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Biomedical subjects

X Xi

Publications and source records attributed to X Xi.

At least 19 recordsLinked to original sources
PubMed2001

A mitogen-activated protein kinase-dependent signaling pathway in the activation of platelet integrin alpha IIbbeta3.

We have recently shown that the platelet integrin alpha(IIb)beta(3) is activated by von Willebrand factor (vWF) binding to its platelet receptor, glycoprotein Ib-IX (GPIb-IX), via the protein kinase G (PKG) signaling pathway. Here we show that GPIb-IX-mediated activation of integrin alpha(IIb)beta(3) is inhibited by dominant negative mutants of Raf-1 and MEK1 in a reconstituted integrin activation model in Chinese hamster ovary (CHO) cells and that the integrin-dependent platelet aggregation induced by either vWF or low dose thrombin is inhibited by MEK inhibitors PD98059 and U0126. Thus, mitogen-activated protein kinase (MAPK) pathway is important in GPIb-IX-dependent activation of platelet integrin alpha(IIb)beta(3). Furthermore, vWF binding to GPIb-IX induces phosphorylation of Thr-202/Tyr-204 of extracellular signal-regulated kinase 2 (ERK2). GPIb-IX-induced ERK2 phosphorylation is inhibited by PKG inhibitors and enhanced by overexpression of recombinant PKG. PKG activators also induce ERK phosphorylation, indicating that activation of MAPK pathway is downstream from PKG. Thus, our data delineate a novel integrin activation pathway in which ligand binding to GPIb-IX activates PKG that stimulates MAPK pathway, leading to integrin activation.

Animals↗
PubMed2001

Detection of soluble urokinase receptor by immunoradiometric assay and its application in tumor patients.

It has recently been found that tumor cells express large amounts of urokinase receptor (uPAR) on their surface and that the blood soluble uPAR (suPAR) level in cancer patients is increased. However, the significance of suPAR in tumor progression is still unclear. To investigate the significance of suPAR in evaluating clinical status of solid tumor patients, an immunoradiometric assay (IRMA) based on using two monoclonal antibodies (McAbs) to different epitopes of uPAR was established to determine the serum levels of suPAR in normal individuals and solid tumor patients. The detectable range of this suPAR IRMA was 1.95-500 microg/l. The affinity constant was 4.75x10(9) l/mol. The mean rate of recovery was 101.3%, and the mean coefficients of variation for intra- and interassay were 6.40+/-2.57% (mean+/-S.D., n = 11) and 10.48+/-2.65% (n = 5), respectively. The serum suPAR levels were 2.71+/-1.12 microg/l in 62 normal individuals, 3.71+/-1.69 microg/l in 30 patients with benign tumors, and 5.82+/-2.27 microg/l in 124 patients with malignant tumors. The serum suPAR levels of these two types of tumor patients were increased in comparison with that of normal individuals (P values less than.01 and.001). The extent of their increase in malignant tumors was much greater than in benign tumors (P < .001). The serum suPAR levels of patients with malignant tumors were correlated with tumor invasion, metastasis, and surgical intervention. Our data suggest that IRMA for suPAR could be a sensitive and specific assay and that the serum suPAR level would be a valuable index for evaluating the condition and prognosis of tumor patients in clinic.

Adolescent↗
PubMed2001

Dynamic photoelastic study of the transient stress field in solids during shock wave lithotripsy.

Photoelastic and shadowgraph imaging techniques were used to visualize the propagation and evolution of stress waves, and the resultant transient stress fields in solids during shock wave lithotripsy. In parallel, theoretical analysis of the wavefront evolution inside the solids was performed using a ray-tracing method. Excellent agreement between the theoretical prediction and experimental results was observed. Both the sample size and geometry were found to have a significant influence on the wave evolution and associated stress field produced inside the solid. In particular, characteristic patterns of spalling damage (i.e., transverse and longitudinal crack formation) were observed using plaster-of-Paris cylindrical phantoms of rectangular and circular cross sections. It was found that the leading tensile pulse of the reflected longitudinal wave is responsible for the initiation of microcracks in regions inside the phantom where high tensile stresses are produced. In addition, the transmitted shear wave was found to play a critical role in facilitating the extension and propagation of the microcrack.

High-Energy Shock Waves↗
PubMed2000

Improvement of stone fragmentation during shock-wave lithotripsy using a combined EH/PEAA shock-wave generator-in vitro experiments.

