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Biomedical subjects

T Hao

Publications and source records attributed to T Hao.

9 recordsLinked to original sources
PubMed2000

Biological potency of microsphere encapsulated plasmid DNA.

We evaluated the utility of three in vitro methods to monitor the biological potency of PLGA encapsulated DNA. For each assay we also determined whether the biological activity was influenced by the structural profile of DNA isomers. Collectively, the results indicate that all three methods can be used to evaluate the biological activity of DNA extracted from PLGA microspheres, but they are differentially sensitive to the structural changes of plasmid DNA that can occur during microencapsulation and microsphere storage. More specifically, mammalian cell transfection followed by an enzyme assay affords an accurate determination of DNA potency over time and is less influenced by DNA isoform than bacterial transformation. Cell-free transcription/translation systems can also be utilized, and the results of this assay are influenced by DNA isoform. Finally, bacterial transformation was found to be more sensitive to DNA isoform than the other assay methods.

Animals↗
PubMed2000

Heat-shock protein 70 can replace viral protein R of HIV-1 during nuclear import of the viral preintegration complex.

Heat-shock proteins (Hsp's) are a family of molecular chaperones that contribute to protection from environmental stress. In this report, we demonstrate that a member of this family, Hsp70, facilitates nuclear import of HIV-1 preintegration complexes (PICs). The mechanism of this activity appears to be similar to the one used by Vpr, an HIV-1 protein regulating viral nuclear import and replication in macrophages. Indeed Hsp70 stimulated binding of HIV-1 matrix antigen to GST-karyopherin alpha fusion protein and rescued nuclear import of a Vpr-defective HIV-1 strain in vitro. Binding studies with truncated forms of GST-karyopherin alpha demonstrated that both Vpr and Hsp70 bind to a region in the amino-terminal part of the karyopherin alpha molecule. This region appears to be distinct from the binding sites for two other karyopherin alpha cargoes, basic-type NLS-containing proteins and transcription factor STAT-1. Vpr competed with Hsp70 for binding to karyopherin alpha. These results suggest the presence of a novel regulatory site on karyopherin alpha which is used by Hsp70 and Vpr to stimulate interaction between the HIV-1 PIC and karyopherin alpha and thus promote viral nuclear import.

Antigens, Polyomavirus Transforming↗
PubMed1999

The CLAVATA1 receptor-like kinase requires CLAVATA3 for its assembly into a signaling complex that includes KAPP and a Rho-related protein.

The CLAVATA1 (CLV1) and CLAVATA3 (CLV3) genes are required to maintain the balance between cell proliferation and organ formation at the Arabidopsis shoot and flower meristems. CLV1 encodes a receptor-like protein kinase. We have found that CLV1 is present in two protein complexes in vivo. One is approximately 185 kD, and the other is approximately 450 kD. In each complex, CLV1 is part of a disulfide-linked multimer of approximately 185 kD. The 450-kD complex contains the protein phosphatase KAPP, which is a negative regulator of CLV1 signaling, and a Rho GTPase-related protein. In clv1 and clv3 mutants, CLV1 is found primarily in the 185-kD complex. We propose that CLV1 is present as an inactive disulfide-linked heterodimer and that CLV3 functions to promote the assembly of the active 450-kD complex, which then relays signal transduction through a Rho GTPase.

Arabidopsis Proteins↗
PubMed1999

Comparison of process parameters for microencapsulation of plasmid DNA in poly(D,L-lactic-co-glycolic) acid microspheres.

Poly(D,L-lactic-co-glycolic) acid (PLGA) microspheres containing plasmid DNA encoding the firefly luciferase gene were prepared using the water-in-oil-in-water (w/o/w) double emulsion and solvent evaporation method. In this study, we investigated the effects of three process parameters on DNA microencapsulation: (1) emulsification method used to generate the primary emulsion, (2) water/oil ratio during formation of the first emulsion, and (3) surfactant concentration used in the preparation of the second emulsion. The resulting formulations were also analyzed for microsphere size, encapsulation efficiency, and kinetics of DNA release. We found that although each process alteration resulted in encapsulation of biologically active, structurally intact DNA, the surfactant and water/oil ratio significantly affected the size, release kinetics and encapsulation efficiency of plasmid DNA.

Biocompatible Materials↗
PubMed1998

The Interfacial Polarization-Induced Electrorheological Effect.

