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Biomedical subjects

G Weissmann

Publications and source records attributed to G Weissmann.

At least 163 records · Page 9Linked to original sources
PubMed1982

The effects of retinoids on neutrophil functions in vitro.

Vitamin A (retinol) and its analogues (retinoids) are clinically effective in cystic acne and psoriasis, diseases in which neutrophils may constitute major components of inflammatory cell infiltrates. We found that the earliest histopathologic alteration in psoriasis is the disappearance of neutrophils at 2 to 4 weeks after the initiation of therapy with etretinate. Since retinoids may exert anti-inflammatory effects by virtue of an action upon neutrophils, we studied the effects of the following retinoids on discrete neutrophil functions in vitro: retinol, retinyl acetate, retinal, tretinoin, isotretinoin, etretinate, and Ro 10-1670. Although they had no significant effects upon aggregation, chemokinesis, or chemotaxis, all of the retinoids, with the exception of etretinate and Ro 10-1670, profoundly inhibited superoxide anion production and lysosomal enzyme release. Tretinoin and isotretinoin were the most effective inhibitors. We propose that these drugs exert their pharmacologic effects (resolution of inflammatory lesions) by inhibiting the release of mediators of inflammation and by preventing the accumulation of neutrophils in acne lesions when applied topically or systemically, respectively.

Cell Aggregation↗
PubMed1982

Degranulation, membrane addition, and shape change during chemotactic factor-induced aggregation of human neutrophils.

Neutrophils stimulated by the chemotactic factor formyl-methionyl-leucyl-phenyl-alanine (FMLP) undergo a transient change in surface properties that permits the cells to adhere more readily to surfaces and to each other. This transient change can be monitored by light scattering as stimulated neutrophils form aggregates while stirred in a platelet aggregometer. Maximum change in light scattering occurs within 1 min and correlates with an increase in the percentage of cells that are in aggregates of four or more cells and a decrease in the percentage of single cells. With time (3-5 min), small aggregates disappear and single cells reappear. The transient change in adhesiveness is accompanied by a persistent change in cell shape; the cells become polarized and protrude ruffles from one sector of the cell surface. During aggregation the cells adhere to one another with smooth sides together and ruffles pointed outward. During disaggregation the cells dissociate laterally with the simultaneous internalization of membrane in the region opposite the ruffles. Particle bound to the surface by charge (thorotrast, cationized ferritin) are concentrated and internalized in this region. The change in cell shape from round to ruffled occurs within seconds, suggesting that membrane is added to the cell surface from an intracellular store. We therefore quantified surface membrane by electron microscopy morphometry and measured a 25% increase within 10 s of adding FMLP. The source of new membrane appeared to be the specific granule membrane since the kinetics of granule discharge (between 30% and 50% of all release occurs in the first 10 s) correlate with the appearance of new membrane. Furthermore, the amount of membrane that appears at the cell surface at 10 s correlates with that lost from intracellular granules in that time. Chemotaxin-induced aggregation thus begins with granule discharge and membrane addition followed by protrusion of ruffles. Adherence is maximal at 60 s and the gradual loss of adhesiveness that follows is associated with uropod formation and enhanced endocytic activity.

Cell Adhesion↗
PubMed1982

Neutrophils: release of mediators of inflammation with special reference to rheumatoid arthritis.

The encounter of neutrophils with immune complexes and complement components, in the bulk phase or on a surface, leads to their secretion of lysosomal hydrolases, especially neutral proteases, which provoke tissue injury. Secretion of lysosomal enzymes and generation of reactive oxygen species (e.g., O(2)) is part of a stimulus-secretion response to a variety of secretagogues, including immune complexes and complement components. However, the pathways of secretion and O(2) generation are stimulus-specific and can be dissected to establish cause and effect relationships by means of: a) kinetic analysis, b) variations in the stimulus, and c) use of impermeant reagents to block discrete responses. Neutrophils also generate products of 11-cyclooxygenase (e.g., PGE2, TxA2) and of the 5-and 15-lipoxygenases (mono-, di-, and tri-HETEs, LTB4, and their isomers). But the cyclooxygenase products (save TxA2) are not phlogistic by themselves: they inhibit the functions of neutrophils, platelets, macrophages, and mast cells. The most potent pro-inflammatory agent yet identified as a product of arachidonate is LTB4. LTB4 is a potent Ca ionophore, constricts airways, is a potent chemoattractant, and induces local inflammation.

