Biomedical subjects

C Cheng

Publications and source records attributed to C Cheng.

At least 91 records · Page 5Linked to original sources

PubMed1998

Conservation of structure and mechanism between eukaryotic topoisomerase I and site-specific recombinases.

Vaccinia DNA topoisomerase breaks and rejoins DNA strands through a DNA-(3'-phosphotyrosyl)-enzyme intermediate. A C-terminal catalytic domain, Topo(81-314), suffices for transesterification chemistry. The domain contains a constellation of five amino acids, conserved in all eukaryotic type IB topoisomerases, that catalyzes attack of the tyrosine nucleophile on the scissile phosphate. The structure of the catalytic domain, consisting of ten alpha helices and a three-strand beta sheet, resembles the catalytic domains of site-specific recombinases that act via a topoisomerase IB-like mechanism. The topoisomerase catalytic pentad is conserved in the tertiary structures of the recombinases despite scant sequence similarity overall. This implies that the catalytic domains of type IB topoisomerases and recombinases derive from a common ancestral strand transferase.

Binding Sites↗

PubMed1998

Electrophysiological and biochemical evidence that DEG/ENaC cation channels are composed of nine subunits.

Members of the DEG/ENaC protein family form ion channels with diverse functions. DEG/ENaC subunits associate as hetero- and homomultimers to generate channels; however the stoichiometry of these complexes is unknown. To determine the subunit stoichiometry of the human epithelial Na+ channel (hENaC), we expressed the three wild-type hENaC subunits (alpha, beta, and gamma) with subunits containing mutations that alter channel inhibition by methanethiosulfonates. The data indicate that hENaC contains three alpha, three beta, and three gamma subunits. Sucrose gradient sedimentation of alphahENaC translated in vitro, as well as alpha-, beta-, and gammahENaC coexpressed in cells, was consistent with complexes containing nine subunits. FaNaCh and BNC1, two related DEG/ENaC channels, produced complexes of similar mass. Our results suggest a novel nine-subunit stoichiometry for the DEG/ENaC family of ion channels.

Animals↗

PubMed1998

Getting the right kind of support: functional differences in the types of social support on depression for Chinese adolescents.

The present study adopted a prospective design to explore relationships among various types of social support and depression. Four types of social support, namely network support, instrumental enacted support, socio-emotional enacted support, and perceived support, were assessed in a sample of Chinese adolescents. Results revealed that perceived support was related to a reduction of subsequent depression for both male and female adolescents. In addition, instrumental enacted support was a significant predictor of subsequent depression for male adolescents, whereas socioemotional enacted support was a significant predictor of subsequent depression for female adolescents. Functional differences in the types of social support for Chinese male and female adolescents, as well as implications for clinical intervention, are discussed.

Adolescent↗

PubMed1998

Results of termino-lateral neurorrhaphy to original and adjacent nerves.

In this comprehensive investigation, we studied three different neurorrhaphy models in an attempt to elucidate the potential of termino-lateral nerve repair to original and adjacent nerves. In experimental group 1, the peroneal nerve was sectioned and then attached to the posterior tibial nerve in a termino-lateral fashion. In experiment group 2, the motor nerves to the gastrocnemius muscle were sectioned and then attached to the posterior tibial nerve in a termino-lateral fashion. In experimental group 3, the obturator nerve (L2-4) was sectioned and attached to the sciatic nerve (L4-6) in a termino-lateral fashion. For the control in each group, the same type of nerve used in each respective group was transected without repair. Experimental groups 1 and 2 showed viable axons in the peroneal nerve distal to the neurorrhaphy site. Experimental group 3 showed no viable axons at these sites. No regeneration was observed in the transected nerve without repair in all three control groups. This study suggests that termino-lateral neurorrhaphy is a viable means of repairing damaged nerves if the distal segment of the sectioned nerve is reattached to its original trunk distal to its original branch point. However, the results from experimental group 3 demonstrate that termino-lateral neurorrhaphy cannot be used to repair nerves when the donor and recipient nerves originate from different spinal cord levels.

Anastomosis, Surgical↗

PubMed1998

Abdominoinguinal incision in adenocarcinoma of the sigmoid or cecum: report of two cases.

