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C H Chang

Publications and source records attributed to C H Chang.

At least 361 records · Page 20Linked to original sources
PubMed1993

Nitric oxide in the sensory function of the carotid body.

Recent studies suggest that nitric oxide (NO) may act as a chemical messenger in the nervous system. Since neurotransmitters are considered necessary for the sensory function of the carotid body, and molecular O2 is a co-factor for NO synthesis, we examined whether (a) chemoreceptor tissue also synthesizes NO and if so, (b) does endogenous NO affect chemosensory activity. Experiments were performed on carotid bodies obtained from anesthetized cats (n = 20). Distribution of nitric oxide synthase (NOS), an enzyme that catalyzes the formation of NO was examined using NADPH-diaphorase histochemistry. Many nerve plexuses innervating the chemoreceptor tissue were positive for NADPH-diaphorase, indicating that the nerve fibers are the primary source of NO production in the carotid body. Radiometric analysis of NOS activity of the chemoreceptor tissue averaged 1.94 pmol [3H]citrulline/min/mg protein. NOS activity was significantly less in low pO2 reaction medium than in room air controls. Chemosensory activity in vitro increased in a dose-dependent manner in response to L-omega-nitro arginine (L-NNA), an inhibitor of NOS activity. The effects of NOS inhibitor were enantiomer selective as evidenced by reversal of the responses by L- but not D-arginine. These observations imply that endogenous NO is inhibitory to carotid body sensory activity. cGMP levels of L-NNA-treated carotid bodies were significantly less than untreated controls, suggesting that the actions of NO are coupled to the cGMP second messenger system, as elsewhere in the nervous system.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Oxidoreductases↗
PubMed1993

Site-specific and compensatory mutations imply unexpected pathways for proton delivery to the QB binding site of the photosynthetic reaction center.

In photosynthetic reaction centers, a quinone molecule, QB, is the terminal acceptor in light-induced electron transfer. The protonatable residues Glu-L212 and Asp-L213 have been implicated in the binding of QB and in proton transfer to QB anions generated by electron transfer from the primary quinone QA. Here we report the details of the construction of the Ala-L212/Ala-L213 double mutant strain by site-specific mutagenesis and show that its photosynthetic incompetence is due to an inability to deliver protons to the QB anions. We also report the isolation and biophysical characterization of a collection of revertant and suppressor strains that have regained the photosynthetic phenotype. The compensatory mutations that restore function are diverse and show that neither Glu-L212 nor Asp-L213 is essential for efficient light-induced electron or proton transfer in Rhodobacter capsulatus. Second-site mutations, located within the QB binding pocket or at more distant sites, can compensate for mutations at L212 and L213 to restore photocompetence. Acquisition of a single negatively charged residue (at position L213, across the binding pocket at position L225, or outside the pocket at M43) or loss of a positively charged residue (at position M231) is sufficient to restore proton transfer activity to the complex. The proton transport pathways in the suppressor strains cannot, in principle, be identical to that of the wild type. The apparent mutability of this pathway suggests that the reaction center can serve as a model system to study the structural basis of protein-mediated proton transport.

Alanine↗
PubMed1993

Oxidized low-density lipoprotein enhances monocyte-endothelial cell binding against shear-stress-induced detachment.

Oxidatively modified low-density lipoprotein may be involved in the adherence of blood monocytes to arterial endothelium in the early atherosclerotic lesion. The present study employed static assays and flow-chamber technique to investigate the adhesive interactions between isolated human blood monocytes and cultured human umbilical vein endothelial cell (EC) monolayer pretreated with Cu(2+)-oxidized human plasma LDL (Ox-LDL) and native LDL (N-LDL). The cell-cell binding force was estimated by the intensity of wall shear stress needed to detach monocytes from an EC monolayer. The number of monocytes attached to EC monolayer was quantitated by microscopic observation, measurement of myeloperoxidase (MPO) activity in monocyte and cellular uptake of Rose Bengal stain. The results show that the proadhesive activity of EC surface for monocytes was strongly induced by Ox-LDL and weakly modulated by N-LDL. Pretreatment of an EC monolayer with Ox-LDL (25 micrograms/ml) for 6 h induced a 2.2-fold increase in the number and an 8-fold increase in the force of monocyte binding to EC monolayer as compared to untreated control. A significant number of monocytes (4.4-times control) were able to maintain their adhesion to Ox-LDL-pretreated EC monolayer under high shear stress (30 dyn/cm2). The cell surface expression of intercellular adhesion molecule 1 (ICAM-1), but not vascular cell adhesion molecule 1 (VCAM-1), in umbilical vein EC was increased by 2.6-fold after treatment of EC with Ox-LDL (50 micrograms/ml) for 6 h compared with non-treated control. On prolonged (> 12 h) incubation, Ox-LDL (> 100 micrograms/ml) was found to have cytotoxic effect on EC as reflected by the loss of EC integrity and detachment at low shear stress. It indicates that a sublethal dose of oxidized LDL may alter vascular endothelium physiology, up-regulate expression of ICAM-1 in EC, enhance monocytes binding against shear-stress-induced detachment, and thus may contribute to atherogenesis.

