The Nonfibrillar Amyloid β-Peptide Induces Apoptotic Neuronal Cell Death

The toxicity of the nonaggregated amyloid beta-peptide (1-40) [A beta(1-40)] on the viability of rat cortical neurons in primary culture was investigated. We demonstrated that low concentrations of A beta peptide, in a nonfibrillar form, induced a time- and dose-dependent apoptotic cell death, including DNA condensation and fragmentation. We compared the neurotoxicity of the A beta(1-40) peptide with those of several A beta-peptide domains, comprising the membrane-destabilizing C-terminal domain of A beta peptide (e.g., amino acids 29-40 and 29-42). These peptides reproduced the effects of the (1-40) peptide, whereas mutant nonfusogenic A beta peptides and the central region of the A beta peptide (e.g., amino acids 13-28) had no effect on cell viability. We further demonstrated that the neurotoxicity of the nonaggregated A beta peptide paralleled a rapid and stable interaction between the A beta peptide and the plasma membrane of neurons, preceding apoptosis and DNA fragmentation. By contrast, the peptide in a fibrillar form induced a rapid and dramatic neuronal death mainly through a necrotic pathway, under our conditions. Taken together, our results suggest that A beta induces neuronal cell death by either apoptosis and necrosis and that an interaction between the nonfibrillar C-terminal domain of the A beta peptide and the plasma membrane of cortical neurons might represent an early event in a cascade leading to neurodegeneration.     

Isolation and characterization of cultivable fermentative bacteria from the intestine of two edible snails, Helixpomatia and Cornu aspersum (Gastropoda: Pulmonata)

The intestinal microbiota of the edible snails Cornu aspersum fSyn: H. aspersa), and Helix pomatia were investigated by culture-based methods, 16S rRNA sequence analyses and phenotypic characterisations. The study was carried out on aestivating snails and two populations of H. pomatia were considered. The cultivable bacteria dominated in the distal part of the intestine, with up to 5.10(9) CFU g -1, but the Swedish H. pomatia appeared significantly less colonised, suggesting a higher sensitivity of its microbiota to climatic change. All the strains, but one, shared >/= 97% sequence identity with reference strains. They were arranged into two taxa: the Gamma Proteobacteria with Buttiauxella, Citrobacter, Enterobacter, Kluyvera, Obesumbacterium, Raoultella and the Firmicutes with Enterococcus, Lactococcus, and Clostridium. According to the literature, these genera are mostly assigned to enteric environments or to phyllosphere, data in favour of culturing snails in contact with soil and plants. None of the strains were able to digest filter paper, Avicel cellulose or carboxymethyl cellulose (CMC). Acetogens and methanogenic archaea were not cultivated, so the fate of hydrogen remains questionable. This microbiota could play important roles in the digestive process (fermentation) and the energy supply of the snail (L-lactate, acetate). The choice of cereals and plants by snail farmers should take into account the fermentative abilities of the intestinal microbiota.     

β-Amyloid Peptide Interacts Specifically with the Carboxyl-Terminal Domain of Human Apolipoprotein E

Abstract : Growing evidence indicates the involvement of apolipoprotein E (apoE) in the development of late-onset and sporadic forms of Alzheimer's disease, although its exact role remains unclear. We previously demonstrated that β-amyloid peptide (Aβ) displays membrane-destabilizing properties and that only apoE2 and E3 isoforms inhibit these properties. In this study, we clearly demonstrate that the carboxy-terminal lipid-binding domain of apoE (e.g., residues 200-299) is responsible for the Aβ-binding activity of apoE and that this interaction involves pairs of apoE amphipathic α-helices. We further demonstrate that Aβ is able to inhibit the association of the C-terminal domain of apoE with lipids due to the formation of Aβ/apoE complexes resistant to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. On the contrary, the amino-terminal receptor-binding domain of apoE (e.g., residues 129-169) is not able to form stable complexes with Aβ. These data extend our understanding of human apoE-dependent binding of Aβ by involving the C-terminal domain of apoE in the efficient formation of apoE/Aβ complex.     

