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Biomedical subjects

X B Wang

Publications and source records attributed to X B Wang.

At least 37 records · Page 2Linked to original sources
PubMed1999

Cell separation on microfabricated electrodes using dielectrophoretic/gravitational field-flow fractionation.

Dielectrophoretic/gravitational field-flow fractionation (DEP/G-FFF) was used to separate cultured human breast cancer MDA-435 cells from normal blood cells mixed together in a sucrose/dextrose medium. An array of microfabricated, interdigitated electrodes of 50 microns widths and spacings, and lining the bottom surface of a thin chamber (0.42 mm H x 25 mm W x 300 mm L), was used to generate DEP forces that levitated the cells. A 10-microL cell mixture sample containing approximately 50,000 cells was introduced into the chamber, and cancerous and normal blood cells were levitated to different heights according to the balance of DEP and gravitational forces. The cells at different heights were transported at different velocities under the influence of a parabolic flow profile that was established in the chamber and were thereby separated. Separation performance depended on the frequency and voltage of the applied DEP field and the fluid-flow rate. It took as little as 5 min to achieve cell separation. An analysis of the DEP/G-FFF results revealed that the separation exploited the difference in dielectric and density properties between cell populations. The DEP/G-FFF technique is potentially applicable to many biological and biomedical problems, especially those related to microfluidic systems.

Algorithms↗
PubMed1999

Membrane dielectric responses of human T-lymphocytes following mitogenic stimulation.

Human peripheral blood T-lymphocytes, normally resting at the G0 phase, were stimulated with phytohemagglutinin (PHA) and interleukin-2 (IL-2) to induce the cell division cycle. The cells were examined at 24-h intervals for up to 96 h by flow cytometry to determine cell cycle distributions and by electrorotation to determine dielectric properties. The average membrane specific capacitance was found to vary from 12 (+/-1.5) mF/m2 prior to stimulation to 10 (+/-1.5) and 16 (+/-3.5) mF/m2 at 24 and 48 h after stimulation, respectively, and to remain unchanged up to 96 h after stimulation. Scanning electron microscopy studies of the cells revealed an increased complexity in cell membrane morphology following stimulation, suggesting that the observed change in the membrane capacitance was dominated by the alteration of cell surface structures. The average electrical conductivity of the cell interior decreased from approximately 1.1 S/m prior to stimulation to approximately 0.8 S/m at 24 h after stimulation and showed little change thereafter. The average dielectric permittivity of the cell interior remained almost unchanged throughout the course of the cell stimulation. The percentage of T-lymphocytes in the S and G2/M phases increased from approximately 4% prior to stimulation to approximately 11 and approximately 34% at 24 and 48 h after stimulation, respectively. The large change in membrane specific capacitance between the 24 and 48 h time period coincided with the large alteration in the cell cycle distribution where the S and G2/M populations increased by approximately 23%. These data, together with an analysis of the variation of the membrane capacitance during the cell cycle based on the cell cycle-dependent membrane lipid accumulation, show that there is a correlation between membrane capacitance and cell cycle phases that reflects alterations in the cell plasma membrane.

Cell Cycle↗
PubMed1999

Dielectric properties of human leukocyte subpopulations determined by electrorotation as a cell separation criterion.

The separation and purification of human blood cell subpopulations is an essential step in many biomedical applications. New dielectrophoretic fractionation methods have great potential for cell discrimination and manipulation, both for microscale diagnostic applications and for much larger scale clinical problems. To discover whether human leukocyte subpopulations might be separable by such methods, the dielectric characteristics of the four main leukocyte subpopulations, namely, B- and T-lymphocytes, monocytes, and granulocytes, were measured by electrorotation over the frequency range 1 kHz to 120 MHz. The subpopulations were derived from human peripheral blood by magnetically activated cell sorting (MACS) and sheep erythrocyte rosetting methods, and the quality of cell fractions was checked by flow cytometry. Mean specific membrane capacitance values were calculated from the electrorotation data as 10.5 (+/- 3.1), 12.6 (+/- 3.5), 15.3 (+/- 4.3), and 11.0 (+/- 3.2) mF/m2 for T- and B-lymphocytes, monocytes, and granulocytes, respectively, according to a single-shell dielectric model. In agreement with earlier findings, these values correlated with the richness of the surface morphologies of the different cell types, as revealed by scanning electron microscopy (SEM). The data reveal that dielectrophoretic cell sorters should have the ability to discriminate between, and to separate, leukocyte subpopulations under appropriate conditions.