Animals↗
PubMed1982

Ceruloplasmin: an acute phase reactant that scavenges oxygen-derived free radicals.

Superoxide anion radicals have been implicated recently as mediators of inflammation and tissue injury. Protection from superoxide anion radicals is provided primarily by a copper-containing, intracellular enzyme (superoxide dismutase) (SOD) that catalyzes the dismutation of superoxide to hydrogen peroxide and oxygen. We have found that the action of cytoplasmic SOD to scavenge superoxide and thereby to inhibit superoxide-mediated reactions can be mimicked by the copper-containing plasma protein and acute-phase reactant, ceruloplasmin. Ceruloplasmin, at concentrations present in normal plasma, inhibited reduction of both cytochrome c and nitroblue tetrazolium (NBT) mediated by the aerobic action of xanthine oxidase on hypoxanthine (a superoxide-generating system). Ceruloplasmin neither inhibited formation of uric acid by xanthine oxidase nor accelerated autooxidation of cytochrome c. Furthermore, in an experimental system in which contact between ceruloplasmin and indicator was prevented by a relatively impermeable lipid membrane barrier, ceruloplasmin inhibited reduction of NBT trapped within liposomes exposed to xanthine oxidase and hypoxanthine. Ceruloplasmin also inhibited reduction of cytochrome c and NBT mediated by the aerobic action of xanthine oxidase on acetaldehyde (another superoxide-generating system) and mimicked the activity of purified human erythrocyte SOD by inhibiting photoreduction of NBT and by accelerating aerobic photooxidation of dianisidine. Ceruloplasmin could be separated from purified human erythrocyte SOD by electrophoresis on alkaline 12% polyacrylamide gels and identified by its superoxide-scavenging activity. These results suggest that ceruloplasmin may function as a circulating scavenger of oxygen-derived free radicals.

Acute Disease↗
PubMed1982

Stimulus-secretion coupling in the human neutrophil: the role of phosphatidic acid and oxidized fatty acids in the translocation of calcium.

Neutrophils, stimulated via their surface receptors by ligands such as f-Met-Leu-Phe or immune complexes, release membrane calcium from intracellular stores and accumulate calcium from the extracellular medium. Both mechanisms provide for a rise in the intracellular concentration of free calcium which appears to be required for later responses of the cell: release of lysosomal enzymes and the generation of superoxide anion as neutrophils undergo an aggregation response. Exogenous ionophores, such as A23187 and PGBx, which move calcium bidirectionally across lipid bilayers, bypass the ligand-receptor step, thereby providing the necessary rise in intracellular calcium. In the course of the remodeling of membrane lipids--within 5 sec after their exposure to a stimulus--neutrophils generate phosphatidic acid, at least in part at the expense of phosphatidyl inositol. Because phosphatidic acid is the only phospholipid whose action in model membranes mimics the action of exogenous ionophores (as it is formed early enough and in sufficient quantities to account for uptake of extracellular calcium), we propose phosphatidic acid as a promising candidate for the role of endogenous ionophore. This ionophoretic action may serve to amplify signals launched by primary changes at the plasma membrane from whence calcium is mobilized during stimulus-secretion coupling. The release of oxidation products of arachidonic acid, be it via the cyclo-oxygenase or lipoxygenase pathway, is a concomitant of neutrophil activation. Indeed, the pathways by which oxidative products of arachidonate are formed may also be influenced by stimulus-specific changes in membrane phospholipids, not the least interesting of which is the generation of phosphatidic acid.

Arachidonate Lipoxygenases↗
PubMed1982

Activation of the human neutrophil: the roles of lipid remodeling and intracellular calcium.

The stimulus-response coupling sequence of neutrophils has been partially elucidated, and a temporal order for some of the initial events in PMN activation has been established; membrane potential, Ca2+ motivation, Ca2+ influx, cAMP pulse, aggregation, O2- . generation and degranulation. Receptor-ligand interaction is followed by membrane hyperpolarization and the mobilization of Ca2+ from intracellular loci. In common with other secretory cells, neutrophils utilize Ca2+ as a second messenger to mediate cellular responses. For optimal activation, neutrophils require an influx of extracellular Ca2+. However, the mechanism by which Ca2+ enters neutrophils or other cells is not known. In view of our recent findings that phosphatidic acid and oxidized trienoic acids can translocate Ca2+ in lipid bilayers, it should be apparent that a study of phospholipid metabolism (particularly changes in phosphatidyl inositol and phosphatidic acid) in human neutrophil activation together with a temporal analysis of Ca2+ influx will contribute to an understanding of the mechanism of stimulus-secretion coupling. Since arachidonic acid metabolites play an important role in inflammation and have recently been suspected of modulating stimulus-secretion coupling, studies of the release of arachidonic acid from membrane phospholipids are important because all prostaglandins and hydroxy acids are derived from this initial step. Finally, the generation, by neutrophils, of free arachidonic acid and its oxygenation products might serve as a model system for other tissues in addition to their important role in inflammation.

