Biomedical subjects

Y Y Chen

Publications and source records attributed to Y Y Chen.

At least 19 recordsLinked to original sources

PubMed2006

Lattice disorder and size-induced kondo behavior in CeAl2 and CePt(2+x).

When the size of CeAl2 and CePt(2+x) particles is reduced to the nanometer scale, antiferromagnetism is suppressed and Kondo behavior predominates, with the Kondo temperature T(K) either decreasing (CeAl2) or increasing (CePt(2+x)) relative to the bulk. Local structure measurements show that these nanoparticles are significantly distorted. While such distortions should strongly affect magnetic and electronic properties, we find they cannot explain the observed changes in T(K). Other size-induced changes to the electronic structure must, therefore, play a significant role.

Journal Article↗

PubMed2006

Short interfering RNA against the PDCD5 attenuates cell apoptosis and caspase-3 activity induced by Bax overexpression.

The programmed cell death 5 (PDCD5) protein plays an important apoptosis-accelerating role in cells undergoing apoptosis. Decreased expression of PDCD5 has been detected in various human carcinomas. Here we describe that one potent short interfering RNA (siRNA) against the PDCD5 (siPDCD5) specifically inhibits the expression of PDCD5 at both the mRNA and protein level. Cells with decreased PDCD5 expression displayed reduced sensitivity to an apoptotic stimulus induced by Bax overexpression in HeLa, HEK293 and 293T cell lines. Furthermore, we also show that siPDCD5 inhibited both caspase-3 activity and procaspase-3 cleavage. Suppressed expression of PDCD5 attenuates the release of cytochrome c from mitochondria to cytosol induced by Bax overexpression. This phenomenon is accompanied by the reduced translocation of Bax from the cytosol to mitochondria. MTT assay shows that targeted suppression of PDCD5 expression markedly promoted cell proliferation in Hela and HEK293 cell lines. Our data suggests that PDCD5 may exert its effects through pathway of mitochondria by modulating Bax translocation, cytochrome c release and caspase 3 activation directly or indirectly, and that decreased PDCD5 expression may be one of the mechanisms by which tumor cells achieve resistance to apoptotic stimulus induced by anticancer drugs.

Apoptosis↗

PubMed2006

Protein tyrosine phosphatase interacting protein 51 (PTPIP51) is a novel mitochondria protein with an N-terminal mitochondrial targeting sequence and induces apoptosis.

Apoptosis is a genetically determined cell suicide program. Mitochondria play a central role in this process and various molecules have been shown to regulate apoptosis in this organelle. In the present study, we firstly identified that protein tyrosine phosphatase interacting protein 51 (PTPIP51) is a novel mitochondrial protein, which may induce apoptosis in HEK293T and HeLa cell lines. PTPIP51 transfection resulted in the externalization of phosphatidylserine (PS), activation of caspase-3, cleavage of PARP, and condensation of nuclear DNA. Further investigation revealed that PTPIP51 over-expression caused a decrease in mitochondrial membrane potential and release of cytochrome c, suggesting that it may be involved in a mitochondria/cytochrome c mediated apoptosis pathway. We also found that a putative TM domain near the N terminus of PTPIP51 is required for its targeting to mitochondria, as evidenced by the finding that deletion of the PTPIP51 TM domain prevented the protein's mitochondiral localization. Furthermore, this deletion significantly influenced the ability of PTPIP51 to induce apoptosis. Taken together, the results of the present study suggest that PTPIP51 is a mitochondrial protein with apoptosis-inducing function and that the N-terminal TM domain is required for both the correct targeting of the protein to mitochondria and its apoptotic functions.

Amino Acid Sequence↗

PubMed2006

Effect of a periodized exercise training and active recovery program on antitumor activity and development of dendritic cells.

