The toxicity of azidothymidine (AZT) on human and animal cells in culture at concentrations used for antiviral therapy

AZT, a chain terminator of DNA synthesis originally developed for chemotherapy, is now prescribed as an antihuman immunodeficiency virus (HIV) drug at 500 to 1500 mg/person/day, which corresponds to 20 to 60 M AZT. The human dosage is based on a study by the manufacturer of the drug and their collaborators, which reported in 1986 that the inhibitory dose for HIV replication was 0.05 to 0.5 M AZT and that for human T-cells was 2000 to 20,000 times higher, i.e. 1000 M AZT. This suggested that HIV could be safely inhibited in humans at 20 to 60 M AZT. However, after the licensing of AZT as an anti-HIV drug, several independent studies reported 20-to 1000-fold lower inhibitory doses of AZT for human and animal cells than did the manufacturer's study, ranging from 1 to 50 M. In accord with this, life threatening toxic effects were reported in humans treated with AZT at 20 to 60 M. therefore, we have re-examined the growth inhibitory doses of AZT for the human CEM T-cell line and several other human and animal cells. It was found that at 10 M and 25 M AZT, all cells are inhibited at least 50% after 6 to 12 days, and between 20 and 100% after 38 to 48 days. Unexpectedly, variants of all cell types emerged over time that were partially resistant to AZT. It is concluded that AZT, at the dosage prescribed as an anti-HIV drug, is highly toxic to human cells.     

A method for assessing alternative effects functions that uses simulation with EMDEX data

A method for evaluating a variety of alternative biologically plausible effects functions through the use of simulation studies conducted on personal-monitor exposure data is described. Using magnetic field time series collected with EMDEX instruments, we demonstrate how the method can be used to explore (1) how the outputs from various effects functions simulations compare to the results obtained by assuming that effects are proportional to time average field strength; (2) how the results of epidemiological studies might be used to assess the relative likelihood that each of the alternative effects functions describes biological reality; and (3) how the results might be used to assess possible health risks. Although the available data are sufficient to demonstrate the general method, they are not yet sufficient to support actual discrimination among possible alternatives. The arguments on the use of the method are for illustrative purposes only. © 1995 Wiley-Liss, Inc.     

Repair mechanisms involved in prophage reactivation and UV reactivation of UV-irradiated phage lambda

Survival of UV-irradiated phage λ is increased when the host is lysogenic for a homologous heteroimmune prophage such as λimm434 (prophage reactivation). Survival can also be increased by UV-irradiating slightly the non-lysogenic host (UV reactivation).Experiments on prophage reactivation were aimed at evaluating, in this recombination process, the respective roles of phage and bacterial genes as well as that of the extent of homology between phage and prophage.To test whether UV reactivation was dependent upon recombination between the UV-damaged phage and cellular DNAs, lysogenic host cells were employed. Such hosts had thus as much DNA homologous to the infecting phage as can be attained. Therefore, if recombination between phage and host DNAs was involved in this repair process, it could clearly be evidenced.By using unexposed or UV-exposed host cells of the same type, prophage reactivation and UV reactivation could be compared in the same genetic background.The following results were obtained: (1) Prophage reactivation is strongly decreased in a host carrying recA mutations but quite unaffected by mutation lex-I known to prevent UV reactivation; (2) In the absence of the recA⁺ function, the red⁺ but not the int⁺ function can substitute for recA⁺ to produce prophage reactivation, although less efficiently; (3) Prophage reactivation is dependent upon the number of prophages in the cell and upon their degree of homology to the infecting phage. The presence in a recA host of two prophages either in cis (on the chromosome) or in trans (on the chromosome and on an episome) increases the efficiency of prophage reactivation; (4) Upon prophage reactivation there is a high rate of recombination between phage and prophage but no phage mutagenesis; (5) The rate of recombination between phage and prophage decreases if the host has been UV-irradiated whereas the overall efficiency of repair is increased. Under these conditions UV reactivation of the phage occurs as in a non-lysogen, as attested by the high rate of mutagenesis of the restored phage.These results demonstrate that UV reactivation is certainty not dependent upon recombination between two pre-existing DNA duplexes. The hypothesis is offered that UV reactivation involves a repair mechanism different from excision and recombination repair processes.     

