Hormonal control of lysosomal enzyme release from human neutrophils. Effects of autonomic agents on enzyme release, phagocytosis, and cylic nucleotide levels

Exchange protein directly activated by cyclic AMP (EPAC) activation reverses neutrophil dysfunction induced by β2-agonists, corticosteroids, and critical illness

BACKGROUND

Neutrophils play a role in the pathogenesis of asthma, chronic obstructive pulmonary disease, and pulmonary infection. Impaired neutrophil phagocytosis predicts hospital-acquired infection. Despite this, remarkably few neutrophil-specific treatments exist.

OBJECTIVES

We sought to identify novel pathways for the restoration of effective neutrophil phagocytosis and to activate such pathways effectively in neutrophils from patients with impaired neutrophil phagocytosis.

METHODS

Blood neutrophils were isolated from healthy volunteers and patients with impaired neutrophil function. In healthy neutrophils phagocytic impairment was induced experimentally by using β2-agonists. Inhibitors and activators of cyclic AMP (cAMP)-dependent pathways were used to assess the influence on neutrophil phagocytosis in vitro.

RESULTS

β2-Agonists and corticosteroids inhibited neutrophil phagocytosis. Impairment of neutrophil phagocytosis by β2-agonists was associated with significantly reduced RhoA activity. Inhibition of protein kinase A (PKA) restored phagocytosis and RhoA activity, suggesting that cAMP signals through PKA to drive phagocytic impairment. However, cAMP can signal through effectors other than PKA, such as exchange protein directly activated by cyclic AMP (EPAC). An EPAC-activating analog of cAMP (8CPT-2Me-cAMP) reversed neutrophil dysfunction induced by β2-agonists or corticosteroids but did not increase RhoA activity. 8CPT-2Me-cAMP reversed phagocytic impairment induced by Rho kinase inhibition but was ineffective in the presence of Rap-1 GTPase inhibitors. 8CPT-2Me-cAMP restored function to neutrophils from patients with known acquired impairment of neutrophil phagocytosis.

CONCLUSIONS

EPAC activation consistently reverses clinical and experimental impairment of neutrophil phagocytosis. EPAC signals through Rap-1 and bypasses RhoA. EPAC activation represents a novel potential means by which to reverse impaired neutrophil phagocytosis.

Renewal of photoreceptor outer segments and their phagocytosis by the retinal pigment epithelium

The discovery of disc protein renewal in rod outer segments, in 1960s, was followed by the observation that old discs were ingested by the retinal pigment epithelium. This process occurs in both rods and cones and is crucial for their survival. Photoreceptors completely degenerate in the Royal College of Surgeons mutant rat, whose pigment epithelium cannot ingest old discs. The complete renewal process includes the following sequential steps involving both photoreceptor and pigment epithelium activity: new disc assembly and old disc shedding by photoreceptor cells; recognition and binding to pigment epithelium membranes; then ingestion, digestion, and segregation of residual bodies in pigment epithelium cytoplasm. Regulating factors are involved at each step. While disc assembly is mostly genetically controlled, disc shedding and the subsequent pigment epithelium phagocytosis appear regulated by environmental factors (light and temperature). Disc shedding is rhythmically controlled by an eye intrinsic circadian oscillator using endogenous dopamine and melatonin as light and dark signal, respectively. Of special interest is the regulation of phagocytosis by multiple receptors, including specific phagocytosis receptors and receptors for neuroactive substances released from the neuroretina. The candidates for phagocytosis receptors are presented, but it is acknowledged that they are not completely known. The main neuromodulators are adenosine, dopamine, glutamate, serotonin, and melatonin. Although the transduction mechanisms are not fully understood, attention was brought to cyclic AMP, phosphoinositides, and calcium. The chapter points to the multiplicity of regulating factors and the complexity of their intermingling modes of action. Promising areas for future research still exist in this field.

The effect of phosphodiesterase III inhibitors on human neutrophil function

OBJECTIVES

Neutrophils play an important role in ridding the body of bacteria and cellular debris. Several neutrophil functions are thought to be regulated by inotropes that increase cellular levels of cyclic adenosine monophosphate, including phosphodiesterase (PDE) inhibitors. We have investigated the effect of amrinone, milrinone, and olprinone, type III PDE (PDE-III) inhibitors, on several human neutrophil functions.

DESIGN

Prospective in vitro study.

SETTING

Academic research laboratory.

SUBJECTS

Neutrophils isolated from 12 healthy adult volunteers.

INTERVENTIONS

We measured chemotaxis, phagocytosis, reactive oxygen species production, intracellular calcium ion concentration, and cyclic adenosine monophosphate levels in neutrophils in the absence and the presence (at clinically relevant concentrations, 10 times, and 100 times those concentrations) of amrinone, milrinone, or olprinone. We also measured reactive oxygen species production under the same condition in a xanthine-xanthine oxidase system

MEASUREMENTS AND MAIN RESULTS

None of the PDE-III inhibitors impaired neutrophil chemotaxis or phagocytosis. Amrinone at clinically relevant or higher concentrations and milrinone at high concentrations reduced superoxide, hydrogen peroxide, and hydroxyl radical levels in neutrophils and in the xanthine-xanthine oxidase system. Olprinone did not have those effects, and none of the PDE-III inhibitors had an effect on intracellular calcium ion concentration or cyclic adenosine monophosphate production in neutrophils stimulated by a chemotactic factor.

CONCLUSIONS

The ability of amrinone to scavenge reactive oxygen species at clinically relevant concentrations while not affecting neutrophil function suggests that the PDE inhibitor can be used without detriment in severely ill patients.

