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Biomedical subjects

V C Yang

Publications and source records attributed to V C Yang.

At least 55 records · Page 3Linked to original sources
PubMed1995

Optical detection of macromolecular heparin via selective coextraction into thin polymeric films.

Thin plasticized polymer films, poly(vinyl chloride) doped with a specific ion pairing quaternary ammonium compound, tridodecylmethylammonium chloride, and a lipophilic pH indicator, 3-hydroxy-4-(4-nitrophenylazo)phenyl octadeconate, are shown to exhibit significant and analytically useful optical response toward macromolecular heparin. The response mechanism is based on favorable extraction of heparin into the bulk organic film, owing to the specific ion-pairing complexation reaction between the quaternary ammonium species and the polyanion. A simultaneous coextraction of hydrogen ions results in protonation of the pH chromophore and hence a change in the optical absorbance of the polymeric film. When used in a limited volume/fixed exposure (10 min) detection mode, film absorbances change as a function of the initial heparin concentration in the range of 0.2-3.0 units/mL (1.2-18 micrograms/mL). The practical measurement response time is controlled by heparin diffusion through the stagnant diffusion layer adjacent to the surface of the film as well as within the bulk of the polymer film and is shown to increase with the molecular weight of the heparin species tested. No optical response to heparin is observed when a strong heparin complexing agent (e.g., protamine) is present in the test solution, suggesting that the polymer film can be used to conveniently monitor heparin-protamine (or other antagonist) titrations. The theory relating to the operation of the sensing film in either the equilibrium or the kinetic mode and the selectivity of the optimized film to heparin relative to small anions are presented.

Anions↗
PubMed1995

Potentiation of growth inhibition due to vincristine by ascorbic acid in a resistant human non-small cell lung cancer cell line.

A human cell subline (PC-9/VCR) resistant to vincristine was established from non-small cell lung cancer PC-9 cells by incremental exposure of the cells to vincristine. The resistant cells showed phenotypic resistance to vincristine (10-fold), colchicine (6.9-fold) and cisplatin (1.4-fold) but they showed sensitivity to other chemotherapeutic agents including melphalan and etoposide VP-16. The characteristics of the vincristine resistance was partially inhibited (5-7-fold) by co-treatment of PC-9/VCR cells with a nontoxic concentration of L-ascorbic acid (25 micrograms/ml). Co-treatment or 96 h pre-treatment with ascorbic acid resulted in potentiation of the vincristine effect on the resistant, but not on the sensitive, cell line. The growth inhibition due to vincristine treatment after 24 or 96 h growth in ascorbic acid-free medium was decreased in the resistant as well as in the sensitive cell line. In both cell lines, enhanced growth rate has been shown after ascorbic acid treatment. Similarly, cross-resistance of PC-9/VCR cells to colchicine could also be blocked by ascorbic acid. In addition, a nontoxic concentration of verapamil, a known multidrug resistance inhibitor, did not affect the resistant phenotype of PC-9/VCR cells. These findings suggest that an ascorbic acid-sensitive mechanism may be involved in drug resistance per se in the human lung cancer cells, which differs from the classical phosphoglycoprotein-mediated or previously reported non-phosphoglycoprotein-mediated multidrug resistance.

Ascorbic Acid↗
PubMed1995

Protamine-sensitive polymer membrane electrode: characterization and bioanalytical applications.

A polymeric membrane electrode that exhibits significant and analytically useful potentiometric response to submicromolar levels of the heparin antagonist, protamine, is reported. The sensor is prepared by incorporating a lipophilic cation exchanger, potassium tetrakis(4-chlorophenyl)borate (KTpClPB) (at 1 wt%), within a specially formulated polymer membrane composed of 33 wt% 2-nitrophenyl octyl ether (2-NPOE), and 66 wt% poly(vinyl chloride) (PVC). When the polymer film is mounted in an appropriate electrode body, the resulting membrane electrode responds reproducibly to protamine via a nonequilibrium quasi-steady-state change in the phase boundary potential at the membrane/sample interface. Such response can be used to directly monitor, via classical potentiometric titrations, the binding between protamine and a variety of native (porcine and beef) as well as low-molecular-weight heparins. Scatchard analysis of the EMF titration data provides binding constants and stoichiometries for protamine-heparin interactions. The electrode can be further used to follow the enzymatic digestion of protamine by trypsin. In the presence of a given level of protamine, initial rates of potential decrease (-dE/dt) are shown to be linearly related to trypsin activity in solution over the range of 0-130 units/ml. The speed and simplicity of the protamine sensor make it an attractive alternative to classical methods for studying the interaction of protamine with other biologically important macromolecules as well as the proteolytic activity and reaction kinetics of trypsin.