Cell Adhesion↗
PubMed1993

Recursive partitioning analysis of prognostic factors in three Radiation Therapy Oncology Group malignant glioma trials.

BACKGROUND: Despite notable technical advances in therapy for malignant gliomas during the past decade, improved patient survival has not been clearly documented, suggesting that pretreatment prognostic factors influence outcome more than minor modifications in therapy. Age, performance status, and tumor histopathology have been identified as the pretreatment variables most predictive of survival outcome. However, an analysis of the association of survival with both pretreatment characteristics and treatment-related variables is necessary to assure reliable evaluation of new approaches for treatment of malignant glioma. PURPOSE: This study of malignant glioma patients used a non-parametric statistical technique to examine the associations of both pretreatment patient and tumor characteristics and treatment-related variables with survival duration. This technique was used to identify subgroups with survival rates sufficiently different to create improvements in the design and stratification of clinical trials. METHODS: We used a recursive partitioning technique to analyze survival in 1578 patients entered in three Radiation Therapy Oncology Group malignant glioma trials from 1974 to 1989 that used several radiation therapy (RT) regimens with and without chemotherapy or a radiation sensitizer. This approach creates a regression tree according to prognostic variables that classifies patients into homogeneous subsets by survival. Twenty-six pretreatment characteristics and six treatment-related variables were analyzed. RESULTS: The years). Patients younger than 50 years old were categorized by histology (astrocytomas with anaplastic or atypical foci [AAF] versus glioblastoma multiforme [GBM]) and subsequently by normal or abnormal mental status for AAF patients and by performance status for those with GBM. For patients aged 50 years or older, performance status was the most important variable, with normal or abnormal mental status creating the only significant split in the poorer performance status group. Treatment-related variables produced a subgroup showing significant differences only for better performance status GBM patients over age 50 (by extent of surgery and RT dose). Median survival times were 4.7-58.6 months for the 12 subgroups resulting from this analysis, which ranged in size from 32 to 256 patients. CONCLUSIONS: This approach permits examination of the interaction between prognostic variables not possible with other forms of multivariate analysis. IMPLICATIONS: The recursive partitioning technique can be employed to refine the stratification and design of malignant glioma trials.

Adult↗
PubMed1993

Melittin potentiates guanylate cyclase activation stimulated by atrial natriuretic factor and ATP.

The biologically relevant receptor for atrial natriuretic factor (ANF) has been shown to be membrane-bound guanylate cyclase. While guanylate cyclase is known to be activated by ANF and ATP, the molecular mechanism of the enzyme activation remains unclear. We now show that melittin, the main peptide toxin of bee venom, activates membrane-bound guanylate cyclase and potentiates ANF- and ATP-stimulated guanylate cyclase activity in rat lung membranes. Melittin stimulated basal guanylate cyclase activity by increasing the Vmax without significantly affecting the Km of the substrate, GTP. However, melittin enhances ANF- and ATP-stimulated enzyme activity by altering both the Vmax and the EC50 of ANF and ATP. Although melittin activates guanylate cyclase in crude membranes, it has little effect on the activity of the purified enzyme. The effect of melittin on guanylate cyclase activation in rat lung membranes is attenuated by the Ca2+ chelator, EGTA. These results suggest that the effects of melittin on guanylate cyclase activation may require the participation of accessory proteins or nonprotein factors. Therefore, melittin would be a valuable tool for exploring the molecular mechanisms of ANF-mediated guanylate cyclase activation.

Adenosine Triphosphate↗
PubMed1993

CT characteristics of patients with brain metastases treated in RTOG study 79-16.

