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Biomedical subjects

Y L Chen

Publications and source records attributed to Y L Chen.

At least 145 records · Page 8Linked to original sources
PubMed1995

Utilization of patterns of biotinyl-polypeptides as a promising analytical target for bacterial identification.

The family of biotin enzymes, which are involved in carboxylation, transcarboxylation, and decarboxylation reactions in cells, is essential and conserved for bacteria. The prosthetic group biotin is stably linked to the biotinyl-polypeptide by an amide bond. Since avidin interacts with biotin in an irreversible manner, the patterns of biotinyl-polypeptides for bacterial cells could be revealed by probing them with an avidin-enzyme complex in Western blots of total cellular proteins. In this way, the family of commonly existing gene products of bacteria could be monitored and compared without the use of specific DNA probes, oligonucleotide primers, or antibodies. In this study, this approach was tested and it was found that different species of bacteria showed different patterns of biotinyl-polypeptides. Our results indicate that patterns of biotinyl-polypeptides can be a promising analytical target for bacterial identification.

Avidin↗
PubMed1995

Design and synthesis of 1-heteroaryl-3-(1-benzyl-4-piperidinyl)propan-1-one derivatives as potent, selective acetylcholinesterase inhibitors.

Herein is described the synthesis and structure--activity relationship of a novel series of aromatic and heteroaromatic 3-(1-benzyl-4-piperidinyl)propan-1-one derivatives that display potent and selective inhibition of the enzyme acetylcholinesterase (AChE). 1-(2-Methyl-6-benzothiazolyl)-3-(N-benzyl-4-piperidinyl)propan-1-one hydrochloride, 6d, is one of the most active compounds within this series exhibiting an IC50 for the inhibition of the AChE enzyme equal to 6.8 nM. Compound 6d has shown a dose-dependent elevation of total acetylcholine (ACh) levels in the mouse forebrain with an oral ED50 = 9.8 mg/kg. In addition, in vivo microdialysis experiments in the rat demonstrate that 6d increases extracellular ACh (100% over basal) 1-3 h postdose with an oral ED50 = 4.8 mg/kg.

Animals↗
PubMed1995

Determination of the structure of two novel echistatin variants and comparison of the ability of echistatin variants to inhibit aggregation of platelets from different species.

Two new variants of short disintegrins were purified from the venom of Echis carinatus leakeyi and named echistatin beta and gamma. These proteins were found to be about 85% similar in amino acid sequence to echistatin alpha which has been well studied. The disulphide pattern of echistatin gamma appeared to be identical with that of echistatin alpha. They all contain the adhesive recognition sequence Arg-Gly-Asp (RGD) but inhibit the aggregation of platelets from human and other mammals with different potencies. Echistatin beta and alpha are far more effective on platelets from humans and guinea pigs than those from rabbits and rats whereas echistatin gamma is less discriminating of the platelets of the species tested. This species-dependent platelet sensitivity to echistatin beta and gamma could be attributed to the variations in residues 15, 21, 22 and 27, which are close to or within the RGD loop, rather than to the C-terminal variations after residue 46. Taking advantage of the presence of methionine residues flanking both sides of the ARGDDM motif in echistatin gamma, we deleted this hexapeptide by CNBr cleavage to produce des-(23-28)-echistatin gamma. The modified protein showed c.d. and fluorescent spectra grossly similar to the intact echistatin but its antiplatelet potency decreased more than 200-fold. We thus propose that a favourable conformation of the RGD region is responsible mainly for the high-affinity binding of echistatin to the platelet glycoprotein IIb-IIIa as shown previously for the binding of medium-size disintegrin.

Amino Acid Sequence↗
PubMed1995

Growth suppression of human colorectal carcinoma in nude mice by monoclonal antibody C27-abrin A chain conjugate.

