Search PubMed⌕ Search

Biomedical subjects

T C Chen

Publications and source records attributed to T C Chen.

At least 199 records · Page 11Linked to original sources
PubMed1992

Unilateral acoustic neuromas in childhood without evidence of neurofibromatosis: case report and review of the literature.

A six-year-old female with a unilateral benign acoustic neuroma and no evidence of neurofibromatosis is presented. Review of the literature revealed only 16 cases of unilateral acoustic neuromas in children less than 15 years old. Children often do not appreciate hearing loss when compared with adults. As a result, they often present with larger tumors, thus adversely affecting outcome. The need for early diagnostic tests and a hearing-conservation surgical approach is emphasized. Routine follow-up imaging studies are crucial to rule out the development of a contralateral acoustic neuroma in neurofibromatosis-2 (NF-2).

Audiometry↗
PubMed1992

[The comparison of microleakage among three different dentin bonding agents in class V cavities].

The use of the etching technique and an enamel bonding agent may effectively reduce microleakage of the cavity wall. However, the reduction of marginal leakage relating to class V cavities, is still unsatisfactory according to the dental literature. Due to the structural difference between the dentin and the enamel, though many new dentin bonding agents have been developed lately, none of them work perfectly. In this experiment, the "silver staining technique" was used to investigate the degree of microleakage in class V resin restorations which were bonded with 3 different dentin bonding agents (Scotchbond, Scotchbond 2 and Denthesive). The sample consists of 21 caries free human molars which were divided into 3 groups: 1) Scotchbond v. s. Scotchbond 2, 2) Scotchbond v. s. Denthesive, 3) Scotchbond 2 v. s. Denthesive. Both buccal and lingual surfaces were prepared for class V cavities. The cavities were then filled with composite resin Silux, and immersed in 50% silver nitrate solution for 2 hours, and followed by washing with distilled water. After that these teeth were immersed in photodeveloping solution under the fluorescent light for 3 hours. On finishing, they were washed again, sectioned vertically into mesial and distal halves with a Isomet sectioner and put under a microscope and evaluated for the degree of microleakage with Dr. Going's method. On statistical analysis, the results of this study showed that the degree of microleakage was not significantly different among the 3 dentin bonding agents in class V resin restorations, either on the gingival wall or the occlusal wall.

Dental Caries↗
PubMed1991

Two bacteriophage T4 base plate genes (25 and 26) and the DNA repair gene uvsY belong to spatially and temporally overlapping transcription units.

The bacteriophage T4 DNA recombination-repair gene uvsY located at or near an origin of DNA replication and adjacent to the late base plate genes 25 and 26. Our present results reveal a complex transcription pattern in the region encompassing these genes. Most significantly, uvsY and two ORFs, downstream of it, all of which are transcribed from a middle promoter before the onset of DNA replication, are also part of a larger late transcription unit which includes the base plate genes 25 and 26. The late genes 25 and 26 are transcribed not only late, but also early from one or several early promoters further upstream. Translation, however, is inhibited by secondary structures which sequester the ribosome binding site in the early transcript. We discuss possible advantages of these transcriptional patterns for T4 DNA recombination, replication, and repair. The predicted and in vivo-expressed 23.9-kDa product of gene 26 is smaller than the reported size of gene 26 protein isolated from base plates, suggesting that nascent gp26 might be processed to a larger protein during assembly.

Base Sequence↗
PubMed1991

The construction of endocardial balloon arrays for cardiac mapping.