The Wagner theory, which describes the interfacial polarization in heterogeneous systems, was employed to model the electrorheological (ER) effect under the presumption that the shear stress increment is induced by the interfacial polarization. The currently observed experimental facts, such as the yield stress of some ER fluids, decreases with the applied field frequency increasing or the environment temperature decreasing, while that of other fluids increases with the frequency decreasing or temperature increasing; the strongest ER effect is usually observed in the suspension with the dispersed particle conductivity around 10(-7) S/m; the particle dielectric loss tangent of a good ER fluid usually is above 0.10 at 1000 Hz; and the fluid with a high conductive particle usually has a short response time, can be satisfactorily understood with the extended Wagner model. The Wagner-polarization-induced maximum yield stress of a heterogeneous-type ER fluid is estimated around 7 kPa under the presumption that the dielectric constants of the solid particle and the liquid medium are 10 and 2, respectively, the particle volume fraction is 35%, and the applied electric field strength is 3 kV/mm. It is concluded that the ER effect may substantially correlate with the Wagner polarization, which would help in understanding the mechanism of the ER effect and would provide a strategy for designing high performance ER fluids. Copyright 1998 Academic Press.

Journal Article↗
PubMed1997

Correlation of the Dielectric Properties of Dispersed Particles with the Electrorheological Effect

The dc field rheological properties and frequency dependent dielectric properties of a set of electrorheological (ER) fluids composed of oxidized polyacrylonitrile or aluminosilicate materials dispersed in silicone oil were examined in this paper. Our experimental investigations show that there is a complicated relationship between the dielectric properties of dispersed particles and the ER effect. The dielectric loss of dispersed particles, which has not attracted much attention in previous work, was found to play a considerable role in ER response. The large dielectric loss tangent, experimentally around 0.10 at 1000 Hz, is found to be needed for a strong ER effect. A good ER solid material should first have large dielectric loss, and then the higher the dielectric constant, the stronger the ER effect. The large dielectric loss would facilitate the turning of dispersed particles, and the high dielectric constant would maintain the fibrillation structure stable and strong. Two processes, the particle turning process and the particle polarization process, are thought to be involved in ER activity. Our findings, in connection with the Wagner model, can better explain why the strongest ER effect occurs at particle conductivity of 10(-7) S/m; why the shear stress of some ER fluids decreases with frequency while with others the shear stress increases with frequency; and why trace water can enhance the ER effect considerably, which would help in understanding the mechanism of the ER effect. Too large a dielectric loss is thought to be unfavorable for the ER effect, and its suitable range is worth further study. The results also present a method of designing high performance ER fluids, which would significantly promote development of electrorheology and its application in industrial areas.

Journal Article↗
PubMed1997

Microstructure-Confined Mechanical and Electric Properties of the Electrorheological Fluids under the Oscillatory Mechanical Field

The dynamic properties of two kinds of aluminosilicate-based electrorheological (ER) fluids were investigated under on-state and off-state electric fields. The dynamic responsive (frequency sweep spectrum and strain sweep spectrum) differences between these two ER suspensions were found under the off-state electric field, whereas similarities were observed once an external electric field was applied. Their dc conductances under an oscillatory mechanical field and their mechanical strengths under an oscillatory electric field were also examined. The periodically varied dc current in an oscillatory mechanical field and the decreased shear stress in an ac field were both found in these ER suspensions. The different in situ microstructures of these two ER fluids suggested on the basis of the percolation model, as well as their different response times measured experimentally, were presented to understand the experimental observations. Our results have a direct implication concerning the practical application of ER fluids.

Journal Article↗
PubMed1996

The Conductivity Confined Temperature Dependence of Water-Free Electrorheological Fluids

The shear stresses and the current densities of four sorts of water-free ER fluids, two oxidized polyacrylonitriles-based and two aluminosilicates-based, were investigated at elevated and reduced temperatures in order to elucidate the operating mechanism. The complicated relationships among the mechanical properties, the current density, and temperature were especially addressed. The Wagner model was introduced to interpret our observations, instead of the commonly used conductivity model. It is found that the conductivity of the dispersed particles determines the temperature dependence of the shear stress and the current density of an ER fluid. Our findings have direct implication for the design of industrially required ER fluids and would be significant for ER applications.

Journal Article↗