The search continues for a favorable subgroup of patients with brain metastases in whom testing of new modalities might show a benefit in overall survival. Complete pre- and post-treatment CT evaluation of the brain was performed in 779 of the 859 patients entered into RTOG protocol 7916, a phase III study of the role of misonidazole combined with radiation therapy in the treatment of brain metastases. Pretreatment scan findings of mass effect, midline shift, massive edema, central necrosis, location of sentinel lesion, and number of lesions were correlated with length of survival for all patients as well as for each treatment group. The only characteristics that showed a statistically significant difference in survival in the overall group were the presence of < or = 3 lesions and the presence of a midline shift. The actual benefit in overall survival, however, was found to be only 3 weeks. The volume of the largest lesion prior to treatment did not correlate well with survival, nor did location of lesions. The time to response, number of responders and absolute decrease in number of lesions were similar for the four treatment arms. Patients who responded to cranial treatment had a significantly prolonged survival over those who did not respond. No CT characteristic evaluated in this study showed value as a clinically relevant prognosticator for patients with brain metastases for the overall group. Patients who fulfilled three of the four favorable clinical characteristics previously described by Diener-West (age < or = 60, KPS > or = 70, primary lesion absent or controlled and brain as sole site of metastasis), were analyzed separately. Those with < or = three lesions had a statistically significantly prolonged survival over those with four or more lesions.

Brain Neoplasms↗
PubMed1993

Thromboxane A2: an endothelium-derived vasoconstrictor in human internal mammary arteries.

The internal mammary artery (IMA) has become the conduct of choice for coronary artery bypass grafting. However, the IMA graft can exhibit vasoconstriction during the perioperative period. Experiments were designed to determine the role of cyclooxygenase products in human IMA during hypoxia. Rings of IMA, with and without endothelium, were suspended in organ baths containing physiologic salt solution. Rings were contracted with norepinephrine and then exposed to hypoxia for 15 minutes. In segments with endothelium, hypoxia induced a transient relaxation followed by contraction. This contraction was associated with a significantly increased production of thromboxane B2, the stable metabolite of thromboxane A2 (n = 10; from 120.7 +/- 3.5 pg/mg wet tissue before hypoxia to 175.8 +/- 5.2 pg/mg during hypoxia; p < 0.05). This hypoxic contraction could be attenuated by indomethacin. However, thromboxane B2 could not be detected in samples from organ baths containing IMA segments without endothelium before or during hypoxia. This study demonstrated that endothelium of human IMA grafts releases thromboxane A2 basally and that production is augmented by hypoxia, which acts to constrict the underlying vascular smooth muscle, increase vascular tone, and promote ischemic events such as vasospasm and thrombosis, particularly in hypoxemic patients.

Endothelins↗
PubMed1993

Surgical management of thrombotic disc valve.

Thrombotic obstruction, a rare but often fatal complication of cardiac valve prostheses, appears to occur more frequently in tilting-disc valves than in other valve designs. Its diagnosis and surgical treatment remain a challenge. Ten consecutive patients who had thrombosis of a tilting-disc valve prosthesis were treated in Chang Gung Memorial Hospital from November 1982 to August 1990. Preoperative clinical features, including exertional dyspnea, new murmur, and absence of a metallic click from the prosthetic valve, occurred in all of the patients. Symptoms were present for 1 week or more before reoperation in 70% of the patients; nevertheless, many patients were referred only after acute exacerbation of heart failure and development of pulmonary edema. Echocardiography confirmed prosthetic valve malfunction in 90% of the patients. One unconfirmed case was later documented by cardiac catheterization. Anticoagulant therapy was in the therapeutic range for only half of the patients at the time of admission. Prompt reoperation was performed for thrombectomy (8 patients, all survived) or valve replacement (2 patients, one death). Long-term outcome was satisfactory in all survivors with a mean follow-up of 31.6 months. These findings emphasize the importance of considering the diagnosis of thrombosis in patients with mechanical heart valve prostheses who are first seen with nonspecific symptoms and minor changes of their physical findings. The diagnosis could be easily made by echocardiography. Thrombectomy is an easy, fast, and safe procedure, especially for these critically ill patients.

Adult↗
PubMed1993

kil-kor regulon of promiscuous plasmid RK2: structure, products, and regulation of two operons that constitute the kilE locus.

