Stimuli which provoke secretion of azurophil enzymes from human neutrophils induce increments in adenosine cyclic 3'-5'-monophosphate

Quantitative Factors Introduced in the Feasibility Analysis of Reactive Oxygen Species (ROS)-Sensitive Triggers

Reactive oxygen species (ROS) are critical for cellular signaling. Various pathophysiological conditions are also associated with elevated levels of ROS. Hence, ROS-sensitive triggers have been extensively used for selective payload delivery. Such applications are predicated on two key functions: (1) a sufficient magnitude of concentration difference for the interested ROS between normal tissue/cells and intended sites and (2) appropriate reaction kinetics to ensure a sufficient level of selectivity for payload release. Further, ROS refers to a group of species with varying reactivity, which should not be viewed as a uniform group. In this review, we critically analyze data on the concentrations of different ROS species under various pathophysiological conditions and examine how reaction kinetics affect the success of ROS-sensitive linker chemistry. Further, we discuss different ROS linker chemistry in the context of their applications in drug delivery and imaging. This review brings new insights into research in ROS-triggered delivery, highlights factors to consider in maximizing the chance for success and discusses pitfalls to avoid.

The PGE2-induced inhibition of the PLD activation pathway stimulated by fMLP in human neutrophils is mediated by PKA at the PI3-Kgamma level

Prostaglandin E2 (PGE2), an eicosanoid that modulates inflammation, inhibits several chemoattractant-elicited functions in neutrophils such as chemotaxis, production of superoxide anions, adhesion, secretion of cytotoxic enzymes and synthesis of leukotriene B4. We previously reported that PGE2 inhibits the fMLP signaling pathway that leads to PLD activation through suppression of PI3-Kgamma activity and the decreased recruitment to membranes of PLD activation factors, PKC, Rho and Arf-GTPases. This effect is mediated via the EP2 receptors known to raise cAMP in cells. The inhibition of most fMLP-induced functional responses by PGE2 via EP2 receptors is mediated by PKA, except the chemotactic response. We have investigated the role of PKA in the EP2-mediated inhibition of the PLD activation pathway. H-89, a selective PKA pharmacological inhibitor suppressed the inhibitory effects of PGE2 at all stages of the PLD pathway activated by fMLP, i.e. PLD activity, translocation to membranes of PKCalpha, Rho and Arf-GTPases, calcium influx, tyrosine phosphorylation of proteins and finally translocation of p110gamma catalytic subunit of PI3-K to membranes. However, neither PLD nor PI3-Kgamma was substrate of PKA. These data provide evidence that PGE2-stimulated PKA activity regulates the PLD pathway stimulated by fMLP at the level of PI3-Kgamma and that the inhibition of PI3-Kgamma activation by PKA is a complex mechanism that remains to be completely elucidated.

L-selectin signaling of neutrophil adhesion and degranulation involves p38 mitogen-activated protein kinase

The adhesion molecules known as selectins mediate the capture of neutrophils from the bloodstream. We have previously reported that ligation and cross-linking of L-selectin on the neutrophil surface enhances the adhesive function of beta(2)-integrins in a synergistic manner with chemotactic agonists. In this work, we examined degranulation and adhesion of neutrophils in response to cross-linking of L-selectin and addition of interleukin-8. Cross-linking of L-selectin induced priming of degranulation that was similar to that observed with the alkaloid cytochalasin B. Activation mediated by L-selectin of neutrophil shape change and adhesion through CD11b/CD18 were strongly blocked by Merck C, an imidazole-based inhibitor of p38 mitogen-activated protein kinase (MAPK), but not by a structurally similar non-binding regioisomer. Priming by L-selectin of the release of secondary, tertiary, and secretory, but not primary, granules was blocked by inhibition of p38 MAPK. Peak phosphorylation of p38 MAPK was observed within 1 min of cross-linking L-selectin, whereas phosphorylation of ERK1/2 was highest at 10 min. Phosphorylation of p38 MAPK, but not ERK1/2, was inhibited by Merck C. These data suggest that signal transduction as a result of clustering L-selectin utilizes p38 MAPK to effect neutrophil shape change, integrin activation, and the release of secondary, tertiary, and secretory granules.

