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Biomedical subjects

Y Chen

Publications and source records attributed to Y Chen.

At least 757 records · Page 42Linked to original sources
PubMed2000

Photoreactivity of 2-pyridones with furan, benzene, and naphthalene. Inter- and intramolecular photocycloadditions.

Pyridones, well-known for their ability to photodimerize, have been found to undergo [4 + 4] photocycloaddition with furan and naphthalene but not with benzene. In some cases these reactions can be highly regio- and stereospecific. Intramolecular reaction with furan produces both cis and trans [4 + 4] products. The cycloaddition with naphthalene can occur both inter- and intramolecularly. The intermolecular reaction yields primarily the cis isomer, whereas the trans isomer is the major product from the intramolecular reaction. A mixture of 4-methoxy-2-pyridone and 2-methoxynaphthalene that could form up to eight regio- and stereoisomers forms largely one [4 + 4] product.

Benzene↗
PubMed2000

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is an inhibitor of autoimmune inflammation and cell cycle progression.

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis of tumor cells but not normal cells; its role in normal nontransformed tissues is unknown. We report here that chronic blockade of TRAIL in mice exacerbated autoimmune arthritis, and that intraarticular TRAIL gene transfer ameliorated the disease. In vivo, TRAIL blockade led to profound hyperproliferation of synovial cells and arthritogenic lymphocytes and heightened the production of cytokines and autoantibodies. In vitro, TRAIL inhibited DNA synthesis and prevented cell cycle progression of lymphocytes. Interestingly, TRAIL had no effect on apoptosis of inflammatory cells either in vivo or in vitro. Thus, unlike other members of the tumor necrosis factor superfamily, TRAIL is a prototype inhibitor protein that inhibits autoimmune inflammation by blocking cell cycle progression.

Animals↗
PubMed2000

[Effect of mercury chloride on the reproductive function and visceral organ of female mouse].

In this paper the effects of mercury chloride on the coefficient of visceral organ of mouse and the meiotic maturation and the fertilization ability of mouse oocyte were studied by in vitro culture and in vitro fertilization (IVF) of mouse oocytes, etc. The results showed that mercury chloride (0.5 and 1.5 mg/kg BW) had obviously toxicity to the liver and the kidney of mouse, and the dose of 1.5 mg/kg BW could damage the ovary function and reduce the number of superovulation oocytes. The results also showed that mercury chloride could inhibit the extruding of the first polar body and affect the quality and the viability of mouse oocyte and reduce the rate of IVF, but little impact on germinal vesicle breakdown (GVBD) of mouse oocyte in vivo. The results indicated that mercury chloride could affect the meiotic maturation of mouse oocyte, obviously block the IVF and injury or make a reduction of reproductive capacity of mouse.

Animals↗
PubMed2000

[Study on plasma lipids, apolipoprotein A1, apolipoprotein B100 in simple obese children].

To investigate the disorder of lipid metabolism and explore the possible mechanism of increasing risk of atherosclerosis(AS) in simple childhood obesity, serum lipids and apolipoprotein were examined. 49 obese children were selected and another 49 non-obese children were selected as control. Their serum lipids (TG, TC, VLDL-ch, HDL-ch and LDL-ch) and apolipoprotein(apoA1 and apoB100) were measured. The results showed TG, VLDL-ch, apoB100, artherosclerosis index (AI) and LDL-ch/HDL-ch ratio in childhood obesity were significantly higher than that in normal children (P < 0.05), while HDL-ch, apoA1, HDL-ch/TC, apoA1/apoB100 ratio in obese children were obviously lower than that in normal ones(P < 0.05). The results suggested that metabolic disorder of lipid and apolipoprotein took place in obese children. The disorder which may increase the risk of AS should be paid great attention.

Adolescent↗
PubMed2000

Comparison of the repeatability of quantitative data measured in high-performance liquid chromatography with UV and atmospheric pressure chemical ionization mass spectrometric detection.

