邵春林，学者全讯担保网主页-全讯担保网

by the method of gel electrophoresis, radiation-induced dna single- and double-strand breaks (ssb, dsb) were studied with a model system of pbr322 solution in vitro in the presence of •oh radical scavengers, mannitol and te (10-2 mol dm-3 tris and 10-3 mol dm-3 ethylene diamine tetra-acetic acid). experiments showed that ssb resulted from one-hit events of radiation energy deposition and dsb resulted from both one-hit and two-hit energy deposition events and so were distinguished into two classes of αdsb and βdsb. moreover, α/β, where a is the number of dsb per unit dose induced in one irradiation event and β the number of dsb per unit squared dose induced by the combination of two independent ssb, was related to the scavenging capacity, s, and for σ<108 s-1, αdsb predominate over dsb. on the other hand, if σ<2´108 s–1, the measured g(αdsb) decreased in parallel with g(ssb), i.e., g(αdsb)/g(ssb) was a constant. when σ>2×108 s-1, g(αdsb) decreased slightly so that the ratio of αdsb to ssb evidently increased. therefore, αdsb could be induced by the radical transfer mechanism for σ<2×108 s-1 and contrarily produced by the local multiply damaged sites (lmds) mechanism for σ larger than this value. in addition, the distance for two independent complementary ssb forming αdsb was deduced, but no apparent variation of it was found in the wide σ range from ～105 to ～109 s-1, which shows that the dna steric structure was not influenced by mannitol.

glow-discharge experiments were performed against water using a graphite rod as the anode and a silver thread as the cathode under an ar atmosphere. uv-spectrum, ft-ir, 1h-nmr spectrum and gc-ms analyses of the solutions irradiated with plasma were studied. it was found that a small amount of carbon was transferred from anode into water and some organic compounds were produced by reaction between carbon and water. among those, formic acid, acetic acid and propanoic acid were identified as the main products.

an arc-discharge was carried out to a mixture of ethanol and heavy water under a nitrogen atmosphere. gc-ms analysis showed that dch2ch2oh and doch2ch2oh were produced. this result implies the decomposition of water molecules, which possibly serves as an initial step for the reaction in aqueous solution. in addition, ch3cood and hoch2ch2nd2 were also identified in the products, and it was considered that the "nitrogen deposition" effect was caused by capture of d from d2o with n

discharge was performed against ammonia water using a graphite rod as the anode and a silver thread as the cathode under an ar atmosphere. hplc and thin layer chromatograph (tlc) analyses showed that three kinds of amino acids were produced in the reaction mixture. as the graphite anode is the solitary source of carbon in the system, it is considered that amino acids have been produced by synthetic reaction between graphite and ammonia water. thus, our results provide a possible way of formation of amino acids from elemental carbon on the primitive earth. in ad-dition, the mechanism for the production of amino acids is discussed and the yields of different amino acids are pre- sented.

i per nuclear traversal, sug-gesting the existence of bystander effects. this low-dose sen-sitivity was increased when gjic was enhanced by treating cells with 8-br-camp, but it was partly reduced by treating cells with dmso, an effective scavenger of reactive oxygen species (ros). moreover, no low-dose sensitivity was observed when cells were treated with 100 μm lindane, an inhibitor of gjic. the survival of irradiated cells was increased by dmso but was not influenced significantly by camp or lin- dane. on the other hand, g1-phase arrest was detected in the irradiated cells, and it was enhanced by camp. in contrast, this arrest was reduced or almost eliminated by dmso or iindane, respectively, even when cells were irradiated with such a high dose that each cell received five nuclear traversals on average. thus the bystander responses occurred after both low-dose and relatively high-dose irradiation. our results in-dicated that both gjic and ros contributed to the radiation- induced bystander effect, but gap junctional channels might play an essential role by modulating the release of radiation-induced signaling factors.

the bystander effect on unirradiated neoplastic human salivary gland (hsgc) cells was investigated by co-culturing them with hsgc cells that had been irradiated with 290 mev/u carbon beams of different linear energy transfer (let) values. it was found that the plating efficiency and proliferation of the unirradiated recipient cells were increased and that these increases were related to the let as well as the radiation dose. exposure of hsgc cells to higher let and higher dose was much more effective in enhancing the plating efficiency and proliferation of the unirradiated cells than exposure to lower let and lower dose. however, when ptio, a nitric oxide (no)-specific scavenger, was present in the coculture medium, the cell growth capacity of the unirradiated recipients was reduced to control level, indicating that no is involved in the bystander response. as an oxidization product of no, nitrite was detected in the coculture medium and its concentration depended on the let and dose of irradiation. using a no-generator sper/ no, it was verified that no at low concentrations indeed enhanced cell proliferation. accordingly, no plays an important role in medium-mediated bystander effects.

