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Biomedical subjects

D C Chen

Publications and source records attributed to D C Chen.

At least 19 recordsLinked to original sources
PubMed2003

Analysis of microcystins in cyanobacteria blooms and surface water samples from Meiliang Bay, Taihu Lake, China.

Taihu Lake is the third largest freshwater lake in China. In recent years, the water pollution of cyanobacteria blooms has become a severe problem in this area. Microcystins (MCs) are an important group of toxic compounds mainly produced by some cyanobacteria species and have both acute and chronic hepatotoxic effects on animals and humans. This paper presents the first data on the identification and detection of MCs in both natural occurring cyanobacteria blooms and surface water samples (0-0.5 m), collected from Meiliang Bay, Taihu Lake, China. A conventional method for extraction and isolation of MCs from cyanobacteria blooms was applied. High-performance liquid chromatography (HPLC) analysis showed that the main toxic component in the cyanobacteria materials was MC-LR. The monoclonal antibody (mAb) against MC-LR produced by hybridoma technique was employed for direct competitive ELISA to detect the concentrations of MCs in bloom and water samples collected in 2001. The results not only revealed the presence of MCs but also temporal variations of MCs levels of three sampling stations in Meiliang Bay in 1 year. It is obvious that the MC contents were relatively higher during warm months and related with the status of eutrophication. Our study indicates the threat associated with MCs in water body of Taihu Lake. To prevent the MCs potential hazard on public health in this area, some necessary measures of monitoring and control of growth of cyanobacteria are urgently needed.

Bacterial Toxins↗
PubMed2003

Effect of circumferential undercut placement in the root canal wall on the retention of a tapered post in large and small root canals.

OBJECTIVES: This study examined the influence of root canal space and circumferential undercut placement in the dentine wall on the retention of a prefabricated Root Keeper post. METHODS: Twenty-four extracted single-rooted teeth, having narrow root canal spaces, were decoronated, treated endodontically, and then centrally embedded in resin blocks. All canal spaces were prepared with a no. 2 Peeso reamer to an 8mm depth, and half the specimens were successively treated with a no. 3 Peeso to depths of 5 and 8mm for the small canal group (SC) and large canal group (LC), respectively. An L-type keeper post (Aichi Steel Co.) was luted to each canal with resin cement. The assembly was thermocycled 2000 times (4-60 degrees C), and post retention was measured. Afterwards the dislodged post with the intact structure was sandblasted, and the canal was cleaned and slightly undercut using an inverted cone bur. Six treated posts were recemented for both grooved large canal (GLC) and grooved small canal (GSC) groups, and the repaired retentive strengths were measured. RESULTS: Keeper posts cemented in SC (84.26+/-31.85N) showed better (p<0.05) retention than those cemented in LC (41.92+/-22.36N). Interestingly, the repaired strengths of the recemented post increased in both GSC (104.29+/-11.89N) and GLC (96.65+/-6.91N). All posts, except for one in the GLC, failed at the keeper-post joint. CONCLUSIONS: Prefabricated Root Keeper posts had lower retentive strength in roots with a large canal space. Placement of a circumferential undercut in the root canal wall significantly enhanced the retention of the short tapered posts.

Cementation↗
PubMed2001

Determination of urine catecholamines by capillary electrophoresis with dual-electrode amperometric detection.

Demonstrated in this study is that without pretreatment and preconcentration nanomolar-level catecholamines in human urine samples can be quantitatively determined with ease by utilizing capillary electrophoresis coupled with amperometric detection. The detector employs a parallel-opposed dual-electrode scheme assembled with an on-capillary electrode and a disk electrode and takes advantage of the redox cycling of analytes between the two working electrodes to improve the limit of detection. The matrix effect of urine samples significantly decreases the detection sensitivity from that obtained in standard solutions. Therefore, calibration curves derived from standard solutions cannot be used in quantitative determination of catecholamines. Methods of standard addition and internal standard have been studied. The results suggest that isoproterenol is a good internal standard to facilitate the measurements of dopamine, epinephrine, and norepinephrine in human urine samples.

Catecholamines↗
PubMed2001

Characterization of a Saccharomyces cerevisiae mutant with oversecretion phenotype.

