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Biomedical subjects

M Zeng

Publications and source records attributed to M Zeng.

At least 19 recordsLinked to original sources
PubMed2006

Inactivation of DNA adenine methyltransferase alters virulence factors in Actinobacillus actinomycetemcomitans.

DNA adenine methyltransferase (DAM) plays critical roles in diverse biological pathways in gram-negative bacteria, and specifically in regulating the expression of virulence genes in several organisms. Actinobacillus actinomycetemcomitans plays an important role in the pathogenesis of juvenile and adult periodontal disease, yet little is known about its mechanisms of gene regulation. DAM is shown here to directly or indirectly affect well-known A. actinomycetemcomitans virulence factors. A mutant A. actinomycetemcomitans strain lacking the dam gene was created by homologous recombination and shows normal growth phenotypes when grown exponentially. This mutant strain has four sixfold increased levels of extracellular leukotoxin, altered cellular levels of leukotoxin, and significant changes in bacterial invasion of KB oral epithelial cells. These results provide a basis for further characterization of regulatory mechanisms that control A. actinomycetemcomitans virulence.

Aggregatibacter actinomycetemcomitans↗
PubMed2003

Requirement of Rac activity for maintenance of capillary endothelial barrier properties.

Our previous experiments indicated that GTPases, other than RhoA, are important for the maintenance of endothelial barrier integrity in both intact microvessels of rats and mice and cultured mouse myocardial endothelial (MyEnd) cell monolayers. In the present study, we inhibited the endothelial GTPase Rac by Clostridium sordellii lethal toxin (LT) and investigated the relation between the degree of inhibition of Rac by glucosylation and increased endothelial barrier permeability. In rat venular microvessels, LT (200 ng/ml) increased hydraulic conductivity from a control value of 2.5 +/- 0.6 to 100.8 +/- 18.7 x 10-7 cm x s(-1) x cm H2O(-1) after 80 min. In cultured MyEnd cells exposed to LT (200 ng/ml), up to 60% of cellular Rac was glucosylated after 90 min, resulting in depolymerization of F-actin and interruptions of junctional distribution of vascular endothelial cadherin (VE-cadherin) and beta-catenin as well as the formation of intercellular gaps. To understand the mechanism by which inhibition of Rac caused disassembly of adherens junctions, we used laser tweezers to quantify VE-cadherin-mediated adhesion. LT and cytochalasin D, an actin depolymerizing agent, both reduced adhesion of VE-cadherin-coated microbeads to the endothelial cell surface, whereas the inhibitor of Rho kinase Y-27632 did not. Stabilization of actin filaments by jasplakinolide completely blocked the effect of cytochalasin D but not of LT on bead adhesion. We conclude that Rac regulates endothelial barrier properties in vivo and in vitro by 1) modulation of actin filament polymerization and 2) acting directly on the tether between VE-cadherin and the cytoskeleton.

Actins↗
PubMed2003

Thrombin increases permeability only in venules exposed to inflammatory conditions.

Thrombin is widely used to stimulate a variety of responses in cultured endothelial cell monolayers as a model of acute vascular endothelial response to inflammatory mediators. However, preliminary results indicated that rat mesenteric venules did not respond acutely to thrombin. We tested the hypothesis that rat venules would respond to thrombin 24 h after prior injury by microperfusion. Vessel responsiveness was measured as hydraulic conductivity (Lp). When venules were exposed to rat thrombin (10 U/ml) within 2 h of initial perfusion with vehicle control, there was no increase in Lp of any vessel from a mean baseline of 1.2 +/- 0.2 x 10(-7) cm.s-1.cmH2O-1. In contrast, when perfused with thrombin at 25-27 h after initial perfusion, every venule responded to thrombin with a transient increase in Lp. The mean peak Lp on day 2 in response to thrombin was 24 +/- 4.2 x 10(-7) cm.s-1.cmH2O-1. Our results suggest that prior endothelial injury modifies the endothelial cell phenotype and alters the response of endothelial cells to thrombin after 24 h. Phenotypic plasticity of endothelial cells may play a key role in the regulation of permeability of some endothelial cells in culture and in intact venules, where localized leaky sites may form where there had been a previous inflammatory response.

