Phorbol myristate acetate induced neutrophil autotoxicity

Microbes and the fate of neutrophils

Neutrophils or polymorphonuclear neutrophils (PMNs) are an important component of innate host defense. These phagocytic leukocytes are recruited to infected tissues and kill invading microbes. There are several general characteristics of neutrophils that make them highly effective as antimicrobial cells. First, there is tremendous daily production and turnover of granulocytes in healthy adults-typically 1011 per day. The vast majority (~95%) of these cells are neutrophils. In addition, neutrophils are mobilized rapidly in response to chemotactic factors and are among the first leukocytes recruited to infected tissues. Most notably, neutrophils contain and/or produce an abundance of antimicrobial molecules. Many of these antimicrobial molecules are toxic to host cells and can destroy host tissues. Thus, neutrophil activation and turnover are highly regulated processes. To that end, aged neutrophils undergo apoptosis constitutively, a process that contains antimicrobial function and proinflammatory capacity. Importantly, apoptosis facilitates nonphlogistic turnover of neutrophils and removal by macrophages. This homeostatic process is altered by interaction with microbes and their products, as well as host proinflammatory molecules. Microbial pathogens can delay neutrophil apoptosis, accelerate apoptosis following phagocytosis, or cause neutrophil cytolysis. Here, we review these processes and provide perspective on recent studies that have potential to impact this paradigm.

The coming of age of neutrophil extracellular traps in thrombosis: Where are we now and where are we headed?

Thrombosis remains a major problem in our society, manifesting across multiple demographic groups and with high associated morbidity and mortality. Thrombus development is the result of a complex mechanism in which multiple cell types and soluble factors play a crucial role. One cell that has gained the most attention in recent years is the neutrophil. This key member of the innate immune system can form neutrophil extracellular traps (NETs) in response to activating stimuli in circulation. NETs form a scaffold for thrombus formation, both initiating the process and stabilizing the final product. As the first responders of the host immune system, neutrophils have the flexibility to recognize a variety of molecules and can quickly interact with a range of different cell types. This trait makes them sensitive to exogenous stimuli. NET formation in response to pathogens is well established, leading to immune-mediated thrombus formation or immunothrombosis. NETs can also be formed during sterile inflammation through the activation of neutrophils by fellow immune cells including platelets, or activated endothelium. In chronic inflammatory settings, NETs can ultimately promote the development of tissue fibrosis, with organ failure as an end-stage outcome. In this review, we discuss the different pathways through which neutrophils can be activated toward NET formation and how these processes can result in a shared outcome: thrombus formation. Finally, we evaluate these different interactions and mechanisms for their potential as therapeutic targets, with neutrophil-targeted therapies providing a future approach to treating thrombosis. In contrast to current practices, such treatment could result in reduced pathogenic blood clot formation without increasing the risk of bleeding.

Staphylococcus aureus and Neutrophil Extracellular Traps: The Master Manipulator Meets Its Match in Immunothrombosis

Over the past 10 years, neutrophil extracellular traps (NETs) have become widely accepted as an integral player in immunothrombosis, due to their complex interplay with both pathogens and components of the coagulation system. While the release of NETs is an attempt by neutrophils to trap pathogens and constrain infections, NETs can have bystander effects on the host by inducing uncontrolled thrombosis, inflammation, and tissue damage. From an evolutionary perspective, pathogens have adapted to bypass the host innate immune response. Staphylococcus aureus (S. aureus), in particular, proficiently overcomes NET formation using several virulence factors. Here we review mechanisms of NET formation and how these are intertwined with platelet activation, the release of endothelial von Willebrand factor, and the activation of the coagulation system. We discuss the unique ability of S. aureus to modulate NET formation and alter released NETs, which helps S. aureus to escape from the host's defense mechanisms. We then discuss how platelets and the coagulation system could play a role in NET formation in S. aureus-induced infective endocarditis, and we explain how targeting these complex cellular interactions could reveal novel therapies to treat this disease and other immunothrombotic disorders.

The action of Echis carinatus and Naja naja venoms on human neutrophils; an emphasis on NETosis

BACKGROUND

Neutrophils are the first line defense cells of the innate immunity. As a final defense, they discharge their de-condensed chromatin/DNA fibers, the NETs (Neutrophil Extracellular Traps), by a process called NETosis. Two types of NETosis have been currently described: the suicidal/delayed/classical-type, which is ROS dependent that results in the ejection of nuclear DNA, and the vital/rapid/early-type, which may or may not require ROS but, eject nuclear/mitochondrial DNA or both. Thus, Echis carinatus and Naja naja venoms are comparatively studied for their NET inducing property.

