Biomedical subjects

C T Chen

Publications and source records attributed to C T Chen.

At least 91 records · Page 5Linked to original sources

PubMed1999

Endoscopically assisted mandibular subcondylar fracture repair.

The endoscope has been widely used in aesthetic surgery in recent years, but rarely has it been used in cases of facial trauma. From July of 1996 to December of 1996, the endoscope was used successfully to assist in the repair of mandibular subcondylar fractures in eight patients (five men and three women). Their ages ranged from 15 to 60 years with an average age of 31 years. Six of the patients had other associated mandibular fractures including angular, parasymphyseal, and contralateral subcondylar fractures. A 4.0-mm, 30-degree telescope was introduced to visualize the fracture site by means of an intraoral incision over the ascending ramus. A miniplate was used to stabilize the fracture site with the help of a percutaneous trocar. Intermaxillary fixation was applied for 3 to 6 days. Functionally, all patients returned to normal range of motion within 8 weeks. A slight deviation to the trauma site was noted on maximal opening in three patients, but this condition returned to normal 3 months after surgery. There was no facial palsy or lip numbness. The benefits of the endoscopic approach include not only the provision of better visualization and precise anatomic alignment of bony segments but also the avoidance of large facial scars and facial nerve injuries.

Adolescent↗

PubMed1999

Endoscopically assisted reconstruction of orbital medial wall fractures.

Traditional surgical approaches to orbital medial wall fractures are either direct extraocular skin incisions or indirect bicoronal flap. However, these methods can leave remarkable orbital scars or scalp alopecia with the possible associated complications. A minimally invasive endoscopic technique with the assistance of a 2.7-mm, 30-degree telescope through a medial transconjunctival incision has been successfully used to reconstruct the orbital medial wall fractures. This technique was applied to four patients who had orbital medial wall fractures. Three patients also had concomitant orbital floor fractures. The other had associated superior orbital fissure syndrome. All patients were presented with limited eye movement, positive forced duction test, horizontal diplopia, and enophthalmos (3 mm to 6 mm) preoperatively. The entrapped periorbital tissues in the ethmoid sinus were completely reduced endoscopically. The bone defect of orbital medial wall was reconstructed with autogenous rib bone grafts under endoscopic control. The patients were followed up for 8 to 16 months with an average of 11 months. Three patients recovered completely without any residual eye symptoms after intervention. Clinically significant residual enophthalmos of 3 mm occurred in the patient with the superior orbital fissure syndrome. His eye movement limitation caused by entrapment of medial rectus muscle was relieved postoperatively. There was no donor-site morbidity or any complications related to the endoscopically assisted procedure. Endoscopically assisted medial transconjunctival approach to the orbital medial wall fractures is an excellent adjunct for the exposure and complete reduction of herniated periorbital tissue and bony reconstruction of the medial orbital wall.

Adult↗

PubMed1999

The blood supply of the reverse temporalis muscle flap: anatomic study and clinical implications.

Although the reverse temporalis muscle flap has been used clinically, the exact vascular connection between the superficial and deep temporal vessels has not been clearly defined. The purpose of this study was to investigate the vascular territory of the reverse temporalis muscle supplied by the superficial temporal vessels. Six cadaver heads were studied using a colored lead oxide injection through the superficial temporal artery. The specimens were examined macroscopically and radiographically. The reverse temporalis muscle flap was then applied to a clinical case presenting with traumatic anterior skull base defect communicating with the nasal cavity. The cadaver specimens demonstrated that the superficial temporal artery formed an average 1.3 +/- 0.2 cm in width of dense vascular zone, which was located within 1.8 cm below the superior temporal line. The dense vascular network further perfused the anterior and posterior deep temporal arteries and the muscular branch of the middle temporal artery to supply the temporalis muscle. The mean perfused area of the temporalis muscle was 83 percent, ranging from 79 to 89 percent, in five cadaver heads. One cadaver revealed only 55 percent of perfused area in the absence of the muscular branch of the middle temporal artery. The consistent area without perfusion was located in the distal third of the posterior portion of the reverse temporalis muscle. In clinical cases, the reverse temporalis muscle flap was used successfully to obliterate the anterior skull base defect without evidence of muscle flap necrosis. The exact blood supply to the distal third of the posterior portion of the reverse temporalis muscle flap needs to be investigated further in vivo. Particular attention was paid to the inclusion of the muscular branch of the middle temporal artery in this flap to augment the blood supply to the temporalis muscle.

