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Biomedical subjects

Yi Chen

Publications and source records attributed to Yi Chen.

At least 145 records · Page 8Linked to original sources
PubMed2004

Determination of nateglinide in animal plasma by micellar electrokinetic chromatography and on-line sweeping technique.

A micellar electrokinetic chromatography (MEKC) method was developed for the determination of nateglinide in animal plasma by on-line sweeping technique, in which plasma samples were simply deproteinized with acetonitrile, and analyzed with 16 mmol/L NaH2PO4 + 6 mmol/L Na2B4O7 + 60 mmol/L sodium dodecyl sulfate (SDS) (pH 7.14) as the running buffer, a fused-silica capillary as the separation tube, 21 kV as the running voltage and UV detection at 214 nm. Under these conditions, more than 100-fold enrichment of nateglinide was obtained with the good linear relation in the range of nateglinide plasma concentration 0.2-7 mg/L (R = 0.998). The method could be applied successfully to determine trace drugs in clinical analysis.

Animals↗
PubMed2004

Novel electrochemical method for sensitive determination of homocysteine with carbon nanotube-based electrodes.

An electrochemical method has been successfully demonstrated for sensitive determination of homocysteine (HcySH) with carbon nanotube (CNT)-modified glassy carbon (GC) electrodes. Cyclic voltammetric results clearly show that carbon nanotubes, especially those pretreated with nitric acid, possess an excellent electrocatalytic activity toward the oxidation of HcySH at a low potential (0.0 V versus Ag/AgCl). The remarkable catalytic property of the acid-pretreated CNTs, which is essentially associated with oxygen-containing moieties introduced on the tube surface, has been further exploited as a sensitive determination scheme for HcySH. Continuous-flow amperometric results suggest that the CNT-based electrodes (p-CNT/Nafion/GC), which were prepared by using Nafion to solubilize and further immobilize CNTs on GC electrodes, show striking analytical properties of good stability and reproducibility and strong ability against electrode fouling. Such analytical properties, along with the low operation potential, substantially enable a reliable and sensitive determination of HcySH with a good dynamic linearity up to 60 microM and a detection limit of 0.06 microM (S/N = 3). The catalytic mechanism and the possible application of the as-prepared p-CNT/Nafion/GC electrodes for the study of the auto-oxidation of HcySH are also demonstrated and discussed.

Biosensing Techniques↗
PubMed2004

Total syntheses of (+)-chloropuupehenone and (+)-chloropuupehenol and their analogues and evaluation of their bioactivities.

Tetracyclic pyrans (+)-chloropuupehenone (1) and (+)-chloropuupehenol (5) and its C8-R-isomer (+)-3 were synthesized via a one-pot condensation of 1-chloro-2-lithio-3,5,6-tris(tert-butyldimethylsilyloxy)benzene (8) with (4aS,8aS)-3,4,4a,5,6,7,8,8a-octahydro-2,5,5,8a-tetramethylnaphthalene-1-carboxaldehyde (7). The major condensation product, (4aS,6aR,12bS)-2H-9,10-bis(tert-butyldimethylsilyloxy)-11-chloro-1,3,4,4a,5,6,6a,12b-octahydro-4,4,6a,12b-tetramethyl-benzo[a]xanthene (4), after desilylation provided tetracyclic pyran (+)-(4aS,6aR,12bS)-2H-11-chloro-1,3,4,4a,5,6,6a,12b-octahydro-4,4,6a,12b-tetramethyl-benzo[a]xanthene-9,10-diol (3). At a dosage of 42 mg/rat over 8 h, pyran diol 3 inhibited the intestinal absorption of cholesterol by 71% in rats. Tetracyclic pyran 4 was also converted to o-quinone 28, which inhibited cholesteryl ester transfer protein (CETP) activity and L1210 leukemic cell viability with IC(50) values of 31 and 2.4 microM, respectively. Diol (+)-5 inhibited CETP activity with an IC(50) value of 16 microM. The minor condensation product, (4aS,6aS,12bS)-2H-9,10-bis(tert-butyldimethylsilyloxy)-11-chloro-1,3,4,4a,5,6,6a,12b-octahydro-4,4,6a,12b-tetramethyl-benzo[a]xanthene (6), was transformed into (+)-5 and (+)-1. A stepwise stereoselective synthesis of (+)-1 was also developed utilizing an oxyselenylation ring-closure reaction. The synthetic sequence also produced four biologically active naturally occurring drimanic sesquiterpenes, (+)-drimane-8alpha,11-diol (34), (-)-drimenol (38), (+)-albicanol (39), and (-)-albicanal (31) as intermediates.