The kil-kor regulon of IncP plasmid RK2 is a complex regulatory network that includes genes for replication and conjugal transfer, as well as for several potentially host-lethal proteins encoded by the kilA, kilB, and kilC loci. While kilB is known to be involved in conjugal transfer, the functions of kilA and kilC are unknown. The coregulation of kilA and kilC with replication and transfer genes indicates a possible role in the maintenance or broad host range of RK2. In this work, we found that a fourth kil locus, designated kilE, is located in the kb 2.4 to 4.5 region of RK2 and is regulated as part of the kil-kor regulon. The cloned kilE locus cannot be maintained in Escherichia coli host cells, unless korA or korC is also present in trans to control its expression. The nucleotide sequence of the kilE region revealed two potential multicistronic operons. The kleA operon consists of two genes, kleA and kleB, predicted to encode polypeptide products with molecular masses of 8.7 and 7.6 kDa, respectively. The kleC operon contains four genes, kleC, kleD, kleE, and kleF, with predicted products of 9.2, 8.0, 12.2, and 11.3 kDa, respectively. To identify the polypeptide products, each gene was cloned downstream of the phage T7 phi 10 promoter and expressed in vivo in the presence of T7 RNA polymerase. A polypeptide product of the expected size was observed for all six kle genes. In addition, kleF expressed a second polypeptide of 6 kDa that most likely results from the use of a predicted internal translational start site. The kleA and kleC genes are each preceded by sequences resembling strong sigma 70 promoters. Primer extension analysis revealed that the putative kleA and kleC promoters are functional in E. coli and that transcription is initiated at the expected nucleotides. The abundance of transcripts initiated in vivo from both the kleA and kleC promoters was reduced in cells containing korA or korC. When korA and korC were present together, they appeared to act synergistically in reducing the level of transcripts from both promoters. The kleA and kleC promoter regions are highly homologous and contain two palindromic sequences (A and C) that are the predicted targets for KorA and KorC proteins. DNA binding studies showed that protein extracts from korA-containing E. coli cells specifically retarded the electrophoretic mobility of DNA fragments containing palindrome A. Extracts from korC-containing cells altered the mobility of DNA fragments containing palindrome C. These results show that KorA and KorC both act as repressors of the kleAand kleC promoters. In the absence of korA and korC, expression of the cloned kleA operon was lethal to E.coli cells, whereas the cloned kleC operon gave rise to slowly growing, unhealthy colonies. Both phenotypes depended on at least one structural gene in each operon, suggesting that the operons encode genes whose products interact with critical host functions required for normal growth and viability. Thus, the kilA, kilC, and kilE loci of RK2 constitute a cluster of at least 10 genes that are coregulated with the plasmid replication initiator and the conjugal transfer system. Their potential toxicity to the host cell indicates that RK2 is able to establish a variety of intimate plasmid-host interactions that may be important to its survival in nature.

Amino Acid Sequence↗
PubMed1993

Structure, function, and regulation of the kilB locus of promiscuous plasmid RK2.

The kil-kor regulon of the self-transmissible, broad-host-range plasmid RK2 is a unique network with eight coregulated operons. Among the genes encoded by the kil-kor regulon are trfA, which encodes the replication initiator, and several kil loci (kilA, kilB, kilC, and kilE), each of which is lethal to the host cell in the absence of appropriate negative regulatory elements encoded by the korA, korB, korC, and korE determinants. We have proposed that the functions of the kil loci are related to RK2 maintenance or host range. Here, we report the nucleotide sequence of a 2.44-kb region that includes the lethal kilB determinant. We identified the first three genes of the kilB operon (designated klbA, klbB, and klbC), and we determined by deletion analysis that the host-lethal phenotype requires klbB. The predicted amino acid sequence of the 34,995-Da klbA product reveals a potential ATP-binding fold. The klbB product is predicted to be a membrane protein with a molecular mass of 15,012 Da with homology to the RK2 KlaC membrane protein encoded by the kilA operon. The amino acid sequence of the 12,085-Da klbC product contains a perfect match to the leucine zipper motif common to eukaryotic regulatory proteins. Primer extension analysis revealed unambiguously that transcription of the kilB operon begins 46 nucleotides upstream of klbA. No transcription was initiated from the sequence previously presumed by other investigators to be the kilB promoter. The abundance of kilB transcripts is reduced in the presence of KorB, consistent with the prediction that KorB acts at the level of transcription. A degenerate KorB-binding site that contains a perfect half-palindrome overlaps the kilB promoter, but this site is insufficient for regulation by KorB. The region containing a KorB-binding site located 183 bp upstream of the transcriptional start is required for regulation by KorB, indicating that KorB acts at a distance to regulate transcription of kilB. Our studies with the mutant plasmid pRP101, a transfer-defective derivative of the RK2-like plasmid RP4, demonstrated that the kilB operon includes the conjugal transfer and surface exclusion genes of the Tra2 region. Nucleotide sequence analysis revealed that the transposon Tn7 insertion in pRP101 is located in the klbC gene, and complementation analysis showed that this mutation has a strong polar effect on the expression of genes for conjugal transfer and surface exclusion located several kilobases downstream. A klbA mutant was constructed and found to be both transfer defective and complementable, thus, demonstrating a requirement was constructed and found to be both transfer defective and complementable, thus demonstrating a requirement for klbA product in plasmid transmissibility. These results have demonstrated a role for the kilB operon in conjugal transfer. The kil-kor regulon of RK2 is the only known example of plasmid-mediated coregulation of replication and transfer.