N-formyl-methionyl-leucyl-phenylalanine (fMLP) inhibits tumour necrosis factor-alpha (TNF-alpha) production on lipopolysaccharide (LPS)-stimulated human neutrophils

During gram-negative infections bacterial components, such as LPS and formylated peptides, exert profound physiological effects on polymorphonuclear neutrophils (PMN) resulting in increased neutrophil effector activities, including the generation of oxidative metabolites, degranulation, phagocytosis and cytokine release. There is not enough evidence about the relationships between LPS and formylated bacterial peptides in the triggering and regulation of the immune inflammatory response. In this study, we present evidence indicating that pretreatment of human PMN with a prototype formylated peptide such as fMLP results in the inhibition of TNF-alpha secretion, a key molecule that plays a central role in the pathogenesis of septic shock. This inhibitory effect of fMLP does not appear to alter the expression of LPS receptors or the transcriptional pathway of the TNF-alpha mRNA, but instead, fMLP reduces the expression of the membrane form of TNF-alpha on the PMN surface. These findings indicate that fMLP, a typical proinflammatory agent, could play, at least in determined conditions, an anti-inflammatory role.

An inhibitor of cyclic AMP-dependent protein kinase enhances the superoxide production of human neutrophils stimulated by N-formyl-methionyl-leucyl-phenylalanine

Intact human neutrophils produced superoxide (O2-) by the stimulation with N-formyl-methionyl-leucyl-phenylalanine (fMLP) even when the extracellular Ca2+ was absent (0.56 +/- 0.13 nmol/min per 10(6) cells). The production by fMLP was enhanced more than twice in the presence of the extracellular Ca2+. Moreover, the O2- production by fMLP in the presence of extracellular Ca2+ was enhanced nearly three times by the treatment of cells with H-89, an inhibitor of cyclic AMP-dependent protein kinase (PKA). The enhancement was not observed when the extracellular Ca2+ was depleted from the reaction mixture. In addition, H-89 did not enhance fMLP-induced O2- production of electropermeabilized neutrophils in which the intracellular Ca2+ concentration was fixed to about 100 nM. These observations suggest that not only Ca2+ influx but the inhibition of PKA is necessary for the maximum O2- production by fMLP and that the O2- production is partially suppressed by the activation of PKA induced by fMLP.

Role of neutrophils in mediating human epithelial cell detachment from native basement membrane

Epithelial cell detachment from underlying basement membrane is a feature of diseases of many organs. In the lungs it is seen in disorders as diverse as bronchiectasis, allograft rejection, and asthma. The potential for different leukocytes to induce this change is not clear. In asthma both eosinophils and neutrophils are found in affected tissues, but the capacity of each of these types of cells to induce detachment of native epithelial cells from basement membrane requires clarification. Although eosinophils damage rather than detach human epithelial cells, the effects of neutrophils on epithelial cells naturally attached to basement membrane have not previously been described. Using the human amnion in vitro model, we tested the hypothesis that neutrophils have the capacity to detach intact human epithelial cells from basement membrane. The data indicate that increasing concentrations of neutrophils are able to detach epithelial cells from their underlying basement membrane. Detachment was increased when the neutrophils were activated in situ with tetradecanoyl phorbol acetate and after longer incubation periods. Platelet activating factor and opsonized zymosan showed similar boosting effects, whereas activated complement and formyl-methyl-leucyl-phenylalanine did not. Physical contact of the neutrophils with the epithelial cells was required to induce detachment. Detachment could be inhibited by glutathione and by soybean trypsin inhibitor, an inhibition pattern similar to cathepsin G and trypsin, but not collagenase, in this system. We conclude that neutrophils are capable of detaching human epithelial cells from basement membrane, which in part involves the release of chymotrypsin-like serine proteases, probably in conjunction with oxidants, and that this detachment can be inhibited.

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)

Regulation of human neutrophil degranulation by LY-83583 and L-arginine: role of cGMP-dependent protein kinase

The effects of guanosine 3',5'-cyclic monophosphate (cGMP) on the secretory response of activated human neutrophils were investigated using LY-83583, an inhibitor of soluble guanylate cyclase, and L-arginine, the precursor of nitric oxide formation. A 30% release of myeloperoxidase (MPO) and lactoferrin (LF) from the primary and specific granules, respectively, was detected by enzyme-linked immunosorbent assay in adhered neutrophils stimulated with 0.1 microM N-formyl-methionyl-leucyl-phenylalanine (FMLP) or 20 microM A-23187. LY-83583 (100 microM) inhibited the release of both LF and MPO after stimulation with FMLP or A-23187. Conversely, preincubation of neutrophils with 0.5 mM L-arginine augmented the release of LF and MPO in FMLP- and A-23187-stimulated cells. Concurrent with the increase in the degranulation response was an elevation of cGMP levels in L-arginine-treated cells, while stimulated cGMP levels were reduced in LY-83583-treated cells. Furthermore, cGMP-dependent protein kinase (G-kinase) activity was reduced in LY-83583-treated cells, as determined by the delay in G-kinase translocation to intermediate filaments and the inhibition of vimentin phosphorylation. Degranulation, elevation of cGMP levels, and targeting of G-kinase were also dependent on the concentration of A-23187 or FMLP. These data suggest that activators of neutrophil degranulation mediate this response through a cGMP-dependent protein kinase mechanism.

