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Biomedical subjects

Y Hu

Publications and source records attributed to Y Hu.

At least 91 records · Page 5Linked to original sources
PubMed2001

Palladium-mediated intramolecular carbonylative annulation of o-alkynylphenols to synthesize benzo[b]furo[3,4-d]furan-1-ones.

[reaction in text] The carbonylative annulation of o-alkynylphenols mediated by PdCl(2)(PPh(3))(2) and dppp in the presence of CsOAc at 55 degrees C in acetonitrile under a balloon pressure of CO generates functionalized benzo[b]furo[3,4-d]furan-1-ones in good yields. This novel synthetic approach provides a highly efficient method for diversification of the benzofuran scaffold for combinatorial synthesis.

Benzofurans↗
PubMed2001

IKKalpha controls formation of the epidermis independently of NF-kappaB.

The IKKalpha and IKKbeta catalytic subunits of IkappaB kinase (IKK) share 51% amino-acid identity and similar biochemical activities: they both phosphorylate IkappaB proteins at serines that trigger their degradation. IKKalpha and IKKbeta differ, however, in their physiological functions. IKKbeta and the IKKgamma/NEMO regulatory subunit are required for activating NF-kappaB by pro-inflammatory stimuli and preventing apoptosis induced by tumour necrosis factor-alpha (refs 5,6,7,8,9,10,11). IKKalpha is dispensable for these functions, but is essential for developing the epidermis and its derivatives. The mammalian epidermis is composed of the basal, spinous, granular and cornified layers. Only basal keratinocytes can proliferate and give rise to differentiated derivatives, which on full maturation undergo enucleation to generate the cornified layer. Curiously, keratinocyte-specific inhibition of NF-kappaB, as in Ikkalpha-/- mice, results in epidermal thickening but does not block terminal differentiation. It has been proposed that the epidermal defect in Ikkalpha-/- mice may be due to the failed activation of NF-kappaB. Here we show that the unique function of IKKalpha in control of keratinocyte differentiation is not exerted through its IkappaB kinase activity or through NF-kappaB. Instead, IKKalpha controls production of a soluble factor that induces keratinocyte differentiation.

Animals↗
PubMed2001

Molecular modeling studies of the Akt PH domain and its interaction with phosphoinositides.

The serine-threonine protein kinase Akt is a direct downstream target of phosphatidylinositol 3-kinase (PI3-K). The PI3-K-generated phospholipids regulate Akt activity via directly binding to the Akt PH domain. The binding of PI3-K-generated phospholipids is critical to the relocalization of Akt to the plasma membrane, which plays an important role in the process of Akt activation. Activation of the PI3-K/Akt signaling pathway promotes cell survival. To elucidate the structural basis of the interaction of PI3-K-generated phospholipids with the Akt PH domain with the objective of carrying out structure-based drug design, we modeled the three-dimensional structure of the Akt PH domain. Comparative modeling-based methods were employed, and the modeled Akt structure was used in turn to construct structural models of Akt in complex with selected PI3-K-generated phospholipids using the computational docking approach. The model of the Akt PH domain consists of seven beta-strands forming two antiparallel beta-sheets capped by a C-terminal alpha-helix. The beta1-beta2, beta3-beta4, and beta6-beta7 loops form a positively charged pocket that can accommodate the PI3-K-generated phospholipids in a complementary fashion through specific hydrogen-bonding interactions. The residues Lys14, Arg25, Tyr38, Arg48, and Arg86 form the bottom of the binding pocket and specifically interact with the 3- and 4-phophate groups of the phospholipids, while residues Thr21 and Arg23 are situated at the wall of the binding pocket and bind to the 1-phosphate group. The predicted binding mode is consistent with known site-directed mutagenesis data, which reveal that mutation of these crucial residues leads to the loss of Akt activity. Moreover, our model can be used to predict the binding affinity of PI3-K-generated phospholipids and rationalize the specificity of the Akt PH domain for PI(3,4)P2, as opposed to other phospholipids such as PI(3)P and PI(3,4,5)P3. Taken together, our modeling studies provide an improved understanding of the molecular interactions present between the Akt PH domain and the PI3-K-generated phospholipids, thereby providing a solid structural basis for the design of novel, high-affinity ligands useful in modulating the activity of Akt.