The advent of multichannel recording systems has enabled clinical mapping to be performed on a beat-by-beat basis using multi-electrode arrays. Surgical ablation of ventricular arrhythmias generally requires endocardial mapping. Clinical usage has indicated that an inflatable balloon array is the most practical design and can obviate the need for ventriculotomy by a transatrial introduction in the deflated state. Successful experience with the left ventricular balloon led to the development of a right ventricular balloon array suitably configured to extend into the outflow tract. Custom moulds are used to create an appropriate balloon from liquid latex. Nylon cloth is cut from a cardboard pattern to fashion a stretchable sock to envelope the balloon. Electrodes are formed by stitching 2-mm silver beads to the balloon sock in a preconfigured pattern. Teflon-coated 31 G multi-strand stainless-steel wires 130 mm in length connect the electrode beads by solder to the multipin connectors for easy hookup to the amplifier inputs. Tygon tubing 0.53 cm in diameter fitted to the balloon allows inflation and pressure monitoring. This basic design has been successfully implemented for the last 6 years.

Arrhythmias, Cardiac↗
PubMed1991

Monostotic fibrous dysplasia of the clivus. Case report.

A case report of monostotic fibrous dysplasia of the clivus in a postadolescent woman is described. Although fibrous dysplasia of craniofacial structures is well documented, involvement of the clivus has not been reported. Diagnosis by clinical, radiographic, and histopathological features is detailed. Implications for the role of surgery and management are discussed.

Adult↗
PubMed1991

Analysis of ras gene mutations in gastrointestinal cancers.

Point mutations of c-Ki-ras genes were analyzed in 33 samples of human gastrointestinal malignancy. DNA extracted from the frozen tissue was amplified by polymerase chain reaction (PCR) and analyzed by direct sequencing and slot-blot hybridization at codons 12, 13 and 61 of c-Ki-ras. In 7 cases out of 19 colorectal cancers, point mutations were found: 3 cases at codon 12, 1 at codon 13, 2 at codon 61 of c-Ki-ras and one case had double mutations at codon 12 and codon 13. In 11 cases of gastric cancer, 4 showed point mutations: 1 at codon 12 and 3 at codon 13 of c-Ki-ras. In 3 pancreatic carcinomas, 2 had point mutations: one at codon 12 and the other at codon 13 of c-Ki-ras. The results indicate that c-Ki-ras gene point mutations are involved in the tumorigenesis of the human gastrointestinal system.

Adult↗
PubMed1991

Serum zinc and copper during long-term total parenteral nutrition.

Changes in serum zinc and copper levels were studied in 17 patients who received 18 courses of total parenteral nutrition for 28 to 89 days. Mean serum zinc levels decreased significantly after 4 weeks of therapy in the group without zinc supplementation when compared with pretreatment levels (p less than 0.05) and in a second group who received about 1.5 mg of zinc per day (p less than 0.05). Serum copper levels fell consistently and significantly in patients of both groups. However, no obvious clinical signs or symptoms of zinc or copper deficiencies were observed. Blood transfusions were not able to significantly change the serum levels of zinc or copper. Although serum alkaline phosphatase has been suggested as a functional indicator of zinc deficiency, the concomitant hepatic or skeletal dysfunction of the patients made its interpretation difficult. These findings indicate that a decrease in serum zinc and copper is common during TPN using solutions unsupplemented with these trace elements. Supplementation of TPN solutions with zinc, copper, and other trace elements is recommended.

Adult↗
PubMed1991

Huge plexiform neurofibroma of the head and liver--case report.

Neurofibromatosis (NF) is a hereditary autosomal dominant disorder. Von Recklinghausen first described NF in 1882, which is now classified as Neurofibromatosis 1 (NF-1). NF-1 is the most commonly encountered NF which affects 1 in 4000 persons. Clinical manifestations of NF-1 include: generalized cutaneous neurofibroma, pigmented skin patches (cafe-au-lait spots), pigmented iris hamartoma (Lisch nodules), skeletal abnormally, CNS tumors, etc. The subject of this case study is a young adult male with a huge plexiform neurofibroma involving both the liver and head regions. The head tumor measured 10 x 8 x 3.5 cm3 in size, weighted approximately 180g with overlying hyperpigmented skin and an underlying congenital skull defect. A CT scan and MRI of the head and neck revealed a well defined lobulated tumor and deformed external ear. A abdominal sonogram, CT scan and MRI showed a huge plexiform neurofibroma with liver invasion. Lisch nodules and multiple cafe-au-lait spots were also found. Surgical removal of the head tumor along with an external ear reconstruction was performed. Satisfactory cosmetic results and improved hearing were achieved.

