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Biomedical subjects

C S Chiu

Publications and source records attributed to C S Chiu.

17 recordsLinked to original sources
PubMed1992

The facial soft tissue profile of the southern Chinese: prosthodontic considerations.

A simple photographic setup was established to produce standardized life-sized black and white prints of Southern Chinese adults. Facial soft tissue profile analysis was performed on 28 men and 31 women aged 19 to 30, dentate Chinese, having class I occlusion and originating from Guangdong province. The facial profile values studied included the profile convexity, the interlabial contour, the nasolabial contour, the columella and upper lip inclination angles to the true horizontal, and the relative positions of upper and lower lips from the Esthetic plane. Data obtained were compared with those from previous Caucasian studies and other accepted empirical values. The lower third of the face presented the greatest ethnic difference: the interlabial contour was more convex and the upper and lower lips were more protrusive among the Southern Chinese. The widely-used standard of a right-angled nasolabial contour proved to be applicable among the Southern Chinese adult males. However, a more obtuse nasolabial angle, almost 100 degrees, occurred among the women.

Adult↗
PubMed1992

Inhibition of mammalian ribonucleotide reductase by cis-diamminedichloroplatinum(II).

Ribonucleotide reductase is a highly regulated, rate-limiting activity in the synthesis of DNA. A previous study has shown that the Escherichia coli enzyme is inhibited by the clinically important antitumor agent cis-diamminedichloroplatinum(II) (DDP), and this has led to the hypothesis that ribonucleotide reductase is an important site of action for this chemotherapeutic agent. This hypothesis has been directly tested in this investigation. We observed that DDP inhibits the mammalian ribonucleotide reductase, with 50% inhibition occurring at 0.3 mM. Unlike the E. coli enzyme where only one of the two protein components is targeted by DDP, we observed that both of the mammalian proteins (R1 and R2) were sites for the inhibitory activity of the drug. Colony-forming experiments, enzyme activity studies, and analyses of R1 and R2 message levels in mutant cell lines containing either high levels of ribonucleotide reductase activity or exhibiting resistance to the cytotoxic effects of DDP were used to further investigate the potential role of ribonucleotide reductase in DDP cytotoxic action and drug resistance. These studies did not support a hypothesis formulated in the earlier investigation that inhibition of ribonucleotide reductase is an important component of DDP cytotoxic activity or that it is a major participant in DDP resistance mechanisms. From a biological point of view, DDP is a very active drug, and in addition to its cytotoxic effects it is capable of inducing a variety of cellular changes. Whether or not the inhibition of mammalian ribonucleotide reductase activity that we have described in this study plays a role in mediating any of these other effects remains to be determined.

Animals↗
PubMed1991

Reproducibility of natural head position.

The orientation of the head, when the natural head position was adopted, was measured relative to the true vertical on standardized black and white profile photographs. Two methods of obtaining the natural head position were compared and their reproducibility tested. No statistically significant difference was found between the two different methods or at different sittings.

Adult↗
PubMed1989

Experience with the management of primary endodermal sinus tumor of the mediastinum.

Ten male patients with extensive primary endodermal sinus tumor of the mediastinum were treated with chemotherapy (with or without surgical excision and radiation therapy) between 1977 and 1985. Three patients, treated with cyclophosphamide-vincristine-based chemotherapy, died 1.5, 2.5, and 6.0 months, respectively, after initial diagnosis. Of the seven patients treated with cisplatin-based chemotherapy, one patient died of septicemia at 2.5 months after diagnosis and was disease-free at autopsy examination. Three other patients died of progressive disease at 7.0, 13.0, and 14.0 months, respectively. The three survivors remain alive at 17.0, 31.0, and 40.0 months from diagnosis; all are without evidence of disease. Of the three patients who underwent excision of the residual mediastinal tumor after cisplatin-based chemotherapy, persistent local disease was found in two patients. One of these two patients died of recurrent disease. All surviving patients had surgical resection of the tumor either before or after cisplatin-based chemotherapy, with or without radiotherapy and the timing of therapeutic interventions was guided by changes in the serum alpha-fetoprotein concentrations after initial therapy and during follow-up. Our experience suggests that the optimal management of patients with primary mediastinal endodermal sinus tumor requires an aggressive multidisciplinary approach guided by the extent of the tumor and the serum tumor marker levels.

Adolescent↗
PubMed1989

Left subclavian arterioesophageal fistula induced by a foreign body.

A left subclavian arterioesophageal fistula was diagnosed in a 35-year-old man at exploratory thoracotomy for suspected aortoesophageal fistula. After successful closure of the arterial fistula the patient developed a mediastinal abscess and esophagopleural fistula. The latter was successfully managed by retrosternal jejunal esophagoplasty followed by excision of the thoracic esophagus. This report documents a case of left subclavian arterioesophageal fistula and illustrates the importance of early diagnosis and surgical intervention of arterial perforation secondary to a foreign body in the esophagus.

