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N Hogg

Publications and source records attributed to N Hogg.

At least 91 records · Page 5Linked to original sources
PubMed1996

Characterization of sulfur-centered radical intermediates formed during the oxidation of thiols and sulfite by peroxynitrite. ESR-spin trapping and oxygen uptake studies.

Using a novel phosphorylated spin trap, 5-diethoxy-phosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO), an analog of the commonly used trap 5,5'-dimethyl-1-pyrroline N-oxide (DMPO), we have investigated the reactions of sulfur-centered radicals produced from the oxidation of thiols and sulfite by peroxynitrite. The predominant species trapped in all cases are the corresponding sulfur-centered radicals, i.e. glutathionyl radical (GS) from glutathione (GSH), N-acetyl-DL-penicillamine thiyl radical (S-NAP) from N-acetyl-DL-penicillamine (NAP) and sulfate anion radical (SO3-) from sulfite. These radicals consume molecular oxygen forming either peroxyl or superoxide anion radicals. GS, S-NAP, and (SO3-)-derived radicals react with ammonium formate to form the carbon dioxide anion radical (CO2-). Further support of spin adduct assignments and radical reactions are obtained from photolysis of S-nitrosoglutathione and S-nitroso-N-acetyl-DL-penicillamine. We conclude that the direct reaction of peroxynitrite with thiols and sulfate forms thiyl and sulfate anion radicals, respectively, by a hydroxyl radical-independent mechanism. Pathological implications of thiyl radical formation and subsequent oxyradical-mediated chain reactions are discussed. Oxygen activation by thiyl radicals formed during peroxynitrite-mediated oxidation of glutathione may limit the effectiveness of GSH against peroxynitrite-mediated toxicity in cellular systems.

Cyclic N-Oxides↗
PubMed1996

T cell adhesion to intercellular adhesion molecule-1 (ICAM-1) is controlled by cell spreading and the activation of integrin LFA-1.

Many leukocyte integrins require activation before they can adhere to their ligands. For example, stimulation of T cells enables the integrin LFA-1 to bind to ligand. This study compares two well known protocols for inducing T cell LFA-1 mediated adhesion to intercellular adhesion molecule-1 (ICAM)-1. We how that treatment with high concentrations of the divalent cation Mg2+ induces a high affinity state of LFA-1, which is reflected in the binding of soluble ICAM-1 and correlates with the expression of the epitope recognized by mAb 24. The second stimulation protocol with the phorbol ester phorbol-12,13-dibutyrate (PDBu) does not induce a high affinity state of LFA-1, and in this situation, adhesion is dependent on cell spreading and intracellular events involving protein kinase C, [Ca2+]i, and actin polymerization. These low affinity LFA-1 receptors are responsible for the initial contact with immobilized ligand because, unlike the Mg2+-stimulated receptors, adhesion is not blocked by soluble ICAM-1. Finally, we used a third method of inducing LFA-1-mediated adhesion by stimulation of T cells through the TCR/CD3 complex. This procedure, which is considered to be a more physiologic trigger for LFA-1 activation, resembles the phorbol ester protocol in that high affinity LFA-1 receptors are not induced and cell adhesion depends on involvement of the cytoskeleton and cell spreading.

Antibodies, Monoclonal↗
PubMed1996

The beta 2 integrin Mac-1 but not p150,95 associates with Fc gamma RIIA.

In this study we have compared the ligand binding activity of the two closely related beta 2 integrins, Mac-1 and p150,95, which are expressed separately as receptors permanently transfected into K562 cells. Mac-1 has previously been shown to associate with Fc gamma R, particularly Fc gamma RIII, but K562 cells express only endogenous Fc gamma RIIA. We have, therefore, taken advantage of this situation to examine a possible relationship between Fc gamma RIIA with Mac-1 and p150,95 in the absence of other Fc gamma R. The main finding is that anti-Fc gamma RII mAb have a profound inhibitory effect on cell adhesion mediated by Mac-1, but not on the adhesion mediated by p150,95. Thus, in spite of the fact that Mac-1 and p150,95 bind to the same or at least a very similar selection of ligands, their association with other receptors on the cellular membrane, and therefore their mode of regulation may be different.

