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Biomedical subjects

Y Tang

Publications and source records attributed to Y Tang.

At least 307 records · Page 17Linked to original sources
PubMed1997

[Comparative study on three different methods in typing hepatitis C virus].

The sea from 120 anti-HCV-positive patients were detected by three different methods to type HCV. In method A, PCR product of 5'-NC region was cut by restriction endonuclease. In method B, PCR with HCV core region type-specific primers was used. In method C, EIA based on HCV genotype I, II (serotype 1) and genotype III, IV (serotype 2) synthetic peptides was used to detect type-specific antibodies. It was showed that HCV genotypes were successfully identified in 96(80%) patients both by method A and method B, with HCV-II 86(89.6%), HCV-III 8(8.3%), HCV-II/III coinfection 2(2.1%). The results of these two methods were completely agreeable. HCV type-specific antibodies were detected in 78(65%) cases by method C, with serotype 1 68(87.2%), serotype 2 6(7.7%), serotype 1 plus 2 positive 4(5.1%). The comparative estimation of 66 patients who were positive for all the three methods showed a remarkable concordance (64/66, 97.0%). Our study demonstrated that the results of different HCV-typing methods mentioned above were fairly consistent and reliable. The abvantages, disadvantages and practical applicable scope of these methods were discussed in the paper.

Genotype↗
PubMed1997

In vivo tissue disposition of 3'-azido-3'-deoxythymidine and its anabolites in control and retrovirus-infected mice.

At present, 3'-azido-3'-deoxythymidine (AZT; zidovudine) remains the drug of choice for initiating AIDS therapy. This drug in itself is inactive; it needs to be converted intracellularly by a series of cellular kinases to AZT 5'-triphosphate (AZT-TP) to exert antiviral activity. The purpose of this study was to examine the in vivo disposition of the phosphorylated AZT anabolites in different target tissues and to investigate the effects of chronic retrovirus infection on the tissue disposition of AZT anabolites. Female C57BL/6 mice at 20 weeks after inoculation with LP-BM5 murine leukemia virus, as well as age-matched control animals, were dosed subcutaneously with 25 mg/kg of AZT. The dosing solution contained [3H]AZT with a specific activity of 87 mCi/mmol. The levels of AZT and its phosphorylated anabolites were determined in tissues collected at different times after AZT administration using an analytical method coupling an ion-pair HPLC separation procedure with radioactivity detection after the separation. The tissue-to-plasma AZT ratios in control mice could be ranked in the following order: kidneys > muscle approximately equal to spleen approximately equal to liver approximately equal to heart approximately equal to lung > thymus > lymph nodes > brain. Similar rank order was observed in infected animals, with the exception that significantly higher AZT levels were found in the lymph nodes, where the tissue-to-plasma AZT ratios in lymph nodes were higher than those in thymus tissues. Tissue AZT 5'-monophosphate profiles tended to parallel the AZT profiles in most tissues examined. Delays in the appearance of AZT 5'-diphosphate and AZT-TP were observed in all tissues tested. AZT-TP content was not detectable in any of the brain samples analyzed. The conversion of AZT to AZT anabolites was found to be highest in the spleen and bone marrow samples from both control and infected animals. Lymph nodes of the control animals showed poor ability to phosphorylate AZT to its active triphosphate moiety. This ability was significantly enhanced in infected animals. We concluded that the in vivo disposition of AZT anabolites after a single dose administration of AZT is tissue-specific in mice and that experimentally induced chronic retrovirus infection resulted in the most significant changes in the distribution of AZT into the lymph nodes and in the phosphorylation of AZT in this important target tissue. Further studies are needed to relate the tissue-specific disposition of AZT anabolites to the therapeutic problems encountered with AZT treatment.

Animals↗
PubMed1997

Immunologic havoc induced by the 60 kD Gag protein of the MAIDS defective virus.

The mechanisms responsible for development of profound immunodeficiency and extensive lymphoproliferation that characterize infection of different species with retroviruses are only partially understood. In mice, it has been shown the activities of an unusual Gag protein are necessary and sufficient to induce these abnormalities in a syndrome designated mouse AIDS (MAIDS). Current studies suggest that complex, antigen-driven interactions between T cells and B cells result in polyclonal activation of both types of lymphocytes, aberrant cytokine production and late lymphomas.

Animals↗
PubMed1997

The carboxyl-terminal cytoplasmic domain of CD36 is required for oxidized low-density lipoprotein modulation of NF-kappaB activity by tumor necrosis factor-alpha.