Amino Acid Sequence↗
PubMed2001

Studies in polyphenol chemistry and bioactivity. 3.(1,2) stereocontrolled synthesis of epicatechin-4alpha,8-epicatechin, an unnatural isomer of the B-type procyanidins.

Oligomeric procyanidins containing 4alpha-linked epicatechin units are rare in nature and have hitherto not been accessible through stereoselective synthesis. We report herein the preparation of the prototypical dimer, epicatechin-4alpha,8-epicatechin (6), by reaction of the protected 4-ketones 11a,b with aryllithium reagents derived by halogen/metal exchange from the aryl bromides 26a,b. Removal of the 4-hydroxyl group from the resulting tertiary benzylic alcohols 27a,b was effected by tri-n-butyltin hydride and trifluoroacetic acid in a completely stereoselective manner, resulting in hydride delivery exclusively from the beta face. If benzyl was chosen for protection of the 3-hydroxyls, all protective groups could subsequently be removed in a single step by hydrogenolysis. tert-Butyldimethylsilyl groups, on the other hand, permitted selective deprotection of the 3-hydroxyls in preparation for their subsequent acylation with tri-O-benzylgalloyl chloride. Only monogalloylation at the "bottom" 3-hydroxyl took place when 28c was acylated under the previously reported conditions, reflecting the increased steric hindrance of the "top" 3-hydroxyl group in 28c compared with its 4beta,8-isomer 3. The preparation of compounds 14 and 17 containing phloroglucinol trimethyl ether in the 4alpha and 4beta linkages to epicatechin is also described. The 8-position of the bromine atom in 19, previously conjectured in analogy to the structurally characterized tetramethyl ether 20, was confirmed by transformation of both compounds into the common derivative 25.

Biflavonoids↗
PubMed2001

The effects of aging on gene expression in the hypothalamus and cortex of mice.

A better understanding of the molecular effects of aging in the brain may help to reveal important aspects of organismal aging, as well as processes that lead to age-related brain dysfunction. In this study, we have examined differences in gene expression in the hypothalamus and cortex of young and aged mice by using high-density oligonucleotide arrays. A number of key genes involved in neuronal structure and signaling are differentially expressed in both the aged hypothalamus and cortex, including synaptotagmin I, cAMP-dependent protein kinase C beta, apolipoprotein E, protein phosphatase 2A, and prostaglandin D. Misregulation of these proteins may contribute to age-related memory deficits and neurodegenerative diseases. In addition, many proteases that play essential roles in regulating neuropeptide metabolism, amyloid precursor protein processing, and neuronal apoptosis are up-regulated in the aged brain and likely contribute significantly to brain aging. Finally, a subset of these genes whose expression is affected by aging are oppositely affected by exposure of mice to an enriched environment, suggesting that these genes may play important roles in learning and memory.

Aging↗
PubMed2001

Association of thrombospondin-1 and cardiac allograft vasculopathy in human cardiac allografts.