Differential regulation of early phase and late phase responses in human neutrophils by cAMP

The elevation of intracellular levels of cyclic AMP by forskolin stimulation of adenylate cyclase regulates early and late phase neutrophil responses differentially. Early phase neutrophil responses as measured by shape change in response to chemotactic factors, transmigration across a polycarbonate membrane and priming were unaffected by forskolin-induced elevation of intracellular cAMP. Late phase neutrophil responses such as release of superoxide anions, activation of phospholipase A2 and platelet activating factor (PAF) synthesis were inhibited by increasing intracellular cAMP through the addition of 10 microM forskolin for 10 min prior to stimulation. N-Formyl-methionyl-leucyl-phenylalanine-stimulated arachidonic acid release fell from 9.3% (untreated cells) to 4.6% in forskolin-treated cells. PAF generation was also inhibited from 430 pg/10(6) cells in untreated cells to background levels in forskolin-treated cells (110 pg/10(6) cells). Also, the reduction of cytochrome c by superoxide anions fell from 4.2 nmol/10(6) cells in the absence of forskolin to 2.0 nmol/10(6) cells following forskolin treatment. These results indicate that in neutrophils the elevation of cAMP acts differentially on cellular responses, not affecting early activation events, but markedly inhibiting late events such as the release of inflammatory mediators.

Nitric oxide, an endothelial cell relaxation factor, inhibits neutrophil superoxide anion production via a direct action on the NADPH oxidase

Nitric oxide provokes vasodilation and inhibits platelet aggregation. We examined the effect of nitric oxide on superoxide anion production by three sources: activated intact neutrophils, xanthine oxidase/hypoxanthine, and the NADPH oxidase. Nitric oxide significantly inhibited the generation of superoxide anion by neutrophils exposed to either FMLP (10(-7)M) or PMA (150 ng/ml) (IC50 = 30 microM). To determine whether the effect of nitric oxide on the respiratory burst was due to simple scavenging of O2+, kinetic studies that compared effects on neutrophils and the cell-free xanthine oxidase system were performed. Nitric oxide inhibited O2+ produced by xanthine oxidase only when added simultaneously with substrate, consistent with the short half-life of NO in oxygenated solution. In contrast, the addition of nitric oxide to neutrophils 20 min before FMLP resulted in the inhibition of O2+ production, which suggests formation of a stable intermediate. The effect of nitric oxide on the cell-free NADPH oxidase superoxide-generating system was also examined: The addition of NO before arachidonate activation (t = -6 min) significantly inhibited superoxide anion production. Nitric oxide did not inhibit O2+ when added at NADPH initiation (t = 0). Treatment of the membrane but not cytosolic component of the oxidase was sufficient to inhibit O2+ generation. The data suggest that nitric oxide inhibits neutrophil O2+ production via direct effects on membrane components of the NADPH oxidase. This action must occur before the assembly of the activated complex.

Ca2+ ionophore-induced cyclic adenosine-3',5'-monophosphate elevation in human neutrophils. A calmodulin-dependent potentiation of adenylate cyclase response to endogenously produced adenosine: comparison to chemotactic agents

The cyclic adenosine-3',5'-monophosphate (cAMP) elevation caused by exposure of human neutrophils to the Ca2+ ionophore A23187 was prevented when endogenously produced adenosine was either removed by preincubation with adenosine deaminase or blocked from binding to the adenosine receptor by antagonists [theophylline or (E)-4-(1,2,3,6-tetrahydro-1,3-dimethyl-2,6-dioxo-9H-purin-8-yl)cinnamic acid]. In the absence of endogenous adenosine, A23187 potentiated the neutrophil cAMP response to 2-chloroadenosine, prostaglandin E1, and isoproterenol. When neutrophil suspensions were preincubated with concentrations of Ro 20-1724, which appeared to maximally inhibit cAMP phosphodiesterase, A23187 was still able to substantially elevate cAMP levels, suggesting that A23187 increases cAMP by amplifying adenylate cyclase responsiveness to the agonist rather than by inhibiting cAMP phosphodiesterase. The ability of A23187 to augment the cAMP elevation caused by 2-chloroadenosine was persistent over a 10-min period. The neutrophil cAMP elevations caused by chemoattractants leukotriene B4, C5a, and N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) were all prevented when endogenously produced adenosine was eliminated from the cell suspensions by the addition of adenosine deaminase. The A23187-induced cAMP elevation was inhibited completely by the calmodulin inhibitors chlorpromazine, trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide, whereas cAMP levels induced by FMLP, leukotriene B4 and C5a were less affected. It appears that A23187 raises cAMP in human neutrophils by a calmodulin-dependent potentiation of adenylate cyclase responsiveness to endogenously produced adenosine while the chemoattractant-induced cAMP elevations (FMLP), leukotriene B4, and C5a), although possibly Ca2+ dependent, are less sensitive to calmodulin inhibitors and may involve additional biochemical events.

