Production of superoxide by phagocytic leukocytes: a paradigm for stimulus-response phenomena

In memoriam: Filippo Rossi (1926-2022)

Description of the scientific life of Filippo Rossi, who died in October 2022.

Review

Production of superoxide anion O2*- by the membrane-bound enzyme NADPH oxidase of phagocytes is a long-known phenomenon; it is generally assumed that O2*-helps phagocytes kill bacterial intruders. The details and the chemistry of the killing process have, however, remained a mystery. Isoforms of NADPH oxidase exist in membranes of nearly every cell, suggesting that reactive oxygen species (ROS) participate in intra- and intercellular signaling processes. What the nature of the signal is exactly, how it is transmitted, and what structural characteristics a receptor of a "radical message" must have, have not been addressed convincingly. This review discusses how the action of messengers is in agreement with radical-specific behavior. In search for the smallest common denominator of cellular free radical activity we hypothesize that O2*- and its conjugate acid, HO2*, may have evolved under primordial conditions as regulators of membrane mechanics and that isoprostanes, widely used markers of "oxidative stress", may be an adventitious correlate of this biologic activity of O2*-/HO2*. An overall picture is presented that suggests that O2*-/HO2* radicals, by modifying cell membranes, help other agents gain access to the hydrophobic region of phospholipid bilayers and hence contribute to lipid-dependent signaling cascades. With this, O2*-/HO2* are proposed as indispensable adjuvants for the generation of cellular signals, for membrane transport, channel gating and hence, in a global sense, for cell viability and growth. We also suggest that many of the allegedly O2*- dependent bacterial pathologies and carcinogenic derailments are due to membrane-modifying activity rather than other chemical reactions of O2*-/HO2*. A consequence of this picture is the potential evolution of the "radical theory of ageing" to a "lipid theory of aging".

Uric acid mediates photodynamic inactivation of caprine alpha-2-macroglobulin

Uric acid (2,6,8 trioxopurine), the end product of purine metabolism in mammalian systems, has shown a wide range of antioxidant properties including scavenging of hydroxyl radical and singlet oxygen. In this study we show that in the presence of visible light, uric acid disrupted caprine alpha-2-macroglobulin (alpha(2) M) structure and antiproteolytic function in vitro. Proteinase cleaves the bait region of caprine inhibitor inducing major conformational changes and entrapping the enzyme within its molecular cage. In contrast to native alpha(2) M, modified antiproteinase lost half of its antiproteolytic potential within 4 hours of uric acid exposure. The changes in uv-absorption spectra of the treated protein suggested possible spatial rearrangement of subunits or conformational change. Analysis of the mechanism by which alpha(2) M was inactivated revealed that the process was dependent on generation of superoxide anion and hydrogen peroxide. Our findings suggest that antiproteolytic activity of caprine alpha(2) M could be compromised via oxidative modification mediated by uric acid. Moreover, low concentrations of alpha(2) M were found to stimulate superoxide production by some unknown mechanism.

Oxidation of defined antigens allows protein unfolding and increases both proteolytic processing and exposes peptide epitopes which are recognized by specific T cells

The participation of oxidative mechanisms in major histocompatibility complex (MHC) class II-restricted antigen presentation was studied in vitro. In general, antigen processing is inhibited when peritoneal macrophages (MO) are incubated with scavengers of reactive oxygen intermediates (ROI): mannitol (an.OH scavenger), dimethylurea (DMTU, which reacts with H2O2 and HOCl) and NCO-700 (an epoxysuccinic acid derivative which inhibits oxidant production by activated phagocytes and can scavenge reactive oxygen species in both NaOCl and hypoxanthine (XOD) systems). However, neither rotenone and antimycins (inhibitors of O-2 production at the NADH dehydrogenase and ubiquinone-cytochrome b regions, respectively) nor aminoguanidine (an inducible nitric oxide synthase inhibitor) impaired antigen presentation, thus indirectly discarding the participation of mitochondrial oxidation and reactive nitrogen intermediates (RNI) in antigen processing. ROI scavengers do not inhibit the MHC class II-restricted presentation of antigens that need processing but have their disulphide bonds reduced. It can be shown that oxidation of protein antigens (either by chlorination or performic acid treatment) allow protein unfolding and enhance both processing and exposure of immunogenic epitopes to specific T cells.

Resistance of spontaneously transformed Syrian hamster embryo cells and their malignant variants to cytotoxic activity of recombinant tumor necrosis factor-alpha