A detailed comparison of the repeatability of the retention times, the peak efficiencies and the peak areas of a dozen probe compounds achieved in HPLC, using either HPLC-UV or HPLC-MS for detection purpose, is reported. Three groups of conventional analytes, each one separated under a different set of experimental conditions, were selected for this study. Most of the compounds are basic, the other ones being neutral. The repeatabilities of the retention times do not exhibit any influence of the mode of detection. However, the repeatabilities of the peak areas and the column efficiencies are generally (although not always) better in HPLC-UV than that in HPLC-MS. On average, the precision for the UV peak area detection was 2.5% versus 6.8% for MS detection. Experimental results show that the response factor of the UV detector is more constant than that of the MS detector, probably because the HPLC flow-rate was sufficiently stable. The results obtained in the different tests are discussed.

Atmospheric Pressure↗
PubMed2000

Mechanism of insulin resistance in A-ZIP/F-1 fatless mice.

Insulin resistance is a major factor in the pathogenesis of type 2 diabetes and may be related to alterations in fat metabolism. Fatless mice have been created using dominant-negative protein (A-ZIP/F-1) targeted gene expression in the adipocyte and shown to develop diabetes. To understand the mechanism responsible for the insulin resistance in these mice, we conducted hyperinsulinemic-euglycemic clamps in awake fatless and wild type littermates before the development of diabetes and examined insulin action and signaling in muscle and liver. We found the fatless mice to be severely insulin-resistant, which could be attributed to defects in insulin action in muscle and liver. Both of these abnormalities were associated with defects in insulin activation of insulin receptor substrate-1 and -2-associated phosphatidylinositol 3-kinase activity and a 2-fold increase in muscle and liver triglyceride content. We also show that upon transplantation of fat tissue into these mice, triglyceride content in muscle and liver returned to normal as does insulin signaling and action. In conclusion, these results suggest that the development of insulin resistance in type 2 diabetes may be due to alterations in the partitioning of fat between the adipocyte and muscle/liver leading to accumulation of triglyceride in the latter tissues with subsequent impairment of insulin signaling and action.

Adipose Tissue↗
PubMed2000

The amyloid precursor protein-binding protein APP-BP1 drives the cell cycle through the S-M checkpoint and causes apoptosis in neurons.

APP-BP1 binds to the amyloid precursor protein (APP) carboxyl-terminal domain. Recent work suggests that APP-BP1 participates in a novel ubiquitinylation-related pathway involving the ubiquitin-like molecule NEDD8. We show here that, in vivo in mammalian cells, APP-BP1 interacts with hUba3, its presumptive partner in the NEDD8 activation pathway, and that the APP-BP1 binding site for hUba3 is within amino acids 443-479. We also provide evidence that the human APP-BP1 molecule can rescue the ts41 mutation in Chinese hamster cells. This mutation previously has been shown to lead to successive S phases of the cell cycle without intervening G(2), M, and G(1), suggesting that the product of this gene negatively regulates entry into the S phase and positively regulates entry into mitosis. We show that expression of APP-BP1 in ts41 cells drives the cell cycle through the S-M checkpoint and that this function requires both hUba3 and hUbc12. Overexpression of APP-BP1 in primary neurons causes apoptosis via the same pathway. A specific caspase-6 inhibitor blocks this apoptosis. These findings are discussed in the context of abnormalities in the cell cycle that have been observed in Alzheimer's disease.

Animals↗
PubMed2000

Coordination of two high-affinity hexamer peptides to copper(II) and palladium(II) models of the peptide-metal chelation site on IMAC resins.