Animals↗
PubMed2003

PAF- and bradykinin-induced hyperpermeability of rat venules is independent of actin-myosin contraction.

We tested the hypothesis that acutely induced hyperpermeability is dependent on actin-myosin contractility by using individually perfused mesentery venules of pentobarbital-anesthetized rats. Venule hydraulic conductivity (Lp) was measured to monitor hyperpermeability response to the platelet-activating factor (PAF) 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine or bradykinin. Perfusion with PAF (10 nM) induced a robust transient high Lp [24.3 +/- 1.7 x 10-7 cm/(s.cmH2O)] that peaked in 8.9 +/- 0.5 min and then returned toward control Lp [1.6 +/- 0.1 x 10-7 cm/(s.cmH2O)]. Reconstruction of venular segments with the use of transmission electron microscopy of serial sections confirmed that PAF induces paracellular inflammatory gaps. Specific inhibition of myosin light chain kinase (MLCK) with 1-10 microM 1-(5-iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine hydrochloride (ML-7) failed to block the PAF Lp response or change the time-to-peak Lp. ML-7 reduced baseline Lp 50% at 40 min of pretreatment. ML-7 also increased the rate of recovery from PAF hyperpermeability measured as the decrease of half-time of recovery from 4.8 +/- 0.7 to 3.2 +/- 0.3 min. Inhibition of myosin ATPase with 5-20 mM 2,3-butanedione 2-monoxime also failed to alter the hyperpermeability response to PAF. Similar results were found using ML-7 to modulate responses. These experiments indicate that an actin-myosin contractile mechanism modulated by MLCK does not contribute significantly to the robust initial increase in permeability of rat venular microvessels exposed to two common inflammatory mediators. The results are consistent with paracellular gap formation by local release of endothelial-endothelial cell adhesion structures in the absence of contraction by the actin-myosin network.

Actins↗
PubMed2001

A metabolic enzyme for S-nitrosothiol conserved from bacteria to humans.

Considerable evidence indicates that NO biology involves a family of NO-related molecules and that S-nitrosothiols (SNOs) are central to signal transduction and host defence. It is unknown, however, how cells switch off the signals or protect themselves from the SNOs produced for defence purposes. Here we have purified a single activity from Escherichia coli, Saccharomyces cerevisiae and mouse macrophages that metabolizes S-nitrosoglutathione (GSNO), and show that it is the glutathione-dependent formaldehyde dehydrogenase. Although the enzyme is highly specific for GSNO, it controls intracellular levels of both GSNO and S-nitrosylated proteins. Such 'GSNO reductase' activity is widely distributed in mammals. Deleting the reductase gene in yeast and mice abolishes the GSNO-consuming activity, and increases the cellular quantity of both GSNO and protein SNO. Furthermore, mutant yeast cells show increased susceptibility to a nitrosative challenge, whereas their resistance to oxidative stress is unimpaired. We conclude that GSNO reductase is evolutionarily conserved from bacteria to humans, is critical for SNO homeostasis, and protects against nitrosative stress.

Aldehyde Oxidoreductases↗
PubMed2001

A study of equivalent source techniques for high-resolution EEG imaging.

High-resolution EEG imaging has been an important topic in recent EEG research, and much work has been done on the two equivalent source imaging techniques: the equivalent distributed dipole-layer source imaging technique (EST) and the equivalent multipole source imaging technique (SAT). In this paper we first develop a forward density formula for a spherical equivalent distributed dipole layer of an arbitrary dipole in a three-concentric-sphere head model. It is clarified using the derived forward formula that the equivalent dipole-layer source and equivalent multipole source are interrelated in theory. Finally, simulation comparisons are conducted, the results of which suggest that EST has a higher spatial resolution than SAT when both of them are implemented by a truncated singular value decomposition algorithm. This is due to the different singularities of the inversion equations involved in the two techniques. An empirical VEP data study also shows that EST is better than SAT in providing higher spatial resolution EEG imaging.