The binding of oxidized low-density lipoprotein (Ox LDL) by monocyte-macrophages causes pleiotropic effects, including changes in gene expression, and is thought to represent an early event in atherogenesis. The integral membrane glycoprotein CD36 appears to play a physiological role in binding and uptake of Ox LDL by monocyte-macrophages, although the molecular events associated with CD36-Ox LDL interaction are unknown. To approach this issue, we used CD36 transfected Chinese hampster ovary (CHO) cells, exposed them to Ox LDL, and determined changes in the activity of the transcription factor NF-kappaB. We report here that Ox LDL enhanced DNA binding activity of nuclear extracts to an NF-kappaB sequence following activation of CD36-producing CHO cells with the proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha). This enhanced DNA binding activity was inhibited by coincubation of CD36 transfected cells with the human CD36-specific antibody OKM5. We also determined that activation of NF-kappaB DNA binding activity required an intact carboxyl-terminal cytoplasmic segment on CD36. Our results support the idea that human CD36 mediates signal transduction events in response to Ox LDL.

Animals↗
PubMed1997

[Morphological changes of intramedullary capillary circulation after fracture].

To investigate the influence of injury of nutrient artery on the blood supply of inner 2/3 of cortical and intramedullary tissue, the experiment was carried out on twenty-four rabbits. Four rabbits were killed and perfused with Chinese ink in femoral artery to survey the blood supply of intramedullary vessels. Others were received fracture on tibia and sacrificed respectively on the third, eighth, eighteenth, twenty-eighth, and forty-second days after fracture. Chinese ink was also perfused through femoral artery on those rabbits. The relative density of capillary vessels were determined. The results were as follows: when the nutrient artery was injured after fracture, blood supply to the intramedullary tissue and the inner 2/3 of cortical bone was interrupted. The intramedullary vessels were increared and dilated. During the whole course of healing of fraeture, the density of intramedullary capillary vessels were higher than normal. It was concluded that the anastomosis between the epiphysis and metaphysis was important in the reconstruction of collateral circulation in healing of fracture.

Animals↗
PubMed1996

Enantioseparation of 3-phenylacetylamino-2,6-piperidinedione and related chiral compounds.

This paper reports HPLC methodology for the first successful enantiomeric separations of 3-phenylacetylamino-2,6-piperidinedione (PAP), a naturally occurring peptide derivative used for inhibiting the growth of cancer tissues. The chiral separation of four related hydrolysates is also described. A commercially available tris-4-methylbenzoate cellulose (Chiralcel OJ) column was used as the chiral stationary phase, operated in the normal-phase, mode. The results demonstrated that hydrolyzed products of PAP, each of which has a carboxylic acid functionality present in its structure, eluted in a reasonable time and are enantiomerically resolved only when a trace amount of organic acid is present in the mobile phase. Different alcohols (ethanol and isopropanol) and acid additives (trifluoroacetic acid, trichloroacetic acid and acetic acid) were evaluated. In general, for the separation of the acidic enantiomers, ethanol is superior to isopropanol and stronger acids enhance the resolution more effectively. However, chiral separation of PAP could only be accomplished with isopropanol in the mobile phase and no acidic additive was needed.

Benzeneacetamides↗
PubMed1996

Investigation on enantiomeric separations of fluorenylmethoxycarbonyl amino acids and peptides by high-performance liquid chromatography using native cyclodextrins as chiral stationary phases.

A systematic study was carried out to investigate enantiomeric separations of fluorenylmethoxycarbonyl (FMOC) amino acids and their peptides. Twenty amino acids were derivatized by 9-fluorenylmethyl chloroformate (FMOC-Cl) and its analogues, FMOC-glycyl-Cl and FMOC-beta-alanyl-Cl. All derivatives were chromatographed on native beta- and gamma-cyclodextrin columns using acetonitrile as the main mobile phase component. The results indicated that glycyl and beta-alanyl groups between FMOC and amino acid moieties enhanced chiral selectivities of amino acid derivatives. The addition of modifiers, triethylamine, acetic acid and methanol, into the mobile phase caused alterations in retention, enantiorecognition and elution order. The structures of amino acids and the type of chiral stationary phase employed exhibited significant impacts on chiral resolutions. It is also found that the number and position of glycyl moieties affect the retentions and enantioselectivities of FMOC derivatized glycyl containing peptides.

Alanine↗
PubMed1996

Release of cerebral acetylcholine increases during visually mediated behavior in monkeys.