AIM: Dendritic cells (DCs) are potent antigen-presenting cells that promote antitumor immunity in vivo when pulsed with tumor antigen. No studies have indicated that exercise training affects DC function. The purpose of this study was to investigate the effect of a 5-week periodized exercise training and active recovery program on the development of DCs, and to test their effect on the antitumor immunity of mononuclear cells (MNC) from blood and spleen against human leukemic U937 and murine lymphoma Yac-1 cells, respectively. METHODS: Male Fisher 344 rats were divided into 2 groups: exercise and non-exercise group. The training protocol consisted of running on a motor-driven treadmill 6 days a week for consecutive 5 weeks, during which the running time, treadmill speed, and incline gradient were increased weekly. Active recovery parameters were set at 30% of the intensity of the previous day. RESULTS: DC numbers increased significantly (P<0.05) in the exercise group compared to controls, but there were no significant changes in the expression of surface antigens CD80 and CD86. In exercise group MNC-conditioned medium (CM) prepared with 50 microg/mL phytohemagglutinin (PHA) significantly inhibited proliferation of U937 cells, and splenocyte-CM with PHA at 20 and 40 microg/mL significantly inhibited proliferation of YAC-1 cells greater than control group. CONCLUSIONS: The 5-week periodized exercise training with active recovery promotes the number of DCs and enhances the activity of DCs against tumor cells.

Animals↗

PubMed2005

Relativistic electromagnetic ion cyclotron instabilities.

The relativistic instabilities of electromagnetic ion cyclotron waves driven by MeV ions are analytically and numerically studied. As caused by wave magnetic field and in sharp contrast to the electrostatic case, interesting characteristics such as Alfve nic behavior and instability transition are discovered and illuminated in detail. The instabilities are reactive and are raised from the coupling of slow ions' first-order resonance and fast ions' second-order resonance, that is an essential extra mechanism due to relativistic effect. Because of the wave magnetic field, the nonresonant plasma dielectric is usually negative and large, that affects the instability conditions and scaling laws. A negative harmonic cyclotron frequency mismatch between the fast and slow ions is required for driving a cubic (and a coupled quadratic) instability; the cubic (square) root scaling of the peak growth rate makes the relativistic effect more important than classical mechanism, especially for low fast ion density and Lorentz factor being close to unity. For the cubic instability, there is a threshold (ceiling) on the slow ion temperature and density (the external magnetic field and the fast ion energy); the Alfve n velocity is required to be low. This Alfve nic behavior is interesting in physics and important for its applications. The case of fast protons in thermal deuterons is numerically studied and compared with the analytical results. When the slow ion temperature or density (the external magnetic field or the fast ion energy) is increased (reduced) to about twice (half) the threshold (ceiling), the same growth rate peak transits from the cubic instability to the coupled quadratic instability and a different cubic instability branch appears. The instability transition is an interesting new phenomenon for instability.

Journal Article↗

PubMed2005

Multiple signaling pathways regulate FGF-2-induced retinal ganglion cell neurite extension and growth cone guidance.

Growth cones use cues in their environment in order to grow in a directed fashion to their targets. In Xenopus laevis, fibroblast growth factors (FGFs) participate in retinal ganglion cell (RGC) axon guidance in vivo and in vitro. The main intracellular signaling cascades known to act downstream of the FGF receptor include the mitogen-activated protein kinase (MAPK), phospholipase Cgamma (PLCgamma) and phosphotidylinositol 3-kinase (PI3K) pathways. We used pharmacological inhibitors to identify the signaling cascade(s) responsible for FGF-2-stimulated RGC axon extension and chemorepulsion. The MAPK, PI3K and PLCgamma pathways were blocked by U0126, LY249002 and U73122, respectively. D609 was used to test a role for the phosphotidylcholine-PLC (PC-PLC) pathway. We determined that the MAPK and two PLC pathways are required for FGF-2 to stimulate RGC neurite extension in vitro, but the response of axons to FGF-2 applied asymmetrically to the growth cone depended only on the PLC pathways.

Animals↗

PubMed2005

Posterior cranial fossa crowdedness is related to age and sex: an magnetic resonance volumetric study.

PURPOSE: To measure 3-dimensional (3D) posterior cranial fossa (PCF) crowdedness and to evaluate the effect of age, sex, and body height on PCF. MATERIAL AND METHODS: Fifty-two healthy volunteers (24 M and 28 F; mean age 55.4 +/- 17.2 years; range 24-82 years) were recruited. Using a semi-automated magnetic resonance technique, we calculated a PCF crowdedness index (CI) as the ratio of hindbrain (HB) volume to PCF volume x 100% and correlated this index with age, sex, body height, and other crowdedness parameters. RESULTS: The mean PCF CI was 93.7 +/- 2.7%. Women had a more crowded PCF than men (95.0+1.7% versus 92.1 +/- 2.7%; P<0.001). PCF CI declined with age for both men (r = -0.61; P=0.002) and women (r = -0.68; P<0.001). The association with age--but not HB volume was maintained after we controlled for sex and body height. On multiple regression, both age and sex accounted for 57.5% of the PCF CI variance. CONCLUSION: Our study shows that PCF CI is associated with age and sex, and can therefore be used as a surrogate to assess hindbrain atrophy in a cross-sectional sample. Moreover, sex- and age-specific normal ranges may be needed to evaluate the PCF CI in clinical practice.