Endogenous catecholamine synthesis, metabolism, storage and uptake in human neutrophils

Evidence is presented that human neutrophils contain catecholamines and several of their metabolites. In vitro, incubation with alpha-methyl-p-tyrosine or pargyline affects intracellular dopamine, norepinephrine and their metabolites, suggesting catecholamine synthesis and degradation by these cells. Reserpine reduces intracellular dopamine and norepinephrine and desipramine reduces intracellular norepinephrine, suggesting the presence of storage and uptake mechanism. In view of the ability of catecholamines to affect neutrophil function, the present results support the hypothesis that autoregulatory adrenergic mechanisms may exist in these cells.

NPC 15669-modulated human polymorphonuclear neutrophil functional responsiveness: effects on receptor-coupled signal transduction

1. The effect of NPC 15669, N-carboxy-L-leucine, N-[(2,7-dimethylfluoren-9-yl)methyl]ester), an inhibitor of human polymorphonuclear neutrophil (PMN) adhesion, on granule exocytosis and the oxidative burst was investigated in PMN activated with receptor-specific pathophysiological stimuli. 2. NPC 15669 caused a concentration-dependent (1-30 microM) inhibition of the extracellular release of azurophil (myeloperoxidase) and specific (vitamin B12-binding protein) granule constitutents from PMN exposed to N-formyl-methionyl-leucyl-phenylalanine (FMLP), leukotriene B4 (LTB4), platelet activating factor (PAF), C5a and interleukin-8 (IL-8). 3. The receptor agonist-triggered PMN oxidative burst, measured as superoxide anion (O2-) production, was suppressed by NPC 15669. 4. Phorbol myristate acetate (PMA)-stimulated degranulation and O2-) production were unaffected by NPC 15669. 5. NPC 15669 (0.1-10 microM) inhibited receptor-triggered inositol 1,4,5-trisphosphate (IP3) production and the IP3-triggered increase in cytosolic-free calcium ([Ca2+]i) in FMLP-activated PMN, but not in cells exposed to the other receptor agonists. 6. NPC 15669 suppressed FMLP but not PMA-stimulated redistribution of protein kinase C (PKC) in PMN. 7. The specific binding of [3H]-FMLP but not [125I]-C5a to PMN was inhibited by NPC 15669. 8. NPC 15669 suppressed O2- production and the rise in [Ca2+]i in PMN treated with the guanine nucleotide-binding protein (G-protein) activators, sodium fluoride (NaF) and mastoparan, respectively. 9. The results show that NPC 15669 inhibits PMN responsiveness to various receptor agonists, and suggest interference with receptor-coupled signal transduction in this inflammatory cell at both the receptor and post-receptor level in a stimulus-specific manner.

Dual effects of formylpeptides on the adhesion of endotoxin-primed human neutrophils

Neutrophils, treated with sequential additions of bacterial products such as endotoxin (E. Coli lipopolysaccharide, LPS) and the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP), undergo to metabolic activation and express membrane-anchoring proteins that promote adhesion to serum-coated culture wells. By investigating the dose-response relationships of these phenomena, we have found that: (a) resting neutrophils do not produce a significant amount of superoxide (O2-) and show only minimal adhesion to serum-coated plastic surfaces; (b) fully activatory doses (> 5 x 10(-8) M) of fMLP induce the release of O2- and a significant increase of the cell adhesion; (c) pretreatment of the cells for 1 h with LPS augments cell adhesion to serum-coated culture wells in the absence of further stimulation and primes the neutrophils to enhanced fMLP-dependent O2- release; (d) addition of low, substimulatory doses of fMLP (from 10(-10) M to 5 x 10(-9) M) inhibits and reverses the adhesion of LPS-treated cells, (e) high fMLP doses ( > 10(-7) M) are additive to LPS in promoting adhesion. Phorbol-myristate acetate (> 10(-9) M) increased adhesion in both normal and LPS-treated neutrophils, but low doses of this stimulant did not inhibit adhesion. Low doses (10(-9) M) of fMLP increased intracellular cyclic AMP in both normal and LPS-treated neutrophils, suggesting that stimulus-induced rises in cAMP may be the negative signal responsible for down-modulation of adhesion.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of Rap1A binding to cytochrome b558 of NADPH oxidase by phosphorylation of Rap1A

Rap1A is a low molecular weight guanosine triphosphate (GTP)-binding protein in human neutrophil membranes whose cellular function is unknown. Rap1A was found to form stoichiometric complexes with the cytochrome b558 component of the phagocyte nicotinamide adenine dinucleotide phosphate (NADPH) oxidase system. The (guanosine-5'-O-(3-thiotriphosphate) (GTP-gamma-S)-bound form of Rap1A bound more tightly to cytochrome b558 than did the guanosine diphosphate-bound form. No complex formation was observed between cytochrome b558 and H-Ras-GTP-gamma-S or Rap1A-GTP-gamma-S that had been heat-inactivated, nor between Rap1A-GTP-gamma-S and hydrophobic proteins serving as controls. Complex formation between Rap1A-GTP-gamma-S and cytochrome b558 was inhibited by phosphorylation of Rap1A with cyclic adenosine monophosphate (cAMP)-dependent protein kinase. These observations suggest that Rap1A may participate in the structure or regulation of the NADPH oxidase system and that this function of the Rap1A protein may be altered by phosphorylation.