PURPOSE: This study illustrates a technique allowing resection of a sigmoid adenocarcinoma with lateral fixation and a cecal adenocarcinoma with involvement of the psoas muscle and ureter. METHODS: The abdominoinguinal incision, an incision used in the resection of a sarcoma of the lower abdominal quadrants, was applied in the case of a sigmoid adenocarcinoma with posterolateral fixation and infiltration of the anterior abdominal wall and in a case of a cecal adenocarcinoma involving the right psoas muscle and ureter. RESULTS: In the first case, resection of the tumor mass en bloc with resection of the sigmoid and lower anterior abdominal wall muscles, including the inguinal ligament, was performed. Reconstruction of the muscular fascial defect was done with the rotation of a right rectus abdominis flap. The patient was well 12 months later. In the second case, the cecal carcinoma was resected en bloc with the right psoas and ureter; a right nephrectomy was also performed. This patient was well eight months later. CONCLUSIONS: The abdominoinguinal incision may provide the exposure needed to allow the resection of a sigmoid or a cecal adenocarcinoma with posterolateral fixation, often considered unresectable with conventional abdominal incisions.

Adenocarcinoma↗

PubMed1998

Laparoscopic adrenalectomy: experience with transabdominal and retroperitoneal approaches.

OBJECTIVES: To study the patient outcomes of various approaches on 14 consecutive patients who had laparoscopic adrenalectomy surgery between October 1995 and March 1997. METHODS: The patients comprised 5 men and 9 women (mean age 46.2 years, range 32 to 61) with varying diagnoses. Eleven patients had Conn's syndrome, 1 had Cushing's syndrome, 1 had a nonfunctioning adrenal adenoma, and 1 had an adrenal myelolipoma. The adenomas were confirmed by hormonal assays, biochemical tests, and computed tomography (CT) imaging. Seven adenomas were sited on the right and seven were sited on the left. We used two alternative approaches: a transabdominal approach (8 patients) and a retroperitoneal approach (6 patients). RESULTS: None of the procedures required conversion to open surgery, nor was there any procedure-related complication. Blood loss was minimal. All the lesions were benign on final histology. The mean operating time was 135 minutes (range 80 to 190). The postoperative period was without significant complications, with patients reporting minimal pain. Patients were able to achieve an early return to oral intake and preoperative activity. The postoperative hospital period ranged from 1 to 10 days. CONCLUSIONS: We believe laparoscopic adrenalectomy to be a viable option in the removal of benign adrenal lesions. It is a safe technique when performed by experienced practitioners and results in faster recovery. The key advantage to this technique is its minimally invasive approach and decreased hospital costs.

Abdomen↗

PubMed1998

Nuclear factor-kappa B activation during cerebral reperfusion: effect of attenuation with N-acetylcysteine treatment.

We examined activation of the transcription factor, nuclear factor-kappaB (NF-kappaB), which participates in the upregulation of endothelial cell adhesion proteins, during reperfusion after temporary middle cerebral artery occlusion (TMCAO). We hypothesized that N-acetylcysteine (NAC), an antioxidant which inhibits NF-kappaB activation, would alter events in brain reperfusion injury. We used a rat model of TMCAO. The left sides of the brains were rendered ischemic for 2 h, and then the area was allowed to reperfuse. The animals were treated with NAC (150 mg/kg) or saline placebo, sacrificed, and activated NF-kappaB was assessed in both the left and right hemispheres, all at varying intervals. Cerebral infarction volume was also measured in each of the hemispheres collected from a separate group of animals. Activated NF-kappaB, consisting of p65 and p50 Rel proteins, was significantly increased 15 min after reperfusion in the affected hemisphere. The activation at 15 min was completely abolished with NAC treatment. NAC treatment 1 h prior to the end of occlusion and at 24 h reduced the percentage infarction volume of the affected hemispheres from 35.5+/-2.8% (S.E.) to 18. 1+/-2.1% (p<0.01). NAC treatment at 1 h after the occlusion (after the NF-kappaB peak) and again at 24 h also significantly reduced the percentage infarction volume from 34.8+/-3.8% to 24.6+/-3.8% (p<0. 05). Thus, while NAC inhibited activation of NF-kappaB at 15 min after reperfusion, the drug acted to reduce cerebral infarction by additional, undefined mechanisms. These results bring into question the various roles of NF-kappaB in cerebral infarction followed by reperfusion.

Acetylcysteine↗

PubMed1998

Structural determination of oxofatty acids by charge-remote fragmentations.

