Induction of Chromosome Aberrations by Monochromatic X-rays with Resonance Energy of Phosphorus K-shell Absorption Edge

The induction of chromosome aberrations by monochromatic soft X-rays with energies corresponding to the K-shell absorption edge of phosphorus has been studied in density-inhibited mouse m5S cells. The frequency of dicentrics was markedly enhanced when the cells were irradiated with energy at the K-shell resonance peak (2·153 keV) as compared to those at below (2·146 keV) or above (2·160 keV) the peak. The quantum efficiency was calculated to be 2·7 × 10^?3 for the induction of dicentrics per photoelectric absorption of phosphorus atom in DNA, which was comparable to the known efficiencies of X- or γ-ray-induced DNA double-strand breaks. However, comparison of the efficiencies based on the absorbed dose indicated that the magnitude of the enhancement was not due solely to the selective photoelectric absorption of the phosphorus atoms in DNA, and suggested the combined contributions of Auger electrons from phosphorus atoms within and outside the DNA molecules.     

Biological Effects of Auger Processes of Bromine on Yeast Cells Induced by Monochromatic Synchrotron X-rays

Summary

The biological effects of inner-shell ionization in bromine atoms incorporated into DNA in the form of bromodeoxyuridine monophosphate (BrdUMP), induced by monochromatized synchrotron X-rays, were studied using a deoxythymidine monophosphate (dTMP)-permeable mutant of yeast, Saccharomyces cerevisiae. The BrdUMP-incorporated yeast cells were irradiated with monochromatic X-rays of 13·51 or 13·45 keV, between which the bromine K-absorption edge (13·47 keV) is located. The cells were 1·07 times more sensitive to irradiation by 13·51 keV X-rays than at 13·45 keV, while dTMP-incorporated cells did not show any difference in sensitivity. In the presence of a radioprotector during irradiation, BrdUMP-incorporated cells showed a larger enhancement (1·20). These enhancements observed in the bromine-incorporated cells cannot be explained only by an increase of the absorbed dose due to a substitution of CH₃ group of thymine by bromine. It may be concluded that a major part of the enhancement was caused by inner-shell photoionization, followed by an Auger cascade of the bromine in the DNA. The quantum yield of lethality caused by the photoabsorption of bromine K-shell is not affected by the presence of cysteamine, suggesting the biological enhancement by the Auger processes may not be influenced by chemical protection.     

The response of high-purity germanium detectors to X-rays with energy in the region of the Ge K-absorption edge.

The response of a high-purity germanium detector to X-rays in the 8-15-keV energy region has been investigated. The w-value and energy resolution dependencies on the X-ray energy have been studied. No abrupt variation of w is observed at the germanium K absorption-edge (11.104-keV). The detector energy resolution follows a characteristic linear dependence on Ex(-1/2) over the whole energy range. Both features are consistent with the absence of intrinsic nonlinearity effects in germanium at the K-edge.     

Inhibitory Effect of Membrane-specific Drugs on Liquid-holding Recovery in U.V.-irradiated E. Coli Cells

The content and biosynthesis of glycosaminoglycans (GAGs) were studied in the pig thigh muscle after acute local γ-irradiation. Seven months following irradiation, the muscular tissue next to the irradiation cone was replaced by severe mutilating fibrosis delimited by an intermediary perifibrotic zone. Fibrosis, perifibrotic tissue and normal muscle, were sampled and incubated with [³H]glucosamine and [³⁵S]sulphate, and GAGs were isolated following pronase digestion. Results showed a parallel increase of collagen and GAG content in perifibrotic and fibrotic tissues. Sulphated GAGs, heparan sulphate and dermatan sulphate were preferentially accumulated in fibrotic tissue, while the hyaluronic acid content increased only slightly. Synthesis of sulphated GAGs was more elevated in fibrotic tissue than in perifibrotic zone as compared with normal muscle. Seven months after irradiation well-developed fibrotic tissue continued to synthesize and to accumulate extracellular matrix macromolecules, indicating the invasive aspect of post-irradiation fibrosis.     

