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Y Huang

Publications and source records attributed to Y Huang.

At least 1,009 records · Page 56Linked to original sources
PubMed1994

[D-TRP32]neuropeptide Y: a competitive antagonist of NPY in rat hypothalamus.

Neuropeptide Y (NPY) is a potent orexigenic peptide. Structure-activity studies have revealed that nearly the entire sequence of NPY is required to elicit feeding responses. Therefore, in order to develop antagonistic peptides for NPY-induced feeding, we synthesized full-length analogs of NPY, substituting D-Trp in the C-terminal receptor binding region, and screened their activity in rat hypothalamus. Although [D-Trp36]NPY and [D-Trp34]NPY inhibited isoproterenol-stimulated hypothalamic membrane adenylate cyclase activity, [D-Trp32]NPY exhibited no intrinsic activity. Furthermore, [D-Trp32]NPY inhibited [125I]NPY binding to rat hypothalamic membranes with a potency comparable to that of NPY. The presence of 30 and 300 nM concentrations of [D-Trp32]NPY shifted the inhibitory dose-response curve of NPY on isoproterenol-stimulated hypothalamic membrane adenylate cyclase activity parallel to the right with comparable KB values. Moreover, in vivo experiments in rats revealed that [D-Trp32]NPY (10 micrograms) significantly attenuated the 1-h feeding response induced by NPY (1 microgram). Several other substitutions at position 32 including 2-D-Nal resulted in agonist activity, suggesting that there are strict structural requirements to induce the antagonistic property in NPY. These findings confirm that [D-Trp32]NPY is a competitive antagonist of NPY in both in vitro and in vivo systems. Analogs based on [D-Trp32]NPY may have potential clinical application, since NPY has been implicated in the pathophysiology of a number of feeding disorders including obesity, anorexia, and bulimia.

Adenylyl Cyclase Inhibitors↗
PubMed1994

A plasma lipoprotein containing only apolipoprotein E and with gamma mobility on electrophoresis releases cholesterol from cells.

Previous studies have identified lipid-poor high density lipoproteins with electrophoretic pre-beta mobility as the initial acceptors of cell-derived cholesterol in human plasma. These lipoproteins contain apolipoprotein A-I (apo A-I) as their sole apolipoprotein. In the present study, incubation of human plasma with [3H]cholesterol-laden skin fibroblasts has led to the identification of another lipoprotein that serves as a potent initial acceptor of cell-derived cholesterol. This lipoprotein, which we term gamma-LpE, exhibits gamma mobility on agarose gel electrophoresis. As determined by nondenaturing PAGE and by electron microscopy, the size of the spherical particle ranges between 12 and 16 nm. SDS/PAGE and subsequent immunoblotting identified apoE as its sole apolipoprotein. Plasma from normal and apoA-I-deficient mice, but not from apoE-deficient mice, released [3H]cholesterol from fibroblasts into a gamma-migrating lipoprotein. Cell culture media from hepatoma cells or mouse peritoneal macrophages, both of which contain apoE of cellular origin, also promoted efflux of [3H]cholesterol from fibroblasts into a gamma-migrating fraction. This was not observed with cell culture medium from fibroblasts alone. In conclusion, our results strongly indicate the presence in human plasma of a lipoprotein containing only apoE, gamma-LpE, which is secreted by peripheral cells and is a potent acceptor of cell-derived cholesterol.

Animals↗
PubMed1994

Binding of malate dehydrogenase and NADH channelling to complex I.

As previously reported, mitochondrial malate dehydrogenase (MDH) binds to purified complex I of the electron transport system. With conditions used in previous reports, MDH binds even more extensively, but probably predominantly non-specifically, to the matrix side of the inner mitochondrial membrane of submitochondrial particles (SMP). Herein we report experimental conditions for highly specific binding of malate dehydrogenase to complex I within SMP. These conditions permit us to demonstrate NADH channelling from malate dehydrogenase to complex I using the competing reaction test. This test, though not ideal for all situations, has several advantages over the enzyme buffering test previously used. These advantages should facilitate further studies elucidating NADH channelling to complex I from MDH and other dehydrogenases. Independent evidence of NADH channelling to the electron transport chain and the potential advantages of substrate channelling in general are also discussed. Substrate channelling from MDH in particular may be especially beneficial because of the unfavourable equilibrium and kinetics of this enzyme reaction.