Abscess↗
PubMed1976

Simultaneous initiation of synthesis of bacteriophage T4 DNA and of deoxyribonucleotides.

In earlier reports we have suggested that bacteriophate T4 DNA replication occurs in a complex composed of the proteins required for polymerization and the system of enzymes synthesizing the deoxyribonucleoside triphosphate precursors of DNA. T4-induced dCMP hydroxymethylase and dTMP synthetase, though demonstrable in extracts soon after infection, are not active in vivo until about 5 min. The in vivo activities increase exponentially for approximately 15 min and then become constant. We have suggested that the exponential period represents the formation of the complexes. This paper shows that the initiation of DNA synthesis and of the two deoxyribonucleotide-synthesizing activities occurs simultaneously and with coinciding exponential kinetics. The in vivo activities of the two enzymes were tested after infection by a number of T4 amber Dna- mutants. Their activities were essentially unchanged compared to the wild-type phage, except on infection by mutants of gene 43 (T4 DNA nucleotidyltransferase or DNA polymerase). With these mutants the rate of increase of dTMP synthetase and dCMP hydroxymethylase activities was always substantially lower than after infection by wild-type phage. It is proposed that an intimate interaction occurs between T4-induced DNA polymerase and the complex of enzymes forming 5-hydroxymethyl-dCMP and dTMP.

Chloramphenicol↗
PubMed1976

Replicative bacteriophage DNA synthesis in plasmolyzed T4-infected cells: evidence for two independent pathways to DNA.

Bacteriophage T4-infected Escherichia coli rendered permeable to nucleotides by sucrose plasmolysis exhibited two apparently separate pathways or channels to T4 DNA with respect to the utilization of exogenously supplied substrates. By one pathway, individual labeled ribonucleotides, thymidine (tdR), and 5-hydroxymethyl-dCMP could be incorporated into phage DNA. Incorporation of each of these labeled compounds was not dependent upon the addition of the other deoxyribonucleotide precursors, suggesting that a functioning de novo pathway to deoxyribonucleotides was being monitored. The second pathway or reaction required all four deoxyribonucleoside triphosphates or the deoxyribonucleoside monophosphates together with ATP. However, in this reaction, dTTP was not replaced by TdR. The two pathways were also distinguished on the basis of their apparent Mg2+ requirements and responses to N-ethylmaleimide, micrococcal nuclease, and to hydroxyurea, which is a specific inhibitor of ribonucleoside diphosphate reductase. Separate products were synthesized by the two channels, as shown by density-gradient experiments and velocity sedimentation analysis. Each of the pathways required the products of the T4 DNA synthesis genes. Furthermore, DNA synthesis by each pathway appeared to be coupled to the functioning of several of the phage-induced enzymes involved in deoxyribonucleotide biosynthesis. Both systems represent replicative phage DNA synthesis as determined by CsCl density-gradient analysis. Autoradiographic and other studies provided evidence that both pathways occur in the same cell. Further studies were carried out on the direct role of dCMP hydroxymethylase in T4 DNA replication. Temperature-shift experiments in plasmolyzed cells using a temperature-sensitive mutant furnished strong evidence that this gene product is necessary in DNA replication and is not functioning by allowing preinitiation of DNA before plasmolysis.

Adenosine Triphosphate↗
PubMed1973

Direct participation of dCMP hydroxymethylase in synthesis of bacteriophage T4 DNA.

In order to retain in an in situ system the control mechanisms involved in synthesis of bacteriophage T4 DNA, infected cells were made permeable to nucleotides by plasmolysis with concentrated sucrose. Such preparations use exogenous deoxyribonucleotides to synthesize T4 phage DNA. As has been observed with in vivo studies, DNA synthesis was drastically reduced in plasmolyzed preparations from cells infected by amber mutants of genes 1, 32, 41, 42, 43, 44, or 45. Added 5-hydroxymethyl dCTP did not bypass either a mutant of gene 42 (dCMP hydroxymethylase) or of gene 1 (phage-induced deoxyribonucleotide kinase). In a phage system lacking deoxycytidine triphosphatase (gene 56) and the gene-46 product, and therefore incorporating dCTP into DNA, dCTP incorporation did not require dCMP hydroxymethylase, in keeping with in vivo results. With a triple amber mutant of genes 1, 46, and 56 only slight incorporation of dCTP occurred. By contrast, in experiments performed in vivo the synthesis of cytosine-containing DNA was unaffected by an amber mutation in gene 1. These studies provide evidence that dCMP hydroxymethylase, in addition to its known catalytic function, has a second, more direct, role in phage T4 DNA synthesis, apparently in recognition of hydroxymethyl dCTP. The role of the phage-induced deoxyribonucleotide kinase in T4 DNA synthesis in the plasmolyzed system remains unresolved.

Adenosine Monophosphate↗