Biomedical subjects

Y Chen

Publications and source records attributed to Y Chen.

At least 523 records · Page 29Linked to original sources

PubMed2001

Extracellular matrix protein 1 (ECM1) has angiogenic properties and is expressed by breast tumor cells.

Tumor growth and metastasis are critically dependent on the formation of new blood vessels. The present study found that extracellular matrix protein 1 (ECM1), a newly described secretory glycoprotein, promotes angiogenesis. This was initially suggested by in situ hybridization studies of mouse embryos indicating that the ECM1 message was associated with blood vessels and its expression pattern was similar to that of flk-1, a recognized marker for endothelium. More direct evidence for the role of ECM1 in angiogenesis was provided by the fact that highly purified recombinant ECM1 stimulated the proliferation of cultured endothelial cells and promoted blood vessel formation in the chorioallantoic membrane of chicken embryos. Immunohistochemical staining with specific antibodies indicated that ECM1 was expressed by the human breast cancer cell lines MDA-435 and LCC15, both of which are highly tumorigenic. In addition, staining of tissue sections from patients with breast cancer revealed that ECM1 was present in a significant proportion of primary and secondary tumors. Collectively, the results of this study suggest that ECM1 possesses angiogenic properties that may promote tumor progression.

Angiogenesis Inducing Agents↗

PubMed2001

Schedule-dependent pulsed paclitaxel radiosensitization for thoracic malignancy.

The objective of this study was to apply preclinical research of paclitaxel radiosensitization to the treatment of thoracic malignancy. Human lung cancer cell line NCI520 and epidermoid cell line A431 were investigated in vitro for radiosensitizing effects of paclitaxel. Optimal schedule of paclitaxel treatment was applied to a clinical protocol as well as off-protocol treatment of thoracic malignancy. Pulsed paclitaxel with concurrent once-daily radiation was delivered every 48 hours during the week using doses of 15 mg/m2, 20 mg/m2, or 25 mg/m2 in a phase I clinical trial of dose escalation. Preclinical data support the finding that low-dose paclitaxel is sufficient for radiosensitization. Data also support that delaying radiation is better than immediate radiation after drug treatment. Twenty-three patients have enrolled in the phase I clinical trial. Seventeen patients completed treatment (6 at 15 mg/m2; 5 at 20 mg/m2; and 6 at 25 mg/m2). Mean tumor shrinkage at 4 to 6 weeks after therapy was 82%, 84%, and 84% for dose levels I, II, and III, respectively [average primary tumor shrinkage was 83% +/- 8% (95% C.I.)]. Locoregional tumor response rate was 100% [12% (2/17) complete response and 88% (15/17) partial response] with low rates of toxicity. It is concluded that pulsed low-dose paclitaxel and radiation is a very effective and well-tolerated regimen for thoracic malignancy.

Adult↗

PubMed2001

The protective effect of ceramide in immature rat brain hypoxia-ischemia involves up-regulation of bcl-2 and reduction of TUNEL-positive cells.

Preconditioning brain with tumor necrosis factor alpha (TNF-alpha) can induce tolerance to experimental hypoxia and stroke and ceramide is a downstream messenger in the TNF-alpha signaling pathway. A hypoxic-ischemic (HI) insult in the immature rat injures brain primarily through apoptosis. Apoptosis is regulated by Bcl-2 family proteins. The authors explored whether ceramide protects against HI in the immature rat, and whether Bcl-2 family protein expression is involved. Hypoxia-ischemia was produced in seven-day-old rats by ligating the right carotid artery, followed by 2 hours of 8% oxygen exposure. Thirty minutes after HI, C2-ceramide (150 microg/kg) was injected intraventricularly. Infarct volume was measured 5 days later. C2-ceramide reduced HI-induced brain damage by 45% to 65% compared with HI/dimethyl sulfoxide (DMSO) (vehicle control) or HI only groups. In separate experiments, brains of sham-operated control and HI only animals and animals subjected to HI plus C2-ceramide or DMSO infusion were sampled 6 hours, 24 hours, and 5 days after treatments and analyzed for Bcl-2, Bcl-xl, and Bax expression (Western blotting), and apoptosis (TUNEL assay). Augmented Bcl-2 and Bcl-xl levels in the C2-ceramide treated group were associated with a significant decrease in TUNEL-positive cells. The results support a protective role for ceramide in neonatal HI.