Animals↗
PubMed1994

Synergistic effects of bombesin and cholecystokinin on cholesterol esterase biosynthesis and secretion by AR42J cells.

This study used the rat pancreatoma AR42J cells as model to study hormonal regulation of cholesterol esterase biosynthesis. Our previous studies (Y. Huang and D. Y. Hui, 1991, J. Biol. Chem. 266, 6720-6725) have demonstrated that the AR42J cells responded to cholecystokinin (CCK) and secretin challenge by increasing cholesterol esterase biosynthesis. The current investigation showed that another gastric peptide hormone, bombesin, was also effective in stimulation of cholesterol esterase biosynthesis. Cholesterol esterase biosynthesis in AR42J cells increased 2- to 3-fold in the presence of 5 to 10 nM bombesin or 4 nM CCK. More significantly, when both bombesin and CCK were added to the incubation medium at these concentrations simultaneously, a 15-fold induction of cholesterol esterase biosynthesis was observed. Slot-blot analysis of RNA isolated from control and hormone-stimulated cells revealed no change in the level of cholesterol esterase mRNA, suggesting the post-transcriptional activation of cholesterol esterase biosynthesis. The synergism between bombesin and CCK was not restricted to cholesterol esterase biosynthesis as the simultaneous addition of the two hormones also dramatically increased amylase secretion by AR42J. The results of these studies indicated that gastric peptide hormones may act in concert to stimulate maximally digestive enzyme biosynthesis. The synergistic effects of bombesin and CCK also suggest that distinctive signal transduction pathways may be responsible for the bombesin and CCK induction of pancreatic protein secretion.

Amylases↗
PubMed1994

Binding of heme-CO to bovine and porcine beta-lactoglobulins.

Two molecules of heme-CO bind to bovine or porcine beta-lactoglobulin (BLG) with an average affinity of 0.5 microM. The affinity increases with pH, with a transition near pH 7.5, indicating a conformational change in the protein. Heme-CO does not bind to the predominantly alpha-helix conformation of BLG, which occurs in solutions with more than 40% ethanol or methanol. Fluorescence energy transfer measurements have been made for the complex of BLG with retinol and/or heme-CO. Two species of BLG were used. While bovine BLG possesses two tryptophans (at positions 19 and 61) which are quenched by about a factor of 2 by either retinol or heme-CO, the porcine species has only one tryptophan (at position 19) whose fluorescence is decreased by a factor of 15 when both hemes are bound, indicating that at least one of the heme-binding sites is near (< 20 A) to this tryptophan. The fluorescence of retinol (complexed to BLG) is also quenched by the addition of heme-CO, indicating that BLG can bind both molecules simultaneously; a separation of 25 A between retinol and heme was calculated. The results suggest at least two hydrophobic pockets for this protein.

Animals↗
PubMed1994

Development of a high-performance liquid chromatographic method for the analysis of enatiomer/enantiomer interaction in oxidative metabolism of bunitrolol in rat liver microsomes.

A high-performance liquid chromatographic method for the assay of enantiomeric 4-hydroxybunitrolol (4-OH-BTL) formed from racemic bunitrolol (BTL) in rat liver microsomes was developed. Racemic bunitrolol was incubated with rat liver microsomes fortified with an NADPH-generating system. Metabolites extracted with ethyl acetate were converted to acetyl derivatives with acetic anhydride in pyridine. The derivatives of 4-OH-BTL were well separated by the liquid chromatography equipped with a chiral column. Using this method, the metabolic interaction of BTL enantiomers was examined. The 4-OH-BTL-forming activities from enantiomeric BTL were higher than those from racemic BTL in rat liver microsomes, while the formation of ratios of 4-OH-BTL enantiomer to its antipode were the same under the two conditions. The Ki values obtained from kinetic studies using each BTL enantiomer as an inhibitor of its antipode were almost the same (ca 0.9 microM), which were close to their Michaelis constants (Km values). Oxidative activities of enantiomeric and racemic BTL were almost equally inhibited by debrisoquine and quinidine, a typical substrate and a selective inhibitor of the CYP2D subfamily, respectively. These results indicate that a BTL enantiomer is a mutual metabolic inhibitor of its antipode and BTL enantiomers compete for the same CYPD2D isozyme in rat liver microsomes.

