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Articles 121 - 135 of 135
Full-Text Articles in Dentistry
A Common Mechanism For Influenza Virus Fusion Activity And Inactivation, João Ramalho-Santos, Shlomo Nir, Nejat Düzgüneş, Arsélio Pato De Carvalho, Maria Conceição Pedroso De Lima
A Common Mechanism For Influenza Virus Fusion Activity And Inactivation, João Ramalho-Santos, Shlomo Nir, Nejat Düzgüneş, Arsélio Pato De Carvalho, Maria Conceição Pedroso De Lima
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The fusion of influenza virus (A/PR/8/34 strain) with PC-12 cells was monitored by a fluorescence assay, and the results were analyzed with a mass-action model which could explain and predict the kinetics of fusion. The model accounted explicitly for the reduction in the fusion rate constant upon exposure of the virus to low pH, either for the virus alone in suspension or for the virus bound to the cells. When the pH was lowered without previous viral attachment to cells, an optimal fusion activity was detected at pH 5.2. When the virus was prebound to the cells, however, reduction of …
Simian Immunodeficiency Virus (Siv(Mac)251) Membrane Lipid Mixing With Human Cd4+ And Cd4- Cell Lines In Vitro Does Not Necessarily Result In Internalization Of The Viral Core Proteins And Productive Infection, L. Stamatatos, Nejat Düzgüneş
Simian Immunodeficiency Virus (Siv(Mac)251) Membrane Lipid Mixing With Human Cd4+ And Cd4- Cell Lines In Vitro Does Not Necessarily Result In Internalization Of The Viral Core Proteins And Productive Infection, L. Stamatatos, Nejat Düzgüneş
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The cell binding site of simian immunodeficiency virus (SIV) is believed to be the CD4 molecule. Several CD4+ cell lines are, however, resistant to infection by SIV(mac)251 in vitro and additional cell membrane molecules have been implicated in SIV(mac)251 entry. We investigated the binding, envelope fusion and entry of the viral core proteins (p27) of SIV(mac)251 into two human CD4+ cell lines (H9 and Sup-T1) which are infectible, and one CD4+ (A3.01) and two CD4- cell lines (K562 and Raji) that are resistant to infection. The fusion of the viral and cellular membranes was monitored by a fluorescence assay for …
Anionic Liposomes Inhibit Human Immunodeficiency Virus Type 1 (Hiv-1) Infectivity In Cd4+ A3.01 And H9 Cells, Krystyna Konopka, B. R. Davis, C. E. Larsen, Nejat Düzgüneş
Anionic Liposomes Inhibit Human Immunodeficiency Virus Type 1 (Hiv-1) Infectivity In Cd4+ A3.01 And H9 Cells, Krystyna Konopka, B. R. Davis, C. E. Larsen, Nejat Düzgüneş
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Immunodeficiency viruses undergo fusion with liposomes containing anionic phospholipids (Larsen et al., 1990). We have investigated the effect of liposomes composed of cardiolipin, phosphatidylserine or phosphatidylinositol, on the infectivity of three strains of HIV-1 in A3.01 and H9 cells, measured by p24 (gag) production in the medium. The infectivity of HIV-1 in A3.01 or H9 cells was inhibited by the presence of cardiolipin liposomes during a 2 h infection period, with IC50's of 23.0, 4.8, and 5.0 μM phospholipid, respectively, for the different strains. Liposomes composed of phosphatidylserine or phosphatidylinositol were ineffective under similar conditions. However, prolonged pre-incubation of the …
Fusion Activity And Inactivation Of Influenza Virus: Kinetics Of Low Ph-Induced Fusion With Cultured Cells, Nejat Düzgüneş, Maria C. Pedroso De Lima, L. Stamatatos, D. Flasher, D. R. Alford, Daniel S. Friend, S. Nir
Fusion Activity And Inactivation Of Influenza Virus: Kinetics Of Low Ph-Induced Fusion With Cultured Cells, Nejat Düzgüneş, Maria C. Pedroso De Lima, L. Stamatatos, D. Flasher, D. R. Alford, Daniel S. Friend, S. Nir
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The kinetics of fusion of influenza virus (A/PR/8/34) with human promyelocytic leukaemia (HL-60), human T lymphocytic leukaemia (CEM) and murine lymphoma (S49) cells were investigated. Fusion was demonstrated by electron microscopy, and monitored by fluorescence dequenching of octadecylrhodamine incorporated in the virus membrane. Rapid fusion was induced upon mild acidification of the medium. At pH 5, all virus particles were capable of fusing with the cells. The initial rate and the extent of fusion were maximal between pH 4.9 and 5.2 and declined sharply below and above this range. The rate constants of adhesion of influenza virus to cells or …