The Influence of Thiols on the Pre-irradiation Incubation Effect of Nitroimidazoles in E. Coli Cells

Summary

The increase in the degree of radiosensitization of Escherichia coli cells following prolonged pre-irradiation incubation with nitroimidazoles is not correlated with the loss of intracellular non-protein thiols (NPSH) alone. The rates of reduction of the nitro compounds and the NPSH removal do not show strong dependencies on the lipophilicities of the nitroimidazoles whereas the highly lipophilic compound RGW-609 effects an increase in radiosensitization in a much shorter incubation time than the other nitroimidazoles. Exogenous dithiothreitol (DTT) increased the rate of reduction of misonidazole in the cells but did not alter the fraction converted to the amine. Added DTT (0·15 mmol dm^?3) completely protected against the pre-irradiation incubation effect of misonidazole (2·5 mmol dm^?3) when added at the start of the incubation but only partially protected when added before irradiation. It is suggested that NPSH can intercept metabolite(s) (or their precursors) of nitroimidazoles which can potentiate cell killing by radiation.     

Photoreactivation of Ionizing-radiation-induced Damage in E. Coli

Since the cytokinesis-block micronucleus assay is very sensitive at low radiation doses, we used it to investigate the in vitro sensitizing effects of two new hypoxic cell sensitizers (KU-2285, a fluorinated 2-nitroimidazole and RP-170, a 2-nitroimidazole nucleoside analogue) at 1–3 Gy in comparison with etanidazole. Exponentially growing EMT6 cells were treated with the drugs under aerobic or hypoxic conditions for 40 min prior to and during irradiation, after which the drugs were removed and cytochalasin B (2 µg/ml) was added to the medium. The number of micronuclei in binucleate cells was counted after 42 h of culture. Under aerobic conditions the three compounds at 5 mm had no sensitizing effect. Under hypoxic conditions the sensitizer enhancement ratio (SER) at 5 mm was 3·8 for KU-2285, 3·2 for RP-170, and 2·3 for etanidazole, while the oxygen enhancement ratio was 2·9. When the cells were pretreated under hypoxic conditions with drugs at 5 mm but then irradiated under aerobic conditions, KU-2285 and RP-170 had a sensitizing effect whereas etanidazole did not. The sensitizers were also tested at 0·5 and 1 mm, and the SER values were compared with those obtained at high doses (15–30 Gy) using a colony assay. The SER at low doses was higher than that at high doses for 1 and 5 mm KU-2285 and 5 mm RP-170, while the SERs were similar for all concentrations of etanidazole and the lower concentrations of KU-2285 and RP-170. These results might suggest the potential usefulness of KU-2285 and RP-170 in clinical radiotherapy.     

Rhodium(III) as a Potentiator of the Effects of X-rays on Cells

Summary

A rhodium compound, Rh(NH₃)₃Cl₃, does not sensitize the spores of Bacillus megaterium to X-rays. However, it is a very effective sensitizer of vegetative cells of Staphylococcus aureus, raising the sensitivity four times in O₂ and over 100 times in anoxia. The inhibition by oxygen of the sensitizing action of Rh(III), which operates over a wide range of [O₂], is noteworthy. These experiments were performed in saline-phosphate buffer using 50kVp X-rays. The results are discussed in terms of the known radiation chemistry of this compound.     

Some Effects of Hypothermia and Hypoxia on the Sensitivity of HeLa Cells to X-rays

Summary

In vivo studies on the alterations in radio-sensitivity produced in hypothermic mammals do not enable a distinction to be drawn between the effects of hypothermia per se and the concomitant hypoxia.

The present experiments on the radio-sensitivity of mammalian (HeLa) cells in vitro have permitted observations to be made on the separate effects of hypoxia and hypothermia.

It is concluded that, whereas hypoxia produces a decrease in radio-sensitivity, hypothermia produces no detectable change.     

Changes in the Survival Curve Shape of E. Coli Cells Following Irradiation in the Presence of Uncouplers of Oxidative Phosphorylation

Summary

Four uncouplers of oxidative phosphorylation (UOP) (carbonyl cyanide m-chlorophenylhydrazone, 2,4-dinitrophenol, 4-hydroxybenzylidenemalonitrile and N-phenylanthranilic acid) have been found to alter the shape of the radiation survival curves of several cell lines of E. coli when present during irradiation in oxia. Incubation of cells with high concentrations of UOP for 30 min before irradiation induced an increase in extrapolation number (n) in cell lines AB 1157(wild-type), AB 1886(uvrA^?) and KMBL(polA^?) but not GR 501(lig^?)ts, AB 2463(recA^?) and AB 2480(uvrA^? recA^?). In addition the UOP all effect a decrease in mean lethal dose (D₀) even when tested at low concentrations or short contact times. Studies with wild-type cells correlate the increase in n with measured increased levels of ATP (above oxic control cells) produced upon incubation with UOP. The increased levels of ATP most likely arise from the UOP overstimulating glycolysis. The decrease in D₀ cannot be associated with any of the repair pathways investigated and it is concluded that the highly lipophilic UOP directly or indirectly potentiate other target(s) to radiation damage as well as DNA under oxic conditions. Treatment of the cells with UOP did not result in the deleterious depletion of energy substrates, loss of non-protein thiols or the production of cytotoxins upon irradiation.     