Adult↗

PubMed1999

Signaling pathway and pepsinogen secretion in Helicobacter pylori-infected human gastric adenocarcinoma.

Although in vitro studies have suggested that Helicobacter pylori not only attaches to cultured cells but also induces signal transduction events in host cells, the underlying mechanism of H. pylori action has yet to be fully investigated. In the present study, a cytotoxin-positive H. pylori was used to infect and examined for its effect on the stimulation of second messengers in human gastric adenocarcinoma (AGS). Results showed that H. pylori increased cytosolic free calcium concentration [Ca2+]i in host cells in a dose-dependent manner. The increase of [Ca2+]i was due to release from the intracellular Ca2+ store as well as entry to the extracellular Ca2+. H. pylori infection on host cells was also found to induce the generations of inositol phosphates, adenosine 3', 5'-cyclic monophosphate, and guanosine 3',5'-cyclic monophosphate, and to stimulate the secretion of pepsinogen.

Adenocarcinoma↗

PubMed1999

Regulation of vascular endothelial growth factor secretion in human meningioma cells.

Previously, we induced vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) secretion in glioma cell lines by using physiologic concentrations of epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), or platelet-derived growth factor-BB (PDGF-BB). We hypothesized that VEGF/VPF might enhance the blood supply required for the unregulated growth of tumors, and that it acts as the central mediator of tumor angiogenesis. The objective of this study was to determine whether the expression of VEGF/VPF by meningiomas is regulated by growth factors or sex hormones. By means of an enzyme-linked immunosorbent assay of CH-157MN meningioma cell supernatants, we demonstrated that EGF and bFGF similarly induce VEGF secretion by CH-157MN meningioma cells. At the maximum concentrations of EGF (50 ng/mL) and bFGF (50 ng/mL) used in this study, VEGF secretion was induced to 140% to 160% above baseline constitutive secretion. PDGF-BB homodimer did not enhance VEGF secretion significantly. Estradiol (up to 10(-7) mol/L), progesterone (up to 10(-5) mol/L), or testosterone (up to 10(-5) mol/L) did not stimulate or inhibit VEGF secretion in CH-157MN meningioma cells (p > 0.05). Furthermore, we demonstrated that dexamethasone decreased VEGF secretion to 32% of baseline constitutive secretion. This might explain the effect of corticosteroids in alleviating peritumoral brain edema in meningiomas. These results suggest that VEGF secretion in CH-157MN meningioma cells is mainly regulated by growth factors and corticosteroids, but not by sex hormones. Understanding the regulation of VEGF/VPF secretion in meningiomas might contribute to the development of a new therapeutic strategy.

Dexamethasone↗

PubMed1999

MIRD Pamphlet No. 14 revised: A dynamic urinary bladder model for radiation dose calculations. Task Group of the MIRD Committee, Society of Nuclear Medicine.