Adult↗

PubMed2004

Pilot point temperature regulation for thermal lesion control during ultrasound thermal therapy.

The fundamental goal of ultrasound thermal therapy is to provide proper thermal lesion formations for effective tumour treatment. The quality of the therapy depends mostly on its positional precision. To date, most ultrasound thermal therapy treatments have focused on the formation of power or temperature patterns. The non-linear and time-delay effects of thermal dose formation prohibit direct control of the thermal dose distribution. In the paper, the control of thermal lesions by regulation of the temperature of a pilot point is proposed. This scheme utilises the high correlation between temperature elevation and thermal dose at the forward boundary of thermal lesions. To verify the feasibility, a 2D ultrasound phased array system was used to generate thermal lesions of various sizes, and the temperature elevation required to generate a thermal dose threshold was investigated. Results showed that the required temperature elevation was found to be a reasonably constant value of 52.5 degrees C under differing conditions when the focal area was small. When the focal area under consideration was large, the required temperature elevation became a monotonic function of blood perfusion rate, ranging from 49.2 to 52.5 degrees C. When the reference temperature of the pilot point was set at a conservative value (52.5 degrees C), the thermal lesions were controlled precisely under a wide range of blood perfusion and power pattern changes, tested by using a more realistic model that takes into account thermal-induced attenuation and blood perfusion changes. This changed the complex thermal dose control problem into a simple temperature regulation problem, which makes implementation of thermal lesion control easier, giving the scheme a high potential for application to current ultrasound thermal therapy systems.

Humans↗

PubMed2004

Adaptive processing bandwidth adjustment for laser Doppler flowmetry.

A novel laser Doppler flowmetry scheme is reported that adjusts the processing bandwidth adaptively to optimise the estimation of flow. To obtain an adequate processing bandwidth, the Doppler spectra is first fitted to the Lorentzian function, and the bandwidth at half the maximum of the Lorentzian function is used as an indicator of the major frequency range of the signal. The processing bandwidth is then tuned accordingly, and a frequency-weighted algorithm is applied to compute the fluid velocity. To investigate the influence of the processing bandwidth, an in vitro experiment was performed. In the experiment, the flow rate was controlled at constant velocity in the range from 0 to 18.52 mm s(-1), and the fluid velocity indices were calculated using adaptive and fixed processing bandwidths, respectively. The results showed that the adaptive processing bandwidth adjustment, not only significantly reduced the biological zero (9.6% of the case using 100 kHz bandwidth), but also enhanced the sensitivity of the laser Doppler measurement (over 20%) and linearly responded to a wider velocity range (R2 = 0.979 for velocity from 0 to 18.52 mm s(-1)).

Algorithms↗

PubMed2003

Responsiveness, affinity constants and beta 2-adrenoceptor reserves for isoprenaline on portal veins from normo- and pre- and hypertensive rats.

