Spontaneous Aggregation and Cytotoxicity of the β-Amyloid Aβ1–40: A Kinetic Model

The time dependency of the spontaneous aggregation of the fibrillogenic β-Amyloid peptide, Aβ^1–40, was measured by turbidity, circular dichroism, HPLC, and fluorescence polarization. The results by all methods were comparable and they were most consistent with a kinetic model where the peptide first slowly forms an activated monomeric derivative (AM), which is the only species able to initiate, by tetramerization, the formation of linear aggregates. The anti-Aβ antibody 6E10, raised against residues 1–17, at concentrations of 200–300 nM delayed significantly the aggregation of 50 μM amyloid peptide. The anti–Aβ antibody 4G8, raised against residues 17–24, was much less active in that respect, while the antibody A162, raised against the C-terminal residues 39–43 of the full-length Aβ was totally inactive at those concentrations. Concomitant with the aggregation experiments, we also measured the time dependency of the Aβ^1–40–induced toxicity toward SH-EP1 cells and hippocampal neurons, evaluated by SYTOX Green fluorescence, lactate dehydrogenase release, and activation of caspases. The extent of cell damage measured by all methods reached a maximum at the same time and this maximum coincided with that of the concentration of AM. According to the kinetic scheme, the latter is the only transient peptide species whose concentration passes through a maximum. Thus, it appears that the toxic species of Aβ^1–40 is most likely the same transient activated monomer that is responsible for the nucleation of fibril formation. These conclusions should provide a structural basis for understanding the toxicity of Aβ^1–40 in vitro and possibly in vivo.     

A rabbit reticulocyte factor which stimulates protein synthesis in several mammalian cell-free systems

Rabbit reticulocyte lysate post-ribosomal supernatant is shown to stimulate protein synthesis in a variety of mammalian cell-free systems, particularly the less efficient systems, such as those from mouse liver, HeLa cells and heat-shocked L cells. This stimulation reflects an increase in the rate of initiation, and is not due to the presence of globin mRNA. The stimulatory activity is unstable to purification, but some conditions favouring stability have been identified and partial purification has been achieved. It is free of eIF-2, but possesses eIF-2B activity. Its purification properties suggest that it is distinct from previously characterized initiation factors, including eIF-2/eIF-2B complex, and its possible relationship to known initiation factors is discussed.     

猫脑干上涎核节前神经元电活动的观察

在麻醉的32只猫记录了电刺激颌下腺神经支引起的上涎核平均场电位和单位放电。逆行电刺激颌下腺神经支引起的上涎核平均场电位分布在同侧脑干背面闩部头端5.5—8mm处,与过去的组织学结果大致符合。用微电极在上涎核记录了68个对刺激颌下腺神经支有反应的单位,其中33个单位作了碰撞试验。有9个单位符合逆向反应标准,它们是真正的颌下腺节前神经元,逆行反应的潜伏期为14.4±2.5ms,其轴突传导速度为2.9±0.1m/s。其他不符合逆向反应标准的单位,对刺激颌下腺神经支仍能发生反应,估计多为中间神经元。在一部分单位观察了电刺激舌神经或味觉刺激舌引起的反应。根据这些观察对上涎核内存在复杂神经元回路的可能性作了讨论。     

Recovery of the Ability to Synthesize DNA in Segments of Normal Size at Long Times After Ultraviolet Irradiation of Human Cells

DNA synthesized in human cells within the first hour after ultraviolet (UV) irradiation is made in segments of lower molecular weight than in nonirradiated cells. The size of these segments approximates the average distance between pyrimidine dimers in the parental DNA. This suggests that the dimers interrupt normal DNA synthesis and result in gaps in the newly synthesized DNA. However, DNA synthesized in human cells at long times after irradiation is made in segments equal or nearly equal to those synthesized by nonirradiated cells. The recovery of the ability to synthesize DNA in segments of normal size occurs in normal human cells, where the dimers are excised, and also in cells of the human mutants xeroderma pigmentosum (XP), where the dimers remain in the DNA. This observation implies that the pyrimidine dimer may not be the lesion that causes DNA to be synthesized in smaller than normal segments.     

