Biomedical subjects

S W Yang

Publications and source records attributed to S W Yang.

At least 55 records · Page 3Linked to original sources

PubMed1996

A eukaryotic enzyme that can disjoin dead-end covalent complexes between DNA and type I topoisomerases.

The covalent joining of topoisomerases to DNA is normally a transient step in the reaction cycle of these important enzymes. However, under a variety of circumstances, the covalent complex is converted to a long-lived or dead-end product that can result in chromosome breakage and cell death. We have discovered and partially purified an enzyme that specifically cleaves the chemical bond that joins the active site tyrosine of topoisomerases to the 3' end of DNA. The reaction products made by the purified enzyme on a variety of model substrates indicate that the enzyme cleanly hydrolyzes the tyrosine-DNA phosphodiester linkage, thereby liberating a DNA terminated with a 3' phosphate. The wide distribution of this phosphodiesterase in eukaryotes and its specificity for tyrosine linked to the 3' end but not the 5' end of DNA suggest that it plays a role in the repair of DNA trapped in complexes involving eukaryotic topoisomerase I.

Binding Sites↗

PubMed1996

Inhibition of human DNA ligase I activity by zinc and cadmium and the fidelity of ligation.

Heavy metals, including zinc (Zn) and cadmium (Cd), are potentially important genotoxic agents in our environment. Here we report that human DNA ligase I, the major form of the enzyme in replicative cells, is a target for Zn and Cd ions. ZnCl2 at 0.8 mM caused complete inhibition of DNA ligase I activity, whereas only 0.04 mM CdCl2 was required to achieve a similar effect. Both metals affected all three steps of the reaction, namely, the formation of ligase-AMP intermediate, the transfer of the AMP to DNA and the ligation reaction that succeeds the formation of the AMP-DNA complex. Unlike F-ara-ATP and the natural protein inhibitor of DNA ligase-I, these metals may affect different domains of the enzyme. Moreover, these metal ions did not increase the rate of misligation of F-ara-A-modified DNA or mismatched DNA substrates, but considerable misligation was observed for the T:C mispairing. These data support the notion of high fidelity of the human DNA ligases and that the major action of these metal ions on the enzyme is their inhibitory function.

Adenosine Monophosphate↗

PubMed1996

Sequential mediation of norepinephrine-and dopamine-induced antinociception at the spinal level: involvement of different local neuroactive substances.

The effects of intrathecally (i.t.) administered opioid antagonist naloxone (Nal), adenosine antagonist aminophylline (Aph), and gamma-aminobutyric acid (GABAA)-receptor antagonist picrotoxin (PTX) or Bicuculline (BIC) on the antinociception produced by i.t. norepinephrine (NE), dopamine (DA), morphine (Mor), 5'-N-ethylcarboxamidoadenosine (NECA, an adenosine agonist) or muscimol (MUS, a selective GABAA-receptor agonist) were studied and compared using the tail-flick test in rats. The results showed that: (1) both i.t. NE (0.3, 0.5 and 1.0 nmol) and DA (5.5, 8.3 and 16.5 nmol) produced significant and dose-dependent increases in tail-flick latencies (antinociception); (2) both Nal (240 nmol) and Aph (120 nmol) blocked the antinociception produced by NE (1.0 nmol); (3) both Nal (240 nmol) and Aph (120 nmol) blocked the antinociception produced by Mor (0.5 nmol), but only Aph (120 nmol) blocked the antinociception produced by NECA (0.5 nmol), while Nal (240 nmol) did not; (4) neither Nal (240 nmol) nor Aph (120 nmol) altered the antinociception produced by DA (16.5 nmol); (5) both i.t. PTX (1.5 nmol) and BIC (0.5 nmol) completely blocked the antinociception produced by DA (16.5 nmol), but showed no effects on that produced by NE (1.0 nmol); and (6) both PTX and BIC blocked the antinociception produced by MUS (1.0 nmol). These results suggest that: (a) endogenous opiate and adenosine may be involved in the mediation of NE-induced, but not DA-induced, antinociception; (b) NE, opioid and adenosine may act in a sequential order in NE-induced antinociception at the spinal level; (c) endogenous GABA may be involved in the mediation of DA-induced antinociception through the GABAA-receptors, but is not involved in NE-induced antinociception at the spinal level.

Animals↗

PubMed1995

Comparison of protein binding to DNA in vivo and in vitro: defining an effective intracellular target.