Animals↗

PubMed2001

Cell permeable exogenous ceramide reduces infarct size in spontaneously hypertensive rats supporting in vitro studies that have implicated ceramide in induction of tolerance to ischemia.

Previous work in primary cell culture has shown that TNF-alpha and ceramide are involved in the signaling that induces tolerance to brain ischemia (Ginis et al., 1999; Liu et al., 2000). To validate the in vitro studies, the authors administered cell permeable analogs of ceramides intracisternally or intravenously to examine their effect on neuroprotection after focal cerebral ischemia. Permanent middle cerebral artery occlusion (MCAO) was performed in spontaneously hypertensive rats. Infarct volumes were assessed at 24 hours after surgery. D-erythro-N-acetylsphingosine (C2-ceramide) or its vehicle was infused intracisternally for 1 hour before MCAO. In a second set of studies, D-erythro-N-octanoylsphingosine (C8-ceramide) or its vehicle was injected intravenously 48 or 24 hours before MCAO to mimic preconditioning (PC) and was also injected 5 minutes after MCAO. C2-ceramide infusion significantly reduced infarct volumes by approximately 14% (P < 0.05). C8-ceramide injection reduced infarct volumes approximately 17% compared with controls. This effect was constant and significant compared with controls over the time periods examined (P < 0.01). This work supports findings in primary brain cell cultures that implicate ceramide as a downstream signal that is proximate to development of tolerance to brain ischemia. Because the degree of protection represents approximately 50% of the maximal infarct reduction observed in this model, there are probably additional signaling pathways that subserve tolerance.

Animals↗

PubMed2001

Intra-hepatic expression of scavenger receptor and CD14 and their relationship with local inflammatory responses in endotoxemia in mice.

Our objective was to investigate the expression of scavenger receptor (SR) and CD14 in the liver and their relationship with local anti-inflammatory and proinflammatory responses in endotoxemia in order to uncover the mechanism for the liver to turn into effector organ from defense one at the level of cell receptors in sepsis. Mouse models of endotoxemia of different severity were reproduced by injection of different doses of lipopolysaccharide (LPS) via tail vein. Expression of SR and CD14 in the liver was assayed by immunohistochemistry and was then analyzed with an image analysis system. The levels of TNFalpha, IL-6, IL-4, and IL-10 in liver tissue were determined with ELISA. Expression of SR in the liver in the high-dose group was markedly decreased 1 h after injection of LPS, and also in low- and medium-dose groups at 3 h. The expression of SR in the liver in the three groups was shown to be progressively decreased with the time prolonged. There was significant difference in average optical density (OD) values of SR among the three groups. The expression of CD14 in the liver in the three groups was shown to be significantly increased 1 h after injection of LPS, and much more with the time prolonged. But there was no significant difference in OD values of CD14 among the three groups. The contents of intrahepatic proinflammatory mediators TNFalpha and IL-6 and anti-inflammatory mediators IL-4 and IL-10 were successively significantly increased after injection of LPS. The release of anti-inflammatory mediators was shown to be later than that of proinflammatory mediators. Correlation analysis indicated that there was negative correlation between expression of SR and CD14, and that changes of TNFalpha, IL-6, IL-4, and IL-10 levels in liver tissues were correlated significantly positively with OD values of CD14 and negatively with OD values of SR. Expression of SR in the liver was shown to be progressively decreased, and that of CD14 increased in endotoxemia, which was closely related to the uncontrolled inflammatory response in liver. This might be an important mechanism for the liver to turn into effector organ from defense one in sepsis.

Animals↗

PubMed2001

Validation of a new algorithm for the BPM-100 electronic oscillometric office blood pressure monitor.

