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Biomedical subjects

Y Luo

Publications and source records attributed to Y Luo.

At least 379 records · Page 21Linked to original sources
PubMed1995

Studies on the distribution of vasopressin-immunoreactive neuronal perikarya and their fibers in the hypothalamus of Tupaia belangeri.

The distribution of vasopressin (VP)-immunoreactive neuronal perikarya and its fibers had been studied in the hypothalamus of Tupaia belangeri using the avidin-biotin complex (ABC) immunocytochemical technique. VP-immunoreactive neurons were found in the hypothalamic paraventricular nucleus (PVN), supraoptic nucleus (SON), accessory supraoptic nucleus (ASN), hypothalamic lateral nucleus (HLN), perifornical nucleus (PFN) and ansa peduncularis (AP) but not in the suprachiasmatic nucleus (SCN). VP neurons of the rostral PVN could be divided into three subnuclei and the caudal PVN could also be divided although not so distinctly into four subnuclei. The VP-immunoreactive neuronal perikarya of SON were divided into three parts, i.e., medioventral, mediodorsal and laterodorsal. Three types of VP neuronal perikarya, i.e., large, medium and small cells, existed in PVN and SON. Between PVN and SON, there were a large number of VP immunopositive nerve fibers. In addition, there were numerous immunopositive fibers projecting into the infundibulum and the neurohypophysis. VP-immunoreactive-positive products localized in the large granular vesicles and on the rough-surfaced endoplasmic reticulum could be seen under electron microscope.

Animals↗
PubMed1995

Crystal and molecular structure of paclitaxel (taxol).

Paclitaxel (formerly called taxol), an important anticancer drug, inhibits cell replication by binding to and stabilizing microtubule polymers. As drug-receptor interactions are governed by the three-dimensional stereochemistries of both participants, we have determined the crystal structure of paclitaxel to identify its conformational preferences that may be related to biological activity. The monoclinic crystals contain two independent paclitaxel molecules in the asymmetric unit plus several water and dioxane solvent molecules. Taxane ring conformation is very similar in both paclitaxel molecules and is similar to the taxane ring conformation found in the crystal structure of the paclitaxel analogue docetaxel (formerly called taxotere). The two paclitaxel molecules have carbon-13 side-chain conformations that differ from each other and from that of the corresponding side chain in the docetaxel crystal structure. The carbon-13 side-chain conformation of one paclitaxel molecule is similar to what was proposed from NMR studies done in polar solvents, while that of the other paclitaxel molecule is different and hitherto unobserved. The paclitaxel molecules interact with each other and with solvent atoms through an extensive network of hydrogen bonds. Analysis of the hydrogen-bonding network together with structure-activity studies may suggest which atoms of paclitaxel are important for binding to microtubule receptors.

Crystallography, X-Ray↗
PubMed1995

Secondary organ allografting after a primary "bridging" xenotransplant.

It remains uncertain whether xenotransplantation can sensitize the recipient to alloantigens, rendering subsequent allotransplantation unsuccessful. This is of considerable importance if a xenograft is to be used as a "bridge" to support the patient until a suitable allograft becomes available. When sera from 9 baboons that had received pig or African green monkey heart or liver xenografts were tested against a panel of lymphocytes from 5 or 6 potential donor baboons, positivity was seen in only 1 baboon (and then to only 2 of the potential 5 donors). In 4 baboons that had undergone previous xenotransplants (1 from this series of 9 baboons and 3 others), subsequent organ allografting was not followed by hyperacute, antibody-mediated, or accelerated cellular rejection. We conclude that organ xenotransplantation using discordant or concordant donor species does not prohibit subsequent allotransplantation.

Animals↗
PubMed1995

Transforming growth factor beta induces a beta-responsive calcium fluxes in neurons.

