Biomedical subjects

C C Yang

Publications and source records attributed to C C Yang.

At least 37 records · Page 2Linked to original sources

PubMed2002

Thermal contraction of au nanoparticles.

A fine Au powder, with a mean particle diameter of 4 nm, has been successfully fabricated. The crystalline structure of the 4 nm Au nanoparticles remains in fcc symmetry. No structural changes were found between 15 and 450 K. A crossover from a positive thermal expansion at low temperatures to a negative thermal expansion at high temperatures was observed in the fcc cell parameter at about 125 K. Anomalies associated with the crossover were also observed in the magnetic response and the heat capacity measurements. The observations can be reasonably well interpreted by accounting for the effects of the valence electron potential on the equilibrium lattice separations, with a weakly temperature dependent level spacing.

Journal Article↗

PubMed2002

The effect of paclitaxel on 2-aminofluorene-DNA adducts formation and arylamine N-acetyltransferase activity and gene expression in human lung tumor cells (A549).

In this study, paclitaxel was used to determine inhibition of arylamine N-acetyltransferase (NAT) activity, gene expression and 2-aminofluorene-DNA adduct formation in a human lung tumor cell line (A549). The activity of NAT was measured by HPLC assaying for the amounts of N-acetyl-2-aminofluorene (2-AAF) and remaining 2-aminofluorene (2-AF). Human lung tumor cell cytosols and intact cells were used for examining NAT activity and carcinogen-DNA adduct formation. The results demonstrated that NAT activity, gene expression (NAT1 mRNA) and 2-AF-DNA adduct formation in human lung tumor cells were inhibited and decreased by paclitaxel in a dose-dependent manner. The effects of paclitaxel on the values of the apparent Km and Vmax of NAT from human lung tumor cells were also determined in both examined systems. The result also indicated that paclitaxel decreased the apparent values of Km and Vmax from human lung tumor cells in both cytosol and intact cells. Thus, paclitaxel is an uncompetitive inhibitor to NAT enzyme.

Acetylation↗

PubMed2002

The effect of paclitaxel on gene expression and activity of arylamine N-acetyltransferase and DNA-2-aminofluorene adduct formation in human leukemia HL-60 cells.

N-Acetylation is recognized as the first step in arylamine metabolism. The enzyme responsible for N-acetylation is called arylamine N-acetyltransferase (NAT),which uses acetyl coenzyme A as the acetyl group donor. Paclitaxel has been shown to exhibit antineoplastic and anticancer activity. In this study, paclitaxel was selected to determine the inhibition of arylamine N-acetyltransferase activity, gene expression (NAT mRNA) and DNA-2-aminofluorene adduct formation in human leukemia HL-60 cell line. Paclitaxel (0.01-l microM) did decrease the level of NAT mRNA in a dose-dependent manner. The results demonstrated that paclitaxel inhibited NAT activity and DNA-2-aminofluorene adduct formation in human leukemia HL-60 cells in a dose-dependent manner. Using standard steady-state kinetic analysis, it was demonstrated that paclitaxel was a possible uncompetitive inhibitor to NAT activity in cytosols based on the decrease in apparent values of K(m) and V(max). This report is the first demonstration that paclitaxel affected human leukemia HL-60 cells NAT activity and DNA-2-aminofluorene adduct formation.

Acetylation↗

PubMed2002

Primary resistance to antibiotics and its clinical impact on the efficacy of Helicobacter pylori lansoprazole-based triple therapies.