The coordination of peptides Ser-Pro-His-His-Gly-Gly (SPHHGG) and (His)6 (HHHHHH) to [PdII(mida)(D2O)] (mida2- = N-methyliminodiacetate) was studied by 1H NMR as model reactions for CuII(iminodiacetate)-immobilized metal affinity chromatography (IMAC) sites. This is the first direct physical description of peptide coordination for IMAC. A three-site coordination is observed which involves the first, third, and fourth residues along the peptide chain. The presence of proline in position 2 of SPHHGG achieves the best molecular mechanics and bonding angles in the coordinated peptide and enhances the interaction of the serine amino nitrogen. Histidine coordination of H1, H3, and H4 of (His)6 and H3 and H4 of SPHHGG was detected by 1H NMR contact shifts and H/D exchange of histidyl protons. The EPR spectra of SPHHGG and HHHHHH attached to the [CuII(mida)] unit were obtained for additional modeling of IMAC sites. EPR parameters of the parent [Cu(mida)(H2O)2] complex are representative: gzz = 2.31; gyy = 2.086; gxx = 2.053; A parallel = 161G; AN = 19G (three line, one N coupling). Increased rhombic distortion is detected relative to the starting aqua complex in the order of [Cu(mida)L] for distortion of HHHHHH > SPHHGG > (H2O)2. The lowering of symmetry is also seen in the decrease in the N-shf coupling, presumably to the imino nitrogen of mida2- in the order 19 G (H2O), 16 G (SPHHGG) and 11 G (HHHHHH). Visible spectra of the [Cu(mida)(SPHHGG)] and [Cu(mida)(HHHHHH)] as a function of pH indicate coordination of one histidyl donor at ca. 4.5, two in the range of pH 5-7, and two chelate ring attachments involving the terminal amino donor for SPHHGG or another histidyl donor of HHHHHH in the pH domain of 7-8 in agreement with the [PdII(mida)L] derivatives which form the two-chelate-ring attachment even at lower pH as shown by the 1H NMR methods.

Catalysis↗
PubMed2000

Increased histamine release and granulocytes within the thalamus of a rat model of Wernicke's encephalopathy.

The current study examined the possible role of increased histamine release and granulocyte activity in the vascular changes that precede the onset of necrotic lesions with the thalamus of the pyrithiamine-induced thiamine deficiency (PTD) rat model of Wernicke's encephalopathy (WE). An increase in histamine release and the number of granulocytes was observed in lateral thalamus on day 9 and in medial thalamus on day 10 of PTD treatment, a duration of thiamine deficiency associated with perivascular edema in this brain region. Within the hippocampus, histamine release was significantly increased on day 9, declined to control levels on days 10-12, and was significantly elevated on days 12-14. No granulocytes were observed in hippocampus of either PTD or control rats. These observations suggest that the release of histamine from nerve terminals and histamine and other vasoactive substances from granulocytes may be responsible for thiamine deficiency-induced vascular breakdown and perivascular edema within thalamus.

Animals↗
PubMed2000

Formation of novel D-ring and E-ring isoprostane-like compounds (D4/E4-neuroprostanes) in vivo from docosahexaenoic acid.

Free radical-mediated oxidant injury and lipid peroxidation have been implicated in a number of neural disorders. We have reported that bioactive prostaglandin D2/E2-like compounds, termed D2/E2-isoprostanes, are produced in vivo by the free radical-catalyzed peroxidation of arachidonic acid. Docosahexaenoic acid, in contrast to arachidonic acid, is the most abundant unsaturated fatty acid in brain. We therefore questioned whether D/E-isoprostane-like compounds (D4/E4-neuroprostanes) are formed from the oxidation of docosahexaenoic acid. Levels of putative D4/E4-neuroprostanes increased 380-fold after oxidation of docosahexaenoic acid in vitro from 15.2 +/- 6.3 to 5773 +/- 1024 ng/mg of docosahexaenoic acid. Subsequently, chemical approaches and liquid chromatography electrospray ionization tandem mass spectrometry definitively identified these compounds as D4/E4-neuroprostanes. We then explored the formation of D4/E4-neuroprostanes from a biological source, rat brain synaptosomes. Basal levels of D4/E4-neuroprostanes were 3.8 +/- 0.6 ng/mg of protein and increased 54-fold after oxidation (n = 4). We also detected these compounds in fresh brain tissue from rats at levels of 12.1 +/- 2.4 ng/g of brain tissue (n = 3) and in human brain tissue at levels of 9.2 +/- 4.1 ng/g of brain tissue (n = 4). Thus, these studies have identified novel D/E-ring isoprostane-like compounds that are derived from docosahexaenoic acid and that are formed in brain in vivo. The fact that they are readily detectable suggests that ongoing oxidative stress is present in the central nervous system of humans and animals. Further, identification of these compounds provides a rationale for examining their role in neurological disorders associated with oxidant stress.

Animals↗
PubMed2000

Evidence for the rate of the final step in the bacteriorhodopsin photocycle being controlled by the proton release group: R134H mutant.

