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Abstract: MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes) is commonly associated with the A3243G mitochondrial DNA (mtDNA) mutation encoding the transfer RNA of leucine (UUR) (tRNA Leu(UUR)). The pathogenetic mechanisms of this mutation are not completely understood. Neuronal functions are particularly vulnerable to alterations in oxidative phosphorylation, which may affect the function of the neurotransmitter glutamate, leading to excitotoxicity. In order to investigate the possible effects of A3243G upon glutamate homeostasis, we assessed glutamate uptake in osteosarcoma-derived cytoplasmic hybrids (cybrids) expressing high levels of this mutation. High-affinity Na+-dependent glutamate uptake was assessed as radioactive [3H]-glutamate influx mediated by specific excitatory amino acid transporters (EAATs). The maximal rate (V max) of Na+-dependent glutamate uptake was significantly reduced in all the mutant clones. Although the defect did not relate to either the mutant load or magnitude of oxidative phosphorylation defect, we found an inverse relationship between A3243G mutation load and mitochondrial ATP synthesis, without any evidence of increased cellular or mitochondrial free radical production in these A3243G clones. These data suggest that a defect of glutamate transport in MELAS neurons may be due to decreased energy production and might be involved in mediating the pathogenic effects of the A3243G mtDNA mutation. [Copyright &y& Elsevier]

The Hopf bifurcation behaviour of a symmetric rotor/seal system was investigated using Muszynska''s non-linear seal fluid dynamic force model. For a perfectly balanced system, the instability from certain critical equilibrium positions is proved to be the result of Hopf bifurcation and only the supercritical type is found for a specific rotor system using Poore''s algebraic criteria. Hence, a stable periodic orbit bifurcates from the critical equilibrium position after the threshold speed is exceeded. Due to the dimensionless whirl frequency being found to be close to 1/2 over quite a large range of system parameters, the periodically perturbed Hopf bifurcation in 1/2 over quite a large range of system parameters, the periodically perturbed Hopf bifurcation in 1/2 subharmonic resonance is dealt with for an imbalanced rotor system. The bifurcation of the averaged system, obtained using the centre manifold procedure and averaging method, is analyzed. The results show that non-synchronized whirl of the imbalanced rotor can either be a quasi-periodic motion resulting from a Hopf bifurcation, or a half-frequency whirl from period doubling bifurcation, determined by the structure parameters of the system and operation conditions. Numerical simulation verifies the analytical results. [Copyright &y& Elsevier]

Globally, regulatory authorities grapple with the challenge of assessing the hazards and risks to human and ecosystem health that may result from exposure to chemicals that disrupt the normal functioning of endocrine systems. Rapidly increasing number of chemicals in commerce, coupled with the reliance on traditional, costly animal experiments for hazard characterization - often with limited sensitivity to many important mechanisms of endocrine disruption -, presents ongoing challenges for chemical regulation. The consequence is a limited number of chemicals for which there is sufficient data to assess if there is endocrine toxicity and hence few chemicals with thorough hazard characterization. To address this challenge, regulatory assessment of endocrine disrupting chemicals (EDCs) is benefiting from a revolution in toxicology that focuses on New Approach Methodologies (NAMs) to more rapidly identify, prioritize, and assess the potential risks from exposure to chemicals using novel, more efficient, and more mechanistically driven methodologies and tools. Incorporated into Integrated Approaches to Testing and Assessment (IATA) and guided by conceptual frameworks such as Adverse Outcome Pathways (AOPs), emerging approaches focus initially on molecular interactions between the test chemical and potentially vulnerable biological systems instead of the need for animal toxicity data. These new toxicity testing methods can be complemented with in silico and computational toxicology approaches, including those that predict chemical kinetics. Coupled with exposure data, these will inform risk-based decision-making approaches. Canada is part of a global network collaborating on building confidence in the use of NAMs for regulatory assessment of EDCs. Herein, we review the current approaches to EDC regulation globally (mainly from the perspective of human health), and provide a perspective on how the advances for regulatory testing and assessment can be applied and discuss the promises and challenges faced in adopting these novel approaches to minimize risks due to EDC exposure in Canada, and our world. [Display omitted] • Traditional testing approaches for endocrine effects are costly and animal-intensive. • Emerging technologies are increasingly available to rapidly and reliably test many chemicals. • Testing and assessment frameworks support use and integration of novel evidence. • Using data from New Approach Methods is critical to modernizing the assessment of EDCs. [ABSTRACT FROM AUTHOR]

Abstract: Alpha-synuclein aggregation plays a central role in Parkinson''s disease pathology. Direct transmission of alpha-synuclein from pathologically affected to healthy unaffected neurons may be important in the anatomical spread of the disease through the nervous system. We have demonstrated that exosomes released from alpha-synuclein over-expressing SH-SY5Y cells contained alpha-synuclein and these exosomes were capable of efficiently transferring alpha-synuclein protein to normal SH-SY5Y cells. Moreover, the incubation of cells with ammonium chloride or bafilomycin A1 to produce the lysosomal dysfunction recently reported in Parkinson''s disease led to an increase in the release of alpha-synuclein in exosomes and a concomitant increase in alpha-synuclein transmission to recipient cells. This study clearly demonstrates the importance of exosomes in both the release of alpha synuclein and its transmission between cells and suggests that factors associated with PD pathology accelerate this process. These mechanisms may play an important role in PD pathology and provide a suitable target for therapeutic intervention. [Copyright &y& Elsevier]