We have quantitatively evaluated the affinity of a set of target sites for the integration host factor (IHF) protein of Escherichia coli by their performance as competitors in an electrophoretic mobility shift assay. We also determined how well each of these sites is filled by IHF in vivo. The data show that several natural sites have an affinity not much greater than that required for intracellular occupancy. The data also indicate that very little of the IHF in a cell is present as free protein available for binding, suggesting that binding to non-specific targets dominates the operation of this system. The correlation between in vitro affinity and in vivo occupancy provides a ready means to assess the likely physiological significance of putative IHF sites. It also provides a general method to assess the importance of non-specific interactions by DNA binding proteins inside a cell.

Bacterial Proteins↗

PubMed1995

Adenosine and opiate-like substances mediates antinociception at the spinal cord.

The effects of intrathecally administered naloxone or aminophylline on the antinociception produced by intrathecal NE, 5-HT, morphine or adenosine receptor agonist, 5'-N-ethylcarboxamidoadenosine (NECA) were observed in rats using the tail-flick test. The results show that: (1) the antinociception produced by NE with doses of 0.5 or 1.0 nmol could be completely blocked by both naloxone (240 nmol) and aminophylline (120 nmol); (2) neither naloxone (240 nmol) nor aminophylline (120 nmol) could alter the antinociception produced by 5-HT with doses of 60 or 120 nmol; and (3) the antinociception produced by morphine (0.5 nmol) could be blocked by both naloxone (240 nmol) and aminophylline (120 nmol), while the antinociception by NECA (0.5 nmol) could be blocked only by aminophylline (120 nmol), but not by naloxone (240 nmol). The results suggest that opiate-like substances (OLS) and adenosine are involved in the mediation of the NE-produced antinociception, but not in 5-HT-produced antinociception. Results also suggest that NE, OLS and adenosine may act in a sequential order in the performance of NE-induced antinociception at the spinal level.

Adenosine↗

PubMed1995

Interaction of serotonin and norepinephrine in spinal antinociception.

The interactions between different doses of serotonin (5-HT) and norepinephrine (NE) in in vivo experiments on rat spinal cord dorsal horn cells was investigated using the integrated electromyography (EMG) measurement of the nociceptive hindlimb flexor reflex (FR). The results indicate that (1) intrathecal (IT) administration of low doses of 5-HT (60 nmol) or NE (1.5 nmol) suppresses the nociceptive FR by 40% for 20 min, respectively; (2) administration of higher doses of 5-HT (240 nmol, IT) multiplies the suppression of the nociceptive FR by 80% for 40 min, and NE (15 nmol, IT) produces similar suppression of the nociceptive FR for 80 min; (3) concomitant administration of low doses of 5-HT (60 nmol, IT) and NE (1.5 nmol, IT) produces a summation of the nociceptive FR suppression both in amplitude and duration; (4) concomitant administration of the higher doses of 5-HT (240 nmol IT) with NE (15 nmol, IT) produces similar effect obtained as 5-HT given separately, and no summation was obtained as observed following the lower dosages; (5) serotonin (240 nmol, IT) given 40 min before NE (15 nmol, IT) attenuates the duration of the suppression induced by NE; (6) pretreatment with a selective 5-HT2 receptor antagonist ketanserin (60 nmol, IT) failed to abolish the 5-HT effects; (7) pretreatment with ketanserin prior to concomitant administration of the higher doses of 5-HT and NE prolongs the time duration of the nociceptive FR suppression.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

PubMed1995

New steroid acids from Antrodia cinnamomea, a fungal parasite of Cinnamomum micranthum.

Three new steroids, zhankuic acids A [1], B [2], and C [3], were isolated from the fruiting bodies of Antrodia cinnamomea by bioassay-guided fractionation. The structures of these compounds were elucidated by chemical reactions and detailed analysis of their 1H- and 13C-nmr spectra. Biological studies revealed that 1 exhibited cytotoxic activity against P-388 murine leukemia cells and 2 showed weak anticholinergic and antiserotonergic activities.

Animals↗

PubMed1994

Specific photocrosslinking of DNA-protein complexes: identification of contacts between integration host factor and its target DNA.

Azide moieties have been specifically placed in the backbone of DNA by chemical coupling between azidophenacyl bromide and uniquely positioned phosphorothioate residues. The derivatized DNA forms specific complexes with a DNA-binding protein and, following irradiation with 302-nm light, makes specific crosslinks to the protein. Isolation of this covalent complex, followed by tryptic digestion and Edman degradation of the resulting crosslinked peptide, identifies the portion of the protein that is near the derivatized segment of the target DNA. We use this method to probe the interaction between a specific DNA sequence and integration host factor (IHF) protein. A single IHF heterodimer is known to contact > 25 bp of DNA and thereby introduce a sharp bend. Two segments of a typical IHF site were derivatized with aryl azide. Although the segments were separated by only 5 bp, they crosslinked to different subunits of IHF. The locations of the crosslinks support our current view for the way IHF protein binds to and bends its specific targets.

