Superoxide production by digitonin-stimulated guinea pig granulocytes. The effects of N-ethyl maleimide, divalent cations; and glycolytic and mitochondrial inhibitors on the activation of the superoxide generating system

Overview of General and Discriminating Markers of Differential Microglia Phenotypes

Inflammatory processes and microglia activation accompany most of the pathophysiological diseases in the central nervous system. It is proven that glial pathology precedes and even drives the development of multiple neurodegenerative conditions. A growing number of studies point out the importance of microglia in brain development as well as in physiological functioning. These resident brain immune cells are divergent from the peripherally infiltrated macrophages, but their precise in situ discrimination is surprisingly difficult. Microglial heterogeneity in the brain is especially visible in their morphology and cell density in particular brain structures but also in the expression of cellular markers. This often determines their role in physiology or pathology of brain functioning. The species differences between rodent and human markers add complexity to the whole picture. Furthermore, due to activation, microglia show a broad spectrum of phenotypes ranging from the pro-inflammatory, potentially cytotoxic M1 to the anti-inflammatory, scavenging, and regenerative M2. A precise distinction of specific phenotypes is nowadays essential to study microglial functions and tissue state in such a quickly changing environment. Due to the overwhelming amount of data on multiple sets of markers that is available for such studies, the choice of appropriate markers is a scientific challenge. This review gathers, classifies, and describes known and recently discovered protein markers expressed by microglial cells in their different phenotypes. The presented microglia markers include qualitative and semi-quantitative, general and specific, surface and intracellular proteins, as well as secreted molecules. The information provided here creates a comprehensive and practical guide through the current knowledge and will facilitate the choosing of proper, more specific markers for detailed studies on microglia and neuroinflammatory mechanisms in various physiological as well as pathological conditions. Both basic research and clinical medicine need clearly described and validated molecular markers of microglia phenotype, which are essential in diagnostics, treatment, and prevention of diseases engaging glia activation.

Bioenergetic regulation of microglia

Microglia have diverse actions, ranging from synapse pruning in development to cytotoxic effects in disease. Brain energy metabolism and substrate availability vary under normal and disease states, but how these variations influence microglial function is relatively unknown. Microglia, like most other cell types, express the full complement of gene products required for both glycolytic and oxidative metabolism. Evidence suggests that microglia increase aerobic glycolysis and decrease respiration when activated by various stimuli. Mitochondrial function, glucose availability, and glycolytic rate influence pro-inflammatory gene expression at both transcriptional and post-translational levels. These effects are mediated through CtBP, an NADH-sensitive transcriptional co-repressor; through effects on NLRP3 inflammasome assembly and caspase-1 activation; through formation of advanced glycation end-products; and by less well-defined mechanisms. In addition to these transcriptional effects, microglial glucose metabolism is also required for superoxide production by NADPH oxidase, as glucose is the obligate substrate for regenerating NADPH in the hexose monophosphate shunt. Microglia also metabolize acetoacetate and β-hydroxybutyrate, which are generated during fasting or ketogenic diet, and respond to these ketones as metabolic signals. β-Hydroxybutyrate inhibits histone de-acetylases and activates microglial GRP109A receptors. These actions suppress microglia activation after brain injury and promote neuroprotective microglia phenotypes. As our understanding of microglial activation matures, additional links between energy metabolism and microglial function are likely to be identified.

Antioxidant cerium oxide nanoparticle hydrogels for cellular encapsulation

Oxidative stress and the resulting radical by-products cause significant toxicity and graft loss in cellular transplantation. Here, the engineering of an auto-catalytic, antioxidant, self-renewing cerium oxide nanoparticle (CONP)-composite hydrogel is reported. This enzyme-mimetic material ubiquitously scavenges ambient free radicals, with the potential to provide indefinite antioxidant protection. The potential of this system to enhance the protection of encapsulated beta cells was evaluated. Co-incubation of CONPs free in solution with beta cells demonstrated potent cytoprotection from superoxide exposure; however, phagocytosis of the CONPs by the beta cells resulted in cytotoxicity at concentrations as low as 1mM. When CONPs were embedded within alginate hydrogels, the composite hydrogel provided cytoprotection to encapsulated beta cells from free radical attack without cytotoxicity, even up to 10mM. This nanocomposite hydrogel has wide applicability in cellular transplantation, with the unique advantage of localization of these potent antioxidant CONPs and their capacity for sustained, long-term scavenging.

The dehydrogenase region of the NADPH oxidase component Nox2 acts as a protein disulfide isomerase (PDI) resembling PDIA3 with a role in the binding of the activator protein p67 (phox.)

The superoxide (O(·-) 2)-generating NADPH oxidase of phagocytes consists of a membrane component, cytochrome b 558 (a heterodimer of Nox2 and p22 (phox) ), and four cytosolic components, p47 (phox) , p67 (phox) , p40 (phox) , and Rac. The catalytic component, responsible for O(·-) 2 generation, is Nox2. It is activated by the interaction of the dehydrogenase region (DHR) of Nox2 with the cytosolic components, principally with p67 (phox) . Using a peptide-protein binding assay, we found that Nox2 peptides containing a (369)CysGlyCys(371) triad (CGC) bound p67 (phox) with high affinity, dependent upon the establishment of a disulfide bond between the two cysteines. Serially truncated recombinant Nox2 DHR proteins bound p67 (phox) only when they comprised the CGC triad. CGC resembles the catalytic motif (CGHC) of protein disulfide isomerases (PDIs). This led to the hypothesis that Nox2 establishes disulfide bonds with p67 (phox) via a thiol-dilsulfide exchange reaction and, thus, functions as a PDI. Evidence for this was provided by the following: (1) Recombinant Nox2 protein, which contained the CGC triad, exhibited PDI-like disulfide reductase activity; (2) Truncation of Nox2 C-terminal to the CGC triad or mutating C369 and C371 to R, resulted in loss of PDI activity; (3) Comparison of the sequence of the DHR of Nox2 with PDI family members revealed three small regions of homology with PDIA3; (4) Two monoclonal anti-Nox2 antibodies, with epitopes corresponding to regions of Nox2/PDIA3 homology, reacted with PDIA3 but not with PDIA1; (5) A polyclonal anti-PDIA3 (but not an anti-PDIA1) antibody reacted with Nox2; (6) p67 (phox) , in which all cysteines were mutated to serines, lost its ability to bind to a Nox2 peptide containing the CGC triad and had an impaired capacity to support oxidase activity in vitro. We propose a model of oxidase assembly in which binding of p67 (phox) to Nox2 via disulfide bonds, by virtue of the intrinsic PDI activity of Nox2, stabilizes the primary interaction between the two components.

Detection of superoxide anion and hydrogen peroxide production by cellular NADPH oxidases

BACKGROUND

The recent recognition that isoforms of the cellular NADPH-dependent oxidases, collectively known as the NOX protein family, participate in a wide range of physiologic and pathophysiologic processes in both the animal and plant kingdoms has stimulated interest in the identification, localization, and quantitation of their products in biological settings. Although several tools for measuring oxidants released extracellularly are available, the specificity and selectivity of the methods for reliable analysis of intracellular oxidants have not matched the enthusiasm for studying NOX proteins.

