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Biomedical subjects

Z Yang

Publications and source records attributed to Z Yang.

At least 73 records · Page 4Linked to original sources
PubMed2001

Cyclodextrin dimers as cleavable carriers of photodynamic sensitizers.

Several phthalocyanines carrying hydrophobic components have been synthesized and shown to bind to a group of cyclodextrin dimers with a carbon-carbon double bond in the linker. The complexes are soluble in water. On irradiation in the presence of oxygen, the singlet oxygen produced cleaves the olefinic linkers in the complexes, resulting in precipitation of the sensitizers. This process concentrates the sensitizers in the light beam, a process that has useful potential in photodynamic therapy.

Cyclodextrins↗
PubMed2001

Study of adaptive mutations in Salmonella typhimurium by using a super-repressing mutant of a trans regulatory gene purR.

Salmonella typhimurium purR encodes a transcriptional repressor regulating gene expression of de novo purine nucleotide biosynthesis. It represses purD gene transcription by binding to the 16-base pair purD operator (PUR box). A S. typhimurium strain carrying a super-repressing mutant of purR, purR(s), has been used as an experimental system to study adaptive mutation. Escherichia coli lac genes were genetically engineered into S. typhimurium chromosome and repressed by purR(s) so that they could be used as an indicator of adaptive mutations in purR(s) or in the purD operator. Mutations in purR(s) or in the purD operator accumulated when the mutant strain was placed on a minimal lactose plate supplemented with 10 microg/ml of adenine during prolonged incubation. These specific mutations reverted the mutant strain from lac(-) to lac(+) phenotype. The lac(+) strains were categorized into the early- and late-arising mutants according to the time for colony appearance. Our genetic studies indicate that (i) Poisson distributed mutations accumulated in the chromosomal regulatory gene purR or the purD operator in very slowly dividing cells under selection; (ii) after about 8 days of selection, the frequency of mutations in purD operator reached the high value of about two mutations per 10(8) cells; (iii) the mutational spectrum in the purD operator during growth was not significantly different from that during selection; (iv) defects in mutL or mutS appeared to have a stronger effect on growth-dependent mutations than on adaptive mutations.

Adaptation, Physiological↗
PubMed2001

Leucine zipper domain of 52 kDa SS-A/Ro promotes protein dimer formation and inhibits in vitro transcription activity.

Two forms of the human 52 kDa SS-A/Ro protein autoantigen, 52alpha and 52beta, are products of alternative mRNA splicing. The 52alpha form is ubiquitously expressed whereas 52beta, lacking the central leucine zipper domain, has been detected at higher levels than 52alpha during certain stages of fetal development. Because 52alpha has sequence similarity with macromolecules associated with transcriptional regulation and the two forms differ only in that 52beta does not contain the leucine zipper, their roles in protein dimer formation and in transcriptional activity were examined. Employing the yeast two-hybrid system, 52alpha was shown to interact with itself but not 52beta. The homodimerization of 52alpha was independently confirmed in gel filtration chromatography using in vitro cDNA template derived translation products and in HL-60 cell extracts; two peaks were observed corresponding to dimer and monomer of 52alpha, while in vitro the translation product of 52beta exhibited only a single monomer peak. In addition, dimer formation was also demonstrated in a chemical cross-linking experiment using HeLa cells transfected with 52alpha. To evaluate effects on transcription, eukaryotic expression plasmids encoding 52alpha or 52beta fused with the GAL4 DNA binding (DB) domain were co-transfected into 293 cells together with a luciferase reporter vector. A 6-fold increase in transcription activity of the reporter was detected with the GAL4-DB-52beta fusion constructs compared to GAL4-DB-52alpha or the empty vector control. We speculate that the ratio of cellular 52alpha and 52beta may play an important role in regulating gene expression as potential repressor and activator respectively.

Autoantigens↗
PubMed2001

Imaging time after Gd-DTPA injection is critical in using delayed enhancement to determine infarct size accurately with magnetic resonance imaging.