Electrodes↗
PubMed1995

Visualization of the transport pathways of low density lipoproteins across the endothelial cells in the branched regions of rat arteries.

The transport pathways of low density lipoproteins (LDL) across the endothelium at the branched and unbranched regions of the artery were studied in high cholesterol diet-fed rats. Rat tissues were analyzed by perfusing in situ human or rat LDL labeled with colloidal gold or fluorescein 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI). Results indicated that more LDL-DiI accumulated in the branched regions than in the unbranched regions of the artery. LDL-gold conjugates were observed in the plasmalemmal vesicles, multivesicular bodies and in the subendothelial space in both the branched and the unbranched regions of the arteries. Quantitative study revealed that the volume densities of plasmalemmal vesicles which contained the LDL-gold particles in the branched regions of the aortic arch were significantly (P < 0.05) higher than the density value in the unbranched regions of the thoracic aorta, whereas there was no marked difference in the density value of multivesicular bodies between these two regions. The open junctions with gap widths of 30-450 nm between adjacent endothelial cells were only observed in the branched regions of the aortic arch, whereas no open junctions were present in the unbranched regions of the thoracic aorta. Moreover, the LDL-gold conjugates were present within most of these open junctions. In all specimens examined, no gold particles were found in the normal intercellular channels (i.e., 25 nm and less) of both regions. These results indicated that the major visible routes for transport of LDL across the endothelium in the branched regions of the arteries are open junctions as well as plasmalemmal vesicles. The region-associated permeability changes of LDL might account for the incidence of atherosclerosis in the branched areas of arteries.

Animals↗
PubMed1995

Inhibition of the growth of a human nasopharyngeal carcinoma cell line by bFGF is mediated via FGFR-1.

The growth of CG-1 human nasopharyngeal carcinoma cell line and five of its randomly selected, single cell-derived subline cells is inhibited by bFGF in an autocrine and paracrine manner. In contrast, aFGF, which has a 55% homology in amino acid sequence with bFGF, stimulates cell growth. Basic FGF binds to specific cell surface high-affinity receptor sites with an apparent Kd of 105 pM. Of the two lines examined, the high-affinity binding sites for bFGF are calculated to be 1200 and 2600 per cell. The biological effect of bFGF is conveyed through its binding to the high-affinity receptor sites and the binding is dependent on the presence of cell surface heparin-like molecules, as treatment of cells with heparitinase or sodium chlorate abolishes high-affinity binding and growth inhibition. In contrast, similar treatment has no obvious effect on the growth-stimulatory effect of aFGF. Experimental results are also presented showing that the growth inhibition by bFGF is mediated through type I FGF receptors. These results suggest that bFGF and aFGF act via distinct receptor types to oppositely regulate the growth of CG-1 and subline cells.

Base Sequence↗
PubMed1994

Ascorbic acid increases drug accumulation and reverses vincristine resistance of human non-small-cell lung-cancer cells.

A human lung-cancer PC-9 subline with acquired resistance to vincristine (VCR), a chemotherapeutic agent, was established with incremental increases of the drug. The resistant PC-9 subline (PC-9/VCR) shows a 12-fold increase in resistance to VCR and a unique cross-resistance pattern: high cross-resistance to the potent VCR analogue colchicine (6.9-fold) and vinblastine (2.5-fold); lower cross-resistance to actinomycin D (1.8-fold), cisplatin (1.2-fold) and adriamycin (1.3-fold) and a sensitivity to melphalan and VP-16 which is similar to that of the parental cell line. A reduced accumulation of VCR in the resistant cells was demonstrated. Interestingly, the VCR resistance of the PC-9/VCR cell line was partially reversed by ascorbic acid, and the drug uptake was enhanced. In contrast, ascorbic acid had no effect on drug tolerance and drug accumulation was not observed in either PC-9 parental cells or known multidrug-resistant (MDR) cells, suggesting that VCR resistance in PC-9/VCR cells results essentially from reduced drug accumulation. It is worth noting that, whereas reduced drug accumulation in the PC-9/VCR cells was susceptible to modulation by ascorbic acid, the increased efflux rate characteristic of the resistant cells was not. Further, there was a higher efflux rate in resistant cells than in parental cells. DNA Southern- and RNA Northern-blot hybridization analyses indicate that PC-9/VCR cells do not contain amplified mdr genes or overexpress P-glycoprotein. In addition, the calcium-channel blocker verapamil, which acts as a competitive inhibitor of drug binding and efflux, did not affect the resistant phenotype of PC-9/VCR cells. These findings suggest an ascorbic acid-sensitive drug uptake mechanism which is important in mediating VCR resistance per se in human lung-cancer cells; this differs from the P-glycoprotein-mediated MDR mechanism.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1994

Response mechanism of polymer membrane-based potentiometric polyion sensors.