METHODS

Formation of NETs, cell viability, ROS, and Ca²⁺ levels are estimated. An in vivo toxicity study and possible cellular signaling have been addressed using immunoblots and pharmacological inhibitors.

RESULTS

E. carinatus and N. naja venoms respectively induce suicidal and vital NETosis. E. carinatus venom induces NETosis by activating NOX and PAD-4 enzymes in a ROS dependent manner via PKC/ERK/JNK signaling axis, while N. naja venom does it by activating PAD-4 enzyme, but independent of ROS requirement and as well as PKC/ERK/JNK activation.

CONCLUSION

For the first time our study demonstrates the distinct action of E. carinatus and N. naja venoms on the process of NETosis. NETosis being a newly explored area in snake venom pharmacodynamics, it is important to study its impact on the various pathophysiological properties induced by snake venoms.

SIGNIFICANCE

Understanding the varied actions of snake venoms on neutrophils/blood cells and the role of DNase are likely to provide insights for better management of snakebite pathophysiology.

[Viewing sepsis and autoimmune disease in relation with infection and NETs-formation]

Neutrophil has been widely recognized as body's first line of defence against pathogens. NETosis was first reported in 2004 as a programmed cell death of neutrophil and distinguished from apoptosis and necrosis. This phenomenon has been already observed in both basic and clinical research. NETosis is induced by various stimulants such as PMA, IL-8, DAMPs/PAMPs, bacteria, and antigen-antibody complex including self-antibody such as ANCA. It is known that there are two types of NETosis following bacterial infections. Although both of them have the ability to capture and kill bacteria, they also damage the host tissues. The inhibition of the NETs-related enzymes prevents the NETs formation at that time. The production of O₂^- from respiratory burst of neutrophils triggers NETs formation. In the first type of NETosis, neutrophils are completely collapsed, while in the second type, they maintain the morphology and the ability of phagocytosis. However, bacteria can escape from NETs by degrading NETs with their secreting nucleases. Thus the animal models of infection, using these bacteria, oftentimes suffer from severe infectious diseases. Human CGD (Chronic Granulomatosis Disease) patients who do not have Nox2 are immunocompromised, and highly susceptible to infection due to the defect of NETs formation. On the other hand, SLE patients are unable to break down the NETs as their serum inhibits the DNase1 activity, which results in autoantibody generation against NETs as well as self-DNA. It is getting clear that there is a relationship between inflammatory diseases, including infectious diseases, Sepsis and autoimmune diseases, and NETs. Therefore, it is important to re-evaluate the inflammatory disorders from NETs' perspective, and to incorporate the emerging concepts for better understanding the mechanisms involved.

A Critical Reappraisal of Neutrophil Extracellular Traps and NETosis Mimics Based on Differential Requirements for Protein Citrullination

NETosis, an antimicrobial form of neutrophil cell death, is considered a primary source of citrullinated autoantigens in rheumatoid arthritis (RA) and immunogenic DNA in systemic lupus erythematosus (SLE). Activation of the citrullinating enzyme peptidylarginine deiminase type 4 (PAD4) is believed to be essential for neutrophil extracellular trap (NET) formation and NETosis. PAD4 is therefore viewed as a promising therapeutic target to inhibit the formation of NETs in both diseases. In this review, we examine the evidence for PAD4 activation during NETosis and provide experimental data to suggest that protein citrullination is not a universal feature of NETs. We delineate two distinct biological processes, leukotoxic hypercitrullination (LTH) and defective mitophagy, which have been erroneously classified as “NETosis.” While these NETosis mimics share morphological similarities with NETosis (i.e., extracellular DNA release), they are biologically distinct. As such, these processes can be readily classified by their stimuli, activation of distinct biochemical pathways, the presence of hypercitrullination, and antimicrobial effector function. NETosis is an antimicrobial form of cell death that is NADPH oxidase-dependent and not associated with hypercitrullination. In contrast, LTH is NADPH oxidase-independent and not bactericidal. Rather, LTH represents a bacterial strategy to achieve immune evasion. It is triggered by pore-forming pathways and equivalent signals that cumulate in calcium-dependent hyperactivation of PADs, protein hypercitrullination, and neutrophil death. The generation of citrullinated autoantigens in RA is likely driven by LTH, but not NETosis. Mitochondrial DNA (mtDNA) expulsion, the result of a constitutive defect in mitophagy, represents a second NETosis mimic. In the presence of interferon-α and immune complexes, this process can generate highly interferogenic oxidized mtDNA, which has previously been mistaken for NETosis in SLE. Distinguishing NETosis from LTH and defective mitophagy is paramount to understanding the role of neutrophil damage in immunity and the pathogenesis of human diseases. This provides a framework to design specific inhibitors of these distinct biological processes in human disease.

