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Biomedical subjects

Yi Chen

Publications and source records attributed to Yi Chen.

At least 199 records · Page 11Linked to original sources
PubMed2003

[Evaluation of different methods in monitoring YMDD motif mutations associated with lamivudine resistance].

OBJECTIVES: To evaluate the three different methods in monitoring the lamivudine-resistant HBV mutants in lamivudine-treated patients with chronic hepatitis B. METHODS: The sensitivity and specialty of melting curve assay and polymerase chain reaction microplate nucleotide hybridization-enzyme linked immunosorbent assay (PCRmnh-ELISA) were compared with those of mismatch polymerase chain reaction-restriction fragment length polymorphism (mPCR-RFLP) and sequence analysis, through detection of HBV YMDD mutants in 44 serums from chronic hepatitis B patients receiving lamivudine monotherapy at the time of viral breakthrough. RESULTS: mPCR-RFLP assay was more sensitive (10(4) copies/ml) than both PCRmnh-ELISA (10(5) copies/ml) and melting curve assay (10(6) copies/ml). 26 YMDD mutants and 18 wild-types were determined by the means of mPCR-RFLP. Among the 26 mutants, only 16 and 18 mutants were found by melting curve assay and PCRmnh-ELISA, respectively. Whereas, out of the 18 wild-types, 2 and 13 mutants were detected by melting curve assay and PCRmnh-ELISA, respectively. To confirm the different results determined by the three methods in 16 samples, sequence analysis was conducted and showed that the rate of consistency with sequencing was 93.8% by mPCR-RFLP, 43.8% by melting curve, and 18.8% by PCRmnh-ELISA, respectively (chi2=18.7, P<0.01). CONCLUSIONS: The mPCR-RFLP assay is reliable to monitor HBV YMDD mutations. Melting curve assay and PCRmnh-ELISA should be further improved to increase their sensitivity and specialty.

Adult↗
PubMed2002

Synthesis of N-glyoxyl prolyl and pipecolyl amides and thioesters and evaluation of their in vitro and in vivo nerve regenerative effects.

The recent discovery that small molecule ligands for the peptidyl-prolyl isomerase (PPIase) FKBP12 possess powerful neuroprotective and neuroregenerative properties in vitro and in vivo suggests therapeutic utility for such compounds in neurodegenerative disease. The neurotrophic effects of these compounds are independent of the immunosuppressive pathways by which drugs such as FK506 and rapamycin operate. Previous work by ourselves and other groups exploring the structure-activity relationships (SAR) of small molecules that mimic only the FKBP binding domain portion of FK506 has focused on esters of proline and pipecolic acid. We have explored amide and thioester analogues of these earlier structures and found that they too are extremely potent in promoting recovery of lesioned dopaminergic pathways in a mouse model of Parkinson's disease. Several compounds were shown to be highly effective upon oral administration after lesioning of the dopaminergic pathway, providing further evidence of the potential clinical utility of a variety of structural classes of FKBP12 ligands.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed2002

Synthesis of ketone analogues of prolyl and pipecolyl ester FKBP12 ligands.

The recently discovered small-molecule ligands for the peptidyl and prolyl isomerases (PPIase) of FKBP12 have been shown to possess powerful neuroprotective and neuroregenerative effects. Ketone analogues of the prolyl and pipecolyl esters, which mimic only the FKBP binding domain portion of FK506, are proposed and an efficient synthetic strategy is presented in this report, along with the preliminary results of in vitro and in vivo biological studies.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed2002

Chiral separation of amino acids derivatized with fluoresceine-5isothiocyanate by capillary electrophoresis and laser-induced fluorescence detection using mixed selectors of beta-cyclodextrin and sodium taurocholate.

Chiral separation of 20 pairs of amino acids derivatized with fluoresceine-5-isothiocyanate (FITC) by capillary electrophoresis and laser-induced fluorescence detection was studied using the mixture of beta-cyclodextrin (beta-CD) and sodium taurocholate (STC) as selector. Resolution was considerably superior to that obtained by using either beta-CD or STC alone. The molar ratio of beta-CD to STC of about 2:3 was found to be critical to achieve maximum separation. At this beta-CD-to-STC ratio, chiral separation occurred at really low total concentration of beta-CD and STC (<0.1 mM). Other impacting factors were investigated including the total concentration of beta-CD and STC, pH, and capillary conditioning procedure between two successive runs. Using a running buffer of 80 mM borate containing 20 mM beta-CD and 30 mM STC at pH 9.3, all of the 20 pairs of FITC-amino acid enantiomers were baseline resolved. The resolutions of the most pairs of the amino acid enantiomers (17 of 20) were higher than 3.0, only three pairs gave a resolution lower than 3.0 but higher than 1.90 (beta-phenylserine, pSer). The highest resolution reached 14.58 (Glu). Two derivatives of beta-CD, 2-hydroxypropyl-beta-CD (HP-beta-CD) and heptakis(2,6-di-O-methyl)-beta-CD (DM-beta-CD) were also explored. HP-beta-CD showed similar cooperative effect with STC, while DM-beta-CD together with STC led to poorer chiral separation.