The beta-amyloid (a beta) peptide is a neurotoxic peptide that accumulates in the brains of Alzheimer patients, but is also present in body fluids at subnanomolar levels. The potential effects of these low levels of a beta are unclear. We have recently shown that physiologic levels of a beta increase tyrosine phosphorylation and induce increases in cytosolic calcium. The basement membrane mixture, Matrigel, is required for observation of the a beta-induced calcium response. We now show that transforming growth factor beta (TGF beta) is the active component in Matrigel eliciting the a beta/calcium response. The response to the type of TGF beta varies depending on the cell type with TGF beta 1 eliciting a beta responsiveness in olfactory neuroblasts, and TGF beta 2 eliciting a beta responsiveness in PC12 cells.

Amyloid beta-Peptides↗
PubMed1995

Auxiliary liver allografting and xenografting in the nonhuman primate.

Auxiliary liver transplantation has been performed in the baboon using allografts (n = 8) and concordant xenografts from donor African green monkeys (n = 8). The native portal vein was ligated in all cases and the native common bile duct was ligated in 5 cases. The immunosuppressive therapy used was identical in both the allografts and xenografts and consisted of triple drug therapy (cyclosporine, cyclophosphamide, and methylprednisolone), all at dosages consistent with clinical use. During the determination of the surgical technique to be applied, there were 5 early failures (3 allografts, 2 xenografts), and 2 deaths at 10 and 20 days from multiorgan failure and sepsis, respectively (xenografts). The remaining 9 baboons (5 allografts, 4 xenografts) were electively euthanized at 16-62 days (allografts) and 35-120 days (xenografts). Hyperacute rejection or antibody-mediated rejection was not seen in the grafted livers. Episodes of acute cellular rejection occurred in the majority of animals within the first 30 days and recurred in the longer-term survivors, but could be controlled by bolus therapy with intravenous methylprednisolone. Satisfactory donor liver function was confirmed using a number of tests, including scintigraphy in 3 cases. We conclude that auxiliary liver transplantation using a closely related donor species is feasible in baboons and might be extended to humans with terminal liver failure. A baboon-to-man auxiliary liver graft may serve as a "bridge" until either a human cadaver donor liver became available or native liver function recovers in patients with fulminant hepatic failure.

Animals↗
PubMed1995

RET mutations in exons 13 and 14 of FMTC patients.

RET is a receptor tyrosine kinase gene which is responsible for three different inherited cancer syndromes namely multiple endocrine neoplasia type 2A (MEN 2A), type 2B (MEN 2B) and familial medullary thyroid carcinoma (FMTC) as well as for Hirschsprung disease (HSCR), a congenital disorder affecting the intestinal motility. Germ-line mutations in the RET exons 10 and 11 were demonstrated in the majority of the MEN 2A and FMTC patients. On the other hand, one codon of RET exon 16 is preferentially changed in MEN 2B patients. Recently, a germ-line mutation in the exon 13 was described in one FMTC family as well as in four sporadic MTCs. In the present study, we observed the same exon 13 mutation in two FMTC families. In addition, we identified a previously unreported substitution of RET exon 14 in two unrelated FMTC families. Both mutations segregate with the disease in these four FMTC families and involve the tyrosine kinase domain of RET. Haplotype analysis using polymorphic markers tightly linked to the RET gene indicates that in each pedigree the mutation arose as an independent event.

Adult↗
PubMed1995

Identification of dihydroetorphine in biological fluids by gas chromatography-mass spectrometry.

A method for the monitoring of dihydroetorphine hydrochloride, a powerful anaesthetic and analgesic drug, in biological fluids was developed, involving GC-MS with multiple selected-ion monitoring. Dihydroetorphine was extracted from human blood and urine with dichloromethane and then derivatized with N-heptafluorobutyrylimidazole after having been concentrated to dryness. A dihydroetorphine monoheptafluorobutyl derivative was formed, which showed good behaviour in GC-MS with electron impact ionization. Its molecular ion, m/z 609, and its main fragments, m/z 576, 534, 522 and 508, were selected as the ions for identification owing to their relative peak intensities and characteristics. The target drug was identified based on its retention time, its selected multiple ions and their relative intensities. This method was successfully used for the detection of dihydroetorphine in blood and urine from a dihydroetorphine addict and a poisoned patient, respectively.