Light absorbed by bacteriorhodopsin (bR) leads to a proton being released at the extracellular surface of the purple membrane. Structural studies as well as studies of mutants of bR indicate that several groups form a pathway for proton transfer from the Schiff base to the extracellular surface. These groups include D85, R82, E204, E194, and water molecules. Other residues may be important in tuning the initial state pK(a) values of these groups and in mediating light-induced changes of the pK(a) values. A potentially important residue is R134: it is located close to E194 and might interact electrostatically to affect the pK(a) of E194 and light-induced proton release. In this study we investigated effects of the substitution of R134 with a histidine on light-induced proton release and on the photocycle transitions associated with proton transfer. By measuring the light-induced absorption changes versus pH, we found that the R134H mutation results in an increase in the pK(a) of the proton release group in both the M (0.6 pK unit) and O (0.7 pK unit) intermediate states. This indicates the importance of R134 in tuning the pK(a) of the group that, at neutral and high pH, releases the proton upon M formation (fast proton release) and that, at low pH, releases the proton simultaneously with O decay (slow proton release). The higher pK(a) of the proton release group found in R134H correlates with the slowing of the rate of the O --> bR transition at low pH and probably is the cause of this slowing. The pH dependence of the fraction of the O intermediate is altered in R134H compared to the WT but is similar to that in the E194D mutant: a very small amount of O is present at neutral pH, but the fraction of O increases greatly upon decreasing the pH. These results provide further support for the hypothesis that the O --> bR transition is controlled by the rate of deprotonation of the proton release group. These data also provide further evidence for the importance of the R134-E194 interaction in modulating proton release from D85 after light has led to its being protonated.

Arginine↗
PubMed2000

In situ biochemical demonstration that P-glycoprotein is a drug efflux pump with broad specificity.

While P-glycoprotein (Pgp) is the most studied protein involved in resistance to anti-cancer drugs, its mechanism of action is still under debate. Studies of Pgp have used cell lines selected with chemotherapeutics which may have developed many mechanisms of resistance. To eliminate the confounding effects of drug selection on understanding the action of Pgp, we studied cells transiently transfected with a Pgp-green fluorescent protein (GFP) fusion protein. This method generated a mixed population of unselected cells with a wide range of Pgp-GFP expression levels and allowed simultaneous measurements of Pgp level and drug accumulation in living cells. The results showed that Pgp-GFP expression was inversely related to the accumulation of chemotherapeutic drugs. The reduction in drug concentration was reversed by agents that block multiple drug resistance (MDR) and by the UIC2 anti-Pgp antibody. Quantitative analysis revealed an inverse linear relationship between the fluorescence of Pgp-GFP and MDR dyes. This suggests that Pgp levels alone limit drug accumulation by active efflux; cooperativity between enzyme, substrate, or inhibitor molecules is not required. Additionally, Pgp-GFP expression did not change cellular pH. Our study demonstrates the value of using GFP fusion proteins for quantitative biochemistry in living cells.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2000

Hybrid cell vaccination for cancer immune therapy: first clinical trial with metastatic melanoma.

Hybrid cell vaccination is a new cancer immune therapy approach that aims at recruiting T cell help for the induction of tumour specific cytolytic immunity. The vaccines are generated by fusion of the patients' tumour cells with allogeneic MHC class II bearing cells to combine the tumour's antigenicity with the immunogenicity of allogeneic MHC molecules. Safety and anti-tumour activity of this treatment were assessed in a clinical trial that has yielded one complete and one partial remission, and 5 cases of stable disease among 16 patients with advanced stage metastatic melanoma. As evidenced by histology, the vaccination induced T cell relocation into tumour nodules. Stable disease could be maintained by repeated booster injections for more than 24 months in some patients. The side effects were minor. Occasional occurrences of vitiligo spots after vaccination were indicative of a restricted therapy induced auto-immune reactivity. The results suggest that hybrid cell vaccination is a safe cancer immune therapy potentially effective for induction of acute anti-tumour response as well as long-term maintenance.

Adult↗
PubMed2000

Detection of gene amplification by genomic hybridization to cDNA microarrays.