BACKGROUND: In patients with acute myocardial infarction (MI), delayed enhancement is seen in MRI 5 to 7 minutes after gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) injection, and the enhancement occurs in regions that later show recovery of function. However, in a canine model of acute MI, delayed enhancement 20 to 30 minutes after injection only occurs in necrotic regions and not in surrounding, reversibly injured myocardium. The objective of the present study was to determine (1) if the size of the enhanced region varies with time after Gd-DTPA injection and (2) if and when the size of the enhanced region corresponds to the true infarct size. METHODS AND RESULTS: The left coronary artery was occluded in 15 Lewis rats for 30 minutes (n=9) or 2 hours (n=6); this was followed by reperfusion. MRI scans were performed 48+/-2 hours after-MI. Midventricular short-axis images were obtained continuously for 40 minutes after Gd-DTPA injection (0.3 mmol/kg). The sizes of enhanced regions at each time were determined by threshold analysis and compared with triphenyltetrazolium chloride-stained sections of the excised rat heart. In all animals, the enhanced region overestimated infarct size (28+/-5%) immediately after the injection of Gd-DTPA, although it then gradually receded to match the size of the infarct. The time required for enhancement to accurately determine infarct size was significantly different between 2-hour infarcts (16+/-2 minutes) and 30-minute (26+/-4 minutes) infarcts (P<0.05). CONCLUSIONS: In reperfused acute MI, accurate determination of infarct size by delayed enhancement MRI requires imaging at specific times after Gd-DTPA injection, and this time varies with the duration of occlusion.

Animals↗
PubMed2001

Determination of the mechanism of human malic enzyme with natural and alternate dinucleotides by isotope effects.

Human malic enzyme was studied by steady state kinetics, deuterium isotope effects, and 13C isotope effects with both the physiological dinucleotide cofactor and several alternate cofactors. The log V vs pH profile with NAD revealed two pK(a) values too close to be separately determined, but with an average value of 7.33. The log V/K vs pH profile with NAD revealed two pK(a) values at 7.4 and 5.6. Deuterium and 13C isotope effects indicate that the mechanism of human malic enzyme is stepwise with both NAD and epsilonNAD, but that hyperconjugation in the transition state for hydride transfer is detectable only with the former. With thioNAD and APAD, the isotope effects do not clearly indicate whether the mechanism is stepwise or concerted. The intrinsic 13C isotope effect for decarboxylation was calculated to be 1.0485 by measurement of the partition ratio of oxaloacetate in the presence of NADH and human malic enzyme (decarboxylation to pyruvate/reduction to malate = 2.33). The isotope effect and partitioning data suggest that the energy barrier for decarboxylation of oxaloacetate is not as high relative to the barrier for reduction of oxaloacetate as with the chicken liver enzyme.

Carbon Isotopes↗
PubMed2001

The 7SK small nuclear RNA inhibits the CDK9/cyclin T1 kinase to control transcription.

The human positive transcription elongation factor P-TEFb, consisting of a CDK9/cyclin T1 heterodimer, functions as both a general and an HIV-1 Tat-specific transcription factor. P-TEFb activates transcription by phosphorylating RNA polymerase (Pol) II, leading to the formation of processive elongation complexes. As a Tat cofactor, P-TEFb stimulates HIV-1 transcription by interacting with Tat and the transactivating responsive (TAR) RNA structure located at the 5' end of the nascent viral transcript. Here we identified 7SK, an abundant and evolutionarily conserved small nuclear RNA (snRNA) of unknown function, as a specific P-TEFb-associated factor. 7SK inhibits general and HIV-1 Tat-specific transcriptional activities of P-TEFb in vivo and in vitro by inhibiting the kinase activity of CDK9 and preventing recruitment of P-TEFb to the HIV-1 promoter. 7SK is efficiently dissociated from P-TEFb by treatment of cells with ultraviolet irradiation and actinomycin D. As these two agents have been shown to significantly enhance HIV-1 transcription and phosphorylation of Pol II (refs 6,7,8), our data provide a mechanistic explanation for their stimulatory effects. The 7SK/P-TEFb interaction may serve as a principal control point for the induction of cellular and HIV-1 viral gene expression during stress-related responses. Our studies demonstrate the involvement of an snRNA in controlling the activity of a Cdk-cyclin kinase.

Cyclin T↗
PubMed2001

Crystal structure of native chicken fibrinogen at 2.7 A resolution.

The crystal structure of native chicken fibrinogen (320 kDa) complexed with two synthetic peptides has been determined at a resolution of 2.7 A. The structure provides the first atomic-resolution view of the polypeptide chain arrangement in the central domain where the two halves of the molecule are joined, as well as of a putative thrombin-binding site. The amino-terminal segments of the alpha and beta chains, including fibrinopeptides A and B, are not visible in electron density maps, however, and must be highly disordered. The alphaC domain is also very disordered. A residue by residue analysis of the coiled coils with regard to temperature factor shows a strong correlation between mobility and plasmin attack sites. It is concluded that structural flexibility is an inherent feature of fibrinogen that plays a key role in both its conversion to fibrin and its subsequent destruction by plasmin.