Amino Acid Sequence↗

PubMed1994

Morphine and norepinephrine-induced antinociception at the spinal level is mediated by adenosine.

The purpose of this study was to examine whether adenosine or serotonin is involved in mediation of the antinociception produced by norepinephrine at the spinal cord level. Aminophylline, an adenosine receptor antagonist and naloxone given intrathecally (i.t.) were used to test the antinociception produced by i.t. norepinephrine, serotonin, morphine or the adenosine receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA) by using the tail-flick assay in rats. It was observed that (1) aminophylline blocked the antinociception produced by norepinephrine, but exhibited no effect on the antinociception produced by serotonin, (2) aminophylline blocked the antinociception produced by morphine similarly to naloxone, (3) aminophylline blocked the antinociception produced by NECA and (4) naloxone failed to block the antinociception produced by NECA and serotonin. The results suggest that adenosine is involved in mediation of the norepinephrine-produced antinociception at the spinal level and that norepinephrine and adenosine may act in a sequential manner in norepinephrine-induced antinociception.

Adenosine↗

PubMed1994

Changes in lumbar disc angles of Chinese subjects from upright to flexion.

STUDY DESIGN: This study analyzed the sizes and angles of vertebrae and discs in Chinese subjects. Lateral lumbar spine radiograph films were taken of subjects in upright and 60 degrees flexion positions to evaluate disc height and angle changes. OBJECTIVES: This study sought to gather data regarding the contribution of each segment to lumbar lordotic curvature in upright posture, and angle changes of individual segments from upright to flexion positions. SUMMARY OF BACKGROUND DATA: Although the dimensions of vertebrae and discs have been measured, little has been done regarding in vivo measurements of lumbar lordotic curvature formation, especially during flexion. In addition, no data are available for the Chinese population. METHODS: Five men and six women were studied. The lateral lumbar spine radiograph films were taken for upright and 60 degrees flexion positions. The dimensions of vertebral bodies and discs and lumbosacral angle were measured. RESULTS: The disc heights ranged from 0.7 to 1.2 cm in upright posture. Mean disc angle ranged from 9 degrees to 14 degrees in men and 6 degrees to 13 degrees in women. The lowest three segments (L3-L5) contributed 80% to 90% of the lumbosacral angle (L1-S1), which was approximately 47 degrees. Mean sacral horizontal angle was 35 degrees. From upright to 60 degrees flexion positions, all disc angles decreased uniformly from a total of 53 degrees +/- 6 degrees to 11 degrees +/- 12 degrees in men and 46 degrees +/- 11 degrees to 0 degrees +/- 18 degrees in women. CONCLUSIONS: The dimensions of lumbar vertebral bodies and discs, in upright and flexion positions, appear to be similar between Chinese and Western populations.

Adult↗

PubMed1994

Materials and design concepts for an intervertebral disc spacer. I. fiber-reinforced composite design.

The intervertebral disc is a complex joint anatomically and functionally. It may be displaced or damaged due to trauma or a disease process. To alleviate this condition, it may be necessary to remove the involved disc surgically and fuse the two adjacent vertebrae. Fusion is one option; however, replacing the damaged disc (or part thereof) with a suitable synthetic equivalent to allow near normal joint motion is more desirable. Unfortunately, the complex mechanical properties of the lumbar disc cannot be duplicated with homogeneous synthetic materials (polymers). To overcome this fundamental problem we have developed rational designs utilizing biocompatible thermoplastic elastomers of various stiffnesses (durometers) with and without fiber reinforcements. Our design consisted of three components analogous to the natural end plates, annulus, and nucleus. In this study only the fiber-reinforced design is considered. The variables examined in the present study included orientation of the fiber layers, number of fiber layers, and order of the reinforcing layers. The results of mechanical testing of the fiber reinforced disc spacer indicate that the range of compressive and torsional properties can be achieved. The results further demonstrate that properly developed, this design results in properties similar to the natural disc. Designs developed provided adequate compression and compression torsion properties for a synthetic spine disc spacer.

Biocompatible Materials↗

PubMed1994

Norepinephrine and serotonin-induced antinociception are blocked by naloxone with different dosages.