Recombinant human granulocyte-macrophage colony-stimulating factor induces granule exocytosis from human polymorphonuclear neutrophils

Exposure of human polymorphonuclear neutrophils (PMNs) to recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF) resulted in a time- and concentration-dependent (3-100 units/ml) extracellular release of a specific (vitamin B12-binding protein) but not azurophil granule constituent (myeloperoxidase). Negligible granule exocytosis occurred if PMNs were not preincubated with cytochalasin B prior to contact with GM-CSF. The extent of degranulation elicited with GM-CSF was reduced but not abolished when PMNs were incubated with EGTA in calcium-free medium. GM-CSF did not stimulate a rise in the cytosolic-free calcium concentration ([Ca2+]i), and it had no effect on PMN protein kinase C (PKC) activity.

Immune complexes in sera from patients with rheumatoid vasculitis induce polymorphonuclear cell-mediated injury to endothelial cells

The ability of sera from 11 patients with rheumatoid arthritis (RA) complicated by leukocytoclastic vasculitis (RV) to induce injury to cultured monolayers of human umbilical vein endothelial cells (HEC) was investigated. Injury was assessed in vitro using assays of cell lysis and cell detachment. Sera from patients with RV produced neither direct injury to HEC monolayers nor indirect injury when cocultured with HEC and normal peripheral blood polymorphonuclear cells (PMN). However, immune complexes (Icx) isolated from these sera induced nonlytic PMN-mediated HEC detachment. The inhibitory effect of serum on PMN-mediated HEC detachment induced by Icx could be attributed both to a different response of PMN to Icx present in serum compared to isolated Icx and to the presence of protease inhibitors in serum. The results of this study show that sera from patients with RV do not contain factors that can injure HEC directly and provide further support for the hypothesis that Icx and PMN play important roles in the pathogenesis of immune vascular injury.

Interaction between PAF-acether and drugs that stimulate cyclic AMP in guinea-pig alveolar macrophages

The PAF-acether (1-alkyl-2-acetyl-sn-glycero-3-phosphocholine)-induced arachidonate release from alveolar macrophages was significantly reduced by prostaglandin E2 (PGE2) and by the beta-adrenoceptor agonist salbutamol. In addition, PAF-acether markedly reduced the increase in intracellular cyclic AMP (cAMP) concentrations induced by PGE2 and salbutamol. Our data indicate an inverse relationship between intracellular cAMP levels and free arachidonate availability in alveolar macrophages treated with PAF-acether. A rise in intracellular cAMP therefore represents an important alternative route for controlling the effects of PAF-acether and the resulting inflammatory alterations in the respiratory system.

Interleukin-1 and tumor necrosis factor are not synergistic for human synovial fibroblast PLA2 activation and PGE2 production

Patterns of arachidonic acid release and metabolism were altered in human synovial fibroblasts following exposure to cytokines. Recombinant interleukin-1 induced an approximate 3-fold increase in [3H]-AA release, a 7-fold increase in PGE2 production and a 2-fold increase in PLA2 activity in human synovial fibroblasts. Recombinant tumor necrosis factor induced similar responses, however, the magnitude was less than that mediated by interleukin-1. A combination of the two cytokines had an additive effect on [3H]-AA release and PLA2 activity while PGE2 production was similar to that detected using interleukin-1 alone. [3H]-AA, was released in substantial amounts when sodium fluoride was used as a stimulus but PGE2 was not. These data show that tumor necrosis factor and interleukin-1 can both activate synovial cell PLA2 and induce generation of PGE2, but act in an additive rather than a synergistic fashion. Furthermore, the data show that PGE2 production is not always concordant with [3H]-AA release, suggesting that appropriate enzyme(s) must be activated.

Phospholipid and arachidonic acid metabolism in zymosan-stimulated human monocytes: modulation by cAMP

Receptor-ligand interaction in mononuclear phagocytes is intimately linked to alterations in membrane phospholipids and release of arachidonic acid (AA). In addition, synthesis of bioactive lipids from released AA can result in further modification of cell responses. Upon challenge with opsonized zymosan, [3H]-arachidonic acid ([3H]-AA)-labeled human monocytes released 25 +/- 2% of their incorporated radiolabel within 30 min. Pretreatment of the monocytes with 5 X 10(-4) M isobutylmethylxanthine (IBMX) or 1 X 10(-3) M dibutyryl cyclic AMP (d-cAMP) inhibited total [3H]-AA release in the presence of zymosan by 47% and 42%, respectively. Analysis of incorporated [3H]-AA in cellular phospholipid pools indicated that significant amounts of label were lost from both phosphatidylcholine (PC) and phosphatidylinositol (PI) during zymosan stimulation. Treatment with d-cAMP substantially inhibited the loss of label from PC, but had no affect on PI. HPLC analysis of cell supernatants from zymosan-treated cells indicated that 5-HETE was the predominant metabolite generated from [3H]-AA, and its production was depressed during treatment with d-cAMP. Phospholipase activity in human monocyte homogenates was not effected by d-cAMP or IBMX at the highest concentrations used, whether these were added directly to the homogenate or by pretreatment of whole cells, demonstrating that inhibition required an intact cell. These results suggest that human monocytes exposed to opsonized zymosan release AA via two mechanisms and that modulation by cAMP is indirectly effecting a phospholipase directed towards PC.

Characterization of adenylate cyclase in human retinal pigment epithelial cells in vitro

Human retinal pigment epithelial cells in culture demonstrate adenylate cyclase activity. It is membrane-bound and modulated by GTP regulatory proteins. It is effectively activated only by beta-adrenergic agonists (L-isoproterenol greater than or equal to L-epinephrine greater than L-norepinephrine) and some prostaglandins (PGE1 and PGE2, but not PGF1 alpha). The adrenergic response appears to be mediated by beta-2 receptors. No inhibitory ligands could be demonstrated. Its characteristics, which are similar to functional adenylate cyclase complexes in other mammalian cells, and its selective and sensitive agonist responsiveness, suggest a possible physiologic role in the regulation of human retinal pigment epithelial-cell function.