Efficacies Of Liposome-Encapsulated Streptomycin And Ciprofloxacin Against Mycobacterium Avium-M. Intracellulare Complex Infections In Human Peripheral Blood Monocyte/Macrophages, S. Majumdar, Diana L. Flasher, Daniel S. Friend, P. Nassos, D. Yajko, W. K. Hadley, Nejat Düzgüneş
Efficacies Of Liposome-Encapsulated Streptomycin And Ciprofloxacin Against Mycobacterium Avium-M. Intracellulare Complex Infections In Human Peripheral Blood Monocyte/Macrophages, S. Majumdar, Diana L. Flasher, Daniel S. Friend, P. Nassos, D. Yajko, W. K. Hadley, Nejat Düzgüneş
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Current treatments of disseminated infection caused by the Mycobacterium avium-M. intracellulare complex (MAC) are generally ineffective. Liposome- mediated delivery of antibiotics to MAC-infected tissues in vivo can enhance the efficacy of the drugs (N. Duzgunes, V. K. Perumal, L. Kesavalu, J. A. Goldstein, R. J. Debs, and P. R. J. Gangadharam, Antimicrob. Agents Chemother. 32:1404-1411, 1988; N. Duzgunes, D. A. Ashtekar, D. L. Flasher, N. Ghori, R. J. Debs, D. S. Friend, and P. R. J. Gangadharam, J. Infect. Dis. 164:143-151, 1991). We investigated the therapeutic efficacies of liposome- encapsulated streptomycin and ciprofloxacin against growth of the MAC inside human …
Enhancement Of Human Immunodeficiency Virus Type 1 Infection By Cationic Liposomes: The Role Of Cd4, Serum And Liposome-Cell Interactions, Krystyna Konopka, L. L. Stamatatos, C. E. Larsen, B. R. Davis, Nejat Düzgüneş
Enhancement Of Human Immunodeficiency Virus Type 1 Infection By Cationic Liposomes: The Role Of Cd4, Serum And Liposome-Cell Interactions, Krystyna Konopka, L. L. Stamatatos, C. E. Larsen, B. R. Davis, Nejat Düzgüneş
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We have reported previously the enhancement of the infectivity of human immunodeficiency virus type 1 (HIV- 1) by liposomes composed of the cationic lipid N[2,3-(dioleyloxy) propyl]-N,N,N-trimethylammonium chloride (DOTMA). To determine the mechanism by which this process occurs, we have investigated the role of CD4, serum concentration and liposome-cell interactions in the DOTMA-mediated stimulation of HIV-1 infection of A3.01 cells. Serum alone significantly inhibited the binding and infectivity of HIV-1, but DOTMA-mediated enhancement of infectivity was more pronounced in the presence of serum than in its absence. HIV-1 binding to cells was increased in the presence of DOTMA liposomes, DEAE-dextran and …
Liposomes Modulate Human Immunodeficiency Virus Infectivity, Krystyna Konopka, B. R. Davis, C. E. Larsen, D. R. Alford, Robert J. Debs, Nejat Düzgüneş
Liposomes Modulate Human Immunodeficiency Virus Infectivity, Krystyna Konopka, B. R. Davis, C. E. Larsen, D. R. Alford, Robert J. Debs, Nejat Düzgüneş
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We have investigated the effects of the fusion of liposomes with human immunodeficiency virus type 1 (HIV-1(LVA)) on the ability of the virus to infect CD4+ and CD4- cells. Fluorescence dequenching measurements indicated that HIV-1 fuses with liposomes composed of either cardiolipin (CL) or N-[2,3-(dioleyloxy) propyl]-N,N,N-trimethyl ammonium chloride (DOTMA) but not appreciably with dioleoylphosphatidylcholine (DOPC) liposomes. Pre-incubation of HIV-1 with DOTMA liposomes enhanced virus production (measured by p24 gag antigen production in the culture medium and in situ) in CD4+ A3.01 and H9 cells in a concentration-dependent manner, but did not mediate the infection of the CD4- cell line, K562. …
Fusion Of Simian Immunodeficiency Virus With Liposomes And Erythrocyte Ghost Membranes: Effects Of Lipid Composition, Ph And Calcium, Charles E. Larsen, D. R. Alford, L. J.T. Young, T. P. Mcgraw, Nejat Düzgüneş
Fusion Of Simian Immunodeficiency Virus With Liposomes And Erythrocyte Ghost Membranes: Effects Of Lipid Composition, Ph And Calcium, Charles E. Larsen, D. R. Alford, L. J.T. Young, T. P. Mcgraw, Nejat Düzgüneş
