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Biomedical subjects

Y M Chang

Publications and source records attributed to Y M Chang.

At least 55 records · Page 3Linked to original sources
PubMed1998

Primary insertion of osseointegrated dental implants into fibula osteoseptocutaneous free flap for mandible reconstruction.

Twelve patients with segmental mandibular defects were reconstructed with fibula osteoseptocutaneous flaps and simultaneous placement of osseointegrated implants. Decision to perform this procedure was based on the facts that all patients had benign diseases, did not require postoperative radiotherapy, were in good general and oral conditions, and were psychologically motivated. A total of 34 fixtures was inserted in the first stage. Eight patients underwent second stage surgery, which consisted of connection of the implant abutments to the fixtures and the use of palatal mucosal grafts around the implants. Final dental prostheses were fixed 1 month later in seven patients, at this time. All flaps survived after surgery, and no implant failure was observed after a mean follow-up period of 25 months. Only one fixture was not used during the subsequent stage and was left as a sleeper. Fixed dental prostheses were used in five patients and removable overlay prostheses in the other two. Chewing function was recovered between 4 and 6 weeks after the start using the definitive dental prosthesis. In contrast to previous results, we conclude that excellent results can be achieved when this combined procedure is used in carefully selected patients. In addition, it is confirmed that the fibula osteoseptocutaneous flap is a versatile, reliable composite tissue that facilitates primary placement of osseointegrated dental implants during mandible reconstruction, thus allowing full oral rehabilitation in a shorter period of time.

Adolescent↗
PubMed1998

Pretreatment of colon carcinoma cells with Tomudex enhances 5-fluorouracil cytotoxicity.

The cytotoxic effect of sequence and dose of Tomudex (TX) and 5-fluorouracil (FUra) on an HCT-8 colon carcinoma cell line using a clonogenic assay was evaluated. Synergistic cell kill was obtained with 24 h of exposure to TX followed by 4 h of exposure to FUra. Marginal synergy was obtained with the same sequence but with a 5-day exposure to FUra. The reverse sequence, FUra (either 4 h or 5 days), followed by TX (24 h), resulted in less-than-additive cell kill. The synergistic effect was not due to augmented inhibition of thymidylate synthase, as determined by the measurement of thymidylate synthase activity by tritium release from [5-3H]2'-deoxyuridine. Surprisingly, an increase in intracellular levels of phosphoribosylpyrophosphate was observed after 24 h of exposure to TX, suggesting the possibility of an indirect effect of TX and/or its polyglutamates on purine biosynthesis. Moreover, we observed an increased formation of FUra nucleotides in the cells preexposed to TX, likely due to the increased intracellular levels of phosphoribosylpyrophosphate, that as a consequence led to an enhanced incorporation of FUra into RNA and increased cell killing.

Adenocarcinoma↗
PubMed1997

Ganglion cyst and synovial cyst of the temporomandibular joint. Two case reports.

Ganglion cysts and synovial cysts are lesions rarely associated with the temporomandibular joint. Ganglion cysts arise from myxoid degeneration of the connective tissue of the joint capsule, are filled with viscoid fluid or gelatinous material, and have a fibrous lining. Synovial cysts also contain gelatinous fluid and are lined with cuboidal to somewhat flattened cells consistent with a synovial origin. One case of a ganglion cyst and one case of a synovial cyst of the temporomandibular joint are presented, and their differential diagnosis and management are discussed.

Adult↗
PubMed1997

Mandibular reconstruction with fibular osteoseptocutaneous free flap and simultaneous placement of osseointegrated dental implants.

Insertion of osseointegrated dental implants several months after mandibular reconstruction using vascularized composite bone grafts has proved to be a successful method to achieve mastication and complete oral rehabilitation. Theoretically with primary placement of implants into the new mandible a better access to the bone is achieved, interdental relationships are easier to determine, and oral rehabilitation can be attained in a shorter period of time. Previous results describing this approach, however, are inconclusive and controversial. This review describes our experience with primary insertion of dental implants into fibular flaps used for mandibular reconstruction during ablative surgery. Adequate selection of patients for this combined procedure depends mainly on the pathological nature of the mandible and perioperative radiotherapy. Preoperative determination of soft-tissue and bone requirements, number of osteotomies, rigid fixation method, and familiarity with the use of osseointegrated implants are important factors that must be considered for adequate surgical planning and to achieve good results.