SCOPE OF REVIEW

Focusing exclusively on superoxide anion and hydrogen peroxide produced by NOX proteins, this review describes the ideal probe for analysis of O2(-) and H2O2 generated extracellularly and intracellularly by NOX proteins. An overview of the components, organization, and topology of NOX proteins provides a rationale for applying specific probes for use and a context in which to interpret results and thereby construct plausible models linking NOX-derived oxidants to biological responses. The merits and shortcomings of methods currently in use to assess NOX activity are highlighted, and those assays that provide quantitation of superoxide or H2O2 are contrasted with those intended to examine spatial and temporal aspects of NOX activity.

MAJOR CONCLUSIONS

Although interest in measuring the extracellular and intracellular products of the NOX protein family is great, robust analytical probes are limited.

GENERAL SIGNIFICANCE

The widespread involvement of NOX proteins in many biological processes requires rigorous approaches to the detection, localization, and quantitation of the oxidants produced. This article is part of a Special Issue entitled Current methods to study reactive oxygen species - pros and cons and biophysics of membrane proteins. Guest Editor: Christine Winterbourn.

Leptin triggers Ca(2+) imbalance in monocytes of overweight subjects

Obesity is a major risk factor in numerous diseases, in which elevated intracellular Ca(2+) plays a major role in increased adiposity. We examined the difference between Ca(2+) signals in monocytes of lean and overweight subjects and the relationship between leptin induced NADPH oxidase activation and intracellular calcium concentration [Ca(2+)](i) homeostasis. Our results are as follows: (1) The basal level of [Ca(2+)](i) in resting monocytes of overweight subjects (OW monocytes) was higher than that in control cells, whereas the leptin-induced peak of the Ca(2+) signal was lower and the return to basal level was delayed. (2) Ca(2+) signals were more pronounced in OW monocytes than in control cells. (3) Using different inhibitors of cellular signaling, we found that in control cells the Ca(2+) signals originated from intracellular pools, whereas in OW cells they were generated predominantly by Ca(2+)-influx from medium. Finally, we found correlation between leptin induced superoxide anion generation and Ca(2+) signals. The disturbed [Ca(2+)](i) homeostasis in OW monocytes was fully restored in the presence of fluvastatin. Statins have pleiotropic effects involving the inhibition of free radical generation that may account for its beneficial effect on elevated [Ca(2+)](i) and consequently on the pathomechanism of obesity.

Measurement of oxidative burst in neutrophils

Polymorphonuclear neutrophils (PMNs) generate reactive oxygen species (ROS) during phagocytosis and in response to soluble agonists. This functional response, termed oxidative burst, contributes to host defense, but it can also result in collateral damage of host tissues. To study this important PMN response, different methods have been developed that are based on the assessment of oxidative burst by measuring intracellular ROS production or formation of ROS in the extracellular space. Among the different methods that were developed, the following two are particularly widely used because of their convenience and accuracy. The first method depends on the reduction of cytochrome c, which can be assessed by photometry, while the second method relies on changes in the fluorescence properties of dihydrorhodamine 123, which can be assessed by flow cytometry.

Copy number of FCGR3B, which is associated with systemic lupus erythematosus, correlates with protein expression and immune complex uptake

Copy number (CN) variation (CNV) has been shown to be common in regions of the genome coding for immune-related genes, and thus impacts upon polygenic autoimmunity. Low CN of FCGR3B has recently been associated with systemic lupus erythematosus (SLE). FcgammaRIIIb is a glycosylphosphatidylinositol-linked, low affinity receptor for IgG found predominantly on human neutrophils. We present novel data demonstrating that both in a family with FcgammaRIIIb-deficiency and in the normal population, FCGR3B CNV correlates with protein expression, with neutrophil uptake of and adherence to immune complexes, and with soluble serum FcgammaRIIIb. Reduced FcgammaRIIIb expression is thus likely to contribute to the impaired clearance of immune complexes, which is a feature of SLE, explaining the association between low FCGR3B CNV and SLE that we have confirmed in a Caucasian population. In contrast, antineutrophil cytoplasmic antibody-associated systemic vasculitis (AASV), a disease not associated with immune complex deposition, is associated with high FCGR3B CN. Thus, we define a role for FCGR3B CNV in immune complex clearance, a function that may explain why low FCGR3B CNV is associated with SLE, but not AASV. This is the first report of an association between disease-related gene CNV and variation in protein expression and function that may contribute to autoimmune disease susceptibility.

The association between angiotensin II-induced free radical generation and membrane fluidity in neutrophils of patients with metabolic syndrome

Angiotensin II (Ang II) is able to induce free radical generation in neutrophils, which is more elevated in neutrophils of patients with hypercholesterolemia (HC). In addition, the signal processing through angiotensin I (Ang I) receptors is altered. In present study, we compared the Ang II-triggered free radical generation of neutrophils obtained from patients with relatively isolated forms of metabolic syndrome (MS) with membrane-bound cholesterol content and membrane fluidity. We determined the enhancement of Ang II-induced superoxide anion and leukotriene C(4) (LTC(4)) generation, membrane fluidity and cell-bound cholesterol content of neutrophils obtained from 12 control subjects, 11 patients with obesity (Ob), 10 patients with type 2 diabetes mellitus (t2-DM) and 12 patients with HC. The alteration of signal processing was studied after preincubation with different inhibiting drugs. Superoxide anion, LTC(4) production and membrane rigidity were increased in the following order: control < Ob < t2-DM < HC. Both Ang II-induced superoxide anion and LTC(4) generation were decreased in control cells by pertussis toxin and fluvastatin (Flu), whereas in each patient group, mepacrin, verapamil and Flu were effective, suggesting alterations in signal pathways, which may be attributed to isoprenylation. The enhancement of superoxide anion and LTC(4) generation correlated significantly with membrane rigidity, independently from the experimental groups and membrane-bound cholesterol content. Membrane rigidity of neutrophils, obtained from patients with MS, plays a role in Ang II-induced free radical generation independent of intracellular cholesterol homeostasis.