Extracellular levels of acetylcholine in inferior temporal cortex (IT), perirhinal cortex (PR), and dentate gyrus (DG) of the hippocampus were monitored using in vivo microdialysis in rhesus monkeys performing two behavioral tasks. Performance on a visual recognition task was associated with 26%, 41% and 24% increases in acetylcholine overflow in IT, PR and DG, respectively, compared with pre-test baseline levels. Performance on a memory-independent task was associated with increases in acetylcholine release of 24%, 34% and 7% above baseline in IT, PR and DG, respectively. The PR-DG differences were significant, but the others were not. The results provide biochemical evidence for cerebral cholinergic system activation during visually mediated behavior in non-human primates, and are consistent with the view that such activation is a prerequisite for visual recognition memory.

Acetylcholine↗
PubMed1996

Selection of linkers for a catalytic single-chain antibody using phage display technology.

Phage display has been evaluated as a means of rapidly selecting tailored linkers for single-chain antibodies (scFvs) from protein linker libraries. Preliminary experiments with a conventional linker failed to yield a functional single-chain version of a catalytic antibody with chorismate mutase activity. A random linker library was therefore constructed in which the genes for the heavy and light chain variable domains were linked by a segment encoding an 18-amino acid polypeptide of variable composition. The scFv repertoire ( approximately 5 x 10(6) different members) was displayed on filamentous phage and subjected to affinity selection with hapten. The population of selected variants exhibited significant increases in binding activity but retained considerable sequence diversity. Screening 1054 individual variants subsequently yielded a catalytically active scFv that was produced efficiently in soluble form. Sequence analysis revealed a conserved proline in the linker two residues after the VH C terminus and an abundance of arginines and prolines at other positions as the only common features of the selected tethers. There are apparently many viable solutions to the problem of linking individual VH and VL domains, but subtle differences in sequence dramatically influence the production, stability, and recognition properties of the scFv. The success of these experiments suggests that phage display will be generally useful for identifying peptide sequences for covalently linking any two protein domains.

Amino Acid Sequence↗
PubMed1996

Conformational analysis of two glycoproteins: a Monte Carlo simulated annealing approach using a soft-sphere potential.

The Monte Carlo simulated annealing method was effectively used to predict the three-dimensional structure of the carbohydrate part of two glycoproteins: 1 vsg and 2 fbj from a protein data bank, utilizing a soft-sphere potential. The result was compared both to the crystal structure and to the structure of the corresponding isolated oligosaccharide structure simulated using an ECEPP/2 force field. A good agreement with crystal structure was reached. The interaction with the protein environment was found to significantly influence the structure of the carbohydrate moiety.

Carbohydrate Conformation↗
PubMed1996

NMR determination of the structure of Julibroside J1.

Julibroside J1 is a new triterpenoid saponin which contains one triterpene, two monoterpenes and nine sugar residues. The structure has been determined almost exclusively by high-resolution NMR methods. The 1H and 13C NMR spectra of Julibroside J1 C5D5N have been assigned by homonuclear and heteronuclear correlation experiments, such as COSY, CH-COSY, TOCSY, HMBC, HMQC-COSY, HMQC-TOCSY and NOESY. Anomeric configurations were obtained by combined use of 1JCH and 3JH1,H2 and NOESY data. The particular sugar residues were identified by utilizing 3JHH values obtained from TOCSY cross-peaks, NOE difference spectra, and several 1D-TOCSY spectra, and three-bond intra-ring cross-peaks from a HMBC spectrum. Linkage assignments were made using the HMBC spectrum, and supplemented by NOE data from the NOESY spectrum. The structure of Julibroside J1 was characterized as 3-O-[beta-D-xylopyranosyl-(1-->2)-alpha-L-arabinopyranosyl-(1-->6) -beta-D- glucopyranosyl]-21-O-((6S)-2-trans-2-hydroxymethyl-6-methyl-6-O-[4-O-((6 S)- 2-trans-2,6-dimethyl-6-O-(6-deoxy-beta-D-glucopyranosyl)-2,7-octadien oyl)-6- deoxy-beta-D-glucopyranosyl]-2,7-octadienoyl)-acacic acid 28-O-(beta-D-glucopyranosyl-(1-->3)-[alpha-L-arabinofuranosyl-(1-->4)]- alpha-L-rhamnopyranosyl-(1-->2))-beta-D-glucopyranosyl ester.

Carbohydrate Conformation↗
PubMed1996

Increased resistance to acetaminophen-induced hepatotoxicity in retrovirus-infected mice.