Amino Acids↗
PubMed2002

Chiral separation of underivatized amino acids by ligand-exchange capillary electrophoresis using a copper(II)-L-lysine complex as selector.

A ligand-exchange capillary electrophoretic method was explored, with L-lysine as the ligand and copper(II) as the central ion. Its applicability was demonstrated with underivatized aromatic amino acids, namely D,L-phenylalanine, D,L-tryptophan, D,L-tyrosine and D,L-beta-phenylserine. Optical resolutions of a single pair of amino acid enantiomers, and of mixed amino acids were obtained with a running buffer of 10 mM NH4Ac, 6.67 mM Cu(II) and 13.33 mM L-lysine, pH 7.0. Sodium dodecylsulfate (SDS) was shown to be necessary for simultaneous separation of the mixed amino acids. The resolution was found to increase with the concentration of the copper(II) complex at a copper(II)-to-lysine ratio of 1:2. If the total concentration of copper(II) and lysine was kept at 20 mM, decreasing the ratio of copper(II) to lysine caused a resolution loss of tryptophan, but a slight resolution improvement of the other three amino acids. The pH of buffer is another important factor controlling the separations. For all the studied amino acids, the optimum pH was 6.0. An interesting phenomenon was observed in this study. SDS induces precipitation at a concentration below 32 mM at room temperature (16+/-2 degrees C), possibly due to the formation of neutral substance from the SDS monomer and the copper(II)-lysine complex.

Amino Acids↗
PubMed2002

Intracoronary retrieval of the dehisced radiopaque ring of a guiding catheter: an unusual complication of coronary angioplasty.

The guiding catheter used in coronary intervention may be damaged or some parts could be dehisced during the procedure, producing adverse effects in the vascular tree. So much so that immediate surgery is usually indicated. We report a case with a dehisced radiopaque ring of the catheter during the procedure. It was retrieved percutaneously without thoracotomy.

Angioplasty, Balloon, Coronary↗
PubMed2002

A carbonyl oxygen migration in electrospray ionization mass spectrometry and its application in differentiating alpha- and beta-alanyl peptides.

A novel rearrangement reaction with a carbonyl oxygen migration was observed in the electrospray ionization tandem mass spectra of N-diisopropyloxyphosphoryl dipeptides and their analogues. A possible mechanism was proposed and supported by the MS/MS study, derivatization of different functional groups and deuterium labeling experiments. It was found that metal ions could catalyze the rearrangement through a five-membered ring intermediate. A strong affinity between the phosphoryl group and oxygen atom in the gas phase was proposed to result in this kind of rearrangement reaction, which might provide some basic information on the nature of phosphorylation in biochemistry. The replacement of N-terminal alpha-alanine by beta-alanine stopped the migration, which provides a simple method for differentiating the alpha- and beta-alanine residues at the N-terminus of peptides.

Alanine↗
PubMed2002

Novel phosphoryl derivatization method for peptide sequencing by electrospray ionization mass spectrometry.

A one-step phosphoryl derivatization method has been used in a peptide sequencing procedure for electrospray ionization tandem mass spectrometry (ESI-MS/MS). The sodiated derivatized peptides exhibit very simple dissociation patterns, in which two kinds of fragment ions, [b(n) + OH + Na]+ and [a(n) + Na]+, are formed. Since the amino acid residues are lost sequentially from the C-terminus, peptide sequences can be identified easily. The fragmentation efficiency of peptides increased as a result of the phosphorylation, and also provided peaks of useful intensity at lower m/z. A peptide with lysine at the C-terminus was derivatized and analyzed by ESI-MS/MS. Similar mass spectra, from which the sequence could be read out, were obtained. This is a novel derivatization method yielding neutral derivatives that should be suitable for peptide sequencing by LC/ESI-MS/MS.

Amino Acid Sequence↗
PubMed2002

Negative-ion electrospray ionization tandem mass spectrometry of N-phosphoryl amino acids and dipeptides.

The negative-ions of N-phosphoryl amino acids were studied by electrospray ionization tandem mass spectrometry (ESI-MS/MS). The negative-ion ESI-MS/MS of N-phosphoryl amino acids showed characteristic fragmentation patterns different from those observed in the corresponding positive-ion ESI-MS/MS and negative-ion fast-atom bombardment mass spectra. For negative-ion ESI-MS/MS, a unique fragmentation from the N-terminal of N-phosphoryl amino acids or peptides containing a free beta-OH or CO(2)H group was observed to yield the characteristic fragment ion (RO)(2)P(O)O(-). The ease of the rearrangement depended on the position of the hydroxyl group in amino acids or peptides, and the N --> O rearrangement mechanism was proposed to involve the participation of the hydroxyl group. From previous solution-phase experiments and theoretical calculations, it was found that the beta-OH group was more active than gamma-OH, and the corresponding difference in negative-ion ESI-MS/MS was consistent with those previous findings.

