Biomedical subjects

E Liang

Publications and source records attributed to E Liang.

12 recordsLinked to original sources

PubMed2001

Investigation of ultrafast laser-driven radiative blast waves.

We have examined the evolution of cylindrically symmetric blast waves produced by the deposition of femtosecond laser pulses in gas jets. In high- Z gases radiative effects become important. We observe the production of an ionization precursor ahead of the shock front and deceleration parameters below the adiabatic value of 1/2 (for a cylinder), an effect expected when the blast wave loses energy by radiative cooling. Despite significant radiative cooling, the blast waves do not appear to develop thin shell instabilities expected for strongly radiative waves. This is believed to be due to the stabilizing effect of a relatively thick blast wave shell resulting in part from electron thermal conduction effects.

Journal Article↗

PubMed2000

Developing a Radiative Shock Experiment Relevant to Astrophysics.

We report on the initial results of experiments being developed on the Falcon laser to simulate radiative astrophysical shocks. Cylindrically diverging blast waves were produced in low-density ( approximately 1018 cm-3), high-Z gas by laser-irradiating Xe gas jets containing atomic clusters. The blast-wave trajectory was measured by Michelson interferometry. The velocity for the blast wave is slightly less than the adiabatic Sedov-Taylor prediction, and an ionization precursor is observed ahead of the shock front. This suggests energy loss through radiative cooling and reduced compression due to preheat deposited ahead of the shock, both consistent with one-dimensional radiation hydrodynamics simulations.

Journal Article↗

PubMed2000

Evaluation of an accelerated Caco-2 cell permeability model.

An accelerated 3-7-day Caco-2 cell permeability model was examined and compared to the traditional 21-25-day model. Caco-2 cell permeability coefficients (P(Caco-2)) of 33 structurally diverse small molecular weight compounds from apical to basolateral (AP-->BL) direction in the accelerated model were approximately twice those in the traditional model. As observed with microscopy and transepithelial electrical resistance measurements, this difference was attributed to less confluent and differentiated Caco-2 cell monolayers in the accelerated model. However, there were no significant differences in rank ordering of the compounds. The expression of P-glycoprotein in the accelerated model was shown to be significantly less than that in the traditional model. This resulted in lower permeability directional ratios defined as the ratio between permeability coefficients from BL-->AP and from AP-->BL for compounds that were cellular efflux pump substrates. The accelerated model may not be suitable for studying cellular efflux pumps such as P-glycoproteins. However, it is a feasible alternative to the traditional model for rank ordering of compounds in the process of drug discovery and development by significantly improving the turnover time and labor efficiency. This makes it an excellent Caco-2 cell permeability model for high throughput screening.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2000

In vitro transport and delivery of antisense oligonucleotides.

A variety of techniques are currently available to enhance the cellular uptake and pharmacological effectiveness of antisense oligonucleotides in the in vitro setting. The choice of technique will depend on the context of investigation, the likelihood of cytotoxity due to the delivery agents, and the ease and convenience of the approach. The considerations for the delivery of antisense molecules in the in vivo setting are likely to be quite different from the cell culture situation emphasized in this article.

Amino Acid Sequence↗

PubMed2000

Biodegradable pH-sensitive surfactants (BPS) in liposome-mediated nucleic acid cellular uptake and distribution.

The impact of biodegradable pH-sensitive surfactant (BPS)-liposomes on nucleic acid, i.e., oligonucleotide and plasmid DNA, cellular delivery was examined. Fluorescein-labeled nucleic acids complexed with 1,2-dioleoyl-3-trimethylammonium propane cationic liposomes and BPS at a charge ratio (+/-) of 10 were incubated in CV-1 cells and analyzed by flow cytometry. The fluorescence intensity of oligonucleotides but not plasmid DNA complexed with BPS-liposomes was higher than those complexed with BPS-free liposomes at early time points. However, when cells were fixed to equalize the intracellular pH since fluorescein, a pH-sensitive fluorophore, has higher fluorescence intensity in alkaline pH than acidic, no difference in intensity was observed. This indicated the incorporation of BPS in liposomes did not increase oligonucleotide cellular uptake over control liposomes, but redistributed oligonucleotides into a more basic environment, e.g., cytoplasm. An explanation consistent with the presented data is the formation of small transient membrane defects within the endosomal membrane as presented previously [Liang, E., Hughes, J.A., 1998a. Membrane fusion and rupture in liposomes: effect of biodegradable pH-sensitive surfactants. J. Membr. Biol. 166, 37-49.]. The above findings suggested that BPS may be effective agents of disrupting one of the major barriers, endosomal membrane, to enhance nucleic acid cellular transport.

Animals↗

PubMed2000

Mechanisms of transport and structure-permeability relationship of sulfasalazine and its analogs in Caco-2 cell monolayers.