Abstract: Friedreich ataxia (FRDA) is a neurodegenerative disorder caused by an unstable GAA repeat expansion mutation within intron 1 of the FXN gene. However, the origins of the GAA repeat expansion, its unstable dynamics within different cells and tissues, and its effects on frataxin expression are not yet completely understood. Therefore, we have chosen to generate representative FRDA mouse models by using the human FXN GAA repeat expansion itself as the genetically modified mutation. We have previously reported the establishment of two lines of human FXN YAC transgenic mice that contain unstable GAA repeat expansions within the appropriate genomic context. We now describe the generation of FRDA mouse models by crossbreeding of both lines of human FXN YAC transgenic mice with heterozygous Fxn knockout mice. The resultant FRDA mice that express only human-derived frataxin show comparatively reduced levels of frataxin mRNA and protein expression, decreased aconitase activity, and oxidative stress, leading to progressive neurodegenerative and cardiac pathological phenotypes. Coordination deficits are present, as measured by accelerating rotarod analysis, together with a progressive decrease in locomotor activity and increase in weight. Large vacuoles are detected within neurons of the dorsal root ganglia (DRG), predominantly within the lumbar regions in 6-month-old mice, but spreading to the cervical regions after 1 year of age. Secondary demyelination of large axons is also detected within the lumbar roots of older mice. Lipofuscin deposition is increased in both DRG neurons and cardiomyocytes, and iron deposition is detected in cardiomyocytes after 1 year of age. These mice represent the first GAA repeat expansion-based FRDA mouse models that exhibit progressive FRDA-like pathology and thus will be of use in testing potential therapeutic strategies, particularly GAA repeat-based strategies. [Copyright &y& Elsevier]

We demonstrate that a quantum-dot cellular automata device can be fabricated using electron beam lithographically defined gates on GaAs/AlGaAs heterostructure materials, and that by tuning the four quantum dot (J. Phys. C: Solid State Phys. 21 (1988) L893) system polarization of one double dot can lead to polarization in the neighboring double dot (Phys. Rev. B 67 (2003) 033302). The polarization is detected using a 1-D or 0-D channel defined next to one pair of double dots which acts as a non-invasive voltage probe (Phys. Rev. Lett. 70 (1993) 1311). Ultimately a cellular automata device should be isolated from reservoirs to prevent charge fluctuations caused by co-tunneling. The non-invasive voltage probe is used to show that coupled double dots isolated from reservoirs can be made to have a sharper polarization transition. By studying the broadening of the polarization signal from a coupled double dot system isolated from reservoirs, we deduce the charge dephasing times for intra dot scattering to be more than 0.2 ns (Phys. Rev. B 67 (2003) 073302). [Copyright &y& Elsevier]

Blade-tip timing (BTT) is a promising method for the detection, measurement and analysis of blade vibrations in rotating bladed assemblies. However, the intricacies of the method when applied to real rotating structures undergoing synchronous (Engine Ordered) vibrations are not yet fully understood. In this paper, a mathematical model is developed to simulate data from typical BTT tests of rotating assemblies. The simulator is then used in order to provide a qualitative analysis of several phenomena that can be associated with the synchronous vibrations of rotating assemblies, including mistuning, coupling, excitation at multiple Engine Orders and simultaneous synchronous and asynchronous responses. It is concluded that none of these phenomena on its own will render the identification of the frequency and amplitude of blade vibrations impossible. However, there is no single BTT data analysis method that is able to deal with all of these phenomena. [Copyright &y& Elsevier]

Endothiapepsin is derived from the fungus Endothia parasitica and is a member of the aspartic proteinase class of enzymes. This class of enzyme is comprised of two structurally similar lobes, each lobe contributing an aspartic acid residue to form a catalytic dyad that acts to cleave the substrate peptide bond. The three-dimensional structures of endothiapepsin bound to five transition state analogue inhibitors (H189, H256, CP-80,794, PD-129,541 and PD-130,328) have been solved at atomic resolution allowing full anisotropic modelling of each complex. The active sites of the five structures have been studied with a view to studying the catalytic mechanism of the aspartic proteinases by locating the active site protons by carboxyl bond length differences and electron density analysis. In the CP-80,794 structure there is excellent electron density for the hydrogen on the inhibitory statine hydroxyl group which forms a hydrogen bond with the inner oxygen of Asp32. The location of this proton has implications for the catalytic mechanism of the aspartic proteinases as it is consistent with the proposed mechanism in which Asp32 is the negatively charged aspartate. A number of short hydrogen bonds (∼2.6 A˚) with ESD values of around 0.01 A˚ that may have a role in catalysis have been identified within the active site of each structure; the lengths of these bonds have been confirmed using NMR techniques. The possibility and implications of low barrier hydrogen bonds in the active site are considered. [Copyright &y& Elsevier]