Biophysical Phenomena↗
PubMed1999

Neuronal localization of the Adenomatous polyposis coli tumor suppressor protein.

Recent biochemical studies have demonstrated that the adenomatous polyposis coli gene, initially identified via its link to colon cancer, is expressed at high levels in the brain. Furthermore, the ability of this tumor suppressor protein to bind to Discs-Large and beta-catenin, proteins implicated in organizing synaptic structure, point to a role for APC in neuronal signalling. However, anatomical studies have provided conflicting results regarding its localization in brain. In situ hybridization studies predict neuronal expression of APC, while immunostaining studies performed with a panel of N-terminal antibodies detected staining of glial cells, especially oligodendrocytes. In this study, we have examined the basis for this discrepancy and provide evidence that the glial staining pattern detected in previous studies reflects cross-reactivity with an unrelated antigen rather than the localization of APC. Furthermore, we have performed immunohistochemical studies with a C-terminal APC antibody which reveal a neuronal pattern of staining closely matching that predicted by the in situ studies. For example, in the hippocampus APC immunostaining is detected in the pyramidal neurons and dentate granule cells, which fits well with the localization of APC mRNA. Examination of APC immunostaining in other regions revealed that particularly intense staining was displayed by large neurons, including layer V cortical pyramidal neurons, cerebellar Purkinje cells, and olfactory bulb mitral cells. Within labeled neurons, APC staining was apparent in the cytoplasm, as well as in dendritic and axonal processes. To help clarify the localization of APC in brain, we have conducted additional in situ hybridization and immunohistochemical studies. These results provide compelling evidence that APC is expressed predominantly in neurons rather than in glial cells as reported previously.

Adenomatous Polyposis Coli Protein↗
PubMed1999

The removal of human breast cancer cells from hematopoietic CD34+ stem cells by dielectrophoretic field-flow-fractionation.

Dielectrophoretic field-flow-fractionation (DEP-FFF) was used to purge human breast cancer MDA-435 cells from hematopoietic CD34+ stem cells. An array of interdigitated microelectrodes lining the bottom surface of a thin chamber was used to generate dielectrophoretic forces that levitated the cell mixture in a fluid flow profile. CD34+ stem cells were levitated higher, were carried faster by the fluid flow, and exited the separation chamber earlier than the cancer cells. Using on-line flow cytometry, efficient separation of the cell mixture was observed in less than 12 min, and CD34+ stem cell fractions with a purity >99.2% were obtained. The method of DEP-FFF is potentially applicable to many biomedical cell separation problems, including microfluidic-scale diagnosis and preparative-scale purification of cell subpopulations.

Bone Marrow Purging↗
PubMed1999

[Effects of mild and moderate hypoxia on event-related potentials and the comparison of different stimulus paradigms].

OBJECTIVE: To investigate the effects of mild and moderate hypoxia on event-related potentials (ERP), and to compare the sensitivity of different stimulus paradigms to hypoxia. METHODS: Twelve subjects performed visual Oddball and memory set size (MSET) 1 and MSET 3 of Sternberg tasks on the ground and at the simulated altitudes of 2500 m and 4300 m by breathing low oxygen mixtures. P3 latency and amplitude of ERP, reaction time (RT) and response error rate (ER) were recorded. RESULTS: During hypoxia at the altitude of 4300 m, P3 latency significantly delayed, and ER was high when the difficulty of task increased (Sternberg paradigm with MSET 3). In contrast, at the altitude of 2500 m no changes were observed. Sternberg paradigm with MSET 1, in comparison with others, could elicit clearer ERP waves, and P3 latency was slower during hypoxia. CONCLUSION: Hypoxia at the altitude of 4300 m has strong influence on ERP. P3 latency can be used as a sensitive index in evaluating the decrement of brain cognitive capacity during hypoxia. ERP elicited by Sternberg paradigm with MSET 1 was more sensitive to hypoxia.

Adolescent↗
PubMed1998

The effect of dietary sulfur-containing amino acids on calcium excretion.