The respiratory burst oxidase

Sbarra and Karnovsky were the first to present evidence suggesting the presence in phagocytes of a special enzyme designed to generate reactive oxidants for purposes of host defense. In the years since their report appeared, a great deal has been learned about this enzyme, now known as the respiratory burst oxidase. It has been found to be a plasma membrane-bound heme- and flavin-containing enzyme, dormant in resting cells, that catalyzes the one-electron reduction of oxygen to O2- at the expense of NADPH: O2 + NADPH----O2- + NADP+ + H+ Its behavior in whole cells and its response to various activating stimuli have been described in detail, although important insights continue to emerge, as for example a very interesting new series of observations on differences in oxidase activation patterns between suspended and adherent cells. The enzyme has been shown by biochemical and genetic studies to consist of at least six components. In the resting cell, three of these components are in the cytosol and three in the plasma membrane, but when the cell passes from its resting to its activated state the cytosolic components are all transferred to the plasma membrane, presumably assembling the oxidase. Of the components initially bound to the membrane, two constitute cytochrome b558, a heme protein characteristic of the respiratory burst oxidase, and the third may represent an oxidase flavoprotein. With regard to the cytosolic components, one is a phosphoprotein and another is the NADPH-binding component, possibly a second oxidase flavoprotein. The nature of the third (p67phox) is a puzzle. Four of the six oxidase components have now been cloned and sequenced. These findings only scratch the surface, however, and many questions remain. How many oxidase components, for example, remain to be discovered, and how do they fit together to form the active enzyme? How is the route of activation of the oxidase integrated into the general signal transduction systems of the cell? How did the oxidase come to be? Could there be a widespread system that generates small amounts of O2- as an intercellular signaling molecule, as recent work is beginning to suggest, and did the ever-destructive respiratory burst oxidase arise from that innocuous system as the creation of some evolutionary Frankenstein--an oxidase from hell? Finally, will it be possible to develop drugs that specifically block the respiratory burst oxidase, and will such drugs prove to be clinically useful as anti-inflammatory agents?(ABSTRACT TRUNCATED AT 400 WORDS)

Neuropeptides induced a pronounced and statin-sensitive dysregulation of mevalonate cycle in human monocytes of patients with hypercholesterolemia

Angiotensin II (Ang II) and leptin generate statin-inhibitable superoxide anion production that accounts for only part of the entire superoxide anion production. In our recent studies, we aimed at elucidating whether Ang II and leptin, affecting the intensity of the mevalonate cycle, are able to increase endogenous cholesterol synthesis. Furthermore, we compared the superoxide anion and cholesterol production capability of monocytes of healthy control volunteers and monocytes obtained from patients with hypercholesterolemia (HC). We also studied the differences of the produced statin-inhibitable superoxide anion and cholesterol synthesis in control and HC-monocytes, depending on the applied stimulating ligands. In control and HC-monocytes--stimulated by Ang II, leptin, fenyl-Me-Leu-Phe (FMLP), phorbol-12-myristate-13-acetate (PMA) and A23187--we determined the proportion of mevalonate cycle-dependent and -independent superoxide and cholesterol production, using lovastatin (Lov), and 25-hydroxycholesterol (25-HC). According to our results; (1) superoxide anion generation in HC-monocytes was elevated after Ang II, leptin and FMLP-stimulation, whereas PMA and A23187-stimulation had lower stimulating effect in HC than in control cells. (2) Cholesterol synthesis was increased only after stimulation with Ang II and leptin. (3) The Ang II and leptin-induced total superoxide anion generation and cholesterol synthesis were more elevated in HC than in control monocytes. (4) In contrast, the increase in Lov and 25-HC sensitive cholesterol synthesis were higher in resting, but lower in stimulated HC monocytes than in control cells. Summarizing our results, we concluded that Ang II and leptin are involved in enhancement of endogenous cholesterol synthesis through a statin-sensitive pathway.

De novo ICAM-1 synthesis in the mouse lung: model of assessment of protein expression in lungs

Because most studies addressing the regulatory mechanisms of intercellular adhesion molecule (ICAM)-1 expression have used cultured endothelial cells, we set out to develop an isolated mouse lung preparation to study gene and protein expression in its proper cellular context in the organ. Lungs from CD1 mice were isolated and perfused (2 ml/min, 37°C) with a recirculating volume of RPMI 1640 solution supplemented with 3 g/100 ml albumin. Lungs maintained their isogravimetric state for 4 h. Tumor necrosis factor (TNF-α; 2,000 U/ml) was added to the perfusate for 0.5, 1, 2, or 3.5 h to induce ICAM-1 expression or lungs received no treatment (control). After quick-freezing the lungs using liquid nitrogen at different time points, the prepared tissue homogenates were analyzed for ICAM-1 protein expression by Western blotting and NF-κB activation by electrophoretic mobility shift assay. TNF-α caused a progressive increase in NF-κB activity after 0.5 h and ICAM-1 protein expression two- to threefold of basal after 2 h. Untreated lungs expressed a low and constant level of ICAM-1 between 0 and 3.5 h. TNF-α failed to induce NF-κB activation and ICAM-1 expression in lungs of NADPH oxidase-deficient mice lacking p47phox. We disaggregated mouse lungs using collagenase and stained the cells for ICAM-1 and VE-cadherin (used as an endothelial marker) to assess the in situ endothelial-specific expression of ICAM-1. We observed that TNF-α challenge resulted in increased ICAM-1 expression in endothelial cells freshly isolated from lungs. These data show the role of NADPH oxidase-derived oxidant signaling in the mechanism of NF-κB activation and ICAM-1 expression in mouse lung endothelial cells. Moreover, the general method presented herein has potential value in assessing mechanisms of gene and protein expression in the isolated-perfused mouse lung model.

Topical H2 antagonist prevents periodontitis in a rabbit model

Cimetidine is a powerful H2 receptor antagonist that eliminates histamine's effects on chemotaxis, phagocytosis, and superoxide anion production by phagocytes. The purpose of this study was to analyze the clinical and histopathological changes associated with experimental periodontitis in rabbits in response to topically applied cimetidine. Experimental periodontitis was induced in 21 New Zealand White rabbits using Porphyromonas gingivalis (10(9) CFU) topically applied three times a week for a 6-week period to previously ligatured teeth. Topical application of cimetidine in a liposome carrier for the prevention of periodontitis was evaluated in four groups of four animals each: 1, 10, and 100 mg/ml and no treatment (positive control). In addition, there was a vehicle group (n = 3) that received liposome preparation (carrier) only, and two animals with ligature application alone served as negative controls. Periodontal disease was quantified by direct visualization and radiographical evaluation of bone loss on defleshed skulls and by histological analyses of sections stained with hematoxylin-eosin and tartrate-resistant acid phosphatase. In the no-treatment (positive control) and liposome (vehicle) groups, direct visualization and radiological measurements revealed statistically significant bone loss compared to the negative control. Application of cimetidine at all concentrations tested inhibited inflammation and bone loss by >90%. Histological findings revealed that ligated sites of the positive control and vehicle groups showed significant reduction in bone level (P < 0.05) compared to the three cimetidine groups, with a marked decrease in inflammation. The findings of this study provide morphological and histological evidence that topically active cimetidine is a potent inhibitor of P. gingivalis-elicited periodontal inflammation, arresting and/or preventing tissue destruction and influencing cell populations present in the inflammatory cell infiltrate.

Synthesis of 2-alkoxy 1,4-naphthoquinone derivatives as antiplatelet, antiinflammatory, and antiallergic agents

In our continuing search for novel antiplatelet, antiallergic, and antiinflammatory agents, 2-alkoxy derivatives of 1,4-naphthoquinone were prepared. Some of these compounds showed significant antiplatelet, antiallergic, and antiinflammatory activities. Among them, 2-propoxy-1,4-naphthoquinone and 2-butoxy-1,4-naphthoquinone exhibited potent inhibitory effect on neutrophil superoxide anion formation. These two compounds are worthy of further exploration.