To control the collapse of cavitation bubbles induced during shock-wave lithotripsy (SWL), a piezoelectric annular array (PEAA) shock-wave generator was fabricated and combined with an experimental electrohydraulic (EH) shock-wave lithotripter with a truncated HM-3 reflector. The PEAA generator consists of eight individual transducers of 200-kHz resonant frequency. At a discharge voltage of 15 kV, the PEAA generator produces a shock wave with a peak positive pressure of 8.2 MPa, a positive half cycle duration of 2.9 micros, and a -6-dB beam width of 5 mm. The trigger of the PEAA generator was controlled via fiberoptic link with reference to the spark discharge of the EH generator. Hence, the PEAA-generated shock wave could be used to interact with cavitation bubbles induced by the EH source at various stages of their oscillation. The duration of bubble oscillation during SWL was monitored by a 2.25-MHz focused hydrophone, and this information was used to control the release timing of the PEAA generator. Stone fragmentation tests in vitro were carried out, and demonstrated that stone comminution could be significantly enhanced when the shock wave-bubble interaction occurred during the collapsing phase of the bubbles. A maximum increment of 60% to 80% in stone fragmentation was achieved when the PEAA-generated shock wave arrives near the collapse of the bubbles. Under these conditions, much intensified collapse of the bubbles near the surface of the stone, with strong secondary shock-wave emission and increased stress concentration at the impact site of the solid boundary, was observed using high-speed shadowgraph and photoelastic imaging.

Calculi↗
PubMed2000

Lipopolysaccharide effects on neuronal activity in rat basal forebrain and hypothalamus during sleep and waking.

Peripheral administration of lipopolysaccharide (LPS) is associated with alterations in sleep and the electroencephalogram. To evaluate potential neuronal mechanisms for the somnogenic effects of LPS administration, we used unanesthetized rats to survey the firing patterns of neurons in various regions of rat basal forebrain (BF) and hypothalamus during spontaneous sleep and waking and during the epochs of sleep and waking that occurred after the intraperitoneal administration of LPS. In the brain regions studied, LPS administration was associated with altered firing rates in 39% of the neurons examined. A larger proportion of LPS-responsive units showed vigilance-related alterations in firing rates compared with nonresponsive units. Approximately equal proportions of LPS-responsive neurons showed increased and decreased firing rates after LPS administration, with some units in the lateral preoptic area of the hypothalamus showing particularly robust increases. These findings are consistent with other studies showing vigilance-related changes in neuronal activity in various regions of BF and hypothalamus and further demonstrate that peripheral LPS administration alters neuronal firing rates in these structures during both sleep and waking.

Animals↗
PubMed1999

Analysis of the roles of 14-3-3 in the platelet glycoprotein Ib-IX-mediated activation of integrin alpha(IIb)beta(3) using a reconstituted mammalian cell expression model.

We have reconstituted the platelet glycoprotein (GP) Ib-IX-mediated activation of the integrin alpha(IIb)beta(3) in a recombinant DNA expression model, and show that 14-3-3 is important in GPIb-IX signaling. CHO cells expressing alpha(IIb)beta(3) adhere poorly to vWF. Cells expressing GPIb-IX adhere to vWF in the presence of botrocetin but spread poorly. Cells coexpressing integrin alpha(IIb)beta(3) and GPIb-IX adhere and spread on vWF, which is inhibited by RGDS peptides and antibodies against alpha(IIb)beta(3). vWF binding to GPIb-IX also activates soluble fibrinogen binding to alpha(IIb)beta(3) indicating that GPIb-IX mediates a cellular signal leading to alpha(IIb)beta(3) activation. Deletion of the 14-3-3-binding site in GPIbalpha inhibited GPIb-IX-mediated fibrinogen binding to alpha(IIb)beta(3) and cell spreading on vWF. Thus, 14-3-3 binding to GPIb-IX is important in GPIb-IX signaling. Expression of a dominant negative 14-3-3 mutant inhibited cell spreading on vWF, suggesting an important role for 14-3-3. Deleting both the 14-3-3 and filamin-binding sites of GPIbalpha induced an endogenous integrin-dependent cell spreading on vWF without requiring alpha(IIb)beta(3), but inhibited vWF-induced fibrinogen binding to alpha(IIb)beta(3). Thus, while different activation mechanisms may be responsible for vWF interaction with different integrins, GPIb-IX-mediated activation of alpha(IIb)beta(3) requires 14-3-3 interaction with GPIbalpha.

14-3-3 Proteins↗
PubMed1999

Recent developments in SWL physics research.