A strategy is described to locate the carbonyl position in oxofatty acids by utilizing charge-remote fragmentations of various molecular ions that are desorbed by fast atom bombardment (FAB). Oxofatty acids were cationized with alkali metal ions (Li+, Na+, K+, Rb+, and Cs+) to form [M + 2Met-H]+ or alkaline earth metal ions (Mg2+, Ca2+, Sr2+ or Ba2+) to from [M + Met-H]+ in the gas phase. The cationized acids undergo charge-remote fragmentations upon high-energy activation, giving a product-ion pattern that has a gap corresponding to the oxo position and bordered by two high-intensity peaks. One of the peaks corresponds to an ion that is formed by the cleavage of the C-C bond beta to the oxo position and proximal to the charge (beta ion), whereas the other is formed from the cleavage of the C-C bond gamma to the oxo position and distal to the charge (gamma' ion). The oxo position is easily determined by identifying the gap and the beta and gamma' ions. Furthermore, there are two competing patterns of fragments in a CAD spectrum of an oxofatty acid or ester [M + Li]+ ion. These arise because Li+ attaches to either the oxo or the carboxylic end, as was confirmed by ab initio molecular orbital calculations. The results demonstrate that control of the fragmentation can be guided by an understanding of metal-ion affinities. Collisional activation of the anionic carboxylates gives results that are similar to those for positive ions, showing that the process is not related to the charge status. Collisional activation of [M + H]+ ions does not give structural information because the charge migrates, leading to charge-mediated fragmentations.

Animals↗

PubMed1998

Fragmentation mechanisms of oxofatty acids via high-energy collisional activation.

Upon high-energy collisional activation, oxofatty-acid ions undergo fragmentations to produce a unique pattern of product ions by which the position of the ketone is revealed. The reactions occurring in the vicinity of the ketone, which are the subject of this article, produce a spectral pattern that is not symmetrical. Although cleavages of alpha, beta, and gamma C-C bonds occur on the side proximal to the charge site, giving alpha, beta, and gamma ions, respectively, there is only a gamma' ion formed on the side distal to the charge site. The resulting lack of symmetry seemingly contradicts the concept that the reactions are independent of the charge (i.e., that they are charge remote). To eliminate any interaction between the charge and the reaction site, oxofatty acids were linked to glycyrrhetic acid, a steroid with a rigid polycyclic system. The fragmentation pattern remains the same, indicating that the effect does not depend on charge but rather on the ketone. Isotopic labeling and MS/MS/MS studies confirm that the fragmentations of C-C bonds in the vicinity of the ketone are complex, charge-remote processes. Formation of [M-H-H2O]- and [M-H-CO2]- anions and the ion that is formed by homolytic cleavage of the beta bond at the side distal to the charge, however, are charge directed.

Fatty Acids↗

PubMed1998

Charge-remote fragmentations are energy-dependent processes.

Fast atom bombardment-produced [M + Na]+ ions of tristearoylglycerol and [M - H]- ions of stearic or nervonic acid undergo charge-remote fragmentations (CRFs) to produce one series of product ions reflecting CnH2n + 2, losses, whereas electrospray ionization-produced ions fragment to give two series of product ions reflecting CnH2n + 2 and CnH2n + 1 losses. These results and those from previous studies show that the mechanisms and energetics of CRFs are complex and unsettled. We demonstrate that several pathways are simultaneously involved in CRFs, and the preference for certain pathways (by CnH2n + 1 and CnH2n + 2 losses) is determined by the internal energy of the compound itself and the ionization and activation energies that are applied to it.

Chemical Phenomena↗

PubMed1998

Calcium-sensitive fluorescent dyes can report increases in intracellular free zinc concentration in cultured forebrain neurons.

