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Biomedical subjects

M C Cheng

Publications and source records attributed to M C Cheng.

At least 19 recordsLinked to original sources
PubMed1999

Controlled acid hydrolysis of colominic acid under microwave irradiation.

The hydrolysis of colominic acid under microwave irradiation was studied and compared with traditional heating methods. The microwave irradiation has several advantages over the heating method in the hydrolysis of colominic acid: (a) products with higher degrees of polymerization are obtained, (b) less lactone byproducts are observed, and (c) the hydrolytic rate is much faster. These advantages are probably due to the microwave effect. Oligosialic acids as the products of the acid hydrolysis of polysialic acid with conventional heating methods were fully lactonized, especially under the conditions of higher temperature and stronger acid.

Hydrolysis↗
PubMed1998

High-performance capillary electrophoretic characterization of different types of oligo- and polysialic acid chains.

We have carried out comparative structural analysis of novel oligo- and polysialic acid chains from diverse sources. Controlled acid hydrolysates of (a) colominic acid, alpha2-->8-linked homopolymer of N-acetylneuraminic acid (Neu5Ac), (b) alpha2-->8-linked oligo/polyNeu5Gc chains present in rainbow trout egg polysialoglycoprotein, and (c) alpha2-->8-linked oligomers of deaminoneuraminic acid (KDN) residues of KDN-rich glycoprotein derived from rainbow trout vitelline envelope were analyzed by high-performance capillary electrophoresis (HPCE). The results showed that three different types of alpha2-->8-linked oligosialic acids having same degree of polymerization can be separated by HPCE. A partial hydrolysate of colominic acid with mild acid was shown by CE to form intramolecular esters during the controlled hydrolysis and the subsequent workup procedure. In contrast, lactonization of (-->5-Oglycolyl-Neu5Gcalpha2-->)n, alpha2-->5-Oglycolyl-linked homopolymer of N-glycolylneuraminic acid (Neu5Gc) present in the egg jelly coat of sea urchin, did not take place as readily as in (-->8Neu5Acalpha2-->)n.

Animals↗
PubMed1998

Novel cytotoxic diterpenes, excavatolides A-E, isolated from the Formosan gorgonian Briareum excavatum.

The chemistry of Briareum excavatum, a Formosan gorgonian coral, was investigated. This study has led to the isolation of five novel marine natural products, excavatolides A-E (1-5), together with brianolide (6). The structures of the above compounds were established by spectral and chemical methods. The relative configuration of excavatolide B (2) was further confirmed by a single-crystal X-ray structure analysis. Cytotoxicity of these compounds toward various cancer cell lines also is described.

Animals↗
PubMed1997

HDR source calibration methods and discrepancies.

PURPOSE: To report the calibration discrepancies observed in HDR sources and our methods of calibration of a new source. METHODS AND MATERIALS: 21 sources have been calibrated since March 1991 to February 1996 and discrepancies are reported in comparison to the certificate value. The calibration methodology used for two different systems: the NEL Farmer system and reentrant well chamber (HDR-1000) are described. A lead shield insert developed for use with the well chamber for timer linearity measurement is described. RESULTS: Eleven sources had discrepancy from 0 to 1%, 7 sources had discrepancy from 1 to 5%, and 3 sources had discrepancy from 5 to 10%. The maximum discrepancy observed was -8.04 % for one source. Our procedure of dealing with situations when discrepancy exceeds the range of +/-5% value is discussed. CONCLUSION: (a) The discrepancies that we observed in our study are compared with other users and found to be within the range of values observed. (b) Due to the easy set up procedure, less prone to error in the use of well chamber and with the use of a new lead insert, we conclude in our case that, the well system can be used for monthly calibration of HDR source and timer linearity measurements. (c) Because the Farmer system has a first generation calibration factor, obtained by interpolation of two calibration energies from ADCL, we prefer to use the Farmer system for determining the activity of the new HDR source.

Brachytherapy↗
PubMed1997

Identification and purification of a spinach chloroplast DNA-binding protein that interacts specifically with the plastid psaA-psaB-rps14 promoter region.