Two projects in our laboratory highlight some recent developments in shockwave lithotripsy (SWL) physics research. In the first project, we developed a prototype of a piezoelectric annular array (PEAA) shockwave generator that can be retrofitted on a Dornier HM-3 lithotripter for active control of cavitation during SWL. The PEAA generator, operating at 15 kV, produces a peak positive pressure of approximately 8 MPa with a -6-dB beam diameter of 5 mm. The shockwave generated by the PEAA was used to control and force the collapse of cavitation bubbles induced by a laboratory electrohydraulic shockwave lithotripter with a truncated HM-3 reflector. With optimal time delay between the lithotripter pulse and the PEAA-generated shockwave, the collapse of cavitation bubbles near the stone surface could be intensified, and the resultant stone fragmentation in vitro could be significantly improved. In the second project, high-speed shadowgraph imaging was used to visualize the dynamics of lithotripter-induced bubble oscillation in a vascular phantom. Compared with the free bubble oscillation in water, the expansion of cavitation bubble(s) produced in silicone tubes and a 200-microm cellulose hollow fiber by either a Nortech EHL or a Dornier XL-1 lithotripter was found to be significantly constrained. Rupture of the cellulose hollow fiber was observed consistently after about 20 shocks from the XL-1 lithotripter at an output voltage of 20 kV. These results confirm experimentally that SWL-induced cavitation in vivo can be significantly constrained by the surrounding tissue, and large intraluminal bubble expansions could cause rupture of capillaries and small blood vessels.

Humans↗
PubMed1999

Shock wave-inertial microbubble interaction: methodology, physical characterization, and bioeffect study.

A method of generating in situ shock wave-inertial microbubble interaction by a modified electrohydraulic shock wave lithotripter is proposed and tested in vitro. An annular brass ellipsoidal reflector (thickness = 28 mm) that can be mounted on the aperture rim of a Dornier XL-1 lithotripter was designed and fabricated. This ring reflector shares the same foci with the XL-1 reflector, but is 15 mm short in major axis. Thus, a small portion of the spherical shock wave, generated by a spark discharge at the first focus (F1) of the reflector, is reflected and diffracted by the ring reflector, producing a weak shock wave approximately 8.5 microseconds in front of the lithotripter pulse. Based on the configuration of the ring reflector (different combinations of six identical segments), the peak negative pressure of the preceding weak shock wave at the second focus (F2) can be adjusted from -0.96 to -1.91 MPa, at an output voltage of 25 kV. The preceding shock wave induces inertial microbubbles, most of which expand to a maximum size of 100-200 microns, with a few expanding up to 400 microns before being collapsed in situ by the ensuing lithotripter pulse. Physical characterizations utilizing polyvinylidene difluoride (PVDF) membrane hydrophone, high-speed shadowgraph imaging, and passive cavitation detection have shown strong secondary shock wave emission immediately following the propagating lithotripter shock front, and microjet formation along the wave propagation direction. Using the modified reflector, injury to mouse lymphoid cells is significantly increased at high exposure (up to 50% with shock number > 100). With optimal pulse combination, the maximum efficiency of shock wave-induced membrane permeabilization can be enhanced substantially (up to 91%), achieved at a low exposure of 50 shocks. These results suggest that shock wave-inertial microbubble interaction may be used selectively to either enhance the efficiency of shock wave-mediated macromolecule delivery at low exposure or tissue destruction at high exposure.

Acoustics↗
PubMed1999

Morbidity and mortality attributable to alcohol, tobacco, and illicit drug use in Canada.

OBJECTIVES: This study estimated morbidity and mortality attributable to substance abuse in Canada. METHODS: Pooled estimates of relative risk were used to calculate etiologic fractions by age, gender, and province for 91 causes of disease or death attributable to alcohol, tobacco, or illicit drugs. RESULTS: There were 33,498 deaths and 208,095 hospitalizations attributed to tobacco, 6701 deaths and 86,076 hospitalizations due to alcohol, and 732 deaths and 7095 hospitalizations due to illicit drugs in 1992. CONCLUSIONS: Substance abuse exacts a considerable toll on Canadian society in terms of morbidity and mortality, accounting for 21% of deaths, 23% of years of potential life lost, and 8% of hospitalizations.

Adult↗
PubMed1999

Studies on biosensor to determine diacetyl.