AIM: To evaluate Helicobacter pylori primary resistance and its clinical impact on the efficacy of two lansoprazole-based eradication triple therapies. METHODS: H. pylori-positive patients (n=228) were randomized to receive one of the 1-week regimens: lansoprazole 30 mg, clarithromycin 500 mg and amoxicillin 1 g (LAC), or lansoprazole 30 mg, clarithromycin 500 mg and metronidazole 500 mg (LMC), each given twice daily. H. pylori status was assessed by 13C-urea breath test and culture at diagnosis and by 13C-urea breath test 6 weeks after therapy. Antibiotic susceptibility was determined by E-test (n=98). RESULTS: The eradication rates with per protocol/ intention-to-treat analyses were: LAC (n=95/114) 83%/69% and LMC (n=96/114) 85%/72%. Primary resistance was 11% for clarithromycin, 41% for metronidazole and 0% for amoxicillin. Eradication in metronidazole-susceptible/-resistant strains was 85%/82% in LAC and 83%/63% in LMC. Significantly lower cure rates were observed in clarithromycin-resistant patients treated with LAC (95% vs. 0%, P < 0.001) and LMC (86% vs. 0%, P < 0.001). CONCLUSIONS: One-week LAC and LMC are similarly effective therapies. Clarithromycin resistance significantly affected H. pylori eradication in both regimens.

2-Pyridinylmethylsulfinylbenzimidazoles↗

PubMed2002

Method for the determination of dialkyl phosphates in urine by strong anion exchange disk extraction and in-vial derivatization.

A method for the determination of four dialkylphosphate metabolites in urine by strong anion exchange disk (SAX) was investigated. Calcium hydroxide was added to a 1-mL urine sample to reduce interference. The aliquot was passed through the SAX disk to accumulate dialkylphosphate metabolites on the disk. The retained dialkylphosphate metabolites were derivatized with methyl iodide in acetonitrile online, and the resulting methyl esters of dialkylphosphate metabolites were directly analyzed by capillary column gas chromatography with flame photometric detection. The recoveries of these dialkylphosphate metabolites were found to be stable. When the intact sample was diluted with deionized water at a 1:1 ratio, the recoveries were both increased and stabilized. The urine samples collected from eight fruit farmers showed that levels of dialkylphosphate metabolites in urine were significantly different before and after pesticide application, indicating the method established in this study is applicable for real sample analysis. Compared with previous studies, this method not only can greatly simplify sample preparation, but it can also significantly reduce the consumption of toxic solvents in sample preparation.

Chromatography, Gas↗

PubMed2002

Effects of garlic components diallyl sulfide and diallyl disulfide on arylamine N-acetyltransferase activity and 2-aminofluorene-DNA adducts in human promyelocytic leukemia cells.

Two components of garlic, diallyl sulfide (DAS) and diallyl disulfide (DADS), inhibited arylamine N-acetyltransferase (NAT) activity and 2-aminofluorene-DNA adduct in human promyelocytic leukemia cells (HL-60). The NAT activity was measured by high performance liquid chromatography assaying for amounts of N-acetyl-2-aminofluorene (2-AAF) and remaining 2-aminofluorene (2-AF). Cellular cytosols and intact cell suspensions were assayed. The inhibition of NAT activity and 2-AF-DNA adduct formation in human leukemia cells by DAS and DADS were dose-dependent and were directly proportional. The data also indicated that DAS and DADS decrease the apparent values of Km and Vmax from human leukemia cells in both assays. This is the first report of garlic components affecting human leukemia cell NAT activity and 2-AF-DNA adduct formation.

Allyl Compounds↗

PubMed2001

Suppression of proline-directed protein kinase F(A) potentiates apoptotic induction and greatly enhances chemosensitivity in human acute lymphoblastic leukemia cells.

BACKGROUND: Previously, the authors reported that specific antisense suppression of overexpressed proline-directed protein kinase (PDPK) F(A) enhances the chemosensitivity of various clinical anticancer drugs up to > 100-fold in human prostate carcinoma cells, suggesting an association of PDPK F(A) with drug resistance in human malignancies. METHODS: In this report, by using a similar approach, the authors demonstrate further that the suppression of PDPK F(A) enhances even more dramatically the chemosensitivity of clinically used anticancer drugs in various types of human acute lymphoblastic leukemia (ALL) cells. RESULTS: Compared with parental and control transfected cells, transduced ALL cells (both Jurkat and CCRF-CEM cells) with low levels of PDPK F(A) displayed an enhanced sensitivity to vincristine, vinblastine, paclitaxel, methotrexate, doxorubicin, and daunorubicin. Estimation of the 50% inhibitory concentration (IC(50)) index further revealed that the transduced cells displayed up to > 3000-fold drug sensitivity, and there was a correlation between suppressed levels of PDPK F(A) and drug sensitivity. A mechanistic study further revealed that the enhanced chemosensitivity in transduced ALL cells was due mainly to the potentiation of apoptotic induction. CONCLUSIONS: Taken together, the results demonstrate that the suppression of overexpressed PDPK F(A) greatly enhances the chemosensitivity of various clinical anticancer drugs in both types of human ALL cells, providing initial evidence for an important role of this PDPK in controlling multidrug resistance of ALL.