1. This study used contractility methods with the portal veins of 5- and 14-week-old Wistar-Kyoto normotensive rats (WKY) and spontaneously hypertensive rats (SHRs). The SHRs are prehypertensive at 5 weeks. 2. The first part of our study was to determine whether the responsiveness to isoprenaline and forskolin was altered in the maturation of portal veins from normo- and prehypertensive rats. The responses to forskolin were similar on the portal veins of 5- and 14-week-old WKY and SHRs. 3. The sensitivity and maximum responses to isoprenaline were similar on portal veins of 5- and 14-week-old WKY. The sensitivity and maximum responses to isoprenaline were lower on the portal veins of 5-week-old SHRs (pD2 = 8.25, maximum = 85%) than age-matched WKY (pD2 = 8.79, maximum = 96%); these differences are not caused by hypertension. At 14 weeks, the sensitivity was similar (WKY pD2 = 8.74, SHR pD2 = 8.65) but the maximum responses to isoprenaline were lower on the portal veins SHRs (77%) than WKY (97%). Thus, the sensitivity to isoprenaline increases with the development of hypertension in the SHR portal vein. 4. The second part of the study was to determine whether the affinity for isoprenaline at beta2-adrenoceptors and the fractional beta2-adrenoceptor occupancy-response relationships on the portal vein were altered in maturation from normo- and pre-hypertensive rats. The effects of bromoacetylalprenololmenthane (BAAM), an irreversible beta-adrenoceptor blocker, on the isoprenaline responses of 5- and 14-week-old WKY and SHRs were studied. Maturation of the WKY portal vein between 5 and 14 weeks was associated with a loss of affinity for isoprenaline (from pKA of 7.13 to 7.87), and increase in beta2-adrenoceptor reserve (from 72 to 92% at the 95% response). There were similar affinity and reserve findings in the maturation of the SHR portal vein. Thus, there are major changes in beta2-adrenoceptor structure and reserve in maturation on the portal vein that are irrespective of the development of hypertension.

Adrenergic beta-2 Receptor Agonists↗

PubMed2001

Theoretical analysis of acoustic stop bands in two-dimensional periodic scattering arrays.

This paper presents a theoretical analysis of the recently reported observation of acoustic stop bands in two-dimensional scattering arrays [Robertson and Rudy, J. Acoust. Soc. Am. 104, 694 (1998)]. A self-consistent wave scattering theory, incorporating all orders of multiple scattering, is used to obtain the wave transmission. The band structures for the regular arrays of cylinders are computed using the plane-wave expansion method. The theoretical results compare favorably with the experimental data.

Journal Article↗

PubMed2001

Allelic imbalance on chromosome 2q and alterations of the caspase 8 gene in neuroblastoma.

We previously reported a high incidence of loss of heterozygosity (LOH) on chromosome 2q33 in neuroblastoma (NB), observed in various types of human cancers including lung cancer, head and neck cancer and follicular thyroid carcinoma. To better elucidate the role of chromosome 2q aberrations in NB, we examined common allelic imbalance (AI) regions on chromosome 2q in 82 NB patients using 10 polymorphic microsatellite markers. AI on 2q was detected in 26 (32%) of 82 NB cases. There was a distinct common AI region between the D2S115 and D2S307 markers on 2q33. The distance between these markers was about 2.0 cM. Recently, the caspase 8 and caspase 10 genes, both of which encode cystein protease, were mapped to chromosome 2q33. Since the common AI region on 2q33 includes the caspase 8 and caspase 10 genes, the alterations of these genes were examined further. Absent or reduced expression of caspase 8 and caspase 10 were found in 19 (70%) of 27 and two (7%) of 27 NB cell lines by reverse transcription-polymerase chain reaction, respectively. A missense mutation was detected at codon 96, GCT (Alanine) to GTT (Valine), of the caspase 8 gene in one of the NB cell lines lacking caspase 8 expression. Thirteen (68%) of 19 cell lines lacking caspase 8 expression displayed methylation of the CpG island of the caspase 8 gene, whereas only one (13%) of eight cell lines with caspase 8 expression showed caspase 8 methylation (P=0.031). Furthermore, there was a significant association between AI at 2q33 and loss of caspase 8 expression (P=0.026). These results indicated that there was a tumor suppressor gene in the common AI region on chromosome 2q33 involved in the pathogenesis of a subset of NB. It is possible that the caspase 8 gene is one of the candidate tumor suppressor genes for NB and inactivation of this gene plays an important role in the tumorigenesis of NB through mainly its methylation.

Allelic Imbalance↗

PubMed2001

X-ray absorption studies of carbon-related materials.

X-ray absorption near-edge structure (XANES) measurements have been performed on nitrogen-doped diamond films with three different dopant concentrations and iron-layer-stabilized carbon nanotube (CNT) structures with various diameters at the C K-absorption edge using the sample drain current mode. The C K-edge XANES spectra of these N-doped diamond films resemble that of the undoped diamond regardless of the dopant concentration, which suggest that the overall bonding configuration of the C atom is unaltered. N dopants are found to reduce the intensities of both the sp2- and sp3-bond-derived resonance features in the XANES spectra. On the other hand, the C K-edge XANES spectra of CNTs indicate that the intensities of the pi* and sigma* bands and the interlayer-state features vary with the diameter of the CNT. This phenomenon may be caused by the Fe-layer-catalysed bending of the graphite sheet and the interaction between C and Fe atoms.