The relationships between dietary protein and sulfur amino acid (methionine and cystine or taurine) intakes and urinary calcium excretion were examined both in animals and in young men. Thirty-two adult Wistar rats were divided into 4 groups, i.e., basal diet (group I), supplemented with albumin (II), methionine and cystine (III), or taurine (IV). During the 5-week feeding period, food consumption was recorded and 48 h urine samples were collected 4 times for each rat. Urinary calcium, creatinine and sulfate were measured. The results showed that the calcium and sulfate excretion in rats in group II and III were significantly higher than rats in the basal diet group. In contrast, supplementing a basal diet with taurine did not increase sulfate excretion and failed to induce hypercalciuria. The same result was also observed in the study carried out in Chinese young men. An increase in protein intake from 67 g to 107 g caused an increase in urinary calcium and sulfate. Supplementation with methionine and cystine in an amount to simulate those in the high protein diet had a similar effect. Adding taurine to the diet had no effect on urinary calcium and sulfate excretion. About 60 percent of the supplemented taurine in the diet was detected in the urine.

Adult↗
PubMed1998

Separation of polystyrene microbeads using dielectrophoretic/gravitational field-flow-fractionation.

The characterization of a dielectrophoretic/gravitational field-flow-fractionation (DEP/G-FFF) system using model polystyrene (PS) microbeads is presented. Separations of PS beads of different surface functionalization (COOH and none) and different sizes (6, 10, and 15 microm in diameter) are demonstrated. To investigate the factors influencing separation performance, particle elution times were determined as a function of particle suspension conductivity, fluid flow rate, and applied field frequency and voltage. Experimental data were analyzed using a previously reported theoretical model and good agreement between theory and experiment was found. It was shown that separation of PS beads was based on the differences in their effective dielectric properties. Particles possessing different dielectric properties were positioned at different heights in a fluid-flow profile in a thin chamber by the balance of DEP and gravitational forces, transported at different velocities under the influence of the fluid flow, and thereby separated. To explore hydrodynamic (HD) lift effects, velocities of PS beads were determined as a function of fluid flow rate in the separation chamber when no DEP field was applied. In this case, particle equilibrium height positions were governed solely by the balance of HD lift and gravitational forces. It was concluded that under the experimental conditions reported here, the DEP force was the dominant factor in controlling particle equilibrium height and that HD lift force played little role in DEP/G-FFF operation. Finally, the influence of various experimental parameters on separation performance was discussed for the optimization of DEP/G-FFF.

Electrophoresis↗
PubMed1998

Subtracted differential display: genes with amphetamine-altered expression patterns include calcineurin.

Genes whose expression changes with administration of abused substances provide candidate biochemical mechanisms for drug-induced long-term brain changes. To identify such genes, and to avoid the false-positive results frequently obtained from differential display PCR, we applied a subtracted differential display (SDD) approach. We subtracted single-stranded cDNA prepared from drug-treated animals with excess mRNA from saline-treated animals, and visa versa, prior to differential display amplifications. Two of initial amphetamine-regulated cDNAs identified in this fashion encoded calcineurin A, a neuron-specific protein phosphatase catalytic subunit whose striatal expression was upregulated ca. 1.5-fold. SDD may enhance the utility of differential display approaches to identifying regulated genes in tissues in which mRNA complexities are high.

Animals↗
PubMed1997

rGbeta1: a psychostimulant-regulated gene essential for establishing cocaine sensitization.

Repeated doses of cocaine or amphetamine lead to long-lasting behavioral manifestations that include enhanced responses termed sensitization. Although biochemical mechanisms that underlie these manifestations currently remain largely unknown, new protein synthesis has been implicated in several of these neuroadaptive processes. To seek candidate biochemical mechanisms for these drug-induced neuroplastic behavioral responses, we have used an approach termed subtracted differential display (SDD) to identify genes whose expression is regulated by these psychostimulants. rGbeta1 is one of the SDD products that encodes a rat G-protein beta subunit. rGbeta1 expression is upregulated by cocaine or amphetamine treatments in neurons of the nucleus accumbens shell region, a major center for psychostimulant effects in locomotor control and behavioral reward. Antisense oligonucleotide treatments that attenuate rGbeta1 expression in regions including the nucleus accumbens abolish the development of behavioral sensitization when they are administrated during the repeated cocaine exposures that establish sensitization. These treatments fail to alter acute behavioral responses to cocaine, and they do not block the expression of cocaine sensitization when it is established before oligonucleotide administrations. Full, regulated rGbeta1 expression is a biochemical component essential to the establishment of a key consequence of repeated cocaine administrations, sensitization.