To study the possible role of the host macrophages in the selection of tumor cells and tumor progression, a series of Syrian hamster tumor cell lines all originating from a single spontaneously transformed Syrian hamster embryo cell line (STHE strain) have been established. These STHE tumor cell variants, selected either in vitro with resident and lipopolysaccharide-activated macrophages or in vivo, differ in tumorigenic and metastatic activity. The selected malignant STHE cells become resistant to cytotoxic activity of activated peritoneal macrophages and of exogenous hydrogen peroxide (H2O2). Since activated macrophages are a known source for both cytotoxic agents H2O2 and tumor necrosis factor (TNF), the purpose of the present study was to define the sensitivity of the STHE tumor cell lines to a direct cytotoxic activity mediated by recombinant TNF-alpha in an attempt to understand the role of the cytokine in in vitro selection of a malignant STHE cells by activated macrophages. The spontaneously transformed STHE cells (selected in vivo and in vitro) as well as the hamster embryo cells transformed in vitro by a tumorigenic Rous sarcoma virus (Schmidt-Ruppin strain) were used as targets. TNF-alpha-sensitive mouse L929 cells were included in the study as a positive control. Sensitivity of actinomycin D-pretreated target cells studied for cytotoxic activity of a recombinant TNF-alpha was examined over 21 h with a crystal violet dye assay. It was found that, in contrast to L929 cells, the spontaneously transformed STHE cells as well as tumorigenic Rous sarcoma virus hamster embryo transformants, were all significantly resistant to the TNF-alpha-mediated cytolysis. This indicates that TNF-alpha is not the single factor responsible in in vitro selection of malignant STHE cell variants by activated macrophages. It appears that H2O2 is involved in the selection of the hamster macrophage-resistant STHE tumor cells.

Functional characterization of equine neutrophils in response to calcium ionophore A23187 and phorbol myristate acetate ex vivo

Equine neutrophils (PMN) play a critical role in inflammatory processes in horses. The objective of this study was to characterize equine PMN function ex vivo following stimulation with calcium ionophore A23187 (A23187) and phorbol myristate acetate (PMA). These stimulants trigger different branches of the PMN activation process that occurs in vivo. Equine PMN were isolated from the whole blood of six clinically normal geldings using a one-step discontinuous Percoll gradient technique. Neutrophil aggregation, degranulation, and superoxide anion production were evaluated in assay systems which had previously been established to quantitate PMN function. Dose-response curves for A23187 and PMA were derived for the three functions. Results indicate that equine PMN aggregation and superoxide anion production are more responsive to activation by PMA as the maximum change in percent transmittance and maximum nanomoles of superoxide anion produced following PMA stimulation (60.8% and 10.4 nmol per 10(6) cells, respectively) were greater than those values stimulated by A23187 (41.5% and 5.2 nmol per 10(6) cells, respectively). However, degranulation was found to be more responsive to A23187 stimulation (maximum percent degranulation: 56.1%) than to PMA stimulation (maximum percent degranulation: 30.7%). Dose-response curves following A23187 and PMA stimulation revealed that superoxide anion production had the lowest threshold concentration among the three functions. Degranulation had the highest threshold concentration among the three functions for both stimulants. Results indicate that equine PMN functions differ in their dependence on second messengers in the activation pathway. These functions also occur in a dose-dependent manner and differ in the threshold concentrations required for their stimulation.

Superoxide and traditional Chinese medicines

In traditional Chinese medicinal practices, herbs are classified as 'cold', 'neutral', or 'hot'. Fluorometric analysis of herbs with 'cold' properties revealed that these herbs produce large amounts of superoxide. In contrast, herbs with 'hot' properties have scavenging activities. We believe that this electron transfer to form superoxide and the scavenging of superoxide may elucidate the phenomena of the 'yin' (represented by 'cold') and 'yang' (represented by 'hot') respectively.

The NADPH oxidase complex of phagocytic leukocytes: a biochemical and cytochemical view

The NADPH oxidase complex catalyzes the formation of superoxide (O2.-) in phagocytic leukocytes. This paper reviews recent advances in our understanding of this enzyme system. Recent studies have defined conditions for reconstitution of this enzymatic activity with purified proteins in a cell-free system. The role of the individual proteins that make up the active complex, their regulation and the effects of mutations in these proteins are discussed. While these studies represent major achievements, it is clear from cytochemical investigations that additional levels of complexity exist in the modulation of the NADPH oxidase complex in vivo. A major role for cytochemical analysis in understanding the cell biological aspects of the generation of reactive oxygen species is discussed.

Stereoselective suppression of neutrophil function by ketamine?

The effects of the commercially available ketamine preparation (Ketanest), the ketamine racemate and of the two enantiomers, the R(-)-racemate and the S(+)-racemate, as well as its drug-free solvent were examined by N-formyl-methionyl-leucyl-phenylalanine-(FMLP)- and zymosan-induced oxygen radical production of polymorphonuclear cells (PMN). The racemate and the two enantiomers of ketamine suppressed FMLP- and zymosan-induced chemiluminescence of PMN in a dose-dependent fashion to the same extent. Therefore suppression of chemiluminescence of PMN by ketamine does not result from a specific receptor interaction.

Participation of intracellular oxidative pathways in antigen processing by dendritic cells, B cells and macrophages

The antigen presentation abilities of antigen presenting cells (APC) from different lineages [mainly macrophages (M phi), B cells and dendritic cells (DC)] were compared. In this review we focus on the participation of intracellular oxidative mechanisms in intracellular degradation of protein antigens: an aspect that is often neglected when the issue of antigen processing is considered. Special emphasis is given to recent findings from our laboratory indicating that in addition to a lysosomal proteolytic step being present in all APC, a previous or simultaneous oxidative step is operative in some APC (M phi) but absent or less important in others (B cells, DC).