Adolescent↗
PubMed1990

Biosynthesis and processing of renal mitochondrial glutaminase in cultured proximal tubular epithelial cells and in isolated mitochondria.

Primary cultures of rat renal proximal tubular epithelial cells were used to characterize the biosynthesis and processing of the mitochondrial glutaminase. When the cells were labeled with [35S]methionine in the presence of 20 microM carbonylcyanide m-chlorophenylhydrazone, only a 72-kDa peptide, which co-migrates with the primary translation product of the glutaminase mRNA, was immunoprecipitated. At lower concentrations of carbonylcyanide m-chlorophenylhydrazone, the 68- and 65-kDa peptides that are characteristic of the mature glutaminase and a 71-kDa peptide were synthesized. Pulse-chase experiments suggest that the 72-kDa cytosolic precursor could be quantitatively chased to generate the mature mitochondrial species. The observed kinetics indicate that the 71-kDa species is an intermediate in the import pathway. In addition, the 65-kDa glutaminase peptide was synthesized more rapidly than the 68-kDa peptide, and the two peptides were produced in a final ratio of 3:1, respectively. These results suggest that one subunit of the tetrameric glutaminase may be subject to covalent modification. In vitro processing was also characterized by incubating isolated rat liver mitochondria with the glutaminase precursor that was produced by in vitro translation of acidotic rat renal poly(A+) RNA. This system produced an identical sequence of processing reactions. The in vitro formation of the 71-kDa intermediate required a transmembrane potential. Both the intermediate and the mature forms of the glutaminase were recovered in the mitochondria and were resistant to trypsin digestion. Thus, the glutaminase precursor is rapidly translocated across the inner mitochondrial membrane and initially processed to yield an intermediate. The intermediate is subsequently processed to yield the two peptides that constitute the mature enzyme.

Animals↗
PubMed1990

Asthma and eczema in children born to women with migraine.

Migraine and asthma have been reported to occur in the same person more commonly than would be expected if they are independent. The large Collaborative Perinatal Project provided an opportunity to see if children born to women with migraine or with the group of disorders characterized by asthma and/or allergies were more likely to manifest asthma or eczema in the first 7 years of life. Among children whose mothers had neither migraine nor asthma/allergies, 3.2% had asthma. Of children whose mothers had migraine, but not asthma/allergies, more than 6% had asthma. The risk of asthma among children born to women who had both migraine and asthma/allergies was greater than the risk associated with each maternal disease. The risk of eczema in children was not appreciably influenced by the mother's propensity to migraine or asthma/allergies. The results of this first study of migraine in one generation and asthma in the next lead to the conclusion that the two disorders are probably related.

Adolescent↗
PubMed1990

Flow cytometry measurement of nuclear RNA content in uveal melanoma.

We retrospectively studied the nuclear RNA content in uveal melanomas with known, long-term follow-up. Thirty patients had spindle cell melanomas, 25 had mixed cell tumors, and 9 had epithelioid cell neoplasms. Epithelioid cell types had a higher nuclear RNA content compared to mixed or spindle cell types (p less than 0.05). Using the Cox proportional hazards model, the nuclear RNA content appeared to be an independent prognostic indicator in uveal melanomas, and an increased nuclear RNA content was associated with a worse prognosis (p = 0.001).

DNA, Neoplasm↗
PubMed1990

A case of zinc deficiency during long-term total parenteral nutrition.