Aerosolization of recombinant SLPI to augment antineutrophil elastase protection of pulmonary epithelium

In a variety of lung diseases the respiratory epithelial surface must contend with an increased burden of neutrophil elastase (NE). One candidate for augmenting epithelial anti-NE protection is the secretory leukoprotease inhibitor (SLPI). In vitro evaluation demonstrated that 96 +/- 1% of the recombinant SLPI (rSLPI) molecules were capable of inhibiting NE, with an association rate constant of 7.1 +/- 0.1 X 10(6) M-1.s-1. Evaluation of rSLPI after in vitro and in vivo aerosolization showed that aerosolization did not alter rSLPI. Aerosolization of a single dose of 50 mg rSLPI to sheep resulted in a fourfold increase of the anti-NE capacity in epithelial lining fluid (ELF) at 3 h, with a half-life in ELF of 12 h. After aerosolization some rSLPI appeared in lung lymph. Simultaneous aerosolization of rSLPI and recombinant alpha 1-antitrypsin (rAAT) demonstrated a molar ratio of the concentration in lymph to the concentration in ELF 3 h after the aerosol eightfold higher for rAAT than for rSLPI. Overall, these observations demonstrate that it is feasible to use aerosolized rSLPI to directly augment the anti-NE capacity of the lung, particularly on the pulmonary epithelial surface.     

Study of the Biological Activity and Phenolic Content of the Ethanol Extract of Phyllogonium viride Brid. (Phyllogoniaceae,Bryophyta)

The present study aimed to examine the phenolic content and evaluate the antimicrobial and antioxidant potential of ethanol extracts from the moss species Phyllogonium viride Brid. on the pathogenic bacteria Salmonella enterica serovar enteritidis, Staphylococcus aureus, Listeria monocytogenes and Escherichia coli, and the pathogenic fungi Candida albicans and Cryptococcus neoformans. The antimicrobial activity was determined from Minimum Inhibitory Concentration (MIC) Minimum Bactericidal Concentration (MBC) and Minimum Fungicidal Concentration (MFC). Antioxidant activity was determined by the DPPH method. Folin-Denis reagent was used for the content of total phenolics and flavonoids and HPLC-DAD for identification of phenolic compounds. The results showed that bacteriostatic and bactericidal activities occurred at concentrations ranging from 9.76 μg/mL–78.13 μg/mL among all evaluated microorganisms. These values, considering the criteria used, suggest the P. viride extract as a potent antimicrobial. For antioxidant activity, P. viride extract was considered weak. Analysis of the phenolic content showed a wide range of compounds, with Kaempferol (0.41 mg/g) being the major compound, followed by t-cinnamic acid and caffeic acid (0.17 mg/g). Although P. viride is a species of moss not yet referenced in scientific publications of biotechnological interest, it has shown promising potential for further studies and possible application as an antimicrobial of natural origin.     

Conversion of cephalosporin-c into 7-phenoxy-acetamido-cephalosporanic acid by acyltransferase of mutants of Penicillium chrysogenum

Summary We have tested the acyl-transferase of penicillin producing strains and penicillin-less mutants of Penicillium chrysogenum for their ability to exchange the d--aminoadipic acid side chain of cephalosporin-C with phenoxyacetic acid. We found the reaction in both types of strains.     

Measurement of chronic toxicity using the opossum shrimpMysidopsis bahia

The chronic toxicity of silver and endosulfan to the opossum shrimpMysidopsis bahia was determined using continuous-flow bioassays. The 28-day bioassays measured survival, fecundity, and growth (length and weight measurements). Maximum acceptable toxicant concentrations (MATC) were estimated from measured toxicant concentrations. MATC values were similar using either brood size or growth as a criterion for sublethal effects. As an alternative to the determination of fecundity impairment, measurement of growth reduction in response to exposure to toxicants may provide a useful tool in the assessment of chronic toxicity inMysidopsis life-cycle bioassays.