Signalling by O2-. and NO.: how far can either radical, or any specific reaction product, transmit a message under in vivo conditions?

With regard to the stability of the NO. radical as a chemical entity, it is without doubt able to serve as an intra- as well as an intercellular messenger. The radical O2-., in contrast, does not seem to be suited to far-range signalling in the vascular system. Its short chemical half-life, which is limited by the presence of various reactive blood constituents to below 50 ms, results in a free diffusion path length of less than 40 microns, i.e. only the distance between just a few cells. While accelerated 'downstream' transport by arterial blood may help to extend the action sphere, there is no possibility for O2-. to serve as a signal in an upstream direction. The estimates presented, however, do not invalidate arguments for a possible role of superoxide anions in intra- or pericellular signalling phenomena. Cross-talk between NO.- and O2-.-dependent signal routes, e.g. by peroxynitrite formation, is unlikely to be a relevant process under the conditions which prevail in the vascular system.

Effect of 5-aminosalicylic acid and analogous substances on superoxide generation and intracellular free calcium in human neutrophilic granulocytes

Activated polymorphonuclear leukocytes (PMNs), which are found in the inflammatory lesions of chronic inflammatory bowel disease, produce tissue-destructive oxygen-derived free radicals. The influence of 5-aminosalicylic acid (5-ASA), its acetylated metabolite (Ac-5-ASA), sulfasalazine (SAZ), and olsalazine (OLZ) (5-ASA dimer linked by an azo group) in pharmacologically relevant concentrations (0.1-10 mM) were tested on PMN superoxide production with either the receptor-specific agent formyl-methionyl-leucyl-phenylalanine (fMLP) or the protein kinase C activator phorbol myristate acetate (PMA). Inhibition of receptor-specific superoxide production occurred at 0.07, 0.32, and 0.63 mM (IC50 values) for 5-ASA, SAZ, and OLZ, respectively. No inhibitory effects of SAZ and OLZ were observed when PMA was applied as stimulus for PMN superoxide production. The results indicate that the signal to which PMNs respond by generating superoxide is primarily due to calcium release from intracellular stores. They further suggest that SAZ and OLZ may affect the oxygen-derived free radical production in human PMNs by unspecific cytotoxicity or by interference with the nicotinamide adenine dinucleotide phosphate, reduced (NADPH) oxidase system, whereas 5-ASA itself is a free radical scavenger.

Bacterial phospholipases C

A variety of pathogenic bacteria produce phospholipases C, and since the discovery in 1944 that a bacterial toxin (Clostridium perfringens alpha-toxin) possessed an enzymatic activity, there has been considerable interest in this class of proteins. Initial speculation that all phospholipases C would have lethal properties has not been substantiated. Most of the characterized enzymes fall into one of four groups of structurally related proteins: the zinc-metallophospholipases C, the sphingomyelinases, the phosphatidylinositol-hydrolyzing enzymes, and the pseudomonad phospholipases C. The zinc-metallophospholipases C have been most intensively studied, and lethal toxins within this group possess an additional domain. The toxic phospholipases C can interact with eukaryotic cell membranes and hydrolyze phosphatidylcholine and sphingomyelin, leading to cell lysis. However, measurement of the cytolytic potential or lethality of phospholipases C may not accurately indicate their roles in the pathogenesis of disease. Subcytolytic concentrations of phospholipase C can perturb host cells by activating the arachidonic acid cascade or protein kinase C. Nonlethal phospholipases C, such as the Listeria monocytogenes PLC-A, appear to enhance the release of the organism from the host cell phagosome. Since some phospholipases C play important roles in the pathogenesis of disease, they could form components of vaccines. A greater understanding of the modes of action and structure-function relationships of phospholipases C will facilitate the interpretation of studies in which these enzymes are used as membrane probes and will enhance the use of these proteins as models for eukaryotic phospholipases C.

The immediate activator of the NADPH oxidase is arachidonate not phosphorylation

Superoxide generation is rapidly triggered following the addition of a stimulus to neutrophils. The signal-transduction pathway culminates in the activation of protein kinase C, whose phosphorylation of a protein component is considered to activate the oxidase. Arachidonate stimulated the oxidase in a concentration-dependent manner but, unlike phorbol-12-myristate-13-acetate (PMA), was not inhibited by staurosporine, a protein kinase inhibitor. Increase protein phosphorylation, apparent with PMA, was not observed when superoxide generation was triggered by arachidonate. Inhibitors of phospholipase A2 inhibit the PMA activation of the oxidase. Therefore, we propose that arachidonate and not phosphorylation is the immediate stimulus for superoxide generation.

The NADPH-oxidase-associated H+ channel is opened by arachidonate

The H+ channel associated with the generation of O2.- by NADPH oxidase and the oxidase itself must both be activated in response to stimuli (e.g. phorbol esters, chemotactic peptides, certain fatty acids). We have investigated the effects of membrane potential, an imposed pH gradient and a combination of the two (the protonmotive force) on the H+ conductivity of the cytoplast membrane. H+ conductivity was observed only in the presence of arachidonate and not in its absence. In the presence of arachidonate, H+ movement was determined by the protonmotive force. The effect of arachidonate was probably on a channel, since this fatty acid did not significantly increase the H+ permeability of artificial phospholipid membranes. It appears, therefore, that arachidonate is required both for the activation of O2.- production and the associated H(+)-channel-mediated efflux.