Myeloperoxidase: Bridging the gap in neurodegeneration

Neurodegenerative conditions present a group of complex disease pathologies mostly due to unknown aetiology resulting in neuronal death and permanent neurological disability. Any undesirable stress to the brain, disrupts homeostatic balance, through a remarkable convergence of pathophysiological changes and immune dysregulation. The crosstalk between inflammatory and oxidative mechanisms results in the release of neurotoxic mediators apparently spearheaded by myeloperoxidase derived from activated microglia, astrocytes, neurons as well as peripheral inflammatory cells. These isolated entities combinedly have the potential to flare up and contribute significantly to neuropathology and disease progression. Recent, clinicopathological evidence support the association of myeloperoxidase and its cytotoxic product, hypochlorous acid in a plethora of neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Amyotrophic lateral sclerosis, Multiple sclerosis, Stroke, Epilepsy etc. But the biochemical and mechanistic insights into myeloperoxidase mediated neuroinflammation and neuronal death is still an uncharted territory. The current review outlines the emerging recognition of myeloperoxidase in neurodegeneration, which may offer novel therapeutic and diagnostic targets for neurodegenerative disorders.

Neutrophil extracellular traps (Nets) impact upon autoimmune disorders

Friend or foe? This is often asked question when it comes to neutrophil extracellular traps studies. There is no simple answer to that. At the time of their discovery they were considered to be protectors of our well-being. Excellent pathogen fighting skills were described as purely beneficial. But it was not long before those guardians of immunity reveal their dark side. What seemed to be profitable could also take its toll. They are perfectly constructed, made from nucleic deoxyribonucleic acid ornamented with cytoplasmic and granular proteins, to fight invaders. But this unique build is prone to become considered by our body as a threat. Since there is a thin line which when crossed turns a savior into enemy, it was postulated that Nets can play a significant role in autoimmune disorders pathogenesis and disease exacerbation. Recent years have brought a new insight into autoimmune disorders trying to connect the old knowledge and suspicions with modern discoveries.

Reactive Oxygen Species, Granulocytes, and NETosis

When pathogens invade the body, neutrophils create the first line of defense. Basic weaponry consists of phagocytosis and degranulation, but these cells have yet another ace in the sleeve, a unique strategy in which invading microorganisms are being destroyed. These cellular warriors are able to release nuclear chromatin and form extracellular structure, known as neutrophil extracellular traps (NET). NET formation is connected with the presence of free radicals. Research has shown that inhibition of free radical formation leads to suppression of NET release. The exact mechanisms controlling cooperation of free radicals with NET still remain unclear. New investigations in this field may contribute to discovery of NET etiology and put a new light on related disorders.

NETosis: how vital is it?

In this review, we examine the evidence that neutrophil extracellular traps (NETs) play a critical role in innate immunity. We summarize how NETs are formed in response to various stimuli and provide evidence that NETosis is not universally a cell death pathway. Here we describe at least 2 different mechanisms by which NETs are formed, including a suicide lytic NETosis and a live cell or vital NETosis. We also evaluate the evidence for NETs in catching and killing pathogens. Finally, we examine how infections are related to the development of autoimmune and vasculitic diseases through unintended but detrimental bystander damage resulting from NET release.

Novel cell death program leads to neutrophil extracellular traps

Neutrophil extracellular traps (NETs) are extracellular structures composed of chromatin and granule proteins that bind and kill microorganisms. We show that upon stimulation, the nuclei of neutrophils lose their shape, and the eu- and heterochromatin homogenize. Later, the nuclear envelope and the granule membranes disintegrate, allowing the mixing of NET components. Finally, the NETs are released as the cell membrane breaks. This cell death process is distinct from apoptosis and necrosis and depends on the generation of reactive oxygen species (ROS) by NADPH oxidase. Patients with chronic granulomatous disease carry mutations in NADPH oxidase and cannot activate this cell-death pathway or make NETs. This novel ROS-dependent death allows neutrophils to fulfill their antimicrobial function, even beyond their lifespan.