UNLABELLED: The constant-volume urinary bladder model in the standard MIRD Pamphlet No. 5 (Revised) phantom has recognized limitations. Various investigators have developed detailed models incorporating more physiologically realistic features, such as expanding bladder contents and residual volume, and variable urinary input rate, initial volume and first void time. We have reviewed these published models and have developed a new model for calculation of radiation absorbed dose to the urinary bladder wall incorporating these aspects. METHODS: The model consists of a spherical source with variable volume to simulate the bladder contents and a wall represented by a spherical shell of constant volume. The wall thickness varies as the source expands or contracts. The model provides for variable urine entry rate (three different hydration states), initial bladder contents volume, residual volume and first void time. The voiding schedule includes an extended nighttime gap during which the urine entry rate is reduced to one-half the daytime rate. RESULTS: Radiation-absorbed dose estimates have been calculated for the bladder wall surface (including photon and electron components) and at several depths in the wall (electron component) for 2-18F-fluoro-2-deoxy-D-glucose, 99mTc-diethylenetriaminepentaacetic acid (DTPA), 99mTc-HEDP, 99mTc-pertechnetate, 99mTc-red blood cells (RBCs), 99mTc-glucoheptonate, 99mTc-mercaptoacetyltriglicine chelator (MAG3), 99mTc-methylene diphosphonate (MDP), 99mTc-hexamethylpropylene amine oxime (HMPAO), 99mTc-human serum albumin (HSA), 99mTc-MIBI (rest and stress), 123I-/124I-/131I-OIH, 123I/131I-NaI, 125I-iothalamate, 111In-DTPA and 89Sr-SrCl. CONCLUSION: The new model tends to give a higher radiation absorbed dose to the bladder wall surface than the previous models. Large initial bladder volumes and higher rates of urine flow into the bladder result in lower bladder wall dose. The optimal first voiding time is from 40 min to 3 hr postadministration, depending on radiopharmaceutical. The data as presented in tabular and graphic form for each compound provide guidance for establishing radiation absorbed dose reduction protocols.

Humans↗

PubMed1999

A probability-based multivariate statistical algorithm for autofluorescence spectroscopic identification of oral carcinogenesis.

A probability-based multivariate statistical algorithm combining partial least-squares (PLS) and logistic regression was developed to identify the development stages of oral cancer through analysis of autofluorescence spectra of oral tissues. Tissues were taken from a 7,12-dimethylbenz[a]anthracene-induced hamster buccal pouch carcinogenesis model. Analyses were conducted at various excitation wavelengths, ranging from 280 nm to 400 nm in 20 nm increments, to assess classification performance at different excitations. For each excitation the PLS analysis and logistic regression were combined, on the basis of cross validation, to calculate the posterior probabilities of samples belonging to four stages of cancer development: normal tissues, hyperplasia, dysplasia and early cancers and frankly invasive cancers. Results showed that the 320 nm excitation wavelength optimally classified the cancer development stages: the accuracy rates for identifying samples at that excitation were 91.7%, 83.3%, 66.7% and 83.3% for the four respective stages. The average accuracy rate was 81.3%. These results suggest that the algorithm described in this study might be useful for the detection of human oral cancers.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1998

Characterization of p96h2bk: immunoreaction with an anti-Erk(extracellular-signal-regulated kinase) peptide antibody and activity in Xenopus oocytes and eggs.

We have shown previously that oncogenic Ras induces cell cycle arrest in activated Xenopus egg extracts [Pan, Chen and Lin (1994) J. Biol. Chem. 269, 5968-5975]. The cell cycle arrest correlates with the stimulation of a protein kinase activity that phosphorylates histone H2b in vitro (designated p96(h2bk)) [Chen and Pan (1994) J. Biol. Chem. 269, 28034-28043]. We report here that p96(h2bk) is likely to be p96(ram), a protein of approx. 96 kDa that immunoreacts with a monoclonal antibody (Mk-1) raised against a synthetic peptide derived from a sequence highly conserved in Erk1/Erk2 (where Erk is extracellular-signal-regulated kinase). This is supported by two lines of evidence. First, activation/inactivation of p96(h2bk) correlates with upward/downward bandshifts of p96(ram) in polyacrylamide gels. Secondly, both p96(h2bk) and p96(ram) can be immunoprecipitated by antibody Mk-1. We also studied the activity of p96(h2bk)/p96(ram) in Xenopus oocytes and eggs. p96(h2bk)/p96(ram) was inactive in stage 6 oocytes, was active in unfertilized eggs, and became inactive again in eggs after fertilization. Since stage 6 oocytes are at G2-phase of the cell cycle, unfertilized eggs arrest at M-phase and eggs exit M-phase arrest after fertilization, the results thus indicate that p96(h2bk)/p96(ram) activity is cell cycle dependent. Moreover, microinjection of oncogenic Ras into fertilized eggs at the one-cell stage arrests the embryos at the two-cell stage, and this induced arrest is correlated with an inappropriate activation of p96(h2bk)/p96(ram). The data are consistent with the concept that inappropriate activation of p96(h2bk)/p96(ram) plays a role in the cell cycle arrest induced by oncogenic Ras.