Dental Implantation, Endosseous↗
PubMed1997

Traumatic brainstem deafness with normal brainstem auditory evoked potentials.

A 48-year-old woman became totally deaf after a head injury. Magnetic resonance imaging showed bilateral contusions around the inferior colliculi and the brainstem auditory evoked potentials (BAEP) failed to show any abnormality. This case demonstrates that small, symmetrical, bilateral lesions around the inferior colliculi may cause deafness and may still be associated with a normal BAEP.

Auditory Pathways↗
PubMed1996

Splinting and local steroid injection for the treatment of ulnar neuropathy at the elbow: clinical and electrophysiological evaluation.

OBJECTIVE: To compare the effects of splinting alone in the treatment of ulnar nerve lesion at the elbow with the effects of applying a local steroid injection in addition to splinting. DESIGN: Twelve nerves of 10 patients were randomly assigned into two groups: 5 nerves in Group A were treated with elbow splinting only; 7 nerves in Group B were treated with local steroid injection in addition to splinting. Therapeutic effects were assessed 1 and 6 months after treatment. SETTING: Patients were selected from an outpatient clinic of a VA Medical Center. PATIENTS: Ten patients (12 nerves) with ulnar neuropathy at the elbow confirmed by electrodiagnostic tests. INTERVENTIONS: Elbow splint was given to patients of both Groups A and B. A single dose of 40 mg triamcinolone plus 1 mL of 1% lidocaine was injected around the ulnar nerve at the elbow of Group A patients. MAIN OUTCOME MEASURES: Clinical evaluation of symptoms and signs, and ulnar motor and sensory nerve conduction studies were performed before, 1 month after, and 6 months after treatment. RESULTS: There was significant improvement in symptoms in both groups at 1 and 6 months after treatment. Ulnar motor nerve conduction velocity across the elbow improved at 1 month in Group A only, but showed improvement at 6 months in both groups. There was no significant change in the other parameters either at 1 or 6 months in both groups. In comparing the differences between Groups A and B regarding the changes at 1 or 6 months after treatment, there was no significant difference between the two groups in all parameters. CONCLUSIONS: Splint application alone is adequate to improve the symptoms and ulnar nerve conduction across the elbow. The addition of a steroid injection did not provide further benefit in the treatment of cubital tunnel syndrome.

Adult↗
PubMed1994

Thaliporphine, a positive inotropic agent with a negative chronotropic action.

The effects of thaliporphine on contractions and electrophysiological properties of cardiac tissues were examined. In driven rat left atria and right ventricular strips, thaliporphine (1-30 microM) increased twitch tension dose-dependently. The positive inotropic effect of thaliporphine was unaffected by atenolol (3 microM) and prazosin (1 microM) but was significantly suppressed by verapamil (1 microM). An electrophysiological study revealed that thaliporphine (3-10 microM) markedly inhibited the action potential upstroke and prolonged the action potential duration (APD50) in rat and guinea pig atrial and ventricular cells. At 1-30 microM, thaliporphine reduced the transient outward current (Ito) of the rat ventricular cells in a dose-dependent manner. The peak Ito in rat ventricular cells and the delayed rectifying K+ current (Ik in guinea pig ventricular cells were reduced by thaliporphine (10 microM) to 37.3 +/- 2.1% (n = 8) and 45.3 +/- 1.8% (n = 4), respectively. In rat ventricular cells and guinea pig atrial cells, thaliporphine (1.5 microM) reduced the Na+ inward current (INa) with a negative shift (4-5 mV) relative to its half inactivation potential. For the Ca2+ inward current (ICa) in rat ventricular cells, 10 microM of thaliporphine caused a smaller increase in the peak ICa than 0.5 microM of Bay K 8644. The increase in ICa elicited by both agents was associated with a negative shift of its half activation potential from -10 +/- 2 mV to -18 +/- 2 mV (n = 6) by thaliporphine and -11 +/- 2 to -19 +/- 2 mV (n = 4) by Bay K 8644. These results indicate that thaliporphine is a weak Ca2+ channel agonist with strong Na+ and K+ channel blocking activities. The positive inotropic effect may be due to an increase in calcium entry mediated via partial activation of calcium channels or by inhibition of K+ efflux. Inhibition of K+ efflux would result in prolongation of APD50 and contribute to the negative chronotropic effect of thaliporphine.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1994

Bovine pancreatic deoxyribonuclease F: isoelectric focusing, peptide mapping and primary structure.