Synthesis and antiplatelet, antiinflammatory, and antiallergic activities of substituted 3-chloro-5,8-dimethoxy-1,4-naphthoquinone and related compounds

2-Amino (6), 2-alkylamino (7-8), 2-methoxy (9), 2-acetamido (10), and 5,8-diacetoxy (11) derivatives of the lead compound 2,3-dichloro-5,8-dimethoxy-1,4-naphthoquinone (4) were synthesized, together with 6,7-dichloro-5,8dimethoxy-1,4-naphthoquinone (5), a positional isomer of 4. Antiplatelet, antiinflammatory, and antiallergic activities were evaluated, and most compounds were quite potent in all assays. Compounds 5 and 9-11 were especially active; however, 5 was ineffective against neutrophil superoxide formation, and 10 was ineffective against mast cell degranulation.

Synthesis and antiplatelet, antiinflammatory, and antiallergic activities of 2-substituted 3-chloro-1,4-naphthoquinone derivatives

A series of 2-substituted 3-chloro-1,4-naphthoquinones was synthesized, and the antiplatelet, antiinflammatory, and antiallergic activities of these compounds were evaluated. The structure-activity relationships in this series were also examined. Most of the 2-alkyl/arylcarboxamido derivatives of 3-chloro-1,4-naphthoquinone showed potent activities with similar trends in each of the activities evaluated.

Functional properties of nonhuman primate antibody to Porphyromonas gingivalis

The nonhuman primate (NHP) serves as a useful model for examining the host-parasite interactions in Porphyromonas gingivalis-associated periodontal disease. This study determined the influence of NHP sera on (i) the direct killing of P. gingivalis, (ii) P. gingivalis-induced superoxide anion (O2-) release from human polymorphonuclear leukocytes (PMNs), and (iii) the ability of PMNs to bind and phagocytize P. gingivalis. Three types of NHP sera were utilized: (i) normal or baseline sera; (ii) sera obtained after ligature-induced periodontitis; and (iii) sera obtained following active immunization with formalinized P. gingivalis. All assays were performed with or without the addition of human complement. Significantly more (P < 0.01) direct killing of P. gingivalis occurred with immunized sera and complement than with any of the other treatments. The sera from ligature-induced periodontitis NHPs had significantly less (P < 0.03) killing capacity than the baseline sera, which contained natural antibody produced to P. gingivalis colonization. Sera from immunized NHPs were used to opsonize P. gingivalis and caused significantly greater (P < 0.01) levels of O2- release from PMNs. Finally, the sera from immunized NHPs significantly enhanced (P < 0.009) the uptake of P. gingivalis by PMNs, although binding of the bacteria to PMNs was similar among all three serum types. Active immunization of NHPs with P. gingivalis elicited a functional antibody that enhanced direct killing, positively influenced the activation of PMNs, and enhanced the ability of PMNs to phagocytize P. gingivalis. Moreover, antibody produced as a sequela of progressing periodontitis appeared to lack these functions. A wide variability in functional capacity of the sera from individual NHPs, which may contribute to an individual's susceptibility to P. gingivalis-induced disease, was noted. This variability suggested that results from functional tests of serum antibody may aid in predicting host susceptibility to disease and response to therapy.

The phosphorylation targets of p47phox, a subunit of the respiratory burst oxidase. Functions of the individual target serines as evaluated by site-directed mutagenesis

The respiratory burst oxidase of phagocytes and B lymphocytes catalyzes the reduction of oxygen to O2- at the expense of NADPH. Dormant in resting cells, the oxidase is activated by exposing the cells to appropriate stimuli. During activation, p47phox, a cytosolic oxidase subunit, becomes extensively phosphorylated on a number of serines located between S303 and S379. To determine whether this phosphorylation is necessary for oxidase activation, we examined phorbol-elicited oxidase activity in EBV-transformed B lymphoblasts deficient in p47phox after transfection with plasmids expressing various S-->A mutants of p47phox. The mutant containing S-->A mutations involving all serines between S303 and S379 [S(303-379)A] was not phosphorylated, did not translocate to plasma membrane during activation and was almost devoid of function. As to individual serines, S379 was of special interest because (a) p47 phox S379 was phosphorylated in phorbol-activated lymphoblasts expressing wild-type p47phox, and (b) p47phox S379A failed to translocate to the membrane, and was as functionless as p47phox S(303-379)A; other single S-->A mutations had little effect on oxidase activity. These findings suggest that the phosphorylation of S379 may be important for oxidase activation in whole cells.

Daphnoretin-induced respiratory burst in rat neutrophils is, probably, mainly through protein kinase C activation

Daphnoretin, a dicoumarin isolated from Wikstroemia indica C.A. Mey. (Thymelaceae), induced superoxide anion (O2-) formation in rat neutrophils in a concentration-dependent manner. Addition of staurosporine reduced daphnoretin-induced respiratory burst. Removal of extracellular free Ca2+ by EGTA did not affect the respiratory burst of neutrophils in response to daphnoretin. Prior exposure of neutrophils to phorbol 12-myristate 13-acetate (PMA) or daphnoretin reduced the O2- formation caused by a subsequent challenge with PMA and daphnoretin, but potentiated the response caused by a subsequent addition of formyl-Met-Leu-Phe (fMLP). Like PMA, daphnoretin did not increase the [Ca2+]i during cell activation. In neutrophil suspension, daphnoretin increased the membrane associated protein kinase C activity. In the presence of Ca2+ and phosphatidyl-serine, daphnoretin also activated protein kinase C isolated from cytosolic fraction of resting neutrophils. Staurosporine inhibited the direct activation of protein kinase C caused by daphnoretin as well as by PMA. Daphnoretin reduced the [3H]Phorbol-12,13-dibutyrate ([3H]PDB) binding to the neutrophil cytosolic protein kinase C in a concentration-dependent manner with an IC50 value of 1.77 +/- 0.37 microM. These results indicate that daphnoretin, like PMA, may direct activation of protein kinase C which in turn activated NADPH oxidase and elicited respiratory burst.