We have previously shown the presence in chloroplasts of sequence-specific DNA-binding proteins that interact specifically with two regions located downstream and upstream from the 5'-transcription start site of the plastid psaA-psaB-rps14 operon. As part of an effort to elucidate the regulatory mechanism of plastid transcription during plant development, we report here the purification and characterization of the chloroplast DNA-binding protein from spinach (Spinacia oleracea L. var. spinosa Ashers et Graeden) leaves that specifically recognizes sequences between positions +64 to +83 relative to the transcription start site. This DNA-binding protein has been highly purified from chloroplasts by using a combination of high-salt extraction, ammonium sulfate precipitation, heparin-agarose chromatography, and sequence-specific DNA-affinity chromatography. The protein exhibited an apparent molecular weight of 59-60 kDa on the basis of gel filtration. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by Southwestern blot analysis further indicated that this DNA-binding protein is dimeric and composed of two approximately 31-kDa subunits. We discuss the properties of this protein in relation to the known chloroplast DNA-binding factors for plastid gene expression.

Base Sequence↗
PubMed1996

Introduction and expression of foreign DNA in isolated spinach chloroplasts by electroporation.

An electroporation-mediated method for the study of foreign gene expression within chloroplasts has been developed. The chloroplast expression vector pHD203-GUS, which consists of coding regions for beta-glucuronidase (GUS) and chloramphenicol acetyltransferase (CAT) separated by a double psbA promoter fragment from pea (in opposite orientation) was electroporated into spinach chloroplasts and the transient gene expression was examined. Conditions for the expression of the reporter genes have been optimized. Both CAT and GUS activities were detected in chloroplasts electroporated with pHD203-GUS, but not with nuclear expression vector pBI221 or negative control pUC18. No GUS activity was detected when pHD203-GUS was electroporated into spinach protoplasts. Dot immunoblot analysis using anti-GUS antibody confirmed the existence of GUS protein in chloroplasts electroporated with chloroplast-specific vector but not the negative controls, excluding the possibilities of endogenous GUS or bacterial contamination. The expression of GUS protein in treated chloroplasts was further confirmed by Western blot analysis.

Cell Fractionation↗
PubMed1996

Characterization of the light-responsive promoter of rice chloroplast psbD-C operon and the sequence-specific DNA binding factor.

The transcription of rice plastid psbD-psbC genes encoding photosystem II reaction center protein D2 and chlorophyll alpha-binding protein CP43 is closely regulated by light. To elucidate the sequence requirement for the light-responsive promoter of psbD-psbC operon, transcriptional analysis of the rice promoter was performed with deleted mutants and site-directed mutants in vitro. Deletion of -546 approximately -100 upstream sequences resulted in 4- to 5-fold decrease in the transcription rate. Further deletion of -99 approximately -40 conserved region of repeated sequences resulted in 2-fold decrease in the transcription rate. The core light-responsive promoter requires "-10" element but not "-35" element for accurate initiation of basal transcription. No downstream promoter element was found in the +4 approximately +111 region. The competitive gel-retardation experiments revealed the presence of DNA-binding protein in the rice chloroplasts, which interacts specifically with the -60 approximately -37 repeated sequences. Southwestern blot analysis further demonstrated that the binding factor is composed of 36-kDa polypeptide(s).

Base Sequence↗
PubMed1995

High dose rate (HDR) brachytherapy technique: for carcinoma of uterine cervix using Nucletron applicators.

This study describes our existing treatment method for high dose rate (HDR) brachytherapy of carcinoma of uterine cervix using Nucletron applicators. Based on our clinical experience with low dose rate (LDR) brachytherapy since 1986, we deliver 40-45Gy by external and 30Gy by internal radiation therapy. The change in regimen using HDR brachytherapy is that internal radiation dose is given in 5 fractions at weekly intervals following external radiotherapy. We have analyzed the dosimetry of 20 patients; total of 100 treatments done at our center using ring-tandem (R-T) and ovoid-tandem (O-T) applicator combinations. Since O-T applicator has more flexibility of using desired tandem length and reduced rectum and bladder dose due to internal shielding inside the ovoids, we have made the transition from R-T to O-T combination of applicator. The dose volume histogram of the isodose curve indicates that there is an increase in isodose volume with the O-T applicator by as much as 1.5 times as compared to R-T applicator. In majority of the treatments, rectum and bladder doses are less than 70% of target dose, however in very few treatments, the bladder dose has increased to more than the target dose, in which case, the applicators were reseated and added more packing or reduced the dose per fraction, for better tolerance of late responding normal tissues. All our dose calculations are checked with an independent calculation method and agreement was obtained with in 5-7% discrepancy.(ABSTRACT TRUNCATED AT 250 WORDS)

Brachytherapy↗
PubMed1995

Seroepidemiological survey of feline retrovirus infections in cats in Taiwan in 1993 and 1994.