BACKGROUND: Despite the expression of angiogenic growth factors in transplanted hearts, neovessel formation appears scant. We therefore hypothesized that cardiac allografts contain endogenous inhibitors of angiogenesis. In particular, we tested the involvement in cardiac allografts of thrombospondin-1 (TSP-1), a matrix glycoprotein that inhibits angiogenesis and facilitates smooth muscle cell (SMC) proliferation. METHODS AND RESULTS: Levels of TSP-1 mRNA in endomyocardial biopsy samples of human cardiac allografts substantially exceeded those in normal hearts. The ratio of TSP to GAPDH mRNA determined with quantitative RT-PCR was 6.54+/-1.6 in cardiac allografts versus 0.26+/-0.02 (P:=0.001) in normal hearts. Analysis in sequential biopsies revealed a strong association between persistent elevation of TSP-1 in allografts and the development of cardiac allograft vasculopathy (CAV). The CAV score was 2.4+/-0.8 in patients with persistent TSP-1 elevation compared with 0.2+/-0.2 in patients without elevation (P:=0.001). Immunohistochemistry demonstrated intense expression of TSP-1 in cardiac allografts, predominantly in cardiac myocytes and neointimal SMCs. In vitro experiments demonstrated that T cells expressed TSP-1, acidic fibroblast growth factor, and vascular endothelial cell growth factor on allogeneic stimulation. Cytokines known to be elevated in cardiac allografts (interleukin-1beta, interferon-gamma, and tumor necrosis factor-alpha) induced TSP-1 in SMCs but inhibited TSP-1 in endothelial cells. CONCLUSIONS: Persistent elevation of TSP-1 in cardiac allografts correlates with the development of CAV. Allogeneic stimulation induces angiogenic growth factors and TSP-1 in T cells. Cytokines differentially regulate TSP-1 expression in SMCs versus endothelial cells. Increased levels of TSP-1 in human cardiac allografts may alter vascular responses to angiogenic growth factors by inhibiting angiogenesis and promoting SMC proliferation characteristic of CAV.

Blotting, Northern↗
PubMed2001

B cell development is arrested at the immature B cell stage in mice carrying a mutation in the cytoplasmic domain of immunoglobulin beta.

The B cell receptor (BCR) regulates B cell development and function through immunoglobulin (Ig)alpha and Ig beta, a pair of membrane-bound Ig superfamily proteins, each of which contains a single cytoplasmic immunoreceptor tyrosine activation motif (ITAM). To determine the function of Ig beta, we produced mice that carry a deletion of the cytoplasmic domain of Ig beta (Ig beta Delta C mice) and compared them to mice that carry a similar mutation in Ig alpha (MB1 Delta C, herein referred to as Ig alpha Delta C mice). Ig beta Delta C mice differ from Ig alpha Delta C mice in that they show little impairment in early B cell development and they produce immature B cells that respond normally to BCR cross-linking as determined by Ca(2+) flux. However, Ig beta Delta C B cells are arrested at the immature stage of B cell development in the bone marrow and die by apoptosis. We conclude that the cytoplasmic domain Ig beta is required for B cell development beyond the immature B cell stage and that Ig alpha and Ig beta have distinct biologic activities in vivo.

Alleles↗
PubMed2001

Comparison of time-frequency distribution techniques for analysis of spinal somatosensory evoked potential.

Spinal somatosensory evoked potential (SSEP) has been employed to monitor the integrity of the spinal cord during surgery. To detect both temporal and spectral changes in SSEP waveforms, an investigation of the application of time-frequency analysis (TFA) techniques was conducted. SSEP signals from 30 scoliosis patients were analysed using different techniques; short time Fourier transform (STFT), Wigner-Ville distribution (WVD), Choi-Williams distribution (CWD), cone-shaped distribution (CSD) and adaptive spectrogram (ADS). The time-frequency distributions (TFD) computed using these methods were assessed and compared with each other. WVD, ADS, CSD and CWD showed better resolution than STFT. Comparing normalised peak widths, CSD showed the sharpest peak width (0.13+/-0.1) in the frequency dimension, and a mean peak width of 0.70+/-0.12 in the time dimension. Both WVD and CWD produced cross-term interference, distorting the TFA distribution, but this was not seen with CSD and ADS. CSD appeared to give a lower mean peak power bias (10.3%+/-6.2%) than ADS (41.8%+/-19.6%). Application of the CSD algorithm showed both good resolution and accurate spectrograms, and is therefore recommended as the most appropriate TFA technique for the analysis of SSEP signals.