The effects of intrathecally (IT) administered naloxone (Nal) on the antinociception produced by IT norepinephrine (NE), serotonin (5-HT), or morphine (Mor) were observed and compared in rats using the tail-flick (TF) assay. The results show that: a) NE, 5-HT, and Mor in doses of 1 nmol, 240 nmol, and 0.5 nmol, respectively, produce similar increases in amplitude and time in TF latency (TFL); b) Nal treatment of 240 and 360 nmol has no effects on TFL; c) the antinociception produced by NE (1 nmol) can be blocked by Nal (240 nmol); d) antinociception produced by Mor (0.5 nmol) can also be blocked by Nal (240 nmol); e) 240 nmol of Nal does not affect the 5-HT (120 nmol)-produced antinociception, while 360 nmol of Nal show a delayed blockade to the 5-HT (120 nmol)-produced antinociception. The results suggest that endogenous opiate-like substances may be involved in both NE- or 5-HT-produced antinociception at the spinal level, and these effects may be mediated through different types of opiate receptors.

Animals↗

PubMed1994

The incidence of IDDM in Seoul from 1985 to 1988.

OBJECTIVE: To determine insulin-dependent diabetes mellitus (IDDM) incidence rates for the first time in Seoul, Korea, from 1985 to 1988. RESEARCH DESIGN AND METHODS: A mail survey was conducted among all hospitals, a total of 136, with > 80 beds in the Seoul area. Of these, (15.4%) hospitals reported patients with newly diagnosed IDDM. RESULTS: The average incidence rate of IDDM from 1985 to 1988 was 0.70/100,000 (95% confidence interval [CI]: 0.55-0.89). When stratified by gender, the average incidence rate in boys was 0.58/100,000 (95% CI: 0.42-0.9), and in girls it was 0.78/100,000 (95% CI: 0.56-1.07). The age at onset was similar to that reported in other countries, i.e., more than 50% of the cases were diagnosed between the ages of 10 and 14. The incidence of IDDM increased in parallel with the age-group (0.4 < 5-9 < 10-14 years). Onset seasonality was also similar to that in other reported countries with the most cases occurring during the winter months and the least number of cases during the summer months. CONCLUSIONS: The incidence rate of IDDM in Seoul is the lowest reported in the world. This might be effectively considered a baseline incidence rate before exposure to environment or other risk factors. The similar pattern of onset characteristics in Korea to those in other countries suggests that the same etiological factors are operative.

Adolescent↗

PubMed1993

Loss of retinoblastoma gene and amplification of N-myc gene in retinoblastoma.

We have analyzed paired samples of genomic DNA from peripheral leukocyte and primary tumor tissue from nine patients with retinoblastoma (RB) and from two RB cell lines, WERI-Rb-1 and Y79, to detect the molecular alterations of the retinoblastoma susceptibility gene (RB-1) and N-myc gene. In Southern analysis, RB-1 deletions in tumor tissues were detected in five patients (56%), one of these revealed a total loss of RB-1. N-myc amplification was found only in one (11.1%) out of nine patients. We also observed a total loss of RB-1 in WERI-Rb-1, and a more than 100-fold amplification of N-myc in Y79. The analysis of the relationship between molecular events and clinical characteristics such as age, sex, tumor laterality did not reveal any specific correlation. These results suggest that genetic backgrounds of RB in Korean patients are quite similar to those of reported cases elsewhere. The high sensitivity of our method in detecting the RB-1 loss indicates that this method can be a useful tool for initially screening a large number of tumors.

Child↗

PubMed1993

Chemosensitization to adriamycin by cyclosporin A and verapamil in human retinoblastoma cell lines.

The chemosensitizing effects of cyclosporin A and verapamil on the cytotoxicity of adriamycin were investigated using MTT assay against two human retinoblastoma cell lines, Y79 and WERI-Rb-1. Y79 and WERI-Rb-1 were totally resistant to doses up to 5.0 micrograms/ml of verapamil. Cyclosporin A inhibited the survival of Y79 and WERI-Rb-1 dose-dependently, however, the maximum inhibition at the highest concentration tested (5.0 micrograms/ml) was less than 50% (% survival at 5.0 micrograms/ml of cyclosporin A: 65.6% and 66.9% in Y79 and WERI-Rb-1, respectively). Combination of cyclosporin A and verapamil did not further inhibit the survival of Y79 and WERI-Rb-1 compared with cyclosporin A alone. Adramycin inhibited the survival of Y79 and WERI-Rb-1 dose-dependently. The chemosensitizing effects of cyclosporin A and verapamil on the cytotoxicity of adriamycin were evaluated in terms of sensitizing index (SI: the ratio of IC50 to adriamycin alone to IC50 to adriamycin in the presence of cyclosporin A and/or verapamil). Cyclosporin A significantly enhanced SI and the addition of verapamil enhanced SI further: SI values at 5.0 micrograms/ml of cyclosporin A, 5.0 micrograms/ml of cyclosporin A plus 1.5 micrograms/ml of cyclosporin A plus 1.5 micrograms/ml of verapamil, 5.0 micrograms/ml of cyclosporin A plus 3.0 micrograms/ml of verapamil were 2.0, 2.6 and 2.8 in Y79 and 2.6, 5.8 and 9.7 in WERI-Rb-1, respectively. These results suggest that cyclosporin A and verapamil are promising chemosensitizers to adriamycin in the treatment of retinoblastoma.