Cerebral Cortex↗
PubMed2001

Streptimonospora salina gen. nov., sp. nov., a new member of the family Nocardiopsaceae.

Actinomycete strain YIM 90002T (= CCTCC 99003T = CCRC 16284T) was isolated from a soil sample collected from a salt lake in the west of China. The aerial mycelium of this organism is well developed but not fragmented and, at maturity, forms short chains of spores. Spores in short chains are oval- to rod-shaped and have wrinkled surfaces. Substrate mycelium is branched with non-fragmenting hyphae and forms single oval to round spores borne on sporophores or dichotomously branching sporophores. Single spores have wrinkled surfaces. Single spores and spores in short chains are non-motile. Strain YIM 90002T contains meso-diaminopimelic acid, DD-diaminopimelic acid, glycine, lysine and aspartic acid in its cell wall and has glucose, galactose, ribose, xylose, arabinose and mannose as whole-cell sugars (no diagnostic sugars). The phospholipids are phosphatidylglycerol, phosphatidylinositol and phosphatidylethanolamine. The major menaquinones are MK-9(H6), MK-10(H2) and MK-10(H4). Phylogenetic data indicate that this strain belongs to the family Nocardiopsaceae. The morphological and physiological characteristics and chemotaxonomic and phylogenetic data for this strain differ from those of previously described actinomycetes. Therefore, a new genus, Streptimonospora, is proposed for this organism; the type species of the genus is Streptimonospora salina gen. nov., sp. nov., and the type strain of S. salina is strain YIM 90002T.

Actinomycetales↗
PubMed2001

Protection against tetanus by needle-free inoculation of adenovirus-vectored nasal and epicutaneous vaccines.

The effectiveness of vaccination programs would be enhanced greatly through the availability of vaccines that can be administered simply and, preferably, painlessly without the need for timed booster injections. Tetanus is a prime example of a disease that is readily preventable by vaccination but remains a major threat to public health due to the problems associated with administration of the present vaccine. Here we show that a protective immune response against live Clostridium tetani infection in mice can be elicited by an adenovirus vector encoding the tetanus toxin C fragment when administered as a nasal or epicutaneous vaccine. The results suggest that these vaccination modalities would be effective needle-free alternatives. This is the first demonstration that absorption of a small number of vectored vaccines into the skin following topical application of a patch can provide protection against live bacteria in a disease setting.

Adenoviridae↗
PubMed2001

[The inhibitory effect of oxymatrine on hepatitis C virus in vitro].

OBJECTIVE: To study the inhibitory effect of oxymatrine on HCV in vitro. METHODS: SMMC-7721 cells transfected with pBK-HCV using lipofectin transfection protocal were treated with oxymatrine. bDNA signal amplification assay and MTT colorimetric assay were used for intracellular HCV RNA and cytotoxicity. RESULTS: The stable HCV expression cell model established here could be used as a tool for medicine screen. Oxymatrine at the concentration of 100~1000 mug/ml could significantly decrease the level of intracellular HCV RNA. No cytotoxicity was shown in such concentrations. CONCLUSIONS: Oxymatrine has an anti-HCV potential activity in vitro.

Alkaloids↗
PubMed2001

[A preliminary study of the combination of noninvasive parameters in the diagnosis of liver fibrosis].

OBJECTIVE: To explore the combination of noninvasive parameters and its significance in the diagnosis of liver fibrosis. METHODS: Liver biopsy was performed on 200 patients with chronic liver diseases, and the biochemical parameters, serum fibrotic markers, and B ultrasound, CT, and MRI were detected in the corresponding period. Then, by the regression, we obtained the combination of the noninvasive parameters and evaluated the significance in the diagnosis of liver fibrosis. RESULTS: Three combinations have been obtained. The parameters in the first combination which was used to differentiate fibrosis and no fibrosis(S0 vs S1+S2+S3+S4) were the parameter of blood flow of portal vein per minute by B ultrasonography, age, the maximum oblique line of right liver by B ultrasound, the wave expression of the surface of liver by CT/MRI and GGT. The parameters in the second combination which was used to evaluated the degree of fibrosis(S1+S2 vs S3+S4) were HA, A/G and the longest length of spleen by B ultrasound. The third combination which was used to distinguish fibrosis with cirrhosis (S1+S2+S3 vs S4) was composed by HA, the little cyst-like change near the intrahepatic duct, thickness of liver capsule by B ultrasound, age and the index of symptoms. All the three combinations were sensitive, specific, and accurate. CONCLUSIONS: The combinations of noninvasive parameters is more valuable than single parameter in the diagnosis of liver fibrosis.