An oversecreting mutant of Saccharomyces cerevisiae was obtained from about 400 meiotic segregants derived from thediploid cells made by crossing the HBsAg-induced mutant NI-C with the wild-type strain Sey6211. When transformed with a plasmid containing mouse alpha-amylase cDNA, the mutant (NI-C-D4) exhibited an increased capacity (up to 13-fold) for the secretion of mouse alpha-amylase, higher than the parental strains and other standard wild-type strains. It was also shown that alpha-amylase secreted by the oversecreting mutant had a higher activity and contained more of the non-glycosylated form than the glycosylated form. This isolated oversecreting, low-glycosylation mutant may prove to be a potential S. cerevisiae host for the production of foreign proteins. Further genetic analysis suggested that the mutation responsible for the mutant's oversecretion was partially dominant and that both the oversecretion and low-glycosylation phenotypes were governed by a single chromosome mutation. These pleiotrophic phenotypes may be attributed to a defect in the synthesis of an ER-resident chaperone.

Endopeptidases↗
PubMed2001

Involvement of the XpsN protein in formation of the XpsL-xpsM complex in Xanthomonas campestris pv. campestris type II secretion apparatus.

The xps gene cluster is required for the second step of type II protein secretion in Xanthomonas campestris pv. campestris. Deletion of the entire gene cluster caused accumulation of secreted proteins in the periplasm. By analyzing protein abundance in the chromosomal mutant strains, we observed mutual dependence for normal steady-state levels between the XpsL and the XpsM proteins. The XpsL protein was undetectable in total lysate prepared from the xpsM mutant strain, and vice versa. Introduction of the wild-type xpsM gene carried on a plasmid into the xpsM mutant strain was sufficient for reappearance of the XpsL protein, and vice versa. Moreover, both XpsL and XpsM proteins were undetectable in the xpsN mutant strain. They were recovered either by reintroducing the wild-type xpsN gene or by introducing extra copies of wild-type xpsL or xpsM individually. Overproduction of wild-type XpsL and -M proteins simultaneously, but not separately, in the wild-type strain of X. campestris pv. campestris caused inhibition of secretion. Complementation of an xpsL or xpsM mutant strain with a plasmid-borne wild-type gene was inhibited by coexpression of XpsL and XpsM. The presence of the xpsN gene on the plasmid along with the xpsL and the xpsM genes caused more severe inhibition in both cases. Furthermore, complementation of the xpsN mutant strain was also inhibited. In both the wild-type strain and a strain with the xps gene cluster deleted (XC17433), carrying pCPP-LMN, which encodes all three proteins, each protein coprecipitated with the other two upon immunoprecipitation. Expression of pairwise combinations of the three proteins in XC17433 revealed that the XpsL-XpsM and XpsM-XpsN pairs still coprecipitated, whereas the XpsL-XpsN pair no longer coprecipitated.

Bacterial Proteins↗
PubMed2000

Asparagine as a nitrogen source for improving the secretion of mouse alpha-amylase in Saccharomyces cerevisiae protease A-deficient strains.

A modified chemically defined medium was achieved by using asparagine as a nitrogen source to increase the production of secreted mouse alpha-amylase in several Saccharomyces cerevisiae protease A-deficient (pep4) strains. The specific productivity (quantity) and the 53 kDa non-glycosylated active form (quality) of mouse salivary alpha-amylase in liquid medium containing asparagine was remarkably improved compared to media containing other nitrogen sources, including ammonium sulphate, glutamic acid, arginine, casamino acids, yeast extract and peptone. Similar improvement was also observed on starch solid agar regarding the clarity and size of the halo zone formed by alpha-amylase activity. Compared with ammonium sulphate, advantages of using asparagine as the nitrogen source in liquid or solid medium included increasing the cell mass of test strains, recovering the viability of protease-deficient strains to levels similar to the wild-type strain, and increasing the copy number of the mouse alpha-amylase expression vector in test strains. In turn, these advantages apparently contributed to the increase of secretion of mouse alpha-amylase in several test strains and especially in the protease A-deficient strains. In addition to demonstrating the use of modified chemically defined medium to improve the quality and quantity of secreted mouse alpha-amylase, this study also provides a new strategy to improve the secretion of heterologous proteins in protease A deficient strains.

Amino Acids↗
PubMed2000

Contributing factors of mandibular deformation during mouth opening.