PURPOSE: The aim of this study was to assess an immunotoxin, monoclonal antibody C27-abrin A chain conjugate (MAAAC), that might be effective in the treatment of colorectal carcinoma. METHODS: The immunotoxin was prepared by a specific monoclonal antibody against carcinoembryonic antigen (CEA), monoclonal antibody C27, linked to N-succinimidyl-3-(2-pyridyldithio)propionate and then coupled covalently to the toxic abrin-A chain to synthesize MAAC. The therapeutic role of this immunotoxin in suppressing the in vitro and in vivo growth of CEA-secreting human colorectal cancer cells (LS174T) was assayed by methods of protein biosynthesis inhibition, cell colony proliferation, and treatment of tumor cells before and after inoculation in nude mice. RESULTS: We found that MAAC effectively suppressed the growth of LS174T in culture medium and completely eradicated cells in inoculated nude mice. In contrast, irrelevant immunotoxin antiferritin-abrin A chain conjugate and isotype-matched monoclonal immunoglobin (MOPC21IgG1)-abrin A chain conjugate did not cause such effects. The in vitro toxicity was highly specific because the conjugate (MAAC) inhibited de novo protein biosynthesis, impeded growth, and caused death of cells possessing surface CEA determinants. The 50 percent inhibition dose values of the conjugate for colonogenic survival and for protein biosynthesis in LS174T cells were 0.09 microgram/ml and 0.06 microgram/ml, respectively. Colon survival was inhibited 96.3 percent after prolonged MAAC treatment. MAAC showed selective cytotoxicity; the inhibitory effect of MAAC to the CEA-secreting LS174T cells over the CEA-nonsecreting human embryonic kidney cells was 16-fold. CONCLUSION: These results indicate that MAAC may be of benefit in therapy during or soon after resection of colorectal carcinoma or in patients who have micrometastasis.

Abrin↗
PubMed1995

Ultrastructural studies on macromolecular permeability in relation to endothelial cell turnover.

Our previous light microscopic studies demonstrated the correlation of focal arterial uptake of macromolecules with the mitosis or death of endothelial cells (ECs). To investigate horseradish peroxidase (HRP) permeability associated with the clefts surrounding these ECs at the ultrastructural level, experiments were performed on rat thoracic aortae by using transmission electron microscopy. In en face preparations of aortic specimens, light microscopy was used first to detect mitotic ECs by hematoxylin staining prior to electron microscopy. Dying (or dead) ECs containing cytoplasmic immunoglobulin G (IgG) were identified by an indirect immunogold technique, HRP was found to permeate from the vessel lumen through the widened junctions around the mitotic and dying cells, as well as some non-widened junctions and the plasma membrane of dying cells. The transiently open junctions during cell turnover lead to an increased transendothelial permeability to macromolecules. In addition to its enhanced passage through the leaky junctions around EC turnover and through the damaged membrane of dying cells. HRP can also traverse many normal intercellular clefts into the subendothelial space of the aorta. These observations show that normal intercellular junctions can provide a significant pathway for the transport of macromolecules with the size of HRP, and that HRP transport is enhanced in transiently open junctions surrounding ECs undergoing turnover. The widened junctions around the mitotic and dying cells provide the pathway for macromolecules larger than HRP, e.g., the low density lipoproteins (LDLs).

Animals↗
PubMed1995

Comparative analysis of the workload in seated and standing horizontal submaximal lifting tasks.

The objective of the present laboratory study was to analyse physiological responses of horizontal lifting tasks when they were performed in sitting and standing positions. Heart rate and blood pressure were used as indices of circulatory strain. Lifting tasks were performed under four lifting positions: sitting-forward lift, sitting-twist lift, standing-forward lift, and standing-twist lift. The weights of the loads were 3, 5 and 7 kg and the frequencies of handling were 1, 4 and 6 lifts/min. This study supports the idea that heart rate is a sensitive measure for evaluating the effects of seated horizontal lifting tasks. The lifting positions and workload (frequency x load x distance) are important parameters in the design of these types of tasks. It appears that within the experimental values examined in this study, a seated position could be recommended while performing horizontal lifting tasks at workloads < or = to 4.6 kg.m.min-1. The results are supported by smaller physiological responses.

Adult↗
PubMed1995

Propofol concentration monitoring in plasma or whole blood by gas chromatography and high-performance liquid chromatography.

We compared the measurement of propofol concentrations in plasma or whole blood by high-performance liquid chromatography (HPLC) to that of gas chromatography (GC). Blood samples were collected from patients who had received bolus injection or continuous infusion of propofol. The results showed that the two methods correlated well both in plasma and whole blood samples. However, significant biphasic differences of propofol concentrations between plasma and whole blood specimens were observed in the bolus injection group. Differences were larger in the infusion group. This discrepancy in concentrations resulted from the infusion or clearance of propofol, and the lag of redistribution across blood cell membranes. In conclusion, monitoring of propofol concentrations by the methods of GC and HPLC gives equivalent results. For propofol concentration monitoring, plasma samples are preferred, but immediate centrifugation is needed.