PURPOSE: To investigate the mechanisms involved in transport of sulfasalazine in Caco-2 cells. METHODS: Permeability coefficients of sulfasalazine and its analogs across Caco-2 cell monolayers were measured as a function of direction of transport, energy and concentration dependence, and in the presence of inhibitors of various cellular efflux pumps and transporters. RESULTS: Permeability coefficients of sulfasalazine across Caco-2 cell monolayers were approximately 342-, 261-, and 176-fold higher from basolateral to apical direction (BL-->AP) than from apical to basolateral direction (AP-->BL) at 100, 200, and 500 microM, respectively. Carrier permeability coefficient, non-saturable membrane permeability coefficient, and Michaelis constant were estimated to be 1.4x10(-5) cm/s, 1.9x10(-8) cm/s, and 369 microM, respectively. The efflux of sulfasalazine was completely blocked at 4 degrees C and in the presence of an uncoupler of oxidative phosphorylation. Using cellular efflux inhibitors, the permeability of sulfasalazine was shown to depend on multidrug resistance-associated protein and anion sensitive transport mechanisms. Structure-permeability studies showed that the affinity of sulfasalazine for the cellular efflux pumps and transporters in Caco-2 cells depended strongly on the carboxylic acid functional group. CONCLUSIONS: The permeability of sulfasalazine across Caco-2 cell monolayer is very low due to its strong interaction with multiple cellular efflux pumps and transporters. This may partially explain its low absorption in vivo.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1999

Oligonucleotide delivery: a cellular prospective.

The use of oligonucleotides (ONs) for gene therapy of certain diseases has been discussed since the late 1970s. ONs are single stranded chains of nucleic acids that can hybridize with target nucleic acid sequences to inhibit specific proteins, and therefore allow selective treatment of various diseases. The use of ONs is limited due to their instability in biological tissues and difficulty in delivery to the intracellular compartments of the cell. Chemical analog approaches have been used to address the instability issue and delivery systems have been developed to increase cellular uptake of ONs. It is generally thought that ONs with or without a delivery system are transported into cells by endocytosis, and then accumulate within endosomes where they are significantly inactivated. The rate and extent of movement of ON from endosomes appears to be important in determining ON effects. Consequently, developing accessory compounds or delivery methods that enhance endosome to cytoplasm transfer may be vital to ON therapy. This review focuses on investigating mechanisms of various delivery approaches at the cellular/intracellular level that have demonstrated utility in increasing ON activity or cellular accumulation. The future prospects of ON delivery are also addressed.

Animals↗

PubMed1998

Membrane fusion and rupture in liposomes: effect of biodegradable pH-sensitive surfactants.

Biodegradable pH-sensitive surfactants (BPS) are a unique family of easily metabolized compounds that demonstrate pH-dependent surface activity. These agents, in combination with other delivery systems, have demonstrated effects in enhancing transnucleic acid activity. The increased activity has been hypothesized to occur from a release of endosomal contents. Simply, the BPS delivery system containing nucleic acids enters the cell through an endocytotoic process. It encounters an acidic pH and becomes surface active leading to defects in the endosomal membrane. In the current study, an in vitro model membrane was used to better understand the liposome defect mechanisms that BPS elicit. Using this system, it is shown that BPS can induce both liposome fusion and rupture depending upon the pH and mole ratio of BPS to membrane lipids. Futhermore, liposome fusion induced by BPS was dependent on the total numbers of liposome particles while rupture was independent of interacting liposome particles. The generated data indicate that BPS agents act differently from other typical surface active agents and fuosgenic compounds. Instead of facilitating membrane fusion through the hexagonal II phase, BPS appeared to contribute and participate in the membrane fusion at different stages.

Biodegradation, Environmental↗

PubMed1998

Characterization of a pH-sensitive surfactant, dodecyl-2-(1'-imidazolyl) propionate (DIP), and preliminary studies in liposome mediated gene transfer.

The inefficiency of non-viral gene delivery systems, relative to viral systems, is likely due, in part, to the failure of endosomes to release DNA before reaching degradative lysosomes. A solution is to incorporate compounds in a delivery vector that will selectively increase the release of endosomally encapsulated DNA. To meet the above criteria, we designed, synthesized, and characterized the physicochemical and biological properties of such a compound, dodecyl-2-(1'-imidazolyl) propionate (DIP) to enhance cationic liposome mediated gene delivery. Several surface active techniques were used to characterize DIP lysing membranes. The critical micelle concentration of DIP was between 0.10-0.18 mM and the effective release and solubilization ratios were 1.0 and 4.0, respectively. DIP facilitated membrane disruption in both a pH and concentration dependent manner. In the presence of esterase at pH 7.0, the hydrolysis rate increased 32-fold indicating DIP can be degraded in the biological milieu. Toxicity of DIP by MTT assay in the SKnSH cell line demonstrated an ID50 of 1.2 mM, which is 30-fold higher than the concentration of DIP used to enhance gene transfection. When incorporated into cationic-liposomes, DIP enhanced transgene expression in vitro by 5-fold. The results of the study indicate that DIP may be a useful adjuvant to increase non-viral gene delivery to cells.