OBJECTIVES: A decrease in mandibular arch width during forced opening has been documented. However, the contributing factors of mandibular deformations are still unclear. This study investigated the mandibular deformation during mouth opening, and searched for contributing factors related to this phenomenon. METHODS: Sixty-two dental students volunteered for this study. A linear variable differential transducer (LVDT) was cemented on the mandibular first molars to record mandibular deformation during mouth opening. Proposed factors including geometric factors of the mandible such as lower gonial angle, mandibular length, symphyseal width and height were measured from cephalometric analysis. Densitometric analysis was performed to detect symphyseal area and bone density. RESULTS: The changes in width between the mandibular first molars ranged from 20 to 437 microm, which was negatively correlated to the symphyseal width, area, and bone density. Where the lower gonial angle had a positive influence, the arch width changed during mouth opening. A multifactorial model showed a significant correlation between the set of predictor variables (symphyseal area, bone density, and mandibular length) and mandibular deformation. CONCLUSIONS: Mandibular arch width narrowed during forced opening. Subjects with smaller symphysis, lower bone density and longer mandible tend to have larger arch width changes.

Adult↗
PubMed2000

Retentive and compressive strengths of modified zinc oxide-eugenol cements.

OBJECTIVES: This investigation sought to improve the handling and physical properties of a commonly used temporary zinc oxide-eugenol cement by changing the base/accelerator (B/A) ratio or combining it with a petroleum jelly or fluoride varnish. METHODS: Twelve modifications of a temporary cement were evaluated in terms of retentive strength, compressive strength at 24 h, film thickness and by scanning electron microscopy. RESULTS: Decreasing the B/A mixing ratio increased the retentive and compressive strengths, but reduced the film thickness of the cement. By increasing the percentage of incorporated petroleum jelly or fluoride varnish in the cement, there was a progressive decrease in the retentive and compressive strengths and in film thickness. CONCLUSIONS: Modifications of a zinc oxide-eugenol temporary cement to change the B/A ratio or to incorporate additives resulted in variations in physical properties. All modified forms of the cement had a film thickness less than 25 microns and a compressive strength below 35 MPa. With a wide range of retentive strength, modified forms of zinc oxide-eugenol cement may be found to have diverse clinical applications.

Analysis of Variance↗
PubMed2000

Association of the cytoplasmic membrane protein XpsN with the outer membrane protein XpsD in the type II protein secretion apparatus of Xanthomonas campestris pv. campestris.

An xps gene cluster composed of 11 open reading frames is required for the type II protein secretion in Xanthomonas campestris pv. campestris. Immediately upstream of the xpsD gene, which encodes an outer membrane protein that serves as the secretion channel by forming multimers, there exists an open reading frame (previously designated ORF2) that could encode a protein of 261 amino acid residues. Its N-terminal hydrophobic region is a likely membrane-anchoring sequence. Antibody raised against this protein could detect in the wild-type strain of X. campestris pv. campestris a protein band with an apparent molecular mass of 36 kDa by Western blotting. Its aberrant slow migration in sodium dodecyl sulfate-polyacrylamide gels might be due to its high proline content. We designated this protein XpsN. By constructing a mutant strain with an in-frame deletion of the chromosomal xpsN gene, we demonstrated that it is required for the secretion of extracellular enzyme by X. campestris pv. campestris. Subcellular fractionation studies indicated that the XpsN protein was tightly associated with the membrane. Sucrose gradient sedimentation followed by immunoblot analysis revealed that it primarily appeared in the cytoplasmic membrane fractions. Immune precipitation experiments indicated that the XpsN protein was coprecipitated with the XpsD protein. In addition, the XpsN protein was co-eluted with the (His)(6)-tagged XpsD protein from the metal affinity chromatography column. All observations suggested that the XpsN protein forms a stable complex with the XpsD protein. In addition, immune precipitation analysis of the XpsN protein with various truncated XpsD proteins revealed that the C-terminal region of the XpsD protein between residues 650 and 759 was likely to be involved in complex formation between the two.

Amino Acid Sequence↗
PubMed2000

Verrucous carcinoma of the uterine cervix.