Virulence factors of the family Legionellaceae

Whereas bacteria in the genus Legionella have emerged as relatively frequent causes of pneumonia, the mechanisms underlying their pathogenicity are obscure. The legionellae are facultative intracellular pathogens which multiply within the phagosome of mononuclear phagocytes and are not killed efficiently by polymorphonuclear leukocytes. The functional defects that might permit the intracellular survival of the legionellae have remained an enigma until recently. Phagosome-lysosome fusion is inhibited by a single strain (Philadelphia 1) of Legionella pneumophila serogroup 1, but not by other strains of L. pneumophila or other species. It has been found that following the ingestion of Legionella organisms, the subsequent activation of neutrophils and monocytes in response to both soluble and particulate stimuli is profoundly impaired and the bactericidal activity of these cells is attenuated, suggesting that Legionella bacterial cell-associated factors have an inhibitory effect on phagocyte activation. Two factors elaborated by the legionellae which inhibit phagocyte activation have been described. First, the Legionella (cyto)toxin blocks neutrophil oxidative metabolism in response to various agonists by an unknown mechanism. Second, L. micdadei bacterial cells contain a phosphatase which blocks superoxide anion production by stimulated neutrophils. The Legionella phosphatase disrupts the formation of critical intracellular second messengers in neutrophils. In addition to the toxin and phosphatase, several other moieties that may serve as virulence factors by promoting cell invasion or intracellular survival and multiplication are elaborated by the legionellae. Molecular biological studies show that a cell surface protein named Mip is necessary for the efficient invasion of monocytes. A possible role for a Legionella phospholipase C as a virulence factor is still largely theoretical. L. micdadei contains an unusual protein kinase which catalyzes the phosphorylation of eukaryotic substrates, including phosphatidylinositol and tubulin. Since the phosphorylation of either phosphatidylinositol or tubulin might compromise phagocyte activation and bactericidal functions, this enzyme may well be a virulence factor. Administration of the L. pneumophila exoprotease induces lesions resembling those of Legionella pneumonia and kills guinea pigs, suggesting that this protein plays a role in the pathogenesis of legionellosis. However, recent work with a genetically engineered strain has convincingly shown that the protease is not necessary for intracellular survival or virulence. As might be expected with a complex process like intracellular parasitism, it appears that the capability of Legionella strains to invade and multiply in host phagocytes is multifactorial and that no single moiety which is responsible for the virulence phenotype will be found.

Phacoanaphylactic endophthalmitis

Phacoanaphylactic endophthalmitis is a rare disease that develops infrequently after lens injury. The recent popularity of extracapsular cataract extraction with intraocular lens implants and the recently described possible association of low-grade infections have stimulated renewed interest in phacoanaphylactic endophthalmitis. It was formerly believed that this disease was due to the rejection of a lens protein that had been sequestered prior to lens injury. Recent observations indicate that this concept is incorrect and that phacoanaphylactic endophthalmitis represents altered tolerance to lens proteins. Clinical and histopathologic features as well as controversies in clinical management are discussed. Recent evidence concerning mechanisms of pathogenesis is reviewed [corrected].

Mechanisms of neutrophil-mediated tissue injury

Neutrophil-mediated tissue injury (NMTI) is a prominent mechanism of host autodestruction. It is defined by a sequence of events including neutrophil adherence and sequestration, diapedesis, activation, and secretion of toxic compounds. Knowledge of this sequence is valuable because it outlines points at which intervention may be sought. A limitation of these studies comes in the misunderstanding and misapplication of the tests used to analyze these events. We now realize that neutrophil adherence, sequestration, diapedesis, and secretion of toxic compounds can each occur alone without promoting generalized tissue injury. NMTI is a normally localized process that has gone systemically awry. Influencing this system must be selective and controlled because the inflammatory system is a critical component of host defense. As we gain insight into the pathophysiology of NMTI, we hope to find new avenues for therapeutic intervention in critical care.

Protein kinase C subtypes in human neutrophils

Protein kinase C from rat brain and human neutrophils was chromatographically separated on a hydroxylapatite column connected to a high-performance liquid chromatography (HPLC) system. Protein kinase C from rat brain was separated into three peaks (types I, II, and III). In contrast, only two types were obtained from human neutrophils matching type II and type III in brain. In cell membranes from unstimulated human neutrophils type III was predominant, but mainly type II was translocated to the membranes upon stimulation with phorbolmyristatacetate (PMA). Both types were equivalently activated by phosphatidylserine, diolein, and magnium and presented identical Km for ATP.