Fluoresceins↗

PubMed1998

Pitfalls in pharmacokinetic multicompartment analysis.

When a pharmacokinetic (PK) two-compartment body model with first-order absorption is fitted to blood levels of a drug, the estimates of the PK parameters may have considerable errors and can cause wrong predictions in other features of the system. The objectives of this report were to illustrate this problem, to provide an easy way to prevent wrong estimation, and to investigate the origin of the mistake. A simple way to prevent wrong interpretation of the calculated PK parameters is to inspect the PK profiles visually. Without observing a clear biphasic profile, one should not apply the two-compartment model if the resulting parameters are to be interpreted and used for further simulations. We investigated the origin of this ambiguity in terms of the relative order of magnitude of microconstants (ka, k12, k21, and k10) and of hybrid constants (A and B). The observed parameter errors will not be of any relevance if the calculated parameters are used only to predict future blood levels over the same time-span. However, if these parameters are used to predict any other characteristic of the system, erroneous predictions may result.

Computer Simulation↗

PubMed1996

Variability of magnetic resonance angiography and computed tomography angiography in grading middle cerebral artery stenosis.

BACKGROUND AND PURPOSE: Magnetic resonance angiography and computed tomography angiography are new, noninvasive methods to provide images of the cerebral vasculature. The reliability of magnetic resonance angiography and computed tomography angiography when used to grade middle cerebral artery stenosis remains to be established. We sought to study the interobserver and intraobserver variabilities of magnetic resonance angiography and computed tomography angiography in grading middle cerebral artery stenosis. METHODS: A total of 50 middle cerebral arteries in 25 patients were studied with magnetic resonance angiography and computed tomography angiography. All patients had a history of ischemic stroke. The films were read independently by two observers on separate occasions. Films were shown again to the same observer 4 weeks after the first reading. The degree of middle cerebral artery stenosis was categorized into four grades: normal/mild, moderate, severe, and occluded. The interobserver and intraobserver variabilities were calculated by the kappa statistic method. RESULTS: Interobserver variability for grading middle cerebral artery stenosis was good (kappa = 0.78) for magnetic resonance angiography and moderate (kappa = 0.51) for computed tomography angiography. There was perfect agreement between two observers in 86% of the vessels shown in magnetic resonance angiography and in 76% of the vessels shown in computed tomography angiography. Intraobserver variability for both imaging methods was good, with the kappa value in the range of 0.70 to 0.76. CONCLUSIONS: Our results suggest that according to our protocol, magnetic resonance angiography is more reliable than computed tomography angiography in grading middle cerebral artery stenosis.

Adult↗

PubMedDate not supplied

Permeability measurement of macromolecules and assessment of mucosal antigen sampling using in vitro converted M cells.

INTRODUCTION: M cells are located in the epithelial layer covering the gut-associated lymphoid tissue and are responsible for delivery of macromolecules and microorganisms to the underlying lymphoid cells. It has been shown that the human colonic cell line Caco-2 can be converted to M cells in vitro following coculture with isolated lymphocytes from murine Peyer's patches. Studies were undertaken to evaluate and characterize the transepithelial transport of select macromolecules across these in vitro derived M cells. METHODS: Caco-2 cells were converted to M cells as reported previously. The morphology of Caco-2 cells and M cells was compared by transmission electron microscopy (TEM). The transport properties of macromolecules such as horseradish peroxidase, FITC-conjugated polystyrene beads, and radiolabeled dextrans were examined. The activation of murine antigen-specific T cells following transport of the antigen ovalbumin across the M-cell barrier was assessed by measuring cytokine production. RESULTS: M cells were shown to be irregular in shape and have fewer and shorter microvilli compared to the Caco-2 cell progenitors. These cells were still able to form tight junctions and monolayers on polycarbonate membranes. Time-course studies demonstrated that the transport of polystyrene beads and large-molecular-weight dextrans at physiological temperature across M-cell-containing monolayers was size dependent and more rapid than across Caco-2 cell monolayers. The transport of dextrans was also shown to be temperature and concentration dependent. Befitting the role of the M cell in mucosal defense, protein antigen could be delivered by these cells in order to be processed and presented to antigen-specific CD4+ T lymphocytes. DISCUSSION: The M-cell permeability model is a functional and practical system for evaluating the transport properties of macromolecules and assessing the potential for intestinal mucosal antigen sampling to elicit immunological responses.

Animals↗