DNAase F is a minor isoform of bovine pancreatic DNAase which can be separated from the other isoforms (DNAases A, B, C and D) present in a commercial preparation by a preparative isoelectric-focusing cell (Rotofor; Bio-Rad). The ampholytes and other contaminating proteins present in DNAase F preparations can be removed by chromatography on an affinity column (Cibacron Blue 3GA-agarose) and a hydrophobic-interaction column (phenyl-Sepharose CL-4B). The complete separation of DNAase F from the other isoforms is demonstrated on a thin-layer isoelectric-focusing gel, DNAase F being the most basic (pI 5.68). A procedure is described for tryptic peptide mapping by h.p.l.c. requiring only picomolar amounts of DNAase F protein. The DNAase F map shows two peptide peaks not present in the DNAase A map, and the DNAase F map does not have a peak at the position where a C-terminal peptide of DNAase A is normally eluted. The amino acid compositions and sequences for the two new peptides suggest that Gly240 in DNAase A is changed to Arg240 in DNAase F.

Amino Acid Sequence↗
PubMed1993

Decreased folylpolyglutamate synthetase expression: a novel mechanism of fluorouracil resistance.

HCT-8 cells become rapidly resistant to either 4-h (HCT-8/4hR) or 7-day (HCT-8/7dR) repeated exposures to fluorouracil (FUra). The HCT-8/7dR cells were studied in more detail to determine their mechanism of resistance to FUra. Thymidylate synthase activity, binding of 5-fluorodeoxyuridylate to thymidylate synthase, and incorporation of FUra into RNA were not different between the parental and resistant sublines. However, folylpolyglutamate synthetase activity was markedly decreased in this subline using tetrahydrofolate, 5,10-methylenetetrahydrofolate, and methotrexate as substrates. Northern blot analysis revealed decreased folylpolyglutamate synthetase mRNA expression in HCT-8/7dR cells as compared to HCT-8 cells. These findings indicate that low-dose continuous exposure schedules to FUra are cytotoxic primarily due to inhibition of thymidylate synthase and underscores the role of 5,10-methylenetetrahydrofolate polyglutamates in this inhibition.

Adenocarcinoma↗
PubMed1992

Calcium and catecholamine interactions with adrenal chromogranins. Comparison of driving forces in binding and aggregation.

The soluble core of catecholamine storage vesicles in the adrenal medulla contains high concentrations of the cations calcium (20 mM) and catecholamine (600 mM). Do these cations interact with the abundant vesicle core anionic proteins, the chromogranins? We investigated the binding of calcium and norepinephrine (NE) to bovine adrenal chromogranins by equilibrium dialysis. Both calcium and NE were bound saturably by chromogranins, with low affinity (Kd values of 1.3 x 10(-4) M and 2.1 x 10(-3) M), but high capacity (17 and 32 mol of ligand/mol of chromogranin A). Both ligands bound maximally at a pH greater than 5.5 and were displaced by competing cations in a pattern (trivalent greater than divalent greater than monovalent) consistent with electrostatic components to the interactions. Binding of calcium and NE was not impaired by prior heat denaturation of the chromogranins, and chromogranin A was involved in both binding reactions. Calcium but not NE binding was enhanced by nonpolar solvents. Temperature dependence studies indicated that calcium binding to chromogranins was largely entropy-driven, while NE binding was driven by a significantly negative (favorable) change in enthalpy (5760 cal/mol), even in the face of an unfavorable entropy. Exposure of chromogranins to calcium or NE resulted in precipitation (aggregation) as analyzed by centrifugation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. NE was a more effective chromogranin precipitant than calcium, and in combination, the NE effect was antagonized by calcium. Precipitation of chromogranins by both calcium and NE was inhibited by NaCl at ionic strengths comparable with those of the ligands. These data suggest that chromogranins bind and are precipitated by calcium and NE at affinities compatible with their in situ concentrations, but that the interactions exhibit different thermodynamic driving forces. Furthermore, NE may trigger an enthalpy-driven conformational change in chromogranins, resulting in aggregation.