Journal Article↗

PubMed2001

No significant association of Epstein-Barr virus infection with invasive breast carcinoma.

We studied 48 cases of invasive breast carcinoma for evidence of Epstein-Barr virus (EBV), which is associated with many human malignancies. In situ hybridization studies to detect the presence of EBV-encoded small nonpolyadenylated RNA (EBER)-1 were performed in paraffin sections. Immunohistochemical studies to detect EBV nuclear antigen (EBNA)-1, latent membrane protein (LMP)-1, and the transactivating immediate-early BZLF1 (ZEBRA) protein were also performed in paraffin sections. The presence of EBV genomic DNA was studied by polymerase chain reaction (PCR) amplification using sets of primers flanking the EBNA-4 and the EBV-LMP-1 genes in frozen tissues. Southern blot analysis using a probe flanking the EBV terminal repeat region was then attempted in cases that were PCR-positive. Five of 48 cases (10%) of breast carcinoma showed focal EBER-positive tumor cells. Twelve cases (25%) were positive for EBNA-1 by immunohistochemistry, all but one different from the EBER-positive cases. None of the cases were positive for LMP-1 or ZEBRA protein by immunohistochemistry. PCR studies for EBNA-4 and LMP-1 were each positive in five cases (including three cases in common). However, Southern blot studies successfully performed in all but one of the PCR-positive cases were completely negative. The identification of EBV by any methodology was not correlated with tumor size, grade, or lymph node status. This study demonstrated evidence of EBV infection in tissues involved by invasive breast carcinomas in a significant subset of cases. However, the lack of localization of EBV infection to a significant population of the tumor cells in any case, the negativity by Southern blot hybridization, and the lack of expression of multiple antigens in any case strongly argue against a significant role for EBV in the pathogenesis of breast carcinoma.

Adaptor Proteins, Signal Transducing↗

PubMed2001

No direct role for Epstein-Barr virus in American hepatocellular carcinoma.

Epstein-Barr virus (EBV) was recently linked to hepatocellular carcinogenesis in Japanese patients. It is not clear whether EBV infection is also associated with hepatocellular carcinoma (HCC) occurring in American patients. We studied 41 cases of HCC from the Los Angeles area for evidence of EBV infection by in situ hybridization, immunohistochemistry, and polymerase chain reaction methods. Of 41 cases, 16 were seropositive for hepatitis B virus surface antigen (39%), 9 of 29 tested were seropositive for hepatitis C virus antibody (31%); in total, 22 cases were seropositive for hepatitis B virus and/or hepatitis C virus (53%). Of 41 cases, 1 was positive for EBV-encoded small nonpolyadenylated RNA (EBER)-1 (2%) by in situ hybridization. By immunohistochemistry, two cases were positive for EBV nuclear antigen (EBNA)-1 (5%), one was positive for the transactivating immediate early BZLF1 (ZEBRA) (2%), and none was positive for latent membrane protein-1. None of the 41 cases was positive for latent membrane protein-1 and EBV nuclear antigen (EBNA)-4 DNAs by polymerase chain reaction assay. All four positive cases showed rare EBER-1-, ZEBRA-, or EBNA-1- positive cells (<0.1%); in none of these cases was there expression of any other EBV viral genes. In the one case each that was positive for EBER-1 and ZEBRA, both of which occurred in patients of non-Asian ethnicity, the staining was limited to infiltrating small lymphocytes, and tumor cells were negative. In the two cases that were positive for EBNA-1, both of which occurred in patients of Asian ethnicity, the staining was limited to tumor cells, and infiltrating small lymphocytes were negative. Our study indicates that rare cases of American HCC may contain EBV-infected cells, but it is unlikely that EBV plays a major role in the carcinogenesis of HCC.

Adolescent↗

PubMed2001

Ocular manifestations of tuberculosis.

