Biomedical subjects

H C Chang

Publications and source records attributed to H C Chang.

At least 91 records · Page 5Linked to original sources

PubMed1999

Differential induction of the androgen receptor transcriptional activity by selective androgen receptor coactivators.

Several new androgen receptor (AR) cofactors, associated to the ligand binding domain of AR, have been identified by our group and named AR associated protein (ARA)70, ARA55, and ARA54. Our previous reports have suggested that the cofactor ARA70 can confer the androgenic effect from 17 beta-estradiol (E2) and antiandrogen to AR. It is of interest for us to compare and determine if the specificity of sex hormones and antiandrogens could be modulated by different coactivators. Our results indicate that ARA70 is the best coactivator to confer the androgenic activity on E2. Only ARA70 and ARA55 could increase significantly the androgenic activity of hydroxyflutamide, a widely used antiandrogen for the treatment of prostate cancer. Furthermore, as compared to the relative specificity of these coactivators to AR in the prostate cancer DU145 cells, our results suggest that ARA70 has a relatively higher specificity. Together, our data suggest that the specificity of sex hormones and antiandrogens can be modulated by some selective AR coactivators. These findings may not only help us to better understand the specificity of the sex hormones and antiandrogens, but also to facilitate the development of better antiandrogens or androgens to fight the androgen-related diseases, such as prostate cancer.

Androgens↗

PubMed1999

Fertilization capability of frozen epididymal sperm for intracytoplasmic sperm injection.

Both microsurgical epididymal sperm aspiration (MESA) and intracytoplasmic sperm injection (ICSI) are great advances in assisted reproductive techniques. By using the ICSI technique, frozen sperm from the epididymis can result in successful fertilization. The epididymal sperm retrieved via MESA can be cryopreserved for an in-vitro fertilization (IVF) procedure, thus, making repeat surgical retrieval of sperm unnecessary. We report a retrospective analysis of 24 ICSI cycles in 16 patients with obstructive or nonreconstructable azoospermia. Fresh epididymal sperm was used in 13 ICSI cycles and frozen-thawed epididymal sperm was used in the other 11. We compared the fertilization capability of ICSI using frozen-thawed epididymal sperm with fresh epididymal sperm. Eleven patients became pregnant and five of these pregnancies resulted from frozen epididymal sperm. The fertilization rate per oocyte was 58% with fresh sperm, and 66% with frozen-thawed sperm. The rate of clinical pregnancy for one embryo transfer was 46% with fresh sperm, and 45% with frozen-thawed sperm. There were no significant differences between fresh and frozen-thawed spermatozoa in the fertilization rate of oocytes or the clinical pregnancy rate. Our results suggest that we should cryopreserve supernumerary spermatozoa during a MESA/ICSI procedure in order to avoid repeated scrotal surgery.

Adult↗

PubMed1999

HELLP syndrome with antepartum pulmonary edema--a case report.

A 44-year-old pregnant female with a gestation of 29 weeks suddenly developed abdominal pain, nausea, vomiting, and laboratory study showed anemia, elevated liver enzymes, and lower platelets. HELLP syndrome was diagnosed and urgent delivery was needed. In order to correct the plasma volume and platelet deficiency, 6 units of both fresh frozen plasma and platelets, were given before operation. However, acute pulmonary edema was noted in the antepartum period. After vigorous treatment, she gave birth to a male infant. The postoperative course was smooth and she and her baby were discharged eleven days later. This case reminded us once again of the importance and necessity of invasive monitoring in fluid management of these patients.

Adult↗

PubMed1999

Cyst-like chylous coagulum in the urinary bladder of a patient with recurrent chyluria.

We report a rare case of recurrent chyluria in a 64-year-old man, who had undergone sclerosing therapy for chyluria with complete remission 40 years previously. The chyluria recurred 4 months before the present hospital admission. The patient presented with acute urine retention and weight loss of 6 kg during the past 6 months. Urine biochemistry studies showed elevated concentrations of albumin (0.7 g/dL), globulin (0.6 g/dL), cholesterol (0.59 mmol/L), and triglyceride (0.89 mmol/L), confirming the diagnosis of chyluria. Intravenous urography showed a substantial filling defect in the urinary bladder. Cystoscopy revealed milky urine flowing out of the right ureteral orifice, and a large chylous coagulum presenting as a cyst-like mass in the urinary bladder. The chyluria was successfully treated with sclerosing therapy with injection of 76% Urografin (Shering AG, Berlin, Germany) into the right upper urinary tract, and the chylous coagulum was evacuated endoscopically. No evidence of chyluria recurrence has been noted during a year of follow-up, and the patient has regained 6 kg of body weight. This particular presentation of chylous coagulum in a chyluria patient has not been previously reported in the literature.