Adrenal Medulla↗
PubMed1992

Cisplatin-based chemotherapy for the treatment of advanced transitional-cell carcinoma of the urinary tract--a preliminary report.

The CMV (cisplatin, methotrexate, and vinblastine) and M-VAC (methotrexate, vinblastine, doxorubicin, and cisplatin) regimens were used to treat 19 patients with advanced transitional-cell carcinoma (TCC) of the urothelial tract. In the CMV group, the partial response rate was 45.5% and the mean response duration was 6.3 months. No complete response was obtained in our series. The median duration of survival was 15.8 and 8.3 months in responders and nonresponders, respectively. The toxic symptoms included one case of sepsis and three cases of renal toxicity. However, nausea and vomiting were experienced by most patients and required the administration of antiemetics. In the M-VAC group, the median duration of survival for responders was longer than that of nonresponders (greater than 10.2 vs 7.2 months), although the number of patients was too small for this difference to reach statistical significance. The toxic symptoms included one case of sepsis, two cases of renal toxicity, and nausea and vomiting in most patients. Bone metastasis in three patients did not respond to chemotherapy (CMV), a finding that is compatible with the results reported by other investigators. In summary, chemotherapy with the CMV or M-VAC regimen was effective in improving the response rate of patients. However, the duration of response was short, toxicity was severe in some cases, and the efficacy against bone lesions was poor. These problems must be solved to improve the outcome of patients with TCC following chemotherapy with the CMV or M-VAC regimens.

Adult↗
PubMed1991

Prediction of antifolate efficacy in a rat sarcoma model.

A methylcholanthrene-induced rat sarcoma propagated both in vitro and in vivo was used to examine the usefulness of a rapid biochemical in situ assay that measures thymidylate synthase (TS) activity in whole cells to predict sensitivity and resistance to the folate antagonists methotrexate (MTX), 10-ethyl-10-deazaaminopterin (10-EDAM) and trimetrexate (TMTX). There was an excellent correlation between the effects of these drugs on inhibiting TS and cytotoxicity as measured by a clonogenic assay, when the exposure time was 4 hr and those when the rat sarcoma cell line was employed (p less than 0.001). When tumor-cell suspensions were prepared from the rat sarcoma propagated in vivo, they were less sensitive to these antifolates, but the relative effectiveness of the 3 antifolates was similar: TMTX much greater than 10-EDAM greater than MTX. As expected, continuous exposure (10 to 12 days) produced cytotoxicity at a much lower dose of these drugs. When the 3 drugs were tested for anti-tumor effectiveness in rats bearing this tumor, the tumor regression measured was best with TMTX; 10-EDAM was intermediate in effectiveness as compared with MTX. These results indicate that the in situ TS assay and clonogenic assay may be used to predict anti-tumor efficacy of antifolates in vivo in this rat sarcoma.

Aminopterin↗
PubMed1991

Application of fluidized bed combustion to industrial waste treatment.

Landfill and sea-dumping appear to be on their way out as acceptable methods for the disposal of untreated industrial wastes in Taiwan. Recently, there has been interest in the application of fluidized bed technology to waste incineration for efficient energy utilization and environmental protection. A pilot fluidized bed combustion system was used to investigate the incineration performance and parametric test for the waste from an industrial park. According to the experimental results, the appropriate operating conditions, including temperatures of 800-840 degrees C, aeration rates of U(0)/Um(f)-2.0 or so, and on-bed feeding, were recommended to treat such waste. The emissions of SO(x), NO(x) and CO in flue gas meet the ROC-EPA regulation.

Journal Article↗
PubMed1991

[Imported case of malaria in Taiwan: analysis of 11 cases].

