 mm 3AB or 4 mm BZ. However, no sensitization was observed at these concentrations in the lung adenocarcinoma cells or osteosarcoma cells. The degree of radiosensitization in vitro by 3AB and BZ correlates well with the clinical radiocurability of these tumours in vivo.     

美军联合战场创伤系统的发展及应用

联合战场创伤系统是美军为了提高伊拉克和阿富汗战场上的战伤救治效果而建立的一种创伤救治系统。2004年美军开始在伊拉克战场应用该系统,2005年开始在伊拉克和阿富汗战场全面应用。本文梳理了美军联合战场创伤系统的发展历史,探讨了该系统的任务、目标及组织构成,分析了其在伊拉克和阿富汗战场上的应用效果。     

Involvement of MAPK activation and ROS generation in human leukemia U937 cells undergoing apoptosis in response to sonodynamic therapy

Abstract

Purpose: To elucidate the underlying events in Chlorin e6 (Ce6)-mediated sonodynamic therapy (SDT) (Ce6-SDT)-induced apoptosis of human leukemia cell line U937.

Materials and methods: The viability of cells was determined by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltertrazolium bromide tetrazolium (MTT) test. Apoptosis was analyzed using a ?ow cytometer as well as ?uorescence microscopy with 4′-6-Diamidino-2-Phenylindole (DAPI) staining. Western blotting was used to analyze the expression of caspase-3, poly ADP- ribose polymerase (PARP) and mitogen-activated protein kinase (MAPK).

Results: Several distinct sonochemical effects were found after SDT treatment. The participation of MAPK signals in SDT which caused U937 cell damage was specifically examined and the inhibition of p38 MAPK and Jun-N-terminal kinase (JNK) both apparently exerted a negative effect on SDT-induced cell death, while extracellular signal-regulating kinase (ERK1/2) inhibition enhanced SDT-induced cell death. The intracellular reactive oxygen species (ROS) was significantly enhanced by SDT, and pre-treatment with ROS scavenger N-acetylcysteine (NAC) partially alleviated SDT-induced cell viability loss, DNA fragmentation, mitochondria membrane potential (MMP) dissipation, caspase-3 activation, but interestingly MAPK activation was not affected much by NAC.

Conclusions: In the present paper, cell apoptosis of U937 cells was markedly enhanced after Ce6-SDT. Meanwhile, p38 MAPK, JNK and ERK were all differently activated in this process. One possible explanation for the induced cell apoptosis could be the increased ROS generation in Ce6-SDT.     

Sensitive CEST agents based on nucleic acid imino proton exchange: detection of poly(rU) and of a dendrimer-poly(rU) model for nucleic acid delivery and pharmacology.

It is shown that the exchange properties of the imino and hydroxyl protons of polyuridilic acid (poly(rU)) allow use of this compound as a chemical-exchange saturation transfer (CEST) contrast agent. A proton/proton sensitivity enhancement factor of over 5000 per imino proton allowed the detection of a few micromolar of polymer (2000 uridine units; 644 kD) with a 50% change in the water signal. The enhancement factor would increase further at even lower concentrations, opening up the submicromolar range. When poly(rU) was complexed to a dendrimer carrying 250 positive charges, the stoichiometry was approximately one RNA for 10 dendrimers. The sensitivity enhancement was reduced but remained large (2300/imino proton), bringing enhanced CEST visibility to the dendrimers. The net charge of the complex was positive, suggesting that the complexed dendrimers would still interact with cell membranes, and that the RNA-dendrimer complex could provide a model for a gene delivery system with good CEST visibility.     

Correction for artifacts induced by B(0) and B(1) field inhomogeneities in pH-sensitive chemical exchange saturation transfer (CEST) imaging.