Gene amplification is one of the major mechanisms of oncogene activation in tumorigenesis. To facilitate the identification of genes mapping to amplified regions, we have used a technique based on the hybridization of total genomic DNA to cDNA microarrays. To aid detection of the weak signals generated in this complex hybridization, we have used a tyramide-based technique that allows amplification of a fluorescent signal up to 1000-fold. Dilution experiment suggests that amplifications of 5-fold and higher can be detected by this approach. The technique was validated using cancer cell lines with several known gene amplifications, such as those affecting MYC, MYCN, ERBB2, and CDK4. In addition to the detection of the known amplifications, we identified a novel amplified gene, ZNF133, in the neuroblastoma cell line NGP. Hybridization of NGP cDNA on an identical array also revealed over expression of ZNF133. Parallel analysis of genomic DNA for copy number and cDNA for expression now provides rapid approach to the identification of amplified genes and chromosomal regions in tumor cells.

Cyclin-Dependent Kinase 4↗
PubMed2000

Laparoscopic hepatic surgery guided by hookwire localization.

Due to recent improvements in radiographic technique, computed tomography (CT) occasionally delineates small hepatocellular carcinomas (HCCs) that are invisible with sonography. However, surgery has not been a viable option for these lesions because of the absence of tumor localization. We describe a new technique of preoperative tumor localization using a hookwire to guide laparoscopic surgery for such HCCs. A 68-year-old man with HCC had tumor recurrence after chemoembolization. Two recurrent lesions, 10 mm or less in diameter, located in segment III were demonstrated; not by sonography but by Lipiodol CT. We successfully placed a hookwire into the tumor through a 21-gauge needle under the guidance of CT. The hookwire instrument provided the only clue of tumor location at laparoscopy. The liver around the hookwire was thoroughly coagulated. The postoperative course was uneventful, and the tumor was completely ablated. Preoperative CT-guided hookwire placement is useful to localize and to laparoscopically treat small hepatic lesions.

Aged↗
PubMed2000

Blockade of U50488H on sodium currents in acutely isolated mice hippocampal CA3 pyramidal neurons.

The effect of opioid agonist U50488H on Na(+) currents was examined in freshly dissociated hippocampal neurons of mice using the whole-cell patch clamp technique. U50488H (1-100 microM) caused a concentration dependent reversible inhibition of the voltage-activated sodium currents. IC50 of 15.5 microM and Hill constant of 1.4 were calculated respectively. The inhibitory actions of U50488H on I(Na) were still observed in the presence of 30 microM naloxone. Moreover, under the action of U50488H, repetitive stimulation induced further inhibition which was frequency-dependent. The activation curve did not change before and after application of 10 microM U50488H. However, after exposure to 10 microM U50488H and repetitive depolarizing at 10 Hz, frequency-dependent inhibition occurred, and a mean shift of half-activation membrane potential by +20 mV could be induced. The inactivation curve was significantly changed toward negative membrane potential with 10 microM U50488H, and further negative shift was observed after repetitive depolarizing at 10 Hz. Our results indicate that U50488H could directly inhibit neuronal Na(+) currents without involvement in the activation of kappa-opioid receptors.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed2000

Biochemical analysis of the arginine methylation of high molecular weight fibroblast growth factor-2.

The post-translational methylation of the N-terminally extended or high molecular weight (HMW) forms of fibroblast growth factor-2 (FGF-2) has been shown to affect the nuclear accumulation of the growth factor. In this study, we determined the extent and position of methyl groups in HMW FGF-2. Using mass spectrometry and amino acid sequence analysis, we have shown that the 22- and 22.5-kDa forms of HMW FGF-2 contain five dimethylated arginines located at positions -22, -24, -26, -36, and -38 using the methionine residue normally used to initiate the 18-kDa form as position 0. The 24-kDa form of HMW FGF-2 contains seven to eight dimethylated arginines located at positions -48, -50, and -52, in addition to positions -22, -24, -26, -36, and -38. In vitro methylation reactions demonstrate that the N-terminal extension of HMW FGF-2 acts as a specific substrate for yeast Hmt1p and human HRMT1L2 arginine methyltransferases. These findings indicate that HMW FGF-2, with the presence of five or more dimethylated Gly-Arg-Gly repeats, contains an RGG box-like domain, which may be important for protein-protein and/or protein-RNA interactions.

3T3 Cells↗