Inhibition by gomisin C (a lignan from Schizandra chinensis) of the respiratory burst of rat neutrophils

1. The possible mechanisms of action of the inhibitory effect of gomisin C on the respiratory burst of rat neutrophils in vitro was investigated. 2. The peptide formyl-Met-Leu-Phe (FMLP) induced superoxide anion (O2-) formation and O2 consumption, which was inhibited by gomisin C in a concentration-dependent manner (IC50 21.5 +/- 4.2 micrograms ml-1 for O2- formation). Gomisin C also suppressed O2- formation and consumption at low concentrations of phorbol myristate acetate (PMA) with an IC50 value of 26.9 +/- 2.1 micrograms ml-1 for O2- formation. However, gomisin C did not affect the responses induced by a high concentration of PMA. 3. Gomisin C had no effect on O2- generation and uric acid formation in the xanthine-xanthine oxidase system, and failed to alter O2- generation during dihydroxyfumaric acid (DHF) autoxidation, indicating that it does not scavenge superoxide. 4. Like trifluoperazine (TFP), gomisin C attenuated the activity of PMA-activated neutrophil particulate NADPH oxidase in a concentration-dependent manner. 5. Gomisin C reduced the elevations of cytosolic free Ca2+ in neutrophils stimulated by FMLP in the presence or absence of EDTA. Cyclopiazonic acid (CPA) induced the release of Ca2+ from intracellular stores and this was also reduced by gomisin C. However, the Ca2+ influx pathway activated by CPA was not affected by gomisin C. 6. The cellular cyclic AMP level was markedly increased by forskolin, but not by gomisin C. Moreover, the inositol phosphate levels in FMLP-activated neutrophils were not affected by gomisin C. 7. These results show that the inhibitory action of gomisin C on the respiratory burst is not mediated by changes in cellular cyclic AMP or in inositol phosphates, or by scavenging O2- released from neutrophils, but may be mediated partly by the suppression of NADPH oxidase and partly by the decrease of cytosolic Ca2+ released from an agonist-sensitive intracellular store.

Inhibitory effect of interferon-alpha on respiratory burst and glucose metabolism in phagocytic cells

Anion superoxide (O2-) production and glucose metabolism was studied in murine macrophages following in vivo or in vitro treatment with human recombinant interferon-alpha 2b (IFN-alpha 2b). The PMA-dependent O2- production was inhibited by IFN-alpha 2b in a concentration- and time-dependent manner. NO2- production by macrophages in culture was slightly inhibited (about 16%) at 30 nM IFN-alpha and a clear decrease (35%) was obtained with 150 nM IFN-alpha. Low doses (0.3 and 3 nM IFN-alpha) had no effect. Also, IFN-alpha 2b inhibited lactate release and 3H2O production from [2-3H] and [3-3H]glucose in macrophages isolated after in vivo treatment for 24 h. The data support an inhibitory role of IFN-alpha in the metabolic activation of macrophages and suggest a putative mechanism for the inhibition of some macrophage functions as previously reported.

Inhibition of macrophage superoxide generation by dehydroepiandrosterone

To understand the anti-atherosclerotic mechanism of the steroid dehydroepiandrosterone (DHEA), the effect of DHEA on rat peritoneal macrophage superoxide generation was studied. Dehydroepiandrosterone (12.5 to 50 microM) inhibited digitonin-stimulated superoxide production in a dose-dependent manner, with 100% inhibition achieved at 50 microM. Dehydroepiandrosterone also inhibited macrophage superoxide production stimulated with phorbol myristate acetate, A23187 (calcium ionophore), sodium fluoride, and arachidonate. Dehydroepiandrosterone did not affect the activity of nicotinamide-adenine dinucleotide phosphate oxidase, which generates superoxide. Dehydroepiandrosterone inhibited superoxide formation in the presence of nicotinamide-adenine dinucleotide phosphate, potassium cyanide, and 2,4-dinitrophinal, suggesting that DHEA does not exert its effects by inhibiting glucose-6-phosphate dehydrogenase activity or mitochondrial respiration. Of the several steroids tested, epiandrosterone was as effective as DHEA in inhibiting macrophage superoxide production. Estrogen, androstenedione, and dihydroxytestosterone showed 25% inhibition, whereas pregnenolone, progesterone, testosterone, etiocholanolone, androstenediol, and DHEA-sulfate had minimal effect. The steroids cortisol and corticosterone had slight stimulatory effect. These results suggest that the anti-atherosclerotic effect of DHEA may be the result of inhibition of superoxide generation in macrophages.

Modulation of the respiratory burst in human neutrophils by isoproterenol and dibutyryl cyclic AMP

The effects of a beta-adrenergic agonist and a cyclic AMP analogue on activation, activity, and termination of FMLP-stimulated superoxide anion production were investigated. Incubation with isoproterenol resulted in a 50% reduction in the maximal rate of superoxide production and a 3-4-fold increase in the rate of termination of superoxide production. Exposure to 1 mM dibutyryl cyclic AMP resulted in a 40% decrease in the maximal rate and a 3-fold increase in the rate of termination of FMLP-induced superoxide production. Neither agent had a significant effect on the lag time prior to superoxide anion generation.

Phagocytic activation of human neutrophils by the detergent component of fluosol

Fluosol (Alpha Therapeutic Corporation, Los Angeles, CA) an emulsion of perfluorocarbons with a high oxygen-carrying capacity, was approved as an adjunct to alleviate myocardial ischemia during coronary angioplasty. This drug also significantly enhances myocardial salvage presumably related to an action on the neutrophil. The mechanism by which fluosol and its individual components, including the detergent Pluronic F-68, affected neutrophil function was examined. During the incubation of neutrophils with fluosol, a rapid stimulation of superoxide anion production and degranulation which progressively increased over a 30-minute period was detected. Neutrophils incubated with only Pluronic F-68 produced similar amounts of superoxide anion. Cytochalasin B, an inhibitor of phagocytosis, significantly inhibited this superoxide anion generation. As shown previously, neutrophils incubated with fluosol for 30 minutes and then subsequently stimulated manifested a reduction in lysozyme release as compared with untreated cells. Results of an electron microscopic examination confirmed the cellular uptake of the fluosol within phagocytic vacuoles. Neutrophil viability determined by trypan blue was unaffected after fluosol treatment. These observations show that the fluosol emulsion, primarily through micelles formed by the detergent Pluronic F-68, activates human neutrophils by serving as a phagocytic stimulus, which produces a cell refractory to subsequent stimulation.

Mechanisms in neutrophil priming: characterization of the oxidative response induced by formylmethionyl-leucyl-phenylalanine in human exudated cells

Exudate human polymorphonuclear neutrophils were isolated and investigated regarding oxidative responsiveness and priming ability. The exudate neutrophils were found to produce an increased amount of O2- and H2O2 when stimulated with formylmethionyl-leucyl-phenylalanine (fMLP), i.e. these cells were metabolically primed. Cytochalasin B (cyt B) pretreatment affected the production of O2- by exudate cells, although to a lesser extent than the production by peripheral blood cells, in which a substantial increase was induced. Addition of N-ethylmaleimide (NEM) to activated exudate and peripheral blood cells revealed no difference in oxidase inactivation rate. To induce further priming, the cells were incubated in vitro with a synthetic diacylglycerol (sn-1,2-didecanoylglycerol; diC10), or the Ca2+ ionophore ionomycin. Results of this procedure showed significant differences between exudate and peripheral blood neutrophils: the peripheral cells expressed a primed response, which was measured as increased fMLP-induced O2- production following incubation with both these substance; whereas the metabolic activity of exudated cells was not affected by diC10, but was significantly primed by ionomycin (P less than 0.01). The exact route for diacylglycerol priming is unknown. However, our results with human neutrophils primed during exudation indicate an exhausted diC10-priming pathway, with a retained sensitivity for priming [Ca2+]i rises.