Amino Acid Sequence↗
PubMed2001

Present-day crustal deformation in China constrained by global positioning system measurements.

Global Positioning System (GPS) measurements in China indicate that crustal shortening accommodates most of India's penetration into Eurasia. Deformation within the Tibetan Plateau and its margins, the Himalaya, the Altyn Tagh, and the Qilian Shan, absorbs more than 90% of the relative motion between the Indian and Eurasian plates. Internal shortening of the Tibetan plateau itself accounts for more than one-third of the total convergence. However, the Tibetan plateau south of the Kunlun and Ganzi-Mani faults is moving eastward relative to both India and Eurasia. This movement is accommodated through rotation of material around the eastern Syntaxis. The North China and South China blocks, east of the Tibetan Plateau, move coherently east-southeastward at rates of 2 to 8 millimeters per year and 6 to 11 millimeters per year, respectively, with respect to the stable Eurasia.

Journal Article↗
PubMed2001

Evidence for involvement of the neural pathway containing the peripheral vagus nerve, medullary visceral zone and central amygdaloid nucleus in neuroimmunomodulation.

It is now evident that a bidirectional communication network exists between the central nervous system (CNS) and immune system (IS). However, the way in which the IS passes inform to the brain is not quite clear.In the present study, one of the neural pathways involved in the cytokine-to-brain communication was investigated in the rat. This pathway starts at the vagal nerve projecting to the medullary visceral zone (MVZ), an arc-shape band from the dorsomedial to ventrolateral area in the middle-caudal segment of the medulla oblongata, and terminates at the central amygdaloid nucleus (Ce) which receives projections from large catecholaminergic neurons in the MVZ. Animals were randomly divided into two experimental groups. Triple-labeling was used in Group I animals to combine wheat germ aggulutinin-conjugated horseradish peroxidase (WGA-HRP) retrograde tracing with anti-Fos and anti-tyrosine hydroxylase (TH) immunostaining. WGA-RP was stereotaxically injected into the unilateral Ce of the animals and, after a survival period of 48 h, intraperitoneal (IP) injection of lipopolysaccharide (LPS) was performed. Seven kinds of labeled neurons were observed in the MVZ, namely, HRP-, Fos- or TH-singly-labeled neurons; Fos/HRP-, Fos/TH- or HRP/TH-doubly-labeled neurons; and Fos/HRP/TH-triply-labeled neurons. As for Group II animals, bilateral subdiaphragmatic vagotomy (SDV) or sham operation was performed, followed 4 weeks later by IP injection of LPS. The number of Fos-positive neurons within the Ce and MVZ was significantly lower (P<0.01) in rats having SDV when compared with those receiving sham operation. Our results suggest that part of the peripheral immune information can be conveyed through the vagus to the catecholaminergic neurons in the MVZ, where it is transported to the Ce. The MVZ is a neural relay station in the immune-to-brain communication and might play a significant role in neuroimmuno-modulation via the vagus-MVZ-Ce pathway.

Amygdala↗
PubMed2001

Thrombin suppresses endothelial nitric oxide synthase and upregulates endothelin-converting enzyme-1 expression by distinct pathways: role of Rho/ROCK and mitogen-activated protein kinase.

An imbalance of nitric oxide and endothelin plays an important role in cardiovascular disease. Thrombin exerts profound effects on endothelial function. The present study investigated the molecular mechanisms by which thrombin regulates endothelial nitric oxide synthase (eNOS) and endothelin-converting enzyme (ECE)-1 expression in human endothelial cells. Incubation of human umbilical vein endothelial cells with thrombin (0.01 to 4 U/mL) for 15 to 24 hours markedly downregulated eNOS and increased ECE-1 protein level in a dose-dependent manner. Thrombin also decreased eNOS mRNA and increased ECE-1 mRNA level. In mRNA stability assay, thrombin shortened the half-life of eNOS mRNA but not that of ECE-1 mRNA. Activation of protease-activated receptor 1 by the agonist (SFLLRN, 10 to 100 micromol/L) had no effect on eNOS expression but increased ECE-1 level as thrombin. Thrombin activated Rho A and extracellular signal-regulated kinase (ERK)1 and ERK2. Inhibition of Rho A by C3 exoenzyme (20 microgram/mL) and ROCK by Y-27632 (10 micromol/L) prevented the downregulation of eNOS expression by thrombin. Y-27632 also prevented the reduction in NOS activity induced by prolonged incubation with thrombin. On the other hand, inhibition of ERK1 and ERK2 activation by PD98059 (50 micromol/L) prevented the upregulation of ECE-1 expression by thrombin as well as the increase in ECE activity and ET-1 accumulation in the medium. Treatment of rat aorta with thrombin overnight impaired endothelium-dependent relaxations but not endothelium-independent relaxations. Thus, thrombin suppresses eNOS and upregulates ECE-1 expression via Rho/ROCK and ERK pathway, respectively. These effects of thrombin may be important for endothelial dysfunction in cardiovascular disease, particularly during acute coronary episodes.