Antineoplastic Agents↗

PubMed2001

Turing model for the patterns of lady beetles.

We simulate the patterns on the hard wings of lady beetles using a reaction-diffusion equation based on the Turing model. A part of a spherical surface is used to approximate the geometry of the hard wings. Various patterns common to lady beetles in Taiwan can be produced on this curved surface by adjusting the parameters of the model.

Animals↗

PubMed2001

Specific binding of the C-terminal Src homology 2 domain of the p85alpha subunit of phosphoinositide 3-kinase to phosphatidylinositol 3,4,5-trisphosphate. Localization and engineering of the phosphoinositide-binding motif.

Phosphoinositide second messengers, generated from the action of phosphoinositide 3-kinase (PI3K), mediate an array of signaling pathways through the membrane recruitment and activation of downstream effector proteins. Although pleckstrin domains of many target proteins have been shown to bind phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) and/or phosphatidylinositol 3,4-bisphosphate (PI(3,4)P(2)) with high affinity, published data concerning the phosphoinositide binding specificity of Src homology 2 (SH2) domains remain conflicting. Using three independent assays, we demonstrated that the C-terminal (CT-)SH2 domain, but not the N-terminal SH2 domain, on the PI3K p85alpha subunit displayed discriminative affinity for PIP(3). However, the binding affinity diminished precipitously when the acyl chain of PIP(3) was shortened. In addition, evidence suggests that the charge density on the phosphoinositol ring represents a key factor in determining the phosphoinositide binding specificity of the CT-SH2 domain. In light of the largely shared structural features between PIP(3) and PI(4,5)P(2), we hypothesized that the PIP(3)-binding site on the CT-SH2 domain encompassed a sequence that recognized PI(4,5)P(2). Based on a consensus PI(4,5)P(2)-binding sequence (KXXXXXKXKK; K denotes Arg, Lys, and His), we proposed the sequence (18)RNKAENLLRGKR(29) as the PIP(3)-binding site. This binding motif was verified by using a synthetic peptide and site-directed mutagenesis. More importantly, neutral substitution of flanking Arg(18) and Arg(29) resulted in a switch of ligand specificity of the CT-SH2 domain to PI(4,5)P(2) and PI(3,4)P(2), respectively. Together with computer modeling, these mutagenesis data suggest a pseudosymmetrical relationship in the recognition of the phosphoinositol head group at the binding motif.

Amino Acid Sequence↗

PubMed2001

On-line concentration of s-triazine herbicides in micellar electrokinetic chromatography using a cationic surfactant.

On-line concentration of neutral species of s-triazine herbicides in micellar electrokinetic chromatography using tetradecylammonium bromide (TTAB) as a cationic surfactant was investigated. Factors affecting the stacking of analytes were examined. The results indicate that the stacking efficiency is markedly improved with addition of phosphate buffer in the sample matrix. It was found that, depending on the nature of the analytes, the most effective stacking of these analytes occurs when the ratio of the conductivity of buffer electrolyte to that of sample matrix is in the range 1.4-1.2, with sample matrix containing phosphate buffer. Micelle concentration in the separation buffer is also a crucial factor to enhance the stacking efficiency and detection sensitivity of analytes. Moreover, the stacking efficiency of each individual analyte depends on its binding constant to TTAB micelles. The concentration effect is primarily based on sweeping mechanism which is operated in a normal stacking mode with reversed electrode polarity in the presence of reversed electroosmotic flow. As a result of concentration enhancement, the detection limits of these herbicides can reach about 9-15 ng/ml with UV detection.