Arachidonic Acids↗
PubMed1981

Phosphatidate and oxidized fatty acids are calcium ionophores. Studies employing arsenazo III in liposomes.

Liposomes which have entrapped the metallochromic dye, arsenazo III, constitute a sensitive assay system for ionophoresis of divalent cations. By this means we have compared known calcium ionophores (A23187, ionomycin) with membrane phospholipids, fatty acids, prostanoids, and retinoids. Added at micromolar concentrations to preformed multilamellar liposomes (phosphatidylcholine 7:dicetyl phosphate 2: cholesterol 1) both A23187 and ionomycin, as well as phosphatidic acid and products derived from linoleic acid, linolenic acid, and two eicosatrienoic acids provoked Ca influx (e.g. phosphatidic acid: 0.13 mol of Ca2+/mol of membrane lipid/5 min). A variety of other phospholipids (e.g. phosphatidylinositol), fatty acids (e.g. arachidonic acid), prostanoids (e.g. PGE1) retinoids (e.g. retinoic acid), and glyceryl ether phosphorylcholines ("platelet-activating factors") were without effect. Phosphatidic acid and oxidized fatty acids translocated divalent cations selectively, demonstrating the same rank order as A23187 or ionomycin: Mn greater than Ca greater than Sr much greater than Mg. Membrane lysis did not contribute to the perceived translocation; the liposomes remained impermeable to EDTA, EGTA, arsenazo III, or Mg. Liposomes with phosphatidic acid or oxidized trienoic acids preincorporated at 1-5 mole % of total lipids also permitted translocation of Ca but not Mg. Reduction of ionophoretic fatty acids or ionomycin with stannous chloride abolished their ionophoretic activity. Release of Ca from liposomes which had entrapped arsenazo III-Ca complexes into a medium rich in EGTA permitted calculation of efflux induced by ionophores, whether these were added to the outside of liposomes or preincorporated. Data suggest that phosphatidic acid and oxidized di- and trienoic fatty acids, which act as calcium ionophores in model bilayers, could serve as "endogenous ionophores" in cells.

Arsenazo III↗
PubMed1981

Liposome uptake by human leukocytes. Enhancement of entry mediated by human serum and aggregated immunoglobulins.

The entry of immunoglobulin-coated liposomes into human leukocytes bearing Fc receptors was evaluated using two methods: (i) the cellular association of liposomal markers (3H-labelled phosphatidylcholine, lipid phase; [14C]inulin, aqueous phase), and (ii) the ultrastructural cytochemistry of cells following incubation of cells with liposomes containing a cytochemical marker (horseradish peroxidase) in the aqueous spaces. The entry of liposomes into a cell population composed predominantly of neutrophils was linear for 10--15 min and was mediated by an active process that appeared to be both energy- and surface-dependent. This uptake could be largely inhibited by incubation at 0 degrees C, and by exposure to glutaraldehyde, iodoacetamide, N-ethylmaleimide, and an excess of aggregated immunoglobulins. Entry into cells of multilamellar liposomes was saturable, displaying affinity constants of 1.1 and 1.7 mM. Ultrastructural analysis of the heterogeneous leukocyte population showed that monocytes took up liposomes more actively than neutrophils and lymphocytes. Moreover, liposomes were almost always found within the leukocytes, rather than adherent to the outer plasma membrane. The relative avidity of monocytes was confirmed by comparing the uptake of radiolabelled liposomes by a 'pure' neutrophil population, a 'mixed' neutrophil population, and a 'mononuclear cell' population. Precoating liposomes with high molecular weight aggregates of human immunoglobulin G resulted in enhanced serum-independent uptake. The fraction of aggregated immunoglobulin G which was most effective in provoking uptake of coated liposomes also stimulated the greatest amount of lysosomal enzyme secretion. These data suggest that the interaction (precoating) of liposomes with either high molecular weight aggregates of immunoglobulin G or with serum enhances their subsequent uptake by human leukocytes.

Blood Proteins↗