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Biomedical subjects

P M Henson

Publications and source records attributed to P M Henson.

At least 19 recordsLinked to original sources
PubMed1992

Different populations of macrophages use either the vitronectin receptor or the phosphatidylserine receptor to recognize and remove apoptotic cells.

One of the key features associated with programmed cell death in many tissues is the phagocytosis of apoptotic bodies by macrophages. Removal of apoptotic cells occurs before their lysis, indicating that these cells, during the development of apoptosis, express specific surface changes recognized by macrophages. We have compared the mechanisms by which four different macrophage populations recognize apoptotic cells. Murine macrophages elicited into the peritoneal cavity with either of two different phlogistic agents were able to phagocytose apoptotic cells. This phagocytosis was inhibited by phosphatidylserine (PS), regardless of the species (human or murine) or type (lymphocyte or neutrophil) of the apoptotic cell. In contrast, the murine bone marrow macrophage, like the human monocyte-derived macrophage, utilized the vitronectin receptor, an alpha v beta 3 integrin, for the removal of apoptotic cells, regardless of their species or type. That human macrophages are capable, under some circumstances, of recognizing PS on apoptotic cells was suggested by the observation that PS liposomes inhibited phagocytosis by phorbol ester-treated THP-1 cells. These results suggest that the mechanism by which apoptotic cells are recognized and phagocytosed by macrophages is determined by the subpopulation of macrophages studied.

Animals↗
PubMed1992

Reversible membrane association of neutrophil 5-lipoxygenase is accompanied by retention of activity and a change in substrate specificity.

Ionophore activation of the human polymorphonuclear neutrophil results in eicosanoid synthesis and the accumulation of inactive 5-lipoxygenase in a membrane compartment. We report here that inhibition of self-inactivation of 5-lipoxygenase in ionophore-treated neutrophils with the reversible inhibitor zileuton, results in the accumulation of active 5-lipoxygenase in the membrane fraction. In zileuton plus ionophore-treated cells, 77% of the specific activity of the cytosolic enzyme from resting cells was diverted to the membrane fraction compared to 22% of the activity translocated when ionophore alone was used to activate the neutrophils. Accumulation of active membrane-associated 5-lipoxygenase was inhibited and reversed by the 5-lipoxygenase translocation inhibitor MK-886. The membrane-associated 5-lipoxygenase was two times more efficient in the production of leukotriene A4 from arachidonate-derived 5-hydroperoxyeicosatetraenoic acid than the cytosolic enzyme. Unlike the cytosolic enzyme, membrane-associated 5-lipoxygenase could metabolize 12(S)- and 15(S)-hydroxyeicosatetraenoic acid to 5(S),12(S)- and 5(S),15(S)-dihydroxyeicosatetraenoic acid, respectively. The ability to metabolize hydroxy fatty acids was dependent upon 5-lipoxygenase-activating protein association, but was lost if 5-lipoxygenase was eluted from the membrane by MK-886. These studies reveal for the first time that significant quantities of active 5-lipoxygenase can be detected in the membrane fraction of activated neutrophils and show that membrane association can alter the substrate specificity of 5-lipoxygenase which is further evidence for the role of the membrane-associated enzyme in the synthesis of 5-lipoxygenase metabolites.

Arachidonate 5-Lipoxygenase↗
PubMed1992

Time-dependent utilization of platelet arachidonic acid by the neutrophil in formation of 5-lipoxygenase products in platelet-neutrophil co-incubations.

The biosynthesis of leukotrienes is known to occur through a series of complex processes which, in part, can be influenced by cell-cell interactions. Several studies have suggested that arachidonic acid availability is a major limiting step for leukotriene biosynthesis and that its transfer between cells can represent a significant source of this precursor. Accordingly, effect of time and source of arachidonic acid on transcellular leukotriene synthesis was studied in mixed platelet/neutrophil populations challenged with the calcium ionophore A23187. A time-dependent contribution of platelet-derived as well as neutrophil-derived arachidonate was found in the selective formation of neutrophil 5-lipoxygenase metabolites. Utilization of platelet or neutrophil arachidonate was followed by incorporation of radiolabeled arachidonic acid into platelet or neutrophil phospholipids prior to stimulation. Specific activity of liberated arachidonic acid along with numerous 5-lipoxygenase products (including LTB4, 20-hydroxy-LTB4, 5-HETE and LTC4) was determined in order to follow mass and radiolabel. A large amount of platelet-derived arachidonic acid was released in the first 1.5 min, whereas 10 min platelet-derived arachidonate was much lower in amount but significantly higher in specific activity, suggesting different precursor pools. The platelet-derived arachidonate was heavily utilized by the neutrophils at the early time points for formation of 5-HETE and delta 6-trans-LTB4 isomers, but appeared to contribute only marginally to the constitutive metabolism of neutrophil arachidonate into LTB4. Results from these experiments suggest different pools of 5-lipoxygenase in the neutrophil and indicate a time and source dependent modulation of arachidonate metabolism in mixed cell interactions.