Chromatography, Micellar Electrokinetic Capillary↗

PubMed2001

IS1550 from Mycoplasma fermentans is transposable in Escherichia coli.

An insertion sequence (IS)-like element (ISMil) was previously isolated from the incognitus strain of Mycoplasma fermentans. With polymerase chain reaction primers corresponding to the left and right terminal inverted repeats of ISMil, a 1.4-kb DNA fragment was amplified from the genome of the M64 strain of M. fermentans. This DNA fragment has structural characteristics similar to those of ISMil and is designated IS1550. One copy of IS1550 encoded two considerable overlapping open reading frames (ORFs), ORF1 and ORF2. A putative translation frame-shift signal AAAAAAG (A6G) was located near the 3'-end of ORF1. This signal might cause a -1 frame-shift to form a fused product of ORF1 and ORF2 with 444 amino acids, which has a significant similarity to the putative transposase of the IS3 family. This copy of IS1550 was shown to be transposable in Escherichia coli ISM612. Its transposition caused a 1465-bp deletion immediately adjacent to the 3'-end of the element and the creation of a pair of 3-bp direct repeats flanking the element at the new insertion site. On the basis of these results, IS1550 was considered a typical transposable element.

Base Sequence↗

PubMed2001

Refolding of Taiwan cobra neurotoxin: intramolecular cross-link affects its refolding reaction.

In order to explore the effect of intramolecular cross-linking in the folding reaction of cobrotoxin from Naja naja atra (Taiwan cobra) venom, the toxin molecule was modified with glutaraldehyde (GA). The monomeric GA-modified cobrotoxin (mGA-cobrotoxin) was separated from the dimeric and trimeric derivatives using gel filtration. The results of electrophoretic and chromatographic analyses revealed that mGA-cobrotoxin comprised two modified derivatives, which contained modified Lys residues at positions 26 and 27 and at positions 26, 27, and 47, respectively. Moreover, an intramolecular cross-linking of loops II and III by Lys residues was noted with the monomeric derivative containing three modified Lys residues. In sharp contrast to cobrotoxin observations, the folding rate of mGA-cobrotoxin decreased in the presence of GSH/ GSSG, but notably increased in the absence of thiol compounds. Particularly, the accelerated effect of GSH/GSSG on the refolding reaction was affected by the presence of the intramolecular cross-link. Comparative analyses on cobrotoxin and mGA-cobrotoxin CD spectra revealed that modification with the GA reagent caused a change in the gross conformation of cobrotoxin. Fluorescence measurement revealed that the stability of the microenvironment around the single Trp-29 in mGA-cobrotoxin and unfolded mGA-cobrotoxin was appreciably higher than in cobrotoxin and unfolded toxin. Moreover, the ordered structure formation around Trp-29 in refolded mGA-cobrotoxin was faster than in refolded cobrotoxin as evidenced by fluorescence quenching studies. Taken together, these results suggest that the structural flexibility of unfolded cobrotoxin should be favorable for the thiol catalyst to exert its action in the refolding reaction after modification with GA.

Amino Acids↗

PubMed2001

Suppression of proline-directed protein kinase F(A) systemically inhibits the growth of human acute leukemia cells.

Initial studies revealed that proline-directed protein kinase F(A) (PDPK F(A)) was overexpressed in various cancerous tissues relative to normal controls. However, the functional role of overexpressed PDPK F(A) in cancer remains to be established. In this report, we explore the potential role of PDPK F(A) in leukemia cell growth by investigating the effects of partial inhibition of this kinase on human acute promyelocytic leukemia (HL-60) and acute lymphoblastic leukemia (Jurkat) cells. Cloning of PDPK F(A) cDNA and its recombinant antisense expression vector and antibody were successfully developed. Several stable antisense clones of HL-60 and Jurkat cells were subcloned, which expressed a low level of PDPK F(A) when compared with the control-transfected clone in immunoblot analysis. Moreover, these antisense clones potently inhibited cell growth, clonogenic growth in soft agar and serum-independent growth. The results taken together demonstrate that suppression of PDPK F(A) is able to interfere with the growth of HL-60 and Jurkat cells, suggesting an essential role of this PDPK in human acute leukemia cell growth.