Neutrophil function and oral disease

The pathological sequela of reduced neutrophil function in the oral cavity and the mechanisms behind dysfunction have added to our understanding of infectious diseases. Numerous examples have been given, and the overriding conclusion must be that any impairment of neutrophil function will lead to some degree of increased susceptibility to infection. Perhaps the tissue most sensitive to pathological changes in the oral cavity is the periodontium. In cases of severe neutrophil dysfunction, there is severe periodontal breakdown, but also in cases of "mild" neutrophil dysfunction, where there is no other infection, such as in individuals with LJP, there is severe periodontal breakdown. The molecular basis of neutrophil dysfunction is beginning to be understood in individuals with LJP, LAD, CGD, and AIDS. It is our hope that further research in this area will help to delineate the pathogenesis of these and other oral diseases.

Activation of the respiratory burst oxidase in neutrophils: on the role of membrane-derived second messengers, Ca++, and protein kinase C

A major bactericidal mechanism of neutrophils involves activation of the respiratory burst oxidase to generate superoxide (O2-). The oxidase is activated rapidly, often within a minute, in response to extracellular signals such as chemoattractants, inflammatory mediators, and invading microorganisms. Increasing evidence indicates that lipases also respond rapidly, releasing potent regulatory molecules from progenitor lipids. Released molecules include potential regulators of protein kinase C--diacylglycerol (DAG), arachidonate, and sphingosine--and levels of one of these, DAG, frequently correlate with O2- production. In this author's view, the available data implicate DAG and protein kinase C as key factors in the regulation of the respiratory burst. Herein, the array of activating agonists, the generation and function of some lipid-derived mediators, and evidence pertaining to the participation of protein kinase C are reviewed.

Stimulation of cAMP accumulation and superoxide production in human neutrophils and monocytes

The effect of sodium fluoride (NaF) on superoxide generation and cyclic adenosine monophosphate (cAMP) levels in human neutrophils and monocytes was investigated. NaF (greater than 10 mM) stimulated superoxide (O2-) production in both cell types in a time dependent manner. NaF (0.5 to 20 mM) increased cAMP levels by 1.5- to 3.-fold in both neutrophils and monocytes. Increases in cAMP levels were time-dependent; the maximal level was attained within 5 minutes after the addition of NaF, and cAMP levels remained elevated for up to 10 minutes. Only high concentrations of NaF (10 and 20 mM) increased both cAMP levels and O2- production. Therefore, a direct role of cAMP in O2- generation is not likely. It is speculated that since NaF (greater than 10 mM) can complex with extracellular Ca++, and thus reduce free Ca++ concentration required for O2- generation, a NaF-dependent increase in cAMP may restore cytosolic free Ca++ by mobilizing intracellular stores of Ca++. Further, in view of the proposed involvement of a phosphorylation-dephosphorylation mechanism in the regulation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, we speculate that NaF, by inhibiting phosphoprotein phosphatase activity, may indirectly activate the NADPH oxidase system and thus superoxide generation.

Neutrophil function disorders

The polymorphonuclear leukocyte (neutrophil) is the most important phagocytic cell that defends the host against acute bacterial infection. Disorders of neutrophil function are suggested by recurrent cutaneous, periodontal, respiratory, or soft tissue infections. Staphylococcus aureus, gram-negative bacilli, and less commonly, Candida albicans, are the causative organisms. Treatment is supportive involving surgical drainage and antibiotics. Bone marrow transplantation offers hope to some patients. The biochemical and molecular defects have been identified for some of these disorders. Identification of these defects and their physiologic consequences have improved our understanding of how the activated neutrophil is attracted and adheres to inflammatory sites, and produces toxic products that destroy bacteria. However, the activated neutrophil may also damage normal tissue and participate in diseases such as rheumatoid arthritis and the adult respiratory distress syndrome (ARDS).

Phosphorylation of partially purified 1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine:acetyl-CoA acetyltransferase from rat spleen

A new improved method for purification of the enzyme 1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine: acetyl-CoA acetyltransferase (EC 2.3.1.67) from rat spleen is described. The catalytic subunit of cyclic AMP-dependent protein kinase in the presence of MgATP stimulated about 3-fold the activity of this partially purified enzyme activity. When [gamma-32P]ATP was included in the assay mixture, the analysis of phosphoprotein products by SDS/polyacrylamide-gel electrophoresis and autoradiography showed the incorporation of [32P]phosphate into a single protein band of about 30 kDa. Analysis of the phosphorylated amino acids indicated that the phosphate was incorporated into a serine residue. Activation of the acetylation reaction by the protein kinase was reversible. The reversal of the activation was coincident with the loss of the [32P]phosphate incorporated into the 30 kDa protein band, which suggests that the acetyltransferase is regulated by a phosphorylation-dephosphorylation mechanism dependent on cyclic AMP.