重组人乙型肝炎病毒核糖核酸酶H基因工程菌的生物活性研究

目的：研究表达乙型肝炎病毒核糖核酸酶H(HBV—RNaseH)工程菌的发酵条件。方法：采用摇瓶发酵，研究不同宿主菌对表达HBV—RNaseH的效果；同时对培养基、诱导时期、诱导时间、初始pH等发酵条件以及质粒稳定性进行研究。结果：选用E coliBL21为宿主菌，在LB培养基中培养至A600为0．6时，诱导表达4．5h，HBV—RNaseH表达量最高达33．6％。而且重组质粒具有良好的分离稳定性和结构稳定性。结论：此发酵条件可以比较好的提高HBV—RNaseH的表达量，为发酵规模的扩大奠定了基础。     

The Analysis of Single-strand Breaks in E. Coli Using a Curve-fitting Procedure

A curve-fitting technique has been used to analyse the activity profiles occurring when the tritium labelled DNA of irradiated E. coli is sedimented in an alkaline sucrose gradient. The fitted curve is a modification of an expression derived elsewhere, which assumes that DNA of unit length undergoes scissions at random positions on the DNA strand. The theoretical curves fit the data well, even after considerable repair or excision of the radiation damage has been effected by cellular enzymes. The profile resulting from sedimentation of unirradiated DNA may be fitted with the same theoretical expression provided that the velocity of centrifugation is not too high. The number of single-strand breaks derived from the analysis is almost unaffected by the presence of extraneous activity at the top or bottom of the sucrose gradient. The method is therefore more reliable than many other methods used to analyse sedimentation data.     

Effects of X-rays on Female Germ-cells of Drosophila Melanogaster

Summary

The sensitivity in terms of dominant-lethal induction (strictly speaking: reduced hatchability) has been measured for successive eggs laid by Drosophila melanogaster after irradiation of the female with 1000, 4000 and 6000 rad.

Hypersensitivity is found in eggs laid by females aged seven days, during the first 12 hours after irradiation. This is attributed to irradiation of Metaphase I. A lower level of sensitivity is found in eggs laid over the next six days. This is attributed to the irradiation of oocytes in all stages prior to Metaphase I.

Finally, a residual incidence of dominant lethals is observed in eggs laid more than six days after irradiation, which are presumed to have been irradiated as oogonia.

Oviposition (i.e. rate of maturation of eggs) shows an entirely different radiation response. 4000 rad produces a slight depression of egg-laying during the period of low dominant-lethal production, a more marked depression coinciding with the main production of dominant lethals, and a particularly severe depression on day 3 after irradiation. The pattern of sensitivity after 6000 rad is the same but more marked. The egg-laying rate more than six days after irradiation is slightly depressed by 4000 rad, and more so with increasing doses until 10 000 rad, when complete sterility is produced. After such a dose the ovarioles are atrophied, without oocytes or oogonia.     

De novo development of presumed cavernomas following resolution of E. Coli subdural empyemas

Cavernomas fall within the group of angiographically occult lesions and may be found in up to 4 % of the population [1]. They may occur at any age, and with the advent of MRI incidental cavernomas are increasingly identified. The pathogenesis is uncertain. Familial cases are well recognised with a reported prevalence of 10–15 % [2–3]. The incidence of new lesions has been reported at 0.4 lesions per patient per year in cases with familial cavernomas [4]. Presumed cavernomas have been documented following radiation for malignancy [5–6], and sterotactic cerebral biopsy [7]. There have been no previously documented cases of de novo genesis of cavernomas following bacterial meningitis and subdural empyemas. Received: 18 November 1999/Accepted: 11 February 2000     

Radiation Protection of E. Coli Strains by Cysteamine in the Presence of Oxygen

Summary

The survival of various E. coli K₁₂ strains with defects in the rec system have been measured after γ-irradiation in air in the presence (0·1 mol dm^?3) or in the absence of cysteamine. The results confirm those of Bresler et al. (1978) indicating that the protection by cysteamine in the presence of oxygen is due to an influence on enzymatic repair. The low protection by cysteamine of wild-type cells pretreated with chloramphenicol which prevents protein synthesis, supports the above conclusion. The reason for the absence of a protective effect by OH radical scavenging and H-atom donation is discussed. It is proposed that DNA peroxyl radicals are formed during irradiation in the presence of oxygen and that they are transformed into hydroperoxides by H-atom donation from the intracellular glutathione and the added cysteamine. These hydroperoxides are still dangerous for the cell as indicated by the protective action of glutathione peroxidase observed by Marklund et al. (1984).     