The potentiometric response mechanism of a previously reported polymer membrane-based electrode sensitive to the polyanion heparin is established. Based on transport and extraction studies, the heparin response is attributed to a nonequilibrium change in the phase boundary potential at the sample/membrane interface. While true equilibrium polyion response, obtained for low heparin concentrations only after very long equilibration times (> 20 h), yields the expected Nernstian response slope of < 1 mV/decade, the observed large and reproducible EMF response to clinically relevant heparin concentrations (approximately 10(-7) M) during typical measurement periods (2-5 min) is ascribed to a steady-state kinetic process defined by the flux of the polyion both to the surface and into the bulk of the polymer membrane. A model describing this nonequilibrium response is presented. With this model, the uniqueness of the polymer membrane composition (e.g., very low plasticizer content, strictly controlled cationic site concentration, etc.) required to achieve analytically useful heparin response becomes clear. Practical working conditions and limitations of the sensor are discussed. To support the generality of the steady-state model proposed, corresponding EMF response data for a newly developed membrane electrode sensitive to a polycationic protein (protamine) are also presented. It is shown that the protamine-responsive membrane electrode appears to operate via the exact same kinetic mechanism as the heparin sensing system.

Biosensing Techniques↗
PubMed1994

A method for the quantitation of protamine in plasma.

A unique and simple colorimetric method for the quantitation of plasma protamine levels has been developed. The method is established on the competitive binding displacement mechanism between protamine and heparin-azure A dye complex, and the metachromatic color change of azure A dye in the presence of heparin. Because the method is based on the clinical specificity of protamine as the heparin antagonist, it is specific for protamine quantitation. Plasma protamine levels determined by this method are within 94% of accuracy when compared with their aqueous counterparts determined by the conventional Lowry protein assay. Since the method measures the protamine excess after heparin neutralization, it potentially could be employed during clinical heparin reversal with protamine to monitor protamine excess. In addition, the method may provide a useful means to identify the mechanism of the so-called "heparin rebound".

Azure Stains↗
PubMed1994

Glycosaminoglycans enhance phorbol ester-induced proteolytic activity and angiogenesis in vitro.

It has been reported that endothelial cells suspended in three-dimensional type I collagen gels can be induced to undergo tube formation by 12-o-tetradecanoyl phorbol 13-acetate (TPA). In this report, we show that TPA-induced endothelial cell tube formation can be further enhanced by the addition of other matrix components in the collagen gels. In the presence of TPA, both high molecular weight hyaluronate and chondroitin sulfate elicit a dose-dependent stimulation of tube formation. The enhanced tube formation appears to be due to an increase in the number of cells undergoing morphogenesis as the average length per tube is not obviously increased. Concomitant with the increased cell morphogenesis, there is an increase in proteolytic activity secreted by the cells. Treatment of cells with cycloheximide suppresses hyaluronate- and chondroitin sulfate-enhanced cell morphogenesis and proteolytic activity suggesting that new protein synthesis, perhaps proteases, is necessary for endothelial cell morphogenesis. The possible role of the production of proteolytic activity in endothelial cell tube formation is discussed.

Cell Differentiation↗
PubMed1994

Ultrastructure and permeability of endothelial cells in branched regions of rat arteries.

The ultrastructure and the permeability to macromolecules of the endothelia in the branched and unbranched regions of the arteries were compared using two different age groups (3 and 12 months) of rats. In the aortic arch, the endothelial cells were longer and thinner and contained fewer intracytoplasmic vesicles than those observed in the unbranched regions of aorta. Quantitative study revealed that the volume density of intracytoplasmic vesicles in the branched regions of aortic arch in 3-month-old rats was significantly (P < 0.01) lower than the density value in the unbranched regions of aorta. The volume densities of vesicles in both regions of the aorta were lower than those in the carotid artery. There was an apparent increase in the frequency of the simple type of interendothelial contacts and a decrease in the complex type in the branched regions as compared with those in the unbranched regions of aorta and carotid artery. In addition to the normal interendothelial contacts, several open junctions with increasing width (25-300 nm) were identified in the branched regions of aortic arch and the bifurcations of carotid artery. For rats at the age of 12 months, local areas of the subendothelial space were expanded. Basal lamina-like and electron-dense materials were accumulated in the subendothelium. The volume densities of vesicles in the aortic endothelia were significantly (P < 0.01) increased as compared with those in the 3-month-old group. The volume density of vesicles in the aortic arch was again significantly (P < 0.01) lower than that in the unbranched regions of aorta. Furthermore, the frequency of the simple type of intercellular contacts was increased, whereas that of the complex type was decreased in both regions of aorta. With regard to the junctional complexes, the frequencies of gap junctions and tight junctions were increased and the junctionless intercellular contacts were decreased compared with those of the 3-month-old group.