In order to investigate the prevalence of infections with three feline retroviruses feline immunodeficiency virus (FIV), feline leukemia virus (FeLV) and feline syncytial virus (FSV) in Taiwan, we collected a total of 75 blood samples from cats from veterinary hospitals, a breeding cattery and a homeless shelter in 1993 and 1994. We examined the presences of anti-FIV and FSV antibodies and FeLV-p27 antigen in these samples by the indirect immunofluorescence and/or enzyme-linked immunosorbent assays. All of the serum samples positive for FIV were obtained from homeless cats and the overall FIV positive rate was 4%. The overall positive rates of FSV and FeLV were 28% and 1.3%, respectively. From these results, together with previous seroepidemiological surveys by others, it was revealed that the prevalence of FIV and FeLV infections appeared to be lower in Taiwan than in the United States or Japan. In contrast, the prevalence of FSV infection in Taiwan was as high as that in Japan.

Animals↗
PubMed1993

Confounded carcinogenicity study of sodium fluoride in CD-1 mice.

To determine its carcinogenic potential, sodium fluoride (NaF) was fed to CD-1 mice for up to 97 weeks. Mice given NaF at a dose of 4, 10, or 25 mg/kg of body weight per day added to a low-fluoride diet were compared to controls given either an unsupplemented low-fluoride diet or laboratory chow. Nonneoplastic changes consistent with those previously recognized from fluoride toxicity were observed in teeth, bones, and joints. Unexpectedly, osteomas occurred in all groups. The incidence of osteomas was similar in groups given the low-fluoride control diet, laboratory chow, or NaF doses of 4 or 10 mg/kg per day. The incidence of osteomas in these groups was increased over that historically experienced at the laboratory and reported in the literature for CD-1 mice. The incidence of osteomas in the mice given 25 mg NaF/kg per day added to a low-fluoride diet was increased over that in the other groups. Osteomas were first observed at Week 55. No malignant bone tumors were observed during the course of the study. The locations, multiplicity, and morphologic features of the osteomas in all groups were similar to those associated with virus-induced bone tumors. Electron microscopic examination revealed abundant retrovirus particles in all osteomas examined from control and test mice. It was concluded that the study was confounded by a retrovirus which contributed to the induction of the osteomas. Because the study was confounded, it cannot be considered a valid bioassay to be used for risk assessment.

Animals↗
PubMed1993

Characterization of the promoter of rice plastid psaA-psaB-rps14 operon and the DNA-specific binding proteins.

Transcriptional analysis of the promoter of rice psaA-psaB-rps14 operon was performed with Bal 31 deleted mutants in spinach chloroplast extracts. Two functional promoters in this operon (denoted as "-175" and "-129" promoters) were revealed to be utilized by the spinach transcription machinery; however only the "-175" promoter is utilized in vivo. The existence of psaA promoter-specific binding factors in the chloroplast extracts was indicated by competitive gel retardation assay and exonuclease III protection analysis. After ammonium sulfate fractionation of the extracts followed by heparin-agarose column chromatography, the sequence-specific binding factors were characterized to be 66-kDa and 31-kDa polypeptides. Southwestern analysis demonstrated that the two protein factors interact independently with the psaA promoter-containing DNA fragment.

Base Sequence↗
PubMed1992

[Dento-facial structural characteristics in Angle Class II malocclusion associated with abnormal facial divergency].