Chyle↗

PubMed1998

CTG repeats show bimodal amplification in E. coli.

Trinucleotide repeats in human genetic disorders showing anticipation follow two inheritance patterns as a function of length. Inheritance of 35-50 repeats show incremental changes, while tracts greater than 80 repeats show large saltatory expansions. We describe a bacterial system that recapitulates this striking bimodal pattern of CTG amplification. Incremental expansions predominate in CTG tracts < Okazaki fragment size, while saltatory expansions increase in repeat tracts > or = Okazaki fragment size. CTG amplification requires loss of SbcC, a protein that modulates cleavage of single-stranded DNA and degradation of duplex DNA from double-strand breaks. These results suggest that noncanonical single strand-containing secondary structures in Okazaki fragments and/or double-strand breaks in repeat tracts are intermediates in CTG amplification.

Bacterial Proteins↗

PubMed1998

Differential thymic selection outcomes stimulated by focal structural alteration in peptide/major histocompatibility complex ligands.

The T lineage repertoire is shaped by T cell receptor (TCR)-dependent positive and negative thymic selection processes. Using TCR-transgenic (N15tg) beta2-microglobulin-deficient (beta2m-/-) RAG-2(-/-) H-2(b) mice specific for the VSV8 (RGYVYQGL) octapeptide bound to Kb, we identified a single weak agonist peptide variant V4L (L4) inducing phenotypic and functional T cell maturation. The cognate VSV8 peptide, in contrast, triggers negative selection. The crystal structure of L4/Kb was determined and refined to 2.1 A for comparison with the VSV8/Kb structure at similar resolution. Aside from changes on the p4 side chain of L4 and the resulting alteration of the exposed Kb Lys-66 side chain, these two structures are essentially identical. Hence, a given TCR recognizes subtle distinctions between highly related ligands, resulting in dramatically different selection outcomes. Based on these finding and the recent structural elucidation of the N15-VSV8/Kb complex, moreover, it appears that the germ-line Valpha repertoire contributes in a significant way to positive selection.

Amino Acid Sequence↗

PubMed1998

One of the CD3epsilon subunits within a T cell receptor complex lies in close proximity to the Cbeta FG loop.

A recent crystal structure of the N15 alpha/beta-T cell receptor (TCR) in complex with an Fab derived from the H57 Cbeta-specific monoclonal antibody (mAb) shows the mAb fragment interacting with the elongated FG loop of the Cbeta domain. This loop creates one side wall of a cavity within the TCR Ti-alpha/beta constant region module (CalphaCbeta) while the CD and EF loops of the Calpha domain form another wall. The cavity size is sufficient to accommodate a single nonglycosylated Ig domain such as the CD3epsilon ectodomain. By using specific mAbs to mouse TCR-beta (H57) and CD3epsilon (2C11) subunits, we herein provide evidence that only one of the two CD3epsilon chains within the TCR complex is located in close proximity to the TCR Cbeta FG loop, in support of the above notion. Moreover, analysis of T cells isolated from transgenic mice expressing both human and mouse CD3epsilon genes shows that the heterologous human CD3epsilon component can replace the mouse CD3epsilon at this site. The location of one CD3epsilon subunit within the rigid constant domain module has implications for the mechanism of signal transduction throughout T cell development.

Animals↗

PubMed1998

The peptidyl-prolyl isomerase domain of the CyP-40 cyclophilin homolog Cpr7 is not required to support growth or glucocorticoid receptor activity in Saccharomyces cerevisiae.

CyP-40 cyclophilins are found in association with molecular chaperone Hsp90.steroid receptor complexes. The amino-terminal portion of these cyclophilins harbors the characteristic peptidyl-prolyl isomerase (PPIase) domain, whereas three copies of the tetratricopeptide (TPR) motif, a structure shown to be involved in protein-protein interactions, and a putative calmodulin-binding domain are located in the carboxyl-terminal half of the protein. The TPR domains mediate binding to Hsp90, but a requirement for the PPIase domain has not been established. To address this, we have investigated the effects of mutations that alter the PPIase domain of the Saccharomyces cerevisiae CyP-40 homolog, Cpr7. Because Cpr7 is required for rapid growth and full Hsp90 activity, a functional assessment of the PPIase domain could be performed in vivo. A mutation in the catalytic domain altering a conserved site predicted to be essential for isomerase activity did not compromise Cpr7 function. Furthermore, deletion of the entire PPIase domain did not significantly affect growth or Hsp90-mediated steroid receptor activity. These results indicate that the TPR-containing carboxyl terminus of Cpr7 is sufficient for fundamental Cpr7-dependent activity.