Adrenergic beta-Antagonists↗
PubMed1994

1-beta-D-arabinofuranosylcytosine-, mitoxantrone-, and paclitaxel-induced apoptosis in HL-60 cells: improved method for detection of internucleosomal DNA fragmentation.

We investigated the ability of different doses and durations of exposure to the chemotherapeutic drugs 1-beta-D-arabinofuranosylcytosine (Ara-C), mitoxantrone (MTN), and paclitaxel (taxol, TXL) to induce internucleosomal DNA fragmentation and apoptosis in human acute myeloid leukemia (AML) HL-60 cells in suspension culture. At clinically achievable concentrations, all three drugs have been shown to induce apoptosis in HL-60 cells. An improved method was developed for the isolation of pure genomic DNA and the detection of drug-induced internucleosomal DNA fragmentation in < 1.0 microgram of DNA sample by agarose gel electrophoresis. Morphologic evidence for apoptosis was determined by light microscopy following Wright staining, and cell viability was assessed by trypan blue dye exclusion. Internucleosomal DNA fragmentation was observed following exposure to 1.0 microM Ara-C for 4 h, which increased with 10 and 50 microM Ara-C. Incubation with 100 microM Ara-C produced internucleosomal DNA fragmentation starting at 3 h, which increased with longer periods of exposure to Ara-C. Utilizing a schedule of 1-h exposure followed by 3-h suspension in drug-free medium, 0.25 microM MTN was found to initiate DNA fragmentation, which increased with exposure to 1.0 and 5.0 microM MTN. However, identical treatment with higher concentrations of MTN resulted in random DNA degradation. Alternatively, continuous exposure to 1.0 microM MTN for 3 h was necessary to initiate internucleosomal DNA fragmentation. This increased with exposure intervals of up to 6 h. Exposure to TXL concentrations as low as 0.01 microM for 24 h caused internucleosomal DNA fragmentation, which increased with dose escalation (0.05, 0.1, 0.5, and 1.0 microM) of TXL. Although continuous exposure to 1.0 microM TXL for a period as short as 8 h produced internucleosomal DNA fragmentation, this increased significantly with longer exposure intervals. In general there appears to be a threshold concentration and duration of exposure below which none of these three drugs activates endonucleolytic internucleosomal DNA fragmentation and apoptosis. This threshold is lower for the DNA-interactive drugs MTN and Ara-C but higher for the non-DNA-interactive drug TXL. Higher doses or prolonged treatments with the drugs produce random DNA fragmentation associated with necrotic cell death. These in vitro results may further improve our understanding of the antileukemic cytotoxic effects of these drugs, which may enable a more rational design of drug regimens for optimal treatment of AML.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1994

A proper transmembrane Ca2+ gradient is essential for the stimulation of adenylate cyclase activity by stimulatory GTP-binding protein.

Stimulatory GTP-binding Protein (Gs) and adenylate cyclase prepared from bovine brain cortices were co-reconstituted into asolectin vesicles with or without 1000-fold transmembrane Ca2+ gradient. The results showed that both basal activity and Gs-stimulated activity of adenylate cyclase were highest in proteoliposomes with a transmembrane Ca2+ gradient similar to physiological condition (1 microM Ca2+ outside and 1 mM Ca2+ inside) and lowest when the transmembrane Ca2+ gradient was in the inverse direction. Such a difference could be diminished following dissipation of the transmembrane Ca2+ gradient by A23187. Comparable conformational changes of Gs in proteoliposomes were also observed when Gs was labeled with the fluorescence probe, acrylodan. These results may indicate that a proper transmembrane Ca2+ gradient is essential not only for higher adenylate cyclase activity but also for its stimulation by Gs.

Adenosine Monophosphate↗
PubMed1994

Comparison of peripheral blood flow patterns associated with the defense reaction and the vigilance reaction in rabbits.