Measurement of phagocytosis and oxidative burst of canine neutrophils: high variation in healthy dogs

Quantitative analysis of phagocytosis and oxidative burst in canine polymorphonuclear (PMN) cells was performed by flow cytometry techniques. Different concentrations of phorbol myristate acetate (PMA) were used to modulate PMN phagocytosis. A low concentration of PMA (3 nmol) resulted in increased phagocytic activity of canine PMN, which could not be enhanced by higher dosages. Experiments with a reference cell population showed high losses of PMN, most probably by adherence to plastic material. It was possible to avoid this loss by layering all ingredients on cushions of Histopaque. However, Histopaque had a negative influence on the phagocytic activity of canine PMN. The use of PMA led to a dosage-dependent increase in the oxidative burst measured by the production of reactive oxygen species (ROS). Cushions of Histopaque were used to avoid cell loss. There was no negative influence of Histopaque on ROS formation. Storage of canine PMN for 24 h at room temperature had no negative influence on phagocytosis or oxidative burst measurements. Variations in the ROS assays conducted by two different examiners could be eliminated by use of a Histopaque-cushion.

Neutrophil survival on biomaterials is determined by surface topography

PURPOSE

Cardiovascular device-centered infections are a major cause of hospital morbidity, mortality, and expense. Caused by opportunistic bacteria, this phenomenon is thought to arise because of a defect in neutrophil bacterial killing. We have shown that neutrophils that adhere to polystyrene remain viable, whereas neutrophils that adhere to the vascular biomaterials expanded polytetrafluoroethylene (ePTFE) and Dacron undergo a rapid nonapoptotic death. This study was designed to test the hypothesis that surface topography is a determinant of the nonapoptotic death response of neutrophils to biomaterials.

METHODS

We took advantage of the ease with which a polystyrene surface can be manipulated to examine the effect of surface topography on neutrophil viability. Neutrophils were exposed to smooth or roughened polystyrene surfaces both in vivo and in vitro. Changes in cell membrane permeability and production of reactive oxygen species by individual cells were monitored with fluorescent dyes.

RESULTS

Host cells and isolated human neutrophils died rapidly after adhesion to roughened polystyrene. Neutrophils adherent to roughened surfaces produced more reactive oxygen intermediates than those adherent to smooth surfaces and were first to die. The cell death response precipitated by expanded polytetrafluoroethylene, Dacron, or the roughened surfaces was significantly reduced with treatment of the neutrophils with catalase, diphenylene iodonium, or the src kinase inhibitor PP2 before adhesion.

CONCLUSIONS

Neutrophil adhesion to roughened materials triggers rapid production of reactive oxygen species and precipitates a nonapoptotic cell death. Understanding the material properties that trigger these responses is essential to development of the next generation of implantable biomaterials.

Oxidative stress in phagocytes--"the enemy within"

Phagocytes represent a powerful defense system against invading microorganisms that threaten the life or functional integrity of the host. The capacity to generate and release substantial amounts of reactive oxygen species is a unique property of activated polymorphonuclear and mononuclear phagocytes. The crucial role of these molecules in killing microorganisms and their consecutive contribution to tissue damage during injury and inflammation is widely known. Although much research has been done to explore the molecular events involved in the interaction of oxygen intermediates with microbes or host tissue, surprisingly little attention has been paid to the effect of reactive metabolites on the phagocyte itself. This fact is especially surprising, since it is apparent that the activated phagocyte is directly exposed to its own toxic metabolites. The potential damage occurring during excessive radical formation might notably alter the vital functions of these primarily immunocompetent cells. Moreover, the critical role of oxygen radicals in apoptosis of leukocytes has been recently revealed. Apoptosis is now supposed to represent a key mechanism in neutrophil deactivation and resolution of inflammation. Therefore, this review will focus on the delicate balance between released oxidants and antioxidative protection within the phagocytes themselves. General and phagocyte-specific antioxidative mechanisms, which have co-evolved with the radical generating machinery of phagocytes, are discussed, since the outcome of local inflammation can directly depend on this antioxidative capacity and might range from adequate elimination of the pathogen with minimal acute tissue damage to progression towards a systemic inflammatory response syndrome.

Cytotoxic effects of peroxynitrite, polymorphonuclear neutrophils, free-radical scavengers, inhibitors of myeloperoxidase, and inhibitors of nitric oxide synthase on bovine mammary secretory epithelial cells

OBJECTIVE

To determine cytotoxic effects of activated polymorphonuclear neutrophils (PMN) and peroxynitrite on bovine mammary secretory epithelial cells before and after addition of nitric oxide synthase inhibitors, myeloperoxidase (MPO) inhibitors, and free-radical scavengers.

SAMPLE POPULATION

Polymorphonuclear neutrophils from 3 lactating cows.