BACKGROUND: To test the accuracy of a new algorithm for the BPM-100, an automated oscillometric blood pressure (BP) monitor, using stored data from an independently conducted validation trial comparing the BPM-100(Beta) with a mercury sphygmomanometer. DESIGN: Raw pulse wave and cuff pressure data were stored electronically using embedded software in the BPM-100(Beta), during the validation trial. The 391 sets of measurements were separated objectively into two subsets. A subset of 136 measurements was used to develop a new algorithm to enhance the accuracy of the device when reading higher systolic pressures. The larger subset of 255 measurements (three readings for 85 subjects) was used as test data to validate the accuracy of the new algorithm. METHODS: Differences between the new algorithm BPM-100 and the reference (mean of two observers) were determined and expressed as the mean difference +/- SD, plus the percentage of measurements within 5, 10, and 15 mmHg. RESULTS: The mean difference between the BPM-100 and reference systolic BP was -0.16 +/- 5.13 mmHg, with 73.7% < or = 5 mmHg, 94.9% < or = 10 mmHg and 98.8% < or = 15 mmHg. The mean difference between the BPM-100 and reference diastolic BP was -1.41 +/- 4.67 mmHg, with 78.4% < or = 5 mmHg, 92.5% < or = 10 mmHg, and 99.2% < or = 15 mmHg. These data improve upon that of the BPM-100(Beta) and pass the AAMI standard, and 'A' grade BHS protocol. CONCLUSION: This study illustrates a new method for developing and testing a change in an algorithm for an oscillometric BP monitor utilizing collected and stored electronic data and demonstrates that the new algorithm meets the AAMI standard and BHS protocol.

Adolescent↗

PubMed2001

A SNP resource for human chromosome 22: extracting dense clusters of SNPs from the genomic sequence.

The recent publication of the complete sequence of human chromosome 22 provides a platform from which to investigate genomic sequence variation. We report the identification and characterization of 12,267 potential variants (SNPs and other small insertions/deletions) of human chromosome 22, discovered in the overlaps of 460 clones used for the chromosome sequencing. We found, on average, 1 potential variant every 1.07 kb and approximately 18% of the potential variants involve insertions/deletions. The SNPs have been positioned both relative to each other, and to genes, predicted genes, repeat sequences, other genetic markers, and the 2730 SNPs previously identified on the chromosome. A subset of the SNPs were verified experimentally using either PCR-RFLP or genomic Invader assays. These experiments confirmed 92% of the potential variants in a panel of 92 individuals. [Details of the SNPs and RFLP assays can be found at http://www.sanger.ac.uk and in dbSNP.]

Base Composition↗

PubMed2001

Iris bulbs express type 1 and type 2 ribosome-inactivating proteins with unusual properties.

Two closely related lectins from bulbs of the Dutch iris (Iris hollandica var. Professor Blaauw) have been isolated and cloned. Both lectins, called Iris agglutinin b and Iris agglutinin r, possess N-glycosidase activity and share a high sequence similarity with previously described type 2 ribosome-inactivating proteins (RIP). However, these lectins show only 57% to 59% sequence identity to a previously characterized type 1 RIP from iris, called IRIP. The identification of the iris lectins as type 2 RIP provides unequivocal evidence for the simultaneous occurrence of type 1 and type 2 RIP in iris bulbs and allowed a detailed comparison of type 1 and type 2 RIP from a single plant, which provides further insight into the molecular evolution of RIP. Binding studies and docking experiments revealed that the lectins exhibit binding activity not only toward Gal/N-acetylgalactosamine, but also toward mannose, demonstrating for the first time that RIP-binding sites can accommodate mannose.

Amino Acid Sequence↗

PubMed2001

Tag surface reconstruction and tracking of myocardial beads from SPAMM-MRI with parametric B-spline surfaces.

Magnetic resonance imaging (MRI) is unique in its ability to noninvasively and selectively alter tissue magnetization, and create tag planes intersecting image slices. The resulting grid of signal voids allows for tracking deformations of tissues in otherwise homogeneous-signal myocardial regions. In this paper, we propose a specific spatial modulation of magnetization (SPAMM) imaging protocol together with efficient techniques for measurement of three-dimensional (3-D) motion of material points of the human heart (referred to as myocardial beads) from images collected with the SPAMM method. The techniques make use of tagged images in orthogonal views by explicitly reconstructing 3-D B-spline surface representation of tag planes (tag planes in two orthogonal orientations intersecting the short-axis (SA) image slices and tag planes in an orientation orthogonal to the short-axis tag planes intersecting long-axis (LA) image slices). The developed methods allow for viewing deformations of 3-D tag surfaces, spatial correspondence of long-axis and short-axis image slice and tag positions, as well as nonrigid movement of myocardial beads as a function of time.