A 54-year-old housewife received total parenteral nutrition (TPN) because of an intestinal fistula and total wound breakdown after an emergency operation for perforation of the ileum and diffuse peritonitis. The TPN regimen reversed the catabolism and resolved the abdominal wound and enterocutaneous fistula. Zinc and copper were not supplemented because there was no licensed parenteral trace element solution available. At week 17 of TPN, eczematoid dermatitis appeared on the face, nasolabial folds and chin, and the perineal area. These changes, coinciding with a serum zinc level of 20 micrograms/dl, were consistent with zinc deficiency. Zinc supplementation was commenced giving 6 mg of elemental zinc intravenously daily. The response to zinc therapy was very dramatic. Not only did the serum zinc level increase, but the skin changes returned to normal within 7 days. The patient gradually resumed her usual diet and TPN was discontinued after an approximate duration of 21 weeks. She was later discharged in good health.

Copper↗
PubMed1989

[Evaluation of the effect of glass ionomer liner on microleakage of light-curing composite resin restoration].

Light-curing composite resin restorations with acid etching technique and bonding agents cannot completely reduce the degree of microleakage. One initial report by Dr. Mclean (1985) describing glass ionomers as Class V cavity liners suggested that this product was superior to a resin/dentin bond to avert marginal leakage under a light curing composite. In this study, Wu's silver staining technique was used to evaluate the effect of glass ionomer liner on microleakage of light curing composite-Silux. Twenty one caries-free human molar teeth were selected for study. The Class V cavities were prepared on the buccal and the lingual surface of each tooth. Teeth were divided into 3 groups. Group I: Scotchbond/Silux and Liner/Scotchbond/Silux. Group II: Scotchbond/Silux and Hybond. Group III: Liner/Scotchbond/Silux and Hybond. The degree of microleakage were evaluated with Dr. Going's method by three dentists. The results of this study indicate that Ketac bond Glass ionomer liner was ineffective as a restoration in resisting microleakage on the gingival wall of cavities.

Composite Resins↗
PubMed1989

Inhibition by volume expansion of phosphate uptake by the renal proximal tubule brush border membrane.

Clearance studies and examination of brush border membrane (BBM) vesicle transport were performed in rats that had been volume expanded by 10% of body weight. The results were compared to those obtained in control animals. The data indicate that the phosphaturia which resulted from the expansion procedure was accompanied by an inhibition of proximal BBM phosphate uptake. The BBM uptake of proline and glucose was unchanged. Furthermore, since plasma calcium did not change, the findings are compatible with the view that the membrane transport changes resulted from alterations induced by the saline loading itself, rather than (or in addition to) any changes caused by parathyroid hormone excretion.

Animals↗
PubMed1989

Characterization of primary cell cultures derived from rat renal proximal tubules.

Proximal tubules were prepared from rat kidney cortex by collagenase digestion and purified by Percoll gradient centrifugation. Their enrichment was estimated by comparing the specific activities of various cell-specific enzymes in homogenates of renal cortex and of the isolated tubules. The tubules were cultured in a 50:50 mixture of Dulbecco's modified Eagle's and Ham's F12 media supplemented with insulin, transferrin, epidermal growth factor, hydrocortisone, and prostaglandin E1. After 2 to 3 d an extensive outgrowth of epithelial cells developed from the attached tubules. After 5 to 7 d near confluent monolayers were obtained. Hormonal responsiveness, marker enzyme activities, and transport properties were determined to further characterize the primary cultures. The cultured cells exhibited increased cyclic AMP production in response to parathyroid hormone but not calcitonin or vasopressin, consistent with the absence of cells derived from distal and collecting tubules. The cells also retained significant levels of 25-hydroxyvitamin D3-1 alpha-hydroxylase, alkaline phosphatase, and gamma-glytamyl-transpeptidase, three enzymes that are primarily associated with the proximal tubule. The cultured epithelial cells also exhibit a Na+-dependent phosphate and glucose transport systems. Therefore, the cells retain many functional properties that are characteristic of proximal tubules. Thus, the primary cultures should be suitable for the study of processes that occur specifically within this segment of the rat nephron.

Animals↗