Adult↗
PubMed1995

Determination of free digoxin in sera of 8 patients with chronic cardiac insufficiency.

AIM: To establish a method for the determination of free digoxin in serum for clinical use and to study the relationship between the free and total digoxin concentrations in chronic cardiac insufficiency patients receiving digoxin with different renal function. METHODS: The ultrafiltration with fluorescence polarization immunoassay was used to determine the concentration of free digoxin. RESULTS: The concentrations of digoxin standards in serum were 0.96, 1.92, and 3.84 nmol.L-1. The relative standard deviation was < 7% for intra-day and < 6% for inter-day determinations. The average recovery was 99.95 +/- 2.18%. The ratio of free/total digoxin in chronic cardiac insufficiency patients with renal dysfunction was lower than that in patients with normal kidneys (63.5 +/- 4.7% vs 75.1 +/- 3.9%, P < 0.01). CONCLUSION: The present method is simple and reliable. In these patients there is an over-measurement for total digoxin concentration, suggesting the presence of elevated endogenous digoxin-like immunoreactive substances.

Aged↗
PubMed1995

[A cohort study and KAP investigation of HIV infected persons in Ruili, and other counties in Yunnan, 1994].

In 1994, an cohort study of drug users had continued in Longchuan and Luxi counties, Ruili city. The cohort study for drug users had been established since 1992 and total 522 drug users were investigated. Sixty five sera samples were collected, including 26 HIV negatives intravenous drug users in 1992 and 39 of them in 1993. The result shown that 10 sera samples are positives. Of sixty five samples tested, the rate of HIV infectious for IVDU in Ruili, Longchuan and Luxi were 25.0%, 16.3% and 0.0% respectively. Total of 46 HIV positives samples were found from 105 blood samples among the IVDU who were newly included in the cohort study in 1994. Of these samples, the rates of HIV infection in Ruili, Longchuan and Luxi were 61.8%, 38.5% and 0.0% respectively. The result of KAP investigation from 522 drug users has shown that there is a marked difference of the rate of HIV infections in the nationalities, occupations, education (P < 0.01). The main reason contributing the low rate of HIV infections in Luxi county is that the IVDU mainly are the Han nationality with higher education level, as well as travelling less to Burma.

China↗
PubMed1995

Comparison of serum CA15-3 and CEA in breast cancer.

The monoclonal antibodies CA15-3 were developed against the two antigens 115D8 of the human milk fat globule membrane and DF3 of breast cancer. CA15-3 was assayed radioimmunologically and CEA was analysed using the enzyme immunoassay. Normal control was achieved in 32 healthy women, the mean values for CA15-3 were 11.5 +/- 3.0 u/ml, range from 7.9 to 16.9 u/ml. We compared serum levels of CA15-3 and CEA in 121 patients with histologically proved breast carcinoma. CA15-3 levels above 25 u/ml and CEA levels above 5 ng/ml were considered positive values. 31 of 121 patients studied had elevated CA15-3 levels (sensitivity: 25.6%) and 21 of 121 patients had positive CEA levels (sensitivity 17.4%). 92 of the breast cancer patients (76%) did not have metastatic disease. In this group CA15-3 sensitivity was 7.6%, while CEA sensitivity was 6.5%. Mean values were 15.1 +/- 6.6 u/ml for CA15-3 and 1.78 +/- 2.47 ng/ml for CEA. 29 patients (24%) had metastatic disease. In this group, CA15-3 sensitivity was 82.8% and CEA sensitivity was 51.7% (P < 0.05). Mean values for CA15-3 were 147.5 +/- 175.9 u/ml and 16.9 +/- 24.0 ng/ml of CEA. With regard to the correlation of two tumor markers with clinical course patients had significantly higher levels of CA15-3 than of CEA in metastatic breast cancer. This result suggests CA15-3 to be the more sensitive and more specific of the two for metastatic breast cancer detection and monitoring.

Adult↗
PubMed1995

[Synthesis and biological activity of dynorphin A-(1-13) analogs].