We studied the purification of diacetyl reductase, the preparation of a biosensor, and its performance. With diacetyl reductase and reduced coenzyme I (NADH) co-immobilized as working membrane, NAD+/NADH produced in the course of diacetyl reduction was connected with Fe2+/Fe to build a biosensor. The biosensor could be used to determine diacetyl concentration within the range from 0.1 microgram/mL to 0.5 microgram/mL and the response time was less than two minutes, and its performance was stable within 9 days. The experiments showed that typical metal ions and organics in nominal concentration did not affect the performance of the biosensor, meanwhile, the interference of dissolved oxygen on the performance of biosensor and regeneration of coenzyme I (NADH) were solved to some extent.

Acetoin Dehydrogenase↗
PubMed1997

High resolution multichannel fluorescence detection for capillary electrophoresis. Application to multicomponent analysis.

A wavelength-resolved fluorescence detector for laser-induced fluorescence detection in capillary electrophoresis (CE) is described that uses a charge injection device (CID) array detector Post-column fluorescence detection occurs using a sheath flow cell. The limit of detection for fluorescein is 4.8 x 10(-11) M (29,000 molecules), the spectral resolution is 0.56 nm/pixel, and the spectrograph/CID monitors a 250 nm spectrum throughout the 250-875 nm range. Custom array readout, data manipulation and data processing methods are described to convert wavelength/spatial CID images into electropherograms. The application of the system to characterizing bilirubins in human serum is described, demonstrating the ability to match electrophoretic peaks to standards using spectral information.

Bilirubin↗
PubMed1997

Simple sheath flow reactor for post-column fluorescence derivatization in capillary electrophoresis.

A system for post-column fluorescence derivatization in capillary electrophoresis is described. The post-column reactor uses a sheath flow detection cell where the reagents, o-phthaldialdehyde and beta-mercaptoethanol, are added to the sheath buffer and mix by diffusion with the analytes effusing from the separation capillary. Reaction progress is monitored and optimized by imaging a large portion of the sheath flow cuvette using an extended UV source and a CCD camera. Significantly, this design provides the ability to switch between the analysis of pre- and post-column derivatized amino acids and peptides easily and without sacrificing system performance. The lack of turbulent flow in this system minimizes post-separation band broadening. The limit of detection for glycine is 9.4 x 10(-8) M (110 amol) with a separation efficiency of 190,000 theoretical plates, without stacking. The performance of the system for a series of amino acids was evaluated using post-column and pre-capillary derivatization.

Amino Acids↗
PubMed1996

Direct and reversible inhibition of platelet factor 4 on megakaryocyte development from CD34+ cord blood cells: comparative studies with transforming growth factor beta1.

Mechanisms of the action of platelet factor 4 (PF4) on the growth of megakaryocyte (MK) progenitor cells in CD34+ cord blood (CB) cells were studied in comparison with transforming growth factor beta1 (TGFbeta1). Development of MK from CD34+ CB cells in both plasma clot culture and liquid culture was significantly inhibited by either purified human PF4 and by recombinant human TGFbeta1. Inhibition of MK colony formation by PF4 was reversible because CD34+ cells preincubated with PF4 could regenerate colonies after washing and replating into secondary cultures. In contrast, TGFbeta1-preincubated CD34+ cells gave rise to few colonies following replating. Moreover, incubation of CD34+ cells with PF4 in liquid culture caused the increased number of both stem cell factor (SCF)-binding cells and CD34 antigen-bearing cells. In addition, PF4-preincubated CD34+ cells exhibited a higher potential in MK colony formation in the presence of 5-fluorouracil (5FU). These results demonstrate that both PF4 and TGFbeta1 inhibit MK development from CD34+ CB cells by different mechanisms, and suggest that PF4, unlike TGFbeta1, exerts its inhibitory effect on the growth of the target cells in a reversible manner which results in a preservation of a more immature and 5FU-resistant cell population.

Antigens, CD34↗
PubMed1995

Differential effects of recombinant human interleukin-13 on the in vitro growth of human haemopoietic progenitor cells.