Free radical damage to proteins: the influence of the relative localization of radical generation, antioxidants, and target proteins

Free radicals were generated at known rates in the aqueous phase (by means of 2,2'-azobis (2-amidinopropane) dihydrochloride [AAPH]) and in a membranous (lipid) phase (by means of 2,2'-azobis (2,4-dimethylvaleronitrile [AMVN]). A soluble protein (bovine serum albumin: BSA), and membranes of lysed mitochondria containing radioactively labeled monoamine oxidase (MAO), were exposed to the resultant radical fluxes. Antioxidants were added to the system, either in the aqueous phase (Trolox) or in a liposomal membrane phase (alpha-tocopherol). Protein damage was assessed as tryptophan oxidation and conformational changes in tryptophan fluorescence of the soluble protein, BSA, and as fragmentation of both BSA and monoamine oxidase. Radicals generated in the aqueous phase, by AAPH, were effective in damaging BSA and MAO. Radicals generated within the liposome membrane phase (by AMVN) were less effective against BSA than those deriving from AAPH. Liposomal AMVN radicals could damage MAO, present in a separate membranous phase, though again, less effectively than could AAPH-derived radicals. BSA could be protected by Trolox, the aqueous soluble antioxidant, but hardly by tocopherol itself. Damage to MAO was limited by Trolox, and also by the hydrophobic antioxidant, tocopherol. Damaging reactions due to radicals generated in a membrane phase were significantly accelerated when the membrane was peroxidizable (soybean phosphatidylcholine) rather than nonperoxidizable (saturated dimyristoyl phosphatidylcholine). Thus lipid radicals also played some role in protein damage in these systems. BSA was attacked similarly in the presence or absence of liposomes by AAPH. Correspondingly, BSA could inhibit the peroxidation of liposomes induced by AAPH and less efficiently that induced by AMVN.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential inhibition by nedocromil sodium of superoxide generation elicited by platelet activating factor in human neutrophils

Nedocromil sodium (10(-10) - 10(-9) M) produced a dose-related inhibition of superoxide anion generation induced by platelet activating factor (PAF) in human polymorphonuclear leukocytes (PMNs). At a higher concentration (3 x 10(-7) M), nedocromil sodium significantly inhibited superoxide generation elicited by N-formyl-methionyl-leucylphenylalanine, but was unable to block the response to phorbol dibutyrate. Nedocromil sodium (10(-11) - 10(-5) M) enhanced PAF-stimulated lysozyme release in a non-concentration-dependent manner, and was completely ineffective in depressing PAF-induced release of [3H]arachidonic acid and the rise in cytosolic Ca2+. The preferential inhibitory effects of nedocromil sodium on PAF-induced activation of superoxide generation may provide insight into the therapeutic action of this drug as an anti-asthmatic agent.

Utility of staurosporine in uncovering differences in the signal transduction pathways for superoxide production in neutrophils

Neutrophils exhibit an intense phosphorylation of a 47 kDa protein and release large quantities of superoxide (O2-) upon stimulation with phorbol 12-myristate 13-acetate (PMA) or fMet-Leu-Phe (fMLP). Antagonists of protein kinases (e.g., 200 microM 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7); 15 nM staurosporine) inhibited these phenomena when the stimulus was PMA (Badwey, J.A. et al. (1989) J. Biol. Chem. 264, 14947-14953). In this paper, we now report that while neutrophils treated with 15 nM staurosporine and PMA release little O2-, cells in the presence of these compounds can be stimulated to release near normal quantities of O2- by the subsequent addition of fMLP. Surprisingly, staurosporine (15 nM) reduced the incorporation of 32P into the 47 kDa protein in fMLP stimulated cells at least as effectively as H-7, yet, while the staurosporine treated cells released substantial amounts of O2-, the cells treated with H-7 did not. These data suggest that a stimulatory pathway exists in neutrophils that contains a protein kinase 'distinct' from that which is activated when PMA is the stimulus and that this pathway may enable the O2- producing system to become functional with little or no phosphorylation of the 47 kDa protein. They further suggest that the steps which are sensitive to H-7 in the signal-transduction pathways utilized by PMA and fMLP may be different.

Continuous phosphorylation of both the 47 and the 49 kDa proteins occurs during superoxide production by neutrophils

Neutrophils stimulated with 4 beta-phorbol 12-myristate 13-acetate release large quantities of superoxide (O2-) and exhibit an intense phosphorylation of two proteins with molecular masses of approx. 47 and 49 kDa. Treatment of unstimulated cells with antagonists of protein kinase C (e.g., staurosporine; 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7)) is known to inhibit both of these phenomena upon stimulation. These antagonists of PKC also cause a rapid cessation of O2- release when added to cells that are already stimulated. In this paper, we report that the addition of staurosporine or H-7 to stimulated neutrophils resulted in a rapid loss of 32P from both the 47 and the 49 kDa phosphoprotein bands, as detected by autoradiography. This suggests that these two proteins may be regulated by a continual cycle of phosphorylation and dephosphorylation in the stimulated cell, with the phosphorylation reactions predominating, or undergo a rapid degradation subsequent to phosphorylation. Either explanation is consistent with the view that protein kinase C activity is necessary to both initiate and maintain O2- production in neutrophils stimulated with tumor promoters.

Calcium in lipid peroxidation: does calcium interact with superoxide?