Characteristics of aggregated immunoglobulin G as an immunologic phagocytic stimulus for granule enzyme release from human neutrophils

Aggregated immunoglobulin G (AggIgG) induced a time- and concentration-dependent phagocytic release of granule-associated lysozyme and myeloperoxidase (MPO) from human neutrophils. Degranulation was significantly enhanced in the presence of calcium or magnesium, and maximum granule exocytosis was observed when both divalent cations were present. AggIgG-stimulated enzyme release was inhibited with the intracellular calcium antagonist, TMB-8[8-(N,N-diethylamino)-octyl-(3,4,5-trimethoxy)benzoate] in the absence of extracellular calcium. DIDS (4,4'-diisothiocyano-2,2'-disulfonic acid stilbene), a permeant anion channel blocker, also suppressed AggIgG-induced degranulation. Cycloheximide, an inhibitor of protein synthesis, enhanced granule exocytosis from AggIgG-treated neutrophils. Two inhibitors of transmethylation reactions, 3-deazaadenosine (3-DZA) and homocysteine thiolactone (HCTL) in combination, suppressed AggIgG-elicited granule enzyme release. These data indicate that AggIgG is a useful probe for investigating the requirements for phagocytic enzyme release from human neutrophils.

Calmodulin-dependency of human neutrophil phosphodiesterase

A recent study has reported that the phosphodiesterases of human neutrophils are calmodulin-insensitive (Smolen and Geosits, Inflammation 8:193-199, 1984). In the present study, two forms of human neutrophil phosphodiesterase were separated by chromatography on DEAE-52. Peak I phosphodiesterase is activated 2.3-fold by calcium and calmodulin but is not stimulated by either calcium or calmodulin alone. Calmodulin-dependent activation of the phosphodiesterase is blocked by both 20 microM trifluoperazine and 20 microM W-7. Peak II is not stimulated by calmodulin. These findings suggest that calmodulin may play an important role in regulating alterations in cyclic nucleotide metabolism that accompany neutrophil activation.

Receptor-specific threshold effects of cyclic AMP are involved in the regulation of enzyme release and superoxide production from human neutrophils

We have investigated the sequence of events leading from the activation of adenylate cyclase and increases in intracellular cyclic AMP to the modulation of enzyme release and superoxide production in human neutrophils. In the isolated plasma membrane, adenylate cyclase is activated by both prostaglandin E1 and isoproterenol. In the whole cell only a small increase in cyclic AMP is observed, though in the presence of the phosphodiesterase inhibitor, methylisobutylxanthine a substantial amplification in intracellular cyclic AMP is observed with both isoproterenol and prostaglandin E1. These conditions are relevant to the regulation of cell function, since fMet-Leu-Phe-stimulated superoxide production is inhibited by either prostaglandin E1 or isoproterenol in the absence of methylisobutylxanthine, while enzyme release is inhibited only via the prostaglandin E1 receptor and then only in the presence of methylisobutylxanthine. For enzyme release and superoxide production, the order of potency for three prostaglandins tested was prostaglandin E1 greater than prostaglandin D2 much greater than prostaglandin F2 alpha. Our results suggest that (a) superoxide production is more sensitive to regulation by cyclic AMP than enzyme release, (b) the type of receptor occupied as well as the threshold level of cyclic AMP attained are important to the regulation of enzyme release, and (c) although elevation in cyclic AMP is inhibitory to neutrophil function, phosphodiesterase inhibition is required in addition to adenylate cyclase activation to effect maximal inhibition.

Effects of D-penicillamine, dichlofenac sodium and gold sodium thiomalate upon the selective release of lysosomal enzymes from human polymorphonuclear leucocytes to immune complex

The selective release of beta-glucuronidase (beta-Gluc) and beta-N-acetylglucosaminidase (beta-Glm) from human polymorphonuclear leucocytes (PMN), initiated with bovine serum albumin/anti-bovine serum albumin (BSA/anti-BSA) immune complex (15 micrograms/ml-1) was significantly reduced by increasing concentrations (10(-7) M, 10(-6) M and 10(-5) M) of D-penicillamine (D-PEN) in a dose-dependent fashion. These effects upon the exocytosis of the lysosomal enzymes studied are in accordance with the results obtained previously in rats with adjuvant arthritis. In contrast, Dichlofenac Sodium (DICHL), which has been found to exert inhibitory activity upon extracellular release of beta-Gluc and beta-Glm in adjuvant arthritic rats in previous studies, had no significant in vitro effect on the exocytosis of these enzymes at the concentrations identical to those of D-PEN. Also, Gold Sodium Thiomalate (GST), in the same concentrations ranging from 10(-7) M-10(-5) M, failed to inhibit selective release of beta-Gluc and beta-Glm in the present investigations. Additionally, BSA/anti-BSA, D-PEN, DICHL and GST did not significantly produce the extracellular release of lactate dehydrogenase (LDH) indicating that under experimental conditions described the cell remained intact. Moreover, neither D-PEN, DICHL, GST or BSA/anti-BSA significantly changed the activities of lysosomal enzyme markers used in these experiments. The possible mechanism(s) of the observed phenomena are discussed.