Dipeptides↗
PubMed2002

Electrospray ionization mass spectrometric studies of phosphorus oxychloride directed synthesis of homo-oligopeptide ester libraries.

With the assistance of phosphorus oxychloride, alpha-amino acids were assembled into homo-peptides, which were analyzed by electrospray ionization mass spectrometry (ESI-MS) and multistage electrospray ionization mass spectrometry (ESI-MS/MS). On quenching with water or various alcohols, the reaction mixtures yielded the corresponding peptides or peptide esters, respectively. This paper reports a simple method to synthesize the homo-oligo-peptide-ester conjugated library by phosphorus oxychloride activation.

Amino Acids↗
PubMed2002

Inducible nitric oxide synthase knockout mouse and low-density lipoprotein oxidation.

We have presented experimental procedures that examine macrophage-mediated LDL oxidation using Ham's F-10 medium. By comparing iNOS-/- and iNOS+/+ macrophages, an antioxidant effect for NO and a prooxidant effect for IFN-gamma were demonstrated. The methods outlined here should allow for the investigation on the mechanism of in vitro LDL oxidation and how the macrophage-mediated LDL oxidation process is affected by various factors, one of which was the effect of iNOS induction by IFN-gamma.

Animals↗
PubMed2002

Expression of Fas, p53 and AFP in development of human fetal germ cells in vitro.

In the present study we employed a two-step culture system to study the expression of Fas, p53 and alpha-fetoprotein (AFP) in the development in vitro of human fetal germ cells. p53 mRNA was determined by Northern blotting, and Fas content was assessed by western blotting. RT-nested polymerase chain reaction (RT-nPCR) analysis was performed to determine the expression of AFP mRNA in different stages of fetal follicular development. Follicular cell apoptosis was evaluated by DNA fragmentation analyses (DNA ladder). The results showed that by day 7 of culture approximately one-sixth of fetal germ cells grew to class C oocytes (primary oocytes) from class B oocytes (primordial oocytes) or class A oocytes. On day 45 of culture, one-third of these primary follicles doubled in size. In the meantime, there was a high proportion apoptosis of follicular cells on days 35 or 45 of culture, as evident by a clear ladder pattern of DNA fragmentation upon electrophoretic analysis. Expression of Fas antigen and p53 mRNA increased in a time-dependent manner, while AFP mRNA was expressed on days 10 to 35, and disappeared on day 45. These results indicate that human fetal germ cells can develop in a two-step culture system and AFP may play an active role in the proliferation of these germ cells. At the late stage of follicular development in vitro, a number of follicular cells became apoptotic. Moreover, apoptosis may be the mechanism responsible for fetal germ cell regression and the Fas antigen and/or p53-mediated death pathway may be central in the induction of germ cell regression.

Female↗
PubMed2002

Volatile compounds in anal gland of Siberian weasels (Mustela sibirica) and steppe polecats (M. eversmanni).

The volatile constituents in anal gland secretions of two sympatric Mustela species, the Siberian weasel (M. sibirica) and steppe polecat (M. eversmanni), were studied by the headspace technique, followed by gas chromatography-mass spectrometry (GC-MS) analysis. Nine sulfur-containing compounds were identified. They were 2,2-dimethylthietane, (Z)- or (E)-2,4-dimethylthietane, (E)-2,3-dimethylthietane, 2-ethylthietane, (E)-2-ethyl-3-methylthietane, (Z)-2-ethyl-3-methylthietane, 2-propylthietane, 3,3-dimethyl-1,2-dithiacyclopentane, and (Z)-3,4-dimethyl-2,2-dithiacyclopentane. Among them, (E)-2-ethyl-3- methylthietanes, (Z)-2-ethyl-3-methylthietanes, and (Z)-3,4-dimethyl-1,2-dithiacyclopentane were present in the polecat but not in the weasel. The predominant compound was 2,2-dimethylthietane in the weasel and (E)- or (Z)-2,4-dimethylthietane in the polecat. These differences were consistent between the two species, regardless of sex and age and, therefore, could possibly be used for species recognition. In the weasel, 2-ethylthietane was found only in the female, and the relative abundance of several compounds was significantly different between males and females. In the polecat, although no sex-specific volatile compounds were found, males and females differed in the relative abundance of several of the compounds. In both species, the relative abundance of some compounds varied with age. We conclude that these volatile compounds can be used to communicate information about species, sex, and age.

Anal Canal↗