Arachidonate 5-Lipoxygenase↗
PubMed1992

Exposure of phosphatidylserine on the surface of apoptotic lymphocytes triggers specific recognition and removal by macrophages.

During normal tissue remodeling, macrophages remove unwanted cells, including those that have undergone programmed cell death, or apoptosis. This widespread process extends to the deletion of thymocytes (negative selection), in which cells expressing inappropriate Ag receptors undergo apoptosis, and are phagocytosed by thymic macrophages. Although phagocytosis of effete leukocytes by macrophages has been known since the time of Metchnikoff, only recently has it been recognized that apoptosis leads to surface changes that allow recognition and removal of these cells before they are lysed. Our data suggest that macrophages specifically recognize phosphatidylserine that is exposed on the surface of lymphocytes during the development of apoptosis. Macrophage phagocytosis of apoptotic lymphocytes was inhibited, in a dose-dependent manner, by liposomes containing phosphatidyl-L-serine, but not by liposomes containing other anionic phospholipids, including phosphatidyl-D-serine. Phagocytosis of apoptotic lymphocytes was also inhibited by the L isoforms of compounds structurally related to phosphatidylserine, including glycerophosphorylserine and phosphoserine. The membranes of apoptotic lymphocytes bound increased amounts of merocyanine 540 dye relative to those of normal cells, indicating that their membrane lipids were more loosely packed, consistent with a loss of membrane phospholipid asymmetry. Apoptotic lymphocytes were shown to express phosphatidylserine (PS) externally, because PS on their surfaces was accessible to derivatization by fluorescamine, and because apoptotic cells expressed procoagulant activity. These observations suggest that apoptotic lymphocytes lose membrane phospholipid asymmetry and expose phosphatidylserine on the outer leaflet of the plasma membrane. Macrophages then phagocytose apoptotic lymphocytes after specific recognition of the exposed PS.

Animals↗
PubMed1992

The mechanism of internalization of platelet-activating factor in activated human neutrophils. Enhanced transbilayer movement across the plasma membrane.

Recent studies suggest that cellular internalization of platelet-activating factor (PAF), a potent ether phospholipid mediator of inflammation, is modulated by, as yet undefined cellular mechanisms. Using an albumin extraction method, the internalization of PAF and several PAF analogues was studied in the resting and stimulated human neutrophil. Our data demonstrate that internalization of these analogues is largely dependent on the state of cellular activation and that the process is not specific for certain unique structural features of the PAF molecule including the 1-position ether linkage, 2-position acetyl substitution, or choline polar head group. Furthermore, the internalization process was shown not to be dependent on the PAF receptor, metabolism of the molecule, or the process of endocytosis. Data are presented to suggest that the route of internalization of PAF is enhanced transbilayer movement (flipping) across the plasma membrane occurring as a result of changes in membrane physical properties accompanying cellular activation. It is proposed that in addition to enhanced internalization of PAF, modulation of PAF biosynthesis and net release from the stimulated neutrophil may be consequences of enhanced transbilayer movement of PAF across the activated plasma membrane.

Biological Transport↗
PubMed1992

Effects of neutrophil depletion and repletion on PAF-induced hyperresponsiveness of canine trachea.