Characterization of cyclic-nucleotide phosphodiesterase activities in resting and N-formylmethionylleucylphenylalanine-stimulated human neutrophils

Cyclic nucleotide phosphodiesterase activities in human neutrophils were characterized. Neutrophil sonicates exhibited high-affinity and low-affinity cAMP phosphodiesterase activities, with apparent Km values of 1.9 microM and 112 microM, respectively. No cGMP phosphodiesterase activity was detected. Approx. 70% of cAMP phosphodiesterase activity measured at 1 microM cAMP was present in the soluble subcellular fraction, and the remainder was localized in the particulate fraction. Chromatography of the soluble subcellular fraction on DE-52 ion-exchange resin yielded a low-affinity cAMP phosphodiesterase activity and a high-affinity cAMP phosphodiesterase activity. The soluble high-affinity cAMP phosphodiesterase activity exhibited moderate calmodulin sensitivity. After incubation of intact neutrophils with N-formylmethionylleucylphenylalanine (fMet-Leu-Phe), a 25-30% increase in the activity of the high-affinity cAMP phosphodiesterase activity was observed in the sonicate and in the soluble fraction. Maximal increases were achieved after 2 min of incubation and the increases persisted for at least 10 min. The increase in activity was independent of calmodulin and guanine nucleotide regulatory proteins. These results indicate that a soluble high-affinity cAMP phosphodiesterase comprises the majority of phosphodiesterase activity in neutrophils and that increases in this activity may contribute to the regulation of cAMP levels in neutrophils during activation.

Effects of anthrax toxin components on human neutrophils

The virulence of Bacillus anthracis has been attributed to a tripartite toxin composed of three proteins designated protective antigen, lethal factor, and edema factor. The effects of the toxin components on phagocytosis and chemiluminescence of human polymorphonuclear neutrophils were studied in vitro. Initially, it was determined that the avirulent Sterne strain of B. anthracis (radiation killed) required opsonization with either serum complement or antibodies against the Sterne cell wall to be phagocytized. Phagocytosis of the opsonized Sterne cells was not affected by the individual anthrax toxin components. However, a combination of protective antigen and edema factor inhibited Sterne cell phagocytosis and blocked both particulate and phorbol myristate acetate-induced polymorphonuclear neutrophil chemiluminescence. These polymorphonuclear neutrophil effects were reversible upon removal of the toxin components. The protective antigen-edema factor combination also increased intracellular cyclic AMP levels. These studies suggest that two of the protein components of anthrax toxin, edema factor and protective antigen, increase host susceptibility to infection by suppressing polymorphonuclear neutrophil function and impairing host resistance.

Cyclic AMP inhibition of fMet-Leu-Phe-dependent metabolic responses in human neutrophils is not due to its effects on cytosolic Ca2+

Cyclic AMP powerfully inhibits the fMet-Leu-Phe-dependent respiratory burst and exocytosis of azurophilic and specific granules without affecting Ca2+ release from intracellular stores. The elevation of [Ca2+]i induced by fMet-Leu-Phe is short-lived in cyclic AMP-treated cells and similar to that of untreated cells stimulated in the absence of external Ca2+. Nevertheless, in these latter cells fMet-Leu-Phe induces metabolic activation. We therefore suggest that the inhibitory action of cyclic AMP on neutrophil responses is not due to its effects on [Ca2+]i homoeostasis.

Activation of the human neutrophil secretory process with 5(S),12(R)-dihydroxy-6,14-cis-8,10-trans-eicosatetraenoic acid

Exposure of human neutrophils to 5(S),12(R)-dihydroxy-6,14-cis-8,10-trans-eicosatetraenoic acid (leukotriene B4, LTB4) resulted in a time- and concentration- (10(-9)-10(-6) M) dependent extracellular release of granule-associated lysozyme and myeloperoxidase (MPO). Enzyme extrusion was negligible if cells were not pretreated with cytochalasin B prior to exposure to LTB4. A time-dependent deactivation of granule exocytosis was observed in neutrophils which were stimulated with LTB4 prior to contact with cytochalasin B. LTB4-induced enzyme release was markedly enhanced in the presence of extracellular calcium. Nevertheless, significant enzyme discharge occurred in the absence of extracellular calcium, and the percent of total activity released was not altered in the presence of EGTA. The calmodulin antagonist, trifluoperazine (TFP), and the intracellular calcium antagonist, 8-(N,N-diethylamino)-octyl-(3,4,5-trimethoxy)benzoate hydrochloride (TMB-8), caused a dose-related inhibition of enzyme release from LTB4-stimulated neutrophils. Degranulation was suppressed by the glycolytic inhibitor, 2-deoxy-D-glucose (2-DG), and the sulfhydryl reagents iodoacetic acid (IA) and N-ethylmaleimide (NEM). Sodium cyanide was inactive. Two inhibitors of transmethylation, 3-deazaadenosine (3-DZA) and L-homocysteine thiolactone (HCTL), alone or in combination, had no effect on LTB4-elicited degranulation. The protein synthesis inhibitor, cycloheximide, was inactive. Neutrophils pretreated with LTB4 or 5(S),12(R),20-trihydroxy-6,14-cis-8,10-trans-eicosatetraenoic acid (20-OH-LTB4, an omega-oxidation metabolite of LTB4) were desensitized to the subsequent exposure to LTB4. Cross-desensitization was also demonstrated between LTB4 and 20-OH-LTB4. The stimulus specific nature of LTB4-induced desensitization of neutrophil degranulation was demonstrated by the fact that cells exposed to 1-O-hexadecyl/octadecyl-2-O-acetyl-sn-glyceryl-3-phosphorylcholine (AGEPC) or N-formyl-methionyl-leucyl-phenylalanine (FMLP) were capable of inducing granule exocytosis from LTB4-pretreated neutrophils. Enzyme release from LTB4-treated cells was suppressed with the phospholipase inhibitor, 4-bromophenacyl bromide (4-BPB), the cyclooxygenase/lipoxygenase inhibitor, ETYA, and the 5-lipoxygenase inhibitor, U-60, 257. However, the cyclooxygenase inhibitor, flurbiprofen, exerted a weak suppressive effect on LTB4-induced degranulation.