Etorphine↗
PubMed1995

Biologic activities of the beta-chemokine TCA3 on neutrophils and macrophages.

Previous in vivo and in vitro studies demonstrated that the murine beta-chemokine TCA3 is a chemoattractant for monocytes/macrophages and neutrophils. The ability of TCA3 to activate these cell populations is now evaluated. Treatment with 10 to 20 nM rTCA3 induced a respiratory burst with the production of superoxide and hydrogen peroxide in both casein-elicited and unstimulated neutrophil and macrophage populations. In addition, TCA3 treatment induced the production of reactive nitrogen intermediates, whereas stimulation with higher concentrations (100 nM) of TCA3 induced the exocytosis of lysozyme and elastase in the presence of cytochalasin B (7 micrograms/ml). Subnanomolar concentrations (100 pM) of TCA3 also caused integrin-mediated increases of adhesiveness to fibrinogen by neutrophils and macrophages. Increased adhesiveness is the most sensitive assay for TCA3 bioactivity. TCA3 treatment appears to involve signaling through a G-protein-linked receptor as Pertussis toxin abolished the TCA3-mediated increase of adhesiveness and the production of reactive nitrogen intermediates. The dose dependence of the TCA3-mediated activities indicate a coordinated inflammatory response mediated by varying concentrations of TCA3.

Animals↗
PubMed1995

Cell-cycle inhibition by independent CDK and PCNA binding domains in p21Cip1.

Mammalian cell-cycle control by antimitogenic signals involves p21Cip1/WAF1 (refs 1-4), p27Kip1 (refs 5, 6) and p57Kip2 (refs 7, 8), a family of proteins that bind to and inhibit cyclin-dependent kinases (CDKs) required for initiation of S phase. The protein p21 also binds to the DNA polymerase delta processivity factor, proliferating-cell nuclear antigen (PCNA), and inhibits in vitro PCNA-dependent DNA replication. The CDK and PCNA inhibitory activities of p21 are shown here to be functionally independent and to reside in separate protein domains. The PCNA binding and inhibitory activities, which are not observed with p27 or p57, reside in the C-terminal domain of p21, whereas the CDK inhibitory activity resides in the conserved N-terminal domains of these proteins. When separately overexpressed in mammalian cells, the CDK and PCNA inhibitory domains prevent DNA replication, demonstrating a dual function of p21 as a cell-cycle inhibitor in vivo.

Amino Acid Sequence↗
PubMed1995

Photoaffinity ADP analogs as covalently attached reporter groups of the active site of myosin subfragment 1.

The enzymatic properties of rabbit skeletal myosin subfragment 1 (S1) have been determined after photoaffinity labeling the active site with two ADP analogs. These analogs, 2-[(4-azido-2-nitrophenyl)-amino]ethyl diphosphate (NANDP) and the fluorescent analog 3'(2')-O-(4-benzoylbenzoyl)-1,N6-ethenoadenosine diphosphate (Bz2 epsilon ADP), label the heavy chain residues Trp 130 and Ser-324, respectively. These residues in the crystal structure of chicken skeletal S1 are on either side of the entrance to the active site pocket (Rayment et al., 1993b). Here S1 was photolabeled with NANDP or Bz2 epsilon ADP after trapping with vanadate (Vi). Both of the photolabeled S1 preparations had normal MgATPase activities after removal of vanadate by actin treatment. These results show that the covalently tethered nucleotide analogs could move out of the active site and be replaced by MgATP. Experiments that monitored the fluorescence emission intensity, polarization, and quenching by acrylamide of S1 photolabeled with Bz2 epsilon ADP show that the covalently linked analog was displaced out of the active site cleft by MgATP (or MgATP and actin) but not by ATP in the absence of Mg2+ ions. The effective concentration of the tethered ethenoadenosine diphosphate at the active site, determined by competition with MgATP, was calculated to be 10 mM. In the absence of Mg2+ ions, ATP was unable to compete with the bound analog. Binding constants of the S1 photolabeled with Bz2 epsilon ADP to actin were 1.5 x 10(5) and 5.8 x 10(5) M-1 at 200 and 20 mM ionic strength, respectively, showing that actin binding affinities are similar to those obtained for S1.ADP. The binding of actin in the absence of MgATP did not produce any change in the emission intensity, polarization, or quenching by acrylamide of the tethered ethenoadenosine diphosphate, indicating that the conformation of the pocket around the adenine ring was unchanged. However, the binding of actin did destabilize Vi, which had been previously trapped in the form of photolabeled S1-Vi complexes. These results indicate that actin binding primarily affects the gamma-phosphate binding site but not the adenine ring binding site.