Humans↗

PubMed2001

Fast LV motion estimation using subspace approximation techniques.

Cardiac motion estimation is very important in understanding cardiac dynamics and in noninvasive diagnosis of heart disease. Magnetic resonance (MR) imaging tagging is a technique for measuring heart deformations. In cardiac tagged MR images, a set of dark lines are noninvasively encoded within myocardial tissue providing the means for measurement of deformations of the heart. The points along tag lines measured in different frames and in different directions carry important information for determining the three-dimensional nonrigid movement of left ventricle. However, these measurements are sparse and, therefore, multidimensional interpolation techniques are needed to reconstruct a dense displacement field. In this paper, a novel subspace approximation technique is used to accomplish this task. We formulate the displacement estimation as a variational problem and then project the solution into spline subspaces. Efficient numerical methods are derived by taking advantages of B-spline properties. The proposed technique significantly improves our previous results reported in [3] with respect to computational time. The method is applied to a temporal sequence of two-dimensional images and is validated with simulated and in vivo heart data.

Algorithms↗

PubMed2001

Simulation of field characteristics of the focused axisymmetrically curved surface transducers.

The acoustical fields produced by a variety of focused axisymmetrically curved surface transducers with large aperture have been investigated on the basis of Fresnel-Kirchhoff diffraction theory. The interrelation of ultrasound characteristics with some structural aspects of the transducers has been calculated and compared. The forms of resulting intensity maxima and their resulting suitability for surgical lesion of tissues are compared through parameters such as "lesioning capability" and "focussing efficiency." Although only modest changes in intensity distribution are possible, some may have applications in making lesions for control of focal cancer and other pathologies.

Biomedical Engineering↗

PubMed2001

A study of sentence stress production in Mandarin speakers of American English.

Acoustic characteristics of American English sentence stress produced by native Mandarin speakers are reported. Fundamental frequency (F0), vowel duration, and vowel intensity in the sentence-level stress produced by 40 Mandarin speakers were compared to those of 40 American English speakers. Results obtained from two methods of stress calculation indicated that Mandarin speakers of American English are able to differentiate stressed and unstressed words according to features of F0, duration, and intensity. Although the group of Mandarin speakers were able to signal stress in their sentence productions, the acoustic characteristics of stress were not identical to the American speakers. Mandarin speakers were found to produce stressed words with a significantly higher F0 and shorter duration compared to the American speakers. The groups also differed in production of unstressed words with Mandarin speakers using a higher F0 and greater intensity compared to American speakers. Although the acoustic differences observed may reflect an interference of L1 Mandarin in the production of L2 American English, the outcome of this study suggests no critical divergence between these speakers in the way they implement American English sentence stress.

Adult↗

PubMed2001

Cocaine blocks HERG, but not KvLQT1+minK, potassium channels.

Cocaine causes cardiac arrhythmias, sudden death, and occasionally long QT syndrome in humans. We investigated the effect of cocaine on the human K(+) channels HERG and KvLQT1+minK that encode native rapidly (I(Kr)) and slowly (I(Ks)) activating delayed rectifier K(+) channels in the heart. HERG and KvLQT1+minK channels were heterologously expressed in human embryonic kidney 293 cells, and whole-cell currents were recorded. Cocaine had no effect on KvLQT1+minK current in concentrations up to 200 microM. In contrast, cocaine reversibly blocked HERG current with half-maximal block of peak tail current of 7.2 microM. By using a protocol to quickly activate HERG channels, we found that cocaine block developed rapidly after channel activation. At 0 mV, the time constants for the development of block were 38.2 +/- 2.1, 15.2 +/- 0.8, and 6.9 +/- 1.1 ms in 10, 50 and 200 microM cocaine, respectively. Cocaine-blocked channels also recovered rapidly from block after repolarization. At -100 mV, recovery from block followed a biphasic time course with fast and slow time constants of 3.5 +/- 0.7 and 100.3 +/- 15.4 ms, respectively. Using N-methyl-cocaine, a permanently charged, membrane-impermeable cocaine analog, block of HERG channels rapidly developed when the drug was applied intracellularly through the patch pipette, suggesting that the cocaine binding site on the HERG protein is located on a cytoplasmic accessible domain. These results indicate that cocaine suppresses HERG, but not KvLQT1+minK, channels by preferentially blocking activated channels, that it unblocks upon repolarization, and does so with unique ultrarapid kinetics. Because the cocaine concentration range we studied is achieved in humans, HERG block may provide an additional mechanism for cocaine-induced arrhythmias and sudden death.