Using a pulse radiolysis approach to generate and observe superoxide anions (O2-.) in the absence and presence of calcium, we have attempted to verify the recent hypothesis of Babizhayev (Arch. Biochem. Biophys. 266, 446-451, 1988) of a Ca2(+)-O2-. interaction during lipid peroxidation. We could not observe rapid scavenging of O2-. or complex formation with Ca2+ to account for an inhibitory effect of this cation on lipid peroxidation. Neither could we agree that the stimulatory effect is due to liberation of catalytic ferrous iron from weak complexes by Ca2+. Drawing on reports in the literature, we propose an alternate explanation for the apparent stimulation of lipid peroxidation by low Ca2+ concentrations. In our view, this is not a direct effect, but reflects independently initiated processes of lipid peroxidation and Ca2+ translocation, which interact subsequently in a synergistic manner. The reported inhibition at high Ca2+ concentrations is considered an artifact as it was observed at levels far in excess of those relevant to animal systems (but not necessarily in some plant compartments).

Functional comparison of the inductions of NADPH oxidase activity and Fc gamma RI in IFN gamma-treated U937 cells

The capacity to generate superoxide anion (O2-) can be induced in U937 cells by various agents known to cause myeloid cell differentiation. Other reported differentiation events include diminished cell proliferation and the induction by gamma-interferon (IFN gamma) of Fc receptors for immunoglobulin G1 (Fc gamma RI). In this study, we differentiated U937 cells and high Fc gamma RI-expression mutants of U937 cells by treating them with IFN gamma. We compared the time courses over which surface Fc gamma RI became maximal, NADPH oxidase activity was induced, and the antiproliferative effect of IFN gamma was detected. Oxidase activity was measured by stimulating cells with PMA or by activating surface Fc gamma RI using aggregated human IgG1 or second antibody crosslinking of mAb 32/Fc gamma RI complexes. We found that IFN gamma in the absence of additional lymphokines induced high levels of oxidase activity in maximally differentiated U937 cells with even higher levels in the fully differentiated high-Fc gamma RI expression mutants (greater than 8 nmoles/10(6) cells/min for A12.13 cells). Over the course of differentiation, maximal induced levels of Fc gamma RI were reached after 1 to 2 days of IFN gamma treatment, prior to the antiproliferative effect of the lymphokine. In contrast, oxidase activity was induced after a lag of approximately 2 days, becoming maximal only after 4 to 6 days of IFN gamma treatment. This comparison of the induction of Fc gamma RI with that of oxidase activity triggered through Fc gamma RI indicated that the rapid increase of surface receptor was not accompanied by a completion of the pathway of Fc gamma RI-mediated oxidase activity. However, the time courses of induction detected by PMA and Fc gamma RI-agonists were coincident suggesting that the development of oxidative capacity could be due to the induction of components required by both the PMA- and surface receptor-mediated pathways. There are several oxidase components that are known to be IFN gamma-inducible, such as the oxidase flavoprotein, a b558 cytochrome peptide, and oxidase-requiring cytosolic components, and it is possible that one or a set of these components could be the limiting factor(s) for IFN gamma-induced oxidase activity.

Protein phosphorylation associated with the stimulation of neutrophils. Modulation of superoxide production by protein kinase C and calcium

Neutrophils and other phagocytic cells of the immune system possess a superoxide-generating oxidase system which is essential for the efficient killing of microbes. The system is activated by a wide variety of stimuli, some of which operate through pathways involving protein kinase C (PKC), while others appear not to. The PKC-dependent pathway is probably the major signal transduction route for most of the stimuli. Alterations in cellular Ca2+ and diglyceride levels can have a pronounced stimulatory effect on this pathway by their ability to synergistically activate PKC. This review discusses PKC, the different interactions of this kinase with the plasmalemma that are important in superoxide production, the synergy between Ca2+ and diglyceride, and the nature of the phosphoproteins involved. Evidence supporting the existence of the PKC-independent pathway is also reviewed.

Inhibition of neutrophil oxidative burst by elastase-generated IgG fragments

IgG1 is cleaved in vitro by granulocyte elastase into Fc, Fab and Fabc fragments. The cleaved products have been isolated by a series of chromatographic procedures and characterized with regard to molecular mass and isoelectric point. The Fc fragment has been previously shown to express at its N-terminal site a neoantigen which is specific for elastase (Kolb, G., Eckle, I., Heidtmann, H.-H., Neurath, F. & Havemann, K. (1988) Scand. J. Rheumatol. S75, 179-189). The production of superoxide radical anions in prestimulated neutrophils is inhibited dose-dependently by the elastase-generated Fc and Fabc fragments. Native IgG1 and Fab fragments show no inhibitory effect, nor do papain-generated Fc fragments. The degree of inhibition depends on the stimulus applied: half-maximal inhibition is obtained by 6 microM Fc after stimulation with 4 beta-phorbol and 2.4 microM after stimulation with fMet-Leu-Phe; neutrophils stimulated with serum-activated zymosan are not inhibited by IgG fragments. The effect of Fc is purely cellular; no inhibition of O2 generation can be produced by applying Fc to the xanthine oxidase/xanthine system. The fragments have no effect on the activation or activity of crude NADPH oxidase, which is the O2-forming enzyme system of neutrophils. Possible mechanisms are discussed by which Fc acts on stimulated neutrophils.