Acrylamides↗
PubMed1995

The structure of human pancreatic alpha-amylase at 1.8 A resolution and comparisons with related enzymes.

The structure of human pancreatic alpha-amylase has been determined to 1.8 A resolution using X-ray diffraction techniques. This enzyme is found to be composed of three structural domains. The largest is Domain A (residues 1-99, 169-404), which forms a central eight-stranded parallel beta-barrel, to one end of which are located the active site residues Asp 197, Glu 233, and Asp 300. Also found in this vicinity is a bound chloride ion that forms ligand interactions to Arg 195, Asn 298, and Arg 337. Domain B is the smallest (residues 100-168) and serves to form a calcium binding site against the wall of the beta-barrel of Domain A. Protein groups making ligand interactions to this calcium include Asn 100, Arg 158, Asp 167, and His 201. Domain C (residues 405-496) is made up of anti-parallel beta-structure and is only loosely associated with Domains A and B. It is notable that the N-terminal glutamine residue of human pancreatic alpha-amylase undergoes a posttranslational modification to form a stable pyrrolidone derivative that may provide protection against other digestive enzymes. Structure-based comparisons of human pancreatic alpha-amylase with functionally related enzymes serve to emphasize three points. Firstly, despite this approach facilitating primary sequence alignments with respect to the numerous insertions and deletions present, overall there is only approximately 15% sequence homology between the mammalian and fungal alpha-amylases. Secondly, in contrast, these same studies indicate that significant structural homology is present and of the order of approximately 70%. Thirdly, the positioning of Domain C can vary considerably between alpha-amylases. In terms of the more closely related porcine enzyme, there are four regions of polypeptide chain (residues 237-250, 304-310, 346-354, and 458-461) with significantly different conformations from those in human pancreatic alpha-amylase. At least two of these could play a role in observed differential substrate and cleavage pattern specificities between these enzymes. Similarly, amino acid differences between human pancreatic and salivary alpha-amylases have been localized and a number of these occur in the vicinity of the active site.

Amino Acid Sequence↗
PubMed1995

Spectral editing with adiabatic pulses.

Amplitude- and frequency-modulated pulses, known as adiabatic pulses, can induce uniform flip angles in the presence of extreme B1 inhomogeneity, which makes them advantageous for in vivo surface-coil studies. This paper describes the conversion of conventional (square pulse-based) spectral-editing sequences into their adiabatic counterparts. Eight adiabatic homo- and heteronuclear sequences are experimentally evaluated for lactate editing. For homonuclear lactate editing, gradient-enhanced multiple-quantum-coherence filtering provides the best overall performance (100% signal recovery with excellent water and lipid suppression in a single acquisition). For heteronuclear [3-(13)C]lactate editing, gradient-enhanced heteronuclear multiple-quantum-coherence filtering provides the best suppression of unwanted signals in a single acquisition, whereas J-modulated spin-echo sequences yield maximum sensitivity.

Animals↗
PubMed1995

A new localization method using an adiabatic pulse, BIR-4.