Carrier Proteins↗

PubMed1998

Identification of a common docking topology with substantial variation among different TCR-peptide-MHC complexes.

Whether T-cell receptors (TCRs) recognize antigenic peptides bound to major histocompatability complex (MHC) molecules through common or distinct docking modes is currently uncertain. We report the crystal structure of a complex between the murine N15 TCR [1-4] and its peptide-MHC ligand, an octapeptide fragment representing amino acids 52-59 of the vesicular stomatitis virus nuclear capsid protein (VSV8) bound to the murine H-2Kb class I MHC molecule. Comparison of the structure of the N15 TCR-VSV8-H-2Kb complex with the murine 2C TCR-dEV8-H-2Kb [5] and the human A6 TCR-Tax-HLA-A2 [6] complexes revealed a common docking mode, regardless of TCR specificity or species origin, in which the TCR variable Valpha domain overlies the MHC alpha2 helix and the Vbeta domain overlies the MHC alpha1 helix. As a consequence, the complementary determining regions CDR1 and CDR3 of the TCR Valpha and Vbeta domains make the major contacts with the peptide, while the CDR2 loops interact primarily with the MHC. Nonetheless, in terms of the details of the relative orientation and disposition of binding, there is substantial variation in TCR parameters, which we term twist, tilt and shift, and which define the variation of the V module of the TCR relative to the MHC antigen-binding groove.

Animals↗

PubMed1998

A piezoelectric quartz crystal sensor for the determination of coagulation time in plasma and whole blood.

A Peizoelectric Quartz Crystal (PQC) system possessing an adequate sensitivity to a slight viscosity change is employed to monitor the blood coagulation. In the case of an anticoagulated plasma specimen, prothrombin time (PT) was determined by the PQC sensor on the basis of the introduction of tissue thromboplastin (TF) and calcium ion. Discussing the PQC data statistically, we found that at 90% of the total frequency shift (delta f) the best linear relationship in a double-logarithmic plot of PT versus TF concentration in the range of 5.466-22.311 unit/ml is shown. The PQC result was compared with commercial optical coagulometry and showed a good linear correlation (ca. 0.98). The clotting and recalcification of whole blood were also studied by the PQC system. The testing time for one measurement could be completed within 20 min. and had a good agreement with that obtained conventionally.

Biosensing Techniques↗

PubMed1998

Atomic structure of an alphabeta T cell receptor (TCR) heterodimer in complex with an anti-TCR fab fragment derived from a mitogenic antibody.

Each T cell receptor (TCR) recognizes a peptide antigen bound to a major histocompatibility complex (MHC) molecule via a clonotypic alphabeta heterodimeric structure (Ti) non-covalently associated with the monomorphic CD3 signaling components. A crystal structure of an alphabeta TCR-anti-TCR Fab complex shows an Fab fragment derived from the H57 monoclonal antibody (mAb), interacting with the elongated FG loop of the Cbeta domain, situated beneath the Vbeta domain. This loop, along with the partially exposed ABED beta sheet of Cbeta, and glycans attached to both Cbeta and Calpha domains, forms a cavity of sufficient size to accommodate a single non-glycosylated Ig domain such as the CD3epsilon ectodomain. That this asymmetrically localized site is embedded within the rigid constant domain module has implications for the mechanism of signal transduction in both TCR and pre-TCR complexes. Furthermore, quaternary structures of TCRs vary significantly even when they bind the same MHC molecule, as manifested by a unique twisting of the V module relative to the C module.

Amino Acid Sequence↗

PubMed1998

Peroxidase-catalyzed oxidation of 2,4,6-trichlorophenol.

2,4,6-Trichlorophenol (TCP) is an environmental contaminant that is toxic, mutagenic, and carcinogenic. We have investigated peroxidase-catalyzed oxidation of TCP as an alternative pathway of TCP bioactivation using horseradish peroxidase (HRP) as a model peroxidase. TCP was shown to function as a reducing substarte for HRP as evidenced by TCP-dependent, HRP-catalyzed reduction of 5-phenyl-4-penten-1-yl hydroperoxide (PPHP) to its corresponding alcohol. In addition, TCP was shown to undergo hydroperoxide (H2O2, ethyl hydroperoxide, or PPHP)-dependent metabolism as evidenced by electronic absorption spectroscopic analysis of reaction mixtures. A single major product was detected by reverse phase HPLC and was identified as 2,6-dichloro-1,4-benzoquinone (2,6-dichloro-2, 5-cyclohexadiene-1,4-dione, CAS no. 697-91-6) on the basis of electronic absorption spectroscopy, mass spectrometry, and cochromatography with synthetic standard. In addition, HRP-catalyzed oxidation of TCP yielded EPR-detectable phenoxyl radical intermediates whose EPR spectrum consisted of a 1:2:1 triplet characterized by proton hyperfine coupling constants aH(3,5) = 2.35 gauss. Mechanisms for the hydroperoxide-dependent, HRP-catalyzed oxidation of TCP are proposed that are consistent with these results.