Animals↗
PubMed2004

Study on photochromic diarylethene with phenolic Schiff base: preparation and photochromism of diarylethene with benzoxazole.

A photochromic diarylethene with phenolic Schiff base 1a can be easily transformed to photochromic diarylethene with benzoxazole 3a in the conditions of base and phototrigger. Both of their photochromic properties are investigated. They show that the conversions of ring-open form to ring-closed form at photostationary equilibrium are ca. 20% and 10% for 3a and 1a, respectively, and the backconversions are in nearly quantitative yield for both compounds. They also show that the response time for photostationary equilibrium is ca. 0.5 and 5 min for 3a and 1a, respectively, in the solution. In addition, a general preparation of 2-arylbenzoxazole from phenolic Schiff base in the conditions of base and phototrigger is demonstrated by employing phenolic Schiff bases with different substituted groups as template, and other conditions (solvents, in the presence and absence of oxygen) for preparation of benzoxazole from phenolic Schiff base are explored as well.

Journal Article↗
PubMed2004

Putting a brake on an autonomous DNA nanomotor.

A strategy was developed to reversibly switch on/off an autonomous DNA nanomotor that contains a DNA enzyme. The multiple RNA cleavage of the DNAzyme powered the motor to move, and a strand displacement mechanism provided the basis for a reversible brake to the motor.

DNA↗
PubMed2004

Syntheses of conformationally constricted molecules as potential NAALADase/PSMA inhibitors.

Two six-membered ring targeted analogues of PSMA inhibitors (4a and 4b) were designed on the basis of a computational analysis and synthesized. (E,Z)-Diene 10 was subjected to the nitroso Diels-Alder reaction to give the 1,4-trans six-membered ring adduct, 4a. The cis isomer 4b was derived from similar nitroso cycloaddition reactions with the corresponding (E,E)-diene and separately from cyclohexadiene. The IC(50) values of 4a and 4b in a NAALADase assay were found to be 0.9 and 0.1 microM, respectively. [reaction: see text]

Antigens, Surface↗
PubMed2004

Long-term retinal transgene expression with FIV versus adenoviral vectors.

PURPOSE: Gene therapy for chronic retinal diseases will require long-term expression of therapeutic transgenes. Lentiviral and adenoviral (Ad) vectors are gene delivery systems with markedly different properties. Lentiviral vectors require integration into the host genome, which facilitates long-term expression, while Ad vectors remain episomal. We compared time course, location, and extent of transgene expression from replication-deficient feline immunodeficiency virus (FIV) vectors and Ad vectors in neonatal rat retina. METHODS: A dose-response study was conducted to determine the optimal subretinal dose for comparison of FIV and Ad vectors with an internal cassette expressing beta-galactosidase under transcriptional control of the CMV immediate-early gene promoter/enhancer. Forty-two five-day old Sprague-Dawley rats received subretinal injections of 2 microl containing 2x10(3) transducing units (TU, n=14), 2x10(4) TU (n=14) or 2x10(5) TU (n=14) of FIV vector (right eye) and Ad vector (left eye). Expression was evaluated 48 h after transduction. In the subsequent long-term expression study, 60 five-day old rats received a subretinal injection of 2x10(5) TU FIV vector (right eye) and Ad vector (left eye). Ten pairs of eyes were analyzed at 1 week, 1 month, 3 months, 6 months, 12 months, and the remainder at 16 months. Eye cups were evaluated in a masked manner for extent of beta-galactosidase expression (graded 0-5) by whole mount microscopy and by cross sectional histology. RESULTS: In the dose-response study, 2x10(5) TU resulted in consistent, widespread retinal transduction with both vectors and was selected as the dose for the subsequent study. In the long-term expression study, FIV vector resulted in a higher grade of expression than Ad at multiple single time points and produced higher overall expression when data from all eyes across the entire 16 month study were analyzed (p=0.01). Retinal expression was present at 16 months with both vectors. beta-galactosidase expression was limited to the retinal pigment epithelium (RPE) until the first month, but later was also found to a lesser extent in neurosensory retina with each vector. In contrast to FIV, most Ad injected eyes showed signs of focal accumulation of macrophage-like cells with disrupted retinal architecture. CONCLUSIONS: Both FIV and Ad vectors result in long-term transgene expression in RPE after subretinal injection. FIV vectors show more promise than Ad as delivery systems for retinal diseases since they transduce greater areas of RPE, result in less cellular infiltrate, and cause less disruption of retinal architecture. The persistent expression at 16 months of follow-up suggests that these lentiviral vectors are useful for gene therapy of chronic retinal diseases.