Antibodies, Monoclonal↗
PubMed1996

Where the outside meets the inside: integrins as activators and targets of signal transduction cascades.

In fibroblasts, signaling through the adhesion receptors known as integrins synergizes with other cellular stimulators such as the growth factors. There is currently great interest in the details of the ensuing 'outside in' signal transduction mechanisms, and the focal adhesion kinase in particular, has been a focus of attention. Less is understood of signalling through integrins on leukocytes which also perform a costimulator role. The activity of these leukocyte integrins is not constitutive but is initiated via signalling through other receptors, termed 'inside out' signalling. These signals cause movement and clustering of integrins in the membrane leading to strengthened adhesion between cells.

Cell Adhesion↗
PubMed1995

Interaction of nitric oxide with photoexcited rose bengal: evidence for one-electron reduction of nitric oxide to nitroxyl anion.

The interaction of nitric oxide (.NO) with Rose Bengal (RB) in the presence of electron donors was investigated. Upon illumination of a mixture of RB and .NO with visible light, an enhancement in the rate of .NO consumption was observed that increased with increasing RB concentration. In the presence of electron donors (NADH, glutathione, or ascorbate), the rates of .NO depletion increased further. NADH enhanced .NO depletion to a greater extent than either glutathione or ascorbate. Photoactivated RB under anaerobic conditions reacts with NADH to form the RB anion radical (RB.-), which has a characteristic visible absorption band centered at 418 nm. Rose Bengal anion radical disporportionates to give RB and a colorless reduced form of RB, RBH-. The net result of this process is the photobleaching of RB. The presence of .NO during irradiation of RB and NADH introduced a lag time into the kinetics of RB photobleaching. The length of this lag time was proportional to the concentration of .NO. A similar lag time, which was also dependent on the .NO concentration, was observed in the kinetics of formation of RB.-. The three-line electron spin resonance (ESR) spectrum of RB.-, with an intensity ratio 1:2:1, was obtained during irradiation of RB and NADH under anaerobic conditions. .NO introduced a concentration-dependent lag time into the kinetics of the appearance of this ESR signal. We propose that .NO oxidizes RB.- to regenerate RB and thus inhibit photobleaching until .NO is consumed. This reaction predicts the formation of NO-, the one-electron reduced form of .NO. Nitrous oxide, a characteristic dimerization product of NO-, was detected by gas chromatography. This evidence indicates the occurrence of a Type I mechanism between photoactivated RB and .NO.

Anions↗
PubMed1995

The S100 family protein MRP-14 (S100A9) has homology with the contact domain of high molecular weight kininogen.

The heterodimeric molecule MRP-8/MRP-14 (S100A8/S100A9) is abundantly expressed in circulating monocytes and neutrophils. We report here an homology between the C-terminal 'tail' region of MRP-14 (S100A9) and sequences within the plasma protein, high molecular weight kininogen (HMWK) which are involved in binding to negatively charged surfaces such as kaolin. MRP-14 also binds to kaolin and is competitively inhibited by HMWK and by peptides corresponding to MRP-14 tail and the HMWK 'contact' regions. Furthermore both MRP-14 and the tail peptide inhibit the coagulation cascade in vitro giving functional relevance to the homology between MRP-14 and HMWK. At inflammatory sites, MRP-8/14 is localised to areas of close contact between myeloid cells and endothelium. The results of this study identify a potential binding region in MRP-14 and suggest that it could function by interfering with fibrin formation at sites of leukocyte transendothelial migration.

Amino Acid Sequence↗
PubMed1995

Spin-labeling study of the oxidative damage to low-density lipoprotein.