Catalysis↗

PubMed1998

Pregnancy achieved by intracytoplasmic sperm injection using cryopreserved vasal-epididymal sperm from a man with spinal cord injury.

Anejaculation and poor semen quality are two major causes of infertility in men with spinal cord injury (SCI). The poor motility of retrieved sperm usually has low fertilization potential and is thought to be unfavorable for cryopreservation. This report describes a pregnancy after intracytoplasmic sperm injection (ICSI) with cryopreserved vasal-epididymal sperm from a man with SCI and anejaculation. An attempt was made to obtain sperm through electroejaculation, but no motile sperm were found in two trials. Therefore, the subject underwent vasal aspiration. The retrieved sperm had a concentration of 26 x 10(6)/mL and a motility of 3%. ICSI was considered to be the best choice for the couple, but the wife did not become pregnant in the first cycle of treatment. A successful pregnancy was achieved by ICSI in the second cycle using frozen-thawed sperm, supernumerary in the previous cycle, with a density of 5 x 10(6)/mL and 1% motility. A set of healthy twins, one boy and one girl, were delivered via cesarean section at 36 weeks of gestation. Complementary to other assisted reproductive techniques, ICSI may provide men with SCI a greater opportunity to father children. The supernumerary sperm, regardless of quality, should be cryopreserved to avoid the necessity and risk of repeated assisted ejaculations and aspirations of the genital tract.

Adult↗

PubMed1998

Point mutations in the beta chain CDR3 can alter the T cell receptor recognition pattern on an MHC class I/peptide complex over a broad interface area.

To study how the T cell receptor interacts with its cognate ligand, the MHC/peptide complex, we used site directed mutagenesis to generate single point mutants that alter amino acids in the CDR3beta loop of a H-2Kb restricted TCR (N30.7) specific for an immunodominant peptide N52-N59 (VSV8) derived from the vesicular stomatitis virus nucleocapsid. The effect of each mutation on antigen recognition was analyzed using wild type H-2Kb and VSV8 peptide, as well as H-2Kb and VSV8 variants carrying single replacements at residues known to be exposed to the TCR. These analyses revealed that point mutations at some positions in the CDR3beta loop abrogated recognition entirely, while mutations at other CDR3beta positions caused an altered pattern of antigen recognition over a broad area on the MHC/peptide surface. This area included the N-terminus of the peptide, as well as residues of the MHC alpha1 and alpha2 helices flanking this region. Assuming that the N30 TCR docks on the MHC/peptide with an orientation similar to that recently observed in two different TCR-MHC/peptide crystal structures, our findings would suggest that single amino acid alterations within CDR3beta can affect the interaction of the TCR with an MHC surface region distal from the predicted CDR3beta-Kb/VSV8 interface. Such unique recognition capabilities are generated with minimal alterations in the CDR3 loops of the TCR. These observations suggest the hypothesis that extensive changes in the recognition pattern due to small perturbations in the CDR3 structure appears to be a structural strategy for generating a highly diversified TCR repertoire with specificity for a wide variety of antigens.

Amino Acid Sequence↗

PubMed1998

Emotional symptoms are secondary to the voice disorder in patients with spasmodic dysphonia.

The aims of this study were to evaluate the emotional status and life quality of the patients with spasmodic dysphonia (SD) before and after botulinum toxin treatment, and to ascertain whether SD is a somatoform disorder. Ten patients with spasmodic dysphonia were injected unilaterally into the vocal cord with botulinum toxin. Before botulinum toxin treatment, two clinician's rating scales--Hamilton Depression Rating Scale (HDRS) and Hamilton Anxiety Rating Scale (HARS), and three self-rating psychometrics--Zung's Self-Rating Depression Scale (SDS), Life Quality Scale (GHQ/QL-12), and Symptom Distress Checklist (SCL-90) were applied. Self-rating scales were also administered in 20 matched normal controls. The patients were reevaluated 1 month after botulinum toxin treatment. The Clinical Global Impression Scale (CGI) was also rated by the patients themselves and a speech pathologist. The mean scores of SD patients were significantly higher than that of controls in SDS, and subscales of somatization, obsessive-compulsive symptoms, depression, anxiety, and psychoticism in SCL-90. The mean score of GHQ/QL-12 was significantly higher in the control group. The scores of HDRS, SDS, GHQ/QL-12 and subscales of somatization, depression, and anxiety in SCL-90 showed significant improvement after botulinum treatment. In CGI, seven patients were rated as improved by patients themselves and the speech pathologist. The patients with SD had more anxiety, depression and somatization symptoms, and poor life quality than normal controls. Their emotional status and life quality improved after botulinum toxin treatment. The results suggest that the emotional symptoms of patients with SD are mainly secondary to voice disorder.