Differential effects of prostaglandin E2 and cyclic AMP on release of arachidonic acid metabolites from resting and lipopolysaccharide-stimulated macrophages

The present study investigated the effect of cyclic adenosine 3',5'-monophosphate (cyclic AMP) and prostaglandin E2 (PGE2) on arachidonic acid metabolism in rat peritoneal macrophages. Dibutyryl cyclic AMP (db-cyclic AMP) caused differential effects on the synthesis of PGE2 and thromboxane. Although db cyclic AMP enhanced the release of PGE2, it inhibited the release of thromboxane. This suggests that cyclic AMP may regulate cellular functions via induction of a shift in the proportion of arachidonic acid metabolites. PGE2, at low concentrations, markedly inhibited thromboxane release in nontreated macrophages, but it had virtually no effect on thromboxane release in cells treated with lipopolysaccharide (LPS). By contrast, db-cyclic AMP inhibited thromboxane release also in LPS-stimulated cells. The interrelationships between PGE2, thromboxane and cyclic AMP, and possible interference of LPS in these interactions are discussed.

Retinal pigment epithelium in culture demonstrates a distinct beta-adrenergic receptor

Retinal pigment epithelial (RPE) cells in culture, as well as freshly dissected embryonic RPE, exhibit a beta-adrenergic receptor. Agonist potency is: L-isoproterenol greater than (-)epinephrine greater than or equal to (-)norepinephrine much greater than dopamine. Propranolol blocks this effect. Hydroxybenzylpindolol (HYP), a beta-antagonist, also blocks the increase in cAMP elicited by L-isoproterenol. Binding of [125I]-hydroxybenzylpindolol, shows a half saturation concentration of 1.1 X 10(-9) M and 2.7 X 10(5) HYP binding sites per cell. The presence of such distinct beta-adrenergic responsiveness indicates a potentially important role for this receptor in RPE cell physiology.

Characteristics of 1-O-hexadecyl- and 1-O-octadecyl-2-O-acetyl-sn-glyceryl-3-phosphorylcholine-stimulated granule enzyme release from human neutrophils

1-O-Hexadecyl-2-O-acetyl-sn-glyceryl-3-phosphorylcholine (C16-AGEPC) and 1-O-octadecyl-2-O-acetyl-sn-glyceryl-3-phosphorylcholine (C18-AGEPC) stimulated a time- and concentration-dependent release of granule-associated lysozyme and beta-glucuronidase from human neutrophils. Maximum discharge of granule enzymes occurred between 30 and 60 sec after neutrophil exposure to C16- or C18-AGEPC (0.01-10 microM). Less than 10% of total enzyme activity is released when cells are not preincubated with cytochalasin B prior to interaction with the AGEPC analogs. A time-dependent desensitization for granule exocytosis was observed in neutrophils which were stimulated with C18-AGEPC prior to contact with cytochalasin B. The rate and amount of enzyme released by C16- and C18-AGEPC activated neutrophils was significantly enhanced in the presence of extracellular calcium. Trifluoperazine, an inhibitor of calmodulin, caused a dose-related suppression of C18-AGEPC-induced degranulation. Granule enzyme extrusion from C18-AGEPC-treated neutrophils was inhibited by the sulfhydryl reagents, N-ethylmaleimide and iodoacetic acid, and by the glycolytic inhibitor, 2-deoxy-D-glucose. Sodium cyanide was inactive. Pretreatment of neutrophils with C16- or C18-AGEPC rendered the cells unresponsive to subsequent exposure to either AGEPC analog. C18-AGEPC-induced desensitization of neutrophil degranulation appears to be stimulus specific in that serum-treated zymosan and N-formyl-methionyl-leucyl-phenylalanine were capable of eliciting granule enzyme release from C18-AGEPC-pretreated cells.

Autonomic nervous system abnormalities in cystic fibrosis

The basic defect in cystic fibrosis, the most common lethal genetic diseases of white Americans, is unknown, but the character of the generalized exocrinopathy suggests some disorder of the regulation and control of the process of glandular secretion. Definite abnormalities in all branches of the autonomic nervous system have been demonstrated in patients with cystic fibrosis, including increased sensitivity to alpha-adrenergically stimulated pupillary dilation; increased responsiveness to cholinergic stimulation of pupillary constriction, parotid saliva secretion, and eccrine sweat secretion; and decreased responsiveness to beta-adrenergic stimulation of the cardiovascular system as well as circulating lymphocytes and granulocytes. Since these abnormalities also occur in asymptomatic heterozygotes for cystic fibrosis (parents of patients), they are likely to be inherited characteristics and not secondarily acquired. This constellation of inherited autonomic abnormalities--alpha-adrenergic and cholinergic hyperresponsiveness and beta-adrenergic resistance--may contribute to the pathophysiology of cystic fibrosis and may also be an important clue to the nature of the basic defect.