Effects of soluble stimuli on human monocyte secretion

We report here that the chemotactic peptide, N-formyl-methionyl-leucyl-phenylalanine (FMLP), and the mitogenic phorbol ester, phorbol myristate acetate (PMA) cause a time- and concentration-dependent, selective, extracellular release of N-acetyl-beta-glucosaminidase and lysozyme from freshly isolated, adherent human peripheral blood monocytes. The inability of the protein synthesis inhibitor, cycloheximide, to influence enzyme release indicates that these enzymes are constitutive secretory products. 1-O-Hexadecyl-/octadecyl-2-O-acetyl-sn-glyceryl-3-phosphorylcholine demonstrated moderate secretory activity, whereas pepstatin A, concanavalin A, and leukotriene B4 were essentially inactive. FMLP- and PMA-induced enzyme release were inhibited with the intracellular calcium antagonist, 8-(N,N-diethylamino)-octyl-(3,4,5-trimethoxy)benzoate hydrochloride and the anion channel blocker, 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene. These results demonstrate the capacity of soluble, surface-active stimuli to activate the human monocyte secretory process.

Inhibition by verapamil of neutrophil responses to formylmethionylleucylphenylalanine and phorbol myristate acetate. Mechanisms involving Ca2+ changes, cyclic AMP and protein kinase C

Verapamil inhibits in human neutrophils the respiratory burst, the secretion and the change of transmembrane potential induced by formylmethionylleucylphenylalanine, a Ca2+-dependent stimulus, and by phorbol myristate acetate, a Ca2+-independent stimulus. Besides the blocking of Ca2+ channels, many mechanisms are responsible for the inhibition of neutrophil responses. In fact, verapamil (i) increases the intracellular cAMP concentration, potentiates the cAMP response induced by the chemotactic peptide and induces the appearance of a cAMP response also when the stimulant is phorbol myristate acetate; (ii) causes a decrease of Ca2+ association to cell membranes, so depleting the pools of exchangeable Ca2+ and depressing the 'Ca2+ response' in terms of rise in [Ca2+]i monitored with Quin 2 and of rapid mobilization from cell membranes monitored by chlorotetracycline fluorescence change; (iii) inhibits the Ca2+-activated phospholipid-dependent protein kinase C. The data, discussed in relation to the biochemical mechanisms of the stimulus-response coupling, are compatible with the hypothesis of an involvement of the activation of protein kinase C as key step in the sequence of transduction events for the induction of many neutrophil functions.

Activation of protein kinase C in neutrophil cytoplasts. Localization of protein substrates and possible relationship with stimulus-response coupling

Treatment of enucleated, granule-free neutrophil cytoplasts with the protein kinase C activator phorbol 12-O-myristate-13-acetate (PMA) causes an increased 32P-incorporation into a variety of polypeptides. Permeabilization of PMA-stimulated, 32P-labeled cytoplasts by 0.01% digitonin fully releases the majority of these phosphorylated proteins. A statistically significant correlation is found between the extent of PMA-induced activation of generation of superoxide anion (O2-) and the phosphorylation of a cytosolic polypeptide with an apparent Mr of 46,000, whose 32P-labeling is also enhanced by the treatment of cytoplasts with 1-oleyl-2-acetylglycerol, the Ca2+ ionophore ionomycin or latex beads. Furthermore, treatment of cytoplasts with the protein kinase C inhibitor trifluoperazine markedly inhibits the 32P-labeling of proteins in the 40 000 Mr range, including the 46 kDa polypeptide, and almost totally abolishes the activation of O2- production by PMA.

Inhibition of receptor-mediated release of arachidonic acid by pertussis toxin

Treatment of guinea pig neutrophils with pertussis toxin (islet-activating protein; IAP) results in inhibition of N-formyl peptide receptor-mediated release of arachidonic acid and granular enzymes. Inhibition by the toxin is specific, in that responses to the calcium ionophore A23187 are not affected. The action of the toxin is not associated with alterations in cellular concentrations of cyclic AMP but is correlated with the ability of the toxin to catalyze the ADP-ribosylation of a 41,000 dalton membrane protein. This protein comigrates on SDS-polyacrylamide gels with the alpha subunit of Gi, the inhibitory guanine nucleotide-binding regulatory component of adenylate cyclase. It is likely that this G protein is involved in receptor-mediated signal transduction in neutrophils by mechanisms that do not involve cyclic AMP.