Chemical exchange saturation transfer (CEST) imaging provides an indirect detection mechanism that allows quantification of certain labile groups unobservable using conventional MRI. Recently, amide proton transfer (APT) imaging, a variant form of CEST imaging, has been shown capable of detecting lactic acidosis during acute ischemia, providing information complementary to that of perfusion and diffusion MRI. However, CEST contrast is usually small, and therefore, it is important to optimize experimental conditions for reliable and quantitative CEST imaging. In particular, CEST imaging is sensitive to B(0) and B(1) field, while on the other hand; field inhomogeneities persist despite recent advances in magnet technologies, especially for in vivo imaging at high fields. Consequently, correction algorithms that can compensate for field inhomogeneity-induced measurement errors in CEST imaging might be very useful. In this study, the dependence of CEST contrast on field distribution was solved and a correction algorithm was developed to compensate for field inhomogeneity-induced CEST imaging artifacts. In addition, the proposed algorithm was verified with both numerical simulation and experimental measurements, and showed nearly complete correction of CEST imaging measurement errors caused by moderate field inhomogeneity.     

颌骨曲面及直线断层摄影在种植牙体中的临床应用

目的:探讨颌骨曲面及直线断层摄影在种植牙体中的临床应用价值。方法:对38例种植牙患者术前进行颌骨曲面及直线断层摄影,根据所得图像测出颌骨受植区的深度、宽度及厚度等相关数值,以指导临床选择合适型号的种植体制定种牙计划;种植牙体后立即重复摄影,对种植效果进行评价,及时纠正种植体植入中存在的角度和深度等问题。结果:本组病例种植牙76颗,其中61颗种植体植入效果满意,14颗种植体角度轻度偏离,但未超出正常偏离值范围,1例种植体角度偏离并穿破颌骨皮质,重新植入后效果满意。术后半年随访所有种植牙体形态位置均无异常改变。结论:颌骨曲面及直线断层摄影相结合能清晰显示受植区三维骨质结构和种植体的植入情况,对种植牙手术计划的制定与实施,提高种植牙体的成功率具有重要的临床应用价值。     

Effect of Electromagnetic Pulses (EMP) on associative learning in mice and a preliminary study of mechanism

Abstract

Purpose: To investigate the effects of electromagnetic pulses (EMP) on associative learning in mice and test a preliminary mechanism for these effects.

Materials and methods: A tapered parallel plate gigahertz transverse electromagnetic (GTEM) cell with a flared rectangular coaxial transmission line was used to expose male BALB/c mice to EMP (peak-intensity 400 kV/m, rise-time 10 ns, pulse-width 350 ns, 0.5 Hz and total 200 pulses). Concurrent sham-exposed mice were used as a control. Associative learning, oxidative stress in the brain, serum chemistry and the protective action of tocopherol monoglucoside (TMG) in mice were measured, respectively.

Results: (1) Twelve hour and 1 day post EMP exposure associative learning was reduced significantly compared with sham control (p < 0.05) but recovered at 2 d post EMP exposure. (2) Compared with the sham control, lipid peroxidation of brain tissue and chemiluminescence (CL) intensity increased significantly (p < 0.05), while the activity of the antioxidant enzymes Superoxide Dismutase [SOD], Glutathione [GSH], Glutathione Peroxidase [GSH-Px], Catalase [CAT]) decreased significantly (p < 0.05) at 3 h, 6 h, 12 h and 1 d post EMP exposure. All these parameters recovered at 2 d post EMP exposure. (3) No significant differences between the sham control group and EMP exposed group were observed in serum cholesterol and triglycerides. (4) Pretreatment of mice with TMG showed protective effects to EMP exposure.

Conclusions: EMP exposure significantly decreased associative learning in mice and TMG acted as an effective protective agent from EMP exposure. This mechanism could involve an increase of oxidative stress in brain by EMP exposure.     

Health technology assessment on the use of magnetic resonance imaging (MRI) and computed tomography (CT) in the diagnosis of multiple sclerosis (MS) and clinically isolated syndromes (CIS)

This work is the result of a health technology assessment for the Flemish regional government, Belgium, performed in 2006. A search of the available literature in the databases Medline and EMBASE was performed to find evidence for a rational choice between CT and MRI techniques in the work-up of patients with clinically isolated syndrome (CIS) with a suspicion for multiple sclerosis (MS), and in follow-up exams performed in such patients. From the presented evidence, in patients referred for CIS or MS, MR is superior to CT for detection and characterization of brain and spine lesions.     