Adenoviridae↗
PubMed2004

A new series of potent oxindole inhibitors of CDK2.

A novel series of oxindole-type inhibitors of CDK2 that have heteroatom substituted alkynyl moieties at their C-4 position is described. These novel 4-alkynyl-substituted inhibitors have superior potency relative to their parent compound in free enzyme and in cell based assays. The crystal structure of CDK2 in complex with one of these analogues was determined and gives insight to their increased potency. The biochemical evaluation of a representative derivative is also described.

CDC2-CDC28 Kinases↗
PubMed2004

Chiral separation of tamsulosin isomers by HPLC using cellulose tris (3,5-dimethhylphenylcarbamate) as a chiral stationary phase.

A high-performance liquid chromatographic (HPLC) method was developed for the chiral separation of an antagonist of alpha1A adrenoceptors, tamsulosin and its S-isomer. Baseline separation of the isomers was achieved within 35 min on a CHIRALCEL OD-RH column with a binary solvent mixture of 50 mmol l(-1) KPF6-acetonitrile (v/v (70:30), pH 5.0) as the optimized mobile phase. The detection limits and quantification limits of both R-isomer and S-isomer were 0.11 and 0.44 ng, respectively. The R.S.D. values of peak-area for the two isomer were 0.42% (of peak-height: 0.77%) for R-isomer and 0.64% (of peak-height:0.92%) for S-isomer (n = 5).

Carbamates↗
PubMed2004

In situ TA-MS study of the six-membered-ring-based growth of carbon nanotubes with benzene precursor.

By using the in situ thermal analysis-mass spectroscopic technique, combined with transmission electron microscopic characterization of the carbon nanotube (CNT) product, we have studied the chemical vapor deposition (CVD) growth of CNTs with Fe-Co/gamma-Al2O3 catalyst and benzene precursor in the range of room temperature to 700 degrees C. The growth process has been clearly illuminated, which starts from the reduction of catalyst around 645 degrees C followed by the dissociation of carbon-hydrogen bonds of benzene and the sequential growth of CNTs. A surprising fact is that no possible hydrocarbon species derived from benzene was detected, indicating that the carbon-carbon bond was not broken under our experimental conditions. All of the experimental results strongly reinforce the six-membered-ring-based growth model, and a schematic elucidation is presented accordingly. This in situ study not only reveals the unique and convincing information directly related to the growth mechanism from the involved chemistry, but also provides a powerful way to clarify the mechanism of CVD synthesis of CNTs with other precursors.

Journal Article↗
PubMed2004

Determination of three compounds in Aloe vera by capillary electrophoresis.

A capillary electrophoretic assay for determining aloe-emodin (AE), methyl p-coumarate (MC), and 3,4-dihydro-6,8-dihydroxyl-[(3s)-2'-acetyl-3'-hydroxyl-5'-methoxy-benzyl]-isocoumarin (DDI) in Aloe vera has been developed. Baseline separation was achieved within 15 min using a running buffer of 20 mm borax containing 10% (v/v) acetonitrile at pH 10.5. A linear relationship between the peak area and the concentration of the analytes was found in the ranges 5-500, 10-1000 and 2-1000 micro g/mL for AE, MC and DDI, respectively, with correlation coefficients of 0.9992-0.9998. The relative standard deviations of migration time and peak area were within 0.17-0.19 and 1.52-3.37%, respectively. The recoveries of AE, MC and DDI were 105, 102 and 96.4%. The contents of AE, MC and DDI in Aloe vera were measured to be 5.13, 0.768 and 1.30 mg/g, respectively.