The "eradication of malaria" in Taiwan was announced by WHO in 1965. From 1966 to 1989, 919 malaria cases were detected in Taiwan. Of these cases, 803 were classified as imported malaria. During 1977 to 1989, our hospital collected 11 cases of imported malaria, 6 of Plasmodium falciparum (PF), including 1 suspicious case, 2 of Plasmodium vivax (PV), 1 of mixed infection (PF plus PV), and 2 unclassified. Most of the patients presented clinically with fever and chills. Hepatosplenomegaly was the most common abnormal finding during the physical examination. Jaundice and anemia occurred in the more severe cases. No cases had lymphadenopathy which is helpful in making a differential diagnosis. Six cases had thrombocytopenia which may be considered as an indirect sign in the diagnosis. The MCV levels were within normal limits in all of the cases. This may indirectly imply a potential protective effect against malaria infection in cases of congenital hemoglobinopathy such as thalassemia or G6PD deficiency. Initially, 10 cases were given "standard treatment", which consisted of chloroquine 450 mg qd for 2 days then 300 mg qd for 2 days and primaquine 15 mg qd for 2 weeks. Four cases of chloroquine resistance were encountered, all in cases with PF infection. Two cases were grade I delayed type resistance and were successfully treated with Fansidar, tetracycline and quinine. Two cases were grade II resistance and presented clinically as cerebral malaria. Intravenous quinine was given plus Fansidar and tetracycline. The cases were resolved without sequele or recurrence. None of the cases, except for 2, received chemoprophylaxis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Circulating chromogranin A as a diagnostic tool in clinical chemistry.

Chromogranin A, measured in the circulation by radioimmunoassay, has emerged as a useful tool in the evaluation of exocytotic sympathoadrenal activity in man, as well as the diagnosis of the presence and extent of neuroendocrine neoplasia. Here we present current thoughts on the structure and function of chromogranin A, and describe known parameters affecting its plasma concentration.

Adrenal Gland Neoplasms↗
PubMed1989

Inherent resistance of human squamous carcinoma cell lines to methotrexate as a result of decreased polyglutamylation of this drug.

Three human squamous carcinoma cell lines (FaDu, A253, and SQCC/Y1) were tested for sensitivity to methotrexate (MTX) and trimetrexate, a second generation folate antagonist in clinical trials. Two of the three cell lines (A253 and SQCC/Y1) showed inherent resistance to methotrexate, when cytotoxicity was evaluated after short term exposure (4 and 24 h). In contrast, all three cell lines were markedly sensitive to trimetrexate, an antifolate which is taken up by cells by a different transport system than is methotrexate and which is not polyglutamylated. The basis for the natural resistance to methotrexate shown by two of the three cell lines was examined. Levels of dihydrofolate reductase activity, inhibition of this enzyme by methotrexate, and influx of MTX did not differ significantly between the three cell lines; however, resistance was correlated to the amounts of polyglutamates of methotrexate synthesized by the three cell lines. After a 24-h incubation with 10 microM MTX, the A253 cell line was able to form only 35.0 pmol/10(7) cells of polyglutamates, compared to 250 pmol/10(7) cells synthesized by the FaDu cell line, while the SQCC/Y1 cell line, intermediate in sensitivity to methotrexate, was able to form 145 pmol/10(7) cells of MTX polyglutamates. The A253 cell line contained less folylpolyglutamate synthetase activity compared to the FaDu and SQCC/Y1 cell lines. However, it is not clear if this difference is sufficient to explain the marked differences in polyglutamates of methotrexate found between the cell lines. We conclude that decreased polyglutamylation of methotrexate in some human squamous cell carcinomas may be the major contributing factor in inherent resistance to high dose pulse administration of this drug.

Antineoplastic Agents↗
PubMed1989

The basis for intrinsic drug resistance or sensitivity to methotrexate.

Natural resistance to MTX in three different types of malignant cells is discussed. Two causes of resistance found were impaired drug uptake and impaired polyglutamylation. These resistance mechanisms have also been described to occur in cell lines with acquired resistance to this drug. In cells with acquired drug resistance, these phenotypic changes may reflect mutations in genes associated with transport of MTX or the enzyme DHFR, or in some circumstances reversion of the cell to a different phenotype without a mutational event. In cells with intrinsic resistance, the genetic mechanism responsible for these phenotypes is not known. Alternate treatment programs, e.g., with TMTX, or with TMTX and CPG2, a folate depleting enzyme, are under evaluation for these MTX resistant neoplasms.

Carcinoma, Squamous Cell↗