Mechanism of vanadate-induced activation of tyrosine phosphorylation and of the respiratory burst in HL60 cells. Role of reduced oxygen metabolites

Vanadate induces phosphotyrosine accumulation and activates O2 consumption in permeabilized differentiated HL60 cells. NADPH, the substrate of the respiratory burst oxidase, was found to be necessary not only for the increased O2 consumption, but also for tyrosine phosphorylation. The effect of NADPH was not due to reduction of vanadate to vanadyl. Instead, NADPH was required for the synthesis of superoxide, which triggered the formation of peroxovanadyl [V(4+)-OO] and vanadyl hydroperoxide [V(4+)-OOH]. One or both of these species, rather than vanadate itself, appears to be responsible for phosphotyrosine accumulation and activation of the respiratory burst. Accordingly, the stimulatory effects of vanadate and NADPH were abrogated by superoxide dismutase. Moreover, phosphorylation was activated in the absence of NADPH by treatment with V(4+)-OO and/or V(4+)-OOH, generated by treatment of orthovanadate with KO2 or H2O2 respectively. The main source of the superoxide involved in the formation of V(4+)-OO and V(4+)-OOH is the NADPH oxidase. This was shown by the inhibitory effects of diphenylene iodonium and by the failure of undifferentiated cells, which lack oxidase activity, to undergo tyrosine phosphorylation when treated with vanadate and NADPH. By contrast, exogenously generated V(4+)-OO induced marked phosphorylation in the undifferentiated cells, demonstrating the presence of the appropriate tyrosine kinases and phosphatases. A good correlation was found to exist between induction of tyrosine phosphorylation and activation of the respiratory burst, suggesting a causal relationship. Therefore an amplification cycle appears to exist in cells treated with vanadate, whereby trace amounts of superoxide initiate the formation of V(4+)-OO and/or V(4+)-OOH. These peroxides promote phosphotyrosine formation, most likely by inhibition of tyrosine phosphatases. Accumulation of critical tyrosine-phosphorylated proteins then initiates a respiratory burst, with abundant production of superoxide. The newly formed superoxide catalyses the formation of additional V(4+)-OO and/or V(4+)-OOH, thereby magnifying the response. Since vanadium derivatives are ubiquitous in animal tissues, V(4+)-OO and/or V(4+)-OOH could be formed in vivo by reduced O2 metabolites, becoming potential endogenous tyrosine phosphatase inhibitors. Because of their potency, peroxides of vanadate may be useful as probes for the study of protein phosphotyrosine turnover.

Superoxide anion release (O2-) after ischemia and reperfusion

Neutrophils have been implicated as mediators of the reperfusion injury following ischemia. In order to measure neutrophil activation, O2- was determined after 2 hr of ischemia followed by 1 hr of reperfusion (no clinical reperfusion injury) and 3 hr of ischemia followed by 1 hr of reperfusion (significant clinical reperfusion injury). Using New Zealand white rabbits, baseline blood samples were drawn from an ear artery. The right iliac and femoral arteries were exposed and clamped. Just prior to clamp release, blood was obtained from the right iliac vein (ischemia). After 1 hr of reperfusion, blood was again taken from the right iliac vein (reperfusion). Neutrophils were isolated from the blood samples. O2- was determined by the reduction of cytochrome c using a spectrophotometer. In the 2-hr group, results (expressed as mumole O2-/min/2 x 10(6) cells) were: baseline, 0.337 +/- 0.025; ischemia, 0.512 +/- 0.039;* and reperfusion, 0.634 +/- 0.064*. (*P less than .05 as compared to baseline). In the 3-hr group, results were: baseline, 0.391 +/- 0.038; ischemia, 0.413 +/- 0.051; and reperfusion, 0.258 +/- 0.043** (**P less than 0.05 as compared to 2 hr reperfusion). A significant increase in O2- was seen after 2 hr of ischemia followed by 1 hr of reperfusion. However, little O2- increase was seen after 3 hr of ischemia and a significant O2- decrease was seen after 1 hr of reperfusion. We conclude: (1) Neutrophil O2- is stimulated early in ischemia followed by reperfusion; (2) after reperfusion injury occurs (3 hr), neutrophils have been activated and O2- can no longer be stimulated; and (3) O2- in this model may be involved in the clinical reperfusion injury seen.

Cytoplasmic lipid bodies of neutrophils: formation induced by cis-unsaturated fatty acids and mediated by protein kinase C

Lipid bodies, nonmembrane-bound cytoplasmic inclusions, serve as repositories of esterified arachidonate and are increased in cells associated with inflammatory reactions. We have evaluated stimuli and mechanisms responsible for lipid body formation within human polymorphonuclear leukocytes (PMNs). Arachidonic acid and oleic acid stimulated dose-dependent formation of lipid bodies over 0.5-1 h. Other C20 and C18 fatty acids were less active and demonstrated rank orders as follows: cis-unsaturated fatty acids were much more active than trans-fatty acids, and activity diminished with decreasing numbers of double bonds. Lipid bodies elicited in vitro with cis-fatty acids were ultrastructurally identical to lipid bodies present in PMNs in vivo. Lipid body induction was not because of fatty acid-elicited oxidants or fatty acid-induced ATP depletion. Cis-fatty acid-induced activation of protein kinase C (PKC) was involved in lipid body formation as evidenced by the capacity of other PKC activators, 1-oleoyl-2-acetyl-glycerol and two active phorbol esters, phorbol myristate acetate, and phorbol 12,13 dibutyrate, but not an inactive phorbol, to induce lipid body formation. The PKC inhibitor, 1-O-hexadecyl-2-O-methyl-glycerol, inhibited PMN lipid body formation induced by oleic and arachidonic acids and by 1-oleoyl-2-acetyl-glycerol and phorbol myristate acetate. Other PKC inhibitors (staurosporine, H-7) also inhibited lipid body formation. Formation of lipid bodies in PMNs is a specific cellular response, stimulated by cis-fatty acids and diglycerides and apparently mediated by PKC, which results in the mobilization and deposition of lipids within discrete, ultrastructurally defined cytoplasmic domains.