Cell Division↗

PubMed2001

Smad proteins function as co-modulators for MEF2 transcriptional regulatory proteins.

An emerging theme in transforming growth factor-ss (TGF-ss) signalling is the association of the Smad proteins with diverse groups of transcriptional regulatory proteins. Several Smad cofactors have been identified to date but the diversity of TGF-ss effects on gene transcription suggests that interactions with other co-regulators must occur. In these studies we addressed the possible interaction of Smad proteins with the myocyte enhancer-binding factor 2 (MEF2) transcriptional regulators. Our studies indicate that Smad2 and 4 (Smad2/4) complexes cooperate with MEF2 regulatory proteins in a GAL4-based one-hybrid reporter gene assay. We have also observed in vivo interactions between Smad2 and MEF2A using co-immunoprecipitation assays. This interaction is confirmed by glutathione S:-transferase pull-down analysis. Immunofluorescence studies in C2C12 myotubes show that Smad2 and MEF2A co-localise in the nucleus of multinuclear myotubes during differentiation. Interestingly, phospho-acceptor site mutations of MEF2 that render it unresponsive to p38 MAP kinase signalling abrogate the cooperativity with the Smads suggesting that p38 MAP Kinase-catalysed phosphorylation of MEF2 is a prerequisite for the Smad-MEF2 interaction. Thus, the association between Smad2 and MEF2A may subserve a physical link between TGF-ss signalling and a diverse array of genes controlled by the MEF2 cis element.

Animals↗

PubMed2001

Sulindac inhibited gene expression and activity of arylamine N-acetyltransferase and DNA-2-aminofluorene adduct formation in T24 human bladder tumor cells.

We demonstrated in vivo that non-steroidal anti-inflammatory drugs including sulindac can act as inhibitors of urinary bladder carcinogenesis in rats. The aim of the present study was to determine whether sulindac affects arylamine N-acetyltransferase (NAT) activity and gene expression and DNA-2-aminofluorene adduct formation in the T24 human bladder tumor cell line. The NAT activity (N-acetylation of 2-aminofluorene) was measured by high performance liquid chromatography assaying for the amount of acetylated 2-aminofluorene and the remaining 2-aminofluorene (AF). The results demonstrated that NAT activity in T24 cells were inhibited by the sulindac in a dose-dependent manner. The apparent values of Km and Vmax of NAT from T24 cells were also decreased by sulindac. This inhibition was not competitive. The amount of DNA-AF adduct formation in T24 cells was also inhibited by sulindac. The data also demonstrated that sulindac inhibited the NAT mRNA level in T24 cells.

Aged↗

PubMed2001

Quantitative pathology of cutaneous nerve terminal degeneration in the human skin.

Pathological diagnosis of neuropathy has traditionally depended on ultrastructural examinations of nerve biopsy specimens, particularly for sensory neuropathies affecting unmyelinated and small-myelinated nociceptive nerves. These sensory nerves terminate in the epidermis of the skin, and the pathology of neuropathy usually begins from nerve terminals. We investigated the feasibility of diagnosing small-fiber sensory neuropathy by evaluating cutaneous innervation. Skin biopsy specimens of 3-mm in diameter were obtained from the distal leg and the distal forearm of 55 healthy controls and 35 patients with sensory neuropathy. In the healthy controls, conventional intraepidermal nerve fiber densities (IENF densities) as measured using the image analysis system in the distal forearm and in the distal leg were correlated (r=0.55, P<0.0001), with significantly higher values in the distal forearm than in the distal leg (17.07+/-6.51 vs 12.92+/-5.33 fibers/mm, P<0.001). Compared to IENF densities of healthy controls, these values of neuropathic patients were significantly reduced in the distal forearm (5.82+/-6.50 fibers/mm, P<0.01) and in the distal leg (2.40+/-2.30, P<0.001). We further explored the possibility of quantifying skin innervation by counting "ocular intraepidermal nerve fiber density" (ocular nerve fiber density) with no aid of an image analysis system. This was based on the fact that the epidermal length on specifically defined sections was very close to the predicted epidermal length of 3 mm, the diameter of skin punches (P=0.14). Ocular nerve fiber densities were significantly correlated with IENF densities as measured by the image analysis system (r=0.99, P<0.0001). Dermal nerve fibers of neuropathic patients either disappeared or became degenerated. These findings were consistent with the notion of early terminal degeneration in neuropathy, and will facilitate quantitative interpretation of epidermal innervation in human neuropathy.