Platelet-activating factor (PAF) has been implicated as a mediator of airway hyperresponsiveness. PAF, infused intra-arterially into the canine cervical trachea, causes adherence of neutrophils to vascular endothelium, increases vascular permeability, and increases the responsiveness of tracheal muscle to parasympathetic stimulation. We hypothesized that the increase in airway responsiveness induced by PAF in this model depends on the presence of neutrophils. To test this hypothesis, we perfused a cervical tracheal segment with autologous blood depleted of leukocytes or with similar leukocyte-depleted blood that had been repleted with its neutrophils. Fifteen minutes after the onset of perfusion with either leukocyte-depleted or neutrophil-repleted blood, PAF infusion was begun into the tracheal arterial vasculature. The contractile response of the tracheal muscle to parasympathetic stimulation was measured before and 15 and 30 min after the onset of PAF infusion. PAF did not significantly change the response of tracheal muscle during perfusion with neutrophil-depleted blood but increased the response of tracheal muscle during perfusion with neutrophil-repleted blood. We conclude that the increase in canine tracheal muscle response induced by intra-arterial PAF depends on neutrophils.

Animals↗
PubMed1992

Platelet-activating factor causes neutrophil accumulation and neutrophil-mediated increased vascular permeability in canine trachea.

Platelet-activating factor (PAF) has potent effects on the respiratory airways that may be mediated through its ability to act as an inflammatory stimulant. To study its inflammatory properties in the airways, we infused PAF into the vasculature of the canine trachea and examined (1) the kinetics of neutrophil transit through the tracheal microcirculation, (2) accompanying changes in vascular permeability, and (3) the dependence of vascular permeability changes on neutrophil accumulation. Neutrophil kinetics were assessed by measuring the transit times of fluorescein isothiocyanate-labeled canine neutrophils by in vivo microscopy. Changes in vascular permeability were measured by the extravascular leakage of radiolabeled albumin and comparison of wet-to-dry weight ratios. The importance of neutrophils in increasing vascular permeability was assessed by perfusing the trachea with either autologous blood depleted of its leukocytes, or leukocyte-depleted blood replenished with neutrophils. Our data indicate that PAF causes rapid and prolonged neutrophil accumulation in the canine trachea and an increase in vascular permeability that is partially mediated by neutrophils.

Animals↗
PubMed1992

Studies on the role of tumor necrosis factor in adult respiratory distress syndrome.

Tumor necrosis factor (TNF), rapidly becoming recognized as a mediator of inflammation, may be important in the pathogenesis of acute lung injury. Its role in the development of the adult respiratory distress syndrome (ARDS) in humans, however, has been difficult to clarify. To determine if TNF could be important early in the development of acute lung injury from multiple causes, we enrolled 103 patients within 8 h of meeting the criteria for an at-risk illness (sepsis, aspiration of gastric contents, severe pancreatitis, hypertransfusion, abdominal trauma, chest trauma, multiple fractures) and obtained multiple frequent blood samples for TNF measurements. Using five methods of TNF analysis, we were unable to find an association between TNF and the development of ARDS. However, we found significant differences in TNF measurements depending on the methods of analysis used, which could, at least in part, account for the inconsistencies in the published literature regarding the relationship between TNF and disease processes.

Adult↗
PubMed1991

A model for the extracellular release of PAF: the influence of plasma membrane phospholipid asymmetry.

Recent studies suggesting that cellular activation leads to enhanced transbilayer movement of phospholipids and loss of plasma membrane phospholipid asymmetry lead us to hypothesize that such events may govern the release of PAF, a potent, but variably release, lipid mediator synthesized by numerous inflammatory cells. To model these membrane events, we studied the transbilayer movement of PAF across the human erythrocyte and erythrocyte ghost plasma membrane, membranes with documented phospholipid asymmetry which can be deliberately manipulated. Utilizing albumin to extract outer leaflet PAF, transbilayer movement of PAF was shown to be significantly enhanced in erythrocytes and ghosts altered to lose membrane asymmetry when compared to movement in those with native membrane asymmetry. Verification of membrane changes was demonstrated using merocyanine 540 (MC540), a dye which preferentially stains loosely packed or hydrophobic membranes, and acceleration of the modified Russell's viper venom clotting assay by externalized anionic phospholipids. Utilizing the erythrocyte ghost loaded with PAF in either the outer or the inner leaflet, enhanced transbilayer movement to the opposite leaflet was seen to accompany loss of membrane asymmetry. Studies utilizing ghosts loaded with albumin intracellularly demonstrated that 'acceptor' molecules binding PAF further influence the disposition of PAF across the plasma membrane. Taken together, these findings suggest that the net release of PAF from activated inflammatory cells will depend on localization of PAF to the plasma membrane, transbilayer movement, which is facilitated by alteration of membrane phospholipid asymmetry, and removal from the membrane by extracellular and intracellular 'acceptor' molecules.

