Physico-chemical requirements and kinetics of membrane fusion of flavivirus-like particles.

Flaviviruses deliver their RNA genome into the host-cell cytoplasm by fusing their lipid envelope with a cellular membrane. Expression of the flavivirus pre-membrane and envelope glycoprotein genes in the absence of other viral genes results in the spontaneous assembly and secretion of virus-like particles (VLPs) with membrane fusion activity. Here, we examined the physico-chemical requirements for membrane fusion of VLPs from West Nile and Japanese encephalitis viruses. In a bulk fusion assay, optimal hemifusion (or lipid mixing) efficiencies were observed at 37 °C. Fusion efficiency increased with decreasing pH; half-maximal hemifusion was attained at pH 5.6. The anionic lipids bis(monoacylglycero)phosphate and phosphatidylinositol-3-phosphate, when present in the target membrane, significantly enhanced fusion efficiency, consistent with the emerging model that flaviviruses fuse with intermediate-to-late endosomal compartments, where these lipids are most abundant. In a single-particle fusion assay, VLPs catalysed membrane hemifusion, tracked as lipid mixing with the cellular membrane, on a timescale of 7-20 s after acidification. Lipid mixing kinetics suggest that hemifusion is a kinetically complex, multistep process.This work was supported by a Senior Research Fellowship from the Wellcome Trust, grant number 101908/Z/13/Z, to Y.M.; grant R01 GM102869 from the National Institutes of Health (NIH) to Y.M.; NIH grant NS079955 to E.R.; NIH grant T32 GM08283 to J.B.N.; and NIH grant T32 GM007223 to D.C.D. We thank Michel Ledizet, Martin Mattessich and Nathalie Bonafé (L2 Diagnostics, LLC) for helpful discussions.This is the author accepted manuscript. The final version is available from the Society for General Microbiology via http://dx.doi.org/10.1099/vir.0.00011

Theoretical Feasibility of Vasodilator-enhanced Local Tumor Heating

Normal arterioles, in contrast to the abnormal microvasculature of many solid tumors, provide a target for selective drug action that can enhance local heat treatment of the tumors. Measurements of tissue blood flow with radioactive microspheres and estimates of changes in blood flow with thermal clearance methods revealed that vasodilator drugs either decreased or did not alter blood flow in hamster melanoma, rat hepatoma, and canine transmissible venereal tumor, while increasing perfusion in adjacent normal tissues 2 to 4-fold. Solutions of the bio-heat transfer equation, which take into account such selective effects of vasodilators on blood flow in normal tissues, clearly demonstrate improved selective heating for spheroidal tumors over 2 cm in diameter. In the presence of vasodilator drug effect, steady-state center tumor temperatures of 45-50°C can be achieved by increased power input, while surrounding normal tissues remain below 42°C

B-Amyloid of Alzheimer\u27s Disease Induces Reactive Gliosis that Inhibits Axonal Outgrowth

Pathological lesions in the brains of patients with Alzheimer\u27s disease (AD) are characterized by dense deposits of the protein ,B-amyloid. The link between the deposition of B-amyloid in senile plaques and AD-associated pathology is, at present, controversial since there have been conflicting reports on whether the 39- 43 amino acid B-amyloid sequence is toxic or trophic to neurons. In this report, we show that B-amyloid peptide when presented as an insoluble substrate which mimics its conformation in vivo can induce cortical glial cells in vitro and in vivo to locally deposit chondroitin sulfate containingproteoglycan. In vitro the proteoglycan-containing matrix deposited by glia on B-amyloid blocks the usual ability of the peptide to allow cortical neurons to adhere and grow. Chondroitin sulfate-containing proteoglycan was also found in senile plaques of human AD tissue. We suggest that an additional effect of B-amyloid in the brain, which compounds the direct effects of ,8- amyloid on neurons, is mediated by the stimulation of astroglia to become reactive. Once in the reactive state, glial cells deposit large amounts of growth-inhibitory molecules within the neuropil which could impair neuronal process survival and regeneration leading to neurite retraction and/or dystrophy around senile plaques in AD

String-Based Methods in Perturbative Gravity

String theory implies a relatively modest growth in computational complexity for perturbative gravity calculations as compared to gauge theory calculations, contrary to field theory expectations. An explicit string-based calculation, which would be extremely difficult using conventional techniques, is presented to illustrate this.Comment: 14 pages (including figure), IASSNS-HEP-93-3

Midisuperspace-Induced Corrections to the Wheeler De Witt Equation

We consider the midisuperspace of four dimensional spherically symmetric metrics and the Kantowski-Sachs minisuperspace contained in it. We discuss the quantization of the midisuperspace using the fact that the dimensionally reduced Einstein Hilbert action becomes a scalar-tensor theory of gravity in two dimensions. We show that the covariant regularization procedure in the midisuperspace induces modifications into the minisuperspace Wheeler DeWitt equation.Comment: 7 page

Dust as a Standard of Space and Time in Canonical Quantum Gravity

The coupling of the metric to an incoherent dust introduces into spacetime a privileged dynamical reference frame and time foliation. The comoving coordinates of the dust particles and the proper time along the dust worldlines become canonical coordinates in the phase space of the system. The Hamiltonian constraint can be resolved with respect to the momentum that is canonically conjugate to the dust time. Imposition of the resolved constraint as an operator restriction on the quantum states yields a functional Schr\"{o}dinger equation. The ensuing Hamiltonian density has an extraordinary feature: it depends only on the geometric variables, not on the dust coordinates or time. This has three important consequences. First, the functional Schr\"{o}dinger equation can be solved by separating the dust time from the geometric variables. Second, the Hamiltonian densities strongly commute and therefore can be simultaneously defined by spectral analysis. Third, the standard constraint system of vacuum gravity is cast into a form in which it generates a true Lie algebra. The particles of dust introduce into space a privileged system of coordinates that allows the supermomentum constraint to be solved explicitly. The Schr\"{o}dinger equation yields a conserved inner product that can be written in terms of either the instantaneous state functionals or the solutions of constraints. Examples of gravitational observables are given, though neither the intrinsic metric nor the extrinsic curvature are observables. Disregarding factor--ordering difficulties, the introduction of dust provides a satisfactory phenomenological approach to the problem of time in canonical quantum gravity.Comment: 56 pages (REVTEX file + 3 postscipt figure files

The Consistency of Causal Quantum Geometrodynamics and Quantum Field Theory

We consider quantum geometrodynamics and parametrized quantum field theories in the framework of the Bohm-de Broglie interpretation. In the first case, and following the lines of our previous work [1], where a hamiltonian formalism for the bohmian trajectories was constructed, we show the consistency of the theory for any quantum potential, completing the scenarios for canonical quantum cosmology presented there. In the latter case, we prove the consistency of scalar field theory in Minkowski spacetime for any quantum potential, and we show, using this alternative hamiltonian method, a concrete example where Lorentz invariance of individual events is broken.Comment: Final version. See also http://www.cosmologia.cbpf.b

Calculation of Graviton Scattering Amplitudes using String-Based Methods

Techniques based upon the string organisation of amplitudes may be used to simplify field theory calculations. We apply these techniques to perturbative gravity and calculate all one-loop amplitudes for four-graviton scattering with arbitrary internal particle content. Decomposing the amplitudes into contributions arising from supersymmetric multiplets greatly simplifies these calculations. We also discuss how unitarity may be used to constrain the amplitudes.Comment: 25 pages +5 figs. , SWAT-94-37 UCLA/TEP/94/30, Plain TeX. (Typos in eqns. fixed