OBJECTIVE: To present the clinical and histopathologic findings in five cases of tuberculosis (TB) with various ocular manifestations. DESIGN: Observational case series. METHODS: Retrospective review of clinical findings, course, and treatment of five patients. Diagnostic techniques, including biomicroscopic, histopathologic, and molecular biologic test results, are presented. MAIN OUTCOME MEASURES: Visual acuity, slit-lamp biomicroscopy, indirect ophthalmoscopy, and fluorescein angiography results. RESULTS: The ocular manifestations of TB in our patients included panophthalmitis, endophthalmitis, posterior uveitis with choroidal tubercles, keratitis, and a lid mass. Mycobacterium tuberculosis was identified in four cases in ocular specimens using acid-fast bacilli microscopy and in three cases by culture. Rapid diagnosis using polymerase chain reaction was obtained in one case. Extraocular foci of TB were identified in three cases with an intraocular infection at presentation. No patients had the human immunodeficiency virus (HIV) and none were immunocompromised. Two eyes could not be saved using antituberculous treatment because of delayed diagnosis and treatment. CONCLUSIONS: In this age of the HIV pandemic, TB is becoming more common. Because it is curable, heightened awareness and better understanding of the disease's ocular manifestations should be of concern to all ophthalmologists.

Aged↗

PubMed2001

Ascitic fluid carcinoembryonic antigen and alkaline phosphatase levels for the differentiation of primary from secondary bacterial peritonitis with intestinal perforation.

BACKGROUND/AIMS: In cirrhotic patients, spontaneous bacterial peritonitis (SBP) may be difficult to distinguish from secondary peritonitis with occult intestinal perforation; Runyon's criteria (based on ascitic fluid glucose, protein and lactate dehydrogenase levels) are sensitive but not specific. Ascitic fluid carcinoembryonic antigen (CEA) and alkaline phosphatase (AP) are potential markers for secondary peritonitis. METHODS: Ascitic fluid CEA and AP levels were prospectively compared among three subject groups--cirrhotic patients with sterile ascites, cirrhotic patients with SBP, and patients (cirrhotic and non-cirrhotic) with perforation-related secondary peritonitis. RESULTS: The secondary peritonitis group (n = 38 including 11 cirrhotic patients) had significantly higher mean CEA and AP levels than the SBP (n = 34) and sterile ascites patients (n = 63). Of secondary peritonitis patients, 92% fulfilled predetermined criteria (either CEA >5 ng/ml or AP >240 units/l) versus only 12% of SBP patients; sensitivity was 92% and specificity 88% for differentiating secondary peritonitis from SBP. Runyon's criteria had a sensitivity of 97% and specificity of 56%. Stratification of secondary peritonitis patients by the presence or absence of cirrhosis did not alter our results. CONCLUSIONS: Ascitic fluid CEA or AP elevations appear to be sensitive and specific markers for perforation-related secondary peritonitis in cirrhotic as well as non-cirrhotic patients.

Adult↗

PubMed2001

Characterization of self-T-cell response and antigenic determinants of U1A protein with bone marrow-derived dendritic cells in NZB x NZW F1 mice.

Systemic lupus erythematosus (SLE) is characterized by the existence of a heterogeneous group of autoantibodies directed against nuclear intact structures, such as nucleosomes and small nuclear ribonucleoproteins (snRNPs). Autoantibodies against snRNPs are of special interest because they are detectable in the majority of SLE patients. Although the B-cell antigenic determinants have been well characterized, very limited data have been reported in regard to the T-cell epitopes of snRNPs. Furthermore, several studies have demonstrated that determination of the auto-T-cell epitopes recognized by freshly isolated T cells is difficult from unprimed lupus mice when self-antigen-pulsed B cells or macrophages are used as antigen-presenting cells (APCs) in vitro. In the present study, we showed a novel approach for determining the auto-T-cell epitopes, using bone marrow-derived dendritic cells (BMDCs) pulsed with the murine U1A protein - an immunodominant antigen of the U1 snRNPs - which is capable of activating freshly isolated T cells from unprimed (NZB x NZW) F1 (BWF1) mice in vitro. The T-cell epitope area was found to be located at the C-terminus of U1A, overlapping the T-cell epitope of human U1A that has been reported in human SLE. Identification of the autoreactive T-cell epitope(s) in snRNPs will help to elucidate how reciprocal T-B determinant spreading of snRNPs emerges in lupus. The results presented here also indicate that it is feasible to use this approach to further explore strategies to design immunotherapy for patients with lupus.

Animals↗