Modulatory role of cyclic AMP in the release of platelet-activating factor from human polymorphonuclear leucocytes

Zymosan coated with complement (Zc) was observed to induce a transient elevation of the intracellular cyclic AMP in human polymorphonuclear cells: a two- to three-fold increase was observed within 1 min after stimulation and approached prestimulation levels by 2 min incubation. These changes in cyclic AMP were not associated with significant changes in cyclic GMP levels. Zymosan caused the release of PAF and beta-glucuronidase and particle uptake, which was initiated about 5 min after stimulation. These results suggest that the transient increase in cyclic AMP content might regulate an early event during mediator release. In an attempt to study further the significance of this rise in cyclic AMP, cells were preincubated with various phosphodiesterase inhibitors. Preincubation of the cells with methylisobutylxanthine (MIX, 10(-6) M to 5 X 10(-5) M), theophylline (3 X 10(-5) to 3 X 10(-3) M) or dipyridamole (10(-6) M to 10(-4) M) enhanced the increase in cyclic AMP levels, but resulted in dose-dependent inhibition of Zc-induced mediator release. Particle uptake and beta-glucuronidase release were less sensitive than PAF release to phosphodiesterase inhibitors, which argues in favour of the independence of both phenomena. Synergistic experiments with MIX and cyclic AMP indicate that the effect of this drug is through its action on cyclic AMP levels. These results suggest that while Zc-induced cyclic AMP elevation might occur in an intracellular place critical to its effect; phosphodiesterase inhibitors may elevate cyclic AMP levels throughout the cell and therefore inhibit the biological response.

The uptake of amines by polymorphonuclear leukocytes

Muscarinic and beta-adrenergic ligands associate with polymorphonuclear leukocytes to show high-affinity, saturable accumulation. This association can be distinguished from specific receptor binding by its temperature dependence, sensitivity to pH, requirement of an energy source, inhibition by ionophores, and inhibition by a variety of permeable basic amines. Our results suggest that these amines accumulate in acidic lysosomes which are plentiful in these cells. This permeable amine effect can be inhibited without affecting specific receptor binding.

Eosinophil degranulation. Monitoring by interference contrast microscopy

A method is described for the quantitative monitoring of human eosinophil degranulation using interference contrast microscopy. Using staphyloccoci as a stimulus, degranulated cells appeared larger than nondegranulating cells, were ameboid in shape and exhibited large nude areas of cytoplasm with prominent nuclei. Granules were observed to marginate along the plasma membrane and discharge into the exterior of the cell. Eosinophils that were not induced to degranulate were spherical in shape and the cytoplasm contained numerous granules that often obscured the nuclei. Pharmacological agents that increase intracellular cAMP prevented degranulation, whereas those that increase cGMP had no effect on degranulation. Colchicine inhibited degranulation but did not interfere with the phagocytosis of staphyloccoci. Endotoxin-activated serum, ECF-A, phytohemagglutinin, concanavalin A, levamisole, and compound 48/80 caused degranulation of eosinophils per se. The presence of disodium cromoglycate prevented this degranulation. Compound 48/80 and disodium cromoglycate had no effect on the level of intracellular cAMP and cGMP.

[Phagocytosis mechanisms of alveolar macrophages and granulocytes (author's transl)]

Alveolar macrophages and granulocytes protect the organism against invaded microorganisms under various conditions. To investigate whether the environmental difference may influence the various phagocytic functions the adherence, chemotaxis, ingestion rate, degranulation as well as the bactericidal activity were determined in alveolar macrophages and granulocytes obtained from guinea pigs. In addition, the cytoskeleton was examined by observing the fluorescence of Concanavalin A receptors. Various functional differences between both cell types have been demonstrated. Both cell types exhibited the same adherence. In contrast, granulocytes demonstrated a greater chemotactic activity and ingestion rate than alveolar macrophages. Following the exposure to opsonized zymosan alveolar macrogphages secreted almost totally the lysosomal enzyme beta-glucuronidase during the degranulation. Nevertheless, alveolar macrophages exhibited a lower bactericidal activity than granulocytes. This functional differences were not caused by an alteration of the cytoskeleton. A random fluorescence distribution of FITC-Concanavalin A receptors was observed in 72% alveolar macrophages and 73% granulocytes, demonstrating polymerisation of the microtubuli. Only 12% alveolar macrophages and 11% granulocytes showed a capped FITC-Concanavalin A fluorescence which is associated with an alteration of the microtubulin. This study demonstrates that the difference in adherence, chemotaxis, ingestion rate, as well as the bactericidal activity of alveolar macrophages and granulocytes is a specific cell-type property.

Biochemical properties of polymorphonuclear neutrophils from venous blood and peritoneal exudates of rabbits

The biochemical properties of polymorphonuclear neutrophils from blood and peritoneal exudates of rabbits were compared. All enzymes measured showed almost identical activities in both types of cells, except for alkaline phosphodiesterase, the activity of which was seven times higher in peritoneal neutrophils. During phagocytosis, blood and peritoneal beta-glucuronidases were released in very similar fashions. Lysozyme, one of the enzymes concerned with killing of bacteria, as well as beta-glucuronidase, showed the same releasing pattern in both types of cells, but peroxidase was hardly released. Although superoxide anion generation in peritoneal neutrophils was two times higher than superoxide generation in blood neutrophils, phagocytic and bactericidal activities were almost the same in blood and peritoneal neutrophils. Blood neutrophils were more resistant to hypotonic lysis than were peritoneal neutrophils. These results show that there are no distinct differences in enzymatic and functional properties between blood and peritoneal polymorphonuclear neutrophils, except for alkaline phosphodiesterase activity, superoxide anion production, and osmotic fragility.