Free radicals and antioxidants in the pathogenesis of eye diseases

There is fairly convincing evidence that free radical mechanisms are involved in the pathogenesis of cataracts and uveitis and that antioxidants may be protective. Studies on retinal degeneration are almost entirely limited to dietary manipulation of vitamins C and D. Unfortunately, antioxidant properties are not easily isolated from other metabolic effects of vitamins. Cataracts, uveitis, and retinal degeneration cause nearly one-third of all blindness. The evidence that free radical mechanisms are important in the pathogenesis of these diseases is compelling incentive to encourage more extensive and detailed investigation.

Diadenosine tetraphosphate (Ap4A) levels in HL-60 cells during differentiation into granulocytes and monocytes

1. Diadenosine tetraphosphate (Ap4A) levels were determined in HL-60 cells differentiating into granulocytes or monocytes after treatment for 0-7 days with retinoic acid (RA) or 4-beta-phorbol-12-myristate-13-acetate (PMA) respectively. 2. The levels increased significantly compared to untreated control cells within 2 days and then declined again. 3. In RA treated cells the levels finally decreased far below those of untreated HL-60 cells and became equal to those found in human granulocytes. 4. PMA treatment had no effect on Ap4A levels in human granulocytes. 5. A possible interaction between Ap4A and ADP-ribosyl transferase is discussed.

Cyclosporin A inhibits phorbol ester-induced activation of superoxide production in resident mouse peritoneal macrophages

Peritoneal resident macrophages from mice are sensitive to inhibition by cyclosporin A (CsA) of phorbol 12-myristate 13-acetate (PMA)-stimulated oxidative burst. Inhibition was assessed in terms of superoxide anion (O2.-) and H2O2 production. Key findings were as follows. (a) CsA inhibited in a dose-dependent manner the production of O2.- when cells were stimulated with PMA. CsA did not alter the respiratory burst induced by other stimuli (zymosan, concanavalin A and fMet-Leu-Phe). It was verified that CsA itself had no scavenger effect. (b) A concomitant decrease in H2O2 liberation following CsA exposure was found. This inhibition was observed both in the initial rate of synthesis and in the accumulation after 15 min of incubation. (c) NADPH oxidase activity in the crude supernatant was unaffected by the previous incubation of macrophages with CsA. CsA does not inhibit glucose transport measured as 14CO2 production. (d) The production of O2.- was strongly dependent on the glucose concentration. Sodium oleate also stimulated O2.- production in resident macrophages. These data might be correlated with the inhibitory effect of CsA upon other functions of macrophages.

Superoxide generation is inhibited by phospholipase A2 inhibitors. Role for phospholipase A2 in the activation of the NADPH oxidase

The stimulation of O2.- generation by phorbol 12-myristate 13-acetate (PMA) in human neutrophil-derived cytoplasts was inhibited by a variety of phospholipase A2 inhibitors in a concentration-dependent manner. Inhibition was found to be independent of the order of addition of the inhibitor and PMA. The most potent inhibitor, RO 31-4639, inhibited O2.- generation with an IC50 value (concentration causing 50% inhibition) of 1.5 microM. The addition of either arachidonic acid or SDS, in the presence of the inhibitors, was able to restore O2.- generation. The results suggest that arachidonic acid, released by phospholipase A2, is necessary for both the activation and the maintenance of O2.- generation by the NADPH oxidase.

Inhibitory effects of sulfasalazine and related compounds on superoxide production by human polymorphonuclear leukocytes

The inhibitory effects of sulfasalazine, some sulfasalazine-related compounds and indomethacin on superoxide production by human polymorphonuclear (PMN) leukocytes were studied. The inhibition of the chemotactic peptide (FMLP)-induced superoxide production, which is membrane receptor-mediated, was strongly dependent on the concentration both of the secretory stimulus and of the test compounds, indicating an interaction between the receptor and the test compound. Furthermore, a positive correlation was found between the lipophilicity of the compound and the degree of inhibition. However, when the receptor was by-passed by direct activation of the receptor-linked G protein by the use of fluoride ions as secretory stimuli, the test compounds still inhibited superoxide production. On the other hand, superoxide production by cells stimulated with phorbol ester was not inhibited by the test compounds. Furthermore, the production of phosphatidic acid was decreased in the presence of sulfasalazine, indicating impaired phosphoinositide metabolism. The inhibition of this metabolism was not due to increased intracellular concentrations of cyclic AMP, although sulfasalazine did inhibit cyclic nucleotide phosphodiesterase. We conclude that sulfasalazine attenuates superoxide production by PMN leukocytes at a post-receptor site of action at a step before the activation of protein kinase C, possibly by interfering with the phosphoinositide metabolism but independent of cyclic AMP.