Two cytosolic components of the human neutrophil respiratory burst oxidase translocate to the plasma membrane during cell activation

The superoxide-forming respiratory burst oxidase of human neutrophils is composed of membrane-associated catalytic components and cytosolic constituents required for oxidase activation. This study concerns the hypothesis that cytosolic oxidase components translocate to a membrane fraction when neutrophils are stimulated and the oxidase is activated. A polyclonal antiserum that recognizes two discrete cytosolic oxidase components of 47 and 67 kD was used to probe transfer blots of electrophoresed membrane and cytosol fractions of resting and stimulated neutrophils. In contrast to their strictly cytosolic localization in unstimulated cells, both proteins were detected in membrane fractions of neutrophils activated by phorbol esters and other stimuli. This translocation event was a function of stimulus concentration as well as time and temperature of exposure to the stimulus. It was inhibited by concentrations of N-ethylmaleimide that blocked superoxide formation but was unaffected by 2-deoxyglucose. There was a correlation between translocation of the cytosolic proteins and activation of the oxidase as determined by superoxide formation. Quantitative analyses suggested that approximately 10% of total cellular p47 and p67 became membrane-associated during phorbol ester activation of the oxidase. Analysis of Percoll density gradient fractions indicated that the target membrane for translocation of both proteins was the plasma membrane rather than membranes of either specific or azurophilic granules. In the cell-free oxidase system arachidonate-dependent but membrane-independent precipitation of the cytosolic oxidase proteins was demonstrated. The data show that activation of the respiratory burst oxidase in stimulated human neutrophils is closely associated with translocation of the 47- and 67-kD cytosolic oxidase components to the plasma membrane. We suggest that this translocation event is important in oxidase activation.

Biochemical events associated with rapid cellular damage during the oxygen- and calcium-paradoxes of the mammalian heart

The O2- and Ca2(+)-paradoxes have a number of features in common and it is suggested that release of cytosolic proteins in both paradoxes is initiated by the activation of a sarcolemma NAD(P)H dehydrogenase which can generate a transmembrane flow of H+ and e- and also oxygen radicals or redox cycling which damage ion channels and membrane proteins (phase I). Entry of Ca2+ through the damaged ion channels then exacerbates the damage by further activating this system, either directly or indirectly, and the redox cycling and/or oxygen radicals cause further damage to integral and cytoskeletal proteins of the sarcolemma resulting in microdamage to the integrity of the membrane (phase II) and the consequent release or exocytosis of cytoplasmic proteins and, under specialised conditions, the blebbing of the sarcolemma. The system may be primed either by removal of extracellular Ca2+ or by raising [Ca2+]i by a variety of measures, these two actions being synergistic. The system is initially activated in the Ca2(+)-paradox by the membrane perturbation associated with removal of extracellular Ca2+; prolonged anoxia in the metabolically active cardiac muscle causes a depletion of the ATP supply, particularly in the absence of glucose, and hence a rise in [Ca2+]i in phase I of the oxygen paradox with the consequent activation of the NAD(P)H oxidase at the sarcolemma. Oxygen radicals are probably generated in both paradoxes and may have a partial role in the genesis of damage, but are not essential in the Ca2(+)-paradox which continues under anoxia. Massive entry of Ca2+ also activates an intracellularly localised dehydrogenase (probably at the SR) which produces myofilament damage by redox cycling.

31P NMR study of intracellular pH during the respiratory burst of macrophages

The metabolic events occurring during the respiratory burst of macrophages previously primed in vivo with lipopolysaccharide were studied by 31P nuclear magnetic resonance, using the P388D1 cell line as a model of the mature macrophages. Using perchloric acid extracts, the presence of phosphocreatine was shown in the primed cells, indicating that in control P388 D1 macrophages, in which no phosphocreatine was seen, in vivo maturation was incomplete. The cells primed in vivo exhibited greater maturation than the control cells, as well as greater creatine kinase activity. Perfusion of gel-embedded macrophages allowed the monitoring of phosphorylated metabolite peak intensities and of the intracellular pH. After the respiratory burst of the primed macrophages had been triggered by concanavalin A, these intensities did not alter significantly, but the intracellular pH decreased. 31P NMR spectra reflected transient acidification in the primed cells, possibly due to the formation of endocytic vesicles and their fusion with lysosomes.

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.

Lectinlike interactions of Fusobacterium nucleatum with human neutrophils

Fusobacterium nucleatum expresses lectinlike adherence factors which mediate binding to a variety of human tissue cells. Adherence is selectively inhibited by galactose, lactose, and N-acetyl-D-galactosamine. In this study, adherence of F. nucleatum to human peripheral blood polymorphonuclear neutrophils (PMNs) was investigated. The results indicated that the fusobacteria adhered to live and metabolically inactivated or fixed PMNs. Adherence of F. nucleatum resulted in activation of PMNs as determined by PMN aggregation, membrane depolarization, increased intracellular free Ca2+, superoxide anion production, and lysozyme release. Transmission electron micrographs showed that F. nucleatum was phagocytized by the PMNs. Microbicidal assays indicated that greater than 98% of F. nucleatum organisms were killed by PMNs within 60 min. Adherence to and activation of PMNs by F. nucleatum were inhibited by N-acetyl-D-galactosamine or lactose greater than galactose, whereas equal concentrations of glucose, N-acetyl-D-glucosamine, mannose, and fucose had little or no effect on F. nucleatum-PMN interactions. Pretreatment of the fusobacteria with heat (80 degrees C, 20 min) or proteases inhibited adherence to and activation of PMNs, but superoxide production was also stimulated by heated bacteria. The results indicate that interaction of F. nucleatum with PMNs is lectinlike and is probably mediated by fusobacterial proteins which bind to other human tissue cells. Adherence of F. nucleatum to PMNs in the absence of serum opsonins, such as antibodies and complement, may play an important role in PMN recognition and killing of F. nucleatum in the gingival sulcus and in the subsequent release of PMN factors associated with tissue destruction.

Activation of electropermeabilized neutrophils by adenosine 5'-[gamma-thio]triphosphate (ATP[S]). Role of phosphatases in stimulus-response coupling

Electrically permeabilized human neutrophils were used to study the mechanism of activation of the NADPH oxidase by chemotactic factors. The respiratory burst elicited by formyl-methionyl-leucyl-phenylalanine (fMLP) was strictly dependent on the addition of ATP. The response was also supported by adenosine 5'-[gamma-thio]triphosphate (ATP[S]), but not by the non-hydrolysable analogue (p[NH]ppA). In the presence of ATP, displacement of fMLP from its receptor by antagonist peptides resulted in the abrupt termination of the O2-consumption burst. In contrast, the response persisted after displacement of fMLP when ATP[S] was present. This finding is consistent with the formation of biologically active thiophosphoproteins which are resistant to cleavage by cellular phosphatases. Accordingly, lower concentrations of ATP[S], as compared with ATP, were required to support the fMLP response. The data indicate that protein phosphatases control the extent and duration of the response in cells stimulated with chemoattractants. Unlike ATP, sub-millimolar concentrations of ATP[S] elicited a spontaneous respiratory burst in the absence of fMLP or other stimuli. This effect was inhibited by p[NH]ppA and was not observed in intact (non-permeabilized) cells, indicating interaction of ATP[S] with an intracellular adenine-nucleotide-binding site, possibly a protein kinase. These results suggest that protein kinases are active in neutrophils in the absence of exogenous stimuli, but that accumulation of the essential phosphoprotein(s) is normally prevented by the ongoing vigorous phosphatase activity. It is conceivable that control of the respiratory burst is exerted by inhibition of phosphatase activity, instead of or in addition to the more commonly postulated activation of protein kinases.