Lateral cephalometric radiographs of 60 adult patients with Angle class 11 malocclusion associated with abnormal facial divergency were collected from the Orthodontic Department of the National Taiwan University Hospital. They were divided into a hyperdivergent group (35 cases) and a hypodivergent group (25 case), according to mandibular plane angle (SN-MP). The 19 landmarks on each cephalometric tracing were digitized into a computer, then computer-aided cephalometric analysis was performed to calculate the 17 skeletal measurements and 13 dentoalveolar measurements. The dento-facial structural characteristics of the hyperdivergent and hypodivergent groups were compared. It was found that the subjects of the hyperdivergent group revealed a greater tendency of divergency in the anterior cranial base plane, Frank-fort horizontal plane, palatal plane, occlusal plane, and mandibular plane. Hyperdivergent facial type, supposedly indicating an open bite or a tendency toward an open bite, has a longer lower anterior facial height, shorter posterior facial height, longer upper anterior and posterior dental height. While, the majority of dentofacial characteristics of the hypodivergent facial type observed in is study were directly opposite to those of the hyperdivergent facial type. The relationships of incisor overbite depth and other skeletal and dentoalveolar parameters were illustrated by Pearson's correlation coefficient and stepwise multiple regression analysis by means of the SPSS/PC statistic program. With the incisor overbite depth as the dependent variable, the independent variables included on the regression analysis were the 10 items of skeletal and dentoalveolar parameters. The compared parameters showed a statistically significant correlation with the incisor overbite depth (P < 0.001). By the stepwise method, the variables included on the regression equation were (1) N-Go-Gn, (2) A-Gn-Ar, (3) N-Ans/ans-Me, and (4) U1L1. The value of R square (R2) in the regression analysis was 0.543. It demonstrated that only a 54.3% variation in incisor overbite depth can be explained by variations in those skeletal and dentoalveolar variables.

Adult↗
PubMed1990

Two-year carcinogenicity study of sodium fluoride in rats.

To determine the carcinogenic potential of sodium fluoride (NaF), we fed Sprague-Dawley rats a diet containing NaF for up to 99 weeks. Rats receiving NaF at a dose of 4, 10, or 25 mg/kg per day added to a low-fluoride diet were compared with controls receiving either a low-fluoride diet or laboratory chow. Each treatment group consisted of 70 rats of each sex. A 30% decrement in weight gain occurred at an NaF dose of 25 mg/kg per day. Evidence of fluoride toxicity was seen in the teeth, bones, and stomach, and the incidence and severity of these changes were related to the dose of NaF and the duration of exposure. Despite clear evidence of toxicity, NaF did not alter the incidence of preneoplastic and neoplastic lesions at any site in rats of either sex. Results from this study indicate that NaF is not carcinogenic in Sprague-Dawley rats.

Animals↗
PubMed1990

Role of surgery in the treatment of cancer of the cervix.

Of the four treatment modalities of invasive cancer of the cervix, surgery and radiotherapy remain the most effective. Surgery is preferred for microinvasive cancers. For stages 1B to 2B, surgery appears to have an edge over radiotherapy, whereas radiotherapy is more widely used for the more advanced cases.

Female↗
PubMed1989

Wertheim's operation--a study of 130 cases.

The Hsu's method of radical hysterectomy and lymphadenectomy procedure is a modification of the Okabayashi's radical hysterectomy. It involves the creation of the pararectal and paravesical spaces completely down to the pelvic floor and the excision en block of the uterus with its appendages, the parametria and the entire cardinal ligaments and the upper 1/3 to 1/2 of the vagina with its paracolpia. The vagina is lengthened by the Hsu's technique of suturing the vagina with a Boston suture incorporating the cut margin of the rectal serosa to the posterior rim of the vagina and stitching the visceral peritoneum 2 cm above the cut margin of the rectal serosa. The ovaries are preserved in young patients. Lymphadenectomy involves the dissection of the anterior and posterior chains of the common iliac nodes, the external iliac, obturator, internal iliac and presacral nodes. The author having been trained in the Hsu's method of radical hysterectomy by Professor Hsu himself, conducted a prospective study of the morbidity, sequelae and survival rates of this operation in Singapore. Between January 1982 and July 1987, 130 cases of cancer of the cervix were operated on by the author. Patients who had lymph node metastasis or parametrial infiltration were given adjuvant post operative irradiation. Every patient was followed up personally by the author. Only six patients were lost to follow-up at varying times after operation. Four cases were excluded from analysis. Of the remaining 126 cases, 67 were stage 1B, 20 stage 2A, 36 stage 2B, 2 were central recurrences following radiotherapy and one corpus cancer stage 2. Eleven patients (8.7%) had operative or post-operative morbidity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