Human neutrophil phosphodiesterase. Calmodulin insensitivity and other properties

Extracts of human neutrophils were examined for phosphodiesterase activity using a radiochemical assay. As reported by other investigators, both high- and low-Km forms of the enzyme were found. Although calmodulin could be measured in these extracts, human neutrophil phosphodiesterase proved not to be calmodulin dependent. Activity of the neutrophil phosphodiesterase was also not altered by physiologic concentrations of indomethacin, p-bromophenacyl bromide, eicosatetraenoic acid, or eicosatetraynoic acid, all inhibitors of arachidonic acid metabolism. These results are relevant to stimulus secretion coupling in neutrophils, wherein calmodulin-dependent reactions play a vital role.

Human leukocyte cyclic AMP and cyclic GMP levels during chemotaxis in delayed type hypersensitivity

Ten nickel-allergic patients and six healthy control subjects participated in a study of the morphology, kinetics and evolution of the cAMP and cGMP concentrations of migrated leukocytes, using an improved skin chamber technique. Also studied was the effect of nickel exposure in the chamber medium during development of an eczematous reaction in the nickel-allergic patients. Nickel exposure had a specific effect on the morphology, from the 24th hour to the end of the 48 h observation period, with a significant increase in the percentages of basophils, eosinophils and lymphocytes and a decrease of neutrophils. A significantly increased leukocyte migration rate (LMR) was observed from the 27th to 39th hour in six of the allergic patients exposed to nickel. There were no specific permanent changes in cAMP and cGMP concentrations during nickel exposure. The control chambers of the allergic patients and healthy controls had identical leukocyte morphology, LMR and leukocyte concentrations of cAMP and cGMP. However, no correlations were found between LMR, cAMP and cGMP in the eczema patients throughout the observation period.

Evidence for N-formyl chemotactic peptide-stimulated GTPase activity in human neutrophil homogenates

Neutrophil homogenates contained a high affinity guanosine triphosphatase (GTPase) that was stimulatable (+27%) by the addition of 100 nM N-formyl chemotactic peptide (CHO-pep), but not by 1 microgram X ml-1 phorbolmyristate acetate (PMA). Kinetic analysis of the stimulation demonstrated an apparent lagtime of 14.3 +/- 6.9 s between the addition of CHO-pep and the optimal GTPase stimulation. The GTPase activity (but not CHO-pep-stimulated GTPase activity) was preserved in a highly purified plasma membrane fraction of the homogenate. From these observations we suggest that both a high affinity guanine nucleotide binding protein and GTPase are closely associated with the plasma membrane CHO-pep receptor. The possibility that GTPase activity may influence guanine nucleotide regulation of adenylate cyclase during CHO-pep stimulation of neutrophils is discussed.

Mechanisms of mediator release from neutrophils

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., O2-. 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.

Nonoxidative antimicrobial reactions of leukocytes

Increasingly abundant evidence supports the hypothesis that PMNs and perhaps alveolar macrophages have antimicrobial mechanisms independent of the presences of molecular oxygen for effective action against an array of bacteria and against some fungi. Eosinophils have mechanisms toxic for schistosomula and Trichinella larvae. In all instances the antimicrobial substances isolated have been cationic proteins and, in PMNs, associated with the azurophil cytoplasmic granules of the PMNs. Several of these substances have thus far demonstrated no enzymic function. Two of these substances are serine proteases but in one, chymotrypsin-like protein, the antimicrobial action depends on the cationic properties of the protein and is independent of the proteolytic action of the substance. In most instances, these proteins are cationic due to relatively large proportions of arginine. In two instances, a large proportion of lysine is present. All have high proportions (about 50%) of hydrophobic amino acid. Such proteins occur in the PMNs of man, rabbit, guinea pig, rat, cow, and chicken. The present view is that they are most active against gram-negative bacteria. At least two of them-37-kd and 57-kd proteins (Shafer and Spitznagel, 1983)-act on S. typhimurium in a manner analogous to that of polymyxin B through binding to lipid A. Currently available results shows that anaerobic PMNs have substantial antimicrobial capacity. Whether this capacity is due to the O2-independent mechanisms discussed in this chapter remains to be established with greater certainty.