In this research we examined the influence of chronic retrovirus infection on the hepatic metabolism of a model substrate, acetaminophen (APAP), and its induced liver injury in mice inoculated with LP-BM5 murine leukemia viruses. Female C57BL/6 mice at 15-17 wks after LP-BM5 retrovirus inoculation and age-matched control animals were used in the studies. APAP treatment (300 mg kg-1, p.o.) resulted in moderate to severe centrilobular necrosis in control animals, with the necrotic area accounting for 40-60% of the total area. In contrast, the APAP-treated (300 mg kg-1, p.o.) infected animals exhibited mild zonal necrosis with the necrotic area accounting for 1-6% of the total area. In the same study, a statistically significant higher percentage of APAP glucuronide and a lower percentage of unchanged APAP were recovered from the urine of the LP-BM5-inoculated animals than from that of controls. No statistically significant differences between infected and uninfected animals in the urinary recovery of APAP sulfate, APAP cysteine, or APAP mercapturate were observed. The formation of APAP metabolites and APAP-associated biochemical changes were also determined from liver slice preparation to avoid in vivo complicating factors. Consistently more significant depletion of the intracellular glutathione levels and K+ content were observed in slices from the uninfected animals at high concentrations of APAP (1 and 2 mM) than in slices from the retrovirus-infected animals. The differences in APAP-associated biochemical changes were accompanied by a 1.4-1.5-fold increase in the formation of APAP glucuronide, sulfate, and glutathione metabolites in slices prepared from animals inoculated with LP-BM5. We concluded that, based on histological examination and hepatic biochemical measurements, the retrovirus-infected animals were more resistant to APAP-induced liver injury. This could be due, in part, to alterations in the detoxification and activation metabolic pathways of APAP.

Acetaminophen↗
PubMed1996

Significance of mobile phase composition in enantioseparation of chiral drugs by HPLC on a cellulose-based chiral stationary phase.

Eight randomly selected pharmaceuticals, which included ibuprofen, ketoprofen, albuterol, acebutolol, propafenone, betaxolol, methylphenidate, and homatropine, were directly separated on a cellulose tris(4-methylbenzoate) chiral stationary phase (CSP) without derivatization via normal phase mode HPLC. Enantioresolution was achieved by the optimization of the type and the ratio of mobile phase modifiers and additives. The modifiers included alcohols; the mobile phase additives were trifluoroacetic acid (TFA) and triethylamine (TEA). It was found that methanol and ethanol were superior to isopropanol as mobile phase modifiers for enhancing chiral separation of some of the chiral drugs. The results also demonstrated that TFA has a dominant effect on chiral separations for both acidic and basic chiral drugs, although for some basic drug such as homatropine, TEA was more beneficial at improving enantioseparation. The separation of acebutolol enantiomers was achieved for the first time by adding both TFA and TEA to the mobile phase. The purpose of this paper is to demonstrate that the applicability of cellulose based CSPs can be expanded by controlling the mobile phase compositions through the addition of trace amounts of achiral additives and the selection of the appropriate alcoholic modifier.

Chromatography, High Pressure Liquid↗
PubMed1996

Simplification and analysis of models of calcium dynamics based on IP3-sensitive calcium channel kinetics.

We study the models for calcium (Ca) dynamics developed in earlier studies, in each of which the key component is the kinetics of intracellular inositol-1,4,5-trisphosphate-sensitive Ca channels. After rapidly equilibrating steps are eliminated, the channel kinetics in these models are represented by a single differential equation that is linear in the state of the channel. In the reduced kinetic model, the graph of the steady-state fraction of conducting channels as a function of log10(Ca) is a bell-shaped curve. Dynamically, a step increase in inositol-1,4,5-trisphosphate induces an incremental increase in the fraction of conducting channels, whereas a step increase in Ca can either potentiate or inhibit channel activation, depending on the Ca level before and after the increase. The relationships among these models are discussed, and experimental tests to distinguish between them are given. Under certain conditions the models for intracellular calcium dynamics are reduced to the singular perturbed form epsilon dx/d tau = f(x, y, p), dy/d tau = g(x, y, p). Phase-plane analysis is applied to a generic form of these simplified models to show how different types of Ca response, such as excitability, oscillations, and a sustained elevation of Ca, can arise. The generic model can also be used to study frequency encoding of hormonal stimuli, to determine the conditions for stable traveling Ca waves, and to understand the effect of channel properties on the wave speed.

Animals↗