Animals↗
PubMed2001

Effects of cytosolic ATP on Ca(2+) sparks and SR Ca(2+) content in permeabilized cardiac myocytes.

Confocal imaging was used to study the influence of cytosolic ATP on the properties of spontaneous Ca(2+) sparks in permeabilized ventricular myocytes. Cells were perfused with mock intracellular solutions containing fluo 3. Reducing [ATP] to <0.5 mmol/L decreased the frequency but increased the amplitude of spontaneous Ca(2+) sparks. In the presence of 20 micromol/L ATP, the amplitude increased by 48.7+/-10.9%, and the frequency decreased by 77.07+/-3.8%, relative to control responses obtained at 5 mmol/L ATP. After exposure to a solution containing zero ATP, the frequency of Ca(2+) sparks decreased progressively and approached zero within 90 seconds. As ATP washed out of the cell, the sarcoplasmic reticulum (SR) Ca(2+) content increased, until reaching a maximum after 3 minutes. Subsequent introduction of adenylyl imidodiphosphate precipitated a burst of large-amplitude Ca(2+) sparks. This was accompanied by a rapid decrease in SR Ca(2+) content to 80% to 90% of the steady-state value obtained in the presence of 5 mmol/L ATP. Thereafter, the SR Ca(2+) content declined much more slowly over 5 to 10 minutes. The effects of ATP withdrawal on Ca(2+) sparks may reflect reduced occupancy of the adenine nucleotide site on the SR Ca(2+) channel. These effects may contribute to previously reported changes in SR function during myocardial ischemia and reperfusion, in which ATP depletion and Ca(2+) overload occur.

Adenosine Triphosphate↗
PubMed2001

Phorbol ester downregulates PDGFbeta receptor via PKCbeta1 in vascular smooth muscle cells.

The role of protein kinase C (PKC) and their isoforms in cell growth regulation remains elusive. Here we showed that in cultured human vascular smooth muscle cells (SMC), the PKC stimulator phorbol 12-myristate 13-acetate (PMA) inhibited [(3)H]thymidine incorporation in response to the growth factor PDGF associated with downregulation of PDGFbeta (but not alpha) receptors, which was recovered to normal level after PKC was depleted. The changes in PDGFbeta receptor were inversely correlated with PKCbeta1 protein levels regulated by PMA. The downregulation of PDGFbeta receptor by PMA was fully prevented by the PKCbeta inhibitor LY379196, however, without recovery of [(3)H]thymidine incorporation to PDGF. In contrast, [(3)H]thymidine incorporation was fully recovered after depletion of PKCs. These results indicate that in human SMC PKCbeta1 mediates PDGFbeta receptor downregulation. Other PKC isoforms activated by phorbol ester also contribute to the inhibitory effects on cell growth.

Cells, Cultured↗
PubMed2001

Simultaneous infection with multiple strains of Mycobacterium tuberculosis.

Drug-susceptible and drug-resistant isolates of Mycobacterium tuberculosis were recovered from 2 patients, 1 with isoniazid-resistant tuberculosis (patient 1) and another with multidrug-resistant tuberculosis (patient 2). An investigation included patient interviews, record reviews, and genotyping of isolates. Both patients worked in a medical-waste processing plant. Transmission from waste was responsible for at least the multidrug-resistant infection. We found no evidence that specimens were switched or that cross-contamination of cultures occurred. For patient 1, susceptible and isoniazid-resistant isolates, collected 15 days apart, had 21 and 19 restriction fragments containing IS6110, 18 of which were common to both. For patient 2, a single isolate contained both drug-susceptible and multidrug-resistant colonies, demonstrating 10 and 11 different restriction fragments, respectively. These observations indicate that simultaneous infections with multiple strains of M. tuberculosis occur in immunocompetent hosts and may be responsible for conflicting drug-susceptibility results, though the circumstances of infections in these cases may have been unusual.

Adult↗
PubMed2001

Features of the two gene pairs RD-SKI2W and DOM3Z-RP1 located between complement component genes factor B and C4 at the MHC class III region.