Adolescent↗
PubMed2000

Ionizing radiation-induced apoptosis via separate Pms2- and p53-dependent pathways.

The cytotoxicity of ionizing radiation (IR) has been associated with both the p53 pathway and with DNA mismatch repair (MMR). p53 mediates cell cycle arrest and apoptosis in response to X-ray damage, whereas the MMR complex is thought to recognize damaged bases and initiate a signal transduction pathway that can include phosphorylation of p53. To determine whether p53 and MMR mediate X-ray cytotoxicity via the same pathway, mice with targeted disruptions in either the p53 gene or the MutL homologue MMR gene Pms2 were interbred and primary fibroblasts were established from the progeny with genotypes of either wild type, p53 null, Pms2 null, or double null. Cells with either p53 or Pms2 separately disrupted showed reduced levels of apoptosis after IR in comparison with wild type, but the double null cells showed even lower levels, consistent with nonoverlapping roles for p53 and PMS2 in the X-ray response. In transformed cell lines established from the primary cells at early passage, similar differences in the apoptotic response to IR were seen, and clonogenic survival assays following low dose rate IR further showed that nullizygosity for Pms2 confers increased survival on cells in both wild-type and p53 null backgrounds. These results indicate that both p53 and MMR contribute to X-ray-induced apoptosis and that the role of MMR in the cytotoxicity of IR does not depend on p53.

Animals↗
PubMed2000

Protection from nitrosative stress by yeast flavohemoglobin.

Yeast hemoglobin was discovered close to half a century ago, but its function has remained unknown. Herein, we report that this flavohemoglobin protects Saccharomyces cerevisiae from nitrosative stress. Deletion of the flavohemoglobin gene (YHB1) abolished the nitric oxide (NO)-consuming activity of yeast cells. Levels of protein nitrosylation were more than 10-fold higher in yhb1 mutant yeast than in isogenic wild-type cells after incubation with NO donors. Growth of mutant cells was inhibited by a nitrosative challenge that had little effect on wild-type cells, whereas the resistance of mutant cells to oxidative stress was unimpaired. Protection conferred by yeast flavohemoglobin against NO and S-nitrosothiols was seen under both anaerobic and aerobic conditions, consistent with a primary function in NO detoxification. A phylogenetic analysis indicated that protection from nitrosative stress is likely to be a conserved function among microorganismal flavohemoglobins. Flavohemoglobin is therefore a potential target for antimicrobial therapy.

Aerobiosis↗
PubMed2000

An apoptotic model for nitrosative stress.

Nitric oxide overproduction has been implicated in the pathogenesis of many disorders, including artherosclerosis, neurodegenerative diseases, inflammatory and autoimmune diseases, and cancer. The common view holds that nitric oxide-induced cellular injury is caused by oxidative stress. This theory predicts that interactions between reactive nitrogen species and reactive oxygen species produce powerful oxidants that initiate cell death programs. Cytokine-treated murine macrophages are the prototype of this form of cellular injury. Here we report that generation of reactive nitrogen species upon lipopolysacharide/interferon-gamma stimulation of RAW 264.7 cells is largely divorced from production of reactive oxygen species, and that oxidative stress is not principally responsible for cell death (in this model). Rather, the death program is induced mainly by a nitrosative challenge, characterized by the accrual of nitrosylated proteins without a major alteration in cellular redox state. Moreover, interactions between reactive oxygen and nitrogen species may alter the balance between pathways that yield nitrite and nitrate, without impacting the level of S-nitrosylation or extent of cell death. Our results thus (1) provide new insights into NO-related metabolic pathways, (2) demonstrate that apoptotic injury can be caused by nitrosative mechanisms, and (3) establish a model for nitrosative stress in mammalian cells.