Cation Transport Proteins↗

PubMed2001

Enterocin P selectively dissipates the membrane potential of Enterococcus faecium T136.

Enterocin P is a pediocin-like, broad-spectrum bacteriocin which displays a strong inhibitory activity against Listeria monocytogenes. The bacteriocin was purified from the culture supernatant of Enterococcus faecium P13, and its molecular mechanism of action against the sensitive strain E. faecium T136 was evaluated. Although enterocin P caused significant reduction of the membrane potential (DeltaPsi) and the intracellular ATP pool of the indicator organism, the pH gradient (DeltapH) component of the proton motive force (Deltap) was not dissipated. By contrast, enterocin P caused carboxyfluorescein efflux from E. faecium T136-derived liposomes.

Adenosine Triphosphate↗

PubMed2001

Comparison of logistic regression and linear regression in modeling percentage data.

Percentage is widely used to describe different results in food microbiology, e.g., probability of microbial growth, percent inactivated, and percent of positive samples. Four sets of percentage data, percent-growth-positive, germination extent, probability for one cell to grow, and maximum fraction of positive tubes, were obtained from our own experiments and the literature. These data were modeled using linear and logistic regression. Five methods were used to compare the goodness of fit of the two models: percentage of predictions closer to observations, range of the differences (predicted value minus observed value), deviation of the model, linear regression between the observed and predicted values, and bias and accuracy factors. Logistic regression was a better predictor of at least 78% of the observations in all four data sets. In all cases, the deviation of logistic models was much smaller. The linear correlation between observations and logistic predictions was always stronger. Validation (accomplished using part of one data set) also demonstrated that the logistic model was more accurate in predicting new data points. Bias and accuracy factors were found to be less informative when evaluating models developed for percentage data, since neither of these indices can compare predictions at zero. Model simplification for the logistic model was demonstrated with one data set. The simplified model was as powerful in making predictions as the full linear model, and it also gave clearer insight in determining the key experimental factors.

Clostridium botulinum↗

PubMed2001

Evidence that mycobacterial PE_PGRS proteins are cell surface constituents that influence interactions with other cells.

The elucidation of the genomic sequence of Mycobacterium tuberculosis revealed the presence of a novel multigene family designated PE/PE_PGRS that encodes numerous, highly related proteins of unknown function. In this study, we demonstrate that a transposon insertion in a PE_PGRS gene (1818(PE_PGRS)) found in Mycobacterium bovis BCG Pasteur, which is the BCG homologue of the M. tuberculosis H37Rv gene Rv1818c, introduces new phenotypic properties to this BCG strain. These properties include dispersed growth in liquid medium and reduced infection of macrophages. Complementation of the 1818(PE_PGRS)::Tn5367 mutant with the wild-type gene restores both aggregative growth (clumping) in liquid medium and reestablishes infectivity of macrophages to levels equivalent to those for the parent BCG strain. Western blot analysis using antisera raised against the 1818(PE_PGRS) protein shows that PE_PGRS proteins are found in cell lysates of BCG and M. tuberculosis H37Ra and in the cell wall fraction of M. tuberculosis H37Rv. Moreover, immunofluorescent labeling of mycobacteria indicates that certain PE_PGRS proteins are localized at the cell surface of BCG and M. tuberculosis. Together these results suggest that certain PE_PGRS proteins may be found at the surface of mycobacteria and influence both cell surface interactions among mycobacteria as well as the interactions of mycobacteria with macrophages.