CTB-mST2融合蛋白在大肠杆菌表达及其生物活性鉴定

目的:表达霍乱毒素B亚单位(CTB)和大肠杆菌突变的热稳定肠毒素(mST)的融合蛋白,并进行抗原性和免疫原性的分析.方法:通过连接肽(linker)将CTB基因和串连的mST连接,然后插入表达载体pET-22b( ),获得克隆,经IPTG诱导获得CTB-mST2融合蛋白.采用多因素正交优选法优化了培养基及培养条件,对表达产物进行包涵体复性后,经过亲合层析纯化得到融合蛋白,并对该融合蛋白抗原性和免疫原性进行了分析.结果与结论:构建了高效表达工程菌,经摇瓶培养,在优化培养基及培养条件下融合蛋白表达量可达320 mg/L,占总蛋白40%.融合蛋白免疫小鼠,可获得高滴度抗CTB和ST血清;将融合蛋白与灭活的O157∶ H7菌体组合免疫小鼠,可产生对O157∶ H7毒株攻击的保护力.本研究可为构建抗ETEC和EHEC复合疫苗提供依据.     

X射线全身照射对小鼠脾细胞转铁蛋白受体表达的影响

目的转铁蛋白受体（ＴｆＲ）是Ｔ淋巴细胞受抗原或丝裂原刺激后表达在细胞表面的重要受体之一,与Ｔ细胞的活化和增殖有着密切关系。目前尚未见国内外有关ＴｆＲ辐射效应研究的报道。研究大剂量电离辐射后ＴｆＲ表达的变化及作用,对阐明辐射抑制机体免疫功能的机制有着重要意义。方法本文采用流式细胞术的方法观察了不同剂量Ｘ射线全身照射对小鼠脾细胞ＴｆＲ表达的影响以及４ＧｙＸ射线全身照射后不同时间ＴｆＲ表达的变化。结果０５～６ＧｙＸ射线全身照射后２４小时,脾脏ＴｆＲ阳性细胞数从１Ｇｙ开始随照射剂量的增加而下降,且呈明显的剂量依赖性。４ＧｙＸ射线全身照射后１２～７２小时,脾脏ＴｆＲ阳性细胞数于照后１２小时开始下降,２４、４８小时降至最低值（Ｐ＜０．０５,Ｐ＜０．０１）,７２小时开始回升。结论大剂量电离辐射抑制小鼠脾细胞ＴｆＲ的表达,并有明显剂量依赖性;ＴｆＲ表达的下降可能与辐射抑制ＩＬ２的分泌和ＩＬ２受体的表达有关。     

Effects of Irradiation with Low-energy X-rays on Resting- and Action-potentials of Skeletal- and Heart-muscle Fibres

Summary

The effects of x-irradiation (50 kv) on resting- and action-potentials of isolated frog sartorius muscles, of heart-muscle fibres (papillary muscles of cats and Purkinje fibres of calves and sheep) were investigated by the intracellular recording technique. On frog sartorius fibres, radiation doses below 160 kr had no effect on the resting-potential; higher doses led to a dose-dependent decrease of about 1 mv per 160 kr. This effect was independent of the dose-rate in a range from 3 up to 85 kr/min. Shape and amplitude of the action-potential of frog sartorius fibres (stimulus frequency: 0·2/min) were not influenced significantly by irradiation of 15 min duration up to doses of 600 kr.

On rhythmically-stimulated (85/min), isolated papillary muscles, irradiation with total doses up to 240 kr had no effect on the resting- and action-potential. Higher doses (345–440 kr) produced a significant fall in the resting-potential, action-potential and rate of rise, as well as a shortening of repolarization-time and a decrease in mechanical tension. These changes were most marked immediately after irradiation and were partly reversible within one hour. Spontaneously-beating Purkinje fibres were at least 10–15 times more sensitive to x-rays than papillary muscles. As in papillary muscle, irradiation caused a decrease in the maximal diastolic potential, the action-potential and the upstroke velocity, the latter effect being most pronounced. At the same time, some decrease in slow diastolic depolarization and frequency was observed. All these changes were reversible within 30 min. The observed effects point to a partial inactivation of the sodium-carrying system as a possible primary mechanism of action.