Lymphocyte-mediated cytotoxicity to cells infected with measles virus: I. Use of in vitro infected leukocytes as autologous target cells; absence of virus-specific cytotoxic lymphocytes

We investigated lymphocyte-mediated cytotoxicity in humans to autologous cells infected with measles virus. Mononuclear leukocytes, isolated from peripheral blood, were stimulated by phytohemagglutinin (PHA) and infected with measles virus. At 72 hr after infection, about 80% of the cells could be lysed by antibodies against measles virus and human complement, which meant that at that time the expression of virus-specific antigens on the cell surface was maximal. Such PHA-stimulated, infected leukocytes were used as target cells in an assay for lymphocyte-mediated cytotoxicity. Effector lymphocytes were obtained from the same donor who had provided the target cells, and were tested for their cytotoxicity directly after isolation.Lymphocytes obtained from adult humans, with a history of natural measles infection contracted during childhood, were not found to be cytotoxic to autologous infected cells, unless antibodies against measles virus were present during the assay. The same response, though to a lesser extent, was observed with cord blood lymphocytes obtained from healthy neonates. This indicates that the observed cytotoxicity does not reflect acquired cellular immunity but rather antibody-dependent cellular cytotoxicity (ADCC).     

罗布麻茶辐照灭菌工艺中的剂量控制

本文给出罗布麻茶灭菌剂量的Ｄ１０值,讨论了产品箱内吸收剂量分布及剂量场空间纵向分布分布,结果表明,罗布麻茶最佳灭菌剂量范围为６－９ＫＧｙ。静态辐照灭菌宜选用水平方向沿等剂量线多层码放,纵向采用不等时多源位辐照处理工艺。可有效地提高产品的剂量均匀性及射线利用率。     

Mechanisms of Reduction of the Stelar Pattern along Barley Roots

The stelar pattern along the seminal and nodal roots of barley (Hordeum vulgare L.) is gradually simplified due to a decreasing frequency of longitudinal cell division in the apical meristem. The decrease involves the proportion of stelar parenchyma, the number of vascular strands on the periphery of the stele and, in nodal roots with a more complex structure, the number of central metaxylem files. In spite of the fact that the stelar parenchyma is reduced in distal parts of the roots to approximately one half, the discontinuity of central and peripheral metaxylem is preserved. Reduction of the number of central metaxylem files is due to fusion. In the reduction of peripheral xylem and phloem strands, the development of certain xylem strands is discontinued and they are terminated blindly. Two phloem strands that had alternated radially with them, approach each other, coalesce and a single phloem strand continues to develop. In this way the regular alternation of phloem and xylem is re-established. The importance of fusions ensuring reduction of the functional continuity in vascular tissue by formation of a network structure must be stressed. This reduction mechanism is involved not only in files of the wide central metaxylem but also in phloem strands which are thus preferred over blindly terminating peripheral xylem strands.     

高温和啶虫脒处理西花蓟马对其F1 代生命表参数的联合作用

【目的】西花蓟马 Frankliniella occidentalis (Pergande) (缨翅目: 蓟马科）是一种危险的入侵害虫,其生长发育受温度影响显著。我们的前期研究表明,高温热激对西花蓟马的杀灭效果并不理想,但高温热激可以改变西花蓟马的药剂敏感性。为了探究高温热激后再进行杀虫剂减量处理能否提高高温对西花蓟马的防治效果,本实验测定了45℃高温热激 2 h后恢复不同时间（8 h 和24 h）啶虫脒对西花蓟马F₁代生命表参数的影响,从控制种群发展的角度探究高温和啶虫脒防治西花蓟马最佳结合方式。【方法】应用特定年龄 龄期及两性生命表的方法,研究45℃高温热激和啶虫脒处理西花蓟马后其F₁代种群的生命表参数。【结果】45℃热激2 h后恢复不同时间用啶虫脒处理西花蓟马亲代,其F₁代卵、1龄幼虫和蛹的平均发育历期均显著长于对照（仅45℃热激2 h）的西花蓟马F₁代（P<0.01）;而且其F₁代雌成虫的寿命和产卵量均显著少于对照（P<0.01）。热激恢复8 h后啶虫脒处理西花蓟马亲代,其F₁代发育历期和雌成虫的寿命虽然与热激恢复24 h的F₁代不存在显著性差异,但是其F₁代的平均产卵前期（adult pre-oviposition period, APOP）和平均总产卵前期（total pre-oviposition period, TPOP）显著长于恢复24 h的F₁代（P<0.01）,单雌平均产卵量显著小于恢复24 h的F₁代（P<0.01）。【结论】相比单一高温防治,高温和杀虫剂综合使用对西花蓟马有更好的防控效果。相比热激后恢复24 h,热激后恢复8 h再进行杀虫剂处理对西花蓟马有更好的防控效果。     