Conversion of active transport vesicles of Escherichia coli into oxidative phosphorylation vesicles

Passage of membrane vesicles of Escherichia coli which catalyze active transport but not oxidative phosphorylation through a French pressure cell yields vesicles which catalyze oxidative phosphorylation but not active transport. The properties of these two species of membrane vesicles are described.     

In vitro and in vivo effects of selenium and selenium with vitamin E on platelet functions in diabetic rats relationship to platelet sorbitol and fatty acid distribution

In vitro 30 min of incubation with selenomethionine (Sm)+vitamin E multiplied by about five platelet selenium (Se) decreased significantly platelet thrombin and ADP-induced aggregation decrease. Four groups of streptozotocin-induced diabetic rats were fed with a supplemented purified diet with an Se-rich yeast (Selenion): DSel, Sm: DSm, Sm α-tocopherol: DSmE or unsupplemented diet: D. After 24 wk of supplementation, only a decrease in thrombin-induced aggregation in group DSel compared to DSm and DSmE and D was observed. However, after 24 wk of diet compared to 14 wk, in group D and DSm, a significant increase in thrombin-induced aggregation occurred (p<0.0001), whereas a significant decrease in groups DSel and DSmE (p<0.0001,p<0.03) was noted. After 21 wk of diet, in DSmE, platelet adhesion to fibronectin was significantly decreased compared to group D (p<0.05). These changes in DSmE were associated with a significant decrease in platelet sorbitol (p<0.02) and a very significant increase in platelet Se (p<0.0005). Sm associated with vitamin E would appear more efficient to prevent oxidative damage of diabetic platelet membrane and thus to modulate its hyperactivity.     

Selection of cells with different chromosomal localizations of the amplified c-myc gene during in vivo and in vitro growth of the breast carcinoma cell line SW 613-S

The c-myc gene is amplified in the human breast carcinoma cell line SW 613-S. At early in vitro passages, the extra copies of the gene were mainly localized in double minute chromosomes (DMs), as shown by in situ hybridization with a biotinylated c-myc probe. However, cells without DMs were also present in which the c-myc genes were found integrated into any of several distinct chromosomes (mainly 7q+, 4 and 4q+, and 1). When this cell line was propagated in vitro, the level of c-myc amplification decreased because cells with DMs and a high amplification level were lost and replaced by cells without DMs and having a low amplification level. On the contrary, when early passage SW 613-S cells were grown in vivo, as subcutaneous tumours in nude mice, cells with numerous DMs and a high level of c-myc amplification were selected for. In one cell line (SW 613-Tu1) established from such a tumour, the DM-containing cells were substituted at late passages for cells with a high number of c-myc copies integrated within an abnormally banded region, at band 17q24 of a 17q+ chromosome. When only cells with integrated genes were present, this cell line was still highly tumorigenic indicating that the localization of the c-myc genes in DMs was not required for these cells to be tumorigenic in nude mice. Furthermore, cells of the secondary tumours induced by SW 613-Tu1 did not contain any DMs showing that in vivo growth did not promote the release of integrated c-myc copies into DMs.     

Dual localization of the human gene encoding hnRNP I/PTB protein to chromosomes 19p13.3 and 14q23

A cDNA probe representative of the human hnRNP I/PTB gene was used to perform fluorescence in situ hybridization (FISH) on metaphases of human chromosomes. A new localization was found on band 19p13.3 in addition to the previously reported localization to band 14q23. Identical results were obtained when FISH analysis was repeated with probes covering different parts of the hnRNP I cDNA clone. This supported the notion that most, if not all, of the sequences of the different parts of this clone are present on both chromosomes. Moreover, Southern blot analysis of DNAs from interspecies somatic hybrids containing chromosomes 19 and 14 revealed that the whole hnRNP I cDNA probe generated very similar patterns in each hybrid DNA. These data suggest that two closely related copies of the hnRNP I gene exist in the human genome. Received: 19 January 1996 / Revised: 9 March 1996     