A new method is described for accomplishing localized spectroscopy with an adiabatic pulse, BIR-4. The method has advantages similar to previously described combinations of outer-volume suppression (OVS) and ISIS, with the additional advantages that localization is achieved with only three radiofrequency pulses and the localization remains accurate even in the presence of intense signals with short relaxation times. This new localization pulse sequence is referred to as integrated OVS-ISIS. Computer simulations, experimental images of the localized volumes, and in vivo 1H spectroscopy measurements demonstrate the high degree of localization achievable with integrated OVS-ISIS.

Animals↗
PubMed1995

Detection of a germline mutation at codon 918 of the RET proto-oncogene in French MEN 2B families.

Multiple endocrine neoplasia type 2A (MEN 2A), type 2B (MEN 2B), and familial medullary thyroid carcinoma (FMTC) are three dominantly inherited disorders linked to the same disease locus on chromosome 10. Two types of germline mutation of the RET proto-onco-gene, which codes for a transmembrane tyrosine kinase, are associated with MEN 2. Missense mutations at cysteine residues in the extra-cytoplasmic domain are exclusively associated with MEN 2A and FMTC. In MEN 2B patients, a single point mutation at codon 918 has recently been characterized, leading to the replacement of a methionine by a threonine within the RET tyrosine kinase domain. We now report the identification of a mutation at codon 918 in the germline of 16 patients out of 18 unrelated MEN 2B families analyzed. In these families we have been able to demonstrate that, in five cases, the mutation arose de novo, and that, in one kindred, it was coinherited with the disease. These results indicate that a unique mutation at codon 918 of the RET gene is the most prevalent genetic defect causing MEN 2B, but also that rare MEN 2B cases are associated with different mutations yet to be defined.

Adolescent↗
PubMed1995

Production and function of monocyte chemoattractant protein-1 and other beta-chemokines in murine glial cells.

Monocyte chemoattractant protein-1 (MCP-1), formerly termed JE, is a member of the beta-chemokine (C-C chemokine) family and has been shown to be produced by a variety of cell types. Recently, mRNA of JE/MCP-1 was detected in astrocytes during the acute phase of experimental allergic encephalomyelitis (EAE). In addition, supernatants collected from human cultured astrocytes have recently been found to be chemotactic for monocytes. However, chemokine production and function in glial cells has not been fully examined. Using a sandwich ELISA assay, we have now quantitated MCP-1 levels and assessed MCP-1 function on murine glial cells. Lipopolysaccharide (LPS), interleukin (IL)-1 beta and tumor necrosis factor (TNF)-alpha induced MCP-1 secretion by astrocytes, but not microglia. In addition, pretreatment with interferon (IFN)-gamma significantly augmented MCP-1 production by either LPS or the above cytokines. In contrast, LPS preferentially induced production of another beta-chemokine, macrophage inflammatory protein-1 alpha (MIP-1 alpha) from microglial cells. MCP-1 induced chemotaxis of microglial cells and macrophages. Similarly, another beta-chemokine, TCA3, which is produced by encephalitogenic T lymphocytes, also induced chemotaxis of microglia and macrophages. These findings suggested that astrocytes and microglial cells differentially produce chemokines in the central nervous system, and that both astrocytes and T cells may facilitate recruitment and activation of microglial cells via production of beta-chemokines.

Animals↗
PubMed1995

Zinc-copper interaction affecting plant growth on a metal-contaminated soil.

In order to assess the effects of metal interactions on plant growth, a greenhouse experiment was conducted, in which spring barley was grown for 48 days in a soil to which cadmium, copper, lead and zinc were added singly and in combination. Plant growth was measured as shoot and root dry matter production. At the end of the experiment the plant material was analysed for metal uptake and the soil was extracted with CaCl(2) solution, to measure the plant-available metal content. The most consistent effect on plant growth was an interaction between copper and zinc, which was also important in determining uptake of these metals and the amounts extractable with CaCl(2) solution. An analysis of the underlying mechanism led to the conclusion that the growth of barley was controlled principally by the amount of plant-available zinc, which depended on the amounts of both added zinc and added copper. The effect of the added copper was to increase the toxicity of the added zinc.

Journal Article↗