Evoked Potentials, Somatosensory↗
PubMed2001

A randomized, controlled, single-blind trial of leflunomide in the treatment of rheumatoid arthritis.

The efficacy and safety of leflunomide (LEF) in the treatment of rheumatoid arthritis (RA) were evaluated and the comparison with methotrexate's (MTX's) was performed in a 12-week, single-blind, randomized, parallel trial for treating 81 patients with RA. There were 56 cases in LEF group and 25 cases in MTX group. The dose of LEF was 20 mg per day and MTX 15 mg per week. All patients took oxaproxin simultaneously at the 4th to 6th week after the trail. The results showed that the general effective rate and notable effective rate were 94.64% and 73.21% in LEF group, 72% and 44% in MTX group, respectively, with the differences being statistically significant between the two groups (P < 0.05). LEF and oxaprozin could obviously improve the symptoms, signs and joint functions. The incidence of side reactions was lower in LEF group (17.86%) than in MTX group (40.00%, P < 0.05). LEF had a good therapeutic effect for RA, especially for refractory RA and had slight side reactions, and could be regarded as a superior immunosuppressive agent used in the treatment of RA and other connective tissue diseases.

Adolescent↗
PubMed2001

Synthesis of (5alpha)-17-azaandrostan-3-ols and (5alpha)-17-aza-D-homoandrostan-3-ols and their N-acylated derivatives.

Two groups of N-acylated D-azasteroids (4 and 5) were synthesized to explore structure-activity relationships for steroid modulation of GABA(A) receptor function. The target compounds were prepared conveniently from (5alpha)-3-hydroxyandrostan-17-ones (6 and 7) via the intermediate (5alpha)-17-aza-D-homoandrostan-3-ols (14 and 15) or (5alpha)-17-azaandrostan-3-ols (18 and 19) precursors in high overall yields. A Beckmann rearrangement and a Hofmann rearrangement were employed as two key steps in the synthetic sequences.

Androstanols↗
PubMed2001

Synergistic inhibitory activity of alpha- and beta-LFA-1 peptides on LFA-1/ICAM-1 interaction.

Interactions of cell-adhesion molecule LFA-1 and its ligand ICAM-1 play important roles during immune and inflammatory responses. Critical residues of LFA-1 for ICAM-1 binding are known to be in the I-domain of the alpha-subunit and the I-like domain of the beta-subunit. On the basis of our previous work demonstrating the inhibitory activity of I-domain cyclic peptide cLAB.L on LFA-1/ICAM-1 interaction, here we have explored the activity of I-like-domain peptide LBE on the binding mechanism of cLAB.L. LBE enhances cLAB.L binding to T-cells and epithelial cells. The adherence of T-cells to epithelial monolayers was suppressed by the two peptides. The addition of LBE to the monolayers prior to the addition cLAB.L produced a better inhibitory effect than the reverse procedure. LBE, but not cLAB.L, changes the ICAM-1 conformation, suggesting that LBE binds to ICAM-1 at sites that are distinct from these of cLAB.L and induces improved conformation in ICAM-1 for binding to cLAB.L.

Caco-2 Cells↗
PubMed2001

Siah-1 mediates a novel beta-catenin degradation pathway linking p53 to the adenomatous polyposis coli protein.

The adenomatous polyposis coli (APC) tumor-suppressor protein, together with Axin and GSK3beta, forms a Wnt-regulated signaling complex that mediates phosphorylation-dependent degradation of beta-catenin by the proteasome. Siah-1, the human homolog of Drosophila seven in absentia, is a p53-inducible mediator of cell cycle arrest, tumor suppression, and apoptosis. We have now found that Siah-1 interacts with the carboxyl terminus of APC and promotes degradation of beta-catenin in mammalian cells. The ability of Siah-1 to downregulate beta-catenin signaling was also demonstrated by hypodorsalization of Xenopus embryos. Unexpectedly, degradation of beta-catenin by Siah-1 was independent of GSK3beta-mediated phosphorylation and did not require the F box protein beta-TrCP. These results indicate that APC and Siah-1 mediate a novel beta-catenin degradation pathway linking p53 activation to cell cycle control.