Aging↗
PubMed1994

Delay of the excision of UV light-induced DNA adducts is involved in the coclastogenicity of UV light plus arsenite.

Chromatid exchanges and chromatid breaks were synergistically increased by a 2-h post-treatment with arsenite (VS treatment) but not with arabinofuranosyl cytosine (VA treatment) of UV-irradiated late-G1 Chinese hamster ovary cells. In order to determine the mechanism of this UV-arsenite coclastogenicity, we have compared the effects of arsenite and arabinofuranosyl cytosine on the generation of DNA strand breaks in UV-irradiated cells by alkaline elution and alkaline sucrose sedimentation. Only very small numbers of DNA breaks were detected immediately after VS treatment, however the breaks in parental strands increased as the cells reached mitosis in drug-free medium, whereas a large number of breaks were detected immediately after VA treatment but the breaks decreased thereafter. By labelling the newly synthesized DNA, we have also shown that the VS-treated cells had more breaks in daughter strands than the VA-treated cells at the time of reaching mitosis. The effect of a 2-h post-treatment with arsenite on the excision of UV-induced DNA adducts was further investigated by using the exponentially growing cells. The results confirmed that very low amount of breaks was detectable immediately after VS treatment, however the amount of breaks increased upon the removal of arsenite. Therefore, the breaks in the daughter strands of VS-treated cells may come from DNA replication using templates containing unexcised adducts, or using broken templates. It is conceivable that gaps in the overlapping regions of parental and daughter strands may result in chromatid breaks and that misreplication, because of unexcised adducts or gaps in the parental strands, may result in chromatid exchanges.

Animals↗
PubMed1993

Electrochemical sensor for heparin: further characterization and bioanalytical applications.

Further studies regarding the potentiometric response to heparin of polymeric membranes doped with lipophilic quaternary ammonium salts are reported. Among a wide range of membrane formulations examined, optimum response toward macromolecular heparin is achieved using tridodecylmethylammonium chloride as the active membrane component within poly(vinyl chloride) or poly(vinyl chloride)/(vinyl acetate) films plasticized with dioctyl sebacate. Although such membranes are shown to exhibit a typical Hofmeister potentiometric selectivity pattern toward small inorganic and organic anions, a very large and reproducible response to heparin at submicromolar levels is observed in the presence of physiological saline (0.12-0.15 M NaCl), as well as in citrated whole blood. Equal response on a mass basis occurs with fragments of heparin's as small as 2500 Da. Complexation of heparin's anionic sites by macromolecules that bind heparin with high affinity (e.g., protamine and poly(L-lysine)) reduces the membrane electrode's heparin response, indicating that the electrode detects biologically available (unbound) heparin levels in solution. Quantitative potentiometric titrations of protamine with porcine mucosa heparin followed by the sensor yield stoichiometric values in good agreement with the literature. The biomedical utility of the sensor is demonstrated by measuring its response in whole blood from patients undergoing open heart surgery before and after heparin therapy and correlating such response to conventional blood clotting time measurements.

Electrochemistry↗
PubMed1993

Acidic FGF and EGF are involved in the autocrine growth stimulation of a human nasopharyngeal carcinoma cell line and sub-line cells.

The growth of a recently established human nasopharyngeal carcinoma cell line, CG-1, and 5 randomly selected, single-cell-derived sub-lines in serum-free medium and in fetal-bovine-serum(FBS)-containing medium was investigated. In basal medium supplemented with insulin, transferrin, fibronectin and high-density lipoprotein, cell growth was moderately stimulated by aFGF and EGF in a dose-dependent manner. In contrast, in medium containing as little as 0.5% FBS, most of the stimulatory effect of the aforementioned growth factors observed was masked. Western blotting analysis of the cell lysates and conditioned media showed that CG-1 and sub-line cells were all capable of synthesizing and releasing aFGF- and EGF-immunoreactive proteins. The amounts of these 2 growth factors synthesized and released appeared to vary among the parental cell line and sub-line cells. Moreover, the rate of basal proliferation of these cells appeared to be positively correlated with the amounts of aFGF- and EGF-immunoreactive proteins produced. Addition of the neutralizing antibodies to aFGF and EGF exerted a dose-dependent suppression on cell growth in medium containing 0.5% FBS. The results suggest a role of aFGF and EGF in autocrine growth stimulation of CG-1 and sub-line cells, and may explain the moderate response of these cells to exogenously added aFGF and EGF.