the observation of radiation-induced bystander responses, in which cells respond to their neighbors being irradiated, has important implications for understanding mechanisms of radiation action particularly after low-dose exposure. much of this questions the current dogma of direct dna damage driving response in irradiated systems. in this study, we have used a charged-particle microbeam to target individual helium ions (3he2) to individual cells within a population of radioresistant glioma cells cultured alone or in coculture with primary human fibroblasts. we found that even when a single cell within the glioma population was precisely traversed through its cytoplasm with one 3he2 ion, bystander responses were induced in the neighboring nonirradiated glioma or fibroblasts so that the yield of micronuclei was increased by 36% for the glioma population and 78% for the bystander fibroblast population. importantly, the yield of bystander-induced micronuclei was independent of whether the cytoplasm or nucleus of a cell was targeted. the bystander responses were fully eliminated when the populations were treated with 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide or filipin, which scavenge nitric oxide (no) and disrupt membrane rafts, respectively. by using the probe 4-amino-5-methylamino-2,7-difluorofluorescein, it was found that the no level in the glioma population was increased by 15% after 1 or 10 cytoplasmic traversals, and this no production was inhibited by filipin. this finding shows that direct dna damage is not required for switching on of important cell-signaling mechanisms after lowdose irradiation and that, under these conditions, the whole cell should be considered a sensor of radiation exposure.

nitric oxide (no) is an important messenger molecule with multiple biological activities. in the present study, sper/no, a no generator, showed a biphasic effect on the proliferation of human salivary gland neoplastic (hsg) cells. sper/no of less than 20 lm stimulated cells to depart from the g2/m phase and so enhanced cell division and cell proliferation. but sper/no at higher concentrations restrained cell proliferation and blocked cell-cycle progression. cells were mainly arrested in the g2/m phase and s phase when they were treated with 100-200 and 300-500 lm sper/no, respectively. aspecial s-phase peak was detected in a histogram of the cell-phase distribution of sper/no-treated hsg. when the concentration of sper/no increased, the s-phase peak shifted from early the g2/m-phase to later the g1–s-phase boundary. sper/no-induced cell-cycle arrests were reversible when the cells were released from no stress for 48 h and hence cell proliferation was recovered. in addition, micronucleus, but no apoptosis, was produced in the sper/no-treated cells, and its yield tended to a saturation value with increasing concentrations of sper/no. the sper/no-induced effects were effectively eliminated or reduced by treating cells with ptio, a no-specific scavenger, indicating that no is the main source of these effects.

evidence has been accumulated for attached cells demonstrating that nonirradiated cells can have a response to the ionization events delivered to their neighbors. in the present study, we first investigated the bystander responses between suspension and neoplastic cells by coculturing l5178y (ly) cells with human salivary gland (hsg) cells that had been irradiated with either 290 mev/u carbon ions or x-rays. after this coculture, the survival of nonirradiated recipient ly cells showed dichotomous responses to the irradiation dose delivered to hsg cells. apoptosis and necrosis were also produced in a 48 h subculture of the recipient ly cells, and their yield increased, but then had a tendency to decrease when the irradiation dose increased. treatment of cells with ptio, a nitric oxide specific scavenger, diminished apoptosis and necrosis of the recipient ly cells to the control level. as an oxidization product of no, nitrite was detected in the coculture medium and its time course corresponded well to the decrease of the viability of irradiated hsg cells. moreover, the relationship of the survival and the apoptotic and necrotic production of the recipient ly cells to the nitrite concentration followed a linear-quadratic model. the present findings of no being involved in the radiation-induced bystander effect may have significance in terms of radiotherapy.

the mechanisms of medium-mediated bystander effects on cell survival and micronucleus (mn) induction were investigated by co-cultivating unirradiated hsg cells with cells irradiated by x-rays or 290 mev/u carbon beams. it was found that the survival of the irradiated cells exponentially decreased along with the dose, and that the plating efficiency (pe) of the unirradiated recipient cells was obviously more enhanced than that of the control cells. moreover, mn was induced in the unirradiated recipient cells and its yield had a maximum distribution corresponding to the donor dose, which was different from the linear-quadratic dose response of the yield of mn in the irradiated cells. the treatment of ptio, a scavenger of nitric oxide (no), decreased both pe and mn of the unirradiated recipient cells to control levels. moreover, nitrite was detected in the co-culture medium, and its concentration was related to the donor dose. these results indicated that no was involved in the above mentioned medium-mediated bystander effects. in addition, an equation was deduced to well fit the induction of mn of the unirradiated recipient cells.