Dynorphin A-(1-13) (I) and its two analogs were synthesized by solid-phase method. Fully-protected peptides were cleaved from the resin with HF. The three products were purified and their analgesic activity (antiwrithing response in mouse) and receptor affinity in mouse vas deferens (MVD) and rabbit vas deferens (RVD) were measured. The biological and pharmacological results showed that the replacement of Gla2, Ile8 and Pro10 by D-Ala8 and D-Pro10 caused an increase in analgesic activity, receptor affinity and selectivity. In analgesia and RVD assay, its activity is 2.6 times and 135 times respectively higher than dynorphin A-(1-13). The structure-activity relationships were briefly discussed.

Analgesics, Opioid↗
PubMed1994

Anti-tumor necrosis factor properties of non-peptide drugs in acute-phase responses.

Dexamethasone (sodium phosphate), pentoxifylline, fusidic acid (sodium salt), pentamidine (isethionate) and R-phenylisopropyladenosine (R-PIA) were tested for their anti-tumor necrosis factor (TNF) activities in an endotoxin-induced shock rat model. All the drugs reduced serum TNF concentrations in a dose-dependent manner, whereas their effects on serum interleukin-6 levels differed. Doses that reduced TNF levels by 50% were 0.012 mg/kg for dexamethasone, 0.06 mg/kg for R-PIA, 0.24 mg/kg for pentamidine, 6.5 mg/kg for fusidic acid and 15 mg/kg for pentoxifylline. Administration of the drugs to rats before intraplantar injection of carrageenan reduced paw edema by 50-70%. Injection of a monoclonal anti-TNF antibody reproduced the inhibitory effect. Moreover, the time course of tissue-associated TNF following carrageenan injection was compatible with mediation of edema by TNF. Results obtained for this acute, non-immunological inflammatory reaction strongly suggest that the model is TNF-dependent. Our results reinforce the idea that TNF is a crucial target in the therapeutics of inflammatory reactions. These drugs, which are able to cross cell barriers, might have clinical applications in localized and/or chronic diseases in which TNF is involved.

Acute-Phase Reaction↗
PubMed1994

Novel benzisoxazole derivatives as potent and selective inhibitors of acetylcholinesterase.

A series of N-benzylpiperidine benzisoxazoles has been developed as potent and selective inhibitors of the enzyme acetylcholinesterase (AChE). The benzisoxazole heterocycle was found to be an appropriate bioisosteric replacement for the benzoyl functionality present in the N-benzylpiperidine class of inhibitors. The title compounds were synthesized by alkylating 3-methyl-1,2-benzisoxazoles with an iodo piperidine derivatives as the key step. Benzisoxazoles 1b-j,o displayed potent inhibition of AChE in vitro with IC50's = 0.8-14 nM. Particularly interesting were N-acetyl and morpholino derivatives 1g (IC50 = 3 nM) and 1j (IC50 = 0.8 nM), respectively, which displayed outstanding selectivity for acetyl-over butyrylcholinesterase, in excess of 3 orders of magnitude. N-Acetyl 1g also displayed a favorable profile in vivo. This analog showed a dose-dependent elevation of total acetylcholine in mouse forebrain after oral administration with an ED50 = 2.4 mg/kg. In addition, 1g was able to reverse amnesia in a mouse passive avoidance model at doses of 3.2 and 5.6 mg/kg with an average reversal of 89.7%. Molecular dynamics simulations were used to study the possible binding modes of N-benzylpiperidine benzisoxazoles to AChE from Torpedo californica. Key structural insights were obtained regarding the potency of this class of inhibitors. Specifically, Asp-72, Trp-84, Trp-279, Phe-288, and Phe-330 are implicated in the binding of these inhibitors. The N-benzylpiperidine benzisoxazoles may be suitable compounds for the palliative treatment of Alzheimer's Disease.

Acetylcholine↗
PubMed1994

Syntheses and anticholinesterase activity of tetrahydrobenzazepine carbamates.

The synthesis of a series of alkylcarbamates of 1,5-methano-2,3,4,5-tetrahydro-1H-2-benzazepin-7-ol is reported. Many of these compounds are potent acetylcholinesterase (AChE) inhibitors. The in vitro AChE inhibition, cholinergic effects, acute toxicity, and elevation of brain acetylcholine levels in vivo of this series of compounds are described. A representative compound, 1d (5.6 mg/kg, po), was able to reverse hemicolinium-3-induced amnesia in the mouse passive avoidance assay.

Administration, Oral↗
PubMed1994

Altered queuine modification of transfer RNA involved in the differentiation of human K562 erythroleukemia cells in the presence of distinct differentiation inducers.