2-Naphthylamine↗
PubMed2000

Dominant role of cAMP in regulation of microvessel permeability.

We reported previously that increasing cAMP levels in endothelial cells attenuated ATP-induced increases in hydraulic conductivity (L(p)), and that the activation of cGMP-dependent pathways was a necessary step to increase L(p) in response to inflammatory mediators. The aim of the present study was to evaluate the role of basal levels of cAMP in microvessel permeability under resting conditions and to evaluate the cross talk between cAMP- and cGMP-dependent signaling mechanisms in regulation of microvessel permeability under stimulated conditions, using individually perfused microvessels from frog and rat mesenteries. We found that reducing cAMP levels by inhibition of adenylate cyclase or inhibiting cAMP-dependent protein kinase through the use of H-89 increased basal L(p) in both frog and rat mesenteric venular microvessels. We also found that 8-bromocAMP (8-BrcAMP, 0.2 and 2 mM) was sufficient to attenuate or abolish the increases in L(p) due to exposure of frog mesenteric venular microvessels to 8-BrcGMP (2 mM) and ATP (10 microM). Similarly, in rat mesenteric venular microvessels, application of 8-BrcAMP (2 mM) abolished the increases in L(p) due to exposure to 8-BrcGMP alone (2 mM) or with the combination of bradykinin (1 nM). In addition, application of erythro-9-(2-hydroxy-3-nonyl)adenine, an inhibitor of cGMP-stimulated phosphodiesterase, significantly attenuated both 8-BrcGMP- and bradykinin-induced increases in L(p). These results demonstrate that basal levels of cAMP are critical to maintaining normal permeability under resting conditions, and that increased levels of cAMP are capable of overcoming the activation of cGMP-dependent pathways, therefore preventing increases in microvessel permeability. The balance between endothelial concentrations of these two opposing cyclic nucleotides controls microvessel permeability, and cAMP levels play a dominant role.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed2000

Leukocyte adhesion and microvessel permeability.

To investigate the direct effect of leukocyte adherence to microvessel walls on microvessel permeability, we developed a method to measure changes in hydraulic conductivity (L(p)) before and after leukocyte adhesion in individually perfused venular microvessels in frog mesentery. In 19 microvessels that were initially free of leukocyte sticking or rolling along the vessel wall, control L(p) was measured first with Ringer-albumin perfusate. Blood flow was then restored in each vessel with a reduced flow rate in the range of 30-116 microm/s to facilitate leukocyte adhesion. Each vessel was recannulated in 45 min. The mean number of leukocytes adhering to the vessel wall was 237 +/- 22 leukocytes/mm(2). At the same time, L(p) increased to 4.7 +/- 0.5 times the control value. Superfusion of isoproterenol (10 microM) after leukocyte adhesion brought the increased L(p) back to 1.1 +/- 0.2 times the control in 5-10 min (n = 9). Superfusing isoproterenol before leukocyte adhesion prevented the increase in L(p) (n = 6). However, the number of leukocytes adhering to the vessel wall was not significantly affected. These results demonstrated that leukocyte adhesion caused an increase in microvessel permeability that could be prevented or restored by increasing cAMP levels in endothelial cells using isoproterenol. Thus cAMP-dependent mechanisms that regulate inflammatory agent-induced increases in permeability also modulate leukocyte adhesion-induced increases in permeability but act independently of mechanisms that regulate leukocyte adhesion to the microvessel wall. Application of ketotifen, a mast cell stabilizer, and desferrioxamine mesylate, an iron-chelating reagent, attenuated the increase in L(p) induced by leukocyte adhesion, suggesting the involvement of oxidants and the activation of mast cells in leukocyte adhesion-induced permeability increase. Furthermore, with the use of an in vivo silver stain technique, the locations of the adherent leukocytes on the microvessel wall were identified quantitatively in intact microvessels.

Adrenergic beta-Agonists↗