The effect of various cations and pH on the adsorption of U(VI) on Amberlite IR-118H resin

The effects of various metal cations and pH on the adsorption of uranium(VI) on strongly acidic cation exchanger Amberlite IR-118H (AIR-118H) were studied. The metal cations suppress U(VI) adsorption differently depending on their ionic radii. Adsorption of U(VI) on AIR-118H peaks at pH 3.4, which was attributed to the occurrence of different forms of U(VI) at different pH values. The adsorption data were then processed using the Frumkin–Fowler–Guggenheim equation, and the standard free energy of adsorption was calculated.     

刺五加制剂对中老年人恒定负荷运动中脂肪利用的影响

以 2 0名 45～ 5 5岁志愿者为试验对象 ,随机分为试验组与对照组进行双盲干预试验 ,研究刺五加制剂对人体运动能力的影响。结果表明 :试验组服用刺五加制剂 80 0mg 14天后 ,在 45 0kg·m/min(75W)持续恒定功率负荷运动时呼吸商由 0 95下降至 0 90 ,使运动时脂肪供能增加 17% ,而对照组无改变。结论 :刺五加制剂可能通过增加运动中的脂肪供能 ,节省肌糖元 ,从而发挥抗疲劳作用。     

Frequency data for the STR loci HumFibra (FGA) and HumACTBP2 (SE33) in a population of Germans and Turks from South-West Germany

Population studies were carried out on German and Turkish individuals from South-West Germany using the short tandem repeat (STR) systems HumFibra (n = 138 Turkish and 1161 German individuals) and HumACTBP2 (n = 202 Turkish and 1338 German individuals). After electrophoresis 19 alleles could be identified for HumFibra and 55 for HumACTBP2. No significant deviations from Hardy-Weinberg equilibrium were observed. Received: 11 February 1998 / Received in revised form: 4 May 1998     

The Effect of Tanespimycin (17-AAG) on Radioiodine Accumulation in Sodium-Iodide Symporter Expressing Cells

Purpose

The heat shock protein 90 inhibitor, tanespimycin, is an anticancer agent known to increase iodine accumulation in normal and cancerous thyroid cells. Iodine accumulation is regulated by membrane proteins such as sodium iodide symporter (NIS) and pendrin (PDS), and thus we attempted to characterize the effects of tanespimycin on those genes.

Methods

Cells were incubated with tanespimycin in order to evaluate ¹²⁵I accumulation and efflux ability. Radioiodine uptake and efflux were measured by a gamma counter and normalized by protein amount. RT-PCR were performed to measure the level of gene expression.

Results

After tanespimycin treatment, ¹²⁵I uptake was increased by ∼2.5-fold in FRTL-5, hNIS-ARO, and hNIS-MDA-MB-231 cells, but no changes were detected in the hNIS-HeLa cells. Tanespimycin significantly reduced the radioiodine efflux rate only in the FRTL-5 cells. In the FRTL-5 and hNIS-ARO cells, PDS mRNA levels were markedly reduced; the only other observed alteration in the levels of NIS mRNA after tanespimycin treatment was an observed increase in the hNIS-ARO cells.

Conclusions

These results indicate that cellular responses against tanespimycin treatment differed between the normal rat thyroid cells and human cancer cells, and the reduction in the ¹²⁵I efflux rate by tanespimycin in the normal rat thyroid cells might be attributable to reduced PDS gene expression.     

中国美利奴(新疆型)新品系羊综合选择指数制定及应用效果分析

本研究分别对中国美利奴羊 (新疆型 )体格大品系和毛质好品系制定出综合选择指数I1=1.97x1+3.32x2 (x1为体重 ,x2 为毛量 )和I2 =2 .2x1+0 .6 7x2 (x1为弯曲评分 ,x2 为毛量 ) ,使用效果表明 ,两个选择指数实用性较为理想。