Adenomatous Polyposis Coli Protein↗
PubMed2001

Effect of p58GTA on beta-1,4-galactosyltransferase 1 activity and cell-cycle in human hepatocarcinoma cells.

Beta-1,4-galactosyltransferase 1 (beta1,4-GT 1) is the key enzyme transferring galactose to the terminal N-acetylglucosamine (GlcNAc) forming Galbeta3-->4GlcNAc structure in the Golgi apparatus. In addition, it also serves as a cell adhesion molecule by recognizing and binding to terminal GlcNAc of glycoconjugates on the adjacent cell surface and matrix through a subpopulation of the enzyme distributed on the cell surface. Transient expression of the p58GTA protein kinase, which belongs to the p34cdc2-related supergene family, could enhance beta1,4-GT 1 total activity in COS cells. In this study, the p58GTA interaction with beta1,4-GT 1 was confirmed using an in vitro assay with the TNT Coupled Reticulocyte Lysate System. An expression vector containing p58GTA was stably transfected into 7721 cells, a human hepatocarcinoma cell line, expression was confirmed by Northern and Western blot analyses. The cells transfected with p58GTA (p58GTA/7721) contained 1.9 times higher total beta1,4-GT 1 activity and 2.6 times higher cell-surface beta1,4-GT 1 activity than the mock transfected cells (pcDNA3/7721). However, Ricinus communis agglutinin-I lectin blot analysis revealed that the enhanced beta1,4-GT1 activity did not increase the Galbetal-->4GlcNAc groups on most of the membrane proteins in p58GTA/7721 cells. By flow cytometry analysis, it was found that the p58GTA/7721 cells were G2/M phase arrested, compared with the pcDNA3/7721 cells. These results suggest that the p58GTA stable transfection into human hepatocarcinoma cells could enhance the two beta1,4-GT1 subcellular pool activities independently and change its cell-cycle without modifying the beta-1,4-linked galactose residues on most membrane proteins.

Animals↗
PubMed2001

Improving the selectivity of HAV-peptides in modulating E-cadherin-E-cadherin interactions in the intercellular junction of MDCK cell monolayers.

PURPOSE: The objective of this work is to understand the sequence specificity of HAV peptides and to improve their selectivity in regulating E-cadherin-E-cadherin interactions in the intercellular junctions. METHODS: Peptide 1 was modified using an alanine scanning method to give peptides 2-6. The ability of these peptides to modulate intercellular junctions was evaluated using Madin-Darby Canine Kidney (MDCK) cell monolayers on Transwell membranes from either the apical (AP) or the basolateral (BL) side. Modulation of the intercellular junctions was measured by the ability to lower the transepithelial electrical resistance (TEER) of MDCK monolayers and by the increase in mannitol flux. Molecular docking experiments were performed to model the binding properties of these peptides to the EC1 domain of E-cadherin. RESULTS: Peptides 5 (Ac-SHAVAS-NH2) and 6 (Ac-SHAVSA-NH2) were found to be more effective than the parent peptide 1 in decreasing the resistance of the cell monolayer. Furthermore, comparative studies with the control and the weak inhibitor peptide 2 indicate that peptide 5 displayed a significant increase in mannitol flux. Molecular docking of peptides 1, 2 and 5 to the EC1 domain suggests that peptide 5 has the lowest binding energy. CONCLUSIONS: HAV peptides have the ability to modulate E-cadherin-E-cadherin interactions in the intercellular junctions of the MDCK cell monolayer, thus indirectly increasing the permeability of the tight junctions. This observation indicates that residues flanking the HAV sequence are important in the binding selectivity of HAV peptides to E-cadherin. Molecular docking can further aid in the design of peptides with better selectivity to the EC1 domain of E-cadherin.