Control of fructose 2,6-bisphosphate levels in rat macrophages by glucose and phorbol ester

The presence of fructose 2,6-bisphosphate (Fru 2,6-P2) in elicited peritoneal macrophages of rat was examined. These cells possess an active phosphofructokinase-2 which is diminished by citrate and only slightly inhibited by glycerol 3-phosphate. Phosphofructokinase-1 submaximal activity was increased 26-fold by the addition of 1 microM Fru 2,6-P2. Incubation of cells without glucose decreased the amount of Fru 2,6-P2 to zero, but further addition of 5 mM glucose increased the levels of the sugar ester 20-fold. In addition, the presence of phorbol ester potentiated the synthesis of Fru 2,6-P2. By contrast phenylisopropyladenosine or prostaglandin F2 alpha inhibited the production of Fru 2,6-P2.

Mechanisms that produce rapid damage to myofilaments of amphibian skeletal muscle

The system causing myofilament damage is separate from the phospholipase A2 pathway, Ca activation of which ultimately causes sarcolemma breakdown in muscle cells. Mitochondrial agents cause myofilament damage in saponin-skinned frog pectoris cutaneous muscle when [Ca] = 0. There are parallels with other systems that generate oxygen radicals. However, a variety of protectors against oxygen radicals, or anoxia, failed to protect; Ca-activated damage was not augmented by diethylthiocarbamate, nor was it accompanied by a respiratory burst. Thus, there is no firm evidence implicating oxygen radicals in myofilament damage. Thiol-oxidizing agents cause contraction damage in skinned muscle that resembles the quasirigor induced in myosin by N-ethylmaleimide. Activation of transmembrane dehydrogenases and electron flow produced damage and increased Ca sensitivity in skinned muscle, and it is suggested that this enzyme system may be implicated in characteristic damage to the myofilaments via redox cycling and modification of sulphydryl groups; its possible location on the sarcoplasmic reticulum is discussed.

Stimulation of guinea pig neutrophil superoxide anion-producing system with thymol

Thymol stimulated O2- production in guinea pig neutrophils. O2- production occurred about 30 sec after the addition of thymol, and its rate was independent of extracellular Ca2+. Thymol-induced activity was inhibited by trifluoperazine (TFP), an inhibitor of protein kinase c, and its IC50 was less than that for 12-O-tetradecanoyl phorbol 13-acetate (TPA) induced activity. After complete activation, O2- production was reversed by addition of TFP or by washing out and resuspending in a stimuli-free medium. The responsiveness of the thymol-pulsed cells to another stimulus, TPA, was somewhat more than resting cells, but the responsiveness of the former cells to thymol was about half that of the latter cells. The ATP level of cells was reduced to one half its initial value during activation by thymol. These data suggest that the magnitude of thymol-induced O2- production in neutrophils is dependent on the initial density of the binding sites of the cells with thymol and the initial intracellular ATP concentration.

Felodipine-induced inhibition of polymorphonuclear leukocyte functions

Felodipine inhibits fMet-Leu-Phe or ionophore A23187-induced exocytosis in rabbit peritoneal polymorphonuclear leukocytes (PMNs), in the concentration range 1-50 microM. Activation of the metabolic burst, and migration of PMNs towards fMet-Leu-Phe are equally inhibited by felodipine in the same concentration range. The effect is not due to blocking of calcium channels in the plasma membrane, because the degree of inhibition remains the same when Ca2+ is omitted from the medium. Felodipine interferes with ionophore A23187-induced association of 45Ca with the PMN but this interference occurs at lower concentrations than the inhibition of exocytosis. Hypotonic hemolysis of erythrocytes is inhibited by felodipine; maximal protection against hemolysis occurs at a concentration of 50 microM felodipine. It is suggested that at least a part of the inhibiting effect on PMN functions might be due to an anesthetic-like membrane effect of felodipine.

Arachidonate 15-lipoxygenase from human eosinophil-enriched leukocytes: partial purification and properties

Arachidonate 15-lipoxygenase was purified from human eosinophil-enriched leukocytes after showing that 15-lipoxygenase activity was 100-fold greater in eosinophils than in neutrophils. Partial purification was achieved using ammonium sulfate precipitation, cation-exchange and hydrophobic-interaction chromatography. New evidence is presented suggesting that 15-lipoxygenase has electrostatic and hydrophobic properties distinct from 5-lipoxygenase. In addition, ATP is shown to inhibit, and phosphatidylcholine is shown to stimulate, 15-lipoxygenase, suggesting a regulatory role for these compounds in the lipoxygenation of arachidonic acid.

The superoxide-forming enzymatic system of phagocytes

The formation of oxygen-derived free radicals by the phagocytes (neutrophils, eosinophils, monocytes and macrophages) is catalysed by a membrane-bound NADPH oxidase which is dormant in resting cells and becomes activated during phagocytosis or following interaction of the cells with suitable soluble stimulants. This enzyme is under investigation in many laboratories but its molecular structure remains to be clarified. Possible components such as flavoproteins, cytochrome b558, and quinones have been proposed on the basis of enzyme purification studies, effects of inhibitors, kinetic properties and analysis of genetic defects of the oxidase. An extensive discussion of the evidence for the participation of these constituents is reported. On the basis of the available information on the structure and the catalytic properties of the NADPH oxidase, a series of possible models of the electron-transport chain from NADPH to O2 is presented. Finally, the triggering mechanism of the respiratory burst is discussed, with particular reference to the stimulus-response coupling and the final modification(s) of the oxidase (phosphorylation, assembly, change of lipid environment, etc.) which are involved in its activation.

Chemiluminescence in human whole blood: modulation by the cocarcinogens phorbol diester and polychlorobiphenyls

A human whole blood chemiluminescence (CL) assay was established using zymosan as cell activator. Aroclor 1254 was found to inhibit this CL response in a direct linear relation to its concentration, (50% inhibitory dose, (ID50) equal to 5 x 10(-4)M) in diluted blood samples of 10 normal human subjects. In comparison the ID50 of other inhibitors was 1.3 x 10(-3)M for ethylenediamine tetraacetic acid, 3.3 x 10(-3)M for ascorbic acid, 4 x 10(-3)M for reduced glutathione, 1.2 x 10(-1)M for ethanol, 2.5 x 10(-1)M for methanol and 3.7 x 10(-1)M for dimethyl sulfoxide. Using 12-o-tetradecanoyl-phorbol-13-acetate (TPA) as cell activator the CL response was likewise inhibited by Aroclor 1254 with an ID50 of 4.5 x 10(-4)M. However, it was found that Aroclor 1254 alone has a stimulatory CL effect on otherwise unactivated cells. To compare the mechanisms involved in the CL elicited by the three stimulants zymosan, TPA and Aroclor 1254, the CL signal was measured in the presence of cytochalasin B. Cytochalasin B inhibited zymosan-induced CL, had a smaller inhibitory effect on TPA-induced CL but it could augment the CL response initiated by Aroclor 1254. This pattern of responses implicates Aroclor 1254 in the activation of eicosanoid metabolism as it matches the differential responses reported for arachidonic acid.