The present study compared the skeletal muscle and visceral blood flow patterns elicited by electrical stimulation of the hypothalamic defense area (HDA) and the hypothalamic vigilance area (HVA) of the rabbit. Electrical stimulation of the HDA evoked a pressor response, tachycardia, hyperventilation, an increase in blood flow to the skeletal muscles and decreased blood flow to visceral organs. Stimulation of the HVA yielded a pressor response, bradycardia, inspiratory apnea and decreased blood flow to both the skeletal muscles and the viscera. Intravenous injections of atropine methyl nitrate significantly reduced the HVA-elicited bradycardia and the HDA-elicited increase in blood flow to the skeletal muscles, thereby providing evidence that the bradycardia was mediated by vagal efferents and that the rabbit has an atropine-sensitive cholinergic vasodilation system. The decrease of blood flow to the visceral organs associated with the defense reaction and vigilance reaction was reversed by intravenous injections of the alpha-1 receptor blocker prazosin.

Animals↗
PubMed1994

Comparative effectiveness of hand-cleansing agents for removing methicillin-resistant Staphylococcus aureus from experimentally contaminated fingertips.

BACKGROUND: Five subjects participated in a study of optimal conditions for removing methicillin-resistant Staphylococcus aureus from contaminated fingertips. METHODS: Fingertips were contaminated experimentally and cleaned by various methods. Bacterial removal was measured as percentage and is given as mean +/- standard error of the mean. RESULTS: Rinsing the fingertips with tap water for 20 seconds and drying them with paper towels removed 95.2% +/- 1.6% of the contamination. Application of hand-cleansing agents to fingertips for 20 seconds, followed by a 20-second tap-water rinse and towel drying, removed bacteria as follows: povidone-iodine detergent, 99.2% +/- 0.4%; chlorhexidine detergent, 97.2% +/- 0.8%; and liquid soap, 96.1% +/- 1.1%. In a modification of the method, 80% ethyl alcohol applied to the fingertips for 20 seconds, followed by air drying for 40 seconds, removed 99.1% +/- 0.8% of the bacteria. Statistical analyses indicated that povidone-iodine and 80% ethyl alcohol were more effective than the other agents. CONCLUSIONS: Rinsing contaminated fingertips with tap water and towel drying them is sufficient to reduce contamination with methicillin-resistant S. aureus by 95%. Washing with povidone-iodine or 80% ethyl alcohol further reduces contamination by an additional 99%.

Adult↗
PubMed1994

The influence of dose, dose-rate and particle fragmentation on cataract induction by energetic iron ions.

Because activities in space necessarily involve chronic exposure to a heterogeneous charged particle radiation field it is important to assess the influence of dose-rate and the possible modulating role of heavy particle fragmentation on biological systems. Using the well-studied cataract model, mice were exposed to plateau 600 MeV/amu 56Fe ions either as acute or fractionated exposures at total doses of 5 - 504 cGy. Additional groups of mice received 20, 360 and 504 cGy behind 50 mm of polyethylene, which simulates body shielding. The reference radiation consisted of 60Co gamma radiation. The animals were examined by slit lamp biomicroscopy over their three year life spans. In accordance with our previous observations with heavy particles, the cataractogenic potential of the 600 MeV/amu 56Fe ions was greater than for low-LET radiation and increased with decreasing dose relative to gamma-rays. Fractionation of a given dose of 56Fe ions did not reduce the cataractogenicity of the radiation compared to the acute regimen. Fragmentation of the beam in the polyethylene did not alter the cataractotoxicity of the ions, either when administered singly or in fractions.

Animals↗
PubMed1994

In vivo morphometry of planum temporale asymmetry in first-episode schizophrenia.

Magnetic resonance imaging is a promising tool for in vivo analysis of the neuropathology underlying schizophrenia. One of the most consistent features emerging from the majority of published studies is the lateralization of pathological findings, and this has led to hypotheses of impaired hemispheric specialization in schizophrenia. In previous work, we have validated morphometry of supratemporal language-related cortex using high-resolution magnetic resonance imaging and analyzed the relation of the so defined planum temporale to functional parameters of hemispheric specialization. In the present study, we examined planum temporale structural asymmetry in first-episode schizophrenics. Asymmetry coefficients obtained in these patients did not differ significantly from those in equally right-handed controls and were not correlated to standard psychopathological measures. These data are contrasted with other studies reporting lateralized brain pathology in schizophrenia with special emphasis on methodological considerations in neuroimaging procedures.