Analysis of Variance↗
PubMed1991

Role of endogenously derived leukotrienes in the regulation of lysosomal enzyme expression in macrophages exposed to beta 1,3-glucan.

The expression of the lysosomal enzyme hexosaminidase has been shown to be stimulated by the exposure of mouse macrophages to beta 1,3-glucan, a particulate component of yeast cell walls and zymosan particles. Exposure of mouse peritoneal macrophages to particulate beta 1,3-glucan (100 micrograms/ml) was also found to stimulate the production of eicosanoids from both the cyclooxygenase (prostaglandin E2) and 5'-lipoxygenase (leukotriene C4) pathways. The objective of this study was to determine the relationship, if any, between the production of arachidonic acid metabolites and the increased expression of lysosomal enzymes. To determine if products of the cyclooxygenase or 5'-lipoxygenase pathway were involved in the regulation of hexosaminidase expression, macrophages were exposed to beta 1,3-glucan in the presence of indomethacin, an inhibitor of cyclooxygenase; 4,7,10,13 ETYA, an inhibitor of both cyclooxygenase and 5'-lipoxygenase; or AA861, a selective inhibitor of 5'-lipoxygenase. While the increased expression of hexosaminidase was not affected in macrophages stimulated with beta 1,3-glucan in the presence of indomethacin, both 4,7,10,13 ETYA and AA861 completely blocked the response, suggesting a role for products of the 5'-lipoxygenase pathway in the regulation of hexosaminidase expression. To further explore the relationship between arachidonate release and the increase expression of hexosaminidase, macrophages were exposed to phospholipase A2 in an attempt to circumvent the interaction between beta 1,3-glucan and the macrophage membrane. Incubation with phospholipase A2 was found both to induce the accumulation of LTC4 in the culture supernatant and to stimulate the increased expression of hexosaminidase. The mechanism of regulation of hexosaminidase expression by products of the 5'-lipoxygenase pathway was investigated by incubating macrophages with purified luekotrienes in either the presence or absence of beta 1,3-glucan. Incubation of macrophages with purified LTC4 or LTB4 in the absence of beta 1,3-glucan failed to stimulate the expression of hexosaminidase. However, challenging macrophage monolayers with LTC4 or LTB4 in the presence of a suboptimal concentration of beta 1,3-glucan (1 microgram/ml) led to a synergistic increase in the expression of hexosaminidase. Collectively these data suggest that the leukotriene products of the 5'-lipoxygenase pathway, LTC4 and LTB4, regulate the expression of lysosomal enzymes by apparently priming macrophages, thereby increasing their sensitivity to triggering agents such as beta 1,3-glucan. Since macrophages produce LTC4, and the increased expression of hexosaminidase is prevented by inhibitors of the 5'-lipoxygenase pathway, the data further suggest that LTC4 may prime macrophages in an autocrine or paracrine fashion.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1991

Selective secretion of azurophil granule contents induced by monovalent cation ionophores in human neutrophils: evidence for direct ionophore effects on the granule membrane.

The study of factors contributing to secretion of neutrophil azurophil granules has previously been complicated by the inability to induce their release without concomitant exocytosis of specific granules. This publication describes the action of the first two agents, the Na-ionophore monensin and the K-ionophore nigericin which elicited only secretion of azurophil granules. Secretion depended on H+/alkali ion antiport by the ionophores since it was abolished in Na(+)- and K(+)-poor choline buffer. The secretagogue effects of both ionophores did not correlate with changes either in cytoplasmic pH or in transmembrane potential and were not associated with Ca-transients, but were closely associated with azurophil granule alkalinization suggesting that the secretory event resulted from alkali ion/H+ antiport at the granule membrane. Addition of zinc inhibited azurophil (but not specific) granule secretion in response to monensin, CB/FMLP, and zymosan, indicating that secretion induced by these agents shares a common step(s).

Azure Stains↗
PubMed1991

Control of local blood flow in pulmonary inflammation: role for neutrophils, PAF, and thromboxane.