PROCEDURE

Cells from the bovine mammary epithelial cell line MAC-T were cultured. Monolayers were treated with activated bovine PMN, lipopolysaccharide (LPS), phorbol 12-myristate 13-acetate (PMA), 3-morpholino-sydnonimine (SIN-1), 4-amino-benzoic acid hydrazide (ABAH), NG-monomethyl-L-arginine, histidine, and superoxide dismutase (SOD). At 24 hours, activity of lactate dehydrogenase in culture medium was used as a relative index of cell death. Tyrosine nitration of proteins in MAC-T cell lysates was determined by visual examination of immunoblots.

RESULTS

Lipopolysaccharide, PMA, and < or = 0.1 mM SIN-1 were not toxic to MAC-T cells. Activated PMN, > or = 6 mg of histidine/ml, and 0.5 mM SIN-1 were toxic. Together, histidine and 500,000 activated PMN/ml also were toxic. NG-monomethyl-L-arginine did not have an effect, but ABAH decreased PMN-mediated cytotoxicity. Ten and 50 U of SOD/ml protected MAC-T cells from cytotoxic effects of 0.5 mM SIN-1. Compared with control samples, nitration of MAC-T tyrosine residues decreased after addition of 500,000 PMN/ml or > or = 6 mg of histidine/ml. Superoxide dismutase increased and SIN-1 decreased tyrosine nitration of MAC-T cell proteins in a dose-responsive manner.

CONCLUSIONS AND CLINICAL RELEVANCE

Peroxynitrite, MPO, and histidine are toxic to mammary secretory epithelial cells. Superoxide dismutase and inhibition of MPO activity mitigate these effects. Nitration of MAC-T cell tyrosine residues may be positively associated with viability.

Neutrophil adhesion to vascular prosthetic surfaces triggers nonapoptotic cell death

OBJECTIVE

To test the hypothesis that neutrophil adhesion to expanded polytetrafluoroethylene (ePTFE) and Dacron triggers cell death.

SUMMARY BACKGROUND DATA

Vascular prosthetic infections are intransigent clinical dilemmas associated with excessive rates of death and complications. Impaired neutrophil function has been implicated in the infection of implanted cardiovascular devices. ePTFE and Dacron are potent neutrophil stimuli able to elicit activation responses such as reactive oxygen species production independent of exogenous/soluble agonists. Reactive oxygen species that are released into the medium when neutrophils are challenged by soluble agonists are known to cause self-destruction. The authors therefore sought to examine whether neutrophil adhesion to prosthetic graft materials decreases neutrophil viability by means of reactive oxygen species production.

METHODS

Neutrophils were adhered to surfaces for up to 6 hours. Cell viability was monitored with propidium iodide staining and lactate dehydrogenase release.

RESULTS

Within 6 hours of adhesion to ePTFE and Dacron, respectively, 59% +/- 11% and 44% +/- 5% (n = 7) of the neutrophils were stained by propidium iodide. Indistinguishable results were obtained with plasma-coated ePTFE and Dacron. In contrast, less than 2% of the neutrophils adherent to fibrinogen-, immunoglobin-, or fetal bovine serum-coated polystyrene surfaces for 6 hours were positive for propidium iodide. The increase in membrane permeability to propidium iodide was accompanied by a two- to threefold increase in lactate dehydrogenase release. Pretreatment of neutrophils with N-acetyl-L-cysteine, cytochalasin D, or cyclosporin A significantly reduced the number of propidium iodide-positive ePTFE and Dacron adherent neutrophils.

CONCLUSIONS

Neutrophil adhesion to ePTFE and Dacron triggers a rapid nonapoptotic cell death. The effect of ePTFE and Dacron on neutrophil viability appears to be caused by reactive oxygen species production. The premature death of graft-adherent neutrophils provides a novel explanation of the defect in neutrophil bacterial killing associated with vascular prosthetic grafts.

Can spin trapping compounds like PBN protect against self-inflicted damage in polymorphonuclear leukocytes?

Polymorphonuclear leukocytes (PMNs) have been suggested to be damaged by superoxide radical generated on their own. The protective capacity of a spin trapping compound, phenyl-N-tert-butyl nitrone (PBN) was evaluated for this damage which occurs after the induction of superoxide generation. The life span of PMNs after superoxide generation was measured in the presence of PBN using the cell counting method, and effects of PBN on the amount of superoxide generated were quantitated using both cytochrome c reduction and spin trapping with DMPO. Results indicated significant extension of life span when PBN was present, and the extension was dose dependent. However, the magnitude of life span extension was not as large as expected from the decrease of superoxide generation. Possible mechanisms for the protection of PMNs by PBN are discussed.