Sorptive removal of Methylene blue from aqueous solution using palm kernel fibre: Effect of fibre dose

The use of palm kernel fibre, a readily available agricultural waste product for the sorption of Methylene blue from aqueous solution and the possible mechanism of sorption has been investigated at various fibre doses. The extent of dye removal and the rate of sorption were analyzed using two kinetic rate models (pseudo-first and pseudo-second-order kinetic models) and two diffusion models (intraparticle and external mass transfer models).

Analysis of the kinetic data at different sorbent dose revealed that the pseudo-first order kinetics fitted to the kinetic data only in the first 5 min of sorption and then deviated from the experimental data. The pseudo-second-order kinetic model was found to better fit the experimental data with high correlation coefficients at the various fibre dose used. The dye sorption was confirmed to follow the pseudo-second-order model by investigating the relationship between the amount of dye sorbed and the change in hydrogen ion concentration of the dye solution and also the dependence of dye uptake with solution temperature. It was found that the change in hydrogen ion concentration and increase in sorption temperature were directly related to the amount of dye sorbed, and activation energy was calculated to be −39.57 kJ/mol, indicating that the dye uptake is chemisorption, involving valence forces through sharing or exchange of electrons between sorbent and sorbate as covalent forces.

The intraparticle diffusion plots showed three sections indicating that intraparticle diffusion is not solely rate controlling. The intraparticle diffusion and mass transfer rate constants where observed to be well correlated with sorbent dose in the first 5 min of sorption, indicating sorption process is complex. It was found that at low sorbent dose the mass transfer is the main rate controlling parameter. However at high sorbent dose, intraparticle diffusion becomes rate controlling.     

Nitric oxide (NO) increase at fertilization in sea urchin eggs upregulates fertilization envelope hardening

Previous studies indicate that the nitric oxide (NO) increase at fertilization in sea urchin eggs is Ca²⁺-dependent and attributed to the late Ca²⁺ rise. However, its role in fertilization still remains unclear. Simultaneous measurements of the activation current, by a single electrode voltage clamp, and NO, using the NO indicator DAF-FM, showed that the NO increase occurred at the time of peak current (t_p) which corresponds to peak [Ca²⁺]_i, suggesting that NO is not related to any other ionic changes besides [Ca²⁺]_i. We measured O₂ consumption by a polarographic method to examine whether NO regulated a respiratory burst for protection as reported in other biological systems. Our results suggested NO increased O₂ consumption. The fluorescence of reduced pyridine nucleotides, NAD(P)H was measured in controls and when the NO increase was eliminated by PTIO, a NO scavenger. Surprisingly, PTIO decreased the rate of the fluorescence change and the late phase of increase in NAD(P)H was eliminated. PTIO also suppressed the production of H₂O₂ and caused weak and high fertilization envelope (FE). Our results suggest that NO increase upregulates NAD(P)H and H₂O₂ production and consolidates FE hardening by H₂O₂.     

Trypanocidal and leishmanicidal activities of different antimicrobial peptides (AMPs) isolated from aquatic animals

Most of the available animal antimicrobial peptides (AMPs) have been tested against bacteria and fungi, but very few against protozoan parasites. In the present study, we investigated the antiparasitic activity of different AMPs isolated from aquatic animals: tachyplesin (Tach, from Tachypleus tridentatus), magainin (Mag, from Xenopus laevis), clavanin (Clav, from Styela clava), penaeidin (Pen, from Litopenaeus vannamei), mytilin (Myt, from Mytilus edulis) and anti-lipopolysaccharide factor (ALF, from Penaeus monodon). The antiparasitic activity was evaluated against the promastigote form of Leishmania braziliensis and epi and trypomastigote forms of Trypanosoma cruzi, through the MTT method. Tach was the most potent peptide, killing completely L. braziliensis and trypomastigote T. cruzi from 12.5microM, whereas Pen and Clav were weakly active against trypomastigotes and Myt against L. braziliensis, only at a high concentration (100microM). Tach and Mag were markedly hemolytic at high concentrations, whereas the other peptides caused only a slight hemolysis (<10% up to 50microM). Our results point to Tach as the only potential candidate for further investigation and potential application as a therapeutic agent.