Located at the 30 kb genomic region between complement factor B and component C4 are four ubiquitously expressed genes RD, SKI2W, DOM3Z and RP1. Besides RP1, the protein products of the other three genes each has highly conserved homologues or related proteins in lower eukaryotes, contains leucine zipper motifs for protein interaction, and plays important roles related to RNA metabolism. RD is a subunit of the negative transcription elongation factor, critical for the regulation of gene expression. It has an RNA recognition motif and 24 copies of Arg-Asp (RD) repeats. Ski2w is a nucleolar and cytoplasmic protein that has a putative RNA helicase domain. Fusion proteins of human Ski2w expressed in insect cells and bacteria have ATPase activity. The cytoplasmic protein of human Ski2w is associated with the polysomes and probably the 40S subunit of ribosomes. Ski2w is probably involved in the regulation of translation and RNA turnover. Dom3z is a nuclear protein whose yeast homologue forms a complex with an exoribonuclease. RP1 (or STK19) is a Ser/Thr nuclear protein kinase. No homologues of RP1 in lower eukaryotes have been discovered. Six polymorphic residues are present in human Ski2w and two in Dom3z. The potential roles of Ski2w and Dom3z on the clearance of degraded nuclear and cytoplasmic RNA raised their possibilities as susceptibility genes of systemic lupus erythematosus that is a disease with flawed processes in the removal of apoptotic materials.

Amino Acid Sequence↗
PubMed2001

The role of glutamate and vasopressin in the excitation of RVL neurones by paraventricular neurones.

Neurones in the paraventricular nucleus of the hypothalamus project to rostral ventrolateral medullary spinally projecting vasomotor neurones. We studied the excitatory action and the role of glutamate and vasopressin in this pathway in anaesthetised rats. A five barrel micropipette assembly was used for extracellular recording of neuronal activity and for microiontophoresis of drugs into the vicinity of identified medullary vasomotor neurones. Iontophoresis of L-glutamate or vasopressin into the vicinity of a vasomotor neurone increased activity, effects which were blocked by simultaneous iontophoretic application of a glutamate receptor antagonist, or a vasopressin V(1a) antagonist respectively. Paraventricular neurones were activated either by microinjecting D,L-homocysteic acid or by disinhibition by microinjecting bicuculline. The excitatory effects on vasomotor neurones, of paraventricular nucleus stimulation at some sites were prevented by simultaneous microiontophoretic application of kynurenic acid or at other sites by application of V(1a) antagonist. Neither antagonist altered the ongoing activity of the vasomotor neurones. Therefore, glutamate or vasopressin may act as excitatory neurotransmitters at synapses of paraventricular neurones on rostral ventrolateral medullary vasomotor neurones.

Action Potentials↗
PubMed2001

Controlled release of clot-dissolving tissue-type plasminogen activator from a poly(L-glutamic acid) semi-interpenetrating polymer network hydrogel.

With the aim of developing an effective therapeutic modality for treatment of thrombosis, a tissue-type plasminogen activator (t-PA)-loaded porous poly(L-glutamic acid) (PLGA) semi-interpenetrating polymer network (semi-IPN) hydrogel was developed as a possible local drug delivery system. Porous structure of hydrogel was essential in this system to yield a large surface area so that t-PA release could be facilitated. This semi-IPN hydrogel was prepared using the method of free-radical polymerization and crosslinking of polyethylene glycol (PEG)-methacrylate through the PLGA network. Sodium bicarbonate (NaHCO(3)) was added to function as a foaming agent under acidic conditions, rendering the semi-IPN hydrogel to be porous. While the added NaHCO(3) provided gas foam in the reaction mixture, the pH in the hydrogel increased to about 7 to 8, which stimulated the polymerization. The porous structure that was presented at both the surface and sublayer was stabilized during hydrogel formation and freeze-drying. The hydrogel thus prepared possessed a porous structure of 10-20 microm in diameter, as determined by scanning electron microscopy. Results showed that the above hydrogel preparation process did not significantly alter the specific activity of the entrapped t-PA with regard to plasminogen activation and fibrin clot lysis ability. The t-PA release from this semi-IPN hydrogel was examined by measuring the plasmin activity using the chromogenic substrate S-2251. Findings in this paper demonstrated that the porous structure of the hydrogel facilitated t-PA release when compared to the dense structure. Aside from the porous structure, other factors including the content of the crosslinker, PLGA and t-PA could all be varied to regulate t-PA release from the hydrogel. These results suggest that a porous PLGA semi-IPN hydrogel could potentially be a useful local delivery system to release active t-PA primarily at the site of a thrombus.

Blood Coagulation↗