Aloe↗
PubMed2004

Novel benzyl rearrangements in electrospray ionization multistage tandem mass spectra of benzyl 2',3'- didehydro-2',3'-dideoxythymidin-5'-yl H-phosphonate.

Several alkyl 2',3'-didehydro-2',3'-dideoxythymidin-5'-yl H-phosphonates were synthesized and analyzed by electrospray ionization multistage tandem mass spectrometry (ESI-MS(n)). Two kinds of novel benzyl rearrangement reactions were observed in ESI - MS(2) of [M + H](+), [M + Na](+) and [M + K](+) of benzyl 2',3'-didehydro-2',3'-dideoxythymidin-5' yl H-phosphonate. Results from tandem mass spectrometry, high-resolution mass spectrometry and control experiments showed that the benzyl migration could undergo a four-membered cyclic rearrangement reaction, and benzyl was essential in the process.

Anti-HIV Agents↗
PubMed2004

Sensitivity improvement of amino acids by N-terminal diisopropyloxyphosphorylation in electrospray ionization mass spectrometry.

With the introduction of a diisopropyloxyphosphoryl (DIPP) group at the N-terminus of amino acids, the signal response in electrospray ionization mass spectrometry can be enhanced by 10-100-fold in positive mode and even more in negative mode. An enhancement of proton affinity due to the N-terminal DIPP derivatization was considered to be responsible for the sensitivity improvement in positive mode, which was supported by kinetic method studies. Two possible mechanisms, i.e., an increase in gas-phase acidity due to the introduction of the electron-withdrawing DIPP group, and the effect of pH on the formation of anions of amino acids and their phosphorylated derivatives, were considered for the signal response enhancement in negative mode.

Amino Acids↗
PubMed2004

Ring contraction reactions of 2,3-dihydro-4H-1,3-oxazin-4-ones under electrospray ionization conditions.

The mass spectral behavior of 2,3-dihydro-4H-1,3-oxazin-4-ones has been investigated using electrospray ionization multi-stage mass spectrometry (ESI-MS(n)). All compounds showed a predominant retro-Diels-Alder (RDA) fragmentation pathway, and a novel ring contraction reaction by loss of isocynates was also found. The fragmentation mechanisms proposed for 4H-1,3-oxazin-4-ones are supported by ESI-MS/MS/MS spectra.

Journal Article↗
PubMed2004

Thyroid storm and ventricular tachycardia.

A 34-year-old woman was brought to our emergency department because of sudden loss of consciousness. Ventricular tachycardia and fibrillation were noted on electrocardiographic monitoring and reverted to sinus rhythm after repeated defibrillation. She was treated as a case of thyroid storm. Although tachycardia and fever normalized after 2 days, she remained comatose and died. This is an unusual case because the patient's initial presentation was cardiac arrest without previous history of cardiac disease. To our knowledge, this is the first reported case where ventricular tachyarrhythmia was the initial presenting sign of thyroid storm.

Adult↗
PubMed2004

Inhibition of NF-kappaB activity by IkappaBbeta in association with kappaB-Ras.

IkappaBbeta, one of the major IkappaB proteins, is only partially degraded in response to most extracellular signals. However, the molecular mechanism of this event is unknown. We show here that IkappaBbeta exists in at least two different forms: one that is bound to the NF-kappaB dimer and the other bound to both NF-kappaB and kappaB-Ras, a Ras-like small G protein. Removal of cellular kappaB-Ras enhances whereas excess kappaB-Ras blocks induced IkappaBbeta degradation. Remarkably, kappaB-Ras functions in both GDP- and GTP-bound states, and mutations of the conserved guanine-binding residues of kappaB-Ras abrogate its ability to block degradation of IkappaBbeta. kappaB-Ras also directly blocks the in vitro phosphorylation of IkappaBbeta by IKKbeta. These observations suggest that IkappaBbeta in the ternary complex is resistant to degradation by most signals. We suggest that specific signals, in addition to those that activate only IKK, are essential for the complete degradation of IkappaBbeta.

Animals↗