Metabolic requirements for maintenance of the chlortetracycline-labeled pool of membrane-bound calcium in human neutrophils

Human neutrophils labeled with chlortetracycline (CTC), commonly used as a probe of membrane-bound calcium, release lysosomal enzymes and exhibit a rapid decrease in fluorescence when exposed to the chemotactic peptide fMet-Leu-Phe or the lectin Con A. This decrease has been attributed to the release of calcium from a membrane-associated "trigger pool." The nature of this putative pool has been further characterized by examining the effects of various inhibitors on the CTC fluorescence response and lysosomal enzyme release from stimulated neutrophils. These agents included inhibitors of glycolysis (2-deoxyglucose and iodoacetate), an uncoupler of oxidative- phosphorylation (KCN), and a sulfhydryl inhibitor (N-ethylmaleimide). Resting neutrophils labelled with CTC demonstrated an enhanced decay of baseline fluorescence when exposed to 2-deoxyglucose or iodoacetate. This suggested that the pool of membrane-bound calcium labelled by this probe was maintained by glycolytic metabolism. Furthermore, 2-deoxyglucose and iodoacetate inhibited both the stimulated decrease in CTC fluorescence and lysosomal enzyme release induced by fMet-Leu-Phe and Con A in a time-dependent manner. KCN did not inhibit either response to stimulation, but did retard the recovery of CTC fluorescence observed when fMet-Leu-Phe was used as the stimulus. High concentrations of N-ethylmaleimide (100 microM) completely inhibited both the CTC fluorescence response and lysosomal enzyme release almost immediately; low concentrations of N-ethylmaleimide (30 microM) inhibited lysosomal enzyme release in a time-dependent manner without significantly affecting changes in CTC fluorescence. These results are consistent with the hypothesis that CTC serves as a probe of membrane-bound "trigger" calcium, the release of which is dependent upon intact glycolysis and is a requirement for lysosomal enzyme release.

The fluorescence response of chlortetracycline-loaded human neutrophils is modulated by prostaglandin E1, but not by cyclic nucleotides

Human neutrophils preloaded with chlortetracycline, commonly used as a probe of membrane-bound calcium, demonstrate a prompt decrease in fluorescence when exposed to surface stimuli such as the chemotactic peptide fMet-Leu-Phe. The fluorescence response was highly sensitive to preincubation with prostaglandin E1. This effect was apparently not due to elevated levels of cAMP since exogenous dibutyryl-cAMP did not alter the chlortetracycline fluorescence response to fMet-Leu-Phe. This is one of the few instances of prostaglandin E1 affecting neutrophils at physiologic concentrations, dissociated from changes in cellular cyclic nucleotide levels.

Myeloperoxidase-dependent effect of amines on functions of isolated neutrophils

Isolated neutrophilic leukocytes were incubated with primary amines and related nitrogenous compounds. Stimulation of neutrophil oxygen (O2) metabolism with phorbol myristate acetate or opsonized zymosan resulted in production of hydrogen peroxide (H2O2), myeloperoxidase-catalyzed oxidation of chloride (C1-) to hypochlorous acid (HOC1), and the reaction of HOC1 with the added compounds to yield nitrogen-chlorine (N-C1) derivatives. Formation of N-C1 derivatives of low lipid solubility resulted in accumulation of the derivatives in the extracellular medium. These oxidizing agents were identified and measured on the basis of their absorption spectra and their ability to oxidize 5-thio-2-nitrobenzoic acid to the disulfide form. The yield of N-Cl derivatives was in the order: taurine greater than Tris greater than spermidine greater than spermine greater than glucosamine greater than putrescine greater than guanidinoacetate. Accumulation of N-C1 derivatives was also observed in the absence of added amines, owing to the reaction of HOC1 with endogenous taurine and other amines that were released from the cells into the medium. In the presence of compounds that yield lipophilic N-C1 derivatives, little or no accumulation of oxidizing agents was observed. Instead, these compounds inhibited the accumulation of N-C1 derivatives that was obtained with taurine, and their effect was competitive with taurine. Inhibition was in the order: methylamine greater than ethanolamine greater than phenylethylamine greater than p-toluenesulfonamide greater than ammonia greater than guanidine. Formation of lipophilic N-C1 derivatives also resulted in inhibition of O2 uptake and glucose metabolism. Inhibition was prevented by adding catalase to eliminate H2O2, dapsone to inhibit myeloperoxidase, taurine to compete for reaction with HOC1, or compounds that are rapidly oxidized by HOC1 or N-C1 derivatives, to reduce these oxidizing agents. The results indicate that: (a) formation of N-C1 derivatives that do not penetrate biological membranes can protect leukocytes against the cytotoxicity of HOC1 and lipophilic N-C1 derivatives, and (b) formation of membrane-permeable N-C1 derivatives in the absence of target cells or readily oxidized substances results in oxidative attack by the N-C1 derivatives on leukocyte components and inhibition of leukocyte functions.