Alanine↗
PubMed2001

Cytotoxicity induced by manipulation of signal transduction pathways is associated with down-regulation of Bcl-2 but not Mcl-1 in MCF-7 human breast cancer.

We examined the role of Mcl-1 and Bcl-2 expression in the induction of apoptosis. through blocking protein tyrosine kinase (PTK), protein kinase C (PKC), phosphatidylinositol 3-kinase (P13-K) and mitogen-activated protein kinase (MAPK)/Erk kinase (MEK) signaling pathways by various kinase inhibitors in MCF-7 breast cancer cells. The PTK inhibitor genistein (GEN) and PKC inhibitor staurosporine (STP) down-regulated Mcl-1 and Bcl-2 expression, and induced growth inhibition by blocking at the G2/M phase of cell cycle, followed by apoptosis, leading to chromatin condensation and DNA fragmentation. LY294002 (LY)-mediated inhibition of P13-K activity down-regulated Bcl-2 but not Mcl-1 expression. triggered growth arrest at the G1/G0 phase of cell cycle and also led to apoptosis marked with chromatin condensation and DNA fragmentation. The MEK inhibitor U0126 (U0) decreased Bcl-2 expression but not Mcl-1 expression, inhibited cells growth and induced G1/G0 arrest. but in this case cell death occurred without significant apoptotic features. The kinase inhibitor concentration dependence of cytotoxicity correlated well with down-regulation of Bcl-2 but not with changes in Mcl-1 levels. This suggests that Bcl-2 plays a predominant role in the regulation of cell death induced by cell signaling alterations whereas Mcl-1 does not appear to control cell survival under these conditions in MCF-7 cells. Further studies showed that the combination of GEN, STP and LY with U0 can produce synergetic cytotoxic effects on MCF-7 cells. Our results suggest that PTK, PKC, P13-K and MEK signaling pathways can regulate Bcl-2 expression and form an integrated network that plays a critical role in cell survival.

Antineoplastic Agents↗
PubMed2001

Effects of salviainolic acid A (SA-A) on liver injury: SA-A action on hepatic peroxidation.

BACKGROUND/AIMS: This study aimed to investigate the actions of salviainolic acid A (SA-A), an antiperoxidative component of Salvia miltiorrhiza (Sm), on rat liver injury and fibrosis. METHODS: Acute and chronic rat liver injury models were established using carbon tetrachloride (CCl4). After 48 h (acute) or during 6 weeks of CCl4 injection, rats were further divided and treated with biphenyl dimethyl-dicarboxylate (BDD) or colchicine, as a control antifibrotic treatment, with Sm, a herbal compound, or SA-A, a water-soluble extract of Sm. Liver function was investigated by assessing alanine transaminase (ALT) and aspartate transaminase (AST) activities, histological analysis, hydroxyproline (Hyp) and malondiadehyde (MDA) content. In vitro, isolated cultured hepatocytes were injured with CCl4 gas for 24 h, followed by treatment with either vitamin E or various concentrations of SA-A. The extent of hepatocyte injury was monitored by analyzing various lipid peroxidative parameters such as superoxide dismutase (SOD), glutathione (GSH), catalase (CAT), lactase dehydrogenase (LDH), and glutathione peroxidase (GSH-PX) levels in hepatocyte supernatants. RESULTS: SA-A significantly decreased abnormal serum ALT activity both in acutely and chronically injured rat livers, decreased abnormal serum AST activity, Hyp and MDA content and attenuated hepatic collagen deposition. After CCl4 incubation and injury, the activities of AST, ALT CAT, GSH-PX and LDH and MDA content in hepatocyte supernatants increased significantly, but GSH levels decreased significantly. SA-A markedly improved these pathological changes in a dose-dependent manner. 10(-4) mol/l SA-A had stronger inhibitory action than vitamin E. CONCLUSIONS: Our studies suggest that SA-A has antiperoxidative effects on injured hepatocytes in liver injury and fibrosis induced by CCl4.

Alanine Transaminase↗