Climatic significance of isotope ratios

The hydrogen and oxygen isotope ratios of water, which can be measured by Isotope Ratio Mass Spectrometry (IRMS), exhibit climatic dependencies and are commonly exploited in hydrogeology. More generally, the overall carbon or hydrogen isotope ratios of plant organic matter, and in particular of tree-ring cellulose, have been frequently used for climatic reconstruction. However, since many physicochemical and biochemical fractionation phenomena are likely to contribute to the isotopic values, the interpretation of the climatic significance of isotopic parameters is not always straightforward. In the case of hydrogen and oxygen for instance, the climatic profile of the source meteoric water is not simply transferred to leaf water and many steps of the biosyntheses are accompanied by kinetic and thermodynamic isotope effects that depend on the individual mechanistic pathways. The information brought about by overall isotope ratios determined by IRMS is averaged over all fractionation effects undergone at the different molecular positions. In contrast, the NMR investigation of Site-specific Natural Isotope Fractionation (SNIF-NMR) gives simultaneous access to isotope ratios specific to individual positions in the molecule. Since the different atoms do not necessarily exhibit the same climatic dependency, the method provides complementary responses to the environmental conditions. In particular, the isotopic parameters of ethanol and water obtained by fermenting sugars in standardized conditions reflect climatic influences which took place at different periods of plant growth. As a consequence, statistical analyses based on multi-site isotopic variables provide powerful criteria for distinguishing geographical regions of cultivation characterized by different climatic features. Although the sensitivity to climatic variations is the most pronounced for plant water and for sugars formed at the first step of photosynthesis, other components such as lipids or minor metabolites also exhibit climatic dependencies. The combination of isotopic values pertaining to different atomic species and either averaged over the whole molecule (IRMS) or associated with different molecular sites (SNIF-NMR), provides complementary criteria, which can be exploited in terms of both climatic significance and mechanistic pathways of the individual atoms.     

Effects of organic and inorganic Ca antagonists on rat platelet arachidonic acid metabolism in the presence of Ca2+, Sr2+ and Ba2+

The effects of Ca-antagonists on the thrombin-induced mobilization of radiolabeled arachidonate preincorporated into rat platelets as well as the subsequent formation of labeled cyclooxygenase and lipoxygenase products were analyzed in the presence of either Call or Ca²⁺-substitutes, Sr²⁺ and Ba²⁺. Results indicate that following thrombin stimulation (0.2 U/ml) in the presence of Ca²⁺, nitrendipine (Nit), Cd²⁺ or Mn²⁺ reduced the release of arachidonate and the biosynthesis of thromboxane 132- Inhibition of arachidonic acid release and metabolism were also obtained by both Nit and Cd2+ in the presence of Sr2+ and Bat+. Results from studies with a semi-purified phospholipase A₂ fraction prepared from rat platelets indicated that the activity was almost unaffected by Nit or Cd²⁺. From these findings, we concluded that inhibition of platelet-induced release and metabolism of arachidonic acid by the Ca-antagonists tested require intact platelets. These data support the hypothesis of an interaction of these agents at an unknown surface membrane level.Abbreviations AA Arachidonic Acid - 5-HT 5-hydroxy-tryptamine - HETE 12-hydroxyeicosatetraenoic acid - HHT 12-hydroxy-heptadecanoic acid - HHT Nitrendipine - TXB₂ Thromboxane B₂     

Acetate Utilization and Macromolecular Synthesis During Sporulation of Yeast

Acetate utilization and macromolecule synthesis during sporulation (meiosis) of Saccharomyces cerevisiae were studied. When diploid cells are transferred from glucose nutrient medium to acetate sporulation medium at early stationary phase, respiration of the exogenously supplied acetate proceeds without any apparent lag. At the completion of ascospore development, 62% of the acetate carbon consumed has been respired, 22% remains in the soluble pool, and 16% is incorporated into lipids, protein, nucleic acids, and other cell components. Measurements of the rate of protein synthesis during sporulation reveal two periods of maximal synthetic activity: an early phase coincidental with increases in deoxyribonucleic acid, ribonucleic acid, and protein cellular content and a later phase during ascospore formation. Experiments in which protein synthesis was inhibited at intervals during sporulation indicate that protein synthesis is required both for the initiation and completion of ascus development.