Amino Acid Sequence↗
PubMed1997

Introducing dielectrophoresis as a new force field for field-flow fractionation.

We present the principle of cell characterization and separation by dielectrophoretic field-flow fractionation and show preliminary experimental results. The operational device takes the form of a thin chamber in which the bottom wall supports an array of microelectrodes. By applying appropriate AC voltage signals to these electrodes, dielectrophoretic forces are generated to levitate cells suspended in the chamber and to affect their equilibrium heights. A laminar flow profile is established in the chamber so that fluid flows faster with increasing distance from the chamber walls. A cell carried in the flow stream will attain an equilibrium height, and a corresponding velocity, based on the balance of dielectrophoretic, gravitational, and hydrodynamic lift forces it experiences. We describe a theoretical model for this system and show that the cell velocity is a function of the mean fluid velocity, the voltage and frequency of the signals applied to the electrodes, and, most significantly, the cell dielectric properties. The validity of the model is demonstrated with human leukemia (HL-60) cells subjected to a parallel electrode array, and application of the device to separating HL-60 cells from peripheral blood mononuclear cells is shown.

Cell Separation↗
PubMed1997

Dielectrophoretic manipulation of cells with spiral electrodes.

Electrokinetic responses of human breast cancer MDA-MB-231 cells were studied in suspensions of conductivities 18, 56, and 160 mS/m on a microelectrode array consisting of four parallel spiral electrode elements energized with phase-quadrature signals of frequencies between 100 Hz and 100 MHz. At low frequencies cells were levitated and transported toward or away from the center of the spiral array, whereas at high frequencies cells were trapped at electrode edges. The frequencies of transition between these characteristic cell behaviors increased with increasing suspension conductivity. Levitation heights and radial velocities were determined simultaneously for individual cells as a function of the applied field magnitude and frequency. Results were compared with theoretical predictions from generalized dielectrophoresis theory applied in conjunction with cell dielectric parameters and simulated electric field distributions corrected for electrode polarization effects. It was shown that the conventional and traveling-wave dielectrophoretic force components dominated cell levitation and radial motion, respectively. Both theoretical predictions and experimental data showed that the cell radial velocity was very sensitive to the field frequency when the in-phase component of the field-induced polarization was close to zero. Applications of spiral electrode arrays, including the isolation of cells of clinical relevance, are discussed.

Breast Neoplasms↗
PubMed1997

Role of transchelation in the uptake of 99mTc-MAb in liver and kidney.

High radioactivity in liver and kidney after administration of 99mTc-labeled antibodies is a major detriment to the use of radiolabeled antibodies for diagnosis and therapy. In the present study, the uptake mechanism of radioactivity by liver and kidney involving 99mTc moiety was investigated. The data of in vitro and in vivo thiol transchelation studies, biodistribution alteration of 99mTc-MAb after specific modulation of endogenous thiol containing compounds, and the finding of 99mTc-labeled cysteine and GSH in bile, urine and kidney after administration of 99mTc-MAb demonstrated that transchelation by thiols (cysteine and GSH) played an important role in the localization of radiotracer from 99mTc MAb in normal tissues such as liver and kidney.

Animals↗
PubMed1996

Membrane changes associated with the temperature-sensitive P85gag-mos-dependent transformation of rat kidney cells as determined by dielectrophoresis and electrorotation.