High concentrations of Zn2+ are found in presynaptic terminals of excitatory neurons in the CNS. Zn2+ can be released during synaptic activity and modulate postsynaptic receptors, but little is known about the possibility that Zn2+ may enter postsynaptic cells and produce dynamic changes in the intracellular Zn2+ concentration ([Zn2+]i). We used fura-2 and magfura-2 to detect the consequences of Zn2+ influx in cultured neurons under conditions that restrict changes in intracellular Ca2+ and Mg2+ concentrations. The resulting ratio changes for both dyes were reversed completely by the Zn2+ chelator, N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine, indicating that these dyes are measuring changes in [Zn2+]i. We found that fura-2 was useful in measuring small increases in [Zn2+]i associated with exposure to Zn2+ alone that may be mediated by a Na+/Ca2+ exchanger. Magfura-2, which has a lower affinity for Zn2+, was more useful in measuring larger agonist-stimulated increases in [Zn2+]i. The coapplication of 300 microM Zn2+ and 100 microM glutamate/10 microM glycine resulted in a [Zn2+]i increase that was approximately 40-100 nM in magnitude and could be inhibited by the NMDA receptor antagonist, MK-801 (30 microM), or extracellular Na+. This suggests that Zn2+ influx can occur through at least two different pathways, leading to varying increases in [Zn2+]i. These findings demonstrate the feasibility of measuring changes in [Zn2+]i in neurons.

Animals↗

PubMed1998

Psychometric properties of the social-conflict scales for Chinese adolescents.

Despite the gradual increase of research on social conflicts, psychometric characteristics of social-conflict scales have not been extensively examined, especially in the adolescent population. In this study, the internal consistency, test-retest reliability, and criterion-related validity of 2 established social-conflict scales were examined in a sample of 581 Chinese adolescents. There were high internal consistencies and test-retest reliabilities for both the Family Conflict Scale and the Friend Conflict Scale. The scales were significantly related to appraisals of the quality of social relations, psychological distress, and trait anxiety.

Adolescent↗

PubMed1998

Effect of hyperbaric oxygen on survival of the composite ear graft in rats.

In this study the authors set out to determine whether postoperative hyperbaric oxygen (HBO) therapy increases the survival rate of the composite graft in the rat ear model. A composite graft (1 x 0.5 cm2) that included skin, subcutaneous tissue, and cartilage was created from the left ear, and was transferred onto the posterior auricular site of the right ear. The animals were divided into two groups: a control group (N = 10) and an experimental group receiving HBO (N = 10). The experimental group was given HBO immediately following reattachment for 4 hours, and then for 6 hours each day for 5 days (2 atm). The results showed the average ear flap survival area in the experimental group was 82%, and it was 26.5% in the control group (p < 0.01). Histology demonstrated the existence of neovascularization in the experimental group. We have concluded that postoperative HBO therapy increases the survival of the rat ear composite graft, and that the effect of this therapy is influenced by the magnitude (size and thickness) of the graft.

Animals↗

PubMed1998

Cyclin partners determine Pho85 protein kinase substrate specificity in vitro and in vivo: control of glycogen biosynthesis by Pcl8 and Pcl10.

In Saccharomyces cerevisiae, PHO85 encodes a cyclin-dependent protein kinase (Cdk) with multiple roles in cell cycle and metabolic controls. In association with the cyclin Pho80, Pho85 controls acid phosphatase gene expression through phosphorylation of the transcription factor Pho4. Pho85 has also been implicated as a kinase that phosphorylates and negatively regulates glycogen synthase (Gsy2), and deletion of PHO85 causes glycogen overaccumulation. We report that the Pcl8/Pcl10 subgroup of cyclins directs Pho85 to phosphorylate glycogen synthase both in vivo and in vitro. Disruption of PCL8 and PCL10 caused hyperaccumulation of glycogen, activation of glycogen synthase, and a reduction in glycogen synthase kinase activity in vivo. However, unlike pho85 mutants, pcl8 pcl10 cells had normal morphologies, grew on glycerol, and showed proper regulation of acid phosphatase gene expression. In vitro, Pho80-Pho85 complexes effectively phosphorylated Pho4 but had much lower activity toward Gsy2. In contrast, Pcl10-Pho85 complexes phosphorylated Gsy2 at Ser-654 and Thr-667, two physiologically relevant sites, but only poorly phosphorylated Pho4. Thus, both the in vitro and in vivo substrate specificity of Pho85 is determined by the cyclin partner. Mutation of PHO85 suppressed the glycogen storage deficiency of snf1 or glc7-1 mutants in which glycogen synthase is locked in an inactive state. Deletion of PCL8 and PCL10 corrected the deficit in glycogen synthase activity in both the snf1 and glc7-1 mutants, but glycogen synthesis was restored only in the glc7-1 mutant strain. This genetic result suggests an additional role for Pho85 in the negative regulation of glycogen accumulation that is independent of Pcl8 and Pcl10.