Animals↗

PubMed1998

Androgen-dependent and -independent human prostate xenograft tumors as models for drug activity evaluation.

The present study evaluated three human prostate xenograft tumors (CWR22, CWR22R, and CWR91) as models for drug activity evaluation. The chemosensitivity and the expression of several proteins (i.e., p-glycoprotein or Pgp, prostate specific antigen or PSA, p53, and Bcl-2) in xenograft tumors were compared with those in patient tumors obtained through radical prostatectomy (n = 26). CWR22 is androgen-dependent, CWR22R is the androgen-independent subline of CWR22, and CWR91 is a separately derived androgen-independent tumor. The results of immunohistochemical and/or Western blot analysis indicate that the expression of PSA, Pgp, p53, and Bcl-2 in the three CWR xenograft tumors are representative of their expression in 100, 85, 90, and 60%, respectively, of patient tumors. The responses of histocultures of xenograft tumors to doxorubicin and paclitaxel, including inhibition of DNA precursor incorporation and cell death induction, were qualitatively similar to the responses of patient tumors. For example, in all three xenograft and patient tumors, doxorubicin produced complete antiproliferation and cytotoxicity (ie., cell kill) whereas paclitaxel produced incomplete effects. A comparison of the concentration-effect relationships in xenograft and patient tumors (population median values) indicates that the chemosensitivity observed in patient tumors is represented by the chemosensitivity of one or more of the three xenograft tumors, as follows: (a) the three xenograft tumors and patient tumors responded equally to doxorubicin-induced antiproliferation; (b) CWR22R, CWR91 and patient tumors responded equally to doxorubicin-induced cytotoxicity, whereas CWR22 was 2-3-fold less sensitive; (c) CWR22 and CWR22R tumors were less sensitive to paclitaxel-induced antiproliferation compared with patient tumors, whereas CWR91 was several-fold more sensitive; and (d) CWR22, CWR22R and patient tumors responded equally to paclitaxel-induced cytotoxicity, whereas CWR91 was 2-3-fold more sensitive. The results of this study indicate that the three xenograft tumors, which show chemosensitivity comparable with the results of > or =50% patient tumors and encompass the majority of the heterogeneous patient prostate tumors in the expression of Pgp, PSA, p53 and Bcl-2 proteins, are useful models for drug activity evaluation.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1998

Pharmacodynamics of immediate and delayed effects of paclitaxel: role of slow apoptosis and intracellular drug retention.