Pharmacological modulation of platelet-activating factor (PAF) release from rabbit leucocytes. I. Role of cAMP

Basophil-rich rabbit leucocytes sensitized by anti-horseradish peroxidase antibodies released platelet-activating factor (PAF) and histamine upon exposure to the specific antigen. This release was preceded and accompanied by a sharp decrease in the intracellular concentration of cyclic AMP. Isoproterenol, a beta-adrenergic agent, and theophylline, a phosphodiesterase inhibitor, used individually or in combination, increased the intracellular concentration of cyclic AMP and inhibited the release of both PAF and histamine. Propranolol, a beta-adrenergic blocking agent, suppressed the effect of isoproterenol on cyclic AMP level and mediator release. Dibutyryl cyclic AMP, an alkylated derivative of cyclic AMP, inhibited PAF and histamine release. These results indicate that cyclic AMP, which is known to control the release of other mediators of immediate hypersensitivity, also regulates the release of PAF. Histamine and PAF followed one another closely in all of our release or inhibition experiments, bringing more evidence for the basophil origin of PAF.

The effect of exercise on the granulocyte response to isoproterenol in the trained athlete and unconditioned individual

Many factors will influence the tissue response to catecholamine stimulation. Isolated human granulocytes (PMNs) release the lysosomal enzyme beta-glucuronidase following incubation with complement-activated zymosan particles. Isoproterenol, histamine, and prostaglandin E1 (PGE1) inhibit this PMN release of beta-glucuronidase. The effect of exercise on this in vitro granulocyte response was studied in two groups: highly conditioned marathon runners (n = 6) and unconditioned subjects (n = 7). A 13-km run did not produce leukocytosis in the highly conditioned marathon runners and the granulocyte response to isoproterenol was unchanged in cells obtained immediately following the run. In contrast, the seven unconditioned subjects exercised to a maximal response on the treadmill. Following exercise there was an increase in plasma catecholamines, a significant leukocytosis, and granulocytes from the immediate postexercise period responded less well to isoproterenol.

Increased levels of cyclic adenosine-3',5'-monophosphate in human polymorphonuclear leukocytes after surface stimulation

Levels of cyclic AMP (cAMP) (but not cyclic GMP) in suspensions of human polymorphonuclear leukocytes (PMN) increased promptly after exposure of the cells to stimuli such as the chemotactic peptide N-formyl methionyl leucyl phenylalanine, the immune complex bovine serum albumin/anti-bovine serum albumin and calcium ionophore A23187. cAMP increased rapidly, reaching a maximum of twice the basal level 10--45 s after stimulation; after 2--5 min the amount of cAMP had subsided to basal levels. Elevations in cAMP levels were concurrent with, or followed, membrane hyperpolarization (measured by uptake of the lipophilic cation triphenylmethyl phosphonium) and always preceded lysosomal enzyme release and superoxide anion (O2) production. Elevated cAMP levels could be uncoupled from these later events by removal of extracellular divalent cations, replacement of extracellular Na+ with K+ or choline+, and by use of low concentrations of stimulus; each of these conditions virtually abolished lysosomal enzyme release and O2 generation, while leaving the stimulated elevation of cAMP levels unimpaired. Calcium ionophore A23187 did not provoke membrane hyperpolarization, thus uncoupling changes in membrane potential from changes in cAMP levels. These data suggested that cAMP is not a critical component in the earliest steps of stimulus-secretion coupling. Surface stimulation of cells pretreated with prostaglandins E1 or I2 yielded very high levels of cAMP; these high levels may be an important part of the mechanism by which stable prostaglandins inhibit lysosomal enzyme release and O2 generation.

An improved method for the isolation of eosinophilic leukocytes from normal human blood

A relatively short and simple method for the isolation of the eosinophils from normal human blood is reported. With a recovery of about 45-55%, cell preparations, showing a degree of purity of 90-98%, are obtained. The isolated cells are morphologically intact and viable, as assessed by the trypan blue exclusion test and by active phagocytosis.

Electric currents, bone remodeling, and orthodontic tooth movement. I. The effect of electric currents on periodontal cyclic nucleotides

Osteogenesis has been found to occur in response to the application of electric currents to bone. The objective of this experiment was to study the effects of D.C. electric currents on periodontal tissues in cats. Cyclic nucleotides, compounds known to be involved in cellular activation, were studied by immunohistochemistry in the involved tissues. Three groups of three young adult cats each were treated for 1, 3, and 7 days, respectively, by a device delivering 15 microamperes of direct current to bone osteoblasts and PDL cells stained intensely for cAMP and cGMP were observed adjacent to the cathode and anode, and bone apposition was found near the cathode. These results suggest that electric stimulation enhances cellular enzymatic phosphorylation activities in periodontal tissues and may be a potent tool in accelerating alveolar bone turnover.