Adhesins, Bacterial↗

PubMed2001

Expression of cytokine and chemokine genes by human middle ear epithelial cells induced by formalin-killed Haemophilus influenzae or its lipooligosaccharide htrB and rfaD mutants.

To define the role of nontypeable Haemophilus influenzae (NTHI) lipooligosaccharide (LOS) in the induction of proinflammatory cytokine gene expression during otitis media, we compared the abilities of formalin-killed NTHI strain 2019 and its LOS htrB and rfaD mutants to stimulate human middle ear epithelial (HMEE) cell cytokine and chemokine gene expression and production in vitro. Strain DK-1, an rfaD gene mutant, expresses a truncated LOS consisting of only three deoxy-D-manno-octulosonic acid residues, a single heptose, and lipid A. Strain B29, an isogenic htrB mutant, possesses an altered oligosaccharide core and an altered lipid A. HMEE cells were incubated with formalin-killed NTHI 2019, B29, or DK-1. The supernatants and the cells were collected at 2, 4, 8, and 24 h after stimulation. Expression of genes for the cytokines tumor necrosis factor alpha (TNF-alpha), interleukin lbeta (IL-1beta), and IL-6 and for the chemokines macrophage inflammatory protein 1beta (MIP-1beta), monocyte chemotactic peptide 1 (MCP-1), and IL-8 was quantitated by real-time PCR. NTHI B29 did not significantly stimulate any cytokine or chemokine mRNA expression in HMEE cells. In striking contrast, NTHI 2019 induced up to 105-, 139-, and 187-fold increases in HMEE cell expression of IL-1beta, TNF-alpha, and MIP-1beta, respectively (P < 0.01 [2019 versus B29]). NTHI 2019 also induced upregulation of IL-8, IL-6, and MCP-1 mRNA expression (by 26-, 44-, and 14-fold, respectively [P < 0.05 (2019 versus B29)]). The significant induction of cytokine genes was confirmed by quantitating the secretion of cytokines in culture supernatants with an enzyme-linked immunosorbent assay. There were no significant differences in mRNA expression of IL-8, IL-6, and MCP-1 between the 2019- and DK-1-treated groups. The low levels of gene transcripts observed after incubation of HMEE cells with B29 indicate that products of the disrupted NTHI htrB LOS gene may play a major role in induction of these particular inflammatory mediators.

Adult↗

PubMed2001

Subunit interactions and glutamine utilization by Escherichia coli imidazole glycerol phosphate synthase.

A selection strategy has been developed to identify amino acid residues involved in subunit interactions that coordinate the two half-reactions catalyzed by glutamine amidotransferases. The protein structures known for this class of enzymes have revealed that ammonia is shuttled over long distances and that each amidotransferase evolved different molecular tunnels for this purpose. The heterodimeric Escherichia coli imidazole glycerol phosphate (IGP) synthase was probed to assess if residues in the substrate amination subunit (HisF) are critical for the glutaminase activity in the HisH subunit. The activity of the HisH subunit is dependent upon binding of the nucleotide substrate at the HisF active site. This regulatory function has been exploited as a biochemical selection of mutant HisF subunits that retain full activity with ammonia as a substrate but, when constituted as a holoenzyme with wild-type HisH, impair the glutamine-dependent activity of IGP synthase. The steady-state kinetic constants for these IGP synthases with HisF alleles showed three distinct effects depending upon the site of mutation. For example, mutation of the R5 residue has similar effects on the glutamine-dependent amidotransfer reaction; however, k(cat)/K(m) for the glutaminase half-reaction was increased 10-fold over that for the wild-type enzyme with nucleotide substrate. This site appears essential for coupling of the glutamine hydrolysis and ammonia transfer steps and is the first example of a site remote to the catalytic triad that modulates the process. The results are discussed in the context of recent X-ray crystal structures of glutamine amidotransferases that relate the glutamine binding and acceptor binding sites.

Amino Acid Sequence↗