Adult↗

PubMed1998

Transforming growth factor beta 1 potently activates CPP32-like proteases in human hepatoma cells.

Induction of apoptosis in Hep3B hepatoma cells by transforming growth factor beta 1 (TGF-beta 1) was accompanied by the activation of interleukin-1-beta-converting-enzyme-like proteases, which have recently been renamed as caspases. The caspase inhibitor ZVAD-FMK, which has a broader specificity for caspase family proteases, blocked TGF-beta 1-induced apoptosis in a concentration-dependent manner. The caspases in this apoptotic process were further characterized by using a more specific caspase inhibitor, DEVD-FMK, for CPP32-like (caspase-3-like) proteases. Our results demonstrated that CPP32-like proteases were activated during apoptosis triggered by TGF-beta 1. Enhancement of CPP32-like activity was clearly detected in TGF-beta 1-treated Hep3B cells. Furthermore, cleavage of poly(ADP-ribose) polymerase, an in vivo substrate for CPP32, in these cells was confirmed by immunoblotting. Thus, we suggest that CPP32-like proteases participate in apoptotic cell death induced by TGF-beta 1.

Amino Acid Chloromethyl Ketones↗

PubMed1998

Structural basis of CD8 coreceptor function revealed by crystallographic analysis of a murine CD8alphaalpha ectodomain fragment in complex with H-2Kb.

The crystal structure of the two immunoglobulin variable-like domains of the murine CD8alphaalpha homodimer complexed to the class I MHC H-2Kb molecule at 2.8 A resolution shows that CD8alphaalpha binds to the protruding MHC alpha3 domain loop in an antibody-like manner. Comparison of mouse CD8alphaalpha/H-2Kb and human CD8alphaalpha/HLA-A2 complexes reveals shared as well as species-specific recognition features. In both species, coreceptor function apparently involves the participation of CD8 dimer in a bidentate attachment to an MHC class I molecule in conjunction with a T cell receptor without discernable conformational alteration of the peptide or MHC antigen-presenting platform.

Amino Acid Sequence↗

PubMed1998

Mechanism for inhibition of thyroid peroxidase by leucomalachite green.

The triphenylmethane dye, malachite green (MG), is used to treat and prevent fungal and parasitic infections in the aquaculture industry. It has been reported that the reduced metabolite of MG, leucomalachite green (LMG), accumulates in the tissues of fish treated with MG. MG is structurally related to other triphenylmethane dyes (e.g., gentian violet and pararosaniline) that are carcinogenic in the liver, thyroid, and other organs of experimental animals. The ability of LMG to inhibit thyroid peroxidase (TPO), the enzyme that catalyzes the iodination and coupling reactions required for thyroid hormone synthesis, was determined in this study. LMG inhibited TPO-catalyzed tyrosine iodination (half-maximal inhibition at ca. 10 microM). LMG also inhibited the TPO-catalyzed formation of thyroxine in low-iodine human goiter thyroglobulin (half-maximal inhibition at ca. 10 microM) using a model system that measures simultaneous iodination and coupling. Direct inhibition of the coupling reaction by LMG was shown using a coupling-only system containing chemically preiodinated thyroglobulin as the substrate. Incubation of LMG with TPO, iodide, and tyrosine in the presence of a H2O2-generating system yielded oxidation products that were identified by using on-line LC/APCI-MS as desmethyl LMG, 2desmethyl LMG, 3desmethyl LMG, MG, and MG N-oxide. Similar products from LMG were observed in incubations with TPO and H2O2 alone. These findings suggest that the anti-thyroid effects (increased serum thyroid-stimulating hormone and decreased serum thyroxine) observed in rats treated with LMG result from blockade of hormone synthesis through alternate substrate inhibition and that chronic exposure could cause thyroid follicular cell tumors through a hormonal mechanism. The observed TPO-catalyzed oxidative demethylation of LMG to a primary arylamine also suggests a genotoxic mechanism for tumor formation is possible.

Aniline Compounds↗