Altered queuine modification of tRNA has been correlated to neoplasia and cell differentiation, but much of the existing evidence is only circumstantial. In the present study, we used several distinct differentiation inducers to measure changes in Q-family tRNA species during the erythroid differentiation of human K562 erythroleukemia cells. Treatment of K562 cells with 3.6 microM 1-beta-D-arabinofuranosylcytosine (ara-C), 1 mM sodium butyrate, 0.1 mM hemin, or 5 microM 5-azacytidine resulted in growth inhibition, erythroid differentiation, and changes in queuine content of tRNA. In the presence of the irreversible inducer ara-C, the queuine content of tRNA increased markedly when the cells differentiated into benzidine-positive erythroid cells, and cell growth was inhibited. The increase in the queuine content of tRNA in differentiated K562 cells was an irreversible event. In cells incubated with the reversible inducer sodium butyrate, an increase in the queuine content of tRNA was correlated with the increase in benzidine-positive erythroid cells throughout the culturing period. After removal of the drug at 48 h, the queuine content of tRNA decreased concomitant with a decrease in benzidine-positive cells. Treatment with another reversible inducer, hemin, caused only a transient increase in the queuine content of tRNA, which was not correlated with the steady increase in benzidine-positive erythroid cells. The agent 5-azacytidine slightly inhibited cell growth but did not significantly change the percentage of benzidine-positive cells and the queuine content of tRNA. We further clarified the changes in queuine content of tRNA by analyzing the Q-containing isoacceptors of Q-family tRNA species including tRNA(Tyr), tRNA(His), tRNA(Asp), and tRNA(Asn) by RPC-5 chromatography, and found that the change in queuine content of tRNA(Tyr) was greater than the other Q-family tRNA species during induction by ara-C, sodium butyrate, and hemin. Our results indicate that the change in queuine content of tRNA is an irreversible event of terminal differentiation in ara-C induction and is a transient event of reversible differentiation in hemin induction. Sodium butyrate induction might represent a status between irreversible and reversible differentiation. Q-containing isoacceptors of tRNA might potentially play an important biological role during K562 cell differentiation.

Aspartate-tRNA Ligase↗
PubMed1994

Dissipation and movement of acaricide chlorobenzilate in the environment.

The dissipation of acaricide chlorobenzilate in selected soil and river water samples was studied. Under incubation conditions at 25 degrees C and 90% field capacity of moisture for 21 days, the residues of chlorobenzilate were 14 and 55% in Lukang silty clay loam and Pincheng clay, respectively. More than 80% of chlorobenzilate remained in the natural water (pH 7.2 and 7.3, respectively) and in the water adjusted to pH 5.0 when water samples collected from Green Lake and Wai-Shuang River near Taipei were treated with chlorobenzilate and then incubated for 34 days. But when the pH was adjusted to 9.0, only 60% was found in Green Lake water and 29% in Wai-Shuang River water. The dissipation of chlorobenzilate in the soil was fitted to first-order kinetics with half-lives of 5 to 36 days under various conditions in the laboratory experiments. No chlorobenzilate was detected in the leachate by a leaching experiment on the soil column for 18 days; most chlorobenzilate remained in the upper 3 cm of the column. According to assessment by the groundwater pollution-potential model (GWP), chlorobenzilate seemed to be safe in regard to groundwater contamination.

Benzilates↗
PubMed1994

Quantitative investigations of cell-bubble interactions using a foam fractionation technique.

Previous work by the authors and others has shown that suspended animal cell damage in bioreactors is caused by cell-bubble interactions, regardless whether the bubbles are from bubble entrainment or direct gas sparging. As approach to measure the adsorptivity of animal cells to bubbles, a modified batch foam fractionation technique has been developed in this work and proven to be applicable. By using this technique, the number of cells absorbed per unit bubble surface area and the adsorption coefficients have been measured to quantify hybridoma cell-bubble interactions, and the preventive effects of serum and Pluronic F68 on these interactions. It was demonstrated quantitatively that the hybridoma cells adhere to bubbles spontaneously and significant numbers exist in the foam, and that both the serum and Pluronic F68 provide strong prevention to these cell-bubble interactions. The results obtained provide criteria for bioreactor operation and medium formulation to prevent cell-bubble interactions and cell damage in the culture processes.

Adsorption↗