The kinetics of the time-dependent antitumor effects of paclitaxel are not fully understood; some literature reports indicate a higher activity by prolonging treatment durations, whereas other reports indicate no enhancement under in vitro conditions. The present study was designed to address this controversy and to determine the mechanism of the higher cytotoxicity associated with longer treatment durations. Six human epithelial cancer cell lines (bladder RT4, breast MCF7, pharynx FaDu, ovarian SKOV3, and prostate PC3 and DU145) were used. To determine whether the higher activity observed for the longer treatment durations is due to a delayed exhibition of drug effects and/or a reflection of cumulative effects that required a continuous drug exposure, cells were treated with paclitaxel for 3-96 h and then either: (a) immediately processed for drug effect measurement; or (b) washed, incubated in drug-free medium, and processed for drug effect measurement at 96 h. The overall drug effect (i.e., combination of cytostatic and apoptotic effects) was determined by the sulforhodamine B assay, which measures the cellular protein. In addition, to determine whether apoptosis occurs with a time delay, apoptosis was measured in cells that were collected immediately after drug treatment for various durations or in cells that were treated with drugs for 3 h but collected at later time points. Apoptosis was determined using agarose gel electrophoresis and by measuring the cytoplasmic DNA-histone complex using ELISA. The contribution of the intracellularly retained drug to the delayed drug effect was studied by characterizing the kinetics of cellular drug uptake and efflux and by examining the effect of removal of the intracellularly retained drug. All six cell lines showed similar results, as follows: (a) paclitaxel produced cytotoxicity that was exhibited immediately after treatment (immediate effect) and after treatment was terminated (delayed effect); (b) the immediate and delayed effects showed different pharmacodynamics. The immediate effect increased with treatment duration and drug concentration. For the delayed effect, all treatments produced the same maximum effect at 96 h, although treatments for < or = 12 h showed higher IC50s than longer treatments, whereas treatments for > or = 24 h showed indistinguishable IC50s; (c) treatment for as brief as 3 h was sufficient to induce apoptosis, which occurred with a lag time of about 24 h, although longer treatments produced a greater extent of apoptosis; (d) The intracellular and extracellular concentrations reached an equilibrium at approximately 5 h, which rules out slow and/or insufficient uptake as the cause of the lower effects at shorter treatment times (i.e., < 24 h); (e) upon removal of drug-containing medium, the amount of drug retained intracellularly was about 10% of the applied dose and was reduced to approximately 0.5% after three successive washes, separated by 3-h equilibration periods; and (f) the delayed effect of the 3-h treatment was largely due to the drug retained intracellularly, whereas the delayed effect of the 24 h treatment was independent of the drug retained intracellularly. In conclusion, in human epithelial cancer cells, paclitaxel-induced cytotoxicity occurred after termination of drug treatment, which was partly due to the slow manifestation of apoptosis and partly due to the significant amount of drug retained intracellularly. Based on these findings and recognizing that some previous studies measured the immediate effect whereas the other studies measured the delayed effect, we propose that the conflicting data in the literature regarding the effect of treatment duration on paclitaxel activity under in vitro conditions are in part due to the different pharmacodynamics of the immediate and delayed drug effects. Furthermore, differences in the delayed effects for treatments of < 24 h and the minimal differences for treatments of > or = 24 h indicate that th

Animals↗

PubMed1998

A unique high-performance wide-range (10-1500 eV) spherical grating monochromator beamline.

A wide-spectral-range high-performance 6 m-spherical grating monochromator (6 m-SGM) beamline has been designed and is under construction at SRRC. Two different entrance slits, instead of additional mirrors, are used to optimize the overall performance. Six gratings are used to cover photon energies from 10 to 1500 eV. Movable entrance slits and bendable vertical focusing mirrors are used to enhance further the beamline performance. A bendable horizontal focusing mirror is used to improve the resolution and to focus the photon beam at the experimental station immediately after the exit slit. Several end-stations can be installed at the same time to utilize the beam time fully. The expected energy-resolving power, with both slit openings set at 10 micro m, is up to 15 000 and 40 000 for the high- and low-energy branches, respectively. A photon flux of 1 x 10(11) photons s(-1) can be obtained with an energy-resolving power of 20 000.

Journal Article↗

PubMed1998

A dynamic local bump system for producing synchrotron radiation with an alternating elliptical polarization.

To facilitate high-sensitivity soft X-ray magnetic circular dichroism experiments, a dynamic local bump system has been developed at the SRRC storage ring. This system was devised to vary dynamically the vertical slope of the electron beam in a bending magnet, producing, in the electron orbit plane, soft X-rays with an alternating elliptical polarization. The local bump was created by using two pairs of vertical correctors located on each side of the bending magnet. The bump strength coefficient was obtained both from calculated estimation and from measured beam-response matrices. Control electronics for proper bump strength settings were designed to incorporate the existing orbit-corrector function. A corresponding graphic user interface was implemented so that the bump amplitude could be easily adjusted. The performance of this system is presented. Disturbance on the stored electron beam orbit was observed while flipping the corrector polarity during EPBM (elliptical polarization from bending magnets) operation. A local feedback loop, developed to eliminate such disturbance on other beamlines, is also described.

Journal Article↗

PubMed1998

A high-performance wide-range beamline for elliptically polarized undulator source.

A high-performance wide-range beamline has been designed for monochromatizing circularly polarized photons with energies from 10 to 1400 eV. A grazing SGM-based beamline with two entrance slits has been employed to optimize the performance. The degree of the circular polarization affected by the beamline optics has been analysed. The horizontal and vertical refocusing mirrors have been specially arranged to improve greatly the polarization degree in the low-energy region. By connecting this beamline to a high-efficiency elliptically polarized undulator, this beamline should be able to provide, in the entire energy range, intensive and high-resolution photons of a high degree of circular polarization.