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Simian immunodeficiency virus from macaques (SIV(mac)) is closely related in its structure and biological activity to human immunodeficiency virus, and is the best animal model for the acquired immunodeficiency syndrome. We investigated the kinetics of membrane fusion between SIV(mac) and phospholipid vesicles and the effects of various parameters on this process. Purified SIV(mac) was labelled with octadecyl rhodamine B chloride, and fusion was continuously monitored as the dilution of the probe in target membranes. These studies show that SIV(mac) fusion is strongly dependent upon the liposome composition. Fusion with pure cardiolipin (CL) liposomes is significantly faster than with CL/dioleoylphosphatidylcholine (DOPC) …
Enhanced Effect Of Liposome-Encapsulated Amikacin On Mycobacterium Avium-M. Intracellulare Complex Infection In Beige Mice, Nejat Düzgüneş, Veluchamy K. Perumal, L. Kesavalu, Jayne A. Goldstein, Robert J. Debs, Pattisapu R.J. Gangadharam
Enhanced Effect Of Liposome-Encapsulated Amikacin On Mycobacterium Avium-M. Intracellulare Complex Infection In Beige Mice, Nejat Düzgüneş, Veluchamy K. Perumal, L. Kesavalu, Jayne A. Goldstein, Robert J. Debs, Pattisapu R.J. Gangadharam
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We examined the therapeutic effects of free and liposome-encapsulated amikacin on Mycobacterium avium-M. intracellulare complex infection by using the beige-mouse model of the disease. In the first series of studies, intravenous administration of four weekly doses of 5 mg of amikacin per kg encapsulated in large (approximately 0.4-μm diameter), unilamellar liposomes arrested the growth of M. avium-M. intracellulare complex organisms in the liver, as measured by CFU counts. M. avium-M. intracellulare complex levels in untreated animals and in those treated with the same dose of free amikacin increased by several orders of magnitude over 8 weeks. Liposome-encapsulated amikacin was also …
La3+-Induced Fusion Of Phosphatidylserine Liposomes. Close Approach, Intermembrane Intermediates, And The Electrostatic Surface Potential, Joe Bentz, D. R. Alford, J. Cohen, Nejat Düzgüneş
La3+-Induced Fusion Of Phosphatidylserine Liposomes. Close Approach, Intermembrane Intermediates, And The Electrostatic Surface Potential, Joe Bentz, D. R. Alford, J. Cohen, Nejat Düzgüneş
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The fusion of large unilamellar phosphatidylserine liposomes (PS LUV) induced by La3+ has been monitored using the 1-aminoapthalene-3,6,8-trisulfonic acid/p-xylenebis(pyridinium bromide) (ANTS/DPX) fluorescence assay for the mixing of aqueous contents. The fusion event is extensive and nonleaky, with up to 95% mixing of contents in the fused liposomes. However, addition of excess EDTA leads to disruption of the fusion products in a way that implies the existence of metastable intermembrane contact sites. The maximal fusion activity occurs between 10 and 100 microM La3+ and fusion can be terminated rapidly, without loss of contents, by the addition of excess La3+, e.g., 1 …
Ph-Sensitive Liposomes Mediate Cytoplasmic Delivery Of Encapsulated Macromolecules, Robert M. Straubinger, Nejat Düzgüneş, Demetrios Papahadjopoulos
Ph-Sensitive Liposomes Mediate Cytoplasmic Delivery Of Encapsulated Macromolecules, Robert M. Straubinger, Nejat Düzgüneş, Demetrios Papahadjopoulos
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Negatively charged liposomes are endocytosed by the coated vesicle system and accumulate in acidic intracellular vesicles. Liposomes that become unstable at acidic pH improve cytoplasmic delivery of membraneimpermeant macromolecules such as calcein (CAL) and FITC dextran (18 or 40 kDa). Oleic acid (OA): phosphatidylethanolamine (PE) (3:7 mole ratio) liposomes become permeable to CAL at pH < 7.0. Control liposomes of phosphatidylserine : PE or OA : phosphatidylcholine are stable at pH 4-8. OA:PE liposomes promote cytoplasmic delivery of encapsulated CAL to CV-1 cells, as evidenced by the emergence of diffuse, cytoplasmic CAL fluorescence. Delivery requires metabolic energy and is partially inhibited by chloroquine or monensin, which raise the pH of intracellular vesicles. © 1985.