Verrucous carcinoma is a variant of squamous cell carcinoma that is often found in the oral cavity, skin and larynx. It rarely occurs in the genital tract, especially in the cervix. A 66-year-old postmenopausal female had undergone a total abdominal hysterectomy and bilateral salpingo-oophorectomy at a local hospital 1 year previously, due to carcinoma in situ of the cervix. The patient complained of profuse discharge from the vagina. Under the impression of chronic inflammation and suspicion of cancer recurrence, the patient was transferred to the Tri-Service General Hospital. A pelvic examination revealed a cauliflower-like, fungating mass about 4 cm in diameter located in the anterior vaginal vault. A biopsy disclosed verrucous carcinoma. Cystoscopy with bladder biopsy also confirmed direct tumor invasion into the bladder trigone. Anterior exenteration was performed including radical cystectomy, ileal conduit, vaginectomy, bilateral pelvic lymph node dissection and appendectomy. The final pathology report was verrucous carcinoma with bladder invasion. The margins of the ureters and vaginal cutting end were free of cancerous cells. Surgical excision is the treatment of choice for verrucous carcinoma. Radiotherapy is contraindicated because it may induce anaplastic transformation with subsequent regional and distant metastasis. Further surgical excision, even exenteration, is required for recurrent tumors.

Aged↗
PubMed1999

Postjunctional alpha2-adrenoceptors in the rat tail artery: effect of sex and castration.

To investigate sex-related differences in vasoconstrictor responses to postjunctional alpha2-adrenoceptor activation, isolated ring segments of tail arteries from Fischer-344 rats were studied. Addition of the alpha2-adrenoceptor agonist, UK-14304 [5-bromo-6-(2-imidazoline-2yl)-aminol-quinoxaline], enhanced vasoconstriction to the selective alpha1-adrenoceptor agonist, methoxamine, in arteries from both males and females. The response to UK-14304 was significantly greater in arteries from males as compared to female arteries. Addition of alpha2-adrenoceptor antagonist, idazoxan or rauwolscine, shifted norepinephrine concentration response curves to the right. Antagonist effects also tended to be greater in arteries from males as compared to females. After gonadectomy, male-female differences persisted; thus, removal of sex hormones in either males or females did not alter responses to either agonists or antagonists of alpha2-adrenoceptors. These findings suggest that sex differences in alpha2-adrenoceptor function are not maintained by either male or female gonadal steroid hormones but may be developmentally regulated.

Adrenergic alpha-2 Receptor Agonists↗
PubMed1999

A variant of Saccharomyces cerevisiae pep4 strain with improved oligotrophic proliferation, cell survival and heterologous secretion of alpha-amylase.

A variant of Saccharomyces cerevisiae pep4 strain 20B12, with improved oligotrophic proliferation, cell survival and secretion of heterologous mouse alpha-amylase, is described. Previously we reported a procedure to enrich NI transformants that are not inhibited by cytotoxic expression of hepatitis B virus surface antigen in the secretion pathway of the protease-A-deficient (pep4) strain. To use the NI cells as a host for heterologous expression, we tried to amend the introduced pYAS/12S vector and obtain a host strain, NI-C, with stable NI phenotype and trp1 marker restored. Southern analysis of genomic DNA of NI-C suggested that the original pYAS/12S was abnormally rearranged and not completely corrected. Further assay showed that the viability and mitotic ability of the NI-C strain were increased. While using the NI-C strain as host for plasmid transformation and heterologous expression of mouse alpha-amylase, we observed that transformed colonies grew more quickly and secreted more alpha-amylase than general yeast strains. A further test showed that the NI-C strain was able to use mouse alpha-amylase as a positive selection marker to form transformed colonies on nitrogen-starved plates that contain starch as the sole carbon source. The results imply that the NI-C variant is an improved pep4 strain that can be used for heterologous expression and for the development of new selective markers in the yeast transformation system.

Animals↗
PubMed1999

Endometriomas: diagnostic performance of US.

PURPOSE: To determine the diagnostic performance of specific ultrasonographic (US) features in discriminating endometriomas from other adnexal masses. MATERIALS AND METHODS: Two sonologists independently reviewed the sonograms of 252 adnexal masses in 226 women and recorded US features by using a standardized checklist. The diagnostic performance of specific US features and overall reviewer impression in discriminating endometriomas from other adnexal masses were evaluated. RESULTS: There were 40 endometriomas. Diffuse low-level internal echoes were present in 38 (95%) endometriomas and 40 (19%) nonendometriomas (positive likelihood ratio, 5). The positive likelihood ratio for the diagnosis of endometrioma increased to 8 if masses with neoplastic features at gray-scale US were excluded, allowing identification of 30 endometriomas (75%). The presence of multilocularity or hyperechoic wall foci further increased the positive likelihood ratio to 48, allowing the identification of 18 endometriomas (45%). CONCLUSION: An adnexal mass with diffuse low-level internal echoes and absence of particular neoplastic features is highly likely to be an endometrioma if multilocularity or hyperechoic wall foci are present. A patient with a mass with diffuse low-level internal echoes and other US features may benefit from additional imaging.