Amino Acid Sequence↗
PubMed1993

Thoracic actinomycosis.

Actinomycotic infection is uncommon and primary actinomycosis of the lung and chest wall has been less frequently reported. This disease may present as chronic debilitating illness with radiographic manifestation simulating lung tumor, pulmonary infiltrating lesion, or chronic suppuration. From 1984 to 1990, we experienced 17 cases of thoracic actinomycosis. There were nine patients who presented with a clinical picture of a suppurative lesions and the remaining eight were suspected of having primary lung tumor initially. In no case was an accurate diagnosis made at the time of hospital admission. Final diagnosis was based on aspiration (n = 3), anaerobic sputum culture (n = 1), bronchoscopic biopsy specimens (n = 4), and histologic examination of the resected tissue in the remaining 9 patients who received surgical excision. Among the 17 patients, 8 were treated medically and the other 9 received surgical intervention followed by antibiotic treatment. Regarding the surgically treated patients, suspected malignancy is the most common indication for operation (seven of nine). However, both medically and surgically treated patients achieved good clinical results, and the postoperative courses were uneventful. We would like to remind physicians of this unusual entity and review our own experience with particular emphasis on the clinical diagnosis and management of this unique disease.

Actinomycosis↗
PubMed1993

Video-assisted thoracic surgery. Manipulation without trocar in 112 consecutive procedures.

Since learning of the video-assisted thoracoscopic techniques in the treatment of thoracic diseases, we have encountered many problems and difficulties because of the limited trocar space and lack of suitable instrumentations. Since March 1992, we have found a simple and easier way to perform this procedure, that is, manipulating through the extended incisional wound without using a trocar. Endoscopic and conventional thoracic instruments are able to pass through the incisional channel freely and manipulate similarly to the technique used in open thoracotomy. All the patients had less postoperative pain, reduced operative time, and prompt return to employment. The technique is effective and is herein described.

Humans↗
PubMed1993

Modified Fontan procedure for complex congenital heart disease.

The Fontan procedure is frequently used for correction of complex congenital heart disease, but the postoperative morbidity and mortality rates are still high. The results in 35 consecutive patients who underwent the Fontan procedure from January 1980 to June 1991 are reviewed. The patients comprised 26 boys and nine girls aged from 1.7 to 14.8 (mean 6.8) years. The underlying diseases were univentricular heart (19 patients), tricuspid atresia (eight), complete atrioventricular canal (three patients, two of whom had straddling atrioventricular valve) and other conditions (five). Valved conduits were implanted in four patients and non-valved in 15. Direct right atrium-pulmonary artery anastomosis was performed in 16 patients. The overall hospital mortality rate was 23% (eight patients); in the final year of the review it was 11%. Follow-up of the survivors ranged from 1 to 120 (mean 25) months. All except two patients attained New York Heart Association functional class I or II. Three patients underwent reoperation for atrioventricular valve regurgitation and conduit stenosis with good results. It is concluded that the Fontan procedure is a good palliative operation for complex congenital heart disease.

Adolescent↗
PubMed1993

A tetrazolium-based(MTT) assay for measuring viability of cultured porcine corneal endothelium.

A tetrazolium-based(MTT) assay was used to evaluate the viability of cultured porcine monolayer corneal endothelial cells. In this study, we tried to find out the best spectra at which scanning multiwell ELISA spectrophometer can obtain the widest range of absorbance (optical density, O.D.) and the ranges of numbers of corneal endothelial cells in which absorbance is in a significant linear relationship with cell numbers. Among the three tested spectra of 450, 540, and 630nm, the widest range of absorbance was at 540 nm, from 0.1193 to 0.6183. At all three tested spectra, numbers of corneal endothelial cells from 50 to 30,000 were in a significant linear relationship with absorbance. Therefore, in the future studies to assay the viability of corneal endothelial cells, we shall choose the spectrum of 540 nm for reading with a scanning multiwell ELISA spectrophotometer, and absorbance(O.D.) from 0.1193 to 0.6183 will be accepted, representing cell numbers from 50 to 30,000.

Animals↗