Conventional dielectrophoresis (cDEP) and electrorotation (ROT) measurements have been used to determine the dielectric properties of a clone of normal rat kidney cells, designated 6m2, that exhibits a transformed phenotype at 33 degrees C and a non-transformed phenotype at 39 degrees C. cDEP measurements of the crossover frequencies at which individual 6m2 cells experienced zero cDEP force performed as a function of the conductivity of the suspension medium revealed that, in response to a temperature shift from 33 degrees C to 39 degrees C for 24 h, the mean specific cell membrane capacitance and conductance fell significantly (P < 0.01) from 42.3 (+/-1.3) to 30.3 (+/-2.9) mF/m2 and 743 (+/-422) to 567 (+/-326) S/m2, respectively. ROT analyses demonstrated a similar reduction for the membrane capacitance from 37.2 (+/-7.3) to 27.4 (+/-6.1) mF/m2, and also showed that accompanying changes in the mean internal electrical conductivity and dielectric permittivity of the cells were insignificant. Scanning electron microscopy was used to examine the surface morphology of the cells and, in agreement with our previous reports for leukemia cells, the observed membrane capacitance values correlated closely with the morphological complexity of the cell membrane surface. The observed changes in the membrane dielectric properties are discussed in terms of their biological significance and their relationship to previously-detected changes in cell surface charge.

Animals↗
PubMed1996

AP-1 DNA-binding activation by methamphetamine involves oxidative stress.

Methamphetamine (METH) caused dose-dependent increases in AP-1 DNA-binding activity in both nontransgenic (Non-Tg) and CuZn-SOD transgenic (SOD-Tg) mice. However, the increases in SOD-Tg mice were less prominent than those observed in Non-Tg animals. The time-course of METH-induced AP-1 changes was similar in both strains of mice. AP-1 binding activity showed an initial increase at 1 h, peaked at 3 h, and then gradually declined. AP-1 binding activity was back to normal by the 72-h time point. Regional analyses of METH effects revealed increases in the caudate putamen and cerebellum, with the striatum showing relatively higher METH-induced AP-1 DNA-binding activation. These regional effects were also attenuated in the SOD-Tg mice. These data indicate that METH-induced stimulation of AP-1 DNA-binding depends on cellular redox status. These results are consistent with in vitro studies that have reported that several transcription factors are regulated through redox mechanisms.

Animals↗
PubMed1996

Methamphetamine-induced neurotoxicity is associated with increased striatal AP-1 DNA-binding activity in mice.

Multiple injections of methamphetamine (METH) produce long-lasting neurotoxic effects on the nigrostriatal dopamine (DA) system. The drug also causes increases in AP-1 DNA-binding activity in mice. In the present study, we tested the idea that toxic doses of METH might cause long-term increases in AP-1 DNA-binding. Mice were given 10 mg/kg of METH 2, 3 or 4 times at a 2 h interval in 1 day. Striatal DA levels were markedly decreased at 3 h and 24 h in all injection groups. After 1 week, striatal DA level recovered to near control in the METH x2 group, but were still significantly decreased in the METH x3 and x4 groups. Similar drug administration schedules caused increases in AP-1 DNA-binding activity at the 3 h time point in all groups. The AP-1-binding activity almost returned back to control level in the x2 and x3 injection groups at the 24 h and 1 week time point, but there were still increased levels of AP-1-binding activity in the METH x4 group. These findings raise the possibility that METH-induced neurotoxicity might involve prolonged activation of AP-1 transcription factor. This might be related to the report that c-fos or c-jun activation may be important in some models of neurodegeneration.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1996

[Effects of tangshenkang capsule on diabetic nephropathy].

To study the effects of Chinese herbal medicine Tangshenkang (TSK) capsule on diabetic nephropathy (DN), 57 patients with DN were randomly divided into two groups, the treated group and the control group, they were treated with TSK capsule and the conventional therapy respectively. There were serious disorders of metabolism in DN patients, that showed the TXB 2/6-keto-PGF1 alpha ratios and lipid peroxidase (LPO) levels were higher than that of healthy people. After 6 weeks treated with TSK capsule the albuminuria levels reduced obviously (decreased 51%), renal plasma flow (RPF) increased, glomerular filtration rate and the LPO levels decreased and a positive correlation was observed between albuminuria levels and TXB 2/6-keto-PGF1 alpha ratios while the clearance rate of creafinin didn't improve significantly. There were no significant difference in the above-mentioned parameters in the control group before and after treatment. These results suggested that TSK capsule possessed a significant effect in improving albuminuria and glomerular function. And the effect of TSK might be due to its adjusting TXB 2/6-keto-PGF1 alpha ratios and its lipid-peroxidation in DN patients.

6-Ketoprostaglandin F1 alpha↗