Journal Article↗

PubMed1998

Design of a high-flux and high-resolution VUV bending-magnet beamline.

A high-flux and high-resolution VUV beamline (4-40 eV) has been designed and is under construction at SRRC. This beamline, which collects 50 mrad of horizontal radiation, uses a 6 m cylindrical-grating monochromator with an incident angle of 70 degrees instead of the conventional normal-incidence-monochromator (NIM) design. Special features, such as movable entrance slit, bendable vertical focusing mirror and movable curved exit slit, are employed to enhance greatly the beamline performance. With both slit openings set at 10 micro m, the energy-resolving power can reach as high as 70000. Photon fluxes of 1 x 10(13) and 1 x 10(10) photons s(-1) are calculated for energy-resolving powers of 1000 and 40000, respectively. The best image size at the sample position is smaller than 0.45 x 0.2 mm.

Journal Article↗

PubMed1998

A compact mirror manipulator in the SRRC beamline.

A compact mirror manipulator which has high stiffness and is easily adjustable has been developed for new beamlines at SRRC. It consists of a vertical stem to support the mirror and allows for six-axis precise positioning. The rotation adjustment is designed with a minimum of cross-coupling between adjustments. An independent support is fixed to the ground to reduce vibration from the chamber and the pump. Some performance test results in vacuum and in atmosphere, including vibration, repeatability, long-term drift etc., are described in this paper.

Journal Article↗

PubMed1998

Identification of neutral and acidic sphingomyelinases in Helicobacter pylori.

We demonstrated for the first time the presence of sphingomyelinase (SMase) in Helicobacter pylori. Activation of SMase has been implicated as the cause of elevation of cellular ceramide levels and consequently of apoptosis. The data indicate that there are two classes of SMase, defined by their optimal pHs and cellular locations, existing in H. pylori. One is an Mg(2+)-dependent membrane-bound enzyme with an optimal activity at pH 7, and the other is an Mg(2+)-independent cytosolic enzyme with an optimal activity at pH 5. Bisalumin, a bismuth salt, was found to inhibit the activities of both forms of SMase regardless of the presence of Mg2+. By Western blot analysis, the membrane-bound SMases of H. pylori and Bacillus cereus were shown to be antigenically related and to have a similar denatured molecular mass of 28 kDa.

Bismuth↗

PubMed1998

Fluorescent, sequence-selective peptide detection by synthetic small molecules.

Small organic sensor molecules were prepared that bind and signal the presence of unlabeled tripeptides in a sequence-selective manner. Sequence-selective peptide binding is a difficult problem because small peptides are highly flexible and there are no clear rules for designing peptide-binding molecules as there are for the nucleic acids. The signaling system involved the application of fluorescence energy transfer and provided large, real-time fluorescence increases (300 to 500 percent) upon peptide binding. With it, these sensors were sensitive enough to detect unlabeled cognate peptides both in organic solution and in the solid state at low micromolar concentrations.

Binding Sites↗

PubMed1998

The Homothorax homeoprotein activates the nuclear localization of another homeoprotein, extradenticle, and suppresses eye development in Drosophila.

The Extradenticle (Exd) protein in Drosophila acts as a cofactor to homeotic proteins. Its nuclear localization is regulated. We report the cloning of the Drosophila homothorax (hth) gene, a homolog of the mouse Meis1 proto-oncogene that has a homeobox related to that of exd. Comparison with Meis1 finds two regions of high homology: a novel MH domain and the homeodomain. In imaginal discs, hth expression coincides with nuclear Exd. hth and exd also have virtually identical, mutant clonal phenotypes in adults. These results suggest that hth and exd function in the same pathway. We show that hth acts upstream of exd and is required and sufficient for Exd protein nuclear localization. We also show that hth and exd are both negative regulators of eye development; their mutant clones caused ectopic eye formation. Targeted expression of hth, but not of exd, in the eye disc abolished eye development completely. We suggest that hth acts with exd to delimit the eye field and prevent inappropriate eye development.

Amino Acid Sequence↗