Effect of auranofin on eicosanoids and protein kinase C in human neutrophils

Auranofin (AF), a lipophilic chrysotherapeutic agent, was investigated for its effect on the formation of lipoxygenase products and the activity of protein kinase C in human neutrophils. We have previously shown that inhibition of LTB4 formation by 5-lipoxygenase (5-LO) inhibitors is intimately associated with a marked increased in 15-HETE in excess of arachidonic acid. The calcium- and phospholipid-dependent protein kinase, protein kinase C, is activated in FMLP- and A23187-stimulated neutrophils, is hypothesized to stimulate superoxide generation, and plays an essential role in eicosanoid production. AF dose-dependently inhibited the generation of leukotriene B4(LTB4) in FMLP-stimulated neutrophils, the ID50 was approximately 4.5 micrograms/ml. Unlike known 5-LO inhibitors, AF did not enhance the production of 15-HETE. In neutrophils stimulated with the calcium ionophore, A23187, AF did not inhibit the generation of LTB4 nor did AF change the 15-HETE levels. AF inhibited superoxide generation in FMLP-stimulated neutrophils dose-dependently, but did not change the activation of protein kinase C in the cells. We therefore conclude, that AF inhibition of LTB4 production in neutrophils is different from 5-lipoxygenase inhibitors and is elicited at a step distal to protein kinase C activation.

Phosphorylation of both 47 and 49kDa proteins accompanies superoxide release by neutrophils

Neutrophils stimulated with activators of protein kinase C (i.e., 4 beta-phorbol 12-myristate 13-acetate; sn-1,2-dioctanoylglycerol) exhibit a dramatic, dose-dependent incorporation of 32P[Pi] into two proteins with molecular weights of ca. 47 and 49kDa. Proteins of the same molecular weights are also labelled when the cells are stimulated with a chemotactic peptide. However, with the latter stimulus, labelling of the 47kDa species is transient whereas that of the 49kDa entity persists. Labelling of both proteins always accompanied the release of O2-stimulated by these agents. The kinetics of labelling are compatible with the involvement of both phosphoproteins in the stimulation of these cells.

Leukocytic oxygen activation and microbicidal oxidative toxins

Following a brief introduction of cellular response to stimulation comprising leukocyte activation, three major areas are discussed: (1) the neutrophil oxidase; (2) myeloperoxidase (MPO)-dependent oxidative microbicidal reactions; and (3) MPO-independent oxidative reactions. Topics included in section (A) are current views on the activation mechanism, redox composition, structural and topographic organization of the oxidase, and its respiratory products. In section (B), emphasis is placed on recent research on cidal mechanisms of HOCl, including the oxidative biochemistry of active chlorine compounds, identification of sites of lesions in bacteria, and attendant metabolic consequences. In section (C), we review the (bio)chemistry of H2O2 and .OH microbicidal reactions, with particular attention being given to addressing the controversial issue of probe methods to identify .OH radical and critical assessment of the recent proposal that MPO-independent killing arises from site-specific metal-catalyzed Fenton-type chemistry.

Oxygen radicals acting as chemical messengers: a hypothesis

Based on a critical reappraisal of the reactions of radicals in a biological milieu, a hypothesis is proposed according to which superoxide anion radicals act as biological messengers rather than as mediators or precursors of cellular damage under oxidative stress conditions.

A time-course study on superoxide generation and protein kinase C activation in human neutrophils

The time course of superoxide generation and membrane association of protein kinase C was studied in human neutrophils stimulated by PMA, FMLP, ionomycin and A23187. The initiation of superoxide generation in PMA; ionomycin- and A23187-stimulated neutrophils was characterized by a lag period of at least 30 s in contrast to a lag period of 10-15 s in FMLP-stimulated cells. The time course of membrane association of protein kinase C in PMA-stimulated neutrophils was highly dependent upon the PMA concentration used for stimulation. However, membrane association of protein kinase C preceded superoxide generation in cells stimulated by 10-300 ng/ml PMA. FMLP, ionomycin and A23187 induced membrane association of protein kinase C in a few seconds and always before superoxide generation. It is concluded that membrane association of protein kinase C in PMA-, FMLP-, ionomycin- and A23187-stimulated neutrophils precedes superoxide generation, and thereby may be part of the mechanism initiating NADPH-oxidase activity. A simple correlation between the two parameters could not be proven, indicating that also other activation mechanisms are decisive in the activation of NADPH-oxidase.

all-trans-Retinal stimulates superoxide release and phospholipase C activity in neutrophils without significantly blocking protein kinase C

all-trans-Retinal was previously shown to stimulate high levels of superoxide release by guinea pig neutrophils. When the cells, previously labeled with [3H]inositol, are treated with all-trans-retinal, they exhibit a decrease in the levels of [3H]inositol phospholipids and an increase in the accumulation of [3H]inositol phosphates. The maximal accumulation of inositol phosphates and the optimal rate of superoxide release occurred together at approximately 7 min after stimulation. The levels of [3H]inositol phosphates accumulated were comparable to those observed when the cells were stimulated with a chemotactic peptide. In direct measurements, using concentrations that stimulate intact cells maximally, all-trans-retinal was found not to inhibit protein kinase C from the cytosol of neutrophils significantly. This contrasts with the situation with this kinase obtained from other sources. These observations represent additional effects of vitamin A on cells.