In this study, we have spin-labeled the lysine and cysteine residues of low-density lipoprotein (LDL) using N-4-(2,2,6,6-tetramethylpiperidinyl-1-oxyl-4-yl) maleimide (MAL-6) and succinimidyl-2,2,5,5-tetramethyl-3-pyrroline-1-oxyl-3-carboxylate (SSL), respectively. The electron spin resonance (ESR) spectrum of SSL bound to LDL indicated that the nitroxide moiety was relatively mobile. In contrast, the ESR spectrum of MAL-6 bound to LDL showed that the nitroxide moiety was rotationally restricted. Using the continuous-wave power saturation technique in the presence of hydrophobic and hydrophilic paramagnetic relaxing agents, we have determined that (i) approximately 60-70% of lysine-bound SSL is exposed to the aqueous phase, (ii) approximately 30-40% of SSL-LDL is buried in a hydrophobic region, and (iii) MAL-6 bound to LDL is localized predominantly in the hydrophobic region. During Cu(2+)-initiated oxidation of spin-labeled LDL, nitroxide labels located in a hydrophobic environment were predominantly degraded. Nitroxide destruction was inhibited by butylated hydroxytoluene, indicating the role of lipid peroxidation in this process. ESR data also showed that Cu2+ binding to lysine is essential for LDL oxidation. The spin label methodology may be useful for the investigation of site-specific radical reactions in LDL.

Apolipoproteins B↗
PubMed1995

Nitric oxide donor compounds inhibit the toxicity of oxidized low-density lipoprotein to endothelial cells.

Photo-oxidized low-density lipoprotein is cytotoxic to bovine aortic endothelial cells in a concentration-dependent manner. Total cell killing occurs at a concentration of 600 mumol/l lipid hydroperoxide (LOOH). Selenium deficiency enhances the toxicity of LOOH such that 300 mumol/l LOOH is cytotoxic. This toxicity is inhibited by desferrioxamine, a transition metal ion chelator, and by butylatedhydroxytoluene, a potent inhibitor of lipid peroxidation. Toxicity is also inhibited by the nitric oxide donors S-nitrosoglutathione and spermine NONOate but not by reduced or oxidized glutathione and spermine. We propose that nitric oxide, released from these compounds, is inhibiting the toxicity of LOOH to selenium-deficient endothelial cells. Furthermore we hypothesize that the mechanism for this inhibition of toxicity is the scavenging of the propagatory peroxyl and alkoxyl free radicals, by nitric oxide, that are generated during peroxidation of cell membranes.

Animals↗
PubMed1995

Photosensitized decomposition of S-nitrosothiols and 2-methyl-2-nitrosopropane. Possible use for site-directed nitric oxide production.

Irradiation of S-nitrosoglutathione (GSNO) with light (lambda = 550 nm) resulted in the homolytic decomposition of GSNO to generate glutathionyl radical (GS.) and nitric oxide (.NO), which were monitored by ESR spectrometry. Inclusion of Rose Bengal (RB) resulted in a 9-fold increase in the quantum yield for .NO production and also an increase in the rate of thiyl radical formation. The bimolecular rate constant for the interaction of triplet RB with GSNO has been estimated to be approximately 1.2 x 10(9) M-1s-1 by competition with oxygen. Hematoporphyrin (HP) also enhanced the rate of .NO production by 2-3-fold. 2-Methyl-2-nitrosopropane (MNP) decomposed on irradiation (lambda = 660 nm) to form .NO and tert-butyl radical. Aluminum phthalocyanine tetrasulphonate enhanced the rate of decomposition of MNP by 10-fold. These studies show that photosensitizers enhance the release of .NO from donor compounds.

Electron Spin Resonance Spectroscopy↗
PubMed1995

Analysis of the binding site on intercellular adhesion molecule 3 for the leukocyte integrin lymphocyte function-associated antigen 1.

Intercellular adhesion molecule 3 (ICAM-3, CD50) is a member of the immunoglobulin superfamily and is a constitutively expressed ligand for the leukocyte integrin LFA-1 (CD11a/CD18). ICAM-3 is expressed at high levels by all resting leukocyte populations and antigen presenting cells and is a major ligand for LFA-1 in the resting immune system. ICAM-3 is a signal transducer and may play a key role in initiating immune responses. Mutant ICAM-3 Fc-chimeric proteins were quantitatively analyzed for their ability to bind COS cells expressing human LFA-1. The LFA-1-binding site on ICAM-3 is located in the N-terminal 2 Ig domains. Domains 3-5 do not significantly contribute to adhesion. The binding site has been further resolved by rational targeting of 14 point mutations throughout domains 1 and 2, coupled with modeling studies. Within domain 1 a cluster of residues (Glu37, Leu66, Ser68, and Gln75), that are predicted to lie on the CC'FG face of the Ig fold, play a dominant role in LFA-1 binding.