Cytotoxicity of fatty acid oxygenase activation in rat basophilic leukemia cells

Apart from the generation of potent inflammatory mediators, the effects of fatty acid oxygenase activation, per se, on the host cell have not been well-delineated. Fatty acid oxygenases were activated in rat basophilic leukemia cells (RBL-1) by incubating them for 2-4 hr with 33-300 microM of arachidonic acid (AA) or linoleic acid (LA). As a control, the cells were incubated with one of two analogs of these fatty acids which are not oxygenase substrates: eicosatetraynoic acid or linoelaidic acid. Effects of oxygenase activation on cell viability were monitored by an assay for mitochondrial function. Cytotoxicity occurred in incubations with exogenous AA or LA in direct proportion to the substrate concentration but was not found in the control incubations or in incubations with the principal monohydroxylated AA products, 5-, 15-, and 12-HETE. Nordihydroguaiaretic acid (80 microM) and alpha-tocopherol (100 microM) significantly decreased the cell death observed during incubations with AA or LA. It is concluded that extensive oxygenase activation can result in cell death from intermediates produced proximal to the stable monohydroxylated derivatives.

Vitamin C and the common cold

The effect of vitamin C on the common cold has been the subject of several studies. These studies do not support a considerable decrease in the incidence of the common cold with supplemental vitamin C. However, vitamin C has consistently decreased the duration of cold episodes and the severity of symptoms. The benefits that have been observed in different studies show a large variation and, therefore, the clinical significance may not be clearly inferred from them. The biochemical explanation for the benefits may be based on the antioxidant property of vitamin C. In an infection, phagocytic leucocytes become activated and they produce oxidizing compounds which are released from the cell. By reacting with these oxidants, vitamin C may decrease the inflammatory effects caused by them. Scurvy, which is caused by a deficiency in vitamin C, is mostly attributed to the decreased synthesis of collagen. However, vitamin C also participates in several other reactions, such as the destruction of oxidizing substances. The common cold studies indicate that the amounts of vitamin C which safely protect from scurvy may still be too low to provide an efficient rate for other reactions, possibly antioxidant in nature, in infected people.

Myeloperoxidase: a myeloid cell nuclear antigen with DNA-binding properties

An antigen histochemically localized in the nuclei and cytoplasmic granules of normal and leukemic human myeloid cells has been identified as myeloperoxidase (MPO; EC 1.11.1.7). The localization and amount of the enzyme was determined by using a murine monoclonal antibody designated H-43-5 raised against nuclear proteins derived from human promyelocytic HL-60 leukemia cells. The highest amount of nuclear MPO (3.5 micrograms per 10(6) nuclei) was found in granulocytes; less than half of this amount was detected in nuclei from HL-60 cells. Still lower levels were found in nuclei from monocytes and a series of human monomyelocytic leukemia cells. MPO from HL-60 cells was purified by immunoaffinity chromatography and fractionated into three components (forms I, II, and III) by CM-cellulose chromatography. Chromatography of these MPO forms on DNA-Sepharose columns confirmed that all three forms of MPO were tightly bound to DNA with apparent relative affinities in the order of form III greater than form II greater than form I. The affinity of MPO form III for DNA was sufficient to enable the formation and elution of DNA-MPO complexes during size-exclusion chromatography at high ionic strength and neutral pH. This form of MPO was also able to shield DNA from strand scission induced by active oxygen species generated by xanthine oxidase acting aerobically on xanthine. These data suggest that intranuclear MPO may help to protect DNA against damage resulting from oxygen radicals produced during myeloid cell maturation and function.

Ascorbate and cysteine-mediated selective neutralisation of extracellular oxidants during N-formyl peptide activation of human phagocytes

The effects of sodium ascorbate and cysteine (2.5 X 10(-5) M-2.5 X 10(-4) M) on the intensity and profile of luminol-enhanced chemiluminescence, superoxide generation, extracellular myeloperoxidase (MPO) activity and auto-iodination were measured in purified human polymorphonuclear leukocytes activated by the leukoattractant FMLP in vitro. Chemiluminescence studies were also performed using a whole-blood method. Cysteine (10(-4) M-2.5 X 10(-4) M) and ascorbate (2.5 X 10(-5) M-2.5 X 10(-4) M) caused significant inhibition of the early extracellular peak of FMLP-activated chemiluminescence and increased the intensity of the later occurring intracellular peak in both PMNL and blood. At the same concentrations both agents scavenged superoxide released by FMLP-activated PMNL, inhibited oxidant generation by extracellular MPO and decreased FMLP-induced auto-oxidation of PMNL. Administration of a single 1 gram oral dose of ascorbate to adult human volunteers was associated with significant reduction and enhancement respectively of the extracellular and intracellular luminol-enhanced chemiluminescence responses of FMLP-activated blood. These results show that the water soluble anti-oxidants cysteine and especially ascorbate selectively neutralise the reactivity of harmful reactive oxidants released by phagocytes, whilst the intracellular generation of antimicrobial oxidants remains intact.