Interaction Of Phosphatidylserine-Phosphatidylcholine Liposomes With Sickle Erythrocytes. Evidence For Altered Membrane Surface Properties, R. S. Schwartz, Nejat Düzgüneş, D. Tsun Yee Chiu, B. Lubin
Interaction Of Phosphatidylserine-Phosphatidylcholine Liposomes With Sickle Erythrocytes. Evidence For Altered Membrane Surface Properties, R. S. Schwartz, Nejat Düzgüneş, D. Tsun Yee Chiu, B. Lubin
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The sickle erythrocyte (RBC) is a pathologic RBC that contains multiple membrane abnormalities. Some of these abnormalities have been implicated in the pathophysiology of vasoocclusive crises characteristic of sickle cell disease; others have yet to be defined in terms of their clinical significance. Recent information has shown that sickle RBC adhere abnormally to cultured endothelial cells yet little is known about the ways in which sickle cells interact with model membranes of defined size and lipid composition. We investigated this phenomenon by interacting sickle RBC with artificial lipid vesicles (liposomes) containing acidic phospholipids. Our results demonstrate that sickle disease (hemoglobin …
Fusion Of Phospholipid Vesicles Arrested By Quick-Freezing. The Question Of Lipidic Particles As Intermediates In Membrane Fusion, E. L. Bearer, Nejat Düzgüneş, Daniel S. Friend, Demetrios Papahadjopoulos
Fusion Of Phospholipid Vesicles Arrested By Quick-Freezing. The Question Of Lipidic Particles As Intermediates In Membrane Fusion, E. L. Bearer, Nejat Düzgüneş, Daniel S. Friend, Demetrios Papahadjopoulos
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We have examined the early events in Ca2+-induced fusion of large (0.2 μm diameter) unilamellar cardiolipin/phosphatidylcholine and phosphatidylserine/phosphatidylethanolamine vesicles by quick-freezing freeze-fracture electron microscopy, eliminating the necessity of using glycerol as a cryoprotectant. Freeze-fracture replicas of vesicle suspensions frozen after 1-2 s of stimulation revealed that the majority of vesicles had already undergone membrane fusion, as evidenced by dumbbell-shaped structures and large vesicles. In the absence of glycerol, lipidic particles or the hexagonal HII phase, which have been proposed to be intermediate structures in membrane fusion, were not observed at the sites of fusion. Lipidic particles were evident in less …
Synexin Facilitates Fusion Of Specific Phospholipid Membranes At Divalent Cation Concentrations Found Intracellularly., K. Hong, Nejat Düzgüneş, R. Ekerdt, Demetrios Papahadjopoulos
Synexin Facilitates Fusion Of Specific Phospholipid Membranes At Divalent Cation Concentrations Found Intracellularly., K. Hong, Nejat Düzgüneş, R. Ekerdt, Demetrios Papahadjopoulos
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The effect of synexin (an adrenal medullary protein) on the kinetics of Ca2+- and Mg2+-mediated membrane fusion was examined. Membrane fusion was studied by monitoring intermixing of the aqueous contents of phospholipid vesicles. Synexin facilitated Ca2+-mediated, but not Mg2+-mediated, fusion of phosphatidate/phosphatidylethanolamine (1:3) and phosphatidate/phosphatidylserine/phosphatidylethanolamine/cholesterol (1:2:3:2) vesicles. The threshold concentration of Ca2+ for fusion was decreased to approximately equal to 10 microM in the presence of synexin at 6 micrograms/ml and 1.5 mM Mg2+ in vesicle suspensions containing 50 microM lipid. This effect of synexin was drastically inhibited by including 25% phosphatidylcholine (mol/mol) in the vesicle membrane. It is proposed …
Modulation Of Membrane Fusion By Calcium-Binding Proteins, K. Hong, Nejat Düzgüneş, Demetrios Papahadjopoulos
Modulation Of Membrane Fusion By Calcium-Binding Proteins, K. Hong, Nejat Düzgüneş, Demetrios Papahadjopoulos
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The effects of several Ca2+-binding proteins (calmodulin, prothrombin, and synexin) on the kinetics of Ca2+-induced membrane fusion were examined. Membrane fusion was assayed by following the mixing of aqueous contents of phospholipid vesicles. Calmodulin inhibited slightly the fusion of phospholipid vesicles. Bovine prothrombin and its proteolytic fragment 1 had a strong inhibitory effect on fusion. Depending on the phospholipid composition, synexin could either facilitate or inhibit Ca2+-induced fusion of vesicles. The effects of synexin were Ca2+ specific. 10 microM Ca2+ was sufficient to induce fusion of vesicles composed of phosphatidic acid/phosphatidylethanolamine (1:3) in the presence of synexin and 1 mM …