Amino Acid Sequence↗
PubMed1995

Antibodies that activate beta 2 integrins can generate different ligand binding states.

A human erythroleukemic cell line (K562) that does not normally express beta 2 integrins has been transfected with the genes encoding these integrins. The resulting cell lines show minimal background adhesion but can be stimulated to bind to appropriate substrates when activated with either of two different antibodies to CD18. The two antibodies appear to generate different ligand binding states in LFA-1 such that different members of the ICAM family are recognized. Antibody-activated complement receptor type 3 and p150,95-transfected cells bind protein-coated surfaces, although they require slightly different activation conditions for optimal binding.

Antibodies, Monoclonal↗
PubMed1995

Leukocyte integrins.

Lymphocytes, monocytes and granulocytes, which are collectively known as 'leukocytes', circulate primarily within the vascular system and lymphoid tissue but are found in essentially all tissues of the body. This mobile lifestyle necessitates the constant making and breaking of adhesive contacts with targets in their immediate environment. The adhesion receptors termed integrins, which are expressed in abundance by leukocytes, are well suited to carry out the transient interactions in which these cells engage. Major advances in the leukocyte integrin field this year have been the realization of the extensive roles for alpha 4 integrins in leukocyte function, the solution of the crystal structure of an I domain and its identification as a major ligand-binding site, and the initial understanding of how divalent cations may function in an active integrin.

Cell Adhesion↗
PubMed1995

Trapping of nitric oxide formed during photolysis of sodium nitroprusside in aqueous and lipid phases: an electron spin resonance study.

Photolytic decomposition of sodium nitroprusside (SNP), a widely used nitrovasodilator, produced nitric oxide (.NO), which was continuously monitored by electron spin resonance (ESR) spectroscopy. The .NO present in the aqueous or the lipid phase was trapped by either a hydrophilic or a hydrophobic nitronyl nitroxide, respectively, to form the corresponding imino nitroxide. The conversion of nitronyl nitroxide to imino nitroxide was monitored by ESR spectrometry. The quantum yield for the generation of .NO from SNP, measured from the rate of decay of nitronyl nitroxide, was 0.201 +/- 0.007 and 0.324 +/- 0.01 (mean +/- SD, n = 3) at 420 nm and 320 nm, respectively. The action spectrum for .NO generation was found to overlap the optical absorption spectrum of SNP closely. A mechanism for the reaction between SNP and nitronyl nitroxide in the presence of light is proposed and computer-aided simulation of this mechanism using published rate constants agreed well with experimental data. The methodology described here may be used to assay .NO production continuously during photoactivation of .NO donors in aqueous and lipid environments. Biological implications of this methodology are discussed.

Electron Spin Resonance Spectroscopy↗
PubMed1995

Reactions of nitric oxide with nitronyl nitroxides and oxygen: prediction of nitrite and nitrate formation by kinetic simulation.