Cyclin-Dependent Kinases↗

PubMed1998

Pharmacological characteristics of MJ-451, a new benzopyran- derived ATP-sensitive potassium channel opener, in guinea pig isolated trachea.

In this study, we determined the pharmacological activities of MJ-451 (6-cyano-3S,4R-dihydro-2, 2-dimethyl-2H-3-hydroxy-4-[2-oxo-5S-1-hydroxmethyl)-1-pyrrolidinyl ]-1 -benzopyran) in guinea pig isolated trachea and compared its effects with those of cromakalim. MJ-451 (0.1-10 micromol/l) and cromakalim (0.01-1 micromol/l) produced concentration-dependent relaxation of guinea pig isolated trachea precontracted with carbachol (0.5 micromol/l) or histamine (1 micromol/l). MJ-451 (0.03-30 micromol/l), as well as cromakalim (0.03-30 micromol/l), caused a complete and concentration-dependent relaxation of guinea pig isolated trachea precontracted with 20 mmol/l KCl, but did not inhibit the spasmogenic effect of 80 mmol/l KCl. However, theophylline (30-3,000 micromol/l) caused a complete and concentration-dependent relaxation of guinea pig isolated trachea precontracted with either 20 or 80 mmol/l KCl. Propranolol (0.1 micromol/l) markedly antagonized the relaxant action of isoprenaline, but not that of MJ-451 in carbachol-contracted isolated trachea. 8-(p)-sulfophenyltheophylline (150 micromol/l), a selective P1 purinoceptor antagonist, had no effect against the tracheal relaxation induced by MJ-451, but markedly depressed the concentration-response curve of 5'-N-ethylcarboxamidoadenosine. Charybdotoxin (10 micromol/l), a large-conductance Ca2+-activated K+ channel blocker, failed to modify the relaxant activity of MJ-451 in carbachol-contracted isolated trachea. The ATP-sensitive K+ channel blocker, glibenclamide (0.1, 1 and 10 micromol/l) concentration-dependently antagonized the relaxant activity of MJ-451 in carbachol-contracted isolated trachea. It is concluded that MJ-451 is a selective ATP-sensitive K+ channel opener in the tracheal smooth muscle of the guinea pig.

Animals↗

PubMed1998

Novel aspects of the regulation of glycogen storage.

The storage polysaccharide glycogen is widely distributed in nature, from bacteria to mammals. Study of its regulated accumulation has resulted in the discovery or elaboration of several important biochemical principles. Many aspects of the control of glycogen storage still remain poorly understood and glycogen metabolism continues to provide interesting models of more general relevance.

Animals↗

PubMed1998

Cryptococcal prostatic abscess in an immunocompromised patient: a case report and review of the literature.

A case of cryptococcal prostatic abscess in a 65-year-old Chinese man with immunosuppression from treatment of myasthenia gravis is presented. The patient was diagnosed to have cryptococcaemia when he presented with fever and urinary symptoms. Further investigations confirmed cryptococcal meningitis and imaging studies showed a hypodense lesion in the prostate. This proved to be an abscess and it was deroofed transurethrally. Histology of the prostatic tissue revealed the presence of Cryptococcus. The prostate can be a site of persistent cryptococcal infection and may take the form of an abscess. It should be drained transurethrally to prevent relapse.

Abscess↗

PubMed1998

Studies on chemical constituents and immunological function activity of hairy root of Astragalus membranaceus.

Using a large-scale culture technique, the hairy roots of Astragalus membranaceus were produced with a yield reaching 10 g/L. The results from RP-HPLC detection showed that the contents of crude saponin and astragaloside i.v. in the hairy roots were 5.81% and 0.14%, respectively. Six isoflavonoid compounds were also determined. Polysaccharide analysis showed that the total polysaccharide content in the hairy roots was 22.97%; of this content, acidic 8.29% and soluble 14.88%. In comparison with the dry roots, the hairy roots contained higher crude saponin and soluble polysaccharide contents, similar astragaloside i.v. content and lower contents of 6 isoflavonoids, total and acidic polysaccharides, showing that the quality of both types of roots was similar. Regaining the immunity function of rats with low immunity after feeding the aqueous extract of the hairy roots produced by large-scale culture showed that its capacity was similar to the dry roots of A. membranaceus in increasing the immunity function. The results in this paper give evidence that the hairy roots may be a new source of A. membranaceus.

Animals↗