Adult↗

PubMed2001

Neurophysiologic testing in chronic pelvic pain syndrome: a pilot study.

OBJECTIVES: Studies of male chronic pelvic pain syndrome (CPPS) have generally centered on the pathologic features of the prostate rather than on the neurology of pain. Electrodiagnostic studies examine the integrity of somatosensory nerve pathways consisting of large, group A fibers. Heat sensation and visceral (autonomic) pain is mediated through small, unmyelinated C fibers, which can be tested cutaneously by thermal sensory analysis. We hypothesized that CPPS pain is mediated by these small C fibers. METHODS: All subjects and controls had no history of neurologic disease and had normal neurologic examinations. Phase I: 14 patients with CPPS underwent electrodiagnostic testing using pudendal somatosensory evoked potentials and bulbocavernosus reflex latency measurements. Phase II: 31 patients with CPPS and 14 controls underwent thermal sensory analysis testing on the perineum and anterior thigh using noxious heat stimuli. Subjects used a computer-generated visual analog scale to dynamically report their discomfort. The peak and slope of the computer-generated visual analog scale were analyzed. RESULTS: Phase I: two patients had delayed latency of the somatosensory evoked potentials, but additional evaluation with magnetic resonance imaging revealed no definable lesion. Phase II: with thermal sensory analysis, men with CPPS reported higher intensity pain at lower temperatures (P = 0.03). Men with CPPS also had higher peak computer-generated visual analog scale scores on perineal testing. No difference in thermal testing on the anterior thigh was found between the two groups. CONCLUSIONS: Large, myelinated somatic fibers do not play a significant role in the pathophysiology of CPPS. Patients with CPPS have an altered sensation of perineal pain elicited by heat, which may represent a C-fiber-mediated effect.

Chronic Disease↗

PubMed2001

Glutaraldehyde cross-linking alters the environment around Trp(29) of cobrotoxin and the pathway for regaining its fine structure during refolding.

Cobrotoxin, purified from the venom of Naja naja atra (Taiwan cobra), was subjected to modification with glutaraldehyde in order to prepare intra- and intermolecule cross-linked derivatives. Monomeric and dimeric derivatives were separated from polymeric derivatives by gel filtration. The results of amino acid analysis and sequence determination revealed that only Lys residues were selectively modified by glutaraldehyde. Glutaraldehyde cross-linking was accompanied by a change in the gross conformation of cobrotoxin as revealed by circular dichroism spectra of the modified derivatives. Compared with cobrotoxin, Trp(29) of monomeric and dimeric derivatives was in an apolar microenvironment. This was in agreement with acrylamide quenching studies showing that the spatial position of the Trp indole ring became buried in the interior of the molecule after glutaraldehyde cross-linking. Moreover, the Trp of modified derivatives was less accessible for iodide than that observed with cobrotoxin. Notably, disulfide reduction could not completely unfold the structure of glutaraldehyde-modified derivatives as evidenced by the results of acrylamide quenching studies and enzyme-linked immunoassay. Study of the characteristic changes in Trp fluorescence after the initiation of refolding suggested that the fine structure around Trp(29) of cobrotoxin and glutaraldehyde-modified derivatives was formed differently. These results suggest that glutaraldehyde cross-linking leads to a change in the microenvironment of cobrotoxin Trp(29) and alters the pathway of its fine structure formation during the refolding of cobrotoxin.

Animals↗