Adnexal Diseases↗
PubMed1999

Radioaerosol scintigraphy in infants and children born to mothers with HIV disease. Pediatric Pulmonary and Cardiovascular Complications (of Vertically Transmitted Human Immunodeficiency Virus) Study Group.

PURPOSE: To determine the usefulness of technetium 99m diethyltriaminepentacetic acid (DTPA) radioaerosol inhalation-clearance scintigraphy for early detection of pulmonary complications of human immunodeficiency virus (HIV) disease in children. MATERIALS AND METHODS: A total of 301 studies were performed in 132 HIV-positive children (group 1; mean age, 46.6 months). In children born to HIV-positive mothers (group 2), 273 studies were performed in 160 children who eventually were proved to be HIV negative (mean age, 10.3 months), and 80 studies were performed in 47 HIV-positive children (mean age, 15.6 months). Radioaerosol studies were performed by using commercially available radioaerosol nebulizers. Pulmonary clearance half-time was measured by using conventional gamma camera computer systems. Radioaerosol results were correlated with indexes of pulmonary health and function. RESULTS: The HIV-negative, group 2 children had a mean radioaerosol clearance half-time (58.1 minutes; 162 studies in 108 children) similar to that reported in healthy adults. Group 1 children with pulmonary involvement exhibited a faster mean clearance half-time (28.6 minutes) than did children without evidence of pulmonary involvement from either group 1 or group 2 (P < .05). A faster pulmonary clearance rate did not simply reflect the presence of chest disease that also was detectable on radiographs (P = .3). CONCLUSION: Quantitative DTPA radioaerosol clearance studies may provide useful information about pulmonary involvement in selected children with HIV disease.

Administration, Inhalation↗
PubMed1999

Inhibitory effects of nitric oxide and interleukin-10 on production of tumor necrosis factor alpha, interleukin-1 beta, and interleukin-6 in mouse alveolar macrophages.

AIM: To observe the effects of nitric oxide and interleukin-10 (IL-10) on inflammatory reaction in mouse alveolar macrophages (AM). METHODS: AM from mice were stimulated by lipopolysaccharides (LPS) 10 mg.L-1 and nitric-oxide synthase inhibitor, S-methylisothiorea sulfate (SMT) or nitric-oxide donor, S-nitroso-N-acetyl-D, L-penicillamine (SNAP). The production of tumor necrosis factor alpha (TNF alpha), IL-1 beta, IL-6, and IL-10 by AM were measured by ELISA. RESULTS: After LPS-stimulation, TNF alpha, IL-1 beta, and IL-6 peaked at 6, 12, and 24 h, respectively by AM. SMT inhibited LPS-induced nitric oxide release and increased IL-1 beta and IL-6 secretions in AM, but the TNF alpha levels remained unchanged. SNAP had inhibitory effects on IL-1 beta and IL-6 secretions in a concentration-dependent manner, but exerted no effect on TNF alpha release. TNF alpha, IL-1 beta, and IL-6 secretions were inhibited by recombinant IL-10, but the cytokines release was upregulated by anti-IL-10 monoclonal antibody. CONCLUSION: Both endogenous and exogenous nitric oxide and IL-10 had inhibitory effects on the LPS-induced TNF alpha, IL-1 beta, and IL-6 secretions in mouse AM.

Animals↗
PubMed1999

[Studies on individual characters of juvenile delinquents in Fujian province].

Ashenk's Character Questionnaire was adopted to study the relationship between juvenile delinquency and individual characters. 621 delinquents at the age of 13-19 and 1371 school students (as control group) were questioned, and results were statistically analyzed. For male delinquents of 16-19, scores of extroversion, psychosomatic and nervosity were significantly higher than for control group (P < 0.01). For male delinquents of 13-15, scores of psychosomatic and nervosity were significantly higher than for control group (P < 0.01). For female delinquents of 16-19, score of nervosity was lower than for control group (P < 0.05). Different types of delinquency had no statistical relations with characters. The study reveals that characters of psychosomatic and nervosity might be related with male delinquent crimes, and that stabilization with female delinquent crimes.

Adolescent↗