Nitric oxide reacts with nitronyl nitroxides (NNO) to form imino nitroxides (INO) and this transformation can be monitored using electron spin resonance spectroscopy. Recently, Akaike et al., reported that NNO such as 2-phenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl (PTIO) and its derivatives (e.g., carboxy-PTIO) react with nitric oxide (.NO) in a 1:1 stoichiometry forming 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl (PTI) or the respective product (e.g., carboxy-PTI) together with nitrite and nitrate (Akaike et al., Biochemistry 32, 827-332, 1993). In this paper, we reevaluate their results and show that the stoichiometry of the reaction between PTIO and .NO is 0.63 +/- 0.06:1.0. The reason for this discrepancy is due to an erroneous assumption by Akaike et al., that the stoichiometry for the reaction between .NO and O2 is 2:1 in aqueous solution. If the data reported by Akaike et al., were recalculated using a 4:1 stoichiometry established for the aqueous oxidation of .NO, the reaction between .NO and PTIO would give a stoichiometry of 0.5:1.0 in closer agreement with our data. We propose mechanism for the reaction between PTIO and .NO in aqueous solution. This mechanism predicts that the stoichiometry between carboxy-PTIO and .NO is dependent on the rate of generation of .NO and is 1:1 only at low rates of .NO generation (i.e., 10(-13) M/s). However the stoichiometry approaches 0.5:1.0 at higher rates of .NO production or when it is added as a bolus. The ratio between nitrite and nitrate also varies as a function of the rate of generation of .NO. The model agrees with previous experimental observations that the aqueous oxidation of .NO in air saturated solutions will exclusively form nitrite and predicts that .NO will only generate substantial amounts of nitrate if it is released at a rate less than 10(-17) M/s. This may have important consequences in cellular systems where the concentration of .NO is typically measured from nitrite production.

Benzoates↗
PubMed1995

Inhibition of macrophage-dependent low density lipoprotein oxidation by nitric-oxide donors.

We have previously shown that nitric oxide donors inhibit the oxidation of low density lipoprotein (LDL) initiated by copper ions or by azo-bis-amidinopropane (Hogg et al., 1993. FEBS Lett. 334: 170-174). In this study, the nitric oxide donors S-nitroso-N-acetylpenicillamine (SNAP), spermine NONOate, and sodium nitroprusside were tested for their ability to inhibit macrophage-dependent oxidation of LDL. SNAP and spermine NONOate inhibited macrophage-dependent oxidation of LDL in a time- and concentration-dependent manner. We propose that nitric oxide is acting as a chain-breaking antioxidant that can inhibit the progression of lipid peroxidation in cell dependent-oxidation of LDL. By this mechanism nitric oxide could be an endogenous defense against atherogenesis. In contrast, sodium nitroprusside enhanced cell-mediated oxidation of LDL by a mechanism dependent on superoxide production and transition metal ions. Sodium nitroprusside also enhanced LDL oxidation by cell culture medium alone by a similar mechanism. The use of sodium nitroprusside as a nitric oxide donor in cellular systems appears to be complicated by the release of iron leading to an enhanced oxidative stress. Thus the effects of sodium nitroprusside in such systems may be unrelated to nitric oxide release.

Animals↗
PubMed1995

Role of apolipoprotein B-derived radical and alpha-tocopheroxyl radical in peroxidase-dependent oxidation of low density lipoprotein.

The peroxidation of low density lipoprotein (LDL) may play an important role in the modification of the lipoprotein to an atherogenic form. The oxidation of LDL by peroxidases has recently been suggested as a model for in vivo transition metal ion-independent oxidation of LDL (Wieland, E., S. Parthasarathy, and D. Steinberg. 1993. Proc. Natl. Acad. Sci. USA. 90: 5929-5933). It is possible that in vivo the peroxidase activities of proteins, such as prostaglandin synthase and myeloperoxidase, promote LDL oxidation. We have used horseradish peroxidase (HRP) and H2O2 as a model of peroxidase-dependent oxidation of LDL and we observed the following during HRP/H2O2-initiated LDL oxidation. i) The oxidation of alpha-tocopherol occurred with the concomitant formation of alpha-tocopheroxyl radical. This was followed by the production of an apolipoprotein B (apoB)-derived radical. The apoB radical and the alpha-tocopheroxyl radical were formed under both aerobic and anaerobic conditions. ii) Inclusion of N-t-butyl-alpha-phenylnitrone (PBN) did not inhibit alpha-tocopheroxyl radical formation. The ESR spectrum of a PBN/LDL-lipid derived adduct was observed after prolonged incubation. iii) There was formation of conjugated dienes, lipid hydroperoxides and thiobarbituric acid reactive substances. Our data indicate that HRP/H2O2 oxidizes both alpha-tocopherol and apoB to the corresponding radicals and concomitantly initiates lipid peroxidation.

Apolipoproteins B↗