The influence of different fixatives and a tumor promoter, 12-0-tetradecanoyl-phorbol-13-acetate (TPA), on the induction of so-called dark cells in mouse epidermis. A light microscopical study

Epidermal "dark cells" (DC) are believed to play a specific role in the so-called promotion phase of experimental skin carcinogenesis. They are recognized by their morphological features both at the light and the electron microscopical level. The possible effects of fixation on the morphology of epidermal cells and hence on the number of DC have not yet been thoroughly studied. In the present light microscopical study we used a semiquantitative method together with simple cell counting to evaluate the influence of fixation on the specific cellular morphology which is traditionally used to determine the number of DC. The use of cacodylate vehicled prefixatives, either formaldehyde or glutaraldehyde, led to a higher incidence of DC, and furthermore both to an increased width of the intercellular spaces (ICS) and a more heavy staining of the keratinocytes than when s-collidine vehicled glutaraldehyde was used. Differences in yield of DC solely due to the prefixative itself (formaldehyde or glutaraldehyde) were not detected. Exposure to TPA or the use of a hyperosmolal prefixative vehicle both yielded higher DC numbers than did controls or conventional prefixative vehicles, respectively. After prefixation with hyperosmolal vehicles, however, TPA treatment did not induce higher DC yield than in a control series. Phenomena usually accompanying exposure to TPA, such as intercellular oedema (widening of the ICS) and cytoplasmic vacuolization, varied in parallel to the number of DC. Hence, there is reason to believe that the induction of epidermal DC is mainly associated with volume reduction of keratinocytes. Such shrinkage may be due to the cytotoxic properties of TPA and degenerative phenomena appearing during tissue processing.

Slow exponential decay of rate of superoxide production in phorbol ester-activated human neutrophils

Proper quantification of the superoxide (O2-) respiratory burst induced in human neutrophils is important for better understanding of the mechanism of action of stimulators and inhibitors. Reexamination of the reaction triggered by phorbol myristate acetate (PMA) indicated that it was a persistent process which lasted over 60 min. Plots of rates versus time show that rates of O2- release decayed logarithmically with a mean half-life (T1/2) of 21 +/- 6 min (SD), N = 12). Calculations of areas under curves indicate an average O2- yield of 217 +/- 99 nmol/10(6) cells. The inclusion of catalase in incubation mixtures did not alter the T1/2 or O2- yield, nor was the latter value affected by the quantitive scavenging of O2- by cytochrome c. Under certain conditions--the presence of excess dimethyl sulfoxide, the substitution of a less potent phorbol ester or activation of cells at high densities--the initial rate was either increased or decreased but a complementary alteration in the T1/2 resulted in little or no change in the total O2- yield. Retinol and retinol acetate decreased the initial rate, but retinoic acid enhanced it. By comparison, total O2- production was markedly reduced by all three agents with the following order of potency: retinoic acid greater than retinol greater than retinol acetate. In contrast, the serine protease inhibitor, TPCK, suppressed both the O2- yield and initial rate to a similar extent. On the basis of present observations, it is proposed that under normal conditions of PMA cellular activation, the logarithmic decay of the rate of O2- release was not due to autoinactivation of the O2--generating system, but rather to another factor, a possibility being the depletion of intracellular NADPH.

Membrane endopeptidases of human neutrophil

Recent studies using inhibitors or synthetic substrates of serine protease suggest that membrane protease activity may be essential for neutrophil chemotaxis, phagocytosis, degranulation, and superoxide production. However, little is known about the nature and localization of the proteases. In this study, we demonstrated that intact human neutrophils hydrolyzed [125I]glucagon. The degradation of glucagon was temperature dependent and was not dependent on the release of lysosomal enzymes. Two endopeptidases were demonstrated: a metalloendopeptidase which accounted for two thirds of the intact cell activity, and a serine endopeptidase, accounting for the rest of the activity. Both enzymes had a neutral to alkaline pH optimum (pH 7-9). The metalloendopeptidase had a Km of 15.3 microM and Vmax of 5.9 nmol/5 X 10(6) cells/45 min. The corresponding values for the serine endopeptidase were 33.3 microM and 5.0 nmol/5 X 10(6) cells/45 min, respectively. Inhibition of the membrane metalloendopeptidase or serine endopeptidase by 1,10-phenanthroline or diisopropylfluorophosphate, respectively, did not inhibit the production of superoxide by phorbol myristate acetate-stimulated neutrophils.