Effects of recombinant human interleukin (IL)-13 on in vitro haemopoiesis from non-adherent mononuclear cells (NAMC) or highly enriched CD34+ cells of human cord blood (CB) were studied. IL-13 significantly increased megakaryocyte (MK) colony formation from either NAMC or CD34+ cells cultured in a plasma clot system supplemented with aplastic anaemia serum (AAS) and phytohaemagglutinin-stimulated human peripheral blood leucocyte-conditioned medium (PHA-LCM) in a dose-dependent manner. Experiments using a modified plasma clot culture, in which normal AB serum and various cytokines were added to replace AAS and PHA-LCM, demonstrated an increased MK colony number in the presence of IL-13, especially in combination with IL-3. However, IL-13 had no stimulatory effect, but rather a slight inhibitory effect in some cases on granulocyte-macrophage (GM) colony formation in both plasma clot cultures. Furthermore, the growth of GM progenitor cells in a methylcellulose culture system in the presence of IL-3, GM-CSF, Epo, G-CSF or in combination was significantly inhibited by the addition of IL-13. On the other hand, high concentrations (100 ng/ml) of IL-13 were needed to cause a slight inhibition on the growth of BFU-E-derived colonies under the same methylcellulose culture. These results indicate that IL-13, alone and synergistically with the effect of IL-3, promotes MK colony formation, but it inhibits the growth of GM and erythroid progenitor cells in vitro.

Cells, Cultured↗
PubMed1995

[ACh and ATP induced calcium mobilization in outer hair cells of the guinea pig cochlea: confocal microscopy].

Effects of acetylcholine (ACh) and ATP as the candidates of efferent neurotransmitter on intracellular Ca2+ concentrations ( [Ca2+]i) of the isolated outer hair cells (OHCs) from guinea pig cochlea were studied with laser scanning confocal microscope. The OHCs were loaded with Ca2+ sensitive dye Fluo-3, whose fluorescent intensity was strongest at the basal end in resting OHC. The presence of ACh gradually increased [Ca2+]i to a higher level at the basal end of OHCs. Continuous application of ATP caused a rapid [Ca2+]i increase followed by a gradual exhaustion throughout the whole OHC. Magnitude of the increase at the apex was greater than that at the base. In OHCs whose calcium had been exhausted by ATP, ACh induced a temporary increase in [Ca2+]i. It seems likely that the ACh-induced [Ca2+]i rise is partly due to an influx of extracellular Ca2+. The bursting nature of ATP-induced [Ca2+]i rise may be a consequence of Ca2+ influx through the ATP-gated cation channels and of the mobilization of intracellular store mediated by ATP.

Acetylcholine↗
PubMed1995

[Confocal images of cochlear outer hair cells in the guinea pigs].

The effects of ACh, ATP and high K+ on intracellular calcium concentration Ca2+ in outer hair cells (OHC) of the guinea pig cochleae were observed with the use of Ca2+ sensitive dye Fluo-3 and laser scanning confocal microscope. Ca2+ increase induced by these chemicals had individual temporal and spatial features. Moreover, high K+ solutions induced contraction and bending of OHC too. Taking advantage of the "optical sectioning" facility of confocal microscopy, morphography of Fluorescein-labelled living OHC and PI-dyed nuclei was reconstructed three-dimensionally. The application of confocal microscopy in OHC physiological and morphological research was discussed.

Animals↗
PubMed1995

[Platelet factor 4, reversible inhibitor of megakaryocytogenesis, protector of megakaryocytes during chemotherapy].

Development of megakaryocyte (MK) from CD34+ cord blood (CB) cells in both plasma clot culture and liquid culture was significantly inhibited by human platelet factor 4 (PF4) and human transforming growth factor beta 1 (TGF beta 1). Inhibition of cell growth by PF4 was reversible judging from the fact that the CD34+ cells preincubated with PF4 could regenerate colonies after washing and replating into the cultures. By contrast, TGF beta 1-pretreated CD34+ cells gave rise to few colonies following replating. Moreover, incubation of CD34+ cells with PF4 in liquid culture caused an increase in the number of both stem cell factor (SCF)-binding cells and CD34 antigen-bearing cells, and exhibited greater capacity to form MK colonies than control after the treatment of 5-FU. In vivo in mice, twice injections of PF4 at 40 micrograms/kg resulted in a significant increase in the number of colony-forming cells with high proliferative potential (HPP-CFC) and colony-forming unit-megakaryocyte (CFU-MK) in bone marrow. In exponentially growing human erythroleukemia cells (HEL), the addition of PF4 prolonged cell cycle progression and therefore resulted in an increased cell population in S phase, as determined by flow cytometric analysis. Different from PF4, TGF beta 1 blocked more cells in G1 phase. These results demonstrate that PF4 and TGF beta 1 inhibit MK development from CD34+ CB cells by different mechanisms and suggest that PF4, unlike TGF beta 1, exerts its inhibitory effect on cell growth in a reversible and S phase-specific manner by which it protects stem cells and MK progenitor cells from 5-FU cytotoxicity.

Animals↗