The in vitro effects of propranolol and atenolol on neutrophil motility and post-phagocytic metabolic activity

Propranolol at concentrations of 1 x 10(-6) to 1 x 10(-4) M consistently increased neutrophil motility as measured in Boyden chambers. The effects were not due solely to stimulation of random migration and chemokinesis but also of directional motility. Propranolol, over a similar concentration range, caused inhibition of post-phagocytic cell metabolic activity (hexose monophosphate shunt, nitro-blue tetrazolium reduction and protein iodination) without any detectable effect on the ingestion rate of Candida albicans. Atenolol had no effect on any of these neutrophil functions. Both drugs were without effect on glycolysis and intracellular cyclic AMP levels. Propranolol however, at concentrations which stimulated cell motility, caused increased intracellular cyclic GMP levels. It is suggested that propranolol may stimulate neutrophil motility by promoting increased intracellular cyclic GMP levels or by decreasing neutrophil superoxide production.

Immuno-histochemical localization of cyclic nucleotides in mineralized tissues: mechanically-stressed osteoblasts in vivo

Previous experiments indicate that bone cells respond to external stimuli with fluctuations of cyclic nucleotide levels. The objective of this experiment was to study the response of alveolar bone to the application of tensile forces through an examination of the osteoblastic staining pattern for cAMP and cGMP. Cat canines were tipped by 80-g force for 0 to 48 hours. Fresh frozen, unfixed, undecalcified jaws were sectioned sagittally and stained immuno-histochemically for cAMP and cGMP. In tension sites, osteoblastic staining intensity for cAMP decreased gradually from one to three hours, and then increased by 24 hours. Intense staining for cGMP, visible in osteoblasts of all treated cats, peaked after three hours of treatment and then again at 24 hours. Generally, groups of cGMP-stained osteoblasts were found adjacent to unstained osteoblasts. The observed fluctuations in the osteoblasts staining pattern for cAMP and cGMP indicates involvement of these substances in the early response of osteoblasts to mechanical stimuli in vivo.

Effects of catecholamines and glucagon on glycogen metabolism in human polymorphonuclear leukocytes

Addition of 10 micron of the alpha-adrenergic agonist phenylephrine to polymorphonuclear leukocytes suspended in glucose-free Krebs-Ringer bicarbonate buffer (pH 6.7) activated phosphorylase, inactivated glycogen synthase R maximally within 30 s, and resulted in glycogen breakdown. Phenylephrine increased 45Ca efflux relative to control of 45Ca prelabelled cells, but did not affect cyclic adenosine 3',5'-monophosphate (cAMP) concentration. The effects of phenylephrine were blocked by 20 micron phentolamine and were absent in cells incubated at pH 7.4. The same unexplained dependency of extracellular pH was observed with 2.5 nM--2.5 micron glucagon, which activated phosphorylase and inactivated synthase-R, but in addition caused a 30-s burst in cAMP formation. 25 nM glucagon also increased 45Ca efflux. The activation of phosphorylase by phenylephrine and possibly also by glucagon are thought mediated by an increased concentration of cytosolic Ca2+ activating phosphorylase kinase. The effects of 5 micron isoproterenol or 5 micron epinephrine were independent of extracellular pH 6.7 and 7.4 and resulted in a sustained increase in cAMP, an activation of phosphorylase and inactivation of synthase-R within 15 s, and in glycogenolysis. The effects of both compounds were blocked by 10 micron propranolol, whereas 10 micron phentolamine had no effect on the epinephrine action. The efflux of 45Ca was not affected by either isoproterenol or epinephrine. The beta-adrenergic activation of phosphorylase is consistent with the assumption of a covalent modification of phosphorylase kinase by the cAMP dependent protein kinase. Phosphorylation of synthase-R to synthase-D can thus occur independently of increase in cAMP, but the evidence is inconclusive with respect to the cAMP dependent protein kinase also being active in this phosphorylation.

Effects of 2-(4-(2-imidazo[1,2-a]pyridyl)phenyl) propionic acid (Y-9213) and anti-inflammatory drugs on erythrocytes, polymorphonuclear leukocytes and lysosomes in vitro

2-(4-(2-Imidazo[1,2-a]pyridyl)phenyl)propionic acid (Y-9213) with analgesic, antipyretic and anti-inflammatory activities significantly inhibited hemolysis of rat erythrocytes. Activity of Y-9213 (100--500 micrometer) on hemolysis was more potent than that of phenylbutazone, and less potent than that of indomethacin. The spontaneous release of enzymes from rat liver lysosomes by incubation alone was significantly inhibited by Y-9213 (1--100 micrometer) to the same degrees as phenylbutazone or tinoridine hydrochloride. Release of enzymes from the lysosomes by addition of phospholipase C (PLC, 0.03 units/ml) was slightly inhibited by Y-9213 (10--100 micrometer) and phenylbutazone (100 micrometer). Dexamethasone, prednisolone, hydrocortisone and tinoridine hydrochloride (1--10 micrometer) inhibited more potently the PLC-induced release than the spontaneous release. Y-9213 (1--100 micrometer) inhibited considerably the release of enzymes from intact lysosomes of rabbit polymorphonuclear (PMN) leukocytes. The release of enzymes from the PMN leukocyte lysosomes preincubated at 37 degrees C for 15 min was strongly inhibited by dexamethasone, prednisolone and hydrocortisone (1--100 micrometer), but not by Y-9213, phenylbutazone and indomethacin (100 micrometer). Y-9213 (0.1--10 micrometer) also inhibited significantly the phagocytic secretion of lysosomal enzymes from PMN leukocytes without affecting phagocytosis of the particles. Activity of this agent was similar to that of phenylbutazone, and less active than that of indomethacin, dexamethasone or prednisolone. Our results suggest that Y-9213 may stabilize membranes of erythrocytes and lysosomes and inhibit phagocytic secretion of lysosomal constitutents from PMN leukocytes.