Cell Survival↗

PubMed1992

Analysis of the formation of AMP-DNA intermediate and the successive reaction by human DNA ligases I and II.

DNA ligation catalyzed by all DNA ligases involves two intermediary steps, the formation of the ligase-AMP and the AMP-DNA complexes. A method was developed to purify and analyze the AMP-DNA intermediate from the DNA ligation reaction catalyzed by DNA ligases. This AMP-DNA complex was maximally accumulated by preincubation of human DNA ligase I or II with ATP, followed by interaction with the DNA substrate for 5 s at 0 degrees C. The gel-purified AMP-DNA complex maintained its property as a ligation intermediate. The AMP was directly linked to the 5'-phosphate of DNA with a pyrophosphate bond. The successive ligation reaction following the AMP-DNA complex formation required DNA ligase and Mg2+ ion but was inhibited by ATP and pyridoxal 5'-phosphate, indicating that the availability of the AMP binding site in the enzyme is essential for the completion of the reaction. Furthermore, the formation of the AMP-DNA complex and the subsequent DNA ligation were substrate specific for human DNA ligases I and II. These data, together with previously reported results, suggest that a major difference between human DNA ligases I and II is in their DNA-binding domains. The methods make it convenient to study in depth the kinetics of the overall DNA ligation.

Adenosine Monophosphate↗

PubMed1992

Identification of a specific inhibitor for DNA ligase I in human cells.

A protein inhibitor for human DNA ligase I has recently been identified. It was copurified with a fraction of the enzymes from HeLa cells through several steps of chromatography. The inhibitor was first identified by the absence of ligation activity of the associated enzyme, while it retained the ability to form the ligase-[32P]AMP adducts. The inhibitor was eluted as a single peak at approximately 0.25-0.30 M NaCl from a Mono S column. It inhibited the ligation of both double-stranded and single-stranded breaks by purified DNA ligase I but not by T4 DNA ligase and DNA ligase II. Subsequent gel-filtration chromatography indicated that this inhibitor, with a molecular mass of 55-75 kDa, could form a complex with DNA ligase I and inhibited the DNA ligation activity. Rechromatography of the ligase I-inhibitor complex in high-salt conditions resulted in the dissociation of the complex and the restoration of enzyme activity, indicating that the physical interaction of inhibitor with DNA ligase I is one of the mechanisms of inhibition. These data indicate that this protein inhibitor for DNA ligase I may play a specific role in regulating DNA ligation during replication, repair, or recombination.

Chromatography, Affinity↗

PubMed1992

Dual mode of inhibition of purified DNA ligase I from human cells by 9-beta-D-arabinofuranosyl-2-fluoroadenine triphosphate.

9-beta-D-Arabinofuranosyl-2-fluoroadenine (F-ara-A) is an analogue of adenosine and deoxyadenosine with potent anti-tumor activity. The mechanism of action for this compound has been elucidated as the inhibition of DNA and RNA synthesis, induction of DNA fragmentation, and genetic damage. This study demonstrated that DNA ligase I, an enzyme involved in DNA replication, is a target for the drug action. F-ara-adenine triphosphate (F-ara-ATP) at 80 microM inhibited the activity of DNA ligase I by more than 90%. In contrast, eight other related nucleoside analogues showed no effect on the enzyme activity at 200 microM. F-ara-ATP inhibited DNA ligation in two distinct ways. First, F-ara-ATP directly interacted with DNA ligase I and inhibited the formation of the ligase-AMP complex. This inhibition could not be reversed when free F-ara-ATP was eliminated from the treated enzyme; however, the addition of pyrophosphate, followed by gel filtration chromatography, restored enzyme activity, indicating that F-ara-ATP bound to the enzyme and altered the AMP-binding site. Secondly, the activity of DNA ligase I was inhibited when F-ara-ATP was incorporated into the 3' terminus of the DNA substrate. The dual mode of inhibition of DNA ligase I by F-ara-ATP indicates that its effect on DNA ligation may be important in the inhibition of DNA synthesis and the cytotoxicity of F-ara-A.

Adenosine Monophosphate↗