The intrapulmonary instillation of C5a results in a local inflammatory response that, in this site, is accompanied by a decrease in local blood flow. Reversal of this decrease by vasodilators or the thromboxane synthesis inhibitor dazmegral has been shown to result in enhanced lung inflammation. In the present study the mechanisms underlying the decrease in flow in pulmonary inflammation were investigated in the rabbit in vivo and in the isolated blood-perfused rabbit lung. In vivo, the decrease in local blood flow was shown to be dependent on circulating neutrophils. In the isolated blood-perfused lung, inflammation induced by airway instillation of C5a was similar histologically to that seen in vivo and was also accompanied by a decrease in local blood flow. The decrease in blood flow appeared to require circulating neutrophils and was prevented by dazmegral and the platelet-activating factor (PAF) antagonists WEB 2086 and L-659,989. Furthermore, no decrease occurred in aspirin-treated lungs perfused with normal blood, suggesting that the source of thromboxane was lung rather than circulating cells. The decrease in blood flow in inflammation did not appear to be a consequence of hypoxic vasoconstriction. Inflammation in the guinea pig lung was also accompanied by a decrease in local blood flow and was also prevented by dazmegral and PAF antagonists. We conclude that local inflammation in the lung is accompanied by a decrease in blood flow that involves neutrophils and the lipid mediators PAF and thromboxane. We suggest that this form of negative feedback by the neutrophil serves to control the inflammatory response.

Animals↗
PubMed1991

Neutrophil kinetics in the pulmonary microcirculation during acute inflammation.

The site of neutrophil interaction with the vasculature during acute lung inflammation is controversial, but has been suggested to occur in the alveolar capillaries, in contrast with its location in postcapillary venules in nonpulmonary tissues. We studied the kinetics of neutrophil accumulation and the site of neutrophil-vascular interaction in the lung by examining directly the behavior of fluorescein isothiocyanate-labeled canine neutrophils utilizing in vivo fluorescence videomicroscopy through a window inserted into the chest wall of anesthetized dogs. The administration of fragments of the fifth component of complement (C5f) into either the airway or pulmonary artery resulted in neutrophil sequestration almost exclusively in pulmonary capillaries. Kinetically, there was a shift in the distribution of neutrophil transit times resulting in a marked prolongation of median transit time. This response occurred within seconds after intravascular C5f and within 5 minutes after airway C5f and was maintained for at least 30 minutes. Ultrastructural studies after airway C5f showed neutrophils in various stages of migration through the alveolar-capillary membrane and more than 90% of these neutrophils were seen to migrate from capillary rather than from venular sites. These data indicate that pulmonary inflammation differs from inflammation in other vascular beds primarily in the site of neutrophil localization and migration. This fundamental difference in the inflammatory response may serve to localize the inflammatory response to the alveolus, and (since cells were retained singly), indicates the inability of leukoaggregation adequately to explain the findings. Leukocyte accumulation in the lung may thus occur through alterations in the balance between delivery of neutrophils to the lung and the transit time of these cells across the capillary bed.

Acute Disease↗
PubMed1990

The subcellular distribution of platelet-activating factor in stimulated human neutrophils.

Exposure of human peripheral blood neutrophils to a variety of phagocytic and soluble stimuli is known to induce the synthesis and secretion of platelet-activating factor (PAF), a unique ether-linked phospholipid. It has recently been observed in this laboratory, that whereas some PAF is secreted to the exterior of the cell, the majority of the newly synthesized PAF is retained intracellularly. This observation led us to investigate the subcellular distribution of intracellular PAF in stimulated human neutrophils, and to question the possible intracellular role of this molecule. Approximately 2 x 10(8) neutrophils were exposed to either the phagocytic stimulus, opsonized zymosan particles (25 particles/cell), the soluble stimulus, Ca2(+)-ionophore A23187 (5 micrograms/ml), or were left unstimulated for up to 30 min. After disruption, the cells were fractionated into nuclei, phagolysosomes, specific granules, azurophil granules, membranes, and cytosol. Fractions were analyzed for representative organellar markers, as well as for total protein, total phospholipid phosphorous, and PAF. In cells that had been exposed to opsonized zymosan particles, the majority of the PAF was localized to the phagolysosomal fraction, with lesser amounts being detected in the membranous and granular fractions of the cells. In neutrophils that had been exposed to A23187, the major portion of the PAF was detected in the membranous fractions with smaller amounts being seen in fractions corresponding to the specific granules. On the basis of these data, combined with the known physicochemical properties of PAF, it is speculated that the PAF detected at discrete intracellular locations in stimulated human neutrophils may play an important role in the endocytic and/or secretory functions of neutrophils.

Calcimycin↗