Adult↗
PubMed1994

Tactile exploration of shape after subcortical ischaemic infarction studied with PET.

We studied the cerebral activations related to restitution of hand function in five patients with first hemiplegic subcortical stroke due to ischaemic infarction in the area of the basal ganglia or thalamus. In two subjects, involvement of the cortico-spinal tract was demonstrated by magnetic evoked potentials. The subjects were requested to discriminate rectangular parallelepipeda of identical mass with their affected hands. Regional cerebral blood flow (rCBF) was measured with PET after intravenous bolus injection of [15O]butanol, at rest and during task execution. Evaluation of the rCBF changes was based on pixel-by-pixel t statistics of spatially standardized and averaged PET images and on a statistical distribution analysis of regions of interest in the individual subjects. For anatomical localization of the significant rCBF changes, a computerized brain atlas (Greitz et al. J Comput Assist Tomogr 1991; 15: 26-38) and a matching procedure that directly aligns individual PET and high resolution magnetic resonance images were used. The rCBF at rest and the task-induced rCBF changes varied from subject to subject, as did the residual neurological deficits at the time of PET scanning. In all subjects there were large activation areas in the motor and the sensory hand area contralateral to the affected hand. Poor performance of the task was correlated with a low rCBF in the contralateral sensorimotor cortex at rest and a bilateral activation of the primary sensorimotor cortex during task performance. The premotor cortex, ipsilateral and anterior cerebellum, contralateral to the affected hand, were also significantly activated. Further activations were observed in the contralateral premotor cortex, supplementary motor area and bilaterally in the posterior cingulate cortex, but were less consistent among the subjects. Our data suggest that recovery from hemiplegic stroke is associated with a marked reorganization of the cerebral activation patterns, including common and subject-specific activation sites. With respect to task-specific information processing a lower discrimination rate of objects compared with controls was associated with diminished activations in parietal lobe.

Adult↗
PubMed1994

A unique p53 intragenic deletion flanked by short direct repeats results in loss of mRNA expression in a human esophageal carcinoma.

A 45 base pair (bp) intragenic deletion of the p53 gene from a human esophageal cancer was analyzed in detail. This deletion contained all RNA splice consensus sequences at the 3' end of intron 7, including the RNA splice branch point, the pyrimidine-rich region and the 3' splice acceptor site. Northern blotting revealed a total lack of p53 mRNA expression in this tumor. Short direct repeats (TACTG) were found at the 5' and 3' breakpoints of the deletion and it removed one complete repeat as well as the entire region between the repeats. These results suggest that a 'slipped mispairing' mechanism occurring during DNA replication may generate p53 intragenic deletion in human esophageal cancer, leading to abolished p53 mRNA expression.

Base Sequence↗
PubMed1994

Physiological role and clinical relevance of high-density lipoprotein subclasses.

Low HDL cholesterol is an important predictor of cardiovascular risk. Considerable effort has been undertaken to improve the predictive value of HDL cholesterol by the quantification of HDL subclasses. Controversy still exists as to whether quantification of apolipoprotein A-I, selective precipitation of HDL2, or differential immunoassays of apolipoprotein A-I-containing particles improve the diagnostic value of HDL cholesterol. Some quantitatively minor subclasses of HDL, namely pre-beta-1-lipoprotein(AI) and gamma-lipoproteinE, contribute significantly to the release of cellular cholesterol into the plasma compartment, and possibly to the antiatherogenic role of HDL. These particles can only be separated from the bulk of HDL by laborious electrophoretic techniques that, although provide important insights into the physiology of reverse cholesterol transport, are not suitable for clinical laboratories. Thus, to date, clinicians are not recommended to extend the measurement of HDL cholesterol to include the determination of HDL subclasses.

Antigens↗