Enhancement of intracellular glutathione protects endothelial cells against oxidant damage

We studied the role of glutathione in the endothelial cell defense against H2O2 damage. Treatment of endothelial cells with buthionine sulfoximine, an irreversible inhibitor of gamma-glutamylcysteine synthetase, depleted the cells of GSH, while L-2-oxothiazolidine-4-carboxylate, an effective intracellular cysteine delivery agent, markedly enhanced endothelial cell GSH concentration. Depletion of intracellular GSH sensitized the endothelial cells to injury by H2O2 either preformed or generated by the glucose-glucose oxidase system. In contrast, an increase of intracellular GSH protected the cells from H2O2 damage. There was an inverse, linear relationship between the intracellular GSH concentrations and killing of endothelial cells by H2O2. Our results suggest that enhancement of endothelial cell GSH may be an alternative approach toward the prevention of oxidant-induced endothelial damage such as adult respiratory distress syndrome.

Oxidation of methionine residues in proteins of activated human neutrophils

A simple assay for the detection of 35S-labeled methionine sulfoxide residues in proteins is described. The assay, which is based on the ability of CNBr to react with methionine but not with methionine sulfoxide, requires the prelabeling of cellular proteins with [35S]methionine. The assay was used to study the extent of methionine oxidation in newly synthesized proteins of both activated and quiescent human neutrophils. In cells undergoing a phorbol 12-myristate 13-acetate-induced respiratory burst, about 66% of all methionine residues in newly synthesized proteins were oxidized to the sulfoxide derivative, as compared with 9% in cells not treated with the phorbol ester. In contrast, quantitation of methionine sulfoxide content in the total cellular protein by means of amino acid analysis showed that only 22% of all methionine residues were oxidized in activated cells as compared with 9% in quiescent cells. It is proposed that methionine residues in nascent polypeptide chains are more susceptible to oxidation than those in completed proteins.

Inhibition of neutrophil sulfhydryl groups by choloromethyl ketones. A mechanism for their inhibition of superoxide production

The inhibition of O2- production by serine protease inhibitors such as chloromethyl ketone derivatives, has been used as evidence to indicate that protease activity is essential for the production of O2- by neutrophils. However, chloromethyl ketones are potent inhibitors of sulfhydryl groups. This study demonstrates that chloromethyl ketones inhibited non-protein sulfhydryl groups as well as O2- production by human neutrophils stimulated with phorbol myristate acetate (PMA). Their inhibition of O2- production could be prevented by reduced glutathione. The results suggest that inhibition of O2- production by chloromethyl ketones is largely due to their inhibition of sulfhydryl groups.

Myeloperoxidase-mediated oxidation of methionine

The myeloperoxidase-mediated oxidation of methionine was studied using a purified canine myeloperoxidase preparation. The system required the simultaneous presence of myeloperoxidase, H2O2, and a halide anion. When 0.1 mM H2O2 was used, the system has a Ph optimum of approximately pH 5-5.5. Bromide and iodide were much more effective than chloride in the myeloperoxidase-mediated oxidation of methionine. Horseradish peroxidase was unable to oxidize methionine whether chloride or iodide was used. In contrast, lactoperoxidase oxidized methionine in the presence of iodide but not chloride. Based on studies of 1) the effect of various inhibitors and singlet oxygen quenchers, as well as 2) the effect of D2O on the oxidation of methionine, by the myeloperoxidase system, OCI-, or methylene blue, it was shown that the oxidation of methionine by the myeloperoxidase system was not mediated by OCI- or 1O2. The mechanism of the myeloperoxidase-mediated oxidation of methionine remains unclear. However, it may be one mechanism by which the myeloperoxidase system damage microorganisms.

Phorbol myristate acetate-induced neutrophil autotoxicity. A comparison with H2O2 toxicity

We have previously shown that in the presence of phorbol myristate acetate (PMA), neutrophils kill neoplastic cells as well as themselves. This PMA-induced neutrophil autotoxicity was markedly inhibited by catalase, suggesting that H2O2 directly or indirectly played an important role. In this study we compared PMA and H2O2 toxicity against human neutrophils. The effect of H2O2 was faster and more sensitive to catalase and serum than that of PMA. Sodium azide markedly enhanced the effect of H2O2 but not that of PMA. In contrast, methionine and histidine prevented the toxicity of PMA, while they had no effect on H2O2 toxicity. The results suggest that PMA-induced neutrophil autotoxicity is not mediated by H2O2 alone.