Carcinoma↗
PubMed1993

Enzyme activities and maturation in unstimulated and exogenous gonadotropin-stimulated human oocytes.

With the advent of new techniques of human in vitro fertilization (IVF), identifying parameters of oocyte quality to allow selection of those most likely to fertilize becomes crucial. Morphology of oocytes, which correlates positively with biological performance, is the currently utilized classification criterion. However, biological links between form and function are tenuous, and underlying mechanisms remain elusive. We investigated whether biochemical activation is quantitatively associated with the stages of maturation in ova obtained from patients undergoing gynecologic surgery during unstimulated cycles and women undergoing IVF after exogenous gonadotropin stimulation. Changes in selected enzymes from protein, lipid, and carbohydrate metabolism (hexokinase, phosphoglucomutase, glycogen synthetase, uridine diphosphoglucose pyrophosphorylase, glucose-6-phosphate dehydrogenase, cytosolic thiolase, beta-hydroxyacyl-CoA dehydrogenase, alanine aminotransferase, and aspartate aminotransferase) were determined simultaneously, in individual oocytes, utilizing a highly sensitive biochemical methodology. Several enzyme activities paralleled maturation grade and were higher in stimulated oocytes after correction for grade. These biochemical findings quantify metabolic and functional changes that increase as ova mature, possibly contributing to their reproductive performance.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1993

Late structural changes in mouse coronary arteries after iron-particle irradiation of the orbital region.

A single dose of 0.1 or 0.2 Gy iron particles was given to B6CF1 female mice at 4 months of age. Degenerative changes in the coronary arteries due to orbital irradiation were observed 15 months after irradiation. The major changes included smooth muscle degeneration with fibrosis and accumulation of debris and extracellular matrix in the medial layer of the vessels. Quantitative analysis indicates that the average fractional volume of degenerated area is 12% in the unirradiated group. The corresponding percentages are 28% (P < 0.01) and 24% (P < 0.01) after 0.1 and 0.2 Gy irradiation, respectively.

Animals↗
PubMed1991

The use of immobilized protamine in removing heparin and preventing protamine-induced complications during extracorporeal blood circulation.

Heparin, currently used in extracorporeal blood circulation procedures, may lead to hemorrhagic complications. Protamine, used for reversal of heparin-induced anticoagulation at the end of such procedures, can cause adverse hemodynamic responses. To prevent both types of complications, we have developed a reactor device containing immobilized protamine (i.e., a protamine bio-reactor) that can be placed at the distal end of the circuit, thus providing simultaneous extracorporeal heparin removal and protamine treatment. In preliminary in vivo studies involving dogs at a blood flow of 100 ml/min, the bio-reactor removed about 50% of the administered dose of heparin (i.e., 100 units/kg) in 10 min. While rapid injection of protamine in dogs anticoagulated with heparin produced a transient and significant (P less than 0.005) decreases in systemic arterial blood pressure (-39.5 +/- 9.2 mmHg), cardiac output (-1.59 +/- 0.23 L/min), and mixed venous oxygen saturation (-7.5 +/- 1.3%) and increases in pulmonary artery systolic (+12.7 +/- 4.4 mmHg) and diastolic pressures (+10.0 +/- 3.6 mmHg), the use of the protamine bio-reactor did not elicit any statistically significant change in any of the variables measured. Hemolysis was not significant, as reflected by a statistically insignificant change of the animals' red blood cell counts, hematocrits, and total hemoglobin values. In addition, hemolytic complement was found to be reduced only by 10% in animals with the protamine bio-reactor, whereas it was reduced rapidly by 20% in animals receiving intravenous protamine administration and progressively by 20% in control animals with a sham reactor that contained no protamine. Furthermore, the use of the protamine bio-reactor also significantly reduced the protamine-induced transient thrombocytopenic and granulocytopenic responses. The white blood cell counts and platelet counts decreased to 87.7 +/- 7.5 and 83.3 +/- 5.0% of baseline, respectively, in dogs with the protamine bio-reactor compared to 35.5 +/- 14.3 and 32.1 +/- 8.1% of baseline in dogs receiving intravenous protamine. The protamine bio-reactor may provide a unique means to simultaneously control both heparin- and protamine-induced complications.

Animals↗